CN114621056B - Process method for separating dimethyl carbonate and methanol azeotrope - Google Patents
Process method for separating dimethyl carbonate and methanol azeotrope Download PDFInfo
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- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 title claims abstract description 283
- 238000000034 method Methods 0.000 title claims abstract description 73
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 title claims abstract description 42
- 238000000605 extraction Methods 0.000 claims abstract description 71
- 238000000746 purification Methods 0.000 claims abstract description 33
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 claims abstract description 31
- 238000000895 extractive distillation Methods 0.000 claims abstract description 23
- 238000004821 distillation Methods 0.000 claims abstract description 16
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 63
- 238000010992 reflux Methods 0.000 claims description 31
- 230000008929 regeneration Effects 0.000 claims description 20
- 238000011069 regeneration method Methods 0.000 claims description 20
- 239000000463 material Substances 0.000 claims description 13
- 239000000203 mixture Substances 0.000 claims description 11
- 230000006835 compression Effects 0.000 claims description 6
- 238000007906 compression Methods 0.000 claims description 6
- 239000007791 liquid phase Substances 0.000 claims description 4
- 238000005265 energy consumption Methods 0.000 abstract description 10
- 239000003795 chemical substances by application Substances 0.000 abstract description 9
- 238000005516 engineering process Methods 0.000 abstract description 2
- 239000000047 product Substances 0.000 description 27
- 239000007788 liquid Substances 0.000 description 24
- 230000009286 beneficial effect Effects 0.000 description 8
- 238000000926 separation method Methods 0.000 description 8
- 239000006227 byproduct Substances 0.000 description 7
- 238000010438 heat treatment Methods 0.000 description 7
- 101150047356 dec-1 gene Proteins 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 5
- 238000004064 recycling Methods 0.000 description 5
- 238000006243 chemical reaction Methods 0.000 description 4
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 3
- DNIAPMSPPWPWGF-UHFFFAOYSA-N Propylene glycol Chemical compound CC(O)CO DNIAPMSPPWPWGF-UHFFFAOYSA-N 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 238000009835 boiling Methods 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- LOMVENUNSWAXEN-UHFFFAOYSA-N Methyl oxalate Chemical compound COC(=O)C(=O)OC LOMVENUNSWAXEN-UHFFFAOYSA-N 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000001502 supplementing effect Effects 0.000 description 2
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 1
- 150000001298 alcohols Chemical class 0.000 description 1
- 238000010533 azeotropic distillation Methods 0.000 description 1
- 239000002826 coolant Substances 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 1
- 239000000284 extract Substances 0.000 description 1
- 231100000053 low toxicity Toxicity 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 239000002032 methanolic fraction Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000003507 refrigerant Substances 0.000 description 1
- 230000001172 regenerating effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 231100000331 toxic Toxicity 0.000 description 1
- 230000002588 toxic effect Effects 0.000 description 1
- 231100000419 toxicity Toxicity 0.000 description 1
- 230000001988 toxicity Effects 0.000 description 1
- 238000005809 transesterification reaction Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
- C07C29/74—Separation; Purification; Use of additives, e.g. for stabilisation
- C07C29/76—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment
- C07C29/80—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment by distillation
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
- C07C29/74—Separation; Purification; Use of additives, e.g. for stabilisation
- C07C29/76—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment
- C07C29/80—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment by distillation
- C07C29/84—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment by distillation by extractive distillation
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C68/00—Preparation of esters of carbonic or haloformic acids
- C07C68/08—Purification; Separation; Stabilisation
Abstract
The application relates to a process method for separating dimethyl carbonate and methanol azeotrope, which comprises extractive distillation and heat pump distillation, wherein diethyl carbonate is used as an extractant in the extractive distillation process; and extracting the dimethyl carbonate and the methanol azeotrope by diethyl carbonate, and then performing a heat pump rectification process on the crude methanol to realize the purification process of the methanol. The process method provided by the application solves the problem of extracting agent selection, diethyl carbonate (DEC) is adopted as the extracting agent, and the purpose of separating DMC-MeOH azeotrope can be achieved by using a smaller extraction ratio; the technology method combining the DEC extraction rectification and the heat pump rectification is adopted, so that the problem of high energy consumption of the device operation is solved.
