A device and method for continuously preparing oxalamide

Abstract

The present invention relates to a device and method for continuously and efficiently preparing oxalamide, the method comprising: S1, after molten dimethyl oxalate and liquid ammonia are pressurized to reach the reaction pressure, they are respectively introduced into a DMO preheater and an alcohol ammonia mixer; after circulating methanol is heated by a circulating methanol heat exchanger, they are respectively sent into an alcohol ester mixer and an alcohol ammonia mixer to obtain an alcohol ester solution and an alcohol ammonia solution; S2, the alcohol ester solution and the alcohol ammonia solution are sent into a reactor to carry out an ammonolysis reaction, and the generated reaction liquid enters a reaction liquid receiving tank, and then enters a flash evaporation device for flash evaporation, and the flash steam in the flash evaporation device is condensed by heat exchange to obtain circulating methanol; S3, the flash evaporation liquid in the flash evaporation device is sent into a solid-liquid separator for solid-liquid separation, and a solid phase and a liquid phase are respectively produced, and the solid phase is dried by a dryer to obtain an oxalamide product. The present invention dissolves dimethyl oxalate and liquid ammonia in a methanol solvent respectively for liquid phase reaction, and has low energy consumption and good safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of oxamide preparation, and in particular relates to a device and method for continuously and efficiently preparing oxamide. Background Art

[0002] Oxamide is an excellent slow-release fertilizer, appearing as a white powder with no odor. It contains 31.8% nitrogen, is non-deliquescent in air, slightly soluble in water, stable, and easy to store. During hydrolysis or biodegradation, it gradually releases ammoniacal nitrogen and carbon dioxide, which are not easily lost or polluted. Its fertilizer utilization rate can reach 65% to 80%.

[0003] Currently, the following methods are primarily used to prepare oxamide: 1. The hydrocyanic acid method, which uses hydrocyanic acid as a raw material to synthesize oxamide. However, this method produces high HCN costs, and HCN is a highly toxic chemical, making industrial production unfeasible. 2. The ammonium oxalate thermal decomposition method, which produces oxamide by heating and dehydrating ammonium oxalate. However, the yield of the ammonium oxalate dehydration step to produce oxamide is low, at only 30-60%, resulting in high costs and unsuitable for industrialization. 3. The oxalate ester method, which produces oxamide and the corresponding alcohol through the aminolysis of oxalate esters. In recent years, with the gradual development of C1 chemical industry, the technology for synthesizing ethylene glycol from dimethyl oxalate using coal gasification CO has achieved breakthroughs and has been widely applied. This has significantly reduced the cost of dimethyl oxalate, and the aminolysis of dimethyl oxalate to synthesize oxamide has great prospects for industrialization.

[0004] Chinese patents with publication numbers CN103288666A and CN110862331A respectively disclose a method for continuous gas-phase synthesis of oxamide. After dimethyl oxalate and liquid ammonia are gasified separately, an ammonolysis reaction occurs in a gas-phase reactor to produce the oxamide product. However, this method requires gasification of dimethyl oxalate first, and the process has high energy consumption.

[0005] Chinese patent publication number CN109569480A discloses a liquid-phase oxalamide synthesis method. This method involves dissolving dimethyl oxalate and liquid ammonia in methanol. The ammonia-methanol solution is then slowly added dropwise to the dimethyl oxalate-methanol solution in a reactor. After the reaction is complete, the product enters a solid-liquid separator. This method suffers from long reaction times, a discontinuous process, and the heat generated during the process cannot be recycled, making it unsuitable for large-scale industrial production.

[0006] Chinese patent publication number CN111153823A discloses a method for preparing oxamide from dimethyl oxalate. This method involves mixing a dimethyl oxalate stream, a methanol feed stream, and a liquid ammonia stream for an ammonolysis reaction to provide an ammonolysis product stream. However, to achieve a liquid-phase reaction in this method, the reaction temperature and pressure must match those of the liquid ammonia. Otherwise, the liquid ammonia feed will vaporize, and the reaction will become a two-phase gas-liquid reaction. This results in a rapid reaction rate, intense heat release, and rapid precipitation of the product oxamide, which can hinder heat transfer, clog equipment and pipelines, and affect process continuity. Low reaction temperatures also result in low feedstock conversion and product selectivity. Summary of the Invention

[0007] The object of the present invention is to provide an apparatus and method for continuously and efficiently preparing oxamide, which can react dimethyl oxalate with liquid ammonia in a liquid phase, achieve continuous reaction, mild reaction conditions, low energy consumption, high conversion rate and stable equipment operation;

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A device for continuously and efficiently preparing oxalamide, comprising a feeding unit, a reaction unit and an oxalamide separation unit.

[0010] The feeding unit includes a dimethyl oxalate feeding tank, a liquid ammonia buffer tank, a dimethyl oxalate preheater, an alcohol-ester mixer, an alcohol-ammonia mixer and a circulating methanol heat exchanger;

[0011] The discharge port of the dimethyl oxalate feed tank is connected to the feed port of the dimethyl oxalate preheater through a pipeline, and the discharge port of the dimethyl oxalate preheater is connected to the alcohol-ester mixer through a pipeline; the discharge port of the liquid ammonia buffer tank is connected to the alcohol-ammonia mixer through a pipeline; the discharge port of the circulating methanol heat exchanger is connected to the alcohol-ester mixer and the alcohol-ammonia mixer through pipelines respectively;

[0012] The reaction unit includes a reactor, a steam drum, a reaction liquid receiving tank and a flash evaporation device;

[0013] The discharge ports of the alcohol-ester mixer and the alcohol-ammonia mixer are both connected to the reactor through pipelines; the reactor is connected to the steam drum through a pipeline, and the discharge port of the reactor is connected to the reaction liquid receiving tank through a pipeline; the liquid outlet of the reaction liquid receiving tank is connected to the flash evaporation device through a pipeline;

[0014] The oxalamide separation unit includes a solid-liquid separator and a dryer.

