A preparation method for synthesizing diethyl oxalate

Abstract

The present application discloses a preparation method for synthesizing diethyl oxalate, which relates to the technical field of diethyl oxalate, and includes the following steps: Step ①, put oxalic acid, ethanol, toluene and a catalytic adsorption solid material into a reaction kettle for mixing; Step ②, gradually raise the temperature of the reaction kettle from room temperature to 105-108 °C, and keep the temperature constant until dehydration is completed to obtain an esterification mixture; Step ③, raise the temperature of the esterification mixture to 128-130 °C, then remove toluene, and then cool down to separate diethyl oxalate and the catalytic adsorption solid material. The present application has the effect of achieving the purpose of reducing the preparation difficulty of diethyl oxalate, simplifying the process and improving the preparation efficiency.

Description

Technical Field

[0001] The present application relates to the technical field of diethyl oxalate, and in particular to a method for preparing synthetic diethyl oxalate. Background Art

[0002] Esterification is an organic reaction in which alcohols react with acids to form esters and water. Among them, the esterification reaction between carboxylic acids and alcohols is reversible and generally reacts very slowly, so concentrated sulfuric acid is often used as a catalyst. Polycarboxylic acids react with alcohols to form a variety of esters. A typical esterification reaction is the reaction between ethanol and acetic acid, which produces ethyl acetate with an aromatic odor, which is a raw material for making dyes and medicines. Esterification reactions are widely used in organic synthesis and other fields.

[0003] The Chinese patent application document with publication number CN108003020A discloses a method for preparing diethyl oxalate using toluene as a solvent. The method for preparing diethyl oxalate using toluene as a solvent comprises the following steps: 1) adding materials: 800 kg of industrial oxalic acid, 1000 L of ethanol, and 1100 L of toluene solvent are sequentially added into a reactor; 2) heating up water separation and ethanol supplementation: opening the reflux valve, and adding 600 L of ethanol when the temperature rises to 84°C, and continuing to separate water; when the temperature rises to 85°C, adding 150 L of ethanol, and continuing to separate water; when the temperature reaches 86°C, adding 150 L of ethanol, and continuing to separate water; 3) acid measurement: when the temperature reaches 9 Take a sample at 6°C to measure the acidity, and start toluene distillation when the acidity is below 1.5%; if the acidity is higher than 1.5%, add ethanol according to the acidity*2000L; 4) Distill toluene: start toluene distillation after the acidity test is qualified, and stop distillation when the temperature reaches 140°C; 5) Cooling: After the toluene distillation is completed, use circulating water to cool down to below 80°C and discharge the material to obtain crude ester; 6) Negative pressure distillation: put the crude ester into the distillation kettle, adjust the vacuum degree to above 0.95MPa, increase the temperature, start negative pressure distillation, collect the solution at 45-108°C as the distillation head, and start collecting the finished product diethyl oxalate after collecting the distillation head. When the reactor temperature reaches 140°C, stop collecting the finished product and the distillation is completed.

[0004] Although the method for preparing diethyl oxalate using toluene as a solvent achieves the purpose of being environmentally friendly and green by using toluene as a solvent, it requires multiple heating steps to supplement ethanol, which leads to the problems of high difficulty in preparing diethyl oxalate and complicated procedures, and needs to be improved. Summary of the invention

[0005] In view of this, the purpose of this application is to provide a method for preparing diethyl oxalate, so as to reduce the difficulty of preparing diethyl oxalate, simplify the process and improve the preparation efficiency. The specific scheme is as follows:

[0006] A method for preparing diethyl oxalate comprises the following steps:

[0007] Step ①: Place oxalic acid, ethanol, toluene, and the catalytic adsorption solid material into a reaction kettle for mixing;

[0008] Step ②: Gradually increase the temperature of the reaction kettle from room temperature to 105 - 108 °C, and keep the temperature constant until dehydration is completed to obtain an esterification mixture;

[0009] Step ③: Raise the temperature of the esterification mixture to 128 - 130 °C, then remove toluene, and then cool down to separate diethyl oxalate and the catalytic adsorption solid material.

[0010] The present invention is further configured as: the catalytic adsorption solid material includes successively performing surface carboxyl treatment of fumed silica, lysine diisocyanate coating treatment, and graphene mixing treatment.

