PROCESS FOR THE SEPARATION OF HYDROGEN FROM GAS MIXTURES

Description

[0001] The present invention relates to a process for separating and compressing hydrogen from gas mixtures. STATE OF THE ART

[0002] The extraction of hydrogen from H2-containing gas mixtures is of essential importance in numerous areas of technology. In particular, the extraction of pure hydrogen from a natural gas network is a promising approach for the future of environmentally friendly mobility using vehicles powered by hydrogen combustion engines or fuel cells. To achieve this, it is necessary to separate the hydrogen as purely and cost-effectively as possible, i.e., energy-efficiently, primarily from methane, but also from other gases contained in the natural gas network, such as lower hydrocarbons (primarily from ethane to butane), N2, and CO2.

[0003] Hydrogen is primarily produced on a large industrial scale via steam reforming from natural gas and steam. The hydrogen must then be separated from the hydrogen-containing gas produced. Numerous processes are known for this, most of which have been in use for many years. On a large industrial scale, this is achieved via pressure swing adsorption (PSA) or cryogenic separation. Pressure swing adsorption is a complex process in terms of equipment, as it requires several cyclically operating adsorbers (vessels) including numerous valves, which entails high investment costs. Nevertheless, it is a standard process for the provision of high-purity gases. In cryogenic separation, the gas mixture is partially liquefied and then separated. However, lowering the temperature is very energy-intensive and cost-intensive.

[0004] In addition to these two separation processes, membrane separation technology using hydrogen-selective membranes is becoming increasingly established, especially for smaller plants due to its high flexibility, good scalability, energy efficiency, and simplicity (low equipment and control requirements). In Liemberger et al., Chem. Eng. Trans. 52, 427-432 (2016), the working group of the present inventors discloses a combination of membrane separation and PSA for the separation of hydrogen from natural gas. In the first step, a partial stream with an increased hydrogen concentration is extracted from the natural gas grid using membrane separation technology. The subsequent pressure swing adsorption ensures the required high hydrogen product gas quality. The remaining gas is compressed to pipeline pressure and fed back into the natural gas grid. In Liemberger et al., J. Clean. Prod. 167, 896-907 (2017), the technical feasibility of the technology is demonstrated experimentally.

[0005] More recently, processes using electrochemical proton exchange membranes (PEMs) have also been described, in which hydrogen is oxidized to protons upon entering the membrane and reduced back to molecular hydrogen upon exiting. In this context, for example, Friebe et al., Angew. Chem. Int. Ed. Engl. 54(27), 7790-7794 (2015), disclose an "inverted fuel cell" by means of which hydrogen can be separated from an exhaust gas mixture in a commercially available PEM fuel cell by applying an electrical voltage, while WO 2014 / 207388 A1 discloses a multi-stage "electrochemical compressor."

[0006] US2014 332405 A1 discloses an improved process for increasing hydrogen recovery in a hydrogen production plant comprising pressure swing adsorption (PSA) and electrochemical membrane separation, wherein the exhaust stream from the PSA is fed to the electrochemical membrane to recover hydrogen, which is combined with the hydrogen-rich stream from the PSA.

[0007] However, the disadvantage of this combination of membrane separation and pressure swing adsorption is the high equipment complexity and the associated high investment costs, which are primarily due to pressure swing adsorption. Another disadvantage is the number of compressors required and their energy consumption.

[0008] Against this background, the aim of the invention was to provide an improved process for obtaining pure hydrogen, by which hydrogen is obtained in high purity of > 99.97% (which is referred to herein as "essentially pure") with the lowest possible energy consumption. DISCLOSURE OF THE INVENTION

[0009] This object is achieved by the present invention by providing a process for the separation and compression of hydrogen from H 2 -containing gas mixtures using membrane separation processes, which is characterized in that a) the H 2 -containing gas mixture is first subjected in a manner known per se to at least one membrane separation step using at least one H 2 -selective polymer membrane, whereby at least one H 2 -enriched permeate is obtained; b) the permeate thus obtained is subsequently humidified to a defined degree of humidity; c) the humidified gas mixture is then subjected to a separation step by means of a proton-transporting electrochemical membrane with simultaneous pressure increase in order to obtain a permeate comprising essentially only H 2 and H 2 O; and d) this permeate is subjected to at least one drying step selected from condensation and membrane drying in order to obtain a gas stream comprising essentially pure hydrogen.

