METHOD AND SYSTEM FOR THE SYNTHESIS OF METHANOL

Abstract

A process for synthesizing methanol may involve supplying a CO2 stream consisting predominantly of carbon dioxide and an H stream consisting predominantly of hydrogen to a methanol reactor arrangement for conversion to methanol. A tail gas stream comprising unreacted hydrogen may be obtained from the methanol reactor arrangement. The unreacted hydrogen may be at least partly recycled to the methanol reactor arrangement. The tail gas stream is supplied to a hydrogen recovery arrangement to obtain a return stream comprising the unreacted hydrogen. The molar proportion of hydrogen in the return stream may be higher than in the tail gas stream.

Claims

1-15. (canceled)

16. A process for synthesizing methanol comprising: supplying a CO2 stream that includes a molar proportion of at least 50% carbon dioxide and an H stream that includes a molar proportion of at least 50% hydrogen to a methanol reactor arrangement for conversion to methanol; obtaining a tail gas stream that comprises unreacted hydrogen from the methanol reactor arrangement; supplying the tail gas stream to a hydrogen recovery arrangement to obtain a return stream that comprises unreacted hydrogen, wherein the return stream includes a molar proportion of at least 50% hydrogen; and returning the return stream or at least the unreacted hydrogen to the methanol reactor arrangement.

17. The process of claim 16 comprising: supplying the return stream as the H stream to the methanol reactor arrangement; and feeding a hydrogen-containing fresh gas stream to the hydrogen recovery arrangement to obtain the return stream.

18. The process of claim 16 wherein the H stream is a fresh gas stream from a hydrogen-obtaining arrangement, the process comprising returning the return stream to the H stream to the methanol reactor arrangement for conversion to methanol.

19. The process of claim 16 wherein the hydrogen recovery arrangement includes a pressure swing adsorption apparatus for obtaining the return stream from the tail gas stream.

20. The process of claim 19 wherein the hydrogen recovery arrangement includes a membrane apparatus for obtaining the return stream from the tail gas stream, wherein the tail gas stream is fed to the membrane apparatus to obtain a membrane hydrogen stream and a membrane tail stream, wherein the membrane tail stream is fed to the pressure swing adsorption apparatus to obtain a pressure swing adsorption hydrogen stream.

21. The process of claim 16 comprising: returning a recycle stream comprising unreacted tail gas from the methanol reactor arrangement to the methanol reactor arrangement for partial conversion to methanol; and pressurizing the recycle stream by a recycle compressor arrangement before returning the recycle stream to the methanol reactor arrangement.

22. The process of claim 21 comprising feeding the return stream to the recycle stream prior to pressurizing by the recycle compressor arrangement.

23. The process of claim 21 wherein the methanol reactor arrangement comprises a methanol separation arrangement for obtaining the tail gas stream and a crude methanol stream, wherein the recycle stream is obtained from the methanol separation arrangement.

24. The process of claim 23 wherein the methanol reactor arrangement has a multitude of reactor stages for methanol synthesis that are connected in series, wherein the methanol separation arrangement has a multitude of methanol separation apparatuses, wherein each methanol separation apparatus is connected downstream of a reactor stage of the multitude of reactor stages.

25. The process of claim 24 comprising obtaining a crude methanol substream and a stage tail gas stream comprising unreacted hydrogen from each of the methanol separation apparatuses of the multitude of methanol separation apparatuses, wherein up to a last reactor stage of the multitude of reactor stages, each stage tail gas stream from one of the methanol separation apparatuses is fed to a downstream reactor stage, the process comprising combining the crude methanol substreams to give the crude methanol stream.

26. The process of claim 24 comprising feeding the CO2 stream, the H stream, the return stream, and the pressurized recycle stream to a first reactor stage of the multitude of reactor stages.

27. The process of claim 26 wherein the tail gas stream is obtained from a methanol separation apparatus that is connected downstream of a tail gas recovery reactor stage, wherein the tail gas recovery reactor stage is connected downstream of the first reactor stage, wherein the tail gas recovery reactor stage is last in series among the multitude of reactor stages.

