CN-121988270-A - Production system and production process for preparing dimethyl carbonate by urea two-step method

CN121988270ACN 121988270 ACN121988270 ACN 121988270ACN-121988270-A

Abstract

The invention relates to the technical field of chemical production, and particularly discloses a production system and a production process for preparing dimethyl carbonate by a urea two-step method. The production system comprises a propylene carbonate reaction system, a catalyst treatment system and a dimethyl carbonate reaction system, wherein the propylene carbonate reaction system comprises a batching tank, a multistage reaction kettle, a thin film evaporator and a PC rectifying tower which are sequentially connected, the catalyst treatment system comprises a catalyst concentration tank, a recovered catalyst replenishing tank and a catalyst mixing tank are respectively connected to the outlet of the catalyst concentration tank, the outlet of the catalyst mixing tank is connected with a filter, the liquid phase outlet of the thin film evaporator is connected with the catalyst concentration tank, the gas phase outlet of the PC rectifying tower is connected with the batching tank, the dimethyl carbonate reaction system comprises a DMC reaction rectifying tower, a DMC pressurizing tower, a DMC purifying tower and a DMC rectifying tower which are sequentially connected, and the inlet of the DMC reaction rectifying tower is respectively connected with the liquid phase outlet of the PC rectifying tower and the filter. The production system and the production process can shorten the catalyst recovery time, reduce the filtration difficulty, reduce the DMC separation and purification energy consumption and increase the DMC purity.

Inventors

WANG DONGBO
LIU HONGMING
CHEN ZONGQIN
ZHOU XIAOQIN
LIANG WEI
MO ZHENGHUI
LUO XIAOQIANG
ZUO KE
WANG YANAN
TANG WEI
ZHANG ZHIHUA
YANG CHAO

Assignees

重庆建峰化工股份有限公司

Dates

Publication Date: 20260508
Application Date: 20260130

Claims (10)