Description
Technical Field
The application belongs to the technical field of dimethyl carbonate and methanol azeotrope, and in particular relates to a process method for separating dimethyl carbonate and methanol azeotrope.
Background
When dimethyl carbonate (dimethyl carbonate, DMC for short) is used for respectively carrying out transesterification with alcohols such as ethanol, ethylene glycol, propylene glycol and the like to produce products such as methyl ethyl carbonate, ethylene carbonate, propylene carbonate and the like, methanol as a byproduct exists in the form of DMC-MeOH azeotrope; if methanol is recycled and purified as a byproduct, not only can economic benefit be generated, but also the consumption of DMC in the raw material can be reduced. The conventional separation method is difficult to meet the requirement of separating products, and the separation of DMC-MeOH azeotrope directly affects the economic benefit of the whole factory. Thus, research into the DMC-MeOH azeotrope separation process is particularly important.
In the prior art, various methods have been proposed for separating DMC-MeOH azeotrope, such as freeze crystallization, pressure distillation, azeotropic distillation, membrane separation, extraction and extractive distillation. Although the process method can achieve the aim of changing the azeotropic composition of DMC-MeOH azeotrope, the operation energy consumption is higher when being implemented.
The relationship between azeotropic composition and azeotropic temperature of DMC-MeOH azeotrope at various pressures is shown in the following Table:
at present, the mature process is pressurized rectification and extractive rectification, and the pressurized rectification process adopts low pressure (such as 0.2MPa to 0.6 MPa), and has larger circulation quantity and larger energy consumption in equipment investment and operation although the azeotropic composition can be changed; if the pressure rectification of more than 1.0MPa is adopted, the temperature of the tower bottom of the extraction tower is up to more than 190 ℃, the temperature requirement on the heating medium is higher, and the public engineering is difficult to match. In addition, the extractive distillation method is successful in industrial application, and can achieve the purpose of separating DMC-MeOH azeotrope, such as JP patent publication No. 4-27024 which uses dimethyl oxalate as extractant and CN 94112211.5 which uses propylene carbonate as extractant. However, the extractants selected in these patents are not very desirable, such as dimethyl oxalate is easily hydrolyzed and is highly toxic, while propylene carbonate has a relatively high boiling point and requires vacuum operation. It is obvious that the energy consumption is large and the method is uneconomical whether the pressure swing rectification or the simple extraction rectification is adopted.
Disclosure of Invention
Aiming at the defects existing in the prior art, the application solves the problem of selecting an extracting agent by a process method for separating dimethyl carbonate and methanol azeotrope, and the aim of separating DMC-MeOH azeotrope can be achieved by using a smaller extraction ratio by adopting diethyl carbonate (DEC) as the extracting agent; the technology method combining the DEC extraction rectification and the heat pump rectification is adopted, so that the problem of high energy consumption of the device operation is solved.
The specific technical scheme is as follows:
the process method for separating the dimethyl carbonate and methanol azeotrope is characterized by comprising extractive distillation and heat pump distillation, wherein diethyl carbonate is used as an extractant in the extractive distillation process; and extracting the dimethyl carbonate and the methanol azeotrope by diethyl carbonate, and then performing a heat pump rectification process on the crude methanol to realize the purification process of the methanol.
The beneficial effects of adopting above-mentioned scheme are: the process method selects diethyl carbonate as the extractant, has rich sources, low price, stable chemical property and lower toxicity, has moderate boiling point of the extractant and 126.8 ℃ of normal pressure boiling point, is convenient for normal pressure operation, and ensures that the extraction, rectification and separation of DMC-MeOH azeotrope can be stably and efficiently carried out under normal pressure and low toxicity; in addition, when the purity of the byproduct methanol is purified by heat pump rectification, the load of a heating medium and a cooling medium is greatly reduced, the operation energy consumption can be greatly reduced, and the heat pump rectification is operated under normal pressure, so that public facilities are easy to match; the purity of the recovered product of the byproduct methanol is higher, and the purity of the recovered byproduct methanol is more than or equal to 99.95 percent.