28. The process of claim 16 wherein the CO2 stream, the H stream, and the return stream, before being fed to the methanol reactor arrangement, are pressurized by a feed gas compressor arrangement, wherein the feed gas compressor arrangement has a multitude of compressor stages that are connected in series, wherein the H stream is supplied to the feed gas compressor arrangement for pressurization between different compressor stages of the multitude of compressor stages.

29. The process of claim 16 wherein a majority of the CO2 stream is carbon dioxide and/or a majority of the H stream is hydrogen.

30. A plant for synthesizing methanol, the plant comprising a methanol reactor arrangement configured to be supplied with a CO2 stream that includes a molar proportion of at least 50% carbon dioxide and an H stream that includes a molar proportion of at least 50% hydrogen for conversion to methanol, wherein the methanol reactor arrangement is configured to produce a tail gas stream comprising unreacted hydrogen and configured to receive the unreacted hydrogen in the tail gas stream that is at least partially returned to the methanol reactor arrangement, wherein the plant includes a hydrogen recovery arrangement configured to be supplied with the tail gas stream and to produce a return stream comprising the unreacted hydrogen, wherein the return stream includes a molar proportion of at least 50% hydrogen.

Description

[0042] Further details, features, aims and advantages of the present invention are elucidated hereinafter with reference to the drawing that shows working examples only. The drawing shows:

[0043] FIG. 1 a schematic of the flow diagram of a plant for execution of the process proposed in a first working example,

[0044] FIG. 2 a schematic of the flow diagram of a plant for execution of the process proposed in a second working example,

[0045] FIG. 3 a schematic of the flow diagram of a plant for execution of the process proposed in a third working example,

[0046] FIG. 4 a schematic of the flow diagram of a plant for execution of the process proposed in a fourth working example,

[0047] FIG. 5 a schematic of the flow diagram of a plant for execution of the process proposed in a fifth working example and

[0048] FIG. 6 a schematic of the flow diagram of a plant for execution of the process proposed in a sixth working example.

[0049] The plant according to a first working example of the plant proposed as shown in FIG. 1 serves for synthesis of methanol 1 and can be operated by the process proposed.

[0050] A CO2 stream 2 consisting essentially of carbon dioxide, an H stream 3 consisting essentially of hydrogen, and a return stream 4 likewise consisting essentially of hydrogen are pressurized by a feed gas compressor arrangement 5 and then fed to a first reactor stage 6a of a methanol reactor arrangement 7.

[0051] This feed gas compressor arrangement 5 is in multistage form. By way of simplification, the feed gas compressor arrangement 5 here is represented by three compressor stages 21a-c of a single compressor that are series-connected in the processing operation, where a feed gas compressor arrangement 5 may regularly have four compressor stages. It is apparent that the CO2 stream 2, the H stream 3 and the return stream 4 are each supplied upstream of a different compressor stage 21a-c. The CO2 stream 2 is fed in at ambient pressure, and therefore is to be pressurized by all compressor stages 21a-c of the feed gas compressor arrangement 5 for attainment of the target pressure for the methanol synthesis, and it is consequently supplied directly to the first compressor stage 21a. The H stream 3 is fed in at a somewhat higher pressure and is therefore fed in downstream of the first compressor stage 21a and upstream of the second compressor stage 21b in the processing operation. Finally, the return stream 4 is fed in at the highest pressure, and therefore between the second compressor stage 21b and the third compressor stage 21c in the processing operation.

[0052] Likewise fed into the first reactor stage 6a is a recycle stream 13. In this first reactor stage 6a consisting of a single isothermal reactor, partial conversion of the carbon dioxide and of the hydrogen to methanol takes place.

[0053] The CO2 stream 2 is obtained from the flue gas from a power plant (not shown here). The H stream 3 is obtained from an electrolysis plant for obtaining hydrogen (likewise not shown here), wherein the H stream 3 in this example could also be obtained at ambient pressure. It is alternatively conceivable that the H stream 3 is provided at a lower pressure than the CO2 stream 2, in which case the feed to the compressor stages 21a-c would be switched. The return stream 4 is obtained from a hydrogen recovery arrangement 8 of the plant, which is supplied for this purpose with a tail gas stream 9 from the methanol reactor arrangement 7, which includes unreacted reactants from the methanol synthesis and therefore unreacted hydrogen in particular.

