CN107915640B - Extractive distillation separation method of dimethyl carbonate and methanol - Google Patents
Extractive distillation separation method of dimethyl carbonate and methanol Download PDFInfo
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- C07C29/84—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment by distillation by extractive distillation
Abstract
The invention relates to an extractive distillation separation method of dimethyl carbonate and methanol, which mainly solves the problems of overhigh energy consumption and environmental pollution in the prior art. The invention better solves the technical problem by adopting the technical scheme that the extractive distillation separation method of dimethyl carbonate and methanol adopts the ionic liquid with the anion of bis (trifluoromethanesulfonimide) as the extractant, and can be used in the industrial production for separating the dimethyl carbonate and the methanol.
Description
Technical Field
The invention relates to an extractive distillation separation method of dimethyl carbonate and methanol.
Background
Dimethyl carbonate (DMC) is an environment-friendly chemical intermediate, is widely used for methylation, carbonylation, methylation of carbonyl, methoxylation and other reactions, and is known as a new base stone of current organic synthesis. Dimethyl carbonate is usually produced industrially by the transesterification method, and during the production process, dimethyl carbonate and methanol form an azeotrope which is difficult to separate by the common rectification method.
In recent years, extraction rectification, pressure rectification, azeotropic rectification, membrane separation and other process technologies are used for producing high-purity dimethyl carbonate. Compared with the latter three processes, the extractive distillation has the advantages of low energy consumption, simple process, wide solvent selection and the like, and is a technical trend for separating dimethyl carbonate and methanol azeotrope with energy conservation and consumption reduction.
Patent CN103159586A discloses a continuous extractive distillation separation method of dimethyl carbonate-methanol azeotropic mixture. Under normal pressure, ethylene glycol is used as an extracting agent, the solvent ratio is 1-3, the separated dimethyl carbonate-methanol mixture is fed into the middle of a tower, the extracting agent is fed into the top of the tower, the reflux ratio is 2, high-purity methanol is extracted from the top of an extraction rectifying tower, dimethyl carbonate and the extracting agent are extracted from the bottom of the tower, distillate at the bottom of the tower enters an extracting agent recovery tower, the reflux ratio is 3, dimethyl carbonate is extracted from the top of the tower, and the extracting agent extracted from the bottom of the tower can be recycled. The extractant ethylene glycol exists in a phase separation zone with dimethyl carbonate and methanol, so that the separation efficiency is reduced and the energy consumption is increased.
Patent CN105037162A discloses a continuous extractive distillation separation method of dimethyl carbonate-methanol azeotropic mixture. The extracting agent is N, N-dimethyl amide, N-formyl morpholine or their mixture in any proportion. The operation conditions of the extraction rectifying tower and the solvent recovery tower are normal pressure or reduced pressure, the ratio of the distillate at the top of the extraction rectifying tower to the extractant is 0.5: 1-10: 1, the feeding ratio (mass) of the extractant to the mixture is 1: 10-5: 1, and the two rectifying towers are used for achieving the recycling of the extractant. The environment pollution problem is easily caused by adopting volatile N, N-dimethyl amide, N-formyl morpholine or a mixture of the N, N-dimethyl amide and the N-formyl morpholine as an extracting agent.
Patent CN1367772A discloses a process for separating methanol and dimethyl carbonate in a distillation column by extractive distillation, from which a vapor side stream is taken. Phenol is used as an extracting agent, but the phenol has a high melting point and is easy to crystallize at normal temperature to cause the problem of pipeline blockage.
In conclusion, the prior art adopts the traditional organic solvent as the extracting agent and separates the dimethyl carbonate and the methanol by extraction and rectification, and has the problems of high energy consumption and environmental pollution.
The ionic liquid is composed of anions and cations, has the excellent properties of non-volatility, excellent thermal stability, designable structure, low melting point and the like, is considered to be a novel green solvent, and is widely applied and researched in the fields of chemical reaction, chemical separation, gas treatment and the like in recent years.
Disclosure of Invention
The invention aims to solve the technical problems of over high energy consumption and environmental pollution in the prior art; the new method for separating dimethyl carbonate from methanol by extractive distillation has the advantages of good separation effect, low energy consumption and environmental protection.
In order to solve the technical problems, the technical scheme of the invention is as follows: an extractive distillation separation method of dimethyl carbonate and methanol adopts ionic liquid with the anion of bis (trifluoromethanesulfonimide) as an extractant.
