A process for separating trimethylbenzene monomers from heavy aromatics

Abstract

A method for separating trimethylbenzene monomers from heavy aromatics, comprising: after adsorption separation of heavy aromatic raw materials, obtaining an extract and a raffinate, recycling the desorbent in the extract, and the stream components being a mixture of three isomers of mesitylene, cymene and trimethylbenzene, with a total purity of not less than 99 mass%; and the mixture stream being sequentially subjected to rectification to obtain corresponding trimethylbenzene monomers; and the adsorption separation raffinate being recycled after recycling of the desorbent and being used as a gasoline blending component or a high-boiling aromatic solvent oil component. The method combines adsorption separation and rectification processes to obtain high-purity mesitylene, cymene and trimethylbenzene monomers, with the characteristics of high yield, good product quality, low operating energy consumption, and high product added value.

Description

Technical Field

[0001] The present invention generally relates to the field of production of fine chemical intermediate monomers, and in particular to a method for simultaneously separating high-purity mesitylene, unsymmetrical trimethylol and trimethylol. Background Art

[0002] C 9+ Heavy aromatics are an important by-product of petrochemical and coal coking units. In recent years, the chemical industry has attached increasing importance to their comprehensive utilization. With the successive commissioning of a number of domestic integrated projects, the reforming unit production capacity will reach 190 million tons in 2022, and the reforming heavy aromatics production capacity is expected to reach more than 30 million tons. At present, there are three ways to utilize heavy aromatics: one is as an oil blending component; the second is to increase the production of light aromatics such as BTX (benzene-toluene-xylene mixture, Benzene-Toluene-Xylene); the third is to produce high-boiling point solvent oil. The last utilization method has a high degree of resource waste and low product added value. In the past decade, the price of heavy aromatics has generally shown a downward trend. In 2021, the price of heavy aromatics per ton has been reduced to 3,200 yuan.

[0003] The most of heavy aromatics is mesitylene, cymene and 1,3,5-trimethylbenzene, which almost accounts for half of heavy aromatics, and is an important fine chemical intermediate with high utilization value. Cymene is currently obtained by multi-tower distillation or extractive distillation, but the requirements for the composition of raw materials are strict, especially for the content of tert-butylbenzene. China is the largest producer and consumer of cymene, and the demand is increasing year by year. Cymene can be used to produce cymene anhydride, further produce environmentally friendly plasticizer, also can produce trimethylhydroquinone, which is an intermediate for the production of vitamin E, or methylate to produce mesitylene, further produce the most promising plastic in the 21st century-polyimide, and is widely used in aerospace, supersonic aircraft, atomic energy industry and electromechanical industry. Mesitylene is currently obtained by extractive distillation, alkylation or isomerization, but each has certain shortcomings, such as high energy consumption of extractive distillation, high cost and large consumption of propylene of alkylation, and product yield of isomerization is only about 15% due to the interference of other C9 components. Mesitylene can be used to produce expensive antioxidants, dyes and environmentally friendly herbicides. China is a large agricultural country, and the demand for environmentally friendly herbicides is also increasing year by year. Mesitylene is currently usually sold as high-boiling solvent oil, and monomer can be obtained by alkylation, extractive distillation, precise distillation-cryogenic crystallization and other methods, but due to the difficulty of separation from indane components, the whole separation process has high energy consumption, and the purity is only 50 mass% to 80 mass%, which is poor in economy. Mesitylene can be used to produce Tibet musk, as a daily chemical used in cosmetics and daily chemical products, or produce aniline dyes, alkyd resin, polyester resin and cumaric acid, or react with benzoyl chloride and phenylacetyl chloride to produce analgesics, platelet anticoagulants and thrombosis inhibitors, etc. But at present, due to the huge investment in separation and purification, the industrial production is less in China.

