PRODUCTION OF SYNGAS FROM METHANOL PRODUCED FROM SYNGAS AND/OR CO2

Abstract

The present invention relates to a process for the production of syngas by thermal catalytic decomposition of methanol produced from a mixture comprising at least a carbon oxide (CO and/or CO2) and hydrogen.

Claims

1. A process for the production of syngas by thermal catalytic decomposition of methanol produced from a mixture comprising at least a carbon oxide (CO and/or CO.sub.2) and hydrogen.

2. A process for the production of syngas according to claim 1, comprising the steps of: (i) Producing methanol from a syngas composition (a), (ii) Optional separation of the methanol, (iii) Optional drying of the methanol, (iv) Optional purification of the methanol, (v) Optional storage of the methanol, (vi) Optional transport of the methanol, (vii) Producing syngas (b) from methanol obtained in step (i) by thermal catalytic decomposition, (viii) Optionally subjecting the syngas (b) to a separation step in a separation unit, wherein at least CO enriched and H.sub.2 enriched streams are obtained, (ix) Optionally subjecting the syngas (b) or any CO enriched and/or H.sub.2 enriched streams obtained therefrom to a Fischer Tropsch (FT) synthesis step. (x) Optionally using the syngas (b) or any CO enriched and/or H.sub.2 enriched streams obtained therefrom for the reduction of any iron oxide to iron, wherein optionally the process is performed by two or more individual parties.

3. A process according to claim 2, wherein the syngas composition (a) used in step (i) comprises a carbon oxide, selected from CO and CO.sub.2, and hydrogen.

4. A process according to any of the previous claims 2 and 3, wherein the syngas composition (a) used in step (i) has a molar ratio of carbon oxide to hydrogen in the range of 1:4 to 1:1 preferably 1:3 to 1:2.

5. A process according to any of the previous claims 2 to 4, wherein the carbon oxide in the syngas composition (a) used in step (i) comprises carbon dioxide (CO.sub.2).

6. A process according to any of the previous claims 2 to 5, wherein the syngas composition (a) used in step (i) is obtained from subjecting carbon dioxide and hydrogen to a reverse water gas shift reaction (CO.sub.2+H.sub.2CO+H.sub.2O).

7. A process according to any of the previous claims 2 to 6, wherein the syngas (b) obtained in step (vii) comprises carbon monoxide and hydrogen, in a molar ratio of more than about 1:1 to about 1:3, preferably of about 1:1 to about 1:2.

8. A process according to any of the previous claims 2 to 7, wherein the syngas (b) obtained in step (vii) is subjected to a separation step in a separation unit, wherein CO enriched or H.sub.2 enriched streams are obtained, which optionally can be used directly in subsequent processes or after recombination with the main stream from the methanol decomposition unit used in step (vii), in particular, to adjust a certain CO/H.sub.2 molar ratio.

9. A process according to any of the previous claims 2 to 8, wherein the syngas (b) obtained in step (vii) is subjected to a separation step in a separation unit, wherein a stream of CO is obtained that is used to polymerise CO to a polyketone.

10. A process according to any of the previous claims 2 to 9, wherein the syngas (b) obtained in step (vii) is used to reduce an iron oxide to iron.

11. A process according to any of the previous claims 2 to 10, wherein the syngas (b) obtained in step (vii) is subjected to a separation step in a separation unit, wherein CO enriched or H.sub.2 enriched streams are obtained, whereby either the one or the other is used for the reduction of iron oxide to iron, and wherein optionally (a)the H.sub.2 content of the CO rich stream used for iron oxide reduction is modified according to an external hydrogen demand, and/or (b)the H.sub.2 rich stream is used to export hydrogen into a grid and/or a storage tank, and/or (c)the H.sub.2 rich stream is used for electricity generation, and/or (d)the H.sub.2 rich stream is used to convert part of the CO.sub.2 from iron oxide reduction to produce methanol.

12. A process according to any of the previous claims 2 to 11, wherein the CO enriched or H.sub.2 enriched streams obtained are combined with a stream selected from: the syngas stream resulting from the methanol decomposing unit used in step (vii) to provide CO or H.sub.2 enriched streams of a certain molar ratio, and any stream leaving a FT reactor in the FT synthesis step (ix), to provide a combined CO/H.sub.2 stream preferably having a molar ratio CO/H.sub.2 of about 1:1 to 1:4, preferably 1:1.5 to 1:3, more preferably 1:1.6 to 1:2, most preferably of about 1:1.7 to 1:1.8.

13. A process according to any of the previous claims 2 to 12, wherein the syngas (b) obtained in step (vii) is transferred into a FT synthesis unit, wherein the syngas (b) is subjected to a FT synthesis step (ix), providing higher molecular products having two or more, preferably three or more carbon atoms selected from the group consisting of alkanes, alkenes or alcohols.