1. A production system for preparing dimethyl carbonate by a urea two-step method, which is characterized by comprising the following steps: The propylene carbonate reaction system comprises a batching tank, a multistage reaction kettle, a thin film evaporator and a PC rectifying tower which are connected in sequence; The catalyst treatment system comprises a catalyst concentration tank, wherein an outlet of the catalyst concentration tank is respectively connected with a recovered catalyst replenishing tank and a catalyst mixing tank, the recovered catalyst replenishing tank is connected with a batching tank, an outlet of the catalyst mixing tank is connected with a filter, a liquid phase outlet of a thin film evaporator is connected with the catalyst concentration tank, and a gas phase outlet of a PC rectifying tower is connected with the batching tank; The dimethyl carbonate reaction system comprises a DMC reaction rectifying tower, a DMC pressurizing tower, a DMC purifying tower and a DMC rectifying tower which are sequentially connected, wherein an inlet of the DMC reaction rectifying tower is respectively connected with a liquid phase outlet of a PC rectifying tower and a filter, a first circulation loop is formed between the DMC pressurizing tower and the DMC purifying tower, and a second circulation loop is formed between the DMC purifying tower and the DMC rectifying tower.
2. The production system for preparing dimethyl carbonate by a urea two-step method according to claim 1, wherein the multi-stage reaction kettle comprises a first-stage reaction kettle, a second-stage reaction kettle and a third-stage reaction kettle which are connected in series, gas phase outlets of the first-stage reaction kettle, the second-stage reaction kettle and the third-stage reaction kettle are all connected with condensers, and a discharge hole of any condenser is connected with a vacuum pump.
3. The system for producing dimethyl carbonate by a urea two-step process according to claim 1, wherein the DMC pressurizing tower is further connected with a methanol purifying tower and forms a circulation loop III, a tower bottom of the methanol purifying tower is connected with a DMC reaction rectifying tower, and the DMC rectifying tower is further connected with a scraper evaporator and forms a circulation loop IV.
4. A process for preparing dimethyl carbonate by a urea two-step method, which is characterized in that a production system for preparing dimethyl carbonate by the urea two-step method according to any one of claims 1-3 comprises the following steps: s1, mixing propylene glycol, urea and a catalyst in a mixing tank, then enabling the mixture to enter a multi-stage reaction kettle for reaction, enabling the mixture to enter a thin film evaporator after the reaction, and evaporating the mixture to obtain a gas-phase material A and a liquid-phase material A; S2, rectifying the gas-phase material A in a PC rectifying tower to obtain a gas-phase component and a side-mining liquid-phase component, returning the gas-phase component to a batching tank, and enabling the liquid-phase component to enter a DMC reaction rectifying tower; S3, concentrating the liquid phase material A by a catalyst concentration tank, returning to a recovered catalyst replenishing tank or entering a catalyst mixing tank, washing the catalyst mixing tank with methanol, filtering by a filter, and enabling filtrate to enter a DMC reaction rectifying tower; S4, adding methanol into the DMC reaction rectifying tower, and reacting with the liquid phase component and the filtrate to obtain a tower top material A and a tower bottom material A; The tower bottom material A is returned to the catalyst concentration tank, and the tower top material A enters the DMC pressurizing tower to be pressurized and separated to obtain a tower top material B and a tower bottom material B; the tower bottom material B enters a DMC purifying tower to be purified to obtain a tower top material D and a tower bottom material D; And sending the tower top material D back to the DMC pressurizing tower, sending the tower bottom material D to the DMC rectifying tower, rectifying to obtain a tower top material E and a tower bottom material E, sending the tower top material E back to the DMC purifying tower, and obtaining pure DMC at the side of the DMC purifying tower.
5. The process for preparing dimethyl carbonate by a urea two-step method according to claim 4, wherein in the step S3, the liquid phase material A is concentrated according to the multiplexing times, if the multiplexing times are 20-40 times, the concentrated liquid phase material A is returned to the recovered catalyst replenishing tank, if the multiplexing times are more than 40 times, the concentrated liquid phase material A is fed into the catalyst mixing tank, and the volume ratio of the concentrated liquid phase material A to the methanol in the catalyst mixing tank is 1:1.
6. The process for preparing dimethyl carbonate by a urea two-step method according to claim 4, wherein in the step S4, the tower top material B is purified by a methanol purification tower to obtain a tower top material C and a tower bottom material C, the tower bottom material C is returned to a DMC pressurizing tower, the tower bottom material C is returned to a DMC reaction rectifying tower, the tower bottom material E is evaporated by a scraper evaporator to obtain a gas phase material B and a liquid phase material B, the gas phase material B is returned to the DMC rectifying tower, and the liquid phase material B is sent out, wherein the temperature at the tower top of the methanol purification tower is 67 ℃, the pressure at the tower top is 17KPa, the temperature at the tower bottom is 70 ℃, and the pressure at the tower bottom is 26KPa.
7. The process for preparing dimethyl carbonate by a urea two-step method according to claim 4, wherein the temperature of a batching tank in the step S1 is 70-80 ℃, the reaction temperature of a primary reaction kettle is 140-148 ℃, the reaction temperature of a secondary reaction kettle is 150-158 ℃, the reaction temperature of a tertiary reaction kettle is 160-168 ℃, the pressure is-50 KPa, the evaporation temperature of a thin film evaporator is 155-160 ℃, and the pressure is-85 KPa.
8. The process for preparing dimethyl carbonate by a urea two-step method according to claim 4, wherein in the step S2, the temperature of the top of the PC rectifying tower is 100-110 ℃, the pressure is-94 KPa, and the temperature of the side-extracted liquid phase is 135-140 ℃.
9. The process for preparing dimethyl carbonate by a urea two-step method according to claim 4, wherein in the step S4, the temperature of the top of the DMC reaction rectifying tower is 65-70 ℃, the pressure of the top of the tower is 15KPa, the temperature of the bottom of the tower is 72-75 ℃, and the pressure of the bottom of the tower is 35KPa; The temperature of the top of the DMC pressurizing tower is 135-140 ℃, the pressure of the top of the tower is 0.95MPa, the temperature of the bottom of the tower is 165-170 ℃, and the pressure of the bottom of the tower is 0.98MPa; The temperature of the top of the DMC purification tower is 65-70 ℃, the pressure of the top of the tower is 15KPa, the temperature of the bottom of the tower is 90-98 ℃, and the pressure of the bottom of the tower is 18KPa; the DMC rectifying tower has top temperature of 94 deg.c, top pressure of 15KPa, tower bottom temperature of 96 deg.c, tower bottom pressure of 20KPa and scraper evaporator evaporating temperature of 150-155 deg.c.
10. The process for preparing dimethyl carbonate by a urea two-step method according to claim 4, wherein in the step S1, the molar ratio of urea to propylene glycol is 1 (1.5-2), and the amount of the catalyst is 2-3% of the mass of urea.

