Melamine grafted chloromethylated resin catalyst for decarbonylation of chloroform and preparation method of alkyl carbonate

Abstract

The application provides a melamine-grafted chloromacrolite-based decarbonylation catalyst and a preparation method of alkyl carbonate, wherein the melamine-grafted chloromacrolite-based decarbonylation catalyst is obtained by subjecting chloromacrolite to nucleophilic substitution to obtain amine group chloromacrolite, and then subjecting the amine group chloromacrolite to Schiff base condensation with aldehyde group-terminated melamine-dialdehyde prepolymers. The melamine with strong coordination ability and chemical stability is chemically grafted to the surface of chloromacrolite resin, and a multiphase decarbonylation catalyst with stable structure and excellent performance is constructed. The catalyst exhibits excellent catalytic activity, selectivity and stability in the decarbonylation reaction of alkyl oxalate, and can realize efficient conversion of alkyl oxalate into alkyl carbonate under mild conditions, thereby providing a new technical scheme for solving the high-value utilization of coal-to-ethylene glycol intermediates and the green synthesis of alkyl carbonate.

Description

A method for preparing a melamine-grafted chlorosphere-based decarbonylation catalyst and an alkyl carbonate ester Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to a method for preparing a melamine-grafted chlorosphere-based decarbonylation catalyst and an alkyl carbonate ester. Background Technology

[0002] Alkyl carbonates, such as dimethyl carbonate (DMC, C3H6O3), are colorless, transparent, low-toxicity liquids with a slightly irritating odor. They have a molecular weight of 90.07 and a density of 1.069 g·cm³. - ³, with a melting point of 2-4 ℃, a boiling point of 90 ℃, and a flash point of 17 ℃, it is immiscible with water but miscible with alcohols, ketones, esters, and aromatics. Its molecules simultaneously contain carbonyl, methoxy, and alkoxy groups, possessing multiple reactive properties such as methylation, carbonylation, and transesterification. Moreover, it is safe and environmentally friendly in terms of transportation, storage, and use, and is recognized as a "new cornerstone of organic synthesis" and a "green chemical raw material." It can also be used as a high-performance fuel additive.

[0003] From a market demand perspective, approximately 65% ​​of global dimethyl carbonate (DMC) is used in polycarbonate (PC) synthesis, with the remainder used in high-value-added products such as electrolyte solvents, developing solutions, pesticide / pharmaceutical intermediates, isocyanates, polycarbonate diols, and long-chain alkyl carbonates. In 2024, my country's apparent consumption of DMC reached 2 million tons per year, with new energy vehicle electrolytes and domestically produced PC accounting for about 70%, and this figure continues to grow at an average annual rate of >15%, leading to a widening supply-demand gap.

[0004] Currently, the traditional synthesis technology for dimethyl carbonate has undergone several generations of route iterations: the phosgene method, due to its highly toxic raw materials and the production of highly corrosive hydrochloric acid as a byproduct, has been explicitly phased out. While the methanol oxidative carbonylation method has achieved industrialization, it suffers from rapid catalyst deactivation, reactor corrosion, flammability, explosiveness, and NO emissions. x Fatal flaws such as pollution and a single-pass conversion rate of ≤20% limit the operation of only a few facilities in China, restricting capacity expansion. While transesterification offers a mild reaction and high yield, its lengthy reaction steps and massive equipment investment, coupled with the chemical equilibrium limitation on dimethyl carbonate yield, result in high production costs. Although urea alcoholysis and direct CO2 / methanol synthesis offer high atom economy, their chemical equilibrium limitations and yields of <10% mean that the generated water leads to catalyst hydrolysis and deactivation, thus these methods remain at the laboratory or small-scale testing stage.

