A catalyst for preparing dimethyl carbonate by decarboxylation of dimethyl oxalate and a preparation method and application thereof

Abstract

The application discloses a catalyst for preparing dimethyl carbonate by decarboxylation of dimethyl oxalate and a preparation method and application thereof. The catalyst is composed of a carrier and a metal loaded on the carrier, the weight ratio of the metal in the catalyst is 0.5-50%, the metal is at least one of first main group metal elements, and the carrier is a core-shell composite carrier with Silicalite-1 as a core and mesoporous silica as a shell. The catalyst uses a Silicalite-1@m-SiO2 core-shell composite carrier, the m-SiO2 mesoporous shell layer grown in situ with Silicalite-1 as a core has a wrinkle type thin wall, forms a deep gully type loop morphology, provides a larger specific surface and more adsorption sites for the attachment of alkali metals on the surface of the carrier, greatly improves the capacity and dispersion of the alkali metal loading, and improves the activity and stability of the dimethyl carbonate catalyst prepared by decarboxylation of dimethyl oxalate.

Description

Technical Field

[0001] This invention belongs to the field of dimethyl carbonate preparation technology, specifically relating to a catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate, its preparation method, and its application. Technical Background

[0002] Dimethyl carbonate (DMC) is a low-toxicity, multi-purpose feedstock widely used in organic synthesis, as a solvent, fuel additive, and battery additive. DMC was originally synthesized primarily via the phosgene-ethanol process, but this was abandoned due to its high toxicity, and transesterification was adopted instead. Recently, alternative synthetic routes have been developed, such as the oxidative carbonylation of methanol and urea alcoholysis; however, these methods are far from perfect because catalysts are prone to deactivation and product separation is energy-intensive. In recent years, the decarbonylation of dimethyl oxalate (DMO) to produce dimethyl carbonate (DMC) has gained increasing attention. Under suitable conditions, obtaining DMC by cleaving CO molecules from DMO has proven thermodynamically feasible. As a coal-to-ethylene glycol intermediate, dimethyl oxalate (DMO) has a large production capacity; therefore, as a promising downstream technology of DMO, developing catalysts and preparation methods for the decarbonylation of dimethyl oxalate to produce dimethyl carbonate is of great significance.

[0003] Regarding catalytic technologies for the decarbonylation of dimethyl oxalate to dimethyl carbonate, patents include: US4544507, which discloses the use of sodium alkoxide as a catalyst; EP0916645, which discloses potassium carbonate as a catalyst; and CN116351467 A, which discloses an alkali metal-alkaline earth metal composite organic salt as a catalyst for the liquid-phase decarbonylation of DMO to prepare DMC. The disadvantages of liquid-phase reactions are obvious: difficult catalyst recovery and high energy consumption for product purification. Supporting alkali metals or alkaline earth metals on a support to create a heterogeneous catalyst facilitates catalyst recovery. Patent CN105478150 A discloses a titanium dioxide-supported alkali metal catalyst, and patent CN113385207 A discloses catalysts prepared using activated carbon as a support and supporting alkali metals such as potassium, rubidium, and cesium. Patent CN113181894 A discloses group III and group IV inorganic acid salt supported catalysts of alkali metals / alkaline earth metals. Applicable supports include activated carbon, molecular sieves, nano-silica, non-metallic organic covalent compounds (COFs), metal-organic frameworks (MOFs), and organic-inorganic composite materials. Furthermore, precious metals have also been explored for enhancing the catalytic activity of DMO decarbonylation. For example, patent CN115487806A discloses an activated carbon supported catalyst using palladium and alkali metal / alkaline earth metal ions as active components, which has shown some effectiveness in catalyzing the decarbonylation reaction of DMO in a fixed-bed reactor.

