A method and apparatus for producing oxamide

Abstract

The application provides a device and a method for producing oxamide, the device comprising: a reaction device; a gas-liquid separation device; a solid-liquid separation device; a drying device; a crude rectification tower; a methanol purification system; a washing condensation tower; and an alcohol-ester mixer. The application uses relatively high-level heat energy generated by an ammonolysis reaction for drying of oxamide powder, uses relatively low-level heat energy for reboiling of the crude rectification tower, introduces second alcohol-ammonia gas phase generated by the drying device into the crude rectification tower to fully utilize the heat energy, and uses adsorption or membrane separation for refining treatment of crude methanol obtained from the crude rectification tower, so that the ammonia content in refined methanol can be reduced to 1 ppm. The process technical solution provided by the application fully utilizes heat of the ammonolysis reaction and waste heat of the drying device, and uses adsorption or membrane separation for methanol refining, so that the production cost of oxamide can be significantly reduced. Furthermore, the solution provided by the application can produce high-purity methanol for sale or return to a dimethyl oxalate synthesis section.

Description

Technical Field

[0001] This application relates to the field of novel fertilizer production technology, and in particular to a method and apparatus for producing oxalamide. Background Technology

[0002] Oxalide is a highly efficient slow-release nitrogen fertilizer with advantages such as non-toxicity, low solubility in water, and long-lasting effects. When used properly, it can effectively promote plant growth and improve crop yield and quality. The preparation of oxalamide via ammonolysis of dimethyl oxalate and liquid ammonia is a commonly used industrial production method, which offers advantages such as mild reaction conditions and readily available raw materials.

[0003] In the process of preparing oxalamide through ammonolysis of dimethyl oxalate and liquid ammonia, methanol is produced as a byproduct of the ammonolysis reaction. To ensure stable operation of the unit, this byproduct methanol needs to be extracted from the oxalamide production unit. If the extracted methanol is to be sold externally, it must meet the specifications stipulated in "Industrial Methanol" (GB / T 338-2011). In plants that co-produce oxalamide from dimethyl oxalate, methanol can be returned to the dimethyl oxalate production section. In this case, the extracted methanol needs to meet the specifications required by the dimethyl oxalate section; for example, to extend the lifespan of the dimethyl oxalate synthesis catalyst, the lower the dimethyl oxalate and ammonia content, the better. Current technology generally uses distillation to separate methanol from ammonia or dimethyl oxalate. However, distillation consumes a large amount of steam, exceeding 0.3 tons per ton of methanol. Moreover, to reduce the dimethyl oxalate or ammonia content in methanol to 1 ppm, a higher reflux ratio is required for distillation, resulting in even greater steam consumption. Summary of the Invention

[0004] In view of this, this application provides a method and apparatus for producing oxamide. When the method and apparatus provided in this application are used to produce oxamide, they make full use of the heat of ammonolysis reaction and the waste heat of the gas in the drying device, which can significantly reduce the production cost of oxamide.

[0005] This application provides an apparatus for producing oxamide, comprising:

[0006] A reaction apparatus for ammonolysis reactions of alcohols in the liquid phase and alcohol esters in the liquid phase;

[0007] A gas-liquid separation device whose material inlet is connected to the material outlet of the reaction apparatus;

[0008] A solid-liquid separation device in which the material inlet is connected to the liquid phase material outlet of the gas-liquid separation device;

[0009] A drying device whose material inlet is connected to the solid material outlet of the solid-liquid separation device;

[0010] A crude distillation column whose liquid material inlet is connected to the liquid material outlet of the solid-liquid separation device, and whose gas material inlet is connected to the gas material outlet of the drying device;

[0011] A methanol purification system in which the liquid material inlet is connected to the liquid material outlet of the crude distillation column;

[0012] A washing and condensing tower is connected to the gas phase material inlet of the crude distillation column, the gas phase material outlet of the gas-liquid separation device, the liquid phase material outlet of the solid-liquid separation device, and the gas phase material outlet of the methanol purification system.

[0013] An alcohol-ester mixer is connected to the liquid material inlet of the washing and condensing tower, the material outlet of the dimethyl oxalate supply unit, the material outlet of the methanol supply unit, and the liquid material outlet of the solid-liquid separation unit. The liquid material outlet of the alcohol-ester mixer is connected to the liquid material inlet of the washing and condensing tower and the liquid material inlet of the reaction unit.

[0014] In some specific implementations, the liquid phase material outlet of the solid-liquid separation device is connected to the material inlet of the reaction device.

[0015] In some specific implementations, the reaction apparatus includes:

[0016] Reactors used for ammonolysis reactions of alcohols in the liquid phase and alcohols in the liquid phase; and

[0017] A purifier has its material inlet connected to the material outlet of the reactor, and the material outlet of the purifier is connected to the material inlet of the gas-liquid separation device. In some specific implementations, the purifier includes a first-stage purifier connected to the material outlet of the reactor and a second-stage purifier connected to the material outlet of the first-stage purifier.

[0018] The relatively high residual heat of the first stage purifier provides thermal energy to the drying device through the first heat transfer device;

[0019] The relatively low residual heat of the second-stage purifier provides thermal energy to the crude distillation column through a second heat transfer device.

[0020] In some specific implementations, the crude distillation column is equipped with a condenser at the top and a reboiler at the bottom.

[0021] In some specific implementations, the relatively low residual heat of the second stage purifier provides thermal energy to the reboiler of the crude distillation column through a second heat transfer device.

[0022] In some specific implementations, the purifier can also be divided into multiple sections, such as a first section, a second section, and a third section connected in series. The heat removed from the first section of the purifier is used for the drying device, the heat removed from the second section of the purifier is used for the reboiler of the crude distillation column, and the heat removed from the third section of the purifier is used for the preheating of the reactants.

[0023] In some specific implementations, the liquid phase material outlet of the solid-liquid separation device is connected to the material inlet of the reactor.

[0024] In some specific implementations, the methanol purification system is an adsorption device or a membrane separation device.

[0025] In some specific implementations, the apparatus further includes a final scrubbing tower connected to the gaseous material outlet of the scrubbing condenser.

[0026] This application also provides a method for producing oxamide, using the system described in the above technical solution, comprising the following steps:

[0027] The first alcohol ester liquid phase mixture produced by the washing and condensing tower, the fourth alcohol ammonia liquid phase mixture produced by the solid-liquid separation device, and dimethyl oxalate are mixed in an alcohol ester mixer to obtain an alcohol ester liquid phase mixture, which is further divided into a third alcohol ester liquid phase mixture and a second alcohol ester liquid phase mixture.

