An adsorbent for separating trimethylbenzene monomers from heavy aromatics and a method for preparing the same

Abstract

The application mixes NaX type molecular sieve with kaolin mineral as a binder, then rolls into a ball, calcines at high temperature, converts kaolin into metakaolin, then treats with alkali, converts into X type molecular sieve in situ, then ion exchanges to prepare high selective adsorbent. The prepared adsorbent has high trimethylbenzene adsorption selectivity, compression strength and bulk density.

Description

Technical Field

[0001] This invention generally relates to highly selective adsorbents, their manufacturing methods, and methods for applying them in adsorption separation. More specifically, it relates to an adsorbent for simultaneously separating high-purity mesitylene, pseudotrimethyllene, and terephthalene, and its preparation method. Background Technology

[0002] C9+ heavy aromatics are important byproducts of petrochemical and coal coking plants, and the chemical industry has increasingly emphasized their comprehensive utilization in recent years. With the commissioning of several integrated projects in China, the reforming unit capacity will reach 190 million tons in 2022, and the reformed heavy aromatics capacity is expected to reach more than 30 million tons. Currently, there are three ways to utilize heavy aromatics: first, as a component in oil blending; second, to increase the production of light aromatics such as BTX (benzene-toluene-xylene mixture); and third, to produce high-boiling-point solvent oils. The last utilization method has a high degree of resource waste and low added value.

[0003] On the one hand, heavy aromatics resources are increasing while raw material prices are decreasing. Over the past decade, heavy aromatics prices have generally trended downwards, reaching 3,200 yuan per ton in 2021. On the other hand, most manufacturers' heavy aromatics utilization units currently involve reactions such as extraction, cryogenic crystallization, and alkylation, coupled with multiple distillation columns. Their products are relatively simple, with relatively low purity and yield, complex processes, high investment costs, high operating energy consumption, low overall extraction efficiency, and low product added value. Therefore, the market urgently needs technological innovation to improve the utilization rate of heavy aromatics resources, maximize the economic added value of heavy aromatics products, and extend the industrial chain.

[0004] The three types of trimethylbenzene constitute the largest proportion of reformed heavy aromatics, accounting for almost half of all heavy aromatics. They are important fine chemical intermediates with high utilization value. Pseudotrimethylbenzene is currently obtained through multi-tower distillation or extractive distillation, but this requires specific raw material composition, particularly stringent requirements regarding the content of tert-butylbenzene. China is the largest producer and consumer of pseudotrimethylbenzene, and demand is increasing year by year. Pseudotrimethylbenzene can be used to produce meta-anhydride, which can be further used to produce environmentally friendly plasticizers. It can also be used to produce trimethylhydroquinone, an intermediate in the production of vitamin E, or methylated to produce mesitylene, which can be further used to produce polyimide, one of the most promising plastics of the 21st century, and widely used in aerospace, supersonic aircraft, nuclear energy, and electromechanical industries. Mesitylene is currently obtained through extractive distillation, alkylation, or isomerization, but each method has its drawbacks. For example, extractive distillation has high energy consumption, alkylation consumes a large amount of propylene and has high costs, and isomerization is easily affected by other C9 components, with a product yield of only about 15%. Methoxymethylbenzene can be used to produce expensive antioxidants, dyes, and environmentally friendly herbicides. my country, as a major agricultural country, has an increasing demand for environmentally friendly herbicides. Currently, methoxymethylbenzene is typically sold as a high-boiling-point solvent oil. The monomer can also be obtained through alkylation, extraction distillation, and precision distillation-cryogenic crystallization. However, due to the extreme difficulty in separating it from indene components, the entire separation process is energy-intensive, and the purity is only 50%–80% by mass, resulting in poor economic efficiency. Methoxymethylbenzene can be used to produce Tibetan musk, used as a daily fragrance in cosmetics and daily chemical products, or to produce aniline dyes, alkyd resins, polyester resins, and triphenyltriic acid. It can also react with benzoyl chloride and phenylacetyl chloride to produce analgesics, platelet anticoagulants, and thromboseptic inhibitors. However, due to the huge investment required for its separation and purification, domestic industrial production is currently limited.

[0005] Adsorption separation technology is characterized by selective adsorption of specific components. Its process flow is relatively simple, with fewer by-products and the product is less susceptible to interference from other components. Compared with multiple distillation columns connected in series, it has lower energy consumption.

[0006] US3558730 discloses a BaKX molecular sieve with significantly higher selectivity for p-xylene (PX) than BaX and KX. US3997620 found that, compared to BaKX, the X molecular sieve, after Sr... 2+ and Ba 2+ After the exchange, although the p-xylene / m-xylene (PX / MX) and p-xylene / o-xylene (PX / OX) ratios decreased, the p-xylene / ethylbenzene (PX / EB) and p-xylene / p-diethylbenzene (PX / PDEB) ratios significantly increased. CN1565718A uses small-crystal X molecular sieves with a particle size of 0.1–0.4 micrometers as the active component of the adsorbent to improve the mass transfer performance and adsorption capacity of the adsorbent.

