Process for separating low hydrogen content from natural gas mixtures - Patents.com

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] While hydrogen can be generated from renewable energy sources (during off-peak hours), there is global consensus that its storage remains the biggest drawback for 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, and transportation, 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 benefits, including sector integration, gas decarbonization, energy storage and easy distribution (using existing infrastructure), and, of course, hydrogen risk reduction. The maximum blending level of hydrogen into the gas grid varies significantly across Europe, ranging from a maximum of 3% in Belgium and the UK to 10–14% (volume percent) in the Netherlands and Germany. A 10% average gas concentration would 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 must be compressed for delivery back to the natural gas grid. Therefore, two mechanical compressors are required in the system: one to reach the adsorption pressure for hydrogen separation, and the second to compress the natural gas back into the grid. However, when such a system is used for the separation of low hydrogen concentrations, the system requires a significant amount of compression energy and power source to reinject the low-hydrogen gas back into the grid, which is highly uneconomical.

[0004] PSA systems work efficiently at large 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 it requires pressurizing 10 volumes of gas per volume of hydrogen to a high-pressure ratio. Because PSA units are sized as a function of the amount of impurities in the gas mixture that needs to be purified, at low hydrogen concentrations, the PSA unit becomes very large. Additionally, the higher the adsorption pressure, the higher the purity of the hydrogen output, but the greater 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 significant. When using hydrogen for fuel cell applications, high purity and low pressure are required, making PSA units even less efficient at separating 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, global energy consumption has been changing, driven by the need for new green energy sources to reduce greenhouse gas emissions. The rapid development of renewable energy as a green technology has created many problems in grid management (due to the intermittency of its production), which can be solved by integrating smart grids and storage systems. A future hydrogen-powered society may offer a possible solution to the energy storage problem. The possibility of producing hydrogen using electrolyzers using renewable electricity surplus production during the day offers one possible solution to the grid / energy storage problem. Therefore, converting electrical energy to chemical energy and storing the generated chemical energy becomes a feasible option. In this regard, the concept of blending hydrogen into natural gas pipeline networks has become more attractive, as it allows pure hydrogen to be delivered to the market using downstream separation and purification technologies close to the point of end use. In addition, a significant expansion of natural gas pipeline networks can be utilized to distribute hydrogen. At relatively low hydrogen concentrations, blending may require minor modifications to the operation of the pipeline network, and building dedicated hydrogen pipelines may be costly. 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 power.

[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 can be supplied to end users.

[0008] Therefore, it is an object 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 capability 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 mole fraction of hydrogen in the permeate is higher than the mole fraction of hydrogen in the retentate; and c) transferring the retentate to an electrochemical hydrogen compressor (EHC) for further hydrogen separation and purification.

[0011] This method provides significant synergistic benefits while improving overall hydrogen recovery, purity, and overall hydrogen cost. In one embodiment of the present invention, natural gas (composed of 10% H, 90% CH, and some impurities) originating from a pipeline is heated to the required temperature for a 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 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 EHC can be combined 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, and easy large-scale feasibility. In addition, the inventors have found that recovery and purity can be tailored, particularly 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 compressing hydrogen via the electrochemical reactions shown in equations (1), (2), and (3) below. [ka] [ka] [ka]

[0013] Because EHCs have no moving parts, the compressed hydrogen is not contaminated with oil, which is needed as a lubricant for moving parts, and the maintenance required for the system is low. The absence of moving parts also 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, which facilitates large-scale feasibility. Typically, in large-scale systems, single units are placed electrically in series and parallel to the gas flow to handle the required volumetric flow rate, with the same current flowing through each cell, ensuring that the cells operate under the same conditions.

[0014] The polarization curve provides information about the electrochemical resistance of the EHC. The voltage loss, commonly referred to as overpotential, can be divided into three regions: the active region, the ohmic region, and the mass-transport-limited region. In the low-current-density region, the active overpotential is significant. In the intermediate region, the cell's internal resistance, primarily due to membrane resistance, is the primary factor in 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 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 step b1), in which the permeate of step b) is fed as an inlet stream to a second membrane unit, producing a second retentate and a second permeate in the second membrane unit, the second permeate having a higher molar fraction of hydrogen than the second retentate, and the second retentate being fed back to the membrane unit of step b) as an inlet stream. Such an embodiment ensures very high hydrogen purity (99.99%) compared to the embodiment with 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 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 operating temperature of the membrane unit is about 400°C, it is preferable 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 noticed that electrochemical hydrogen compressors (EHC) offer good performance at higher temperatures, but proper moisture management for humidifying 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 unit.