[0004] CN109627140A and CN102924212B report methods for preparing mesitylene by extractive distillation, which have high energy consumption and low purity. CN110803974A provides a method for obtaining high-purity mesitylene by multi-stage cryogenics, but the energy consumption of cryogenics is high and the yield is low. CN1900034A proposes to alkylate the mesitylene in the raw material with a catalyst, cut the alkyl mesitylene fraction after vacuum distillation, and then dealkylate and vacuum distillate to finally obtain mesitylene with a purity of 92%. Its catalyst life is short and its economy is poor. CN105837394B uses a process-integrated differential pressure coupling design process to purify mesitylene, but it requires two parts: raw material pretreatment and extractive distillation, including a pre-light removal tower, a pre-heavy removal tower, an extractive distillation tower and a solvent recovery tower. The process flow is cumbersome, especially the extractive distillation tower has a large number of plates, high investment cost and high operating energy consumption. CN101704706A discloses a method for separating and purifying trimethylol and indane from heavy aromatic hydrocarbons. The method first uses rough cutting to obtain a stream rich in trimethylol and indane. The indane component is separated from the heavy aromatic hydrocarbons through adsorption separation. The residual oil is then subjected to precise fractionation to obtain a trimethylol product with a purity of 95%. This method is cumbersome and difficult to industrialize.

[0005] On the one hand, heavy aromatic resources are increasing and raw material prices are decreasing. On the other hand, most manufacturers' heavy aromatic utilization devices currently involve extraction, cryogenic crystallization, alkylation and other reactions and the coupling of multiple distillation towers. Their products are relatively single, with relatively low purity and yield, complex process flow, high investment cost, high operating energy consumption, low comprehensive extraction degree and low product added value. Therefore, the current market urgently needs to improve the utilization rate of heavy aromatic resources through technological innovation, maximize the economic added value of heavy aromatic products, and extend the industrial chain. Summary of the Invention

[0006] The invention aims to obtain three high-purity trimethylbenzene isomer monomers simultaneously in an economical and low-energy manner, thereby improving the utilization rate of heavy aromatic hydrocarbon resources and increasing the economic added value of heavy aromatic hydrocarbons.

[0007] In order to solve the above technical problems, the present invention provides a method for separating trimethylbenzene monomers from heavy aromatic hydrocarbons, characterized in that it includes adsorption separation and distillation processes, wherein the heavy aromatic hydrocarbon raw material is subjected to the adsorption separation process, and the extract is recycled and utilized by a desorbent to obtain a three-isomer mixture flow of mesitylene, unsymmetrical trimethylbenzene and trimethylbenzene, and then the three-isomer mixture flow is subjected to a distillation process to obtain the corresponding monomers, and the extract of the adsorption separation process is recycled by a desorbent and utilized as a gasoline blending component or a high-boiling point aromatic hydrocarbon solvent oil component, wherein the adsorption separation process uses a modified X-type, Y-type or A-type molecular sieve adsorbent, and the adsorbent is selected from Mg 2+ , Ca 2+ 、Sr 2+ 、Fe2+ 、Co 2+ 、Ni 2+ and Zn 2+ At least one cation and optionally selected from Li + 、Na + , K + , Rb + and Cs + At least one cationic modification.

[0008] The method of the present invention combines adsorption separation and distillation processes. The total purity of mesitylene, paratrimethylbenzene and tertiary trimethylbenzene obtained by the adsorption separation process is not less than 99% by mass. The distillation process can further simultaneously produce high-purity paratrimethylbenzene, mesitylene and tertiary trimethylbenzene monomers. The yield is high, the process is relatively simple, the product quality is good, the energy consumption is low, the resource utilization efficiency can be improved, the economic added value of heavy aromatic hydrocarbon products is greatly increased, and considerable economic benefits are brought to enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a pulse diagram of the adsorption separation of heavy aromatics using a pulse device, where n-nonane is used as a tracer, and the heavy aromatic components are p-ethylmethylbenzene, m-ethylmethylbenzene, o-ethylmethylbenzene, propylbenzene, p-propylmethylbenzene, m-propylmethylbenzene, o-propylmethylbenzene, p-diethylbenzene, mesitylene, unitylene, trimethylbenzene, 2-ethyl-p-xylene, 4-ethyl-m-xylene, and indane.

[0010] Figure 2 This is a schematic diagram of the small-scale simulated moving bed adsorption separation process of the present invention.

