Membrane-based separation of hydrogen

Abstract

The invention relates to a device (200, 300, 312) for efficiently separating hydrogen (H2) from biogas streams (410) in biogas plants (100, 200, 300) in order to optimise the liquefaction processes of methane and carbon dioxide, the device comprising a separation membrane (216, 318) which is based on the differing permeances of hydrogen, carbon dioxide, and methane in order to selectively remove hydrogen (310) and to maximise the purity of methane and carbon dioxide in subsequent processing.

Description

MEMBRANE-BASED SEPARATION OF HYDROGEN AREA OF TECHNOLOGY

[0001] The invention relates to a method for the selective separation of hydrogen (H₂). z ) from gas mixtures, especially in the application of processing biogas into liquefied methane (Bio-LNG) and / or liquefied carbon dioxide (Bio-LCO₂) z ). STATE OF THE ART

[0002] Biogas is produced through the anaerobic digestion of organic substrates and can be used for a variety of purposes, e.g., for the production of biomethane. Raw biogas consists primarily of methane (CH4) and carbon dioxide (CO2). Z ), but also contains other components such as water vapor (H Z O), hydrogen sulfide (H Z S), oxygen (O z ), nitrogen (N z ) and possibly traces of other gases, e.g. hydrogen (H₂) z ) or various noble gases.

[0003] For the injection of biomethane into natural gas networks or for its use as a fuel or for the production of other end products such as bio-ICO z (Liquefied Carbon Dioxide) requires extensive processing of the raw biogas. This involves, in particular, enriching the methane and removing accompanying gases such as CO. Z and H Z The goal is to obtain highly purified product fractions that can be economically utilized and stored, transported, or used directly. While some of these gas components can be separated relatively easily by condensation, adsorption, or absorption, so-called non-condensable gases pose a particular challenge.

[0004] Typical examples of non-condensable gases are nitrogen (N₂). z ) and oxygen (O2), which can enter the biogas system, for example, through air intake during substrate preparation or through leaks, or hydrogen (H z), the formation of which is mainly due to microbiological activity during anaerobic fermentation. Any noble gases present in trace amounts are also non-condensable.

[0005] Due to the physical properties of these gases, they are not condensable under normal process conditions. Removing these non-condensable associated gases during the processing of biogas and gas mixtures of similar composition can, among other things, help to meet the quality requirements for biomethane.

[0006] In the context of biogas processing, a CC liquefaction plant (LCO2 plant) can also be used. This plant further purifies a gas stream with a high CC content originating from a gas processor and serves to produce liquid CO2, which can be used for various purposes. Hydrogen is undesirable not only in the processed methane but also in the processed CO2 and is limited depending on the intended use of the CO2 and the applicable standards and limits (e.g., the EIGA standard for food-grade CO2).

[0007] Separating hydrogen from biogenic gas mixtures presents a particular technical challenge because methane and hydrogen have similar physical properties (small, nonpolar molecules), hydrogen has a low density and high diffusivity, and it is often present in gas mixtures only in very low concentrations. Separating gases that are only present in trace amounts makes economically viable separation using conventional methods technically complex, inefficient, and therefore uneconomical. Consequently, hydrogen is often not removed intentionally. Furthermore, due to the risk of explosion when mixed with oxygen, hydrogen imposes increased safety requirements on the design and operation of processing plants.

[0008] Especially in CCh liquefaction plants, which are often used in the context of processing raw biogas, the problem is that hydrogen can accumulate in the low-temperature processes that take place during liquefaction: For example, H remains z At -160 °C, the typical condensation temperature of methane, hydrogen completely condenses into a gas and accumulates in the so-called "boil-off" gas of the reboiler stage of carbon dioxide liquefaction plants. During the liquefaction of carbon dioxide, which typically takes place at approximately -25 °C and 15-20 bar, hydrogen remains in gaseous form in the reboiler and can then pass into the headspace of the condenser or storage tank and accumulate there.

[0009] Currently, various processes are being used, such as pressurized water scrubbing (PWS - physical absorption of CO2 in water under pressure), amine scrubbing (chemical absorption of CO2 and H2), and other methods. ZS in solutions based on monoethanolamine (MEA) or methyldiethanolamine (MDEA)), or pressure swing adsorption (PSA - Adsorptive separation of gas components on zeolite or activated carbon basis under cyclically changing pressure levels) is used for the separation of hydrogen.

[0010] Additionally or alternatively, general degassing systems for non-condensable gases can be used, which thermally utilize, flare off or release the non-condensable components, but which are not specifically designed for separation. or are designed for hydrogen enrichment. Furthermore, in practice, this (residual) gas stream obtained from the general degassing system is at least materially lost.

[0011] Physical washing processes, amine scrubbing, and PSA systems have the disadvantage that hydrogen enters the product streams during the process steps. Membrane processes, on the other hand, prevent hydrogen from entering the product streams. zDuring the separation of raw biogas in a gas processor into a methane-enriched retentate stream and a carbon dioxide-enriched permeate stream, the carbon dioxide is usually separated along with the retentate and transferred to the carbon dioxide-enriched permeate stream. There, unlike in the methane-enriched retentate stream produced by the gas processor, it does not represent an economically viable component. Rather, it hinders CO2 liquefaction because it lowers the partial pressure, alters the condensation dynamics, and reduces the purity of the product.

[0012] According to another method known in the prior art, the gas mixture produced in the stripper-reboiler stage of an LCO plant (typically consisting of CO2, O2, CH4, H2) is separated and either thermally utilized or partially recycled back into the fermenter. However, the focus here is usually on removing other, non-condensable gases, not on removing hydrogen.

[0013] Both approaches – the removal of hydrogen into the CO2-containing permeate stream of the biogas upgrading plant and the use of a stripper-reboiler stage in a CO2 liquefaction plant – result in losses: either the hydrogen is burned without being utilized, or it accumulates in the process. Targeted, selective separation of hydrogen does not occur.

[0014] Patent application EP4321237A1 generally describes concepts for separating gas mixtures using membranes, but not with the aim of selectively separating H2. Rather, the system described in patent application EP4321237A1 aims to separate methane and carbon dioxide from a gas stream with the goal of enriching the methane.

[0015] Document EP0410845 Al discloses a process for recovering CO2 from the exhaust gas of a carbon dioxide liquefaction plant by means of membrane separation and recycling a carbon dioxide-enriched permeate into the plant feed. The document does not address the removal of hydrogen from the process. SUMMARY

[0016] An improved method and device for processing gas mixtures consisting of at least methane, carbon dioxide and hydrogen are described here.

[0017] One aspect described here is a device for the efficient separation of hydrogen (H2) from biogas streams in biogas plants to optimize the liquefaction processes of methane and carbon dioxide (CO2). The device comprises a special separation membrane, also called a "membrane," which is based on the different permeances of H2, CO2, and CH4 to selectively remove H2 and subsequently maximize the purity of CH4 and CO2.

[0018] Examples of applications of the invention include the advantage that the non-condensable gas fractions (NCGs) produced in a CO2 liquefaction plant contain small amounts of hydrogen, which accumulate during operation and negatively impact the efficiency, process stability, purity, and safety of the plants. By integrating the separation membrane described above into the process or into a biogas power generation plant, the problems associated with hydrogen accumulation can be reduced or completely avoided. Suitable separation membranes are available on the market (e.g., EVONIK, Noble from UBE, H2 Separation Membrane, or from Airrane, Meritair). If these are integrated into the process at a suitable point, hydrogen accumulation can be prevented, and the hydrogen can potentially even be used for energy recovery or material recovery.The device in which the aforementioned membrane is integrated can be either a micro-plant or a macro-plant. Micro-plants can be, for example, smaller units for processing biogas electricity, such as those used in university settings or in some biogas processing plants. Macro-plants can be facilities that process larger quantities of biogas on an industrial scale, such as plants for processing biogas produced in large wastewater treatment plants or digesters for organic waste or manure.

[0019] The biogas stream from which the hydrogen is separated can be, in particular, a CO2-rich gas stream from a biogas plant, especially a gas stream that arises at a point in the biogas processing process where non-condensable residual gases – for example, from a reboiler or condenser – occur and have so far been thermally utilized or flared without being used.

[0020] Removing the hydrogen not only reduces the risk of explosion but also increases the purity of the CO2 stream, allowing a higher proportion of CC (carbon dioxide) in the initially produced biogas to be liquefied. Since methane penetrates the membrane less effectively... Since the hydrogen permeates the methane, methane losses are also avoided, so examples of the invention can also have the advantage of improved methane yield.

[0021] In contrast to conventional biogas upgrading processes, which H zWhile other methods treat or tolerate hydrogen as a non-condensable inert gas requiring thermal disposal, examples of the invention treat hydrogen as a component to be selectively separated. Examples of the invention can prevent accumulated hydrogen from causing increased pressure in the liquefaction system, bubble formation, and concentration in the LNG or LCO. Z - Headspace leads to this. This can result in yield losses in the extraction of LCO. Z and / or LCH4, as well as safety risks (explosive oxyhydrogen gas can be produced in the event of leaks in tanks and pipes), are avoided or reduced. The CO z -Electricity is produced by the H z -Removal inerted.

[0022] According to some examples, the liquefied CO Z as food CO zIt is used, for example, in the production of carbonated beverages. Here, the use of a separation membrane can have the advantage of requiring less equipment and energy for the subsequent purification of the food-grade CO₂. z s must be operated because the proportion of hydrogen in the process and therefore also in the LCO Z thanks to the separation membrane, CO₂ emissions can be reduced. This is especially important in food-grade CO₂. z Strict purity requirements must be met for these applications (e.g., < 10 ppm H₂). z For example, the use of the separation membrane of the H z - Content in CO Z - Electricity generated from a CO₂ z -Liqueflux plant for the production of liquid CO Z The CO₂ level used should be reduced to below 100 ppm, which is the usual limit for suitability for food, technical or medical applications. z -Applications corresponds.

[0023] Compared to the system described in patent application EP4321237A1 for separating methane and carbon dioxide from a gas stream with the aim of enriching methane, several advantageous differences arise: In the aforementioned document, the membranes are specifically designed for CO z -permeation designed to retain CH4. Such membranes are poorly suited, if at all, for the targeted separation of hydrogen in particular, since, according to examples of the invention, separation membranes with a high H z / CO z -Selectivity and H zThe membranes in EP4321237A1 exhibit CH4 selectivity and, consequently, unlike those in EP4321237A1, are intended to selectively permeate hydrogen, thus enabling efficient hydrogen removal from the biogas processing process. The intended use of the membrane described in EP4321237A1 is entirely different: to recover valuable methane, while carbon dioxide is to be permeated as efficiently as possible. Membrane design The process objective and the process goal are therefore fundamentally different. Furthermore, the process steps shown in EP4321237A1 are optimized for the concentration ratios (5-25% methane in CO2) and do not offer economically viable separation performance for hydrogen in the ppm to percent range. The gas separation process described in EP4321237A1 is not suitable for the targeted separation of hydrogen due to the opposing separation objective, the different membrane selectivity, and the specific process conditions. Compared to the process described in EP4321237A1, examples of the invention not only have the advantage that hydrogen is effectively removed from the process, but also that the recovered hydrogen is much more concentrated and thus, according to some implementation variants, may also be suitable for material utilization.Examples of the invention have the advantage over this publication that an improved biomethane yield is enabled in further biogas processing, but for a different reason, namely because after efficient hydrogen separation the separation of carbon dioxide and methane can also proceed more efficiently.

[0024] Compared to the process for recovering CO2 from the exhaust gas of a carbon dioxide liquefaction plant described in publication EP0410845 Al, examples of the invention have the advantage that hydrogen can be selectively removed from the process, which can bring about the advantages described above with regard to safety and process efficiency. EP0410845 Al describes the recycling of a carbon dioxide-enriched permeate into the plant feed. This publication does not address the removal of hydrogen from the process. In particular, EP0410845 Al focuses exclusively on CO2 selectivity (CO2 permeate). The separation factor diagrams (CO2 / H2 as a function of T) shown in EP0410845 Al do not support the conclusion that slightly elevated temperatures increase the H2 permeability relative to CO2 and thus optimize H2 separation. The trend of the curve suggests the opposite.

[0025] The separation membrane can, for example, be configured so that, despite its affinity to permeate CO2 more quickly, it allows crucial H2 to permeate, while CO2 and CH4 are largely retained.

[0026] This can have the advantage of producing a hydrogen-enriched permeate stream, which, depending on the plant design, can be flared, used for energy and / or material recovery, or – in the case of power-to-gas concepts – fed back into the methanization process of power-to-gas plants. Furthermore, a retentate can be produced, which consists, for example, almost exclusively of... CO2, CH4 and optionally small amounts of O2, which can be returned to a processing stage upstream of the separation membrane in the biogas electricity processing.

[0027] For example, the device can be configured to provide the separated gases (CH4 and CO2) in marketable purity and to significantly reduce the proportion of non-condensable gases.

[0028] The separation membrane can be integrated, for example, in an additional step or module after the stripper-reboiler stage of a CO2 liquefaction plant.

[0029] The stripper-reboiler stage is also referred to here as the "reboiler stage" or "reboiler." This can have the advantage that a previously technically problematic stream (reboiler residual gas stream with non-condensable gases), which was previously simply discarded, is made energetically and / or usable for the first time. The integration takes place at a position in the system that has been previously overlooked in the prior art, namely at or after the outlet of a reboiler in a CO2 liquefaction plant. Because, according to examples of the invention, hydrogen is separated via the membrane precisely at this strategically advantageous position, CO2 from the reboiler can be made available for liquefaction in a particularly energy-efficient manner, without hydrogen accumulating in the process.

[0030] For example, the separation membrane or a module containing this and possibly other elements can be directly integrated into a degassing stage of a CO2 liquefaction plant.

[0031] The degassing stage is a component of a CO2 liquefaction plant, and degassing is a process step typically controlled by the CO2 liquefaction plant's control unit along with other process steps. A degassing stage in an LCO2 plant serves to remove unwanted gases from the liquid CO2. After CO2 liquefaction (i.e., cooling and compressing CO2 from biogas to approximately -50 to -80 °C and ~20 bar), the liquid CO2 may still contain residual gases that were not completely removed during the previous purification or condensation. The degassing stage ensures that non-condensable gases as well as volatile organic compounds (e.g., traces of sulfur compounds or siloxanes) are removed from the liquefied CO2.

[0032] The integration of the separation membrane into the device can be achieved, for example, by using the reboiler's pressure regulator to also determine the pressure on the feed side of the separation membrane. This has the advantage that no additional components are required for feed-side pressure regulation. The inventor has observed that, as a rule, the pressure of the reboiler's residual gas flow, as generated by the reboiler's pressure regulator, is already sufficient for efficient hydrogen separation at the separation membrane. Figure 3 shows an example of an implementation variant in which the pressure on the feed gas side of the separation membrane is determined by the reboiler's pressure regulator. For example, the separation membrane, or the module containing it and any other elements, can be integrated between the reboiler and a degassing valve of the LCO2 system.

[0033] The separation membrane can also be integrated at other points in the residual gas stream from a reboiler of a CO₂ liquefaction plant. For example, the separation membrane, or the module containing it and any other components, can be installed downstream of the reboiler and within a return line for the residual gas stream. This return line can, for example, be a line used to return the residual gas stream from the reboiler to the LCO system or to another component of the device. Preferably, in this case, the membrane module includes an additional pressure sensor and pressure regulator, such as a pressure control valve, for regulating the pressure on the feed gas side of the separation membrane. This allows the pressure on the feed gas side of the separation membrane to be controlled independently of the reboiler pressure.

[0034] In both implementation variants, the membrane module can optionally include a pressure sensor on the permeate side of the separation membrane and a pressure regulator to regulate the pressure on the permeate side of the separation membrane.

[0035] The membrane module can be implemented as a retrofittable membrane module, in particular as a so-called "bolt-on module". A bolt-on module is a pre-assembled, self-contained functional unit ("plug-and-play module") that can be retrofitted to an existing device (e.g., a biogas processing plant, CO2 liquefaction plant, LNG plant, etc.) to expand its performance or functionality without having to fundamentally modify the main plant.

[0036] In particular, the separation membrane or the module that contains this and possibly other components can It contains elements that can be integrated as an "inline module" into existing gas pipelines.

[0037] According to further examples, the biogas stream or gas mixture with which the separation membrane is exposed can be one of the following gas streams: • the entire non-condensable residual gas stream from the reboiler of a CO2 liquefaction plant; or • only a portion of the non-condensable residual gas stream from the reboiler of a CO2 liquefaction plant; the other portion can, for example, be released into the atmosphere or returned to the LCO2 process or biogas processing process; • Partial or total flows of non-condensable residual gases from the reboilers of several COj liquefaction plants.

