A method for purification of mesitylene by suspension melt crystallization

Abstract

This invention provides a method for purifying mesitylene through suspension melt crystallization, belonging to the field of fine chemical separation technology. By adding a crystallization aid to assist in the suspension melt crystallization of mesitylene, this invention overcomes the limitations of traditional crystallization separation. The addition of the crystallization aid interacts with impurities in the crude product, effectively altering the crystallization behavior of the impurities and inhibiting their entry into the mesitylene lattice during crystal growth. This reduces the amount of impurities trapped during mesitylene crystallization, accelerates the crystallization process, and reduces the number of multi-stage crystallization. Without altering the main molecular configuration of mesitylene, this invention achieves highly efficient separation and purification of mesitylene, significantly improving its purity and yield. It solves the problem of isomer separation and overcomes the technical bottleneck of low efficiency in the existing mesitylene purification and separation process.

Description

Technical Field

[0001] This invention relates to the field of fine chemical separation technology, and in particular to a method for purifying mesitylene by suspension melt crystallization. Background Technology

[0002] 1,2,4,5-Tetramethylbenzene, with the molecular formula C2... 10 H 14 It has a molecular weight of 134.22, CAS number 95-93-2, melting point of 79.4±0.9℃, a camphor-like odor, and is a white crystalline solid. It is soluble in organic solvents such as ether and ethanol, but insoluble in water. Its structural formula is as follows: .

[0003] Methionylene is an important chemical raw material, mainly used to produce pyromellitic acid (PMA) and pyromellitic dianhydride (PMDA, 1,2,4,5-benzoic acid dianhydride). Pyromellitic acid is primarily used in the synthesis of polyimide (PI) resins and films, epoxy resin curing agents, powder coating matting agents, polyester resin crosslinking agents, high-insulation, heat-resistant plasticizers, and intermediates in pharmaceuticals, pesticides, and dyes. Pyromellitic dianhydride can also be used to produce polyimide, making it the most economical and ideal raw material for producing polyimide insulating films. Polyimide holds a crucial position among heat-resistant engineering plastics, being one of the most heat-resistant thermoplastic engineering plastics currently available, and is widely used in aerospace, electromechanical, and electronic fields. Furthermore, methionylene is also used in the production of water treatment agents, metal corrosion inhibitors, additives in leather preparations, low-temperature performance improvers for diesel fuels, color tone improvers for electronic photography, electrode materials, and dyes.

[0004] Currently, the main production methods of mesitylene can be divided into two categories: separation method and synthesis method. The separation method mainly uses the "crystallization-pressing" process with C10 heavy aromatics as raw materials. The synthesis methods mainly include the chloromethylation method of pseudotrimethylbenzene, the disproportionation isomerization method of pseudotrimethylbenzene, the direct synthesis of mesitylene from methanol, and the methanol alkylation method of pseudotrimethylbenzene.

[0005] The separation and purification of mesitylene produced by the above methods generally fall into the following categories: 1. Mesitylene is obtained through a process of freeze crystallization-centrifugation-pressing, with a product purity generally of 70-80% and a low content; 2. Due to the low purity of the product in method 1, the process is improved by distillation, freeze crystallization, pressure filtration, first crushing, stirring, pressing, and second crushing to produce mesitylene with a purity of 99%, but the yield of mesitylene obtained is low; 3. A multi-stage crystallization method is adopted, with primary and secondary crystallization being layer-by-layer melt crystallization. Primary crystallization yields a product purity of up to 99.4%, and secondary crystallization recovers the mother liquor, but the operation process is complex and involves many processing procedures; 4. A two-stage distillation-isomerization-stepwise crystallization (multi-stage layer-by-layer melt crystallization) method is used to produce mesitylene products with a purity of over 99%.

[0006] The above purification and separation processes for xylene are complex, involve numerous pieces of equipment, and are all intermittent operations. In particular, the pressure filtration process cannot be completely sealed, resulting in a poor operating environment that can harm the health of operators. In contrast, the continuous distillation process is prone to coking due to prolonged high temperatures, leading to high energy consumption and a long process. Furthermore, the layered melting and crystallization process contains a large number of impurities, requiring post-treatment methods such as sweating and washing, which are time-consuming and inefficient.

[0007] Therefore, providing a method for the purification and separation of mesitylene with good separation performance and high purification efficiency has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to provide a method for purifying mesitylene by suspension melt crystallization. The method provided by this invention enables mesitylene to crystallize more purely from the melt, with good separation properties, and the obtained high-quality mesitylene product has a purity of over 99%, resulting in excellent purification effect.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for purifying mesitylene through suspension melt crystallization, comprising the following steps: (1) Distill the mesitylene raw material to obtain a distillate, and then cool and separate the distillate under vacuum to obtain the mother liquor and crude mesitylene. (2) Melt the crude mesitylene obtained in step (1) to obtain a homogeneous melt, then add a crystallization aid to perform suspension melting crystallization, and finally perform vacuum separation. Repeat the above operations 1 to 3 times to obtain high-purity mesitylene crystals and mother liquor containing aids and impurities.

[0010] Preferably, by mass percentage, the mesitylene raw material in step (1) includes 20-30% mesitylene, 2-5% tetramethylbenzene, 7-8% trimethylbenzene, and the balance being impurities.

[0011] Preferably, the initial temperature of distillation in step (1) is 180°C and the final temperature of distillation is ≤210°C.

[0012] Preferably, the cooling temperature in step (1) is ≤0℃.

[0013] Preferably, the melting operation in step (2) is as follows: crude mesitylene is placed in a jacketed crystallizer, circulating water is introduced into the jacket, the circulating water is then heated, the temperature of the circulating water is controlled by a circulating water bath, and the temperature is displayed by a probe thermometer. The crystallizer is heated evenly by a digital display mechanical stirrer to form a turbulent state, and finally heated to complete melting to form a homogeneous melt.

[0014] Preferably, the crystallization aid in step (2) includes any one of zinc chloride, zinc carbonate, zinc oxide, zinc acetate, copper chloride, aluminum trichloride, aluminum hydroxide, sodium hydroxide, sorbitan monooleate, triphenyl phosphite, and tetraethylammonium hydroxide.

[0015] Preferably, the mass of the crystallization aid in step (2) is 0.1-1% of the crude mesitylene mass.

[0016] Preferably, the suspension melting crystallization operation in step (2) is as follows: the circulating water bath is cooled by a program, and the crystallizer is heated evenly by a digital display mechanical stirrer; the cooling rate of the program cooling is 0.1~0.5℃ / min.

