Method for separating cresol mixture and synthesizing 2, 3, 6-tricresol by hydrocarbonylation method

Abstract

The invention discloses a method for separating a cresol mixture and synthesizing 2, 3, 6-tricresol by adopting an alkylation method, and relates to the technical field of separation of cresol mixtures. The technical problems that in the prior art, during alkylation separation of 2, 4, 2, 5-xylenol, the obtained 2, 5-xylenol is narrow in application and small in dosage, and the synthesis cost of 2, 3, 6-tricresol is relatively high are solved. According to the method, the isobutene reacts with the mixture of the 2, 4-xylenol and the 2, 5-xylenol to generate the 6-tert-butyl-2, 4-xylenol and the 4-tert-butyl-2, 5-xylenol, so that the partial separation of the 2, 4-xylenol and the 2, 5-xylenol is realized; and carrying out methylation reaction on the separated intermediate and methanol to generate 2, 3, 6-trimethylphenol. According to the method disclosed by the invention, the application range of the 2, 5-xylenol is remarkably widened, the use amount of the mixture of the 2, 4-xylenol and the 2, 5-xylenol is increased, and the dependency degree on m-cresol in the synthesis of the vitamin E is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of separation of cresol mixtures, and in particular to a method for separating the cresol mixtures and synthesizing 2,3,6-trimethylphenol by adopting an alkylation method. Background Art

[0002] The traditional methods for synthesizing 2,3,6-trimethylol mainly include: m-cresol is methylated with methanol in a fixed bed under the catalysis of an iron-based catalyst to produce 2,3,6-trimethylol (Northwest Institute of Chemical Technology, Shanxi Ruicheng Foster, etc.); phenol and p-tert-butylphenol are reacted with methanol in a fixed bed or fluidized bed in the presence of different positioned catalysts to obtain 2,3,6-trimethylol (Hubei Nengte Technology, etc.); 2,3,6-trimethylol is separated from coal tar mixed phenol. Due to the low content of 2,3,6-trimethylol in crude phenol and the large number of other phenol impurities with similar boiling points, there are technical problems such as great separation difficulty and low yield, so there are currently no research reports in this area in China.

[0003] There are more or less 2,4-dimethylphenol and 2,5-dimethylphenol in the crude phenol extracted from coking phenolic coal tar, pyrolysis and gasification phenolic coal tar, coal liquefaction phenolic tar, etc., and the crude phenol from gasification. Due to their similar boiling points, they cannot be separated by conventional distillation, and only a mixture of 2.4 and 2,5-dimethylphenol can be obtained. 2,4-dimethylphenol and 2,5-dimethylphenol are important pharmaceutical intermediates with certain value, so choosing an appropriate method to separate them has practical economic and social benefits.

[0004] 2,5-Dimethylphenol (CAS#95874) is an organic medicine and dye intermediate, used to synthesize lipid-lowering drug Gemfibrozil, vitamin E intermediate 2,3,6-trimethylphenol, etc. In the current prior art, the 2,5-dimethylphenol obtained by alkylation separation of 2,4 and 2,5-dimethylphenol has a narrow application and a small amount, while when 2,5-dimethylphenol is directly used to synthesize 2,3,6-trimethylphenol, there are more by-products (more useless substances such as 2,3,4,6-tetramethylphenol), and the separation requirements are high and the difficulty is also higher. Therefore, the technical problems existing in the above prior art limit the application of 2,5-dimethylphenol, and further limit the separation prospects of mixed 2,4 and 2,5-dimethylphenol. It is necessary to open up a new technical route for the separation of 2,4 and 2,5-dimethylphenol. Summary of the invention

[0005] The object of the present invention is to provide a method for separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by an alkylation method, which solves the technical problems in the prior art that 2,5-dimethylphenol obtained by alkylation separation of 2,4 and 2,5-dimethylphenol has a narrow application and a small amount, and also solves the technical problems that the cost of synthesizing 2,3,6-trimethylphenol by the prior art method is relatively high and the quality is relatively poor.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by an alkylation method, wherein the cresol mixture is a mixture of 2,4-xylenol and 2,5-xylenol, and the method comprises the following steps:

[0008] (1) reacting a cresol mixture, a strongly acidic polyacrylic acid resin and isobutylene to obtain 6-tert-butyl-2,4-dimethylphenol and 4-tert-butyl-2,5-dimethylphenol, filtering the filter cake resin, and distilling the filtrate obtained by filtration to obtain 4-tert-butyl-2,5-dimethylphenol with a mass fraction of 99.5%;