[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 consisting of Pd-based ceramic supported membranes and Pd-based metal supported membranes, which have lower hydrogen permeation but higher permeation selectivity than 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 increasing the retentate pressure increases purity by requiring a lower surface area but by providing a higher driving force for the hydrogen-containing stream to permeate. A smaller membrane surface area is required because the driving force across the membrane is greater due to the greater 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 have found that increasing the H concentration of the hydrogen-containing stream results in a decrease in membrane area and a slight increase in 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 results in 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 present invention further relates to an apparatus for separating low hydrogen content from a natural gas mixture, the apparatus 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 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, compressors, and vacuum pumps. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a process flow diagram of a first embodiment of the present invention. [Figure 2] FIG. 1 is a process flow diagram of a second embodiment of the present invention. [Figure 3] FIG. 1 is a process flow diagram of a third embodiment of the present invention. [Figure 4] 10 shows the results of calculations of the performance of an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] In order to allow those skilled in the art to better understand the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described in the following embodiments 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, outlet permeate and retentate streams, and an overall support structure. The flow through the membrane is called permeate. The material rejected by the membrane is called retentate. In this description, the mole fraction of hydrogen in the permeate is higher than that in the retentate.

[0031] Three different embodiments are proposed for the separation and purification of hydrogen from a mixture of 10% H2 and 90% CH4 by combining palladium membrane, vacuum pump, mechanical compressor, and electrochemical hydrogen compressor technologies. The basis for all 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] 1 shows a process flow diagram 10 for embodiment 1 of the present invention. Incoming Stream 1 (originating from the piping network) at 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 needed to reach the membrane working temperature of 400°C. After heater 3, stream 4 is passed through a 1.2 m 2 The selected membrane has a surface area of ​​2.2*10 at 400°C. 6 mol / s / m 2The Pd-based ceramic support membrane has a hydrogen permeability of 1 / Pa and an ideal permselectivity of 20,000 (experimentally obtained), 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 (the same as the stream coming from the piping network), while the permeate side is maintained at 100 mbar by using a vacuum pump 9 (to increase the driving force through the membrane). The permeate stream 7 is cooled in a cooler 8 before entering the vacuum pump 9 (the 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 cooled downstream 12 is sent to an electrochemical hydrogen compressor 13 (EHC) with a proton membrane resistance of 6 mΩ and 350 parallel batteries 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. Additionally, hydrogen 11 emerging from the outlet cathode side of 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. Next, after depressurization of stream 11 from electrochemical hydrogen compressor 13, purified hydrogen 15 from the permeate side of membrane module 5 and hydrogen 11 from the cathode side of electrochemical hydrogen compressor 13 are combined as stream 16. The outlet anode side stream 14 of 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 a process flow diagram 20 of embodiment 2 of the present invention, which combines two membrane modules of carbon molecular sieving 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 the same as 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 passed through 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, making it a large surface area. The permeate side is maintained at 3 bar to provide sufficient driving force for membrane module 5 and maintain a pressure differential with the second membrane module 17. The permeate side 7 is heated in heat exchanger 8 and further heated in heater 16, and the temperature of the thus heated stream 18 is approximately 400°C, which is the operating temperature of the second membrane module 17, which is made of a Pd-based membrane. The membrane selected exhibits a selectivity of 2.2-10 at 400°C and a pressure differential of 1 bar. 6 mol / s / m 2 / Pa and an ideal selectivity of 20,000. To achieve a final separation of 25 kg per day, a 0.62 m 2A membrane area of ​​1000 mbar 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 was recycled and used as the inlet stream of the first membrane module 5. The outlet retentate 6 of the first membrane module 5 was 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 consisting of a Pd-based membrane, the mixed stream 24 was sent to an end user, while the retentate stream 14 was 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 ultrathin (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 a hydrogen permeation rate 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. Stream 1 originating from the pipeline has the same feed rate and composition as in embodiments 1 and 2, and is first heated in heat exchanger 2 and heater 3, where the outlet retentate stream 12 of the first membrane module 5 is cooled to 65°C, 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 pipeline. After heater 3, the stream is passed through a 1.2 m 2The permeate side was maintained at a pressure of 100 mbar, which was achieved using a vacuum pump 20. The permeate stream 7 from the first membrane module 5 was sent to a heat exchanger 30, and stream 25 was sent to the vacuum pump 20. The outlet stream 27 of the vacuum pump 20 was then compressed to 8 bar in a compressor 28 and then passed through two heat exchangers 30, 31 in cascade to a 0.15 m3 permeate as stream 29. 2 The purified hydrogen from the second membrane module 17 is then sent to the second membrane module 17 having a surface area of ​​1000 sq. m. 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 stream 11 from the cathode side of the electrochemical hydrogen compressor 13 (EHC) are then combined 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 A Pd-based membrane with a surface area of ​​1.0 sq. m recovered 328.9 mol / h of H2 and 0.3 mol / h of CH4. Concentration polarization in the retentate side served as the driving force for hydrogen; the higher the retentate pressure, the higher the mass transfer limit between the bulk and the palladium surface. The retentate side was then sent to an electrochemical hydrogen compressor (EHC), where an additional 191.9 mol / h of hydrogen with 100% purity was separated. The hydrogen recovery from the EHC could be varied by varying the applied voltage (the efficiency of the EHC was considered to be 60% (optimal for energy consumption), while the voltage was varied accordingly).

