METHOD AND SYSTEM FOR THE PRODUCTION OF METHANOL

Abstract

A process for preparing methanol by a methanol synthesis reaction of carbon dioxide with hydrogen may involve a distillation step and a condensation step following the synthesis of a crude methanol. A volatile component and water may be separated off from a methanol-containing product stream, and a gas stream containing a volatile component that has been separated off may be discharged at least partially as offgas. At least part of the gas stream that has been separated off may be recirculated into the methanol synthesis reaction. A plant for preparing methanol can store or utilize electric power generated from renewable energy sources and provide facilities for discharging the offgas stream, which can be purified by catalytic after-combustion. Alternatively, the plant can be configured without discharge of an offgas substream, or the offgas streams are so small that they can be released without treatment into the environment at a suitable position.

Claims

1.-35. (canceled)

36. A process for preparing methanol by reaction of carbon dioxide with hydrogen, the process comprising: feeding a product stream obtained in a methanol synthesis reaction to at least one of a high-pressure separator or a low-pressure separator where a gas stream is separated off from a methanol-containing product stream; feeding the methanol-containing product stream, after the gas stream is separated off, to a distillation step where water is separated off from the methanol-containing product stream; and recirculating volatile components that have been separated off in the distillation step at least partly into a mixing and compression section located upstream of the methanol synthesis reaction.

37. The process of claim 36 comprising at least one of at least partially discharging a gas stream that contains at least one of the volatile components as offgas, or recirculating at least part of the gas stream that contains the at least one of the volatile components to the methanol synthesis reaction.

38. The process of claim 36 comprising feeding at least one substream of the gas stream to a catalytic offgas purification.

39. The process of claim 38 wherein the catalytic offgas purification comprises a catalytic after-combustion with introduction of a supplementary combustion component.

40. The process of claim 39 wherein oxygen obtained by electrolysis is introduced as the supplementary combustion component.

41. The process of claim 36 comprising obtaining the hydrogen used as a starter material in the methanol synthesis reaction by electrolysis of water.

42. The process of claim 41 wherein water that has been separated off from the methanol-containing product stream in the distillation step, water that has been separated off by condensation, or water that has been separated off via another method is at least partially recirculated for the electrolysis.

43. The process of claim 41 comprising treating water that is used as a starter material for the electrolysis by at least one of ion exchange or reverse osmosis.

44. The process of claim 36 wherein liquid carbon dioxide is used as a starter material in the methanol synthesis reaction.

45. The process of claim 36 comprising vaporizing and heating the carbon dioxide with heat from a return stream of a cooling medium.

46. The process of claim 36 comprising: feeding the product stream obtained in the methanol synthesis reaction to the low-pressure separator; and feeding the gas stream that has been separated off in the low-pressure separator to the distillation step.

47. The process of claim 36 wherein the mixing and compression section includes one or more compressors or compressor stages connected in series.

48. The process of claim 36 comprising discharging a substream of the volatile components separated off in the distillation step as offgas.

49. The process of claim 36 comprising: feeding the product stream obtained in the methanol synthesis reaction to the high-pressure separator; at least partially recirculating the gas stream that has been separated off in the high-pressure separator as recycle gas to the methanol synthesis reaction; and feeding a substream from the high-pressure separator to the distillation step.

50. The process of claim 36 wherein the gas stream is a first gas stream, the process further comprising: feeding the product stream obtained in the methanol synthesis reaction to the high-pressure separator where the first gas stream is separated off from the methanol-containing product stream; feeding the methanol-containing product stream to the low-pressure separator where a second gas stream is separated off from the methanol-containing product stream; at least partially recirculating the first gas stream as recycle gas to the methanol synthesis reaction; and feeding the second gas stream and a remainder of the methanol-containing product stream to the distillation step.

51. The process of claim 36 comprising supplying the mixing and compression section with carbon monoxide or hydrogen or a synthesis gas containing carbon oxides and hydrogen from outside a plant where the process occurs.