[0028] The first alcohol-ammonia liquid phase mixture produced by the solid-liquid separation device is mixed with liquid ammonia to obtain a third alcohol-ammonia liquid phase mixture;

[0029] The third alcohol ester liquid phase mixture and the third alcohol ammonia liquid phase mixture are mixed and then subjected to ammonolysis to obtain the first slurry. The first slurry is then subjected to gas-liquid separation to obtain the second slurry and the first alcohol ammonia gas phase mixture.

[0030] The second slurry is subjected to solid-liquid separation to obtain a third slurry and an alcohol-ammonia liquid phase mixture. The third slurry is dried to obtain oxalamide solid product and a second alcohol-ammonia gas phase mixture. The alcohol-ammonia liquid phase mixture is divided into a first alcohol-ammonia liquid phase mixture, a second alcohol-ammonia liquid phase mixture, a fourth alcohol-ammonia liquid phase mixture and a fifth alcohol-ammonia liquid phase mixture.

[0031] The second alcohol-ammonia liquid mixture and the second alcohol-ammonia gas mixture are processed in a crude distillation column to obtain a third alcohol-ammonia gas mixture and crude methanol, and the crude methanol is then purified.

[0032] The fifth alcohol-ammonia liquid phase mixture, the third alcohol-ammonia gas phase mixture, the first alcohol-ammonia gas phase mixture, and the regenerated gas are washed in a washing and condensing tower to obtain the first alcohol ester liquid phase and process tail gas.

[0033] In some specific implementations, dimethyl oxalate is in slight excess relative to ammonia in the washing condenser, and the pressure is slightly positive.

[0034] In some specific implementations, the liquid ammonia meets or exceeds the specifications of superior grade of "Anhydrous Liquid Ammonia" (GB / T536-2017) and has undergone fine dehydration treatment.

[0035] The apparatus for producing oxamide provided in this application includes: a reaction apparatus for ammonolysis of alcohols in liquid phase and alcohol esters in liquid phase; a gas-liquid separation apparatus with its material inlet connected to the material outlet of the reaction apparatus; a solid-liquid separation apparatus with its material inlet connected to the liquid phase material outlet of the gas-liquid separation apparatus; a drying apparatus with its material inlet connected to the solid phase material outlet of the solid-liquid separation apparatus; a crude distillation column with its liquid phase material inlet connected to the liquid phase material outlet of the solid-liquid separation apparatus, wherein the gas phase material inlet of the crude distillation column is connected to the gas phase material outlet of the drying apparatus; and a liquid phase material inlet connected to the crude distillation column. The application includes a methanol purification system connected to the liquid phase material outlet; a washing and condensing tower connected to the gas phase material outlets of the crude distillation column, the gas phase material outlet of the gas-liquid separation device, the liquid phase material outlet of the solid-liquid separation device, and the methanol purification system; an alcohol-ester mixer connected to the liquid phase material outlets of the washing and condensing tower, the dimethyl oxalate supply device, and the solid-liquid separation device; and a liquid phase material outlet of the alcohol-ester mixer connected to the liquid phase material inlet of the washing and condensing tower and the reaction device. This application utilizes the relatively high-grade heat energy generated by the ammonolysis reaction for drying oxalamide powder, and the relatively low-grade heat energy for reboiling the crude distillation column. The alcohol-ammonia gas phase generated by the drying device is introduced into the distillation column to fully utilize its heat energy. The crude methanol obtained from the distillation column is purified by adsorption or membrane separation to obtain refined methanol. The process technology provided by this application can fully utilize the heat of the ammonolysis reaction and the waste heat of the drying device, reducing the consumption of utilities for oxalamide drying and alcohol-ammonia separation, thereby reducing the production cost of oxalamide. Furthermore, the apparatus provided in this application can produce high-purity methanol for external sale or be returned to the dimethyl oxalate synthesis section for use. Attached Figure Description

[0036] Figure 1 A schematic diagram of the production apparatus provided in the embodiments of this application;

[0037] Figure 2 This is a schematic diagram of the methanol purification device provided in this application;

[0038] The following labels are shown in the attached diagram:

[0039] 1-Methanol-ammonia mixer, 2-Reactor, 3-Purifier, 4-Flash tank, 5-Filter, 6-Dryer, 7-Raw distillation column, 8-Methanol purification system, 9-Washing condenser, 10-Methanol-ester mixer, 11-Final washing column, 111-Raw methanol buffer tank, 112-Methanol-ammonia separation unit. Detailed Implementation

[0040] It should be understood that the expression “one or more of…” individually includes each of the objects described after the expression, as well as various different combinations of two or more of the described objects, unless otherwise understood from the context and usage. The expression “and / or” combined with three or more described objects should be understood to have the same meaning, unless otherwise understood from the context.

[0041] The terms “including,” “having,” or “containing,” including the use of their grammatical synonyms, should generally be understood as open-ended and non-restrictive, for example, not excluding other unstated elements or steps, unless otherwise specifically stated or understood from the context.

[0042] It should be understood that the order of steps or the sequence of actions is not important as long as this application remains operational. Furthermore, two or more steps or actions can be performed simultaneously.

[0043] The use of any and all instances or exemplary language such as “e.g.” or “including” herein is merely intended to better illustrate the application and does not constitute a limitation on the scope of the application unless the claims are made. No language in this specification should be construed as indicating that any unclaimed element is essential to the practice of this application.

[0044] Furthermore, the numerical ranges and parameters used to define this application are approximate values, and the relevant values ​​in the specific embodiments have been presented as precisely as possible. However, any numerical value inevitably contains standard deviations due to individual test methods. Therefore, unless otherwise explicitly stated, it should be understood that all ranges, quantities, values, and percentages used in this disclosure are modified with the word "approximately." Here, "approximately" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a specific value or range.

[0045] This application provides an apparatus for producing oxamide, comprising:

[0046] A reaction apparatus for ammonolysis reactions of alcohols in the liquid phase and alcohol esters in the liquid phase;

[0047] A gas-liquid separation device whose material inlet is connected to the material outlet of the reaction apparatus;

[0048] A solid-liquid separation device in which the material inlet is connected to the liquid phase material outlet of the gas-liquid separation device;

[0049] A drying device whose material inlet is connected to the solid material outlet of the solid-liquid separation device;

[0050] A crude distillation column whose liquid material inlet is connected to the liquid material outlet of the solid-liquid separation device, and whose gas material inlet is connected to the gas material outlet of the drying device;

[0051] A methanol purification system in which the liquid material inlet is connected to the liquid material outlet of the crude distillation column;

[0052] A washing and condensing tower is connected to the gas phase material inlet of the crude distillation column, the gas phase material outlet of the gas-liquid separation device, the liquid phase material outlet of the solid-liquid separation device, and the gas phase material outlet of the methanol purification system.

