Method for separating low hydrogen content from natural gas mixture

Abstract

To provide a method for extracting hydrogen from a natural gas mixture.SOLUTION: A method comprises: a) a step for providing a stream including hydrogen to a first heat exchanger, for generating a heated stream; b) a step for transferring as an inlet stream, the heated stream including the hydrogen in the a) to a first film unit, for acquiring first holding liquid and first permeation liquid, where a molar fraction of the hydrogen in the first permeation liquid is higher than that in the first holding liquid, and is higher than that in the inlet stream; c) a step for transferring the first holding liquid to an electrochemical hydrogen compressor (EHC) for further separating the hydrogen and purification of the hydrogen for providing an EHC output stream; d) a step for combining the EHC output stream to the first permeation liquid, for providing a purified hydrogen output stream.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for separating low hydrogen content from a natural gas mixture. [Background technology]

[0002] There is a global consensus on the fact that although hydrogen can be produced from renewable energy sources (during off-peak times), its storage remains the biggest drawback in any power-to-gas application. Various projects have foreseen injecting hydrogen into existing natural gas grids for initial (or long-term) storage and subsequent use in a variety of different applications (power generation, heating, transport applications, e.g. gas-fueled city buses or passenger cars). The maximum blending level of hydrogen is 5-20%, potentially even 25%, depending on the infrastructure of the gas grid. Injecting green hydrogen into the gas grid offers numerous advantages such as sector interlocking, gas decarbonization, energy storage and easy distribution (with the existing infrastructure), and of course hydrogen risk reduction. The maximum blending level of hydrogen into the gas grid varies greatly between European countries, for example up to 3% in Belgium and the UK, and 10-14% (volume percent) in the Netherlands and Germany. As an average gas concentration, 10% will be the benchmark for large-scale deployment of hydrogen injection. However, the main challenge here is how the injected hydrogen can be efficiently and cheaply separated and purified from the natural gas grid. Therefore, another important aspect is to separate this low concentration hydrogen from the natural gas mixture for further use.

[0003] The conventional technology for hydrogen separation is Pressure Swing Adsorption (PSA). This unit is based on an adsorbent material used to adsorb non-hydrogen components at high pressure. In a PSA system, the separated and purified hydrogen is delivered at high pressure, while the non-hydrogen compounds are discharged at a lower pressure. However, if the incoming gas mixture is from a high pressure stream (natural gas grid), the non-hydrogen stream needs to be compressed to be pumped back to the natural gas grid. Therefore, two mechanical compressors are required in the system. The first compressor is to reach the adsorption pressure for the separation of hydrogen, and the second compressor is needed to compress the natural gas back to the grid. However, when such a system is used for the separation of low hydrogen concentration, the system requires a significant amount of compression energy and power source to reinject the low hydrogen gas back to the grid, which is very uneconomical.

[0004] PSA systems work efficiently at larger scales and higher hydrogen concentrations, but are inefficient at lower concentrations. For example, below 10% hydrogen in the stream, PSA is an inefficient option because 10 volumes of gas per volume of hydrogen must be pressurized to a high pressure ratio. At low hydrogen concentrations, the PSA units are very large, since they are sized as a function of the amount of impurities in the gas mixture that needs to be purified. In addition, the higher the adsorption pressure, the higher the purity of the hydrogen output, but the higher the energy consumption required to pressurize (non-hydrogen compounds) back into the grid.

[0005] While PSA units are commercially available on the market for large-scale systems, for small-scale units, the hydrogen separation costs of such systems are quite high. When using hydrogen for fuel cell applications, high purity and low pressure are required, making PSA units even less efficient for separation of low hydrogen concentrations. Hydrogen separation from natural gas grids with low hydrogen concentrations (less than 25%, typically 10%) is costly, energy intensive, and inefficient.

[0006] In recent years, the world's energy consumption has changed, driven by the need for new green energy sources to reduce greenhouse gas emissions. The rapid development of renewable energies as green technologies has created many problems in the management of the grid (due to the intermittency of their production), which can be solved by integrating smart grids and storage systems. A future hydrogen energy society may present a possible solution to solve the energy storage problem. The possibility of producing hydrogen by electrolyzers using renewable electricity excess production that may occur during the day provides one possible solution to solve the grid / energy storage problem. Thus, the conversion of electrical energy to chemical energy and the storage of the produced chemical energy becomes a feasible option. In that respect, the concept of blending hydrogen into the natural gas pipeline grid becomes more attractive, since it allows the delivery of pure hydrogen to the market using separation and purification technologies downstream, close to the point of end use. In addition, a significant expansion of the natural gas pipeline grid can be used to distribute hydrogen. At relatively low hydrogen concentrations, blending may require minor changes in the operation of the pipeline grid, and it may be costly to build a dedicated hydrogen pipeline. Overall, adding hydrogen to the natural gas grid can significantly reduce greenhouse gas emissions if the hydrogen is produced from low-carbon energy sources such as biomass, solar, wind, or nuclear.