[0011] The present invention is further configured as: the surface carboxyl treatment of fumed silica uses nitric acid and sulfuric acid with a volume ratio of 1:2 - 3 as the mixed treatment solvent, and the concentration of nitric acid is 68%, and the concentration of sulfuric acid is 98%; place the fumed silica into the mixed treatment solvent for mixing for at least 1 h, then after centrifugation treatment, wash, dry, and obtain carboxylated fumed silica.

[0012] The present invention is further configured as: the mass of the fumed silica used is ng, and the volume of the nitric acid used is 40 to 60 n mL, where n is a positive integer.

[0013] The present invention is further configured as: the lysine diisocyanate coating treatment uses N,N - dimethylacetamide as the coating treatment solvent. After placing the carboxylated fumed silica and the coating treatment solvent into the reaction kettle, control the temperature of the reaction kettle to 70 - 80 °C and maintain continuous mixing vibration. Then, gradually drop a certain amount of lysine diisocyanate into the reaction kettle. After reacting for 6 - 12 h, after centrifugation treatment, wash, dry, and obtain the coated fumed silica.

[0014] The present invention is further configured as: the mass of the carboxylated fumed silica used is ng, the volume of the N,N - dimethylacetamide used is 90 - 120 n mL, and the mass of the lysine diisocyanate used is 1.36n to 1.42n, where n is a positive integer.

[0015] The present invention is further configured as: the graphene mixing treatment uses sulfuric acid with a concentration of 98% as a treatment agent to treat graphite powder. After the treated graphite powder is ground, add it to an HF solution with a concentration of 0.1 - 10% and keep it at 25 °C for etching treatment for 1 h to obtain surface - treated graphene; then mix the surface - treated graphene with the coated fumed silica.

[0016] The present invention is further configured as: the mass ratio of HF to graphite powder is 0.2 - 3:100.

[0017] The present invention is further configured such that: the mass ratio of the coated fumed silica to the surface-treated graphene is 2:0.6 - 1.1.

[0018] The present invention is further configured such that: in step ①, the mass ratio of the oxalic acid, ethanol, toluene, and the catalytic adsorption solid material is 100:120 - 130:8 - 9:0.3 - 1.

[0019] As can be seen from the above solutions, the present application provides a preparation method for synthesizing diethyl oxalate. The preparation method for synthesizing diethyl oxalate has the following beneficial effects:

[0020] 1. By mixing oxalic acid, ethanol, toluene, and the catalytic adsorption solid material and then separating toluene and the catalytic adsorption solid material, the prepared diethyl oxalate is obtained, which improves the reaction yield of oxalic acid and ethanol, and at the same time achieves the purposes of reducing the preparation difficulty of diethyl oxalate, simplifying the process, and improving the preparation efficiency;

[0021] 2. By using the catalytic adsorption solid material to improve the reaction yield of oxalic acid and ethanol, the purposes of reducing the preparation difficulty of diethyl oxalate, simplifying the process, and improving the preparation efficiency are achieved;

[0022] 3. The surface-treated graphene obtained by mixing with graphene has its surface first treated with sulfuric acid and then etched with HF to improve, so that the content of F element on the surface increases, and the purpose of improving the reaction yield of oxalic acid and ethanol to obtain a high yield of diethyl oxalate is achieved;

[0023] 4. Through the surface carboxyl treatment of fumed silica with nitric acid and sulfuric acid, the isocyanate group of lysine diisocyanate undergoes a nucleophilic addition reaction with the surface carboxyl group of fumed silica, and lysine diisocyanate is coated on the surface of fumed silica to form a bilayer structure. Then, the coated fumed silica with a bilayer structure and the surface-treated graphene are mixed in proportion to effectively adsorb oxalic acid and ethanol for esterification reaction, and the purpose of significantly improving the reaction yield is achieved, and at the same time, the purposes of reducing the preparation difficulty of diethyl oxalate, simplifying the process, and improving the preparation efficiency are achieved. Detailed Embodiments

[0024] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present application.

[0025] It should be noted that the preparation method of synthetic diethyl oxalate of the present application will be specifically described below. The reaction kettle used is a conventional equipment such as a three-necked flask or a four-necked flask.

[0026] A preparation method of synthetic diethyl oxalate includes the following steps:

[0027] Step ①: Place oxalic acid, ethanol, toluene, and a catalytic adsorption solid material into the reaction kettle and mix them.

