System and method for preparing oxalic acid by hydrolyzing dimethyl oxalate

Abstract

The invention relates to a system and a method for preparing oxalic acid through hydrolysis of dimethyl oxalate, and aims to solve the technical problems of low conversion rate and high energy consumption of oxalic acid produced through hydrolysis of dimethyl oxalate in the prior art. An oxalic acid-rich material extracted from the tower bottom is separated and dried to output an oxalic acid product, a material at the tower top enters a pre-rectifying tower for methanol concentration, an extracted material at the tower top of the pre-rectifying tower is sent to a pressurizing tower for methanol refining, and a gas-phase refined methanol material extracted from the tower top is output as a refined methanol product after heat exchange. And feeding the material extracted from the tower bottom to an atmospheric tower for refining the residual methanol. The dimethyl oxalate conversion rate is high, the oxalic acid product quality is good, the replenishment amount of desalted water is the same as the total consumption amount, balance is achieved, the process is optimized and integrated, heat coupling and waste heat recycling are fully considered, the overall energy consumption is reduced, and then the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of oxalic acid preparation, and particularly relates to a system and method for preparing oxalic acid by hydrolyzing dimethyl oxalate. Background Art

[0002] Oxalic acid is an important chemical product with a wide range of applications, including medicine, printing and dyeing, fine chemicals and other fields. There are many production processes for oxalic acid, mainly sodium formate method, polysaccharide oxidation method, carbon monoxide coupling method oxalate hydrolysis and glyoxal oxidation method. At present, the most widely used oxalic acid production process in China is the traditional sodium formate method. Since the sodium formate method requires the consumption of sulfuric acid and caustic soda and has lead pollution, it is gradually being replaced by other new processes. The synthesis of oxalate esters by carbon monoxide gas phase coupling method and then the production of oxalic acid by oxalate hydrolysis is not only low in production cost and environmentally friendly, but also can provide more flexible product solutions for enterprises producing ethylene glycol and oxalate esters, which is conducive to alleviating the current problem of overcapacity of ethylene glycol and the survival difficulties of related enterprises.

[0003] The currently disclosed or applied processes for producing oxalic acid by hydrolysis of dimethyl oxalate have the problems of high energy consumption, low conversion rate of dimethyl oxalate, low yield of oxalic acid, and complex process or equipment. When the conversion rate of dimethyl oxalate is low, unreacted dimethyl oxalate and intermediate product monomethyl oxalate will be included in the oxalic acid product during oxalic acid crystallization, resulting in a decrease in the quality of the oxalic acid product. Patent CN 104892389B discloses a process for preparing oxalic acid by continuous reactive distillation hydrolysis of dimethyl oxalate, in which dimethyl oxalate is directly introduced into a reactive distillation bulkhead tower in a molten state without pre-hydrolysis, which will result in a low conversion rate in the tower and complex equipment and process. Patent CN 104892400B discloses a combined process of catalytic synthesis of oxalic acid by intermittent reaction and continuous reaction distillation, and patent CN 105152916A discloses a process for synthesizing oxalic acid from oxalate. In both processes, the synthesis reaction, product separation and alcohol purification are realized in one tower, which has very high requirements for the tower and is difficult to realize in industrial production. In addition, it is difficult to realize energy coupling through equipment integration of these two processes, and the energy consumption is high. Patent CN110713437B discloses a device and preparation method for preparing oxalic acid by hydrolysis of oxalate, which has high energy consumption and low conversion rate of dimethyl oxalate. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems and provide a system and method for preparing oxalic acid by hydrolyzing dimethyl oxalate.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A system for preparing oxalic acid by hydrolyzing dimethyl oxalate, comprising a reactive distillation device, a pre-distillation device, a pressurizing device and a normal pressure device;

[0007] The reactive distillation device comprises a DMO preheater, a prereactor, a reactive distillation tower, a compressor, a reactive distillation tower reboiler A and a reactive distillation tower reboiler B, wherein the inlet of the DMO preheater is externally connected to a dimethyl oxalate raw material, and the outlet is connected to the inlet of the prereactor, the outlet of the prereactor is connected to the inlet of the reactive distillation tower, the gas phase outlet at the top of the prereactor is connected to the gas phase inlet of the reactive distillation tower, the reactive distillation tower is externally connected to desalted water and low-pressure steam, the bottom outlet of the reactive distillation tower is connected to the inlet of the reactive distillation tower reboiler A, the outlet of the reactive distillation tower reboiler A is connected to the inlet of the reactive distillation tower reboiler B, the outlet of the reactive distillation tower reboiler B is connected to the reactive distillation tower, the top gas phase outlet of the reactive distillation tower is connected to the inlet of the compressor, the outlet of the compressor is connected to the hot side inlet of the reactive distillation tower reboiler A, and the compressor is externally connected to desalted water;

[0008] The pre-distillation device comprises a pre-distillation tower, a pre-distillation tower condenser and a pre-distillation tower reboiler, the top gas phase outlet of the pre-distillation tower is connected to the pre-distillation tower condenser, the outlet of the pre-distillation tower condenser is connected to the inlet of the pre-distillation tower, the bottom outlet of the pre-distillation tower is connected to the inlet of the pre-distillation tower reboiler, the outlet of the pre-distillation tower reboiler is connected to the inlet of the pre-distillation tower, the hot side outlet of the reaction distillation tower reboiler A is connected to the hot side inlet of the pre-distillation tower reboiler, and the hot side outlet of the pre-distillation tower reboiler is connected to the pre-distillation tower;