[0053] An alcohol-ester mixer is connected to the liquid material inlet of the washing and condensing tower, the material outlet of the dimethyl oxalate supply unit, the material outlet of the methanol supply unit, and the liquid material outlet of the solid-liquid separation unit. The liquid material outlet of the alcohol-ester mixer is connected to the liquid material inlet of the washing and condensing tower and the liquid material inlet of the reaction unit.

[0054] See Figure 1 , Figure 1 The diagram below shows the structure of the production apparatus provided in the embodiments of this application, wherein 1 is an alcohol-ammonia mixer, 2 is a reactor, 3 is a purifier, 4 is a flash tank, 5 is a filter, 6 is a dryer, 7 is a crude distillation column, 8 is a methanol purification system, 9 is a washing and condensing column, 10 is an alcohol-ester mixer, and 11 is a final washing column.

[0055] The apparatus provided in this application includes a reaction unit for ammonolysis reactions of alcohols in ammonia and alcohols in a liquid phase. In some specific implementations, the reaction unit includes a reactor 2 and a purifier 3 connected in series. Dimethyl oxalate and ammonia undergo a first ammonolysis reaction in reactor 2, and the product of the first ammonolysis reaction enters purifier 3 for a second ammonolysis reaction to obtain a first slurry. In some specific implementations, reactor 2 is an adiabatic reactor, which is beneficial for improving the heat energy grade of the reaction.

[0056] In some specific implementations, purifier 3 is a purifier with heat exchange function, which not only performs deep ammonolysis but also removes the heat of reaction. In some specific implementations, purifier 3 includes a first-stage purifier (i.e., stage A) connected to the material outlet of reactor 2 and a second-stage purifier (i.e., stage B) connected to the material outlet of the first-stage purifier. The first-stage purifier can reduce the temperature of the reactants to approximately 100°C; the removed heat (i.e., waste heat) is referred to as relatively higher heating energy. The second-stage purifier reduces the temperature of the reactants to approximately 80°C; the removed heat (i.e., waste heat) is referred to as relatively lower heating energy. In some specific implementations, the relatively higher heating energy of the first-stage purifier provides heat energy to the drying device through a first heat transfer device. The relatively lower heating energy of the second-stage purifier provides heat energy to the crude distillation column through a second heat transfer device.

[0057] Furthermore, the purifier 3 includes a first-stage purifier connected to the material outlet of reactor 2, a second-stage purifier connected to the material outlet of the first-stage purifier, and a third-stage purifier connected to the material outlet of the second-stage purifier. That is, it includes the first-stage purifier, the second-stage purifier, and the third-stage purifier connected in series. The heat removed from the first-stage purifier is used for a drying device, the heat removed from the second-stage purifier is used for the reboiler of the crude distillation column, and the heat removed from the third-stage purifier is used for preheating the reactants. The apparatus for producing oxalamide provided in this application includes an alcohol-ammonia mixer 1. The material inlet of the alcohol-ammonia mixer 1 is connected to the material outlet of a methanol supply device, the material outlet of a liquid ammonia supply device, and the liquid phase outlet of a filter 5. During the initial operation of the apparatus, no first alcohol-ammonia liquid phase mixture is produced at the liquid phase outlet of the filter 5. At this time, the methanol supply device needs to provide methanol and anhydrous liquid ammonia to mix and obtain a third alcohol-ammonia liquid phase. When the liquid phase outlet of the filter 5 can produce the first alcohol-ammonia liquid phase, the methanol supply device does not need to supply methanol. The material outlet of the alcohol-ammonia mixer 1 is connected to the material inlet of the reactor 2, providing alcohol-ammonia feedstock to the reactor 2. In some specific implementations, the methanol can be industrial methanol, whose quality meets or exceeds the superior grade specifications in "Industrial Methanol" (GB / T 338-2011) and has undergone fine dehydration treatment.

[0058] The apparatus provided in this application includes an alcohol-ester mixer 10. The material inlet of the alcohol-ester mixer 10 is connected to the material outlet of a dimethyl oxalate supply unit, the material outlet of a methanol supply unit, the liquid phase material outlet of a washing condenser 9, and the liquid phase material outlet of a filter 5. The purpose of the alcohol-ester mixer 10 is to mix dimethyl oxalate and methanol to obtain a methanol solution containing dimethyl oxalate, and to supply the methanol solution to the reaction unit and the washing condenser for ammonolysis and washing of ammonia-containing tail gas, respectively. During the initial operation of the apparatus, no fourth alcohol-ammonia liquid phase mixture is produced at the liquid phase outlet of the filter 5. At this time, the methanol supply unit needs to supply methanol and dimethyl oxalate to obtain a methanol solution containing dimethyl oxalate. Part of the methanol solution containing dimethyl oxalate is sent to the washing condenser 9, and part is sent to the reactor 2. As the reaction proceeds, the fourth alcohol-ammonia liquid phase mixture is produced at the liquid phase outlet of the filter 5 and sent to the alcohol-ester mixer 10, and the flow rate gradually increases. The methanol supply from the methanol supply unit can be gradually reduced until it is completely stopped.

[0059] The apparatus provided in this application includes a flash tank 4, the material inlet of which is connected to the material outlet of a purifier 3. It is used for gas-liquid separation of the first slurry obtained after the ammonolysis reaction, yielding a first alcohol-ammonia gas phase and a second slurry. In other implementations, the flash tank 4 can be replaced with other gas-liquid separation devices capable of separating the gas and liquid phases; this application has no particular limitations. This application utilizes the heat of reaction to flash-concentrate the first slurry and enrich ammonia in the gas phase, facilitating subsequent separation of ammonia and methanol.

[0060] The apparatus provided in this application includes a filter 5, the material inlet of which is connected to the liquid phase outlet of a flash tank 4, for filtering the second slurry to achieve solid-liquid separation and obtain an alcohol-ammonia liquid phase and a third slurry. The liquid phase outlet of the filter 5 is connected to the liquid phase material inlets of an alcohol-ammonia mixer 1, a crude distillation column 7, and an alcohol-ester mixer 10, respectively. In some specific implementations, the filter can be a horizontal screw centrifuge, a plate filter, etc., as long as it can achieve inert gas sealing of the filter to prevent the material inside the filter from contacting air and achieve effective filtration. In other implementations, the filter 5 can be replaced with other solid-liquid separation devices that can separate the solid and liquid phases; this application has no special limitations.