[0007] The hydrogen blended compound can then be extracted downstream and used directly in automotive or fuel cell applications, or as an energy carrier for power generation via conventional power plants. The blended hydrogen can be separated and purified for different applications (e.g., fuel cells), and natural gas grids with low or no hydrogen concentration can be supplied to end users.

[0008] Therefore, it is an objective of the present invention to design different system configurations for separating and purifying hydrogen from blended natural gas grids.

[0009] Another object of the present invention is to provide a method for separating low hydrogen content from natural gas mixtures that offers better efficiency, low cost, excellent separation capacity at low concentrations, easy large-scale feasibility, and simplicity. Summary of the Invention

[0010] Thus, the present invention relates to a method for separating low hydrogen contents from a natural gas mixture, the method comprising the steps of: a) providing a hydrogen-containing stream; b) transferring the hydrogen-containing stream as an inlet stream to a first membrane unit to obtain a retentate and a permeate, wherein the molar fraction of hydrogen in the permeate is higher than the molar fraction of hydrogen in the retentate; and c) transferring the retentate to an electrochemical hydrogen compressor (EHC) for further hydrogen separation and purification.

[0011] The method provides considerable synergy with each other while improving the overall hydrogen recovery, purity, and total cost of hydrogen. In one embodiment of the present invention, natural gas (composed of 10% H2, 90% CH4, and some impurities) coming from the piping network is heated to the required temperature of the membrane separation unit. Impurities such as sulfur can be first removed using a desulfurization unit. In the first membrane module, most of the hydrogen is separated. The retentate side from the first membrane module is then sent to an electrochemical hydrogen compressor (EHC) for further recovery of the remaining hydrogen. The separated and purified hydrogen from the membrane module and the EHC can be mixed and sent for further use. The inventors have found that some advantages of the present invention are high hydrogen recovery, high purity, high efficiency, low energy consumption, easy large-scale feasibility. In addition, the inventors have found that the recovery and purity can be tailored, especially by changing the type and size of the membrane and electrochemical compressor.

[0012] Thanks to a proton membrane that only allows the permeation of protons and very small amounts of other contaminants, electrochemical hydrogen compressors (EHCs) can simultaneously compress and purify hydrogen while purifying it from other contaminants. EHCs consist of the compression of hydrogen via the electrochemical reactions shown in the following equations (1), (2), and (3): [ka] [ka] [ka]

[0013] Since EHCs have no moving parts, the compressed hydrogen is not contaminated with oils required as lubricants for the moving parts, and the maintenance required for the system is low. The absence of moving parts avoids noise generation, making EHCs more suitable for many applications where sound emission is a constraint. EHCs also have the advantage of being compact devices that facilitate large-scale feasibility. Typically, in large-scale systems, the single units are placed in electrical series and parallel to the gas flow to handle the required volumetric flow rates, with the same current flowing through each cell so that the cells operate under the same conditions.

[0014] The polarization curves provide information on the electrochemical resistance of the EHC. The voltage loss, usually called overpotential, can be divided into three regions: active, ohmic, and mass transport limited. In the low current density region, the active overpotential was observed to be significant. In the intermediate region, the internal resistance of the cell, mainly due to the membrane resistance, is the main factor leading to the linear trend of the discharge curve in this region. In the high current density region, the overall cell reaction rate is limited by the lack of reactants. As a result, the mass transport limited overpotential becomes the dominant factor, causing a rapid decline in the current density at a constant applied voltage. Electrochemical hydrogen compressors (EHCs) typically operate at a temperature of 65 °C and a pressure of 8 bar on the anode and cathode sides. The applied voltage is 0.3 V.

[0015] According to one embodiment, the method further comprises a step b1), in which the permeate of step b) is fed as an inlet stream to a second membrane unit, in which a second retentate and a second permeate are produced, the molar fraction of hydrogen in the second permeate being higher than the molar fraction of hydrogen in the second retentate, and the second retentate is fed back to the membrane unit of step b) as an inlet stream. Such an embodiment ensures a very high hydrogen purity (99.99%) compared to the embodiment of only the first membrane unit, thanks to the additional purification achieved by the second membrane module. Such an embodiment ensures a relatively high purity due to the two membrane modules in series, which ensures a substantial purification of the hydrogen-containing stream.