In the above technical solution, preferably, the cation of the ionic liquid is at least one selected from the group consisting of an alkyl imidazole cation, an alkyl ether imidazole cation, an alkyl pyridine cation, a quaternary ammonium cation, and a quaternary phosphonium cation.
In the above technical solution, more preferably, the cation of the ionic liquid is selected from 1, 3-alkyl substituted imidazolium [ R ]1R3im]+1, 2, 3-alkyl-substituted imidazolium cations [ R ]1R2R3im]+1-alkyl ether-3-alkylimidazolium cation [ R1OR2R3im]+N-alkylpyridinium [ Rpy]+Alkyl quaternary ammonium cation [ N ]R1R2R3R4]+And alkyl quaternary phosphonium cations [ P ]R1R2R3R4]+At least one of (1).
In the above technical solution, it is further preferable that the alkyl group in the cation of the ionic liquid is selected from the group consisting of a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, a hexyl group, a heptyl group, and an octyl group.
In the above technical solution, preferably, the molar ratio of the ionic liquid to the mixture of dimethyl carbonate and methanol is 0.2 or more, preferably 0.5 to 1.5, and more preferably 0.7 to 1.
In the above technical scheme, preferably, the mass concentration of dimethyl carbonate in the mixture of dimethyl carbonate and methanol is 1-60%, preferably 20-50%.
In the above technical scheme, preferably, the extractant is added from the upper part of the extractive distillation column, the dimethyl carbonate and methanol are added from the lower part of the extractive distillation column, the product at the top of the column is methanol, and the product at the bottom of the column is a mixture of dimethyl carbonate and ionic liquid.
In the above technical scheme, preferably, the product at the bottom of the column is sent to a solvent recovery flash tower, after flash evaporation, dimethyl carbonate is obtained at the top of the column, and the ionic liquid obtained at the bottom of the column is circulated to the extractive distillation column.
In the technical scheme, preferably, the operating pressure of the extractive distillation tower is normal pressure to 0.5MPa, the reflux ratio is 0.5 to 5, the temperature of a tower kettle is 60 to 150 ℃, and the number of theoretical plates is 20 to 50.
In the above technical scheme, preferably, the operating pressure of the solvent recovery flash tower is 0.001-0.05 MPa, and the operating temperature is 100-200 ℃.
The ionic liquid can be selected from 1-hexyl-3-methylimidazole bistrifluoromethanesulfonylimide salt ([ hmim)][NTf2]) 1-butyl-2-methyl-3-methylimidazolium bistrifluoromethylsulfonyl imide salt ([ bmnim ])][NTf2]) 1-Ethyl ether-3-methylimidazolium bistrifluoromethanesulfonimide salt ([ EOEmim [ ]][NTf2]) 1-hexylpyridine bis (trifluoromethanesulfonylimide) salt ([ hpy)][NTf2]) Tributylmethylammonium bistrifluoromethanesulfonylimide salt ([ N)1444][NTf2]) And tetrabutylphosphonium bistrifluoromethanesulfonylimide salt ([ P ]4444][NTf2]) Preferably at least one of 1-hexyl-3-methylimidazole bistrifluoromethanesulfonimide salt and 1-hexylpyridine bistrifluoromethanesulfonimide salt.
The extraction and rectification tower can be a plate tower or a packed tower. The plate tower comprises a bubble cap tower, a sieve plate tower and a float valve tower, and is preferably a sieve plate tower; the packing used by the packed tower comprises loose packing and structured packing, and the packing is preferably pall ring packing or wire mesh structured packing.
FIG. 1 shows an ionic liquid 1-hexyl-3-methylimidazolium bistrifluoromethylsulfonylimide salt ([ hmim [ ])][NTf2]) Influence on dimethyl carbonate-methanol gas-liquid equilibrium curve under different solvent ratio conditions; FIG. 2 is a schematic view of an ionLiquid 1-hexylpyridine bis (trifluoromethanesulfonylimide) [ hpy ]][NTf2]) Influence on dimethyl carbonate-methanol gas-liquid equilibrium curve under different solvent ratio conditions. When [ hmim][NTf2]The solvent ratio of the mixture of dimethyl carbonate and methanol is 0.25, [ hpy ]][NTf2]When the solvent ratio of the ionic liquid to the dimethyl carbonate-methanol mixture is 0.42, the concentration of methanol in gas and liquid is improved by the ionic liquid, and the azeotropic composition of dimethyl carbonate and methanol is broken, so that high-purity dimethyl carbonate can be obtained by a rectification method.
