Catalytic synthesis method of propylene carbonate
By subjecting activated carbon support to acid-base treatment and tetraethyl orthosilicate sol-gel treatment, a highly selective and stable catalyst was constructed, which solved the problem of insufficient conversion and selectivity in the synthesis of propylene carbonate from 1,2-propanediol and CO2, and enabled the stable recycling of the catalyst under high temperature and high pressure conditions.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANDONG LIXING ADVANCED MATERIAL TECH CO LTD
- Filing Date
- 2026-02-02
- Publication Date
- 2026-05-12
AI Technical Summary
Existing catalytic systems for the synthesis of propylene carbonate from 1,2-propanediol and CO2 suffer from insufficient conversion, selectivity, and catalyst recycling stability. In particular, under high temperature and high pressure conditions, the catalyst is prone to deactivation, structural collapse, and metal species migration.
Using activated carbon as a carrier, a highly polar ionic microenvironment is formed through acid-base treatment. This microenvironment combines tetraethyl orthosilicate and Lewis acid sites to construct stable Zn/Ti-related Lewis acid sites, promoting CO2 enrichment and 1,2-propanediol reaction, suppressing side reactions, and forming a highly selective and stable catalyst.
It improves the conversion and selectivity of propylene carbonate and maintains a high level of catalytic activity after multiple cycles of regeneration, thus solving the problem of catalyst stability under high temperature and high pressure conditions.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of propylene carbonate synthesis technology, and more specifically to a catalytic synthesis method for propylene carbonate. Background Technology
[0002] Propylene carbonate (PC) is an organic carbonate compound with high dielectric constant, low volatility, and good chemical stability. It is often used as an important solvent in lithium-ion battery electrolytes, a high-boiling-point solvent in polymer synthesis, and an intermediate in fine chemicals such as pharmaceuticals and pesticides. It can also be used as an environmentally friendly solvent in coatings, inks, and cleaning agents. The synthesis of propylene carbonate from carbon dioxide and 1,2-propanediol can realize the resource utilization of CO2 and avoid high-risk raw materials such as phosgene, which has a green and sustainable development direction. However, due to the high thermodynamic stability and strong chemical inertness of CO2 molecules and the large -OH bond energy in the 1,2-propanediol molecule, the two are difficult to spontaneously undergo efficient condensation and cyclization under mild conditions. The reaction requires an efficient catalytic system to reduce the activation energy of the reaction and suppress side reactions.
[0003] Currently, catalytic systems for the synthesis of propylene carbonate from 1,2-propanediol and CO2 include homogeneous quaternary ammonium salts, quaternary phosphine salts, organic bases, or ionic liquid systems, as well as heterogeneous metal oxides, metal salt supported catalysts, heteropolyacids, and their salts supported catalysts. Homogeneous catalytic systems typically have advantages such as high initial activity and easy formulation adjustment. However, in industrial applications, the homogeneous catalyst and product are in the same liquid phase, making it difficult to separate and recover them after the reaction. Some organic catalysts or ionic liquids have insufficient thermal stability and are prone to decomposition or deactivation under high temperature and high pressure CO2 environments, making it difficult to achieve multiple recycling.
[0004] Heterogeneous solid catalysts have significant advantages in recycling and process scale-up. However, traditional heterogeneous solid catalysts have low specific surface area or unreasonable pore structure, resulting in insufficient accessibility of effective active sites and limited external and internal mass transfer, making it difficult to achieve both high conversion rate and high selectivity. In addition, many supported metal catalysts are prone to metal species migration, aggregation or leaching in high temperature, high pressure CO2 and water / alcohol environments. Problems such as pore blockage and structural collapse are prominent during regeneration, leading to significant decline in activity and selectivity during catalyst recycling.
[0005] To address this technical deficiency, a solution is proposed. Summary of the Invention
[0006] The purpose of this invention is to provide a catalytic synthesis method for propylene carbonate, which addresses the technical problem that the conversion rate, selectivity, and stability of catalyst recycling in the prior art for the catalytic reaction of 1,2-propanediol and carbon dioxide to prepare propylene carbonate need further improvement.
[0007] The objective of this invention can be achieved through the following technical solution: a catalytic synthesis method for propylene carbonate, comprising the following steps: 1,2-Propanediol and the cyclization catalyst were added to a high-pressure reactor and stirred. Inert gas was introduced into the high-pressure reactor to replace and remove the air. The high-pressure reactor was heated to 115-125℃, and carbon dioxide was introduced into the reactor. The pressure of the high-pressure reactor was adjusted to 4-5 MPa, and the reaction was maintained at this temperature for 6-8 hours. The high-pressure reactor was then cooled to room temperature and filtered to obtain the propylene carbonate reaction solution and the recovered cyclization catalyst.
[0008] Further, tetraethyl orthosilicate and purified water were mixed and stirred. The reaction system was heated to 70-80℃, hydrochloric acid was added to the reaction system to adjust the pH to 3.5-4.5, and the reaction was maintained at this temperature for 50-70 min. Oxalic acid was added to the reaction system, and the reaction was maintained for 50-60 min. The reaction system was then cooled to 50-55℃, zinc acetate and tetrabutyl titanate were added to the reaction system, and the mixture was stirred for 45-55 min. Ionic salt modified activated carbon was added to the reaction system, and the mixture was kept at this temperature and stirred for 16-18 h. After post-treatment, the cyclized catalyst was obtained.