[0005] Furthermore, my country's annual ethylene glycol (EG) production capacity has exceeded 18 million tons, with over 50% using the dimethyl oxalate (DMO) route, a coal-to-ethylene glycol process. This process produces approximately 0.15-0.20 tons of dimethyl oxalate as a byproduct for every ton of ethylene glycol produced. The national surplus of dimethyl oxalate has reached 2-3 million tons per year, and the raw material is inexpensive. However, there is currently no high-value utilization method, which has become a bottleneck for the development of coal-to-ethylene glycol enterprises.

[0006] The decarbonylation of dimethyl oxalate to dimethyl carbonate (DMO→DMC+CO) is a green reaction route that has emerged in recent years: dimethyl oxalate, the raw material, is widely available and low in cost; the reaction is completed in one step, with an atom economy of >90%; the byproduct CO can be used as fuel gas or a raw material for carbonyl synthesis; the entire process produces no wastewater or salt residue, perfectly aligning with the development direction of green chemistry; however, this route still faces the following technical bottlenecks:

[0007] (1) Under high temperature (>240 ℃) conditions, dimethyl oxalate is easily pyrolyzed to generate oxalic acid, CO2 and methyl formate, which leads to a decrease in the selectivity of the target product;

[0008] (2) Although traditional homogeneous base catalysts (K2CO3, CH3ONa) have high activity, they have problems such as difficulty in separation and easy hydrolysis and deactivation.

[0009] (3) Conventional heterogeneous catalysts (alkali metal supported on activated carbon) are easy to separate and recover, but they face industrialization obstacles such as loss of active centers and service life of <100 h. Summary of the Invention

[0010] Based on the technical problems existing in the background technology, this invention proposes a method for preparing a melamine-grafted chlorosphere-based decarbonylation catalyst and alkyl carbonate. By chemically grafting melamine, which has both strong coordination ability and chemical stability, onto the surface of chlorosphere resin, a structurally stable and high-performance heterogeneous decarbonylation catalyst is constructed. It exhibits excellent catalytic activity, selectivity and stability in the decarbonylation reaction of alkyl oxalate, and can achieve efficient conversion of alkyl oxalate to alkyl carbonate under mild conditions. This provides a new technical solution for solving the high-value utilization of coal-to-ethylene glycol intermediates and the green synthesis of alkyl carbonate.

[0011] This invention proposes a melamine-grafted chlorosphere-based decarbonylation catalyst, which is obtained by nucleophilic substitution of chlorospheres with polyamines to obtain amination-modified chlorospheres, followed by Schiff base condensation with aldehyde-terminated melamine-dialdehyde prepolymer.

[0012] In this invention, chloromethylated polystyrene-divinylbenzene crosslinked resin (e.g., chloromethylated polystyrene-divinylbenzene crosslinked resin) is rich in highly active chloromethyl (-CH2Cl) on its surface. It can be functionalized to introduce specific functional groups and become a core substrate in the fields of adsorption materials and catalyst supports. Melamine (molecular formula C3H6N6) contains three primary amino groups (-NH2) and a highly conjugated six-membered triazine ring, which has both strong coordination ability and chemical stability. Grafting it onto the surface of chloromethylated resin can construct a structurally stable and high-performance heterogeneous catalytic system.

[0013] This invention addresses the problem of insufficient amino activity in melamine by using a dialdehyde-mediated amination modification pathway. The prepared melamine-grafted chlorosphere-based heterogeneous decarbonylation catalyst exhibits excellent catalytic activity, selectivity, and stability in the decarbonylation reaction of alkyl oxalate. It can achieve efficient conversion of alkyl oxalate to alkyl carbonate under mild conditions, providing a new technical solution for the high-value utilization of coal-to-ethylene glycol intermediates and the green synthesis of alkyl carbonate.

[0014] The melamine-grafted chlorosphere-based decarbonylation catalyst of this invention is essentially a melamine-grafted chlorosphere resin modified by dialdehyde-mediated amination. Its core structure is a covalent linkage system of "chlorosphere-linking arm (polyamine)-dialdehyde-melamine", and the stable grafting of melamine and chlorosphere resin is achieved through Schiff base reaction.