[0011] Figure 3 Schematic diagram of the device for the combined adsorption separation and distillation process of the present invention. DETAILED DESCRIPTION

[0012] The present application will be further described in detail below through the accompanying drawings and examples, through which the features and advantages of the present application will become more clear and distinct.

[0013] The word "exemplary" is used exclusively herein to mean "serving as an example, example, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise indicated.

[0014] In addition, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0015] The present invention uses heavy aromatic hydrocarbons as raw materials, which enter the adsorption separation device. The adsorption separation device is a simulated moving bed. The active component of the adsorbent is a Y-type, X-type or A-type molecular sieve, and the modified metal cation is Mg 2+ , Ca 2+ 、Sr 2+ 、Fe 2+ 、Co 2+ 、Ni 2 + and Zn 2+ One of them, can also be used with Li + 、Na + , K + , Rb + and Cs + At least one of them is subjected to composite modification, preferably Sr 2+ . The desorbent is an alkylbenzene, preferably toluene. The operating pressure is 0.5MPa~1.2MPa, and the operating temperature is 120℃~200℃. After adsorption separation, the raw material flow obtains an extract flow and a raffinate flow, which enter the extract tower and the raffinate tower respectively. After the desorbent is recovered and recycled, a mixture of three trimethylbenzene isomers with a purity of not less than 99% by mass is obtained at the bottom of the extract tower, and enters the distillation system for separation, and can obtain mesitylene, partial trimethylbenzene and trimethylbenzene with a purity of not less than 97.0% by mass, 98.0% by mass and 95.0% by mass respectively. Heavy aromatic components other than trimethylbenzene are obtained at the bottom of the raffinate tower, which can be further utilized as gasoline blending components or high-boiling point aromatic solvent oil components.

[0016] According to an exemplary embodiment of the present invention, the raw materials that can be processed by the present invention are heavy aromatics, especially C9 + Heavy aromatics (i.e., heavy aromatics rich in C9 and higher aromatics) are derived from reformate, pyrolysis gasoline, naphtha, ethylbenzene plant byproducts, and catalytic cracking gasoline. Reformed heavy aromatics are preferred, and more preferably, the reformed heavy aromatic fraction with a boiling point above 150°C. The feedstock that can be processed may also preferably include heavy aromatics containing mesitylene, unitylene, and tri-trimethylbenzene, with the combined mass fraction of the three trimethylbenzenes exceeding 20%.

[0017] According to the exemplary embodiments of the present application, the active component of the adsorbent loaded in the adsorption separation device of the present application is modified X-type, Y-type or A-type molecular sieve, preferably X-type molecular sieve. The X-type molecular sieve has a crystal grain size of 0.2-3.0 microns and a molar ratio of silicon oxide to aluminum oxide of 2.0-2.6, preferably 2.0-2.4. Without wishing to be bound by theory, it is believed that the crystal grain size of the molecular sieve affects the mass transfer and strength of the adsorbent, and the larger the crystal grain size, the worse the mass transfer of the heavy aromatic hydrocarbon feedstock and the desorbent in the adsorbent, which in turn affects the efficiency of the adsorption separation, and the smaller the crystal grain size, the lower the strength of the adsorbent, which in turn affects the service life of the adsorbent. Similarly, without wishing to be bound by theory, it is believed that the molar ratio of silicon oxide to aluminum oxide in the molecular sieve also has a significant effect on the adsorption capacity of the adsorbent, and a too high molar ratio will result in poor selectivity of the adsorbent, and a too low molar ratio will not only reduce the adsorption capacity of the adsorbent, but also change the internal structure of the molecular sieve. Through long-term research and practice, the present application has obtained the range of the crystal grain size of the molecular sieve and the range of the molar ratio of silicon oxide to aluminum oxide suitable for separating trimethylbenzene monomers.

[0018] According to the exemplary embodiments of the present application, the adsorbent loaded in the adsorption separation device of the present application is modified by at least one metal cation of Mg 2+ , Ca 2+ , Sr 2+ , Fe 2+ , Co 2+ , Ni 2+ and Zn 2+ , preferably Sr 2+ , and can also be modified by at least one metal cation of Li + , Na + , K + , Rb + and Cs + , preferably K + .

