Amorphous silica-alumina solid acid catalyst as well as preparation method and application thereof, and method for preparing durene by adopting sanding method
By combining amorphous silica-alumina solid acid catalysts with sand milling and microreactor technology, the problems of catalyst corrosion and clogging in existing mesitylene production have been solved, achieving efficient and stable mesitylene production and improving conversion rate and yield.
Patent Information
- Application Number
- CN202511747949.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-25
- Publication Date
- 2026-02-24
AI Technical Summary
In existing mesitylene production technologies, liquid acid catalysts are highly corrosive, microporous molecular sieve catalysts are prone to clogging, and solid superacid catalysts have a single active center, resulting in low production efficiency, high cost, and poor environmental performance, making it difficult to meet the needs of stable production.
Amorphous silica-alumina solid acid catalysts are used to prepare nanoscale suspensions via sand milling. These suspensions are then combined with microreactors for alkylation reactions, avoiding catalyst corrosion and clogging. The abundant Lewis acid catalytic active centers are utilized to improve conversion and yield.
It has achieved efficient and stable production of mesitylene, with long catalyst life, fast reaction rate, reduced production costs and environmental risks, and improved production efficiency.
Smart Images
Figure CN121550987A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of catalysis and organic synthesis technology, and in particular to an amorphous silica-alumina solid acid catalyst, its preparation method and application, and a method for preparing mesitylene by sand milling. Background Technology
[0002] 1,2,4,5-Tetramethylbenzene is a key raw material for the preparation of pyromellitic dianhydride. Its downstream product, polyimide, holds an irreplaceable position in high-end fields such as aerospace, microelectronics, and military due to its excellent thermal stability, mechanical strength, and chemical resistance. With the surge in demand for polyimide, the market has placed higher demands on the production efficiency, cost control, and environmental friendliness of 1,2,4,5-tetramethylbenzene.
[0003] Currently, the mainstream industrial production of mesitylene relies on the physical separation method of C10 heavy aromatics. However, this method is limited by the low mesitylene content in the feedstock (usually <5%), high separation energy consumption, and unstable feedstock supply. Among chemical synthesis methods, pseudotrimethylbenzene and methanol alkylation are considered the most promising alternative routes for producing mesitylene. However, current mainstream alkylation catalysts have significant shortcomings: sulfuric acid liquid catalysts, although highly active, are highly corrosive, requiring large amounts of alkali for neutralization after the reaction, generating polluted wastewater and corroding equipment, increasing safety risks and maintenance costs; microporous molecular sieve catalysts have small pore sizes, and large molecular products or carbon species easily accumulate and clog the pores, leading to rapid catalyst deactivation and difficulty in meeting stable production requirements; solid superacid catalysts have a single active center and excessive acidity, with a large amount of Brønsted acid inducing side reactions, reducing the selectivity of the target product and increasing purification difficulty. Summary of the Invention
[0004] In view of this, the purpose of this invention is to provide an amorphous silica-alumina solid acid catalyst, its preparation method and application, and a method for preparing mesitylene using a sand milling method. The amorphous silica-alumina solid acid catalyst prepared by this invention not only avoids corrosion of the equipment, but also exhibits advantages such as high mesitylene conversion and yield, as well as good stability in catalyzing the alkylation of pseudotrimethylbenzene to mesitylene.
[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing an amorphous silica-alumina solid acid catalyst, comprising the following steps: Amorphous silicon source, soft template agent, growth inhibitor, hexadecyltrimethylammonium bromide and water are mixed to obtain the first mixture; The organoaluminum and organic solvent are mixed to obtain a second mixture; The first mixture and the second mixture are mixed, and the resulting third mixture is subjected to hydrothermal crystallization. After solid-liquid separation, the hydrothermal crystallization product is obtained. The molar ratio of amorphous silicon source, organoaluminum, soft template agent, growth inhibitor, hexadecyltrimethylammonium bromide, organic solvent and water in the third mixture is 1:(0.005~0.1):(0.05~0.5):(0.05~0.4):(0.01~0.05):(1~2):(10~30), and the amorphous silicon source is calculated as SiO2. The hydrothermal crystallization product was dried and calcined sequentially to obtain the amorphous silica-alumina solid acid catalyst.
[0006] Preferably, the amorphous silicon source includes one or more of tetraethyl orthosilicate, sodium silicate, and silica sol; the soft template agent includes tetrapropylammonium hydroxide and dimethyl dipropylammonium hydroxide, wherein the mass of the tetrapropylammonium hydroxide is 50-80% of the total mass of the tetrapropylammonium hydroxide and dimethyl dipropylammonium hydroxide; the growth inhibitor includes one or more of L-lysine, arginine, and histidine; and the organoaluminum includes one or more of aluminum acetylacetonate, trimethylaluminum, and triphenylaluminum.
[0007] Preferably, the hydrothermal crystallization temperature is 90~150℃ and the time is 24~72h; the calcination temperature is 550℃ and the time is 2~4h.
[0008] This invention provides an amorphous silica-alumina solid acid catalyst prepared by the preparation method described above, wherein the specific surface area of the amorphous silica-alumina solid acid catalyst is ≥700 m². 2 / g, mesopore volume is 4~10nm, and mesopore size is 0.5~0.7cm³. 3 / g, the ratio of Lewis acidity to Brønsted acidity is ≥50.
[0009] This invention provides the application of the amorphous silica-alumina solid acid catalyst described above in the catalytic alkylation of pseudotrimethylbenzene to prepare mesitylene.
[0010] This invention provides a method for preparing mesitylene using a sand milling method, comprising the following steps: The solid catalyst and methanol were mixed and then milled to obtain a suspension with a D90 particle size of less than 50 nm; the suspension was mixed with pseudotrimethylbenzene and subjected to an alkylation reaction to obtain mesitylene; the solid catalyst was the amorphous silica-alumina solid acid catalyst described in the above technical solution.
[0011] Preferably, the mass ratio of the solid catalyst to methanol is 1:(20~100), and the molar ratio of the pseudotrimethylbenzene to methanol is 1:(1~1.5).