[0054] Connected downstream of the first reactor stage 6a in the processing operation, albeit not directly, is a second reactor stage 6b of the methanol reactor arrangement 7, which second reactor stage 6b here likewise consists of a single isothermal reactor. The methanol reactor arrangement 7 has a methanol separation arrangement 10 which, through condensation of crude methanol, is set up to obtain the tail gas stream 9 and a crude methanol stream 12. The methanol separation arrangement 10 in turn consists here of a first methanol separation apparatus 11a connected between the first reactor stage 6a and the second reactor stage 6b in the processing operation, and a second methanol separation apparatus 11b connected downstream of the second reactor stage 6b in the processing operation.

[0055] The gas mixture comprising methanol and unreacted tail gas from the first reactor stage 6a is fed to the first methanol separation apparatus 11a, and a first crude methanol substream 14a, consisting essentially of crude methanol, and a first stage tail gas stream 15a comprising the unreacted tail gases from the first reactor stage 6a are obtained from this methanol separation apparatus 11a. The first stage tail gas stream 15a is fed to the second reactor stage 6b for methanol synthesis. Correspondingly, the gas mixture from the second reactor stage 6b is fed to the second methanol separation apparatus 11b, and a second crude methanol substream 14b and a second stage tail gas stream 15b are obtained therefrom. The first crude methanol substream 14a and the second crude methanol substream 14b are combined to give the crude methanol stream 12, which is in turn fed to a distillation 16 to obtain the methanol 1.

[0056] The second stage tail gas stream 15b is divided into the tail gas stream 9, which is of course fed to the hydrogen recovery arrangement 8, and the recycle stream 13. In this way, both the tail gas stream 9 and the recycle stream 13 are obtained from the methanol separation arrangement 10. The recycle stream 13 is fed to a recycle compressor arrangement 17 for increasing the pressure and then to the first reactor stage 6a. Since the tail gas stream 9 from the second reactor stage 6b is thus obtained directly downstream here, the second reactor stage 6b can be referred to as tail gas-obtaining reactor stage 20.

[0057] In the working example of FIG. 1, the hydrogen recovery arrangement 8 is a pressure swing adsorption apparatus 18 that affords the return stream 4 from the tail gas stream 9. Likewise obtained is a purge stream 19, which is fed to a firing apparatus (not shown here) of a separate chemical plant, where it is incinerated. The composition of the purge stream 19 corresponds essentially to the composition of the tail gas stream 9 minus the return stream 4. The hydrogen fed back to the methanol reactor arrangement 7 via the return stream 4 is not fired with the purge stream 19 but is available for the methanol synthesis.

[0058] The plant according to a second working example of the plant proposed as shown in FIG. 2 may be operated by the process proposed. This working example corresponds in principle to the first working example of FIG. 1, except that the return stream 4 from the hydrogen recovery arrangement 8 is not pressurized by the feed gas compressor arrangement 5 before being fed to the first reactor stage 6a. Instead, the return stream 4 is fed into the recycle stream 13. This feed is effected upstream of the recycle compressor arrangement 17 in the processing operation, such that the return stream 4 is pressurized by the recycle compressor arrangement 17 together with the recycle stream 13. Compared to the working example of FIG. 1, this firstly reduces the burden on the feed gas compressor arrangement 5. It may likewise be the case that the pressure of the return stream 4 is close to the pressure of the recycle stream 13, such that the latter has to be expanded only slightly, and therefore combination of the return stream 4 with the recycle stream 13 is more favorable than supply of the return stream to the feed gas compressor arrangement 5.

[0059] The plant according to a third working example of the plant proposed as shown in FIG. 3 may be operated by the process proposed. This working example likewise corresponds in principle to the first working example of FIG. 1, except that the hydrogen recovery arrangement 8 here consists of a membrane apparatus 22 for obtaining the return stream 4 and the purge stream 19. Especially when a relatively large pressure drop of the return stream 4 compared to the tail gas stream 9 is accepted—which can in principle be compensated for by the increase in pressure in the feed gas compressor arrangement 5—it is possible to recover a particularly high proportion of the hydrogen in the tail gas stream 9 via the return stream 4. Correspondingly, the loss of hydrogen in the purge stream 19 is low.

