Preparation method and application of synthetic core-shell halogen catalyst

Abstract

A preparation method of a catalyst for synthesizing cyclic carbonate comprises the following steps: (1) mixing a bromine source and an alkali source in water to prepare a first solution; (2) mixing the first solution with an organic silicon source to obtain turbid liquid; and (3) separating the turbid liquid, collecting solid substances, and washing and drying solid lower-layer substances to obtain the catalyst. The method comprises the following steps: carrying out heterogeneity on a homogeneous quaternary ammonium salt bromine source catalyst, and forming a micelle structure by using a quaternary ammonium salt surfactant; the concentration of the precursor is accurately regulated and controlled, so that the microporous silicon oxide shell layer rationally grows on the surface of the micelle, the active center of the bromine source is limited in the silicon oxide shell layer, a core-shell structure is formed, and the problem of loss of a homogeneous catalyst is solved. No organic solvent is used for synthesis of the catalyst, when the catalyst is applied, a limited bromine source and hydroxyl on the surface of silicon oxide have a synergistic effect, a C = O bond of epoxypropane can be efficiently activated and broken, the yield of propylene carbonate exceeds 90% under a mild condition, and the loss of the bromine source is remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and in particular to a catalyst for synthesizing cyclic carbonates and a preparation method thereof. Background Art

[0002] Propylene carbonate (PC) is an important intermediate in chemical production, with advantages such as high boiling point, good solubility, and biodegradability. It can be used for the purification of natural gas and synthetic ammonia raw gas, and can also be used as a solvent in the petrochemical and new energy industries. At present, the main methods for producing propylene carbonate include phosgene method, urea alcoholysis method, 1,2-propylene glycol method, etc., but these methods are difficult to apply to industrial production due to the high price of raw materials and environmentally unfriendly production processes. In current industrial production, the propylene oxide cycloaddition method has become the mainstream production process of propylene carbonate with the help of the polyethylene glycol / KI catalyst system. However, this method has obvious disadvantages. Halogen needs to be continuously added during the reaction process, which not only significantly increases the energy consumption of product separation, but also greatly increases the production cost.

[0003] In recent years, in order to overcome the loss problem of homogeneous catalysts and reduce separation energy consumption, the research on immobilizing highly active homogeneous catalytic components to construct heterogeneous catalysts has attracted widespread attention. CN106732768A discloses a method of using graphene oxide as a carrier to immobilize a halide-containing ion liquid for carbon dioxide cycloaddition reaction. Under the conditions of 2MpaCO2 and 100°C, the yield of propylene carbonate can reach 82.2%, and the catalyst remains stable after three recycling. CN118852469A discloses a cellulose-supported organic catalyst for fixing carbon dioxide. The organic ion pair catalyst composed of cellulose acetoacetate anion and the conjugate acid of a common organic base can achieve an epoxide conversion rate of 99% and a selectivity of 99% under the conditions of 120°C, 24h and 0.58ml of epoxide. CN113582963A assembles HBD groups, organic bases, nucleophilic reagents and polyether chains on Merrifield resin materials. Through the synergistic effect of multiple active sites, a conversion rate of 92.7% of styrene oxide and a selectivity of 99% of cyclic carbonate can be achieved under the conditions of 100°C, 1.2Mpa CO2, and 2h. This catalyst not only maintains the high catalytic activity and selectivity of ionic liquid catalysts, but also enables efficient separation and recycling of catalysts. However, the synthesis process of the solid-supported catalyst disclosed in the prior art is complicated and requires a large amount of organic solvents. The cost of solid support is high and it is difficult to achieve industrial mass production. At the same time, core-shell structure catalysts are regarded as ideal carrier structures for achieving efficient heterogeneity and confinement of homogeneous active centers due to their unique confinement utility, high stability, and abundant designable active sites. CN111013661B uses NH2-UiO-66 as the core and the porous organic polymer CoTPy-CAP as the shell to construct a MOF@POP core-shell catalyst. The catalyst can achieve a 98% propylene oxide conversion rate under mild conditions without a co-catalyst, without a solvent, and without a catalyst. However, the catalyst has poor selectivity for cyclic carbonates. CN114433228A uses imidazole ionic liquid monomers to polymerize on the surface of an inorganic carrier silica to form a core-shell ionic liquid catalyst. The catalyst can obtain a 95.5% propylene carbonate yield under the conditions of 120°C and 2MpaCO2, but the catalyst synthesis conditions are harsh and require the introduction of highly toxic azobisisobutyronitrile. Therefore, there is an urgent need to develop a new type of core-shell solid-supported heterogeneous catalyst.