[0009] Furthermore, the ratio of tetraethyl orthosilicate, purified water, oxalic acid, zinc acetate, tetrabutyl titanate, and ion salt modified activated carbon is 5g:50mL:0.2-0.3g:0.4-0.5g:1.1-1.5g:20g. The post-treatment includes: after the reaction is complete, the reaction system is cooled to room temperature, filtered, the filter cake is washed three times with purified water and then transferred to a drying oven at 110-120℃ and dried to constant weight to obtain the cyclized catalyst.
[0010] Furthermore, ion salt modified activated carbon is obtained through the following steps: A1. Epoxy-modified activated carbon, ethyl acetate, and 1,4-diazacyclo[2.2.2]octane-2-acetamide were mixed and stirred. The reaction system was heated to 60-70℃ and kept at that temperature for 60-80 min. The reaction system was then cooled to 50-55℃. 1,3-propanesulfonate lactone was added to the reaction system, and the mixture was stirred and kept at that temperature for 20-22 h. After post-treatment, the ion salt-modified activated carbon precursor was obtained. The synthesis reaction formula for ion salt modified activated carbon precursor is as follows: A2. Mix the ion salt modified activated carbon precursor and sulfuric acid and stir for 20-30 minutes. Heat the reaction system to 75-85℃ and keep it at that temperature for 8-10 hours. After post-treatment, the ion salt modified activated carbon is obtained.
[0011] The synthesis reaction formula for ion salt modified activated carbon is as follows: Further, in step A1, the ratio of epoxy-modified activated carbon, ethyl acetate, 1,4-diazacyclo[2.2.2]octane-2-acetamide and 1,3-propanesulfonic acid lactone is 5g:30mL:0.8g:1.3g. The post-treatment includes: after the reaction is complete, the reaction system is cooled to room temperature, filtered, the filter cake is washed three times with purified water and then dried, the filter cake is transferred to a drying oven at 65-75℃ and dried to constant weight to obtain the ion salt modified activated carbon precursor.
[0012] Furthermore, in step A2, the solid-liquid ratio of the ion salt modified activated carbon precursor and sulfuric acid is 1:10, the concentration of the sulfuric acid is 2-3 mol / L, and the post-treatment includes: after the reaction is completed, the reaction system is cooled to room temperature, filtered, the filter cake is washed three times with purified water and then transferred to a drying oven at a temperature of 85-95℃ and dried to constant weight to obtain ion salt modified activated carbon.
[0013] Furthermore, the preparation method of epoxy-modified activated carbon is as follows: pretreated activated carbon, anhydrous ethanol and KH-560 are mixed and stirred, the reaction system is heated to 50-60℃, an alkaline catalyst is added to the reaction system, the reaction is kept at the temperature for 50-70 min, and then post-treated to obtain epoxy-modified activated carbon.
[0014] The synthesis reaction formula for epoxy-modified activated carbon is as follows: In the formula, The activated carbon particles are pretreated. Further, the ratio of the pretreated activated carbon, anhydrous ethanol, KH-560, and alkaline catalyst is 5g:50mL:0.9-1.1g:8mL, and the alkaline catalyst is a 2-3mol / L sodium hydroxide solution. The post-treatment includes: after the reaction is complete, cooling the reaction system to room temperature, filtering, washing the filter cake with purified water until neutral, drying it, transferring the filter cake to a drying oven at 70-80℃, and drying it to constant weight to obtain epoxy-modified activated carbon.
[0015] Furthermore, the pretreated activated carbon is obtained by the following steps: B1. Mix activated carbon and hydrochloric acid solution, heat the reaction system to 50-60℃, keep it at the temperature for 120-150 min, and then perform post-treatment to obtain acid-treated activated carbon. B2. Mix the acid-treated activated carbon and the alkaline solution, heat the reaction system to 40-50℃, keep it at the temperature for 10-12 hours, and then perform post-treatment to obtain the pretreated activated carbon. B3. Spread the pretreated activated carbon evenly in a tube furnace. Under the protection of an inert gas atmosphere, heat the tube furnace to 750-800℃ and keep it at that temperature for 2-3 hours. Then perform post-treatment to obtain pretreated activated carbon.
[0016] Further, in step B1, the solid-liquid ratio of the activated carbon and hydrochloric acid solution is 1:5-6, and the hydrochloric acid solution is composed of 1-2 mol / L hydrochloric acid and sodium dodecyl sulfate at a ratio of 100 mL:2-3 g. The post-treatment includes: after the reaction is completed, the reaction system is cooled to room temperature, filtered, the filter cake is washed with purified water until neutral and then dried, the filter cake is transferred to a drying oven at a temperature of 80-90℃ and dried to constant weight to obtain acid-treated activated carbon.
[0017] Further, in step B2, the solid-liquid ratio of the acid-treated activated carbon and the alkaline solution is 1:5-6, the alkaline solution is a 2-3 mol / L potassium hydroxide solution, and the post-treatment includes: after the reaction is complete, filtration is performed, the filter cake is transferred to a drying oven at a temperature of 100-110℃, and dried to constant weight to obtain pretreated activated carbon; in step B3, the heating rate of the tube furnace is 3-5℃ / min, and the post-treatment includes: after the reaction is complete, the tube furnace is cooled to room temperature, the calcined material is washed with purified water until neutral, then dried, and then transferred to a drying oven at a temperature of 80-90℃, and dried to constant weight to obtain pretreated activated carbon.