Further, after the diethyl carbonate is subjected to extractive distillation, the diethyl carbonate enters an extractant regeneration tower to regenerate the extractant, and the diethyl carbonate regenerated by the extractant returns to the extractive distillation process to be recycled.
The beneficial effects of adopting above-mentioned scheme are: the mixed fraction of DMC and DEC extracted from the extraction and rectification process is returned to the extraction tower for recycling after the extraction agent regeneration is realized by the extraction agent regeneration tower, so that the utilization rate of the extraction agent is improved; DMC products recovered by the extractant regenerating tower can enter other reaction working sections to be used as reaction raw materials.
Further, the heat pump rectification process uses two heat pump rectification towers, namely a light component removal tower and an alcohol purification tower; crude methanol obtained by extracting dimethyl carbonate and methanol azeotrope through diethyl carbonate enters a light component removing tower, residual dimethyl carbonate in the crude methanol is separated by the light component removing tower and then is extracted from the top of the light component removing tower, and the crude methanol returns to the extraction rectification process in the form of dimethyl carbonate and methanol azeotrope, and the material extracted from the bottom of the light component removing tower enters an alcohol purifying tower for purifying the purity of the methanol, and finally methanol products are extracted from the alcohol purifying tower.
The beneficial effects of adopting above-mentioned scheme are: the crude methanol extracted from the extractive distillation process contains 10% DMC, a light component removal tower is used for removing residual DMC and methanol azeotrope, and the residual DMC and methanol azeotrope is returned to the extractive distillation process; materials (methanol and DEC) extracted from the tower bottom of the light component removal tower enter an alcohol purification tower, so that the purification of the methanol purity can be realized, and a methanol product is extracted; the DEC extracted from the tower bottom of the alcohol purifying tower is returned to the extraction and rectification process for recycling, so that the utilization rate of the extractant is improved.
Further, the extraction and rectification process is carried out in an extraction and rectification tower which is divided into an upper section, a middle section and a lower section, wherein the upper section is a rectification section, and the theoretical plate number is between 3 and 5; the middle section is an extraction section, and the theoretical plate number is 15-20; the lower section is a stripping section, and the theoretical plate number is between 6 and 10; the feed inlet of the extractant is the boundary layer between the rectifying section and the extracting section, and the feed inlet of the azeotrope is the boundary layer between the extracting section and the stripping section.
The beneficial effects of adopting above-mentioned scheme are: the extraction rectifying tower breaks the composition of DMC-MeOH azeotrope, the rectifying section reduces or prevents the extractant from being carried out of the top of the extraction rectifying tower, the extraction section realizes the extraction of dimethyl carbonate by diethyl carbonate, and the stripping section extracts methanol from the tower bottom of the extraction rectifying tower; the extractant and the azeotrope material are fully contacted and reacted by the specific feed locations of the extractant and the azeotrope.
Further, the feeding mole ratio of the extractant to the azeotropic mixture is 0.3-2.0, and the reflux ratio of the top of the tower is 0.4-5.0.
The beneficial effects of adopting above-mentioned scheme are: the purpose of the extractive distillation column is to destroy the DMC-MeOH azeotrope composition, rather than requiring a high purity methanol product from the top of the extractive distillation column, which can properly reduce the extraction ratio and the overhead reflux ratio in order to reduce heat load and cold load consumption.
Further, the extractant and the azeotrope are both liquid-phase feed, and the feed temperature of the extractant is 50-60 ℃; the feed temperature of the azeotrope is 50-90 ℃.
Furthermore, the extraction rectifying tower is operated at normal pressure, the temperature of the tower bottom is less than 110 ℃, and the temperature of the tower top is 64 ℃.
Further, the light component removing tower can be operated at normal pressure or at negative pressure, and the compression ratio of the heat pump of the light component removing tower is 1.3-3.0; the alcohol purifying tower is an atmospheric tower, and the compression ratio of the heat pump is 1.3-3.0.