[0015] Preferably, the polyamine is at least one of ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, phenylenediamine, cyclohexanediamine, or diethylenetriamine, and is preferably ethylenediamine.

[0016] Preferably, the aldehyde-terminated melamine-dialdehyde prepolymer is obtained by polycondensation reaction of melamine and dialdehyde;

[0017] The dialdehyde is at least one of glyoxal, glutaraldehyde, adipaldehyde, terephthalaldehyde, or isophthalaldehyde, preferably glutaraldehyde; the molar ratio of melamine to dialdehyde is 1:1.2-1:1.5; preferably, the polycondensation reaction temperature is 30-40 °C and the time is 2-3 h.

[0018] Preferably, the molar ratio of the chlorinated spheres to the polyamine is 1:1 to 1:3; and the mass ratio of the amino-modified chlorinated spheres to the aldehyde-terminated melamine-dialdehyde prepolymer is 1:2 to 1:3.

[0019] Preferably, the decarbonylation catalyst is prepared by the following method:

[0020] S1. After swelling the chlorine balls in an amide solvent, add polyamine and alkaline regulator and stir to react, thus obtaining amino-modified chlorine balls;

[0021] S2. After the amination-modified chlorine spheres are swollen in a mixed solvent of amide and alcohol, aldehyde-terminated melamine-dialdehyde prepolymer is added and stirred to react, thereby obtaining the melamine-grafted chlorine sphere-based decarbonylation catalyst.

[0022] In this invention, the chloromethyl group on the surface of the chloromethyl group is first swollen to fully remove the steric hindrance of the pores. Then, the chloromethyl group on the surface of the chloromethyl group is converted into an amino group through an SN2 nucleophilic substitution reaction of the polyamine linker arm. Then, the amino group of melamine undergoes a nucleophilic addition reaction with the aldehyde group of dialdehyde to generate an active intermediate containing a residual aldehyde group. Finally, the amino-modified chloromethyl group and the active intermediate containing the residual aldehyde group are covalently linked through a Schiff base reaction to obtain the melamine-grafted chloromethyl group decarbonylation catalyst.

[0023] Preferably, in step S1, the amide solvent is at least one of N,N-dimethylformamide or N,N-dimethylacetamide, and the alkalinity regulator is at least one of sodium hydroxide, sodium carbonate or potassium carbonate;

[0024] The alkaline regulator adjusts the pH of the reaction to 8-9; the stirring reaction temperature is 40-60 ℃, and the time is 4-8 h.

[0025] Preferably, in step S2, the alcohol is at least one of methanol, ethanol, or isopropanol;

[0026] The stirring reaction is carried out at a temperature of 60-80 ℃ for 4-12 h.

[0027] The present invention also proposes a method for preparing alkyl carbonate, comprising: contacting alkyl oxalate with the above-mentioned decarbonylation catalyst to carry out a decarbonylation reaction, thereby obtaining the alkyl carbonate.

[0028] Preferably, the molecular structural formulas of the alkyl carbonate ester and the alkyl oxalate ester are as follows:

[0029]

[0030] In this context, R and R' are each independently a straight-chain alkyl, branched alkyl, or alkyl containing an aromatic ring with 1-8 carbon atoms.

[0031] Preferably, the preparation method specifically includes: passing the raw material liquid of alkyl oxalate into a fixed-bed reactor packed with a decarbonylation catalyst, carrying out a decarbonylation reaction under set temperature and pressure conditions, and obtaining the product by distillation to obtain alkyl carbonate;

[0032] The set temperature is 90-170 ℃, the set pressure is 0.1-0.8 MPa, and the residence time is 0.5-4 h.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) Excellent catalytic performance: The melamine grafted chlorinated sphere-based decarbonylation catalyst prepared in this invention achieves covalent connection through Schiff base bonds, has a stable structure, and the active center is not easily lost. The catalyst service life can reach more than 500 h. Under the preferred process parameters, the conversion rate of dimethyl oxalate can reach up to 92.3%, the yield of dimethyl carbonate can reach up to 95.3%, and the product is easy to separate from the raw material.