[0018] Furthermore, the weight ratio of 1,2-propanediol to the cyclization catalyst is 50:3-5.
[0019] The present invention has the following beneficial effects: This invention uses activated carbon as a carrier and first treats it with acid and then with alkali to prepare pretreated activated carbon. Epoxysilanes undergo hydrolysis-condensation under alkaline conditions to form a firmly anchored layer with oxygen-containing groups on the surface of the pretreated activated carbon, introducing exposed epoxy groups into the pore walls. Then, covalent grafting is achieved through nucleophilic ring-opening of the epoxy groups by nitrogen-containing components, followed by ring-opening alkylation with propane sulfonate lactone to form a quaternary ammonium cation-sulfonate ionic salt structure. Subsequently, sulfuric acid treatment causes protonation and ion exchange, converting the sulfonate group to -SO3. H+ forms stable ion pairs between the quaternary ammonium sites and HSO4- / SO2-, while simultaneously removing unfixed or weakly bound small molecule residues. This creates a highly polar, strongly hydrogen-bonded / acid-regulated ion microenvironment within the pores of the activated carbon support, which can enrich CO2. It can directionally adsorb and activate glycols and stabilize key intermediates, promote the consumption of propylene glycol to preferentially follow the target cyclization pathway, inhibit side reactions such as dehydration and condensation, improve the conversion rate and selectivity of propylene carbonate, and maintain a high level even after multiple regenerations. This invention also utilizes activated carbon as a support. The support itself has low density, rough particle surface, and well-developed pores, making it easier to form a suspended dispersion under stirring conditions rather than rapid sedimentation. This allows the catalyst to be more easily wetted in the reaction medium and form a stable suspended dispersion, enhancing three-phase mass transfer and the accessibility of active sites, thereby promoting conversion. It also indirectly stabilizes the ionic microenvironment and works synergistically with Lewis acids, helping to maintain high selectivity and better regeneration performance. Furthermore, by employing a hydrochloric acid and surfactant synergistic acid washing process, ash and inorganic impurities in the activated carbon are removed, and pore wetting is improved, simultaneously cleaning the inner and outer surfaces of the pores and reducing impurity-induced degradation. The non-selective side reactions and the shielding effect of subsequent loading are mitigated; then, chemical activation and pore structure shaping are achieved through alkali treatment and high-temperature calcination in an inert atmosphere, forming a more developed and interconnected pore system and enhancing the thermal / chemical stability of the carbon skeleton. After calcination, washing to neutrality reduces the risk of residual salt precipitation, pore blockage, or interference with ion layer / metal sites during reaction and regeneration, making the active sites more uniformly dispersed in the pores and easier to contact with reactants. At the same time, the support can maintain the integrity of the pore structure and the accessibility of the sites even under repeated ethanol washing, dilute acid washing, and water washing regeneration conditions, supporting the slowed activity decay and more stable performance of the cyclized catalyst during recycling. This invention also promotes the hydrolysis and condensation of tetraethyl orthosilicate under acidic conditions to form a -Si-O-Si- network, and introduces oxalic acid complexation to regulate the hydrolysis rate of metal species. This allows zinc acetate and tetrabutyl titanate to be anchored in the -Si-O-Si- network with higher dispersion during gelation, forming stable Zn / Ti-related Lewis acid sites. These Lewis acid sites activate the hydroxyl coordination of 1,2-propanediol, increasing the cyclization reaction rate, while the pore wall ion salt / -SO3 The H microenvironment provides CO2 Enrichment and ion polarity stabilization promote CO2 Insertion and closure of the ring suppress side reactions, thereby achieving a balance between high selectivity and efficient conversion. At the same time, the anchoring of metal sites and structural support of the organic ion layer by the -Si-O-Si- network reduces the probability of site migration, aggregation and leaching, making it easier for the catalyst to maintain its structure and activity during recycling and regeneration. This results in a slower decline in activity and more stable performance of the cyclized catalyst after multiple regenerations, improving the good recycling performance of the cyclized catalyst. Detailed Implementation
[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0021] In this application, the activated carbon is virgin carbon, and the material of virgin carbon is wood chips, fruit shells, coconut shells, etc., with a particle size of 200 mesh, selected from commercially available products of Changge Changhao Environmental Protection Technology Co., Ltd. In this application, KH-560 is γ-glycidoxypropyltrimethoxysilane, CAS number 2530-83-8; In this application, the CAS number of 1,4-diazacyclic [2.2.2]octane-2-acetamide is 171351-29-4; In this application, the purity of carbon dioxide is ≥99.9%. Example
[0022] This embodiment provides a method for preparing a cyclization catalyst for the catalytic synthesis of propylene carbonate, comprising the following steps: Step 1: Preparation of pretreated activated carbon Mix 1 mol / L hydrochloric acid and sodium dodecyl sulfate at a ratio of 100 mL: 2 g to obtain a hydrochloric acid solution; Activated carbon and hydrochloric acid solution were added to a reaction flask at a solid-liquid ratio of 1:5 and stirred. The reaction flask was heated to 50°C and kept at this temperature for 120 minutes. The reaction flask was then cooled to room temperature and filtered. The filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at 80°C and dried to constant weight to obtain acid-treated activated carbon. During the acid treatment process, hydrochloric acid solution dissolves inorganic ash, metal oxides, carbonates and other impurities in activated carbon. Sodium dodecyl sulfate, under acidic conditions, can reduce the surface tension of the aqueous phase, enhance the wetting of carbon pores by the solution, and promote the removal rate of impurities in activated carbon. By removing inorganic impurities from activated carbon through acid treatment, the side reaction sites caused by non-selective base / acid centers and metal impurities in subsequent reactions are reduced.