14. A process according to any of the previous claims 2 to 13, wherein the syngas (b) obtained in step (vii) is transferred to a FT synthesis unit consisting of one or more, preferably 2 or more, more preferably 2 to 3 FT reactors.

15. A process according to any of the previous claims 2 to 14, wherein the syngas (b) obtained in step (vii) is transferred to a FT synthesis unit, consisting of one or more, preferably two or more FT reactors and wherein a CO enriched stream leaving a FT reactor is recombined with a H.sub.2 enriched stream preferably resulting from the separation step (viii), so as to preferably provide a stream having a molar ratio CO/H.sub.2 of about 1:1 to 1:4, preferably 1:1.5 to 1:3, more preferably 1:1.6 to 1:2, most preferably of about 1:1.7 to 1:1.8.

16. A process according to any of the previous claims 2 to 15, wherein at least part of the process heat of the methanol producing step (i) and/or of the FT synthesis step (ix) are transferred to the methanol decomposition step (vii).

17. A process according to any of the previous claims 2 to 16, wherein the syngas composition (a) used in step (i) is obtained from a source selected from the group consisting of natural gas, coal, biomass, other hydrocarbon feedstocks, syngas obtained by reaction with steam (steam reforming), syngas obtained from carbon dioxide (dry reforming) or oxygen (partial oxidation or autothermal reforming) of carbon sources, syngas obtained from waste-to-energy gasification facilities, preferably from biomass sources.

18. A process according to any of the previous claims 2 to 17, wherein the syngas composition (a) used in step (i) is supplemented by hydrogen.

19. A process according to any of the previous claims 2 to 18, wherein the syngas composition (a) used in step (i) is provided with or without using a shift reactor to produce hydrogen from CO and H.sub.2O (CO+H.sub.2OCO.sub.2+H.sub.2).

20. A process according to any of the previous claims 2 to 19, wherein step (ix) is carried out and wherein the tail gas of the FT-reactor(s) is combusted to provide heat for the methanol decomposition step (vii), and optionally the CO.sub.2 from the combustion gas is recycled into the methanol synthesis step (i), wherein the tail gas preferably comprises CO.sub.2, H.sub.2 and CO.

21. A process according to any of the previous claims 2 to 20, wherein step (ix) is carried out and wherein the tail gas of the FT-reactor(s) is recycled back into step (i), wherein the tail gas preferably comprises CO.sub.2, H.sub.2 and CO.

22. A process according to any of the previous claims 2 to 21, wherein the syngas (b) obtained in step (vii) is used for the production of hydrogen, ammonia, synthetic hydrocarbons for use as a fuel or lubricant, in particular via the Fischer-Tropsch process.

23. A process according to any of the previous claims 2 to 22, wherein step (vii) is carried out with one or more of the following conditions: (a) a temperature in the range of 100 C. to 400 C., preferably of 200 C. to 350 C., more preferably of 220 C. to 300 C. and most preferably of 240 C. to 270 C., (b) a pressure in the range of 1 bar to 70 bar, preferably 20 bar to 50 bar, more preferably 35 bar to 45 bar, (c) the use of dried methanol comprising less than 10 wt.-% water, preferably less than 1 wt.-% water, more preferably less than 0.5 wt.-% water, most preferably less than 0.2 wt.-% water, (d) a catalyst selected from the group consisting of compounds of the elements Rh, Pd, Pt, Ir, Ru, Fe, Zn, Co, Ni, Cu and Mn, preferably from the elements Zn, Cu, Fe, Pt, Pd and Rh, more preferably from the elements Zn, Cu and Fe and most preferably catalysts containing either ZnO, a combination of ZnO and Cu or iron oxides, in particular Cu/ZnO, Cu/ZnO/Al.sub.2O.sub.3, doped Cu/ZnO, doped Cu/Zn/Al.sub.2O.sub.3, Fe.sub.2O.sub.3 or Fe.sub.3O.sub.4.

24. A process for the thermal catalytic decomposition of methanol into carbon monoxide and hydrogen, said process comprises the step of reacting methanol in a methanol decomposition reactor, optionally under one or more of the following conditions: (a) a temperature in the range of 100 C. to 400 C., preferably of 200 C. to 350 C., more preferably of 220 C. to 300 C. and most preferably of 240 C. to 270 C., (b) a pressure in the range 10 bar to 70 bar, preferably 20 bar to 50 bar, more preferably 35 bar to 45 bar, (c) the use of dried methanol comprising less than 10 wt.-% water, preferably less than 1 wt.-% water, more preferably less than 0.5 wt.-% water, most preferably less than 0.2 wt.-% water, (d) a catalyst selected from the group consisting of compounds of the elements Rh, Pd, Pt, Ir, Ru, Fe, Zn, Co, Ni, Cu and Mn, preferably from the elements Zn, Cu, Fe, Pt, Pd and Rh, more preferably from the elements Zn, Cu and Fe and most preferably catalysts containing either ZnO, a combination of ZnO and Cu or iron oxides, Cu/ZnO, Cu/ZnO/Al.sub.2O.sub.3, doped Cu/ZnO, doped Cu/Zn/Al.sub.2O.sub.3, Fe.sub.2O.sub.3 or Fe.sub.3O.sub.4, optionally separating at least part of the resulting mixture into CO enriched and H.sub.2 enriched gas streams, e.g. by means of a membrane separation unit, optionally recombining the CO enriched and H.sub.2 enriched gas streams with each other and/or the main stream resulting from the decomposition unit.