[0015] The liquid outlet of the flash evaporation device is connected to the solid-liquid separator through a pipeline; the material outlet of the solid-liquid separator is connected to the dryer through a pipeline.

[0016] Preferably, the flash evaporation device includes a primary flash tank and a secondary flash tank, the liquid outlet of the primary flash tank is connected to the secondary flash tank through a pipeline, and the gas outlet of the primary flash tank is connected to the circulating heat exchanger, the dimethyl oxalate preheater and the final cooler in sequence through an outlet pipe; the dimethyl oxalate preheater and the final cooler are both connected to the circulating methanol buffer tank through pipelines; the liquid outlet of the secondary flash tank is connected to the solid-liquid separator through a pipeline, and the gas outlet of the secondary flash tank is connected to the flash condenser through a pipeline; the flash condenser is connected to the flash condensate tank through a pipeline; the flash condensate tank is connected to the circulating heat exchanger through a pipeline; the circulating heat exchanger and the circulating methanol buffer tank are both connected to the circulating methanol heat exchanger through pipelines.

[0017] Preferably, it further comprises a methanol separation unit, wherein the methanol separation unit comprises a methanol condenser, a methanol condensate tank, a filtrate tank, a feed preheater, a methanol distillation tower, a methanol distillation tower condenser and a reboiler;

[0018] The air outlet of the dryer is connected to the methanol condenser through a pipeline; the methanol condenser is connected to the methanol condensate tank through a pipeline; the liquid outlet of the solid-liquid separator is connected to the filtrate tank through a pipeline; the filtrate tank and the methanol condensate tank are both connected to the flash condensate tank through pipelines, and the filtrate tank is also connected to the feed preheater through a pipeline; the feed preheater is connected to the feed port of the methanol distillation tower, and the first liquid outlet at the bottom of the methanol distillation tower is connected to the feed preheater through a pipeline; the second liquid outlet at the bottom of the methanol distillation tower is connected to the reboiler feed port of the methanol distillation tower through a pipeline through a reboiler; the air outlet at the top of the methanol distillation tower is connected to the methanol distillation tower condenser; the methanol distillation tower condenser is connected to the flash condensate tank through a pipeline.

[0019] Preferably, the solid-liquid separator is any one of a filter press, a centrifuge or a filter; and the dryer is any one of a disc dryer, a paddle dryer or a vacuum dryer.

[0020] Preferably, the solid-liquid separator and the dryer are a separation-drying integrated machine.

[0021] A continuous and efficient method for preparing oxamide comprises the following steps:

[0022] S1, dimethyl oxalate and liquid ammonia are passed through a dimethyl oxalate feed tank and a liquid ammonia buffer tank respectively, and the dimethyl oxalate feed tank heats the dimethyl oxalate to keep the dimethyl oxalate in a molten state; then the molten dimethyl oxalate and liquid ammonia are pressurized respectively, and after reaching the reaction pressure, they are respectively passed into a dimethyl oxalate preheater and an alcohol ammonia mixer; dimethyl oxalate is preheated in the dimethyl oxalate preheater and then passed into an alcohol ester mixer; circulating methanol is heated in a circulating methanol heat exchanger and then respectively passed into an alcohol ester mixer and an alcohol ammonia mixer to obtain an alcohol ester solution and an alcohol ammonia solution; wherein the mass ratio of dimethyl oxalate to methanol in the alcohol ester solution is 1:0.7-5; the mass ratio of ammonia to methanol in the alcohol ammonia solution is 1:4-8, and the molar ratio of ammonia to dimethyl oxalate in the alcohol ester solution and the alcohol ammonia solution is greater than 2;

[0023] S2, placing the alcohol ester solution and the alcohol ammonia solution in a reactor at a temperature of 100-200°C, a reaction time of 10-60 minutes, and a reaction pressure of 1.0-5.0 MPa for ammonolysis reaction, while collecting the heat released by the reaction through a steam drum to produce 0.1-2.0 MPag of steam; the generated reaction liquid enters a reaction liquid receiving tank, and then enters a flash evaporation device for flash evaporation to obtain flash steam and flash liquid, and the flash steam in the flash evaporation device is condensed by heat exchange to obtain circulating methanol;

[0024] S3, sending the flash liquid in the flash evaporation device into a solid-liquid separator for solid-liquid separation, producing a solid phase and a liquid phase respectively, and the solid phase is dried in a dryer to obtain oxalamide.

[0025] Preferably, in S2, the flash evaporation device includes a primary flash tank and a secondary flash tank, the reaction liquid in the reaction liquid receiving tank first enters the primary flash tank for flash evaporation to obtain a primary flash liquid and a primary flash steam, and then the primary flash liquid is sent to the secondary flash tank 13b for flash evaporation to obtain a secondary flash liquid and a secondary flash steam, the secondary flash steam is passed into the flash condenser 14 for condensation and then sent to the flash condensate tank 15 to obtain a flash steam condensate; at the same time, the secondary flash liquid is sent to the solid-liquid separator 16 for solid-liquid separation to obtain a solid phase and a liquid phase.

[0026] Preferably, the solid phase is dried in a dryer to obtain methanol vapor, which is sent to a methanol condenser for condensation to obtain methanol condensate, and then the methanol condensate enters a methanol condensate tank; the liquid phase enters a filtrate tank, and the liquid phase in the filtrate tank is divided into two parts, one part of the liquid phase is mixed with the methanol condensate in the methanol condensate tank to obtain a methanol mixed liquid, which is sent to a flash condensate tank, and the other part is heated by a feed preheater and passed into a methanol distillation tower for methanol refining; a methanol and ammonia mixed gas is obtained at the top of the methanol distillation tower, and after condensation in a methanol distillation tower condenser, a methanol distillation tower top condensate is obtained, which is sent to a flash condensate tank; refined methanol is obtained at the bottom of the methanol distillation tower, and the refined methanol is divided into two parts, one part is returned to the methanol distillation tower through a reboiler, and the other part is passed through a feed preheater and cooled after heat exchange with the liquid phase to obtain a methanol product.

