Device and process for preparing dimethyl carbonate by ester exchange method
阅读说明：本技术 一种酯交换法制备碳酸二甲酯的装置和工艺 (Device and process for preparing dimethyl carbonate by ester exchange method ) 是由 肖福魁 栗进涛 刘磊 李绍果 赵宁 王峰 刘聪 庞小飞 杜彦革 杨直 于 2019-11-15 设计创作，主要内容包括：本发明公开了一种酯交换法制备碳酸二甲酯的装置和工艺,特别是由含有1,2-丙二醇的碳酸丙烯酯混合物或含有乙二醇的碳酸乙烯酯混合物或碳酸丙烯酯或碳酸乙烯酯与甲醇进行酯交换反应制备碳酸二甲酯的工艺,包括：一级配料、二级配料、预反应、反应、反应产物提浓、加压精馏和碳酸二甲酯精制步骤。本发明具有原料适用范围广、碳酸丙烯酯或碳酸乙烯酯的转化效率高、碳酸二甲酯的选择性高,以及生产过程高效、节能、连续稳定、易操作和产品纯度高等优点。(The invention discloses a device and a process for preparing dimethyl carbonate by a transesterification method, in particular to a process for preparing the dimethyl carbonate by carrying out a transesterification reaction on a propylene carbonate mixture containing 1, 2-propylene glycol or an ethylene carbonate mixture containing ethylene glycol or propylene carbonate or ethylene carbonate and methanol, which comprises the following steps: the method comprises the steps of first-stage material preparation, second-stage material preparation, pre-reaction, reaction product concentration, pressurized rectification and dimethyl carbonate refining. The invention has the advantages of wide raw material application range, high conversion efficiency of propylene carbonate or ethylene carbonate, high selectivity of dimethyl carbonate, high efficiency of production process, energy conservation, continuity and stability, easy operation, high product purity and the like.)
1. A device for preparing dimethyl carbonate by a transesterification method is characterized in that: the system comprises a primary pipeline mixer, a secondary pipeline mixer, a pre-reactor, a reaction tower reboiler, a concentration tower reboiler, a primary air cooler, a secondary air cooler, a concentration tower condensate tank, a cooler, a primary heat exchanger, a secondary heat exchanger, a pressurizing tower feeding heater, a pressurizing tower condensate tank, a pressurizing tower top condenser, a pressurizing tower reboiler, a refining tower top condenser, a refining tower condensate tank and a refining tower reboiler;
one end of the first-stage pipeline mixer is provided with a methanol solution inlet of sodium methoxide or potassium methoxide, the side wall of the pipeline close to the inlet of the methanol solution of sodium methoxide or potassium methoxide is provided with an inlet of fresh methanol, and the other end of the first-stage pipeline mixer is provided with a mixed liquid outlet which leads to the second-stage pipeline mixer;
one end of the secondary pipeline mixer is provided with an inlet for receiving the mixed liquid flowing out of the primary pipeline mixer, the side wall of the pipeline close to the inlet is provided with an inlet for a propylene carbonate mixture containing 1, 2-propylene glycol or a ethylene carbonate mixture containing ethylene glycol or propylene carbonate or ethylene carbonate liquid, and the other end of the secondary pipeline mixer is provided with a mixed liquid outlet leading to the pre-reactor;
one end of the pre-reactor is provided with an inlet for receiving the liquid flowing out of the secondary pipeline mixer, and the other end of the pre-reactor is provided with an outlet which leads to the middle upper part of the reaction tower;
the top of the reaction tower is provided with a gas phase outlet which leads to the middle part of the concentration tower; the bottom of the reaction tower is provided with a liquid outlet which is connected with a liquid phase inlet arranged at the bottom of a reboiler of the reaction tower and is used for extracting the mixture of methanol, sodium methoxide or potassium methoxide and polyalcohol; the top of the reboiler of the reaction tower is provided with a gas phase outlet which is connected with a gas phase inlet arranged at the middle upper part of the tower kettle of the reaction tower; a liquid outlet at the bottom of the reaction tower, a reboiler of the reaction tower and a gas phase inlet at the bottom of the reaction tower form a circulation loop;
the top of the concentration tower is provided with a gas phase outlet which leads to a first-stage air cooler; the top of the first-stage air cooler is provided with a gas-phase outlet which leads to the second-stage air cooler; liquid outlets are arranged at the bottoms of the first-stage air cooler and the second-stage air cooler and lead to a concentration tower condensate tank; the bottom of the concentrating tower condensate tank is provided with 2 liquid outlets, one of which is connected with a reflux port arranged at the top of the concentrating tower and the other of which is communicated with the first-stage heat exchanger; the gas phase outlet at the top of the concentration tower is connected with the primary air cooler, the secondary air cooler, the concentration tower condensate tank and the reflux port at the top of the concentration tower to form a circulation loop; the bottom of the concentration tower is provided with a liquid outlet which is connected with a liquid phase inlet arranged at the bottom of a reboiler of the concentration tower and is used for extracting the circulating methanol; the top of the reboiler of the concentration tower is provided with a gas phase outlet which is connected with a gas phase inlet arranged at the middle upper part of the tower kettle of the concentration tower, and a liquid outlet at the bottom of the concentration tower, the reboiler of the concentration tower and the gas phase inlet at the middle upper part of the tower kettle of the concentration tower form a circulation loop; the middle part of the concentration tower is provided with a liquid inlet for receiving liquid from the cooler;
the other liquid outlet at the bottom of the concentrating tower condensate tank is connected with the inlet of the first-stage heat exchanger; the outlet of the first-stage heat exchanger is connected with the inlet of the second-stage heat exchanger; the outlet of the secondary heat exchanger is connected with a feed heater of the pressurizing tower; the outlet of the pressurizing tower feeding heater is connected with the feeding hole in the middle of the pressurizing tower;
the tower top of the pressurizing tower is provided with a gas phase outlet which is connected with a condenser at the tower top of the pressurizing tower; the top condenser of the pressurizing tower is connected with a condensing tank of the pressurizing tower, 2 liquid outlets are arranged at the bottom of the condensing tank of the pressurizing tower, and one of the liquid outlets is connected with a reflux inlet arranged at the upper part of the pressurizing tower; a gas phase outlet at the top of the pressurizing tower, a condenser at the top of the pressurizing tower, a liquid outlet of a condensing tank of the pressurizing tower and a reflux inlet of the pressurizing tower form a loop; the other outlet at the bottom of the condensate tank of the pressurizing tower is connected with a secondary heat exchanger, and the secondary heat exchanger is connected with a cooler; the cooler is connected with a liquid inlet arranged in the middle of the concentration tower;