25. A process according to any of the previous claims 2 to 24, wherein dried methanol, preferably methanol comprising less than 10 wt.-% water, more preferably less than 1 wt.-% water, even more preferably less than 0.5 wt.-% water, most preferably less than 0.2 wt.-% water, is used in the methanol decomposition step (vii) and fed into the methanol decomposition unit, and wherein the reaction is carried out at a temperature below 300.

26. A process according to any of the previous claims 2 to 25, wherein in step (i) and step (vii) the same reactor type is used, differentiated by the presence of a cooling device for step (i) and a heating device for step (vii), respectively.

27. A process according to any of the previous claims 2 to 26, wherein step (i) and step (vii) are operated with the same reactor type with the following differences: (a) a methanol evaporating, compressing and heating unit, (b) a heating device for the main temperature regulating cycle, (c) reversal of the post-reactor recyclization unit so that the gaseous phase (syngas) is sent downstream and the liquid stream (methanol) is recycled back into the reactor.

28. A process according to any of the previous claims 2 to 24 and 26 to 27, wherein 1 wt.-% to 90 wt.-% water based on the amount by weight of methanol, preferably 10 wt.-% to 85 wt.-%, more preferably 20 wt.-% to 70 wt.-%, most preferably 20 wt.-% to 50 wt.-% water in addition to methanol is added in step (vii).

29. A process according to any of the previous claims 2 to 27, wherein the methanol decomposition of step (vii) is performed in a methanol decomposer with dry and CO.sub.2 free methanol, wherein a hydrogen enriched stream, preferably comprising at least 90 mol-% of H.sub.2, is separated from the syngas stream obtained from step (vii), and wherein the remaining CO enriched stream, preferably comprising at least 10 mol-% of CO, is fed into a shaft furnace for the reduction of iron oxides to iron of step (x).

30. The process according to the previous claims 2 to 24 and 26 to 28, wherein the catalyst used in the thermal catalytic decomposition of methanol in step (vii) is a ZnO-containing catalyst, preferably containing ZnO/Al.sub.2O.sub.3, more preferably containing Cu/ZnO/Al.sub.2O.sub.3, and an amount of water is added to the methanol subjected to decomposition in step (vii), preferably 1 wt.-% to 90 wt.-% water based on the amount by weight of methanol, preferably 10 wt.-% to 85 wt.-%, more preferably 20 wt.-% to 70 wt.-%, most preferably 20 wt.-% to 50 wt.-% water in addition to methanol is added.

31. The process according to any of the previous claims 2 to 30, wherein step (vii) is performed in a shaft furnace upon vapourizing methanol and feeding it hot into the shaft furnace, followed by the reduction of iron oxides to iron of step (x).

32. The process according to the previous claim 31, wherein step (vii) and step (x) are performed at temperatures between 500 C. and 950 C., preferably between 550 C. and 850 C., more preferably between 550 C. and 700 C. and most preferably between 550 C. and 650 C.

Description

DESCRIPTION OF THE FIGURES

[0154] FIG. 1: Design of a PtL-plant according to the present invention. The methanol synthesis-decomposition unit is displayed inside the black-circled box.

[0155] FIG. 2: Design of a PtL-plant according to the present invention. The methanol synthesis is performed by DHC (direct hydrogenation of CO.sub.2).

[0156] FIG. 3: Design of a PtL-plant according to the present invention. The syngas composition is regulated by a syngas separation unit.

[0157] FIG. 4: Design of a PtL-plant according to the present invention. The methanol is synthesised from CO.sub.2 and hydrogen (DHC). The syngas composition is regulated by a syngas separation unit.

[0158] FIG. 5: Schematic view of a membrane filtering unit used in the invention.

[0159] FIG. 6: Possible Mechanism of the formation of methanol from CO.sub.2.

[0160] FIG. 7: Possible Mechanism of the formation of syngas from methanol.

[0161] FIG. 8: Design of a prior art syngas-to-methanol reactor and a methanol-to-syngas reactor according to the present invention.

