阅读说明：本技术 一种甲醇和二甲苯制均四甲苯的方法 (Method for preparing durene from methanol and xylene ) 是由 王刃 王相珣 张伶超 徐连海 吴昊 袁麟 于 2019-09-12 设计创作，主要内容包括：本发明提供一种甲醇和二甲苯制均四甲苯的方法,将二甲苯与部分甲醇混合,从顶部主线进入反应器,其余甲醇采用侧线多段进料方式进入反应器,物料在温度250～400℃,压强0.5～2.0MPa下转化为富含均四甲苯的混合烃类组分,经分离得到富含均四甲苯的重芳烃,再经过多级冷冻结晶、离心分离压榨系统得到高纯度为的均四甲苯。本发明采用侧线甲醇多段进料来控制烷基化时床层温升,且充分利用反应器上段床层的反应热给中段、末段床层保温,并使用改性纳米ZSM-5分子筛催化剂而降低反应温度；二甲苯及其混合芳烃与甲醇不断多次进行烷基化反应提高了均四甲苯在油相产物中的选择性。而且充分利用反应副产物提高了均四甲苯收率。(The invention provides a method for preparing durene from methanol and xylene, which comprises the steps of mixing the xylene with part of methanol, feeding the mixture into a reactor from a main line at the top, feeding the rest of the methanol into the reactor in a lateral line multi-section feeding mode, converting the material into a mixed hydrocarbon component rich in durene at the temperature of 250-400 ℃ and under the pressure of 0.5-2.0 MPa, separating to obtain heavy aromatic hydrocarbon rich in durene, and obtaining high-purity durene through a multi-stage freezing crystallization and centrifugal separation squeezing system. The invention adopts side methanol multi-section feeding to control the bed temperature rise during alkylation, fully utilizes the reaction heat of the upper section bed of the reactor to preserve the heat of the middle section bed and the last section bed, and reduces the reaction temperature by using a modified nano ZSM-5 molecular sieve catalyst; the xylene and mixed aromatics thereof are continuously subjected to alkylation reaction with methanol for many times, so that the selectivity of durene in an oil phase product is improved. But also fully utilizes the reaction by-products to improve the yield of durene.)

1. A method for preparing durene from methanol and xylene is characterized in that: the method comprises the following steps:

s1, mixing dimethylbenzene and part of methanol in a raw material storage tank, feeding the mixture into a reactor (1) filled with a multilayer modified nano ZSM-5 molecular sieve catalyst from a top main line through a preheater, feeding the rest of methanol into the reactor (1) in a lateral line multi-stage feeding mode, and controlling the reaction temperature to be 250-400 ℃, the pressure to be 0.5-2.0 MPa and the mass space velocity of the dimethylbenzene to be 0.2-2.0 h^-1The mass space velocity of the methanol is 0.2-1.0 h^-1To a durene-rich mixed hydrocarbon component;

s2, separating the durene-rich mixed hydrocarbon component by an oil-water separator (2), a liquefied gas removal tower (3), a product separation tower (4) and a purification tower (5) to obtain water, dry gas, liquefied gas, durene-rich heavy aromatic hydrocarbon, C7-C9 aromatic hydrocarbon and C5-C6 light hydrocarbon;

s3, taking the dry gas as circulating gas to drive the raw materials in the reactor to flow; the C7-C9 aromatic hydrocarbon enters a raw material storage tank to be used as a reaction raw material;

s4, subjecting the durene-rich heavy aromatic hydrocarbons to multistage freezing crystallization and centrifugal separation squeezing system (6) to obtain solid durene and heavy aromatic hydrocarbon raffinate;

s5, discharging the solid durene serving as a product out of the system, and feeding the heavy aromatic residual liquid into a mixed aromatic storage tank (7) to serve as a reaction raw material;

the modified nano ZSM-5 molecular sieve catalyst comprises a ZSM-5 molecular sieve carrier and active metal, wherein the grain size of the ZSM-5 molecular sieve carrier is 210 nm-300 nm, the active metal is one or more of zinc, iron, magnesium, calcium and rare earth elements, and the mass fraction of the active metal is 0.1-2.0%.