[0012] Preferably, the alkylation reaction is carried out in a plate-type mixing microreactor, wherein the mixing channel of the plate-type mixing microreactor is a serpentine channel with an inner diameter of 0.25~0.5 mm.
[0013] Preferably, the alkylation reaction is carried out at a temperature of 200-300°C and a pressure of 0.5-1.5 MPa, and the residence time of the mixture of suspension and pseudotrimethylbenzene in the mixing channel of the plate mixing microreactor is 10-120 min.
[0014] Preferably, after the alkylation reaction, the resulting reaction solution is further subjected to sedimentation and separation.
[0015] This invention provides a method for preparing an amorphous silicon-aluminum solid acid catalyst, comprising the following steps: mixing an amorphous silicon source, a soft template agent, a growth inhibitor, hexadecyltrimethylammonium bromide, and water to obtain a first mixture; mixing an organoaluminum compound and an organic solvent to obtain a second mixture; mixing the first and second mixtures; subjecting the resulting third mixture to hydrothermal crystallization; and separating the solid and liquid phases to obtain a hydrothermal crystallization product; and sequentially drying and calcining the hydrothermal crystallization product to obtain the amorphous silicon-aluminum solid acid catalyst. This invention utilizes in-situ synthesis of solid acid catalysts from amorphous silicon, and controls crystal growth by introducing a soft template agent and a growth inhibitor to obtain an amorphous solid catalyst. Simultaneously, the acidity of the catalyst is controlled by adjusting the amount of organoaluminum (controlling the aluminum to be non-framework aluminum), resulting in a catalyst with suitable acidity (the amount of L-acid is much higher than that of Brønsted acid, and the acidity is mainly at weak acid sites). The amorphous silica-alumina solid acid catalyst synthesized in situ in this invention has abundant L-acids, a large specific surface area, stable active centers, and abundant mesopores, which can avoid corrosion of the equipment. It has the characteristics of controllable acidity and high catalyst performance. When applied to the catalytic alkylation of pseudotrimethylbenzene to prepare mesitylene, it has the advantages of high pseudotrimethylbenzene conversion and mesitylene yield, as well as good stability.
[0016] This invention provides a method for preparing mesitylene using a sand milling process, achieving high conversion and yield of mesitylene. Furthermore, this invention utilizes the excellent mass and heat transfer capabilities of a microreactor, combined with the easy separation characteristics of heterogeneous catalysis by solid catalysts, to significantly improve the reaction rate, shorten the reaction time, increase the reaction yield, and improve production efficiency and safety. Attached Figure Description
[0017] Figure 1 This is a schematic diagram of the apparatus for preparing mesitylene by alkylation of pseudotrimethylbenzene in an embodiment of the present invention; Figure 2 This is a schematic diagram of the plate-type mixing microreactor in this invention; Figures 1-2In the middle: 1-Sand mill, 2-Raw material storage tank, 3-First conveying pump, 4-Second conveying pump, 5-Plate mixing microreactor, 51-First inlet, 52-Second inlet, 53-Mixing channel, 54-First branch channel, 55-Second branch channel, 6-Back pressure valve, 7-Settling tank; Figure 3 The XRD patterns are for solid catalyst A and solid catalyst B. Figure 4 The N2 adsorption-desorption curves are for solid catalyst A. Figure 5 This is a diagram showing the mesopore distribution of solid catalyst A. Figure 6 The results of NH3-TPD analysis for solid catalyst A and solid catalyst B are shown. Figure 7 The image shows the infrared analysis results of pyridine for solid catalyst A. Detailed Implementation
[0018] This invention provides a method for preparing an amorphous silica-alumina solid acid catalyst, comprising the following steps: Amorphous silicon source, soft template agent, growth inhibitor, hexadecyltrimethylammonium bromide and water are mixed to obtain the first mixture; The organoaluminum and organic solvent are mixed to obtain a second mixture; The first mixture and the second mixture are mixed, and the resulting third mixture is subjected to hydrothermal crystallization. After solid-liquid separation, the hydrothermal crystallization product is obtained. The molar ratio of amorphous silicon source, organoaluminum, soft template agent, growth inhibitor, hexadecyltrimethylammonium bromide, organic solvent and water in the third mixture is 1:(0.005~0.1):(0.05~0.5):(0.05~0.4):(0.01~0.05):(1~2):(10~30), and the amorphous silicon source is calculated as SiO2. The hydrothermal crystallization product was dried and calcined sequentially to obtain the amorphous silica-alumina solid acid catalyst.
[0019] Unless otherwise specified, all raw materials involved in this invention are commercially available products well known in the art.
[0020] The present invention mixes an amorphous silicon source, a soft template agent, a growth inhibitor, hexadecyltrimethylammonium bromide and water to obtain a first mixture.
[0021] In this invention, the amorphous silicon source preferably includes one or more of tetraethyl orthosilicate, sodium silicate, and silica sol. In this invention, the soft template agent preferably includes tetrapropylammonium hydroxide and dimethyl dipropylammonium hydroxide, wherein the mass of the tetrapropylammonium hydroxide is 50-80% of the total mass of the tetrapropylammonium hydroxide and dimethyl dipropylammonium hydroxide, which can be 55%, 58%, 60%, 70%, or 75%; the function of the soft template agent is to control crystal growth during the synthesis process and increase the specific surface area. In this invention, the growth inhibitor preferably includes one or more of L-lysine, arginine, and histidine; the function of the growth inhibitor is to prevent the growth of ZSM-5 molecular sieves during the synthesis process. In this invention, the first mixture is an aqueous phase, the second mixture is an oil phase, and the hexadecyltrimethylammonium bromide acts as a surfactant, allowing the oil and water phases to mix (organoaluminum can enter the aqueous phase for reaction).
[0022] In this invention, the amorphous silicon source, soft template agent, growth inhibitor, hexadecyltrimethylammonium bromide and water are preferably mixed by stirring to ensure that all components are stirred evenly.
[0023] The present invention mixes organoaluminum and organic solvent to obtain a second mixture.