[0035] (2) High raw material utilization rate: The alkyl oxalate raw material used in this invention can be directly adopted as a by-product of the coal-to-ethylene glycol process, realizing the high-value utilization of industrial intermediates, reducing raw material costs, and solving the problem of by-product accumulation in coal-to-ethylene glycol enterprises.

[0036] (3) Mild reaction conditions: The decarbonylation reaction temperature of this invention is controlled at 90-170℃ and the pressure is 0.1-0.8MPa. Compared with traditional high temperature reactions (>200℃), the requirements for equipment are greatly reduced, and energy consumption and side reactions are reduced.

[0037] (4) Great industrialization potential: The raw materials for the catalyst preparation of this invention (chlorine balls, ethylenediamine, glutaraldehyde, melamine, etc.) are all bulk chemical products, which are inexpensive and readily available; the reaction adopts a fixed-bed reactor, which can realize continuous production, with strong process controllability and stable product quality, making it suitable for large-scale industrial promotion. Attached Figure Description

[0038] Figure 1 is a schematic diagram of the structure of the melamine grafted chlorosphere-based decarbonylation catalyst of the present invention;

[0039] Figure 2 is the infrared spectrum of the melamine-grafted chlorosphere-based decarbonylation catalyst described in Example 1 of this invention. Detailed Implementation

[0040] The technical solution of the present invention will be described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and are not to be construed as limiting the scope of the present invention.

[0041] In the following examples, the chlorine balls had a crosslinking degree of 6%, a particle size of 200-400 mesh, and a chlorine content of 18% (dry weight); ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, glutaraldehyde (50% aqueous solution), melamine, ethanol, acetone, sodium hydroxide, and N,N-dimethylformamide (DMF) were all of analytical grade; dimethyl oxalate was derived from coal-based ethylene glycol.

[0042] In the following embodiments, the instruments include: a 250 mL four-necked flask, a constant temperature water bath, a vacuum drying oven, a Buchner funnel, a circulating water vacuum pump, an electronic balance (accuracy 0.0001 g), a pH meter (accuracy ±0.01 pH), a conductivity meter, a fixed-bed reactor (with a back pressure valve and a gas-liquid separator), and a distillation apparatus.

[0043] In the following embodiments, the decarbonylation reaction is carried out in a fixed-bed reactor, specifically including: loading a certain amount of catalyst into the fixed-bed reactor, the catalyst loading amount being adjusted according to the reactor specifications; activating the catalyst by vacuum drying at 80 °C for 8 h after loading; pumping molten alkyl oxalate into the fixed-bed reactor through a metering pump at a set flow rate; adjusting the reaction system to a set pressure through the back pressure valve of the tail gas system; simultaneously heating the reaction device to a set reaction temperature for the decarbonylation reaction; the alkyl oxalate undergoes a decarbonylation reaction under the action of the catalyst to generate alkyl carbonate and CO as a byproduct; during the reaction, when the system pressure is higher than the set pressure, the back pressure valve automatically opens to exhaust gas, and the CO is collected by condensation and can be recycled; after the reaction, the gas and condensate collected in the gas-liquid separator are combined and distilled to obtain high-purity alkyl carbonate.

[0044] In the following examples, the conversion rate of dimethyl oxalate and the yield of dimethyl carbonate were calculated using the internal standard method:

[0045] The conversion rate of dimethyl oxalate = (moles of dimethyl oxalate before reaction - moles of dimethyl oxalate after reaction) / moles of dimethyl oxalate before reaction × 100%;

[0046] The yield of dimethyl carbonate = (moles of dimethyl carbonate / moles of dimethyl oxalate converted) × 100%.