[0010] Through this previously unknown combination of two different membrane separation steps, ie gas membranes and electrochemical membranes, with additional intermediate humidification and final drying, it is quite surprisingly possible to obtain hydrogen in an extremely high purity of practically 100%, namely > 99.99 vol.%, from a natural gas stream containing only 4 vol.% hydrogen, e.g. from a natural gas network.

[0011] As the following examples demonstrate using preferred embodiments, this process can produce an H2 product stream containing only minimal traces of H2O and no CH4 at all. At the same time, a methane stream with a purity of up to 99.9% is obtained, which can be easily fed back into the natural gas grid.

[0012] In such preferred embodiments of the invention, the H 2 -containing gas mixture in step a) is subjected at least in part, but preferably entirely, to two membrane separation steps using two H 2 -selective polymer membranes, wherein at least a portion of the permeate from the first membrane, preferably all of the permeate, is fed as feed to a second membrane and the permeate from the second separation step is fed to the humidification step. In this way, it is possible to minimize the proportion of hydrogen in the retentate (of the second membrane separation stage), i.e. in the off-stream, which in practice can be returned to the natural gas grid. In the examples, a residual amount of H 2 contained in the methane of only 5 ppm was achieved.

[0013] Furthermore, in preferred embodiments, the permeate from the electrochemical membrane separation step c) is subjected to drying both by means of a condenser and by means of a third, H2O-selective membrane in order to achieve the above-mentioned extremely low H2O content. All conventional condensation dryers can be used as condensers, although tube bundle or plate heat exchangers with suitable condensate removal are preferably used.

[0014] According to the present invention, in step a) the currently common, commercially available, highly selective aromatic polyimide membranes are generally used as H 2 -selective polymer membranes, although in the future ceramic membranes could possibly also serve this purpose if it is possible in the next few years to eliminate the currently known mechanical stability problems in order to make them suitable for continuous operation.

[0015] In step c), a Nafion membrane is preferably used as the proton-transporting electrochemical membrane, more preferably with a noble metal catalyst, in particular a platinum catalyst, as is known in principle, in order to achieve high throughputs through the electrochemical membrane.

[0016] In step d), commercially available H 2 O-selective membranes can also be used in the membrane drying stage, preferably in this case also aromatic polyimide membranes, which are commercially available with high selectivities.

[0017] Taken together, this means that no novel membranes are required for the practice of the present invention, but rather commercially available products can be used in all steps. The concrete results disclosed in the examples herein were all the more surprising.

[0018] According to natural gas grid regulations, natural gas may only have a very low residual moisture content. If water vapor is present in the natural gas grid, it will be enriched along with the hydrogen in the first membrane separation step, but the moisture level required for the electrochemical membrane will not be reached. Therefore, in step b) of the process according to the invention, the gas mixture is preferably humidified to a humidity level that corresponds to at least 40%, more preferably at least 50%, in particular at least 60%, and not more than 99%, of the relative humidity at the respective temperature of the gas mixture. This ensures uninterrupted operation of the proton-transporting electrochemical membrane, even at high throughputs.

[0019] The method of humidification is not specifically restricted and can be achieved, for example, by injecting water vapor or by using a separate humidification membrane.

[0020] Water management plays a crucial role in ensuring stable and safe operation of the electrochemical membrane, since i) if the relative humidity is too low, the transport process through the membrane will not function as desired, and ii) if the relative humidity is too high, there is a risk of flooding the membrane. This increases the specific energy consumption related to the product hydrogen.