FURTHER PREFERRED EMBODIMENTS

Embodiment 1

[0162] In a preferred first embodiment of the invention a gas mixture containing carbon dioxide and at least the same molar amount of hydrogen is fed into a RWGS (reverse water gas shift) reactor and shifted to a syngas containing at least carbon monoxide, hydrogen and water.

[0163] The water-gas shift reaction (WGSR) describes the reaction of carbon monoxide and water vapor to form carbon dioxide and hydrogen:

##STR00014##

or as RWGS (reverse water gas shift reaction) the other way around:

##STR00015##

Using an excess of hydrogen in such reverse water gas shift reaction will lead to a syngas composition comprising CO and H.sub.2.

[0164] As the RWGS reaction is an equilibrium reaction, not all of the CO.sub.2 reacts and the product syngas will contain some CO.sub.2. The resulting syngas is dried by condensing the water out and then fed into a methanol synthesis reactor, where the syngas is converted to methanol e.g. according to the following stoichiometry, which reflects the maximum CO.sub.2 content for methanol synthesis using modern Cu/ZnO/Al.sub.2O.sub.3 catalysts:

##STR00016##

[0165] The methanol is separated, dried and ultimately fed again into a methanol decomposition reactor used in step (vii).

[0166] In the methanol decomposition reactor, the methanol is thermally decomposed (with the use of catalysts) to form syngas, in particular, of the composition CO+2 H.sub.2, which process is described in more detail below.

[0167] The syngas stream (b) from the methanol decomposition step (vii) optionally can be fed into a separation unit. The separation unit for example divides the syngas stream into a CO rich stream and a hydrogen rich stream. One way to achieve this is to utilise a membrane filtering unit that with the aid of a pressure drop across a membrane, lets the fast-moving gas (here hydrogen) pass through the membrane while the slow moving gas (here CO) does not pass through the membrane and leaves the unit through another exit. After the separation unit, the two gas streams can be re-mixed in a way so that a CO rich syngas stream of preferred composition (e.g. of a molar ratio CO/H.sub.2 of about 1:1 to 1:4, preferably 1:1.5 to 1:3, more preferably 1:1.6 to 1:2, most preferably of about 1:1.7 to 1:1.8) results.

[0168] The syngas of a preferred composition is then preferably fed into a string of one or more, preferably two or more, more preferably 2-3 FT-reactors. The flue gas from the first FT-reactor is very CO enriched and is mixed with enough of the hydrogen rich gas stream from the separation unit to reach again a preferred composition (e.g. of a molar ratio CO/H.sub.2 of about 1:1 to 1:4, preferably 1:1.5 to 1:3, more preferably 1:1.6 to 1:2, most preferably of about 1:1.7 to 1:1.8) before it enters the second FT-reactor. The procedure is repeated for the third and any subsequent FT-reactor, if required.

Embodiment 2

[0169] The RWGS reactor in embodiment 1 is replaced by a DHC-reactor (DHC: direct hydrogenation of CO.sub.2). A mixture of 25% (v/v) CO.sub.2 and 75% (v/v) H.sub.2 is fed into the reactor. The products methanol and water are condensed out and are fed into a distillation apparatus and the methanol is distilled from the water. The unreacted feedstock gases (CO.sub.2 and H.sub.2) are topped up and recycled back into the DHC-reactor.

Embodiment 3

[0170] The RWGS-reactor in embodiment 1 is replaced by a biomass gasifier. The product gas mixture from a biomass gasifier containing at least carbon monoxide, an insufficient amount of hydrogen and typically some CO.sub.2 is fed-together with additional hydrogen (to convert all CO and usually contained CO.sub.2 into methanol)-into a methanol synthesis reactor according to step (i). In the methanol synthesis reactor, the syngas is converted to methanol, for example according to the following equation, which reflects the maximum CO.sub.2 content for methanol synthesis using modern Cu/ZnO/Al.sub.2O.sub.3 catalysts:

##STR00017##

[0171] The methanol is separated, dried and ultimately (optionally after further purification, storage or transport to another place) fed into a methanol decomposition reactor used in step (vii). In the methanol decomposition reactor, the methanol is thermally decomposed (with the use of catalysts) to form syngas, in particular, of the composition CO+2 H.sub.2. The syngas stream can then be fed into a separation unit as described before. The separation unit divides the syngas stream into a CO rich stream and a hydrogen stream. One way to achieve this is to utilise a membrane filtering unit that with the aid of a pressure drop across a membrane, lets the fast moving gas (here hydrogen) pass through the membrane while the slow moving gas (here CO) does not pass through the membrane and leaves the unit through another exit. After the separation unit, the two gas streams can be re-mixed in a way so that a CO poor syngas stream of preferred composition (e.g. of a molar ratio CO/H.sub.2 of about 1:1 to 1:4, preferably 1:1.5 to 1:3, more preferably 1:1.6 to 1:2, most preferably of about 1:1.7 to 1:1.8) results, as described before.