[0007] The three trimethylbenzene isomers in reformed heavy aromatics share certain commonalities in their configuration and electrostatic potential. Therefore, a combination of adsorption separation and distillation processes can be used to simultaneously separate the three trimethylbenzene isomers from the heavy aromatics, followed by distillation to obtain high-yield and high-purity monomer products. Currently, adsorbents with X-type molecular sieves as the active component are mostly used for the adsorption and separation of para-aromatics. However, adsorbents that simultaneously exhibit selectivity for all three trimethylbenzene isomers, along with high bulk density and high compressive strength, have not yet been reported. Summary of the Invention

[0008] This invention provides a highly selective adsorbent and its preparation method, which has high bulk density and high compressive strength, and preferential selectivity for three types of trimethylbenzene, making it suitable for adsorbing and separating high-purity trimethylbenzene monomers from heavy aromatic hydrocarbons.

[0009] This invention provides a highly selective adsorbent, characterized in that the adsorbent is a modified NaX type molecular sieve, modified by at least one of Group IIA and VIIIB metals, or modified by at least one of Group IIA and VIIIB metals and at least one of Group IA metals; the adsorbent has a 130N crushing rate of 0.3% to 1.0% and a bulk density of 0.40 to 0.95 g / cm³. 3 .

[0010] This invention provides a method for preparing a highly selective adsorbent, characterized by comprising the following steps:

[0011] (1) Spherical molding: NaX molecular sieve and kaolin mineral are mixed evenly at a mass ratio of 91-98:2-9, spherical molding is performed, and after drying, the mixture is calcined at 500℃-680℃.

[0012] (2) In-situ crystallization: The calcined microspheres are treated with a mixed solution of sodium hydroxide and potassium hydroxide to crystallize the kaolin minerals in situ into X molecular sieves. After drying, matrix microspheres are obtained. The K / (Na+K) molar ratio in the mixed solution of sodium hydroxide and potassium hydroxide is 0 to 0.50, and the concentration of hydroxide ions is 0.2 mol / L to 2.0 mol / L.

[0013] (3) Ion exchange: The microsphere matrix obtained by in-situ crystallization is subjected to cation exchange with a compound solution containing at least one metal from Group IIA and Group VIIIB or a compound solution containing at least one metal from Group IIA and Group VIIIB and at least one metal from Group IA. The solid after ion exchange is then dried and activated.

[0014] This invention also provides a method for separating a mixture of trimethylbenzene from heavy aromatics, characterized in that, using heavy aromatics as raw materials, a combined adsorption separation and distillation process is used to obtain high-purity, high-yield mesitylene, pseudotrimethylbenzene, and terephthalene monomers, wherein the adsorption separation process uses a highly selective adsorbent provided by this invention.

[0015] The highly selective adsorbent of this invention not only has high compressive strength and bulk density, but also exhibits extremely high adsorption selectivity for all three trimethylbenzene isomers. It is suitable for use in combined adsorption separation and distillation processes to separate trimethylbenzene mixtures from heavy aromatics, obtaining mesitylene, pseudotrimethylbenzene, and terylene monomers with high purity and high yield, while consuming less energy. Attached Figure Description

[0016] Figure 1 The image shows a pulse diagram of the adsorption and separation of heavy aromatics using a pulse device and the highly selective adsorbent of this invention, wherein n-nonane is used as a tracer, and the heavy aromatic components are p-toluene, m-toluene, o-toluene, propane, p-toluene, m-toluene, o-toluene, p-diethylbenzene, mesitylene, pseudotrimethylbenzene, thionylbenzene, 2-ethyl-p-xylene, 4-ethyl-m-xylene, and indene.

[0017] Figure 2 This is a schematic diagram of the small-scale simulated moving bed adsorption separation process of the present invention.

[0018] Figure 3 This is a schematic diagram of an apparatus for the combined adsorption separation and distillation process of the present invention. Detailed Implementation

[0019] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present application will become clearer and more apparent.

[0020] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0021] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0022] This invention involves mixing NaX-type molecular sieves with kaolin minerals as a binder, rolling the mixture into balls, and then calcining it at high temperature to convert the kaolin into metakaolin. The kaolin is then treated with alkali to crystallize it in situ into X-type molecular sieves, which are then subjected to ion exchange to obtain a highly selective adsorbent. The prepared adsorbent has high trimethylbenzene adsorption selectivity, compressive strength, and bulk density.

[0023] According to an exemplary embodiment of the present invention, a highly selective adsorbent is prepared by the following method:

[0024] (1) Spherical molding: NaX molecular sieve and kaolin mineral are mixed evenly at a mass ratio of 91-98:2-9, spherical molding is performed, and after drying, the mixture is calcined at 500℃-680℃.

[0025] (2) In-situ crystallization: The calcined microspheres are treated with a mixed solution of sodium hydroxide and potassium hydroxide to crystallize the kaolin minerals in situ into X molecular sieves. After drying, matrix microspheres are obtained. The K / (Na+K) molar ratio in the mixed solution of sodium hydroxide and potassium hydroxide is 0 to 0.50, and the concentration of hydroxide ions is 0.2 mol / L to 2.0 mol / L.

[0026] (3) Ion exchange: The matrix microspheres obtained by in-situ crystallization are subjected to cation exchange with a compound solution containing at least one metal from Group IIA and Group VIIIB or a compound solution containing at least one metal from Group IIA and Group VIIIB and at least one metal from Group IA. The solid after ion exchange is then dried and activated.