[0023] Acid-treated activated carbon and 2 mol / L potassium hydroxide solution were added to a reaction flask at a solid-liquid ratio of 1:5 and stirred. The reaction flask was heated to 40°C and kept at this temperature for 10 hours. The mixture was then filtered, and the filter cake was transferred to a drying oven at 100°C and dried to constant weight to obtain pretreated activated carbon. The pretreated activated carbon was spread evenly in a tube furnace. Under argon protection, the tube furnace was heated to 750°C at a heating rate of 3°C / min and calcined for 2 hours. The tube furnace was then cooled to room temperature. The calcined material was washed with purified water until neutral and then dried. It was then transferred to a drying oven at 80°C and dried to constant weight to obtain pretreated activated carbon.
[0024] During heating, activated carbon and KOH undergo a series of reduction / oxidation reactions, generating K, K2CO3, and CO2 which are embedded or corroded in the carbon skeleton. This process etches new pores into the carbon skeleton and opens up existing blind pores. After cooling, water washing removes K, K2CO3, and other substances as soluble salts, making the microporous / mesoporous system more developed and interconnected. This significantly increases the specific surface area and pore volume while preventing salting out / clogging in subsequent processes. Furthermore, after calcination and shaping, the activated carbon is less prone to collapse under subsequent acid washing / organic treatments, thus improving the structural stability of the carbon skeleton and the cycle stability of the catalyst material.
[0025] Step 2: Preparation of epoxy-modified activated carbon Weigh out 50g of pretreated activated carbon, 500mL of anhydrous ethanol and 9g of KH-560 and add them to the reaction flask. Stir the mixture and heat the reaction flask to 50℃. Add 80mL of 2mol / L sodium hydroxide solution to the reaction flask and keep it at this temperature for 50min. After the reaction is complete, cool the reaction flask to room temperature, filter it, wash the filter cake with purified water until neutral, and then dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight to obtain epoxy-modified activated carbon.
[0026] In the reaction, KH-560 undergoes hydrolysis in ethanol and alkaline water to form silanol. Then, the silanol bonds with the active reaction sites on the surface of the pretreated activated carbon, forming epoxy groups on the pretreated activated carbon to prepare epoxy-modified activated carbon.
[0027] Step 3: Preparation of ion salt modified activated carbon Weigh out 50g of epoxy-modified activated carbon, 300mL of ethyl acetate and 8g of 1,4-diazacyclo[2.2.2]octane-2-acetamide and add them to a reaction flask. Stir the mixture and heat it to 60℃. Keep the mixture at this temperature for 60min. Cool the mixture to 50℃ and add 13g of 1,3-propanesulfonate lactone. Keep the mixture at this temperature and stir for 20h. Cool the mixture to room temperature and filter it. Wash the filter cake three times with purified water and then dry it. Transfer the filter cake to a drying oven at 65℃ and dry it to constant weight to obtain the ion salt modified activated carbon precursor.
[0028] In the reaction, the strong nucleophilic tertiary amine site on the 1,4-diazacyclic [2.2.2]octane molecule undergoes ring-opening condensation with the epoxy group modified on the epoxy-modified activated carbon, thereby bonding triethylenediamine onto the epoxy-modified activated carbon support. Then, 1,3-propanesulfonate lactone undergoes ring-opening bonding with the ammonia on the triethylenediamine molecule to form quaternary ammonium and sulfonic acid ion salt modification, thus obtaining the ion salt modified activated carbon precursor.
[0029] Ion salt modified activated carbon precursor and 2 mol / L sulfuric acid were added to a reaction flask at a solid-liquid ratio of 1:10 and stirred for 20 min. The reaction flask was heated to 75 °C and kept at this temperature for 8 h. The reaction flask was then cooled to room temperature, filtered, and the filter cake was washed three times with purified water and then transferred to a drying oven at 85 °C and dried to constant weight to obtain ion salt modified activated carbon.
[0030] In the reaction, the ion salt modified activated carbon precursor is mixed with sulfuric acid, and the sulfonate ions on the ion salt modified activated carbon precursor are converted by H+. + The protons are converted to -SO3H, and the original anions around the quaternary ammonium cation are replaced by HSO4- / SO2-, resulting in ion salt modified activated carbon.
[0031] The quaternary ammonium cation and the strong polar field formed around -SO3H / HSO4 are conducive to the adsorption of polar / polarizable molecules, such as CO2, increasing the local concentration of CO2 in the reaction system, thereby effectively increasing the collision probability of molecules and promoting the insertion reaction. -SO3H provides a strong Brønsted acid, forming hydrogen bonds with the hydroxyl groups on the 1,2-propanediol molecule, promoting the dissociation of -OH and enhancing nucleophilicity. The electric field around the quaternary ammonium cation also helps to stabilize the transition state / intermediate, suppress side reactions, and improve selectivity.