[0021] Furthermore, according to the present invention, it is preferred that the water separated in the drying step d) is recycled to the humidification step b), which minimizes water consumption and ideally reduces it to zero. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In Fig. 1A simplified process of the present invention is shown schematically. In Fig. 2 Somewhat more complex process configurations according to preferred embodiments of the present invention are schematically illustrated, in which the drying step d) was carried out using a combination of condenser and drying membrane. Several such embodiments were computer-simulated and calculated in the following examples. EXAMPLES

[0023] The present invention is described in detail below using specific examples. These are computer simulations of the process sequence selected in each example under the following general basic conditions: Initial feed f1: Natural gas stream consisting of 96 vol.% methane and 4 vol.% hydrogen at a pressure of 51 bar and a temperature of 300 K; 0.725 m 3 / h and 725 m 3 / h, respectively. General overview

[0024] In Examples 1 to 3, it was assumed that a hydrogen-enriched permeate stream p1 is separated from a very low volume flow (0.73 m³ / h; see Table 4) of an H²-containing natural gas feed f1 in a first membrane separation stage Mem_1. The remaining gas, retentate r1, is kept at line pressure and combined with the process-derived (retentate) stream r2, consisting of almost pure methane, before being returned to the natural gas grid. Therefore, care must be taken to ensure that the total moisture content of this combined stream to be recycled, the "off" stream, meets the grid regulation criteria before refeeding. Fig. 1 shown dryer_2 is intended.

[0025] The permeate p1 from Mem_1 is either fed as input stream b1 to a mixer Mix_1, where it is partially saturated with a defined amount of water vapor ( Fig. 1), or p1 is fed at least partially as sweep gas stream s2 to a second membrane separation stage Mem_2. The permeate p2 produced there is then also fed - together with the remainder of p1 or instead of p1 - to the mixer Mix_1 for humidification ( Fig. 2 ).

[0026] The humidified gas is then fed as feed to the electrochemical membrane separation stage (Mem_el). In this separation stage, the majority of the hydrogen, including some of the moisture, is separated as permeate (pel) and simultaneously compressed, depending on the design. The remaining gas leaves the electrochemical membrane (Mem_el) as retentate (rel) at the same pressure level.

[0027] In order to achieve the necessary product gas qualities, the permeate pel must be dried, for which Dryer_1 ( Fig. 1 ) or capacitor Kond_2 ( Fig. 2). The separated water can then be recycled and fed back into the process as water stream w3.

[0028] The retentate rel from the electrochemical membrane separation stage must be compressed to natural gas pipeline pressure level, for which the compressor Komp_1 is provided in all versions. Furthermore, it may also need to be dried before it can be fed back into the natural gas network. For this purpose, Fig. 1 Dryer_2 and in Fig. 2 the condenser Kond_1 is provided. The water produced here can also be reused in the process as water stream w2. Both recirculated water streams w2 and w3 can be combined and fed to a flow divider Spilt_1, from where they are either removed from the process (wout) or mixed as water recycle stream wr in a mixer Mix_2, possibly with externally fed water win, but in any case fed to the humidifier ( Fig. 1) or mixer Mix_1 ( Fig. 2 ) can be supplied.

[0029] Moisture management plays a crucial role in the process. Therefore, it is planned that initial or additional water can be introduced from outside (water input flow win) or excess water can be removed (water output flow wout). This allows for flexible response to moisture requirements.

[0030] In addition to the simplest process management from Fig. 1 with only one gas membrane separation stage Mem_1 is in Fig. 2As a preferred embodiment of the invention, an alternative with two additional gas membrane separations (Mem_2 and Mem_3) is specified. In both separation stages, moisture recovery is the primary focus. However, in the event that not all of the hydrogen has been separated by the electrochemical membrane Mem_el, at least a portion of the hydrogen contained in its retentate rel can be separated by Mem_2 and reintroduced into the process. This increases the overall process yield of hydrogen. For further yield optimization, optional sweep gas streams s2, s3 are provided for Mem_2 and Mem_3, respectively. As can be seen from Fig. 2 As can be seen, for example, a part of the product gas retentate stream r3 from Mem_3 can be fed back to the membrane Mem_3 as sweep stream s3. Example 1

[0031] This - as well as examples 2 to 6 - in Fig. 2The schematically illustrated example is based on the assumption that the permeate p1 from the first membrane stage Mem_1 is fed entirely as sweep stream s2 to a second membrane separation stage Mem_2 before the resulting second permeate p2 is humidified in the mixer Mix_1.