[0024] In this invention, the organoaluminum preferably includes one or more of aluminum acetylacetonate, trimethylaluminum, and triphenylaluminum; the organic solvent preferably includes toluene. Preferably, the organoaluminum is added to an organic solvent and stirred to dissolve, obtaining the second mixture.
[0025] After obtaining the first mixture and the second mixture, the present invention mixes the first mixture and the second mixture, and performs hydrothermal crystallization on the resulting third mixture. After solid-liquid separation, the hydrothermal crystallization product is obtained.
[0026] In this invention, the molar ratio of amorphous silicon source, organoaluminum, soft template agent, growth inhibitor, hexadecyltrimethylammonium bromide, organic solvent and water in the third mixture is 1:(0.005~0.1):(0.05~0.5):(0.05~0.4):(0.01~0.05):(1~2):(10~30), preferably 1:(0.05~0.1):(0.05~0.1):(0.05~0.1):(0.01~0.02):(1~1.5):(10~20), and more preferably 1:(0.06~0.1):(0.06~0.1):(0.07~0.1):(0.01~0.02):(1~1.2):(11~20), wherein the amorphous silicon source is SiO2.
[0027] In this invention, the temperature of the hydrothermal crystallization is preferably 90~150℃, which can be 100 or 120℃, and the time is preferably 24~72h, which can be 24, 36 or 72h; the hydrothermal crystallization is specifically carried out in a crystallization kettle.
[0028] In this invention, the solid-liquid separation method can be centrifugation, and the solid obtained by solid-liquid separation is the hydrothermal crystallization product.
[0029] After obtaining the hydrothermal crystallization product, the present invention sequentially dries and calcines the hydrothermal crystallization product to obtain an amorphous silicon-aluminum solid acid catalyst.
[0030] In this invention, the drying is preferably freeze-drying.
[0031] In this invention, the calcination temperature is preferably 550°C, and the calcination time is preferably 2 to 4 hours, which can be 2, 3 or 4 hours; during the calcination process, the template agent is burned off, and the pores are activated.
[0032] This invention provides an amorphous silica-alumina solid acid catalyst prepared by the preparation method described above, wherein the specific surface area of the amorphous silica-alumina solid acid catalyst is ≥700 m². 2 / g, mesopore size 4~10nm, mesopore volume 0.5~0.7cm³ 3 / g, the ratio of Lewis acidity to Brønsted acidity is ≥50.
[0033] The amorphous silica-alumina solid acid catalyst provided by this invention possesses abundant Li-acids, a large specific surface area, and abundant mesopores. Alkylation reactions can be catalyzed by either Beta-acids or Li-acids. Compared to Beta-acids, Li-acid catalysis features milder reaction conditions, longer catalyst lifetime, and higher yield of the target product. It can avoid corrosion from liquid acids, and suitable acidity and pore structure can reduce carbon deposition and extend the catalyst's lifespan.
[0034] This invention provides the application of the amorphous silica-alumina solid acid catalyst described above in the catalytic alkylation of pseudotrimethylbenzene to prepare mesitylene. Applying the amorphous silica-alumina solid acid catalyst to the catalytic alkylation of pseudotrimethylbenzene to prepare mesitylene offers advantages such as high pseudotrimethylbenzene conversion and mesitylene yield, as well as good stability.
[0035] This invention provides a method for preparing mesitylene using a sand milling method, comprising the following steps: The solid catalyst and methanol were mixed and then milled to obtain a suspension with a D90 particle size of less than 50 nm; the suspension was mixed with pseudotrimethylbenzene and subjected to an alkylation reaction to obtain mesitylene; the solid catalyst was the amorphous silica-alumina solid acid catalyst described in the above technical solution.
[0036] In this invention, the mass ratio of the solid catalyst to methanol is preferably 1:(20~100), which can be 1:20, 1:30, 1:50 or 1:80; the molar ratio of the pseudotrimethylbenzene to methanol is preferably 1:(1~1.5), which can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4 or 1:1.5.
[0037] In this invention, the sand milling process is specifically carried out in a sand mill. In this embodiment, the sand mill used is a Toppa HNM6. This invention does not have special requirements for the process conditions of the sand milling process; it is sufficient to obtain a suspension with a D90 particle size of less than 50 nm. In this invention, the D90 particle size can be 30~50 nm.
[0038] In this invention, the alkylation reaction is preferably carried out in a plate-type mixing microreactor. The mixing channel (i.e., the reaction channel) of the plate-type mixing microreactor is preferably a serpentine channel, and the inner diameter of the serpentine channel is preferably 0.25~0.5 mm, which can be 0.25, 0.3, 0.4 or 0.5 mm. In this invention, the suspension and pseudotrimethylbenzene are preferably transported to the inlet of the plate-type mixing microreactor by separate pumps, mixed at the inlet, and then enter the mixing channel of the plate-type mixing microreactor for the alkylation reaction. The molar ratio of pseudotrimethylbenzene to methanol at the inlet of the plate-type mixing microreactor can be 1:(1~1.5) by controlling the flow rates of the suspension and pseudotrimethylbenzene pumps respectively. The total flow rate of the suspension and pseudotrimethylbenzene is preferably 1~4 mL / min, which can be 1, 2, 3 or 4 mL / min. In this invention, the preferred temperature of the alkylation reaction is 200~300℃, which can be 200, 250, 280, 290 or 300℃. The plate-type mixing microreactor can be completely immersed in heat transfer oil to control the reaction temperature at 200~300℃. The preferred pressure of the alkylation reaction is 0.5~1.5MPa, which can be 0.5, 0.7, 0.8, 1.0, 1.2 or 1.5MPa. The pressure inside the plate-type mixing microreactor can be controlled at 0.5~1.5MPa by a back pressure valve. The preferred residence time of the mixture of suspension and pseudotrimethylbenzene in the mixing channel of the plate-type mixing microreactor is 10~120min, which can be 20, 25, 30, 40, 50 or 100min. The required residence time can be achieved by controlling the length of the mixing channel of the plate-type mixing microreactor or by connecting multiple plate-type mixing microreactors in series.