[0028] Step ②: Gradually raise the temperature of the reaction kettle from room temperature to 105 - 108 °C, and keep the temperature constant until dehydration is completed to obtain an esterification mixture.

[0029] Step ③: Raise the temperature of the esterification mixture to 128 - 130 °C, then remove toluene, and then cool down to separate diethyl oxalate and the catalytic adsorption solid material.

[0030] Among them, the mass ratio of oxalic acid, ethanol, toluene, and the catalytic adsorption solid material is 100:120 - 130:8 - 9:0.3 - 1, so as to efficiently obtain diethyl oxalate with a high reaction yield. The catalytic adsorption solid material includes surface carboxyl treatment of fumed silica, lysine diisocyanate coating treatment, and graphene mixing treatment in sequence.

[0031] It should be noted that for the surface carboxyl treatment of fumed silica, nitric acid and sulfuric acid with a volume ratio of 1:2 - 3 are used as the mixed treatment solvent, and the concentration of nitric acid is 68%, and the concentration of sulfuric acid is 98%; place the fumed silica into the mixed treatment solvent and mix for at least 1 h, then after centrifugation, wash, dry, and obtain carboxylated fumed silica.

[0032] Among them, the mass of the fumed silica used is ng, the volume of the nitric acid used is 40 to 60 n mL, and n is a positive integer.

[0033] For the lysine diisocyanate coating treatment, N,N-dimethylacetamide is used as the coating treatment solvent. After placing the carboxylated fumed silica and the coating treatment solvent into the reaction kettle, control the temperature of the reaction kettle at 70 - 80 °C and keep continuous mixing vibration. Then gradually drop a certain amount of lysine diisocyanate into the reaction kettle. After reacting for 6 - 12 h, then after centrifugation, wash, dry, and obtain the coated fumed silica.

[0034] Among them, the mass of the carboxylated fumed silica used is ng, the volume of N,N-dimethylacetamide used is 90 - 120 n mL, and the mass of lysine diisocyanate used is 1.36n to 1.42n, and n is a positive integer.

[0035] The graphene hybrid treatment uses sulfuric acid with a concentration of 98% as a treatment agent to treat graphite powder. After the treated graphite powder is ground, it is added to an HF solution with a concentration of 0.1 - 10% and etched at 25°C for 1 hour to obtain surface-treated graphene. Then, the surface-treated graphene is mixed with coated fumed silica.

[0036] Among them, the mass ratio of HF to graphite powder is 0.2 - 3:100, and the mass ratio of coated fumed silica to surface-treated graphene is 2:0.6 - 1.1.

[0037] Example 1

[0038] A preparation method for synthesizing diethyl oxalate includes the following steps:

[0039] Step ①: Place oxalic acid, ethanol, toluene, and a catalytic adsorption solid material into a reaction kettle and mix them.

[0040] Step ②: Gradually raise the temperature of the reaction kettle from room temperature to 105°C and keep the temperature constant until dehydration is completed to obtain an esterification mixture.

[0041] Step ③: Raise the temperature of the esterification mixture to 128°C, then remove toluene, and then cool down to separate diethyl oxalate and the catalytic adsorption solid material.

[0042] Among them, the mass ratio of oxalic acid, ethanol, toluene, and the catalytic adsorption solid material is 100:120:8:0.3 to achieve the purpose of efficiently obtaining diethyl oxalate with a high reaction yield. The catalytic adsorption solid material includes the surface carboxyl treatment of fumed silica, the lysine diisocyanate coating treatment, and the graphene hybrid treatment carried out in sequence.

[0043] It should be noted that the surface carboxyl treatment of fumed silica uses a mixed treatment solvent of nitric acid and sulfuric acid with a volume ratio of 1:2, and the concentration of nitric acid is 68% and the concentration of sulfuric acid is 98%. The fumed silica is placed in the mixed treatment solvent and mixed for 1 hour, and then after centrifugation, it is washed, dried, and carboxylated fumed silica is obtained.

[0044] Among them, the mass of the used fumed silica is 2 g, and the used volume of nitric acid is 80 mL.