[0061] The apparatus provided in this application includes a dryer 6, the material inlet of which is connected to the solid material outlet of a filter 5, for drying a third slurry to prepare oxalamide powder and a second alcohol ammonia gas phase. The dryer 6 can be a combination dryer of atmospheric pressure drying and high vacuum drying, or a single-stage high vacuum dryer. Drying the powder under high vacuum can reduce the temperature required for drying, thereby reducing the requirements of the dryer on the grade of the drying heat source; it can also remove impurities such as methanol and ammonia from the oxalamide powder to the greatest extent possible, thus obtaining high-purity oxalamide powder.

[0062] The apparatus provided in this application includes a crude distillation column 7. The liquid material inlet of the crude distillation column 7 is connected to the liquid material outlet of the filter 5, and the gaseous material inlet of the crude distillation column 7 is connected to the gaseous material outlet of the dryer 6. The second alcohol-ammonia gas phase generated by the dryer 6 does not need to be cooled before entering the crude distillation column 7. It enters directly from the lower middle part of the crude distillation column 7, so that its internal energy can be fully utilized, thereby reducing the heat input of the reboiler.

[0063] In some specific implementations, the liquid inlet of the crude distillation column 7 is located in the upper middle part of the column, while the gas inlet is located in the lower middle part. In some specific implementations, a condenser is installed at the top of the crude distillation column 7 to partially condense the gas at the top of the column. The condensed liquid phase is used for reflux in the distillation column, while the uncondensed ammonia-containing gas is sent to the lower part of the washing and condensing column 9. In some specific implementations, a reboiler is installed in the bottom section of the column. Its heat is obtained from the second section of the purifier 3. Heat can be obtained from the purifier 3 using heat transfer media such as heat transfer oil or water to provide heat for the reboiler, or the bottom liquid can be pressurized and directly exchanged with the reactants in the purifier 3.

[0064] The apparatus provided in this application includes a methanol purification system 8, the liquid material inlet of which is connected to the liquid material outlet of the crude distillation column 7 for purifying methanol. Specifically, the methanol purification system 8 can be an adsorption purification system, a membrane separation purification system, or another low-energy-consumption purification system, rather than a high-energy-consumption traditional purification system such as distillation.

[0065] In one specific implementation, the methanol purification system 8 includes:

[0066] A crude methanol buffer tank whose material inlet is connected to the liquid material outlet of crude distillation column 7;

[0067] An alcohol-ammonia separation unit whose material inlet is connected to the liquid phase material outlet of a crude methanol buffer tank.

[0068] See Figure 2 , Figure 2This is a schematic diagram of the methanol purification system provided in an embodiment of this application. The methanol purification system 8 includes a crude methanol buffer tank 111, which can buffer the methanol produced by the crude distillation column 7. The methanol purification system 8 includes an alcohol-ammonia separation device 112, which is used to further refine the crude methanol. The alcohol-ammonia separation device uses non-distillation processes such as adsorption separation or membrane separation, and the ammonia content of the refined methanol can be reduced to 1 ppm. The regeneration gas outlet of the alcohol-ammonia separation device 112 is connected to the washing and condensing column 9 and returns to the washing and condensing column 9 to participate in the reaction.

[0069] The apparatus provided in this application includes a washing and condensing tower 9. The gaseous material inlet of the washing and condensing tower 9 is connected to the gaseous material outlet of the crude distillation tower 7 and the methanol purification system 8, respectively. The liquid material inlet is connected to the liquid material outlet of the methanol supply device, the filter 5, and the alcohol-ester mixer 10. The second alcohol-ester liquid phase in the alcohol-ester mixer 10 and the fourth alcohol-ammonia liquid phase in the filter 5 are used to wash the third alcohol-ammonia gas phase in the crude distillation tower 7 and the regeneration gas in the methanol purification system 8. In some specific implementations, the gaseous material inlet of the washing and condensing tower 9 is also connected to other gas supply devices. The sealing gas, safety valve discharge gas, and other inert gases required by the device discharged from other gas supply devices are washed, condensed, and separated in the washing and condensing tower 9. Ammonia is reacted and transferred to the liquid phase, methanol is partially condensed, and part of it goes to the final washing tower 11 with the uncondensed process tail gas.

[0070] In some specific implementations, the washing and condensing tower 9 has a three-section structure, consisting of a methanol condensation section, a gas washing section, and a reboiler section from top to bottom. The gaseous material inlet is located at the bottom of the gas washing section, and the gaseous material enters the washing and condensing tower 9 from the bottom of the gas washing section. The liquid material, including the second alcohol ester liquid phase and the fifth alcohol ammonia liquid phase, enters the reboiler section and mixes with the washing liquid cascading down from the gas washing section to obtain a circulating liquid. After pressurization, part of the circulating liquid enters the upper part of the gas washing section to wash the gaseous material from top to bottom, while the other part is transported as the second alcohol ester liquid phase to the alcohol ester mixer 10. The process tail gas containing non-condensable gases such as methanol and nitrogen obtained at the top of the washing and condensing tower is sent to the final washing tower 11.

[0071] In some specific implementations, the cooling medium for methanol condensation in the methanol condensation section can be circulating water or other cooling media. It can be staged condensation or single-stage condensation. The cooling medium for the last stage of condensation is preferably chilled water.

[0072] The apparatus provided in this application includes a final scrubbing tower 11, the gaseous material inlet of the final scrubbing tower 11 is connected to the gaseous material outlet of the scrubbing condensing tower 9, the process gas obtained from the scrubbing condensing tower 9 is treated with demineralized water, the resulting gas phase is discharged into the atmosphere, and the liquid phase is treated as wastewater and then used as a carbon source supplement for biochemical treatment.

[0073] To reduce energy loss, the external components of the alcohol-ammonia mixer, alcohol-ester mixer, reactor, purifier, flash evaporator, dryer, and corresponding pipelines for conveying the above substances in this application are preferably insulated. This application does not impose any special restrictions on the insulation measures, and commonly used insulation measures by those skilled in the art are acceptable.

[0074] This application also provides a method for producing oxamide, using the system described in the above technical solution, comprising the following steps:

[0075] The first alcohol ester liquid phase mixture produced by the washing and condensing tower, the fourth alcohol ammonia liquid phase mixture produced by the solid-liquid separation device, and dimethyl oxalate are mixed in an alcohol ester mixer to obtain an alcohol ester liquid phase mixture, which is further divided into a third alcohol ester liquid phase mixture and a second alcohol ester liquid phase mixture.