[0004] In view of the above problems, this application is filed. Summary of the Invention

[0005] The first purpose of the present application is to prepare a catalyst used in a system for synthesizing cyclic carbonates (such as propylene carbonate). During the process of synthesizing cyclic carbonates using the catalyst, no additional supplementation of quaternary ammonium salt ionic liquid is required.

[0006] A second object of the present application is to provide a catalyst having a long service life in a system for synthesizing cyclic carbonates (such as propylene carbonate).

[0007] The third object of the present application is that no organic solvent is used in the process of the catalyst, and the process steps are simple.

[0008] A catalyst for synthesizing cyclic carbonate has a shell-core structure, wherein the shell is composed of a silicon-containing material and the core is a quaternary ammonium salt ionic liquid; the quaternary ammonium salt ionic liquid comprises one of tetrabutylammonium bromide, hexadecyltrimethylammonium bromide, tetraethylammonium bromide, and tetramethylammonium bromide, or a mixture of two or more thereof.

[0009] The catalyst is used in a system for synthesizing cyclic carbonates. It effectively utilizes the active component (halogen) of the catalyst during the reaction and reduces the loss of the active component during the production process. Therefore, during the synthesis of cyclic carbonates, there is no need to supplement with a quaternary ammonium salt ionic liquid.

[0010] The preparation method of the catalyst for synthesizing cyclic carbonate of the present application comprises:

[0011] (1) mixing a bromine source and an alkali source in water to obtain a first solution;

[0012] (2) mixing the first solution with the organosilicon source to obtain a suspension;

[0013] (3) After the suspension is separated, the solid matter is collected, and the solid matter is washed with water and dried to obtain the catalyst.

[0014] The solvent used in the preparation process of the catalyst is water, and no organic solvent is used, which will not cause pollution to the environment.

[0015] The catalyst prepared in this application is used in the reaction system for synthesizing cyclic carbonates. Through the synergistic effect of halide ions and hydrogen bond donors, efficient activation and cleavage of propylene oxide C=O are achieved, and a propylene carbonate yield of more than 90% can be achieved under mild conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the TEM image of the catalyst prepared in Example 1.

[0017] Figure 2 This is a diagram showing the N2- physical adsorption and desorption of the catalyst prepared in Example 1.

[0018] Figure 3 This is the pore size distribution diagram of the catalyst prepared in Example 1.

[0019] Figure 4 This is the XRD pattern of the catalyst prepared in Example 1.

[0020] Figure 5 This is the infrared image of the catalyst prepared in Example 1. DETAILED DESCRIPTION

[0021] Below, synthetic cyclic carbonate catalyst of the present invention and preparation method thereof are further described in detail.Do not limit the protection scope of the present application, its protection scope is defined with the claims.Some disclosed specific details provide a comprehensive understanding to each disclosed embodiment.Yet those skilled in the art know that, do not adopt one or more of these specific details, and adopt the situation of other materials etc. and also can realize embodiment.

[0022] Unless the context requires otherwise, in the specification and claims, the terms "include" and "comprising" should be understood as having an open and inclusive meaning, that is, "including, but not limited to".

[0023] The terms "embodiment," "one embodiment," "another embodiment," or "certain embodiments" mentioned in the specification mean that the specific features, structures, or characteristics described in connection with the embodiment are included in at least one embodiment. Therefore, "embodiment," "one embodiment," "another embodiment," or "certain embodiments" do not necessarily all refer to the same embodiment. Specific features, structures, or characteristics may be combined in any manner in one or more embodiments. Each feature disclosed in the specification may be replaced by any alternative feature that can provide the same, equal, or similar purpose. Therefore, unless otherwise specified, the disclosed features are merely general examples of equal or similar features.

[0024] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. The experimental methods in the following examples, for which specific conditions are not specified, are generally based on conventional conditions or the conditions recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or parts are by weight.

[0025] The units of weight-volume percentage in this application are well known to those skilled in the art, for example, refer to the weight of the solute in 100 ml of solution.

[0026] In this application, the concentration unit "M" of a solution represents mol / L.

[0027] In this application, the term "bromine source" is selected from organic bromine salts that are soluble or slightly soluble in water. The term "silicon source" is selected from silicon-containing compounds that can disperse or decompose in water. The term "alkali source" is selected from compounds that are readily soluble in water and can ionize to produce hydroxide in aqueous solution without generating other anions.

[0028] The term "calcination" unless otherwise specified refers to the process of treating a substance at a high temperature in an air atmosphere.

[0029] The term “not less than” in the present application refers to a range that includes the numerical value, for example, not less than 10°C includes 10°C.