[0016] According to one embodiment, before transferring the hydrogen-containing stream to the membrane unit, the hydrogen-containing stream is heated in a heat exchanger to the operating temperature of the membrane unit. Since the working temperature of the membrane unit is about 400° C., it is preferred to heat the hydrogen-containing stream to the operating temperature of the membrane unit before transferring the hydrogen-containing stream to the membrane unit. Such an embodiment applies to the first membrane unit and / or the second membrane unit.

[0017] According to one embodiment, before transferring the retentate to the electrochemical hydrogen compressor (EHC), the retentate obtained in step b) is cooled in a heat exchanger to the operating temperature of the electrochemical hydrogen compressor (EHC). The retentate outlet stream is preferably cooled in said heat exchanger while heating the hydrogen-containing stream. The inventors have realized that the electrochemical hydrogen compressor (EHC) offers good performance at higher temperatures, but proper moisture management for humidification of the proton membrane must be taken into account when selecting the operating conditions.

[0018] According to one embodiment, a vacuum unit is used to increase the driving force through the first and / or second membrane units.

[0019] According to one embodiment, the second retentate stream originating from the second membrane unit is heated in a heat exchanger before being transferred to the inlet of the first membrane unit. Since the working temperature of the second membrane unit is about 400° C., it is preferred to heat the second retentate stream originating from the second membrane unit in a heat exchanger before being transferred to the inlet of the first membrane unit.

[0020] According to one embodiment, the first membrane unit is selected from the group of Pd-based ceramic supported membranes and Pd-based metal supported membranes, which have lower hydrogen permeation but higher permeation selectivity compared to ceramic supported membranes.

[0021] According to one embodiment, the inlet pressure of the hydrogen-containing stream in a) is at least 5 bar. The inventors have found that by increasing the retentate pressure, a lower surface area is required, but the purity is increased due to a higher driving force for the hydrogen-containing stream to permeate. A smaller membrane surface area is required because the driving force is greater along the membrane due to the larger pressure difference.

[0022] According to one embodiment, the pressure of the permeate of the first membrane unit is lower than 130 mbar. The inventors have found that to reach the same HRF, a lower vacuum is used to reduce the membrane surface area. Since the investment cost of an electrochemical hydrogen compressor (EHC) has a relevant impact on the overall distribution, a lower pressure of the retentate of the first membrane unit is beneficial.

[0023] According to one embodiment, the hydrogen concentration of the hydrogen-containing stream in a) is at least 10% by volume. The inventors found that increasing the H2 concentration of the hydrogen-containing stream resulted in a reduction in the membrane area and a slight increase in the final purity. The inventors assume that this effect is related to the driving force of higher contaminants (higher methane concentration at the inlet).

[0024] According to one embodiment, the pressure of the permeate of the first membrane unit is lower than 5 bar. The reduction in the pressure of the permeate of the first membrane unit leads to a reduction in the surface area of ​​the first module, thereby reducing energy consumption.

[0025] According to one embodiment, the pressure of the retentate of the second membrane unit is below 10 bar. Such a reduction in the pressure of the retentate of the second membrane unit has a positive impact on the overall energy consumption.

[0026] The invention further relates to an apparatus for separating low hydrogen content from a natural gas mixture, the apparatus including a first membrane unit having an inlet for a hydrogen-containing stream, an outlet for a retentate, and an outlet for a permeate, wherein the mole fraction of hydrogen in the permeate is higher than the mole fraction of hydrogen in the retentate, and an electrochemical hydrogen compressor (EHC) having an inlet for the retentate, an outlet cathode site, and an outlet anode site, wherein the mole fraction of hydrogen at the outlet cathode site is higher than the mole fraction of hydrogen at the outlet anode site.

[0027] In one embodiment, the apparatus further includes a second membrane unit having an inlet for a hydrogen-containing stream, an outlet for a second retentate, and an outlet for a second permeate, wherein the mole fraction of hydrogen in the second permeate is higher than the mole fraction of hydrogen in the second retentate, and the outlet for the retentate of the first membrane unit is connected to the inlet of the second membrane unit.