[0009] (2) adding a certain proportion of methanol to a bed reactor containing an iron-based catalyst mainly composed of iron oxide and carrying out a methylation reaction with the 4-tert-butyl-2,5-dimethylphenol, wherein when the reaction is complete, 4-tert-butyl-2,3,6-trimethylphenol is generated, and the unreacted methanol is recycled; when the reaction is incomplete, a mixture of 4-tert-butyl-2,3,6-trimethylphenol and 4-tert-butyl-2,5-dimethylphenol is generated;

[0010] (3) When the reaction of step (2) is complete, 4-tert-butyl-2,3,6-trimethylphenol is added to a bed reactor containing silicon oxide and an acidic alumina catalyst for adsorbing acidic substances, and isobutylene is removed at a certain temperature. After cooling, a crude 2,3,6-trimethylphenol is obtained, and 2,3,6-trimethylphenol with a mass fraction of more than 99.5% is obtained by distillation; when the reaction of step (2) is not complete, a mixture of 4-tert-butyl-2,3,6-trimethylphenol and 4-tert-butyl-2,5-xymethylphenol is added to a bed reactor containing silicon oxide and an acidic alumina catalyst for adsorbing acidic substances, and isobutylene is removed at a certain temperature. After cooling, a mixture of 2,3,6-trimethylphenol and 2,5-xymethylphenol is obtained, and 2,5-xymethylphenol with a mass fraction of 99.5% and 2,3,6-trimethylphenol with a mass fraction of 99.5% are obtained by distillation.

[0011] The above-mentioned method of separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by a hydrocarbonization method, wherein the mixture of 2,4-dimethylphenol and 2,5-dimethylphenol is derived from the extraction and purification of crude phenol from phenol-containing tar in coal liquefaction, coal gasification, and coal pyrolysis, and the extraction and purification of crude phenol from gasification condensate and wastewater; in step (1), the cresol mixture and a strongly acidic polyacrylic acid resin are reacted with isobutylene at a temperature of 100 to 120°C.

[0012] The above-mentioned method of separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by a hydrocarbonization method, wherein the mixture of 2,4-xylenol and 2,5-xylenol is derived from the extraction and purification of crude phenol from coal liquefaction phenol-containing tar, and the components in the mixture of 2,4-xylenol and 2,5-xylenol are composed of 0-1% of o-cresol, 0-5% of m-p-cresol, 90-100% of 2,4-xylenol and 2,5-xylenol, and 0-5% of 2,3-xylenol in terms of mass percentage.

[0013] In the above-mentioned method of separating a cresol mixture by hydrocarbonization and synthesizing 2,3,6-trimethylphenol, in step (2), the preparation method of the iron-based catalyst mainly composed of iron oxide is as follows: at least one of aluminum nitrate, iron nitrate and potassium nitrate is dissolved in water, the pH is adjusted to 7-9, the obtained precipitate is aged, filtered, washed and dried in sequence, and then silica sol is added for mixing and kneading, extruded into strips, and then dried and calcined.

[0014] The above-mentioned method of separating a cresol mixture by alkylation and synthesizing 2,3,6-trimethylphenol, in step (2), the temperature of the methylation reaction is 300-400°C, the molar ratio of 4-tert-butyl-2,5-dimethylphenol to methanol is 1:1-7; and the pH is adjusted by dripping ammonia water.

[0015] The above-mentioned method of separating the cresol mixture and synthesizing 2,3,6-trimethylphenol by alkylation has an aging time of 1 to 2 hours and is extruded into strips with a diameter of 1 to 2 mm and a length of 2 to 3 mm.

[0016] The above-mentioned method of separating the cresol mixture by alkylation and synthesizing 2,3,6-trimethylphenol has the following characteristics: the drying temperature is 110-130°C, the roasting temperature is 500-800°C; the methylation reaction temperature is 320-350°C, and the mass ratio of 4-tert-butyl-2,5-dimethylphenol to methanol is 1:3-5.

[0017] In the above-mentioned method of separating a cresol mixture by alkylation and synthesizing 2,3,6-trimethylphenol, in step (3), the temperature for removing isobutylene is 300-600° C., and the weight ratio of silicon oxide to acidic aluminum oxide is 0.5-10:1.

[0018] In the above-mentioned method of separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by alkylation, the temperature for removing isobutylene is 350-450° C., and the weight ratio of silicon oxide to acidic aluminum oxide is 2-5:1.

[0019] In the above-mentioned method of separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by alkylation, the bed reactor described in steps (2) and (3) is a fixed bed reactor, a fluidized bed reactor or an ebullient bed reactor.