[0017] Preferably, step (2) further includes purifying the high-purity mesitylene crystals; the purification operation is to put the high-purity mesitylene crystals into a jacketed crystallizer, circulate water into the jacket, then heat the circulating water, control the temperature of the circulating water through a circulating water bath, and display the temperature with a probe thermometer. The crystals are heated evenly by a digital display mechanical stirrer in the crystallizer, and the heating endpoint temperature is set to be 1~9℃ lower than the melting temperature for sweating purification. After separation, high-purity mesitylene crystals are obtained.

[0018] Preferably, the temperature for sweating purification is 69~79℃, and the time for sweating purification is 60~120min.

[0019] The present invention provides a method for purifying mesitylene by suspension melt crystallization, comprising the following steps: (1) distilling mesitylene raw material to obtain distillate, and then cooling and vacuum separating the distillate sequentially to obtain mother liquor and crude mesitylene; (2) melting the crude mesitylene obtained in step (1) to obtain homogeneous melt, then adding crystallization aid to perform suspension melt crystallization, and finally performing vacuum separation. The above operations are performed 1 to 3 times to obtain high-purity mesitylene crystals and mother liquor containing aid and impurities. This invention overcomes the limitations of traditional crystallization separation by adding a crystallization aid to assist in the suspension-melt crystallization of mesitylene. The addition of the crystallization aid interacts with impurities in the crude product, effectively altering the crystallization behavior of the impurities and inhibiting their entry into the mesitylene lattice during crystal growth. This reduces the amount of impurities trapped during mesitylene crystallization, accelerates the crystallization process, and reduces the number of multi-stage crystallization levels. Without altering the bulk molecular configuration of mesitylene, this invention achieves highly efficient separation and purification of mesitylene, significantly improving its purity and yield. It solves the problem of isomer separation and overcomes the technical bottleneck of low efficiency in the purification and separation process of mesitylene in existing technologies. The results of the embodiments show that the method provided by this invention enables mesitylene to crystallize more purely from the melt, obtaining a refined mesitylene product with a purity of over 99%, demonstrating excellent purification effects. Attached Figure Description

[0020] Figure 1 The results show the comparison of chromatographic data of crude mesitylene and raw mesitylene in Example 1; Figure 2 The purity and crystallization yield of high-purity mesitylene crystals in Examples 1-4 and Comparative Examples 1-3; Figure 3 The purity of the high-purity mesitylene crystals in Examples 5-10 and Comparative Example 4; Figure 4 The purity and crystallization yield of the high-purity mesitylene crystals obtained in Examples 11-14 and Comparative Example 5; Figure 5 A graph showing the relationship between the concentration and crystallinity of different concentrations of crude mesitylene provided in Example 15; Figure 6 The graph shows the effect of the concentration difference of the crude mesitylene provided in Example 15 on the crystallization-assisted effect of the crystallization aid. Figure 7 To determine the purity and single-stage yield of the mesitylene product obtained at different stages in Comparative Example 6; Figure 8 XRD patterns of the mesitylene product obtained at each stage in Comparative Example 6; Figure 9 FTIR plots of the mesitylene product obtained at each stage in Comparative Example 6; Figure 10 A polarizing microscope image of the high-purity sitylene crystals obtained in Example 16; Figure 11 This is a comparison chart of the crystallization yields of mesitylene products obtained at different stages in three parallel experiments and a blank experiment in Example 16. Figure 12 This is a comparison chart of the crystallization purity of the mesitylene product obtained at different stages in three parallel experiments in Example 16. Figure 13 This is a comparison chart of the total crystallization yield of three parallel experiments and a blank experiment in Example 16; Figure 14 The XRD patterns of the xylene products at each stage obtained in the first parallel experiment of Example 16 are shown. Figure 15 The XRD patterns of the xylene products at each stage obtained from the second parallel experiment in Example 16 are shown. Figure 16 The XRD patterns of the xylene products at each stage obtained in the third parallel experiment of Example 16 are shown. Figure 17 The image shows the XRD pattern of the mesitylene product obtained by primary crystallization in three parallel experiments in Example 16. Figure 18 The image shows the XRD pattern of the mesitylene product obtained by secondary crystallization in three parallel experiments in Example 16. Figure 19 The image shows the XRD pattern of the mesitylene product obtained by sweating purification and crystallization in three parallel experiments in Example 16. Figure 20 The following are FTIR chromatograms of the tetramethylbenzene products at each stage obtained from the first parallel experiment in Example 16. Figure 21 The following are FTIR chromatograms of the tetramethylbenzene products at each stage obtained from the second parallel experiment in Example 16. Figure 22 The following are FTIR chromatograms of the tetramethylbenzene products at each stage obtained from the third parallel experiment in Example 16. Figure 23 The image shows the FTIR spectrum of the mesitylene product obtained by primary crystallization in three parallel experiments in Example 16. Figure 24 The image shows the FTIR spectrum of the mesitylene product obtained by secondary crystallization in three parallel experiments in Example 16. Figure 25 The image shows the FTIR spectrum of the mesitylene product obtained by sweating purification and crystallization in three parallel experiments in Example 16. Figure 26 The mesitylene product obtained in Example 16 1 H NMR spectrum. Detailed Implementation

[0021] This invention provides a method for purifying mesitylene through suspension melt crystallization, comprising the following steps: (1) Distill the mesitylene raw material to obtain a distillate, and then cool and separate the distillate under vacuum to obtain the mother liquor and crude mesitylene. (2) Melt the crude mesitylene obtained in step (1) to obtain a homogeneous melt, then add a crystallization aid to perform suspension melting crystallization, and finally perform vacuum separation. Repeat the above operations 1 to 3 times to obtain high-purity mesitylene crystals and mother liquor containing aids and impurities.

[0022] The present invention involves distilling mesitylene raw material to obtain a distillate, and then cooling and separating the distillate sequentially to obtain a mother liquor and crude mesitylene.

[0023] In this invention, the mesitylene feedstock is preferably a mesitylene product prepared by hydrodealkylation of reformed heavy aromatics or shape-selective alkylation of C6-C9 aromatics. In this invention, the mesitylene feedstock preferably comprises, by mass percentage, 20-30% mesitylene, 2-5% tetramethylbenzene, 7-8% trimethylbenzene, and the balance being impurities.