[0027] According to an exemplary embodiment of the present invention, the spheroidizing step involves mixing NaX molecular sieves and kaolin minerals and spheroidizing them, which can be performed using equipment such as a high-intensity mixing spheroidizing machine. During spheroidizing, the uniformly mixed solid raw materials are placed in a rotating device, with the stirring paddle and drum rotating in opposite directions. Water is sprayed while the paddle is rolling. The high-speed rotating stirring paddle generates localized high pressure upon contact with the materials, causing some of the materials to adhere together. Under the action of the drum, the solid powder adheres and agglomerates into small balls, making the balls more compact. The amount of water added during spheroidizing is 5% to 30% of the total solid mass, preferably 10% to 20%.

[0028] In the spheroidizing step, all NaX molecular sieves preferably have a grain size of 0.5 μm to 2.0 μm, more preferably 0.7 to 1.5 μm, and a molar ratio of silica to alumina in the NaX molecular sieve is 2.0 to 2.6, preferably 2.0 to 2.4. It is believed, rather than being limited by theory, that the grain size of the molecular sieve affects the mass transfer and strength of the adsorbent. Larger grain sizes result in poorer mass transfer of heavy aromatic hydrocarbon feedstocks and desorbents within the adsorbent, thus affecting the adsorption and separation efficiency. Conversely, excessively small grain sizes lead to reduced adsorbent strength, thereby affecting the adsorbent's lifespan. Similarly, it is believed, rather than being limited by theory, that the molar ratio of silica to alumina in the molecular sieve also significantly affects the adsorption capacity of the adsorbent. A high molar ratio leads to poorer selectivity, while a low molar ratio not only reduces the adsorption capacity but also alters the internal structure of the molecular sieve. Through long-term research and practice, this invention has obtained a suitable range of molecular sieve crystal sizes and a suitable range of molar ratios of silicon oxide to aluminum oxide for separating trimethylbenzene monomers.

[0029] In this invention, the kaolin mineral is selected from kaolinite, dickite, perlite, refractory stone, halloysite, or mixtures thereof. The mass fraction of crystallized material in the kaolin mineral is at least 92%, preferably 94% to 99%. The kaolin mineral binder causes the initial NaX-type molecular sieve powder to adhere and agglomerate into small balls during the ball-forming step, and has enhanced mechanical strength.

[0030] After forming small spheres in the spheroidizing step, they are sieved to obtain spheres within a certain particle size range, which are then dried and calcined. The drying temperature is 50℃~100℃, and the time is 2 hours~10 hours. To convert kaolinite minerals into metakaolinite, calcination is required at a temperature of 500℃~680℃ for 2.0 hours~5.0 hours. After calcination, the kaolinite within the spheres is converted into metakaolinite, which facilitates its transformation into X molecular sieves in the in-situ crystallization step.

[0031] According to an exemplary embodiment of the present invention, the kaolin mineral in the calcined microspheres needs to be crystallized in situ into X molecular sieves. In-situ crystallization uses a mixed solution of sodium hydroxide and potassium hydroxide. The calcined microspheres are then subjected to a cooking treatment, which is beneficial for improving the adsorption capacity of the final adsorbent for trimethylbenzene. In a preferred embodiment, the concentration of hydroxide ions in the mixed solution of sodium hydroxide and potassium hydroxide is preferably 0.2 mol / L to 1.6 mol / L, and the K / (Na+K) molar ratio is preferably 0.10 to 0.50, more preferably 0.15 to 0.40. Although not wishing to be limited by theory, it is believed that using a mixed solution of sodium hydroxide and potassium hydroxide helps to increase the bulk density of the highly selective adsorbent and reduce its crushing rate. A high bulk density and a low crushing rate are extremely advantageous for the adsorption and separation process of trimethylbenzene, as they can increase the loading of the adsorbent, thereby increasing the production capacity of the adsorption and separation process and extending the service life of the adsorbent. In a preferred embodiment, the liquid / solid ratio of the sodium hydroxide and potassium hydroxide mixed solution to the kaolin mineral in the in-situ crystallization step is 1.5 L / kg to 5.0 L / kg, the crystallization temperature is 80°C to 100°C, and the treatment time is 1 hour to 8 hours. It is believed that by selecting appropriate in-situ crystallization conditions, such as the composition and concentration of the alkaline solution, the liquid / solid ratio, and the crystallization temperature, the efficiency of in-situ crystallization can be improved, the crystallization effect can be enhanced, and the adsorption capacity of the final adsorbent for trimethylbenzene can be increased.

[0032] Then, the in-situ crystallized microspheres are dried to obtain matrix microspheres. The drying temperature is 50℃~100℃ and the time is 2 hours~10 hours. The particle size of the matrix microspheres obtained after drying is 400 micrometers~950 micrometers.

[0033] According to an exemplary embodiment of the present invention, cation exchange is required on the in-situ crystallized matrix microspheres. The in-situ crystallized matrix microspheres are exposed to a selected cation solution, thereby exchanging the selected cations to cation sites in the molecular sieve. In a preferred embodiment, the cation solution is a compound solution containing at least one metal from Group IIA and VIIIB metals.

[0034] In an exemplary embodiment, at least one metal cation from Group IIA and VIIIB metals is selected from Mg. 2+ Ca 2+ 、Sr 2+ Fe 2+ Co 2+ and Ni 2+ At least one of them, wherein Sr 2+ It is a particularly preferred choice, which can significantly increase the selectivity of the adsorbent for the three types of trimethylbenzene.