[0020] Compared with the prior art, the present invention brings the following beneficial technical effects:

[0021] (1) The raw material mixture of 2,4-dimethylphenol and 2,5-dimethylphenol of the present invention has a wide range of sources, and can be derived from the refining of crude phenol from gasification and water, can also be derived from the refining of crude phenol extracted from phenol-containing coal tar directly or indirectly liquefied from coal, and can also be derived from the refining of crude phenol extracted from phenol-containing coal tar by pyrolysis of coal, and has a wide range of applications.

[0022] (2) The method of the present invention uses solid catalysts throughout, has good methylation selectivity, high yield of target products, few side reactions, simple separation after reaction, very little three wastes, easy to achieve continuous operation, and high overall efficiency.

[0023] (3) The present invention utilizes isobutylene to react with a mixture of 2,4-dimethylphenol and 2,5-dimethylphenol to generate 6-tert-butyl-2,4-dimethylphenol and 4-tert-butyl-2,5-dimethylphenol, thereby achieving partial separation of 2,4-dimethylphenol and 2,5-dimethylphenol; wherein the separated intermediate 4-tert-butyl-2,5-dimethylphenol has high purity (can reach 99.5%), and 4-tert-butyl-2,5-dimethylphenol is catalyzed by methanol to produce The selectivity of 2,3,6-trimethylphenol is significantly better than that of the reaction of m-cresol, 2,5-xylenol, 2,3-xylenol with methanol. The production of other trimethylols and tetramethylols is very small, and the product purity is significantly better than that of several other methods for synthesizing 2,3,6-trimethylphenol. This can significantly broaden the application of 2,5-xylenol, increase the use of a mixture of 2,4-xylenol and 2,5-xylenol, and reduce the dependence on m-cresol in the synthesis of vitamin E.

[0024] (4) The present invention can produce 99.5% high-purity 2,5-xylenol and 2,3,6-trimethylphenol at the same time as required. It is only necessary to control the conversion rate of 4-tert-butyl-2,5-xylenol to 4-tert-butyl-2,3,6-trimethylphenol within a required range. The mixture of 4-tert-butyl-2,5-xylenol in incomplete methylation reaction and methylation product 4-tert-butyl-2,3,6-trimethylphenol is subjected to de-tert-butylation reaction to remove isobutylene to obtain a mixture of 2,5-xylenol and 2,3,6-trimethylphenol, and finally distilled to obtain high-purity 2,5-xylenol and 2,3,6-trimethylphenol. DETAILED DESCRIPTION

[0025] The present invention proposes a method for separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by an alkylation method. In order to make the advantages and technical solutions of the present invention clearer and more specific, the present invention is further described below in conjunction with specific embodiments.

[0026] The mixture of raw materials 2,4-xylenol and 2,5-xylenol described in the present invention is derived from the extraction and refining of crude phenol from phenol-containing tar in coal liquefaction, coal gasification and coal pyrolysis, and the extraction and refining of crude phenol from gasification condensed water and wastewater. It is preferably derived from the extraction and refining of crude phenol from phenol-containing tar in coal liquefaction. In terms of mass percentage, the mixture of 2,4-xylenol and 2,5-xylenol consists of: 0-1% of o-cresol, 0-5% of m-cresol, 90-100% of 2,4-xylenol and 2,5-xylenol, and 0-5% of 2,3-xylenol; preferably 0-2% of m-cresol, 96-100% of 2,4-xylenol and 2,5-xylenol, and 0-2% of 2,3-xylenol.

[0027] Unless otherwise specified, the raw materials described in the present invention can be purchased through commercial channels.

[0028] The main technical concept of the present invention is as follows: First, in the prior art, when 2,5-dimethylphenol is directly used to synthesize 2,3,6-trimethylphenol, more by-products are produced, and the separation requirements and difficulty are high; however, the present application uses 4-tert-butyl-2,5-dimethylphenol and methanol to react to produce 2,3,6-trimethylphenol, which can better avoid these problems, and the produced 2,3,6-trimethylphenol has high purity and reliable quality. Second, 2,3,6-trimethylphenol is a raw material for synthesizing 2,3,5-trimethylhydroquinone, the main ring of vitamin E, and is also a raw material for synthesizing 2,3,5-trimethylphenol, a pharmaceutical intermediate. This further expands the use of 2,5-dimethylphenol obtained by alkylation and separation of 2,4 and 2,5-dimethylphenol, and solves the technical problems of its narrow use and small dosage.