[0024] In this invention, the initial temperature of distillation is preferably 180°C; the final temperature of distillation is preferably ≤210°C, more preferably 200~210°C, and even more preferably 205°C; the distillation is preferably carried out within a distillation system. This invention does not have a specific limitation on the heating rate from the initial temperature to the final temperature, which can be determined based on the technical knowledge of those skilled in the art. This invention does not have a specific limitation on the distillation time, which can be determined based on the technical knowledge of those skilled in the art, until no distillate is produced. In this invention, since the boiling point of mesitylene is 196.8°C, controlling the initial and final temperatures of distillation within the range of 180~210°C can improve the recovery rate of mesitylene.

[0025] In this invention, the cooling temperature is preferably ≤0℃, more preferably -2℃. The cooling time is not specifically limited and can be determined based on the technical knowledge of those skilled in the art. By cooling at low temperatures, this invention promotes the precipitation and crystallization of mesitylene in the distillate, facilitating subsequent separation.

[0026] In this invention, the vacuum separation method is preferably vacuum filtration. This invention utilizes vacuum filtration for separation. A vacuum pump creates negative pressure within the filtration device, resulting in a pressure difference across the filter membrane. External atmospheric pressure then pushes the filtrate through the filter membrane, thereby accelerating the filtration process and enhancing separation selectivity through molecular-level interactions.

[0027] In this invention, the crude mesitylene is preferably stored in a sealed container for later use.

[0028] In this invention, the mother liquor is preferably returned to the distillation separation equipment system for recycling.

[0029] After obtaining crude mesitylene, the present invention melts the crude mesitylene to obtain a homogeneous melt, then adds a crystallization aid for suspension melting crystallization, and finally performs vacuum separation. The above operation is performed 1 to 3 times to obtain high-purity mesitylene crystals and mother liquor containing aids and impurities.

[0030] In this invention, the temperature of the homogeneous melt is preferably 55-60°C; the melting is preferably carried out in a jacketed crystallizer; the melting operation is preferably as follows: crude mesitylene is placed in the jacketed crystallizer, circulating water is introduced into the jacket, the circulating water is then heated, the temperature of the circulating water is controlled by a circulating water bath and displayed by a probe thermometer, the crystallizer is heated uniformly by a digital display mechanical stirrer to form a turbulent state, and finally heated until completely melted to form a homogeneous melt. In this invention, the heating rate of the circulating water is preferably 2-15°C / min. As one embodiment of this invention, the heating rate of the circulating water can be 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, 13°C / min or 14°C / min. By adopting the above method, this invention can form a homogeneous melt.

[0031] In this invention, the crystallization aid preferably includes zinc chloride (ZnCl2), zinc carbonate (ZnCO3), zinc oxide (ZnO), zinc acetate (Zn(OAc)2), copper chloride (CuCl2), aluminum trichloride (AlCl3), aluminum hydroxide (Al(OH)3), sodium hydroxide (NaOH), and sorbitan monooleate (C 24 H 44 O6), triphenyl phosphite (C 18 H 15 O3P) and tetraethylammonium hydroxide (C8H) 21Any one of NO), more preferably zinc chloride; the mass of the crystallization aid is preferably 0.1-1% of the crude mesitylene. As one embodiment of the present invention, the mass of the crystallization aid can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, or 0.95% of the crude mesitylene. The present invention, by adding a crystallization aid, can react with trace amounts of active impurities in the crude mesitylene to generate colored complexes or polymers. These byproducts do not enter the crude mesitylene and are discharged with the mother liquor, thereby improving the purity of the mesitylene crystals.

[0032] In this invention, the suspension melt crystallization is preferably carried out in a crystallization apparatus with circulation, and more preferably in a jacketed crystallizer. By carrying out suspension melt crystallization in the above-mentioned apparatus, this invention can maintain a small temperature difference between the crystallizer and the jacket, achieving a constant and controllable temperature.

[0033] In this invention, the suspension melt crystallization is preferably carried out under stirring conditions. The suspension melt crystallization operation involves controlling the temperature of the circulating water bath to cool down, while the crystallizer is uniformly heated by a digitally displayed mechanical stirrer. The cooling rate of the programmed cooling is preferably 0.1~0.5℃ / min, more preferably 0.2~0.4℃ / min, and even more preferably 0.3℃ / min. This invention does not impose any special limitation on the stirring rate, as long as it ensures uniform mixing of the components without splashing. This invention, through programmed cooling, allows mesitylene crystals to precipitate and grow.

[0034] In this invention, the vacuum separation method is preferably vacuum filtration.

[0035] In this invention, the repetition is preferably performed twice.

[0036] The present invention preferably further includes separating the mother liquor containing additives and impurities to obtain an impurity-free mother liquor, and then returning the impurity-free mother liquor to the distillation product for cooling and crystallization separation. The present invention does not have specific limitations on the specific separation operation, as long as the impurities in the mother liquor are removed. Through the above operations, the present invention can recycle and reuse the mother liquor, thereby reducing costs and wastewater discharge, meeting environmental protection requirements.

[0037] The present invention preferably further includes purifying the high-purity mesitylene crystals after obtaining them. The purification process preferably involves placing the high-purity mesitylene crystals into a jacketed crystallizer, circulating water through the jacket, and then heating the circulating water. The temperature of the circulating water is controlled by a circulating water bath and displayed by a probe thermometer. A digital display mechanical stirrer is used inside the crystallizer to ensure uniform heating of the crystals. The final heating temperature is set 1-9°C below the melting temperature for perspiration purification. After separation, high-purity mesitylene crystals are obtained. In this invention, the preferred heating rate of the circulating water is 2-15°C / min; the preferred temperature for perspiration purification is 69-79°C; and the preferred time for perspiration purification is 60-120 min. In one embodiment of the present invention, the heating rate of the circulating water can be 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, or 14℃ / min; the temperature for sweating purification can be 69℃, 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, or 79℃; and the time for sweating purification can be 65min, 70min, 75min, 80min, 85min, 90min, 95min, 100min, 105min, 110min, or 115min. In this invention, the separation is preferably performed by vacuum filtration. By employing the above-described purification method, the purity of mesitylene crystals can be further improved.

[0038] This invention overcomes the limitations of traditional crystallization separation by adding a crystallization aid to assist in the suspension melt crystallization of mesitylene. The addition of the crystallization aid can interact with impurities in the crude product, effectively changing the crystallization behavior of the impurities and inhibiting their entry into the mesitylene lattice during the crystal growth stage. This reduces the amount of impurities trapped during mesitylene crystallization, accelerates the crystallization process, and reduces the number of multi-level crystallization stages. Without changing the main molecular configuration of mesitylene, this invention achieves high selectivity and efficient separation and purification of mesitylene, significantly improving the purity and yield of mesitylene. It solves the problem of isomer separation and overcomes the technical bottleneck of low efficiency in the purification and separation process of mesitylene in the prior art.