[0039] After the alkylation reaction is completed, the resulting reaction solution is preferably subjected to sedimentation separation, and the resulting liquid is a product liquid containing mesitylene. In this invention, the sedimentation separation is preferably carried out in a sedimentation tank, the inlet of which is connected to the outlet of the plate mixing microreactor. Specifically, the reaction solution flowing out of the plate mixing microreactor after the alkylation reaction flows into the sedimentation tank for sedimentation separation, and the clear liquid above is the product liquid containing mesitylene.
[0040] In this invention, the sand mill, plate-type mixing microreactor, and settling tank together constitute the apparatus for the preparation of mesitylene by the alkylation of pseudotrimethylbenzene, as described above. Figure 1 As shown below, Figure 1 Please provide a detailed explanation: like Figure 1 As shown, the apparatus used in this invention to prepare mesitylene includes a pretreatment module, a raw material supply module, a plate-type mixing microreactor 5, and a sedimentation collection module. Figure 2 This is a schematic diagram of the plate-type mixing microreactor in this invention.
[0041] In this invention, the pretreatment module includes a sand mill 1 and a first delivery pump 3, which are connected by a pipeline. The first delivery pump 3 is also connected by a pipeline to the first inlet 51 of the plate-type mixing microreactor 5. In this embodiment, the sand mill 1 is a Toppa HNM6 model. The sand mill 1 is used to grind the solid catalyst to reduce its particle size (e.g., nanometer level) and to mix the solid catalyst with a liquid additive (e.g., methanol) to form a suspension containing the catalyst (e.g., nanofluid), thereby ensuring smooth flow of the solid catalyst and avoiding clogging of the microchannels of the plate-type mixing microreactor 5. In this invention, the first delivery pump 3 is preferably a horizontal flow pump, and its flow rate is adjustable from 0 to 10 mL / min. The first delivery pump 3 is used to pass the suspension containing the catalyst prepared in the sand mill 1 into the plate-type mixing microreactor 5.
[0042] In this invention, the raw material supply module includes a raw material storage tank 2 and a second transfer pump 4, which are connected by a pipeline. The second transfer pump 4 is also connected by a pipeline to the second inlet 52 of the plate-type mixing microreactor 5. Preferably, the raw material storage tank 2 is made of stainless steel and is used to store reactants (such as pseudotrimethylbenzene). The second transfer pump 4 is preferably a horizontal flow pump with a flow rate adjustable range of 0-10 mL / min, and is used to introduce the reactants from the raw material storage tank 2 into the plate-type mixing microreactor 5.
[0043] In this invention, the plate-type mixing microreactor 5 includes a microreactor body, a first branch channel 54, a second branch channel 55, and a mixing channel 53. The first branch channel 54, the second branch channel 55, and the mixing channel 53 are all located inside the microreactor body. One end of the first branch channel 54 is the first inlet 51 of the plate-type mixing microreactor 5, and the second end of the first branch channel 54 is connected to the first end of the mixing channel 53. One end of the second branch channel 55 is the second inlet 52 of the plate-type mixing microreactor 5, and the second end of the second branch channel 55 is connected to the first end of the mixing channel 53. The substances at the first inlet 51 and the second inlet 52 are then introduced into the mixing channel 53, where they are fully mixed and reacted. The second end of the mixing channel 53 is connected to the inlet of the sedimentation collection module. In this invention, the first end of the mixing channel 53 is located near one side of the plate-type mixing microreactor 5, and the second end of the mixing channel 53 is located near the other side of the plate-type mixing microreactor 5. The mixing channel 53 is a serpentine channel, which can extend the reaction path and ensure thorough mixing of the solid catalyst and reactants. In this invention, the mixing channel 53, the first branch channel 54, and the second branch channel 55 have the same inner diameter. In this invention, the first inlet 51 of the plate-type mixing microreactor 5 is used to connect to the outlet of the pretreatment module, and the second inlet 52 of the plate-type mixing microreactor 5 is used to connect to the outlet of the raw material supply module, thereby facilitating the mixing of substances in the pretreatment module and the raw material supply module through the plate-type mixing microreactor 5; the plate-type mixing microreactor 5 is used to mix and react the suspension containing the catalyst and the reactants to obtain a mixture of reaction products (such as mesitylene) and catalyst, and then transport it to the sedimentation collection module. Compared with directly adding the solid catalyst into the plate-type mixing microreactor 5, by reducing the particle size of the solid catalyst and allowing the solid catalyst and reactants to move while reacting in the plate-type mixing microreactor 5, the solid catalyst and reactants can be fully contacted and mixed.
[0044] In this invention, the sedimentation collection module includes a back pressure valve 6 and a sedimentation tank 7. The sedimentation tank 7 is connected to the outlet of the plate-type mixing microreactor 5 via a pipeline, and the back pressure valve 6 is installed on the pipeline between the sedimentation tank 7 and the plate-type mixing microreactor 5. In this invention, the back pressure valve 6 is used to regulate the reaction pressure inside the plate-type mixing microreactor, with a pressure regulation range of 0~1.5MPa. The sedimentation tank 7 is preferably made of stainless steel and is used to separate the mixture of reaction products and catalyst through sedimentation, thereby collecting the reaction products. In this invention, after the reaction is completed, the solid catalyst and reaction products flow out of the plate-type mixing microreactor 5 together, fundamentally avoiding clogging of the plate-type mixing microreactor 5, and the catalyst can be easily recovered by centrifugation or filtration.
[0045] In this invention, the sedimentation collection module is used to separate the mixture of reaction products and catalyst by sedimentation, thereby collecting the reaction products and ultimately enabling heterogeneous catalytic reaction to be carried out in the plate-type mixing microreactor 5. This not only enhances the reaction performance and improves the heterogeneous catalytic performance, but also avoids the phenomenon of heterogeneous catalyst blockage in the plate-type mixing microreactor 5.
