EP-4735411-A1 - METHANOL SYNTHESIS PROCESS

EP4735411A1EP 4735411 A1EP4735411 A1EP 4735411A1EP-4735411-A1

Abstract

A process for synthesis of methanol including formation of a crude stream of methanol in a methanol converter and purification of said crude stream, wherein the purification process includes distillation of a methanol-containing stream in a distillation column (2, 28); a gaseous stream (3, 37) containing methanol vapour is withdrawn from said column; a portion of said gaseous stream is compressed in a vapour compressor (19, 38); the compressed gaseous stream (20, 39) is subject to a heat exchange step wherein at least part of the methanol vapour is condensed and heat is transferred to an aqueous stream (15, 31) withdrawn from said column; the heated aqueous stream is reintroduced into said column (2, 28).

Inventors

Moreo, Pietro
MUSCIONICO, Isabella
POLETTI, Riccardo

Assignees

CASALE SA

Dates

Publication Date: 20260506
Application Date: 20240628

Claims (1)

CLAIMS 1 ) A process for catalytic synthesis of methanol including formation of a crude stream of methanol and a purification process of said crude stream to obtain a purified methanol stream, wherein the purification process includes: distillation of a methanol-containing stream in a distillation column (2), wherein a gaseous stream (3) containing methanol vapour is withdrawn from a first location of said column, said gaseous stream (3) having a first temperature; said gaseous stream is sent to a vapour compressor (19) where it is compressed obtaining a compressed gaseous stream (20) at a second temperature which is greater than said first temperature; said compressed gaseous stream (20) is subject to a heat exchange step wherein at least part of the methanol vapour contained in the stream is condensed and heat removed from said gaseous stream (20) is transferred to a liquid stream (15) withdrawn from a second location of said column, obtaining a heated stream (13) which is reintroduced into said column (2). 2) Process according to claim 1 , wherein a first liquid stream (15) withdrawn from said second location of said column (4) is heated by said heat exchange step with the compressed gaseous stream (20) and a second liquid stream (14) withdrawn from the column is heated in at least one additional heater (25), preferably including at least one electric heater, in parallel to said heat exchange step with the compressed gaseous stream and before reintroduction into the column. 3) Process according to claim 1 or 2 wherein: said compressed gaseous stream, after said heat exchange step and condensation, results in an effluent stream (21 ) containing condensed methanol; said effluent stream (21 ) is subject to a separation step obtaining a liquid methanol product (23) and a gaseous stream (24) containing methanol vapours, at least part of said gaseous stream is sent to said vapour compressor (19). 4) Process according to any of claims 1 to 3 wherein: distillation of said methanol-containing stream is performed in a plurality of distillation columns including at least a first distillation column (2) and a second distillation column (28), wherein said methanol containing stream (1 ) is sent to the first column (2) and an aqueous solution (27) withdrawn from said first column (2) is further processed in the second column (28). 5) Process according to claim 4 wherein: the gaseous stream sent to said vapour compressor is withdrawn from the first distillation column (2), and the liquid stream which is heated by heat exchange with said compressed gaseous stream is a liquid stream (15) collected from the first column and reintroduced into said first column after heating. 6) Process according to claim 4 wherein: the gaseous stream sent to said vapour compressor is withdrawn from the second distillation column (28), and the liquid stream which is heated by heat exchange with said compressed gaseous stream is a liquid stream (41 ) collected from the second column and reintroduced into said second column after heating. 7) Process according to claim 4 wherein: a first methanol-containing gaseous stream (3), which is withdrawn from the first distillation column (2), is sent to a first vapour compressor (19) obtaining a first compressed gaseous stream, a liquid stream (15) withdrawn from said first column is heated by heat exchange with said first compressed gaseous stream, and reintroduced into said first column after heating, and a second methanol-containing gaseous stream (37), which is withdrawn from the second distillation column (28), is sent to a second vapour compressor (38) obtaining a second compressed gaseous stream (39), a liquid stream (41 ) is withdrawn from said second column, heated by heat exchange with said second compressed gaseous stream and reintroduced into said second column after heating. 8) A process according to any of claims 4 to 7 wherein a liquid stream (31 ) withdrawn from the second column (28) is heated by heat exchange with a non-compressed methanol-containing gaseous stream (5) withdrawn from the first column (2), and said liquid stream is reintroduced into the second column after heating. 9) A process according to any of the previous claims wherein: in at least one distillation column (2), a first portion (14) of a liquid stream (4) withdrawn the column is heated in a heat exchanger (11 ), which is preferably steam-heated, and the so obtained heated stream (16) is reintroduced directly into said column (2); a remaining portion (15) of said liquid stream (4) is heated separately by heat exchange with the methanol-containing compressed gaseous stream (20) withdrawn from the same column, and reintroduced into the column (2) after heating. 10)Process according to any of the previous claims wherein said compression of methanol containing gaseous stream is performed to a pressure of in the range between 7 and 16 bar g. 11 )Process according to any of the previous claims wherein condensation of methanol vapours, after compression, is carried out at a temperature in the range 130 to 170 °C. 12) Process according to any of the previous claims wherein crude methanol is produced by reacting a make-up gas containing not more than 10% CO in volume, preferably not more than 7% and more preferably not more than 5%. 13)Process according to claim 12 wherein some or all of the CO2 contained in the CO-free make-up gas is obtained from a CO2 capture process and/or biogenic CO2, and/or wherein some or all of the hydrogen contained in said CO-free make-up gas is hydrogen produced from water electrolysis, preferably powered by a renewable source of energy, or from a hydrogen production process with no emissions of CO2. 