[0028] The apparatus further includes one or more heat exchangers, a compressor, and a vacuum pump. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a process flow diagram of a first embodiment of the present invention. [Diagram 2] FIG. 1 is a process flow diagram of a second embodiment of the present invention. [Diagram 3] FIG. 1 is a process flow diagram of embodiment 3 of the present invention. [Figure 4] 13 is a calculation result of the performance of an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] In order to allow those skilled in the art to better understand the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described in the following embodiment of the present invention in combination with the drawings. The term module is used to describe a complete unit consisting of a membrane, a pressure support structure, a feed inlet, an outlet permeate and retentate streams, and an overall support structure. The flow through the membrane is called the permeate. The material rejected by the membrane is called the retentate. In this description, the mole fraction of hydrogen in the permeate is higher than that in the retentate.

[0031] By combining palladium membrane, vacuum pump, mechanical compressor and electrochemical hydrogen compressor technologies, three different embodiments are proposed for the separation and purification of hydrogen from a mixture of 10% H2 and 90% CH4. The basis for all the different embodiments was the production of 25 kg H2 per day, and all membrane surface areas and feed rates were based on this production.

[0032] FIG. 1 shows a process flow diagram 10 for embodiment 1 of the present invention. Incoming stream 1 (originating from a piping network) with a total flow rate of 6246.1 mol / h is first preheated in heat exchanger 2 using outlet retentate stream 6 (while outlet retentate stream 6 is cooled), then heater 3 provides the additional heat required to reach the membrane working temperature of 400° C. After heater 3, stream 4 is fed to a 1.2 m 2 The selected membrane has a surface area of ​​2.2*10 at 400° C. 6 mol / s / m 2The membrane is a Pd-based ceramic supported membrane with a hydrogen permeation of 10000 / Pa and an ideal permeation selectivity of 20,000 (obtained experimentally), defined as the ratio between H2 and CH4 at a pressure difference of 1 bar. The retentate side of the membrane is at 8 bar (same as the stream coming from the piping network), while the permeate side is kept at 100 mbar (to increase the driving force through the membrane) by using a vacuum pump 9. The permeate stream 7 is cooled in a cooler 8 before entering the vacuum pump 9 (maximum inlet temperature of the vacuum pump is 75° C.). The retentate stream 6 of the membrane module 5 is then sent to a heat exchanger 2, and the so-cooled downstream 12 is sent to an electrochemical hydrogen compressor 13 (EHC) with a proton membrane resistance of 6 mΩ and 350 cells in parallel, at a working temperature of 65° C., for further hydrogen separation and purification. The retentate outlet stream 6 is cooled in the aforementioned heat exchanger 2 while heating the stream 1 coming from the piping network. In addition, the hydrogen 11 coming from the outlet cathode side of the electrochemical hydrogen compressor 13 is held at 8 bar to ensure proper proton membrane humidification, which may otherwise be difficult to obtain at atmospheric pressure. Then, after depressurization of stream 11 from the electrochemical hydrogen compressor 13, the purified hydrogen 15 from the permeate side of the membrane module 5 and the hydrogen 11 from the cathode side of the electrochemical hydrogen compressor 13 are mixed as stream 16. The outlet anode side stream 14 of the electrochemical hydrogen compressor 13 is sent back to the grid, with zero or low hydrogen concentration in stream 14 (depending on which configuration is selected).

[0033] FIG. 2 shows the process flow diagram 20 of embodiment 2 of the present invention, which combines two membrane modules of molecular sieving carbon membrane (CMSM) and Pd-based ceramic support membrane, a vacuum pump, and an EHC. This configuration is proposed for a high pressure gas piping network (about 40-80 bar) that allows the connection between the two membrane modules without any mechanical compressor in between. The considered piping network pressure is 40 bar, and the total feed rate is similar to embodiment 1. Feed 1 is first heated in heat exchanger 2 to reach the operating temperature of 70° C. Then, after heat exchanger 2 and heater 3, the heated stream 4 is pumped to a 5.02 m 2 The hydrogen permeation rate of CMSM is 7-10 at 70° C. 8 mol / s / m 2 / Pa and has an ideal selectivity of 550 at 40 bar, so it is a large surface area. The permeate side is kept at 3 bar to give sufficient driving force to the membrane module 5 and to maintain the pressure difference with the second membrane module 17. The permeate side 7 is heated in a heat exchanger 8 and further heated in a heater 16, the temperature of the so heated stream 18 is about 400°C, which is the operating temperature of the second membrane module 17 consisting of a Pd-based membrane. The membrane selected has a selectivity of 2.2-10 at 400°C and 1 bar pressure difference. 6 mol / s / m 2 / Pa, and an ideal selectivity of 20,000. 2of membrane area is required. The permeate side 20 of the second membrane module 17 (using a vacuum pump 22) was kept the same as in embodiment 1 by using a heater 21. The outlet retentate 19 of the second membrane module 17 is recycled and used as the inlet stream of the first membrane module 5. The outlet retentate 6 of the first membrane module 5 is heated in a heat exchanger 2 and then sent to an electrochemical hydrogen compressor 13 (EHC) for further hydrogen purification. After mixing the separated hydrogen 11 stream from the electrochemical hydrogen compressor 13 (EHC) with the hydrogen 23 stream coming from the second membrane module 17 made of Pd-based membrane, the mixed stream 24 is sent to the end user, while the retentate stream 14 is fed back to the piping network.

