EP4045172A1

EP4045172A1 - Method and plant for producing a carbon-monoxide-rich gas product

Info

Publication number: EP4045172A1
Application number: EP20786449.7A
Authority: EP
Inventors: Andreas Peschel; Benjamin HENTSCHEL
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2019-10-18
Filing date: 2020-09-22
Publication date: 2022-08-24
Also published as: TW202116674A; WO2021073769A1; KR20220079511A; US20220235478A1; CA3143870A1; JP2022552039A; CN113939612A; DE102019007265A1

Abstract

The invention relates to a method for producing a carbon-monoxide-rich gas product (6), in which method at least carbon dioxide is subjected to electrolysis (E), so as to obtain an untreated gas (3) comprising at least carbon monoxide and carbon dioxide, and in which method the untreated gas (3) is subjected to a separation process, which comprises an adsorption (A) and membrane separation (M), so as to obtain a recycling stream (7), which comprises the major part of the carbon dioxide contained in the untreated gas (3), a residual gas (8), and the carbon-monoxide-rich gas product (6), wherein the recycling stream (7) is partially or entirely recirculated to the electrolysis (E), wherein the untreated gas (3) is partially or entirely subjected to the adsorption (A) so as to obtain the recycling stream (7) and an intermediate product stream (5) which is carbon-monoxide-enriched and carbon-dioxide-depleted in relation to the untreated gas (3), and the intermediate product stream (5) is partially or entirely subjected to the membrane separation (M) so as to obtain the gas product (6) and the residual gas (8), wherein the residual gas (8) is partially or entirely recirculated to the adsorption (A). A plant for carrying out such a method is also proposed.

Description

description

Process and plant for the production of a carbon monoxide rich

Gas product

The invention relates to a method and a plant for the production of a carbon monoxide-rich gas product according to the respective preambles of the independent claims.

State of the art

Carbon monoxide can be produced using a number of different processes, for example together with hydrogen by steam reforming natural gas and subsequent purification from the synthesis gas formed, or by gasifying feedstocks such as coal, natural gas, crude oil or biomass and subsequent purification from the synthesis gas formed.

The electrochemical production of carbon monoxide from carbon dioxide is also known and appears particularly attractive for applications in which the classic production by means of steam reforming is oversized and therefore uneconomical. For this purpose, for example, high-temperature electrolysis, which is carried out using one or more solid oxide electrolysis cells, can be used. Oxygen is formed on the anode side and carbon monoxide on the cathode side according to the following generalized reaction equation:

C0 ₂ - CO + ^_1/2 0 ₂ (1)

As a rule, in the electrochemical production of carbon monoxide, there is no complete conversion of carbon dioxide to carbon monoxide with a single pass through the electrolysis cell (s), which is why carbon dioxide is typically at least partially separated from a raw gas formed during electrolysis and returned to the electrolysis. The explained electrochemical production of carbon monoxide from carbon dioxide is described, for example, in WO 2014/154253 A1, WO 2013/131778 A2, WO 2015/014527 A1 and EP 2 940 773 A1. Separation of the crude gas formed during electrolysis using absorption, adsorption, membrane and cryogenic separation processes is also disclosed in the cited publications, but no details are given on the specific design or on a combination of the processes. A combination of adsorption and membrane separation is known from DE 10 2017 005681 A1 and WO 2018 / 228717A1, but the separation sequence disclosed here is different from that in the present invention.

In solid oxide electrolysis cells, in addition to carbon dioxide, water can also be subjected to electrolysis, so that a synthesis gas containing hydrogen and carbon monoxide can be formed. Details on this can be found, for example, in an article by Foit et al., Angew. Chem. 2017, 129, 5488-5498, DOI:

10.1002 / anie.201607552. Such methods can also be used in the context of the present invention.