[0076] The first alcohol-ammonia liquid phase mixture produced by the solid-liquid separation device is mixed with liquid ammonia to obtain a third alcohol-ammonia liquid phase mixture;

[0077] The third alcohol ester liquid phase mixture and the third alcohol ammonia liquid phase mixture are mixed and then subjected to ammonolysis to obtain the first slurry. The first slurry is then subjected to gas-liquid separation to obtain the second slurry and the first alcohol ammonia gas phase mixture.

[0078] The second slurry is subjected to solid-liquid separation to obtain a third slurry and an alcohol-ammonia liquid phase mixture. The third slurry is dried to obtain oxalamide solid product and a second alcohol-ammonia gas phase mixture. The alcohol-ammonia liquid phase mixture is divided into a first alcohol-ammonia liquid phase mixture, a second alcohol-ammonia liquid phase mixture, a fourth alcohol-ammonia liquid phase mixture and a fifth alcohol-ammonia liquid phase mixture.

[0079] The second alcohol-ammonia liquid mixture and the second alcohol-ammonia gas mixture are processed in a crude distillation column to obtain a third alcohol-ammonia gas mixture and crude methanol, and the crude methanol is then purified.

[0080] The fifth alcohol-ammonia liquid phase mixture, the third alcohol-ammonia gas phase mixture, the first alcohol-ammonia gas phase mixture, and the regenerated gas are washed in a washing and condensing tower to obtain the first alcohol ester liquid phase and process tail gas.

[0081] This application uses a first alcohol ester liquid phase mixture produced by a washing and condensing tower, a fourth alcohol ammonia liquid phase mixture produced by a solid-liquid separation unit, and a third alcohol ester liquid phase mixture obtained by mixing dimethyl oxalate as alcohol ester raw materials. Oxalide is prepared by ammonolysis using a third alcohol ammonia liquid phase mixture obtained by mixing the first alcohol ammonia liquid phase produced by the solid-liquid separation unit and liquid ammonia as alcohol ammonia raw materials. During initial startup, the first, fourth, and fifth alcohol ammonia liquid phases from the filtration unit can be replaced with industrial methanol. The industrial methanol must meet or exceed the superior grade specifications in "Industrial Methanol" (GB / T 338-2011) and undergo fine dehydration treatment.

[0082] In some specific implementations, the third alcohol ester liquid phase mixture mainly comprises dimethyl oxalate, methanol, a small amount of ammonium methyl oxalate and oxalamide, with the mass fraction of dimethyl oxalate being 5%wt to 60%wt. In some specific implementations, the third alcohol ester liquid phase going to the reactor can be preheated, preferably at a temperature of 65℃ to 100℃, more preferably 70℃ to 90℃.

[0083] In some specific implementations, the third alcohol-ammonia liquid phase mixture includes liquid ammonia and methanol, wherein the mass fraction of liquid ammonia is 5% to 50%.

[0084] This application involves mixing the liquid phase of a third alcohol ammonia and the liquid phase of a third alcohol ester, and then carrying out an ammonolysis reaction in a reactor and a purifier. The pressure of the ammonolysis reaction in the reactor is 0.05 MPa to 5.0 MPa, preferably 1.0 MPa to 2.0 MPa; the temperature is 65℃ to 180℃, preferably 110℃ to 150℃; and the residence time of the reactants in the reactor is 0.5 min to 60 min. In some specific implementations, the pressure of the ammonolysis reaction in the purifier is 0.05 MPa to 5.0 MPa, preferably 1.0 MPa to 2.0 MPa; and the temperature is 65℃ to 180℃, preferably 80℃ to 150℃.

[0085] In some specific implementations, this application uses a heat-conducting medium to cool the purifier, thereby recovering and reusing the heat of the ammonolysis reaction. This application does not have any special limitations on the heat-conducting medium; it can be heat-conducting oil, demineralized water, or the process medium within the device, such as the bottom liquid of a distillation column.

[0086] In some specific implementations, the inlet temperature of the heat transfer medium in the first stage of the purifier is preferably 80℃~110℃; the outlet temperature is preferably 110℃~140℃. The heat gained by the heat transfer medium is used for the subsequent drying of oxamide, which can reduce the external heat consumption of oxamide drying. In some specific implementations, the heat transfer medium in the second stage of the purifier is the bottom liquid of a distillation column. After being pressurized, the bottom liquid of the distillation column exchanges heat with the reaction medium in the second stage of the purifier, reducing the temperature of the reaction medium to 70℃~90℃.

[0087] In some specific implementations, when the alcohol ester and alcohol amine undergo ammonolysis in the reactor, the molar ratio of ammonia to dimethyl oxalate is greater than 2.05, preferably 2.05 to 2.3.

[0088] After the ammonolysis reaction is complete, the obtained first slurry is subjected to gas-liquid separation, for example, by flash evaporation, to obtain a first alcohol-ammonia gas phase and a second slurry. The first alcohol-ammonia gas phase includes ammonia and methanol, wherein the ammonia content is preferably 1 wt% to 15 wt%. The second slurry mainly includes oxalamide, methanol, and ammonia, wherein the oxalamide content is preferably 3 wt% to 35 wt%.

[0089] After obtaining the second slurry, the second slurry is subjected to solid-liquid separation to obtain an alcohol-ammonia liquid phase and a third slurry. The alcohol-ammonia liquid phase includes methanol and liquid ammonia, wherein the content of liquid ammonia is preferably 0.01wt%~1wt%, more preferably 0.05wt%~0.5wt%; the third slurry contains methanol, ammonia, and oxalamide, wherein the content of oxalamide is preferably 55wt%~75wt%, more preferably 60wt%~70wt%. After obtaining the alcohol-ammonia liquid phase, it is divided into a first alcohol-ammonia liquid phase, a second alcohol-ammonia liquid phase, a fourth alcohol-ammonia liquid phase, and a fifth alcohol-ammonia liquid phase. The first alcohol-ammonia liquid phase is returned to the alcohol-ammonia mixer to be mixed with liquid ammonia to obtain the third alcohol-ammonia liquid phase. The second alcohol-ammonia liquid phase is sent to the crude distillation column for processing. The fourth alcohol-ammonia liquid phase replaces industrial methanol in the alcohol-ester mixer, and the fifth alcohol-ammonia liquid phase replaces industrial methanol in the washing condenser.

[0090] After obtaining the third slurry, the third slurry is dried to obtain oxalamide powder product and second alcohol ammonia gas phase. This application does not impose any special limitations on the drying process; it can be a combination of an atmospheric pressure dryer and a high-vacuum dryer, or it can be a standalone high-vacuum dryer. In some specific implementations, the operating pressure of the high-vacuum dryer is 0.01 PaA to 50 PaA, preferably 0.1 PaA to 10 PaA.