[0027] Preferably, the flash condensate in the flash condensate tank, the condensate from the top of the methanol distillation tower and the methanol mixed liquid are mixed and then placed in a circulating heat exchanger.

[0028] Preferably, the first-stage flash steam is sequentially condensed with the circulating heat exchanger and the dimethyl oxalate preheater for heat exchange. If it has been condensed into a liquid, the first-stage flash steam condensate is obtained. If not, it is condensed in the final cooler. The first-stage flash steam condensate passes through the circulating methanol buffer tank, is mixed with the mixed liquid of the circulating heat exchanger, and is then sent to the circulating methanol heat exchanger to provide circulating methanol for recycling.

[0029] The present invention provides a device and method for preparing continuous and efficient oxamide, which has the following advantages over the prior art:

[0030] (1) Dissolving dimethyl oxalate and liquid ammonia in methanol solvent respectively for liquid phase reaction, which has lower energy consumption, milder reaction, better heat removal, better safety, and more complete reaction than the gas phase method; achieving reaction at higher temperature and pressure, thereby improving raw material conversion rate and reaction yield;

[0031] (2) By using a suitable methanol ratio, the oxalamide methanol solution is more conducive to the transportation of oxalamide and prevents the blockage of system equipment;

[0032] (3) By setting up a steam drum, the by-product steam released by the reaction heat is recovered. The by-product steam can be used for drying the product oxalamide, distillation reboiler, heating circulating methanol, etc. The flash vapor is condensed by preheating circulating methanol, dimethyl oxalate, and liquid ammonia. The overall heat utilization is sufficient and reasonable, which greatly reduces production energy consumption and production costs;

[0033] (4) The flash evaporation process is used to gradually reduce the material pressure to normal pressure. The subsequent solid-liquid separation and distillation equipment are all low-pressure or normal-pressure equipment with low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0036] like Figure 1 As shown, a device for continuously and efficiently preparing oxalamide includes a feeding unit, a reaction unit and an oxalamide separation unit.

[0037] The feeding unit includes a dimethyl oxalate feeding tank 1, a liquid ammonia buffer tank 4, a dimethyl oxalate preheater 2, an alcohol ester mixer 3, an alcohol ammonia mixer 6 and a circulating methanol heat exchanger 9; the discharge port of the dimethyl oxalate feeding tank 1 is connected to the feed port of the dimethyl oxalate preheater 2 through a pipeline, and the discharge port of the dimethyl oxalate preheater 2 is connected to the alcohol ester mixer 3 through a pipeline; the discharge port of the liquid ammonia buffer tank 4 is connected to the alcohol ammonia mixer 6 through a pipeline; the discharge port of the circulating methanol heat exchanger 9 is connected to the alcohol ester mixer 3 and the alcohol ammonia mixer 6 through pipelines, respectively, so that circulating methanol can be passed into the alcohol ester mixer 3 and the alcohol ammonia mixer 6;

[0038] The reaction unit includes a reactor 10, a steam drum 11, a reaction liquid receiving tank 12 and a flash evaporation device 13; the discharge ports of the alcohol-ester mixer 3 and the alcohol-ammonia mixer 6 are connected to the reactor 10 through pipelines; the boiler feed water inlet and steam outlet of the jacket of the reactor 10 are connected to the steam drum 11 through pipelines, and the discharge port of the reactor 10 is connected to the reaction liquid receiving tank 12 through a pipeline; the liquid outlet of the reaction liquid receiving tank 12 is connected to the flash evaporation device 13 through a pipeline;

[0039] The oxalamide separation unit includes a solid-liquid separator 16 and a dryer 17. The liquid outlet of the flash evaporation device 13 is connected to the solid-liquid separator 16 through a pipeline; the material outlet of the solid-liquid separator 16 is connected to the dryer 17 through a pipeline.

[0040] In this embodiment, the flash evaporation device 13 includes a primary flash tank 13a and a secondary flash tank 13b, the liquid outlet of the primary flash tank 13a is connected to the secondary flash tank 13b through a pipeline, and the gas outlet of the primary flash tank 13a is connected to the circulating heat exchanger 7, the dimethyl oxalate preheater 2 and the final cooler 5 in sequence through an outlet pipe; the dimethyl oxalate preheater 2 and the final cooler 5 are both connected to the circulating methanol buffer tank 8 through a pipeline, wherein the flash steam of the primary flash tank 13a exchanges heat with the circulating heat exchanger 7, the dimethyl oxalate preheater 2 and the final cooler 5, saving energy, reducing production energy consumption, and reducing production costs;

[0041] The liquid outlet of the secondary flash tank 13b is connected to the solid-liquid separator 16 through a pipeline, and the gas outlet of the secondary flash tank 13b is connected to the flash condenser 14 through a pipeline; the flash condenser 14 is connected to the flash condensate tank 15 through a pipeline; the flash condensate tank 15 is connected to the circulating heat exchanger 7 through a pipeline; the circulating heat exchanger 7 and the circulating methanol buffer tank 8 are both connected to the circulating methanol heat exchanger 9 through a pipeline.