[0032] The water vapor mixed with the permeate p1 in Mix_1 is only initially added from outside. During operation, however, a large portion of the required water is recycled from the condenser Cond_2 and, if necessary, from the condenser Cond_1. This reuse of the "auxiliary moisture" significantly reduces the process's fresh water requirements.

[0033] The gas mixture humidified in Mix_1 and enriched with H 2 is then fed as feed fel to the electrochemical membrane Mem_el, where the hydrogen H 2 is oxidized to protons H +<, passed through the membrane in proton form and reduced back to H 2 as permeate pel upon exiting the membrane.

[0034] This permeate is first fed to a condenser Kond_2, where an initial drying process takes place by condensing the water vapor contained in the H2 stream. The resulting water is produced as stream w3, which is fed to a further mixer Mix_2 at a stream divider Split_1 either as recycled stream wr, where it can be mixed with an external water feed win or fed directly back into the mixer Mix_1 as stream w1 without external water feed to further reduce the fresh water requirement, or, if necessary, discarded at Split_1 as stream wout. In both the present Example 1 and the following Example 2, it was assumed that - apart from an initial fresh water feed - the water requirement in the process can be fully covered by recycling the two condensate streams w3 and w2.

[0035] In this preferred embodiment of the invention, the already almost pure H2 gas stream f3 dried in the condenser Kond_2 is subjected to a further gas membrane separation using an H2O-selective membrane Mem_3, whereby the now practically 100% pure hydrogen arises here as retentate r3 and can be recovered as product gas stream prod. In the event that the moisture content in the retentate r3 is too high, the separation efficiency of the membrane separation stage Mem_3 can be increased by separating off a partial stream of the product as sweep gas stream s3. The gas mixture of hydrogen and small amounts of water vapor thus separated is fed back into the process. In the present Example 1, this optimization measure was taken, as can be seen from the values ​​in Table 1.

[0036] Furthermore, in preferred embodiments of the invention, the retentate rel from the electrochemical membrane separation stage can be fed to a compressor Komp_1 and subsequently, as compressed stream c1, to a condenser Kond_1, where it is dried and introduced as feed f2 into the second membrane separation stage Mem_2 to increase the overall process yield of H 2. The water accumulating in the condenser Kond_1 is also fed to the stream divider Split_1 as stream w2 and recycled if necessary. This was taken into account in the present Example 1, as was the recycling of the permeate p3 from the third gas membrane separation stage Mem_3 to Mix_1 to subject it to electrochemical separation again at Mem_el.