52. The process of claim 36 comprising: recirculating a gas stream that has been separated off in the distillation step to the mixing and compression section; and recirculating water that has been separated off in the distillation step as process water for electrolytic production of hydrogen.

53. The process of claim 36 comprising: recirculating a gas stream that has been separated off in the distillation step into the mixing and compression section where the gas stream is compressed in a first compressor or a first compressor stage, which generates a compressed recirculated stream; combining at least one of the carbon dioxide or the hydrogen as feed gases with the compressed recirculated stream, which generates a resulting combined mixture; feeding the resulting combined mixture to a second compressor or a second compressor stage; and feeding the resulting combined mixture, after the second compressor or the second compressor stage, to the methanol synthesis reaction.

54. The process of claim 36 comprising supplying the mixing and compression section from outside a plant where the process occurs with carbon monoxide or hydrogen or a synthesis gas containing carbon oxides and hydrogen, hydrogen produced by electrolysis, gaseous carbon dioxide produced from cryogenic dioxide by vaporization, and/or a stream of the volatile components that has been separated off in the distillation step and recirculated.

55. A plant for preparing methanol by reaction of carbon dioxide with hydrogen, the plant comprising: a reactor unit for synthesis of methanol; a first separation apparatus located downstream of the reactor unit, the first separation apparatus for separating off volatile and/or liquid constituents from a methanol-containing product stream; a second separation apparatus located downstream of the first separation apparatus, the second separation apparatus for separating off volatile constituents and water by distillation; and a return conduit connected to the second separation apparatus for at least partial recirculation of a gas stream separated off in the second separation apparatus to a region upstream of the reactor unit.

56. The plant of claim 55 comprising: an offgas conduit connected to the second separation apparatus for at least partial discharge of an offgas stream; and an apparatus for catalytic offgas purification of at least one of the offgas stream or a purge gas stream to be discharged, wherein the apparatus for catalytic offgas purification is indirectly or directly in active communication with the reactor unit via the offgas conduit.

57. The plant of claim 56 comprising at least one of: a gas conduit from a high-pressure separator to the apparatus for catalytic offgas purification, a gas conduit from a low-pressure separator to the apparatus for catalytic offgas purification, or a gas conduit from a distillation apparatus to the catalytic offgas purification.

58. The plant of claim 55 comprising: an electrolysis apparatus for producing hydrogen from water; and means for feeding the hydrogen produced by way of the electrolysis apparatus to the reactor unit for the synthesis of methanol.

59. The plant of claim 58 comprising a compressor disposed between the electrolysis apparatus and the reactor unit.

60. The plant of claim 58 comprising: an apparatus for treating water by removing substances dissolved in the water; and means for feeding the treated water to the electrolysis apparatus.

61. The plant of claim 55 wherein the first separation apparatus comprises a high-pressure separator that is located downstream of the reactor unit and is configured to separate gaseous constituents from the methanol-containing product stream.

62. The plant of claim 55 wherein the first separation apparatus comprises a low-pressure separator that is located downstream of the reactor unit and is configured to separate liquid and/or gaseous constituents from the methanol-containing product stream.

63. The plant of claim 55 wherein the second separation apparatus comprises a distillation apparatus and the return conduit for recirculating the gas stream that has been separated off in the distillation apparatus to the region upstream of the reactor unit.

64. The plant of claim 55 comprising: an apparatus for providing carbon dioxide; a vaporizer located downstream of the apparatus for providing carbon dioxide; a compressor located downstream of the vaporizer; and means for feeding carbon dioxide from the vaporizer and/or the compressor to the reactor unit.

65. The plant of claim 55 comprising a return conduit that extends from a high-pressure separator and conveys gases to an entry region of the reactor unit and a compressor disposed in a flow path between the high-pressure separator and the entry region of the reactor unit.

66. The plant of claim 65 comprising a branch conduit branching off from the return conduit for feeding a substream of volatile constituents separated off in the high-pressure separator into a top region of a distillation apparatus.