Further, when the operating pressure of the light component removal tower is-0.05 MPa (G), the temperature of the tower top is 47 ℃, and the temperature of the tower bottom is 49 ℃; after the vapor at the top of the light component removing tower is compressed by a light component removing tower compressor, the outlet pressure of the light component removing tower compressor is normal pressure, and the outlet temperature of the light component removing tower compressor is 64 ℃.
The beneficial effects of adopting above-mentioned scheme are: the light component removal tower can be operated at normal pressure or at negative pressure, for example: when the operating pressure of the light component removing tower is-0.05 MPa (G), the temperature of the tower top is 47 ℃, and the temperature of the tower bottom is 49 ℃; after the vapor at the top of the light component removing tower is compressed by a light component removing tower compressor, the outlet pressure of the light component removing tower compressor is normal pressure, the outlet temperature of the light component removing tower compressor is 64 ℃, the vapor at the outlet of the light component removing tower compressor is used as a heat source of a reboiler of a heat pump of the light component removing tower to heat a light component removing tower system, condensed liquid enters a reflux tank of the light component removing tower, after being pressurized by the reflux pump of the light component removing tower, a part of the condensed liquid returns to the top of the light component removing tower as reflux liquid, a part of the condensed liquid is used as a supplementing liquid of the light component removing tower compressor to the light component removing tower compressor, and the other part of the condensed liquid is extracted and returns to the extraction process.
Further, the temperature of the top of the alcohol purifying tower is 64.5 ℃ and the temperature of the tower bottom is 70 ℃; after the vapor at the top of the alcohol purification tower is compressed by the compressor of the alcohol purification tower, the outlet pressure of the compressor of the alcohol purification tower is 0.06MPa (G), and the outlet temperature of the compressor is 76 ℃.
The beneficial effects of adopting above-mentioned scheme are: the alcohol purification tower is an atmospheric tower, the tower top temperature is 64.5 ℃, the tower bottom temperature is 70 ℃, after the vapor at the tower top of the alcohol purification tower is compressed by an alcohol purification tower compressor, the outlet pressure of the alcohol purification tower compressor is 0.06MPa (G), the outlet temperature of the alcohol purification tower compressor is 76 ℃, the vapor at the outlet of the alcohol purification tower compressor is used as a heat source of an alcohol purification tower heat pump reboiler to heat an alcohol purification tower system, condensed liquid enters an alcohol purification tower reflux tank, after being pressurized by the alcohol purification tower reflux pump, part of the condensed liquid is used as reflux liquid to return to the tower top of the alcohol purification tower, part of the condensed liquid is used as a supplementary liquid of the alcohol purification tower compressor to go to the alcohol purification tower compressor, and the other part of the condensed liquid is used as a methanol product.
Compared with the prior art, the application has the following beneficial effects:
(1) The process method solves the problem of extracting agent selection, adopts DEC as the extracting agent, and can achieve the purpose of separating DMC-MeOH azeotrope by using smaller extraction ratio;
(2) The process method provided by the application adopts a process method combining DEC extraction rectification and heat pump rectification, the device can stably operate under normal pressure and low temperature, the heat medium and refrigerant loads of the heat pump rectification are greatly reduced, and the problem of high energy consumption of the device operation is solved; 1 ton of methanol product is recovered, and only 1.87 tons of steam is consumed; and the pressure swing rectification is used for recycling 1 ton of methanol, so that 4.22 tons of steam is consumed;
(3) The purity of the recovered product of the byproduct methanol in the process method provided by the application is higher, and the purity of the recovered byproduct methanol is more than or equal to 99.95%.
Drawings
FIG. 1 is a schematic diagram of a process flow for separating dimethyl carbonate from methanol azeotropes in an embodiment of the application;
FIG. 2 is a schematic diagram of the production process flow for separating dimethyl carbonate and methanol azeotrope by pressure swing distillation in comparative example.