[0035] In an exemplary embodiment, the cation exchange solution may contain, in addition to at least one metal from Group IIA and VIIIB, a Group IA metal such as Li. + Na + K + 、Rb + and Cs + At least one metal cation, preferably K + Metal cations are added to the cation solution in the form of metal compounds. The compound solution containing at least one metal from Group IIA and VIIIB is selected from its nitrate or chloride solution, and the compound solution containing at least one metal from Group IA is selected from its nitrate, chloride, and carbonate solutions.

[0036] In an exemplary embodiment, cation exchange can be carried out in a batch or column container, preferably continuously in a column container. The exchange temperature is 80°C to 120°C, preferably 90°C to 100°C, the time is 8 hours to 25 hours, preferably 10 hours to 15 hours, and the volume hourly space velocity (LHSV) is 2 h⁻¹. -1 ~8h -1 , 3h preferred -1 ~5h -1 .

[0037] Then, the cation-exchanged matrix microspheres are dried and activated to obtain a highly selective adsorbent. Drying and activation can be carried out in flowing hot air or nitrogen, with a drying temperature of 50℃~100℃, preferably 60℃~90℃, and a time of 10 hours~20 hours. The activation temperature is 150℃~260℃, preferably 180℃~250℃, and a time of 5 hours~10 hours. According to an exemplary embodiment of the present invention, the metal ion exchange capacity of the adsorbent is not less than 76%, preferably not less than 85%, more preferably not less than 93%; the water content of the adsorbent is 1~10% by mass, preferably 2~8%, more preferably 3~6%.

[0038] According to an exemplary embodiment of the present invention, the highly selective adsorbent provided by the present invention has high compressive strength, bulk density, and preferential adsorption selectivity for trimethylbenzene isomers. Using a DL-II type particle strength meter from the Dalian Chemical Research and Design Institute, the compressive strength is characterized by measuring the breakage rate of a certain volume of sample under packing pressure. The crushing rate of the adsorbent at 130N was measured to be 0.3%–1.0%, preferably 0.3%–0.6%. Using a tap density meter, a certain mass of adsorbent particles is vibrated and compacted under specified conditions. The tapped volume is measured, and the natural basis bulk density is obtained by dividing the sample mass by the tapped volume. The natural basis bulk density is then multiplied by the igneous basis percentage of the sample to obtain its igneous basis bulk density. The igneous basis bulk density was measured to be 0.40–0.95 g / cm³. 3 The preferred value is 0.75–0.78 g / cm³. 3 This is very advantageous for the adsorption and separation of trimethylbenzene mixtures from heavy aromatics.

[0039] According to an exemplary embodiment of the present invention, the highly selective adsorbent of the present invention is particularly suitable for separating trimethylbenzene mixtures from heavy aromatics. Heavy aromatics, preferably reformed heavy aromatics, are fed into an adsorption separation device, which is a simulated moving bed. The adsorbent is the highly selective adsorbent of the present invention, and the desorbent is alkylbenzene, preferably toluene. The operating pressure is preferably 0.5 MPa to 1.2 MPa, more preferably 0.6 MPa to 1.0 MPa, and the operating temperature is preferably 120°C to 200°C, more preferably 140°C to 180°C. Figure 2 As shown, the simulated moving bed adsorption separation device of the present invention contains multiple adsorption beds filled with adsorbent, for example... Figure 2The simulated moving bed consists of 24 adsorption beds. Each bed has its own material inlet and outlet pipelines. The materials entering and exiting the simulated moving bed divide the adsorption bed into desorption, purification, adsorption, and isolation zones. The adsorption bed between desorbent injection and extractant collection is the desorption zone; the adsorption bed between extractant collection and feed injection is the purification zone; the adsorption bed between heavy aromatic feed injection and raffinate collection is the adsorption zone; and the adsorption bed between raffinate collection and desorbent injection is the isolation zone. The ratio of the number of beds in the adsorption, purification, desorption, and isolation zones is 29±10%:37±15%:21±5%:13±4%. During operation, the positions of the materials entering and exiting the adsorption beds change periodically. Multi-port rotary valves or programmable valve groups can be used to control the entry and exit of each material into different adsorption beds. At a certain moment, each material is connected to a specific bed. Every certain time interval, i.e., a step time, the entry and exit position of each material moves down one adsorption bed. The time required for a material to return to its starting position after passing through all adsorption beds is a cycle. A cycle is usually 18 minutes to 60 minutes, preferably 25 minutes to 35 minutes.

[0040] In one embodiment of the present invention, such as Figure 3 As shown, after the heavy aromatics feedstock undergoes adsorption separation, the extracted liquid and raffinate streams are fed into the extractor tower and raffinate tower, respectively. After desorption and recycling, a mixture of three types of trimethylbenzene with a purity of not less than 99% by mass is obtained at the bottom of the extractor tower, which then enters the distillation process for further separation. Figure 3 As shown, the distillation process can use a wall-mounted column. The bottom stream of the effluent from the adsorption separation process enters the wall-mounted column. Mesitylene is collected at the top of the wall-mounted column, pseudotrimethylbenzene is collected from the side stream, and terephthalene is collected from the bottom. In another embodiment of the invention, the distillation process can also use two distillation columns connected in series. The bottom stream of the effluent from the adsorption separation process enters the first distillation column, with mesitylene as the top product and a mixture of pseudotrimethylbenzene and terephthalene as the bottom product. This mixture then enters the second distillation column, with pseudotrimethylbenzene as the top product and terephthalene as the bottom product.