the bottom of the pressurizing tower is provided with two liquid outlets, and one of the two liquid outlets is connected with a liquid inlet of a reboiler of the pressurizing tower; the gas phase outlet of the reboiler of the pressurized tower is connected with the gas phase inlet arranged at the middle upper part of the tower kettle of the pressurized tower, and the links form a circulation loop; the other liquid outlet of the tower kettle of the pressurizing tower is connected with a first-stage heat exchanger, and the first-stage heat exchanger is connected with the refining tower;
the top of the refining tower is provided with a gas phase outlet which is connected with a condenser at the top of the refining tower; the refining tower top condenser is connected with the refining tower condensate tank; a liquid phase outlet is arranged at the bottom of the refining tower condensate tank and is respectively connected with a reflux inlet arranged at the upper part of the refining tower and a condensate tank of the concentration tower; a gas phase outlet at the top of the refining tower, a condenser at the top of the refining tower and a reflux inlet arranged at the upper part of the refining tower form a circulation loop; the bottom of the refining tower is provided with 2 liquid outlets, one of the liquid outlets is connected with a reboiler of the refining tower, and the other liquid outlet is used for extracting a dimethyl carbonate product; the reboiler of the refining tower is provided with a gas phase outlet which is connected with a gas phase inlet arranged at the middle upper part of the tower kettle of the refining tower; the liquid phase outlet at the bottom of the refining tower, the reboiler of the refining tower and the gas phase inlet at the middle upper part of the tower kettle of the refining tower form a circulation loop.
2. A process for preparing dimethyl carbonate by ester exchange method, which adopts the device for continuously preparing high-purity dimethyl carbonate by ester exchange method as claimed in claim 1, and is characterized in that: the method comprises the following steps:
(1) first-stage batching: feeding the circulating methanol and a methanol solution of 20-31 wt% of sodium methoxide or potassium methoxide into a primary pipeline mixer together, and introducing fresh methanol into the primary pipeline mixer to enable the concentration of the sodium methoxide or potassium methoxide in the outlet liquid of the primary pipeline mixer to reach 0.1-10 wt%;
(2) secondary batching: mixing the raw material A and a mixture flowing out of the primary pipeline mixer through a secondary pipeline mixer, wherein the molar ratio of propylene carbonate or ethylene carbonate to methanol in an outlet liquid of the secondary pipeline mixer is 1: 4-20;
the raw material A comprises any one of ① propylene carbonate mixture containing 1, 2-propylene glycol, ② ethylene carbonate mixture containing ethylene glycol, ③ propylene carbonate and ④ ethylene carbonate, wherein the content of the 1, 2-propylene glycol is 5-60 wt%;
(3) pre-reaction: the mixture flowing out of the secondary pipeline mixer enters a pre-reactor, and part of propylene carbonate or ethylene carbonate in the mixture reacts with methanol to generate dimethyl carbonate and 1, 2-propylene glycol or ethylene glycol;
(4) reaction: the liquid flowing out of the pre-reactor enters a reaction tower, and dimethyl carbonate generated in the pre-reaction process forms the lowest azeotrope with methanol in the reaction tower and flows out of the top of the reaction tower in a gas phase form; 1, 2-propylene glycol or ethylene glycol generated in the pre-reaction and reaction processes, and catalyst sodium methoxide or potassium methoxide and unvaporized methanol are evaporated and vaporized by a reboiler of a tower kettle of the reaction tower, and then reaction tower kettle liquid F containing a small amount of methanol is sent to a catalyst recovery or treatment process;
(5) and (3) concentrating a reaction product: feeding the lowest azeotrope formed by dimethyl carbonate and methanol flowing out of the top of the reaction tower into a concentration tower for concentration;
distilling a dimethyl carbonate methanol gas-phase mixture with the concentration of 25-35 wt% of dimethyl carbonate from the top of the concentration tower, condensing the mixture by a primary air cooler and a secondary air cooler, feeding the condensed mixture into a concentration tower condensate tank, feeding one part of liquid in the concentration tower condensate tank back to the concentration tower as reflux liquid, and feeding the other part of the liquid to a pressurizing tower; one part of the methanol tower kettle liquid in the concentration tower is used for reboiling, and the other part of the methanol tower kettle liquid is sent to a first-stage pipeline mixer for first-stage batching;
(6) and (3) pressurized rectification: liquid from a condensate tank of the concentration tower is sent to a liquid of a dimethyl carbonate refining tower through a first-stage heat exchanger and a tower kettle of a pressurizing tower for heat exchange, then is sent to the top condensate of the pressurizing tower from the condensate tank of the pressurizing tower for heat exchange, is heated to 60-120 ℃ through a feeding heater of the pressurizing tower, and is sent to the pressurizing tower for pressurizing rectification; condensing the gas phase component distilled from the top of the pressurizing tower by a condenser at the top of the pressurizing tower, then feeding the condensed liquid component into a condensing tank of the pressurizing tower, refluxing one part of the condensed liquid component, exchanging heat of the other part of the condensed liquid component by a secondary heat exchanger, cooling the heat exchanged liquid component to 45-70 ℃ by a cooler, and then feeding the cooled liquid component into a concentration tower for concentrating dimethyl carbonate; the tower bottom liquid of the pressurizing tower is sent to a refining tower for refining the dimethyl carbonate after heat exchange by a primary heat exchanger;
(7) refining dimethyl carbonate: the tower bottom liquid from the pressurizing tower enters a refining tower for refining the dimethyl carbonate after heat exchange by a primary heat exchanger; condensing and collecting distillate at the top of the refining tower, refluxing one part of the distillate, and sending the other part of the distillate to a condensate tank of a concentration tower; and distilling the dimethyl carbonate product E with the purity of 99.5-99.99 wt% from the tower kettle of the refining tower.