The electrochemical production of carbon monoxide from carbon dioxide is also possible by means of low-temperature electrolysis on aqueous electrolytes. The following reactions generally take place here:

C0 ₂ + 2e- + 2M ⁺ + H ₂ 0 - CO + 2 MOH (2)

2 MOH - ^_1/2 0 ₂ + 2M ⁺ + 2e- (3)

In the case of a corresponding low-temperature electrolysis, a membrane is used through which the positive charge carriers (M ⁺ ) required according to reaction equation 2 or formed according to reaction equation 3 diffuse from the anode to the cathode side. In contrast to high-temperature electrolysis, the positive charge carriers are not transported in the form of oxygen ions but, for example, in the form of positive ions of the electrolyte salt used (a metal hydroxide, MOH). An example of a corresponding electrolyte salt can be potassium hydroxide. In this case, the positive charge carriers are potassium ions. Further embodiments of the low-temperature electrolysis include, for example, the use of proton exchange membranes through which protons migrate or of so-called anion exchange membranes. Different variants of corresponding processes are described, for example, in Delacourt et al., J. Electrochem. Soc. 2008, 155, B42-B49, DOI: 10.1149 / 1.2801871.

Due to the presence of water in the electrolyte solution, hydrogen is partially formed at the cathode according to:

2 H ₂ 0 + 2M ⁺ + 2e- - H ₂ + 2 MOH (4)

Depending on the catalyst used, additional products of value can also be formed in the low-temperature electrolysis. In particular, a low-temperature electrolysis can be carried out with the formation of different amounts of hydrogen. Corresponding methods and devices are described, for example, in WO 2016/124300 A1 and WO 2016/128323 A1.

In high-temperature (HT) co-electrolysis, which is carried out using solid oxide electrolysis cells (SOEC), the following cathode reactions are observed or postulated:

C0 ₂ + 2 e- - CO + O ² - (5) H ₂ 0 + 2 e- - »H ₂ + O ² - (6)

The following anode reaction also takes place:

2 O ^2- - 0 ₂ + 4 e- (7)

The oxygen ions are essentially selectively conducted from the cathode to the anode via a ceramic membrane.

It has not been fully clarified whether the reaction according to reaction equation 5 takes place in the manner shown. It is also possible that only hydrogen is formed electrochemically and carbon monoxide is formed in the presence of carbon dioxide according to the reverse water-gas shift reaction: C0 ₂ + H ₂ ^ H ₂ 0 + CO (8)

As a rule, the gas mixture formed in the high-temperature co-electrolysis is in the water-gas shift equilibrium (or close to it). However, the specific manner in which the carbon monoxide is formed has no influence on the present invention.

The separation process disclosed in the already mentioned DE 102017005681 A1 for separating the crude gas formed during the electrolysis comprises only a separation of the unconverted carbon dioxide, the electrolysis products pass together into the gas product. With this process, the production of carbon monoxide is only possible with impurities in a non-negligible amount.

The separation process known from the aforementioned WO 2018/228717 A1 can lead to disadvantageous effects in certain cases, in particular with larger amounts of product.

The present invention therefore sets itself the task of improving the purity of a gas product rich in carbon monoxide in a corresponding separation and at the same time improving the yield in relation to the amount of raw material used.

Disclosure of the invention

Against this background, the present invention proposes a method for producing a gas product rich in carbon monoxide and a corresponding plant having the features of the respective independent claims. Preferred configurations are the subject matter of the dependent claims and the description below.

Before further explanation of the present invention and its advantageous embodiments, the terms used are defined and further principles of the present invention are explained.

All information about proportions of mixtures used in the context of the present disclosure relate in each case to the volume fraction. A “gas product rich in carbon monoxide” is understood here in particular to mean carbon monoxide of different purities which is formed by means of the method according to the invention. Accordingly, in addition to carbon monoxide, other gas components can also be contained, but which have a volume fraction of less than 40%, 30%, 20%, 10%, 5%, 3%, 2%, 1%,

0.5%, 0.3%, 0.2%, 0.1%, 100 ppm or 10 ppm, each based on the total product volume of the gas product. Such other gas components can in particular be carbon dioxide and / or hydrogen.

Any gas mixture provided using electrolysis to which (among other things or exclusively) is subjected to carbon dioxide is referred to as “raw gas” in the language used here. In addition to the explicitly mentioned components, the raw gas can also contain, for example, oxygen or unconverted inert components, with “inert” in the language used here being understood as “not converted in the electrolysis” and is not limited to classic inert gases.

The electrolysis carried out in the context of the present invention can be carried out using one or more electrolysis cells, one or more electrolysers each with one or more electrolysis cells or one or more other structural units suitable for electrolysis. This is or are set up in the context of the present invention in particular to carry out a low-temperature electrolysis with aqueous electrolytes, as was explained at the beginning.