2. The method of claim 1, wherein the method comprises the following steps: step S1 further includes mixing the dry gas with xylene and a portion of methanol, and passing the mixture through a preheater to enter the reactor from the top main line.

3. The method of claim 1, wherein the method comprises the following steps: in the step S1, the reaction temperature is 250-340 ℃.

4. The method of claim 1, wherein the method comprises the following steps: the preparation method of the modified nano ZSM-5 molecular sieve catalyst comprises the following steps:

s1, uniformly mixing a silicon source, an aluminum source, an alkali source, n-butylamine, deionized water and ZSM-5 seed crystals to form a mixed solution, crystallizing the mixed solution at 40-190 ℃ for 12-120 h, and washing, drying and roasting a solid product obtained by crystallization to obtain a ZSM-5 molecular sieve carrier;

s2, carrying out alkali treatment, ammonium exchange, extrusion molding, acid treatment and metal salt solution impregnation on the ZSM-5 molecular sieve carrier in the step S1, and roasting to obtain the modified nano ZSM-5 molecular sieve catalyst;

OH in the step S1 Mixed liquid System^-:SiO₂:A1₂O₃The molar ratio of n-butylamine to water is 2-4:7-15:0.1-1:0.5-5: 300-1100.

5. The method of claim 4, wherein the methanol and the xylene are used for preparing durene, and the method comprises the following steps: step S1 mixed liquid system OH in preparation method of modified nano ZSM-5 molecular sieve catalyst^-:SiO₂:A1₂O₃The molar ratio of n-butylamine to water is 2.3-3.5:10-13.5:1:2.5-5.5: 250-.

Technical Field

The invention relates to a preparation method of durene in the technical field of aromatic hydrocarbon production chemical industry, in particular to a method for preparing durene from methanol and xylene.

Background

Durene (1,2,4, 5-tetramethylbenzene) is commonly called durene, is an important organic chemical raw material, and is mainly used for producing pyromellitic dianhydride and further producing polyimide. With the increasing market usage of polyimide, durene is used as the main raw material for synthesizing polyimide, and the demand is increasing.

The existing synthesis method of durene comprises the alkylation of pseudocumene methanol; isomerizing and disproportionating trimethylbenzene; chloromethylating trimethyl benzene; isomerizing tetramethylbenzene; methanol to durene, and the like. The demand of durene is increasing, and thus the search for new raw materials and process routes for preparing durene is imminent.

Chinese patent document CN106565406A reports a one-step process for preparing durene from synthesis gas, which simplifies the process flow and reduces the reaction temperature.

Chinese patent document CN106076404A reports a method for preparing durene by an alkylation reaction of methanol and pseudocumene under the conditions of 350-400 ℃ and 0.6-1.5 MPa.

However, the above method has high reaction temperature and reaction pressure and high cost. The preparation of durene by using methanol with surplus productivity and xylene which is cheaper than pseudocumene and mixed aromatics thereof has important significance for reducing the preparation cost of durene.

Disclosure of Invention

In order to solve the technical problems, the invention provides a method for preparing durene from methanol and xylene, which has the advantages of low cost of raw materials, low reaction temperature and pressure and simple reaction device.