[0046] This invention utilizes the aforementioned apparatus for the alkylation of pseudotrimethylbenzene to prepare mesitylene, which enhances reaction performance, improves heterogeneous catalytic performance, and avoids the blockage of heterogeneous catalysts within the microreactor. Figure 1 The overall process for preparing mesitylene using the apparatus shown is as follows: the solid catalyst and methanol are thoroughly ground in a sand mill 1, and the resulting suspension is fed into a plate-type mixing microreactor 5 via a first transfer pump 3 and a pseudotrimethylbenzene via a second transfer pump 4. The mixture is thoroughly mixed in the plate-type mixing microreactor 5 and undergoes an alkylation reaction (moving while reacting). The reaction mixture (including the solid catalyst and mesitylene) flows out of the plate-type mixing microreactor 5 together and settles and separates in a settling tank 7 to obtain a product liquid containing mesitylene.
[0047] Existing alkylation processes (fixed-bed or reactor processes) suffer from drawbacks such as low reaction efficiency, high methanol ratios (methanol / pyrimethene molar ratios often reach 3:1 to 6:1), rapid catalyst deactivation, and poor product selectivity. Microreactors, with their micron-scale microchannel structure, can achieve precise mixing of reactants at the molecular level, millisecond-level temperature control, and efficient heat and mass transfer, potentially overcoming the inherent limitations of traditional reactors, improving the conversion rate of pyrimethene and the yield of mesitylene, and reducing the amount of methanol used in the reaction. However, heterogeneous catalytic reactions with solid catalysts in microreactors are highly prone to reactor clogging. Researchers have attempted to address this problem by fixing the catalyst in the microreactor and adding surfactants to disperse the solid catalyst. However, these methods are applicable to microreactors with a characteristic size greater than or equal to 1 mm. Furthermore, as the reaction proceeds, these methods all carry the risk of increasing the pressure drop in the microreactor and clogging it, making it impossible to completely avoid clogging. In particular, pressurized reactions within microreactors further exacerbate the clogging risk. Currently, there are no mature case reports of pressurized heterogeneous catalytic processes in microreactors smaller than 1 mm. It is well known that the smaller the characteristic size of a microreactor, the stronger its effect on the reaction process, especially for heterogeneous catalytic processes. External diffusion is often the rate-determining step, and reducing the characteristic size can significantly enhance the external diffusion rate. Researchers have used catalyst coating on the walls of microreactors to effectively solve the problem of blockage in heterogeneous catalytic processes within microreactors; however, this method suffers from issues such as catalyst loss and low catalytic efficiency. Furthermore, conventional supported acidic catalysts suffer from the drawback of easily lost active sites, which is further accelerated when used in continuous reactions within microreactors.
[0048] This invention synthesizes in situ an amorphous silica-alumina solid acid catalyst rich in L-acids. This catalyst possesses a large specific surface area, controllable acidity, stable active centers, and abundant mesopores, which can significantly improve the performance of alkylation of pseudotrimethylbenzene to mesitylene. Furthermore, this invention uses sand milling to prepare the catalyst and methanol into a nanoscale solid catalyst fluid, effectively solving the problem of microreactor clogging. During the microreactor process, methanol and pseudotrimethylbenzene undergo an alkylation reaction to generate mesitylene under the action of the nanocatalyst. Mass transfer between reactants and catalyst is enhanced within the confined space of a microscale, significantly improving the conversion rate of pseudotrimethylbenzene and the yield of mesitylene. After the reaction, the catalyst and reaction product flow out of the microreactor together, fundamentally avoiding microreactor clogging, and the catalyst can be easily recovered by centrifugation or filtration.
[0049] To further illustrate the present invention, the following detailed descriptions, in conjunction with examples, illustrate the amorphous silica-alumina solid acid catalyst provided by the present invention, its preparation method and application, and the method for preparing mesitylene by sand milling. However, these descriptions should not be construed as limiting the scope of protection of the present invention.
[0050] Example 1 Weigh 5.21g tetraethyl orthosilicate, 0.25g tetrapropylammonium hydroxide, 0.18g dimethyl dipropylammonium hydroxide, 0.38g L-lysine, 0.18g hexadecyltrimethylammonium bromide, and 9g water, and mix them thoroughly. Weigh 0.81g aluminum acetylacetonate and add it to 2.5g toluene, stirring to dissolve. Mix the two solutions and transfer them to a crystallization vessel. Crystallize at 120℃ for 24 hours. After centrifugation, obtain the solid, freeze-dry it, and calcine it at 550℃ for 4 hours to obtain an amorphous silica-alumina solid acid catalyst, denoted as solid acid catalyst A.
[0051] Example 2 Weigh out 5g of sodium silicate, 0.32g of tetrapropylammonium hydroxide, 0.13g of dimethyldipropylammonium hydroxide, 0.50g of histidine, 0.15g of hexadecyltrimethylammonium bromide, and 8.0g of water, and mix them thoroughly. Weigh out 0.65g of triphenylaluminum and add it to 4.0g of toluene, stirring to dissolve. Mix the two solutions and transfer them to a crystallization vessel. Crystallize at 100℃ for 36 hours. After centrifugation, obtain the solid, freeze-dry it, and calcine it at 550℃ for 3 hours to obtain an amorphous silica-alumina solid acid catalyst, denoted as solid acid catalyst B.
[0052] Examples 3-7 show the preparation of mesitylene in... Figure 1 The apparatus shown includes a sand mill 1 for sand milling a solid catalyst and methanol, a first transfer pump 3 for conveying the suspension from the sand mill outlet, a raw material storage tank 2 and a second transfer pump 4 for storing and conveying pseudotrimethylbenzene, a plate-type mixing microreactor 5 for mixing the raw materials and carrying out the reaction (the plate-type mixing microreactor 5 includes a first branch channel 54, a second branch channel 55 and a mixing channel 53, wherein the mixing channel 53 is a serpentine channel and the inner diameters of the first branch channel 54, the second branch channel 55 and the mixing channel 53 are the same), and a settling tank 7 for collecting the reaction products.
