A kind of polyphase catalyst and oxalate alkyl decarbonyl preparation alkyl carbonate in application

Abstract

This invention proposes a heterogeneous catalyst and its application in the decarbonylation of alkyl oxalate to alkyl carbonate. The heterogeneous catalyst is a transition metal-modified organic amine-grafted polystyrene resin obtained by grafting chloromethylated polystyrene resin with an organic tertiary amine, followed by modification with a transition metal anion complex. This invention utilizes the heterogeneous catalyst to fully utilize dimethyl oxalate, an important intermediate in the coal-to-ethylene glycol process. By decarbonylating dimethyl oxalate, it can be efficiently converted to dimethyl carbonate and its derived alkyl esters under mild conditions.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and more particularly to a heterogeneous catalyst and its application in the decarbonylation of alkyl oxalate to alkyl carbonate. 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, melting point 2-4 ℃, boiling point 90 ℃, flash point 17 ℃, immiscible with water, but miscible with alcohols, ketones, esters, and aromatics. Its molecule simultaneously contains carbonyl, methoxy, and alkoxy groups, exhibiting multiple reactive properties such as methylation, carbonylation, and transesterification. Furthermore, its transportation, storage, and use are safe and environmentally friendly, making it widely 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] Globally, approximately 65% ​​of DMC is used in polycarbonate (PC) synthesis, with the remainder used in high-value-added products such as electrolyte solvents, developers, pesticide / pharmaceutical intermediates, isocyanates, polycarbonate diols, and long-chain alkyl carbonates. In 2024, my country's apparent DMC consumption 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 over 15%, leading to a widening supply-demand gap.

[0004] Since the advent of the phosgene process (COCl2 + CH3OH) in 1918, DMC synthesis technology has undergone several generations of iterations, including the phosgene process, methanol oxidative carbonylation, transesterification, urea alcoholysis, and direct CO2 / methanol synthesis. While the methanol oxidative carbonylation process (liquid-phase slurry, nitrite ester, direct gas phase) 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 its operation, with only a few units running domestically, restricting expansion. The transesterification method (ethylene oxide / CO2 → ethylene carbonate + CH3OH) The DMC + ethylene glycol reaction is mild and has a high yield, but the process is lengthy, requires large equipment, and involves high investment. Furthermore, the DMC yield is limited by equilibrium conditions, resulting in high production costs. Although the urea alcoholysis method and the direct CO2 / methanol synthesis method have high atom economy, they are limited by chemical equilibrium, have yields of <10%, and the water generated leads to catalyst hydrolysis and deactivation. Currently, these methods remain at the laboratory or small-scale testing stage.

[0005] The decarbonylation of dimethyl oxalate to DMC (DMO→DMC+CO) is a novel reaction route that has emerged in recent years: the raw material DMO 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, and there is no wastewater or salt residue, which aligns with the direction of green chemistry; however, this route still faces the following technical bottlenecks:

[0006] (1) At high temperatures (>240 ℃), DMO is easily pyrolyzed to generate oxalic acid, CO2 and methyl formate, which leads to a decrease in selectivity;

[0007] (2) Traditional homogeneous base catalysts (K2CO3, CH3ONa) have high activity but are difficult to separate and are easily deactivated by hydrolysis;

[0008] (3) Conventional heterogeneous catalysts (alkali metal supported on activated carbon) are easy to separate, but they face industrialization obstacles such as loss of active centers and lifespan of <100 h.

[0009] Therefore, developing a novel, efficient, long-term, and easily scalable decarbonylation technique for the production of dimethyl carbonate from dimethyl oxalate, coupled with a low-energy separation scheme, is currently a pressing need. The decarbonylation of dimethyl oxalate to produce dimethyl carbonate and its derived alkyl esters is a novel approach, which is of great practical significance for reducing the production cost of alkyl carbonates and improving the comprehensive utilization of coal-to-ethylene glycol intermediates. Summary of the Invention

[0010] Based on the technical problems existing in the background technology, the present invention proposes a heterogeneous catalyst and its application in the decarbonylation of alkyl oxalate to alkyl carbonate. The heterogeneous catalyst can make full use of dimethyl oxalate, an important intermediate in the coal-to-ethylene glycol process. By decarbonylating dimethyl oxalate, dimethyl oxalate can be efficiently converted into dimethyl carbonate and its derived alkyl esters under mild conditions.