[0004] The key to the process route of decarbonylation of dimethyl oxalate (DMO) to dimethyl carbonate (DMC) is the catalytic reaction technology. The catalyst needs to meet the stringent requirements of the process conditions: (1) High activity: The decarbonylation reaction activity of dimethyl oxalate (DMO) is related to the type and loading of alkali metal salts. Under the same type of alkali metal salt, appropriately increasing the loading has a significant effect on improving the alkali catalytic activity; (2) High selectivity: Since the reaction temperature is above 200 °C, the reaction product dimethyl carbonate (DMC) can further lose carbonyl to generate the byproduct dimethyl ether. A small amount of water in the system will also lead to the generation of byproducts such as methanol and methyl formate; (3) High stability: The main active components of traditional decarbonylation catalysts are alkali metals or alkaline earth metals. However, at high temperatures, the catalyst is prone to carbon deposition and deactivation, and the higher the loading, the more significant the loss. Therefore, it is of great significance to develop a high-loading heterogeneous catalyst with both high activity and high stability suitable for the decarbonylation of dimethyl oxalate (DMO) to dimethyl carbonate (DMC). Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate, its preparation method, and its application. By using a core-shell inorganic support, the loading capacity and dispersion of alkali metals are improved, giving the catalyst higher catalytic activity, selectivity, and stability.

[0006] A catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate, the catalyst comprising a support and a metal supported on the support, wherein the metal accounts for 0.5-50% of the catalyst by weight; the metal is at least one of Group I metal elements; the support is a core-shell composite support with Silicalite-1 as the core and mesoporous silica as the shell, the support being represented as Silicalite-1@m-SiO2.

[0007] Preferably, the amounts of the core and shell are both calculated as SiO2, and the molar ratio of the core to the shell in the carrier is 0.1-10.

[0008] Preferably, the metal is at least one selected from cesium, potassium, rubidium, and sodium.

[0009] The preparation method of the catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate includes the following steps:

[0010] (1) Preparation of core-shell composite carrier:

[0011] (1.1) Mix template agent A and deionized water, then slowly add silicon source, stir until silicon source hydrolyzes, let stand at room temperature for 2-12 h, then hydrothermally react the obtained gel at 60-180℃ for 2-48 h, then wash with water until pH value is neutral, dry and calcine to obtain Silicalite-1 molecular sieve.

[0012] (1.2) Mix template agent B, sodium carboxylate and deionized water, stir at 45-85℃ until transparent and clear, add the Silicalite-1 molecular sieve, sonicate for 25-40 min, add silicon source while stirring, continue to stir at 45-85℃ for 3-5 h, keep warm in an oven at 80-140℃ for 4-24 h, filter, wash, dry and calcine to obtain the core-shell composite carrier;

[0013] (2) Loading metal:

[0014] The catalyst is obtained by mixing the core-shell composite support and the metal precursor solution using an equal-volume impregnation method, stirring and refluxing at 40-85℃ for 0.5-10 hours, filtering, washing, drying, and calcining.

[0015] Preferably, in step (1.1), the amount of silicon source is SiO2, and the molar ratio of template agent A, silicon source and deionized water is (10-500): 100: (100-6200).

[0016] In step (1.2), the amount of silicon source and Silicalite-1 molecular sieve are both calculated as SiO2, and the molar ratio of template agent B, sodium carboxylate, deionized water, silicon source and Silicalite-1 molecular sieve is (2-10): (1-5): (100-6200):100: (10-1000).

[0017] Preferably, template agent A is tetraalkylammonium hydroxide or triethylamine, template agent B is tetrapropylammonium bromide or hexadecylammonium bromide, silicon source is silica sol or tetraethyl orthosilicate, and sodium carboxylate is sodium benzoate, sodium trifluoroacetate or sodium salicylate.

[0018] Preferably, in step (1), the drying conditions are drying at 60-120℃ for 2-24 hours, and the calcination conditions are calcination at 400-660℃ for 2-24 hours; in step (2), the drying conditions are drying at 50-110℃ for 2-24 hours, and the calcination conditions are calcination at 400-660℃ for 4-24 hours.

[0019] Preferably, the precursor of the metal is a corresponding carbonate, nitrate, or acetate.