[0032] Step 4: Preparation of cyclization catalyst Weigh 25g of tetraethyl orthosilicate and 250mL of purified water and add them to a reaction flask. Stir the mixture and heat the flask to 70℃. Add 3mol / L hydrochloric acid to the reaction flask to adjust the pH of the system to 3.5. Keep the mixture warm for 50min. Add 1g of oxalic acid to the reaction flask and keep the mixture warm for 50min. Cool the reaction flask to 50℃ and add 2g of zinc acetate and 5.5g of tetrabutyl titanate. Stir for 45-55min. Add 100g of ion salt modified activated carbon to the reaction flask and keep the mixture warm and stirred for 16h. Cool the reaction flask to room temperature and filter the mixture. Wash the filter cake three times with purified water and transfer it to a drying oven at 110℃. Dry the cake to constant weight to obtain the cyclization catalyst.
[0033] In the reaction, tetraethyl orthosilicate hydrolyzes and condenses under acidic conditions to form a -Si-O-Si- network. Upon the addition of oxalic acid, it condenses with the silanols in the -Si-O-Si- network, introducing acetic acid groups into the -Si-O-Si- network. Upon the addition of zinc acetate, it reacts with the hydrolyzed free Zn. 2+Complexation is achieved, forming a zinc-containing complex modification. After hydrolysis, tetrabutyl titanate can bond with silanol, allowing Zn and Ti to be anchored in a highly dispersed manner within the -Si-O-Si- network. Adding ion-salt-modified activated carbon to the Zn / Ti-SiO2 system still in a sol state allows the sol to penetrate and gel / solubilize within the pores and on the outer surface of the activated carbon carrier, forming a reinforced network coating with Zn / Ti-related Lewis acid sites, primarily composed of the -Si-O-Si- network. This coating prevents gold from being damaged under high temperature, high pressure, and water / alcohol environments. The genus species migration and aggregation reduce metal leaching and improve the structural and activity stability of the catalyst after multiple regenerations. At the same time, the -Si-O-Si- network coating layer also provides some support and protection for the organic ion layer, slowing down the shedding and degradation of organic functional groups and improving the cyclic regeneration stability of the catalyst material. The Zn / Ti associated Lewis acid sites have a strong coordination ability to the hydroxyl groups on the 1,2-propanediol molecule, which polarizes the hydroxyl groups on the 1,2-propanediol molecule, making it easier for dehydration or insertion with CO2 to occur, thereby increasing the reaction rate. Example
[0034] This embodiment provides a method for preparing a cyclization catalyst for the catalytic synthesis of propylene carbonate, comprising the following steps: Step 1: Preparation of pretreated activated carbon Mix 1.5 mol / L hydrochloric acid and sodium dodecyl sulfate at a ratio of 100 mL: 2.5 g to obtain a hydrochloric acid solution; Activated carbon and hydrochloric acid solution were added to a reaction flask at a solid-liquid ratio of 1:5.5 and stirred. The reaction flask was heated to 55°C and kept at this temperature for 135 minutes. The reaction flask was then cooled to room temperature and filtered. The filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at 85°C and dried to constant weight to obtain acid-treated activated carbon. Acid-treated activated carbon and 2.5 mol / L potassium hydroxide solution were added to a reaction flask at a solid-liquid ratio of 1:5.5 and stirred. The reaction flask was heated to 45°C and kept at this temperature for 11 hours. The mixture was then filtered, and the filter cake was transferred to a drying oven at 105°C and dried to constant weight to obtain pretreated activated carbon. The pretreated activated carbon was spread evenly in a tube furnace. Under argon protection, the tube furnace was heated to 775°C at a heating rate of 4°C / min and calcined for 2.5 hours. The tube furnace was then cooled to room temperature. The calcined material was washed with purified water until neutral and then dried. It was then transferred to a drying oven at 85°C and dried to constant weight to obtain pretreated activated carbon.
[0035] Step 2: Preparation of epoxy-modified activated carbon Weigh out 50g of pretreated activated carbon, 500mL of anhydrous ethanol and 10g of KH-560 and add them to the reaction flask. Stir the mixture and heat the reaction flask to 55℃. Add 80mL of 2.5mol / L sodium hydroxide solution to the reaction flask and keep it at this temperature for 60min. After the reaction is complete, cool the reaction flask to room temperature, filter it, wash the filter cake with purified water until neutral, and then dry it. Transfer the filter cake to a drying oven at 75℃ and dry it to constant weight to obtain epoxy-modified activated carbon.
[0036] Step 3: Preparation of ion salt modified activated carbon Weigh out 50g of epoxy-modified activated carbon, 300mL of ethyl acetate and 8g of 1,4-diazacyclo[2.2.2]octane-2-acetamide and add them to a reaction flask. Stir the mixture and heat it to 65℃. Keep the mixture at this temperature for 70min. Cool the mixture to 53℃ and add 13g of 1,3-propanesulfonate lactone. Keep the mixture at this temperature and stir for 21h. Cool the mixture to room temperature and filter it. Wash the filter cake three times with purified water and dry it. Transfer the filter cake to a drying oven at 70℃ and dry it to constant weight to obtain the ion salt modified activated carbon precursor.