[0047] Example 1

[0048] A melamine-grafted chlorosphere-based decarbonylation catalyst is prepared by the following method:

[0049] (1) 10.000 g of dried chlorine beads were added to a 250 mL four-necked flask, and then 80 mL of DMF was added. After stirring and swelling at room temperature for 18 h, 7.0 mL of ethylenediamine (the molar ratio of chlorine beads to ethylenediamine was 1:2) was added. The pH of the system was adjusted to 8.5 with 2 mol / L sodium hydroxide solution. The temperature was raised to 50 °C, and the reaction was carried out in a closed container for 6 h under the condition of stirring at 250 r / min. After the reaction was completed, the filter was filtered under reduced pressure. The filter cake was washed twice with DMF and washed with deionized water until neutral. It was then filtered for later use to obtain amination-modified chlorine beads.

[0050] (2) Add 3.6 g of melamine to a 100 mL beaker, then add 40 mL of ethanol and stir until completely dissolved. Then slowly add 7 mL of 50 wt% glutaraldehyde aqueous solution (the molar ratio of melamine to glutaraldehyde is 1:1.3). Place the beaker in a 35 ℃ constant temperature water bath and react for 2.5 h under the condition of magnetic stirring speed of 300 r / min to obtain aldehyde-terminated melamine-dialdehyde prepolymer.

[0051] (3) The above-mentioned amination chlorine spheres were added back into a 250 mL four-necked flask, and then 30 mL of DMF and 30 mL of ethanol (volume ratio 1:1) were added. After stirring and swelling at room temperature for 0.5 h, the above-mentioned aldehyde-terminated melamine-dialdehyde prepolymer (mass ratio of amination chlorine spheres to aldehyde-terminated melamine-dialdehyde prepolymer 1:2.5) was added. The temperature was raised to 70 °C, and the reaction was sealed and reacted for 10 h under the condition of stirring rate of 250 r / min. After the reaction was completed, the mixture was filtered under reduced pressure. The filter cake was washed 4 times with ethanol, washed with deionized water until pH 7.0, washed once with acetone, and dried under vacuum at 70 °C for 10 h to obtain the melamine grafted chlorine sphere-based decarbonylation catalyst, which is denoted as catalyst A. As shown in Figure 2, compared to chloroballs (Ball) and amination-modified chloroballs (NH2-Ball), the melamine-grafted chloroball-based decarbonylation catalyst (C=N-Ball) exhibits an imine C=N bond elution peak.

[0052] Example 2

[0053] A melamine-grafted chlorosphere-based decarbonylation catalyst is prepared by the method described in Example 1, except that 1,3-propanediamine is used instead of ethylenediamine in step (1), thus obtaining the melamine-grafted chlorosphere-based decarbonylation catalyst, denoted as catalyst B.

[0054] Example 3

[0055] A melamine-grafted chlorosphere-based decarbonylation catalyst is prepared by the method described in Example 1, except that glyoxal is used instead of glutaraldehyde in step (2), thus obtaining the melamine-grafted chlorosphere-based decarbonylation catalyst, denoted as catalyst C.

[0056] Example 4

[0057] A melamine-grafted chlorosphere-based decarbonylation catalyst is prepared by the method described in Example 1, except that in step (1) the molar ratio of chlorospheres to ethylenediamine is adjusted to 1:1.5, and in step (2) the mass ratio of amination-modified chlorospheres to aldehyde-terminated melamine-dialdehyde prepolymer is adjusted to 1:2, thus obtaining the melamine-grafted chlorosphere-based decarbonylation catalyst, denoted as catalyst D.

[0058] Example 5

[0059] A melamine-grafted chlorosphere-based decarbonylation catalyst is prepared by the method described in Example 1, except that in step (1) the molar ratio of chlorospheres to ethylenediamine is adjusted to 1:2.5, and in step (2) the mass ratio of amination-modified chlorospheres to aldehyde-terminated melamine-dialdehyde prepolymer is adjusted to 1:3, thus obtaining the melamine-grafted chlorosphere-based decarbonylation catalyst, denoted as catalyst E.