[0020] A method for catalytic decarbonylation of dimethyl oxalate to dimethyl carbonate: A catalyst is packed in a fixed-bed reactor, preheated under a high-purity N2 atmosphere, and then methanol and dimethyl oxalate are introduced. The reaction is carried out at a reaction temperature of 180-300℃, a reaction pressure of 0.2-3.5 MPa, and a high-purity N2 atmosphere, and the product is collected; wherein the preheating temperature is ≤10℃ higher than the reaction temperature; the catalyst is the catalyst described in claim 1.

[0021] Preferably, the mass hourly space velocity (MSV) of the dimethyl oxalate is 0.1-3.0 h⁻¹. -1 The molar ratio of methanol to dimethyl oxalate is 1:(1-10).

[0022] Advantages of this invention:

[0023] The catalyst provided by this invention utilizes a Silicalite-1@m-SiO2 core-shell composite support. The m-SiO2 mesoporous shell layer grown in situ with Silicalite-1 as the core has a wrinkled thin wall and forms a deep-groove loop morphology, providing a larger specific surface area and more adsorption sites for alkali metals to adhere to the support surface. This greatly improves the capacity and dispersion of alkali metal loading, thereby achieving a balance between activity and stability. It enhances the activity and stability of the catalyst for the decarbonylation of dimethyl oxalate (DMO) to dimethyl carbonate (DMC), resulting in high product selectivity. Attached Figure Description

[0024] Figure 1 The results of the catalyst activity durability test in Example 1 are as follows: Figure 1 In this context, 'a' represents the conversion rate of the raw material DMO. Figure 1 In the middle, b represents the selectivity for DMC;

[0025] Figure 2 The results of CO2-TPD characterization of the catalysts in Example 1 and Comparative Example 2 are shown.

[0026] Figure 3 XRD characterization of the catalysts in Example 1 and Comparative Example 2;

[0027] Figure 4 Here is a SEM image of the catalyst from Example 1;

[0028] Figure 5 The image shows the TEM characterization of the catalyst in Example 1.

[0029] Figure 6 The N2- adsorption-desorption curves of the catalyst in Example 1 are shown. Detailed Implementation

[0030] Example 1

[0031] 1. A catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate, the catalyst comprising a support and metal Cs supported on the support, wherein the metal Cs accounts for 10% by weight of the catalyst; the support is a core-shell composite support with Silicalite-1 as the core and mesoporous silica as the shell, wherein the amount of the core and shell is calculated as SiO2, the molar ratio of the core and shell in the support is 0.5, and the support is represented as Silicalite-1@m-SiO2;

[0032] 2. The catalyst is prepared by the following method:

[0033] (1) Preparation of core-shell composite carrier:

[0034] (1.1) Mix 500 mmol tetrapropylammonium hydroxide (TPAOH) and 6200 mmol deionized water, then slowly add 100 mmol silica sol (as SiO2), stir vigorously until the silica source is hydrolyzed, let stand at room temperature for 12 h, transfer the resulting gel to a stainless steel autoclave lined with polytetrafluoroethylene, and then perform a hydrothermal reaction in an oven at 180 °C for 2 h. Wash the product with water until the pH value is neutral, dry at 120 °C for 2 h, and calcine at 660 °C for 2 h to obtain Silicalite-1 molecular sieve;

[0035] (1.2) Mix 10 mmol of template agent cetyl ammonium bromide, 5 mmol of sodium benzoate and 6200 mmol of deionized water, stir at 85 °C until transparent and clear, add 50 mmol of the Silicalite-1 molecular sieve, sonicate for 40 min, add 100 mmol of silica sol (calculated as SiO2) while stirring, continue to stir at 85 °C for 5 h, keep warm in an oven at 140 °C for 4 h, filter, wash, dry at 120 °C for 2 h and calcine at 660 °C for 2 h to obtain the core-shell composite carrier, represented as 0.5Silicalite-1@m-SiO2;

[0036] (2) Loading metal:

[0037] The core-shell composite support and cesium acetate solution were mixed using an equal-volume impregnation method, stirred and refluxed at 40°C for 10 h, filtered, washed, dried at 110°C for 2 h, and calcined at 660°C for 4 h to obtain the catalyst, which is represented as 10%Cs / 0.5Silicalite-1@m-SiO2.