[0030] In the description of numerical ranges in this application, a range above or below a certain value includes values ​​equal to the value, and a range between two numerical ranges includes the values ​​of the two endpoints.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods and materials similar or equivalent to those described herein can be applied to the methods of the present invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0032] In the system of preparing cyclic carbonate, when taking quaternary ammonium salt type ionic liquid as catalyst, CO2 efficient conversion can be realized under mild conditions. Unfortunately, quaternary ammonium salt type ionic liquid can form homogeneous solution with reaction solution after reaction ends, and needs to be separated by methods such as extraction. Therefore, in actual production, it is necessary to continuously supplement quaternary ammonium salt ionic liquid to ensure the continuous and stable carrying out of propylene oxide cycloaddition reaction. In addition, simple quaternary ammonium salt ionic liquid causes the C=O activation rate in propylene oxide to be slow due to the absence of hydrogen bond donors, which causes the need to improve residence time or to carry out circulation treatment of reaction solution to realize efficient conversion of propylene oxide in reaction process. The core of the application is to design a core-shell structure by exquisite, highly active homogeneous halogen catalytic center effectively confined in shell layer inside, combine simple, green synthesis process and cheap and easy-to-get raw materials, significantly suppress the loss of halogen active center in catalytic reaction process, thus efficiently catalyze propylene oxide and CO2 cycloaddition to generate propylene carbonate under mild conditions. In addition, the core-shell catalyst disclosed in the present invention affects the hydrolysis rate of the silicon source by adjusting the micelle concentration, thereby precisely controlling the shell structure to 20-30 nm, for example 25 nm, thereby effectively reducing halogen loss. The catalyst of the present application can be easily separated from the reaction solution and reused; it can also increase the C=O activation rate of propylene oxide, thereby improving the reaction efficiency of propylene oxide.

[0033] A method for preparing a catalyst for synthesizing cyclic carbonates, comprising:

[0034] (1) mixing a bromine source and an alkali source in water to obtain a first solution;

[0035] (2) mixing the first solution with the organosilicon source to obtain a suspension;

[0036] (3) After the suspension is separated, the solid matter is collected, and the solid matter is washed with water and dried to obtain the catalyst.

[0037] The bromine source includes one or a mixture of two or more of tetrabutylammonium bromide (TBAB), cetyltrimethylammonium bromide (CTAB), tetraethylammonium bromide (TEAB), and tetramethylammonium bromide (TMAB).

[0038] Alternatively, the bromine source is a mixture of cetyltrimethylammonium bromide and lower alkyl ammonium bromide.

[0039] The lower alkyl ammonium bromide includes one or a mixture of two or more of tetrabutylammonium bromide, tetraethylammonium bromide, and tetramethylammonium bromide.

[0040] Preferably, the bromine source is a mixture of tetrabutylammonium bromide and cetyltrimethylammonium bromide.

[0041] In certain embodiments, when cetyltrimethylammonium bromide and lower alkyl ammonium bromide are mixed, the molar ratio of lower alkyl ammonium bromide to cetyltrimethylammonium bromide is 1:(0.1-10).

[0042] Optionally, the molar ratio of lower alkyl ammonium bromide to hexadecyltrimethylammonium bromide is 1:(0.1-5).

[0043] Preferably, the molar ratio of lower alkyl ammonium bromide to hexadecyltrimethylammonium bromide is 1:(1-4).

[0044] By selecting an appropriate bromine source, a mixture of hexadecyltrimethylammonium bromide and low-carbon alkylammonium bromide can form micelles in water under certain conditions. The micelles formed by the quaternary ammonium salt are wrapped around the main silicon-containing material in the formed shell, and the bromide ions in the shell can maintain a certain concentration.

[0045] In step (1), the molar ratio of the bromine source to water is 1:(50-300). Preferably, the molar ratio of the bromine source to water is 1:(100-300).

[0046] Alternatively, in the first solution, the molar concentration of the bromine source (including hexadecyltrimethylammonium bromide and lower alkylammonium bromide) is about 0.18-0.5 mol / L, such as 0.21 mol / L.

[0047] At the above concentration, micelles with uniform particle size distribution and stable performance can be formed.

[0048] In certain embodiments, the alkaline source includes one of tetrabutylammonium hydroxide (TBAOH), tetrapropylammonium hydroxide (TPAOH), aqueous ammonia, sodium hydroxide, sodium carbonate, sodium bicarbonate, or a mixture of two or more thereof.

[0049] Preferably, the alkali source is aqueous ammonia.

[0050] The molar ratio of the alkali source to the bromine source is 1:(1-10); optionally, the molar ratio of the alkali source to the bromine source is 1:(1-5). Preferably, the molar ratio of the alkali source to the bromine source is 1:(1-3).

[0051] The amount of the added alkaline source can adjust the pH of the first mixed solution to 9-12.