[0172] The syngas of a preferred composition is then preferably fed into a string of one or more, preferably two or more, more preferably 2-3 FT-reactors. The flue gas from the first FT-reactor is very CO enriched and is mixed with enough of the hydrogen rich gas stream from the separation unit to reach again a preferred composition (e.g. of a molar ratio CO/H.sub.2 of about 1:1 to 1:4, preferably 1:1.5 to 1:3, more preferably 1:1.6 to 1:2, most preferably of about 1:1.7 to 1:1.8) before it enters the second FT-reactor. The procedure is repeated for the third and any subsequent FT-reactor, if required as described before.

Embodiment 4

[0173] Dry and CO.sub.2 free methanol is fed into a methanol decomposer according to the present invention. From the stream of syngas, a stream of hydrogen is separated and sent downstream for further use. The remaining CO containing stream is fed into a shaft furnace, where it reduces iron oxides to iron (HBI; hot briquetted iron).

[0174] The CO containing stream is a syngas of composition CO+ (2-x) H.sub.2, where x is the amount of hydrogen removed from the original amount of hydrogen. The amount x is variable and can be adjusted according to the changing hydrogen needs of external consumers. Thus, embodiment 4 serves as a flexible hydrogen source and has the same effect as a hydrogen storage device with the advantage that it does not rely on extensive hydrogen transport and storage infrastructure.

Embodiment 5

[0175] The facilities of embodiment 4 with the alterations that the catalyst is a ZnO containing catalyst and an amount of water, preferably 1 wt.-% to 90 wt.-% water based on the amount by weight of methanol, more preferably 10 wt.-% to 85 wt.-%, even more preferably 20 wt.-% to 70 wt.-%, most preferably 20 wt.-% to 50 wt.-% water is added to the methanol. The water will decompose the methanol to CO.sub.2 and hydrogen with the effect that more methanol is decomposed to produce the same amount of CO and at the same time, an increased mount of hydrogen can be distributed to external consumers.

[0176] The hydrogen distribution capacity has increased compared to embodiment 4.

[0177] The CO.sub.2 that is co-produced with the CO will pass through the shaft furnace without interfering with the steel production process.

Embodiment 6

[0178] The facilities from embodiment 4, but without the methanol decomposer. The methanol is vapourised and fed hot into the shaft furnace. There, it is decomposed to CO and hydrogen by the iron oxides acting as catalysts. The reducing gases CO and hydrogen then proceed to reduce the iron oxides to HBI.

[0179] The process is operated at temperatures between 500 C. and 950 C., preferably between 550 C. and 850 C., more preferably between 550 C. and 700 C. and most preferably between 550 C. and 650 C.

[0180] At high temperatures of the iron oxide bed, both CO and hydrogen react. At high temperatures of the iron oxide bed, only CO reacts and most of the hydrogen passes through unchanged. The hydrogen can be separated from the flue gas and sent downstream for further use. In embodiment 6, the shaft furnace itself acts as methanol decomposer according to the present invention.

Mechanism of Methanol Synthesis

[0181] Regarding the direct hydrogenation of CO.sub.2 to methanol, it follows the equation:

##STR00018##

[0182] In accordance with the process of the invention the methanol can be decomposed again to syngas according to equation:

##STR00019##

with the equilibrium constant depending on temperature and pressure.

[0183] It is well known to the expert in the field that methanol can be steam reformed to obtain hydrogen. However, the presence of water in this reaction oxidises the methanol to CO.sub.2 (CH.sub.3OH+H.sub.2O.fwdarw.CO.sub.2+3 H.sub.2). For this reason, the present invention proposes the use of dry methanol, which has a higher yield, lower energy consumption and no CO.sub.2 formation. Methanol formation is generally favoured at high pressure and low temperature (irrespective whether CO or CO.sub.2 is the starting material) and occurs in a temperature window between T=100 C. and T=400 C. At the high end of this temperature window, the catalyst can be permanently damaged by sintering.

[0184] The corresponding methanol synthesis from syngas (hydrogenation of CO)

##STR00020##

is greatly aided by addition of CO.sub.2 and proceeds very reluctantly in the absence of CO.sub.2. For this reason, a small amount of CO.sub.2 is preferably added or contained in the syngas composition (a) to start the reaction to form methanol. In the process, some H.sub.2O is formed, which may temporarily poison the catalyst. At higher water concentrations (depending on the exact catalyst composition, but with a current maximum concentration of about 10%), the reaction is terminated. Termination occurs because the methanol forming reaction CO.sub.2+3 H.sub.2.fwdarw.CH.sub.3OH+H.sub.2O is in equilibrium with the methanol decomposition reaction CH.sub.3OH+H.sub.2O.fwdarw.CO.sub.2+3 H.sub.2.