[0038] Example 2

[0039] 1. A catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate, the catalyst comprising a support and metal Cs supported on the support, wherein the metal Cs accounts for 10% by weight of the catalyst; the support is a core-shell composite support with Silicalite-1 as the core and mesoporous silica as the shell, wherein the amount of the core and shell is calculated as SiO2, the molar ratio of the core and shell in the support is 0.5, and the support is represented as Silicalite-1@m-SiO2;

[0040] 2. The catalyst is prepared by the following method:

[0041] (1) Preparation of core-shell composite carrier:

[0042] (1.1) Mix 10 mmol of template agent A tetrapropylammonium hydroxide TPAOH and 100 mmol of deionized water, then slowly add 100 mmol of silica sol (calculated as SiO2), stir vigorously until the silica source is hydrolyzed, let stand at room temperature for 2 h, transfer the obtained gel to a stainless steel autoclave lined with polytetrafluoroethylene, and then perform hydrothermal reaction in an oven at 60 °C for 48 h. Wash the product with water until the pH value is neutral, dry at 60 °C for 24 h, and calcine at 400 °C for 24 h to obtain Silicalite-1 molecular sieve;

[0043] (1.2) Mix 2 mmol template agent B hexadecyl ammonium bromide, 1 mmol sodium benzoate and 100 mmol deionized water, stir at 85 °C until transparent and clear, add 50 mmol of the Silicalite-1 molecular sieve, sonicate for 25 min, add 100 mmol of silica sol (calculated as SiO2) while stirring, continue to stir at 85 °C for 3 h, keep warm in an oven at 80 °C for 24 h, filter, wash, dry at 60 °C for 24 h, calcine at 400 °C for 24 h to obtain the core-shell composite carrier, represented as 0.5Silicalite-1@m-SiO2;

[0044] (2) Loading metal:

[0045] The core-shell composite support and cesium acetate solution were mixed using an equal-volume impregnation method, stirred and refluxed at 85°C for 0.5 h, filtered, washed, dried at 50°C for 24 h, and calcined at 400°C for 24 h to obtain the catalyst, which is represented as 10%Cs / 0.5 Silicalite-1@m-SiO2.

[0046] Example 3

[0047] The molar ratio of the core and shell in the carrier is 5. In step (1.2), 500 mmol of Silicalite-1 molecular sieve is taken. The rest is the same as in Example 1. The carrier is denoted as 5 Silicalite-1@m-SiO2.

[0048] Example 4

[0049] The precursor solution used was cesium nitrate solution, and the rest was the same as in Example 1.

[0050] Example 5

[0051] The supported metal is potassium, the precursor solution used is potassium acetate solution, the metal accounts for 10% of the weight of the catalyst, and other aspects are the same as in Example 1.

[0052] Example 6

[0053] The supported metal is rubidium (Rb), and the precursor solution used is rubidium acetate solution. The metal accounts for 10% of the weight of the catalyst, and other aspects are the same as in Example 1.

[0054] Example 7

[0055] The metal accounts for 0.5% of the weight of the catalyst, and the rest is the same as in Example 1.

[0056] Example 8

[0057] The metal accounts for 50% of the weight of the catalyst, and the rest is the same as in Example 1.

[0058] Example 9

[0059] Sodium salicylate was used instead of sodium benzoate in the preparation of the carrier, and the rest was the same as in Example 1.

[0060] Example 10

[0061] In preparing the carrier, tetraethyl orthosilicate was used instead of silica sol, and the rest was the same as in Example 1.

[0062] Example 11

[0063] Template agent A uses triethylamine instead of tetrapropylammonium hydroxide, and the rest is the same as in Example 1.

[0064] Example 12

[0065] Template agent B uses tetrapropylammonium bromide instead of hexadecylammonium bromide, otherwise it is the same as in Example 1.

[0066] Example 13

[0067] The molar ratio of the core and shell in the carrier is 0.1. In step (1.2), 10 mmol of Silicalite-1 molecular sieve is taken. The rest is the same as in Example 1. The carrier is recorded as 0.1 Silicalite-1@m-SiO2.