[0034] FIG. 3 shows a process flow diagram 30 of embodiment 3 of the present invention, in which two membrane modules with a mechanical compressor between them, a vacuum pump, and an EHC are combined. The first membrane module 5 is a Pd-based ceramic support membrane with an ultra-thin (1-3 pm) palladium layer that allows high hydrogen permeation at lower selectivity compared to the membranes employed in embodiments 1 and 2. The hydrogen permeation and ideal permeation selectivity are 4*10, respectively. 6 mol / s / m 2 / Pa and 4000. The second membrane module 17 connected in series with the previous membrane module had a pressure of 2*10 6 mol / s / m 2 The first membrane module 5 is a Pd-based double-skinned membrane with hydrogen permeation of 1.2 m / Pa and an ideal permeation selectivity of 60,000. The second membrane module 17 is mainly responsible for increasing the hydrogen purity. The stream 1 coming from the grid has the same feed rate and composition as in the first and second embodiments, and is first heated in the heat exchanger 2 and heater 3, where the outlet retentate stream 12 of the first membrane module 5 is cooled to 65° C., which is the working temperature of the electrochemical hydrogen compressor 13 (EHC). The outlet anode side 14 of the electrochemical hydrogen compressor 13 (EHC) is sent back to the natural gas grid. After the heater 3, the stream is passed through a 1.2 m 2The first membrane module 5 has a surface area of ​​0.15 m3 while the permeate side is kept at a pressure of 100 mbar, which was achieved using a vacuum pump 20. The permeate stream 7 from the first membrane module 5 is sent to a heat exchanger 30 and stream 25 is sent to the vacuum pump 20. The outlet stream 27 of the vacuum pump 20 is then compressed to 8 bar in a compressor 28 and then, after two heat exchangers 30, 31 in cascade, is passed through a 0.15 m3 suction well as stream 29. 2 The so obtained stream 32 is the feed stream for the second membrane module 17. The retentate stream 33 from the second membrane module 17 (mainly some impurities and remaining unrecoverable H2) is sent back to the first membrane module 5 for further purification. The purified hydrogen stream 36 from the second membrane module 17 and the stream 11 from the cathode side of the electrochemical hydrogen compressor 13 (EHC) are then mixed as stream 37 and sent to the end user.

[0035] The inventors calculated the performance of different configurations. In this description, Configuration A refers to embodiment 1, Configuration B refers to embodiment 2, and Configuration C refers to embodiment 3. The results are shown in Table 1.

[0036] Configuration A, which included a ceramic-supported Pd-based membrane connected to a vacuum pump and an electrochemical hydrogen compressor, yielded 83.39% recovery at 99.93% purity. 2 The Pd-based membrane with a surface area of ​​1.0 MPa recovers 328.9 mol / h H2 and 0.3 mol / h CH4. The concentration polarization in the retentate side helps in terms of the driving force for hydrogen, i.e. the higher the retentate pressure, the higher the mass transfer limitation between the bulk and the palladium surface. The retentate side is then sent to an electrochemical hydrogen compressor (EHC), where an additional 191.9 mol / h hydrogen with 100% purity was separated. By varying the applied voltage it is possible to vary the hydrogen recovery from the EHC (the efficiency of the EHP was considered to be 60% (optimum value for energy consumption), while the voltage was changed as a consequence).

[0037] Configuration B guarantees a very high hydrogen purity (99.99%) compared to configuration A, thanks to the further purification achieved with the second membrane module. The membrane is responsible for separating 52.66% of the hydrogen, 6.32 m 2 and a purity of 91.61%. The final purity achieved is higher than in configuration A, since it is easier to further purify the stream when it contains 91.61% hydrogen. The required electricity consumption, related only to the heat required to reach the working temperature of the system, was 5.62 kWh / kg H2. The total hydrogen production separated in this configuration is 25 kg per day, with only 1.81% hydrogen being sent back to the grid. Thus, with configuration B it is even possible to produce hydrogen of high purity (99.99) with an electricity consumption lower than 6 kWh / kg H2.