[0039] Meanwhile, the method provided by this invention has simple equipment requirements. It only requires adding a trace amount of additives and separation steps to the existing suspension melt crystallization process. Without the need for complex equipment modifications, it can significantly improve product purity and yield. The process steps are simple, the amount of additives is small, and the effect is significant. It is suitable for continuous or intermittent suspension melt crystallization processes and provides an innovative and effective way for the purification of mesitylene.

[0040] The method provided by this invention enables mesitylene to crystallize more purely from the melt, resulting in a high-quality mesitylene product with a purity of over 99% and excellent purification effect.

[0041] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0042] Example 1 A method for purifying mesitylene through suspension melt crystallization comprises the following steps: (1) The raw material (containing 26 wt% of mesitylene, 3 wt% of tetramethylbenzene, 7 wt% of trimethylbenzene and the balance of impurities, denoted as raw material) is placed in a distillation system for distillation. The initial temperature of distillation is 180°C and the final temperature of distillation is 200°C, resulting in a distillate with a distillation temperature in the range of 180~200°C. The distillate is then cooled at -2°C. After no crystals are precipitated, it is vacuum filtered to obtain the mother liquor and crude mesitylene (denoted as crude product). The purity of the crude mesitylene is 68 wt%. The crude mesitylene is stored in a sealed container for later use. The raw material is a mesitylene product obtained by the hydrodealkylation reaction of reformed heavy aromatics. By mass percentage, the raw material contains 26% mesitylene, 4% tetramethylbenzene, 8% trimethylbenzene and the balance of impurities. (2) Place the 35g crude mesitylene obtained in step (1) into a jacketed crystallizer. Circulating water is introduced into the jacket. The circulating water is then heated at a rate of 5℃ / min. The temperature of the circulating water is controlled by a circulating water bath and displayed by a probe thermometer. The crystallizer is heated evenly by a digital display mechanical stirrer to form a turbulent state. Finally, it is heated to a homogeneous melt at a temperature of 60℃ after complete melting. A crystallization aid is added to the homogeneous melt and the mixture is cooled at a rate of 0.2℃ / min under stirring conditions to carry out suspension melting crystallization. Finally, vacuum filtration is performed to obtain high-purity mesitylene crystals and a mother liquor containing aids and impurities. The crystallization aid is zinc chloride (ZnCl2). The mass of the crystallization aid is 0.5% of the crude mesitylene mass.

[0043] The purity of the crude mesitylene and the raw mesitylene in Example 1 was tested. The test method was as follows: the purity of mesitylene was determined using a GC-2014C gas chromatograph (Shimadzu). The test conditions were as follows: detector: FID; column type: SE-54 (30m×0.32mm×0.25μm); carrier gas and flow rate: N2, 1.0ml / min; temperature program set to 70℃ (hold for 2.5min); heating rate: 8℃ / min; final temperature: 280℃ (hold for 5min); injection port temperature... 240℃, detector temperature: 290℃, split ratio: 20:1; 0.1 g of crude mesitylene and raw mesitylene prepared in Example 1 were rapidly weighed into 10 mL volumetric flasks. The flasks were then diluted to volume with the prepared internal standard solution (0.5 g of benzene was added to a 50 mL volumetric flask, diluted to volume with dichloromethane, and shaken well). 0.2 μL of the solution was then drawn sequentially using a sampling needle and injected into the gas chromatograph. The peak areas of mesitylene and benzene were integrated to obtain the peak area ratio. A graph was plotted between the peak area ratio of mesitylene and benzene and the concentration of the standard solution. The chromatographic data comparison results are shown below. Figure 1 As shown. By Figure 1 It can be seen that after distillation, the content of mesitylene in the crude mesitylene product is significantly increased, while the height and peak area of ​​the impurity peaks are significantly reduced.

[0044] Example 2 The crystallization aid is aluminum hydroxide (Al(OH)3), and other conditions are the same as in Example 1.

[0045] Example 3 The crystallization aid is triphenyl phosphite (TPP), and other conditions are the same as in Example 1.

[0046] Example 4 The crystallization aid is tetraethylammonium hydroxide (TEAH), and other conditions are the same as in Example 1.

[0047] Comparative Example 1 A method for purifying mesitylene through suspension melt crystallization comprises the following steps: (1) The raw material (containing 26 wt% of mesitylene, 3 wt% of tetramethylbenzene, 7 wt% of trimethylbenzene and the balance of impurities, denoted as raw material) is placed in a distillation system for distillation. The initial temperature of distillation is 180°C and the final temperature of distillation is 200°C, resulting in a distillate with a distillation temperature in the range of 180~200°C. The distillate is then cooled at -2°C. After no crystals are precipitated, it is vacuum filtered to obtain the mother liquor and crude mesitylene (denoted as crude product). The purity of the crude mesitylene is 68 wt%. The crude mesitylene is stored in a sealed container for later use. The raw material is a mesitylene product obtained by the hydrodealkylation reaction of reformed heavy aromatics. By mass percentage, the raw material contains 26% mesitylene, 4% tetramethylbenzene, 8% trimethylbenzene and the balance of impurities. (2) Place the 35g crude mesitylene obtained in step (1) into a jacketed crystallizer. Circulating water is introduced into the jacket. Then, the circulating water is heated at a rate of 5℃ / min. The temperature of the circulating water is controlled by a circulating water bath and displayed by a probe thermometer. The crystallizer is heated evenly by a digital display mechanical stirrer to form a turbulent state. Finally, it is heated to complete melting to form a homogeneous melt at a temperature of 60℃. Under stirring conditions, the temperature is reduced at a rate of 0.2℃ / min for suspension melting and crystallization. Finally, vacuum filtration is performed to obtain high-purity mesitylene crystals and mother liquor containing additives and impurities (blank group).

[0048] Comparative Example 2 The crystallization aid is cellulose acetate (CA), and other conditions are the same as in Example 1.

[0049] Comparative Example 3 The crystallization aid is L-lysine (Lys), and other conditions are the same as in Example 1.

[0050] The purity of the high-purity mesitylene crystals in Examples 1-4 and Comparative Examples 1-3 was tested using the same methods as described above. The product purity and crystallization yield of the obtained high-purity mesitylene crystals are as follows: Figure 2 As shown in Table 1.