[0052] In certain embodiments, as in step (1), the bromine source and the alkali source are mixed in water at a temperature of 25° C. to 100° C. The mixing process is accompanied by stirring.

[0053] Preferably, the mixing is carried out at a temperature of 25°C to 50°C.

[0054] The stirring time does not have much effect on the properties of the catalyst, as long as it is mixed evenly. In certain embodiments, such as in step (1), the stirring time is 10 minutes to 3 hours, preferably, the stirring time is 10 minutes to 1.5 hours, and more preferably, the stirring time is 10 minutes to 1 hour.

[0055] In certain embodiments, the silicon source is selected from one of tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), sodium silicate, silicon tetrachloride (STC), or a mixture of two or more thereof. Preferably, the silicon source is tetraethyl orthosilicate.

[0056] The molar ratio of the silicon source to the bromine source is 1:(0.4-10).

[0057] Optionally, the molar ratio of the silicon source to the bromine source is 1:(0.6-5), for example: 1:0.8, 1:1, 1:1.6, 1:2.2.

[0058] Within the aforementioned dosage ranges and mixing conditions of the silicon source and bromine source, the thickness and density of the silica shell can be controlled within appropriate limits, allowing the active components of the catalyst to function effectively. Excessive silicon source content can result in overly dense silica coating, reducing contact between propylene oxide and the active sites within the silica, thereby reducing catalyst activity.

[0059] In step (2), the pH of the suspension is 7-11. Alternatively, the pH of the suspension is 8-11.

[0060] In step (2), the pH during mixing is controlled at 7-11 to control the hydrolysis process of the organosilicon source in the aqueous solution, which is conducive to the formation of a silicon oxide shell layer of appropriate thickness.

[0061] In certain embodiments, as in step (2), the first solution and the silicon source are mixed at a temperature of 25° C. to 100° C. The mixing process is accompanied by stirring.

[0062] Preferably, the mixing is carried out at a temperature of 25°C to 50°C.

[0063] In particular, mixing under the above temperature conditions can further control the hydrolysis process of the silicone, thereby facilitating the formation of a shell layer with an appropriate thickness and pore size.

[0064] The stirring time does not significantly affect the properties of the catalyst, as long as the catalyst is mixed evenly. In certain embodiments, such as in step (2), the stirring time is 30 minutes to 13 hours; preferably, the stirring time is 2 hours to 10 hours; more preferably, the stirring time is 3 hours to 7 hours.

[0065] The pH of the suspension is 7-10, preferably, the pH of the suspension is 8-10.

[0066] In step (3), the suspension is centrifuged to obtain a solid substance, which is then washed with water to obtain a first solid.

[0067] In certain embodiments, the first solid is dried at a temperature of 25°C to 170°C; preferably, the first solid is dried at a temperature of 50°C to 120°C.

[0068] By controlling the stirring time, pH, and temperature, the silicon source is fully hydrolyzed to form silicon oxide. This silicon oxide is then grown on the surface of the bromine source via a sol-gel method, encapsulating the bromine source within a uniform shell. Subsequently, continuous water washing removes the short-chain bromine source trapped within the pores, creating an appropriate pore size for the core-shell catalyst. This allows the active ions to pass through the pores and catalyze the synthesis of cyclic carbonates.

[0069] In the catalyst method used in the preparation and synthesis of cyclic carbonates in this application, a homogeneous quaternary ammonium salt bromine source catalyst is heterogeneously transformed, a quaternary ammonium salt surfactant is used to form a micellar structure, and the homogeneous active component, the quaternary ammonium salt bromine source, is in situ immobilized within the micelles through electrostatic interaction. Precisely controlling the precursor concentration allows for the rational growth of a microporous silica shell on the micelle surface, confining the bromine source active center within the silica shell, forming a "core-shell" structure and addressing the issue of homogeneous catalyst loss.

[0070] The catalyst obtained by the above-mentioned preparation method of the present application has a core-shell structure. The shell layer is composed of silicon-containing material, and the core is a quaternary ammonium salt ionic liquid.

[0071] Preferably, the quaternary ammonium salt ionic liquid is a mixture of hexadecyltrimethylammonium bromide and lower alkyl ammonium bromide, wherein the molar ratio of lower alkyl ammonium bromide to hexadecyltrimethylammonium bromide is 1:(0.1-10).

[0072] Optionally, the molar ratio of lower alkyl ammonium bromide to hexadecyltrimethylammonium bromide is 1:(0.1-5).

[0073] Preferably, the molar ratio of lower alkyl ammonium bromide to hexadecyltrimethylammonium bromide is 1:(1-4).

[0074] On the other hand, the catalyst prepared above is used to synthesize cyclic carbonates, such as propylene carbonate.