[0038] On the other hand, configuration C provided higher hydrogen purity compared to configurations A and B, but required the highest energy consumption (7.95 kWh / kg H2).

[0039] In configuration "A1", the membrane type selected is a Pd-based metal supported membrane, which has lower hydrogen permeation but higher permeation selectivity compared to ceramic supported membranes. For this reason, the membrane area required to separate 25 kg per day is 2.92 m in the current configuration. 2 The purity increases to 99.99% while the energy consumption is similar to configuration "A" and lower than "B" and "C". Additionally, the retentate pressure was varied for proper understanding of HRF and purity.

[0040] Configuration "A2" is based on an inlet pressure of 15 bar originating from the natural gas grid instead of 8 bar. The results show that the master configuration "A" (1.62 m 2 ) compared to a smaller surface area (1.43m 2) is required, but it can be noticed that the purity drops from 99.93% to 99.88% due to the higher driving force for the entrained gas to permeate. Due to the larger driving force along the membrane resulting from the higher pressure difference, a smaller membrane surface area is required and the energy consumption is very similar to the master configuration "A".

[0041] In configuration "A3", the permeate pressure is changed from 100 mbar to 70 mbar to demonstrate the effect of different vacuums on the overall system performance in terms of purity. To reach the same HRF, the membrane surface area is increased from 1.62 m2 in the master configuration "A" at 70 mbar vacuum. 2 From 1.54m 2 has been reduced to.

[0042] Configuration “A4” takes into account a H2 concentration from the natural gas grid of 15%, instead of 10% as in the previous case, which reduces the H2 concentration from 1.62 to 1.56 m 2 This resulted in a reduction in the membrane area to 0.1 and a slightly higher final purity (99.96%) compared to the master configuration (99.93%). According to the inventors, this effect is related to the driving force of higher contaminants (higher methane concentration at the inlet).

[0043] Configuration "A5" is based on a lower total flow rate from the grid of 1784.6 mol / h, of which 10% is H2 and 90% is CH4. At a purity of 99.77%, it is possible to increase the membrane HRF from 48.80% to 79.67% and the total HRF from 79.52% to 91.86%. The hydrogen purity decreases from a combination of two different reasons. The first reason is related to less hydrogen being separated from the EHP, which may guarantee a purity of 100%, while the second reason is the higher mass transfer limitations that arise at lower flow rates. The main advantage of configuration "A5" is the better quality of the natural gas grid, resulting from a lower hydrogen concentration (0.90%) returning to the natural gas grid.

[0044] The objective of configuration "A6" is to reduce the flow rate of hydrogen separated by the EHP and thus reduce energy consumption, at the expense of membrane surface and final separation cost. The membrane area to hold the same HRF is 2.41 m 2 and the energy consumption is reduced from 5.19 in configuration “A” to 4.72 kWh / kg H2.

[0045] Configuration "B1" differs from configuration "B" in terms of the type of membrane used. In configuration B, a molecular sieving carbon membrane with a permeation selectivity of 550 is considered, while in case "B1", an ultra-thin Pd-based ceramic support membrane with a selectivity of 5000 is employed in the first membrane module. In contrast to the molecular sieving carbon membrane (CMSM), the energy consumption increases due to the higher operating temperature of the Pd-based membrane (400°C). The energy consumption is 6.03 instead of 5.62 kWh / kg H2. Even if a smaller surface area is required in case "B1", it becomes less economically convenient to employ a Pd-based membrane in the first membrane module due to the higher membrane cost and higher energy consumption. On the other hand, molecular sieving carbon membranes appear to be promising, especially for separating hydrogen in high-pressure piping networks.

[0046] Configuration "B2" is based on configuration "B", with the main difference being the lower permeate pressure in the first membrane module (2 bar instead of 3 bar). The surface area of ​​the first module is reduced thanks to a more relevant driving force, while the membrane surface of the second module is increased due to the reduced retentate inlet pressure.

[0047] Configuration "C" can guarantee a relatively high purity due to the two membrane modules in series which ensures substantial purification of the stream. Configuration "C1" is based on a lower retentate pressure in the second membrane module, which is 4 bar instead of 8 bar. In this configuration, the membrane area is reduced from 2.42 to 1.87 m 2 and energy consumption decreases from 7.95 to 6.38 kWh / kg H2.