[0042] The reaction liquid in the reaction liquid receiving tank 12 enters the flash evaporation device 13 for flash evaporation, wherein the flash evaporation device 13 can be a single-stage flash evaporation or a two-stage flash evaporation, or a multi-stage flash evaporation. The material pressure is reduced to normal pressure by the flash evaporation device, and the subsequent solid-liquid separation and distillation equipment can be low-pressure or normal-pressure equipment, which has a low cost. The reaction liquid passes through the flash evaporation process, and part of the material (mainly methanol) in the reaction liquid is flashed and returned to the feed. The subsequent product solid-liquid separation and methanol distillation material processing volume is small, further reducing the equipment size and saving energy.

[0043] In this embodiment, a methanol separation unit is further included, which includes a methanol condenser 18, a methanol condensate tank 19, a filtrate tank 20, a feed preheater 21, a methanol distillation tower 22, a methanol distillation tower condenser 23 and a reboiler 24;

[0044] The gas outlet of the dryer 17 is connected to the methanol condenser 18 through a pipeline; the methanol condenser 18 is connected to the methanol condensate tank 19 through a pipeline; the liquid outlet of the solid-liquid separator 16 is connected to the filtrate tank 20 through a pipeline; the filtrate tank 20 and the methanol condensate tank 19 are both connected to the flash condensate tank 15 through a pipeline, and the filtrate tank 20 is also connected to the feed preheater 21 through a pipeline; the feed preheater 21 is connected to the feed port of the methanol distillation tower 22, and the first liquid outlet at the bottom of the methanol distillation tower 22 is connected to the methanol distillation tower 22 through a pipeline. The pipeline is connected to the feed preheater 21; the second liquid outlet at the bottom of the methanol distillation tower 22 is connected to the reboiler feed port of the methanol distillation tower 22 through a pipeline through a reboiler 24. The liquid methanol is heated by the reboiler to be vaporized, thereby ensuring the gas-liquid phase balance between the rising gas phase and the reflux liquid phase in the distillation tower, while also maintaining the heat balance in the tower; the gas outlet at the top of the methanol distillation tower 22 is connected to the methanol distillation tower condenser 23; the methanol distillation tower condenser 23 is connected to the flash condensate tank 15 through a pipeline;

[0045] Furthermore, the solid-liquid separator 16 is any one of the devices that can separate solids from liquids, such as a filter press, a centrifuge, or a filter; the dryer 17 is any one of the devices that can dry oxalamide, such as a disc dryer, a paddle dryer, or a vacuum dryer.

[0046] Furthermore, the solid-liquid separator 16 and the dryer 17 are a separation and drying integrated machine.

[0047] The present invention also provides a continuous and efficient method for preparing oxalamide, which can be implemented using the above-mentioned device for preparing continuous and efficient oxalamide, comprising the following steps:

[0048] S1, dimethyl oxalate and liquid ammonia are passed through a dimethyl oxalate feed tank 1 and a liquid ammonia buffer tank 4 respectively, and the dimethyl oxalate feed tank 1 heats the dimethyl oxalate to keep the dimethyl oxalate in a molten state; then the molten dimethyl oxalate and liquid ammonia are pressurized respectively, and after reaching the reaction pressure, they are respectively passed into a dimethyl oxalate preheater 2 and an alcohol ammonia mixer 6; dimethyl oxalate is preheated in the dimethyl oxalate preheater 2 and then enters an alcohol ester mixer 3; circulating methanol is heated in a circulating methanol heat exchanger 9 and then respectively fed into the alcohol ester mixer 3 and the alcohol ammonia mixer 6 to obtain an alcohol ester solution and an alcohol ammonia solution; wherein the mass ratio of dimethyl oxalate to methanol in the alcohol ester solution is 1:0.7-5; the mass ratio of ammonia to methanol in the alcohol ammonia solution is 1:4-8, and the molar ratio of ammonia to dimethyl oxalate in the alcohol ester solution and the alcohol ammonia solution is greater than 2;

[0049] S2, placing the alcohol ester solution and the alcohol ammonia solution in the reactor 10 at a temperature of 100-200° C., a reaction time of 10-60 min, and a reaction pressure of 1.0-5.0 MPa for ammonolysis reaction, while collecting the heat released by the reaction through the steam drum 11 to produce 0.1-2.0 MPa of steam; the generated reaction liquid enters the reaction liquid receiving tank 12, and then enters the flash evaporation device 13 for flash evaporation to obtain flash steam and flash liquid. After the flash steam in the flash evaporation device 13 is condensed by heat exchange, circulating methanol is obtained;

[0050] S3, sending the flash liquid in the flash evaporation device 13 to the solid-liquid separator 16 for solid-liquid separation, producing a solid phase and a liquid phase respectively, and the solid phase is dried in the dryer 17 to obtain oxamide.

[0051] Furthermore, in S2, the flash evaporation device 13 includes a primary flash tank 13a and a secondary flash tank 13b. The reaction liquid in the reaction liquid receiving tank 12 first enters the primary flash tank 13a for flash evaporation, and then the primary flash liquid in the primary flash tank 13a is sent to the secondary flash tank 13b for flash evaporation. The obtained secondary flash steam is passed into the flash condenser 14 for condensation and then sent to the flash condensate tank 15 to obtain flash steam condensate; at the same time, the secondary flash liquid in the secondary flash tank 13b is sent to the solid-liquid separator 16 for solid-liquid separation to obtain a solid phase and a liquid phase.

[0052] Furthermore, the solid phase is dried by the dryer 17 to obtain methanol vapor, which is sent to the methanol condenser 18 for condensation to obtain methanol condensate, and then the methanol condensate enters the methanol condensate tank 19; the liquid phase enters the filtrate tank 20, and the liquid phase in the filtrate tank 20 is divided into two parts. One part of the liquid phase is mixed with the methanol condensate in the methanol condensate tank 19 to obtain a methanol mixed liquid, which is sent to the flash condensate tank 15, and the other part is heated by the feed preheater 21 and passed into the methanol distillation tower 22 for methanol refining; methanol and ammonia mixed gas is obtained at the top of the methanol distillation tower 22, and after condensation by the methanol distillation tower condenser 23, a methanol distillation tower top condensate is obtained, which is sent to the flash condensate tank 15; refined methanol is obtained at the bottom of the methanol distillation tower 22, and the refined methanol is divided into two parts, one part is returned to the methanol distillation tower 22 through the reboiler 24, and the other part passes through the heat exchange tube of the feed preheater 21, exchanges heat with the liquid phase and is cooled to obtain a methanol product.