67. The plant of claim 66 wherein the branch conduit opens into a conduit that serves to feed volatile constituents separated off in a low-pressure separator into the top region of the distillation apparatus.

68. The plant of claim 55 comprising a mixing and compression section that is disposed upstream of the reactor unit and is in active communication with the reactor unit, wherein the mixing and compression section includes one or more compressors or compressor stages and that mixes and compresses a carbon dioxide gas stream supplied from a vaporizer with a hydrogen gas stream produced by electrolysis of water and/or a feed gas stream comprising carbon dioxide and or carbon monoxide and/or hydrogen and/or a synthesis gas from outside the plant.

69. The plant of claim 55 comprising a store for hydrogen that is disposed downstream of an electrolysis apparatus for producing hydrogen from water.

70. The plant of claim 55 comprising an offgas conduit connected to the second separation apparatus for at least partial discharge of an offgas stream.

Description

[0054] The present invention will be illustrated below with the aid of working examples with reference to the accompanying drawings. The drawings show:

[0055] FIG. 1 a schematic flow diagram of a first illustrative plant for the preparation of methanol with incineration of part of the purge gases/offgases;

[0056] FIG. 2 a schematic flow diagram of a second illustrative plant for the preparation of methanol with catalytic combustion of part of the purge gases/offgases;

[0057] FIG. 3 a schematic flow diagram of a third illustrative plant for the preparation of methanol;

[0058] FIG. 4 a schematic flow diagram of a fourth illustrative plant for the preparation of methanol with discharge of part of the purge gases/offgases;

[0059] FIG. 5 a schematic flow diagram of a fifth illustrative plant for the preparation of methanol without discharge of an offgas stream;

[0060] FIG. 6 a schematic flow diagram of a sixth illustrative plant for the preparation of methanol with introduction of further feed gases into the methanol synthesis;

[0061] FIG. 7 a schematic flow diagram of a seventh illustrative plant for the preparation of methanol with a simplified plant configuration.

[0062] In the following, reference is made firstly to FIG. 1. In the working example, this is, in particular, a small-scale plant for methanol production having a capacity in the order of, for example, up to several 10 000 t/a. An external source of carbon dioxide is provided; this carbon dioxide can, for example, be present cryogenically and is fed to a vaporizer 10 from where the CO.sub.2 goes via a conduit 11 into the compressor 12. The second starter material for the preparation of methanol is hydrogen, which is obtained electrolytically from water. Electric power 13 obtained from renewable energy sources is preferably used to operate the electrolysis apparatus 14. The starter material for the electrolysis is water which is conveyed via a conduit 15 firstly optionally into a work-up apparatus 16 in which, for example, a reverse osmosis and/or an ion exchange is provided. From there, the treated water goes via the conduit 17 as starter material into the electrolysis apparatus 14. At this point, a substream of freshwater for a possible steam and condensate system and/or a closed cooling medium circuit can, for example, be branched off. The wastewater from the treatment apparatus can in the simplest case be discharged from the system via the wastewater conduit 42.

[0063] The electrolysis of water forms not only hydrogen but also oxygen which can be discharged via a conduit 18 from the electrolysis apparatus 14 and either be used as supplementary combustion component in the catalytic after-combustion of the purged gases/offgases or else is passed to another use outside the system. The hydrogen produced in the electrolysis is fed via the conduit 20 to the compressor 12 to which the CO.sub.2 is also fed via the conduit 11. From the compressor 12, the combined feed mixture of CO.sub.2 and H.sub.2 is then fed via the conduit 21 into the methanol synthesis reactor 22.