Alternatively, as mentioned, high-temperature electrolysis can also be provided. In such a case, it goes without saying that the one or more electrolysis cell (s) are also set up for such a method. In this case, in particular, no aqueous electrolytes are provided, but solid electrolytes, for example of a ceramic type and / or based on transition metal oxides.

In general, substance flows, gas mixtures, etc. in the language used here can be “enriched” or “depleted” in one or more components, whereby these terms each refer to a corresponding content in a starting mixture. They are “enriched” if they are at least 1.1 times, 1.5 times, 2 times, 5 times, 10 times, 100 times or 1000 times the salary, “depleted” if they are at most contain 0.9 times, 0.75 times, 0, 5 times, 0.1 times, 0.01 times or 0.001 times the content of one or more components, based on the starting mixture.

In the language used here, material flows, gas mixtures, etc. can also be “rich” or “poor” in one or more components, with the indication “rich” for a content of at least 50%, 60%, 75%, 90%, 99 %, 99.9% or 99.99% and the indication "poor" for a content of at most 50%, 40%, 25%,

Can stand for 10%, 1%, 0.1%, 0.01% or 0.001%. If several components are given, the specification “rich” or “poor” refers to the sum of these components. If, for example, “carbon monoxide” is mentioned here, it can be a pure gas or a mixture rich in carbon monoxide. A mixture that “predominantly” contains one or more components is particularly rich in one or more of these in the sense explained.

A “permeate” is understood here and below to mean a gas mixture obtained in a membrane separation which predominantly or exclusively comprises components that are not or not completely retained by the membrane used in the membrane separation, that is to say at least partially pass through the membrane In accordance with the invention, membranes are used that preferentially retain carbon monoxide and preferentially allow other components to pass through. In this way, these other components are enriched in the permeate. Such membranes can, for example, be commercial polymer membranes which are used on an industrial scale for the separation of hydrogen and / or carbon dioxide Correspondingly, a “retentate” in the sense of this disclosure is a mixture which consists predominantly or exclusively of components which are at least partially retained by the membranes used in the membrane separation will be. A passage of the respective components can be adjusted by the appropriate choice of the membrane. Refinements and advantages of the invention

Overall, the present invention proposes a method for producing a carbon monoxide-rich gas product in the sense explained above, in which at least carbon dioxide is subjected to electrolysis to obtain a raw gas containing at least carbon monoxide and carbon dioxide.

With regard to the electrolysis processes that can be used in the process, reference is made to the above explanations. The present invention is described below in particular with reference to low-temperature electrolysis, but high-temperature electrolysis is also readily possible in various embodiments, in which case, as already mentioned, hydrogen, for example, can arise in the raw gas.

If it is said here that “at least carbon dioxide” is subjected to electrolysis, this does not exclude that further components of a feed mixture, in particular, for example, water, can also be fed to and subjected to electrolysis. In particular, in the case of high-temperature electrolysis, the supply of hydrogen and carbon monoxide to the electrolysis can have a positive effect on the service life of the electrolysis cell (s) due to the resulting setting of reducing conditions.

In the context of the present invention, electrolysis can take place in the form of high-temperature electrolysis using one or more solid oxide electrolysis cells or as low-temperature electrolysis, for example using a proton exchange membrane and an electrolyte salt in aqueous solution, in particular a metal hydroxide. In principle, the low-temperature electrolysis can be carried out using different liquid electrolytes, for example on an aqueous basis, in particular with electrolyte salts, on a polymer basis, on an organic solvent basis, on the basis of ionic liquids or in other configurations. In the case of low-temperature electrolysis, due to the presence of water, in particular as a component of the electrolyte, there is always a certain formation of hydrogen, which is variable depending on the design of the process. In high-temperature electrolysis, too, hydrogen can occur in the raw gas, for example through the formation of hydrogen due to the presence of water vapor as an impurity in the used Raw materials or by the targeted addition of hydrogen for electrolysis, as described above. Typically, no targeted co-electrolysis of carbon dioxide and water is performed in the present invention.

To set the temperature in the electrolysis and / or the membrane separation, heat exchangers and / or other heating devices or

Cooling devices are used. Corresponding heat exchangers can particularly advantageously be designed in such a way that a mixture that leaves a process step transfers its thermal energy to a mixture that is fed to the process step (“feed-effluent heat exchanger”).