[0037] From the results of this embodiment of the invention listed in Table 1 - with a permeate from Mem_1 completely separated in Mem_2 - it can be seen that with this process procedure a large part of the hydrogen contained in f1, namely around 71%, obtained by the calculation (n H2 in stream f1 / n H2 in stream prod) x 100, can be continuously separated and recovered. Table 1 - Accounting data for Example 1 H 2 CH4 H2O SUM n mol / s x n mol / s x n mol / s x n mol / s x Electricity f1 3,60E-04 4,00E-02 8,64E-03 9,60E-01 6,93E-07 7,70E-05 9,00 E-03 1 win 1,50E-06 1,00E+00 1,50E-06 1 prod 2,54E-04 1,00E+00 2,34E-09 9,21E-06 2,54E-04 1 off 1,06E-04 1,22E-02 8,64E-03 9,88E-01 4,52E-08 5,17E-06 8,75E-03 1 r1 1,04E-04 1,22E-02 8,42E-03 9,88E-01 3,93E-08 4,61E-06 8,52E-03 1 p1 2,56E-04 5,37E-01 2,20E-04 4,62E-01 6,54E-07 1,37E-03 4,77E-04 1 s2 2,56E-04 5,37E-01 2,20E-04 4,62E-01 6,54E-07 1,37E-03 4,77E-04 1 b1 w1 1,08E-05 1,00E+00 1,08E-05 1 fel 3,93E-04 6,29E-01 2,20E-04 3,52E-01 1,16E-05 1,85E-02 6, 25 E-04 1 pel 2,95E-04 1,00E+00 1,23E-07 4,18E-04 2,95E-04 1 rel 9,84E-05 2,98E-01 2,20E-04 6,67E-01 1,14E-05 3,47E-02 3,30E-04 1 f3 2,95E-04 1,00E+00 4,53E-08 1,54E-04 2,95E-04 1 w3 7,81E-08 1,00E+00 7,81E-08 1 r3 2,54E-04 1,00E+00 2,34E-09 9,21E-06 2,54E-04 1 s3 2,54E-08 1,00E+00 2,34E-13 9,21E-06 2,54E-08 1 p3 4,14E-05 9,97E-01 1,21E-07 2,92E-03 4,15E-05 1 wr 9,32E-06 1,00E+00 9,32E-06 1 c1 9,84E-05 2,98E-01 2,20E-04 6,67E-01 1,14E-05 3,47E-02 3,30E-04 1 w2 1,08E-05 1,00E+00 1,08E-05 1 f2 9,84E-05 3,09E-01 2, 20 E-04 6,91E-01 5,07E-08 1,59E-04 - 3,19E-04 1 r2 2,34E-06 1,05E-02 2,20E-04 9,89E-01 5,98E-09 2,69E-05 2,22E-04 1 p2 3,52E-04 6,15E-01 2,20E-04 3,84E-01 6,99E-07 1,22E-03 5,73E-04 1 wout 2,15E-06 1,00E+00 2,15E-06 1 Water requirements -6,47E-07 mol / s Circulating water 1,09E-05 mol / s Circulating water relative to feed 0,12 % Circulating water based on product 4,30 % Relative humidity in fel 52,06 % Relative humidity in pel 60,00 % Relative humidity in rel 97,58 % H2 yield of the electrochemical membrane 75 % H2 total yield 70,47 % Specific energy consumption 0,72 kWh / m3< Example 2