[0019] According to the exemplary embodiments of the present application, the adsorption separation process of the present application uses a simulated moving bed device, and the pressure is 0.5-1.2 MPa and the temperature is 120-200°C, preferably the pressure is 0.8-1.0 MPa and the temperature is 140-180°C, and the desorbent is alkylbenzene, preferably toluene. By optimizing the operating conditions of the adsorption separation process, the extract of the adsorption separation can basically contain only three trimethylbenzene isomers, and the content of other components is very low.

[0020] According to an exemplary embodiment of the present invention, after the extract obtained by adsorption separation is recycled and reused with a desorbent, the total purity of the three isomers of mesitylene, unsymmetrical trimethylene, and tri-trimethylbenzene in the mixed stream is no less than 99% by mass. This mixed stream is then subjected to a distillation process to obtain the corresponding monomers, with mesitylene, unsymmetrical trimethylene, and tri-trimethylbenzene having purities of no less than 97.0%, 98.0%, and 95.0% by mass, respectively. The raffinate from the adsorption separation, after being recycled with a desorbent, can be used as a gasoline blending component or a high-boiling-point aromatic solvent oil component.

[0021] According to an exemplary embodiment of the present invention, Figure 2 As shown, the simulated moving bed apparatus of the present invention contains a plurality of adsorption beds filled with adsorbents, for example Figure 2 The 24 adsorption beds shown in the figure have their own feed and discharge lines. The flow of material into and out of the simulated moving bed divides the adsorption beds into desorption, purification, adsorption, and isolation zones. The adsorption bed between desorbent injection and extract withdrawal is the desorption zone; the bed between extract withdrawal and feed injection is the purification zone; the bed between feed injection and raffinate withdrawal is the adsorption zone; and the bed between raffinate withdrawal and desorbent injection is the isolation zone. The ratio of the adsorption, purification, desorption, and isolation zones is 29±10%, 37±15%, 21±5%, and 13±4%. During operation of the simulated moving bed, the positions of the various feed streams entering and exiting the adsorption tower beds can be periodically changed. Multi-way rotary valves or programmable on / off valves can be used to control the flow of feed streams into and out of the various adsorption beds. At a certain moment, each stream of material is connected to a specific bed layer. At a certain interval, that is, a step time, the entry and exit positions of each stream of material move down one adsorption bed layer, such as Figure 2 As shown in the figure, the time required for a certain stream of material to move from the solid arrow to the dotted arrow position and then pass through all the adsorption beds to return to the starting position is one cycle. One cycle is usually 18 minutes to 60 minutes, preferably 25 minutes to 35 minutes.

[0022] According to an exemplary embodiment of the present invention, the mass flow rate ratio of the desorbent to the heavy aromatic feedstock used in the adsorption separation process of the present invention is no greater than 3.5, preferably no greater than 3.0, and more preferably no greater than 2.8. The heavy aromatic feedstock flow rate per unit mass of adsorbent is no less than 0.16 kg / (h·kg adsorbent), preferably no less than 0.20 kg / (h·kg adsorbent), and more preferably no less than 0.23 kg / (h·kg adsorbent).

[0023] According to an exemplary embodiment of the present invention, Figure 3As shown, after the heavy aromatic hydrocarbon feed stream is subjected to adsorption separation, the extracted liquid stream and the raffinate stream are respectively fed into the extract tower and the raffinate tower. After the desorbent is recycled, a mixture of three trimethylbenzenes with a purity of not less than 99% by mass is obtained at the bottom of the extract tower. The mixture enters the distillation process for separation. The other heavy aromatic hydrocarbons except trimethylbenzenes obtained at the bottom of the raffinate tower are further utilized as gasoline blending components or high-boiling point aromatic solvent oil components. In an exemplary embodiment, as Figure 3 As shown, the distillation process apparatus of the present invention can use two distillation towers connected in series. The three isomer mixture streams obtained by the adsorption separation process enter the first distillation tower. The overhead product of the first distillation tower is mesitylene, and the bottom product is a stream of an isomer mixture of unsymmetrical trimethylene and tert-trimethylbenzene. The stream enters the second distillation tower. The overhead product of the second distillation tower is unsymmetrical trimethylene, and the bottom product is tert-trimethylbenzene. In another exemplary embodiment, the distillation process apparatus of the present invention can also use a bulkhead tower. The three isomer mixture streams obtained by the adsorption separation process enter the bulkhead tower. Mesitylene is produced from the top of the tower, unsymmetrical trimethylene is produced from the side line of the tower, and tert-trimethylbenzene is produced from the bottom of the tower.