[0037] Configuration B guarantees a very high hydrogen purity (99.99%) compared to configuration A, thanks to the additional 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 operating 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% of the 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, instead of 8 bar, coming from the natural gas network. The results show that by increasing the retentate pressure, the master configuration "A" (1.62 m 2 ) compared to a smaller surface (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 across the membrane resulting from the higher pressure difference, a smaller membrane surface area is required, and the energy consumption is very similar to 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 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 15% H2 concentration from the natural gas network instead of 10% as in the previous case, which results in a difference of 1.62 to 1.56 m 2 This resulted in a reduction in membrane area to 99.96%, 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 for 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 99.77% purity, 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 for a combination of two different reasons. The first reason is related to less hydrogen being separated from the EHP, which can ensure 100% purity, 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 the lower hydrogen concentration (0.90%) returned to the grid.

[0044] The objective of configuration "A6" is to reduce the flow rate of hydrogen separated by the EHP and thereby reduce energy consumption, at the expense of membrane surface and final separation cost. The membrane area required to retain 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 the type of membrane used. In configuration B, a molecular sieving carbon membrane with a permselectivity of 550 is considered, while in case "B1," an ultrathin 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 kWh / kg H2 instead of 5.62 kWh / kg H2. In case "B1," even though a smaller surface area is required, the higher membrane cost and higher energy consumption make it less economically feasible to employ a Pd-based membrane in the first membrane module. On the other hand, molecular sieving carbon membranes appear promising, especially for separating hydrogen in high-pressure pipelines.

[0046] Configuration "B2" is based on configuration "B", with the main difference being a lower permeate pressure in the first membrane module (2 bar instead of 3 bar). The surface area of ​​the first module is reduced due 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 method for separating a low hydrogen content from a natural gas mixture, the method 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 the mole fraction of hydrogen in the permeate is higher than the 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), wherein the permeate of step b) is transferred as an inlet stream to a second membrane unit, where a second retentate and a second permeate are produced in the second membrane unit, 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 returned as an inlet stream to the first membrane unit of step b). 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 the operating temperature of the first membrane unit or the second membrane unit. The method described in item 2. [Item 4] 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). 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 before being transferred 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 items 1 to 6, 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 items 1 to 9, wherein the hydrogen concentration of the hydrogen-containing stream of a) is at least 10% by volume. [Item 11] the pressure of the permeate of 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 higher 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, wherein the mole fraction of hydrogen at the outlet cathode site is 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, 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; Item 14. The device 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 heated 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 the mole fraction of hydrogen in the first permeate is higher than the mole fraction of hydrogen in the first retentate and higher than the 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. Before 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. 3. The method of claim 1, wherein the first membrane unit is selected from the group consisting 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 method of 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 and 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, wherein the mole fraction of hydrogen in the first permeate is higher than the mole fraction of hydrogen in the first retentate and higher 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, wherein the mole fraction of hydrogen at the outlet cathode section of the EHC is higher 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 the mole fraction of hydrogen in the first permeate is higher than the 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 the mole fraction of hydrogen in the second permeate is higher than the mole fraction of hydrogen in the second retentate and higher than the 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 before 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, said 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 and 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, wherein the mole fraction of hydrogen in the first permeate is higher than the mole fraction of hydrogen in the first retentate and higher 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 that extracts a second permeate from the first permeate leaving a second retentate, wherein the mole fraction of hydrogen in the second permeate is higher than the mole fraction of hydrogen in the second retentate and higher than the 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 section of the EHC, wherein the mole fraction of hydrogen at the outlet cathode section of the EHC is greater than the mole fraction of hydrogen at an outlet anode section of the EHC; means for combining the EHC output stream with the 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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