[0029] A method for separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by an alkylation method, the method specifically comprising the following steps:

[0030] Step 1: Synthesis of 4-tert-butyl-2,5-dimethylphenol by alkylation

[0031] A mixture of 2,4-dimethylphenol and 2,5-dimethylphenol and a strongly acidic polyacrylic acid resin are put into a reactor, and isobutylene is introduced at a temperature of 100-120° C. to react to obtain 6-tert-butyl-2,4-dimethylphenol and 4-tert-butyl-2,5-dimethylphenol, and the filter cake is filtered and the resin is used, and the filtrate is distilled to obtain 4-tert-butyl-2,5-dimethylphenol with a mass percentage of 99.5%.

[0032] Step 2: Preparation of catalyst and synthesis of 4-tert-butyl-2,3,6-trimethylphenol

[0033] Preparation of catalyst: chemically pure aluminum nitrate, iron nitrate, potassium nitrate and one or more nitrates of other promoters are dissolved in distilled water under stirring, and ammonia water is added dropwise to pH 7-9. The resulting precipitate is aged for 1-2 hours, filtered, washed, and dried, and silica sol (30%) is added and kneaded. The catalyst is extruded into strips with a diameter of 1-2 mm and a length of 2-3 mm, and then dried at 120°C overnight and calcined at 500-800°C to obtain an iron-based catalyst mainly composed of iron oxide. In the obtained iron-based catalyst, Al:Fe=0-1:1 (mol).

[0034] Synthesis of 4-tert-butyl-2,3,6-trimethylphenol: In a bed reactor equipped with the above-mentioned iron-based catalyst mainly composed of iron oxide, at a temperature of 300-400°C, preferably at a temperature of 320-350°C, a mixed solution of 4-tert-butyl-2,5-dimethylphenol and methanol in a molar ratio of 1:1-7, preferably a molar ratio of 1:3-5, is pumped into the bed reactor by a metering pump to perform a methylation reaction to generate 4-tert-butyl-2,3,6-trimethylphenol, and the generated gas is condensed by a condenser and subjected to gas-liquid separation to remove volatile gases such as methanol to obtain a cooled warm liquid material 4-tert-butyl-2,3,6-trimethylphenol solution, and the uncondensed methanol is cooled by a first-level water cooling and a first-level refrigerant cooling to obtain liquid methanol for application. The temperature of the warm liquid material is 80-250°C, preferably 150-200°C.

[0035] When the methylation reaction of 4-tert-butyl-2,5-dimethylphenol is incomplete, the warm liquid material obtained after cooling down is a mixture of 4-tert-butyl-2,3,6-trimethylphenol and 4-tert-butyl-2,5-dimethylphenol.

[0036] Step 3: When the reaction is complete, 2,3,6-trimethylphenol is prepared

[0037] The 4-tert-butyl-2,3,6-trimethylphenol solution obtained when the reaction in step 2 is completed is pumped into a bed reactor filled with silicon oxide for adsorbing acidic substances and acidic alumina catalyst by a metering pump, and isobutylene is removed at a certain temperature. The product after cooling is crude 2,3,6-trimethylphenol, which is then distilled to obtain 2,3,6-trimethylphenol with a mass fraction of more than 99.5%.

[0038] When the reaction is not complete, 2,3,6-trimethylphenol and 2,5-dimethylphenol are prepared

[0039] The above-mentioned 4-tert-butyl-2,3,6-trimethylphenol and 4-tert-butyl-2,5-xylenol solutions are pumped into a bed reactor filled with silicon oxide and acidic alumina catalyst for adsorbing acidic substances by a metering pump, the weight ratio of silicon oxide to acidic alumina is 0.5-10:1, preferably 2-5:1, and isobutylene is removed at a temperature of 300-600°C, preferably 350-450°C. After cooling, the product is a mixture of 2,3,6-trimethylphenol and 2,5-xylenol, which is then distilled to obtain 99.5% by mass of 2,5-xylenol and 99.5% by mass of 2,3,6-trimethylphenol.

[0040] The bed reactor in the above steps 2 and 3 is a fixed bed reactor, a fluidized bed reactor or an ebullient bed reactor, preferably a fixed bed reactor.