[0024] According to an exemplary embodiment of the present invention, the method for separating trimethylbenzene monomers from heavy aromatics provided by the present invention can be further coupled with an isomerization process so as to optimize the composition of the three trimethylbenzenes obtained according to market needs. In one embodiment, the three isomer mixture logistics obtained by the adsorption separation process enters the isomerization process unit, and the composition of the three isomer mixture obtained by the adsorption separation process is optimized by isomerization, and then enters the distillation process to obtain the corresponding monomer, so that the trimethylbenzene monomers required by the market can be obtained. In another embodiment, the single monomer component obtained by the distillation process enters the isomerization unit and isomerized into other trimethylbenzene components.

[0025] The present invention is further described below by way of examples, but the present invention is not limited thereto.

[0026] Example 1

[0027] Preparation of adsorbents used in adsorption separation processes:

[0028] An X-type molecular sieve with a silicon-aluminum ratio of 2.3 and a kaolin mineral were mixed uniformly in a mass ratio of 93:7, rolled into balls, dried, and calcined at 550°C for 3 hours. The calcined balls were treated with a mixed solution of sodium hydroxide and potassium hydroxide (hydroxyl ion concentration of 0.4 mol / L, K / (Na+K) molar ratio of 0.3) at 90°C for 3 hours. The alkaline-treated and dried balls were cation exchanged with a 0.40 mol / L strontium chloride hexahydrate solution for 8 hours at a temperature of 96°C. The liquid-to-solid ratio of the solution to the adsorbent was 40, and the exchange degree calculated based on the residual sodium content after the exchange was 99.9 mol%. The exchanged balls were dried and activated at 180°C for 3 hours.

[0029] Example 2

[0030] To evaluate the adsorption selectivity of the adsorbent material, a dynamic pulse test apparatus was used to measure its adsorption selectivity and the adsorption and desorption rates of the target product. This apparatus consists of a feed system, adsorption column, heating furnace, and pressure control valve. The adsorption column is a Ø8 x 900 mm stainless steel tube. The lower inlet of the column is connected to the feed and nitrogen system, and the upper outlet is connected to a pressure control valve, which is then connected to the effluent collector.

[0031] The method for determining the adsorption selectivity of the adsorbent is as follows: weigh the adsorbent particles to be tested with a particle size of 800μm to 1000μm and put them into the adsorption column for compaction, and remove the gas in the system in a nitrogen atmosphere. Raise the system pressure to 0.85MPa, the temperature to 145°C, stop introducing the desorbent, and introduce 5mL to 10mL of pulse feed liquid at a liquid flow rate of 1.5mL / h. The feed liquid contains a non-adsorbed tracer. Then, introduce the desorbent at the same volumetric air velocity for desorption. Take 3 drops of desorbed liquid sample every 2mL and analyze it by gas chromatography. Use the volume of the desorbent used for desorption as the horizontal axis and the concentration of each component of the pulse feed liquid as the vertical axis to draw the desorption curve of each component of the pulse feed liquid, as shown below. Figure 1 As shown. Among them, the tracer that is not adsorbed can be used to obtain the dead volume of the adsorption system. The midpoint of the tracer's half-peak width is taken as the zero point, and the net retention volume from the midpoint of the half-peak width to the zero point of each component is measured. The net retention volume of any component is proportional to the distribution coefficient at the adsorption equilibrium, reflecting the interaction between each component and the adsorption material. The ratio of the net retention volume of the two components is the separation coefficient β. For example, the ratio of the net retention volume of trimethylbenzene to the net retention volume of indane is the ratio of the adsorption performance of the adsorption material for the two, which is the separation coefficient of trimethylbenzene relative to indane, recorded as β 连三甲苯 / 茚满Separation degree can also be used as one of the indicators of adsorbent separation efficiency, especially when evaluating the adsorption separation performance of different adsorbents under the same operating parameters. Separation degree is equal to the ratio of the difference between the net retention volumes of adjacent pulse peaks to the average half-peak width of the two pulse peaks. For example, the ratio of the difference between the net retention volume of trimethylbenzene and the net retention volume of indane to the average half-peak width of the two pulse peaks is the separation degree between the two peaks, which is recorded as R 连三甲苯 / 茚满 .