[0051] Table 1. Purity and crystallization yield of high-purity mesitylene crystals in Examples 1-4 and Comparative Examples 1-3.

[0052] Example 5 The mass of the crystallization aid is 0.3% (1-ZnCl2) of the crude mesitylene, and other conditions are the same as in Example 1.

[0053] Example 6 The mass of the crystallization aid was 0.6% (2-ZnCl2) of the crude mesitylene, and other conditions were the same as in Example 1.

[0054] Example 7 The crystallization aid is copper chloride (CuCl2), and other conditions are the same as in Example 1.

[0055] Example 8 The crystallization aid is aluminum trichloride (AlCl3), and other conditions are the same as in Example 1.

[0056] Example 9 The crystallization aid is sodium hydroxide (NaOH), and other conditions are the same as in Example 1.

[0057] Example 10 The crystallization aid was sorbitan monooleate (Span 80), and other conditions were the same as in Example 1.

[0058] Comparative Example 4 The crystallization aid is calcium chloride (CaCl2), and other conditions are the same as in Example 1.

[0059] The purity of the high-purity mesitylene crystals in Examples 5-10 and Comparative Example 4 was tested using the same methods as described above. The product purity and crystallization yield of the obtained high-purity mesitylene crystals are as follows: Figure 3 As shown in Table 2.

[0060] Table 2 shows the purity and crystallization yield of high-purity mesitylene crystals in Examples 5-10 and Comparative Example 4.

[0061] Example 11 A method for purifying mesitylene through suspension melt crystallization comprises the following steps: (1) The raw material (containing 30 wt% of mesitylene, 2 wt% of tetramethylbenzene, 7 wt% of trimethylbenzene and the balance of impurities, denoted as raw material) is placed in a distillation system for distillation. The initial temperature of distillation is 180°C and the final temperature of distillation is 200°C, resulting in a distillate with a distillation temperature in the range of 180~200°C. The distillate is then cooled at -2°C. After no crystals are precipitated, it is vacuum filtered to obtain the mother liquor and crude mesitylene (denoted as crude product). The purity of the crude mesitylene is 74 wt%. The crude mesitylene is stored in a sealed container for later use. The raw material is a mesitylene product obtained by the hydrodealkylation reaction of reformed heavy aromatics. By mass percentage, the raw material contains 26% mesitylene, 4% tetramethylbenzene, 8% trimethylbenzene and the balance of impurities. (2) Place the 35g crude mesitylene obtained in step (1) into a jacketed crystallizer. Circulating water is introduced into the jacket. The circulating water is then heated at a rate of 5℃ / min. The temperature of the circulating water is controlled by a circulating water bath and displayed by a probe thermometer. The crystallizer is heated evenly by a digital display mechanical stirrer to form a turbulent state. Finally, it is heated to a homogeneous melt at a temperature of 60℃ after complete melting. A crystallization aid is added to the homogeneous melt and the temperature is lowered at a rate of 0.2℃ / min under stirring to carry out suspension melting crystallization. Finally, vacuum filtration is performed to obtain high-purity mesitylene crystals and a mother liquor containing aids and impurities. The crystallization aid is zinc carbonate (ZnCO3). The mass of the crystallization aid is 0.5% of the crude mesitylene mass.

[0062] Example 12 The crystallization aid is zinc oxide (ZnO), and other conditions are the same as in Example 11.

[0063] Example 13 The crystallization aid is zinc acetate (Zn(OAc)2), and other conditions are the same as in Example 11.

[0064] Example 14 The crystallization aid is zinc chloride (ZnCl2), and other conditions are the same as in Example 11.

[0065] Comparative Example 5 A method for purifying mesitylene through suspension melt crystallization comprises the following steps: (1) The raw material (containing 30 wt% of mesitylene, 2 wt% of tetramethylbenzene, 7 wt% of trimethylbenzene and the balance of impurities, denoted as raw material) is placed in a distillation system for distillation. The initial temperature of distillation is 180°C and the final temperature of distillation is 200°C, resulting in a distillate with a distillation temperature in the range of 180~200°C. The distillate is then cooled at -2°C. After no crystals are precipitated, it is vacuum filtered to obtain the mother liquor and crude mesitylene (denoted as crude product). The purity of the crude mesitylene is 74 wt%. The crude mesitylene is stored in a sealed container for later use. The raw material is a mesitylene product obtained by the hydrodealkylation reaction of reformed heavy aromatics. By mass percentage, the raw material contains 26% mesitylene, 4% tetramethylbenzene, 8% trimethylbenzene and the balance of impurities. (2) Place the 35g crude mesitylene obtained in step (1) into a jacketed crystallizer. Circulating water is introduced into the jacket. Then, the circulating water is heated at a rate of 5℃ / min. The temperature of the circulating water is controlled by a circulating water bath and displayed by a probe thermometer. The crystallizer is heated evenly by a digital display mechanical stirrer to form a turbulent state. Finally, it is heated to complete melting to form a homogeneous melt at a temperature of 60℃. Under stirring conditions, the temperature is reduced at a rate of 0.2℃ / min for suspension melting and crystallization. Finally, vacuum filtration is performed to obtain high-purity mesitylene crystals and mother liquor containing additives and impurities (blank group).

[0066] The purity of the high-purity mesitylene crystals in Examples 11-14 and Comparative Example 5 was tested using the same methods as described above. The product purity and crystallization yield of the obtained high-purity mesitylene crystals are as follows: Figure 4 As shown in Table 3.

[0067] Table 3 shows the purity and crystallization yield of high-purity mesitylene crystals in Examples 11-14 and Comparative Example 5.

[0068] Depend on Figures 2-4 As can be seen from Tables 1-3, the purification effect of mesitylene varies significantly when different types of crystallization aids are used in this invention. When the crystallization aids are cellulose acetate and L-lysine, the purity and crystallization yield of the high-purity mesitylene crystals are even lower than those of the blank group. When the crystallization aid is zinc chloride, the product purity and crystallization yield are the highest, indicating that zinc chloride has a better crystallization-aiding effect than other crystallization aids.