[0041] Embodiment 1:

[0042] A method for separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by an alkylation method, the method specifically comprising the following steps:

[0043] Step 1: Synthesis of 4-tert-butyl-2,5-dimethylphenol by alkylation

[0044] In a 1000mL four-necked bottle, add 2000g of cresol mixture (containing 61.5% of 2,4-dimethylphenol and 38.5% of 2,5-dimethylphenol) and 200g of strongly acidic acrylic resin, replace with nitrogen three times, start stirring, heat the oil bath to 90°C and start passing 1800g of isobutylene for 8 hours. After the dripping is completed, keep warm for 2 hours and take samples for analysis. The 2,4-dimethylphenol content is 0.18%, which is qualified. Recover 754g of isobutylene for application; filter, apply solid catalyst, add distillation to the material layer In the kettle, 121.3 g of the first portion was distilled off at 10 KPa, and then vacuum distilled to obtain 1737.1 g of 6-tert-butyl-2,4-dimethylphenol with a mass fraction of 99.6%, 75.5 g of the intermediate fraction (28.6 g of 6-tert-butyl-2,4-dimethylphenol and 46.3 g of 4-tert-butyl-2,5-dimethylphenol), 955.8 g of 4-tert-butyl-2,5-dimethylphenol with a mass fraction of 99.5%, and 106.5 g of the kettle residue (105.7 g of 4-tert-butyl-2,5-dimethylphenol).

[0045] Step 2: Preparation of catalyst and synthesis of 4-tert-butyl-2,3,6-trimethylphenol

[0046] 2000 parts of chemically pure iron nitrate, 800 parts of aluminum nitrate and 200 parts of potassium nitrate were added to a preparation kettle, dissolved in 12000 parts of distilled water under stirring, and ammonia water was added dropwise to pH 7-9. The obtained precipitate was aged for 1-2 hours, filtered, washed and dried, and 2000 parts of silica sol (30%) were added and kneaded, and extruded into strip catalysts with a diameter of 1-2 mm (length of 2-3 mm), and then dried at 110-120°C for 12 hours, and calcined and activated at 500-800°C for 8 hours to obtain 1502 parts of a catalyst composed of iron and aluminum oxides. Fe:Al:K in the obtained catalyst is 1:0.45:0.24 (mol).

[0047] In a fixed-bed reactor with a built-in cooling tube (inner tube diameter 25 mm, height 2000 mm, outer tube diameter 32 mm, a jacket formed between the inner and outer tubes, steam or hot water heating, cooling tube is a copper tube with a diameter of 6 mm), 300 g of a catalyst composed of iron aluminum oxide is loaded into the inner tube, circulating water is appropriately introduced into the cooling tube according to the reaction needs to transfer the reaction heat, and 1017 g of a mixture of 4-tert-butyl-2,5-xylenol and methanol (535 g 4-tert-butyl-2,5-xylenol, 482 g methanol) with a mass fraction of 99.5% obtained by alkylation and separation of the cresol mixture is pumped into the The reaction is carried out in a fixed bed reactor preheated to 350°C, with 4-tert-butyl-2,5-dimethylphenol:methanol=1:5 (molar ratio), the feed rate is controlled to 200g / h, and the temperature is adjusted to about 320°C so that the 4-tert-butyl-2,5-dimethylphenol content detected at the discharge port is 0.38%, and the tetramethylphenol content is 0.11%. The material is initially condensed by a condenser and then separated by a gas-liquid separator. The obtained warm liquid at about 180°C is 556.4g of crude 4-tert-butyl-2,3,6-trimethylphenol with a content of 97.6%. The uncondensed methanol gas is condensed by a primary water cooling and a primary refrigerant to obtain methanol for use.

[0048] Step 3: Preparation of 2,3,6-trimethylphenol

[0049] In another fixed-bed reactor with a built-in cooling tube (inner tube diameter 18 mm, height 1500 mm, outer tube diameter 25 mm, a jacket is formed between the inner and outer tubes, steam or hot water is passed for heating, and the cooling tube is a copper tube with a diameter of 6 mm), circulating water is appropriately introduced into the cooling tube to control the reaction temperature, and the inner tube is filled with thin strips of small solids kneaded by aluminum oxide and silicon dioxide (50 g of acidic aluminum oxide and 100 g of silicon oxide). 556.4 g of the slightly cooled hot liquid (4-tert-butyl-2,3,6-trimethylphenol content 97.6%) from the previous step is pumped into the fixed bed reaction by a peristaltic pump. The fixed bed temperature is 400° C. The reaction product coming out of the fixed bed reactor is cooled and enters a 2000 mL four-necked receiving bottle. The isobutylene produced by the reaction is returned to the 2,4,2,5-dimethylphenol alkylation synthesis reactor. The condensate is vacuum distilled to obtain 378.5 g of 2,3,6-trimethylphenol with a mass fraction of 99.7% and a yield of 92.8%.