[0037] Ion salt modified activated carbon precursor and 2.5 mol / L sulfuric acid were added to a reaction flask at a solid-liquid ratio of 1:10 and stirred for 25 min. The reaction flask was heated to 80 °C and kept at that temperature for 9 h. The reaction flask was then cooled to room temperature, filtered, and the filter cake was washed three times with purified water and then transferred to a drying oven at 90 °C and dried to constant weight to obtain ion salt modified activated carbon.
[0038] Step 4: Preparation of cyclization catalyst Weigh out 25g of tetraethyl orthosilicate and 250mL of purified water and add them to a reaction flask. Stir the mixture and heat the flask to 75℃. Add 4mol / L hydrochloric acid to the reaction flask to adjust the pH of the system to 4.0. Keep the mixture warm for 60min. Add 1.3g of oxalic acid to the reaction flask and keep the mixture warm for 55min. Cool the reaction flask to 53℃ and add 2.3g of zinc acetate and 6.5g of tetrabutyl titanate. Stir for 50min. Add 100g of ion salt modified activated carbon to the reaction flask and keep the mixture warm and stirred for 17h. Cool the reaction flask to room temperature and filter the mixture. Wash the filter cake three times with purified water and transfer it to a drying oven at 115℃. Dry the cake to constant weight to obtain the cyclization catalyst. Example
[0039] This embodiment provides a method for preparing a cyclization catalyst for the catalytic synthesis of propylene carbonate, comprising the following steps: Step 1: Preparation of pretreated activated carbon Mix 2 mol / L hydrochloric acid and sodium dodecyl sulfate at a ratio of 100 mL: 3 g to obtain a hydrochloric acid solution; Activated carbon and hydrochloric acid solution were added to a reaction flask at a solid-liquid ratio of 1:6 and stirred. The reaction flask was heated to 60°C and kept at this temperature for 150 min. The reaction flask was then cooled to room temperature and filtered. The filter cake was washed with purified water until neutral and then dried. The filter cake was transferred to a drying oven at 90°C and dried to constant weight to obtain acid-treated activated carbon. Acid-treated activated carbon and 3 mol / L potassium hydroxide solution were added to a reaction flask at a solid-liquid ratio of 1:6 and stirred. The reaction flask was heated to 50°C and kept at this temperature for 12 hours. The mixture was then filtered, and the filter cake was transferred to a drying oven at 110°C and dried to constant weight to obtain pretreated activated carbon. The pretreated activated carbon was spread evenly in a tube furnace. Under argon protection, the tube furnace was heated to 800°C at a heating rate of 5°C / min and calcined for 3 hours. The tube furnace was then cooled to room temperature. The calcined material was washed with purified water until neutral and then dried. It was then transferred to a drying oven at 90°C and dried to constant weight to obtain pretreated activated carbon.
[0040] Step 2: Preparation of epoxy-modified activated carbon Weigh out 50g of pretreated activated carbon, 500mL of anhydrous ethanol and 11g of KH-560 and add them to the reaction flask. Stir the mixture and heat the reaction flask to 60℃. Add 80mL of 3mol / L sodium hydroxide solution to the reaction flask and keep it at this temperature for 70min. After the reaction is complete, cool the reaction flask to room temperature, filter it, wash the filter cake with purified water until neutral, and then dry it. Transfer the filter cake to a drying oven at 80℃ and dry it to constant weight to obtain epoxy-modified activated carbon.
[0041] Step 3: Preparation of ion salt modified activated carbon Weigh out 50g of epoxy-modified activated carbon, 300mL of ethyl acetate and 8g of 1,4-diazacyclo[2.2.2]octane-2-acetamide and add them to a reaction flask. Stir the mixture and heat it to 70℃. Keep the mixture at this temperature for 80min. Cool the mixture to 55℃ and add 13g of 1,3-propanesulfonate lactone. Keep the mixture at this temperature and stir for 22h. Cool the mixture to room temperature and filter it. Wash the filter cake three times with purified water and then dry it. Transfer the filter cake to a drying oven at 75℃ and dry it to constant weight to obtain the ion salt modified activated carbon precursor.
[0042] Ion salt modified activated carbon precursor and 3 mol / L sulfuric acid were added to a reaction flask at a solid-liquid ratio of 1:10 and stirred for 30 min. The reaction flask was heated to 85 °C and kept at this temperature for 10 h. The reaction flask was then cooled to room temperature, filtered, and the filter cake was washed three times with purified water and then transferred to a drying oven at 95 °C and dried to constant weight to obtain ion salt modified activated carbon.