The invention adopts the ionic liquid with the anion of bis (trifluoromethanesulfonimide) as the extractant, improves the relative volatility of dimethyl carbonate and methanol, obtains high-purity dimethyl carbonate, obtains better technical effect, and can be used in industrial production for continuously separating dimethyl carbonate and methanol. By adopting the technical scheme of the invention, the separation effect of the dimethyl carbonate and the methanol is good, and the method has the characteristics of low energy consumption and environmental protection.
Drawings
FIG. 1 is [ hmim][NTf2]Isothermal (60 ℃) vapor-liquid equilibrium curves for the three-component system dimethyl carbonate-methanol.
In fig. 1, the methanol concentration represents the mole fraction of methanol obtained by normalizing the concentrations of methanol and dimethyl carbonate after removing the ionic liquid in the ternary system of methanol-dimethyl carbonate-ionic liquid. [ hmim][NTf2]The solvent ratio to the dimethyl carbonate-methanol mixture was 0.25, 0.42 and 1, respectively.
FIG. 2 is [ hpy ]][NTf2]Isothermal (60 ℃) vapor-liquid equilibrium curves for the three-component system dimethyl carbonate-methanol.
In fig. 2, the methanol concentration represents the mole fraction of methanol obtained by normalizing the concentrations of methanol and dimethyl carbonate after removing the ionic liquid in the ternary system of methanol-dimethyl carbonate-ionic liquid. [ hpy][NTf2]The solvent ratio to the dimethyl carbonate-methanol mixture was 0.42 and 1, respectively.
FIG. 3 is a flow chart of the extractive distillation separation process.
In fig. 3, T1 is an extractive distillation column; t2 is a flash tower; 1 is a mixture of dimethyl carbonate and methanol; 2 is ionic liquid; 3 is methanol; 4 is dimethyl carbonate. Adding an extractant ionic liquid from the upper part of an extraction rectifying tower, adding a mixture of raw materials dimethyl carbonate and methanol from the lower part of the extraction rectifying tower, extracting and separating, wherein the top product of the extraction rectifying tower is methanol, the bottom product of the extraction rectifying tower is a mixture of dimethyl carbonate and the ionic liquid, conveying the bottom product of the extraction rectifying tower to a solvent recovery flash tower through a pump, carrying out high-temperature flash evaporation to obtain high-purity dimethyl carbonate at the top of the tower, and refluxing the ionic liquid extracted from the bottom of the tower to the extraction rectifying tower for recycling.
The present invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.
Detailed Description
[ example 1 ]
Such as the extractive distillation scheme shown in figure 3. The extractive distillation column has 25 theoretical plates (the number of plates is from top to bottom), and the extractant ionic liquid 1-hexyl-3-methylimidazolium bistrifluoromethylsulfonyl imide salt ([ hmim [)][NTf2]) The feed was taken from tray 2 at a flow rate of 11kg/h, and a mixture of the starting materials dimethyl carbonate and methanol was taken from tray 23 at a dimethyl carbonate content of 30% by weight and a methanol content of 70% by weight, with a total flow rate of 1kg/h, at which time the extractant/starting material molar solvent ratio was 0.87. The extractive distillation tower is operated under normal pressure, the top of the tower is fully condensed, the reflux ratio is 1, the extraction amount at the top of the tower is 0.7kg/h, and 99.85 wt% of methanol and 0.15 wt% of dimethyl carbonate can be obtained. The temperature of the top of the extraction and rectification tower is 40 ℃, and the temperature of the bottom of the extraction and rectification tower is 99 ℃. The product at the bottom of the extraction and rectification tower is conveyed to a solvent recovery flash tower by a pump, the operation pressure is 1kPa, the heating temperature is 120 ℃, the flow at the top of the tower is 0.3kg/h, and 99.85 wt% of dimethyl carbonate and 0.15 wt% of methanol can be obtained.