[0009] The pressurizing device comprises a pressurizing tower and a pressurizing tower reboiler, the outlet of the pre-distillation tower condenser is connected to the inlet of the pressurizing tower, the bottom outlet of the pressurizing tower is connected to the inlet of the pressurizing tower reboiler, and the outlet of the pressurizing tower reboiler is connected to the pressurizing tower;

[0010] The atmospheric pressure device comprises an atmospheric pressure tower reboiler, an atmospheric pressure tower and an atmospheric pressure tower condenser, the top outlet of the atmospheric pressure tower is connected to the inlet of the atmospheric pressure tower condenser, the outlet of the atmospheric pressure tower condenser is divided into two streams, one stream is connected to the atmospheric pressure tower, and the other stream outputs a refined methanol product, the bottom outlet of the atmospheric pressure tower is connected to the inlet of the atmospheric pressure tower reboiler, the outlet of the atmospheric pressure tower reboiler is connected to the atmospheric pressure tower, and the bottom outlet of the pressurized tower is connected to the atmospheric pressure tower;

[0011] It also includes an oxalic acid crystallization separation and drying device, a crystallization liquid preheater and a mother liquor preheater. The bottom outlet of the reactive distillation tower is connected to the inlet of the oxalic acid crystallization separation and drying device. One outlet of the oxalic acid crystallization separation and drying device outputs an oxalic acid product, and the other outlet is connected to the inlet of the crystallization liquid preheater. The crystallization liquid preheater outlet, the bottom outlet of the pre-distillation tower and the atmospheric tower are all connected to the inlet of the mother liquor preheater. The mother liquor preheater outlet is connected to the inlet of the pre-reactor. The top gas phase outlet of the pressurizing tower is connected to the hot side inlet of the atmospheric tower reboiler. The hot side outlet of the atmospheric tower reboiler is divided into two streams, one of which is connected to the inlet of the pressurizing tower, and the other is connected to the hot side inlet of the crystallization liquid preheater. The hot side outlet of the crystallization liquid preheater outputs a refined methanol product.

[0012] A method for preparing oxalic acid by hydrolyzing dimethyl oxalate comprises the following steps:

[0013] Step S1: the dimethyl oxalate raw material is preheated by a DMO preheater and then enters a pre-reactor. The circulating mother liquor obtained by mixing the bottom produced materials from the pre-rectification tower and the atmospheric tower with the crystallization liquid of the oxalic acid crystallization separation and drying device is preheated by a mother liquor preheater and then enters the pre-reactor. The dimethyl oxalate raw material and the circulating mother liquor undergo a pre-hydrolysis reaction in the pre-reactor. The gas phase generated by the reaction in the pre-reactor is transported to the reactive distillation tower through the top gas phase outlet, and the material at the outlet of the pre-reactor is transported to the reactive distillation tower.

[0014] Step S2: the material from the pre-reactor is subjected to reactive distillation in a reactive distillation tower, so that dimethyl oxalate and the intermediate product monomethyl oxalate are further reacted and converted into oxalic acid, desalted water required to be supplemented by the system is added to the top of the reactive distillation tower, and this part of the desalted water is also used as the reflux liquid of the reactive distillation tower, low-pressure steam is added to the bottom of the reactive distillation tower to supplement the heat required for reboiling of the tower kettle, and this part of the steam is liquefied in the tower and also used as the desalted water required to be supplemented by part of the system, the gaseous material taken out from the top of the reactive distillation tower is pressurized and heated by the compressor, and then enters the reboiler A of the reactive distillation tower to exchange heat with the tower kettle material to provide the heat required for reboiling of the tower kettle, the tower kettle material from the reboiler A of the reactive distillation tower is then heated by the reboiler B of the reactive distillation tower and returned to the reactive distillation tower, wherein desalted water is added to the inlet of the compressor to avoid the outlet gas phase from being too high in overheating temperature, and this part of the desalted water is also used as the desalted water required to be supplemented by part of the system, and the oxalic acid-rich material taken out from the bottom of the reactive distillation tower passes through the oxalic acid crystallization, separation and drying device to output the oxalic acid product;

[0015] Step S3: the gaseous material after heat exchange in the reboiler A of the reaction distillation tower is further heat exchanged with the material in the bottom of the pre-distillation tower through the reboiler of the pre-distillation tower to provide the heat required for the reboiling of the bottom of the tower, and then enters the pre-distillation tower for methanol concentration; the gaseous material containing 70-80wt% of methanol is taken out from the top of the pre-distillation tower, and is condensed in the condenser of the pre-distillation tower and divided into two streams, one of which is refluxed to the pre-distillation tower, and the other is sent to the pressure tower; the material with a methanol content of ≤0.01wt% is taken out from the bottom of the pre-distillation tower;

[0016] Step S4: the material produced from the top of the pre-distillation tower is sent to the pressure tower for methanol refining. The gaseous refined methanol material produced from the top of the pressure tower is condensed and divided into two streams after heat exchange with the material in the kettle of the atmospheric pressure tower in the reboiler of the atmospheric pressure tower to provide the heat required for reboiling the kettle of the atmospheric pressure tower, one stream is refluxed to the pressure tower, and the other stream is output as a refined methanol product after heat exchange with the crystallization liquid preheater. The material containing 55-65wt% of methanol produced from the bottom of the pressure tower is sent to the atmospheric pressure tower for refining of the remaining methanol. The refined methanol material produced from the top of the atmospheric pressure tower is condensed in the atmospheric pressure tower condenser and divided into two streams, one stream is refluxed to the atmospheric pressure tower, and the other stream is output as a refined methanol product. The material with methanol content ≤0.01wt% is produced from the bottom of the atmospheric pressure tower.