3. The process for preparing dimethyl carbonate by the ester exchange method according to claim 2, wherein: in the step (1), when the circulating methanol and the fresh methanol and the methanol solution of the sodium methoxide or the potassium methoxide with the concentration of 20wt% -30 wt% are mixed through the primary pipeline mixer, the circulating methanol completely enters the primary pipeline mixer and is mixed with the methanol solution of the sodium methoxide or the potassium methoxide with the concentration of 20wt% -30 wt%, and the insufficient methanol in the mixture is supplemented by the fresh methanol.
4. The process for preparing dimethyl carbonate by the ester exchange method according to claim 2, wherein: in the step (3), in the pre-reactor, methoxy negative ions and sodium positive ions or potassium positive ions dissociated from sodium methoxide or potassium methoxide in a methanol solution are used as initiators of the pre-reaction.
5. The process for preparing dimethyl carbonate by the ester exchange method according to claim 2, wherein: in the pre-reaction process, the pre-reaction temperature is 50-85 ℃, the pre-reaction pressure is consistent with the pressure of the reaction tower, and the pre-reaction residence time is 5-40 minutes.
6. The process for preparing dimethyl carbonate by the ester exchange method according to claim 2, wherein: in the reaction process, the temperature of a tower kettle of the reaction tower is 55-150 ℃, the pressure is 0.02-0.5 MPa, and the reaction residence time is 20-120 minutes; in the reaction tower, methoxy negative ions and sodium positive ions or potassium positive ions dissociated from sodium methoxide or potassium methoxide in methanol solution are used as reaction initiators.
7. The process for preparing dimethyl carbonate by the ester exchange method according to claim 2, wherein: in the step (4), the reboiler of the reaction tower is a forced circulation reboiler.
8. The process for preparing dimethyl carbonate by the ester exchange method according to claim 2, wherein: in the process of concentrating the reaction product, the operation temperature of the tower kettle of the concentrating tower is 55-80 ℃, the operation temperature of the tower top is 45-70 ℃, the operation pressure is 0.02-0.3 MPa, and the reflux ratio is 0.5-6.
9. The process for preparing dimethyl carbonate by the ester exchange method according to claim 2, wherein: in the process of pressure rectification, the operating conditions of the pressure tower are as follows: the temperature of the tower kettle is 140-170 ℃, the temperature of the tower top is 130-160 ℃, the pressure is 0.8-1.8 MPa, and the reflux ratio is 0.5-6.
10. The process for preparing dimethyl carbonate by the ester exchange method according to claim 1, wherein: in the refining process of the dimethyl carbonate, the operating conditions of a refining tower are as follows: the temperature of the tower kettle is 90-140 ℃, the temperature of the tower top is 80-130 ℃, the reflux ratio is 0.5-5, and the pressure is 0.1-0.5 MPa.
Technical Field
The invention relates to a device and a process for preparing dimethyl carbonate by a transesterification method, in particular to a process for preparing dimethyl carbonate by carrying out a transesterification reaction on a propylene carbonate mixture containing 1, 2-propylene glycol or an ethylene carbonate mixture containing ethylene glycol or propylene carbonate or ethylene carbonate and methanol, belonging to the field of chemical industry.
Background
Dimethyl carbonate is a novel low-toxicity environment-friendly green basic chemical raw material, and can replace a toxic solvent to be used in the industries of paint, coating, adhesive, spraying agent, leather tanning, printing ink and the like; can be used as raw materials for synthesizing medicines, pesticides, polycarbonate and other substances; it can also be used as gasoline/diesel oil additive, and electrolyte of lithium ion battery.
The preparation method of the dimethyl carbonate mainly comprises a methanol phosgene method, a methanol gas phase oxidation carbonylation method, a methanol liquid phase oxidation carbonylation method, a propylene carbonate or ethylene carbonate methanol ester exchange method, a urea methanol alcoholysis method, a carbon dioxide methanol direct synthesis method, a dimethyl ether oxidation carbonylation method and the like. The transesterification method is favored by the industry because of mild reaction conditions and high concentration of dimethyl carbonate in reaction products, and is also a main preparation method of dimethyl carbonate in China industry.
U.S. Pat. No. 6,63, 767 discloses a process for the synthesis of dialkyl carbonates from alkylene carbonates and alkanols in a molar ratio of 1 to 20 in the presence of an alkali metal, alkaline earth metal or mixture thereof catalyst at 20 to 300 ℃ and 14 to 4000psig (0.097 to 27.576 MPa).
