METHOD AND PLANT FOR PRODUCING A CARBON-MONOXIDE-RICH GAS PRODUCT

Abstract

A method for producing a carbon-monoxide-rich gas product, in which method at least carbon dioxide is subjected to electrolysis, so as to obtain an untreated gas comprising at least carbon monoxide and carbon dioxide, and in which method the untreated gas is subjected to a separation process, which comprises an adsorption and membrane separation, so as to obtain a recycling stream, which comprises the major part of the carbon dioxide contained in the untreated gas, a residual gas, and the carbon-monoxide-rich gas product. A plant for carrying out such a method is also proposed.

Claims

1-12. (canceled)

13. A method for producing a carbon-monoxide-rich gas product, in which method at least carbon dioxide is subjected to electrolysis, so as to obtain an untreated gas comprising at least carbon monoxide and carbon dioxide, and in which method the untreated gas is subjected to a separation process, which comprises an adsorption and membrane separation, so as to obtain a recycling stream, which comprises the majority of the carbon dioxide contained in the untreated gas, a residual gas, and the carbon-monoxide-rich gas product, wherein the recycling stream is partially or entirely recirculated to the electrolysis, wherein the untreated gas is partially or entirely subjected to the adsorption so as to obtain the recycling stream and an intermediate product stream which is carbon-monoxide-enriched and carbon-dioxide-depleted in relation to the untreated gas, and that the intermediate product stream is partially or entirely subjected to the membrane separation so as to obtain the gas product and the residual gas, wherein the residual gas is partially or entirely recirculated to the adsorption.

14. The method according to claim 13, wherein the adsorption comprises pressure swing adsorption, vacuum pressure swing adsorption and/or temperature swing adsorption.

15. The method according to claim 13, wherein some of the residual gas is discharged from the method.

16. The method according to claim 13, wherein the adsorption separates 90%-100% of the carbon dioxide contained in the untreated gas into the recycling stream.

17. The method according to claim 13, wherein the membrane separation comprises at least a first membrane separation step and a second membrane separation step, wherein the retentate of the first membrane separation step is separated further partially or entirely in the second membrane separation step, wherein the gas product is formed using the retentate of the second membrane separation step, and wherein the residual gas is formed using permeate portions of the at least two membrane separation steps.

18. The method according to claim 13, wherein the pressure at which the electrolysis is carried out is not more than 100 kPa, 200 kPa, 300 kPa or 500 kPa different from the pressure at which the adsorption is carried out.

19. The method according to claim 13, wherein the pressure at which the adsorption is carried out is 0.5 MPa to 3 MPa higher than the pressure at which the electrolysis is carried out.

20. The method according to claim 13, wherein the carbon monoxide gas product contains 90%-100% carbon monoxide.

21. The method according to claim 13, wherein at least 20 Nm.sup.3/h of the carbon monoxide gas product is formed.

22. The method according to claim 13, wherein some of the untreated gas is recirculated to the electrolysis.

23. A plant for producing a carbon monoxide gas product having an electrolysis unit, which is configured to subject at least carbon dioxide to an electrolysis so as to obtain an untreated gas containing at least carbon monoxide and carbon dioxide, and having means configured to subject the untreated gas to a separation process, which comprises an adsorption and membrane separation, so as to obtain a recycling stream, which comprises the majority of the carbon dioxide contained in the untreated gas, a residual gas, and the carbon monoxide gas product, with means configured to partially or entirely recirculate the recycling stream to the electrolysis, wherein means which are configured to partially or entirely subject the untreated gas to the adsorption so as to obtain the recycling stream and an intermediate product stream which is carbon-monoxide-enriched and carbon-dioxide-depleted in relation to the untreated gas, and means which are configured to partially or entirely subject the intermediate product stream to the membrane separation so as to obtain the gas product and the residual gas, with means configured to partially or entirely recirculate the residual gas to the adsorption.

24. A plant for producing a carbon monoxide gas product having an electrolysis unit, which is configured to subject at least carbon dioxide to an electrolysis so as to obtain an untreated gas containing at least carbon monoxide and carbon dioxide, and having means configured to subject the untreated gas to a separation process, which comprises an adsorption and membrane separation, so as to obtain a recycling stream, which comprises the majority of the carbon dioxide contained in the untreated gas, a residual gas, and the carbon monoxide gas product, with means configured to partially or entirely recirculate the recycling stream to the electrolysis, wherein means which are configured to partially or entirely subject the untreated gas to the adsorption so as to obtain the recycling stream and an intermediate product stream which is carbon-monoxide-enriched and carbon-dioxide-depleted in relation to the untreated gas, and means which are configured to partially or entirely subject the intermediate product stream to the membrane separation so as to obtain the gas product and the residual gas, with means configured to partially or entirely recirculate the residual gas to the adsorption, wherein said plant for producing a carbon monoxide gas product having an electrolysis is configured to carry out the method according to claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] FIG. 1 illustrates a method according to an embodiment of the invention.

[0061] FIG. 2 illustrates a method according to an embodiment of the invention.

[0062] FIG. 3 illustrates a method according to an embodiment of the invention.

[0063] FIG. 4 illustrates a method according to an embodiment of the invention.