Reference numerals illustrate: 1. DEC; 2. DMC-MeOH azeotrope; 3. an extraction rectifying tower; 4. an extractant regeneration tower; 5. a light component removing tower; 6. an alcohol purification tower; 7. a heat exchanger; 8. an extractant feed cooler; 9. a reboiler of the extraction rectifying tower; 10. extracting pump from the bottom of extraction rectifying tower; 11. extracting pump from tower bottom of extractant regeneration tower; 12. an extractant regeneration column condenser; 13. an extractant regeneration tower reflux tank; 14. reflux/extraction pump of extractant regeneration tower; 15. a DMC product; 16. an extractant regeneration column reboiler; 17. an extraction rectifying tower condenser; 18. reflux tank of extraction rectifying tower; 19. reflux/extraction pump at the top of the extraction rectifying tower; 20. a light component removal tower compressor; 21. a light component removal tower heat pump reboiler; 22. a light component removal tower reflux drum; 23. reflux/extraction pump of light component removing tower; 24. an auxiliary reboiler of the light component removing tower; 25. extracting a pump from the tower bottom of the light component removing tower; 26. an alcohol purification column compressor; 27. an alcohol purification tower heat pump reboiler; 28. an alcohol purifying tower reflux tank; 29. reflux/extraction pump of alcohol purifying tower; 30. a methanol product cooler; 31. a methanol product; 32. an auxiliary reboiler of the alcohol purifying tower; 33. a pump is extracted from the tower bottom of the alcohol purifying tower; 34. a pressurized rectifying tower; 35. a normal pressure rectifying tower; 36. an azeotrope feed preheater; 37. a tower kettle reboiler of the normal pressure rectifying tower; 38. a pressure rectifying tower top condenser; 39. pressurizing a reboiler of the rectifying tower.
Detailed Description
The principles and features of the present application are described below with reference to the following examples and drawings, which are provided for the purpose of illustrating the application and are not to be construed as limiting the scope of the application.
Example 1
A process for separating an azeotrope of dimethyl carbonate and methanol, referring to fig. 1, comprises the following steps:
diethyl carbonate is used as an extractant in the extraction and rectification process, and is carried out in an extraction and rectification tower 3; the extraction rectifying tower 3 is divided into an upper section, a middle section and a lower section, wherein the upper section is a rectifying section, and the number of the tower plates is 5; the middle section is an extraction section, and the number of the tower plates is 18; the lower section is a stripping section, and the number of the tower plates is 8; the extractant DEC 1 enters the extractive distillation column 3 through the heat exchanger 7 and the extractant feed cooler 8, and the feed inlet of the DEC 1 is the boundary layer between the distillation section and the extraction section; the feed inlet of DMC-MeOH azeotrope 2 is the boundary layer of the extraction section and stripping section;
the extractant DEC 1 and DMC-MeOH azeotrope 2 are all liquid-phase feed, the feed mole ratio of the extractant DEC 1 to DMC-MeOH azeotrope 2 is 0.3, and the reflux ratio at the top of the tower is 0.5; the feed temperature of extractant DEC 1 was 60 ℃; the DMC-MeOH azeotrope 2 feed temperature was 90 ℃; the extraction rectifying tower 3 is operated at normal pressure, the temperature of the tower bottom is 105 ℃, and the temperature of the tower top is 64 ℃;
the material in the tower kettle of the extraction rectifying tower 3 is heated by an extraction rectifying tower reboiler 9 in the tower kettle, and the materials are separated; extracting a pump 10 from the tower kettle of the extraction rectifying tower 3, extracting mixed fractions of DMC and DEC, removing the extractant regeneration tower 4 to realize the regeneration of the extractant, extracting a pump 11 from the tower kettle of the extractant regeneration tower, and returning to the extraction rectifying tower 3 for recycling; the steam at the top of the extractant regeneration tower 4 flows back to the top of the extractant regeneration tower 4 by the extractant regeneration tower condenser 12, the extractant regeneration tower reflux tank 13 and the extractant regeneration tower reflux/extraction pump 14, and part of the steam is extracted into DMC product 15 and can enter other reaction working sections to be used as reaction raw materials; the material in the tower kettle of the extractant regeneration tower 4 is heated by the reboiler 16 of the extractant regeneration tower in the tower kettle, and the materials are separated;