Chinese patent CN1235865C discloses a process for the combined production of dimethyl carbonate and propylene glycol, which relates to a process for preparing dimethyl carbonate from propylene carbonate and methanol. In the patent, propylene carbonate, methanol and a methanol alkali metal catalyst are mixed in a raw material preparation tank, the molar ratio of the methanol to the propylene carbonate in the mixture is 6-12: 1, and the content of the methanol alkali metal catalyst is 0.05-1.0 wt% of the total weight of the mixture. And (3) feeding the obtained mixture into a reactive distillation tower, and introducing 1 strand of methanol from the gas-phase condensate at the top of the propylene glycol crude distillation tower into the tower kettle of the reactive distillation tower. The propylene carbonate and methanol react in a reaction rectifying tower to prepare the dimethyl carbonate, the reaction temperature is 55-85 ℃, the pressure is 0-0.7 MPa, the reflux ratio is 0.1-7.0, and the reaction residence time is 0.5-2 hours. And (3) distilling a dimethyl carbonate-containing substance from the top of the reaction rectifying tower, feeding the dimethyl carbonate-containing substance into an azeotrope pressurized rectifying tower, and feeding tower bottom liquid into a propylene glycol crude distillation tower. The process has the defects of large reaction rectification load, low efficiency, high energy consumption and the like.
Chinese patent CN104557554A discloses a method for continuously producing dimethyl carbonate and co-producing 1, 2-propylene glycol by a transesterification method, which relates to a method for preparing dimethyl carbonate from propylene carbonate and methanol. The method is characterized in that propylene carbonate, methanol and a methanol alkali metal catalyst are fed into a mixing tank to be mixed, the molar ratio of the methanol to the propylene carbonate in the mixture is 6-12: 1, and the content of the methanol metal catalyst is 0.05-1.0 wt% of the total weight of the mixture. The obtained mixture is sent into a reaction rectifying tower, and 1 strand of liquid-phase methanol obtained by condensing the gas phase at the top of the methanol recovery tower is introduced into the tower kettle of the reaction rectifying tower. The reaction temperature of the propylene carbonate and the methanol in a synthesis tower (a reaction rectifying tower) is 70-75 ℃, the pressure is normal pressure, the reflux ratio is 1.0-3.0, and the reaction residence time is 0.5 hour. The azeotropic composition product of methanol and dimethyl carbonate is extracted from the top of the reactive distillation tower and sent to a pressurizing tower, and the tower bottom liquid is sent to a methanol recovery tower. Chinese patent CN101774888A discloses a new purification process of high quality propylene glycol in the production process of dimethyl carbonate, which relates to the rectification reaction of methanol and propylene carbonate to prepare dimethyl carbonate, and specifically comprises the following steps: mixing propylene carbonate, methanol and a catalyst sodium methoxide, feeding the mixture into a reaction rectifying tower, controlling the molar ratio of the methanol to the propylene carbonate in the reaction rectifying tower to be 8-15: 1, and controlling the content of the catalyst sodium methoxide on each layer of tower tray in the reaction rectifying tower to be 0.20-0.80% (mass percentage). The azeotrope of methanol and dimethyl carbonate obtained from the top of the reactive rectifying tower is extracted, rectified and separated. The methanol separated from the top of the extraction and rectification tower is used for mixing propylene carbonate, methanol and catalyst sodium methoxide, and then enters the reaction and rectification tower. And (4) carrying out subsequent separation on the kettle liquid of the reactive distillation column. The methanol separated subsequently is used for mixed ingredients of propylene carbonate, methanol and catalyst sodium methoxide, and then enters a reaction rectifying tower. The two methods have the defects of large reaction rectification load, low efficiency, high energy consumption and the like.
Chinese patent CN2032810566U discloses a separation device for azeotrope of dimethyl carbonate and methanol in the process of producing dimethyl carbonate by ester exchange method, which is characterized in that after the material at the top of the pressurized rectifying tower exchanges heat by a reboiler of the reactive rectifying tower, one part of the material flows back to the pressurized rectifying tower, and the other part of the material directly enters the reactive rectifying tower to carry out normal pressure rectification and participate in the reaction. However, the heat carried by the gas phase at the top of the pressurized rectifying tower is difficult to be accurately matched with the heat required by the reboiler at the bottom of the reactive rectifying tower, so that the reactive rectifying tower and the pressurized tower are difficult to be stably operated.
Chinese patent CN106699565A discloses an energy-saving method for a dimethyl carbonate device, which is characterized in that a mixed material of propylene carbonate, methanol and a methanol alkali catalyst enters a reaction rectifying tower after passing through a heat exchanger for preliminary reaction and flow splitting, propylene glycol generated by the reaction is discharged from the bottom of a tower kettle and enters a propylene glycol refining tower, a part of generated dimethyl carbonate and methanol azeotrope is condensed by a tower top condenser and then flows back to the reaction rectifying tower, and a part of azeotrope enters a pressurizing rectifying tower for pressurizing and rectifying. After the tower top gas-phase component of the pressurized rectifying tower exchanges heat with a tower kettle reboiler of the reactive rectifying tower, one part of the obtained liquid-phase component is used for tower top reflux of the pressurized rectifying tower, and the other part of the obtained liquid-phase component enters the methanol rectifying tower for separation. Crude methanol recovered from a tower kettle in a methanol rectifying tower is recycled, a gas-phase component at the top of the tower is heated and pressurized by a rectifying heat pump and then is used as a heat source of a reboiler of the methanol rectifying tower, the effluent of the reboiler is respectively cooled by a feed preheater and a condenser of the reactive rectifying tower, the cooled azeotrope is divided into two paths, one path is sent to the reactive rectifying tower to be refluxed, and the other path is sent to a subsequent reaction unit. Although the method can comprehensively utilize heat, the whole system is difficult to operate stably due to heat matching and the like, and the efficiency of the reactive distillation column is influenced.