[0011] This invention proposes a heterogeneous catalyst, which is a transition metal-modified organic amine-grafted polystyrene resin obtained by grafting chloromethylated polystyrene resin with an organic tertiary amine and then modifying it with a transition metal anion complex.

[0012] Preferably, the organic tertiary amine is at least one of trimethylamine, triethylamine, tributylamine, dodecyl dimethyl tertiary amine, tetradecyl dimethyl tertiary amine, polyethylene polyamine, or polyethyleneimine, and more preferably at least one of trimethylamine, dodecyl dimethyl tertiary amine, or polyethyleneimine.

[0013] Preferably, the transition metal anion complex is CuCl4. 2- CoCl4 2- SnCl4 2- ZnCl42- or NiCl4 2- At least one of the anionic complexes, preferably CuCl4 2- CoCl4 2- or ZnCl4 2- At least one of the anionic complexes.

[0014] Preferably, the mass ratio of the chloromethylated polystyrene resin to the organic tertiary amine is 20:1-2:1, more preferably 10:1-5:1, and the mass ratio of the chloromethylated polystyrene resin to the transition metal anion complex is 50:1-5:1, more preferably 20:1-10:1.

[0015] Preferably, the grafting process includes: adding chloromethylated polystyrene resin to an organic solvent to fully swell, then adding an organic tertiary amine and an inorganic base and stirring to react, thereby obtaining an organic amine-grafted polystyrene resin;

[0016] The organic solvent is at least one of N,N-dimethylformamide or N,N-dimethylacetamide, the inorganic base is at least one of potassium carbonate, sodium carbonate or potassium phosphate, and the stirring reaction temperature is 80-120 °C for 8-12 h.

[0017] Preferably, the modification includes: dispersing the organic amine-grafted polystyrene resin evenly in an alcohol solvent, then adding a transition metal anion complex and stirring to react, thereby obtaining the transition metal-modified organic amine-grafted polystyrene resin.

[0018] The alcohol solvent is at least one of ethanol, methanol or isopropanol, and the stirring reaction temperature is 20-40 °C for 1-3 h.

[0019] The present invention also proposes the application of the above-mentioned heterogeneous catalyst in the decarbonylation of alkyl oxalate to alkyl carbonate.

[0020] In this invention, intermediates from the coal-to-ethylene glycol process can be fully utilized to achieve co-production with the coal-to-ethylene glycol process.

[0021] Preferably, the molecular structure of the alkyl oxalate is as follows:

[0022]

[0023] The molecular structural formula of the alkyl carbonate is shown below:

[0024]

[0025] In this context, R and R' are each an alkyl group having 1-8 carbon atoms.

[0026] The specific application includes: passing a raw material liquid of alkyl oxalate into a fixed-bed reactor containing a multiphase catalyst, pressurizing and heating it to carry out a decarbonylation reaction, and then distilling the resulting reaction liquid to obtain alkyl carbonate.

[0027] Preferably, the decarbonylation reaction is carried out at a temperature of 100-180 °C, more preferably 120-160 °C, at a pressure of 0.1-1.0 MPa, more preferably 0.1-0.5 MPa, and at a residence time of 0.5-5 h, more preferably 0.5-2 h.

[0028] Preferably, the fixed-bed reactor is a fixed-bed reactor with a back pressure valve and a gas-liquid separator in the tail gas system.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The method for preparing dimethyl carbonate provided by the present invention uses dimethyl oxalate as a raw material to prepare dimethyl carbonate through one-step decarbonylation. This method is environmentally friendly, easy to operate, has high dimethyl oxalate conversion efficiency, and dimethyl carbonate is easy to separate from the reaction raw materials. The raw material used in this method can be dimethyl oxalate, an intermediate product in the coal-to-ethylene glycol process, which is convenient for use in conjunction with existing coal-to-ethylene glycol production to achieve large-scale industrial production.