[0038] In contrast to Example 1 – with the same process – a larger membrane area was assumed for the first gas membrane separation stage Mem_1 and a smaller area for the second stage Mem_2 (see Table 4 below). By increasing the area of ​​Mem_1, it is possible to extract even more hydrogen from the natural gas network, which is then purified, significantly increasing the overall yield to around 93%. However, since more methane is also transported through the first membrane separation stage Mem_1, it must be recompressed, which increases the overall energy consumption. In addition, a larger amount of circulating water is required. The rest of the process was identical to Example 1 and is also Fig. 2 can be found. Table 2 - Accounting data for Example 2 H 2 CH4 H2O SUM n mol / s x n x n mol / s x n mol / s x mol / s Electricity f1 3,60E-04 4,00E-02 8,64E-03 9,60E-01 6,93E-07 7,70E-05 9,00E-03 1 win 3,00E-06 1,00E+00 3,00E-06 1 prod 3,34E-04 1,00E+00 8,06E-09 2,41E-05 3,34E-04 1 off 2,59E-05 2,99E-03 8,64E-03 9,97E-01 8,56E-09 9,88E-07 8,67E-03 1 r1 2,20E-05 2,69E-03 8,15E-03 9,97E-01 4,49E-10 5,49E-08 8,17E-03 1 p1 3,38E-04 4,07E-01 4,92E-04 5,92E-01 6,93E-07 8,34E-04 8,31E-04 1 s2 3,38E-04 4,07E-01 4,92E-04 5,92E-01 6,93E-07 8,34E-04 8,31E-04 1 b1 w1 1,86E-05 1,00E+00 1,86E-05 1 fel 5,01E-04 4,95E-01 4,92E-04 4,86E-01 1,94E-05 1,92E-02 1,01E-03 1 pel 3,75E-04 1,00E+00 1,57E-07 4,18E-04 3,76E-04 1 rel 1,25E-04 1,97E-01 4,92E-04 7,73E-01 1,93E-05 3,03E-02 6,37E-04 1 f3 3,75E-04 1,00E+00 5,77E-08 1,54E-04 3,76E-04 1 w3 9,94E-08 1,00E+00 9,94E-08 1 r3 3,34E-04 1,00E+00 8,06E-09 2,41E-05 3,34E-04 1 s3 3,34E-08 1,00E+00 8,06E-13 2,41E-05 3,34E-08 1 p3 4,14E-05 9,96E-01 1,49E-07 3,59E-03 4,15E-05 1 wr 1,56E-05 1,00E+00 1,56E-05 1 c1 1,25E-04 1,97E-01 4,92E-04 7,73E-01 1,93E-05 3,03E-02 6,37E-04 1 w2 1,86E-05 1,00E+00 1,86E-05 1 f2 1,25E-04 2,03E-01 4,92E-04 7,97E-01 9,77E-08 1,58E-04 6,17E-04 1 r2 3,96E-06 7,98E-03 4,92E-04 9,92E-01 8,11E-09 1,64E-05 4,96E-04 1 p2 4,59E-04 4,82E-01 4,92E-04 5,17E-01 7,83E-07 8,22E-04 9,52E-04 1 wout 3,68E-06 1,00E+00 3,68E-06 1 Water requirements -6,78E-07 mol / s Circulating water 1,87E-05 mol / s Circulating water relative to feed 0,21 % Circulating water based on product 5,61 % Relative humidity in fel 53,98 % Relative humidity in pel 60,00 % Relative humidity in rel 85,14 % H 2 yield of the electrochemical membrane 75 % H 2 total yield 92,80 % Specific energy consumption 0,87 kWh / m3< Example 3