Chinese patent CN201848113U discloses a novel dimethyl carbonate reaction rectifying tower, which is characterized in that the rectifying tower comprises an air cooler, and the air cooler is connected between the packing layer and the water cooler. Chinese patent CN201848231U discloses a dimethyl carbonate mixing and feeding device, which comprises 1 pipeline mixer and a reaction tower, and is characterized by comprising parallel feeding pipelines. The three materials enter the pipeline mixer at the same time, and are preheated by electric tracing, so that the concentration of the local catalyst is over-concentrated easily to cause the generation of byproducts.
Disclosure of Invention
The invention aims to provide a device and a process for continuously preparing high-purity dimethyl carbonate by a transesterification method, which are easy to operate stably, energy-saving, efficient, high in conversion rate of propyl carbonate, few in byproducts, wide in application range of raw materials and feasible.
The invention provides a device for preparing dimethyl carbonate by a transesterification method, which comprises a primary pipeline mixer, a secondary pipeline mixer, a pre-reactor, a reaction tower reboiler, a concentration tower reboiler, a primary air cooler, a secondary air cooler, a concentration tower condensate tank, a cooler, a primary heat exchanger, a secondary heat exchanger, a pressurized tower feeding heater, a pressurized tower condensate tank, a pressurized tower top condenser, a pressurized tower reboiler, a refining tower top condenser, a refining tower condensate tank and a refining tower reboiler, wherein the primary pipeline mixer is connected with the secondary pipeline mixer;
one end of the first-stage pipeline mixer is provided with an inlet of a methanol solution of sodium methoxide or potassium methoxide, the side wall of the pipeline close to the inlet of the methanol solution of sodium methoxide or potassium methoxide is provided with an inlet of fresh methanol, and the other end of the first-stage pipeline mixer is provided with a mixed liquid outlet which leads to the second-stage pipeline mixer;
one end of the secondary pipeline mixer is provided with an inlet for receiving the mixed liquid flowing out of the primary pipeline mixer, the side wall of the pipeline close to the inlet is provided with an inlet for a propylene carbonate mixture containing 1, 2-propylene glycol or a ethylene carbonate mixture containing ethylene glycol or propylene carbonate or ethylene carbonate liquid, and the other end of the secondary pipeline mixer is provided with a mixed liquid outlet which leads to the two pre-reactors;
one end of the pre-reactor is provided with an inlet for receiving the liquid flowing out of the secondary pipeline mixer, and the other end of the pre-reactor is provided with an outlet which leads to the middle upper part of the reaction tower;
the top of the reaction tower is provided with a gas phase outlet which leads to the middle part of the concentration tower. The bottom of the reaction tower is provided with a liquid outlet which is connected with a liquid phase inlet arranged at the bottom of a reboiler of the reaction tower and is used for extracting methanol, sodium methoxide or potassium methoxide and the mixture of polyhydric alcohol. The top of the reboiler of the reaction tower is provided with a gas phase outlet which is connected with a gas phase inlet arranged at the middle upper part of the tower kettle of the reaction tower. The liquid outlet at the bottom of the reaction tower, the reboiler of the reaction tower and the gas phase inlet at the bottom of the reaction tower form a circulation loop.
The top of the concentration tower is provided with a gas phase outlet leading to a first-stage air cooler. And a gas phase outlet is formed in the top of the first-stage air cooler and leads to the second-stage air cooler. Liquid outlets are arranged at the bottoms of the first-stage air cooler and the second-stage air cooler and lead to a concentration tower condensate tank. The bottom of the concentrating tower condensate tank is provided with 2 liquid outlets, one of which is connected with a reflux port arranged at the top of the concentrating tower, and the other of which leads to the first-stage heat exchanger. The gas phase outlet at the top of the concentration tower is connected with the first-stage air cooler, the second-stage air cooler, the concentration tower condensate tank and the reflux port at the top of the concentration tower to form a circulation loop. The bottom of the concentration tower is provided with a liquid outlet which is connected with a liquid phase inlet arranged at the bottom of a reboiler of the concentration tower and is used for extracting the circulating methanol. The top of the reboiler of the concentration tower is provided with a gas phase outlet which is connected with a gas phase inlet arranged at the middle upper part of the tower kettle of the concentration tower, and the liquid outlet at the bottom of the concentration tower and the reboiler of the concentration tower and the gas phase inlet at the middle upper part of the tower kettle of the concentration tower form a circulation loop. The middle part of the concentration tower is provided with a liquid inlet for receiving liquid from the cooler;
and the other liquid outlet at the bottom of the concentrating tower condensate tank is connected with the inlet of the primary heat exchanger. The outlet of the first-stage heat exchanger is connected with the inlet of the second-stage heat exchanger. The outlet of the secondary heat exchanger is connected with a feed heater of the pressurizing tower. The outlet of the pressurizing tower feeding heater is connected with the feeding hole in the middle of the pressurizing tower.
