Method for producing methanol from synthesis gas without the emission of carbon dioxide

Patent metadata

Field	Value
Publication number	US-11292717-B2
Application number	US-201917273478-A
Country	US
Kind code	B2
Filing date	Aug 26, 2019
Priority date	Sep 4, 2018
Publication date	Apr 5, 2022
Grant date	Apr 5, 2022

Abstract

A process for preparing methanol from a carbon-containing feedstock by producing synthesis gas therefrom in a synthesis gas production unit, converting the synthesis gas to methanol in a methanol synthesis unit and working up the reaction mixture obtained stepwise to isolate the methanol, wherein the carbon monoxide, carbon dioxide, dimethyl ether and methane components of value from the streams separated off in the isolation of the methanol are combusted with an oxygenous gas, and the carbon dioxide in the resultant flue gas is separated off in a carbon dioxide recovery unit and recycled to the synthesis gas production unit and/or to the methanol synthesis unit.

First claim

The invention claimed is:

1. A process for preparing methanol by
(a) producing a synthesis gas comprising carbon monoxide, carbon dioxide and hydrogen from a carbonaceous feedstock in a synthesis gas production unit;
(b) feeding the synthesis gas from step (a) to a methanol synthesis unit and converting it at a temperature of 150 to 300° C. and a pressure of 5 to 10 MPa abs in the presence of a methanol synthesis catalyst to a reaction mixture containing methanol, water, carbon monoxide, carbon dioxide, hydrogen, dimethyl ether and methane, condensing a methanol- and water-enriched crude methanol stream out of said reaction mixture, and conducting the crude methanol stream and a gaseous stream comprising carbon monoxide, carbon dioxide, hydrogen and methane out of the methanol synthesis unit;
(c) expanding the crude methanol stream from step (b) in an expansion unit to a pressure of 0.1 to 2 MPa abs, and obtaining an expansion gas comprising carbon dioxide and methane and a degassed crude methanol stream enriched with methanol and water;
(d) separating a carbon dioxide- and dimethyl ether-comprising low boiler stream by distillation from the degassed crude methanol stream from step (c) in a distillation apparatus, and obtaining a methanol- and water-enriched bottom stream; and
(e) separating a water-containing high boiler stream from the bottom stream from step (d) in a further distillation apparatus, and obtaining methanol by distillation as an output stream,
which comprises
(f) feeding the carbon monoxide, carbon dioxide, dimethyl ether and methane components of value in the degassed crude methanol stream and in at least one of the expansion gas and the low boiler steam to a combustion unit and combusting them therein with supply of an oxygenous gas having an oxygen content of 30% to 100% by volume, forming carbon dioxide-containing flue gas;
(g) separating a carbon dioxide-enriched stream from the carbon dioxide-containing flue gas from step (f) in a carbon dioxide recovery unit to form an offgas stream; and
(h) recycling the carbon dioxide-enriched stream separated off in the carbon dioxide recovery unit from step (g) to the synthesis gas production unit of step (a) and/or to the methanol synthesis unit of step (b).

2. The process according to claim 1 , wherein the hydrocarbonaceous feedstock used in step (a) is natural gas, biogas, coal, wood, plastics, mineral oil, bionaphtha or hydrocarbonaceous streams from mineral oil or natural gas processing, from chemical production processes, from renewable raw materials or from plastics recycling.

3. The process according to claim 1 , wherein a methane-containing feedstock is used in stage (a) and the synthesis gas is produced by steam reforming, autothermal reforming, a combination of steam reforming and autothermal reforming, or by partial oxidation.

4. The process according to claim 1 , wherein the synthesis gas comprises methane.

5. The process according to claim 1 , wherein a copper- and zinc-containing heterogeneous catalyst is used as methanol synthesis catalyst in the methanol synthesis unit in step (b).

6. The process according to claim 1 , wherein the methanol synthesis unit in step (b) comprises a compressor for compression of the synthesis gas, a reactor for conversion of the synthesis gas, a condenser for condensing out the crude methanol stream, and a conduit for recycling of uncondensed gas to the reactor.

7. The process according to claim 1 , wherein in step (f), the carbon monoxide, carbon dioxide, dimethyl ether and methane components of value in the gaseous stream, the expansion gas, and the low boiler steam are fed to the combustion unit.

8. The process according to claim 1 , wherein the oxygenous gas has an oxygen content of 90% to 100% by volume.

9. The process according to claim 1 , wherein the combustion unit in step (f) comprises a combustion chamber and a condenser, water is condensed out of the combustion gas obtained in the combustion chamber in the condenser and conducted out of the combustion unit as a combustion output stream, and the remaining gaseous stream constitutes the carbon dioxide-containing flue gas.

10. The process according to claim 1 , wherein, in the carbon dioxide recovery unit in step (g), carbon dioxide is absorbed from the carbon dioxide-containing flue gas in an absorber in a basic solvent to form the offgas stream, the carbon dioxide-enriched stream is released from the carbon dioxide-laden solvent in a desorber, and the carbon dioxide-depleted solvent is returned to the absorber.

11. The process according to claim 10 , wherein the basic solvent used is an aqueous solution of an organic amine.

12. The process according to claim 11 , wherein the organic amine used is monoethanolamine, piperazine, 2-amino-2-methyl-1-propanol, triethylenediamine, N-methyldiethanolamine or tert-butylaminoethoxyethanol.

13. The process according to claim 1 , wherein, in step (h), the carbon dioxide-enriched stream (XIV) from step (g) is recycled to the methanol synthesis unit of step (b).

14. The process according to claim 1 , wherein the carbon dioxide-enriched stream from step (g) comprises oxygen, and the carbon dioxide-enriched stream, before it is recycled to the synthesis gas production unit or to the methanol synthesis unit, is catalytically hydrogenated to deplete the oxygen.

15. The process according to claim 1 , wherein, before the gaseous stream is fed to the combustion unit, hydrogen is separated off in a hydrogen recovery unit and recycled to the methanol synthesis unit of step (b).

16. The process according to claim 15 , wherein the hydrogen is separated off by pressure swing adsorption in the hydrogen recovery unit.

17. The process according to claim 1 , wherein the methanol synthesis unit in step (b) is supplied with further hydrogen in addition to the hydrogen supplied via the synthesis gas.

Assignees

• Basf Se

Inventors

• Vicari Maximilian
• Geiger Thomas
• Katz Torsten

Classifications

• Y02P20/129

  Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines · CPC title

• C07C29/80

  by distillation · CPC title

• C01B2203/148

  involving a recycle stream to the feed of the process for making hydrogen or synthesis gas · CPC title

• C07C29/1518

  one step being the formation of initial mixture of carbon oxides and hydrogen for synthesis · CPC title

• C01B2203/061

  Methanol production · CPC title