The technical scheme of the invention is as follows:

a method for preparing durene from methanol and xylene comprises the following steps:

s1, mixing dimethylbenzene (stored in a raw material storage tank) with part of methanol, feeding the mixture into a reactor filled with a multilayer modified nano ZSM-5 molecular sieve catalyst from a top main line through a preheater, feeding the rest methanol into the reactor in a lateral line multi-stage feeding mode, and controlling the reaction temperature to be 250-400 ℃, the pressure to be 0.5-2.0 MPa and the mass space velocity of the dimethylbenzene to be 0.2-2.0 h^-1The mass space velocity of the methanol is 0.2-1.0 h^-1To a durene-rich mixed hydrocarbon component;

s2, separating the durene-rich mixed hydrocarbon component by an oil-water separator, a liquefied gas removal tower, a product separation tower (separating components with boiling points lower than durene) and a purification tower (separating components with boiling points lower than xylene) to obtain water, dry gas, liquefied gas, durene-rich heavy aromatic hydrocarbon, C7-C9 aromatic hydrocarbon and C5-C6 light hydrocarbon;

s3, taking the dry gas as circulating gas to drive the raw materials in the reactor to flow; the C7-C9 aromatic hydrocarbon enters a raw material storage tank to be used as a reaction raw material;

s4, subjecting the durene-rich heavy aromatic hydrocarbons to multistage freezing crystallization and centrifugal separation squeezing system to obtain solid durene and heavy aromatic hydrocarbon raffinate;

s5, discharging the solid durene serving as a product out of the system, and feeding the heavy aromatic residual liquid into a mixed aromatic storage tank to serve as a reaction raw material.

The water is discharged out of the system through an oil-water separator; discharging the liquefied gas from the system through a liquefied gas removal tower; and C5-C6 light hydrocarbon is discharged out of the system through the purification tower.

Step S1 further includes mixing the dry gas with xylene and a portion of methanol, and passing the mixture through a preheater to enter the reactor from the top main line.

The modified nano ZSM-5 molecular sieve catalyst comprises a ZSM-5 molecular sieve carrier and active metal, wherein the grain size of the ZSM-5 molecular sieve carrier is 210 nm-300 nm, the active metal is one or more of zinc, iron, magnesium, calcium and rare earth elements, and the mass fraction of the active metal is 0.1-2.0%.

The xylene in the invention is from pure xylene or mixed aromatic hydrocarbon containing xylene, i.e. the pure xylene or mixed aromatic hydrocarbon containing xylene is used as reaction raw material.

Preferably, the reaction temperature in step S1 is 250-340 ℃.

The preparation method of the modified nano ZSM-5 molecular sieve catalyst comprises the following steps:

s1, uniformly mixing a silicon source, an aluminum source, an alkali source, n-butylamine, deionized water and ZSM-5 seed crystals to form a mixed solution, crystallizing the mixed solution at 40-190 ℃ for 12-120 h, and washing, drying and roasting a solid product obtained by crystallization to obtain a ZSM-5 molecular sieve carrier;

s2, carrying out alkali treatment, ammonium exchange, extrusion molding, acid treatment and metal salt solution impregnation on the ZSM-5 molecular sieve carrier in the step S1, and roasting to obtain the modified nano ZSM-5 molecular sieve catalyst;

OH in the step S1 Mixed liquid System (crystallization reaction System)^-:SiO₂:A1₂O₃The molar ratio of n-butylamine to water is 2-4:7-15:0.1-1:0.5-5: 300-1100.

Preferably OH in the mixed liquid system (crystallization reaction system) of step S1^-:SiO₂:A1₂O₃The molar ratio of n-butylamine to water is 2.3-3.5:10-13.5:1:2.5-5.5: 250-.

The silicon source is one or a mixture of tetraethyl orthosilicate, silica sol and water glass; the aluminum source is one or more of aluminum sulfate, aluminum isopropoxide and sodium metaaluminate; the alkali source is at least one of sodium hydroxide and potassium hydroxide.

Preferably, the seed crystal is added in the step S1 in an amount of 1-8% of the yield of the durene-producing catalyst.

Preferably, the crystallization temperature in the step S1 is 140-190 ℃, and the crystallization time is 12-120 h.