[0069] Example 15 A method for purifying mesitylene through suspension melt crystallization comprises the following steps: (1) The raw material (containing 26 wt% of mesitylene, 3 wt% of tetramethylbenzene, 7 wt% of trimethylbenzene and the balance of impurities, denoted as raw material) is placed in a distillation system for distillation. The initial temperature of distillation is 180°C and the final temperature of distillation is 200°C, resulting in a distillate with a distillation temperature in the range of 180~200°C. The distillate is then cooled at -2°C. After no crystals are precipitated, it is vacuum filtered to obtain the mother liquor and crude mesitylene (denoted as crude product). The purity of the crude mesitylene is 68 wt%. The crude mesitylene is stored in a sealed container for later use. The raw material is a mesitylene product obtained by the hydrodealkylation reaction of reformed heavy aromatics. By mass percentage, the raw material contains 26% mesitylene, 4% tetramethylbenzene, 8% trimethylbenzene and the balance of impurities. (2) Add the crude mesitylene obtained in step (1) to different doses of pure mesitylene or mesitylene raw material, then heat and cool to obtain different concentrations ( Figure 6 crude xylene; (3) The crude mesitylene products (35g) of different concentrations obtained in step (2) are placed into jacketed crystallizers. Circulating water is introduced into the jacket. The circulating water is then heated at a rate of 5℃ / min. The temperature of the circulating water is controlled by a circulating water bath and displayed by a probe thermometer. The crystallizer is heated evenly by a digital display mechanical stirrer to form a turbulent state. Finally, it is heated to complete melting to form a homogeneous melt at a temperature of 60℃. A crystallization aid is added to the homogeneous melt and the temperature is lowered at a rate of 0.2℃ / min under stirring to carry out suspension melting crystallization. Finally, vacuum filtration is performed to obtain high-purity mesitylene crystals and mother liquor containing aids and impurities. The crystallization aid is zinc chloride (ZnCl2). The mass of the crystallization aid is 0.5% of the mass of crude mesitylene.

[0070] The relationship between the concentration and crystallinity of different concentrations of crude mesitylene provided in Example 15 is as follows: Figure 5 As shown; the effect of the concentration difference of the crude mesitylene provided in Example 15 on the crystallization-assisted effect of the crystallization aid is as follows. Figure 6 As shown.

[0071] Depend on Figure 5 and Figure 6 It can be seen that the purity of crude mesitylene has a certain impact on the effect of crystallization aid. The results show a stepwise trend: product purity and yield increase with the increase of raw material concentration. In terms of processing requirements, the lowest raw material purity condition that meets both purity and yield requirements is 72%. Moreover, the data shows that crystallization rate and product purity have a linear relationship.

[0072] Comparative Example 6 (Blank Experiment) A method for purifying mesitylene comprises the following steps: (1) The raw material (containing 26 wt% of mesitylene, 3 wt% of tetramethylbenzene, 7 wt% of trimethylbenzene and the balance of impurities, denoted as raw material) is placed in a distillation system for distillation. The initial temperature of distillation is 180°C and the final temperature of distillation is 200°C, resulting in a distillate with a distillation temperature in the range of 180~200°C. The distillate is then cooled at -2°C. After no crystals are precipitated, it is vacuum filtered to obtain the mother liquor and crude mesitylene (denoted as crude product). The purity of the crude mesitylene is 68 wt%. The crude mesitylene is stored in a sealed container for later use. The raw material is a mesitylene product obtained by the hydrodealkylation reaction of reformed heavy aromatics. By mass percentage, the raw material contains 26% mesitylene, 4% tetramethylbenzene, 8% trimethylbenzene and the balance of impurities. (2) Place 100g of crude mesitylene obtained in step (1) into a jacketed crystallizer. Circulating water is introduced into the jacket. Then, the circulating water is heated at a rate of 5℃ / min. The temperature of the circulating water is controlled by a circulating water bath and displayed by a probe thermometer. The crystallizer is heated evenly by a digital display mechanical stirrer to form a turbulent state. Finally, it is heated to complete melting to form a homogeneous melt at a temperature of 60℃. Under stirring conditions, the temperature is reduced at a rate of 0.2℃ / min for suspension melting crystallization. Finally, vacuum filtration is performed. The above operation is performed three times (first stage, second stage and third stage in sequence) to obtain mesitylene crystals and mother liquor. (3) The mesitylene product obtained in step (2) is placed in a jacketed crystallizer. Circulating water is introduced into the jacket. The circulating water is then heated at a rate of 5°C / min. The temperature of the circulating water is controlled by a circulating water bath and displayed by a probe thermometer. The crystals are heated evenly in the crystallizer by a digital display mechanical stirrer. The temperature in the crystallizer is controlled at 74°C for sweating purification for 90 minutes. After vacuum filtration, a high-purity mesitylene product is obtained.

[0073] The purity and single-stage yield of the mesitylene product obtained at different stages by the method provided in Comparative Example 6 are as follows: Figure 7 As shown in Table 4, Figure 7 PC is crude mesitylene obtained by primary suspension melt crystallization, SC is crude mesitylene obtained by secondary suspension melt crystallization, TC is crude mesitylene obtained by tertiary suspension melt crystallization, and Sweating is the final mesitylene crystal (i.e., the product purified by sweating).

[0074] Table 4 shows the purity and single-stage yield of the mesitylene product obtained at different stages using the method provided in Comparative Example 6.

[0075] Depend on Figure 7 As can be seen from the comparison with Table 4, during the multi-stage crystallization purification process, the purity of mesitylene in the mesitylene product increases as the purification process progresses, and the single-stage yield also increases.

[0076] X-ray diffraction (XRD) was used to characterize the mesitylene products obtained at each stage in Comparative Example 6. During this process, the samples needed to be kept dry, and slow scanning at a small angle at room temperature was selected to determine the effect of the crystallization aid on the crystal structure. The results are as follows: Figure 8 As shown. Figure 8 The image shows the XRD patterns of the mesitylene product obtained at each stage in Comparative Example 6. Figure 8 As can be seen, all diffraction peaks in the XRD pattern are accurately identified without any impurities, the diffraction peaks are very sharp, and the baseline is flat, indicating that the product has high crystallinity, good crystal quality, uniform size, and a stable crystallization process.

[0077] The characteristic functional groups of the mesitylene products obtained at each stage of Comparative Example 6 were characterized using Fourier transform infrared spectroscopy (FTIR) at wavelengths ranging from 4000 to 400 cm⁻¹. -1 The sample and potassium bromide binder were kept dry. After thoroughly mixing and grinding the potassium bromide with the sample, the mixture was compressed into tablets. The compressed mixture was then placed in the sample chamber for measurement, and the results were as follows. Figure 9 . Figure 9 The image shows the FTIR spectra of the mesitylene product obtained at each stage in Comparative Example 6. Figure 9 As can be seen from the data, the main absorption peak positions of all samples are highly consistent, proving that the target product throughout the entire crystallization and purification process is always mesitylene, without any change in chemical structure. The purification effect is very obvious, and the characteristic fingerprint peak of mesitylene (~688 cm⁻¹) is clearly visible. -1 Significantly enhanced and sharpened.