[0017] Furthermore, in the circulating mother liquor of step S1, the methanol content is ≤0.01wt%, the dimethyl oxalate content is ≤0.01wt%, and the monomethyl oxalate content is ≤0.001wt%.

[0018] Furthermore, in step S1, the total molar ratio of water and dimethyl oxalate entering the pre-reactor is 15-25:1, the material residence time is 20-50 min, the operating pressure is 0.005-0.02 MPa, and the temperature is 85-95°C.

[0019] Furthermore, in step S2, the reactive distillation tower is a packed tower with a total theoretical number of 25 to 40 plates, a top temperature of 95 to 105° C., a pressure of 0.005 to 0.02 MPa, a bottom temperature of 100 to 110° C., and a pressure of 0.01 to 0.03 MPa.

[0020] Furthermore, in step S2, the methanol content in the gaseous material extracted from the top of the reaction distillation tower is 25-35wt%, and the purity of the oxalic acid product outputted from the oxalic acid-rich material at the bottom of the reaction distillation tower after passing through the oxalic acid crystallization separation and drying device is ≥99.6wt%.

[0021] Furthermore, in step S2, the amount of desalted water added to the top of the reactive distillation tower to supplement the system is 30-45wt% of the total amount of water added to the system, and the compression ratio of the compressor is 1.7-1.9.

[0022] Furthermore, the methanol content of the gas phase material extracted from the top of the pre-distillation tower in step S3 is 70-80wt%.

[0023] Furthermore, in step S3, the pre-distillation tower is a packed tower with a total theoretical number of 20 to 40 plates, a top temperature of 50 to 60° C., a pressure of -0.04 to -0.06 MPa, a bottom temperature of 75 to 85° C., and a pressure of -0.035 to -0.055 MPa.

[0024] Furthermore, in step S4, the pressure tower is a packed tower with a total theoretical number of plates of 15 to 35, a top temperature of 115 to 125°C, a pressure of 0.5 to 0.65 MPa, a bottom temperature of 130 to 140°C, and a pressure of 0.5 to 0.7 MPa; the atmospheric pressure tower is a packed tower with a total theoretical number of plates of 20 to 40, a top temperature of 65 to 75°C, a pressure of 0.005 to 0.02 MPa, a bottom temperature of 100 to 110°C, and a pressure of 0.01 to 0.03 MPa.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention has a high conversion rate of dimethyl oxalate and a good quality of oxalic acid product. Desalted water required for supplementation of the system is added to the top of the reaction distillation tower, and this part of the desalted water is also used as the reflux liquid of the reaction distillation tower, so as to avoid using a large amount of materials containing methanol extracted from the top of the reaction distillation tower for reflux, so that the methanol content in the upper section of the reaction distillation tower can be kept at a low level, and the equilibrium reaction can be promoted to proceed in the positive direction, and the conversion rate can be improved. Impurities such as dimethyl oxalate and oxalic acid monoester in the oxalic acid solution extracted from the reaction distillation tower are controlled at an extremely low level to ensure the conversion rate of dimethyl oxalate and the oxalic acid product index; at the same time, the water content of the subsequent materials entering the crystallization system can be reduced, the energy consumption of the crystallization system can be reduced, and the amount of crystallization mother liquor and the amount of oxalic acid circulated back to the pre-reactor can be reduced;

[0027] 2. The desalted water consumed by the whole system of the present invention is replenished through the top of the reaction distillation tower, the tower kettle, and the compressor inlet respectively. The desalted water plays its own role at each replenishment position. At the same time, the total replenishment amount is the same as the total consumption of the system. No excess process wastewater is discharged from the whole system, and the system water is balanced;

[0028] 3. The present invention optimizes and integrates the whole process, fully considers the coupling of heat in the production process and the recovery and utilization of waste heat, reduces the overall energy consumption, and thus reduces the production cost; fully utilizes the latent heat of the gas phase at the top of the reaction distillation tower, which can provide heat for its own reboiler after pressurization, and the surplus heat can be used as the heat source of the reboiler of the pre-distillation tower, greatly reducing energy consumption; methanol recovery adopts the differential pressure distillation process to further reduce energy consumption; the cascade utilization of waste heat can also greatly reduce the cooling capacity required by the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the present invention;

[0030] In the figure: 1-DMO preheater; 2-prereactor; 3-reaction distillation tower; 4-compressor; 5-reaction distillation tower reboiler A; 6-reaction distillation tower reboiler B; 7-pre-distillation tower; 8-pre-distillation tower condenser; 9-pre-distillation tower reboiler; 10-pressure tower; 11-pressure tower reboiler; 12-atmospheric pressure tower reboiler; 13-atmospheric pressure tower; 14-atmospheric pressure tower condenser; 15-oxalic acid crystallization separation and drying device; 16-crystallization liquid preheater; 17-mother liquor preheater. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0032] Example 1

[0033] like Figure 1 As shown, a system for preparing oxalic acid by hydrolyzing dimethyl oxalate includes a reactive distillation device, a pre-distillation device, a pressurizing device and a normal pressure device;