[0060] The plant according to a fourth working example of the plant proposed as shown in FIG. 4 proceeds from the third working example of FIG. 3 and can likewise be operated by the process proposed. Here, the hydrogen recovery apparatus 8 comprises both a membrane apparatus 22 and a pressure swing adsorption apparatus 18. Specifically, the tail gas stream 9 is fed to the membrane apparatus 22. A hydrogen-enriched membrane hydrogen stream 23 and a correspondingly low-hydrogen membrane tail stream 24 are obtained from the membrane apparatus 22. The membrane tail stream 24 is fed to the pressure swing adsorption apparatus 18, such that a PSA hydrogen stream 25 consisting essentially of hydrogen and the purge stream 19 are obtained therefrom in turn. The PSA hydrogen stream 25 is combined here with the membrane hydrogen stream 23 to give the return stream 4. But it would also be possible to guide only the membrane hydrogen stream 23 as return stream 4 and the PSA hydrogen stream 25 separately as further return stream to the feed gas compressor arrangement 5. In this case, it would be possible to feed in the membrane hydrogen stream 23 and the PSA hydrogen stream 25 upstream of different compressor stages 21a-c owing to their different pressure. Because the membrane apparatus 22 is connected upstream of the pressure swing adsorption apparatus 18 in the manner described for the fourth working example, the burden on the pressure swing adsorption apparatus 18 is reduced to such an extent that can have a smaller design. It is thus possible to return a very high proportion of the hydrogen in the tail gas stream 9 overall.

[0061] The plant according to a fifth working example of the plant proposed as shown in FIG. 5 may be operated by the method proposed and proceeds in principle from the first working example of FIG. 1, except that—as will be described in detail—the H stream 3 is not obtained from an electrolysis. However, the hydrogen recovery arrangement 8 designed as a pressure swing adsorption apparatus 18 is also used here for the hydrogen-containing fresh gas stream 26, which fresh gas stream 26 is obtained from a hydrogen-obtaining arrangement 27. The hydrogen-obtaining arrangement 27 consists of a steam reformer 28 which is supplied with a natural gas stream 31 and from which a synthesis gas stream 32 comprising carbon oxides and hydrogen is obtained. This synthesis gas stream 32, in order to increase its hydrogen content, is fed to a reactor 29 of the hydrogen-obtaining arrangement 27 for the water-gas shift reaction, from which reactor 29 the fresh gas stream 26 is then obtained. The purge gas 19 from the pressure swing adsorption apparatus 18 can then be used together with a fuel gas 30 for operation of the steam reformer 28. In a departure from the working examples of FIGS. 1 to 4, the pressure swing adsorption apparatus 18 and the hydrogen-obtaining arrangement 27 added in this working example are also part of a chemical plant 33, with the pressure swing adsorption apparatus 18 being part of this chemical plant 33 and part of the plant proposed for synthesis of methanol.

[0062] By virtue of the common use of the pressure swing adsorption apparatus 18, the return stream 4 from the hydrogen recovery arrangement 8 forms the H stream 3, such that the return stream 4 is thus fed as H stream 3 to the methanol reactor arrangement 7. As shown in FIG. 5, only a portion of the hydrogen obtained from the hydrogen recovery arrangement 8 forms the return stream 4, and the further hydrogen can be fed to a use in the chemical plant 33.

[0063] Finally, the plant according to a sixth working example of the plant proposed as shown in FIG. 6 may likewise be operated by the process proposed and proceeds from the fifth working example. However, the hydrogen recovery arrangement 8 here, similarly to the fourth working example, has a membrane apparatus 22 and a pressure swing adsorption apparatus 18. In accordance with the fourth working example, the membrane tail stream 24 here too is fed to the pressure swing adsorption apparatus 18, specifically together with the fresh gas stream 26. The PSA hydrogen stream 25 then forms the return stream 4 which, after its pressure has been increased by the feed gas compressor arrangement 5, is fed as H stream 3 to the methanol reactor arrangement 7. The membrane hydrogen stream 23 forms a further return stream 34 which, after its pressure has been increased by the feed gas compressor arrangement 5, is fed to the methanol reactor arrangement 7.