[0048] [Item 1] 1. A process for separating a low hydrogen content from a natural gas mixture, the process comprising: a) providing a stream comprising hydrogen; b) transferring the hydrogen-containing stream of a) as an inlet stream to a first membrane unit to obtain a retentate and a permeate, wherein a mole fraction of hydrogen in the permeate is greater than a mole fraction of hydrogen in the retentate; c) transferring the retentate to an electrochemical hydrogen compressor (EHC) for further hydrogen separation and purification. method. [Item 2] The method further comprises step b1), in which the permeate of step b) is transferred as an inlet stream to a second membrane unit, in which a second retentate and a second permeate are produced, the mole fraction of hydrogen in the second permeate being higher than the mole fraction of hydrogen in the second retentate, and the second retentate is sent back to the first membrane unit of step b) as an inlet stream. The method according to item 1. [Item 3] Prior to transferring the inlet stream containing hydrogen to the first membrane unit or the second membrane unit, the inlet stream containing hydrogen is heated in a heat exchanger to an operating temperature of the first membrane unit or the second membrane unit. The method according to item 2. [Item 4] Prior to transferring the retentate to the electrochemical hydrogen compressor (EHC), the retentate obtained in step b) is cooled in a heat exchanger to an operating temperature of the electrochemical hydrogen compressor (EHC). 4. The method according to any one of items 1 to 3. [Item 5] A vacuum unit is used to increase the driving force through the first membrane unit and / or the second membrane unit; The method according to item 2 or 3. [Item 6] a second retentate stream originating from the second membrane unit is heated in a heat exchanger prior to transferring the second retentate stream to the inlet of the first membrane unit; The method according to item 2 or 3. [Item 7] 7. The method according to any one of the preceding claims, wherein the first membrane unit is selected from the group consisting of Pd-based ceramic supported membranes and Pd-based metal supported membranes. [Item 8] a) the inlet pressure of the hydrogen-containing stream is at least 5 bar; 8. The method according to any one of items 1 to 7. [Item 9] the pressure of the permeate of the first membrane unit is less than 130 mbar; 9. The method according to any one of items 1 to 8. [Item 10] 10. The process according to any one of the preceding claims, wherein the hydrogen concentration of the hydrogen-containing stream of a) is at least 10% by volume. [Item 11] the pressure of the permeate in the first membrane unit is less than 5 bar; 11. The method according to any one of items 1 to 10. [Item 12] the pressure of the retentate in the second membrane unit is less than 10 bar; The method according to item 2 or 3. [Item 13] 1. An apparatus for separating a low hydrogen content from a natural gas mixture, comprising: a first membrane unit having an inlet for a hydrogen-containing stream, an outlet for a retentate, and an outlet for a permeate, wherein the mole fraction of hydrogen in the permeate is greater than the mole fraction of hydrogen in the retentate; an electrochemical hydrogen compressor (EHC) having an inlet for the retentate, an outlet cathode site, and an outlet anode site, the mole fraction of hydrogen at the outlet cathode site being higher than the mole fraction of hydrogen at the outlet anode site; Device. [Item 14] a second membrane unit having an inlet for a hydrogen-containing stream, an outlet for a second retentate, and an outlet for a second permeate, the mole fraction of hydrogen in the second permeate being higher than the mole fraction of hydrogen in the second retentate, and the outlet for the retentate of the first membrane unit being connected to the inlet of the second membrane unit. Item 14. The apparatus according to item 13.

Claims

1. 1. A method for extracting hydrogen from a natural gas mixture, the method comprising: a) providing a hydrogen-containing stream to a first heat exchanger to produce a heating stream; b) transferring the heated hydrogen-containing stream of a) as an inlet stream to a first membrane unit to obtain a first retentate and a first permeate, wherein a mole fraction of hydrogen in the first permeate is higher than a mole fraction of hydrogen in the first retentate and higher than a mole fraction of hydrogen in the inlet stream; c) transferring the first retentate to an electrochemical hydrogen compressor (EHC) for further hydrogen separation and purification to provide an EHC output stream; d) combining the EHC output stream with the first permeate to provide a purified hydrogen output stream; A method comprising:

2. Prior to transferring the first retentate to the electrochemical hydrogen compressor (EHC), the first retentate obtained in step b) is cooled in the first heat exchanger to an operating temperature of the electrochemical hydrogen compressor (EHC). The method of claim 1.

3. The method according to claim 1 or 2, wherein the first membrane unit is selected from the group of Pd-based ceramic supported membranes and Pd-based metal supported membranes.