[0031] (2) The method for preparing dimethyl carbonate provided by the present invention adopts a continuous reaction and uses a fixed-bed reaction device, which is beneficial to reducing production costs and is easy to realize industrial production. The entire reaction process is carried out under mild conditions, which greatly reduces the requirements of the reaction equipment and has broad industrial application prospects. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the heterogeneous catalyst described in this invention;

[0033] Figure 2 The image shows the UV-vis spectrum of the heterogeneous catalyst described in Example 1 of this invention. Detailed Implementation

[0034] 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 intended to limit the scope of the present invention.

[0035] In the following examples, dimethyl oxalate was obtained from the coal-to-ethylene glycol process; N,N-dimethylformamide and potassium carbonate were purchased from Tianjin Kemeio Reagent Co., Ltd.; dimethyl carbonate, chloromethyl crosslinked polystyrene resin (chloromethylated polystyrene resin, crosslinking degree of 6%, particle size of 200-400 mesh, chlorine content of 18%), trimethylamine, triethylamine, tributylamine, dodecyl dimethyl tertiary amine, tetradecyl dimethyl tertiary amine, polyethylene polyamine, and polyethyleneimine were purchased from Shanghai Aladdin Reagent Co., Ltd.; copper chloride, cobalt chloride, tin chloride, zinc chloride, and nickel chloride were purchased from Shanghai Guoyao Reagent Co., Ltd.

[0036] In the following examples, when the heterogeneous catalyst is used in the decarbonylation of alkyl oxalate to produce alkyl carbonate, it is first dried in air at 120°C for 8 h.

[0037] In the following embodiments, the decarbonylation reaction is carried out in a fixed-bed reactor. A certain amount of heterogeneous catalyst is loaded into the fixed-bed reactor, molten dimethyl oxalate is pumped into the reactor at a certain residence time, and the reaction system is adjusted to a set pressure through a tail gas back pressure valve. The reaction device is heated to a certain temperature to carry out the decarbonylation reaction. After the reaction is completed, the gas condensate and reaction liquid filtrate obtained from the gas-liquid separator are distilled to obtain dimethyl carbonate.

[0038] In the following examples, the internal standard method was used to calculate the conversion rate of dimethyl oxalate and the yield of dimethyl carbonate:

[0039] 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%;

[0040] The yield of dimethyl carbonate = (moles of dimethyl carbonate / moles of dimethyl oxalate converted) × 100%.

[0041] Example 1

[0042] A heterogeneous catalyst is prepared by the following method:

[0043] 50 g of chloromethyl crosslinked polystyrene resin was added to N,N-dimethylformamide and allowed to swell completely. Then, 10 g of polyethyleneimine (molecular weight MW 600, a partially branched polymer containing tertiary amines) and 2 g of inorganic base K₂CO₃ were added. The mixture was stirred at 90 °C for 10 h. The resulting solid was washed with water until neutral, then washed with anhydrous ethanol and filtered for later use to obtain organic amine-grafted polystyrene resin. This organic amine-grafted polystyrene resin was added to 200 mL of anhydrous ethanol solution and dispersed evenly. 5 g of copper chloride was then added to the resulting suspension and stirred at room temperature for 2 h. The copper chloride formed an anionic complex CuCl₄ in the reaction solution. 2-The solid is adsorbed onto the surface of the organic amine-grafted polystyrene resin. After being filtered, the solid is washed multiple times with anhydrous ethanol and then dried under vacuum to obtain the transition metal-modified organic amine-grafted polystyrene resin, which is the heterogeneous catalyst, denoted as catalyst A.

[0044] Reference Figure 2 It can be seen that, compared to organic amine grafted polystyrene resin (N-Ball), transition metal modified organic amine grafted polystyrene resin (CuCl4) 2- - N-Ball) has a distinct CuCl4 content 2- Absorption peak.

[0045] Example 2

[0046] A heterogeneous catalyst, prepared by the method described in Example 1, except that cobalt chloride is used instead of copper chloride, is obtained as catalyst B.

[0047] Example 3

[0048] A heterogeneous catalyst, prepared by the method described in Example 1, except that zinc chloride is used instead of copper chloride, is used to obtain the heterogeneous catalyst, denoted as catalyst C.

[0049] Example 4

[0050] A heterogeneous catalyst, prepared by the method described in Example 1, except that trimethylamine is used instead of polyethyleneimine, is used to obtain the heterogeneous catalyst, denoted as catalyst D.