[0078] Example 16 A method for purifying mesitylene through suspension melt crystallization comprises the following steps: (1) The raw material (containing 26 wt% of mesitylene, 3 wt% of tetramethylbenzene, 7 wt% of trimethylbenzene and the balance of impurities, denoted as raw material) is placed in a distillation system for distillation. The initial temperature of distillation is 180°C and the final temperature of distillation is 200°C, resulting in a distillate with a distillation temperature in the range of 180~200°C. The distillate is then cooled at -2°C. After no crystals are precipitated, it is vacuum filtered to obtain the mother liquor and crude mesitylene (denoted as crude product). The purity of the crude mesitylene is 68 wt%. The crude mesitylene is stored in a sealed container for later use. The raw material is a mesitylene product obtained by the hydrodealkylation reaction of reformed heavy aromatics. By mass percentage, the raw material contains 26% mesitylene, 4% tetramethylbenzene, 8% trimethylbenzene and the balance of impurities. (2) Place 100g of crude mesitylene obtained in step (1) into a jacketed crystallizer. Circulating water is introduced into the jacket. The circulating water is then heated at a rate of 5℃ / min. The temperature of the circulating water is controlled by a circulating water bath and displayed by a probe thermometer. The crystallizer is heated evenly by a digital display mechanical stirrer to form a turbulent state. Finally, it is heated to a homogeneous melt at 60℃ after complete melting. A crystallization aid is added to the homogeneous melt and the temperature is lowered at a rate of 0.2℃ / min under stirring conditions to carry out suspension melting crystallization. Finally, vacuum filtration is performed. The above operation is performed twice (first stage and second stage, respectively) to obtain mesitylene crystals and mother liquor containing aids and impurities. The crystallization aid is zinc chloride (ZnCl2). The mass of the crystallization aid is 0.5% of the crude mesitylene mass. (3) Place the mesitylene crystals obtained in step (2) into a jacketed crystallizer, and circulate water into the jacket. Then, heat the circulating water at a rate of 5°C / min. Control the temperature of the circulating water through a circulating water bath and display the temperature with a probe thermometer. The mesitylene crystals are heated evenly in the crystallizer by a digital display mechanical stirrer. Control the temperature in the crystallizer to 74°C for sweating purification. The sweating purification time is 90 min. After vacuum filtration, high-purity mesitylene crystals are obtained.

[0079] A polarizing microscope (POM) image of the high-purity mesitylene crystals obtained in Example 16 of this invention is shown below. Figure 10 As shown. By Figure 10 It can be seen that the foliated shape of the mesitylene crystals indicates that they are monoclinic crystals.

[0080] The scheme of Example 16 was repeated three times in parallel. The crystallization yield of the three parallel experiments and the blank experiment (Comparative Example 6) at different stages is compared in the following figure. Figure 11 As shown in Table 5, Figure 11In the diagram, R1 represents the total crystallization yield of the first parallel experiment, R2 represents the total crystallization yield of the second parallel experiment, R3 represents the total crystallization yield of the third parallel experiment, and Blank represents the total crystallization yield of the blank experiment; the comparison of the crystallization purity of the mesitylene product obtained at different stages of the three parallel experiments is as follows: Figure 12 As shown in Table 6, Figure 12 PC represents crude mesitylene obtained from primary suspension melt crystallization, SC represents crude mesitylene obtained from secondary suspension melt crystallization, and Sweating represents the final mesitylene crystals (i.e., the product purified by sweating). The comparison of the total crystallization yield from three parallel experiments and a blank experiment is as follows: Figure 13 As shown in Table 7, Figure 13 In the diagram, R1 represents the total crystallization yield of the first parallel experiment, R2 represents the total crystallization yield of the second parallel experiment, R3 represents the total crystallization yield of the third parallel experiment, and Blank represents the total crystallization yield of the blank experiment.

[0081] Table 5. Crystallization yields of mesitylene products obtained at different stages from three parallel experiments and a blank experiment in Example 16.

[0082] Table 6. Crystallization purity of mesitylene products obtained at different stages in three parallel experiments of Example 16.

[0083] Table 7. Overall crystallization yield of three parallel experiments and a blank experiment in Example 16

[0084] Depend on Figures 11-13 As can be seen from Tables 5-7, by adding a small amount of zinc chloride crystallization aid, this invention can not only reduce the number of suspension melt crystallization operations and improve efficiency, but also significantly improve the total crystallization yield. This indicates that the addition of the crystallization aid can accelerate the purification process of mesitylene, significantly improve the total crystallization yield, and reduce certain cost inputs.

[0085] The mesitylene products obtained at each stage in Example 16 were characterized using X-ray diffraction (XRD). During this process, the samples needed to be kept dry, and slow scanning at a small angle at room temperature was selected to determine the effect of the crystallization aid on the crystal structure. The results are as follows: Figures 14-19 As shown. Figure 14 The XRD patterns of the xylene products at each stage obtained in the first parallel experiment of Example 16 are shown. Figure 15 The XRD patterns of the xylene products at each stage obtained from the second parallel experiment in Example 16 are shown. Figure 16 The XRD patterns of the xylene products at each stage obtained in the third parallel experiment of Example 16 are shown. Figure 17The image shows the XRD pattern of the mesitylene product obtained by primary crystallization in three parallel experiments in Example 16. Figure 18 The image shows the XRD pattern of the mesitylene product obtained by secondary crystallization in three parallel experiments in Example 16. Figure 19 The image shows the XRD pattern of the mesitylene product obtained from three parallel experiments of sweating purification and crystallization in Example 16. Figures 14-19 As can be seen, all diffraction peaks in the XRD pattern are accurately identified without any impurities, the diffraction peaks are very sharp, and the baseline is flat—the product has high crystallinity, good crystal quality, uniform size, and a stable crystallization process, indicating that the method provided by this invention effectively purifies mesitylene.