The raw gas formed in the electrolysis can have a content of 0% to 20% hydrogen, 10% to 90% carbon monoxide and 10% to 90% carbon dioxide, especially in the non-aqueous portion (ie "dry"). Its water content depends on the temperature and the pressure and can be, for example, 10% to 60% at 80 ° C. and 100 kPa. Here and below, percentages relate to the volume or molar fraction.

In the context of the present invention, it is further provided that the raw gas partially or completely adsorbs the raw gas while receiving a recycling stream enriched in carbon dioxide and depleted in carbon monoxide and other components compared to the raw gas and an intermediate product depleted in carbon dioxide and enriched in carbon monoxide and other components compared to the raw gas is subjected. According to the invention, the intermediate product is furthermore partially or completely a membrane separation as a permeate, while obtaining a gas product enriched in carbon monoxide and depleted in hydrogen and other components, rich in carbon monoxide as retentate and a residual gas depleted in carbon monoxide and enriched in hydrogen and other components compared to the intermediate product subjected, wherein the recycling stream and thus the carbon dioxide contained therein is at least partially returned to the electrolysis and the residual gas is at least partially returned together with the raw gas for adsorption. An essential aspect of the present invention is therefore to use a raw gas from electrolysis, which due to the electrolysis conditions used contains at least carbon monoxide and carbon dioxide, but can also contain significant proportions of hydrogen, initially using adsorption, in particular pressure swing adsorption, vacuum pressure swing adsorption and / or a temperature swing adsorption, before a membrane separation is carried out.

The water contained in the raw gas is advantageously partially or completely removed from the raw gas before it is fed to the adsorption. In one embodiment of the present invention, the separated water can be partially or completely returned to the electrolysis.

The inventive arrangement of the adsorption upstream of the membrane separation results in several advantages which have a positive effect on the separation performance. In this way, water is removed from the raw gas before the membrane is separated, which saves energy in the process. The (almost) quantitative separation of the carbon dioxide contained in the raw gas by adsorption results in a lower volumetric load on the membrane in the downstream membrane separation, whereby a higher resistance and better separation performance can be achieved there. Because a larger amount of by-products, such as hydrogen, can be discharged in the residual gas, the yield of carbon monoxide is also increased in relation to the amount of carbon dioxide used.

As mentioned, an intermediate product is formed in adsorption, as is a gas mixture referred to here as the "recycling stream". The former is particularly heavily depleted in carbon dioxide, since this adsorbs to the adsorbent used in adsorption. Carbon monoxide is distributed in particular between the intermediate product and the recycling stream The proportions can be influenced by choosing appropriate adsorption conditions.

On the other hand, hydrogen, if present, is predominantly converted into the intermediate product. The intermediate product is therefore low in or free of carbon dioxide and can consist predominantly or exclusively of carbon monoxide and possibly hydrogen consist. For example, the intermediate contains less than 5%, 4%, 3%,

2%, 1%, 0.5%, 0.1%, 500 ppm, 100 ppm, 50 ppm, 10 ppm or 1 ppm carbon dioxide and otherwise contains 50% to 99% carbon monoxide, 0% to 20% hydrogen and any inert Components and impurities that were not removed by adsorption, such as methane, nitrogen and / or argon.

In the membrane separation, the carbon monoxide-rich gas product is formed as retentate as well as a gas mixture, referred to here as residual gas, which is formed using permeate fractions.

In the carbon monoxide-rich gas product, hydrogen and carbon dioxide are depleted and carbon monoxide is enriched compared to the intermediate product. In particular, carbon dioxide is hardly contained in any significant amount. The gas product contains, for example, 90% to 100% carbon monoxide, 0% o to 1% o carbon dioxide,

0% to 1% hydrogen and any inert components and impurities that were not separated in the membrane separation, for example methane,

Nitrogen and / or argon.

The residual gas contains the majority of the hydrogen contained in the intermediate product and is otherwise essentially composed of carbon monoxide and carbon dioxide. However, since the latter has already been removed for the most part in the adsorption, the residual gas is low in carbon dioxide.