[0039] In contrast to the two previous examples, the membrane area of ​​the first gas separation membrane Mem_1 was further increased, reaching the largest value in Examples 1 to 3 (see Table 4). The membrane area of ​​the second membrane Mem_2 was also significantly increased compared to Example 1. The larger areas make the separation less selective, but to the benefit of the H 2 yield, which has a positive effect on the overall yield, which is increased to around 96%. However, this further increases the total energy requirement, primarily due to the lower selectivity of the first membrane separation stage Mem_1. As in Example 2, the amount of circulating water also increases. The remaining process, however, was identical to Examples 1 and 2 and is also Fig. 2 can be found. Table 3 - Accounting data for Example 3 H 2 CH4 H2O SUM n x n mol / s x n mol / s x n mol / s x mol / s Electricity f1 3,60E-04 4,00E-02 8,64E-03 9,60E-01 6,93E-07 7,70E-05 9,00E-03 1 win 3,00E-06 1,00E+00 3,00E-06 1 prod 3,46E-04 1,00E+00 9,23E-09 2,67E-05 3,46E-04 1 off 1,44E-05 1,66E-03 8,64E-03 9,98E-01 8,77E-09 1,01E-06 8,65E-03 1 r1 9,96E-06 1,24E-03 8,02E-03 9,99E-01 4,01E-11 4,99E-09 8,03E-03 1 p1 3,50E-04 3,62E-01 6,16E-04 6,37E-01 6,93E-07 7,17E-04 9,67E-04 1 s2 3,50E-04 3,62E-01 6,16E-04 6,37E-01 6,93E-07 7,17E-04 9,67E-04 1 b1 w1 2,33E-05 1,00E+00 2,33E-05 1 fel 5,16E-04 4,46E-01 6,16E-04 5,33E-01 2,42E-05 2,09E-02 1,16E-03 1 pel 3,87E-04 1,00E+00 1,62E-07 4,18E-04 3,87E-04 1 rel 1,29E-04 1,68E-01 6,16E-04 8,01E-01 2,40E-05 3,12E-02 7,69E-04 1 f3 3,87E-04 1,00E+00 5,95E-08 1,54E-04 3,87E-04 1 w3 1,02E-07 1,00E+00 1,02E-07 1 r3 3,46E-04 1,00E+00 9,23E-09 2,67E-05 3,46E-04 1 s3 3,46E-08 1,00E+00 9,23E-13 2,67E-05 3,46E-08 1 p3 4,14E-05 9,96E-01 1,53E-07 3,67E-03 4,15E-05 1 wr 2,03E-05 1,00E+00 2,03E-05 1 c1 1,29E-04 1,68E-01 6,16E-04 8,01E-01 2,40E-05 3,12E-02 7,69E-04 1 w2 2,33E-05 1,00E+00 2,33E-05 1 f2 1,29E-04 1,73E-01 6,16E-04 8,27E-01 1,18E-07 1,58E-04 7,45E-04 1 r2 4,40E-06 7,10E-03 6,16E-04 9,93E-01 8,73E-09 1,41E-05 6,20E-04 1 p2 4,75E-04 4,35E-01 6,16E-04 5,64E-01 8,03E-07 7,35E-04 1,09E-03 1 wout 3,67E-06 1,00E+00 3,67E-06 1 Water requirements -6,72E-07 mol / s Circulating water 2,35E-05 mol / s Circulating water relative to feed 0,26 % Circulating water based on product 6,80 % Relative humidity in fel 58,86 % Relative humidity in pel 60,00 % Relative humidity in rel 87,90 % H 2 yield of the electrochemical membrane 75 % H 2 total yield 96,01 % Specific energy consumption 0,96 kWh / m3< Table 4 - Membrane areas and volume flows of examples 1 to 3 Example 1 Example 2 Example 3 Areas in m 2< A(Mem_1) 0,036 0,08 0,1 A(Mem_2) 0,02125 0,017 0,17 A(Mem_3) 0,000085 0,000085 0,000085 Areas related to A(Mem_1) from Example 1 A(Mem_1) 100,0% 222,2% 277,8% A(Mem_2) 59,0% 47,2% 472,2% A(Mem_3) 0,2% 0,2% 0,2% Area ratio A(Mem_2) / A(Mem_1) 0,59 0,21 1,70 A(Mem_3) / A(Mem_1) 0,0024 0,0011 0,0009 Standard volume flows in m 3 < / h f1 0,73 0,73 0,73 p1 0,04 0,07 0,08 prod 0,02 0,03 0,03

[0040] As shown in Table 4, as already mentioned, a very low volume flow of only 0.73 m 3 / h was assumed as the output feed f1, which would be sufficient for a small hydrogen filling station of a private household, for example.

[0041] Table 5 below, however, shows the corresponding values ​​for inventive examples 4 to 6, in which a 1000-fold higher volume flow of 725 m³ / h and 1000-fold larger membrane areas for the membranes of the three gas membrane separation stages Mem_1, Mem_2, and Mem_3 were assumed as the starting feed f1. These embodiments of the invention are representative, for example, of a large-scale plant for hydrogen purification from a contaminated natural gas stream or of a public hydrogen filling station. Table 5 - Membrane areas and volume flows of examples 4 to 6 Example 4 Example 5 Example 6 Areas in m 2< A(Mem_1) 36,00 80,00 100,00 A(Mem_2) 21,25 17,00 170,00 A(Mem_3) 0,085 0,085 0,085 Areas related to A(Mem_1) from Example 4 A(Mem_1) 100,0% 222,2% 277,8% A(Mem_2) 59,0% 47,2% 472,2% A(Mem_3) 0,2% 0,2% 0,2% Area ratio A(Mem_2) / A(Mem_1) 0,59 0,21 1,70 A(Mem_3) / A(Mem_1) 0,0024 0,0011 0,0009 Standard volume flows in m 3 < / h f1 725,76 725,76 725,76 p1 38,45 67,00 77,96 prod 20,46 26,94 27,87

[0042] For these examples 4 to 6, the amounts of substance in the respective streams as well as the water requirement in Tables 1 to 3 naturally increase by a factor of 1000. The other relative values, such as the molar fractions and, above all, the respective volume-related energy requirement, remain the same, so that in example 6, as previously in the analogous example 3, hydrogen can be separated with the highest yield of over 96% - and this with only a relatively slightly increased energy requirement compared to the examples with a smaller area of ​​the first separation membrane Mem_1 (examples 1 and 2 or examples 4 and 5).