[0068] Example 14

[0069] The molar ratio of the core and shell in the carrier is 10. In step (1.2), 1000 mmol of Silicalite-1 molecular sieve is taken. The rest is the same as in Example 1. The carrier is recorded as 10 Silicalite-1@m-SiO2.

[0070] Comparative Example 1

[0071] The carrier used was commercially available SiO2, and other aspects were the same as in Example 1.

[0072] Comparative Example 2

[0073] The carrier used was the Silicalite-1 molecular sieve from Example 1, and the rest was the same as in Example 1.

[0074] I. Catalytic performance and stability testing

[0075] 1. Catalytic performance testing

[0076] A method for catalytic decarbonylation of dimethyl oxalate (DMO) to dimethyl carbonate (DMC) involves: loading a catalyst into a fixed-bed reactor, preheating it under a high-purity N2 atmosphere, then introducing methanol and dimethyl oxalate; reacting at a reaction temperature of 180-300℃, a reaction pressure of 0.2-3.5 MPa, and a high-purity N2 atmosphere; and collecting the product. The mass hourly space velocity (WHSV) of the dimethyl oxalate is 0.1-3.0 h⁻¹. -1 The molar ratio (ethanol-ester ratio) of methanol to dimethyl oxalate is 1:(1-10); the preheating temperature is the same as the reaction temperature, and the specific reaction conditions and results are shown in Table 1;

[0077] Table 1. Reaction results under different reaction conditions

[0078] .

[0079] 2. Stability testing

[0080] The catalysts of Example 1, Comparative Example 1, and Comparative Example 2 were subjected to activity and durability evaluation tests under the following reaction conditions: 220°C, 0.2 MPa, alcohol-ester ratio 1:1, and DMO space velocity 1.0 h⁻¹. -1 The reaction was carried out for 216 hours, and the results are shown in [the table below]. Figure 1 .Depend on Figure 1As can be seen, after a cumulative reaction of 216 hours, the catalyst activity of Example 1 remained basically stable, with a conversion rate of 95.8% and a DMC selectivity of 98.3%, showing no significant decrease compared to the activity after 2 hours of reaction (conversion rate of 99.7% and DMC selectivity of 98.4%). With the extension of reaction time, the catalyst activities of Comparative Example 1 and Comparative Example 2 both showed a significant decrease.

[0081] 3. CO2-TPD characterization

[0082] The catalysts of Example 1 and Comparative Example 2 were characterized by CO2-TPD, see [see details]. Figure 2 .Depend on Figure 2 It can be seen that both the catalyst of Example 1 and the catalyst of Comparative Example 2 showed CO2 desorption peaks around 195°C, and the desorption peak area of ​​the former was significantly larger than that of the latter. This indicates that, under the same preparation conditions, using the core-shell composite material 0.5Silicalite-1@m-SiO2 as a support can actually provide more basic sites.

[0083] 4. XRD characterization

[0084] The catalysts of Example 1 and Comparative Example 2 were characterized by XRD, see [see details]. Figure 3 .Depend on Figure 3 It can be seen that the XRD diffraction peak characteristics of the catalyst in Example 1 and the catalyst in Comparative Example 2 are basically the same, but the diffraction peak intensity of Example 1 is relatively lower, indicating that the mesoporous shell layer of the core-shell material weakens the diffraction characteristic peaks of the core Silicalite-1.

[0085] 5. SEM characterization

[0086] The catalyst of Example 1 was examined by scanning electron microscopy (SEM), see [see details]. Figure 4 .Depend on Figure 4 It is evident that the material surface has wrinkled thin walls, forming a deep groove-type loop morphology.

[0087] 6. TEM characterization

[0088] The catalyst of Example 1 was examined by transmission electron microscopy (TEM), see [see details]. Figure 5 .Depend on Figure 5 It is evident that it has a clear core-shell structure. The dark core region is believed to be Silicalite-1 molecular sieve, while the lighter outer region is believed to be m-SiO2 with a porous structure. The shell thickness is approximately 45~55 nm.