the crude methanol extracted from the top of the extraction rectifying tower 3 contains 10 percent of DMC, and part of DMC is refluxed to the top of the extraction rectifying tower 3 through an extraction rectifying tower condenser 17, an extraction rectifying tower reflux tank 18 and an extraction rectifying tower top reflux/extraction pump 19, and part of DMC is extracted into a light component removal tower 5 in the heat pump rectifying process;
wherein, the light component removing tower 5 is used for removing residual DMC-MeOH azeotrope and returns to the front of the extraction rectifying tower 3; the light component removing tower 5 is operated by negative pressure, and the operating pressure of the light component removing tower 5 is minus 0.05MPa (G); the temperature of the top of the light component removing tower 5 is 47 ℃ and the temperature of the tower kettle is 49 ℃; the vapor at the top of the light component removing tower 5 is compressed by a light component removing tower compressor 20, the outlet pressure of the light component removing tower compressor 20 is normal pressure, and the outlet temperature of the light component removing tower compressor 20 is 64 ℃; the outlet steam of the lightness-removing column compressor 20 is used as a heat source of a lightness-removing column heat pump reboiler 21 to heat the lightness-removing column 5 system, condensed liquid enters a lightness-removing column reflux tank 22, after being pressurized by a lightness-removing column reflux/extraction pump 23, one part of the condensed liquid returns to the top of the lightness-removing column 5 as reflux liquid, the other part of the condensed liquid is used as the supplementing liquid of the lightness-removing column compressor 20 to the lightness-removing column compressor 20, and the other part of the condensed liquid is extracted to return to the extraction rectifying column 3; the heat pump compression ratio of the light component removal tower 5 is 1.4; the material at the tower bottom of the light component removing tower 5 is heated by an auxiliary reboiler 24 of the light component removing tower to separate the material;
an alcohol purifying tower 6 in the heat pump rectification process for purifying the purity of the methanol; materials (methanol and DEC) extracted from the tower bottom of the light component removal tower 5 enter an alcohol purification tower 6 through a pump 25 extracted from the tower bottom of the light component removal tower; the alcohol purifying tower 6 is an atmospheric tower, the tower top temperature is 64.5 ℃, and the tower bottom temperature is 70 ℃; the vapor at the top of the alcohol purifying column 6 is compressed by an alcohol purifying column compressor 26, the outlet pressure of the alcohol purifying column compressor 26 is 0.06MPa (G), and the outlet temperature of the alcohol purifying column compressor 26 is 76 ℃; the steam at the outlet of the alcohol purifying column compressor 26 is used as a heat source of the alcohol purifying column heat pump reboiler 27 to heat the alcohol purifying column 6 system, the condensed liquid enters the alcohol purifying column reflux tank 28, after being pressurized by the alcohol purifying column reflux/extraction pump 29, part of the condensed liquid returns to the top of the alcohol purifying column 6 as reflux liquid, the other part of the condensed liquid is used as the supplementary liquid of the alcohol purifying column compressor 26 to remove the alcohol purifying column compressor 26, and the other part of the condensed liquid passes through the methanol product cooler 30 to extract the methanol product 31; the heat pump compression ratio of the alcohol purification column 6 is 1.6; the tower kettle materials of the alcohol purifying tower 6 are heated by an auxiliary reboiler 32 of the alcohol purifying tower of the tower kettle, and the materials are separated;
the DEC extracted from the tower kettle of the alcohol purifying tower 6 is returned to the extraction rectifying tower 3 for recycling through the extracting pump 33 of the tower kettle of the alcohol purifying tower.
The index of the methanol in the recovered methanol product 31 is more than or equal to 99.95 percent through the production process.
Example 2
Referring to example 1, the difference from example 1 is that the light component removal column 5 is operated at normal pressure, the column top temperature is 64.5 ℃ and the column bottom temperature is 66 ℃; the vapor at the top of the light component removing tower 5 is compressed by a light component removing tower compressor 20, the outlet pressure of the light component removing tower compressor 20 is 0.05MPa (G), and the outlet temperature of the light component removing tower compressor 20 is 73 ℃;
the other technical features are the same as those of example 1.