[0034] The reactive distillation device comprises a DMO preheater 1, a prereactor 2, a reactive distillation tower 3, a compressor 4, a reactive distillation tower reboiler A5 and a reactive distillation tower reboiler B6, wherein the inlet of the DMO preheater 1 is externally connected to a dimethyl oxalate raw material, and the outlet is connected to the inlet of the prereactor 2, the outlet of the prereactor 2 is connected to the inlet of the reactive distillation tower 3, the top gas phase outlet of the prereactor 2 is connected to the gas phase inlet of the reactive distillation tower 3, the reactive distillation tower 3 is externally connected to desalted water and low-pressure steam, the bottom outlet of the reactive distillation tower 3 is connected to the inlet of the reactive distillation tower reboiler A5, the outlet of the reactive distillation tower reboiler A5 is connected to the inlet of the reactive distillation tower reboiler B6, the outlet of the reactive distillation tower reboiler B6 is connected to the reactive distillation tower 3, the top gas phase outlet of the reactive distillation tower 3 is connected to the inlet of the compressor 4, the outlet of the compressor 4 is connected to the hot side inlet of the reactive distillation tower reboiler A5, and the compressor 4 is externally connected to desalted water;

[0035] The pre-distillation device comprises a pre-distillation tower 7, a pre-distillation tower condenser 8 and a pre-distillation tower reboiler 9, the top gas phase outlet of the pre-distillation tower 7 is connected to the pre-distillation tower condenser 8, the outlet of the pre-distillation tower condenser 8 is connected to the inlet of the pre-distillation tower 7, the bottom outlet of the pre-distillation tower 7 is connected to the inlet of the pre-distillation tower reboiler 9, the outlet of the pre-distillation tower reboiler 9 is connected to the inlet of the pre-distillation tower 7, the hot side outlet of the reaction distillation tower reboiler A5 is connected to the hot side inlet of the pre-distillation tower reboiler 9, and the hot side outlet of the pre-distillation tower reboiler 9 is connected to the pre-distillation tower 7;

[0036] The pressurizing device includes a pressurizing tower 10 and a pressurizing tower reboiler 11, the outlet of the pre-distillation tower condenser 8 is connected to the inlet of the pressurizing tower 10, the bottom outlet of the pressurizing tower 10 is connected to the inlet of the pressurizing tower reboiler 11, and the outlet of the pressurizing tower reboiler 11 is connected to the pressurizing tower 10;

[0037] The atmospheric pressure device comprises an atmospheric pressure tower reboiler 12, an atmospheric pressure tower 13 and an atmospheric pressure tower condenser 14, the top outlet of the atmospheric pressure tower 13 is connected to the inlet of the atmospheric pressure tower condenser 14, the outlet of the atmospheric pressure tower condenser 14 is divided into two streams, one stream is connected to the atmospheric pressure tower 13, and the other stream outputs a refined methanol product, the bottom outlet of the atmospheric pressure tower 13 is connected to the inlet of the atmospheric pressure tower reboiler 12, the outlet of the atmospheric pressure tower reboiler 12 is connected to the atmospheric pressure tower 13, and the bottom outlet of the pressurized tower 10 is connected to the atmospheric pressure tower 13;

[0038] It also includes an oxalic acid crystallization, separation and drying device 15, a crystallization liquid preheater 16 and a mother liquid preheater 17. The bottom outlet of the reaction distillation tower 3 is connected to the inlet of the oxalic acid crystallization, separation and drying device 15. One outlet of the oxalic acid crystallization, separation and drying device 15 outputs an oxalic acid product, and the other outlet is connected to the inlet of the crystallization liquid preheater 16. The outlet of the crystallization liquid preheater 16, the bottom outlet of the pre-distillation tower 7 and the atmospheric tower 13 are all connected to the inlet of the mother liquid preheater 17. The outlet of the mother liquid preheater 17 is connected to the inlet of the pre-reactor 2. The top gas phase outlet of the pressurizing tower 10 is connected to the hot side inlet of the atmospheric tower reboiler 12. The hot side outlet of the atmospheric tower reboiler 12 is divided into two streams, one of which is connected to the inlet of the pressure tower 10, and the other is connected to the hot side inlet of the crystallization liquid preheater 16. The hot side outlet of the crystallization liquid preheater 16 outputs a refined methanol product.

[0039] A method for preparing oxalic acid by hydrolyzing dimethyl oxalate comprises the following steps:

[0040] Step S1: The dimethyl oxalate raw material is preheated in the DMO preheater 1 and then enters the pre-reactor 2. The bottom material from the pre-distillation tower 7 and the atmospheric tower 13 is mixed with the crystal liquid from the oxalic acid crystallization separation and drying device 15 to obtain a methanol content of 4.2e - 3 wt%, dimethyl oxalate content 5.8e -3 wt%, monomethyl oxalate content 3.1e -4 wt% of circulating mother liquor is preheated by mother liquor preheater 17 and enters pre-reactor 2. The total molar ratio of water and dimethyl oxalate in the feed is 15:1. The dimethyl oxalate raw material and the circulating mother liquor undergo a pre-hydrolysis reaction in the pre-reactor 2. The operating pressure is 0.02MPa, the temperature is 95°C, and the material residence time is 50min. The gas phase generated by the reaction in the pre-reactor 2 is transported to the reaction distillation tower 3 through the top gas phase outlet, and the material at the outlet of the pre-reactor 2 is transported to the reaction distillation tower 3;