[0038] This application of only portions of the residual gas stream from one or more CO₂ liquefaction plants to the separation membrane can be achieved, for example, by integrating a distribution module, such as a distribution valve, upstream of the membrane module and downstream of the reboiler(s). This distribution module diverts the portion of the residual gas stream not directed onto the separation membrane back into the biogas processing or LCO₂ process. Preferably, the distribution module is automatically and / or manually controllable, allowing it to direct varying proportions of the residual gas stream onto or around the membrane, depending on the system condition and requirements.

[0039] This can have the advantage that, under certain operating conditions of the plant, e.g., when fluctuations result in a particularly large amount of residual gas and / or the CO2 liquefaction plant is operated at or above its capacity limit, the increased amount of residual gas, which the separation membrane may no longer be able to process, can be bypassed. If the separation membrane is exposed to an excessive amount of residual gas, the resulting permeate and / or retentate may have a composition that no longer meets the required quality criteria. To ensure that the capacity of the separation membrane is sufficient in all cases, especially in plants with high fluctuations or high utilization, a correspondingly large membrane area would have to be selected, which increases costs and equipment complexity.By using a distribution module and directing only a portion of the reboiler residual gas to the separation membrane if necessary, it is possible to reduce material and costs, especially in larger systems. with high fluctuation of the amount of gas processed or in the case of plant operation up to the capacity limit ("machine reserve") of the plant and beyond.

[0040] The pressure and temperature conditions typically prevailing in this residual gas stream (in many cases 10 to 18 bar absolute, below 25 °C, often below 5 °C) enable, according to examples of the invention, a highly efficient, selective separation of H zwithout additional primary energy input or, in some examples, with only minimal use of additional primary energy, depending on the plant design. For instance, due to the upstream liquefaction processes, the residual gas stream from the reboiler typically already has high pressures of over 10 bar absolute, particularly 10 to 20 bar absolute, preferably 15 to 18 bar absolute, so that this residual gas stream can be fed directly to the feed side of the separation membrane without the use of additional compressors. The temperature can be below zero or only slightly above zero, so that the residual gas from the reboiler often requires little or no heating before it reaches the separation membrane.Optionally, additional components such as valves, pressure sensors and pressure regulators can be integrated into the device for fine-tuning and / or maintaining a constant pressure at an optimal setpoint for the separation membrane and / or to avoid pressure fluctuations.

[0041] In some examples, temperature and / or pressure control within the membrane module is achieved without the use of primary energy. This means that existing pressure and temperature conditions of the gas mixture are utilized, so that by creating suitable pressure and temperature conditions on the feed side of the membrane module, the overall energy consumption of the device—for example, a biogas processing plant or a CC liquefaction plant—does not increase. In particular, the non-condensable residual stream from a reboiler of a carbon dioxide liquefaction plant, also known as "reboiler NCG stream," typically exhibits temperature and pressure conditions that are already suitable for hydrogen capture. Therefore, additional compression and / or the use of additional heating elements can be avoided, for example, when the module is installed in the non-condensable residual stream of a reboiler of a carbon dioxide liquefaction plant.This can also be done retroactively, i.e., after completion and commissioning of the system ("retrofit module").

[0042] According to some examples of the invention, the module with the separation membrane is free of heating elements for actively heating the gas mixture and / or is free of a compressor or other devices for increasing the pressure of the gas mixture.

[0043] In other examples, while a heating element and / or pressure regulator are present, the membrane module also includes temperature and / or pressure sensors and is designed to automatically detect that, under suitable pressure and / or temperature conditions in the gas mixture acting on the feed side of the membrane, the compressor or heating element can be omitted. In addition to or as an alternative to this automatic control of the heating element and / or compressor, the module can also have a user interface that allows a user to activate or deactivate the compressor or heating element, depending on the process (e.g., a carbon dioxide liquefaction plant) and the module's position within the process.Preferably, the heating element is a heat exchanger, in particular one that uses process heat from biogas power processing to bring the gas mixture on the feed side of the separation membrane to the target temperature.

[0044] Modules that do not have their own compressor and / or heating elements can have the advantage of being cheaper to manufacture, requiring less space, and having fewer connectivity issues, making them particularly suitable for retrofitting into existing systems. Modules with integrated and / or operationally connectable heating elements and / or compressors, on the other hand, have the advantage of being able to generate suitable temperatures and pressures for hydrogen separation even when the temperature and / or pressure of the gas mixture reaching the module is not yet suitable or optimal for selective hydrogen separation.

[0045] For example, the biogas produced during a fermentation process, which typically contains small amounts of hydrogen, can first undergo an initial separation of the binary gas mixture CH4 / CO2 before passing through the separation membrane. Specifically, the separation membrane can be exposed to the carbon dioxide-enriched gas mixture obtained through this separation.

[0046] The total mass flow to be reused typically consists of 70-80% CO2, 15-18% CH4, 7-10% O2 and 0.2-0.4% H2, with the hydrogen content being selectively separated by the separation membrane at the corresponding concentration.

[0047] This can mean, in particular, that the H2 content is selectively separated by the separation membrane to such an extent that the retentate contains only the aforementioned concentration of 0.2-0.4% H2 (volume%).

[0048] According to examples of the invention, the non-condensable gases, which usually have to be thermally utilized, can be significantly reduced by separating the hydrogen, leading to an increase in efficiency and a significant reduction in operating costs of the entire plant system.

[0049] According to examples of the invention, the gases remaining in the retentate are reintroduced into the process after their separation, with CO2 and CH4 passing through the process again and O2 being consumed in the fermentation or adsorbed with H2S, while H2 does not accumulate adversely.

[0050] This can have the advantage that biogas processing to LCO2 and / or LCH4 can take place without significant losses of CH4 or CO2. In particular, the CO2 fraction previously lost in the reboiler electricity of a CO2 liquefaction plant can be fed back into the biogas processing process and thus made available for use or liquefaction in a CO2 liquefaction plant.

[0051] EP4321237A1 does not provide for the targeted recirculation of gases into the process. Compared to this document, this offers the advantage that valuable methane can be recirculated into the biogas processing process without hydrogen accumulation.

[0052] By utilizing electricity that was previously lost in terms of energy and materials, depending on the plant design, for example 10% additional CO2 and CH4 yield can be achieved.

[0053] According to examples of the invention, the separation membrane has a permeability ratio (selectivity) for H z relative to CO2 and CH4, at least 3, in particular at least 5, for example at least 10. This means that per unit of time 3 times (or 5 times or 10 times) more hydrogen than CO2 or CH4 passes through the membrane.

[0054] The separation membrane can be, for example, a polymer membrane. Polyamide, polyimide, or polyetherimide membranes can be used, for instance. These offer the advantage of being inexpensive, easy to manufacture, and flexibly scalable. Due to its molecular properties (small kinetic diameter, high diffusion rate), hydrogen permeates polymer membranes and various other types of membranes significantly faster than CO2 or CH4. The separation membrane can, for example, be a thermostable polyamide membrane.

[0055] The separation membrane can also be an inorganic membrane, particularly a ceramic one. For example, there are ceramic membranes based on zeolites, silicates, and γ-Al₂O₃-coated supports. This type of membrane can offer the advantage of particularly high thermal and chemical stability and good separation performance. Palladium-based membranes, such as Pd or Pd alloys on a support material, can also be used. These can exhibit very high selectivity for hydrogen, but they are somewhat more susceptible to impurities, especially sulfur. Furthermore, so-called mixed matrix membranes (MMMs), typically comprising a polymer matrix with inorganic fillers (e.g., zeolites, MOFs), can also be used. These combine the advantages of polymers and inorganic membranes.

[0056] The separation membrane can be, in particular, a temperature-controlled separation membrane. A temperature-controlled separation membrane is a membrane whose selectivity and / or permeability is specifically controlled, or at least partially influenced, by temperature. The membrane is either heated or cooled to optimize its separation properties. For example, the separation membrane can be coupled to a heating element, such as a heat exchanger, and a temperature controller, enabling dynamic, active control of the membrane temperature by the heating element and thus allowing for dynamic adaptation to process-specific requirements (e.g., adjustments to fluctuating hydrogen concentrations depending on fermentation parameters).Furthermore, the separation performance can be optimized, since the temperature affects the molecular mobility and solution / diffusion in the membrane, so that the permeability of the membrane can be increased or decreased as needed.

[0057] Another advantage of using a temperature-controlled separation membrane is that the temperatures of the feed gas, e.g., the temperature of a non-condensable residual gas stream from a reboiler of a carbon dioxide liquefaction plant, are less prone to fluctuations. These can be subject to dynamic fluctuations, so that the temperature of the feed stream to the separation membrane can be kept close to a target temperature.

[0058] According to examples of the invention, the device is configured to effect the separation of hydrogen from the biogas streams by subjecting the separation membrane to one of the biogas streams, which comprises at least hydrogen (H2), carbon dioxide (CO2) and methane (CH4) and is also referred to here as a “gas mixture”, such that hydrogen preferably permeates the membrane and thereby produces a hydrogen-enriched permeate and a hydrogen-reduced retentate.

[0059] The device into which the separation membrane is integrated or will be integrated can be, for example, a biogas plant with bio-LNG production, a plant for liquefying the carbon dioxide contained in biogas (“bio-LCO2 liquefaction plant”), a plant for biogas refining, or a biogas processing plant based on power-to-gas (P2G) technology.

[0060] According to examples of the invention, the biogas stream from which the hydrogen is extracted through the separation membrane is the non-condensable residual gas stream of a CO2 liquefaction plant.

[0061] According to examples of the invention, the biogas stream from which hydrogen is extracted by the separation membrane contains less than 5 vol% H2, in particular less than 2.5 vol% H2, and in particular less than 1 vol% H2. Examples of the invention are therefore capable of efficiently separating hydrogen even from gas streams with a very low hydrogen content, which, due to its tendency to accumulate, can nevertheless pose a significant problem in biogas processes. Membrane configurations primarily designed for the separation of other gases are not capable of extracting hydrogen from gas mixtures with a low hydrogen concentration so effectively that the accumulation problem would be significantly reduced.

[0062] According to examples of the invention, the device is configured to produce a permeate and a retentate at the separation membrane, the permeate:retentate of which has a volume ratio of < 1:2, e.g. between 1:2 and 1:5, in particular between 1:2 and 1:4, e.g. between 1:2 and 1:3.

[0063] According to examples of the invention, the separation membrane is located within the residual gas stream of a CO2 liquefaction plant.

[0064] According to preferred examples of the invention, the device containing the separation membrane is configured (e.g. by suitable positioning of the separation membrane within one of the biogas streams of the device or plant and / or by the use of heating elements) such that the biogas stream, when it hits the feed side of the separation membrane, has a temperature of 0°C to 45°C, preferably 0°C to 25°C, preferably 0°C to 5°C.

[0065] Additionally or alternatively, the device is configured (e.g., by suitable positioning of the separation membrane within one of the biogas streams of the device or plant and / or by using one or more pressure regulators on the feed side and optionally also the permeate side of the membrane) so that the biogas stream, when it hits the feed side of the separation membrane, has a pressure of a maximum of 40 bar absolute, in particular a maximum of 25 bar absolute, preferably 2 bar to 25 bar absolute, in particular 16 to 20 bar absolute, in particular a maximum of 18 bar absolute.

[0066] In contrast, EP4321237A1 recommends an optimum operating temperature for the membrane that is significantly higher than an optimum temperature for hydrogen deposition.

[0067] The process described in EP0410845 Al takes place at very low temperatures (approx. -2 °F or -18 °C) and high pressures (250-350 psia, i.e., 17-24 bar) to optimize CO₂ / impurity selectivity. In contrast, examples of the invention utilize moderate, and comparatively significantly higher, temperatures, preferably above 0 °C, and / or preferably feed pressures up to a maximum of approximately 18 bar, to achieve specifically high H₂ / CO₂ selectivity – an operating range that is neither mentioned in EP0410845 Al nor would be practical with regard to the CO₂ recovery intended therein.

[0068] The device can, for example, include a heating element configured to heat the biogas stream from which hydrogen is extracted through the separation membrane when it hits the feed side of the separation membrane to a temperature of 0°C to 45°C, preferably 0°C to 25°C, preferably 0°C to 5°C.

[0069] The biogas stream used to feed the separation membrane can, for example, be the residual gas stream from a CO2 liquefaction plant. Depending on the plant design, manufacturer, and reboiler size, this residual gas stream has varying temperatures and pressures. Often, this gas stream has an absolute pressure of approximately 18 bar and is significantly colder than 0°C, with a temperature of approximately -5 to -10°C. These specifications therefore refer to the residual gas stream before... it hits the separation membrane or before it is heated by optional heating elements of the membrane module. To enable efficient hydrogen separation at the separation membrane, it is advantageous to increase the temperature on the feed side of the separation membrane to the aforementioned temperature range of 0°C to 45°C, preferably 0°C to 25°C, preferably 0°C to 5°C, wherein for many membrane types, especially for polymer-based membranes, the optimal temperature range for hydrogen separation in the context of the process and its boundary conditions lies in the range of 0°C to 5°C.

[0070] The device can be, for example, a CO2 liquefaction plant or include one. The CO2 liquefaction plant contains a reboiler with a reboiler pressure regulator. The device is configured to use only the reboiler pressure regulator to regulate the pressure on the feed side of the separation membrane. In particular, this variant of the device can be designed such that the separation membrane is integrated into a degassing stage of the CO2 liquefaction plant that includes the reboiler. An example of a device in which the reboiler pressure regulator is used to regulate the pressure on the feed side of the membrane is shown in Figure 3.

[0071] According to some examples, the device is a CO2 liquefaction plant with a reboiler including a reboiler pressure regulator. The device includes an additional pressure regulator and is configured to use the additional pressure regulator to regulate the pressure on the feed side of the separation membrane. A corresponding example is shown in Figure 6.

[0072] For example, the separation membrane can be integrated into a line for transporting the non-condensable residual gas stream from the CO2 liquefaction plant. This line can be located, for example, inside or outside the degassing stage of the CO2 liquefaction plant. The position of the separation membrane within the line can be selected, for example, based on the prevailing temperature and pressure conditions in the line, in such a way as to minimize the energy required to set a target temperature and / or pressure on the feed side of the separation membrane for hydrogen removal.

[0073] For example, the selectivity for hydrogen over carbon dioxide (H2 / CO2) typical for polyimide membranes is approximately 3.0 at 25 °C. If the feed gas operating temperature is set to 5 °C, the selectivity increases to approximately 4.3 – this corresponds to a relative increase of about 43%. For the H2 / CH4 ratio, the selectivity increases from 5.0 (25 °C) to approximately 9.1. (0-5 °C), i.e., by about 82%. The selectivities for other polymer membranes show very similar values ​​and have the same preferred operating temperature ranges.

[0074] The device may, for example, include a heating element configured to heat the biogas stream from which hydrogen is extracted through the separation membrane so that it has a target temperature when it hits the feed side of the separation membrane, with the heating element operating exclusively by means of process heat and without the use of additional primary energy.

[0075] In particular, the heating element can include a heat exchanger that, for example, transfers the heat from gas compressors of a CO₂ plant. z -uses a liquefaction plant.

[0076] The device can, for example, include a pressure regulator configured to control the pressure of the biogas stream from which the hydrogen is extracted through the separation membrane, such that this biogas stream has a pressure of at most 40 bar absolute on the feed side of the separation membrane, in particular at most 25 bar absolute, preferably 2 bar to 25 bar absolute, in particular 16 to 20 bar absolute, in particular at most 18 bar absolute.

[0077] According to some examples of the invention, the pressure on the feed side of the separation membrane corresponds to the pressure of a residual gas stream of non-condensable gases originating from the reboiler of a carbon dioxide liquefaction plant.

[0078] The gas mixture could in particular be a gas mixture of an LCO. z -process, in particular the non-condensable residual stream from a reboiler of a carbon dioxide liquefaction plant, which has an LCO z -process, i.e., a process for the liquefaction of CO Z . At the LCO z The process can particularly involve a bio-LCO. z - process, i.e., to create an LCO z -Process for the liquefaction of biogas. From the non-condensable residual stream of the reboiler, the CO₂ is extracted. z -The liquefaction plant can then selectively separate hydrogen for further material or energy recovery.