The index of the methanol in the recovered methanol product 31 is more than or equal to 99.95 percent through the production process.
Example 3
Referring to example 1, the difference from example 1 is that in extractive distillation, the feed molar ratio of extractant DEC 1 to DMC-MeOH azeotrope 2 is 1.5 and the overhead reflux ratio is 0.8; the extraction rectifying tower 3 is operated at normal pressure, the temperature of the tower bottom is 110 ℃, and the temperature of the tower top is 64 ℃; the DMC content in the crude methanol extracted from the top of the extraction rectifying tower 3 is less than 0.05 percent, and the crude methanol fraction extracted from the top of the extraction rectifying tower is directly removed to an alcohol purifying tower 6;
the other technical features are the same as those of example 1.
The index of the methanol in the recovered methanol product 31 is more than or equal to 99.9 percent through the production process.
Comparative example
The aim of changing the DMC-MeOH azeotropic composition is achieved by changing the operating pressure, and referring to FIG. 2, the process method for separating DMC-MeOH azeotrope by pressure swing distillation is specifically as follows:
DMC-MeOH azeotrope 2 (DMC content about 30%, methanol content about 70%) was preheated by azeotrope feed preheater 36 and fed to pressurized rectifying column 34 at an operating pressure of 0.8MPa (G), a column top temperature of 132.6 ℃, a column bottom temperature of about 178 ℃, and a column top operating reflux ratio of 3.5; DMC-MeOH azeotropic composition (DMC content about 15.7%, methanol content about 84.3%) extracted from the top of the pressurized rectifying tower 34 enters the normal pressure rectifying tower 35; DMC product 15 is extracted from the tower bottom of the pressurized rectifying tower 34;
the DMC-MeOH azeotropic composition (DMC content about 15.7% and methanol content about 84.3%) extracted from the top of the pressure rectifying tower 34 enters the normal pressure rectifying tower 35, the operating temperature of the top of the normal pressure rectifying tower 35 is 63.8 ℃, the operating temperature of the tower kettle is 66 ℃, the operating reflux ratio is 6, the DMC-MeOH azeotropic composition (DMC content about 30% and methanol content about 70%) extracted from the top of the normal pressure rectifying tower 35 returns to the pressure rectifying tower 34 for rectifying; the methanol product 31 is extracted from the tower bottom of the normal pressure rectifying tower 35.
In order to save energy consumption, the pressure rectifying tower 34 and the normal pressure rectifying tower 35 adopt pressure swing coupling rectification, namely, the steam at the top of the pressure rectifying tower 34 can be used as a heat source of a reboiler 37 at the bottom of the normal pressure rectifying tower, and the reboiler 37 at the bottom of the normal pressure rectifying tower can be used as a heat source of a condenser 38 at the top of the pressure rectifying tower; only the pressurized rectifying column reboiler 39 needs one heating medium heating; if steam heating is adopted, the saturated steam heating pressure is higher than 1.3MPa (G), and the requirement on heating media is higher.
According to the production process, 4.22 tons of steam (P is more than or equal to 1.3MPa, T is more than or equal to 195 ℃) is required to be consumed for recovering each ton of methanol, and the purity of a methanol product 31 is more than or equal to 99%; because methanol is extracted from the liquid phase of the tower kettle, the chromaticity of the methanol product 31 is poor. If the requirement on the methanol index is high, the methanol product 31 extracted from the tower bottom of the normal pressure rectifying tower 35 is required to be purified by a methanol purifying tower, and the methanol is extracted from the tower top of the methanol purifying tower; the operation energy consumption is higher due to the addition of the methanol purification tower.
The results illustrate:
the results of comparing the energy consumption of the operation of separating DMC-MeOH azeotrope (in terms of recovered methanol product per ton) using the extractive distillation+heat pump distillation combination process of example 1 of the present application with the comparative pressure swing distillation separation process are shown in Table 1.
TABLE 1
As can be seen from table 1, the process of the present application recovers 1 ton of methanol product, only consumes 1.87 tons of steam; and the pressure swing distillation is used for recovering 1 ton of methanol, so that 4.22 tons of steam are consumed.