[0041] According to embodiments of the present invention, after distillation, mesitylene, pseudotrimethyllene, and terephthalene can be obtained with purities of not less than 97.0% by mass, 98.0% by mass, and 95.0% by mass, respectively, preferably not less than 98.5% by mass, 99.3% by mass, and 97.0% by mass, respectively.

[0042] According to embodiments of the present invention, such as Figure 3As shown, the bottom of the raffinate column yields other heavy aromatic components besides trimethylbenzene, which can be further utilized as gasoline blending components or high-boiling-point aromatic solvent oil components, significantly increasing the economic added value of heavy aromatic products and bringing considerable economic benefits.

[0043] The present invention is further illustrated below by way of examples, but the present invention is not limited thereto.

[0044] Example 1

[0045] The highly selective adsorbent of the present invention was prepared.

[0046] The highly selective adsorbent was prepared by the following steps:

[0047] (1) Ball rolling: 93 kg (on ignition basis weight) of NaX molecular sieve powder with a particle size of 0.5 μm to 1.0 μm and a SiO2 / Al2O3 molar ratio of 2.3 was mixed evenly with 7 kg of kaolin mineral and placed in a high-power ball rolling machine. While stirring, an appropriate amount of deionized water was sprayed in to make the solid powder aggregate into small balls. The amount of water sprayed during ball rolling was 10% of the mass of the solid powder. After sieving, small balls with a particle size of 500 μm to 800 μm were taken, dried at 90℃ for 5 hours, and calcined at 550℃ for 3 hours.

[0048] (2) In-situ crystallization: 65 kg of spheroids after calcination in the spheroid forming step were placed in a 210 L mixed solution of sodium hydroxide and potassium hydroxide. The hydroxide ion concentration in the mixed solution was 0.4 mol / L and the K / (Na+K) molar ratio was 0.3. The spheroids were crystallized in-situ at 90 °C for 3 hours. The crystallized spheroids were washed with water until the pH of the washing solution was less than 10. The spheroids were dried at 90 °C for 3 hours to obtain matrix spheroids.

[0049] (3) Ion exchange: 600 mL of in-situ crystallized and dried matrix beads were loaded into an ion exchange column for cation exchange, using 0.40 M strontium chloride solution at a concentration of 5.0 h. -1 The volume hourly space velocity (VHSV) was continuously exchanged at 0.1 MPa and 96 °C for 8 hours, with a total strontium chloride solution volume of 24 L. After ion exchange, the solid was washed with 6 L of deionized water at 80 °C, dried at 70 °C under a nitrogen atmosphere for 16 hours, and activated at 180 °C under a nitrogen atmosphere for 3 hours to obtain a highly selective adsorbent.

[0050] The water content of the prepared highly selective adsorbent was determined by slowly heating the adsorbent to 600℃ and holding it for several hours until the mass no longer changed. The mass after cooling was taken as the ignition mass. The ratio of the difference between the mass of the adsorbent after activation at different temperatures and the mass of the ignition mass to the adsorbent mass was taken as the water content of the adsorbent. The exchange degree of the prepared highly selective adsorbent was determined by using X-ray fluorescence spectrometry to determine the mass fraction of oxides such as strontium oxide, potassium oxide, and sodium oxide in the adsorbent. The ratio of the mass fraction of strontium oxide to the sum of the mass fractions of the three oxides was taken as the metal exchange degree of the adsorbent. The water content, bulk density, crushing rate, and exchange degree of the adsorbent are shown in Table 1.

[0051] Comparative Example 1

[0052] The comparative adsorbent was prepared by the following steps:

[0053] (1) Ball rolling: 93 kg (on ignition basis weight) of NaX molecular sieve powder with a particle size of 0.5 μm to 1.0 μm and a SiO2 / Al2O3 molar ratio of 2.3 was mixed evenly with 7 kg of kaolin mineral and placed in a high-power ball rolling machine. While stirring, an appropriate amount of deionized water was sprayed in to make the solid powder aggregate into small balls. The amount of water sprayed during ball rolling was 10% of the mass of the solid powder. After sieving, small balls with a particle size of 500 μm to 800 μm were taken, dried at 90℃ for 5 hours, and calcined at 550℃ for 3 hours.

[0054] (2) In-situ crystallization: 65 kg of small balls after calcination in the rolling sphere molding step were placed in 210 L of sodium hydroxide solution with a hydroxide ion concentration of 0.4 mol / L. The small balls were crystallized in-situ at 90 °C for 3 hours. The crystallized small balls were washed with water until the pH of the washing solution was less than 10. The small balls were dried at 90 °C for 3 hours to obtain matrix small balls.