Another essential aspect of the present invention is to recycle portions of the recycling stream (together with fresh input) into the electrolysis and / or recycle portions of the residual gas (together with the raw gas) for adsorption. In this way, advantageous conditions can be set for the process steps by adapting the composition of the respective insert. In particular, carbon dioxide for electrolysis and carbon monoxide can be returned to the separation process in a targeted or targeted manner. This is advantageous because, depending on the design, the electrolysis of Carbon dioxide is favored to carbon monoxide when there is an excess of carbon dioxide.

In this way, carbon dioxide contained in the raw gas can be used to improve the yield of a corresponding process by partially or completely returning it to the electrolysis. In this context, too, when there is talk of returning “carbon dioxide” to the electrolysis, this does not exclude the possibility that other components, intentionally or unintentionally, can also be returned to the electrolysis.

The return of the carbon monoxide contained in the residual gas to the adsorption increases the product yield, since this can ultimately be converted into the gas product in this way and is not lost via the residual gas. In addition, the admixture of residual gas to the raw gas reduces the concentration of carbon dioxide before entering the adsorption, which has an advantageous effect on the process management, in particular with regard to the pressure setting.

In the context of the present invention, a simple, inexpensive on-site production of carbon monoxide by carbon dioxide electrolysis according to one of the techniques explained is possible. In this way, carbon monoxide can be made available to a consumer without having to resort to the possibly oversized, known methods such as steam reforming. High demands on the purity of the carbon monoxide-rich gas product can be met. The on-site production means that cost-intensive and safety-critical transports of carbon monoxide can be dispensed with. In the context of the present invention, the flexible purification of a raw gas provided by means of electrolysis of carbon dioxide to carbon monoxide products of high purity with recycling of carbon dioxide to the electrolysis and particularly efficient process control is possible.

In the context of the present invention, in addition to the recycling stream, a fresh feed containing at least predominantly carbon dioxide can also be fed to the electrolysis. This fresh use can for example have a content of more than 90%, 95%, 99%, 99.9% or 99.99% of carbon dioxide. The higher this proportion, the fewer by-products there are in the electrolysis formed and the lower the proportion of non-product components that have to be separated from the raw gas. As already mentioned, however, it can be advantageous for the service life of the electrolysis cell (s) if, in addition to carbon dioxide, hydrogen and / or carbon monoxide are also supplied for electrolysis, so that under certain conditions further components, for example advantageous for process control, are specifically introduced into the fresh use can be.

As already mentioned, the use of a suitable membrane separation downstream of the adsorption can prevent undesirably high amounts of by-products from getting into the carbon monoxide-rich gas product. By returning the recycling stream to the electrolysis while avoiding the membrane separation, in particular the separation performance and the service life of the membrane can be improved.

In one embodiment of the method according to the invention, the membrane separation comprises at least a first and a second membrane separation step, the permeate being formed using permeate fractions from the first and / or second separation step. According to one embodiment of the present invention, it can also be provided that the membrane separation comprises a first and a second membrane separation step and that the permeate of one of the membrane separation steps is fed to the input mixture of another of the membrane separation steps to increase the yield and / or purity while increasing the pressure by means of a compressor.

It is particularly advantageous within the scope of the present invention that at least part of the residual gas (which is otherwise returned to the process) is discharged from the process. For example, it can be provided within the scope of the present invention that a partial flow is branched off from the residual gas in the form of a so-called purge. The components contained in a corresponding purge are removed from the process and thus removed from the process. By discharging components which, in particular, are inert and / or are undesirable in the carbon monoxide gas product, it can be avoided that they accumulate in the circuits formed by the recirculations. According to one embodiment of the present invention, it can also be provided with particular advantage that the membrane separation comprises a first and a second membrane separation step, wherein in one of the two membrane separation steps a membrane is used that generates a permeate that is particularly rich in by-products, in particular hydrogen and / or inert components. In such an embodiment according to the invention, it is particularly advantageous to form the purge using the correspondingly enriched permeate and discharge it from the process, since this is particularly low in carbon monoxide and carbon dioxide and thus the loss of carbon monoxide and / or carbon dioxide can be minimized.