4. a) the inlet pressure of the hydrogen-containing stream is at least 5 bar; 4. The method according to any one of claims 1 to 3.

5. the pressure of the first permeate of the first membrane unit is less than 130 mbar; 5. The method according to any one of claims 1 to 4.

6. 6. The process according to claim 1, wherein the hydrogen-containing stream of a) has a hydrogen concentration of at least 25%.

7. 7. The method of claim 1, wherein the pressure of the first permeate is reduced using a vacuum pump to increase the driving force of the first permeate through the membrane of the first membrane unit.

8. 1. An apparatus for extracting hydrogen from a natural gas mixture, comprising: a first heat exchanger for heating a hydrogen-containing stream to produce a heated stream; a first membrane unit having a first inlet for the heating stream and a first hydrogen-selective membrane for extracting a first permeate from the heating stream leaving a first retentate, the first membrane unit further having a retentate outlet for the first retentate and a permeate outlet for the first permeate, the mole fraction of hydrogen in the first permeate being greater than the mole fraction of hydrogen in the first retentate and greater than the mole fraction of hydrogen in the heating stream; an electrochemical hydrogen compressor (EHC) having an inlet for a first retentate for further separation and purification of the first retentate to provide an EHC output stream to an outlet cathode section of the EHC, the mole fraction of hydrogen at the outlet cathode section of the EHC being greater than the mole fraction of hydrogen at an outlet anode section of the EHC; means for combining the EHC output stream with the first permeate to provide a purified hydrogen output stream; An apparatus comprising:

9. 10. The apparatus of claim 8, further comprising a vacuum pump for reducing the pressure of the first permeate to increase the driving force of the first permeate through the first hydrogen-selective membrane.

10. 1. A method for extracting hydrogen from a natural gas mixture, the method comprising: a) providing a hydrogen-containing stream to a first heat exchanger to produce a heated stream; b) transferring the heated hydrogen-containing stream of a) as a first inlet stream to a first membrane unit to obtain a first retentate and a first permeate, wherein a mole fraction of hydrogen in the first permeate is greater than a mole fraction of hydrogen in the first retentate; c) transferring the first retentate to an electrochemical hydrogen compressor (EHC) for further hydrogen separation and purification to provide an EHC output stream; d) transferring the first permeate as a second inlet stream to a second membrane unit to obtain a second retentate and a second permeate, wherein a mole fraction of hydrogen in the second permeate is greater than a mole fraction of hydrogen in the second retentate and greater than a mole fraction of hydrogen in the first permeate; e) combining the EHC output stream with the second permeate to provide a purified hydrogen output stream; A method comprising:

11. The method of claim 10 , wherein the second retentate is sent back to the first membrane unit as an inlet stream.

12. 12. The method of claim 10 or 11, wherein the second retentate produced from the second membrane unit is heated in an additional heat exchanger prior to transferring the second retentate to the first membrane unit.

13. 13. The method of any one of claims 10 to 12, wherein the pressure of the first permeate is reduced using a vacuum pump to increase the driving force of the first permeate through the membrane of the first membrane unit.

14. 1. An apparatus for extracting hydrogen from a natural gas mixture, the apparatus comprising: a first heat exchanger for heating a hydrogen-containing stream to produce a heated stream; a first membrane unit having a first inlet for the heating stream and a first hydrogen-selective membrane for extracting a first permeate from the heating stream leaving a first retentate, the first membrane unit further having a retentate outlet for the first retentate and a permeate outlet for the first permeate, the mole fraction of hydrogen in the first permeate being greater than the mole fraction of hydrogen in the first retentate and greater than the mole fraction of hydrogen in the heating stream; a second membrane unit having a second inlet for the first permeate and a second hydrogen-selective membrane for extracting a second permeate from the first permeate leaving a second retentate, wherein a mole fraction of hydrogen in the second permeate is higher than a mole fraction of hydrogen in the second retentate and higher than a mole fraction of hydrogen in the first permeate; an electrochemical hydrogen compressor (EHC) having an inlet for the first retentate for further separating and purifying hydrogen from the first retentate to provide an EHC output stream at an outlet cathode site of the EHC, wherein a mole fraction of hydrogen at the outlet cathode site of the EHC is greater than a mole fraction of hydrogen at an outlet anode site of the EHC; means for combining said EHC output stream with said second permeate to provide a purified hydrogen output stream; An apparatus comprising:

15. 15. The apparatus of claim 14, further comprising a vacuum pump for reducing the pressure of the first permeate to increase the driving force of the first permeate through the membrane of the first membrane unit.

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