[0045] The lysine diisocyanate coating treatment uses N,N-dimethylacetamide as a coating treatment solvent. After the carboxylated fumed silica and the coating treatment solvent are placed in a reaction kettle, the temperature of the reaction kettle is controlled at 70°C and continuous mixing vibration is maintained. Then, a certain amount of lysine diisocyanate is gradually dropped into the reaction kettle. After reacting for 6 hours, it is centrifuged, washed, dried, and coated fumed silica is obtained.

[0046] Among them, the mass of the carboxylated fumed silica used is 2 g, the volume of N,N-dimethylacetamide used is 180 nmL, and the mass of lysine diisocyanate used is 2.72 g.

[0047] For the graphene hybrid treatment, sulfuric acid with a concentration of 98% is used as a treatment agent to treat graphite powder. After the treated graphite powder is ground, it is added to an HF solution with a concentration of 0.1% and kept at 25 °C for etching treatment for 1 h to obtain surface-treated graphene; then the surface-treated graphene is mixed with the coated fumed silica.

[0048] Among them, the mass ratio of HF to graphite powder is 0.2:100, and the mass ratio of the coated fumed silica to the surface-treated graphene is 2:0.6.

[0049] After testing, the yield of diethyl oxalate obtained through this example is 99.3%, and the catalytic adsorption solid material is suitable for recycling more than 75 times.

[0050] Example Two

[0051] A preparation method for synthesizing diethyl oxalate includes the following steps:

[0052] Step ①: Put oxalic acid, ethanol, toluene, and the catalytic adsorption solid material into a reaction kettle and mix them.

[0053] Step ②: Gradually raise the temperature of the reaction kettle from room temperature to 107 °C and keep the temperature constant until dehydration is completed to obtain an esterification mixture.

[0054] Step ③: Raise the temperature of the esterification mixture to 129 °C, then remove toluene, and then cool down to separate diethyl oxalate and the catalytic adsorption solid material.

[0055] Among them, the mass ratio of oxalic acid, ethanol, toluene, and the catalytic adsorption solid material is 100:125:8.5:0.7 to achieve the purpose of efficiently obtaining diethyl oxalate with a high reaction yield. The catalytic adsorption solid material includes sequential surface carboxylation treatment of fumed silica, coating treatment with lysine diisocyanate, and graphene hybrid treatment.

[0056] It should be noted that for the surface carboxylation treatment of fumed silica, a mixed treatment solvent of nitric acid and sulfuric acid with a volume ratio of 1:2.5 is used, and the concentration of nitric acid is 68% and the concentration of sulfuric acid is 98%; the fumed silica is placed in the mixed treatment solvent and mixed for 2 h, and then after centrifugation treatment, it is washed, dried, and carboxylated fumed silica is obtained.

[0057] Among them, the mass of the fumed silica used is 2 g, and the volume of nitric acid used is 100 mL.

[0058] For the lysine diisocyanate coating treatment, N,N-dimethylacetamide is used as the coating treatment solvent. After carboxylated fumed silica and the coating treatment solvent are placed into the reaction kettle, the temperature of the reaction kettle is controlled at 75 °C and continuous mixing vibration is maintained. Then, a certain amount of lysine diisocyanate is gradually dropped into the reaction kettle. After reacting for 9 h, it is centrifuged, washed, dried, and the coated fumed silica is obtained.

[0059] Among them, the mass of the carboxylated fumed silica used is 2 g, the volume of N,N-dimethylacetamide used is 200 mL, and the mass of lysine diisocyanate used is 2.8 g.

[0060] For the graphene mixing treatment, sulfuric acid with a concentration of 98% is used as the treatment agent to treat graphite powder. After the treated graphite powder is ground, it is added to a 5% HF solution and etched at 25 °C for 1 h to obtain surface-treated graphene. Then, the surface-treated graphene is mixed with the coated fumed silica.

[0061] Among them, the mass ratio of HF to graphite powder is 1.4:100, and the mass ratio of the coated fumed silica to the surface-treated graphene is 2:0.8.

[0062] After testing, the yield of diethyl oxalate obtained through this example is 99.5%, and the catalytic adsorption solid material is suitable for recycling more than 75 times.

[0063] Example 3

[0064] A preparation method for synthesizing diethyl oxalate includes the following steps:

[0065] Step ①: Oxalic acid, ethanol, toluene, and the catalytic adsorption solid material are placed into the reaction kettle and mixed.

[0066] Step ②: The temperature of the reaction kettle is gradually raised from room temperature to 108 °C and kept constant until dehydration is completed to obtain an esterification mixture.