[0060] Comparative Example 1

[0061] A decarbonylation catalyst is prepared by the following method: 10.000 g of dried chlorine balls are added to a 250 mL four-necked flask, followed by 30 mL of DMF and 30 mL of ethanol (volume ratio 1:1). After stirring and swelling at room temperature for 0.5 h, 3.6 g of melamine is added, the temperature is raised to 70 °C, and the reaction is sealed and reacted for 10 h under stirring at 250 r / min. After the reaction is completed, the mixture is filtered under reduced pressure. The filter cake is washed four times with ethanol, washed with deionized water until the pH reaches 7.0, and washed once with acetone. The mixture is then dried under vacuum at 70 °C for 10 h to obtain the decarbonylation catalyst, denoted as catalyst F.

[0062] Application Example 1

[0063] A method for preparing dimethyl carbonate, specifically comprising:

[0064] Molten dimethyl oxalate was fed into a fixed-bed reactor packed with a decarbonylation catalyst, with a catalyst loading of 50 mL. The decarbonylation reaction was carried out under set reaction temperature and system pressure conditions. The resulting reaction solution was then distilled to obtain dimethyl carbonate. The feed rate of dimethyl oxalate was 25 mL / h, the set reaction temperature was 150 °C, the set system pressure was 0.3 MPa, and the residence time was 2 h.

[0065] Referring to Application Example 1, the decarbonylation catalyst was selected as catalyst A, B, C, D, or E, respectively. The conversion rate of dimethyl oxalate and the yield of dimethyl carbonate obtained under different catalysts are shown in Table 1 below:

[0066] Table 1. Effect of decarbonylation catalyst on the decarbonylation of dimethyl oxalate to dimethyl carbonate

[0067]

[0068] As shown in Table 1 above, catalyst F, prepared with ethylenediamine as the linker and glutaraldehyde as the crosslinking agent, at a molar ratio of chlorine spheres to ethylenediamine of 1:2 and a mass ratio of amino-modified chlorine spheres to intermediates of 1:2.5, exhibits the best catalytic performance, with a single-pass conversion rate of dimethyl oxalate of 92.3% and a yield of dimethyl carbonate of 95.1%.

[0069] Referring to Application Example 1, the decarbonylation catalyst was catalyst A. The reaction performance was tested by adjusting the residence time of dimethyl oxalate, and the results are shown in Table 2 below:

[0070] Table 2. Effect of raw material residence time on the decarbonylation of dimethyl oxalate to dimethyl carbonate

[0071]

[0072] As shown in Table 2 above, the conversion rate of dimethyl oxalate gradually increases with the extension of residence time. However, the yield of dimethyl carbonate begins to decrease after the residence time exceeds 2 h. This is because the excessive residence time leads to excessive decarbonylation of dimethyl carbonate. The optimal residence time is 1-2 h.

[0073] Referring to Application Example 1, the decarbonylation catalyst is catalyst A. The reaction performance was tested by changing the reaction temperature, and the results are shown in Table 3 below:

[0074] Table 3. Effect of different reaction temperatures on the decarbonylation of dimethyl oxalate to dimethyl carbonate.

[0075]

[0076] As shown in Table 3 above, the reaction temperature has a significant effect on the conversion rate of dimethyl oxalate. The conversion rate gradually increases with increasing temperature. When the reaction temperature is between 130 and 150 °C, the yield of dimethyl carbonate remains at around 95%. Above 150 °C, the yield begins to decrease because the high temperature intensifies the pyrolysis side reaction of dimethyl oxalate. The optimal reaction temperature is 130-150 °C.

[0077] Referring to Application Example 1, catalysts A and F were used as research objects. The reaction temperature was fixed at 150 °C, the system pressure at 0.3 MPa, and the residence time of dimethyl oxalate at 2 h. The system was run continuously for 500 h, and samples were taken for analysis at regular intervals. The results are shown in Table 4.