[0053] Furthermore, the flash condensate in the flash condensate tank 15 , the condensate from the top of the methanol distillation tower and the methanol mixed liquid are mixed and then placed in the circulating heat exchanger 7 .

[0054] Furthermore, the first-stage flash tank 13a flashes out first-stage flash steam, which is sequentially heat-exchanged and condensed with the circulating heat exchanger 7 and the dimethyl oxalate preheater 2. If the first-stage flash steam has been condensed into a liquid, the first-stage flash steam condensate is obtained. If not, the first-stage flash steam condensate is condensed through the final cooler 5. The first-stage flash steam condensate passes through the circulating methanol buffer tank 8, is mixed with the mixed liquid of the circulating heat exchanger 7, and is then sent to the circulating methanol heat exchanger 9 to provide circulating methanol for recycling.

[0055] The method provided by the present invention is illustrated below with several embodiments.

[0056] Example 1

[0057] S1, dimethyl oxalate and liquid ammonia are passed through the dimethyl oxalate feed tank 1 and the liquid ammonia buffer tank 4 respectively, the dimethyl oxalate feed tank 1 heats the dimethyl oxalate to keep the dimethyl oxalate in a molten state; then the molten dimethyl oxalate and liquid ammonia are pressurized respectively, and after reaching the reaction pressure, they are respectively passed into the dimethyl oxalate preheater 2 and the alcohol ammonia mixer 6; dimethyl oxalate is preheated in the dimethyl oxalate preheater 2 and then enters the alcohol ester mixer 3; the circulating methanol is heated in the circulating methanol heat exchanger 9 and then respectively fed into the alcohol ester mixer 3 and the alcohol ammonia mixer 6 to obtain an alcohol ester solution and an alcohol ammonia solution; wherein the mass ratio of dimethyl oxalate to methanol in the alcohol ester solution is 1:2; the mass ratio of ammonia to methanol in the alcohol ammonia solution is 1:4, and the molar ratio of ammonia to dimethyl oxalate in the alcohol ester solution and the alcohol ammonia solution is 2.3:1;

[0058] S2, placing the alcohol ester solution and the alcohol ammonia solution in the reactor 10 at a temperature of 130°C, a reaction time of 45 minutes, and a reaction pressure of 1.5 MPa for ammonolysis reaction. During the reaction, the heat released by the reaction is collected by the steam drum 11 to produce 0.3 MPa of steam; the resulting reaction liquid enters the reaction liquid receiving tank 12, and then enters the flash evaporation device 13 for flash evaporation;

[0059] Under this reaction pressure, only one-stage flash evaporation is adopted; the reaction liquid enters the flash evaporation device 13 for flash evaporation, which will produce flash steam and flash liquid; the flash steam in the flash evaporation device 13 is heat exchanged and condensed with the circulating heat exchanger 7, the dimethyl oxalate preheater 2 and the final cooler 5 respectively to obtain flash steam condensate, which then enters the circulating methanol buffer tank 8; the condensate at the top of the methanol distillation tower in the flash condensate tank 15 is mixed with the methanol mixed liquid and then enters the circulating heat exchanger 7; the flash steam condensate in the circulating methanol buffer tank 8 is mixed with the mixed liquid of the circulating heat exchanger 7 and then sent to the circulating methanol heat exchanger 9 to provide circulating methanol for recycling, wherein the mixed liquid in the circulating heat exchanger 7 is mainly methanol, and the rest is a trace amount of liquid ammonia;

[0060] S3, sending the flash liquid in the flash evaporation device 13 to a filter press for solid-liquid separation, producing a solid phase and a liquid phase respectively, and drying the solid phase in a paddle vacuum dryer to obtain oxalamide and methanol vapor; in the preparation process, the conversion rate of dimethyl oxalate is 100%, and the yield of oxalamide is 97.8%;

[0061] Methanol vapor is sent to the methanol condenser 18 for condensation to obtain methanol condensate, which is then sent to the methanol condensate tank 19; the liquid phase enters the filtrate tank 20, and the liquid phase in the filtrate tank 20 is divided into two parts. One part of the liquid phase is mixed with the methanol condensate in the methanol condensate tank 19 to obtain a methanol mixed liquid, which is sent to the flash condensate tank 15, and the other part is heated by the feed preheater 21 and passed into the methanol distillation tower 22 for methanol refining; methanol and ammonia mixed gas is obtained at the top of the methanol distillation tower 22, and after condensation in the methanol distillation tower condenser 23, a methanol distillation tower top condensate is obtained, which is sent to the flash condensate tank 15; refined methanol is obtained at the bottom of the methanol distillation tower 22, and the refined methanol is divided into two parts. One part passes through the reboiler 24 and returns to the distillation tower, and the other part passes through the feed preheater 21, exchanges heat with the liquid phase and is cooled to obtain a methanol product.