In the step S2, the alkali treatment is to soak the ZSM-5 molecular sieve carrier in an alkali solution at 60-90 ℃ for 15-200min, wherein the alkali solution is one or two of a sodium hydroxide solution and a potassium hydroxide solution, and the concentration of the alkali solution is 0.05-0.3 mol/L.

In the step S2, the ammonium exchange is to perform ion exchange on the ZSM-5 molecular sieve carrier subjected to alkali treatment for 30-200min at 60-90 ℃ by using ammonium nitrate, and the concentration of the ammonium nitrate solution is 0.05-0.3 mol/L.

In the step S2, the acid treatment is to soak the ion exchanged ZSM-5 molecular sieve carrier for 1-5h at 60-80 ℃, wherein the acid solution is one or more of sulfuric acid, hydrochloric acid, hydrofluoric acid and acetic acid, and the concentration of the acid solution is 0.1-2.0 mol/L.

In the step S2, the metal salt solution is one or more of copper nitrate, magnesium nitrate and zinc nitrate, and the mass fraction of the impregnated metal salt is 0.01-0.05%.

The method comprises the steps of mixing dimethylbenzene and part of methanol, feeding the mixture into a reactor from a main line at the top through a preheater, feeding the rest of methanol into the reactor (alkylation reactor) in a lateral line multistage feeding mode, reacting the materials at the temperature of 250-400 ℃ and under the pressure of 0.5-2.0 MPa to convert the materials into mixed hydrocarbon components rich in durene, and separating the mixed hydrocarbon components to obtain water, dry gas, liquefied gas, heavy aromatic hydrocarbons rich in durene, C7-C9 aromatic hydrocarbons and C5-C6 light hydrocarbons. The heavy aromatic hydrocarbon rich in durene is subjected to multistage freezing crystallization and centrifugal separation squeezing system to obtain solid durene and heavy aromatic hydrocarbon residual liquid with the purity of 97%, and the C7-C9 aromatic hydrocarbon and heavy aromatic hydrocarbon residual liquid are returned to the raw material storage tank. Wherein the durene content in the oil phase of the reacted mixed hydrocarbon component reaches 19 percent.

Compared with the prior durene synthesis technology, the method has the following advantages: 1) the reaction temperature is reduced, at present, the reaction temperature of trimethylbenzene and methanol is 350-400 ℃, under the condition of the same molar weight, xylene consumes one more methanol than trimethylbenzene, so that the reaction temperature is further increased to be unfavorable for reaction (the catalyst is easy to deposit carbon), and byproducts are increased, the temperature rise of a bed layer during alkylation can be controlled by a way of adding side-line methanol multi-stage feeding in the reactor, so that the reaction can be carried out at lower temperature and pressure, the reaction heat of an upper-stage bed layer of the reactor can be fully utilized to keep the temperature of a middle-stage bed layer and a last-stage bed layer, and the reaction temperature is further reduced, the reaction temperature is further reduced by using the modified nano ZSM-5 molecular sieve catalyst, and the reaction temperature can be stably controlled at 250-360 ℃ due to high specific surface, high activity and high stability, so that the byproducts are effectively reduced; xylene and mixed aromatics (C7-C9 aromatic hydrocarbon and heavy aromatic hydrocarbon raffinate) thereof and methanol are continuously subjected to alkylation reaction for many times, so that the selectivity of durene in an oil phase product is improved to 45%; C7-C9 aromatic hydrocarbon and heavy aromatic hydrocarbon residual liquid are returned to the raw material storage tank, and the yield of durene is improved by fully utilizing reaction byproducts and can reach 35 percent.

Drawings

FIG. 1 is a flow chart of the process for preparing durene from methanol and xylene according to the present invention;

wherein 1 is a reactor, 2 is an oil-water separator, 3 is a liquefied gas removal tower, 4 is a product separation tower, 5 is a purification tower, 6 is a freezing crystallization and centrifugal separation squeezing system, and 7 is a heavy aromatic hydrocarbon storage tank.

The invention is further illustrated by the following examples.

Detailed Description