[0079] In the case of an "LCO" Z The "process" refers to a process for the liquefaction of CO₂. Z (e.g., after separation from flue gas or biogas) to make it usable for purposes such as transport or storage. In this process, CO₂ is removed. ZThe gas is brought to temperatures below approximately -20 °C and pressures above 15 bar. The reboiler is the boiling vessel of a rectification column. The reboiler stream refers to the gas stream exiting the reboiler, typically rich in lighter substances. Components such as hydrogen, methane, or nitrogen. The non-condensable residual stream of a CO₂ z The liquefaction plant is also referred to as "NCG stream" - "Non-Condensable Gases". It mostly comprises the gases H z , CH4, N z , O z In the LCO z NCGs are not liquefied during the process because they remain gaseous under the given temperature / pressure conditions. The NCG stream is therefore the gaseous fraction that remains after the separation and liquefaction of CO. Z is disconnected. The "reboiler NCG current of the LCO" z "Process" thus refers to a gas stream that occurs during the liquefaction of CO ZThis residue remains because it rises in the column's reboiler. It typically contains residual volatile components and non-condensable gases (NCGs). It is mostly CO. z -low and usually contains hydrogen, methane, nitrogen or oxygen.

[0080] According to some embodiments of the invention, the device comprises a pressure regulator on the permeate side of the separation membrane, wherein the device is configured to generate a partial pressure differential across the separation membrane, the pressure on the permeate side of the separation membrane being regulated by the pressure regulator on the permeate side. The pressure regulator may, for example, be or comprise a pressure regulating valve.

[0081] According to some examples of the invention, the partial pressure difference Ap_H is z at least 2 bar between the feed and permeate sides of the separation membrane.

[0082] According to some embodiments of the invention, the device includes a sensor for the hydrogen concentration in at least one of the biogas streams and is configured to receive a measured hydrogen concentration from the sensor and use it to control the pressure regulator on the permeate side of the separation membrane. This pressure is used to adjust the pressure on the permeate side of the membrane in order to regulate the hydrogen concentration in the permeate as a function of the measured hydrogen concentration. The regulation of the transmembrane pressure can be achieved, for example, by comparing a measured hydrogen concentration with a setpoint and increasing, maintaining, or decreasing the transmembrane pressure depending on the difference between the measured hydrogen concentration and the setpoint.

[0083] This can have the advantage of allowing adjustment of partial pressure differences across the membrane. This makes it possible to react to fluctuations in hydrogen concentration. Fluctuations in hydrogen concentration in biogas streams often occur when there are changes in the composition of the feedstock. Fermentation of degraded organic material and / or in the composition of microorganisms and / or the process conditions of fermentation change something.

[0084] The separation membrane can be one of several parallel-oriented separation membranes within a membrane module. For example, the multiple membranes can be designed as a separate, possibly retrofittable, separation stage, also referred to as a "membrane module".

[0085] Due to the modular and preferably energy-independent / neutral operation of the membrane module according to examples of the invention, the membrane module can be used both in new system design and for retrofitting existing systems. According to examples of the membrane module, no process switching or additional process stages are required. Rather, in some examples, the existing flow, temperature, and pressure conditions can be utilized. In systems where, for example, the length of the pipeline or other factors result in temperature or pressure conditions that deviate too much from the target temperatures for hydrogen separation, the integration of additional temperature and / or pressure regulation elements can ensure that hydrogen separation can be carried out reliably and efficiently.

[0086] For example, the retrofittable module can include one or more separation membranes, a heating element that enables temperature control of the membrane, and an associated temperature controller. Optionally, the module can also have its own pressure regulator on the permeate side of the separation membrane. These components can preferably all be integrated together in a single step into an existing carbon dioxide liquefaction plant. The membrane module in question is therefore particularly suitable for integration into existing or new gas processing plants where biogas is converted into marketable products through pressure, cooling, and gas separation.

[0087] For example, the device may include or be operationally coupled to a carbon dioxide liquefaction plant. The carbon dioxide liquefaction plant may be configured to separate a carbon dioxide-enriched gas mixture obtained from a gas conditioner into a gas mixture fraction to be used for the production of liquid carbon dioxide and the non-condensable residual gas stream. The device may be configured to check whether the gas mixture fraction has a hydrogen content of <0.1 vol.%, and only if this is the case, to proceed with the production of liquid carbon dioxide. The gas mixture fraction is used for the liquefaction of CO2. If this is not the case, the gas mixture fraction is further processed and optionally treated as an additional non-compressible residual gas stream, and the separation membrane is supplied with this additional non-compressible residual gas stream.

[0088] Device according to one of the preceding claims, wherein the device is configured to feed the retentate stream of the separation membrane back to a fermentation process which is the source of the biogas streams, and / or to a gas processor for the biogas of the fermentation process. For example, the retentate can be fed continuously and / or iteratively to the fermentation process or the gas conditioner until a termination criterion is met. The termination criterion can be, for example, one of the following: the hydrogen content in the retentate is below a limit value, wherein the limit value is in particular below 10 ppm, in particular below 1 ppm, especially 0.1 ppm; or a predefined minimum proportion of the hydrogen initially contained in the gas mixture (upon first exposure of the separation membrane) has been removed, wherein the predefined minimum proportion is in particular at least 80 vol%, in particular at least 90 vol% of the initial hydrogen content; or a predefined CO2 purity level in the retentate is achieved, wherein the predefined purity level is in particular at least 98 vol%, in particular at least 99.0 vol%, and in particular at least 99.9 vol%.

[0090] Recycling the retentate back into the biogas processing process can have the advantage of increasing the CO2 product quality. Furthermore, it reduces explosion risks associated with H2 / O2 mixtures, which can occur during CO2 liquefaction, storage, and transport of liquid CO2. In some cases, the hydrogen concentration in the process stream processed by a carbon dioxide liquefaction plant is reduced to below the detection limit of gas chromatography.

[0091] The detection limit of hydrogen in gas mixtures depends strongly on the measurement method. For gas chromatography, the detection limit is approximately 0.1–1 ppm (parts per million); for mass spectrometry, it is < 0.1 ppm.

[0092] The retentate of the separation membrane can, for example, have the following composition: 20-99% by volume carbon dioxide, - 0.1 - 70 vol. -% methane, 0.1-10.0 vol.% oxygen, and - 0.1— 5.0 Vol. -% H2.

[0093] In particular, the retentate may have the following composition: 70-80% carbon dioxide, 15-18% methane, 7-10% oxygen and 0.2-0.4% hydrogen.

[0094] Optionally, the retentate may contain other gases in some cases, e.g. hydrogen sulfide H2S: 0.1-500 ppm, nitrogen (N2) 0.1-10 vol%, whereby the respective concentrations may vary depending on the composition of the starting gas and the selected operating conditions of the plant.

[0095] For example, the separation membrane can have a selectivity a_{H2 / CO2} of at least 3, in particular at least 5.

[0096] In some examples, the membrane has an area between 0.5 m² 2 and 10 m 2 However, given the rapid developments in the field of membrane technologies, even smaller areas may be sufficient in the future.

[0097] According to some examples, the device includes a membrane module with several parallel separation membranes, wherein the separation membrane is one of the several separation membranes.

[0098] The production of the hydrogen-enriched permeate of the separation membrane and the hydrogen-reduced retentate of the separation membrane can be carried out, in particular, without the use of additional primary energy to heat the biogas stream directed to the feed side of the separation mixture.

[0099] According to some implementation examples, the device is configured to direct the permeate from the separation membrane to a drain and / or disposal. For example, the permeate can be released into the atmosphere or used for energy recovery, e.g., by combustion in a district heating plant. It is also possible to flare the permeate and the flammable gases it contains. Another possible use is to further concentrate or purify the hydrogen in the permeate and use it as a raw material. Direct material use of the hydrogen in the gas mixture that feeds the separation membrane is also possible. Given the significantly lower hydrogen concentration, this would hardly be technically possible or economically viable.

[0100] According to examples of the invention, the device is configured to return the retentate of the separation membrane to a biogas gas processing process used for the liquefaction of carbon dioxide and / or the liquefaction of methane.

[0101] According to examples of the invention, the device comprises a carbon dioxide liquefaction plant or is operationally coupled to one. Optionally, the device can include a gas conditioner for separating biogas into a carbon dioxide-enriched gas mixture and a methane-enriched gas mixture, or be operationally coupled to one. The carbon dioxide liquefaction plant is configured to liquefy a methane-poor, carbon dioxide-rich gas mixture produced from the biogas by a gas conditioner, with the non-liquefied portion of this gas mixture produced by the gas conditioner forming a non-condensable residual gas stream from the carbon dioxide liquefaction plant. This residual gas stream from the carbon dioxide liquefaction plant is used as the biogas stream with which the separation membrane is fed, and from which the separation membrane removes the hydrogen.

[0102] According to other examples, the device is a membrane module or a plant for processing biogas.

[0103] In another aspect, the invention relates to a method for separating hydrogen (H2) from biogas streams in biogas plants to optimize liquefaction processes of methane (CH4) and / or carbon dioxide (CO2). The method comprises: using a separation membrane having different permeances of hydrogen, carbon dioxide, and methane (H4) to selectively remove hydrogen from a biogas stream containing hydrogen, carbon dioxide, and methane, and subsequently maximizing the purity of the methane and carbon dioxide.

[0104] The separation membrane can, for example, be configured to allow hydrogen to permeate more rapidly, despite its affinity for permeating carbon dioxide, while largely retaining carbon dioxide and methane.

[0105] For example, the process can be used to provide the separated gases methane and carbon dioxide in a purity suitable for marketing and to significantly reduce the proportion of non-condensable gases.

[0106] The separation membrane can be integrated, in particular, in an additional module after the stripper-reboiler stage of a carbon dioxide liquefaction plant.

[0107] The method can further comprise, according to examples of the invention: integration of an additional module after the stripper-reboiler stage of a CC liquefaction plant, wherein the additional module contains the separation membrane.

[0108] For example, the procedure may also include: Provision of biogas, which is produced during a fermentation process and typically contains small amounts of H2, The biogas undergoes an initial separation of the two gases methane and carbon dioxide before passing through the separation membrane.

[0109] According to examples of the invention, the process can further comprise: targeted separation of the hydrogen content by the separation membrane; and reuse of a total mass flow typically consisting of 70-80% CO2, 15-18% CH4, 7-10% O2 and 0.2-0.4% H2.

[0110] For example, the non-condensable gases, which usually have to be thermally utilized, can be significantly reduced by separating the hydrogen, which can lead to an increase in efficiency and a significant reduction in operating costs for the entire plant system.

[0111] In some examples, the process involves reintroducing the gases remaining in the retentate after their separation into the process, with carbon dioxide and methane passing through the process again and oxygen being consumed in the fermentation or adsorbed with hydrogen sulfide, while hydrogen does not accumulate adversely.

[0112] The use of the separation membrane to remove the hydrogen can, for example, involve exposing the separation membrane to one of the biogas streams, which includes at least hydrogen (H2), carbon dioxide (CO2) and methane (CH4), so that hydrogen preferentially permeates the membrane, thereby producing a hydrogen-enriched permeate and a hydrogen-reduced retentate.

[0113] For example, the biogas stream from which hydrogen is extracted through the separation membrane is the non-condensable residual gas stream of a CO2 liquefaction plant.

[0114] This can be advantageous because the feed side of the separation membrane often has a pressure in the range of 10–20 bar absolute, particularly 16–18 bar absolute, and this existing pressure can be used directly to pressurize the gas mixture to the membrane's feed side at suitable pressure conditions. In this case, no additional energy is required to generate the necessary pressure on the membrane's feed side. If the pressure of the non-condensable residual gas stream from a CO2 liquefaction plant is outside the desired range, either a certain loss of efficiency in hydrogen separation can be accepted, or the desired pressure on the membrane's feed side can be actively generated.However, the inventor has observed that, as a rule, the existing pressure conditions in the non-condensable residual gas stream of a CO2 liquefaction plant are already suitable as they are to effectively separate hydrogen into the permeate when the separation membrane is exposed to this gas stream.

[0115] Examples of the invention specifically utilize the thermal and hydraulic conditions of the CO2 condensate system (e.g., heat exchangers for the use of process heat, use of the pressure of the NCG stream) to achieve selective hydrogen permeation without additional primary energy consumption.

[0116] The process can also include, for example: integration of the separation membrane within the residual gas stream of a CO2 liquefaction plant during or after the construction of the CO2 liquefaction plant.

[0117] The process can, for example, further include: controlling a heating element in such a way that the biogas stream from which hydrogen is extracted through the separation membrane when it hits the feed side of the separation membrane is heated to a target temperature.

[0118] The target temperature can in particular be a temperature in a temperature range of 0°C to 45°C, preferably 0°C to 25°C, preferably 0°C to 5°C.

[0119] The heating element can, for example, be a heating element that operates exclusively using process heat and without the use of additional primary energy. In particular, the heating element can include a heat exchanger that utilizes the heat from gas compressors of a CO2 liquefaction plant.

[0120] The method can further include, for example, controlling a pressure regulator such that the pressure of the biogas stream from which the hydrogen is extracted through the separation membrane has a maximum pressure of 40 bar absolute, in particular a maximum pressure of 25 bar absolute, preferably 2 bar to 25 bar absolute, in particular 16 to 20 bar absolute, in particular a maximum pressure of 18 bar absolute, in some examples 2 - 16 bar absolute.

[0121] The method may, for example, involve using a reboiler pressure regulator from a CO2 liquefaction plant as the pressure regulator to control the pressure on the feed side of the separation membrane. In particular, the method may also involve integrating the separation membrane into a degassing stage of the CO2 liquefaction plant that includes the reboiler.

[0122] In other examples, the method involves using a pressure regulator contained in a membrane module containing the separation membrane, in addition to a reboiler pressure regulator of a reboiler of a CO2 liquefaction plant into which the separation membrane is integrated or coupled, to set the pressure on the feed side of the separation membrane to a setpoint pressure.

[0123] The separation membrane can be integrated, in particular, into a line for transporting the non-condensable residual gas stream from the CO2 liquefaction plant. The line can be located inside or outside a degassing stage of the CO2 liquefaction plant. Preferably, the method includes positioning the separation membrane within the line based on the prevailing temperature and pressure conditions in the line such that the energy required to set a target temperature and / or pressure on the feed side of the separation membrane for hydrogen removal is minimized.

[0124] The method can further include, for example: controlling a pressure regulator on the permeate side of the separation membrane such that a partial pressure difference is established across the separation membrane, wherein the pressure on the permeate side of the separation membrane is controlled by the pressure regulator on the permeate side, wherein in particular the partial pressure difference Ap_H z The pressure between the feed and permeate sides of the separation membrane must be at least 2 bar.

[0125] The method may, for example, further include: receiving a hydrogen concentration measured by a sensor in at least one of the biogas streams; and using the received hydrogen concentration to control a pressure regulating valve on the permeate side of the separation membrane to adjust the pressure on the permeate side of the separation membrane in order to adjust the concentration of hydrogen in the permeate depending on the measured hydrogen concentration.

[0126] In another aspect, the invention relates to a method for the selective separation of hydrogen (H₂). z ) from a gas mixture (410) produced during the processing of biogas, wherein the gas mixture contains at least hydrogen (H z ), carbon dioxide (CO₂) Z The process involves the application of the gas mixture to at least one separation membrane, wherein the separation membrane has a higher permeability for hydrogen than for carbon dioxide and methane, such that hydrogen preferentially permeates the separation membrane, thereby producing a hydrogen-enriched permeate (418) and a hydrogen-reduced retentate. The gas mixture can, for example, be the biogas stream described above. For instance, the gas mixture can be derived from the non-condensable residual gas stream of a CO₂ plant. Z- originate from a liquefaction plant. At least one separation membrane can be located, for example, within the residual gas stream of a CO₂ plant. z -Liqueflux plant.

[0127] According to examples of the invention, the at least one separation membrane is exposed to the gas mixture at a temperature of 0°C to 45°C, preferably 0°C to 25°C, preferably 0°C to 5°C.

[0128] According to examples of the invention, the exposure of the at least one separation membrane to the gas mixture comprises increasing the temperature of the gas mixture before the separation membrane is exposed to the gas mixture, exclusively by means of TI Process heat and without the use of additional primary energy, in particular by means of a Heat exchanger that utilizes the heat from gas compressors of a CO2 liquefaction plant.

[0129] In particular, the application of the gas mixture to the at least one separation membrane can take place at a pressure on the feed side of the at least one separation membrane of a maximum of 40 bar absolute, in particular of a maximum of 25 bar absolute, preferably 2 bar to 25 bar absolute, in particular 16 to 20 bar absolute, in particular a maximum of 18 bar absolute, in some examples 2 - 16 bar absolute.

[0130] The method may, for example, involve using a reboiler pressure regulator from a CO2 liquefaction plant as the pressure regulator to control the pressure on the feed side of the separation membrane. In particular, the method may also involve integrating the separation membrane into a degassing stage of the CO2 liquefaction plant that includes the reboiler.