14) A distillation section for the purification of a crude stream of methanol, said distillation section including: a distillation column (2); a line arranged to withdraw a gaseous stream (3) containing methanol vapour from a first location of said distillation column; a vapour compressor (19) arranged to provide compression of said gaseous stream and to obtain a compressed gaseous stream (20) at a higher temperature than the temperature of extraction from the column; a first heat exchanger (17) arranged to provide condensation of at least part of the methanol vapour contained in said compressed gaseous stream (20) and to transfer heat removed form said gaseous stream to a liquid stream (15) withdrawn from said column (2), obtaining a heated stream, and a line arranged to reintroduce the so obtained heated stream into the column. 15) A distillation section according to claim 14 including a second heat exchanger or an electrical heater (25) in parallel to said first heat exchanger (17); a line (15, 13) arranged to heat a first portion of a liquid stream withdrawn from said column in said first heat exchanger and to reintroduce the so obtained heated stream in the column; a line (14, 16) arranged to heat a second portion of said liquid stream in the second heat exchanger to reintroduce the so obtained heated stream in the column. 16) A distillation section according to claim 14 or 15 including: a first distillation column (2) and a second distillation column (28), and a line arranged to send an aqueous solution (27) withdrawn from said first column (2) to the second column (28) for further processing; a first vapour compressor (19) arranged to compress a methanol-containing gaseous stream (3) withdrawn from the first distillation column (2); a heat exchanger arranged to transfer heat from a compressed gaseous stream delivered by said first compressor to a liquid stream (15) withdrawn from said first column, and a line arranged to reintroduce the so obtained heated stream in said first column; a second vapour compressor (36) arranged to compress a methanolcontaining gaseous stream withdrawn from the second distillation column (28); a heat exchanger arranged to transfer heat from a compressed gaseous stream delivered by said second compressor to a liquid stream withdrawn from said second column, and a line arranged to reintroduce the so obtained heated stream in said second column. 17) A distillation section according to claim 16 additionally including a heat exchanger (6) configured to heat a liquid stream (31 ) withdrawn from the second column (28) by heat exchange with a non-compressed methanolcontaining gaseous stream (5) withdrawn from the first column (2), and including a line to reintroduce the so obtained heated liquid stream into the second column. 18)A methanol plant including at least a methanol synthesis section and a distillation section arranged to process a stream of crude methanol obtained after synthesis, for purification of said stream of crude methanol, the distillation section being in accordance with any of claims 14 to 17. )A procedure of revamping a methanol plant, wherein the methanol plant includes at least a methanol synthesis section and a distillation section arranged for purification of a stream of crude methanol obtained after synthesis, wherein the distillation section includes at least one distillation column, wherein the procedure includes modifying the distillation section to include at least: a line arranged to withdraw a gaseous stream (3) containing methanol vapour from a first location of said distillation column; a vapour compressor (19) arranged to provide compression of said gaseous stream and to obtain a compressed gaseous stream (20) at a higher temperature than the temperature of extraction from the column; a first heat exchanger (17) arranged to provide condensation of at least part of the methanol vapour contained in said compressed gaseous stream (20) and to transfer heat removed form said gaseous stream to a liquid stream (15) withdrawn from said column (2), obtaining a heated stream, and a line arranged to reintroduce the so obtained heated stream into the column. )A procedure according to claim 19 wherein the distillation section is modified to include a second heat exchanger or an electrical heater (25) in parallel to said first heat exchanger (17); a line (15, 13) arranged to heat a first portion of a liquid stream withdrawn from said column in said first heat exchanger and to reintroduce the so obtained heated stream in said distillation column; a line (14, 16) arranged to heat a second portion of said liquid stream in the second heat exchanger to reintroduce the so obtained heated stream in said distillation column. )A procedure according to claim 19 or 20, wherein the distillation section includes a second distillation column, or a second distillation column in added to the distillation section, and the distillation section is modified to include: a line arranged to send an aqueous solution (27) withdrawn from said first column (2) to the second column (28) for further processing; a first vapour compressor (19) arranged to compress a methanol-containing gaseous stream (3) withdrawn from the first distillation column (2); a heat exchanger arranged to transfer heat from a compressed gaseous stream delivered by said first compressor to a liquid stream (15) withdrawn from said first column, and a line arranged to reintroduce the so obtained heated stream in said first column; a second vapour compressor (36) arranged to compress a methanolcontaining gaseous stream withdrawn from the second distillation column (28); a heat exchanger arranged to transfer heat from a compressed gaseous stream delivered by said second compressor to a liquid stream withdrawn from said second column, and a line arranged to reintroduce the so obtained heated stream in said second column. )A procedure according to any of claims 19 to 21 , wherein the distillation section is modified to include: a heat exchanger (6) configured to heat a liquid stream (31 ) withdrawn from the second column (28) by heat exchange with a non-compressed methanolcontaining gaseous stream (5) withdrawn from the first column (2); a line to reintroduce the so obtained heated liquid stream into the second column.