[0041] Step S2: The material from the pre-reactor 2 is subjected to reactive distillation in the reactive distillation tower 3, so that dimethyl oxalate and the intermediate product monomethyl oxalate are further reacted and converted into oxalic acid. The reactive distillation tower 3 is a packed tower with a total theoretical number of 40 plates, a tower top temperature of 105°C, a pressure of 0.02MPa, a tower bottom temperature of 110°C, and a pressure of 0.03MPa. Desalted water required to be supplemented by the system is added to the top of the reactive distillation tower 3, and the added amount is 30wt% of the total amount of water added to the system. This part of the desalted water is also used as the reflux liquid of the reactive distillation tower 3. Low-pressure steam is added to the bottom of the reactive distillation tower 3 to supplement the heat required for reboiling the kettle. This part of the steam is liquefied in the tower and is also used as a part of the system. The desalted water required to be supplemented by the system, the gaseous material containing 35wt% of methanol is extracted from the top of the reaction distillation tower 3, and after being pressurized and heated by the compressor 4, it enters the reaction distillation tower reboiler A5 and exchanges heat with the tower bottom material to provide the heat required for the tower bottom reboiling. The compression ratio of the compressor 4 is 1.7. The tower bottom material from the reaction distillation tower reboiler A is heated by the reaction distillation tower reboiler B6 and then returns to the reaction distillation tower 3, wherein desalted water is added to the inlet of the compressor 4 to avoid the outlet gas phase from being overheated. This part of the desalted water is also used as part of the desalted water required to be supplemented by the system. The oxalic acid-rich material extracted from the bottom of the reaction distillation tower 3 passes through the oxalic acid crystallization, separation and drying device 15 and outputs an oxalic acid product with a purity of 99.7wt%;

[0042] Step S3: The gaseous material after heat exchange in the distillation tower reboiler A5 is further heat exchanged with the material in the bottom of the pre-distillation tower 7 in the pre-distillation tower reboiler 9 to provide the heat required for the reboiling of the bottom of the tower, and then enters the pre-distillation tower 7 for methanol concentration. The pre-distillation tower 7 is a packed tower with a total theoretical number of 20 plates, a top temperature of 50°C, a pressure of -0.06MPa, a bottom temperature of 75°C, and a pressure of -0.055MPa. The gaseous material containing 80wt% of methanol is extracted from the top of the pre-distillation tower 7, and is condensed in the pre-distillation tower condenser 8 and then divided into two streams, one of which is refluxed to the pre-distillation tower 7, and the other is sent to the pressure tower 10. The methanol content of the extracted gaseous material at the bottom of the pre-distillation tower 7 is 4.8e -3 wt% of material;

[0043] Step S4: The extracted material from the top of the pre-distillation tower 7 is sent to the pressure tower 10 for methanol refining. The pressure tower 10 is a packed tower with a total theoretical number of 15 plates, a top temperature of 115°C, a pressure of 0.5 MPa, a bottom temperature of 130°C, and a pressure of 0.505 MPa. The gaseous refined methanol material extracted from the top of the pressure tower 10 is heat exchanged with the material in the bottom of the atmospheric pressure tower 13 by the atmospheric pressure tower reboiler 12 to provide the heat required for reboiling the bottom of the atmospheric pressure tower 13, and then condensed and divided into two streams, one of which is refluxed to the pressure tower 10, and the other is exchanged with the crystallization liquid by the crystallization liquid preheater 16. After heating, it is output as a refined methanol product. The material containing 65wt% of methanol is extracted from the bottom of the pressure tower 10 and sent to the atmospheric pressure tower 13 for refining the remaining methanol. The atmospheric pressure tower 13 is a packed tower with a total theoretical number of 20 plates, a top temperature of 65°C, a pressure of 0.005MPa, a bottom temperature of 100°C, and a pressure of 0.01MPa. The refined methanol material extracted from the top of the atmospheric pressure tower 13 is condensed by the atmospheric pressure tower condenser 14 and divided into two streams, one of which is refluxed to the atmospheric pressure tower 13, and the other is output as a refined methanol product. The methanol content of the extracted material at the bottom of the atmospheric pressure tower 13 is 3.9e -3 wt% of material.

[0044] In this embodiment, the conversion rate of dimethyl oxalate is 99.96 wt %.

[0045] The methanol content in the circulating mother liquid of step S1 can also be any value of ≤0.01wt%, the dimethyl oxalate content can also be any value of ≤0.01wt%, and the monomethyl oxalate content can also be any value of ≤0.001wt%;

[0046] The total molar ratio of water and dimethyl oxalate entering the pre-reactor 2 in step S1 can also be any value between 15 and 25:1, the material residence time can also be any value between 20 and 50 min, the operating pressure can also be any value between 0.005 and 0.02 MPa, and the temperature can also be any value between 85 and 95° C.;

[0047] The total theoretical plate number of the reactive distillation tower 3 can also be any value between 25 and 40, the tower top temperature can also be any value between 95 and 105° C., the pressure can also be any value between 0.005 and 0.02 MPa, the tower bottom temperature can also be any value between 100 and 110° C., and the pressure can also be any value between 0.01 and 0.03 MPa;

[0048] The methanol content in the gaseous material extracted from the top of the reactive distillation tower 3 in step S2 can also be any value between 25 and 35 wt %;

[0049] The amount of desalted water added to the top of the reaction distillation tower 3 in step S2 can also be any value between 30 and 45 wt% of the total amount of water added to the system, and the compression ratio of the compressor 4 can also be any value between 1.7 and 1.9;

[0050] The methanol content of the gas phase material extracted from the top of the pre-distillation tower 7 in step S3 can also be any value between 70 and 80 wt %;