[0131] In other examples, the method involves using a pressure regulator contained in a membrane module containing the separation membrane, in addition to a reboiler pressure regulator of a reboiler of a CO2 liquefaction plant into which the separation membrane is integrated or coupled, to set the pressure on the feed side of the separation membrane to a setpoint pressure.

[0132] The separation membrane can be integrated, in particular, into a line for transporting the non-condensable residual gas stream from the CO2 liquefaction plant. The line can be located inside or outside a degassing stage of the CO2 liquefaction plant. Preferably, the method includes positioning the separation membrane within the line based on the prevailing temperature and pressure conditions in the line such that the energy required to set a target temperature and / or pressure on the feed side of the separation membrane for hydrogen removal is minimized.

[0133]

[0134] For example, the gas mixture can be applied to at least one separation membrane at a pressure determined on the feed side of the separation membrane by the pressure of a reboiler residual gas stream of non-condensable gases from a carbon dioxide liquefaction plant.

[0135] According to some examples, the gas mixture is applied to at least one separation membrane at a transmembrane pressure difference that is regulated on the permeate side by a pressure regulator on the permeate side of the separation membrane.

[0136] According to some examples, the procedure includes: Measuring the hydrogen concentration in biogas, or in the gas mixture, or in another gas mixture that arises in an intermediate processing step of the biogas processing into the gas mixture; and Control of the pressure regulator on the permeate side of at least one separation membrane to adjust the pressure on the permeate side of the separation membrane in order to adjust the concentration of hydrogen in the permeate depending on the measured hydrogen concentration.

[0137] This can have the advantage that partial pressure differences across the separation membrane can be adjusted with fine granularity. This makes it possible to respond to fluctuations in hydrogen concentration. The separation membrane can be at least one, or it can be multiple. For example, the multiple separation membranes can be configured as a separation stage with several parallel membranes.

[0138] According to some examples, the carbon dioxide liquefaction plant can separate a carbon dioxide-enriched gas mixture obtained from a gas processor into a gas mixture fraction to be used for the production of liquid carbon dioxide and the non-condensable residual gas stream. The process can further include: checking whether the gas mixture fraction has a hydrogen content of <0.1 vol.%; only if this is the case: using the gas mixture fraction for the liquefaction of CO2. If this is not the case: using the gas mixture fraction as a further non-compressible residual gas stream, and applying this further non-compressible residual gas stream to at least one separation membrane.

[0139] The retentate stream from at least one separation membrane can then be fed back into a fermentation process, which is the source of the biogas, and / or a biogas processor. For example, the retentate can be fed continuously and / or iteratively to the fermentation process or the biogas processor until a The termination criterion is met. For example, the termination criterion can be one of the following: The hydrogen content in the retentate is below a limit value, wherein the limit value is in particular below 10 ppm, in particular below 1 ppm, in particular 0.1 ppm; or: a predefined minimum proportion of the hydrogen initially contained in the gas mixture has been removed, wherein the predefined minimum proportion is in particular at least 80 vol%, in particular at least 90 vol%; or: a predefined CO2 purity level in the retentate is achieved, wherein the predefined purity level is in particular a value of at least 98 vol%, in particular at least 99.0 vol%, and in particular at least 99.9 vol%.

[0140] Repeated recirculation of the retentate into the process stream and repeated exposure of the separation membrane to remove hydrogen can improve CO2 product quality and reduce explosion risks. Explosion risks can arise during CO2 liquefaction or during the storage and transport of liquid CO2, as, for example, small leaks can lead to the escape of hydrogen from pipes and containers, potentially resulting in the formation of H2 / O2 mixtures.

[0141] The pressure applied to the separation membrane can be carried out, for example, in such a way that the partial pressure difference Ap_H2 between the feed and permeate side of at least one separation membrane is at least 2 bar.

[0142] The retentate produced by exposing at least one separation membrane to the gas mixture can, for example, have the following composition: 20-99% by volume carbon dioxide, - 0.1 - 70 vol. -% methane, 0.1-10.0 vol.% oxygen, and - 0.1-5.0 Vol. -% H2,

[0143] In particular, the retentate can have the following composition: 70-80% carbon dioxide, 15-18% methane, 7-10% oxygen and 0.2-0.4% hydrogen.

[0144] Optionally, other gases may be included, e.g.: H2S: 0.1-500 ppm, N2: 0.1-10 vol.%, whereby the respective concentrations may vary depending on the composition of the starting gas and the selected operating conditions of the fermentation plant.

[0145] The at least one separation membrane can, for example, have a selectivity a_{H2 / CO2} of at least 3, in particular at least 5.

[0146] According to some examples, the separation membrane or the several parallel separation membranes have an area of ​​between 0.5 m² 2 and 10 m 2 on.

[0147] The application of the at least one separation membrane and the production of the hydrogen-enriched permeate and the hydrogen-reduced retentate can be carried out in particular without the use of additional primary energy to heat the gas mixture.

[0148] The permeate produced by the gas mixture crossing the separation membrane can be, for example, discharged and / or disposed of. Specifically, the permeate can be released into the atmosphere or used for thermal or material recovery. In some cases, the hydrogen in the permeate is used for material purposes, for example, by further concentrating the hydrogen and possibly liquefying and storing it.

[0149] The retentate can, for example, be recycled into a biogas upgrading process, which serves to liquefy carbon dioxide and / or methane.

[0150] In another aspect, the invention relates to a device for separating hydrogen (H2) from a gas mixture (410) produced during the processing of biogas (402), wherein the gas mixture includes at least hydrogen (H2), carbon dioxide (CO2) and methane (CH4), comprising at least one separation membrane (216, 318) having different permeances of H2, CO2 and CH4 and configured to selectively remove H2 from the gas mixture and maximize the purity of CH4 and CO2.

[0151] The gas mixture could, for example, be a biogas stream. This gas mixture could be a byproduct of biogas processing in a biogas plant. Hydrogen separation can, for example, be used to optimize the liquefaction processes of methane (CH4) and carbon dioxide (CO2). The separation membrane could, for example, be a specialized membrane based on the different permeances of H2, CO2, and CH4, in order to selectively remove H2 and subsequently maximize the purity of CH4 and CO2.

[0152] The separation membrane can, in particular, be a membrane suitable for separating hydrogen from other components of the gas mixture or for removing it (at least partially) from the gas mixture. Separation or removal can, for example, be understood as the complete or near-complete removal of hydrogen from the gas mixture after a single exposure of the separation membrane to the gas mixture. However, separation or removal can also refer to a clearly measurable reduction of the hydrogen content in the gas mixture, i.e., a reduction of the volume fraction of hydrogen by at least 5 vol.%. Preferably, the separation membrane is designed to remove at least 50 vol.% of the hydrogen from the gas mixture with which the membrane is exposed.

[0153] At least one separation membrane can be configured to allow hydrogen to permeate while largely retaining carbon dioxide and methane. The separation membrane can therefore exhibit some permeance for all three gases, but the permeance for hydrogen should be higher than that for methane and carbon dioxide.

[0154] The separation membrane can be configured, for example, so that despite its affinity to permeate CO2 more quickly, it allows (e.g., especially) H2 to permeate significantly, while CO2 and CH4 are largely retained, i.e., remain in the retentate.

[0155] The device can be, for example, a CO2 liquefaction plant or include a CO2 liquefaction plant. The at least one separation membrane can be integrated downstream of the stripper-reboiler stage of a CO2 liquefaction plant (e.g., in an additional stage or membrane module). The device can include a carbon dioxide liquefaction plant or be operationally coupled to one. The carbon dioxide liquefaction plant can be configured to liquefy a methane-poor, carbon dioxide-rich gas mixture produced from biogas by a gas processor, with the non-liquefied portion of this gas mixture being the residual gas stream from the carbon dioxide liquefaction plant. The residual gas stream from the carbon dioxide liquefaction plant is the gas mixture from which the at least one separation membrane removes the hydrogen.For example, the biogas produced during the fermentation process, which typically contains small amounts of H2, is first subjected to an initial separation of the binary gas mixture CH4 / CO2 before passing through the separation membrane.

[0156] At least one separation membrane can be configured, for example, to allow hydrogen to permeate when exposed to the gas mixture, resulting in a hydrogen-enriched permeate, while carbon dioxide and methane are largely retained, producing a hydrogen-reduced retentate. The retentate produced by the separation membrane consists primarily of 70-80% carbon dioxide, 15-18% methane, 7-10% oxygen, and 0.2-0.4% hydrogen.

[0157] For example, the retentate is a gas mixture whose total mass flow is to be reused in the biogas processing process from which it originated. Typically, the total mass flow to be reused consists of 70-80% CO2, 15-18% CH4, 7-10% O2, and 0.2-0.4% H2. For instance, the H2 content is selectively separated at the appropriate concentration by at least one separation membrane. The device can be configured, for example, to reduce non-condensable gases by separating the H2 from the gas mixture. The device can be configured to significantly reduce non-condensable gases, which would normally require thermal treatment, by separating the H2. This can lead to increased efficiency and significant reductions in the operating costs of the entire plant system.

[0158] The device can also be configured to feed the gases remaining in the retentate of the at least one separation membrane back into a fermenter or gas processor of a biogas plant after their separation.

[0159] The at least one separation membrane can, in particular, have a higher permeability for hydrogen than for carbon dioxide and methane, so that hydrogen preferentially permeates the at least one separation membrane and a hydrogen-enriched permeate and a hydrogen-reduced retentate are produced by the separation membrane.

[0160] The device can, for example, include a gas line for receiving the gas mixture (e.g., from a reboiler of a CO₂ liquefaction plant). The device can further include a module comprising at least one separation membrane. This module is connected to the gas line and configured to supply the at least one separation membrane with the gas mixture received via the gas line. The device can also include a temperature controller configured to adjust the temperature of the received gas mixture so that the feed side of the separation membrane is supplied at a setpoint temperature. The setpoint temperature can, for example, be between 0°C and 45°C. The temperature range is preferably 0°C to 25°C, preferably 0°C to 5°C. The temperature controller preferably uses process heat to adjust the temperature of the gas mixture without requiring additional primary energy. The temperature controller may, in particular, include a heat exchanger.

[0161] Additionally or alternatively, the device can include a pressure regulator, which is designed, for example, as a pressure-maintaining valve in the reboiler stage of the CO₂ liquefaction plant and which is configured to adjust the pressure of the received gas mixture on the feed side of the at least one separation membrane. This pressure is, in particular, a maximum absolute pressure of 40 bar, more specifically a maximum absolute pressure of 25 bar, preferably 2 bar to 25 bar, more specifically 16 bar to 20 bar, more specifically a maximum absolute pressure of 18 bar, and in some examples, 2 to 16 bar.

[0162] According to some examples, the device may include a pressure regulator that controls the pressure on the permeate side of the separation membrane.

[0163] The at least one separation membrane can be positioned in the non-condensable residual gas stream of a carbon dioxide liquefaction plant. The at least one separation membrane can be installed during or after the installation of the device. For example, the module with the at least one separation membrane can be designed as a retrofittable membrane module.

[0164] The device may, for example, include one or more of the following elements or be operationally coupled to them: A fermenter for the production of biogas; and / or a gas processor, wherein the gas processor is configured to separate biogas produced during a fermentation process, which typically contains small amounts of H2, into a first, methane-rich and carbon dioxide-poor gas mixture and a second, methane-poor and carbon dioxide-rich gas mixture; and / or a carbon dioxide liquefaction plant configured to liquefy the second, methane-poor and carbon dioxide-rich gas mixture, wherein the non-liquefied portion is produced as a non-condensable residual gas stream from the carbon dioxide liquefaction plant; the residual gas stream from the carbon dioxide liquefaction plant may, for example, be the gas mixture with which the separation membrane is exposed to remove the hydrogen.

[0165] Here, "biogas flow" refers, for example, to a flow of a gas mixture containing at least methane, carbon dioxide, and hydrogen, which is either biogas or is produced during biogas processing (e.g., for the extraction or liquefaction of methane and / or carbon dioxide). For instance, the biogas flow could be the non-condensable residual gas flow from a reboiler of a carbon dioxide liquefaction plant.

[0166] In this context, a "gas mixture" refers to a mixture of gases that includes at least carbon dioxide and methane, and initially also hydrogen, and may optionally contain other components such as oxygen, nitrogen, and other gases. The exact composition can vary depending on the application.

[0167] "Biogas" can, for example, be a gas mixture produced by the microbial decomposition of organic substances under anaerobic conditions (i.e., without oxygen). This process is called anaerobic digestion (fermentation). Biogas typically contains methane (CH4), typically around 50-70% by volume, and carbon dioxide (CO2), typically... Volume fraction approx. 30-50%, water vapor (H Z O) and optionally also various other gases present in trace amounts, typically less than 1% by volume, e.g., hydrogen, hydrogen sulfide, oxygen, and / or nitrogen. Biogas can originate, for example, from a fermenter, a landfill, an anaerobic wastewater treatment plant, an orthotunnel (a reactor-geometric unit with optimized flow in which microorganisms work particularly efficiently), or other sources.

[0168] The biogas in question is primarily biogas produced under normal biogas fermentation conditions (methane fermentation), as distinct from dark-field fermentation: the main fermentation products found in the resulting biogas are methane (CH4) and carbon dioxide (CO2), and not organic acids. Methanogens (archaea) typically play a central role in this fermentation process. The hydrogen content in biogas from normal biogas fermentation is typically below 5% by volume, usually below 1% by volume, and often in the range of 0.1–0.5% by volume.

[0169] A "separation membrane," also called a "membrane," is understood here to be a selectively permeable layer of material that preferentially allows certain gas components to pass through, thus causing a relative change in the gas component concentrations (and therefore separation). For example, a membrane is arranged within a device such that when the feed side of the membrane is exposed to a gas mixture, a Permeate and a retentate are formed, with the components that can preferentially pass through the membrane being enriched in the permeate compared to their original concentrations in the gas mixture and reduced in the retentate.

[0170] In this context, a "polymer membrane" is understood to be a selectively permeable layer of polymeric material that preferentially allows certain gas components to pass through.

[0171] In this context, a "permeate" refers to the gas stream that permeates the polymer membrane. In the claimed process, it is enriched with hydrogen and contains reduced proportions of CO2 and CH4 compared to the original gas mixture.

[0172] In this context, a "retentate" refers to the gas flow that is retained by the polymer membrane.

[0173] The term “non-condensable gases (NCG)” refers here to components of a gas mixture that do not transition into the liquid phase under the given temperature and pressure conditions.

[0174] A "plant" can be, for example, a technical facility whose components are jointly controlled by one or more control devices in such a way as to achieve a specific goal, e.g., the liquefaction of CO2 and / or methane. This can be achieved, for example, by ensuring that certain boundary conditions are met, such as a minimum purity of the product, a maximum permissible energy consumption of the plant, etc.

[0175] In this context, a "CO2 liquefaction plant" refers to a technical facility for the separation, purification, drying and subsequent liquefaction of carbon dioxide.

[0176] The term "absolute pressure" refers to the total pressure including atmospheric pressure. The system can, for example, be designed so that the membrane process operates at pressures up to, but not above, a predefined maximum pressure.

[0177] The temperature limit for contacting the polymer membrane with the gas mixture refers to the gas temperature at the point of entry into the polymer membrane. Preferably, no external heating or cooling elements are used, provided the ambient conditions permit.

[0178] The term "selectivity a_{H2 / CO2}" refers to the ratio of the permeabilities of hydrogen to carbon dioxide through the polymer membrane. A selectivity of >5 means that hydrogen permeates the separation membrane at least five times faster than CO2.

[0179] Here, a "module" is understood to be a structural and / or functional unit that integrates, for example, the polymer membrane, chambers, gas lines, and, if applicable, control and monitoring devices. It can be designed, for example, as a retrofit unit for existing carbon dioxide liquefaction plants. The term "membrane module" is to be understood as meaning that the membrane module can be provided as a structural unit and integrated into an existing system, but this is not mandatory. The module can also be composed of several separate components (separation membrane, possibly a heating element and pressure regulator, pressure and / or temperature sensors, lines and / or shut-off valves, etc.) that were or are installed successively and form a functional unit after installation.

[0180] An "iterative process" is understood here to be a process in which a gas separation step is applied multiple times until a specific target (e.g., defined H2 content in the retentate) is achieved.

[0181] A "reboiler" (German: "Sumpferhitzer") is a heat exchanger used in distillation columns to re-evaporate the liquid mixture collected at the bottom of the column. The aim is to retain the less volatile components and feed the more volatile ones back into the distillation column.

[0182] A reboiler stream refers to the liquid or vapor stream exiting the reboiler - typically a return stream to the column or a product stream, depending on the system design.