[0185] The generally agreed mechanism is depicted in FIG. 6.

[0186] The key step is the formation of the deoxogenyl-complex by a synchronized CO bond breakage, formyl rotation and OO bond formation sequence. If the delicate last step, OO bond formation, fails to eventuate, a formyl-complex is formed that is unstable and decomposes to CO+H.sub.2.

[0187] Although the agreed mechanism would suggest the reversibility of this step in the presence of water, it is not discussed in the literature. This is maybe not surprising realizing that normally dry syngas is utilized for methanol synthesis. Dry syngas fails to react to methanol, unless CO.sub.2 is added.

[0188] It is not the CO.sub.2 that enables methanol synthesis, but the water that is formed from it, when the CO.sub.2 is hydrogenated.

[0189] Likewise, when dry and CO.sub.2 free methanol is thermally decomposed to syngas (CH.sub.3OH.fwdarw.CO+2 H.sub.2) as part of the present invention, the syngas cannot react back to methanol. There is no water present that would facilitate formation of the deoxogenyl-complex from the H.sub.2CO entity or the formiate complex from the formyl-complex by addition of water as part of the sequence of the reaction mechanism (FIG. 7). The formyl-complex, once formed, can only decompose back to CO and hydrogen. Water acts as a co-catalyst in the synthesis of methanol and its absence converts the apparent equilibrium reaction into a quasi-irreversible reaction that can only decompose methanol into syngas, but no longer converts syngas into methanol. It should be mentioned that the presence of water and/or CO.sub.2 does not prevent the decomposition of methanol to syngas, but it allows the re-formation of methanol during methanol decomposition. This lowers the single pass rate (SPR) and thus the syngas yield. As a consequence, during the process of the current invention, much more syngas is formed at lower temperature and/or higher pressure than calculated by conventional computer simulations, if dry and CO.sub.2 free methanol is used.

[0190] In a preferred embodiment of the invention the methanol decomposed in step (vii) is preferably dried and CO.sub.2 free methanol, preferably comprising less than 10 wt.-% water, preferably less than 1 wt.-% water, more preferably less than 0.5 wt.-% water, most preferably less than 0.2 wt.-% water. The specifications of dry and CO.sub.2 free methanol are given by standard methanol data sheets such as they are provided by the Methanol Institute (Methanol-Technical-Data-Sheet.pdf). Specifically, for the properties of dry and CO.sub.2 free methanol reference is made to the IMPCA Methanol Reference Specifications Version 9, dated 10 Jun. 2021 and the methods referred to in there. Dry and CO.sub.2 free methanol can be produced by distillation and verified by standard spectroscopic means and density measurements (Lange's Handbook of Chemistry, 10th ed. and CRC Handbook of Chemistry and Physics 44th ed.). The catalyst is a commercial Cu/ZnO/Al.sub.2O.sub.3 catalyst.

[0191] Optionally, the methanol decomposer is used to produce hydrogen in addition to the amount of CO required. In this case, 1 wt.-% to 90 wt.-% water based on the amount by weight of methanol, preferably 10 wt.-% to 85 wt.-%, more preferably 20 wt.-% to 70 wt.-%, most preferably 20 wt.-% to 50 wt.-% water in addition to methanol is used.

[0192] Although the above reaction mechanism of the formation of methanol from CO.sub.2 is generally known and discussed in academic circles (Chemical Society Reviews, 2020, 1385), its consequences are generally unknown. The academic literature has identified the formation of the dioxogenyl-complex from the formiate-complex as the rate determining step and even sees the failure to form the dioxogenyl-complex as the main reason for the formation of the formyl-complex (and subsequently CO in a RWGS analogous reaction), but fails to realize that it is the absence of waterand not the absence of CO.sub.2that prevents the direct hydrogenation of CO (syngas-to-methanol) reaction in conventional methanol synthesis from syngas.

[0193] In accordance with the present invention, the methanol decomposition in step (vii) is preferably carried out with dried and CO.sub.2 free methanol. It comprises for example less than 10 wt.-% water, preferably less than 1 wt.-% water, more preferably less than 0.5 wt.-% water, most preferably less than 0.2 wt.-% water.

[0194] The process of the methanol decomposition to form the syngas (b) of the invention thus allows, in particular: [0195] The efficient decomposition of methanol to syngas, and [0196] The generation of syngas at low reaction temperatures.