[0091] In some specific implementations, the ammonia content in the second alcohol-ammonia gas phase is preferably 0.01wt%~1wt%, and more preferably 0.05wt%~0.5wt%.

[0092] This application feeds the second alcohol ammonia gas phase and the second alcohol ester liquid phase into a crude distillation column for processing. In some specific implementations, the second alcohol ammonia gas phase enters the crude distillation column from the lower middle section, and the second alcohol ester liquid phase enters from the upper middle section. A third alcohol ammonia gas phase containing ammonia and methanol is obtained at the top of the column, and crude methanol is obtained at the bottom. In some specific implementations, the ammonia content in the crude methanol is less than 200 ppm. In some specific implementations, the third alcohol ammonia gas phase contains ammonia and methanol, wherein the ammonia content is approximately 0.1 wt% to 15 wt%. In some specific implementations, a reboiler is installed at the bottom of the crude distillation column, and a condenser is installed at the top of the crude distillation column. This application utilizes the methanol and ammonia vapors generated during the drying process of the third slurry and the relatively low heat energy of the second stage of the purifier to process the second alcohol-ammonia liquid phase separated by the filtration device, obtaining crude methanol with a purity of less than 200 ppm. The crude methanol is then refined using a non-distillation process, which not only improves the purity of the by-product methanol but also significantly reduces the energy consumption required to obtain refined methanol. In other words, the refined by-product methanol can be obtained without consuming any additional steam or heat source, thereby reducing steam consumption and lowering production costs.

[0093] This application purifies the crude methanol to obtain refined methanol with an ammonia content of less than 1 ppm. This application does not impose any particular limitation on the purification method; it can be an adsorption process or a membrane separation process, or any process that does not consume a large amount of steam. In some specific implementations, the purification process is an adsorption process, for example, using 3A molecular sieves. In some specific implementations, the regeneration gas generated during adsorbent regeneration is returned to a washing and condensing tower for further treatment.

[0094] This application feeds a third alcohol-ammonia gaseous mixture, a first alcohol-ammonia gaseous mixture, and regenerated gas into a scrubbing condenser for treatment, yielding a first alcohol ester liquid phase and process tail gas. In some specific implementations, this application also feeds sealing gas and safety valve exhaust gas into the scrubbing condenser.

[0095] In some specific implementations, the washing and condensing tower has a three-section structure, consisting of a methanol condensation section, a gas washing section, and a reboiler section from top to bottom. The gaseous material enters the washing and condensing tower 9 from the lower part of the gas washing section. The liquid material, including the second alcohol ester liquid phase and the fifth alcohol ammonia liquid phase, enters the reboiler section and mixes with the washing liquid cascading from the gas washing section to form a circulating liquid. After pressurization, part of the circulating liquid enters the upper part of the gas washing section to wash the gaseous material from top to bottom, while the other part is transported as the second alcohol ester liquid phase to the alcohol ester mixer 10. The process tail gas containing non-condensable gases such as methanol and nitrogen, obtained at the top of the washing and condensing tower, is sent to the final washing tower 11.

[0096] In some specific implementations, the pressure of the washing condenser is slightly positive; in the washing condenser, dimethyl oxalate is in slight excess, that is, to remove as much ammonia as possible from the ammonia-containing gas. In some specific implementations, the molar ratio of dimethyl oxalate to ammonia is approximately 0.505~0.51:1. In some specific implementations, the cooling medium of the washing condenser can be circulating water or other cooling media; the condensation can be single-stage condensation or staged condensation, with the final stage using chilled water.

[0097] In some specific implementations, the second alcohol ester liquid phase mixture mainly includes dimethyl oxalate, methanol, a small amount of ammonium methyl oxalate and oxalamide, wherein the mass fraction of dimethyl oxalate is 5%wt to 60%wt, preferably 30%wt to 45%wt.

[0098] After processing in the washing and condensing tower, a first alcohol ester liquid phase and process gas are obtained. The main components of the first alcohol ester liquid phase include dimethyl oxalate, methanol, a small amount of ammonium methyl oxalate and oxalamide. The mass fraction of dimethyl oxalate is 0.1%wt to 5%wt, preferably 0.5%wt to 2%wt.

[0099] In some specific implementations, when the washing condenser is first started up, a portion of industrial methanol needs to be added to maintain the bottom liquid level and dimethyl oxalate concentration of the washing condenser at appropriate levels; during normal operation, the bottom liquid level and dimethyl oxalate concentration of the washing condenser are maintained at appropriate levels by adding the fifth alcohol-ammonia liquid phase.

[0100] This application mixes a first alcohol ester liquid phase, a fourth alcohol ammonia liquid phase, and dimethyl oxalate to obtain a third alcohol ester liquid phase, which is used as a raw material for the ammonolysis reaction. The third alcohol ester liquid phase is as described above and will not be repeated here.

[0101] After obtaining the process tail gas, it is washed with demineralized water. The washed gas phase is non-condensable and can be discharged into the atmosphere at high altitude. The liquid phase is a process condensate containing methanol, which can be used as a carbon source for biochemical treatment after wastewater treatment.

[0102] This application proposes an integrated process route encompassing "reaction-separation-waste heat-exhaust gas," with the following core innovations and significant advantages:

[0103] 1. Adiabatic reactors improve the grade of thermal energy and couple the reaction heat to make full use of the reaction heat.

[0104] This application uses an adiabatic reactor, in which the majority of the ammonolysis reaction of dimethyl oxalate takes place. Depending on the concentration and ratio of the reactants, the temperature rise of the reactants in the reactor varies, and industrially, the temperature rise range is generally controlled between 20℃ and 80℃. The reaction apparatus of this application includes a reactor and a purifier. The use of an adiabatic reactor can improve the heat energy grade. The purifier is a two-stage heat exchange reactor. The relatively high heat energy removed from stage A of the purifier is used for drying oxalamide, and the use of high heat energy can reduce the heat exchange area of ​​the dryer. The relatively low heat energy removed from stage B of the purifier is used for the reboiler of the distillation column with lower heat energy grade requirements.

[0105] 2. The reboiler of the crude distillation column utilizes the relatively low heat energy of the reactor and the latent heat of the gas to achieve crude ammonia removal with "zero external steam".