[0183] An "NCG stream" is a gas stream discharged from a process section and consisting primarily of components that are not condensable within that section. Non-condensable gases (NCGs) are gaseous components that do not condense under the given conditions, such as nitrogen (N₂), oxygen (O₂), hydrogen (H₂), and carbon monoxide (CO), depending on the temperature and pressure. They remain in the gaseous state even if other components condense or liquefy.

[0184] A reboiler / NCG stream is a combined stream containing both reboiler vapor and non-condensable gases – for example, in CO2 capture plants with solvent regeneration. In CO2 scrubbing processes (e.g., with amines), the loaded scrubbing liquid stream is heated in the regenerator (with a reboiler). The resulting reboiler vapor contains CO2 and often also non-condensable gases – this stream is then discharged as a reboiler / NCG stream.

[0185] A "temperature-controlled membrane" is a membrane device in which the temperature near or within the membrane structure is controlled and maintained within a predetermined temperature range. This can be achieved actively through integrated heating / cooling elements or passively through thermostatic control to ensure optimal separation or permeation properties.

[0186] An “LCO2” process is understood to be a technical procedure for the production, purification, liquefaction and, if applicable, use or storage of carbon dioxide.

[0187] A "bio-LCO2" process is understood to be a technical procedure for the production, purification, liquefaction, and, if applicable, use or storage of carbon dioxide from biogenic sources. Biogenic sources include, for example, biogas upgrading (e.g., after anaerobic digestion), fermentation processes in the food or biotechnology industries (e.g., breweries, bioethanol production), biomass gasification, or pyrolysis.

[0188] It is understood that one or more of the examples described here can be combined with each other, as long as the examples do not exclude each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0189] The following examples are explained in more detail using the drawings. They show:

[0190] Fig. 1 shows a block diagram of a biogas processing device before the separation membrane was integrated;

[0191] Fig. 2 shows a block diagram of a device according to Figure 1 after the separation membrane has been integrated.

[0192] Fig. 3 shows a block diagram of a module for removing hydrogen from a non-condensable residual stream according to an example of the invention.

[0193] Fig. 4 shows the block diagram according to Figure 2, supplemented by exemplary Gas mixtures,

[0194] Fig. 5 shows a flowchart of a process for removing hydrogen from a gas mixture according to an example of the invention, and

[0195] Fig. 6 shows a block diagram of a module for removing hydrogen from a non-condensable residual stream according to another example of the invention. DETAILED DESCRIPTION

[0196] Figure 1 shows a block diagram of a device 200 for processing biogas before the separation membrane for hydrogen separation was installed. Figure 2 shows the corresponding system after the separation membrane was installed according to an example of the invention. Figure 4 shows the biogas streams occurring, processed, or generated in the device according to some examples.

[0197] The system and the process carried out in it are described below with reference to the references in Figures 1, 2 and 4.

[0198] The device 200 can, for example, include a plant 206 for the production of liquid biomethane (LNG plant) 408 and a plant 212 for the production of liquid carbon dioxide 412 (CO2 liquefaction plant) from biogas 402. The plant can include or be coupled to a fermenter 202 in which the biogas is produced.

[0199] In the plant shown in Figure 1, the biogas 402 produced in the fermenter is first directed to a gas processor 204. In this processor, the biogas is separated into a methane-enriched gas mixture fraction 406, which is forwarded to the LNG plant 206, and a carbon dioxide-enriched gas mixture fraction 404, which is forwarded to a CC liquefaction plant 212.

[0200] The LNG plant produces liquid methane 408 from the gas mixture fraction 406, which can be stored in an LNG tank. The process can be cyclical, and there can be return lines leading from the LNG plant and / or the LNG tank that feed the components of the processed gases back into the process or the gas processor 204 via a gas recirculation system 210.

[0201] The CO2 liquefaction plant 212 produces liquid carbon dioxide 412 from the gas mixture fraction 404, which can be stored permanently or temporarily in an LCC storage tank. The process can be cyclical, and there can be return lines leading from the CO2 liquefaction plant and / or the LCC tank, which feed the components of the processed gases back into the process or the gas conditioner 204 via a gas recirculation system 218. For example, the recirculation can take place via the fermenter 202, as shown in Figures 1, 2, and 4.

[0202] Preferably, the separation membrane 216, or a membrane module containing this separation membrane, is integrated into the system 200 such that a residual gas stream 410 from the CC liquefaction plant is directed to the feed side of the separation membrane. The separation membrane 216 splits this gas stream into a hydrogen-enriched permeate 418, which can be removed from the process and used, for example, for energy recovery or material recovery, and a hydrogen-reduced retentate 414. The retentate is preferably returned to the process. This can be done, for example, via a line 416a directly into the digester 202 or via a line 416b into the biogas stream coming from the digester 202.

[0203] The gas processor 204 can use different technologies for separating CO2 and methane, and the composition of the gas fractions 404 and 406 can vary depending on the separation efficiency of the technology used. For example, a three-stage membrane separation can be used. This typically results in a carbon dioxide-enriched gas fraction 404 with >99% CO2 and <1% CH4. Other processes, such as two-stage membrane separation or pressure swing adsorption (PSA), have lower separation efficiency and result in a gas fraction 404 with up to 10% methane. Since methane is highly valuable, it should be recovered from the carbon dioxide-enriched gas fraction 404 whenever possible. Releasing such methane-rich exhaust gases into the atmosphere is also undesirable from an environmental and climate protection perspective.

[0204] The CO2-rich gas fraction 404 can be liquefied in a CO2 liquefaction plant 212, as shown in the apparatus 200, wherein the CO2 stream 404 is liquefied by compression and cooling in order to be stored or transported in liquid form 412. In the CO2 liquefaction plant 212, water is removed by condensation and drying to prevent ice formation. A purification stage can be used to remove impurities when high purity is required. A refrigeration cycle can be used for the liquefaction of the CO2.

[0205] In the operation of a CO2 liquefaction plant 212, a gas stream 410 containing non-condensable gases is removed to produce pure liquid CO2 412. This is done, for example, via a stripper column that includes a reboiler, based on the different volatilities of the components. This gas stream 410 typically contains traces of CO2, methane, and hydrogen, and often also nitrogen and / or oxygen. It is usually discharged at an evaporator (reboiler) where CO2 with high purity 412, often exceeding 99.997% purity, is collected.

[0206] In gas processors with three-stage membrane systems, the CO2 stream (404) for liquefaction often consists of >99% CO2. A significant portion of this gas stream (404) is considered non-condensable. A deterioration in CO2 quality (e.g., due to increased methane, nitrogen, or hydrogen content) increases the proportion of non-condensable gases. In two-stage membrane systems, methane slip and the slip of other gases such as hydrogen are considerably higher. The CO2 liquefaction process further increases the methane content in the gas stream intended for CO2 liquefaction, meaning that up to 50% of the incoming gas stream (404) arrives at the CO2 liquefaction plant as non-condensable gas.

[0207] The separation membrane 216 is integrated into the residual gas stream of a reboiler in the CO2 liquefaction plant and optionally equipped with further components for temperature and / or pressure control of the feed stream impinging on the separation membrane, such that the gas stream 410 impinging on the separation membrane is present at a pressure of preferably 2-18 bar absolute, in some examples 2-16 bar absolute, and a temperature of 0-45°C, particularly 0-15°C. This can enable efficient separation of hydrogen, energetic and / or material utilization of hydrogen, and the recovery of methane and / or CO2 from a flue gas stream 410 of biomethane production. The driving force for hydrogen separation at the separation membrane 216 is the partial pressure difference between the feed stream side and the permeate side of the separation membrane.

[0208] The separation membrane 216 can be retrofitted as an additional stage into existing systems 200, i.e., after the system has been erected. Optionally, the separation membrane or membrane module can include further components for fine-tuning pressure and / or temperature conditions, as exemplified in Figure 3.

[0209] The residual gas stream 410 can in some cases have temperatures of -25 °C or lower – typically adapted to the condenser conditions of CO2 liquefaction. In In these cases, raising the temperature to temperatures above 0°C using a heating element can be advantageous to ensure efficient hydrogen separation.

[0210] The hydrogen-enriched permeate stream 418 can be released into the atmosphere, as it contains little methane - or further processed and used, for example, for energy or material purposes.

[0211] The gas mixture 410, with which the separation membrane 212 is exposed, can contain, for example, 10–50 vol% carbon dioxide, 20–60 vol% methane, and less than 10 vol%, e.g., 0.01% to 10%, hydrogen. Preferably, the gas mixture has a temperature within the specified range when it reaches the separation membrane. If the gas mixture does not already have this target temperature or pressure, the membrane module 212 preferably includes appropriate sensors and controllers for adjusting the temperature and / or pressure to the target value.

[0212] For example, the reboiler residual gas stream 410 can have a pressure of 20 bar and be reduced to 16 bar by valves of the membrane module 212 before it reaches the separation membrane. Alternatively, the reboiler residual gas stream 410 can have a temperature of -20°C and be raised to 5°C by a heating element of the membrane module 212 before it reaches the separation membrane.

[0213] By returning the hydrogen-reduced retentate 414 to the process via appropriate gas recirculation lines 416a, 416b, the residual gases (CO2, CH4, O2) still contained therein can be completely or largely recovered for LCO2 liquefaction and LNG production without increasing the hydrogen content in the process. This is preferably achieved without the need for additional primary energy by utilizing the existing pressure and temperature conditions of the gas stream as they are or, at most, by making minor adjustments.

[0214] In one example, the device 200 and the hydrogen deposition method implemented in it are realized as follows:

[0215] CO2-rich residual gas 410 from the stripper-reboiler unit of a CO2 liquefaction plant 212 is passed over a thermostable polyamide membrane 216. The feed pressure, i.e., the pressure of the gas mixture, is 16–20 bar absolute, and the temperature is 15 °C. The membrane area is preferably dimensioned such that at least 75 vol% of the gas entering the separation membrane passes over it. fitting feed gas stream 410 contained H z pass into the permeate stream. Only 25 vol.% remain in the retentate. Since the separation membrane is less permeable to methane and carbon dioxide, the relative ratio of hydrogen to the other gases shifts in favor of hydrogen in the permeate, and in favor of the other gases in the retentate.

[0216] The separation membrane can be used for micro-LNG plants (e.g., 50-150 Nm²). 3 / h biogas input) can be used, but also, with appropriately scaled membrane area, for industrial bioenergy parks with several thousand Nm² 3throughput per hour.

[0217] When the gas mixture comes into contact with the polymer membrane, individual gas components diffuse through a dense, selectively permeable membrane matrix at different rates based on their molecular properties. Gas permeation through non-porous polymer membranes generally occurs via the solubility-diffusion mechanism, also known as the "solution-diffusion model." This means that the gas first dissolves in the separation membrane on the high-pressure side (absorption), then diffuses through the polymer matrix (migration), and finally desorbs on the low-pressure side.

[0218] The permeability P_i of a gas i is defined as the product of the diffusion coefficient DJ and the solubility of this gas SJ in the separation membrane: PJ = DJ • SJ [Unit: mol-m / (m 2 -spa)]

[0219] This value describes how well a gas is transported through a specific membrane material under given pressure and temperature conditions. For typical polymer membranes (e.g., polyamide), the permeability of hydrogen is in the range of 10⁻⁶. 18 up to 10" 16 mol-m / (m 2 -s-Pa), depending on temperature, pressure, polymer structure and humidity.

[0220] The selectivity ai / j} between two gases i and j is given by the ratio of their permeabilities: ai / j} = PJ / PJ = (DJ • S_i) / (DJ • SJ)

[0221] High selectivity means that one gas diffuses through the separation membrane significantly more readily than the other. For hydrogen-containing mixtures, the following ratios are particularly advantageous (typical for polyamide at 20 °C): a_{H2 / CH4} ~ 50-100 a_{H2 / CO2} ~ 5-15

[0222] This means that hydrogen permeates 5 to 15 times faster than CO2 and up to 100 times faster than CH4.

[0223] The permeability of a gas is strongly temperature-dependent and follows an Arrhenius relationship:

[0224] P_i(T) = P_{0, i} • exp(-E_{A,i] / (R • T)) with:

[0225] P_{0,i} =pre-exponential factor [mol-m / (m 2 -s-Pa)]; E_{A, i} = activation energy of permeation [J / mol]; R = universal gas constant ~ 8.314 J / mol-K; T = absolute temperature in Kelvin. Hydrogen has a comparatively high activation energy (approx. 20-30 kJ / mol). This means that its permeability increases disproportionately with temperature. At the same time, at low temperatures, the permeation of CO2 and CH4 decreases more sharply than that of H2.

[0226] Calculation example for H2 through polyamide:

[0227] Po ~ 1 x IO' 13 mol-m / (m 2 -s-Pa) E_A ~ 25,000 J / mol

[0228] T, = 288 K (15 °C) -> P ~ 2.92 x IO' 18 mol-m / (m 2-s-Pa) T2= 298 K (25 °C) -> P ~ 4.15 x IO' 18 mol-m / (m 2 -spa)

[0229] This means that an increase of just 10 K (~10 °C) leads to a permeability increase of approximately 42%. Conversely, temperature-controlled operation in the range of 0-15 °C allows for preferential permeation of H2 while simultaneously minimizing permeation of CO2 / CH4.

[0230] The effective mass flow rate 'm_i' of a gas i through the separation membrane is given by:

[0231] ' m J = A • (P_i / I) • ApJ with:

[0232] A = Membrane area [m²] 2 ]; I = membrane thickness [m]; ApJ = partial pressure difference of gas i across the separation membrane [Pa],

[0233] Example:

[0234] A = l,0 m 2

[0235] I = 100 pm = 1.0 x 10' 4 m

[0236] P_H2(288 K) = 2.92 x IO' 18 mol-m / (m 2 -spa)

[0237] Ap_H2 = 4 bar = 4 x 10 5 Pa

[0238] ' m_H2= 1 • (2.92 x IO' 18 / 1.0 x IO' 4 ) • 4 x IO 5 = 1.17 x 10" 8 mol / s. This corresponds to approximately 4.2 x IO" 4 mol / h per m 2 or approximately 1.0 Nm 3 / h with a membrane module of 1 m 2 Area. With appropriate expansion (e.g. 5 m²) 2 Membrane area) allows H2 currents in the range of 5-10 N 3 / h selectively separate - sufficient for typical reboiler quantities in bio-LCO2 plants.

[0239] Embodiments also utilize the characteristic volume flow ratios in biogas plants. Preferably, a biogas process stream from the biogas processing plant is selected for feeding the separation membrane 216, containing a hydrogen content of 0.2–0.4 vol.% and a carbon dioxide content of approximately 75–80 vol.%. These volume ratios are typically found in the residual gas stream of a reboiler of a CO2 liquefaction plant.

[0240] With a total gas flow in feed gas 410 of a CO2 liquefaction plant with a gas throughput of 100 Nm³ 3 / h (e.g. in a medium-sized LCO2 plant) results in the following H2 mass flow rate according to an example:

[0241] Hz volume fraction: 0.3 vol.%

[0242] H2 volume flow rate: approx. 0.3 Nm 3 / h

[0243] Mass flow (H2 at 0 °C, 1 atm): 0.3 / 22.4 ~ 0.013 mol / s

[0244] Thus, according to examples of the invention, membrane systems with approximately 1-2 m 2 The area is sufficient to separate almost the entire H2 flow.

[0245] The separation efficiency of the separation membrane also depends on the pressure difference across the separation membrane Ap, the temperature T, and the membrane material and its thickness according to the following relationships:

[0246] Pressure difference Ap: a higher pressure difference Ap increases the driving force of hydrogen separation and enables more efficient separation of the hydrogen into the Permeate.

[0247] Temperature T: higher temperatures correlate with higher permeability, but lower selectivity for carbon dioxide.

[0248] Membrane material and thickness: Thinner membranes (I < 100 pm) with high a_{H z / CO Z} are therefore particularly suitable for efficiently separating hydrogen.

[0249] According to examples of the invention, a targeted H z -Separation with efficient separation performance is possible even under mild process conditions (especially P < 18 bar, T < 15 °C).

[0250] An embodiment of the invention is described below, which illustrates the use of the separation membrane and the associated process in the industrial context of a bio-LCO. z - Annex 212 describes the process. Reference is also made to elements in Figures 1, 2, and 4. The biogas plant can process raw biogas 402 from a mesophilic fermentation process. The separation membrane 216 is integrated into this plant according to one embodiment. The raw biogas 402 consists of approximately 52–55 vol% methane and 43–46 vol% CO. Z 0.2–0.3 vol% hydrogen and traces of O₂ z , N z , H ZS, NH3 and siloxanes. After processing using a three-stage membrane plant 204 and subsequent methane liquefaction in an LNG plant 206, a CO₂ remains. z -rich gas stream 404 with the following typical composition: 75.0 vol.% CO Z , 16.2 vol.% CH4, 8.4 vol.% O z , and 0.3 vol.% H z .