[0053] Example 3 Solid catalyst A from Example 1 was mixed with methanol at a mass ratio of 1:20. The mixture was then milled using a sand mill until the D90 particle size of the solid particles in the methanol mixture (suspension) at the mill outlet was 45 nm. The methanol mixture and pseudotrimethylbenzene were pumped to the inlet of a plate-type mixing microreactor (entering the serpentine mixing channel through the first and second branch channels of the plate-type mixing microreactor, respectively). The flow rates of the pseudotrimethylbenzene delivery pump and the methanol mixture delivery pump were controlled to ensure that the molar ratio of pseudotrimethylbenzene to methanol at the inlet of the plate-type mixing microreactor was 1:1, and the total flow rate of the two pumps was 1 mL / min. The inner diameter of the channels in the plate-type mixing microreactor was 0.5 mm. The residence time in the serpentine channel was adjusted to 30 min by changing the length of the reaction channel. The reaction temperature was controlled at 300 °C, and the reaction pressure was 1.0 MPa. After the reaction, the clear liquid above the settling tank was filtered and the contents of pseudotrimethylbenzene and mesitylene were detected by chromatography. The conversion rate of pseudotrimethylbenzene and the yield of mesitylene were calculated.
[0054] Example 4 Solid catalyst A from Example 1 was mixed with methanol at a mass ratio of 1:50. The mixture was then milled using a sand mill until the D90 particle size of the solid particles in the methanol mixture at the mill outlet was 35 nm. The methanol mixture and pseudotrimethylbenzene were pumped to the inlet of a plate-type mixing microreactor. The flow rates of the pseudotrimethylbenzene pump and the methanol mixture pump were controlled to ensure that the molar ratio of pseudotrimethylbenzene to methanol at the inlet of the plate-type mixing microreactor was 1:1.1, and the total flow rate of the two pumps was 1 mL / min. The inner diameter of the flow channel in the plate-type mixing microreactor was 0.5 mm. The residence time in the serpentine flow channel was adjusted to 40 min by changing the length of the reaction channel. The reaction temperature was controlled at 300 °C, and the reaction pressure was controlled at 0.8 MPa. After the reaction, the clear liquid above the settling tank was filtered and the contents of pseudotrimethylbenzene and mesitylene were detected by chromatography. The conversion rate of pseudotrimethylbenzene and the yield of mesitylene were calculated.
[0055] Example 5 Solid catalyst B from Example 2 was mixed with methanol at a mass ratio of 1:80, and then milled in a sand mill until the D90 particle size of the solid particles in the methanol mixture at the mill outlet was 35 nm. The methanol mixture and pseudotrimethylbenzene were pumped to the inlet of a plate-type mixing microreactor. The flow rates of the pseudotrimethylbenzene pump and the methanol mixture pump were controlled to ensure that the molar ratio of pseudotrimethylbenzene to methanol at the inlet of the plate-type mixing microreactor was 1:1.5, and the total flow rate of the two pumps was 2 mL / min. The inner diameter of the flow channel of the plate-type mixing microreactor was 0.25 mm. By changing the length of the reaction channel, the residence time in the serpentine flow channel was 20 min. The reaction temperature was controlled at 280 °C and the reaction pressure at 1.2 MPa. After the reaction, the clear liquid above the settling tank was filtered and the contents of pseudotrimethylbenzene and mesitylene were detected by chromatography. The conversion rate of pseudotrimethylbenzene and the yield of mesitylene were calculated.
[0056] Example 6 Solid catalyst B from Example 2 was mixed with methanol at a mass ratio of 1:30. The mixture was then milled using a sand mill until the D90 particle size of the solid particles in the methanol mixture at the mill outlet was 46 nm. The methanol mixture and pseudotrimethylbenzene were pumped to the inlet of a plate-type mixing microreactor. The flow rates of the pseudotrimethylbenzene pump and the methanol mixture pump were controlled to ensure that the molar ratio of pseudotrimethylbenzene to methanol at the inlet of the plate-type mixing microreactor was 1:1.2, and the total flow rate of the two pumps was 1.1 mL / min. The inner diameter of the flow channels in the plate-type mixing microreactor was 0.5 mm. The residence time in the serpentine flow channel was adjusted to 25 min by changing the length of the reaction channel. The reaction temperature was controlled at 290 °C, and the reaction pressure was controlled at 0.7 MPa. After the reaction, the clear liquid above the settling tank was filtered and the contents of pseudotrimethylbenzene and mesitylene were detected by chromatography. The conversion rate of pseudotrimethylbenzene and the yield of mesitylene were calculated.
[0057] Example 7 Solid catalyst A from Example 1 was mixed with methanol at a mass ratio of 1:20. The mixture was then milled using a sand mill until the D90 particle size of the solid particles in the methanol mixture at the mill outlet was 45 nm. The methanol mixture and pseudotrimethylbenzene were pumped to the inlet of a plate-type mixing microreactor. The flow rates of the pseudotrimethylbenzene and methanol mixture pumps were controlled to maintain a molar ratio of pseudotrimethylbenzene to methanol of 1:1 at the inlet of the plate-type mixing microreactor, with a total flow rate of 1 mL / min. The inner diameter of the flow channels in the plate-type mixing microreactor was 0.5 mm. The residence time in the serpentine flow channel was adjusted to 30 min by changing the reaction channel length. The reaction temperature was controlled at 300 °C, and the reaction pressure at 1.0 MPa. After the reaction, the catalyst was collected, dried, and reused once more using the same process. This process was repeated until the catalyst was reused five times. The contents of pseudotrimethylbenzene and mesitylene in each reaction product were measured, and the conversion rate of pseudotrimethylbenzene and the yield of mesitylene were calculated.