Description

Methanol synthesis process DESCRIPTION Field of application The invention is in the field of industrial production of methanol. Prior art Methanol is produced industrially by reacting a make-up gas comprising hydrogen (H2) and carbon oxides (CO2 and CO) at elevated temperature and pressure through one or more beds of a suitable methanol synthesis catalyst. The catalytic beds are contained in one or more reactors (methanol converters). The product of the reaction is a methanol-containing gas which is cooled to a temperature below the dew point of methanol so that a stream of crude methanol can be separated. Part of the gaseous fraction separated from the converter effluent is reintroduced in the converter, thus forming a so-called synthesis loop. The circulation in the loop is maintained by a suitable compressor (circulator). Crude methanol is in a liquid state and contains by-products of the synthesis including ethanol, ketones, higher alcohols, and some dissolved gases including H2, CO, CO2, N2 and CH4. To meet the purity specification required by the market, a purification of the crude methanol is necessary. The purification is typically carried out by distillation. A distillation process may use one or more distillation column. In a distillation column, an overhead gaseous stream (“light gas”) is withdrawn from top of the column and an aqueous solution is collected from the bottom of the same column. A portion of the bottom solution is heated in a suitable heat exchanger (“bottom reboiler”) and reintroduced into the column to provide the distillation heat. The heat source of the reboiler is typically hot steam. In the distillation of crude methanol, the light gas contains vapours of methanol which can be condensed to obtain a pure methanol product. If required, more than one distillation column may be used. A known configuration includes two distillation columns, namely a preliminary treatment column, known as topping column or pre-run column, followed by a second distillation column known as refining column. The topping column substantially has the purpose of separating the more volatile components contained in the crude methanol. The topping column receives the crude methanol and separates the lighter components (light ends) at the top and an aqueous solution at the bottom. The refining column carries out the actual distillation separating a refined methanol at the top and an aqueous stream at the bottom. Another stream known as "fusel oil" is separated from the second column, typically at intermediate elevation. The fusel oil contains water, residual methanol (ca. 1-1.5% of the total) and most of the by-products of the synthesis reaction. Fusel oil has a certain heating value and is commonly used as a fuel. Each column comprises a respective bottom reboiler that heats the bottom of the column and maintains the distillation process. The heat is typically provided by steam, or by a process gas, when available at a suitable thermal level. Moreover, each column may have a top reflux, which means that part of the distilled methanol is condensed and reintroduced in the top of the column. For this purpose, each column is equipped with a respective top condenser which uses air or water as heat sink. The above two-column layout is simple and achieves a satisfactory purification but has the major drawback of consuming a substantial amount of energy. The energy consumption is due predominantly to the heat supplied to the bottom reboilers and the cooling water and/or electricity (for pumps and/or cooling air fans) required by the top condensers. Another drawback is a relatively large diameter of the distillation columns, in relation to the production capacity, and the consequent high cost. The order of magnitude of the heat consumption of the two bottom reboilers is in the range of 1.0-1 .5 MWh per ton of refined methanol, depending on raw methanol composition. The amount of heat removed in the condensers is comparable with the amount of heat exchanged in the reboilers. A known attempt to reduce the heat consumption is the use of three distillation columns at different pressure, as disclosed in US 4 210 495. A preliminary treatment column or topping column is followed by a medium-pressure distillation columns and a final distillation column. The medium-pressure column is operated at about 7-8 bar whilst the topping and final columns a are operated at atmospheric pressure or slightly above, such as 1 .5 bar. The advantage of this configuration is the possibility to condense the top vapors of the medium-pressure column in the bottom reboiler of the subsequent column with the advantage of recovering heat. However, both the topping column and the intermediate column must be heated, resulting in a high specific heat consumption. Furthermore, the intermediate column requires a heat input at a higher temperature than the other columns at lower pressure. A typical energy consumption of this configuration is around 0.