[0251] This gas stream is fed into the stripper-reboiler stage of the CO₂ z -Liqueflux plant 212, where non-liquefiable components are to be removed by controlled condensation. The residual gas stream 410, which contains these non-liquefiable components, typically has a pressure level of 15-18 bar (absolute) and a gas temperature of 12-18 °C.

[0252] According to embodiments of the invention, the membrane module 216 for separating the hydrogen is inserted directly into the NCG line, which carries the residual gas stream 410.

[0253] The membrane module comprises, in addition to the separation membrane (which may also include several parallel separation membranes), preferably a pressure-resistant housing, e.g., made of stainless steel, into which the separation membrane(s) are integrated. The separation membrane integrated into the housing can be, for example, a polyamide membrane, such as a spiral-wound membrane or a hollow fiber membrane, depending on the system size.

[0254] The operation is preferably entirely passive, without additional compressors, pumps, or temperature control systems. At the specified location within the NCG pipeline, the temperature and pressure conditions are suitable for the selective separation of hydrogen, as illustrated by the following calculation:

[0255] For a given temperature and pressure difference (feed / permeate '16 / 1 bar), a partial pressure difference Ap_H results. z of approximately 4-5 bar. This results in a pressure of approximately 4-5 bar. z- Mass flow rate m_{H z} from:

[0256] m_{H z} ~ 2.4 x 10“ 7 mol / s per m 2 ; at 2.5 m 2 The membrane area corresponds to approximately 6.0 x 10⁻⁵. 7 mol / s. This in turn corresponds to ~1.3 Nl / h hydrogen, which is >90% of the originally contained H z in the reboiler stream. NI stands for standard liter, i.e., 1 liter volume for gaseous fluids at a temperature of 0°C and 0% relative humidity. Thus, >90% of the hydrogen originally contained in the reboiler stream 410 has passed into the permeate 418. The retentate 414 then contains <0.05 vol% H₂ z By separating the H z The thermal energy from the reboiler electricity, which is otherwise thermally wasted in state-of-the-art technology, is used productively. The CO Z - CH4 yield of the entire plant increases by up to 8-10%.

[0257] Another advantageous aspect is the possibility of additional safety devices (e.g., H). z-flare, inerting) are not required. For example, the CO z The liquefaction plant, or at least the part of the plant used for separating non-condensable gases, must be free of hydrogen flares and / or other components for hydrogen inerting. Furthermore, the quality of the liquefied CO₂ may be affected. Z 412 significantly improve, as hydrogen enrichment in the storage tank is avoided.

[0258] The process can be modularly adapted to different plant capacities:

[0259] For micro systems (e.g. for 20-40 Nm) 3 / h residual gas) can often be 0.5-1 m 2 The membrane area must be sufficient. For medium-sized systems (e.g., 80-150 Nm) 3 / h) are 2-5 m 2 Membrane area is usually sufficient. For large systems >200 Nm² 3In each configuration, several separation membranes are preferably connected in parallel or in series according to embodiments of the invention (series connection e.g. in the form of hollow fiber arrays). The physical and energy requirements remain low in all variants, since no additional pressure or heat input is required according to embodiments of the invention.

[0260] The separation of H z before the CO z Liquefaction can have the advantage of significantly reducing the risk of forming explosive mixtures. The hydrogen-oxygen- The mixture that forms in conventional systems, especially at low pressures and elevated temperatures, can pose a significant safety risk. The use of the membrane device according to embodiments of the invention can significantly increase safety: The hydrogen content in the carbon dioxide gas stream, which is recycled back into the process and then liquefied, is typically below 30 ppm. The need for activated carbon with the exothermic hydrogen reactions occurring on it is thus eliminated. z Reactions can be avoided. Exothermic reactions of hydrogen in tank rooms can also be avoided, and the degassing effort in the LCO can be reduced. z -Tank 214 can be reduced.

[0261] The example shows how a membrane module according to examples of the invention can be integrated into an existing biogas upgrading and CO₂ treatment plant under real conditions. Z- A liquefaction plant can be integrated. This allows for the effective, energy-efficient, economical, and safe use of a previously underutilized gas stream.

[0262] According to examples of the invention, no additional energy is required for compressors or heating. Preferably, no additional components are used to generate the required pressure or temperature. Expensive measures to increase safety or purity can be avoided or reduced. The CO Z and CH4 yield can be increased, and costs for the safe disposal of non-condensable gases can be avoided.

[0263] By using a separation membrane in an NCG line of a CO Z- According to examples of the invention, the liquefaction plant enables almost complete removal of hydrogen without additional heating elements or capacitors and thus without additional energy expenditure, thereby increasing the purity of the CO Z - CH4 electricity can be significantly improved and subjected to efficient and standard-compliant liquefaction.

[0264] Figure 3 shows a block diagram of a module 312 for removing hydrogen from a non-condensable residual stream of a CO₂ z -Liqueflux plant according to an example of the invention.

[0265] The module can be designed, for example, as a retrofittable module, or already during the initial planning and construction of the CO z -Liquefication plant as part of the CO Z - The liquefaction plant is designed as follows. Part 300 of the CC liquefaction plant, which contains the membrane module, is also shown.

[0266] In particular, the module can be configured as a component of a reboiler 302 of the CO2 liquefaction plant or as a module operationally coupled to the reboiler. The reboiler can contain a pressure sensor 336 that measures the pressure of the non-condensable residual gas flow 410 when it is fed into the module 312 via the interface 330.

[0267] The system 200, 212, 216 is preferably configured such that the temperature, pressure, and volumetric flow rate of the gas mixture impinging on the separation membrane 216, 318 are selected to maximize the permeability of the separation membrane for hydrogen, while minimizing the permeability for CO2 and CH4. This results in a high separation efficiency, which is not achievable with other processes (such as PSA, amine scrubbing, or cryogenics) under comparable conditions.

[0268] In many plants, it is possible to install the separation membrane at a position within plant 200, 212, or within the biogas processing chain, such that the temperatures and pressures already present in the gas stream directed onto the separation membrane are sufficient to separate hydrogen with adequate efficiency. This can be the case, in particular, in the non-condensable residual stream of a CO2 liquefaction plant.

[0269] In the embodiment shown in Figure 3, the pressure regulator 304, already present in the reboiler, and preferably also an associated pressure sensor 336, are used to determine the pressure of the residual reboiler flow directed onto the membrane 318. The membrane module utilizes the elements 336 and 304 already present in the reboiler of a CO2 liquefaction plant, or rather, it uses the pressure determined by these elements in the residual reboiler flow to set the pressure on the feed side of the membrane. The membrane module 312, or the device 300, thus has the advantage that few additional components are required and existing pressure regulation elements can be advantageously used to efficiently separate hydrogen from existing plants with minimal structural modifications.

[0270] The membrane module 312 can accommodate further optional components 322, 324, 328, 320, 316, in particular sensors and control elements for regulating temperature and / or for The system includes pressure control on the permeate side of the separation membrane. This allows for further optimization of the process conditions with regard to efficient hydrogen separation and for compensation of process-related fluctuations in temperature and / or pressure. These elements also enable the separation membrane to be installed in systems where the pressure and / or temperature conditions in the reboiler residual stream are not sufficiently favorable for efficient hydrogen separation. A membrane module 312 is described below, which, in addition to the separation membrane 318, also includes further optional components 322, 324, 328, 320, 316 for temperature and / or pressure regulation, as well as optional shut-off valves 326, 314.

[0271] The pressure measured by the pressure sensor 336 of the reboiler can be used by the CO2 liquefaction plant to control the pressure regulating valve 304 already present in the reboiler, ensuring that the pressure of the residual gas flow on the feed side of at least one separation membrane 318 remains within a setpoint range. The pressure regulator 304 can be configured, in particular, as a pressure maintenance valve in the reboiler stage of the CO2 liquefaction plant. This pressure maintenance valve 304 of a reboiler in an LCO2 plant, also referred to as the reboiler pressure regulating valve, has the function and is configured to control and stabilize the reboiler pressure in a CO2 liquefaction plant in order to ensure the desired thermodynamic separation of liquid CO2 and gaseous residues (NCG).According to examples of the invention, the existing pressure regulator 304 and the pressure of the NCG residual gas flow, which is directed as a gas mixture to the feed side of the at least one separation membrane, are adjusted to a setpoint suitable for hydrogen separation. This setpoint can be, in particular, a pressure of a maximum of 40 bar absolute, more specifically a maximum of 25 bar absolute, preferably 2 bar to 25 bar absolute, more specifically 16 to 20 bar absolute, more specifically a maximum of 18 bar absolute, and in some examples, 2 to 16 bar absolute. Often, the configuration of the pressure regulator 304 does not need to be changed for this purpose. In some systems, minor adjustments to the setpoint pressure to be achieved by the regulator 304 are sufficient, so that a compromise is found between optimal separation of liquid CO2 and gaseous residues (NCG) on the one hand and efficient hydrogen separation on the other.

[0272] An optional additional pressure regulator 316 is located on the permeate side of the A separation membrane can be used to reduce the pressure on the permeate side of the The pressure regulator 316 is used to control the separation membrane, thereby enabling even more precise control and dynamic adjustment of the pressure conditions at the separation membrane and thus improving the efficiency of hydrogen separation. The pressure regulator 316 can preferably be a pressure regulator that controls the pressure on the permeate side depending on the hydrogen concentration in one of the gas streams 402, 404, 410, 418, 414 processed by the system. The pressure regulator 316 can be operationally coupled to a pressure sensor 320 on the permeate side and use the sensor to determine whether a desired setpoint has already been reached.

[0273] The pressure regulator on the permeate side can, for example, offer the advantage that the membrane module can be integrated into a wider range of systems and system configurations without having to adjust the pressure set by the reboiler's pressure regulating valve. The pressure set by the reboiler's pressure regulating valve is generally optimized for the separation of non-condensable gases. This pressure is often, but not always, also very suitable for hydrogen separation. By using an additional pressure regulator on the permeate side, the transmembrane pressure can be adjusted, at least within a certain pressure range, to optimize it for hydrogen separation without having to change the pressure on the feed side of the membrane, which is optimized for NCG gas separation.

[0274] The residual gas stream 410 received via interface 330 is raised by an optional heating element 324 to a temperature that enables efficient removal of the hydrogen from the gas mixture via the separation membrane 318. This temperature is typically in the range of 0°C to 45°C, particularly 0°C to 25°C or 0°C to 5°C. The heating element 324 is preferably designed to utilize existing process heat and operate without the need for additional primary energy input. For example, the heating element can be configured as a heat exchanger that receives warm water via interface 332, uses the heat contained therein to raise the temperature of the residual gas stream, and returns the cooled water via interface 334. The warm water received via interface 332 can originate, for example, from gas compressors of the carbon dioxide liquefaction plant or from other heat-generating processes of the CO₂ liquefaction plant.

[0275] Optionally, one or more shut-off valves 326, 314 may be present, which Maintenance of the module, and especially the separation membrane, is facilitated by the ability to selectively and temporarily interrupt the residual gas flow. For example, in the In cases where the module 312 is designed as a retrofit module, a maintenance valve may optionally be installed in front of and / or behind the module at the point where a line was cut to integrate the module 312.

[0276] The separation membrane and the pipework are designed in such a way that the hydrogen, which permeates the separation membrane faster than all other gases in the residual gas stream, accumulates in the permeate, whereby the hydrogen content in the retentate decreases relative to all other gas mixture components.

[0277] Preferably, the module can include the aforementioned additional pressure sensor 320, which is installed on the permeate side of the separation membrane 318 and measures the pressure in the permeate stream of the separation membrane. The module can also include the aforementioned permeate-side pressure regulator 316, which increases or decreases the pressure on the permeate side of the separation membrane depending on the pressure measured by sensor 320. For example, the permeate-side pressure can be further reduced to increase the transmembrane pressure differential to the feed side of the separation membrane and thus also the hydrogen removal rate. This can have the further advantage that the pressure can be variably adjusted depending on the hydrogen concentration in the residual gas, e.g., to increase the hydrogen separation rate when a high hydrogen concentration is present in the residual gas stream.The hydrogen content in biogas can fluctuate depending on the type of fermented biomass and the state and composition of the microorganisms carrying out the fermentation. Thanks to the pressure sensor 320 and the pressure control valve 316, it is possible to dynamically adjust the hydrogen separation rate to changing conditions. Furthermore, it allows the use of module 312 across a wider range of LCO2 plants and plant configurations without requiring adjustment of the pressure generated by the reboiler pressure regulator 304.

[0278] Depending on the implementation example or configuration, the pressure generated on the permeate side can be, for example, a pressure that increases or decreases the transmembrane pressure.

[0279] The hydrogen-enriched permeate can be discharged into the environment via interface 310 or used for thermal or material recovery. The hydrogen-reduced retentate can be output from module 312 via interface 308. For example, the Retentate is fed to the source of the biogas, e.g. a fermenter, or to the pipeline leading from the fermenter to a gas processor 204.

[0280] Figure 4 shows the block diagram according to Figure 2, supplemented by example gas mixtures. The biogas 402, produced in the fermenter 202, is fed to a gas processor 204, which separates it into a methane-enriched gas mixture 406 and a carbon dioxide-enriched gas mixture 404. The gas mixture 406 is fed to an LNG plant 206, where the methane is further enriched and the nearly pure methane 408 is liquefied and transferred to an LNG storage tank 208. The gas mixture 404 is fed to a CO2 liquefaction plant, where the carbon dioxide is further concentrated or purified of other gas components, and the resulting nearly pure carbon dioxide 412 is liquefied and fed to an LCO2 storage tank 214.

[0281] The non-condensable gases remaining after carbon dioxide liquefaction are fed as a non-condensable residual gas stream 410 to a membrane module 312 and the separation membrane 318, 216 contained therein. The separation membrane allows hydrogen to permeate faster than the other gases, resulting in a hydrogen-enriched permeate 418 and a hydrogen-reduced retentate 414. The retentate can be returned via a gas recirculation line 218, either through line 416a to the fermentation source (e.g., a fermenter 202) or through line 416b to the feed stream of the gas conditioner 406. The gas component concentrations of the gas mixtures 402, 404, 406, 410, 412, 414, and 418 are shown below as examples for one implementation variant:

[0282] Figure 5 shows a method for separating hydrogen (H2) from biogas streams 410 in biogas plants 200, 300. The method can be used to optimize liquefaction processes of methane (CH4) and / or carbon dioxide (CO2) and includes the use 502 of a separation membrane 216, 318 which has different permeances of hydrogen, carbon dioxide and methane H4 to selectively remove hydrogen from a biogas stream containing hydrogen, carbon dioxide and methane and to further maximize the purity of methane and carbon dioxide.

[0283] Figure 6 shows another variant of the membrane module 312. Unlike the module shown in Figure 3, this variant does not use the pressure regulator 304 of the reboiler stage to regulate the gas pressure on the feed side of the separation membrane, but instead has its own pressure regulator 602 for this purpose. The membrane module 312 of Figure 6 can have essentially the same elements, including optional elements, as the membrane module described in Figure 3. However, it additionally includes its own pressure regulator 602 on the feed side of the separation membrane 318. This pressure regulator is therefore present in addition to the pressure regulator of the reboiler of the CO2 liquefaction plant. Preferably, the module 312 also includes a pressure sensor 606 on the feed side of the membrane, which measures the pressure of the gas mixture on the feed side of the membrane. The sensor 606 is operationally connected to the pressure regulator 602 via a communication link 604, e.g.a wireless or wired interface, coupled and enables the controller to determine whether the desired target pressure on the feed side has already been reached or even exceeded.

[0284] Here too, the pressure regulator 316 and pressure sensor 320 described in Figure 3 can optionally be present on the permeate side.

[0285] Thanks to the additional pressure regulator 602, the membrane module shown in Figure 6 does not rely on the pressure regulator of the reboiler stage to generate a pressure in the residual NCG gas that directly, or at least after generating additional pressure on the permeate side, provides a transmembrane pressure suitable for hydrogen separation. Thus, the membrane module shown in Figure 6 can be integrated at any point within the line for the non-condensable gases of the CO2 liquefaction plant, even at a considerable distance from the reboiler. This can be advantageous in some systems, for example, where space is limited in or near the reboiler. Often, the pressure in the residual NCG gas decreases with increasing distance from the reboiler, while the temperature increases. Because some variants of the membrane module have their own pressure regulation, the pressure on the reboiler can be adjusted accordingly. Since the membrane-guided gas mixture is located on the feed side of the membrane, it is possible to flexibly integrate the membrane module within the line for the non-condensable gases of the CO2 liquefaction plant, where the pressure and temperature conditions best suited for hydrogen separation are already present, thus minimizing the energy required to generate suitable temperature and pressure conditions at the separation membrane.