In the context of the present invention it is provided that the electrolysis is carried out on an electrolysis pressure level, the adsorption on an adsorption pressure level and the membrane separation on a membrane pressure level. The adsorption pressure level and the membrane pressure level are each the entry pressures in the respective process steps. In the parlance used here, a first pressure level is “at” a second pressure level if the two pressure levels do not differ from one another by more than 0.1 MPa, 0.2 MPa, 0.3 MPa or 0.5 MPa. In the parlance used here, a first pressure level is “above” a second pressure level if it is in particular more than 0.5 MPa and up to 3 MPa above the first pressure level.

According to the invention, the electrolysis can be operated at the (entry or upper) pressure level of the adsorption (which in the case of pressure swing adsorption is, for example, 1 MPa to 8 MPa, preferably 1 MPa to 4 MPa), or at a lower pressure level. In the first case, the raw gas does not have to be compressed, or only to a small extent. For this, the recycling stream has to be compressed to the electrolysis pressure level, since it leaves the adsorption at a desorption pressure level which, in the case of pressure swing adsorption, is significantly below the adsorption pressure level. In the second case, the raw gas or its adsorption portion has to be compressed to the adsorption pressure level, whereby it may be possible to dispense with compressing the recycling stream before it is fed to the electrolysis. In a further embodiment according to the present invention, the adsorption can take the form of vacuum pressure swing adsorption be executed. The adsorption pressure level is then at the electrolysis pressure level (for example 100 kPa to 1000 kPa, preferably 100 to 500 kPa) and the desorption pressure level (for example 20 kPa to 90 kPa, preferably 30 kPa to 70 kPa) is below the electrolysis pressure level. As a result, only relatively weak compressors are required, which results in an advantage in terms of investment, safety and maintenance costs. Depending on the priority, the person skilled in the art selects the most advantageous variant for the specific application, weighing the individual advantages.

In one embodiment of the present invention, the permeate from the membrane separation can be returned to the electrolysis via the same compressor as the recycling stream from the adsorption. This means that a compressor can be saved.

In the context of the present invention, a raw gas is advantageously formed which has a content of 10% to 95% carbon monoxide, 0% to 10% hydrogen and 5% to 90% carbon dioxide.

To increase the conversion of carbon dioxide, a return of part of the raw gas to the electrolysis can advantageously be provided.

The present invention also extends to a plant for the production of a carbon monoxide-rich gas product according to the corresponding independent claim.

Regarding features and advantages of the system proposed according to the invention, express reference is made to the above explanations relating to the method according to the invention and its configurations. This also applies to a system according to a particularly preferred embodiment of the present invention, which is set up to carry out a method as explained above in its configurations.

The invention is explained in more detail below with reference to the accompanying drawings, which illustrate preferred embodiments of the present invention. Brief description of the drawings

FIG. 1 illustrates a method according to an embodiment of the invention.

Figure 2 illustrates a method according to an embodiment of the invention.

FIG. 3 illustrates a method according to an embodiment of the invention.

FIG. 4 illustrates a method according to an embodiment of the invention.

In the figures, process steps, technical units, apparatus and the like that correspond to one another functionally and / or structurally or structurally are indicated with identical reference symbols and are not explained repeatedly for the sake of clarity. Although methods according to the invention are illustrated in the figures and are explained in more detail below, these figures and explanations apply equally to the corresponding systems according to the invention.

Detailed description of the drawings

In Figure 1, a method according to an embodiment of the invention is illustrated schematically.

An electrolysis E, which can be carried out as explained at the beginning, is provided as an essential process step of the process.

A carbon dioxide-rich electrolysis insert 2 fed to the electrolysis contains carbon dioxide. This is partially converted in the electrolysis E to carbon monoxide, which passes from the cathode side of the electrolysis unit (s) into the raw gas 3, which, depending on the electrolysis conditions and the components of the electrolysis insert 2, may also contain other components. The oxygen produced on the anode side, as explained at the outset, is not shown in the figures and is removed from the process. The addition, separation and discharge or recycling of water are also not shown any heat exchangers and / or external heat sources that can be used as described above.