[0043] Step 4: Preparation of cyclization catalyst Weigh out 25g of tetraethyl orthosilicate and 250mL of purified water and add them to a reaction flask. Stir the mixture and heat the flask to 80℃. Add 5mol / L hydrochloric acid to the reaction flask to adjust the pH of the system to 4.5. Keep the mixture warm for 70min. Add 1.5g of oxalic acid to the reaction flask and keep the mixture warm for 60min. Cool the reaction flask to 55℃ and add 2.5g of zinc acetate and 7.5g of tetrabutyl titanate. Stir for 55min. Add 100g of ion salt modified activated carbon to the reaction flask and keep the mixture warm and stirred for 18h. Cool the reaction flask to room temperature and filter the mixture. Wash the filter cake three times with purified water and transfer it to a drying oven at 120℃. Dry the cake to constant weight to obtain the cyclization catalyst. Example
[0044] This embodiment provides a catalytic synthesis method for propylene carbonate, specifically as follows: Weigh 500g of 1,2-propanediol and 30g of the cyclization catalyst prepared in Example 1 and add them to a high-pressure reactor. Stir the reactor and introduce argon gas into it to replace and remove the air. Heat the reactor to 115°C and continuously introduce carbon dioxide into it until the pressure rises to 4MPa. Maintain the reaction temperature for 6 hours. Cool the reactor to room temperature and filter to obtain the propylene carbonate reaction solution and the recovered cyclization catalyst. Example
[0045] This embodiment provides a catalytic synthesis method for propylene carbonate, specifically as follows: Weigh 500g of 1,2-propanediol and 40g of the cyclization catalyst prepared in Example 2 and add them to a high-pressure reactor. Stir the reactor and introduce argon gas into it to replace and remove the air. Heat the reactor to 120°C and continuously introduce carbon dioxide into it until the pressure rises to 4.5MPa. Maintain the reaction temperature for 7 hours. Cool the reactor to room temperature and filter the mixture to obtain the propylene carbonate reaction solution and the recovered cyclization catalyst. Example
[0046] This embodiment provides a catalytic synthesis method for propylene carbonate, specifically as follows: Weigh 500g of 1,2-propanediol and 50g of the cyclization catalyst prepared in Example 3 and add them to a high-pressure reactor and stir. Introduce argon gas into the high-pressure reactor to replace and remove the air in the reactor. Heat the high-pressure reactor to 125°C and continuously introduce carbon dioxide into the reactor until the pressure in the reactor rises to 5MPa. Maintain the reaction temperature for 8 hours. Cool the high-pressure reactor to room temperature and filter to obtain propylene carbonate reaction solution and recovered cyclization catalyst.
[0047] Comparative Example 1 The difference between this comparative example and Example 6 is that, in the preparation of the cyclization catalyst, step 1 is omitted, and the activated carbon in step 1 is used instead of the pretreated activated carbon in step 2 to participate in the reaction.
[0048] Comparative Example 2 The difference between this comparative example and Example 6 is that, in the preparation of the cyclization catalyst, step 2 is omitted, the pretreated activated carbon prepared in step 1 is used instead of the epoxy-modified activated carbon in step 3, and the subsequent post-treatment operation is adjusted to vacuum distillation to remove low-boiling substances.
[0049] Comparative Example 3 The difference between this comparative example and Example 6 is that, in the preparation of the cyclization catalyst, the ion salt modified activated carbon precursor prepared in step 3 is used instead of the ion salt modified activated carbon in step 4, and hydrochloric acid is used instead of sulfuric acid in the subsequent recovery of the cyclization catalyst to prepare the regenerated cyclization catalyst.
[0050] Comparative Example 4 The difference between this comparative example and Example 6 is that tetrabutyl titanate was not added in step 4 during the preparation of the cyclization catalyst.
[0051] Performance testing: The composition of the propylene carbonate reaction solutions prepared in Examples 4-6 and Comparative Examples 1-4 was determined by gas chromatography, and the composition of the propylene carbonate reaction solutions was quantified by the correction normalization method; refer to formula Determine the conversion rate of 1,2-propanediol; refer to the formula. The selectivity of 1,2-propanediol was determined; where, This refers to the molar amount of 1,2-propanediol added to the high-pressure reactor. This refers to the molar amount of 1,2-propanediol in the propylene carbonate reaction solution. This represents the molar amount of propylene carbonate in the propylene carbonate reaction solution. After washing the recovered cyclization catalysts obtained in Examples 4-6 and Comparative Examples 1-4 three times with anhydrous ethanol, they were washed three times with dilute sulfuric acid at 60°C, and then washed three times with purified water. The filter cake was transferred to a drying oven at 90°C and dried to constant weight to obtain the regenerated cyclization catalyst. The recovered cyclization catalyst was repeatedly regenerated, and the conversion rate and selectivity of the recovered cyclization catalyst in the reaction of 1,2-propanediol and carbon dioxide to prepare propylene carbonate were measured during the 9th regeneration. The specific measurement data are shown in Table 1 below.
[0052] Data Analysis: Comparative analysis of the data in Table 1 shows that the cyclization catalyst prepared in this invention achieves a conversion rate of 28.6-29.6% and a selectivity of 98.5-98.9% in the reaction of 1,2-propanediol and carbon dioxide to propylene carbonate. After recycling, the cyclization catalyst regenerated for the 9th time achieves a conversion rate of 26.6-27.4% and a selectivity of 97.3-97.9% in the reaction of 1,2-propanediol and carbon dioxide to propylene carbonate. All performance test data are superior to those of the comparative example. This indicates that the present invention constructs a cyclization catalyst with activated carbon as the support by pretreating the activated carbon support with acid and then alkali and introducing an epoxysilane-ion salt microenvironment, combined with the highly dispersed immobilization of tetraethyl orthosilicate sol-gel and Lewis acid centers. This not only effectively improves the conversion rate and selectivity of the reaction of 1,2-propanediol and carbon dioxide to propylene carbonate, but also improves the stability of the cyclization catalyst during recycling.
[0053] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.