[0064] The methanol synthesis takes place in the methanol synthesis reactor 22 and the product stream leaving this reactor is fed via the conduit 23 to a high-pressure separator 24. From this, it is possible to provide a return conduit 25 to a compressor 19 in which a starter material-containing gas mixture which has been separated off from the product stream in the high-pressure separator 24 is compressed and, after compression, recirculated and fed back into the methanol synthesis reactor 22. In the present example, this methanol synthesis reactor 22 operates at an elevated temperature, for example in the order of from 200 C. to 300 C., and at an elevated pressure which can be, for example, in the range from about 30 bar to 100 bar. In addition, a catalyst is generally used for the methanol synthesis. The methanol-containing product stream leaving the methanol synthesis reactor 22 is fed into a high-pressure separator 24, leaves the latter via the conduit 27 and is then optionally fed to a low-pressure separator 28 in which further separation of gases from the methanol-containing product stream occurs.

[0065] Further purification of this crude methanol takes place in a distillation apparatus 30 which is connected via a conduit to the low-pressure separator 38 and in which volatile components are separated off and are discharged from the top of the distillation apparatus 30 via a conduit 33 and in the simplest case can optionally be discharged as offgas from the system. Furthermore, a second conduit 31 extending from the low-pressure separator 28 is provided; volatile components separated off there can likewise be introduced via this conduit into the offgas stream. These volatile components can, particularly when small amounts are obtained, be burnt by means of a flare 39 and the offgas can be discharged from the system via the conduit 40.

[0066] Apart from the volatile components, water can be separated off from the methanol at the bottom of the distillation apparatus 30 and the waste water can in the case of this simple plant be discharged from the system via the conduit 41. The methanol is then discharged from the system in a high purity via the conduit 32 and can, for example, be stored in tanks.

[0067] Part of the volatile components separated off in the high-pressure separator 24 is conveyed as recycle gas via the return conduit 25 to a further compressor 19 and then from there fed into the conduit 21 for starter materials, so that these components can be recirculated to the methanol synthesis reactor 22.

[0068] A second working example of a plant according to the invention for preparing methanol is described below with reference to FIG. 2. The structure is similar to the working example described above with the aid of FIG. 1, since this is also a relatively small plant (small-scale) in a basic configuration, but, as a difference from the example of FIG. 1, an offgas purification is provided. All plant components which correspond to the structure according to the figure are not explained again here. In this respect, reference is made to what has been said above. The difference from the example of FIG. 1 is that an apparatus 36 for catalytic offgas purification is provided instead of the flare 39.

[0069] The gas stream leaving the top of the distillation apparatus 30 is conveyed via the gas conduit 33 (see FIG. 1) to a catalytic after-combustion 36. The proportion of volatile components separated off in the high-pressure separator 24 is taken as purge gas stream from the circuit and fed via conduit 35 to the apparatus 36 for catalytic after-combustion. This can be fed together with oxygen, which is obtained as by-product in the electrolysis apparatus 14, via the conduit 18, so that, depending on the composition of the purge gases, the oxygen introduced as supplementary combustion component can serve to promote the combustion. The catalytic after-combustion occurs in the apparatus 36, so that a purified offgas stream which leaves the plant via the discharge conduit 37 is produced.

[0070] A third working example of the present invention is explained below with reference to FIG. 3. This variant differs from the two above-described working examples firstly in that the formation of offgas has been minimized. The fluid stream of the volatile components separated off in the distillation apparatus 30 is here recirculated as recycle stream via the return conduit 34 into a region located upstream of a first compressor or a first compressor stage 12 and upstream of the methanol synthesis reactor 22. Unlike the above-described variants, a first compressor (compressor stage) 12 to which firstly the hydrogen from the electrolysis 14 and also this recycle stream is fed is provided here. The mixture leaving the first compressor 12 is then fed together with the carbon dioxide supplied from the vaporizer 10 via the conduit 11 to a further compressor or a further compressor stage 26, since multiple compression is necessary in order to bring the feed gases to the pressure envisaged for the methanol synthesis. From the outlet of this further compressor 26, the feed stream then goes into the methanol synthesis reactor 22 which is additionally supplied with the recycle gas recirculated from the high-pressure separator 24 via the return conduit 25 after it has been compressed in the compressor 19.