[0062] Example 2

[0063] S1, dimethyl oxalate and liquid ammonia are passed through a dimethyl oxalate feed tank 1 and a liquid ammonia buffer tank 4 respectively, and the dimethyl oxalate feed tank 1 heats the dimethyl oxalate to keep the dimethyl oxalate in a molten state; then the molten dimethyl oxalate and liquid ammonia are pressurized respectively, and after reaching the reaction pressure, they are respectively passed into a dimethyl oxalate preheater 2 and an alcohol ammonia mixer 6; dimethyl oxalate is preheated in the dimethyl oxalate preheater 2 and then enters an alcohol ester mixer 3; circulating methanol is heated in a circulating methanol heat exchanger 9 and then respectively fed into the alcohol ester mixer 3 and the alcohol ammonia mixer 6 to obtain an alcohol ester solution and an alcohol ammonia solution; wherein the mass ratio of dimethyl oxalate to methanol in the alcohol ester solution is 1:4; the mass ratio of ammonia to methanol in the alcohol ammonia solution is 1:8, and the molar ratio of ammonia to dimethyl oxalate in the alcohol ester solution and the alcohol ammonia solution is 2.05:1;

[0064] S2, placing the alcohol ester solution and the alcohol ammonia solution in the reactor 10 at a temperature of 150°C, a reaction time of 30 minutes, and a reaction pressure of 2.5 MPa for ammonolysis reaction, while collecting the heat released by the reaction through the steam drum 11 to produce 0.5 MPa steam;

[0065] The generated reaction liquid enters the reaction liquid receiving tank 12, and then enters the first-level flash tank 13a for flash evaporation, wherein the first-level flash steam flashed out is sequentially heat-exchanged and condensed with the circulating heat exchanger 7 and the dimethyl oxalate preheater 2. If it has been condensed into a liquid, a first-level flash steam condensate is obtained. If not, it is condensed through the final cooler 5, and the first-level flash steam condensate passes through the circulating methanol buffer tank 8. The flash steam condensate in the flash condensate tank 15 and the methanol distillation tower top condensate are mixed with the methanol mixed liquid and placed in the circulating heat exchanger 7; the first-level flash steam condensate of the circulating methanol buffer tank 8 is mixed with the liquid of the circulating heat exchanger 7 and sent to the circulating methanol heat exchanger 9 to provide circulating methanol for recycling; the first-level flash liquid in the first-level flash tank 13a is then sent to the second-level flash tank 13b for flash evaporation to obtain second-level flash steam and second-level flash liquid. The second-level flash steam is passed into the flash condenser 14 and condensed and then sent to the flash condensate tank 15 to obtain flash steam condensate;

[0066] S3, the secondary flash liquid in the secondary flash tank 13b is sent to a centrifuge for solid-liquid separation, producing a solid phase and a liquid phase respectively. The solid phase is dried in a disc vacuum dryer to obtain oxalamide and methanol vapor; during the preparation process, the conversion rate of dimethyl oxalate is 100%, and the yield of oxalamide is 97.8%.

[0067] Methanol vapor is sent to the methanol condenser 18 for condensation to obtain methanol condensate, which is then sent to the methanol condensate tank 19; the liquid phase enters the filtrate tank 20, and the liquid phase in the filtrate tank 20 is divided into two parts. One part of the liquid phase is mixed with the methanol condensate in the methanol condensate tank 19 to obtain a methanol mixed liquid, which is sent to the flash condensate tank 15, and the other part is heated by the feed preheater 21 and passed into the methanol distillation tower 22 for methanol refining; methanol and ammonia mixed gas is obtained at the top of the methanol distillation tower 22, and after condensation in the methanol distillation tower condenser 23, a methanol distillation tower top condensate is obtained, which is sent to the flash condensate tank 15; refined methanol is obtained at the bottom of the methanol distillation tower 22, and the refined methanol is divided into two parts. One part passes through the reboiler 24 and returns to the distillation tower, and the other part passes through the feed preheater 21, exchanges heat with the liquid phase and is cooled to obtain a methanol product.

[0068] Example 3:

[0069] S1, dimethyl oxalate and liquid ammonia are passed through the dimethyl oxalate feed tank 1 and the liquid ammonia buffer tank 4 respectively, the dimethyl oxalate feed tank 1 heats the dimethyl oxalate to keep the dimethyl oxalate in a molten state; then the molten dimethyl oxalate and liquid ammonia are pressurized respectively, and after reaching the reaction pressure, they are respectively passed into the dimethyl oxalate preheater 2 and the alcohol ammonia mixer 6; dimethyl oxalate is preheated in the dimethyl oxalate preheater 2 and then enters the alcohol ester mixer 3; the circulating methanol is heated in the circulating methanol heat exchanger 9 and then respectively fed into the alcohol ester mixer 3 and the alcohol ammonia mixer 6 to obtain an alcohol ester solution and an alcohol ammonia solution; wherein the mass ratio of dimethyl oxalate to methanol in the alcohol ester solution is 1:08; the mass ratio of ammonia to methanol in the alcohol ammonia solution is 1:6, and the molar ratio of ammonia to dimethyl oxalate in the alcohol ester solution and the alcohol ammonia solution is 2.5:1;

[0070] S2, placing the alcohol ester solution and the alcohol ammonia solution in the reactor 10 at a temperature of 180°C, a reaction time of 20 minutes, and a reaction pressure of 3.0 MPa for ammonolysis reaction, while collecting the heat released by the reaction through the steam drum 11 to produce 1.0 MPa steam;

[0071] The generated reaction liquid enters the reaction liquid receiving tank 12, and then enters the first-level flash tank 13a for flash evaporation, wherein the first-level flash steam flashed out is sequentially heat-exchanged and condensed with the circulating heat exchanger 7 and the dimethyl oxalate preheater 2. If it has been condensed into a liquid, a first-level flash steam condensate is obtained. If not, it is condensed through the final cooler 5, and the first-level flash steam condensate passes through the circulating methanol buffer tank 8. The flash steam condensate in the flash condensate tank 15 and the methanol distillation tower top condensate are mixed with the methanol mixed liquid and placed in the circulating heat exchanger 7; the first-level flash steam condensate of the circulating methanol buffer tank 8 is mixed with the liquid of the circulating heat exchanger 7 and sent to the circulating methanol heat exchanger 9 to provide circulating methanol for recycling; the first-level flash liquid in the first-level flash tank 13a is then sent to the second-level flash tank 13b for flash evaporation to obtain second-level flash steam and second-level flash liquid. The second-level flash steam is passed into the flash condenser 14 and condensed and then sent to the flash condensate tank 15 to obtain flash steam condensate;