Claims
1. A catalytic synthesis method for propylene carbonate, characterized in that, Includes the following steps: 1,2-Propanediol and the cyclization catalyst were added to a high-pressure reactor and stirred. Inert gas was introduced into the high-pressure reactor to replace and remove the air. The high-pressure reactor was heated to 115-125℃, and carbon dioxide was introduced into the reactor. The pressure of the high-pressure reactor was adjusted to 4-5 MPa, and the reaction was maintained at this temperature for 6-8 hours. The high-pressure reactor was then cooled to room temperature and filtered to obtain the propylene carbonate reaction solution and the recovered cyclization catalyst.
2. The catalytic synthesis method of propylene carbonate according to claim 1, characterized in that, Ethyl orthosilicate and purified water were mixed and stirred. The reaction system was heated to 70-80℃. Hydrochloric acid was added to the reaction system to adjust the pH to 3.5-4.
5. The reaction was maintained at this temperature for 50-70 min. Oxalic acid was added to the reaction system, and the reaction was maintained for 50-60 min. The reaction system was then cooled to 50-55℃. Zinc acetate and tetrabutyl titanate were added to the reaction system, and the mixture was stirred for 45-55 min. Ionic salt modified activated carbon was added to the reaction system, and the mixture was kept at this temperature and stirred for 16-18 h. After post-treatment, the cyclization catalyst was obtained.
3. The catalytic synthesis method of propylene carbonate according to claim 2, characterized in that, The ratio of tetraethyl orthosilicate, purified water, oxalic acid, zinc acetate, tetrabutyl titanate, and ionic salt modified activated carbon is 5g:50mL:0.2-0.3g:0.4-0.5g:1.1-1.5g:20g.
4. The catalytic synthesis method of propylene carbonate according to claim 2, characterized in that, Ion salt modified activated carbon is obtained through the following steps: A1. Epoxy-modified activated carbon, ethyl acetate, and 1,4-diazacyclo[2.2.2]octane-2-acetamide were mixed and stirred. The reaction system was heated to 60-70℃ and kept at that temperature for 60-80 min. The reaction system was then cooled to 50-55℃. 1,3-propanesulfonate lactone was added to the reaction system, and the mixture was stirred and kept at that temperature for 20-22 h. After post-treatment, the ion salt-modified activated carbon precursor was obtained. A2. Mix the ion salt modified activated carbon precursor and sulfuric acid and stir for 20-30 minutes. Heat the reaction system to 75-85℃ and keep it at that temperature for 8-10 hours. After post-treatment, the ion salt modified activated carbon is obtained.
5. The catalytic synthesis method of propylene carbonate according to claim 4, characterized in that, In step A1, the ratio of the amount of epoxy-modified activated carbon, ethyl acetate, 1,4-diazacyclo[2.2.2]octane-2-acetamide and 1,3-propanesulfonate lactone is 5g:30mL:0.8g:1.3g; in step A2, the solid-liquid ratio of the ion salt-modified activated carbon precursor and sulfuric acid is 1:10, and the concentration of the sulfuric acid is 2-3mol / L.
6. The catalytic synthesis method of propylene carbonate according to claim 4, characterized in that, The preparation method of epoxy-modified activated carbon is as follows: pretreated activated carbon, anhydrous ethanol and KH-560 are mixed and stirred, the reaction system is heated to 50-60℃, an alkaline catalyst is added to the reaction system, the reaction is kept at the temperature for 50-70 min, and then post-treatment is performed to obtain epoxy-modified activated carbon.
7. The catalytic synthesis method of propylene carbonate according to claim 6, characterized in that, The ratio of the pretreated activated carbon, anhydrous ethanol, KH-560 and alkaline catalyst is 5g:50mL:0.9-1.1g:8mL, and the alkaline catalyst is a 2-3mol / L sodium hydroxide solution.
8. The catalytic synthesis method of propylene carbonate according to claim 6, characterized in that, Pretreated activated carbon is obtained by the following steps: B1. Mix activated carbon and hydrochloric acid solution, heat the reaction system to 50-60℃, keep it at the temperature for 120-150 min, and then perform post-treatment to obtain acid-treated activated carbon. B2. Mix the acid-treated activated carbon and the alkaline solution, heat the reaction system to 40-50℃, keep it at the temperature for 10-12 hours, and then perform post-treatment to obtain the pretreated activated carbon. B3. Spread the pretreated activated carbon evenly in a tube furnace. Under the protection of an inert gas atmosphere, heat the tube furnace to 750-800℃ and keep it at that temperature for 2-3 hours. Then perform post-treatment to obtain pretreated activated carbon.
9. The catalytic synthesis method of propylene carbonate according to claim 8, characterized in that, In step B1, the solid-liquid ratio of the activated carbon and hydrochloric acid solution is 1:5-6, and the hydrochloric acid solution is composed of 1-2 mol / L hydrochloric acid and sodium dodecyl sulfate at a ratio of 100 mL: 2-3 g; in step B2, the solid-liquid ratio of the acid-treated activated carbon and alkaline solution is 1:5-6, and the alkaline solution is a 2-3 mol / L potassium hydroxide solution; in step B3, the heating rate of the tube furnace is 3-5 °C / min.
10. The catalytic synthesis method of propylene carbonate according to claim 1, characterized in that, The weight ratio of 1,2-propanediol to the cyclization catalyst is 50:3-5.