[0071] Furthermore, the water obtained at the bottom in the distillation is in this variant not discharged from the system but instead circulated via the return conduit as process water back into the water electrolysis 14. This water separated off in the distillation can optionally also firstly be treated, for example to remove methanol by means of a membrane process. Substances dissolved in the water or other impurities can optionally be separated off by suitable methods. If no treatment of the water separated off in the distillation is necessary, the reaction can be carried out without wastewater being formed in this variant of the process. If treatment of the water is necessary, the wastewater from the treatment 16 is discharged from the system via the wastewater conduit 42.

[0072] A further difference in the variant as shown in FIG. 3 is that cooling medium from a closed cooling circuit 46 is used to vaporize the cryogenic CO.sub.2 in the vaporizer 10 and heat it before it is conveyed via the conduit 11 to the second compressor stage 26. A glycol/water mixture can be used as coolant. The heated cooling medium thus does not have to be cooled separately but instead the heat present in the cooling medium can be utilized for the vaporization of CO.sub.2.

[0073] A fourth embodiment of the present invention is explained below with reference to FIG. 4. This plant concept for the methanol synthesis corresponds essentially to that described above with reference to FIG. 3, with the difference than in the variant as per FIG. 4 an offgas stream is provided and is discharged from the system. From the return conduit 34, which recirculates the recycle stream from the top of the distillation apparatus 30 into the region upstream of the first compressor (or the compressor stage) 12, a substream is branched off via an offgas conduit 37 and discharged from the system. However, the amount of offgas can be minimized since, both in the variant as per FIG. 4 and in that as per FIG. 3, the gas phase from the low-pressure separator 28 is passed directly via a further conduit 45 into the distillation apparatus (distillation column) 30. The total efficiency of the plant is increased thereby. The variant as per FIG. 4 also discloses the possibility of additionally providing a small offgas stream 47 which is branched off from the conduit 25 via which the recycled gas is recirculated to the methanol synthesis. Due to the offgas stream 47, the recycled gas stream does not become too large and the ratio of H.sub.2 to CO.sub.2 in the reactor can be set within certain limits. A further manipulated variable for setting the desired H.sub.2 to CO.sub.2 ratio is the introduction of the two starter materials CO.sub.2 and H.sub.2 upstream of the mixing and compression section.

[0074] A fifth working example of the present invention is explained below with reference to FIG. 5. This plant concept for the methanol synthesis represents a variant in which no stream of offgas, or a minimal stream of offgas, is discharged from the system. It differs from the above-described variant as per FIG. 3 in that a substream is branched off via conduit 44, which opens into the further conduit 45, from the recycle gas which is recirculated from the high-pressure separator 24 via the return conduit 25 and the compressor 19 to the methanol synthesis 22. An alternative to this would be direct introduction into the distillation apparatus 30. In this way, this substream can be mixed into the gas stream which goes directly from the low-pressure separator 28 to the distillation apparatus 30. Taking off a substream from the recycle gas enables a constant stream to be recirculated via the recycle compressor 19 to the methanol reactor 22. The division of the stream creates flexibility in respect of the amount recirculated.

[0075] The return conduit 34 provided in the variants as per FIGS. 3 to 7 conveys the gas stream from the distillation apparatus 30 back to a point upstream of the compressor 12 by means of which the feed gas is compressed. The gas stream from the low-pressure separator 28 is fed into the distillation apparatus 30. A substream of the gas stream from the high-pressure separator 24 can, as is shown in the working examples as per FIGS. 5 to 7, likewise be fed via the conduits 44 and 45 to the distillation apparatus 30. As an alternative, the gas stream from the high-pressure separator 24 can, however, be recirculated either in its entirety as in the variants shown in FIGS. 3 and 4 or partly as in the variants shown in FIGS. 5 to 7, optionally with compression by means of the further compressor 19, to the inlet of the methanol synthesis reactor 22. The efficiency of the methanol plant of the invention is significantly improved by these measures.