Description

Production system and production process for preparing dimethyl carbonate by urea two-step method Technical Field The invention relates to the technical field of chemical production, and particularly discloses a production system and a production process for preparing dimethyl carbonate by a urea two-step method. Background In the prior art for preparing cyclic carbonate by urea method, CN201410327072.7 discloses a continuous reaction process for synthesizing cyclic carbonate by urea, which comprises a raw material mixer with an external forced circulation pump, a plurality of serially connected kettle reactors with external forced circulation pumps, a vacuum pump, a reaction liquid heater, a gas phase condenser in the reaction process and a vacuum switching discharge tank. The method has the advantages that the preparation process of urea, polyol and catalyst is continuous, the reaction time required in the reaction process is ensured, meanwhile, the byproduct ammonia gas can be removed in time, the forward reaction is promoted, and the purposes of improving the conversion rate and the selectivity, being easy for automatic control and realizing large-scale continuous and stable production are achieved. The yield of the cyclic carbonate synthesized by the process reaches over 96 percent. However, the recycling of the catalyst is not mentioned in the prior art disclosed. In the industrial urea method, the catalyst used is alkali metal oxide, so that the catalyst can be reused, but after repeated use, the recovery and filtration difficulties are increased due to the fact that the catalyst contains polymers such as PG, DPG and the like. The conventional operation is that a filter press is adopted for direct filtration, but in practice, the direct filtration by adopting equipment such as a plate-and-frame filter press, a cloth bag filter, a metal microporous filter, a centrifugal machine and the like is found to be difficult to be filtered due to the fact that equipment is easily blocked due to the fact that the viscosity is too large. 2. The organic matters such as water and alcohols can be used for washing, diluting and filtering by adopting the addition volume dilution and filtering, considering the condition of a reaction system, but the filtering needs to be separated and purified by using a rectifying tower and the like, so that a large amount of energy consumption is increased. In addition, because the purity of PC produced by the urea method is lower, impurities such as DPG, MOZD and the like are contained, DMC purity is lower when a primary transesterification technology is adopted, and the condition that a rectifying tower kettle is blocked by a polymer when the DMC product is purified finely, so that DMC production is influenced. Disclosure of Invention The invention provides a production system and a production process for preparing dimethyl carbonate by a urea two-step method, which can shorten the catalyst recovery time, reduce the filtration difficulty, reduce the DMC separation and purification energy consumption, increase the DMC purity and solve the problem of blockage of pipelines and equipment at the bottom of a rectifying tower. The invention is realized by the following technical scheme: In one aspect, the invention provides a production system for preparing dimethyl carbonate by a urea two-step method, comprising: The propylene carbonate reaction system comprises a batching tank, a multistage reaction kettle, a thin film evaporator and a PC rectifying tower which are connected in sequence; The catalyst treatment system comprises a catalyst concentration tank, wherein an outlet of the catalyst concentration tank is respectively connected with a recovered catalyst replenishing tank and a catalyst mixing tank, the recovered catalyst replenishing tank is connected with a batching tank, an outlet of the catalyst mixing tank is connected with a filter, a liquid phase outlet of a thin film evaporator is connected with the catalyst concentration tank, and a gas phase outlet of a PC rectifying tower is connected with the batching tank; The dimethyl carbonate reaction system comprises a DMC reaction rectifying tower, a DMC pressurizing tower, a DMC purifying tower and a DMC rectifying tower which are sequentially connected, wherein an inlet of the DMC reaction rectifying tower is respectively connected with a liquid phase outlet of a PC rectifying tower and a filter, a first circulation loop is formed between the DMC pressurizing tower and the DMC purifying tower, and a second circulation loop is formed between the DMC purifying tower and the DMC rectifying tower. Further, multistage reation kettle includes the one-level reation kettle of establishing ties, second grade reation kettle and tertiary reation kettle, and the gaseous phase export of one-level reation kettle, second grade reation kettle and tertiary reation kettle all is connected with the condenser, and the discharge gate of arbitrary c