[0055] (3) Ion exchange: 600 mL of in-situ crystallized and dried matrix beads were loaded into an ion exchange column for cation exchange, using 0.40 M strontium chloride solution at a concentration of 5.0 h. -1 The volume hourly space velocity (VHSV) was continuously exchanged at 0.1 MPa and 96 °C for 8 hours, with a total strontium chloride solution volume of 24 L. After ion exchange, the solid was washed with 6 L of deionized water at 80 °C, dried at 70 °C under a nitrogen atmosphere for 16 hours, and activated at 180 °C under a nitrogen atmosphere for 3 hours to obtain a highly selective adsorbent.

[0056] The prepared adsorbent was measured, and its water content, bulk density, crushing rate and exchange degree are shown in Table 1.

[0057] Table 1

[0058] Instance number Moisture content (%) Crushing rate (130N), % <![CDATA[Bulk density, g / cm 3 > commutativity Example 1 5.48 0.5 0.76 99.9 Comparative Example 1 5.45 0.6 0.74 99.9

[0059] As can be seen from Table 1, in-situ crystallization using a mixed solution of sodium hydroxide and potassium hydroxide increases the bulk density of the adsorbent and reduces its crushing rate.

[0060] Example 2

[0061] To evaluate the adsorption selectivity of the highly selective adsorbent of this invention, a dynamic pulse experimental setup was used to determine its adsorption selectivity and the adsorption and desorption rates of the target product. The setup consists of a feed system, an adsorption column, a heating furnace, and a pressure control valve. The adsorption column is a stainless steel tube measuring Ф8×900 mm. The lower inlet of the adsorption column is connected to the feed and nitrogen system, and the upper outlet is connected to the pressure control valve, which in turn connects to an effluent collector.

[0062] The adsorption selectivity of the adsorbent is determined as follows: Weigh the adsorbent particles to be tested and pack them into the adsorption column. Purge the system of gases under a nitrogen atmosphere. Increase the system pressure to 0.85 MPa and temperature to 145 °C. Stop the desorbent flow and introduce a pulsed feed solution of 5 mL to 10 mL at a flow rate of 1.5 mL / h. The feed solution contains unadsorbed tracers. Then, introduce the desorbent at the same volume hourly space velocity (VHSV) for desorption. Take 3 drops of the desorbate sample every 2 mL and analyze by gas chromatography. Plot the desorption curves of each component in the pulsed feed solution with the volume of the desorbent on the x-axis and the concentration of each component on the y-axis. (Example:) Figure 1 As shown. The unadsorbed tracer can be used to obtain the dead volume of the adsorption system. Taking the midpoint of the tracer's half-peak width as the zero point, the net retention volume from the midpoint of the half-peak width of each component to the zero point is measured. The net retention volume of any component is proportional to the partition coefficient at adsorption equilibrium, reflecting the interaction force between each component and the adsorbent material. The ratio of the net retention volumes of the two components is the separation coefficient β. For example, the ratio of the net retention volume of thallium to that of indane is the ratio of the adsorption performance of the adsorbent material for both components, and is the separation coefficient of thallium relative to indane, denoted as β. 连三甲苯 / 茚满 Resolution is often used as an indicator of adsorbent separation efficiency, especially for evaluating the adsorption and separation performance of different adsorbents under the same operating parameters. Resolution is equal to the ratio of the difference in net retention volume between adjacent pulse peaks to the average half-width at half-maximum (WHM) of the two pulse peaks. For example, the ratio of the difference in net retention volume between thiamine and indane to the average WHM of their pulse peaks is the resolution between the two peaks, denoted as R. 连三甲苯 / 茚满 .

[0063] 26 mL of the highly selective adsorbent prepared in Example 1 was used to conduct a liquid-phase pulse experiment to determine its adsorption selectivity, resolution, and adsorption and desorption rates for ethylbenzene. The desorbents used in the experiment were 50% by mass toluene and 50% by mass n-heptane. The pulse feed solution consisted of 2% by mass each of the three isomers of ethylbenzene, three isomers of trimethylbenzene, three isomers of methylpropylbenzene, propylbenzene, p-diethylbenzene, indane, 2-ethyl-p-xylene, 4-ethyl-m-xylene, and n-nonane (NC9), and 70% by mass of the desorbent, wherein n-nonane was used as a tracer. The obtained desorption curves are shown below. Figure 1 As shown in Table 2, the separation coefficients and separation degrees between mesitylene, pseudotrimethyllene, thionylene and other components are shown in Table 2.

[0064] Table 2

[0065]

[0066]

[0067] from Figure 1 As can be seen from Table 2, the highly selective adsorbent of the present invention has a much higher adsorption capacity for the three types of trimethylbenzene than for other heavy aromatic hydrocarbons, and exhibits preferential selectivity for the adsorption of the three types of trimethylbenzene.

[0068] Example 3

[0069] A small-scale simulated moving bed apparatus was used for the liquid-phase adsorption separation of heavy aromatic hydrocarbons, separating the trimethylbenzene isomers. The apparatus consisted of 24 columns connected in series, forming the adsorption bed. The internal cavity of each column, 200 mm high and 40 mm in diameter, contained the selective adsorbent of this invention, and was filled with a total of 2400 g of adsorbent. The 24th column was connected to the first column via a pump, allowing fluid circulation within the column. Material could be introduced or extracted at the connection points of each column. There were 7 columns between the raffinate outlet and the feed inlet, forming the adsorption zone; 9 columns between the feed inlet and the raffinate outlet, forming the purification zone; 5 columns between the raffinate outlet and the desorbent inlet, forming the desorption zone; and 3 columns between the desorbent inlet and the raffinate outlet, forming the isolation zone. The inlet and outlet positions changed according to the step time; every step time, the inlet / outlet advanced by one column. Figure 2 As shown, the position moves from the solid arrow to the dashed arrow, and the next step advances in the predetermined direction. This process continues, changing the positions of the inlet and outlet until they return to their starting positions, constituting one cycle. One step time is 80 seconds, and one cycle is 32 minutes.