[0072] S3, the secondary flash liquid in the secondary flash tank 13b is sent to a separation and drying integrated machine for solid-liquid separation, producing a solid phase and a liquid phase respectively. After the solid phase is dried, oxalamide and methanol vapor are obtained, wherein the solid-liquid separator 16 and the dryer 17 are a separation and drying integrated machine; during the preparation process, the conversion rate of dimethyl oxalate is 100%, and the yield of oxalamide is 99.8%;

[0073] Methanol vapor is sent to the methanol condenser 18 for condensation to obtain methanol condensate, which is then sent to the methanol condensate tank 19; the liquid phase enters the filtrate tank 20, and the liquid phase in the filtrate tank 20 is divided into two parts. One part of the liquid phase is mixed with the methanol condensate in the methanol condensate tank 19 to obtain a methanol mixed liquid, which is sent to the flash condensate tank 15, and the other part is heated by the feed preheater 21 and passed into the methanol distillation tower 22 for methanol refining; methanol and ammonia mixed gas is obtained at the top of the methanol distillation tower 22, and after condensation in the methanol distillation tower condenser 23, a methanol distillation tower top condensate is obtained, which is sent to the flash condensate tank 15; refined methanol is obtained at the bottom of the methanol distillation tower 22, and the refined methanol is divided into two parts. One part passes through the reboiler 24 and returns to the distillation tower, and the other part passes through the feed preheater 21, exchanges heat with the liquid phase and is cooled to obtain a methanol product.

Claims

1. A device for continuously preparing oxalamide, characterized in that: It includes a feeding unit, a reaction unit and an oxalamide separation unit. The feeding unit comprises a dimethyl oxalate feeding tank (1), a liquid ammonia buffer tank (4), a dimethyl oxalate preheater (2), an alcohol ester mixer (3), an alcohol ammonia mixer (6) and a circulating methanol heat exchanger (9); The discharge port of the dimethyl oxalate feed tank (1) is connected to the feed port of the dimethyl oxalate preheater (2) through a pipeline, and the discharge port of the dimethyl oxalate preheater (2) is connected to the alcohol ester mixer (3) through a pipeline; the discharge port of the liquid ammonia buffer tank (4) is connected to the alcohol ammonia mixer (6) through a pipeline; and the discharge port of the circulating methanol heat exchanger (9) is connected to the alcohol ester mixer (3) and the alcohol ammonia mixer (6) through pipelines respectively; The reaction unit comprises a reactor (10), a steam drum (11), a reaction liquid receiving tank (12) and a flash evaporation device (13); The discharge ports of the alcohol-ester mixer (3) and the alcohol-ammonia mixer (6) are both connected to the reactor (10) through pipelines; the reactor (10) is connected to the steam drum (11) through pipelines, and the discharge port of the reactor (10) is connected to the reaction liquid receiving tank (12) through pipelines; the liquid outlet of the reaction liquid receiving tank (12) is connected to the flash evaporation device (13) through pipelines; The oxalamide separation unit comprises a solid-liquid separator (16) and a dryer (17), The liquid outlet of the flash evaporation device (13) is connected to the solid-liquid separator (16) through a pipeline; the material outlet of the solid-liquid separator (16) is connected to the dryer (17) through a pipeline; The flash evaporation device (13) comprises a primary flash evaporation tank (13a), the gas outlet of the primary flash evaporation tank (13a) being connected to a circulating heat exchanger (7), a dimethyl oxalate preheater (2) and a final cooler (5) in sequence through a gas outlet pipe; the dimethyl oxalate preheater (2) and the final cooler (5) are both connected to a circulating methanol buffer tank (8) through pipelines; the circulating heat exchanger (7) and the circulating methanol buffer tank (8) are both connected to a circulating methanol heat exchanger (9) through pipelines.

2. The device for continuously preparing oxalamide according to claim 1, characterized in that: The flash device (13) further comprises a secondary flash tank (13b), wherein the liquid outlet of the primary flash tank (13a) is connected to the secondary flash tank (13b) via a pipeline, the liquid outlet of the secondary flash tank (13b) is connected to a solid-liquid separator (16) via a pipeline, and the gas outlet of the secondary flash tank (13b) is connected to a flash condenser (14) via a pipeline; the flash condenser (14) is connected to a flash condensate tank (15) via a pipeline; and the flash condensate tank (15) is connected to a circulating heat exchanger (7) via a pipeline.

3. The device for continuously preparing oxalamide according to claim 1, characterized in that: The invention also comprises a methanol separation unit, wherein the methanol separation unit comprises a methanol condenser (18), a methanol condensate tank (19), a filtrate tank (20), a feed preheater (21), a methanol distillation tower (22), a methanol distillation tower condenser (23) and a reboiler (24); The gas outlet of the dryer (17) is connected to the methanol condenser (18) through a pipeline; the methanol condenser (18) is connected to the methanol condensate tank (19) through a pipeline; the liquid outlet of the solid-liquid separator (16) is connected to the filtrate tank (20) through a pipeline; the filtrate tank (20) and the methanol condensate tank (19) are both connected to the flash condensate tank (15) through pipelines, and the filtrate tank (20) is also connected to the feed preheater (21) through a pipeline; the feed preheater (21) is connected to the methanol condensate tank (19) through a pipeline. The methanol distillation tower (22) is connected to the feed port of the methanol distillation tower (22), and the first liquid outlet at the bottom of the methanol distillation tower (22) is connected to the feed preheater (21) through a pipeline; the second liquid outlet at the bottom of the methanol distillation tower (22) is connected to the reboiler feed port of the methanol distillation tower (22) through a pipeline through a reboiler (24); the gas outlet at the top of the methanol distillation tower (22) is connected to the methanol distillation tower condenser (23); the methanol distillation tower condenser (23) is connected to the flash condensate tank (15) through a pipeline.