[0286] The embodiment shown in Figure 6 has the further advantage of being particularly suitable for the device 600, into which the membrane 318 is integrated, to contain one or more distribution modules (not shown) that ensure that only a portion of the residual NCG flow from one or more CO2 liquefaction plants is directed to the membrane. This can allow, for example, in the case of short-term, significantly increased gas flow (fluctuations) or when the plant is operating at its capacity limit, only a portion of the residual gas to be directed to the membrane in order to achieve a sufficient degree of hydrogen separation across the membrane. The device 600 can, for example, be part of a biogas processing plant, including an existing line for the residual NCG gas from a reboiler (here: line between elements 330 and 308, into which the module 312 is integrated).

[0287] Although the invention is illustrated and described in detail in the drawings and the preceding description, this illustration and description is to be regarded as exemplary and not limiting; the invention is not limited to the disclosed examples.

[0288] In another aspect, a device for the efficient separation of hydrogen (H2) from biogas streams in biogas plants is described here, in order to optimize the liquefaction processes of methane (CH4) and carbon dioxide (CO2). The device comprises a special separation membrane based on the different permeances of H2, CO2, and CH4 in order to selectively remove H2 and subsequently maximize the purity of CH4 and CO2.

[0289] The device can be used for the efficient separation of hydrogen (H2) from biogas streams in biogas plants. In particular, the device can be used to optimize the liquefaction processes of methane (CH4) and carbon dioxide (CO2) in order to improve their purity and marketability.

[0290] Small amounts of H₂ are produced during the fermentation processes in biogas plants. In the first stage of gas processing (separation of the binary gas mixture CH₄ / CO₂), most of this hydrogen is converted into the CCh fraction. When the CCh stream is liquefied, the majority of the hydrogen remains, leading to operational challenges. Non-condensable gases must be regularly removed from current liquefaction plants and often thermally utilized. This results in approximately 10% of the total mass flow intended for liquefaction being unmarketable. This stream typically consists of 70–80% CO₂, 15–18% CH₄, 7–10% O₂, and 0.2–0.4% H₂.

[0291] Conventional CCh liquefaction plants use a stripper-reboiler stage to remove non-condensable gases. In this process, some of the gas mixture can be recycled back into the fermentation, with CO2 and CH4 passing through the process again and O2 being consumed in the fermentation or adsorbed with H2S. However, H2 continues to accumulate, leading to increased operating costs and losses.

[0292] By implementing an additional step, as illustrated by the examples of the device and method described here, a special separation membrane is used, based on the different permeances of the molecules. This separation membrane enables the efficient removal of H2, while largely retaining CO2 and CH4. Despite the separation membrane's natural affinity for rapidly permeating CO2, its operation is optimized to selectively remove a significant proportion of the H2.

[0293] Examples of this device thus contribute significantly to improving the purity and marketability of CH4 and CO2 by reducing the amount of non-condensable gases and increasing the efficiency of the liquefaction process. This can lead to a substantial reduction in operating costs and improved economic viability of these biogas plants.

[0294] For example, a device for the efficient separation of hydrogen can be used in accordance with the following clauses:

[0295] 1. Device for the efficient separation of hydrogen (H2) from biogas streams in biogas plants for optimizing the liquefaction processes of methane (CH4) and carbon dioxide (CO2), comprising a special separation membrane which is applied to the different The permeances of H2, CO2 and CH4 are used to selectively remove H2 and subsequently maximize the purity of CH4 and CO2.

[0296] 2. Device according to clause 1, wherein the separation membrane is configured to allow H2 to permeate decisively despite its affinity to permeate CO2 more rapidly, while retaining CO2 and CH4 to a large extent.

[0297] 3. Device according to clause 1 or 2, wherein the separated gases (CH4 and CO2) are made available for marketing in marketable purity and the proportion of non-condensable gases is significantly reduced.

[0298] 4. Device according to any of the preceding clauses, wherein the separation membrane is integrated in an additional step after the stripper-reboiler stage of a CCh liquefaction plant.

[0299] 5. Device according to any of the preceding clauses, wherein the biogas produced during the fermentation process, which typically contains small amounts of H2, is first subjected to an initial separation of the binary gas mixture CH4 / CO2 before passing through the separation membrane.

[0300] 6. Device according to one of the preceding clauses, wherein the total mass flow to be reused typically consists of 70-80% CO2, 15-18% CH4, 7-10% O2 and 0.2-0.4% H2, and wherein the H2 content is selectively separated by the separation membrane to the corresponding concentration.

[0301] 7. Device according to one of the preceding clauses, wherein the non-condensable gases, which usually have to be thermally treated, are significantly reduced by the separation of the H2. This can lead to an increase in efficiency and a significant reduction in the operating costs of the entire plant system.

[0302] 8. Device according to any of the preceding clauses, wherein the gases remaining in the retentate can be reintroduced into the process after their separation, with CO2 and CH4 passing through the process again and O2 being consumed in the fermentation or adsorbed with H2S, while H2 does not accumulate adversely. LIST OF REFERENCE MARKS 100 Device for biogas processing before membrane installation 200 Device for biogas processing after membrane installation 202 fermenters for biogas production 204 gas processors for separating methane and CO2 206 LNG plant for methane liquefaction 208 LNG storage facilities 210 Gas recirculation of the LNG plant 212 CO2 liquefaction plant (LCO2 plant) 213 Stripper-reboiler stage of the CO2 liquefaction plant 214 LCO2 storage 216 Separation membrane for hydrogen separation 218 Gas recirculation 300 parts of a biogas plant containing a membrane module 302 Reboiler (swamp heater) 304 Reboiler pressure regulator as a pressure regulator on the feed side of the diaphragm 308 Retentate outlet of the membrane module 310 Permeate outlet of the membrane module 312 Membrane module (e.g., retrofittable) 314 Shut-off valve 316 Pressure regulators on the permeate side 318 Separation membrane 320 Pressure sensor on the permeate side 322 Temperature sensor 324 Heating element (e.g. heat exchanger) 326 Shut-off valve 328 Temperature controller 330 Interface for gas inlet (e.g. from the reboiler) 332 Interface for heat input (e.g. hot water) 334 Interface for heat outlet (e.g. cooled water) 336 Pressure sensor in the reboiler 402 Raw biogas electricity from the fermenter 404 CO2-rich gas fraction (e.g. feed for LCO2 plant) 406 Methane-rich gas fraction (e.g. feed for LNG plant) 408 Liquefied methane (LNG) 410 Residual gas stream (reboiler / NCG stream) for hydrogen separation 412 Liquefied carbon dioxide (LCO₂) Z ) 414 Retentate after membrane separation (low hydrogen) 416a Return line to the fermenter 416b Return line to the gas processor 418 Permeate after membrane separation (hydrogen-rich) 600 Device 602 Pressure regulator for gas mixture on feed side of the diaphragm (in addition to Reboiler gas pressure regulator) 604 Data connection 606 Pressure sensor for gas mixture on feed side of the diaphragm

Claims

REQUIREMENTS 1. Device (200, 300, 312, 600) for the efficient separation of hydrogen (H2) from biogas streams (410) in biogas plants (200, 300) for the optimization of the liquefaction processes of methane (CH4) and carbon dioxide (CO2), comprising a separation membrane (216, 318) based on the different permeances of H2, CO2 and CH4 to selectively remove H2 (310) and subsequently maximize the purity of CH4 and CO2.

2. Device according to claim 1, wherein the separation membrane is configured such that, despite its affinity to permeate CO2 more rapidly, it allows H2 to permeate significantly while retaining CO2 and CH4 to a large extent.

3. Device according to one of the preceding claims, wherein the separated gases (CH4 and CO2) are provided in marketable purity and the proportion of non-condensable gases is significantly reduced.

4. Device according to one of the preceding claims, wherein the separation membrane is integrated in an additional step after the stripper-reboiler stage (213) of a CO2 liquefaction plant (212).

5. Device according to one of the preceding claims, wherein biogas (402) produced during a fermentation process and typically containing small amounts of H2 is first subjected to a first separation (204) of the binary gas mixture CH4 / CO2 before passing through the separation membrane (216, 318).

6. Device according to one of the preceding claims, wherein the total mass flow (414) to be reused typically consists of 70-80% CO2, 15-18% CH4, 7-10% O2 and 0.2-0.4% H2, and the H2 content is selectively separated by the separation membrane to the corresponding concentration.

7. Device according to one of the preceding claims, wherein the non-condensable gases (410), which usually have to be thermally utilized, are significantly reduced by the separation of the H2, resulting in an increase in efficiency and a significant reduction in operating costs of the entire system (100, 200).

8. Device according to one of the preceding claims, wherein the gases remaining in the retentate (414) are reintroduced into the process (416a, 416b) after their separation, wherein CO2 and CH4 are reintroduced into the process and O2 is consumed in the fermentation (202) or adsorbed with H2S, while H2 does not accumulate adversely.

9. Device (200, 300, 312) according to one of the preceding claims, wherein the device is configured to effect the separation of hydrogen from the biogas streams by applying a (410) of the biogas streams to the separation membrane (216, 318) comprising at least hydrogen (H2), carbon dioxide (CO2) and methane (CH4), such that hydrogen preferably permeates the membrane and thereby produces a hydrogen-enriched permeate (418) and a hydrogen-reduced retentate (414).

10. Device according to one of the preceding claims, wherein the pressure on the feed side of the separation membrane is determined by the pressure of a residual gas stream of non-condensable gases originating from the reboiler of a carbon dioxide liquefaction plant (212), wherein the pressure is in particular a pressure of a maximum of 40 bar absolute, in particular a maximum of 25 bar absolute, preferably 2 bar to 25 bar absolute, in particular 16 to 20 bar absolute, in particular a maximum of 18 bar absolute, in some examples 2 to 16 bar absolute; and / or wherein the temperature on the feed side of the separation membrane is determined by the temperature of a residual gas stream of non-condensable gases originating from the reboiler of a carbon dioxide liquefaction plant (212), wherein the temperature is in particular a temperature of 0°C to 45°C, preferably 0°C to 25°C, preferably 0°C to 5°C.

11. Device according to one of the preceding claims, wherein the device comprises a CO2 liquefaction plant with a reboiler including a reboiler pressure regulator (304), wherein the device is configured to use exclusively the reboiler pressure regulator to regulate the pressure on the feed side of the separation membrane, wherein in particular the separation membrane is integrated into a degassing stage of the CO2 liquefaction plant which contains the reboiler.

12. Device (300) according to any one of the preceding claims 1-10, wherein the device comprises a CO2 liquefaction plant with a reboiler including a reboiler pressure regulator (304), wherein the device comprises an additional pressure regulator (602) and is configured to use the additional pressure regulator (602) to regulate the pressure on the feed side of the separation membrane.

13. Device according to claim 12, wherein the separation membrane is integrated into a line for transporting the non-condensable residual gas stream of the CO2 liquefaction plant, wherein the line is located inside or outside the degassing stage of the CO2 liquefaction plant, wherein in particular the position of the separation membrane within the line is selected on the basis of the temperature and pressure conditions prevailing in the line such that the energy expenditure for setting a target temperature and / or a target pressure on the feed side of the separation membrane for hydrogen removal is minimized.

14. Device according to one of the preceding claims, wherein the device has a heating element (324, 328) configured to heat to a set temperature the (410) of the biogas streams from which the hydrogen is extracted by the separation membrane when it hits the feed side of the separation membrane, wherein the set temperature is in particular a temperature of 0°C to 45°C, preferably 0°C to 25°C, preferably 0°C to 5°C.

15. Device according to claim 14, wherein the heating element operates exclusively by means of process heat and without the use of additional primary energy, wherein the heating element in particular comprises a heat exchanger (324) which utilizes the heat from gas compressors of a CO2 liquefaction plant (212).

16. Device according to one of the preceding claims, wherein the device has a pressure regulator (304, 602) on the feed side of the separation membrane, which is configured to regulate the pressure of that of the biogas streams from which the hydrogen is extracted by the separation membrane, such that this biogas stream has a setpoint pressure on the feed side of the separation membrane, wherein the setpoint pressure is in particular a pressure of a maximum of 40 bar absolute, in particular a maximum of 25 bar absolute, preferably 2 bar to 25 bar absolute, in particular 16 to 20 bar absolute, in particular a maximum of 18 bar absolute, in some examples 2 - 16 bar absolute.

17. Device according to one of the preceding claims, wherein the device comprises a pressure regulator (316) on the permeate side of the separation membrane and wherein the device is configured to produce a partial pressure difference across the separation membrane, wherein the pressure on the permeate side of the separation membrane is regulated by the pressure regulator (316) on the permeate side.

18. Device according to claim 17, wherein the partial pressure difference Ap_H2 between the feed and permeate side of the separation membrane is at least 2 bar.

19. Device according to claim 17 or 18, wherein the device has a sensor for the hydrogen concentration in at least one of the biogas streams (402, 404, 410) and is configured to receive a measured hydrogen concentration from the sensor and to use it to control the pressure regulator (316) on the permeate side of the separation membrane to adjust the pressure on the permeate side of the separation membrane in order to adjust the concentration of hydrogen in the permeate depending on the measured hydrogen concentration.

20. Device according to one of the preceding claims, wherein the (410) of the biogas streams from which the hydrogen is extracted by the separation membrane is the non-condensable residual gas stream (410) of a CO2 liquefaction plant (212).

21. Device according to one of the preceding claims, wherein the (410) of the biogas streams from which the hydrogen is extracted by the separation membrane contains less than 5 vol% H2, in particular less than 2.5 vol% H2, in particular less than 1 vol% H2.

22. Device according to one of the preceding claims, wherein the separation membrane is located within the residual gas stream of a CO2 liquefaction plant (212).

23. Device according to one of the preceding claims, wherein the device is configured to refeed the retentate stream (414) of the separation membrane to a fermentation process (202) which is the source of the biogas streams, and / or to a gas processor (204) for the biogas (402) of the fermentation process (416a, 416b).

24. Device according to one of the preceding claims, wherein the retentate (414) of the separation membrane has the following composition: 20-99% by volume carbon dioxide, 0.1 - 70 vol.-% Methane, 0.1-10.0 vol.% oxygen, and - 0.1-5.0 vol. -% Hz, wherein the retentate has in particular the following composition: 70-80% carbon dioxide, 15-18% methane, 7-10% oxygen and 0.2-0.4% hydrogen.

25. Device according to one of the preceding claims, wherein the separation membrane has a selectivity a_{H2 / CO2} of at least 3, in particular at least 5.

26. Device according to one of the preceding claims, wherein the device includes a membrane module (318) with several parallel separation membranes, wherein the separation membrane is one of the several separation membranes, wherein the membrane module is preferably designed as a retrofittable membrane module, in particular as a “bolt-on module”.

27. Device according to one of the preceding claims, wherein the production of the hydrogen-enriched permeate of the separation membrane and the hydrogen-reduced retentate of the separation membrane is carried out without the use of additional primary energy to heat the biogas stream (410) directed to the feed side of the separation mixture.

28. Device according to one of the preceding claims, wherein the device is configured to supply the permeate of the separation membrane to a discharge and / or disposal, in particular a discharge of the permeate into the atmosphere, a supply of the permeate to an energy use or a supply of the hydrogen in the permeate to a material use.

29. Device according to one of the preceding claims, wherein the device is configured to return the retentate of the separation membrane to a biogas gas processing process used for the liquefaction of carbon dioxide and / or the liquefaction of methane.

30. Device according to one of the preceding claims, wherein the device is, comprises, or is operationally coupled to a carbon dioxide liquefaction plant (212), wherein the carbon dioxide liquefaction plant (212) is in particular configured to liquefy a methane-poor and carbon dioxide-rich gas mixture (404) produced from the biogas by a gas processor (204), wherein the non-liquefied portion (410) of this gas mixture produced by the gas processor is the residual gas stream of the carbon dioxide liquefaction plant; and wherein the residual gas stream of the carbon dioxide liquefaction plant is the biogas stream (410) from which the separation membrane removes the hydrogen; and / or wherein the device is or comprises a membrane module (312); and / or wherein the device is a plant (200) for processing biogas;wherein the device optionally includes or is operationally coupled to a gas processor (204) for separating biogas into a carbon dioxide-enriched gas mixture (412) and a methane-enriched gas mixture (406).