[0078] Table 4. Continuous stability test results of catalyst A

[0079]

[0080] As shown in Table 4 above, after 500 hours of continuous operation, catalyst A maintained a dimethyl oxalate conversion rate of 89.5% and a dimethyl carbonate yield of 88.7%, exhibiting excellent stability and meeting the requirements for continuous industrial production, without significant deactivation. However, verifying the stability of catalyst F revealed that it lost activity immediately after the first sampling at 2 hours, with the dimethyl oxalate conversion rate essentially reaching zero. This verifies the catalytic stability of the melamine-grafted chlorosphere-based decarbonylation catalyst.

[0081] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing an alkyl carbonate, characterized in that, include: The alkyl oxalate was reacted with a melamine-grafted chlorosphere-based decarbonylation catalyst to undergo a decarbonylation reaction, yielding the alkyl carbonate. The melamine-grafted chlorosphere-based decarbonylation catalyst is obtained by nucleophilic substitution of chlorospheres with polyamines to obtain amination-modified chlorospheres, followed by Schiff base condensation with aldehyde-terminated melamine-dialdehyde prepolymer; the aldehyde-terminated melamine-dialdehyde prepolymer is obtained by polycondensation reaction of melamine and dialdehyde.

2. The method for preparing alkyl carbonate according to claim 1, characterized in that, The polyamine is at least one of ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, phenylenediamine, cyclohexanediamine, or diethylenetriamine.

3. The method for preparing alkyl carbonate according to claim 1, characterized in that, The dialdehyde is at least one of glyoxal, glutaraldehyde, adipaldehyde, terephthalaldehyde, or isophthalaldehyde; the molar ratio of melamine to dialdehyde is 1:1.2-1:1.

5.

4. The method for preparing alkyl carbonate according to any one of claims 1-3, characterized in that, The molar ratio of the chlorinated spheres to the polyamine is 1:1 to 1:3; the mass ratio of the amino-modified chlorinated spheres to the aldehyde-terminated melamine-dialdehyde prepolymer is 1:2 to 1:

3.

5. The method for preparing alkyl carbonate according to any one of claims 1-3, characterized in that, The melamine-grafted chlorosphere-based decarbonylation catalyst is specifically prepared by the following method: S1, chlorospheres are swollen in an amide solvent, and then polyamine and alkaline regulator are added and stirred to react, resulting in amination-modified chlorospheres; S2, the amination-modified chlorospheres are swollen in a mixed solvent of amide and alcohol, and then aldehyde-terminated melamine-dialdehyde prepolymer is added and stirred to react, thus obtaining the melamine-grafted chlorosphere-based decarbonylation catalyst.

6. The method for preparing alkyl carbonate according to claim 5, characterized in that, In step S1, the amide solvent is at least one of N,N-dimethylformamide or N,N-dimethylacetamide, and the alkalinity regulator is at least one of sodium hydroxide, sodium carbonate or potassium carbonate; the alkalinity regulator adjusts the reaction pH to 8-9; the stirring reaction temperature is 40-60 ℃, and the time is 4-8 h.

7. The method for preparing alkyl carbonate according to claim 6, characterized in that, In step S2, the alcohol is at least one of methanol, ethanol, or isopropanol; the stirring reaction temperature is 60-80 °C, and the time is 4-12 h.

8. The method for preparing alkyl carbonate according to claim 1, characterized in that, The molecular structural formulas of the alkyl carbonate ester and the alkyl oxalate ester are shown below: In this context, R and R' are each independently a straight-chain alkyl, branched alkyl, or alkyl containing an aromatic ring with 1-8 carbon atoms.

9. The method for preparing alkyl carbonate according to claim 1 or 8, characterized in that, The preparation method specifically includes: passing the raw material liquid of alkyl oxalate into a fixed-bed reactor packed with a decarbonylation catalyst, and carrying out a decarbonylation reaction under set temperature and pressure conditions. The obtained product is then distilled to obtain alkyl carbonate. The set temperature is 90-170 °C, the set pressure is 0.1-0.8 MPa, and the residence time is 0.5-4 h.

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