The top of the pressurizing tower is provided with a gas phase outlet which is connected with a condenser at the top of the pressurizing tower. The top condenser of the pressurizing tower is connected with a condensing tank of the pressurizing tower, 2 liquid outlets are arranged at the bottom of the condensing tank of the pressurizing tower, and one of the liquid outlets is connected with a reflux inlet arranged at the upper part of the pressurizing tower. The gas phase outlet on the top of the pressurizing tower, the condenser on the top of the pressurizing tower, a liquid outlet of the pressurizing tower condensate tank and a reflux liquid inlet of the pressurizing tower form a loop. And the other outlet at the bottom of the condensate tank of the pressurizing tower is connected with a secondary heat exchanger, and the secondary heat exchanger is connected with a cooler. The cooler is connected with a liquid inlet arranged in the middle of the concentration tower.
The bottom of the pressurizing tower is provided with two liquid outlets, and one of the two liquid outlets is connected with a liquid inlet of a reboiler of the pressurizing tower. The gas phase outlet of the reboiler of the pressurized column is connected to a gas phase inlet provided in the upper middle part of the vessel of the pressurized column, and these connections constitute a circulation loop. The other liquid outlet of the tower kettle of the pressurizing tower is connected with a first-stage heat exchanger, and the first-stage heat exchanger is connected with the refining tower.
The top of the refining tower is provided with a gas phase outlet which is connected with a condenser at the top of the refining tower. The top condenser of the refining tower is connected with the condensing tank of the refining tower. The bottom of the refining tower condensate tank is provided with a liquid phase outlet which is respectively connected with a reflux inlet arranged at the upper part of the refining tower and a condensate tank of the concentration tower. The gas phase outlet at the top of the refining tower, the condenser at the top of the refining tower and the reflux inlet arranged at the upper part of the refining tower form a circulation loop. The bottom of the refining tower is provided with 2 liquid outlets, one of which is connected with a reboiler of the refining tower, and the other is used for extracting a dimethyl carbonate product. The reboiler of the refining tower is provided with a gas phase outlet which is connected with a gas phase inlet arranged at the middle upper part of the tower kettle of the refining tower. The liquid phase outlet at the bottom of the refining tower, the reboiler of the refining tower and the gas phase inlet at the middle upper part of the tower kettle of the refining tower form a circulation loop.
The invention provides a process for preparing dimethyl carbonate by an ester exchange method, which comprises the following steps:
(1) first-stage batching: feeding the circulating methanol and a methanol solution of 20-31 wt% of sodium methoxide or potassium methoxide into a primary pipeline mixer together, and introducing fresh methanol into the primary pipeline mixer to enable the concentration of the sodium methoxide or potassium methoxide in the outlet liquid of the primary pipeline mixer to reach 0.1-10 wt%;
(2) secondary batching: mixing the raw material A and a mixture flowing out of the primary pipeline mixer through a secondary pipeline mixer, wherein the molar ratio of propylene carbonate or ethylene carbonate to methanol in an outlet liquid of the secondary pipeline mixer is 1: 4-20;
the raw material A comprises any one of ① propylene carbonate mixture containing 1, 2-propylene glycol, ② ethylene carbonate mixture containing ethylene glycol, ③ propylene carbonate and ④ ethylene carbonate, wherein the content of the 1, 2-propylene glycol is 5-60 wt%;
(3) pre-reaction: the mixture flowing out of the secondary pipeline mixer enters a pre-reactor, and part of propylene carbonate or ethylene carbonate in the mixture reacts with methanol to generate dimethyl carbonate and 1, 2-propylene glycol or ethylene glycol; the pre-reaction temperature is 50-85 ℃, the pre-reaction pressure is consistent with the pressure of the reaction tower, and the pre-reaction residence time is 5-40 minutes;
(4) reaction: the liquid flowing out of the pre-reactor enters a reaction tower, and dimethyl carbonate generated in the pre-reaction process forms the lowest azeotrope with methanol in the reaction tower and flows out of the top of the reaction tower in a gas phase form; 1, 2-propylene glycol or ethylene glycol generated in the pre-reaction and reaction processes, and catalyst sodium methoxide or potassium methoxide and unvaporized methanol are evaporated and vaporized by a reboiler of a tower kettle of the reaction tower, and then reaction tower kettle liquid F containing a small amount of methanol is sent to a catalyst recovery or treatment process; the temperature of a tower kettle of the reaction tower is 55-150 ℃, the pressure is 0.02-0.5 MPa, and the reaction residence time is 20-120 minutes.
(5) And (3) concentrating a reaction product: the lowest azeotrope formed by dimethyl carbonate and methanol flowing out from the top of the reaction tower is sent into a concentration tower for concentration. Distilling a dimethyl carbonate methanol gas-phase mixture with the concentration of 25-35 wt% of dimethyl carbonate from the top of the concentration tower, condensing the mixture by a primary air cooler and a secondary air cooler, feeding the condensed mixture into a concentration tower condensate tank, feeding one part of liquid in the concentration tower condensate tank back to the concentration tower as reflux liquid, and feeding the other part of the liquid to a pressurizing tower; one part of the methanol tower kettle liquid in the concentration tower is used for reboiling, and the other part of the methanol tower kettle liquid is sent to a first-stage pipeline mixer for first-stage batching; the operation temperature of the tower kettle of the concentration tower is 55-80 ℃, the operation temperature of the tower top is 45-70 ℃, the operation pressure is 0.02-0.3 MPa, and the reflux ratio is 0.5-6.