[ example 2 ]
Such as the extractive distillation scheme shown in figure 3. The extractive distillation column has 25 theoretical plates (the number of plates is from top to bottom), and the extractant ionic liquid 1-hexyl-3-methylimidazolium bistrifluoromethylsulfonyl imide salt ([ hmim [)][NTf2]) Fed from tray 2 at a flow rate of 10kg/h, and fed from tray 23 as a mixture of dimethyl carbonate and methanol, the dimethyl carbonate content being 40% by weight, methanolThe content was 60% by weight, the total flow was 1kg/h, and the extractant/starting material molar solvent ratio was 0.857. The extractive distillation tower is operated under normal pressure, the top of the tower is fully condensed, the reflux ratio is 1, the extraction amount at the top of the tower is 0.6kg/h, and 99.9 wt% of methanol and 0.1 wt% of dimethyl carbonate can be obtained. The temperature of the top of the extraction and rectification tower is 40 ℃, and the temperature of the bottom of the extraction and rectification tower is 96 ℃. The product at the bottom of the extraction and rectification tower is conveyed to a solvent recovery flash tower by a pump, the operation pressure is 1kPa, the heating temperature is 120 ℃, the flow at the top of the tower is 0.4kg/h, and 99.89 wt% of dimethyl carbonate and 0.11 wt% of methanol can be obtained.
[ example 3 ]
Such as the extractive distillation scheme shown in figure 3. The extractive distillation column has 25 theoretical plates (the number of plates is from top to bottom), and the extractant ionic liquid 1-hexyl-3-methylimidazolium bistrifluoromethylsulfonyl imide salt ([ hmim [)][NTf2]) The feed was taken from tray 2 at a flow rate of 8kg/h, and a mixture of the starting materials dimethyl carbonate and methanol was taken from tray 23 at a dimethyl carbonate content of 50 wt% and a methanol content of 50 wt% with a total flow rate of 1kg/h, at which time the extractant to starting material molar solvent ratio was 0.75. The extractive distillation tower is operated under normal pressure, the top of the tower is fully condensed, the reflux ratio is 1, the extraction amount at the top of the tower is 0.5kg/h, and 99.93 wt% of methanol and 0.07 wt% of dimethyl carbonate can be obtained. The temperature of the top of the extraction and rectification tower is 40 ℃, and the temperature of the bottom of the extraction and rectification tower is 89 ℃. The product at the bottom of the extraction and rectification tower is conveyed to a solvent recovery flash tower by a pump, the operation pressure is 1kPa, the heating temperature is 120 ℃, the flow at the top of the tower is 0.5kg/h, and 99.90 wt% of dimethyl carbonate and 0.10 wt% of methanol can be obtained.
[ example 4 ]
Such as the extractive distillation scheme shown in figure 3. The extractive distillation column has 25 theoretical plates (the number of plates is from top to bottom), and the extractant ionic liquid 1-hexyl-3-methylimidazolium bistrifluoromethylsulfonyl imide salt ([ hmim [)][NTf2]) The feed was taken from tray 2 at a flow rate of 6kg/h, a mixture of the starting materials dimethyl carbonate and methanol was taken from tray 23 at a dimethyl carbonate content of 40% by weight and a methanol content of 60% by weight, with a total flow rate of 1kg/h, at which time the extractant/starting material molar solvent ratio was 0.51. The extractive distillation tower is operated under normal pressure, the top of the tower is fully condensed, the reflux ratio is 1.6, and the top of the tower is used for extractingThe amount was 0.6kg/h, 99.50 wt% methanol and 0.50 wt% dimethyl carbonate were obtained. The temperature of the top of the extraction and rectification tower is 40 ℃, and the temperature of the bottom of the extraction and rectification tower is 96 ℃. The product at the bottom of the extraction and rectification tower is conveyed to a solvent recovery flash tower through a pump, the operation pressure is 1kPa, the heating temperature is 120 ℃, the flow at the top of the tower is 0.4kg/h, and 99 wt% of dimethyl carbonate and 1 wt% of methanol can be obtained.
[ example 5 ]
Such as the extractive distillation scheme shown in figure 3. The extractive distillation column has 30 theoretical plates (the number of plates is from top to bottom), and the extractant ionic liquid 1-butyl-2-methyl-3-methylimidazole bistrifluoromethylsulfonyl imide salt ([ bmnim ]][NTf2]) The feed was from tray 2 at a flow rate of 13kg/h, a mixture of the starting materials dimethyl carbonate and methanol was fed from tray 28 at a dimethyl carbonate content of 20% by weight and a methanol content of 80% by weight, with a total flow rate of 1kg/h, at which time the extractant to starting material molar solvent ratio was 0.976. The extractive distillation tower is operated under normal pressure, the top of the tower is fully condensed, the reflux ratio is 0.9, the extraction amount at the top of the tower is 0.8kg/h, and 99.95 wt% of methanol and 0.1 wt% of dimethyl carbonate can be obtained. The temperature of the top of the extraction and rectification tower is 40 ℃, and the temperature of the bottom of the extraction and rectification tower is 108 ℃. The product at the bottom of the extraction and rectification tower is conveyed to a solvent recovery flash tower by a pump, the operation pressure is 2kPa, the heating temperature is 160 ℃, the flow at the top of the tower is 0.2kg/h, and 99.88 wt% of dimethyl carbonate and 0.12 wt% of methanol can be obtained.