[0051] The total theoretical plate number of the pre-distillation tower (7) can also be any value between 20 and 40, the tower top temperature can also be any value between 50 and 60° C., the pressure can also be any value between -0.04 and -0.06 MPa, the tower bottom temperature can also be any value between 75 and 85° C., and the pressure can also be any value between -0.035 and -0.055 MPa;

[0052] The total theoretical plate number of the pressurized tower 10 can also be any value between 15 and 35, the tower top temperature can also be any value between 115 and 125° C., the pressure can also be any value between 0.5 and 0.65 MPa, the tower bottom temperature can also be any value between 130 and 140° C., and the pressure can also be any value between 0.5 and 0.7 MPa;

[0053] The atmospheric pressure tower 13 is a packed tower, and the total theoretical plate number can also be any value between 20 and 40, the tower top temperature can also be any value between 65 and 75°C, the pressure can also be any value between 0.005 and 0.02 MPa, the tower bottom temperature can also be any value between 100 and 110°C, and the pressure can also be any value between 0.01 and 0.03 MPa.

[0054] Example 2

[0055] The difference between this embodiment and embodiment 1 is that:

[0056] The methanol content in the circulating mother liquor of step S1 is 3.5e -3 wt%, dimethyl oxalate content 4.1e -3 wt%, monomethyl oxalate content 2.9e -4 wt%, the total molar ratio of water and dimethyl oxalate in the feed is 20:1, the operating pressure of the pre-reactor 2 is 0.01MPa, the temperature is 88°C, and the material residence time is 35min;

[0057] In step S2, the total theoretical number of plates of the reaction distillation tower 3 is 32, the top temperature is 98° C., the pressure is 0.01 MPa, the bottom temperature is 104° C., the pressure is 0.017 MPa, the amount of desalted water added to the reaction distillation tower 3 is 38wt% of the total amount of water added to the system, the methanol content of the gas phase material extracted from the top of the reaction distillation tower 3 is 31wt%, the compression ratio of the compressor 4 is 1.8, and the oxalic acid-rich material extracted from the bottom of the reaction distillation tower 3 passes through the oxalic acid crystallization separation and drying device 15, and the purity of the oxalic acid product output is 99.8wt%;

[0058] In step S3, the total theoretical number of plates of the pre-distillation tower 7 is 33, the top temperature is 55°C, the pressure is -0.05MPa, the bottom temperature is 80°C, the pressure is -0.045MPa, the methanol content of the material taken out from the top of the pre-distillation tower 7 is 76wt%, and the methanol content of the material taken out from the bottom is 3.6e -3 wt%;

[0059] In step S4, the total theoretical number of plates of the pressure tower 10 is 27, the tower top temperature is 121°C, the pressure is 0.58MPa, the tower bottom temperature is 136°C, the pressure is 0.587MPa, and the methanol content of the material taken out from the bottom of the pressure tower 10 is 61wt%. The total theoretical number of plates of the atmospheric tower 13 is 34, the tower top temperature is 71°C, the pressure is 0.013MPa, the tower bottom temperature is 106°C, the pressure is 0.019MPa, and the methanol content of the material taken out from the bottom of the atmospheric tower 13 is 3.6e -3 wt%;

[0060] In this embodiment, the conversion rate of dimethyl oxalate is 99.96 wt %.

[0061] Example 3

[0062] The difference between this embodiment and embodiment 1 is that:

[0063] The methanol content in the circulating mother liquor of step S1 is 1.3e -3 wt%, dimethyl oxalate content 2.4e -3 wt%, monomethyl oxalate content 2.2e -4 wt%, the total molar ratio of water and dimethyl oxalate in the feed is 25:1, the operating pressure of the pre-reactor 2 is 0.005MPa, the temperature is 85°C, and the material residence time is 20min;

[0064] In step S2, the total theoretical number of plates of the reaction distillation tower 3 is 25, the top temperature is 95° C., the pressure is 0.005 MPa, the bottom temperature is 103° C., the pressure is 0.01 MPa, the desalted water added to the top of the reaction distillation tower 3 is 45wt% of the total water added to the system, the gas phase material extracted from the top of the reaction distillation tower 3 contains 25wt% methanol, the compression ratio of the compressor 4 is 1.9, and the oxalic acid-rich material extracted from the bottom of the reaction distillation tower 3 passes through the oxalic acid crystallization separation and drying device 15, and the purity of the oxalic acid product output is 99.8wt%;

[0065] In step S3, the total theoretical number of plates of the pre-distillation tower 7 is 40, the top temperature is 60°C, the pressure is -0.04MPa, the bottom temperature is 85°C, the pressure is -0.035MPa, the material taken out from the top of the pre-distillation tower 7 contains 70wt% methanol, and the methanol content in the material taken out from the bottom is 1.9e -3 wt%;

[0066] In step S4, the total theoretical number of plates of the pressure tower 10 is 35, the tower top temperature is 125°C, the pressure is 0.65MPa, the tower bottom temperature is 140°C, the pressure is 0.66MPa, and the material taken out from the bottom of the pressure tower 10 contains 55wt% methanol. The total theoretical number of plates of the atmospheric tower 13 is 40, the tower top temperature is 75°C, the pressure is 0.02MPa, the tower bottom temperature is 110°C, the pressure is 0.03MPa, and the methanol content of the material taken out from the bottom of the atmospheric tower 13 is 2.1e -3 wt%.

[0067] In this embodiment, the conversion rate of dimethyl oxalate is 99.98 wt %.