[0070] The adsorbent was reformed heavy aromatics. The temperature of the adsorbent entering the adsorption bed was controlled at 160°C, and the operating pressure was 0.88 MPa. The adsorbent was the highly selective adsorbent prepared in Example 1, and the desorbent was 99.9% by mass toluene. The feed rate was 0.50 kg / h, the desorbent injection rate was 1.52 kg / h, the effluent rate was 0.70 kg / h, and the raffinate rate was 1.32 kg / h. The mass flow rate ratio of desorbent to heavy aromatic feed entering the simulated moving bed was 3.04, and the heavy aromatic feed flow rate per unit mass of adsorbent was 0.21 kg / (h·kg adsorbent).

[0071] After the simulated moving bed operation stabilized, mixed samples of the extract and raffinate from one cycle were collected and their composition analyzed. Based on the analytical results, the purity and yield of the trimethylbenzene mixture were calculated as follows:

[0072]

[0073] Where X is the mass fraction of each component in the extract;

[0074]

[0075] Where X 三甲苯，抽出液 Q is the sum of the mass fractions of the three types of trimethylbenzene in the extract. 抽出液 X is the mass flow rate of the extracted liquid. 三甲苯，抽余液 Q is the sum of the mass fractions of trimethylbenzene in the raffinate. 抽余液 This represents the mass flow rate of the residual liquid.

[0076] The yields and purities of the three target trimethylbenzenes obtained were 89.31% and 99.09% by mass, respectively.

[0077] Example 4

[0078] like Figure 3 As shown, three types of trimethylbenzene monomers were obtained using a combined adsorption separation and distillation process. The heavy aromatics feed rate was 20 t / h, the adsorption separation unit temperature was 160℃, the pressure was 0.8 MPa, the desorbent was toluene, and the loaded adsorbent was the highly selective adsorbent from Example 1. The distillation process was carried out using a wall-mounted column with a top temperature of 165℃ (mesotribenzene was collected from the top), a side stream temperature of 173℃ (partially trimethylbenzene was collected from the side stream), and a bottom stream of terylene. The pressure inside the wall-mounted column was 0.1 MPa. The purity and yield of mesotribenzene, partially trimethylbenzene, and terylene are shown in Table 3.

[0079] Table 3

[0080]

[0081] As shown in Table 3, by using the highly selective adsorbent of the present invention, high-purity and high-yield mesitylene, pseudotrimethyllene, and trimethyllene monomers can be obtained through a combined adsorption separation and distillation process. In particular, the purity and yield of the three trimethylbenzenes are extremely high, enabling the high-purity three high-value-added trimethylbenzene products to be obtained in high yield. This not only reduces the process operating cost and improves the resource utilization rate of heavy aromatics, but also maximizes the economic added value of heavy aromatic products and extends the industrial chain.

[0082] The present application has been described above with reference to preferred embodiments; however, these embodiments are merely exemplary and illustrative. Various substitutions and modifications can be made to the present application based on these embodiments, all of which fall within the protection scope of the present application.

Claims

1. A method for separating a mixture of trimethylbenzene from heavy aromatics, characterized in that, Using heavy aromatics as raw materials, high-purity and high-yield mesitylene, pseudotrimethyllene, and terephthalene monomers are obtained through a combined adsorption separation and distillation process. The heavy aromatics are used as raw materials and enter an adsorption separation unit, which is a simulated moving bed, and the desorbent is alkylbenzene. The adsorption separation process uses a highly selective adsorbent, which is a NaX-type molecular sieve, processed with Sr... 2+ Modification, or via Sr 2+ The adsorbent 130 N is modified with at least one of Group IA metals, and has a crushing rate of 0.3% to 1.0% and a bulk density of 0.40 to 0.95 g / cm³. 3 ; The NaX-type molecular sieve has a crystal size of 0.5 micrometers to 2.0 micrometers and a molar ratio of silica to alumina of 2.0 to 2.

6.

2. The method as described in claim 1, characterized in that, At least one of the group IA metals is Li. + Na + K + 、Rb + and Cs + At least one of them.