[0058] Comparative Example 1 use Figure 1 The apparatus shown involves mixing a silica solid catalyst loaded with 5 wt% zinc chloride with methanol at a mass ratio of 1:30. The mixture is then milled using a sand mill until the D90 particle size of the solid particles in the methanol mixture at the mill outlet is 46 nm. The methanol mixture and pseudotrimethylbenzene are pumped to the inlet of a plate-type mixing microreactor. By controlling the flow rates of the pseudotrimethylbenzene and methanol mixture pumps, the molar ratio of pseudotrimethylbenzene to methanol at the inlet of the plate-type mixing microreactor is maintained at 1:1.2, with a total flow rate of 1.1 mL / min. The inner diameter of the flow channels in the plate-type mixing microreactor is 0.5 mm. By varying the reaction channel length, the residence time in the serpentine flow channel is maintained at 25 min. The reaction temperature is controlled at 290 °C, and the reaction pressure at 0.7 MPa. After the reaction, the supernatant from the settling tank is filtered and the contents of pseudotrimethylbenzene and mesitylene are determined by chromatography. The conversion rate of pseudotrimethylbenzene and the yield of mesitylene are calculated.
[0059] Comparative Example 2 Solid catalyst A from Example 1 was mixed with methanol at a mass ratio of 1:20, and then milled in a sand mill until the D90 particle size of the solid particles in the methanol mixture at the mill outlet was 45 nm. This methanol mixture was added to a reaction vessel, followed by the addition of pseudotrimethylbenzene, with a molar ratio of pseudotrimethylbenzene to methanol of 1:1. The total mass of pseudotrimethylbenzene, methanol, and solid catalyst A was 30 g. Nitrogen gas was introduced into the reaction vessel, the reaction temperature was controlled at 300 °C, and the pressure was adjusted to 1.0 MPa. After reacting for 1 hour, the upper layer of liquid in the reaction vessel was collected, and the contents of pseudotrimethylbenzene and mesitylene were determined by chromatography. The conversion rate of pseudotrimethylbenzene and the yield of mesitylene were calculated.
[0060] Comparative Example 3 Two g of the solid catalyst A from Example 1 was loaded into a fixed-bed reactor with an inner diameter of 8 cm. Methanol and pseudotrimethylbenzene were mixed uniformly at a molar ratio of 3:1, and then pumped into the fixed-bed reactor at a flow rate of 1.1 mL / min using a horizontal flow pump. The reaction temperature was controlled at 370 °C, and the back pressure valve was adjusted to maintain a reaction pressure of 0.8 MPa. The liquid after the reaction was collected, and the contents of pseudotrimethylbenzene and mesitylene were determined by chromatography. The conversion rate of pseudotrimethylbenzene and the yield of mesitylene were calculated.
[0061] Comparative Example 4 Two g of the solid catalyst A obtained in Example 1 was loaded into a microreactor tube with an inner diameter of 3 mm. Pseudotrimethylbenzene and methanol were mixed uniformly at a molar ratio of 1:1.1, and then pumped into the microreactor using a horizontal flow pump at a flow rate of 1 mL / min. The residence time was adjusted to 25 min by varying the length of the reactor tube. The reaction temperature was controlled at 300 °C using an oil bath, and the reaction pressure was adjusted to 0.8 MPa using a back pressure valve. The collected liquid was analyzed by chromatography to determine the content of pseudotrimethylbenzene and mesitylene, and the conversion rate of pseudotrimethylbenzene and the yield of mesitylene were calculated. The pressure drop in the reaction tube increased significantly after 40 min of reaction, and the tube became clogged after 60 min of reaction.
[0062] Comparative Example 5 use Figure 1 The apparatus shown (excluding the sand mill) mixed solid catalyst A obtained in Example 1 with methanol at a mass ratio of 1:20, then added 1% by mass of sodium dodecylbenzenesulfonate, and sonicated for 2 hours. The resulting suspension and pseudotrimethylbenzene were pumped to the inlet of a plate-type mixing microreactor. The flow rate was controlled to maintain a molar ratio of pseudotrimethylbenzene to methanol of 1:1 at the inlet of the plate-type mixing microreactor. The total flow rate of the two pumps was 1 mL / min. The inner diameter of the flow channels in the plate-type mixing microreactor was 0.5 mm. By changing the length of the reaction channel, the residence time in the serpentine channel was maintained at 30 min. The reaction temperature was controlled at 300 °C, and the reaction pressure at 1.0 MPa. After 15 min of reaction, the pressure drop in the reaction tube increased significantly, and after 20 min of reaction, the reaction tube became blocked. No product was obtained.
[0063] Comparative Example 6 use Figure 1The apparatus shown involves mixing a ZSM-5 molecular sieve solid catalyst loaded with 5 wt% zinc chloride with methanol at a mass ratio of 1:20. The mixture is then milled using a sand mill until the D90 particle size of the solid particles in the methanol mixture at the mill outlet is 45 nm. The methanol mixture and pseudotrimethylbenzene are pumped to the inlet of a plate-type mixing microreactor. The flow rates of the pseudotrimethylbenzene and methanol pumps are controlled to maintain a 1:1 molar ratio of pseudotrimethylbenzene to methanol at the inlet of the plate-type mixing microreactor. The total flow rate of the two pumps is 1 mL / min. The inner diameter of the flow channels in the plate-type mixing microreactor is 0.5 mm. By varying the reaction channel length, the residence time in the serpentine flow channel is maintained at 30 min. The reaction temperature is controlled at 300 °C, and the reaction pressure at 1.0 MPa. After the reaction, the catalyst is separated and collected. The collected catalyst is dried and reused once more using the same process. This process is repeated until the catalyst has been reused five times. The contents of pseudotrimethylbenzene and mesitylene in each reaction product were determined, and the conversion rate of pseudotrimethylbenzene and the yield of mesitylene were calculated.
[0064] Figure 3 The images show the XRD patterns of solid catalyst A and solid catalyst B. Figure 3 In this context, A represents solid catalyst A, and B represents solid catalyst B. (From...) Figure 3 It can be seen that the catalyst synthesized in this invention is an amorphous silicon-aluminum catalyst.
[0065] Figure 4 The N2 adsorption-desorption curves are for solid catalyst A. Figure 5 This is a mesopore distribution diagram of solid catalyst A. The specific surface area of solid catalyst A is 789 m². 2 / g, mesoporous pore volume is 0.65cm³ 3 / g, mesopore size 5nm. (From) Figure 4 and Figure 5 It can be seen that the obtained solid catalyst has a typical mesoporous structure.