[0051] Example 5

[0052] A heterogeneous catalyst, prepared by the method described in Example 1, except that dodecyl dimethyl tertiary amine is used instead of polyethyleneimine, is obtained as catalyst E.

[0053] Comparative Example 1

[0054] A heterogeneous catalyst, which is prepared by the method described in Example 1, is obtained by grafting an organic amine onto a polystyrene resin and then directly used as the heterogeneous catalyst, is denoted as catalyst F.

[0055] Comparative Example 2

[0056] A heterogeneous catalyst, prepared by the method described in Example 1, except that copper oxide is used instead of copper chloride, is obtained as catalyst G.

[0057] Comparative Example 3

[0058] A heterogeneous catalyst, prepared by the method described in Example 1, except that dimethylamine is used instead of polyethyleneimine, is used to obtain the heterogeneous catalyst, denoted as catalyst H.

[0059] Comparative Example 4

[0060] A heterogeneous catalyst, prepared by the method described in Example 1, except that lithium chloride is used instead of copper chloride, is obtained as catalyst I.

[0061] Application Example 1

[0062] The application of a heterogeneous catalyst in the decarbonylation of dimethyl oxalate to dimethyl carbonate includes:

[0063] Molten dimethyl oxalate was fed into a fixed-bed reactor containing a heterogeneous catalyst and subjected to decarbonylation reaction under pressure and heating. The resulting reaction solution was then distilled to obtain dimethyl carbonate. The heterogeneous catalyst was added in an amount of 50 mL, the reaction temperature was 150 °C, the system pressure was 0.2 MPa, the dimethyl oxalate feed rate was 25 mL / h, and the residence time was 2 h.

[0064] Referring to Application Example 1, the heterogeneous catalyst was selected as catalyst A, B, C, D, E, F, G, or H, respectively. The conversion rate of dimethyl oxalate and the yield of dimethyl carbonate obtained under different catalysts are shown in Table 1 below:

[0065] Table 1. Effect of heterogeneous catalysts on the decarbonylation of dimethyl oxalate to dimethyl carbonate

[0066]

[0067] As shown in Table 1, among the cross-linked polystyrene resin catalysts grafted with different transition metal-modified organic amines, copper-modified polyethyleneimine and dodecyl dimethyl tertiary amine grafted cross-linked polystyrene resins exhibited relatively high single-pass conversion rates for dimethyl oxalate decarbonylation and yields for dimethyl carbonate. In catalysts F and G, the decarbonylation effect was significantly reduced when using either organic amine-grafted cross-linked polystyrene resin catalysts alone or those grafted with a mixture of metal oxides and organic amines, further verifying the influence of transition metal anion complexes and their types on the activity of the decarbonylation catalysts. In catalyst H, the nucleophilic substitution reaction of chloromethylated polystyrene resin with secondary amines failed to form quaternary ammonium salt-grafted chloromethylated polystyrene resin. Therefore, even with transition metal modification, a complex modification structure of quaternary ammonium salt and transition metal could not be formed, resulting in a decrease in the activity of the obtained catalyst.

[0068] Referring to Application Example 1, the residence time of dimethyl oxalate was adjusted to verify the reaction effect of catalyst A. The results are shown in Table 2 below:

[0069] Table 2. Effect of feedstock residence time on the decarbonylation of dimethyl oxalate to dimethyl carbonate

[0070]

[0071] As shown in Table 2 above, using catalyst A and increasing the residence time of the raw materials can improve the single-pass conversion rate of the reaction; however, excessively extending the residence time will cause excessive decarbonylation of dimethyl carbonate, which will affect the yield of dimethyl carbonate.

[0072] Referring to Application Example 1, the catalytic activity of catalyst A was verified by changing the reaction temperature. The results are shown in Table 3 below:

[0073] Table 3. Effect of different reaction temperatures on the decarbonylation of dimethyl oxalate to dimethyl carbonate.

[0074]

[0075] As shown in Table 3 above, catalyst A is used and the reaction temperature has a significant effect on the conversion rate of dimethyl oxalate. The reaction is activated above 140 °C. As the reaction temperature increases, the conversion rate of dimethyl oxalate gradually increases, while the yield of dimethyl carbonate tends to decrease with increasing temperature. The optimal reaction temperature is 150-160 °C.