[0197] Since the decomposition of dry and CO.sub.2 free methanol to syngas according to the present invention is not an equilibrium reaction, as described in the literature, but an irreversible process, the decomposition proceeds uni-directional without reformation of methanol. It is therefore possible to decompose dry and CO.sub.2 free methanol at low temperatures (T<350 C., preferably <250 C. and more preferably at T<200 C.) in a reactor with a longer catalyst bed or with a lower feedstock velocity than the respective syngas-to-methanol reactor for methanol synthesis. In that way, catalyst degradation by sintering (at T>300 C.) and problems with heat transfer (the kinetics of heat transfer to the catalyst bed and/or the methanol feedstock) can be avoided.

[0198] Unreacted methanol can be condensed, separated from the syngas and sent back into the reactor.

Thermal-Catalytical Decomposition of Methanol

[0199] The formation of methanol and its thermal-catalytical decomposition to syngas again in accordance with the process of the invention is described in the following in further detail.

Synthesis of Methanol

[0200] Methanol is produced preferably either from syngas (StM: syngas-to-methanol) or from CO.sub.2 (DHC direct hydrogenation of CO.sub.2). Both technologies preferably use a pipe-bundle reactor with the same or similar catalyst (Cu/ZnO/Al.sub.2O.sub.3) filling and the same or similar reaction conditions (pressure of 10 bar to 70 bar, preferably 30 bar to 50 bar and more preferably 40 bar; temperature of 100 C. to 400 C., preferably of 200 C. to 350 C., more preferably of 220 C. to 300 C. and most preferably of 240 C. to 270 C.) and intensive cooling to remove the process heat.

[0201] A key step in the DHC route is the recycling of the unreacted feedstock gases with a SPR (single pass rate) of about 10% to 15%, depending on the actual Cu/ZnO/Al.sub.2O.sub.3 catalyst used. The products methanol and water are removed by condensation (cooling of the product gas) and the residual gas (CO.sub.2 and H.sub.2) topped up prior to refeeding it into the synthesis reactor. The cooling cycle can be connected to a heat exchanger that operates as a secondary cooling cycle.

[0202] The DHC-process can be reversed and is then known as the MSR (methanol-steam-reforming) process. Theoretically, there are two possible mechanisms for the MSR-process

##STR00021##

[0203] Despite extensive experimental research, no traces of CO as the intermediate of the two-step mechanism has ever been observed (Liu et al). It is therefore generally recognised that the MSR-process proceeds according to the one-step mechanism.

[0204] The WGS (water gas shift) reaction is also performed with the MSR-reactor, but from CO rather than methanol as starting material

##STR00022##

[0205] It was the WGS-reaction that has given rise to the assumption that the MSR-reaction might proceed by decomposition followed by WGS of the CO to CO.sub.2. This assumption was disproven. However, the present invention shows that despite the teachings of the state-of-the-art, dry methanol (methanol in the absence of water) can be decomposed to CO+2 H.sub.2. What is more, as water is consumed in the MSR-reaction, dry decomposition of methanol (to CO+2 H.sub.2) occurs after all the water is consumed, when wet methanol is used.

Prior Art Reactor

[0206] It is known that the synthesis of methanol is a temperature dependent equilibrium reaction with decomposition dominating at higher temperatures (see FIGS. 6 and 7). The two standard prior art reactors (StM and DHC) differ in their SPR (StM: 65-85%, DHC: 10-15%), their process heat (StM: H=90.8 KJ/mol; DHC: H=49.6 KJ/mol), the capacity of their cooling system and their recyclation system. The difference in the cooling system reflects the higher process heat liberated by the StM-reactor and the difference in the recycling system reflects the much larger amount of unreacted feedgas recycled by the DHC reactor.

[0207] For the purpose of the methanol decomposer (methanol-to-syngas MtS reactor) of the present invention, a hybrid system that uses components of both methanol synthesis reactors is utilised and additional modifications introduced.

Methanol Decomposer of the Present Invention

[0208] The standard commercial StM-reactor is fed with gaseous methanol. The pipe-bundle catalyst bed is filled with the same commercial Cu/ZnO/Al.sub.2O.sub.3 catalyst as the original StM-reactor. The temperature of the pipe-bundle catalyst bed is regulated with the same steam cycle, but at a higher temperature.

[0209] The methanol decomposition reaction: CH.sub.3OH.fwdarw.CO+2 H.sub.2 is endotherm and requires heating, whereas the methanol synthesis reaction: CO+2 H.sub.2.fwdarw.CH.sub.3OH is exotherm and requires the same amount of cooling. For this reason, the StM-reactor is chosen as the base and the steam cycle of the present invention is equipped with a heat exchanger and a standard steam heating system outside the reactor. The expert in the art also knows of ways to incorporate the heating system inside the reactor and an interior heating system is within the scope of the invention.