[ example 6 ]
Such as the extractive distillation scheme shown in figure 3. The extractive distillation column has 35 theoretical plates (the number of plates is counted from top to bottom), and the extractant ionic liquid 1-ethyl ether-3-methylimidazole bistrifluoromethanesulfonylimide salt ([ EOEmim [ ])][NTf2]) The feed was taken from tray 2 at a flow rate of 10kg/h, and a mixture of the starting materials dimethyl carbonate and methanol was taken from tray 38 at a dimethyl carbonate content of 30 wt%, a methanol content of 70 wt% and a total flow rate of 1kg/h, at which time the extractant to starting material molar solvent ratio was 0.808. The extractive distillation column is operated at 3bar, the top of the column is fully condensed, the reflux ratio is 1.6, the extraction amount at the top of the column is 0.7kg/h, and 99.81 wt% of methanol and 0.19 wt% of dimethyl carbonate can be obtained. The temperature of the top of the extraction and rectification tower is 76 ℃, and the temperature of the bottom of the extraction and rectification tower is 142 ℃. Extraction ofThe product at the bottom of the rectifying tower is conveyed to a solvent recovery flash tower by a pump, the operation pressure is 2kPa, the heating temperature is 160 ℃, the flow at the top of the tower is 0.3kg/h, and 99.70 wt% of dimethyl carbonate and 0.3 wt% of methanol can be obtained.
[ example 7 ]
Such as the extractive distillation scheme shown in figure 3. The extractive distillation column has 35 theoretical plates (the number of plates is from top to bottom), and the extractant ionic liquid 1-hexylpyridine bis (trifluoromethanesulfonimide) [ hpy ]][NTf2]) The feed was taken from tray 2 at a flow rate of 9kg/h, a mixture of the starting materials dimethyl carbonate and methanol was taken from tray 32 at a dimethyl carbonate content of 30% by weight and a methanol content of 70% by weight, with a total flow rate of 1kg/h, at which time the extractant/starting material molar solvent ratio was 0.8. The extractive distillation column is operated under 1bar, the top of the column is fully condensed, the reflux ratio is 1.4, the extraction amount at the top of the column is 0.7kg/h, and 99.9 wt% of methanol and 0.1 wt% of dimethyl carbonate can be obtained. The temperature of the top of the extraction and rectification tower is 40 ℃, and the temperature of the bottom of the extraction and rectification tower is 105 ℃. The product at the bottom of the extraction and rectification tower is conveyed to a solvent recovery flash tower by a pump, the operation pressure is 2kPa, the heating temperature is 160 ℃, the flow at the top of the tower is 0.3kg/h, and 99.82 wt% of dimethyl carbonate and 0.18 wt% of methanol can be obtained.
[ example 8 ]
Such as the extractive distillation scheme shown in figure 3. The extractive distillation column has 35 theoretical plates (the number of plates is from top to bottom), and the extractant ionic liquid 1-hexylpyridine bis (trifluoromethanesulfonimide) [ hpy ]][NTf2]) The feed was taken from tray 2 at a flow rate of 9kg/h, a mixture of the starting materials dimethyl carbonate and methanol was taken from tray 32 at a dimethyl carbonate content of 30% by weight and a methanol content of 70% by weight, with a total flow rate of 1kg/h, at which time the extractant/starting material molar solvent ratio was 0.8. The extractive distillation column is operated under 1bar, the top of the column is fully condensed, the reflux ratio is 1.4, the extraction amount at the top of the column is 0.7kg/h, and 99.9 wt% of methanol and 0.1 wt% of dimethyl carbonate can be obtained. The temperature of the top of the extraction and rectification tower is 40 ℃, and the temperature of the bottom of the extraction and rectification tower is 105 ℃. The product at the bottom of the extraction and rectification tower is conveyed to a solvent recovery flash tower by a pump, the operation pressure is 2kPa, the heating temperature is 160 ℃, the flow at the top of the tower is 0.3kg/h, and 99.82 wt% of dimethyl carbonate and 0.18 wt% of methanol can be obtained.