[0076] Referring to Application Example 1, catalysts A and I were used as the research objects. The reaction temperature was fixed at 150℃, the system pressure was 0.2MPa, and the residence time of dimethyl oxalate was 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.

[0077] Table 4. Continuous stability test results of catalyst A

[0078]

[0079] Table 4 shows that after 500 hours of continuous operation, catalyst A maintained a high conversion rate of dimethyl oxalate and a dimethyl carbonate yield of 89.2%, without significant deactivation, demonstrating excellent stability and meeting the requirements for continuous industrial production. Furthermore, the stability of catalyst I was verified; the catalyst essentially lost its activity after the first sampling at 2 hours, indicating that alkali metal salts cannot achieve the complexation loading effect of transition metals.

[0080] 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. The application of a heterogeneous catalyst in the decarbonylation of alkyl oxalate to alkyl carbonate, characterized in that, The heterogeneous catalyst is a transition metal-modified organic amine-grafted polystyrene resin obtained by grafting chloromethylated polystyrene resin with an organic tertiary amine and then modifying it with a transition metal anion complex. The transition metal anion complex is CuCl4. 2- CoCl4 2- SnCl4 2- ZnCl4 2- or NiCl4 2- At least one of the anionic complexes.

2. The application of the heterogeneous catalyst according to claim 1 in the decarbonylation of alkyl oxalate to alkyl carbonate, characterized in that, The organic tertiary amine is at least one of trimethylamine, triethylamine, tributylamine, dodecyl dimethyl tertiary amine, tetradecyl dimethyl tertiary amine, or polyethyleneimine.

3. The application of the heterogeneous catalyst according to claim 1 or 2 in the decarbonylation of alkyl oxalate to alkyl carbonate, characterized in that, The mass ratio of the chloromethylated polystyrene resin to the organic tertiary amine is 20:1-2:1, and the mass ratio of the chloromethylated polystyrene resin to the transition metal anion complex is 50:1-5:

1.

4. The application of the heterogeneous catalyst according to claim 1 or 2 in the decarbonylation of alkyl oxalate to alkyl carbonate, characterized in that, The grafting process includes: adding chloromethylated polystyrene resin to an organic solvent to fully swell, then adding an organic tertiary amine and an inorganic base and stirring to react, thereby obtaining organic amine-grafted polystyrene resin; The organic solvent is at least one of N,N-dimethylformamide or N,N-dimethylacetamide, the inorganic base is at least one of potassium carbonate, sodium carbonate or potassium phosphate, and the stirring reaction temperature is 80-120 °C for 8-12 h.

5. The application of the heterogeneous catalyst according to claim 4 in the decarbonylation of alkyl oxalate to alkyl carbonate, characterized in that, The modification includes: dispersing the organic amine-grafted polystyrene resin evenly in an alcohol solvent, then adding a transition metal anion complex and stirring to react, thereby obtaining the transition metal-modified organic amine-grafted polystyrene resin. The alcohol solvent is at least one of ethanol, methanol or isopropanol, and the stirring reaction temperature is 20-40 °C for 1-3 h.

6. The application of the heterogeneous catalyst according to claim 1 in the decarbonylation of alkyl oxalate to alkyl carbonate, characterized in that, The molecular structure of the alkyl oxalate is shown below: The molecular structural formula of the alkyl carbonate is shown below: In this context, R and R' are each an alkyl group with 1 to 8 carbon atoms.

7. The application of the heterogeneous catalyst according to claim 1 or 6 in the decarbonylation of alkyl oxalate to alkyl carbonate, characterized in that, The specific application includes: passing a raw material liquid of alkyl oxalate into a fixed-bed reactor containing a multiphase catalyst, pressurizing and heating it to carry out a decarbonylation reaction, and then distilling the resulting reaction liquid to obtain alkyl carbonate.

8. The application of the heterogeneous catalyst according to claim 7 in the decarbonylation of alkyl oxalate to alkyl carbonate, characterized in that, The decarbonylation reaction is carried out at a temperature of 100-180 °C, a pressure of 0.1-1.0 MPa, and a residence time of 0.5-5.0 h.

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