[0050] Embodiment 2:

[0051] A method for separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by an alkylation method, the method specifically comprising the following steps:

[0052] Step 1: Synthesis of 4-tert-butyl-2,5-dimethylphenol by alkylation

[0053] In a 1000mL four-necked bottle, add 2000g mixed xylenol (containing 61.5% 2,4-xylenol and 38.5% 2,5-xylenol) and 200g strongly acidic acrylic resin, replace with nitrogen three times, start stirring, heat the oil bath to 90°C and start passing 1800g isobutylene for 8 hours. After the dripping is completed, keep warm for 2 hours and take samples for analysis. The 2,4-xylenol content is 0.18%, which is qualified. Recover 754g isobutylene for application; filter, apply solid catalyst, add distillation to the material layer In the kettle, 121.3 g of the first portion was distilled off at 10 KPa, and then vacuum distilled to obtain 1737.1 g of 6-tert-butyl-2,4-dimethylphenol with a mass fraction of 99.6%, 75.5 g of the intermediate fraction (28.6 g of 6-tert-butyl-2,4-dimethylphenol and 46.3 g of 4-tert-butyl-2,5-dimethylphenol), 955.8 g of 4-tert-butyl-2,5-dimethylphenol with a mass fraction of 99.5%, and 106.5 g of the kettle residue (105.7 g of 4-tert-butyl-2,5-dimethylphenol).

[0054] Step 2: Synthesis of 4-tert-butyl-2,3,6-trimethylphenol

[0055] The preparation method of the catalyst is the same as the preparation method of the catalyst in Example 1 above.

[0056] In a fixed bed reactor with a built-in cooling tube (inner tube diameter 25 mm, height 2000 mm, outer tube diameter 32 mm, a jacket formed between the inner and outer tubes, steam or hot water heating, cooling tube is a copper tube with a diameter of 6 mm), 300 g of a catalyst composed of iron aluminum oxide is loaded into the inner tube, circulating water is appropriately introduced into the cooling tube according to the reaction needs to transfer the reaction heat, and 570 g (420 g) of a mixture of 4-tert-butyl-2,5-dimethylphenol and methanol with a mass fraction of 99.5% obtained by alkylation and separation of 2,4,2,5-dimethylphenol is stirred by a peristaltic pump. 4-tert-butyl-2,5-dimethylphenol and methanol (150 g) were introduced into a fixed bed reactor preheated to 300°C for reaction, 4-tert-butyl-2,5-dimethylphenol: methanol = 1:2 (molar ratio), the feed rate was controlled at 100 g / h, the temperature was adjusted at about 300°C, the content of 4-tert-butyl-2,5-dimethylphenol was detected at the outlet and was 34.6%, the material was preliminarily condensed by the condenser and then separated by the gas-liquid separator, and the obtained warm liquid at about 220°C was a mixture of 4-tert-butyl-2,5-dimethylphenol and 4-tert-butyl-2,3,6-trimethylphenol (164.9 g of 4-tert-butyl-2,5-dimethylphenol, 265.8 g of 4-tert-butyl-2,3,6-trimethylphenol, and 5.1 g of others); the uncondensed methanol gas was condensed by primary water cooling and primary refrigerant to obtain methanol for use.

[0057] Step 3: Synthesis of 2,5-dimethylphenol and 2,3,6-trimethylphenol

[0058] In another fixed bed reactor with a built-in cooling tube (inner tube diameter 18 mm, height 1500 mm, outer tube diameter 25 mm, inner and outer tubes formed a jacket, steam or hot water heating, cooling tube is a copper tube with a diameter of 6 mm), circulating water is appropriately introduced into the cooling tube to control the reaction temperature, the inner tube is filled with thin strips of small solids kneaded by acidic alumina and silicon dioxide (acidic alumina 50 g, silicon dioxide 100 g), and a peristaltic pump is used to pump 435.8 g of the hot liquid (4-tert-butyl 2,5-dimethylphenol 164. 9g, 4-tert-butyl-2,3,6-trimethylphenol 265.8g, and the rest 5.1g) were pumped into a fixed bed for reaction at a fixed bed temperature of 400°C. The reaction product coming out of the fixed bed reactor was cooled and entered into a 500mL four-necked receiving bottle. The isobutylene produced by the reaction was returned to the 2,4,2,5-dimethylphenol alkylation synthesis reactor. The condensate was distilled under reduced pressure at 10KPa to obtain 104.3g of 2,5-dimethylphenol with a mass fraction of 99.8% and 154.4g of 2,3,6-trimethylphenol with a mass fraction of 99.5%.