[0210] The decomposed methanol is a syngas of the composition CO+2 H.sub.2 (defined by the chemical equation) and can be removed with the same recycling loop known from methanol synthesis by DHC (90% recycling of CO.sub.2+3 H.sub.2). Except this time, the gas phase is the product and the liquid phase (CH.sub.3OH) is recycled back into the reactor. For this reason, the liquid methanol is brought into the gas phase and recycled back into the MtS-reactor; the syngas is sent downstream.

[0211] It is possible to use a standard MSR-reactor and operate it with dry and CO.sub.2 free methanol. It then serves as a methanol decomposer according to the present invention, after due adjustment of the heating system.

Reactor Modifications

[0212] The customary pipe-bundle reactor of both the DHC and the StM pathways has the pipe-bundle submerged in the cooling medium inside the pressure container of the reactor.

[0213] The cooling medium itself is either steam, thermal oil or liquid salt.

[0214] For safety reasons, the pressure limit of the cooling medium should be above the default pressure of the pipe-bundle and thus above the methanol synthesis operating pressure, which is usually between 10 bar and 70 bar, preferably between 20 bar and 60 bar and more preferably between 35 bar and 50 bar.

[0215] Switching the reactor from synthesis mode at a temperature of 200 C. to 400 C., preferably of 220 C. to 350 C., more preferably of 230 C. to 300 C. and most preferably of 240 C. to 270 C. to decomposition mode at a temperature range of 100 C. to 400 C., preferably of 200 C. to 350 C., more preferably of 220 C. to 300 C. and most preferably of 240 C. to 270 C. has consequences for the thermal fluid. In the case of steam, overheating the saturated steam from 250 C. to 350 C. increases the pressure to near the safety limit of 40 bar to 50 bar of the outer pressure wall. In the case of thermal oil and liquid salt, the material may not be thermally stable at 350 C. In both cases, the fluid can be replaced by a thermal oil or liquid salt of higher thermal stability. In most cases, retrofitting of a methanol synthesis reactor to decomposition mode will be possible with no or only minor modifications to the reactor itself.

Embodiment 7

[0216] A commercially available pipe-bundle StM-reactor with a capacity of 4 t/h syngas (CO+2 H.sub.2 with a CO.sub.2 content of 3% v/v) and a SPR of 75% produces 3 t/h methanol at a reaction temperature of 240 C. and a pressure of 40 bar using a commercial Cu/Zn/Al.sub.2O.sub.3 catalyst. The process heat of 2,357 kWh is taken out of the reactor by a steam cooling cycle. The gaseous products consisting of 3 t/h methanol and 1 t/h syngas (CO+2 H.sub.2 containing water and CO.sub.2) are sent to a recyclization unit that cools the product gas until the water and the methanol condenses. The condensed liquid phase is removed from the recyclisation unit and sent to a distillation apparatus. The gaseous phase (CO, H.sub.2, CO.sub.2) is recycled, topped up to 4 t/h and fed back into the StM-reactor.

[0217] For the process of the present invention, the StM-reactor is retrofitted to serve as a MtS-reactor for the decomposition of methanol to syngas. A methanol storage tank is used to dispense 4 t/h dry and CO.sub.2 free methanol to an evaporation, compression and heating unit to provide gaseous dry and CO.sub.2 free methanol at the reaction pressure of 10 bar to 70 bar, preferably 20 bar to 50 bar, more preferably 35 bar to 45 bar and the reaction temperature of 100 C. to 400 C., preferably of 200 C. to 350 C., more preferably of 220 C. to 300 C. and most preferably of 240 C. to 270 C. The dry and CO.sub.2 free methanol vapour is sent through the MtS-reactor where it is decomposed to 3 t/h syngas (CO+2 H.sub.2) and a SPR of 75%. The necessary process heat is provided by a steam heating device that heats the steam in the steam cycle of the MtS-reactor at a point outside the reactor to the reaction temperature. For this purpose, the steam cooling cycle of the original StM-reactor is retrofitted with a heating device outside the reactor. During the decomposition of the methanol and while the steam flows through the reactor, the methanol decomposition reaction draws heat from the steam and causes the steam to cool down. Subsequently, the heating device heats the steam back up to its default value.

[0218] The MtS-reactor is retrofitted with a new recycling unit that is very similar to the original one in as much as it condenses the methanol (CH.sub.3OH) and separates the liquid methanol from the gaseous syngas (CO+2 H.sub.2). The methanol is recycled back to the methanol evaporation, compression and heating unit, where it is topped up to 4 t/h. The difference in the recycling unit is the capacity for processing the liquid phase (drops from 75% or 3 t/h to 25% or 1 t/h) whereas the gaseous phase increases accordingly (from 25% or 1 t/h to 75% or 3 t/h). The other difference is that now the liquid phase is recycled and the gaseous phase sent downstream. The retrofitted recycling unit resembles in its relative capacities that of an equivalent DHC-reactor for methanol synthesis.