(6) And (3) pressurized rectification: liquid from a condensate tank of the concentration tower is sent to a liquid of a dimethyl carbonate refining tower through a first-stage heat exchanger and a tower kettle of a pressurizing tower for heat exchange, then is sent to the top condensate of the pressurizing tower from the condensate tank of the pressurizing tower for heat exchange, is heated to 60-120 ℃ through a feeding heater of the pressurizing tower, and is sent to the pressurizing tower for pressurizing rectification; operating conditions of the pressurized column: the tower kettle is 140-170 ℃, the tower top is 130-160 ℃, the pressure is 0.8-1.8 MPa, and the reflux ratio is 0.5-6. Condensing the gas phase component distilled from the top of the pressurizing tower by a condenser at the top of the pressurizing tower, then feeding the condensed liquid component into a condensing tank of the pressurizing tower, refluxing one part of the condensed liquid component, exchanging heat of the other part of the condensed liquid component by a secondary heat exchanger, cooling the heat exchanged liquid component to 45-70 ℃ by a cooler, and then feeding the cooled liquid component into a concentration tower for concentrating dimethyl carbonate; the tower bottom liquid of the pressurizing tower is sent to a refining tower for refining the dimethyl carbonate after heat exchange by a primary heat exchanger;
(7) refining dimethyl carbonate: and the tower bottom liquid from the pressurizing tower enters a refining tower for refining the dimethyl carbonate after heat exchange by a primary heat exchanger. Operating conditions of the refining column: the temperature of the tower kettle is 90-140 ℃, the temperature of the tower top is 80-130 ℃, the reflux ratio is 0.5-5, and the pressure is 0.1-0.5 MPa. Condensing and collecting distillate at the top of the refining tower, refluxing one part of the distillate, and sending the other part of the distillate to a condensate tank of a concentration tower; and distilling the dimethyl carbonate product E with the purity of 99.5-99.99 wt% from the tower kettle of the refining tower.
The above process is further described below:
in the step (1), when the circulating methanol and the fresh methanol and the methanol solution of the sodium methoxide or the potassium methoxide with the concentration of 20wt% -30 wt% are mixed through the primary pipeline mixer, the circulating methanol completely enters the primary pipeline mixer and is mixed with the methanol solution of the sodium methoxide or the potassium methoxide with the concentration of 20wt% -30 wt%, and the insufficient methanol in the mixture is supplemented by the fresh methanol.
In the step (3), in the pre-reactor, methoxy negative ions and sodium positive ions or potassium positive ions dissociated from sodium methoxide or potassium methoxide in a methanol solution are used as initiators of the pre-reaction.
In the step (4), methoxy negative ions and sodium positive ions or potassium positive ions dissociated from sodium methoxide or potassium methoxide in a methanol solution in the reaction tower are used as reaction initiators.
In the step (4), the reboiler of the reaction tower is a forced circulation reboiler.
The invention has the beneficial effects that:
1. the whole production process is continuous and stable and is easy to operate: materials with higher temperature distilled from the top and the bottom of the pressurizing tower are used for heating the condensate at the top of the concentrating tower with relatively lower temperature entering the pressurizing tower, and the heat compensation is carried out through a feeding heater of the pressurizing tower, so that the operation is easier and the process is more stable;
2. the raw materials have wide application range: the used cyclic carbonate can be propylene carbonate or ethylene carbonate with high purity, or propylene carbonate containing 1, 2-propylene glycol or ethylene carbonate containing ethylene glycol;
3. the conversion efficiency of the propylene carbonate or the ethylene carbonate is high, and the byproducts are less: the two-stage material mixing enables the raw material and the catalyst to be mixed more fully, and reduces the occurrence of side reactions caused by the local over-concentration of the catalyst; the whole reaction process is divided into two steps of pre-reaction and reaction, so that the reaction is carried out more thoroughly;
4. the production process is more efficient: the load of the reaction tower is greatly reduced due to the pre-reaction, and the efficiency of the reaction tower is improved; the top of the reaction tower is not refluxed, so that the dimethyl carbonate and methanol generated by the reaction can be vaporized and quickly leave the reaction tower in the form of the lowest azeotrope, the reaction is facilitated, the generation of byproducts is avoided, and the reaction efficiency is higher than that of the traditional catalytic distillation; the reaction product is specially concentrated by a concentration tower, rather than being concentrated while reacting, so that the concentration efficiency is higher; the pressure of the pressurizing rectifying tower is increased, so that the concentration of the dimethyl carbonate in the tower kettle of the pressurizing tower is higher, and the separation efficiency of dimethyl carbonate and methanol azeotrope is improved; the purification tower special for the dimethyl carbonate is added, so that the purity of the dimethyl carbonate product is higher.
5. The process is more energy-saving: materials with higher temperature distilled from the top and the bottom of the pressurizing tower are used for heating the condensate at the top of the concentrating tower with relatively lower temperature entering the pressurizing tower, so that the process is more energy-saving; the produced liquid in the tower kettle of the concentrating tower with heat is directly mixed with the methanol solution of sodium methoxide or potassium methoxide without heat exchange, so that the energy consumption can be saved.
Drawings
FIG. 1 is a schematic diagram of a process flow for preparing dimethyl carbonate by a transesterification method;
in the figure: 1: a primary pipeline mixer; 2: a secondary pipeline mixer; 3: a pre-reactor; 4: a reaction tower; 5: a reaction tower reboiler; 6: a concentration tower; 7: a concentration tower reboiler; 8: a primary air cooler; 9: a secondary air cooler; 10: a concentration tower condensate tank; 11: a cooler; 12: a primary heat exchanger; 13: a secondary heat exchanger; 14: a pressurized column feed heater; 15: a pressurized tower condensate tank; 16: a condenser at the top of the pressurized tower; 17: a pressurized column; 18: a pressurized column reboiler; 19: a refining tower; 20: a condenser at the top of the refining tower; 21: refining the tower condensate tank; 22: refining tower reboiler.