31. Methods for separating hydrogen (H2) from biogas streams (410) in biogas plants (200, 300) for optimizing liquefaction processes of methane (CH4) and / or carbon dioxide (CO2), comprising: Using a separation membrane (216, 318) that has different permeances of hydrogen, carbon dioxide and methane H4 to selectively remove hydrogen from a biogas stream (410) containing hydrogen, carbon dioxide and methane (310) and to further maximize the purity of methane and carbon dioxide.

32. The method of claim 30, wherein the separation membrane is configured such that, despite its affinity to permeate carbon dioxide more rapidly, it allows hydrogen to permeate significantly, while carbon dioxide and methane are largely retained.

33. Method according to one of claims 30-32, wherein the separated gases methane and carbon dioxide are provided in marketable purity and the proportion of non-condensable gases is significantly reduced.

34. Method according to one of claims 30-33, wherein the separation membrane is integrated in an additional module (312) after the stripper-reboiler stage (213) of a CO2 liquefaction plant (212).

35. Method according to one of claims 30-34, further comprising: integration of an additional module (312) after the stripper-reboiler stage (213) of a CO2 liquefaction plant (212), wherein the additional module contains the separation membrane (318).

36. Method according to any one of claims 30-35, comprising: Provision of biogas (402) produced during a fermentation process and typically containing small amounts of H2, The biogas undergoes an initial separation (204) of the two gases methane and carbon dioxide before passing through the separation membrane (216, 318).

37. A method according to any one of claims 30-36, comprising: targeted separation of the hydrogen content by the separation membrane; and reuse of a total mass flow (414) typically consisting of 70-80% CO2, 15-18% CH4, 7-10% O2 and 0.2-0.4% H2.

38. Method according to one of claims 30-37, wherein the non-condensable gases (410), which usually have to be thermally utilized, are significantly reduced by the separation of the hydrogen, resulting in an increase in efficiency and a significant reduction in the operating costs of the entire plant system (100, 200).

39. Method according to any one of claims 30-38, further comprising: Re-introduction (416a, 416b) of the gases remaining in the retentate (414) after their separation into the process, whereby carbon dioxide and methane re-pass through the process (202, 204, 206, 212) and oxygen is consumed in the fermentation (202) or adsorbed with hydrogen sulfide, while hydrogen does not accumulate adversely.

40. A method according to any one of claims 30-39, wherein the use of the separation membrane (216, 318) for removing the hydrogen comprises: applying a (410) of the biogas streams to the separation membrane (216, 318), comprising at least hydrogen (H2), carbon dioxide (CO2) and methane (CH4), such that hydrogen The separation membrane preferably permeates, resulting in a hydrogen-enriched solution. Permeate (418) and a hydrogen-reduced retentate (414) are produced.

41. Method according to one of claims 30-40, wherein the biogas stream from which the hydrogen is extracted by the separation membrane is the non-condensable residual gas stream of a CO2 liquefaction plant (212).

42. Method according to one of claims 30-41, further comprising: integration of the separation membrane within the residual gas stream of a CO2 liquefaction plant (212) during or after the construction of the CO2 liquefaction plant.

43. Method according to one of claims 30-42, further comprising: control of a heating element (324, 328) such that the one of the biogas streams from which the hydrogen is extracted through the separation membrane when it hits the feed side of the separation membrane is heated to a target temperature of 0°C to 45°C, preferably 0°C to 25°C, preferably 0°C to 5°C.

44. Method according to one of claims 30-43, further comprising: control of a heating element (324, 328) such that the biogas stream from which hydrogen is extracted by the separation membrane when it hits the feed side of the separation membrane is heated to a setpoint temperature, wherein the heating element operates exclusively by means of process heat and without the use of additional primary energy, wherein the heating element in particular comprises a heat exchanger (324) which utilizes the heat from gas compressors of a CO2 liquefaction plant (212).

45. Method according to one of claims 30-44, further comprising: control of a pressure regulator (304, 602) on the feed side of the separation membrane such that the pressure of that of the biogas streams from which the hydrogen is extracted by the separation membrane has a pressure on the feed side of the separation membrane of a maximum of 40 bar absolute, in particular of a maximum of 25 bar absolute, preferably 2 bar to 25 bar absolute, in particular 16 to 20 bar absolute, in particular a maximum of 18 bar absolute, in some examples 2 - 16 bar absolute.

46. ​​The method of claim 45, further comprising: using a reboiler pressure regulator (304) of a reboiler of a CO2 liquefaction plant as the pressure regulator for regulating the pressure on the feed side of the separation membrane, wherein in particular the method furthermore includes: integration of the separation membrane into a degassing stage of the CO2 liquefaction plant, which contains the reboiler.

47. Method according to claim 46, further comprising: using a pressure regulator (602) contained in a membrane module (312) containing the separation membrane and provided in addition to a reboiler pressure regulator (304) of a reboiler of a CO2 liquefaction plant in which the separation membrane is integrated or coupled, to adjust the pressure on the feed side of the separation membrane to a setpoint pressure.

48. A method according to claim 46 or 47, wherein the separation membrane is integrated into a line for transporting the non-condensable residual gas stream of the CO2 liquefaction plant, wherein the line is located inside or outside a degassing stage of the CO2 liquefaction plant, wherein the method particularly comprises: positioning the separation membrane inside the line based on the temperature and pressure conditions prevailing in the line such that the energy expenditure for setting a target temperature and / or a target pressure on the feed side of the separation membrane for hydrogen removal is minimized.

49. A method according to any one of claims 30-48, further comprising: controlling a pressure regulator (316) on the permeate side of the separation membrane such that a partial pressure difference is produced across the separation membrane, wherein the pressure on the permeate side of the separation membrane is controlled by the pressure regulator (316) on the permeate side, wherein in particular the partial pressure difference Ap_H z The pressure between the feed and permeate sides of the separation membrane must be at least 2 bar.

50. Method according to any one of claims 30-49, further comprising: receiving a hydrogen concentration measured by a sensor in at least one of the biogas streams (402, 404, 410); and using the received hydrogen concentration to control a pressure regulator (316) on the permeate side of the separation membrane to adjust the pressure on the permeate side of the separation membrane in order to adjust the concentration of hydrogen in the permeate as a function of the measured hydrogen concentration.

51. Process for the selective separation of hydrogen (H z ) from a gas mixture (410) produced during the processing of biogas (402), wherein the gas mixture contains at least The process includes hydrogen (Hz), carbon dioxide (CO2) and methane (CH4), and comprises: Exposure of at least one separation membrane (216, 318) with the gas mixture, wherein the separation membrane has a higher permeability for hydrogen than for carbon dioxide and methane, so that hydrogen preferentially permeates the separation membrane and thereby produces a hydrogen-enriched permeate (418) and a hydrogen-reduced retentate (414).

52. Method according to claim 51, wherein the gas mixture is derived from the non-condensable residual gas stream of a CO2 liquefaction plant (212).

53. Method according to one of the preceding claims 51-52, wherein the at least one separation membrane is located within the residual gas stream of a CO2 liquefaction plant (212).

54. Method according to any of the preceding claims 51-53, wherein the exposure of the at least one separation membrane to the gas mixture takes place at a temperature of 0°C to 45°C, preferably 0°C to 25°C, preferably 0°C to 5°C.

55. Method according to any one of the preceding claims 51-54, wherein the exposure of the at least one separation membrane to the gas mixture comprises: increasing the temperature of the gas mixture before the separation membrane is exposed to the gas mixture, exclusively by means of process heat from the processing of the biogas and without the use of additional primary energy, in particular by means of a heat exchanger (324) which utilizes the heat from gas compressors of a CO2 liquefaction plant (212).

56. Method according to one of the preceding claims 51-55, wherein the at least one separation membrane is supplied with the gas mixture at a pressure on the feed side of the at least one separation membrane of a maximum of 40 bar absolute, in particular of a maximum of 25 bar absolute, preferably 2 bar to 25 bar absolute, in particular 16 to 20 bar absolute, in particular a maximum of 18 bar absolute, e.g. 2 - 16 bar absolute.

57. Method according to any one of the preceding claims 51-56, wherein the at least one separation membrane is supplied with the gas mixture at a pressure determined on the feed side of the separation membrane by the pressure of a reboiler residual gas stream of non-condensable gases from a carbon dioxide liquefaction plant (212).

58. A method according to any one of the preceding claims 51-57, further comprising: using a pressure regulator (316) on the permeate side of the separation membrane to adjust the pressure on the permeate side of the separation such that the at least one separation membrane is supplied with the gas mixture at a transmembrane pressure difference corresponding to a setpoint, wherein the setpoint is in particular a partial pressure difference Ap_H z The pressure between the feed and permeate sides of the separation membrane must be at least 2 bar.

59. The method of claim 58, further comprising: Measuring the hydrogen concentration in the biogas (402), or in the gas mixture (410), or in another gas mixture (404) that is produced in an intermediate processing step of the processing of the biogas into the gas mixture; and Control of the pressure regulator (316) on the permeate side of the at least one separation membrane to adjust the pressure on the permeate side of the separation membrane in order to adjust the concentration of hydrogen in the permeate depending on the measured hydrogen concentration.

60. Method according to any one of the preceding claims 51-59, wherein the retentate stream (414) of the at least one separation membrane is fed back to a fermentation process which is the source of the biogas, and / or to a gas processor (204) for the biogas.

61. Method according to any one of the preceding claims 51-60, wherein the application is carried out such that the partial pressure difference Ap_H zbetween the feed and permeate sides, the pressure between at least one separation membrane must be at least 2 bar.

62. A method according to any one of the preceding claims 51-61, wherein the retentate (414) has the following composition after exposure of the at least one separation membrane to the gas mixture: 20-99% by volume carbon dioxide, 0.1 - 70 vol.-% Methane, 0.1-10.0 vol.% oxygen, and - 0.1-5.0 vol. -% Hz, wherein the retentate has in particular the following composition: 70-80% carbon dioxide, 15-18% methane, 7-10% oxygen and 0.2-0.4% hydrogen.

63. Method according to any one of the preceding claims 51-62, wherein the at least one separation membrane has a selectivity a_{H2 / CO2} of at least 5.

64. Method according to any one of the preceding claims 51-63, wherein the application of the at least one separation membrane and the production of the hydrogen-enriched permeate and the hydrogen-reduced retentate are carried out without the use of additional primary energy for heating the gas mixture.

65. Method according to any one of the preceding claims 51-64, further comprising: supplying the permeate to a discharge and / or disposal, in particular discharge of the permeate into the atmosphere, supplying the permeate to an energy use or supplying the hydrogen in the permeate to a material use.

66. Method according to any one of the preceding claims 51-65, further comprising: recycling the retentate into a biogas gas processing process which serves to liquefy carbon dioxide and / or liquefy methane.

67. Device (200, 300, 312, 600) for separating hydrogen (H2) from a gas mixture (410) produced during the processing of biogas (402), wherein the gas mixture comprises at least hydrogen (H2), carbon dioxide (CO2) and methane (CH4), wherein the device comprises at least one separation membrane (216, 318) which has a higher permeability for hydrogen than for carbon dioxide and methane, such that when the gas mixture is applied to the at least one separation membrane (216, 318), hydrogen preferably permeates the separation membrane and thereby produces a hydrogen-enriched permeate (418) and a hydrogen-reduced retentate (414).

68. Device according to claim 67, wherein the device is selected from a group comprising: a membrane module (316), a CO2 liquefaction plant (212), a plant (200, 300) comprising a CC liquefaction plant, a plant (200) for processing biogas.

69. Device according to one of claims 61-62, wherein the device comprises a CO2 liquefaction plant (212) and wherein the at least one separation membrane is integrated after the stripper-reboiler stage of a CC liquefaction plant.

70. Device according to any one of the preceding claims 67-69, wherein the device comprises or is operationally coupled to a carbon dioxide liquefaction plant (212), wherein the carbon dioxide liquefaction plant (212) is configured to liquefy a methane-poor and carbon dioxide-rich gas mixture (404) produced from the biogas by a gas processor (204), wherein the non-liquefied portion (410) of this gas mixture produced by the gas processor is formed as the residual gas stream of the carbon dioxide liquefaction plant; and wherein the residual gas stream of the carbon dioxide liquefaction plant is the gas mixture (410) with which the at least one separation membrane is acted upon.

71. Device according to any one of the preceding claims 67-70, wherein the at least one separation membrane is configured such that, when the separation membrane is exposed to the gas mixture (410), hydrogen permeates, resulting in a hydrogen-enriched permeate (418), while carbon dioxide and methane are largely retained, resulting in a hydrogen-reduced retentate (414), wherein the retentate produced by the separation membrane consists in particular of 70-80% carbon dioxide, 15-18% methane, 7-10% oxygen and 0.2-0.4% hydrogen.

72. Device according to any one of the preceding claims 67-71 wherein the device is configured to reduce non-condensable gases by separating the H2 from the gas mixture.

73. Device according to one of the preceding claims 67-72, wherein the gases remaining in the retentate of the at least one separation membrane are fed back to a fermenter (202) or a gas processor (204) of a biogas plant (200) after their separation.

74. Device according to any one of the preceding claims 67-73, wherein the at least one separation membrane has a higher permeability for hydrogen than for carbon dioxide and methane, such that hydrogen preferably permeates the at least one separation membrane and a hydrogen-enriched permeate and a hydrogen-reduced retentate are produced through the separation membrane.

75. Device according to any one of the preceding claims 67-74, wherein the device comprises: A gas pipeline for receiving the gas mixture; A module (312) which includes at least one separation membrane (216, 318) and is connected to the gas line and is configured to apply the gas mixture received via the gas line to the at least one separation membrane, A temperature controller (328, 324) configured to adjust the temperature of the received gas mixture so that the application can be carried out at a temperature of 0°C to 45°C, preferably 0°C to 25°C, preferably 0°C to 5°C on the feed side of the at least one separation membrane; and / or A pressure regulator (304) designed as a pressure-maintaining valve in the reboiler stage of the CO2 liquefaction plant and configured to adjust the pressure of the received gas mixture on the feed side of the at least one separation membrane, wherein this pressure is a maximum of 40 bar absolute, in particular a maximum of 25 bar absolute, preferably 2 bar to 25 bar absolute, in particular 16 to 20 bar absolute, in particular 18 bar absolute; and / or A pressure regulator (316) that regulates the pressure of the permeate side of the separation membrane.

76. Device according to claims 67-75, wherein the temperature controller uses process heat to adjust the temperature of the gas mixture without accessing additional primary energy, wherein the temperature controller is in particular a heat exchanger.

77. Device according to claims 67-76, wherein the at least one separation membrane is positioned in the non-condensable residual gas stream of a carbon dioxide liquefaction plant, wherein in particular the at least one separation membrane is in a retrofittable The device contains the membrane module and the device contains the membrane module, wherein the retrofittable membrane module is implemented in particular as a "bolt-on module".

78. Device according to any one of the preceding claims 67-77, wherein the device (200) comprises or is operationally coupled to one or more of the following elements: A fermenter (202) for the production of biogas; a gas processor (204) wherein the gas processor is configured to separate biogas produced during a fermentation process and typically containing small amounts of H2 into a first, methane-rich and carbon dioxide-poor gas mixture and a second, methane-poor and carbon dioxide-rich gas mixture; a carbon dioxide liquefaction plant (212) configured to liquefy the second, methane-poor and carbon dioxide-rich gas mixture, wherein the non-liquefied portion is formed as a non-condensable residual gas stream from the carbon dioxide liquefaction plant; and wherein the residual gas stream from the carbon dioxide liquefaction plant is the gas mixture with which the separation membrane is exposed to remove the hydrogen.

79. Device (300) according to any one of the preceding claims 67-78, wherein the device comprises a CO2 liquefaction plant with a reboiler including a reboiler pressure regulator (304), wherein the device is configured to use exclusively the reboiler pressure regulator to regulate the pressure on the feed side of the separation membrane, wherein in particular the separation membrane is integrated into a degassing stage of the CO2 liquefaction plant which contains the reboiler.

80. Device (300) according to any one of the preceding claims 67-79, wherein the device comprises a CO2 liquefaction plant with a reboiler including a reboiler pressure regulator (304), wherein the device comprises an additional pressure regulator (602) and is configured to use the additional pressure regulator (602) to regulate the pressure on the feed side of the separation membrane.

81. Device according to any one of the preceding claims 67-80, wherein the separation membrane is integrated into a line for transporting the non-condensable residual gas stream of the CO2 liquefaction plant, wherein the line is located inside or outside the The degassing stage of the CO2 liquefaction plant is located, in particular the position of the separation membrane within the line is chosen based on the temperature and pressure conditions prevailing in the line so that the energy expenditure for setting a target temperature and / or a target pressure on the feed side of the separation membrane for hydrogen removal is minimized.

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