[ example 9 ]
Such as the extractive distillation scheme shown in figure 3. The extractive distillation column has 25 theoretical plates (the number of plates is from top to bottom), and the extractant ionic liquid 1-hexyl-3-methylimidazolium bistrifluoromethylsulfonyl imide salt ([ hmim [)][NTf2]) And 1-hexylpyridine bistrifluoromethanesulfonylimide salt ([ hpy)][NTf2]) The mixed solvent was fed from tray 2 at 5kg/h and 6kg/h, respectively, and a mixture of raw materials, dimethyl carbonate and methanol, was fed from tray 23 at 30 wt% dimethyl carbonate, 70 wt% methanol and a total flow of 1kg/h, at which time the molar solvent ratio of extractant to raw material was 0.93. The extractive distillation column is operated under 1bar, the top of the column is fully condensed, the reflux ratio is 1.2, the extraction amount at the top of the column is 0.7kg/h, and 99.91 wt% of methanol and 0.09 wt% of dimethyl carbonate can be obtained. The temperature of the top of the extraction and rectification tower is 40 ℃, and the temperature of the bottom of the extraction and rectification tower is 102 ℃. The product at the bottom of the extraction and rectification tower is conveyed to a solvent recovery flash tower by a pump, the operation pressure is 2kPa, the heating temperature is 160 ℃, the flow at the top of the tower is 0.3kg/h, and 99.9 wt% of dimethyl carbonate and 0.1 wt% of methanol can be obtained.
[ example 10 ]
Such as the extractive distillation scheme shown in figure 3. The extractive distillation column has 25 theoretical plates (the number of plates is from top to bottom), and the extractant ionic liquid tributyl methyl ammonium bistrifluoromethylsulfonyl imide salt ([ N ]1444][NTf2]) The feed was taken from tray 2 at a flow rate of 8kg/h, and a mixture of the starting materials dimethyl carbonate and methanol was taken from tray 23 at a dimethyl carbonate content of 30% by weight and a methanol content of 70% by weight, with a total flow rate of 1kg/h, at which time the extractant/starting material molar solvent ratio was 0.66. The extractive distillation tower is operated under normal pressure, the top of the tower is fully condensed, the reflux ratio is 1.6, the extracted quantity at the top of the tower is 0.7kg/h, and 99.70 wt% of methanol and 0.30 wt% of dimethyl carbonate can be obtained. The temperature of the top of the extraction and rectification tower is 40 ℃, and the temperature of the bottom of the extraction and rectification tower is 96 ℃. The product at the bottom of the extraction and rectification tower is conveyed to a solvent recovery flash tower by a pump, the operation pressure is 1kPa, the heating temperature is 120 ℃, the flow at the top of the tower is 0.4kg/h, and 99.5 wt% of dimethyl carbonate and 0.5 wt% of methanol can be obtained.
[ example 11 ]
Such as the extractive distillation scheme shown in figure 3. The extractive distillation column has 25 theoretical plates (the number of plates is from top to bottom), and the extractant ionic liquid tetrabutyl phosphine bistrifluoromethylsulfonyl imide salt ([ P ]4444][NTf2]) The feed was taken from tray 2 at a flow rate of 10kg/h, and a mixture of the starting materials dimethyl carbonate and methanol was taken from tray 23 at a dimethyl carbonate content of 30% by weight and a methanol content of 70% by weight, with a total flow rate of 1kg/h, at which time the extractant/starting material molar solvent ratio was 0.74. The extractive distillation tower is operated under normal pressure, the top of the tower is fully condensed, the reflux ratio is 1, the extraction amount at the top of the tower is 0.7kg/h, and 99.8 wt% of methanol and 0.2 wt% of dimethyl carbonate can be obtained. The temperature of the top of the extraction and rectification tower is 40 ℃, and the temperature of the bottom of the extraction and rectification tower is 96 ℃. The product at the bottom of the extraction and rectification tower is conveyed to a solvent recovery flash tower by a pump, the operation pressure is 1kPa, the heating temperature is 120 ℃, the flow at the top of the tower is 0.4kg/h, and 99.5 wt% of dimethyl carbonate and 0.5 wt% of methanol can be obtained.