[0076] The integrated configuration of the methanol plant in the working examples shown in FIGS. 3 to 5 has the advantage that the amount of offgas obtained in the process can be significantly reduced. In addition, the amount of the feed gases carbon dioxide and hydrogen can be reduced considerably, for example by a few percentage points, at the same amount of methanol produced. The quantity of electric power required in the electrolysis for obtaining the hydrogen is also reduced in this way.

[0077] The vaporizer 10 for vaporizing the cryogenic carbon dioxide, as shown in the working examples as per FIGS. 2 to 6, produces cold which can, for example, be used for cooling the stream of hydrogen from the electrolysis. The stream of hydrogen can in this way be cooled down to temperatures in the region of, for example, less than 5 C. As a result, it is possible to recover a high proportion of water which can then be conveyed back into the electrolysis apparatus 14 for the water electrolysis. A glycol/water mixture, for example, serves as cooling medium here.

[0078] Furthermore, the process water obtained as coproduct in the process can advantageously be recirculated to the electrolysis apparatus 14, for example via the return conduit 43 depicted in FIG. 3.

[0079] Further advantages of the process are given by the apparatus 36 for catalytic offgas purification as described above with the aid of FIG. 2.

[0080] A sixth working example of the present invention will be explained below with reference to FIG. 6. This plant concept for the methanol synthesis provides for discharge of a small offgas stream 37 from the return conduit 34 via which the recycle stream is recirculated to the region upstream of the compressor 12. Such a small offgas stream 37 can, for example, be obtained when a catalyst having poor selectivity is used or unfavorable operating parameters are selected when deactivation of the catalyst has progressed and by-products are thus formed to an increased extent.

[0081] This embodiment as per FIG. 6 also differs from the above-described variants in that further feed gases are introduced from outside the system into the mixing and compression section which comprises the two compressors 12 and 26 or compressor stages. A further conduit 48 which leads from outside to the mixing and compression section and via which CO, H.sub.2 or a synthesis gas comprising CO, CO.sub.2 and H.sub.2 can be introduced is provided. These further gases are mixed in the mixing and compression section with the hydrogen from the electrolysis 14 and/or the carbon dioxide from the vaporizer and the mixture is then fed to the methanol synthesis reactor 22.

[0082] A seventh working example of the present invention is explained below with reference to FIG. 7. This variant relates to a somewhat simplified plant concept for the synthesis of methanol. Here, carbon dioxide is fed from outside the system in the gaseous state via the conduit 11 into a region which is arranged downstream of the first compressor or the first compressor stage 12. The hydrogen is not produced in the system by electrolysis but is instead also supplied from outside via the conduit 20, which comes into consideration when, for example, hydrogen is available at a site. Any other combinations for provision of the feed gases are also possible, for example the use of H.sub.2 from the electrolysis in combination with gaseous CO.sub.2 or, for example, the use of H.sub.2 from outside in combination with cryogenic CO.sub.2. In FIG. 7, too, an offgas stream 37 can be provided in a manner analogous to that described above in the case of FIG. 6.

[0083] The two feed gases go into the region between the first compressor or the first compressor stage 12 and the second compressor or the second compressor stage 26. Here, the way in which compression is carried out is also dependent on the pressure level of the gases present. Introduction downstream of the first compressor stage represents one of several alternative possibilities. The gases can, in a manner analogous to FIG. 7, be introduced into the mixing and compression section at any point, depending on the pressure level at which the gas is present. The recycle stream recirculated from the distillation apparatus 30 via the return conduit 34 is, on the other hand, fed into a region upstream of the first compressor 12 and is there firstly compressed and then, at the outlet end of the first compressor 12, mixed with the fresh feed gases hydrogen and carbon dioxide introduced from the outside and this mixture is fed into the second compressor 26. The recycle gas is, as described above in the case of the variant of FIG. 1, conveyed from the high-pressure separator 24 via the return conduit 25 through the compressor 19, compressed there and then mixed in the region downstream of the second compressor 26 with the fluid stream produced there and fed into the methanol synthesis reactor 22.