[0075] A method for synthesizing propylene carbonate comprises the following steps: using carbon dioxide and propylene oxide as raw materials, reacting them in the presence of the above catalyst at a temperature ranging from 80° C. to 200° C. to obtain propylene carbonate.

[0076] During the reaction, the mass ratio of the catalyst to propylene oxide is 1:(15-30).

[0077] When the catalyst prepared in the present application is used, there is no need to add quaternary ammonium bromide salt in the reaction system.

[0078] The catalyst of the present application is a solid material with a core-shell structure. In the reaction system, it is in a different phase from the reactants or products, and the reacted substances and the catalyst can be separated by filtration. Moreover, the catalyst can be reused after simple alcohol washing and drying.

[0079] Therefore, the present invention uses a solid-supported halogen-containing catalyst synthesized from inexpensive raw materials to efficiently achieve the cycloaddition reaction of carbon dioxide and propylene oxide to produce propylene carbonate. The preparation of the solid-supported catalyst is simple, the synthesis speed is fast, and it is suitable for large-scale industrial production.

[0080] The solid-supported catalyst synthesized in the present application can maintain substantially the same performance after being recycled five times, which can reduce the loss of Br and reduce production costs in future production processes.

[0081] The catalyst of the present invention and its catalytic effect are further described below in conjunction with specific examples. The substances used in the following examples are all chemically pure standards. The quaternary ammonium salt, sodium carbonate, sodium hydroxide and silicon source used in the examples are all chemically pure substances.

[0082] Example 1

[0083] TBAB, CTAB, and aqueous ammonia (ammonia monohydrate) were added to 140 mL of water at a molar ratio of 1:2:1.6. The bromine source concentration was 0.21 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 15 minutes, a mixed solution A with a pH of 9.8 was obtained. To mixed solution A, 3 mL of TEOS was slowly added. The molar ratio of the sum of TBAB and CTAB to TEOS was 2.2:1. After stirring at room temperature for 5 hours, a suspension B with a pH of 8.9 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0084] The catalyst prepared in Example 1 was subjected to transmission electron microscopy (TEM) analysis. Figure 1 As shown, the obtained catalyst exists in a core-shell form, with silica encapsulating the bromine source forming micelles inside the catalyst. The shell thickness is about 25 nm.

[0085] The specific surface area and pore size distribution of the catalyst prepared in Example 1 were analyzed by N2-physical adsorption desorption method. The results are shown in the attached figure. Figure 2 As shown in Figure 2, the catalyst has a small specific surface area because it has not been calcined. Figure 3 As shown, the pore size of the catalyst is relatively small.

[0086] The catalyst prepared in Example 1 was subjected to X-ray powder diffraction (XRD). Figure 4 As shown, there is a crystalline peak of Br source in the catalyst.

[0087] The catalyst prepared in Example 1 was analyzed by infrared spectrum. Figure 5 As shown, the catalyst contains hydroxyl groups.

[0088] Example 2

[0089] TBAB, CTAB, and aqueous ammonia (ammonia monohydrate) were added to 140 ml of water at a molar ratio of 1:1.5:1.3. The bromine source concentration was 0.18 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 30 minutes, a mixed solution A with a pH of 9.5 was obtained. To mixed solution A, 3 ml of TEOS was slowly added. The molar ratio of the sum of TBAB and CTAB to TEOS was 1.85:1. After stirring at room temperature for 5 hours, a suspension B with a pH of 8.9 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0090] Example 3

[0091] TEAB, CTAB, and aqueous ammonia (ammonia monohydrate) were added to 140 mL of water at a molar ratio of 1:2:1.6. The bromine source concentration was 0.21 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 15 minutes, a mixed solution A with a pH of 9.7 was obtained. To mixed solution A, 3 mL of TEOS (the molar ratio of the sum of TBAB and CTAB to TEOS was 2.2:1) was slowly added. After stirring at room temperature for 5 hours, a suspension B with a pH of 8.8 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0092] Example 4

[0093] TEAB, CTAB, and TPAOH (based on the molar ratio of solutes) were added to 140 mL of water at a molar ratio of 1:2:1. The bromine source concentration was 0.21 mol / L, and the mass concentration of the TPAOH solution was 25%. After stirring at room temperature for 15 minutes, a mixed solution A with a pH of 11.1 was obtained. To mixed solution A, 3 mL of TEOS was slowly added, with a molar ratio of TEAB, CTAB, and TEOS of 2.2:1. After stirring at room temperature for 5 hours, a suspension B with a pH of 10.1 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0094] Example 5