Claims

1. A system for preparing oxalic acid by hydrolyzing dimethyl oxalate, characterized in that: It includes a reactive distillation device, a pre-distillation device, a pressurizing device and a normal pressure device; The reactive distillation device comprises a DMO preheater (1), a prereactor (2), a reactive distillation tower (3), a compressor (4), a reactive distillation tower reboiler A (5) and a reactive distillation tower reboiler B (6), wherein the inlet of the DMO preheater (1) is externally connected to a dimethyl oxalate raw material, and the outlet is connected to the inlet of the prereactor (2), the outlet of the prereactor (2) is connected to the inlet of the reactive distillation tower (3), the gas phase outlet at the top of the prereactor (2) is connected to the gas phase inlet of the reactive distillation tower (3), and the reactive distillation tower (3) is externally connected to a degassing tower (4). salt water and low-pressure steam, the bottom outlet of the reaction distillation tower (3) is connected to the inlet of the reaction distillation tower reboiler A (5), the outlet of the reaction distillation tower reboiler A (5) is connected to the inlet of the reaction distillation tower reboiler B (6), the outlet of the reaction distillation tower reboiler B (6) is connected to the reaction distillation tower (3), the top gas phase outlet of the reaction distillation tower (3) is connected to the inlet of the compressor (4), the outlet of the compressor (4) is connected to the hot side inlet of the reaction distillation tower reboiler A (5), and the compressor (4) is externally connected to desalted water; The pre-distillation device comprises a pre-distillation tower (7), a pre-distillation tower condenser (8) and a pre-distillation tower reboiler (9), the tower top gas phase outlet of the pre-distillation tower (7) is connected to the pre-distillation tower condenser (8), the outlet of the pre-distillation tower condenser (8) is connected to the inlet of the pre-distillation tower (7), the tower bottom outlet of the pre-distillation tower (7) is connected to the inlet of the pre-distillation tower reboiler (9), the outlet of the pre-distillation tower reboiler (9) is connected to the inlet of the pre-distillation tower (7), the hot side outlet of the reaction distillation tower reboiler A (5) is connected to the hot side inlet of the pre-distillation tower reboiler (9), and the hot side outlet of the pre-distillation tower reboiler (9) is connected to the pre-distillation tower (7); The pressurizing device comprises a pressurizing tower (10) and a pressurizing tower reboiler (11), the outlet of the pre-distillation tower condenser (8) is connected to the inlet of the pressurizing tower (10), the bottom outlet of the pressurizing tower (10) is connected to the inlet of the pressurizing tower reboiler (11), and the outlet of the pressurizing tower reboiler (11) is connected to the pressurizing tower (10); The atmospheric pressure device comprises an atmospheric pressure tower reboiler (12), an atmospheric pressure tower (13) and an atmospheric pressure tower condenser (14); the top outlet of the atmospheric pressure tower (13) is connected to the inlet of the atmospheric pressure tower condenser (14); the outlet of the atmospheric pressure tower condenser (14) is divided into two streams, one stream is connected to the atmospheric pressure tower (13), and the other stream outputs a refined methanol product; the bottom outlet of the atmospheric pressure tower (13) is connected to the inlet of the atmospheric pressure tower reboiler (12); the outlet of the atmospheric pressure tower reboiler (12) is connected to the atmospheric pressure tower (13); and the bottom outlet of the pressurized tower (10) is connected to the atmospheric pressure tower (13); The invention also comprises an oxalic acid crystallization separation and drying device (15), a crystallization liquid preheater (16) and a mother liquid preheater (17). The bottom outlet of the reaction distillation tower (3) is connected to the inlet of the oxalic acid crystallization separation and drying device (15). One outlet of the oxalic acid crystallization separation and drying device (15) outputs an oxalic acid product, and the other outlet is connected to the inlet of the crystallization liquid preheater (16). The outlet of the crystallization liquid preheater (16), the bottom outlet of the pre-distillation tower (7) and the atmospheric tower (13) are all connected to the inlet of the mother liquid preheater (17). The outlet of the mother liquid preheater (17) is connected to the inlet of the pre-reactor (2). The top gas phase outlet of the pressure tower (10) is connected to the hot side inlet of the atmospheric tower reboiler (12). The hot side outlet of the atmospheric tower reboiler (12) is divided into two streams, one of which is connected to the inlet of the pressure tower (10) and the other is connected to the hot side inlet of the crystallization liquid preheater (16). The hot side outlet of the crystallization liquid preheater (16) outputs a refined methanol product.