The comparison of the operating costs (in terms of recovered methanol product per ton) for separating DMC-MeOH azeotrope using the extractive distillation+heat pump distillation combined process and the pressure swing distillation separation process of example 1 of the present application is shown in Table 2.
TABLE 2
As can be seen from Table 2, the present application adopts the combination of extractive distillation and heat pump distillation to save about 2000 ten thousand yuan per year compared with the pressure swing distillation separation process, which means that the process of the present application has low operation cost; the larger the device is, the more obvious the advantage of the combined process method of extractive distillation and heat pump distillation is.
The foregoing description of the preferred embodiments of the application is not intended to limit the application to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the application are intended to be included within the scope of the application.
Claims (8)
1. The process method for separating the dimethyl carbonate and methanol azeotrope is characterized by comprising extractive distillation and heat pump distillation, wherein diethyl carbonate is used as an extractant in the extractive distillation process; after the dimethyl carbonate and the methanol azeotrope are extracted by diethyl carbonate, the crude methanol is subjected to a heat pump rectification process to realize the purification process of the methanol;
the diethyl carbonate enters an extractant regeneration tower to regenerate the extractant after extraction and rectification, and the diethyl carbonate regenerated by the extractant returns to the extraction and rectification process to be recycled;
the heat pump rectification process uses two heat pump rectification towers, namely a light component removal tower and an alcohol purification tower; crude methanol obtained by extracting dimethyl carbonate and methanol azeotrope through diethyl carbonate enters a light component removing tower, residual dimethyl carbonate in the crude methanol is separated by the light component removing tower and then is extracted from the top of the light component removing tower, and the crude methanol returns to the extraction rectification process in the form of dimethyl carbonate and methanol azeotrope, and the material extracted from the bottom of the light component removing tower enters an alcohol purifying tower for purifying the purity of the methanol, and finally methanol products are extracted from the alcohol purifying tower;
the extraction and rectification process is carried out in an extraction and rectification tower, and the extraction and rectification tower is operated at normal pressure; the light component removing tower is operated at normal pressure or at negative pressure, and the alcohol purifying tower is an atmospheric tower.
2. The process according to claim 1, wherein the extractive distillation column is divided into an upper section, a middle section and a lower section, wherein the upper section is a distillation section, and the theoretical plate number is between 3 and 5; the middle section is an extraction section, and the theoretical plate number is 15-20; the lower section is a stripping section, and the theoretical plate number is between 6 and 10; the feed inlet of the extractant is the boundary layer between the rectifying section and the extracting section, and the feed inlet of the azeotrope is the boundary layer between the extracting section and the stripping section.
3. The process according to claim 2, wherein the molar ratio of the extractant to the azeotropic mixture is 0.3 to 2.0 and the reflux ratio at the top of the column is 0.4 to 5.0.
4. A process according to claim 3, wherein the extractant and azeotrope are both liquid phase feeds, the feed temperature of the extractant being 50 to 60 ℃; the feeding temperature of the azeotrope is 50-90 ℃.
5. The process according to claim 4, wherein the temperature of the bottom of the extractive distillation column is not more than 110 ℃ and the temperature of the top of the extractive distillation column is 64 ℃.
6. The process of claim 1, wherein the lightness-removing column has a heat pump compression ratio of 1.3 to 3.0; the heat pump compression ratio of the alcohol purifying tower is 1.3-3.0.
7. The process of claim 6, wherein the operating pressure of the light ends column is-0.05 MPa, the overhead temperature is 47 ℃, and the bottom temperature is 49 ℃; after the vapor at the top of the light component removing tower is compressed by a light component removing tower compressor, the outlet pressure of the light component removing tower compressor is normal pressure, and the outlet temperature of the light component removing tower compressor is 64 ℃.
8. The process of claim 6, wherein the alcohol purification column has a top temperature of 64.5 ℃ and a bottom temperature of 70 ℃; after the vapor at the top of the alcohol purification tower is compressed by the compressor of the alcohol purification tower, the outlet pressure of the compressor of the alcohol purification tower is 0.06MPa, and the outlet temperature of the compressor is 76 ℃.
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