[0067] Step ③: The esterification mixture is heated to 130 °C to remove toluene, and then cooled to separate diethyl oxalate and the catalytic adsorption solid material.

[0068] Among them, the mass ratio of oxalic acid, ethanol, toluene, and the catalytic adsorption solid material is 100:130:9:1 to achieve the purpose of efficiently obtaining diethyl oxalate with a high reaction yield. The catalytic adsorption solid material includes surface carboxyl treatment of fumed silica, lysine diisocyanate coating treatment, and graphene mixing treatment carried out in sequence.

[0069] It should be noted that for the surface carboxylation treatment of fumed silica, nitric acid and sulfuric acid with a volume ratio of 1:3 are used as the mixed treatment solvent, where the concentration of nitric acid is 68% and the concentration of sulfuric acid is 98%. The fumed silica is placed in the mixed treatment solvent and mixed for 5 h, and then after centrifugation, it is washed, dried to obtain carboxylated fumed silica.

[0070] Among them, the mass of fumed silica used is 2 g, and the volume of nitric acid used is 120 mL.

[0071] For the lysine diisocyanate coating treatment, N,N-dimethylacetamide is used as the coating treatment solvent. After the carboxylated fumed silica and the coating treatment solvent are placed in the reaction kettle, the temperature of the reaction kettle is controlled at 80 °C and continuous mixing vibration is maintained. After gradually dropping a certain amount of lysine diisocyanate into the reaction kettle, after reacting for 12 h, it is then centrifuged, washed, dried to obtain the coated fumed silica.

[0072] Among them, the mass of carboxylated fumed silica used is 2 g, the volume of N,N-dimethylacetamide used is 240 mL, and the mass of lysine diisocyanate used is 2.84 g.

[0073] For the graphene mixing treatment, sulfuric acid with a concentration of 98% is used as the treatment agent to treat graphite powder. After the treated graphite powder is ground, it is added to a 10% HF solution and etched at 25 °C for 1 h to obtain surface-treated graphene. Then the surface-treated graphene is mixed with the coated fumed silica.

[0074] Among them, the mass ratio of HF to graphite powder is 3:100, and the mass ratio of the coated fumed silica to the surface-treated graphene is 2:1.1.

[0075] After testing, the yield of diethyl oxalate obtained through this example is 99.4%, and the catalytic adsorption solid material is suitable for recycling more than 75 times.

[0076] Comparative Example 1

[0077] The difference between Comparative Example 1 and Example 1 is that in step ① of Comparative Example 1, no catalytic adsorption solid material was placed in the reaction kettle, and in step ③, only diethyl oxalate was separated after removing toluene. After testing, the yield of diethyl oxalate obtained through Comparative Example 1 is 92.6%.

[0078] Comparative Example 2

[0079] The difference between Comparative Example 2 and Example 1 lies in that in step ① of Comparative Example 2, the catalytic adsorption solid material placed in the reaction kettle only has surface-treated graphene. After testing, the yield of diethyl oxalate obtained through Comparative Example 2 is 98.4%, and the catalytic adsorption solid material is suitable for recycling more than 40 times.

[0080] In summary, the present application provides a preparation method for synthesizing diethyl oxalate. The preparation method for synthesizing diethyl oxalate obtains the prepared diethyl oxalate by mixing oxalic acid, ethanol, toluene, and a catalytic adsorption solid material and then separating toluene and the catalytic adsorption solid material, which improves the reaction yield of oxalic acid and ethanol, and at the same time achieves the purposes of reducing the preparation difficulty of diethyl oxalate, simplifying the process, and improving the preparation efficiency.

[0081] Among them, the catalytic adsorption solid material used has the effect of improving the reaction yield of oxalic acid and ethanol, thereby achieving the purposes of reducing the preparation difficulty of diethyl oxalate, simplifying the process, and improving the preparation efficiency. Specifically, the surface-treated graphene obtained by graphene mixing treatment has its surface first treated with sulfuric acid and then etched with HF to improve, so that the content of F element on the surface increases, and the purpose of improving the reaction yield of oxalic acid and ethanol to obtain a high yield of diethyl oxalate is achieved; and through the surface carboxyl treatment of fumed silica with nitric acid and sulfuric acid, the isocyanate group of lysine diisocyanate then undergoes a nucleophilic addition reaction with the surface carboxyl group of fumed silica, and lysine diisocyanate is coated on the surface of fumed silica to form a bilayer structure. Then, through the proportionate mixing of the coated fumed silica with the bilayer structure and the surface-treated graphene, oxalic acid and ethanol can be effectively adsorbed for esterification reaction, and the purpose of significantly improving the reaction yield is achieved, and the purposes of reducing the preparation difficulty of diethyl oxalate, simplifying the process, and improving the preparation efficiency are achieved.

