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CN-122006611-A - System and method for preparing oxalic acid by hydrolyzing dimethyl oxalate

CN122006611ACN 122006611 ACN122006611 ACN 122006611ACN-122006611-A

Abstract

The invention provides a system and a method for preparing oxalic acid by hydrolyzing dimethyl oxalate, wherein the system comprises a pre-reaction kettle, a methanol tower, a hydrolysis tower, a methanol tower condenser, a mother liquor heat exchanger and a crystallization unit which are mutually connected through pipelines. The invention sends the mixed solution of fresh dimethyl oxalate and desalted water and the thermally coupled circulating mother liquor into a pre-reaction kettle together for preliminary hydrolysis reaction, then sends the mixed solution to a methanol tower for reaction rectification, returns the tower bottom liquid to the hydrolysis tower for feeding, then carries out reaction rectification, returns the gas phase at the top of the hydrolysis tower to the bottom of the methanol tower for feeding, extracts refined methanol at the top of the methanol tower, mixes one strand of oxalic acid hydrolysis liquid with the mother liquor into the pre-reaction kettle, and sends one strand of oxalic acid hydrolysis liquid into a crystallization unit after thermal coupling with the mother liquor, thus obtaining refined oxalic acid. The invention has high conversion rate of dimethyl oxalate, high purity of methanol, low content of monomethyl oxalate in oxalic acid hydrolysate, contribution to oxalic acid crystallization, heat coupling of mother liquor and hydrolysate, and reduced overall energy consumption.

Inventors

  • XU ZEHU
  • WU XIAOBIN
  • CHEN XIN
  • HUANG SHIQUAN

Assignees

  • 荆州诚亿化工科技有限公司

Dates

Publication Date
20260512
Application Date
20260211

Claims (10)