In the exemplary embodiment shown, the raw gas contains, for example, approximately 1% hydrogen, 34% carbon monoxide and 65% carbon dioxide, based on the dry raw gas. It is formed, for example, in an amount of approx. 500 Nm ³ / h and is present at the electrolysis pressure level of approx. 0 kPa to 100 kPa above atmospheric pressure, for example approx. 150 kPa absolute. After compression to the adsorption pressure level (for example 2 MPa), it is completely fed to an adsorption A as part of an adsorption insert 4 explained below according to the present embodiment according to the invention. The temperatures used in an electrolysis are, for example, in a range from 20 ° C to 80 ° C, for example approx. 60 ° C. Complete conversion of the carbon dioxide used is generally not desired in order to protect the electrolysis material or is not possible in terms of reaction kinetics, which is why the raw gas also contains carbon dioxide.

In adsorption A, the adsorption insert 4, which contains, for example, approx. 3% hydrogen, 38% carbon monoxide and 58% carbon dioxide and is provided, for example, in a mass flow of approx. 550 Nm ³ / h, is processed. An intermediate product 5, which contains, for example, approx. 9% hydrogen, 91% carbon monoxide and 0.1% carbon dioxide, is used in an amount of, for example, approx. 160 Nm ³ / h and a recycling stream 7, which is made up, for example, of approx. 4% hydrogen, 17% carbon monoxide and 82% carbon dioxide and ^{comprises, for example, approx. 390 Nm 3} / h.

The recycling stream 7 is from the desorption pressure level, which is, for example, approx.

120 kPa is compressed to the electrolysis pressure level by means of a compressor and with a fresh insert 1, which ^{comprises, for example, approx. 110 Nm 3} / h of pure carbon dioxide, to the electrolysis insert 2, which contains approx. 0.2% hydrogen,

14% carbon monoxide and 86% carbon dioxide and is provided in an amount of about 500 Nm ³ / h, mixed.

The intermediate product 5 is according to the embodiment of the invention illustrated here downstream of the adsorption A without adjusting the pressure of a Membrane separation M supplied. The membrane pressure level is accordingly at the adsorption pressure level, as explained above. In the membrane separation according to the embodiment of the invention shown in FIG. 1, for example, approx. 100 Nm ³ / h of a carbon monoxide gas product 6 with a composition of, for example, approx. 0.1% hydrogen, 99.9% carbon monoxide and 100 ppm carbon dioxide and approx. 60 Nm ³ / h of a residual gas 8 and 9, which is composed, for example, of approx. 22% hydrogen, 78% carbon monoxide and 0.2% carbon dioxide.

In the embodiment of the invention illustrated in FIG. 1, a portion of the residual gas, for example approx. 10 Nm ³ / h, is withdrawn as a purge 9 with the same composition as the residual gas from the process. The remaining portion of the residual gas 8 is mixed and compressed downstream of the electrolysis E with the raw gas 3 while retaining the adsorption insert 4.

The method illustrated in FIG. 2 according to an embodiment of the present invention differs from the method illustrated in FIG. 1 in particular by the multi-stage execution of the membrane separation. The intermediate product 5 is accordingly processed in a first membrane separation step M1 to obtain a first retentate 12 and a first permeate 14. The first membrane separation step M1 is carried out, for example, in such a way that a high concentration of hydrogen in the first permeate 14, for example a proportion of more than 25%, is achieved. The first retentate is processed in a second membrane separation step M2 to obtain a second retentate 13 and the carbon monoxide gas product 6. The residual gas 8, which is formed using the permeates 13 and 14, is mixed and compressed downstream of the electrolysis E together with the raw gas 3 to the adsorption insert 4. The removal of the purge 9 to be removed from the process can in this embodiment of the process take place with particular advantage from the first permeate 14, since in this way the loss of carbon monoxide and carbon dioxide, as already described, can be minimized.

In Figure 3, an embodiment of the method according to the invention is illustrated in which the adsorption is carried out in the form of a vacuum pressure swing adsorption VA. In this case, the raw gas 3 is subjected to vacuum pressure swing adsorption VA, and compression of the adsorption insert can be dispensed with. The In this embodiment of the invention, the electrolysis pressure level essentially corresponds to the adsorption pressure level of approximately 150 kPa, for example. In the illustrated embodiment of the invention, the residual gas 8 formed in the membrane separation M is compressed together with the intermediate product 5 to the membrane pressure level of, for example, approximately 2 MPa and returned to the membrane separation M.