[0106] The crude distillation column operates under slightly positive pressure, with a bottom operating temperature of approximately 64°C. This application divides the purifier into two sections, A and B. The reactant temperature exiting section A of the purifier is approximately 100°C, which meets the heat energy grade requirements of the crude distillation column reboiler. This application also directly introduces the second alcohol-ammonia gas phase generated by the drying unit into the lower middle section of the distillation column, fully utilizing its heat energy for alcohol-ammonia separation. The crude distillation column reboiler of this application utilizes relatively low heating energy and latent heat of the gas, achieving a reduction of ammonia content in the bottom liquid to <200 ppm with "zero external steam replenishment."

[0107] 3. Methanol purification uses adsorption / membrane separation, which can reduce separation energy consumption;

[0108] This application introduces crude methanol with an ammonia concentration of <200 ppm into an adsorption (molecular sieve or resin) or membrane separation unit. After purification, the ammonia content in the methanol can be reduced to 1 ppm, thus enabling high-purity methanol to be sold externally or returned to the dimethyl oxalate synthesis section. Low ammonia concentration methanol significantly improves the catalyst lifespan in dimethyl oxalate synthesis. Since the ammonia content in the distilled methanol is already very low, the amount of adsorbent can be reduced, or not reduced at all, thus reducing the number of adsorbent regeneration cycles. Both methods are significantly more energy-efficient than distillation.

[0109] 4. A three-stage scrubbing condensing tower can reduce investment costs.

[0110] The washing and condensing tower is arranged from top to bottom as "methanol condensation section - gas washing section - tower bottom section". One unit can perform both washing and condensation functions, which can reduce equipment investment.

[0111] Calculation results show that the process provided in this application can achieve a steam consumption of less than 0.4t per ton for oxamide production, improve the quality of by-product methanol, and significantly reduce the production cost of oxamide.

[0112] The present invention is further illustrated below with reference to the embodiments. The scope of protection of the present invention is not limited to the following embodiments.

[0113] Example 1

[0114] This embodiment provides an apparatus for producing oxamide, see [link to apparatus]. Figure 1 It includes:

[0115] An alcohol-ammonia mixer 1 is used for mixing the first alcohol-ammonia liquid phase and liquid ammonia or for mixing methanol and liquid ammonia during operation;

[0116] An insulated reactor 2 connected to the material outlet of the alcohol-ammonia mixer 1;

[0117] The purifier 3 is connected to the material outlet of the reactor 2. The purifier 3 includes a first-stage purifier and a second-stage purifier connected in series. The waste heat of the first-stage purifier is transferred to the dryer 6 through heat transfer oil, and the waste heat of the second-stage purifier is transferred to the reboiler of the crude distillation column 7 through heat transfer oil.

[0118] The flash tank 4 is connected to the material outlet of the purifier 3, and the gas phase outlet of the flash tank 4 is connected to the gas phase inlet of the washing and condensing tower 9.

[0119] A filter 5 is connected to the liquid phase outlet of the flash tank 4; the liquid phase outlet of the filter 5 is connected to the alcohol-ammonia mixer 1 and the crude distillation column 7 respectively.

[0120] A dryer 6 is connected to the solid outlet of the filter 5, and the liquid outlet of the dryer 6 is connected to the liquid inlet of the crude distillation column 7.

[0121] A methanol purification system 8 is connected to the liquid phase outlet of the crude distillation column 7;

[0122] The washing and condensing tower 9 is connected to the gas phase outlet of the flash tank 4, the gas phase outlet of the crude distillation tower 7, and the regeneration gas outlet of the methanol purification system 8, respectively. The liquid phase outlet of the washing and condensing tower 9 is connected to the liquid phase inlet of the alcohol-ester mixer 10. The liquid phase inlet of the washing and condensing tower is connected to the liquid phase outlet of the alcohol-ester mixer 10, the liquid phase outlet of the filter 5, and the material outlet of the methanol supply unit.

[0123] An alcohol-ester mixer 10 is connected to the liquid phase material inlet of the washing and condensing tower 9, the material outlet of the dimethyl oxalate supply device, the material outlet of the methanol supply device, and the liquid phase material outlet of the filter 5. The liquid phase outlet of the alcohol-ester mixer 10 is connected to the liquid phase inlet of the reactor 2 and the washing and condensing tower 9, respectively.

[0124] Example 2

[0125] The preparation of oxamide using the system provided in Example 1 includes the following steps:

[0126] Liquid ammonia and the first alcohol-ammonia liquid phase from filter 5 are mixed in alcohol-ammonia mixer 1 to obtain a third alcohol-ammonia liquid phase, wherein the mass fraction of liquid ammonia in the third alcohol-ammonia liquid phase is approximately 43%;

[0127] The first alcohol-ammonia liquid phase, the first alcohol-ester liquid phase, and dimethyl oxalate from the washing condenser 9 are mixed in the alcohol-ester mixer 10 to obtain the third alcohol-ester liquid phase, wherein the mass fraction of dimethyl oxalate in the third alcohol-ester liquid phase is approximately 44%.

[0128] The third alcohol ammonia liquid phase and the third alcohol ester liquid phase are mixed and reacted in adiabatic reactor 2. The reacted material enters purifier 3 for cooling and purification to obtain the first slurry. The pressure of adiabatic reactor 2 is 1.5 MPa, and the molar ratio of ammonia to dimethyl oxalate is 2.2. The outlet temperature of adiabatic reactor 2 is about 143℃. The temperature of the reactant material exiting the first purifier is controlled at 105℃, and the temperature of the reactant material exiting the second purifier is controlled at 80℃.

[0129] The first slurry is flash-distilled to obtain a gas phase containing ammonia and methanol, and a liquid phase containing oxalamide, methanol and ammonia.

[0130] The second slurry is filtered through a plate filter to obtain a liquid phase and a third slurry. The liquid phase is an alcohol-ammonia liquid phase. In the third slurry, oxalamide accounts for approximately 65 wt%. The alcohol-ammonia liquid phase is divided into a first alcohol-ammonia liquid phase, a second alcohol-ammonia liquid phase, a fourth alcohol-ammonia liquid phase, and a fifth alcohol-ammonia liquid phase. The first alcohol-ammonia liquid phase is returned to the alcohol-ammonia mixer 1 to be mixed with liquid ammonia to obtain the third alcohol-ammonia liquid phase. The second alcohol-ammonia liquid phase enters the crude distillation column 7. The fourth alcohol-ammonia liquid phase replaces industrial methanol in the alcohol-ester mixer 10. The fifth alcohol-ammonia liquid phase replaces industrial methanol in the washing and condensing column 9.