[0089] 7. N2- adsorption-desorption experiment

[0090] N2- adsorption-desorption experiments were performed on the catalyst of Example 1. The adsorption-desorption isotherm results are shown in [Figure 1]. Figure 6 .like Figure 6 As shown, the adsorption isotherm of the core-shell material exhibits a significant H4-type hysteresis loop, indicating that the material has a mesoporous structure containing narrow slit pores.

Claims

1. A catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate, characterized in that: The catalyst consists of a support and a metal oxide supported on the support, wherein the metal element in the metal oxide accounts for 0.5-50% of the catalyst by weight; the support is a core-shell composite support with Silicalite-1 as the core and mesoporous silica as the shell; the amount of the core and shell is SiO2, and the molar ratio of the core and shell in the support is 0.1-10; the metal is at least one of cesium, potassium, rubidium, and sodium.

2. The method for preparing the catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 1, characterized in that: Includes the following steps: (1) Preparation of core-shell composite carrier: (1.1) Mix template agent A and deionized water, then slowly add silicon source, stir until silicon source hydrolyzes, let stand at room temperature for 2-12 h, then hydrothermally react the obtained gel at 60-180℃ for 2-48 h, then wash with water until pH value is neutral, dry and calcine to obtain Silicalite-1 molecular sieve. (1.2) Mix template agent B, sodium carboxylate and deionized water, stir at 45-85℃ until transparent and clear, add the Silicalite-1 molecular sieve, sonicate for 25-40 min, add silicon source while stirring, continue to stir at 45-85℃ for 3-5 h, keep warm in an oven at 80-140℃ for 4-24 h, filter, wash, dry and calcine to obtain the core-shell composite carrier; (2) Loading metal: The catalyst is obtained by mixing the core-shell composite support and the metal precursor solution using an equal-volume impregnation method, stirring and refluxing at 40-85℃ for 0.5-10 hours, filtering, washing, drying, and calcining.

3. The method for preparing the catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 2, characterized in that: In step (1.1), the amount of silicon source is SiO2, and the molar ratio of template agent A, silicon source and deionized water is (10-500): 100: (100-6200). In step (1.2), the amount of silicon source and the amount of Silicalite-1 molecular sieve are both calculated as SiO2, and the molar ratio of template agent B, sodium carboxylate, deionized water, silicon source and Silicalite-1 molecular sieve is (2-10): (1-5): (100-6200): 100:(10-1000).

4. The method for preparing the catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 3, characterized in that: The template agent A is tetraalkylammonium hydroxide or triethylamine, the template agent B is tetrapropylammonium bromide or hexadecylammonium bromide, the silicon source is silica sol or tetraethyl orthosilicate, and the sodium carboxylate is sodium benzoate, sodium trifluoroacetate or sodium salicylate.

5. The method for preparing the catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 4, characterized in that: In step (1), the drying conditions are drying at 60-120℃ for 2-24 hours, and the calcination conditions are calcination at 400-660℃ for 2-24 hours; in step (2), the drying conditions are drying at 50-110℃ for 2-24 hours, and the calcination conditions are calcination at 400-660℃ for 4-24 hours.

6. The method for preparing the catalyst for the decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 5, characterized in that: The precursor of the metal is the corresponding carbonate, nitrate or acetate.

7. A method for catalytic decarbonylation of dimethyl oxalate to dimethyl carbonate, characterized in that: The catalyst is packed into a fixed-bed reactor, preheated under a high-purity N2 atmosphere, and then methanol and dimethyl oxalate are introduced. The reaction is carried out at a reaction temperature of 180-300℃, a reaction pressure of 0.2-3.5MPa, and a high-purity N2 atmosphere, and the product is collected. The preheating temperature is the same as the reaction temperature. The catalyst is the catalyst described in claim 1.

8. The method for catalytic decarbonylation of dimethyl oxalate to dimethyl carbonate according to claim 7, characterized in that: The mass hourly space velocity (MSV) of the dimethyl oxalate is 0.1–3.0 h⁻¹. -1 The molar ratio of methanol to dimethyl oxalate is 1:(1-10).

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