[0066] Figure 6 The results of NH3-TPD analysis for solid catalyst A and solid catalyst B are shown below. Figure 6 In this context, A represents solid catalyst A, and B represents solid catalyst B. Figure 7 This is the infrared analysis result of pyridine for solid catalyst A. Figure 6 It can be seen that the acid properties of the catalyst are mainly weak acid sites, due to Figure 7 It can be seen that the amount of Lewis acid in the catalyst is much higher than that of Brønsted acid (the ratio of Lewis acid to Brønsted acid is about 60).
[0067] Table 1 lists the conversion rates of pseudotrimethylbenzene and the yields of mesitylene in Examples 3-6 and Comparative Examples 1-4; Table 2 lists the stability comparison data of the catalysts in Example 7 and Comparative Example 6.
[0068] Table 1 lists the conversion rate of pseudotrimethylbenzene and the yield of mesitylene under different conditions.
[0069] Table 2 Comparison of catalyst lifetime
[0070] As shown in Table 1, the synthesis of mesitylene from pseudotrimethylbenzene using the solid acid catalyst synthesized in this invention combined with a microreactor heterogeneous catalytic process significantly improves both the pseudotrimethylbenzene conversion and the mesitylene yield. Comparing Example 6 and Comparative Example 1, it can be seen that the solid acid catalyst synthesized in this invention significantly improves both the pseudotrimethylbenzene conversion and the mesitylene yield due to its suitable acidity. Comparing Example 4 and Comparative Example 4, it can be seen that the packing microreactor has a weaker effect on enhancing the reaction process, and the reaction tube still suffers from clogging. Comparing Example 3 and Comparative Example 5, it can be seen that adding a sand mill to the device to control the solid catalyst size can effectively solve the microreactor clogging problem.
[0071] By comparing Example 7 and Comparative Example 6 in Table 2, it can be found that the introduction of L acid during the synthesis of the catalyst of the present invention significantly improves the performance and lifespan of the catalyst.
[0072] This invention synthesizes a mesoporous solid acid catalyst with controllable acidity. It innovatively prepares the reactants, namely nanofluids containing solid catalysts, using a sand mill, and then conducts a heterogeneous alkylation reaction in a microreactor to prepare mesitylene. This significantly enhances the reaction process, resulting in a marked improvement in both the conversion rate of pseudotrimethylbenzene and the yield of mesitylene.
[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing an amorphous silica-alumina solid acid catalyst, characterized in that, Includes the following steps: Amorphous silicon source, soft template agent, growth inhibitor, hexadecyltrimethylammonium bromide and water are mixed to obtain the first mixture; The organoaluminum and organic solvent are mixed to obtain a second mixture; The first mixture and the second mixture are mixed, and the resulting third mixture is subjected to hydrothermal crystallization. After solid-liquid separation, the hydrothermal crystallization product is obtained. The molar ratio of amorphous silicon source, organoaluminum, soft template agent, growth inhibitor, hexadecyltrimethylammonium bromide, organic solvent and water in the third mixture is 1:(0.005~0.1):(0.05~0.5):(0.05~0.4):(0.01~0.05):(1~2):(10~30), and the amorphous silicon source is calculated as SiO2; The hydrothermal crystallization product was successively dried and calcined to obtain the amorphous silica-alumina solid acid catalyst.
2. The preparation method according to claim 1, characterized in that, The amorphous silicon source includes one or more of tetraethyl orthosilicate, sodium silicate, and silica sol; the soft template agent includes tetrapropylammonium hydroxide and dimethyl dipropylammonium hydroxide, wherein the mass of tetrapropylammonium hydroxide is 50-80% of the total mass of tetrapropylammonium hydroxide and dimethyl dipropylammonium hydroxide; the growth inhibitor includes one or more of L-lysine, arginine, and histidine; and the organoaluminum includes one or more of aluminum acetylacetonate, trimethylaluminum, and triphenylaluminum.
3. The preparation method according to claim 1, characterized in that, The hydrothermal crystallization temperature is 90~150℃ and the time is 24~72h; the calcination temperature is 550℃ and the time is 2~4h.
4. The amorphous silica-alumina solid acid catalyst prepared by the method according to any one of claims 1 to 3, wherein the specific surface area of the amorphous silica-alumina solid acid catalyst is ≥700 m². 2 / g, mesopore size 4~10nm, mesopore volume 0.5~0.7cm³ 3 / g, the ratio of Lewis acidity to Brønsted acidity is ≥50.
5. The application of the amorphous silica-alumina solid acid catalyst according to claim 4 in the catalytic alkylation of pseudotrimethylbenzene to prepare mesitylene.
6. A method for preparing mesitylene using a sand milling method, characterized in that, Includes the following steps: The solid catalyst and methanol were mixed and then milled to obtain a suspension with a D90 particle size of less than 50 nm; the suspension was mixed with pseudotrimethylbenzene and subjected to an alkylation reaction to obtain mesitylene; the solid catalyst was the amorphous silica-alumina solid acid catalyst of claim 4.
7. The method according to claim 6, characterized in that, The mass ratio of the solid catalyst to methanol is 1:(20~100), and the molar ratio of the pseudotrimethylbenzene to methanol is 1:(1~1.5).
8. The method according to claim 6, characterized in that, The alkylation reaction is carried out in a plate-type mixing microreactor; the mixing channel of the plate-type mixing microreactor is a serpentine channel with an inner diameter of 0.25~0.5 mm.
9. The method according to claim 8, characterized in that, The alkylation reaction is carried out at a temperature of 200-300℃ and a pressure of 0.5-1.5MPa. The residence time of the suspension and the mixture of pseudotrimethylbenzene in the mixing channel of the plate-type mixing microreactor is 10-120 min.
10. The method according to claim 6, 8 or 9, characterized in that, The alkylation reaction is followed by sedimentation and separation of the resulting reaction solution.