[0095] TBAB, CTAB, and aqueous ammonia (based on ammonia monohydrate) were added to 140 mL of water in a molar ratio of 1:2:1.6. The bromine source concentration was 0.21 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 30 minutes, a mixed solution A with a pH of 9.8 was obtained. To mixed solution A, 3 mL of TEOS was slowly added, with a molar ratio of TBAB, CTAB, and TEOS of 2.2:1. After stirring at room temperature for 6 hours, a suspension B with a pH of 8.5 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0096] Example 6

[0097] TBAB, CTAB, and aqueous ammonia (based on ammonia monohydrate) were added to 140 mL of water at a molar ratio of 1:2:1.6. The bromine source concentration was 0.21 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 15 minutes, a mixed solution A with a pH of 9.8 was obtained. To mixed solution A, 3 mL of TMOS was slowly added, with a molar ratio of TBAB, CTAB, and TMOS of 1.5:1. After stirring at room temperature for 6 hours, a suspension B with a pH of 8.1 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. The white solid was then dried in an 80°C oven for 12 hours to obtain the catalyst.

[0098] Example 7

[0099] TBAB, CTAB, and aqueous ammonia (in terms of monohydrated ammonia) were added to 140 mL of water at a molar ratio of 1:2:1.6. The bromine source concentration was 0.21 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 15 minutes, a mixed solution A with a pH of 9.8 was obtained. To mixed solution A, 6 mL of TEOS was slowly added, with a molar ratio of TBAB, CTAB, and TEOS of 1.1:1. After stirring at room temperature for 5 hours, a suspension B with a pH of 7.9 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0100] Example 8

[0101] TBAB, CTAB, and aqueous ammonia (based on ammonia monohydrate) were added to 140 mL of water in a molar ratio of 1:2:1.6. The bromine source concentration was 0.21 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 15 minutes, a mixed solution A with a pH of 9.8 was obtained. To mixed solution A, 6 mL of TEOS was slowly added, with a molar ratio of TBAB, CTAB, and TEOS of 1.1:1. After stirring at room temperature for 6 hours, a suspension B with a pH of 7.5 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0102] Comparative Example 1

[0103] TBAB, CTAB, and aqueous ammonia (in terms of monohydrated ammonia) were added to 140 mL of water at a molar ratio of 1:2:1.6. The bromine source concentration was 0.21 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 15 minutes, a mixed solution A with a pH of 9.8 was obtained. To mixed solution A, 3 mL of TEOS was slowly added, with a molar ratio of TBAB, CTAB, and TEOS of 1.1:1. After stirring at room temperature for 5 hours, a suspension B with a pH of 7.5 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. The white solid was then dried in an 80°C oven for 12 hours. The catalyst was then calcined in a muffle furnace at 250°C (at a heating rate of 10°C / min) for 1 hour.

[0104] Comparative Example 2

[0105] TBAB, CTAB, and sodium carbonate were added to 140 ml of water at a molar ratio of 1:2:150, with a bromine source concentration of 0.21 mol / L. After stirring at room temperature for 15 minutes, mixed solution A was obtained with a pH of 13.0. 3 ml of TEOS was slowly added to mixed solution A, resulting in a molar ratio of bromine source to silicon source of 1.6:1. After stirring at room temperature for 5 hours, suspension B was obtained with a pH of 12.8. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0106] Comparative Example 3

[0107] TBAB, TEAB, and aqueous ammonia (based on ammonia monohydrate) were added to 140 mL of water in a molar ratio of 1:2:1.6. The bromine source concentration was 0.21 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 15 minutes, a mixed solution A with a pH of 8.9 was obtained. To mixed solution A, 6 mL of TEOS was slowly added, with a molar ratio of TBAB, TEAB, and TEOS of 1.1:1. After stirring at room temperature for 5 hours, a suspension B with a pH of 7.8 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0108] Comparative Example 4

[0109] TBAB, TEAB, and aqueous ammonia (based on ammonia monohydrate) were added to 140 mL of water in a molar ratio of 1:2:1.6. The bromine source concentration was 0.21 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 15 minutes, a mixed solution A with a pH of 8.9 was obtained. To mixed solution A, 3 mL of TEOS was slowly added, with a molar ratio of TBAB, TEAB, and TEOS of 2.2:1. After stirring at room temperature for 5 hours, a suspension B with a pH of 7.8 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0110] Comparative Example 5

[0111] TBAB, CTAB, and aqueous ammonia (based on ammonia monohydrate) were added to 140 ml of water at a molar ratio of 1:40:1.6. The bromine source concentration was 2.93 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 30 minutes, a mixed solution A with a pH of 10.5 was obtained. To mixed solution A, 3 ml of TEOS was slowly added, with a molar ratio of TBAB, CTAB, and TEOS of 30:1. After stirring at room temperature for 5 hours, a suspension B with a pH of 9.4 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0112] Comparative Example 6