4. The device for continuously preparing oxalamide according to any one of claims 1 to 3, characterized in that: The solid-liquid separator (16) is any one of a filter press, a centrifuge or a filter; the dryer (17) is any one of a disc dryer, a paddle dryer or a vacuum dryer.

5. The device for continuously preparing oxalamide according to any one of claims 1 to 3, characterized in that: The solid-liquid separator (16) and the dryer (17) are a separation and drying integrated machine.

6. A continuous oxalamide preparation method, characterized in that: The following steps are involved: S1, dimethyl oxalate and liquid ammonia are passed through a dimethyl oxalate feed tank (1) and a liquid ammonia buffer tank (4) respectively, and the dimethyl oxalate feed tank (1) heats the dimethyl oxalate to keep the dimethyl oxalate in a molten state; then the molten dimethyl oxalate and liquid ammonia are pressurized respectively, and after reaching the reaction pressure, they are respectively passed into a dimethyl oxalate preheater (2) and an alcohol ammonia mixer (6); dimethyl oxalate is preheated in the dimethyl oxalate preheater (2) and then enters an alcohol ester mixer (3); circulating methanol is heated in a circulating methanol heat exchanger (9) and then respectively sent into an alcohol ester mixer (3) and an alcohol ammonia mixer (6) to obtain an alcohol ester solution and an alcohol ammonia solution; wherein the mass ratio of dimethyl oxalate to methanol in the alcohol ester solution is 1:0.7-5; the mass ratio of ammonia to methanol in the alcohol ammonia solution is 1:4-8, and the molar ratio of ammonia to dimethyl oxalate in the alcohol ester solution and the alcohol ammonia solution is greater than 2; S2, placing the alcohol ester solution and the alcohol ammonia solution in a reactor (10) at a temperature of 100 to 200° C., a reaction time of 10 to 60 minutes, and a reaction pressure of 1.0 to 5.0 MPa to carry out an ammonolysis reaction, while collecting the heat released by the reaction through a steam drum (11) to produce 0.1 to 2.0 MPag of steam; the generated reaction liquid enters a reaction liquid receiving tank (12), and then enters a flash evaporation device (13) for flash evaporation to obtain flash steam and flash liquid, and after the flash steam in the flash evaporation device (13) is condensed by heat exchange, circulating methanol is obtained; S3, sending the flash liquid in the flash evaporation device (13) to a solid-liquid separator (16) for solid-liquid separation, producing a solid phase and a liquid phase respectively, and the solid phase is dried in a dryer (17) to obtain oxalamide.

7. The continuous oxalamide preparation method according to claim 6, characterized in that: In S2, the flash evaporation device (13) comprises a primary flash tank (13a) and a secondary flash tank (13b). The reaction liquid in the reaction liquid receiving tank (12) first enters the primary flash tank (13a) for flash evaporation to obtain primary flash liquid and primary flash steam. The primary flash liquid is then sent to the secondary flash tank (13b) for flash evaporation to obtain secondary flash liquid and secondary flash steam. The secondary flash steam is passed into a flash condenser (14) for condensation and then sent to a flash condensate tank (15) to obtain flash steam condensate. At the same time, the secondary flash liquid is sent to a solid-liquid separator (16) for solid-liquid separation to obtain a solid phase and a liquid phase.

8. The continuous oxalamide preparation method according to claim 6 or 7, characterized in that: The solid phase is dried by the dryer (17) to obtain methanol vapor, which is then sent to the methanol condenser (18) for condensation to obtain methanol condensate, which is then sent to the methanol condensate tank (19); the liquid phase enters the filtrate tank (20), and the liquid phase in the filtrate tank (20) is divided into two parts, one part of the liquid phase is mixed with the methanol condensate in the methanol condensate tank (19) to obtain a methanol mixed liquid, which is then sent to the flash condensate tank (15), and the other part is heated by the feed preheater (21). , and is passed into a methanol distillation tower (22) for methanol refining; a methanol and ammonia mixed gas is obtained at the top of the methanol distillation tower (22), and after condensation in a methanol distillation tower condenser (23), a methanol distillation tower top condensate is obtained, which is sent to a flash condensate tank (15); refined methanol is obtained at the bottom of the methanol distillation tower (22), and the refined methanol is divided into two parts, one part is returned to the methanol distillation tower (22) through a reboiler (24), and the other part is passed through a feed preheater (21), and after heat exchange with the liquid phase and cooling, a methanol product is obtained.

9. The continuous oxalamide preparation method according to claim 8, characterized in that: The flash condensate in the flash condensate tank (15), the condensate from the top of the methanol rectification tower and the methanol mixed liquid are mixed and then passed into the circulating heat exchanger (7).

10. The continuous oxalamide preparation method according to claim 9, characterized in that: The first-stage flash steam is sequentially heat exchanged and condensed with the circulating heat exchanger (7) and the dimethyl oxalate preheater (2). If the first-stage flash steam has been condensed into liquid, the first-stage flash steam condensate is obtained. If not, the first-stage flash steam condensate is condensed in the final cooler (5). The first-stage flash steam condensate passes through the circulating methanol buffer tank (8), is mixed with the mixed liquid of the circulating heat exchanger (7), and is then sent to the circulating methanol heat exchanger (9) for heating, thereby providing circulating methanol for recycling.

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