3. The method as described in claim 2, characterized in that, At least one of the group IA metals is K. + .

4. A method for separating a mixture of trimethylbenzene from heavy aromatics, characterized in that, Using heavy aromatics as raw materials, high-purity and high-yield mesitylene, pseudotrimethyllene, and terephthalene monomers are obtained through a combined adsorption separation and distillation process. The heavy aromatics are used as raw materials and enter an adsorption separation unit, which is a simulated moving bed, and the desorbent is alkylbenzene. The adsorption separation process uses a highly selective adsorbent, which is prepared by the following method: (1) Ball rolling: NaX type molecular sieve and kaolin mineral are mixed evenly at a mass ratio of 91 ~ 98: 2 ~ 9, ball rolling is formed, and after drying, it is calcined at 500 ℃ ~ 680 ℃; (2) In-situ crystallization: The calcined microspheres are treated with a mixed solution of sodium hydroxide and potassium hydroxide to crystallize the kaolin minerals in situ into X molecular sieves. After drying, matrix microspheres are obtained. The K / (Na+K) molar ratio in the mixed solution of sodium hydroxide and potassium hydroxide is 0.10 ~ 0.50, and the concentration of hydroxide ions is 0.2 mol / L ~ 2.0 mol / L. (3) Ion exchange: using Sr-containing 2+ Compound solutions or Sr 2+ A solution of at least one metal from Group IA was used to cation exchange the matrix microspheres obtained by in-situ crystallization, and then the ion-exchanged solid was dried and activated. The NaX-type molecular sieve has a crystal size of 0.5 micrometers to 2.0 micrometers and a molar ratio of silica to alumina of 2.0 to 2.

6.

5. The method as described in claim 4, characterized in that, The molar ratio of silica to alumina in the NaX-type molecular sieve is 2.0 to 2.

4.

6. The method as described in claim 4, characterized in that, The kaolin mineral is selected from kaolinite, dickite, perlite, refractory stone, halloysite, or mixtures thereof.

7. The method as described in claim 4, characterized in that, In the in-situ crystallization step, the concentration of hydroxide ions in the mixed solution of sodium hydroxide and potassium hydroxide is 0.2 mol / L ~ 1.6 mol / L.

8. The method as described in claim 4, characterized in that, In the in-situ crystallization step, the K / (Na+K) molar ratio in the mixed solution of sodium hydroxide and potassium hydroxide is 0.15 ~ 0.

40.

9. The method as described in claim 4, characterized in that, In the in-situ crystallization step, the liquid / solid ratio of the sodium hydroxide and potassium hydroxide mixed solution to the kaolin mineral is 1.5 L / kg ~ 5.0 L / kg.

10. The method as described in claim 4, characterized in that, In the in-situ crystallization step, the kaolin mineral is crystallized into X molecular sieve at a crystallization temperature of 80 ℃ ~ 100 ℃.

11. The method as described in claim 4, characterized in that, In the in-situ crystallization step, the particle size of the matrix microspheres obtained after drying is 400 micrometers to 950 micrometers.

12. The method as described in claim 4, characterized in that, In the ion exchange step, the Sr-containing 2+ The compound solution is selected from its nitrate or chloride, and the compound solution of at least one metal of the Group IA metal is selected from its nitrate, chloride and carbonate.

13. The method as described in claim 4, characterized in that, In the ion exchange step, at least one of the Group IA metals is Li. + Na + K + 、Rb + and Cs + At least one of them.

14. The method as described in claim 13, characterized in that, In the ion exchange step, the Group IA metal is K. + .

15. The method as described in claim 4, characterized in that, The metal ion exchange degree of the adsorbent is not less than 76%.

16. The method as described in claim 15, characterized in that, The metal ion exchange rate of the adsorbent is not less than 85%.

17. The method as described in claim 16, characterized in that, The metal ion exchange degree of the adsorbent is not less than 93%.

18. The method as described in claim 4, characterized in that, The water content of the adsorbent is 1-10% by mass.

19. The method as described in claim 18, characterized in that, The water content of the adsorbent is 2-8% by mass.

20. The method as described in claim 19, characterized in that, The water content of the adsorbent is 3-6% by mass.

21. The method for separating a mixture of trimethylbenzene from heavy aromatics according to any one of claims 1 to 20, characterized in that, The distillation process uses a wall-mounted column. The bottom stream of the extract from the adsorption separation process enters the wall-mounted column. Trimethylbenzene is collected from the top of the wall-mounted column, metatrimethylbenzene is collected from the side stream of the wall-mounted column, and tert-methylbenzene is collected from the bottom of the wall-mounted column.

22. The method for separating a mixture of trimethylbenzene from heavy aromatics according to any one of claims 1 to 20, characterized in that, The distillation process uses two distillation columns connected in series. The bottom stream of the effluent from the adsorption separation process enters the first distillation column. The top product of the first distillation column is mesitylene, and the bottom product of the first distillation column is a mixture of pseudotrimethylbenzene and terephthalene. The bottom product of the first distillation column enters the second distillation column. The top product of the second distillation column is pseudotrimethylbenzene, and the bottom product of the second distillation column is terephthalene.

23. The method for separating a mixture of trimethylbenzene from heavy aromatics according to any one of claims 1 to 20, characterized in that, The total purity of the three isomers, mesitylene, pseudotrimethyllene, and terephthalene, obtained by the adsorption separation process is not less than 99% by mass.

24. The method for separating a mixture of trimethylbenzene from heavy aromatics according to any one of claims 1 to 20, characterized in that, The purity of mesitylene, pseudotrimethylbenzene, and terephthalene obtained by the distillation process is not less than 97.0% by mass, 98.0% by mass, and 95.0% by mass, respectively.

25. The method for separating a mixture of trimethylbenzene from heavy aromatics as described in claim 24, characterized in that, The purity of mesitylene, pseudotrimethylbenzene, and terephthalene obtained by the distillation process is not less than 98.5% by mass, 99.3% by mass, and 97.0% by mass, respectively.

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