[0131] After the third slurry is dried in dryer 6, oxalamide powder product and second alcohol ammonia gas phase are obtained;

[0132] The second ammonia liquid phase enters from the upper middle part of the crude distillation column 7, and the second ammonia gas phase enters from the lower middle part of the crude distillation column 7. The liquid in the bottom of the column is pressurized and sent to the second-stage purifier for heat exchange before returning to the bottom of the crude distillation column. Crude methanol with an ammonia content of less than 200 ppm and the third ammonia gas phase are obtained in the bottom of the crude distillation column. The crude methanol is purified using a 3A molecular sieve to obtain refined methanol with an ammonia content of less than 1 ppm.

[0133] The washing and condensing tower is configured from top to bottom as follows: "methanol condensation section - gas washing section - tower bottom section". The third methanol-ammonia gas phase, the first methanol-ammonia gas phase, the regeneration gas from the methanol purification system, as well as sealing gas and safety valve exhaust gas, enter from the lower part of the gas washing section of the washing and condensing tower 9 and are washed by a mixed liquid phase containing dimethyl oxalate. The operating pressure of the washing and condensing tower 9 is slightly positive, and the dimethyl oxalate content is greater than the dimethyl oxalate content required for the ammonia reaction, meaning the ammonia reaction is complete according to chemical equilibrium. The ammonia in the methanol is washed to produce oxalamide or ammonium oxalate methyl ester. Methanol vapor flows from the gas washing section to the methanol condensation section, where it is condensed in two stages: the first stage uses circulating water for cooling, and the second stage uses chilled water for cooling.

[0134] The first alcohol ester liquid phase mixture, the fourth alcohol ammonia liquid phase mixture, and dimethyl oxalate are mixed in alcohol ester mixer 10. The process tail gas is washed with demineralized water. The methanol content in the gas phase is lower than the limit required by environmental regulations and can be directly discharged at high altitude. The liquid phase contains methanol, which is used to supplement the carbon source after wastewater treatment.

[0135] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in this application, based on the technical solution and inventive concept of this application, should be included within the scope of protection of this application.

Claims

1. An apparatus for producing oxalamide, characterized in that, include: A reaction apparatus for ammonolysis reactions of alcohols in the liquid phase and alcohol esters in the liquid phase; A gas-liquid separation device whose material inlet is connected to the material outlet of the reaction apparatus; A solid-liquid separation device in which the material inlet is connected to the liquid phase material outlet of the gas-liquid separation device; A drying device whose material inlet is connected to the solid material outlet of the solid-liquid separation device; A crude distillation column whose liquid material inlet is connected to the liquid material outlet of the solid-liquid separation device, and whose gas material inlet is connected to the gas material outlet of the drying device; A methanol purification system in which the liquid material inlet is connected to the liquid material outlet of the crude distillation column; A washing and condensing tower is connected to the gas phase material inlet of the crude distillation column, the gas phase material outlet of the gas-liquid separation device, the liquid phase material outlet of the solid-liquid separation device, and the gas phase material outlet of the methanol purification system. An alcohol-ester mixer is connected to the liquid material inlet of the washing and condensing tower, the material outlet of the dimethyl oxalate supply unit, the material outlet of the methanol supply unit, and the liquid material outlet of the solid-liquid separation unit. The liquid material outlet of the alcohol-ester mixer is connected to the liquid material inlet of the washing and condensing tower and the liquid material inlet of the reaction unit.

2. The apparatus according to claim 1, characterized in that, The liquid phase material outlet of the solid-liquid separation device is connected to the material inlet of the reaction device.

3. The apparatus according to claim 1, characterized in that, The reaction apparatus includes: Reactors used for ammonolysis reactions of alcohols in the liquid phase and alcohols in the liquid phase; and A purifier whose material inlet is connected to the material outlet of the reactor, and whose material outlet is connected to the material inlet of the gas-liquid separation device.

4. The apparatus according to claim 3, characterized in that, The purifier includes a first-stage purifier connected to the material outlet of the reactor and a second-stage purifier connected to the material outlet of the first-stage purifier. The relatively high residual heat of the first stage purifier provides thermal energy to the drying device through the first heat transfer device; The relatively low residual heat of the second-stage purifier provides thermal energy to the crude distillation column through a second heat transfer device.

5. The apparatus according to claim 4, characterized in that, The crude distillation column is equipped with a condenser at the top and a reboiler at the bottom.

6. The apparatus according to claim 5, characterized in that, The relatively low residual heat of the second stage purifier provides thermal energy to the reboiler of the crude distillation column through the second heat transfer device.

7. The apparatus according to any one of claims 1 to 6, characterized in that, The methanol purification system is an adsorption device or a membrane separation device.

8. The apparatus according to claim 1, characterized in that, It also includes a final scrubbing tower connected to the gaseous material outlet of the scrubbing condenser.

9. A method for producing oxalamide, characterized in that, Production using the apparatus according to any one of claims 1 to 8 includes the following steps: The first alcohol ester liquid phase mixture produced by the washing and condensing tower, the fourth alcohol ammonia liquid phase mixture produced by the solid-liquid separation device, and dimethyl oxalate are mixed in an alcohol ester mixer to obtain an alcohol ester liquid phase mixture, which is further divided into a third alcohol ester liquid phase mixture and a second alcohol ester liquid phase mixture. The first alcohol-ammonia liquid phase mixture produced by the solid-liquid separation device is mixed with liquid ammonia to obtain a third alcohol-ammonia liquid phase mixture; The third alcohol ester liquid phase mixture and the third alcohol ammonia liquid phase mixture are mixed and then subjected to ammonolysis to obtain the first slurry. The first slurry is then subjected to gas-liquid separation to obtain the second slurry and the first alcohol ammonia gas phase mixture. The second slurry is subjected to solid-liquid separation to obtain a third slurry and an alcohol-ammonia liquid phase mixture. The third slurry is dried to obtain oxalamide solid product and a second alcohol-ammonia gas phase mixture. The alcohol-ammonia liquid phase mixture is divided into a first alcohol-ammonia liquid phase mixture, a second alcohol-ammonia liquid phase mixture, a fourth alcohol-ammonia liquid phase mixture and a fifth alcohol-ammonia liquid phase mixture. The second alcohol-ammonia liquid mixture and the second alcohol-ammonia gas mixture are processed in a crude distillation column to obtain a third alcohol-ammonia gas mixture and crude methanol, and the crude methanol is then purified. The fifth alcohol-ammonia liquid phase mixture, the third alcohol-ammonia gas phase mixture, the first alcohol-ammonia gas phase mixture, regeneration gas, sealing gas, and safety valve exhaust gas are washed in a scrubbing condenser to obtain the first alcohol ester liquid phase and process tail gas.

10. The method according to claim 9, characterized in that, In the washing and condensing tower, dimethyl oxalate is in excess relative to ammonia, and the pressure is slightly positive.

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