FIG. 4 illustrates an embodiment within the scope of the present invention in which the electrolysis E is carried out in the form of high pressure electrolysis at an electrolysis pressure level of, for example, approximately 2 MPa. Compression of the raw gas to form the adsorption insert 4 can also be dispensed with in this embodiment. The adsorption A is carried out at the electrolysis pressure level. In the illustrated embodiment, the residual gas 8 from the membrane separation M is compressed together with the recycling stream 7 to form a recycling insert 10, which is returned to the electrolysis E together with the fresh insert 1 as an electrolysis insert 2. By combining the various flows to be returned and the pressure levels of electrolysis E, adsorption A and membrane separation M, compression steps can be saved.

Claims

1. A method for producing a carbon monoxide-rich gas product (6), in which at least carbon dioxide is subjected to electrolysis (E) to obtain a raw gas (3) containing at least carbon monoxide and carbon dioxide, and in which the raw gas (3) is subjected to a recycling stream ( 7) containing most of the carbon dioxide contained in the raw gas (3), a residual gas (8) and the carbon monoxide-rich gas product (6) is subjected to a separation process comprising adsorption (A) and membrane separation (M) , wherein the recycling stream (7) is partially or completely returned to the electrolysis (E), characterized in that the raw gas (3) while retaining the recycling stream (7) and a carbon monoxide enriched and depleted in carbon dioxide compared to the raw gas (3) Intermediate product stream (5) is partially or completely subjected to adsorption (A), and that the intermediate product stream (5) is partially or completely subjected to the membrane separation (M) while retaining the gas product (6) and the residual gas (8), the residual gas (8) being partially or completely returned to the adsorption (A).

2. The method according to claim 1, wherein the adsorption (A) comprises a pressure swing adsorption, a vacuum pressure swing adsorption and / or a temperature swing adsorption.

3. The method according to any one of the preceding claims, in which part of the residual gas (8) is discharged from the process.

4. The method according to any one of the preceding claims, in which the adsorption (A)

90% -100% of the carbon dioxide contained in the raw gas (3) is separated into the recycling stream (7).

5. The method according to any one of the preceding claims, wherein the membrane separation (M) comprises at least a first (M1) and a second membrane separation step (M2), wherein the retentate (12) of the first membrane separation step (M1) partially or completely in the second membrane separation step (M2) is further separated, wherein the gas product (6) is formed using the retentate of the second membrane separation step (M2) and wherein the residual gas (8) using permeate fractions (13, 14) of the at least two membrane separation steps (M1, M2) is formed.

6. The method according to any one of the preceding claims, wherein the pressure at which the electrolysis (E) is carried out by not more than 100 kPa, 200 kPa, 300 kPa or 500 kPa from the pressure at which the adsorption (A ) differs.

7. The method according to any one of claims 1 to 5, wherein the pressure at which the adsorption (A) is carried out is 0.5 MPa to 3 MPa higher than the pressure at which the electrolysis (E) is carried out.

8. The method according to any one of the preceding claims, wherein the carbon monoxide gas product (6) contains 90% -100% carbon monoxide.

9. The method according to any one of the preceding claims, in which at least 20 Nm ³ / h of the carbon monoxide gas product (6) are formed.

10. The method according to any one of the preceding claims, in which part of the raw gas (3) is returned to the electrolysis (E).

11. Plant for the production of a carbon monoxide gas product (6) with an electrolysis unit which is set up to subject at least carbon dioxide to an electrolysis (E) while obtaining a raw gas (6) containing at least carbon monoxide and carbon dioxide with means that are set up for the raw gas (3) while receiving a recycling stream (7) which contains the majority of the carbon dioxide contained in the raw gas (3), a residual gas (8) and the carbon monoxide gas product (6) a separation process that an adsorption (A) and a membrane separation (M) comprising, with means which are set up to return the recycling stream (7) partially or completely to the electrolysis (E), characterized by

Means which are set up to partially or completely subject the raw gas (3) to adsorption (A) while retaining the recycling flow (7) and an intermediate product flow (5) which is enriched in carbon monoxide and depleted in carbon dioxide compared to the raw gas (3) and

Means which are set up to partially or completely subject the intermediate product stream (5) to the membrane separation (M) while retaining the gas product (6) and the residual gas (8), with means which are set up partially to subject the residual gas (8) or completely returned to the adsorption (A).

12. Plant according to claim 11, which has means which are set up for carrying out a method according to one of claims 1 to 10.