[0113] TBAB, CTAB, and aqueous ammonia (based on ammonia monohydrate) were added to 140 ml of water at a molar ratio of 1:40:1.6. The bromine source concentration was 2.93 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 15 minutes, a mixed solution A with a pH of 10.2 was obtained. To mixed solution A, 3 ml of TEOS was slowly added. The molar ratio of the sum of TBAB and CTAB to TEOS was 30:1. After stirring at room temperature for 15 hours, a suspension B with a pH of 8.4 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0114] Comparative Example 7

[0115] TBAB, TEAB, and aqueous ammonia (based on ammonia monohydrate) were added to 140 ml of water in a molar ratio of 1:2:1.6. The bromine source concentration was 0.21 mol / L, and the mass concentration of aqueous ammonia was 25%. After stirring at room temperature for 15 minutes, a mixed solution A with a pH of 9.9 was obtained. To mixed solution A, 7.8 g of sodium silicate was slowly added, with a molar ratio of TBAB, TEAB, and sodium silicate of 0.5:1. After stirring at room temperature for 5 hours, a suspension B with a pH of 11.1 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0116] Comparative Example 8

[0117] TBAB, CTAB, and sodium hydroxide were added to 140 ml of water at a molar ratio of 1:2:150 to achieve a bromine source concentration of 0.21 mol / L. After stirring at room temperature for 15 minutes, a mixed solution A with a pH of 13.5 was obtained. To this mixed solution A, 25 ml of TEOS was slowly added at a molar ratio of 0.3:1 between the sum of TBAB and CTAB and TEOS. After stirring at room temperature for 5 hours, a suspension B with a pH of 11.2 was obtained. Suspension B was centrifuged, and the solid was collected and washed with water to obtain a white solid. Finally, the white solid was dried in an 80°C oven for 12 hours to obtain the catalyst.

[0118] Catalyst performance testing

[0119] Experimental Example 1

[0120] The cycloaddition reaction of carbon dioxide and propylene oxide was carried out in a 25 mL autoclave. 5 mL of propylene oxide and 0.23 g of catalyst were added sequentially to a polytetrafluoroethylene-lined container at room temperature. The autoclave was then sealed and 1.5 MPa of CO2 was introduced. The reaction temperature was then raised to 100°C. After 2 hours of reaction, the autoclave was allowed to cool naturally to room temperature, unreacted CO2 was vented, and the catalyst was separated from the reaction solution using a sand-core funnel. The separated reaction solution was then analyzed for composition (see Table 1).

[0121] In this experimental example, the liquid after the reaction in Examples 1-8 and Comparative Examples 1-8 was passed through a gas chromatograph for analysis. The gas chromatographic conditions were the same, and the results are shown in Table 1 below.

[0122] Table 1 Results of Examples and Comparative Examples

[0123]

[0124]

[0125] Experimental Example 2

[0126] In this experimental example, a catalyst stability test was conducted on the catalyst of Example 1.

[0127] After the reaction in Experimental Example 1, the catalyst separated was washed with ethanol several times and dried in a vacuum oven at 60°C overnight. The catalyst stability was then evaluated according to the conditions of Experimental Example 1 (see Table 2 for the results). This cycle was repeated multiple times, and the catalyst maintained excellent catalytic performance.

[0128] Table 2 Catalyst cycle performance test results

[0129] Number of cycles Propylene oxide conversion rate / % Propylene carbonate selectivity / % 1 92.3 99.5 2 91.9 99.5 3 92.0 98.7 4 91.8 98.9 5 90.9 97.5

[0130] The propylene oxide conversion and propylene carbonate selectivity in Tables 1 and 2 were calculated as follows:

[0131] Propylene oxide conversion rate = (n PC +n PG ) / (n PO剩余 n PC +n PG )

[0132] Selectivity of propylene carbonate = n PC / (n PC +n PG )

[0133] By-product selectivity = n PG / (n PC +n PG )

[0134] n PC Refers to the molar amount of propylene carbonate, n PG Refers to the molar amount of 1,2-propylene glycol, n PO剩余 Refers to the molar amount of propylene oxide that has not participated in the reaction after the reaction is completed.

[0135] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the substantive technical content of the present invention. The substantive technical content of the present invention is broadly defined in the scope of the claims of the application. Any technical entity or method completed by others, if it is exactly the same as that defined in the scope of the claims of the application or is an equivalent variation, will be deemed to be included in the scope of the claims.

Claims

1. A method for preparing a catalyst for synthesizing cyclic carbonates, comprising: (1) mixing a bromine source and an alkali source in water to obtain a first solution; (2) mixing the first solution with the organosilicon source to obtain a suspension; (3) collecting solid matter after separation of the suspension, washing the solid matter with water, and drying it to obtain a catalyst; Preferably, the drying is carried out at a temperature of 25°C to 170°C; Preferably, the drying is carried out at a temperature of 50°C to 120°C.