  1. 1. The system for preparing oxalic acid by hydrolyzing dimethyl oxalate is characterized by comprising a pre-reaction kettle, a methanol tower, a hydrolysis tower, a methanol tower condenser, a mother liquor heat exchanger and a crystallization unit which are connected with each other through pipelines; An inlet of the pre-reaction kettle is connected with fresh dimethyl oxalate raw material and desalted water through a pipeline, an outlet of the pre-reaction kettle is connected with a pre-reaction liquid inlet of the methanol tower through a pipeline, and an outlet at the bottom of the methanol tower is connected with a tower top inlet of the hydrolysis tower through a pipeline; The bottom of the hydrolysis tower outputs oxalic acid hydrolysis liquid, and the oxalic acid hydrolysis liquid is divided into two paths, wherein one path is input into the first inlet of the mother liquid heat exchanger through a pipeline; The first outlet of the mother liquor heat exchanger is connected with the inlet of the crystallization unit through a pipeline, and the crystallization unit outputs low-temperature centrifugal mother liquor and oxalic acid products; the low-temperature centrifugal mother liquor is connected with a second inlet of the mother liquor heat exchanger through a pipeline, the heat exchange mother liquor obtained after heat exchange of the mother liquor heat exchanger flows out from a second outlet of the mother liquor heat exchanger, and is mixed with another oxalic acid hydrolysate which is not subjected to heat exchange and is connected with an inlet of the pre-reaction kettle through a pipeline; The top gas phase outlet of the hydrolysis tower is connected with the bottom inlet of the methanol tower through a pipeline, the top gas phase outlet of the methanol tower is connected with the inlet of the methanol tower condenser through a pipeline, the outlet pipeline of the methanol tower condenser is divided into two paths, one path is connected to the top of the methanol tower in a return way, and the other path outputs refined methanol products.
  2. 2. The system for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 1, wherein a methanol tower reboiler is connected in series between the bottom of the methanol tower and one side of the lower part of the methanol tower, and the methanol tower is connected with low-pressure steam through a pipeline of the methanol tower reboiler, so that a reflux loop is formed at the bottom of a tower kettle of the methanol tower.
  3. 3. The system for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 1, wherein a hydrolysis tower reboiler is connected in series between the bottom of the hydrolysis tower and one side of the lower part of the hydrolysis tower, and the hydrolysis tower is connected with low-pressure steam through a hydrolysis tower reboiler pipeline, so that a reflux loop is formed at the bottom of a tower kettle of the hydrolysis tower.
  4. 4. The system for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 1, wherein the pre-reaction liquid inlet is positioned at 1/4-1/3 of the height of the methanol tower.
  5. 5. The system for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 1, wherein the methanol tower is a packed tower, and the total theoretical plate number of the methanol tower is 30-40.
  6. 6. The system for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 1, wherein the hydrolysis tower is a packed tower, and the total theoretical plate number of the hydrolysis tower is 35-50.
  7. 7. A method for preparing oxalic acid by hydrolyzing dimethyl oxalate is characterized in that, the system for preparing oxalic acid by hydrolyzing dimethyl oxalate according to any one of claims 1-6 comprises the following steps: S1, introducing raw materials of dimethyl oxalate and desalted water into a pre-reaction kettle, and mixing one path of oxalic acid hydrolysis liquid from the outlet of a hydrolysis tower kettle with heat exchange mother liquid from the outlet of a mother liquid heat exchanger to obtain mother liquid mixed liquid, wherein the mother liquid mixed liquid is introduced into the pre-reaction kettle, and the dimethyl oxalate, the desalted water and the mother liquid mixed liquid undergo preliminary hydrolysis reaction in the pre-reaction kettle to obtain pre-reaction liquid, wherein the reaction temperature is 90-95 ℃, and the reaction time is 30-50 min; S2, conveying the pre-reaction liquid into a methanol tower for reaction rectification, carrying out further hydrolysis reaction on dimethyl oxalate and monomethyl oxalate to produce oxalic acid and methanol, wherein refined methanol is extracted from a gas phase outlet at the top of the methanol tower, is condensed by a methanol tower condenser and then is divided into two parts, one part is refluxed into the methanol tower, and the other part is extracted from refined methanol, wherein the temperature at the top of the methanol tower is 65-67 ℃, the pressure at the top of the tower is 0.015-0.02 MPa, the temperature at the bottom of the tower is 85-95 ℃, and the pressure at the bottom of the tower is 0.02-0.03 MPa; S3, conveying tower kettle materials of the methanol tower to a hydrolysis tower for re-hydrolysis reaction, collecting gas materials at the top of the hydrolysis tower, returning to feed from the bottom of the methanol tower, mixing oxalic acid hydrolysis liquid collected at the tower kettle of the hydrolysis tower into two paths, mixing one path with heat exchange mother liquor, entering the pre-reaction kettle, conveying the other path to a mother liquor heat exchanger for heat exchange, and then entering a crystallization unit to obtain oxalic acid products, wherein the temperature at the top of the hydrolysis tower is 95-100 ℃, the pressure at the top of the tower is 0.02-0.04 MPa, the temperature at the bottom of the tower is 100-105 ℃, and the pressure at the bottom of the tower is 0.02-0.04 MPa.
  8. 8. The method for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 7, wherein in the step S1, the feed composition of the pre-reaction kettle comprises, by mass, 10% -15% of dimethyl oxalate, 8% -14% of monomethyl oxalate, 2% -5% of methanol, 5% -8% of oxalic acid and the balance desalted water.
  9. 9. The method for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 7, wherein in the step S2, the content of refined methanol extracted from the gas phase outlet at the top of the methanol tower is 99.8wt% to 99.9wt%, and the content of methanol in the tower bottom material of the methanol tower is 20wt% to 35wt%.
  10. 10. The method for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 7, wherein in the step S3, the oxalic acid hydrolysate mixed with the heat exchange mother liquor accounts for 12-18 wt% of the total amount of the oxalic acid hydrolysate extracted from the bottom of the hydrolysis tower.