[0059] Embodiment 3:

[0060] A method for separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by an alkylation method, the method specifically comprising the following steps:

[0061] Step 1: Synthesis of 4-tert-butyl-2,5-dimethylphenol by alkylation

[0062] In a 1000mL four-necked bottle, add 2000g mixed xylenol (containing 61.5% 2,4-xylenol and 38.5% 2,5-xylenol) and 200g strongly acidic acrylic resin, replace with nitrogen three times, start stirring, heat the oil bath to 90°C and start passing 1800g isobutylene for 8 hours. After the dripping is completed, keep warm for 2 hours and take samples for analysis. The 2,4-xylenol content is 0.18%, which is qualified. Recover 754g isobutylene for application; filter, apply solid catalyst, add distillation to the material layer In the kettle, 121.3 g of the first portion was distilled off at 10 KPa, and then vacuum distilled to obtain 1737.1 g of 6-tert-butyl-2,4-dimethylphenol with a mass fraction of 99.6%, 75.5 g of the intermediate fraction (28.6 g of 6-tert-butyl-2,4-dimethylphenol and 46.3 g of 4-tert-butyl-2,5-dimethylphenol), 955.8 g of 4-tert-butyl-2,5-dimethylphenol with a mass fraction of 99.5%, and 106.5 g of the kettle residue (105.7 g of 4-tert-butyl-2,5-dimethylphenol).

[0063] Step 2: Synthesis of 4-tert-butyl-2,3,6-trimethylphenol

[0064] The preparation method of the catalyst is the same as the preparation method of the catalyst in Example 1 above.

[0065] In a fixed-bed reactor with a built-in cooling tube (inner tube diameter 25 mm, height 2000 mm, outer tube diameter 32 mm, a jacket formed between the inner and outer tubes, steam or hot water heating, the cooling tube is a copper tube with a diameter of 6 mm), 300 g of a catalyst composed of iron aluminum oxide was loaded into the inner tube, circulating water was appropriately introduced into the cooling tube to transfer the reaction heat according to the reaction needs, and 164.5 g of a mixture of the kettle residue (4-tert-butyl-2,5-xylenol) and methanol obtained by alkylation and separation of 2,4 and 2,5-xylenol [106.5 g of kettle residue (105.7 g of 4-tert-butyl-2,5-xylenol), 58 g of methanol] was pumped into the reactor by a peristaltic pump. The mixture was fed into a fixed bed reactor preheated to 300°C for reaction, with 4-tert-butyl-2,5-dimethylphenol:methanol=1:3 (molar ratio), the feed rate was controlled at 50g / h, the temperature was adjusted at about 350°C, the content of 4-tert-butyl-2,5-dimethylphenol was detected at the outlet and it was 0.43%, the material was preliminarily condensed by the condenser and then separated by the gas-liquid separator, and the obtained warm liquid at about 200°C was 113.1g of 4-tert-butyl-2,3,6-trimethylphenol mixture (110.6g of 4-tert-butyl-2,3,6-trimethylphenol and 2.5g of others); the uncondensed methanol gas was condensed by primary water cooling and primary refrigerant to obtain methanol for use.

[0066] Step 3: Synthesis of 2,5-dimethylphenol and 2,3,6-trimethylphenol

[0067] In another fixed bed reactor with a built-in cooling tube (inner tube diameter 18 mm, height 1500 mm, outer tube diameter 25 mm, inner and outer tubes formed a jacket, steam or hot water heating, cooling tube is a copper tube with a diameter of 6 mm), the cooling tube is appropriately introduced with circulating water to control the reaction temperature, the inner tube is filled with thin strips of small solids kneaded from acidic alumina and silicon dioxide (125 g of acidic alumina, 25 g of silicon dioxide, silicon dioxide: acidic alumina = 1:5), and the above step is pumped into the reactor by a peristaltic pump. After being cooled slightly, 113.1 g of hot liquid (110.6 g of 4-tert-butyl-2,3,6-trimethylphenol and 2.5 g of the others) was pumped into a fixed bed reactor. The fixed bed temperature was 400°C. The reaction product coming out of the fixed bed reactor was cooled and entered into a 500 mL four-necked receiving bottle. The isobutylene produced by the reaction was returned to the 2,4,2,5-dimethylphenol alkylation synthesis reactor. The condensate was distilled under reduced pressure at 10 KPa to obtain 71.7 g of 2,3,6-trimethylphenol with a mass fraction of 99.6%.

[0068] Parts not described in the present invention can be implemented by referring to the existing technology.

[0069] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not intended to be limiting of the present application. As long as they are within the spirit and scope of the present application, appropriate changes and modifications to the above embodiments are within the scope of protection of the claims of the present application.