[0032] Take 26 ml of the adsorbent prepared in Example 1, fluidize and dehydrate it to a water content of 5.48%, and conduct a liquid pulse experiment to determine its adsorption selectivity and separation. The desorbents used in the experiment are 50% by mass of toluene and 50% by mass of n-heptane. The pulse feed liquid consists of 2% by mass of each of the three isomers of methyl and ethyl benzene, the three isomers of trimethylbenzene, the three isomers of methyl and propyl benzene, propylbenzene, p-diethylbenzene, indane, 2-ethyl p-xylene, 4-ethyl m-xylene, n-nonane (NC9) and 70% by mass of the desorbent, wherein n-nonane is a tracer. The desorption curve obtained is as shown in FIG. Figure 1 As shown in Table 1, the separation coefficients and separation degrees between mesitylene, unsymmetrical trimethylol, trimethylol and other components are shown in Table 1.

[0033] Table 1

[0034]

[0035]

[0036] Example 3

[0037] A small simulated moving bed device is used to carry out liquid phase adsorption separation of heavy aromatic hydrocarbons to separate the trimethylbenzene isomers therein. The device is composed of 24 columns connected in series as an adsorption bed. The cavity inside the column for accommodating the selective adsorbent of the present invention is 200 mm high and 40 mm in diameter, with a total of 2,400 g of adsorbent filled. The 24th column is connected to the 1st column by a pump to circulate the fluid in the column. Materials can be introduced or extracted at the connection points of each column. There are 7 columns between the residual liquid outlet and the raw material inlet, which is the adsorption zone; there are 9 columns between the raw material inlet and the extracted liquid outlet, which is the purification zone; there are 5 columns between the extracted liquid outlet and the desorbent inlet, which is the desorption zone; there are 3 columns between the desorbent inlet and the residual liquid outlet, which is the isolation zone. The inlet and outlet positions of the materials change according to the step time. The inlet and outlet are advanced by one column every step time. The inlet and outlet are arranged as follows: Figure 2 As shown in the figure, the position of the solid arrow moves to the dotted arrow position, and the next step time advances in the predetermined direction. Similarly, the position of the inlet and outlet is changed until the inlet and outlet return to the starting position, which is one cycle. One step time is 80 seconds, and one cycle is 32 minutes.

[0038] The adsorption raw material is reformed heavy aromatics, and the raw material composition is shown in Table 2. The temperature of the adsorption raw material entering the adsorption bed is controlled to be 145°C, and the operating pressure is 0.88 MPa. The adsorbent is the adsorbent of Example 1, the desorbent is 99.9% by mass toluene, the raw material feed rate is 0.50 kg / h, the desorbent injection rate is 1.52 kg / h, the extracted liquid rate is 0.70 kg / h, the residual liquid rate is 1.32 kg / h, the mass flow rate ratio of the desorbent entering the simulated moving bed to the heavy aromatic raw material is 3.04, and the heavy aromatic raw material flow rate per unit mass of adsorbent is 0.21 kg / (h·kg adsorbent). The yield and purity of the three target products, three trimethylbenzenes, are 90.97% and 99.208% by mass, respectively.

[0039] After the simulated moving bed runs stably, take mixed samples of the extract and raffinate for one cycle and analyze their composition. Based on the analysis results, the purity and yield of the trimethylbenzene mixture are calculated as follows:

[0040]

[0041] Where X is the mass fraction of each component in the extract;

[0042]

[0043] 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 is the mass flow rate of the extracted liquid, X 三甲苯，抽余液 Q is the sum of the mass fractions of trimethylbenzene in the raffinate, 抽余液 is the mass flow rate of the raffinate.