[0043] The above examples demonstrate that, depending on the process design, different overall yields can be achieved with different energy consumption. Any moisture present in the natural gas network preferentially permeates through the first membrane separation stage, Mem_1. Since the water should ultimately only be present in traces in the product and offgas, it must be removed. This is reflected in the negative water demand. However, a certain amount of circulating water is required for stable operation. The amount of this circulating water depends on the process design and the overall yield. The examples show that more moisture is required to achieve a higher overall yield.

[0044] The above computer-simulated examples thus clearly demonstrate that by means of the process of the present invention a stream of practically pure hydrogen, i.e. > 99.9% pure H 2 , since the mole fraction x of H 2 in the product stream prod is rounded to 1.00, can be diverted from a municipal natural gas network, while at the same time methane with a purity of up to 99.9% can be fed back into the network, as can be seen from the mole fractions x of CH 4 in the stream off of 0.988, 0.997 and 0.998.

[0045] Such a high separation efficiency and purity of the separated gas streams cannot be achieved with the state of the art.

Claims

1. A method for separating and compacting hydrogen from H2-containing gas mixtures by the application of membrane separation methods, characterized in that a) the H2-containing gas mixture (f1) is initially subjected to a membrane separation step using at least one H2-selective polymer membrane (Mem_1, Mem_2) in a well-known manner, resulting in at least one H2-enriched permeate (p1, p2); b) the permeate (p1, p2) thus obtained is subsequently humidified to a defined humidity level; c) the humidified gas mixture (fel) is then subjected to a separation step by means of a proton-transporting electrochemical membrane (Mem_el) while simultaneously increasing the pressure in order to obtain a permeate (pel) containing essentially only H2 and H2O; and d) this permeate (pel) is subjected to at least one drying step selected from condensation (Kond 1) and membrane drying (Mem_3) in order to obtain a gas stream (prod) comprising essentially pure hydrogen.

2. The method according to claim 1, characterized in that the H2-containing gas mixture (f1) in step a) is at least partially subjected to two membrane separation steps by the use of two H2-selective polymer membranes (Mem_1, Mem_2), wherein at least a part of the permeate (p1) of the first membrane (Mem_1) is supplied as a feed (s2) to a second membrane (Mem_2) and the permeate (p2) of the second separation step is supplied to the humidification step.

3. The method according to claim 1 or 2, characterized in that the permeate (pel) of the electrochemical membrane separation step c) is subjected to drying both by means of a condenser (Kond_1) and by means of a third H2O-selective membrane (Mem_3).

4. The method according to any one of the claims 1 to 3, characterized in that, in step a), aromatic polyimide membranes are used as said H2-selective polymer membranes (Mem_1, Mem_2).

5. The method according to any one of the claims 1 to 4, characterized in that, in step c), a Nafion membrane is used as said proton-transporting electrochemical membrane (Mem_el).

6. The method according to any one of the claims 1 to 5, characterized in that, in step c), a precious metal catalyst is used in said proton-transporting electrochemical membrane (Mem_el).

7. The method according to claim 6, characterized in that a platinum catalyst is used.

8. The method according to any one of the claims 1 to 7, characterized in that, in step b), the gas mixture is humidified to a humidity level corresponding to at least 40% of the relative humidity at the respective temperature of the gas mixture.

9. The method according to claim 8, characterized in that the gas mixture is humidified to at least 50% RH.

10. The method according to claim 9, characterized in that the gas mixture is humidified to at least 60% RH.

11. The method according to claim 10, characterized in that the gas mixture is humidified to not more than 95% RH.

12. The method according to any one of the claims 1 to 11, characterized in that the water separated in the drying step d) is recycled to the humidification step b).