Description

System and method for preparing oxalic acid by hydrolyzing dimethyl oxalate Technical Field The invention relates to the technical field of oxalic acid preparation, in particular to a system and a method for preparing oxalic acid by hydrolyzing dimethyl oxalate. Background Oxalic acid is an important organic chemical raw material and is widely applied to the fields of medicine, metallurgy, rare earth, fine chemical industry and the like. Currently, the methods for industrially preparing oxalic acid mainly include a sodium formate method, a carbohydrate oxidation method, an ethylene glycol oxidation method and the like. However, these conventional methods generally have problems of complicated process flow, high energy consumption, more byproducts, serious environmental pollution, and the like. For example, the sodium formate method requires high temperature and high pressure conditions, which are demanding on equipment, and the carbohydrate oxidation method usually uses nitric acid as an oxidant, which can produce a large amount of nitrogen oxide waste gas, and has large treatment difficulty and high cost. Along with the increasingly strict environmental protection requirements and the continuous pursuit of production efficiency and product quality, the development of a novel efficient, green and economic oxalic acid preparation process has important significance. Dimethyl oxalate is used as an important organic intermediate, and hydrolysis reaction of the dimethyl oxalate generates oxalic acid and methanol, and the reaction has potential advantages of high atom economy, few byproducts and the like, so that the development of an oxalic acid preparation system and method based on the hydrolysis reaction of the dimethyl oxalate becomes one of hot spot directions of current researches. The existing technology for preparing oxalic acid by hydrolyzing dimethyl oxalate still has the problems of low complete hydrolysis efficiency of dimethyl oxalate, high content of monomethyl oxalate in hydrolysate and high energy consumption. When the conversion rate of dimethyl oxalate is low, the methyl oxalate and oxalic acid are easy to form co-crystallization when oxalic acid is crystallized, so that the purity of the product is reduced, the subsequent separation and purification difficulty is increased, and the quality and application of oxalic acid products are affected. Meanwhile, the hydrolysis reaction in the prior art often needs higher temperature and pressure conditions, so that the energy consumption is high, which is unfavorable for reducing the production cost and realizing green production. Therefore, in view of the above problems, there is a need to develop a system and a method for preparing oxalic acid by hydrolyzing dimethyl oxalate, which can significantly improve the hydrolysis efficiency of dimethyl oxalate, reduce energy consumption and optimize the separation effect of the product. Disclosure of Invention In view of the technical problems in the background art, the invention provides a system and a method for preparing oxalic acid by hydrolyzing dimethyl oxalate, and aims to solve the technical problems of low complete hydrolysis efficiency of dimethyl oxalate, high content of monomethyl oxalate in hydrolysate and high energy consumption in the existing process for preparing oxalic acid by hydrolyzing dimethyl oxalate. In a first aspect, the invention provides a system for preparing oxalic acid by hydrolyzing dimethyl oxalate, which comprises a pre-reaction kettle, a methanol tower, a hydrolysis tower, a methanol tower condenser, a mother liquor heat exchanger and a crystallization unit which are connected with each other through pipelines; An inlet of the pre-reaction kettle is connected with fresh dimethyl oxalate raw material and desalted water through a pipeline, an outlet of the pre-reaction kettle is connected with a pre-reaction liquid inlet of a methanol tower through a pipeline, and an outlet at the bottom of the tower kettle of the methanol tower is connected with a tower top inlet of a hydrolysis tower through a pipeline; the bottom outlet of the hydrolysis tower is connected with the first inlet of the mother liquor heat exchanger through a pipeline, oxalic acid hydrolysate is output from the bottom of the hydrolysis tower and is divided into two paths, and one path of oxalic acid hydrolysate is input into the first inlet of the mother liquor heat exchanger through a pipeline; The low-temperature centrifugal mother liquor is connected with a second inlet of the mother liquor heat exchanger through a pipeline, and the heat exchange mother liquor obtained after heat exchange of the mother liquor heat exchanger flows out from the second outlet of the mother liquor heat exchanger and is mixed with another oxalic acid hydrolysate which is not subjected to heat exchange through a pipeline to be connected with an inlet of a pre-reaction kettle; The gas phase outlet of the top of the hydrolysis towe