[0084] The process water is not recycled in this variant since no production of hydrogen by electrolysis is provided in the system but instead, as in the variant in accordance with FIG. 1, the water separated off in the distillation apparatus 30 can be discharged from the system via a conduit 31 from the bottom of the column. In an alternative variant of the invention, it is also possible to provide an additional H.sub.2 store in the plant, with, for example, the H.sub.2 being stored under superatmospheric pressure in a vessel. For example, in a plant concept as has been described above with reference to FIG. 3, the H.sub.2 store can be arranged in the region of the first compressor 12, with, for short-term equalization of relatively small fluctuations, a conduit which leads to the inlet side of the H.sub.2 store being branched off downstream of the first compressor 12 and upstream of the second compressor 26 and a conduit being able to lead back from the outlet side of the H.sub.2 store into the region upstream of the first compressor 12. Thus, for example, when there is low power availability, the capacity of the actual methanol plant can be adapted in a regulated manner. This is especially advantageous for the distillation column 30. Pure hydrogen is not stored by means of the branch downstream of the first compressor stage 12. However, the H.sub.2 content is, for example, above 98%. Further components such as CO.sub.2, CO, methanol, dimethyl ether and methyl formate get in via the recycle stream. In return, however, there is the advantage that no additional compressor is necessary.

[0085] When, for example, proton exchange membrane electrolyzers (PEM electrolyzers) are used, the H.sub.2 is obtained at relatively high pressures (for example up to 35 bar) and can then be stored directly without a compressor stage.

[0086] When relatively large storage capacities for hydrogen are necessary, an alternative variant can be chosen. For example, a branched conduit for hydrogen which branches off downstream of the water electrolysis 14 and upstream of the first compressor 12 and leads firstly to a further compressor in order to bring the hydrogen to a higher pressure and store it at a higher pressure can be provided in the plant flow diagram depicted in FIG. 3. The hydrogen store from the outlet of which a conduit leads into the region between the first compressor 12 and the second compressor 26 is then arranged downstream of this further compressor (see plant flow diagram in FIG. 3). In this way, pure H.sub.2 can be stored at higher pressures by means of the additional compressor. Here too, the introduction can also be effected, as an alternative, upstream of the first compressor 12.

LIST OF REFERENCE NUMERALS

[0087] 10 Vaporizer [0088] 11 Conduit for CO.sub.2 [0089] 12 Compressor [0090] 13 Inlet conduit for stream [0091] 14 Electrolysis apparatus [0092] 15 Feed conduit for water [0093] 16 Water treatment [0094] 17 Feed conduit for water [0095] 18 Conduit for oxygen [0096] 19 Compressor [0097] 20 Conduit for hydrogen [0098] 21 Conduit for starter materials [0099] 22 Methanol synthesis reactor [0100] 23 Conduit for product [0101] 24 High-pressure separator [0102] 25 Return conduit (recycle gas conduit) [0103] 26 Compressor [0104] 27 Conduit [0105] 28 Low-pressure separator [0106] 29 Conduit [0107] 30 Distillation apparatus [0108] 31 Second conduit [0109] 32 Outlet conduit for methanol [0110] 33 Conduit [0111] 34 Return conduit [0112] 35 Conduit to after-combustion [0113] 36 Apparatus for catalytic offgas purification [0114] 37 Outlet conduit [0115] 38 Crude methanol tank [0116] 39 Flare [0117] 40 Offgas conduit [0118] 41 Wastewater conduit [0119] 42 Wastewater conduit [0120] 43 Return conduit for process water [0121] 44 Conduit for substream [0122] 45 Conduit [0123] 46 Coolant circuit [0124] 47 Offgas stream [0125] 48 Further conduit to mixing and compression section