2. A method for preparing oxalic acid by hydrolyzing dimethyl oxalate using the system for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 1, characterized in that: The steps include: Step S1: the dimethyl oxalate raw material is preheated by a DMO preheater (1) and then enters a pre-reactor (2); the circulating mother liquor obtained by mixing the bottom extraction materials from the pre-rectification tower (7) and the atmospheric tower (13) with the crystallization liquid of the oxalic acid crystallization separation and drying device (15) is preheated by a mother liquor preheater (17) and then enters the pre-reactor (2); the dimethyl oxalate raw material and the circulating mother liquor undergo a pre-hydrolysis reaction in the pre-reactor (2); the gas phase generated by the reaction in the pre-reactor (2) is transported to a reactive distillation tower (3) through a top gas phase outlet; and the outlet materials of the pre-reactor (2) are transported to the reactive distillation tower (3); Step S2: The material from the pre-reactor (2) is subjected to reactive distillation in a reactive distillation tower (3) so that dimethyl oxalate and the intermediate product monomethyl oxalate are further reacted and converted into oxalic acid. Desalted water required to be supplemented by the system is added to the top of the reactive distillation tower (3). This part of the desalted water also serves as the reflux liquid of the reactive distillation tower (3). Low-pressure steam is added to the bottom of the reactive distillation tower (3) to supplement the heat required for reboiling of the tower kettle. This part of the steam is liquefied in the tower and also serves as a part of the desalted water required to be supplemented by the system. The gaseous material extracted from the top of the reactive distillation tower (3) is compressed to obtain a reflux liquid. After the compressor (4) is pressurized and heated, the water enters the reboiler A (5) of the reaction distillation tower and exchanges heat with the bottom material to provide the heat required for the bottom reboiling. The bottom material from the reboiler A (5) of the reaction distillation tower is heated by the reboiler B (6) of the reaction distillation tower and then returns to the reaction distillation tower (3). Desalted water is added to the inlet of the compressor (4) to avoid excessive overheating of the outlet gas phase. This part of desalted water is also used as a part of the desalted water required to be supplemented by the system. The oxalic acid-rich material extracted from the bottom of the reaction distillation tower (3) passes through the oxalic acid crystallization separation and drying device (15) and then outputs the oxalic acid product. Step S3: the gaseous material after heat exchange in the reaction distillation tower reboiler A (5) is further heat exchanged with the bottom material of the pre-distillation tower (7) through the pre-distillation tower reboiler (9) to provide the heat required for the bottom reboiling and then enters the pre-distillation tower (7) for methanol concentration. The gaseous material containing 70-80 wt% of methanol is extracted from the top of the pre-distillation tower (7) and condensed by the pre-distillation tower condenser (8) and then divided into two streams, one of which is refluxed to the pre-distillation tower (7) and the other is sent to the pressure tower (10). The material with a methanol content of ≤0.01 wt% is extracted from the bottom of the pre-distillation tower (7); Step S4: the material extracted from the top of the pre-distillation tower (7) is sent to the pressure tower (10) for methanol refining. The gaseous refined methanol material extracted from the top of the pressure tower (10) is condensed and divided into two streams after heat exchange with the material in the bottom of the atmospheric pressure tower (13) in the atmospheric pressure tower reboiler (12) to provide the heat required for reboiling the bottom of the atmospheric pressure tower (13) and then refluxed to the pressure tower (10). The other stream is output as a refined methanol product after heat exchange with the crystallization liquid in the crystallization liquid preheater (16). The material containing 55-65wt% of methanol extracted from the bottom of the pressure tower (10) is sent to the atmospheric pressure tower (13) for refining the remaining methanol. The refined methanol material extracted from the top of the atmospheric pressure tower (13) is condensed in the atmospheric pressure tower condenser (14) and then divided into two streams. One stream is refluxed to the atmospheric pressure tower (13) and the other stream is output as a refined methanol product. The material with a methanol content of ≤0.01wt% is extracted from the bottom of the atmospheric pressure tower (13).

3. The method for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 2, characterized in that: The circulating mother liquid in step S1 has a methanol content of ≤0.01 wt%, a dimethyl oxalate content of ≤0.01 wt%, and a monomethyl oxalate content of ≤0.001 wt%.

4. The method for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 2, characterized in that: In the step S1, the total molar ratio of water and dimethyl oxalate entering the pre-reactor (2) is 15-25:1, the material residence time is 20-50 min, the operating pressure is 0.005-0.02 MPa, and the temperature is 85-95°C.

5. The method for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 2, characterized in that: The reactive distillation tower (3) in step S2 is a packed tower with a total theoretical number of 25 to 40 plates, a top temperature of 95 to 105° C., a pressure of 0.005 to 0.02 MPa, a bottom temperature of 100 to 110° C., and a pressure of 0.01 to 0.03 MPa.

6. The method for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 2, characterized in that: In the step S2, the methanol content in the gaseous material extracted from the top of the reaction distillation tower (3) is 25-35wt%, and the purity of the oxalic acid product outputted from the oxalic acid-rich material extracted from the bottom of the reaction distillation tower (3) after passing through the oxalic acid crystallization separation and drying device (15) is ≥99.6wt%.

7. The method for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 2, characterized in that: In the step S2, the amount of desalted water added to the top of the reaction distillation tower (3) to supplement the system is 30-45 wt% of the total amount of water added to the system, and the compression ratio of the compressor (4) is 1.7-1.

9.

8. The method for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 2, characterized in that: The methanol content of the gas phase material extracted from the top of the pre-distillation tower (7) in step S3 is 70-80 wt%.

9. The method for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 2, characterized in that: The pre-distillation tower (7) in step S3 is a packed tower with a total theoretical number of 20 to 40 plates, a top temperature of 50 to 60°C, a pressure of -0.04 to -0.06 MPa, a bottom temperature of 75 to 85°C, and a pressure of -0.035 to -0.055 MPa.

10. The method for preparing oxalic acid by hydrolyzing dimethyl oxalate according to claim 2, characterized in that: In the step S4, the pressure tower (10) is a packed tower with a total theoretical number of plates of 15 to 35, a top temperature of 115 to 125° C., a pressure of 0.5 to 0.65 MPa, a bottom temperature of 130 to 140° C., and a pressure of 0.5 to 0.7 MPa. The atmospheric pressure tower (13) is a packed tower with a total theoretical number of plates of 20 to 40, a top temperature of 65 to 75° C., a pressure of 0.005 to 0.02 MPa, a bottom temperature of 100 to 110° C., and a pressure of 0.01 to 0.03 MPa.

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