[0086] The mesitylene products obtained at each stage in Example 16 were characterized using Fourier transform infrared spectroscopy (FTIR) at wavelengths of 4000–400 cm⁻¹. -1 The sample and potassium bromide binder were kept dry. After thoroughly mixing and grinding the potassium bromide with the sample, the mixture was compressed into tablets. The compressed mixture was then placed in the sample chamber for measurement, and the results were as follows. Figures 20-25 As shown. Figure 20 The following are FTIR chromatograms of the tetramethylbenzene products at each stage obtained from the first parallel experiment in Example 16. Figure 21 The following are FTIR chromatograms of the tetramethylbenzene products at each stage obtained from the second parallel experiment in Example 16. Figure 22 The following are FTIR chromatograms of the tetramethylbenzene products at each stage obtained from the third parallel experiment in Example 16. Figure 23 The image shows the FTIR spectrum of the mesitylene product obtained by primary crystallization in three parallel experiments in Example 16. Figure 24 The image shows the FTIR spectrum of the mesitylene product obtained by secondary crystallization in three parallel experiments in Example 16. Figure 25 The image shows the FTIR spectrum of the mesitylene product obtained from three parallel experiments of sweating purification and crystallization in Example 16. Figures 20-25 As can be seen from the data, the main absorption peak positions of all samples are highly consistent, proving that the target product throughout the entire crystallization and purification process is always mesitylene, without any change in chemical structure. The purification effect is very obvious, and the characteristic fingerprint peak of mesitylene (~688 cm⁻¹) is clearly visible. -1 The significant enhancement and sharpening demonstrate that the method provided by this invention is highly effective and successful in removing specific impurities from mesitylene.

[0087] Using a liquid nuclear magnetic resonance spectrometer ( 1 The mesitylene product obtained in Example 16 was characterized by 1H NMR to determine the changes before and after purification. Tritium-modified chloroform was used as the solvent. One-dimensional 1H NMR spectra were measured at 400 M / 500 M and room temperature. The results are as follows: Figure 26 As shown.

[0088] Depend on Figure 26 As can be seen, high-purity mesitylene exhibits only two singlets in the 1H NMR spectrum. This is due to the extremely high symmetry of the mesitylene molecule (symmetry about the two diagonals), making the two hydrogen atoms on the benzene ring completely equivalent and located in the same chemical environment. The 12 hydrogen atoms on the four methyl groups (-CH3) are also completely equivalent, located in a different chemical environment. The characteristic chemical shift of the hydrogen atoms on the aromatic ring is ~6.9 ppm (singlet, s). Because the ortho and para positions on the benzene ring of mesitylene are replaced by methyl groups, the electron-donating effect of the methyl groups increases their electron cloud density, thus their chemical shift shifts slightly towards a higher field compared to the hydrogens on the benzene ring (~7.3 ppm). The typical chemical shift of the methyl group directly attached to the aromatic ring (aryl methyl group) is ~2.3 ppm (singlet, s). The integral curve shows that the ratio of the area of ​​the low-field aromatic hydrogen signal to the area of ​​the high-field methyl hydrogen signal is approximately 2:12, or 1:6. This quantitatively confirms the ratio of the number of the two types of hydrogen atoms.

[0089] At the same time Figure 26 It can be seen that, compared with high-purity samples 1 The comparison of H NMR data showed that the test data of mesitylene before purification had a significant chemical shift and another small impurity peak, indicating that it contained a lot of impurities. The test data after purification had a flat spectrum baseline and no visible impurity peaks except for the characteristic peak of mesitylene. The ratio of the area of ​​the low-field aromatic hydrogen signal to the area of ​​the high-field methyl hydrogen signal was about 2:12, indicating that the sample purity was very high.

[0090] In summary, the suspension melt crystallization purification method for mesitylene provided by this invention can effectively improve the crystallization purity and yield of mesitylene, and the process is stable and feasible, providing an innovative technical solution for the industrial production of high-purity mesitylene.

[0091] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle 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 purifying mesitylene through suspension melt crystallization, comprising the following steps: (1) Distill the mesitylene raw material to obtain a distillate, and then cool and separate the distillate under vacuum to obtain the mother liquor and crude mesitylene. (2) Melt the crude mesitylene obtained in step (1) to obtain a homogeneous melt, then add a crystallization aid to perform suspension melting crystallization, and finally perform vacuum separation. Repeat the above operations 1 to 3 times to obtain high-purity mesitylene crystals and mother liquor containing aids and impurities.

2. The method according to claim 1, characterized in that, The mesitylene raw material in step (1) comprises 20-30% mesitylene, 2-5% tetramethylbenzene, 7-8% trimethylbenzene, and the balance being impurities, by mass percentage.

3. The method according to claim 1, characterized in that, The initial temperature of distillation in step (1) is 180℃, and the final temperature of distillation is ≤210℃.

4. The method according to claim 1, characterized in that, The cooling temperature in step (1) is ≤0℃.

5. The method according to claim 1, characterized in that, The melting operation in step (2) is as follows: crude mesitylene is placed in a jacketed crystallizer, circulating water is introduced into the jacket, the circulating water is then heated, the temperature of the circulating water is controlled by a circulating water bath, and the temperature is displayed by a probe thermometer. The crystallizer is heated evenly by a digital display mechanical stirrer to form a turbulent state, and finally heated to complete melting to form a homogeneous melt.

6. The method according to claim 1, characterized in that, The crystallization aid in step (2) includes any one of zinc chloride, zinc carbonate, zinc oxide, zinc acetate, copper chloride, aluminum trichloride, aluminum hydroxide, sodium hydroxide, sorbitan monooleate, triphenyl phosphite, and tetraethylammonium hydroxide.

7. The method according to claim 1, characterized in that, In step (2), the mass of the crystallization aid is 0.1-1% of the crude mesitylene.

8. The method according to claim 1, characterized in that, The suspension melting crystallization operation in step (2) is as follows: the circulating water bath is programmed to cool down, and the crystallizer is heated evenly by digital display mechanical stirring; the cooling rate of the programmed cooling is 0.1~0.5℃ / min.

9. The method according to claim 1, characterized in that, Step (2) also includes purifying high-purity mesitylene crystals; the purification operation is to put high-purity mesitylene crystals into a jacketed crystallizer, circulate water into the jacket, then heat the circulating water, control the temperature of the circulating water through a circulating water bath, and display the temperature with a probe thermometer. The crystals are heated evenly by a digital display mechanical stirrer in the crystallizer, and the heating endpoint temperature is set to be 1~9℃ lower than the melting temperature. The crystals are purified by sweating and separated to obtain high-purity mesitylene crystals.

10. The method according to claim 9, characterized in that, The temperature for the sweating purification process is 69~79℃, and the time for the sweating purification process is 60~120min.

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