Claims

1. A method for separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by an alkylation method, wherein the cresol mixture is a mixture of 2,4-xylenol and 2,5-xylenol, characterized in that: The method comprises the following steps: (1) reacting a cresol mixture, a strongly acidic polyacrylic acid resin and isobutylene to obtain 6-tert-butyl-2,4-dimethylphenol and 4-tert-butyl-2,5-dimethylphenol, filtering the filter cake resin, and distilling the filtrate obtained by filtration to obtain 4-tert-butyl-2,5-dimethylphenol with a mass fraction of 99.5%; (2) adding a certain proportion of methanol to a bed reactor containing an iron-based catalyst mainly composed of iron oxide and carrying out a methylation reaction with the 4-tert-butyl-2,5-dimethylphenol, wherein when the reaction is complete, 4-tert-butyl-2,3,6-trimethylphenol is generated, and the unreacted methanol is recycled; when the reaction is incomplete, a mixture of 4-tert-butyl-2,3,6-trimethylphenol and 4-tert-butyl-2,5-dimethylphenol is generated; (3) When the reaction of step (2) is complete, 4-tert-butyl-2,3,6-trimethylphenol is added to a bed reactor containing silicon oxide for adsorbing acidic substances and an acidic alumina catalyst, and isobutylene is removed at a certain temperature. After cooling, a crude 2,3,6-trimethylphenol is obtained, and a mass fraction of 2,3,6-trimethylphenol of more than 99.5% is obtained by distillation; When the reaction of step (2) is incomplete, a mixture of 4-tert-butyl-2,3,6-trimethylphenol and 4-tert-butyl-2,5-xylenol is added to a bed reactor containing silicon oxide for adsorbing acidic substances and an acidic alumina catalyst, and isobutylene is removed at a certain temperature. After cooling, a mixture of 2,3,6-trimethylphenol and 2,5-xylenol is obtained, and 2,5-xylenol with a mass fraction of 99.5% and 2,3,6-trimethylphenol with a mass fraction of 99.5% are obtained by distillation.

2. The method of claim 1, wherein the methylphenol mixture is separated and synthesized by alkylation method, wherein: The mixture of 2,4-xylenol and 2,5-xylenol is derived from the extraction and purification of crude phenol from phenol-containing tar in coal liquefaction, coal gasification and coal pyrolysis, and the extraction and purification of crude phenol from gasification condensate and wastewater; in step (1), the cresol mixture and strongly acidic polyacrylic acid resin are reacted with isobutylene at a temperature of 100-120°C.

3. The method of claim 2, wherein the methylphenol mixture is separated and synthesized by alkylation method, wherein: The mixture of 2,4-dimethylphenol and 2,5-dimethylphenol is derived from the extraction and refining of crude phenol from coal liquefaction phenol-containing tar. In terms of mass percentage, the components in the mixture of 2,4-dimethylphenol and 2,5-dimethylphenol are as follows: 0-1% of o-cresol, 0-5% of m-para-cresol, 90-100% of 2,4-dimethylphenol and 2,5-dimethylphenol, and 0-5% of 2,3-dimethylphenol.

4. The method of claim 1, wherein: In step (2), the preparation method of the iron-based catalyst mainly composed of iron oxide is as follows: at least one of aluminum nitrate, iron nitrate and potassium nitrate is dissolved in water, the pH is adjusted to 7-9, the obtained precipitate is aged, filtered, washed and dried in sequence, and then silica sol is added and kneaded, extruded into strips, and then dried and calcined.

5. The method of claim 4, wherein: In step (2), the temperature of the methylation reaction is 300-400° C., the molar ratio of 4-tert-butyl-2,5-dimethylphenol to methanol is 1:1-7; and the pH is adjusted by dripping ammonia water.

6. A method for separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by alkylation according to claim 4 or 5, characterized in that: The aging time is 1 to 2 hours, and the product is extruded into strips with a diameter of 1 to 2 mm and a length of 2 to 3 mm.

7. A method for separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by alkylation according to claim 4 or 5, characterized in that: The drying temperature is 110-130°C, the roasting temperature is 500-800°C; the temperature of the methylation reaction is 320-350°C, and the mass ratio of 4-tert-butyl-2,5-dimethylphenol to methanol is 1:3-5.

8. The method of claim 1 for separating a cresol mixture and synthesizing 2,3,6-trimethylphenol by alkylation, characterized in that: In step (3), the temperature for removing isobutylene is 300-600° C., and the weight ratio of silicon oxide to acidic aluminum oxide is 0.5-10:

1.

9. The method of claim 7, wherein: The temperature for removing isobutylene is 350-450°C, and the weight ratio of silicon oxide to acidic aluminum oxide is 2-5:

1.

10. The method of claim 1, wherein: The bed reactor in steps (2) and (3) is a fixed bed reactor, a fluidized bed reactor or an ebullating bed reactor.