A: propylene carbonate mixtures containing 1, 2-propylene glycol or ethylene carbonate mixtures containing ethylene glycol or propylene carbonate or ethylene carbonate; b, fresh methanol; c: a methanol solution of sodium methoxide or potassium methoxide with the concentration of 20-31 wt%; d: recycling the methanol; e: a dimethyl carbonate product; f: methanol, sodium methoxide or potassium methoxide, and a mixture of polyols.
Detailed Description
The present invention is further illustrated by, but is not limited to, the following examples.
As shown in fig. 1, a device for preparing dimethyl carbonate by a transesterification method comprises a primary pipeline mixer 1, a secondary pipeline mixer 2 and a pre-reactor 3 which are connected in sequence, wherein an outlet of the pre-reactor 3 is connected with a reaction tower 4, the bottom of the reaction tower 4 is provided with a reaction tower reboiler 5 for refluxing a part of reaction liquid into the reaction tower, an outlet at the top of the reaction tower 4 is connected with a concentration tower 6, the bottom of the concentration tower 6 is provided with a concentration tower reboiler 7, an outlet at the top of the concentration tower 6 is connected with a primary air cooler 8 and a secondary air cooler 9 in sequence, and outlets of the primary air cooler 8 and the secondary air cooler 9 are connected with a concentration tower condensate tank 10; one liquid outlet of the concentrating tower condensate tank 10 is sequentially connected with a primary heat exchanger 12, a secondary heat exchanger 13, a pressurizing tower feeding heater 14 and a pressurizing tower 15, and the other liquid outlet of the concentrating tower condensate tank 10 is connected with the concentrating tower 6 to form reflux circulation; a gas phase outlet at the top of the pressurizing tower 17 forms reflux circulation with a condenser 16 at the top of the pressurizing tower and a condensing tank 15 of the pressurizing tower, and the other outlet of the condensing tank 15 of the pressurizing tower is sequentially connected with a secondary heat exchanger 13, a cooler 11 and a concentration tower 6; one liquid outlet at the bottom of the pressurizing tower 17 is circulated back to the tower through a pressurizing tower reboiler 18, and the other outlet of the tower bottom liquid of the pressurizing tower 17 is connected with a refining tower 19 after passing through a primary heat exchanger 12; the distillate outlet at the top of the refining tower 19 is respectively connected with the refining tower 19 and the concentrating tower condensate tank 10 through a refining tower top condenser 20 and a refining tower condensate tank 21.
Specifically, the method comprises the following steps:
one end of the primary pipeline mixer 1 is provided with a methanol solution inlet of sodium methoxide or potassium methoxide, the side wall of the pipeline close to the methanol solution inlet of the sodium methoxide or potassium methoxide is provided with a fresh methanol inlet, and the other end of the primary pipeline mixer is provided with a mixed liquid outlet which leads to the secondary pipeline mixer;
one end of the secondary pipeline mixer 2 is provided with an inlet for receiving the mixed liquid flowing out of the primary pipeline mixer, the side wall of the pipeline close to the inlet is provided with an inlet for a propylene carbonate mixture containing 1, 2-propylene glycol or a ethylene carbonate mixture containing ethylene glycol or propylene carbonate or ethylene carbonate liquid, and the other end of the secondary pipeline mixer is provided with a mixed liquid outlet which leads to the pre-reactor;
one end of the
the top of the reaction tower 4 is provided with a gas phase outlet which leads to the middle part of the concentration tower 6; the bottom of the reaction tower 4 is provided with a liquid outlet which is connected with a liquid inlet arranged at the bottom of a reboiler 5 of the reaction tower and is used for extracting the mixture of methanol, sodium methoxide or potassium methoxide and polyalcohol; the top of the reaction tower reboiler 5 is provided with a gas phase outlet which is connected with a gas phase inlet arranged at the middle upper part of the tower kettle of the reaction tower 4; a liquid outlet at the bottom of the reaction tower 4, a reaction tower reboiler 5 and a gas phase inlet at the bottom of the reaction tower form a circulation loop;
the top of the concentration tower 6 is provided with a gas phase outlet which leads to a first-stage air cooler 8; the top of the primary air cooler 8 is provided with a gas phase outlet which leads to the secondary air cooler 9; liquid outlets are arranged at the bottoms of the first-stage air cooler 8 and the second-stage air cooler 9 and lead to a condensate tank 10 of the concentration tower; the bottom of a condensing tank 10 of the concentrating tower is provided with 2 liquid outlets, one of which is connected with a reflux port arranged at the top of the concentrating tower 6 and the other of which is communicated with a first-stage heat exchanger 12; a gas phase outlet at the top of the concentration tower 6 is connected with a primary air cooler 8, a secondary air cooler 9, a concentration tower condensate tank 10 and a reflux port at the top of the concentration tower 6 to form a circulation loop; the bottom of the concentration tower 6 is provided with a liquid outlet which is connected with a liquid phase inlet arranged at the bottom of a reboiler 7 of the concentration tower and is used for extracting the circulating methanol; the top of the reboiler 7 of the concentration tower is provided with a gas phase outlet which is connected with a gas phase inlet arranged at the middle upper part of the tower kettle of the concentration tower 6, and a liquid outlet at the bottom of the concentration tower 6, the reboiler of the concentration tower and the gas phase inlet at the middle upper part of the tower kettle of the concentration tower form a circulation loop; the middle part of the concentration tower is provided with a liquid inlet for receiving liquid from the cooler;
the other liquid outlet at the bottom of the concentrating tower condensate tank 10 is connected with the inlet of the primary heat exchanger; the outlet of the
a gas phase outlet is arranged at the top of the pressurizing
the bottom of the pressurizing
the top of the
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