[0044] The yield and purity of the three target trimethylbenzenes were 90.97% and 99.21% by mass, respectively.

[0045] Table 2

[0046]

[0047] Example 4

[0048] The trimethylbenzene isomer mixture was separated by adsorption according to the method of Example 3, except that the simulated moving bed apparatus used 12 adsorption columns. The yield and purity of the three trimethylbenzenes were 88.15% and 99.23% by mass, respectively.

[0049] Example 5

[0050] Three types of trimethylbenzene monomers were obtained using a combined adsorption separation process and distillation process. The heavy aromatics feed rate was 20 t / h. The operating temperature of the adsorption separation device was 160°C and the pressure was 0.8 MPa. The desorbent was toluene, and the adsorbent loaded was the adsorbent of Example 1. The top temperature of the first distillation tower was 166°C and the number of plates was 100. The top temperature of the second distillation tower was 170°C and the number of plates was 90. The pressure in each distillation tower was 0.1 MPa. The purities and yields of mesitylene, unitylene, and trimethylbenzene are shown in Table 3.

[0051] Table 3

[0052]

[0053] Comparative Example 1

[0054] Three types of trimethylbenzene monomers were obtained using a distillation unit, with a heavy aromatic feed rate of 20 t / h. After pretreatment to remove C8 residues, the heavy aromatic feedstock was fed to the first distillation tower, where mesitylene was produced overhead. The bottoms were fed to the second distillation tower, where unsegmented trimethylbenzene was produced overhead and tert-trimethylbenzene was produced at the bottom. The top temperature of the first distillation tower was 166°C, with 100 plates, while the top temperature of the second distillation tower was 170°C, with 90 plates. The pressure in each distillation tower was 0.1 MPa. The purities of mesitylene, unsegmented trimethylbenzene, and tert-trimethylbenzene are shown in Table 4.

[0055] Table 4

[0056]

[0057] As shown in Tables 3 and 4, conventional distillation processes are unable to produce the three trimethylbenzenes at high purity, thus failing to meet the requirements for subsequent utilization. However, the combined adsorption separation and distillation process yields high-purity, high-yield mesitylene, unsimilar trimethylbenzene, and trimethylbenzene monomers. In particular, the purity and yield of all three trimethylbenzenes are extremely high, enabling the production of high-purity, high-value-added trimethylbenzene products at high yields. This not only reduces process operating costs and improves heavy aromatics resource utilization, but also maximizes the economic added value of heavy aromatics products, extending the industrial chain.

[0058] The present application has been described above in conjunction with preferred embodiments, but these embodiments are merely exemplary and serve only as an illustrative example. On this basis, various replacements and improvements can be made to the present application, all of which fall within the scope of protection of the present application.

Claims

1. A method for separating trimethylbenzene monomers from heavy aromatic hydrocarbons, characterized in that: The invention comprises an adsorption separation and distillation process, wherein the heavy aromatic hydrocarbon raw material is subjected to the adsorption separation process, and the extracted liquid is recycled and utilized by a desorbent to obtain a mixture flow of three isomers of mesitylene, unsymmetrical trimethylol and trimethylol, and then the mixture flow of the three isomers is subjected to a distillation process to obtain the corresponding monomers, and the raffinate of the adsorption separation process is recycled and utilized as a gasoline blending component or a high-boiling point aromatic hydrocarbon solvent oil component by a desorbent, wherein the adsorption separation process uses a modified X-type molecular sieve adsorbent, and the adsorbent is recycled by Mg 2+ , Ca 2+ 、Sr 2+ 、Fe 2+ 、Co 2+ 、Ni 2+ and Zn 2+ At least one cation and optionally selected from Li + 、Na + , K + , Rb + and Cs + wherein the adsorption separation process adopts a simulated moving bed device, and The distillation process uses two distillation towers connected in series. The three isomer mixture flow enters the first distillation tower, the top product is mesitylene, and the bottom product is a mixture of two isomers, unsymmetrical trimethylol and thimerosal, and enters the second distillation tower, the top product is unsymmetrical trimethylol and the bottom product is thimerosal.