[0064] In the figures, method steps, technical units, apparatuses, and the like, which correspond to one another in terms of their function and/or design or structure, bear identical reference signs and, for the sake of clarity, are not repeatedly explained. Although methods according to the invention are illustrated in the figures and are explained in more detail below, these figures and explanations apply in the same way to the corresponding plants according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0065] FIG. 1 schematically shows a method according to an embodiment of the invention.

[0066] An electrolysis E, which can be carried out as explained at the outset, is provided as an essential step of the method.

[0067] An electrolysis feed 2, which is rich in carbon dioxide and is supplied to the electrolysis, contains carbon dioxide. The carbon dioxide is partially reacted to carbon monoxide during electrolysis E, which carbon monoxide passes from the cathode side of the electrolysis unit(s) into the untreated gas 3 where further components may also be contained depending on the electrolysis conditions and the components of the electrolysis feed 2. The oxygen arising on the anode side as explained at the beginning is not shown in the figures and is removed from the method. Also not shown are the addition, separation, and discharge or recycling of water, as well as possible heat exchangers and/or external heat sources, which can be used as described above.

[0068] In the exemplary embodiment shown, the untreated gas contains, for example, about 1% hydrogen, 34% carbon monoxide and 65% carbon dioxide, based on the dry untreated gas. It is formed, for example, in an amount of approximately 500 Nm.sup.3/h and is present at the electrolysis pressure level of approximately 0 kPa to 100 kPa above the atmospheric pressure, for example approximately 150 kPa absolute. After compression to the adsorption pressure level (for example, 2 MPa), it is fed entirely to an adsorption A as part of an adsorption feed 4 explained below according to the present embodiment according to the invention. The temperatures used in an electrolysis are, for example, in a range of 20° C. to 80° C., for example approximately 60° C. Complete conversion of the carbon dioxide used is generally not desired in order to protect the electrolysis material or is not possible from a reaction kinetics point of view, which is why the untreated gas also contains carbon dioxide.

[0069] During adsorption A, the adsorption feed 4, which contains, for example, approximately 3% hydrogen, 38% carbon monoxide and 58% carbon dioxide and which is provided, for example, in a quantity stream of approximately 550 Nm.sup.3/h, is processed. Here, an intermediate product 5, which contains, for example, approximately 9% hydrogen, 91% carbon monoxide and 0.1% carbon dioxide, is formed in a quantity of, for example, approximately 160 Nm.sup.3/h and a recycling stream 7 is formed, which consists, for example, of approximately 0.4% hydrogen, 17% carbon monoxide and 82% carbon dioxide and comprises, for example, approximately 390 Nm.sup.3/h.

[0070] The recycling stream 7 is compressed by the desorption pressure level, which is, for example, approximately 120 kPa, by means of a compressor to the electrolysis pressure level and is mixed with a fresh feed 1, which comprises, for example, approximately 110 Nm.sup.3/h pure carbon dioxide, to give the electrolysis feed 2, which has about 0.2% hydrogen, 14% carbon monoxide and 86% carbon dioxide and is provided in an amount of about 500 Nm.sup.3/h.

[0071] According to the embodiment of the invention illustrated herein, the intermediate product 5 is fed to a membrane separation M downstream of the adsorption A without adjusting the pressure. 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 approximately 100 Nm.sup.3/h of a carbon monoxide gas product 6 having a composition of, for example, approximately 0.1% hydrogen, 99.9% carbon monoxide and 100 ppm carbon dioxide and approximately 60 Nm.sup.3/h of a residual gas 8 and 9, which consists, for example, of approximately 22% hydrogen, 78% carbon monoxide and 0.2% carbon dioxide, are formed.

[0072] In the embodiment of the invention illustrated in FIG. 1, some of the residual gas, for example approximately 10 Nm.sup.3/h, is removed from the process as purge 9 having the same composition as the residual gas. The remaining portion of the residual gas 8 is mixed with the untreated gas 3 downstream of the electrolysis E to obtain the adsorption feed 4 and is compressed.

[0073] The method according to an embodiment of the present invention illustrated in FIG. 2 differs from the method illustrated in FIG. 1 in particular by the multi-stage design 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 is achieved in the first permeate 14, for example a proportion of more than 25%. 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 with the untreated gas 3 downstream of the electrolysis E to form the adsorption feed 4 and is compressed. In this embodiment of the process, the purge 9 to be removed from the process can be particularly advantageously removed from the first permeate 14 since the loss of carbon monoxide and carbon dioxide can thus be minimized, as already described.

[0074] FIG. 3 illustrates an embodiment of the method according to the invention in which adsorption is carried out in the form of a vacuum pressure swing adsorption VA. In this case, the untreated gas 3 is subjected to vacuum pressure swing adsorption VA, wherein compression of the adsorption feed can be dispensed with. In this embodiment of the invention, the electrolysis pressure level essentially corresponds to the adsorption pressure level of, for example, approximately 150 kPa. 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 is recirculated to the membrane separation M.

[0075] FIG. 4 illustrates an embodiment in the context 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 untreated gas to form the adsorption feed 4 can also be dispensed with in this embodiment. Adsorption A is carried out at the electrolysis pressure level. In the embodiment illustrated, the residual gas 8 from the membrane separation M is compressed together with the recycling stream 7 to form a recycling feed 10, which, together with the fresh feed 1, is recirculated as electrolysis feed 2 to the electrolysis E. Compression steps can be saved by combining the various streams to be recirculated as well as the pressure levels of electrolysis E, adsorption A and membrane separation M.