2. The preparation method according to claim 1, characterized in that The bromine source includes one or a mixture of two or more of tetrabutylammonium bromide, hexadecyltrimethylammonium bromide, tetraethylammonium bromide, and tetramethylammonium bromide; Preferably, the bromine source is a mixture of hexadecyltrimethylammonium bromide and a lower alkyl ammonium bromide, wherein the lower alkyl ammonium bromide includes one or a mixture of two or more of tetrabutylammonium bromide, tetraethylammonium bromide, and tetramethylammonium bromide; Preferably, the bromine source is a mixture of tetrabutylammonium bromide and cetyltrimethylammonium bromide.

3. The preparation method according to claim 2, characterized in that When cetyltrimethylammonium bromide and lower alkyl ammonium bromide are mixed, the molar ratio of lower alkyl ammonium bromide to cetyltrimethylammonium bromide is 1:(0.1-10); Preferably, the molar ratio of lower alkyl ammonium bromide to hexadecyltrimethylammonium bromide is 1:(0.1-5); Preferably, the molar ratio of lower alkyl ammonium bromide to hexadecyltrimethylammonium bromide is 1:(1-4); Preferably, in step (1), the molar ratio of the bromine source to water is 1:(50-300); Preferably, the molar ratio of the bromine source to water is 1:(100-300).

4. The preparation method according to any one of claims 1 to 3, characterized in that The alkaline source includes one of tetrabutylammonium hydroxide, tetrapropylammonium hydroxide, ammonia water, sodium hydroxide, sodium carbonate, sodium bicarbonate, or a mixture of two or more thereof; Preferably, the alkali source is aqueous ammonia; Preferably, an alkaline source is added to adjust the pH of the first mixed solution to 9-12; Preferably, the molar ratio of the alkali source to the bromine source is 1:(1-10); preferably, the molar ratio of the alkali source to the bromine source is 1:(1-5); more preferably, the molar ratio of the alkali source to the bromine source is 1:(1-3).

5. The preparation method according to any one of claims 1 to 3, characterized in that In step (1), a bromine source and an alkali source are mixed in water at a temperature of 25° C. to 100° C.; Preferably, the mixture is mixed at a temperature of 25°C to 50°C; Preferably, the stirring time is 10 min to 3 h, more preferably, the stirring time is 10 min to 1.5 h, and more preferably, the stirring time is 10 min to 1 h.

6. The preparation method according to any one of claims 1 to 5, characterized in that The silicon source is selected from one of tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), sodium silicate, and silicon tetrachloride (STC), or a mixture of two or more thereof. Preferably, the silicon source is tetraethyl orthosilicate; The molar ratio of the silicon source to the bromine source is 1:(0.4-10). Preferably, the molar ratio of the silicon source to the bromine source is 1:(0.6-5).

7. The preparation method according to any one of claims 1 to 6, characterized in that In step (2), the pH of the suspension is 7-11, preferably, the pH of the suspension is 8-11.

8. The preparation method according to any one of claims 1 to 6, characterized in that In step (2), the first solution is mixed with a silicon source at a temperature of 25° C. to 100° C.; Preferably, the mixture is mixed at a temperature of 25°C to 50°C; Preferably, in step (2), the mixing time is 30 min to 13 h; preferably, the stirring time is 2 h to 10 h; more preferably, the stirring time is 3 h to 7 h.

9. A catalyst obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The catalyst has a core-shell structure, the shell is composed of silicon-containing material, and the core is a quaternary ammonium salt ionic liquid; Preferably, the quaternary ammonium salt ionic liquid is a mixture of hexadecyltrimethylammonium bromide and lower alkyl ammonium bromide, wherein the molar ratio of lower alkyl ammonium bromide to hexadecyltrimethylammonium bromide is 1:(0.1-10); Preferably, the molar ratio of lower alkyl ammonium bromide to hexadecyltrimethylammonium bromide is 1:(0.1-5); Preferably, the molar ratio of lower alkyl ammonium bromide to hexadecyltrimethylammonium bromide is 1:(1-4).

10. A catalyst obtained by the preparation method according to any one of claims 1 to 8, used in the synthesis of cyclic carbonates; the cyclic carbonates include propylene carbonate; Preferably, the catalyst is used to synthesize propylene carbonate, comprising: using carbon dioxide and propylene oxide as raw materials, reacting in the presence of the catalyst at a temperature range of 80°C-200°C to obtain propylene carbonate; During the reaction, the mass ratio of the catalyst to propylene oxide is 1:(15-30).

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