2. The method according to claim 1, wherein The heavy aromatics raw material comes from reforming products, pyrolysis gasoline, naphtha, ethylbenzene unit by-products or catalytic cracking gasoline.

3. The method according to claim 2, wherein The heavy aromatics raw material is reformed heavy aromatics.

4. The method according to claim 2, wherein The heavy aromatic hydrocarbon raw material is a reformed heavy aromatic hydrocarbon fraction with a boiling point above 150°C.

5. The method according to claim 2, wherein The heavy aromatics raw material is reformed heavy aromatics in which the sum of the mass fractions of the three isomers of mesitylene, unsymmetrical trimethylol and trimethylol is greater than 20%.

6. The method according to any one of claims 1 to 5, characterized in that The total purity of mesitylene, unsymmetrical trimethylol and trimethylol in the three isomer mixture stream obtained by the adsorption separation process is not less than 99% by mass.

7. The method according to any one of claims 1 to 5, characterized in that The purities of mesitylene, para-trimethylbenzene and tri-trimethylbenzene obtained by the distillation process are not less than 97.0% by mass, 98.0% by mass and 95.0% by mass, respectively.

8. The method according to claim 7, wherein The purities of mesitylene, para-trimethylbenzene and tri-trimethylbenzene obtained by the distillation process are not less than 98.5% by mass, 99.3% by mass and 97.0% by mass, respectively.

9. The method according to claim 1, wherein The X-type molecular sieve has a particle size of 0.2 microns to 3.0 microns.

10. The method according to claim 1, wherein The molar ratio of silicon oxide to aluminum oxide of the X-type molecular sieve is 2.0 to 2.

6.

11. The method according to any one of claims 1 to 5, characterized in that The desorbent is alkylbenzene.

12. The method according to claim 11, wherein The desorbent is toluene or p-xylene.

13. The method according to claim 1, wherein The pressure of the simulated moving bed device is 0.5 MPa ~ 1.2 MPa, and the temperature is 120 ℃ ~ 200 ℃.

14. The method according to claim 1, wherein The simulated moving bed device includes multiple adsorption beds filled with adsorbents, each bed has its own material inlet and outlet pipelines, and the materials entering and leaving the simulated moving bed device divide the adsorption beds therein into a desorption zone, a purification zone, an adsorption zone and an isolation zone. The adsorption bed between desorbent injection and extractant production is the desorption zone, the adsorption bed between extractant production and raw material injection is the purification zone, the adsorption bed between raw material injection and residual liquid production is the adsorption zone, and the adsorption bed between residual liquid production and desorbent injection is the isolation zone.

15. The method according to claim 1, wherein The mass flow rate ratio of the desorbent to the heavy aromatic hydrocarbon feedstock entering the simulated moving bed device is not greater than 3.

5.

16. The method according to claim 1, wherein The mass flow rate ratio of the desorbent to the heavy aromatic hydrocarbon feedstock entering the simulated moving bed device is not greater than 3.

0.

17. The method according to claim 1, wherein The flow rate of heavy aromatic hydrocarbon feedstock relative to unit mass of adsorbent is not less than 0.16 kg / (h·kg adsorbent).

18. The method according to claim 17, wherein The flow rate of heavy aromatic hydrocarbon feedstock relative to unit mass of adsorbent is not less than 0.20 kg / (h·kg adsorbent).

19. The method according to claim 1, wherein The simulated moving bed device includes an adsorption zone, a purification zone, a desorption zone and an isolation zone, and the ratio of the number of bed layers is 29±10%: 37±15%: 21±5%: 13±4%.

20. The method of claim 1, wherein One cycle of the simulated moving bed device is 18 minutes to 60 minutes.

21. The method according to claim 20, wherein One cycle of the simulated moving bed device is 25 minutes to 35 minutes.

22. The method according to any one of claims 1 to 5, characterized in that A coupled isomerization process is also included to optimize the composition of the three trimethylbenzenes.

23. The method according to any one of claims 1 to 5, characterized in that The three isomer mixture flow obtained by the adsorption separation process enters the isomerization process unit for composition optimization, and then enters the distillation process to obtain the corresponding monomer, or the single monomer component obtained by the distillation process enters the isomerization unit and isomerized into other three toluene components.

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