[0082] At the same time, when the coated fumed silica and the surface-treated graphene are proportionately mixed as the catalytic adsorption solid material, it has the effect of increasing the number of recycling times of the catalytic adsorption solid material.

[0083] The "first", "second", "third", "fourth", etc. (if any) involved in the present application are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments described here can be implemented in an order other than that described here. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, or devices.

[0084] It should be noted that in this application, the descriptions involving "first", "second", etc. are only for descriptive purposes, and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. Additionally, the technical solutions between various embodiments may be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0085] Specific examples are used in this article to elaborate on the principles and implementation manners of this application. The descriptions of the above embodiments are only for helping to understand the method and its core idea of this application; at the same time, for those of ordinary skill in the art, according to the idea of this application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to this application.

Claims

1. A preparation method of synthetic diethyl oxalate, characterized in that, it comprises the following steps: Step ①: Put oxalic acid, ethanol, toluene and a catalytic adsorption solid material into a reaction kettle for mixing; Step ②: Gradually raise the temperature of the reaction kettle from room temperature to 105 - 108 °C, and keep the temperature constant until dehydration is completed to obtain an esterification mixture; Step ③: Raise the temperature of the esterification mixture to 128 - 130 °C, then remove toluene, and then cool down to separate diethyl oxalate and the catalytic adsorption solid material; Wherein: The catalytic adsorption solid material includes surface carboxyl treatment of fumed silica, lysine diisocyanate coating treatment and graphene mixing treatment in sequence; the surface carboxyl treatment of fumed silica uses nitric acid and sulfuric acid with a volume ratio of 1:2 - 3 as a mixed treatment solvent, and the concentration of nitric acid is 68%, and the concentration of sulfuric acid is 98%; and put fumed silica into the mixed treatment solvent for mixing for at least 1 h, then after centrifugation, wash, dry and obtain carboxylated fumed silica; the lysine diisocyanate coating treatment uses N,N - dimethylacetamide as a coating treatment solvent, then after putting the carboxylated fumed silica and the coating treatment solvent into a reaction kettle, control the temperature of the reaction kettle to 70 - 80 °C and keep continuous mixing vibration, then gradually drop a certain amount of lysine diisocyanate into the reaction kettle, after reacting for 6 - 12 h, then after centrifugation, wash, dry and obtain coated fumed silica; the graphene mixing treatment uses sulfuric acid with a concentration of 98% as a treatment agent to treat graphite powder, and after grinding the treated graphite powder, add it to an HF solution with a concentration of 0.1 - 10% and keep it at 25 °C for etching treatment for 1 h to obtain surface - treated graphene; then mix the surface - treated graphene with the coated fumed silica.

2. The preparation method of synthetic diethyl oxalate according to claim 1, characterized in that: The mass of the fumed silica used is ng, and the volume of the nitric acid used is 40×n to 60×n mL, where n is a positive integer.

3. The preparation method of synthetic diethyl oxalate according to claim 1, characterized in that: The mass of the carboxylated fumed silica used is ng, the volume of the N,N - dimethylacetamide used is 90×n - 120×n mL, and the mass of the lysine diisocyanate used is 1.36n g to 1.42n g, where n is a positive integer.

4. The preparation method of synthetic diethyl oxalate according to claim 1, characterized in that: The mass ratio of HF to graphite powder is 0.2 - 3:

100.

5. The preparation method of synthetic diethyl oxalate according to claim 1, characterized in that: The mass ratio of the coated fumed silica to the surface - treated graphene is 2:0.6 - 1.

1.

6. The preparation method of synthetic diethyl oxalate according to claim 1, characterized in that: In step ①, the mass ratio of the oxalic acid, ethanol, toluene and the catalytic adsorption solid material is 100:120 - 130:8 - 9:0.3 - 1.