[ COMPARATIVE EXAMPLE 1 ]
Taking anion as tetrafluoroborate ion liquid [ BF ]4]For example, [ omim]BF4At a solvent ratio of 0.42 to the dimethyl carbonate-methanol mixture, the relative volatility of dimethyl carbonate to methanol at the specified concentration was 1.668. Under the same conditions, the ionic liquid [ hmim ] used in this example][NTf2]、[bmmim][NTf2]And [ EOEmim][NTf2]The relative volatility of dimethyl carbonate and methanol is 2, 2.2 and 1.8, which is better than [ omim]BF4。
[ COMPARATIVE EXAMPLE 2 ]
Such as the extractive distillation scheme shown in figure 3. The extractive distillation column has 25 theoretical plates (the number of plates is from top to bottom), and the extractant ionic liquid 1-decyl-3-methylimidazolium tetrafluoroborate ([ omim][BF4]) The feed was taken from tray 2 at a flow rate of 6.4kg/h, and a mixture of the starting materials dimethyl carbonate and methanol was taken from tray 23 at a dimethyl carbonate content of 30% by weight and a methanol content of 70% by weight, with a total flow rate of 1kg/h, at which point the extractant to starting material molar solvent ratio was 0.92. The extractive distillation tower is operated under normal pressure, the top of the tower is fully condensed, the reflux ratio is 1.5, the extraction amount at the top of the tower is 0.7kg/h, and 99.3 wt% of methanol and 0.7 wt% of carbonic acid can be obtainedAnd (3) dimethyl ester. The temperature of the top of the extraction and rectification tower is 40 ℃, and the temperature of the bottom of the extraction and rectification tower is 99 ℃. The product at the bottom of the extraction and rectification tower is conveyed to a solvent recovery flash tower by a pump, the operation pressure is 1kPa, the heating temperature is 120 ℃, the flow at the top of the tower is 0.3kg/h, and 98.50 wt% of dimethyl carbonate and 1.50 wt% of methanol can be obtained.
Claims (8)
1. An extractive distillation separation method of dimethyl carbonate and methanol adopts ionic liquid with the anion of bis (trifluoromethanesulfonimide) as an extractant; the ionic liquid is at least one of 1-hexyl-3-methylimidazole bistrifluoromethanesulfonimide salt and 1-hexylpyridine bistrifluoromethanesulfonimide salt; the molar ratio of the ionic liquid to a mixture of dimethyl carbonate and methanol is more than 0.2, and the mass concentration of dimethyl carbonate in the mixture of dimethyl carbonate and methanol is 1-60%.
2. The method for the extractive distillation separation of dimethyl carbonate and methanol according to claim 1, wherein the molar ratio of the ionic liquid to the mixture of dimethyl carbonate and methanol is 0.5 to 1.5.
3. The method for the extractive distillation separation of dimethyl carbonate and methanol according to claim 2, wherein the molar ratio of the ionic liquid to the mixture of dimethyl carbonate and methanol is 0.7-1.
4. The method for the extractive distillation separation of dimethyl carbonate and methanol according to claim 1, wherein the mass concentration of dimethyl carbonate in the mixture of dimethyl carbonate and methanol is 20-50%.
5. The method for the extractive distillation separation of dimethyl carbonate and methanol according to any one of claims 1 to 4, wherein the extractant is fed from the upper part of the extractive distillation column, the dimethyl carbonate and methanol are fed from the lower part of the extractive distillation column, the top product is methanol, and the bottom product is a mixture of dimethyl carbonate and ionic liquid.
6. The method for the extractive distillation separation of dimethyl carbonate and methanol according to claim 5, wherein the product from the bottom of the column is sent to a solvent recovery flash column, dimethyl carbonate is obtained from the top of the column after flash evaporation, and the ionic liquid obtained from the bottom of the column is recycled to the extractive distillation column.
7. The method for the extractive distillation separation of dimethyl carbonate and methanol according to claim 5, wherein the operating pressure of the extractive distillation column is from atmospheric pressure to 0.5MPa, the reflux ratio is from 0.5 to 5, the temperature of the column bottom is from 60 to 150 ℃, and the number of theoretical plates is from 20 to 50.
8. The method for the extractive distillation separation of dimethyl carbonate and methanol according to claim 6, wherein the operating pressure of the solvent recovery flash tower is 0.001-0.05 MPa, and the operating temperature is 100-200 ℃.
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|---|---|---|---|
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