Method for refining 2, 3, 5-tricresol and 3-methyl-5-ethyl phenol from tricresol mixture

Abstract

The invention belongs to the technical field of coking product extraction and organic separation, and particularly relates to a method for refining 2, 3, 5-tricresol and 3-methyl-5-ethyl phenol from a tricresol mixture. According to the method for refining the 2, 3, 5-tricresol and the 3-methyl-5-ethyl phenol from the tricresol mixture, the tricresol mixture is rectified to obtain the mixed tricresol, the mixed tricresol and the isobutene are subjected to the tert-butylation reaction under the action of the catalyst, and due to the fact that the 2, 3, 5-tricresol and the 3-methyl-5-ethyl phenol do not react with the isobutene, the 2, 3, 5-tricresol and the 3-methyl-5-ethyl phenol are not reacted with the isobutene. The method comprises the following steps: taking 2, 3, 5-trimethylphenol as a raw material, reacting other phenols with isobutene to generate corresponding tert-butyl phenol, boiling point of a tert-butyl product is obviously higher than that of 2, 3, 5-trimethylphenol and 3-methyl-5-ethyl phenol, performing rectification to obtain a 3-ethyl-5-cresol crude product and a 2, 3, 5-trimethylphenol crude product, and performing solvent refining and melt crystallization to obtain 3-ethyl-5-cresol of which the content is greater than or equal to 99% and 2, 3, 5-trimethylphenol of which the content is greater than or equal to 99%.

Description

Technical Field

[0001] The invention belongs to the technical field of coking product extraction and organic separation, and specifically relates to a method for refining 2,3,5-trimethylol and 3-methyl-5-ethylphenol from a trimethylol mixture. Background Art

[0002] Crude phenol is distilled to obtain phenol, o-cresol, tri-mixed cresols, m-cresol containing 55% meta-position, 99% m-cresol, and industrial xylenol. They are sold directly as products without good fine separation. In fact, m-cresol, 2,4 / 2,5-xylenol, 3,5-xylenol / m-p-ethylphenol, m-p-ethylphenol, and industrial xylenol can be further treated, distilled, refined, crystallized, alkylated and separated to obtain PU-grade 3,5-xylenol, mixed m-p-ethylphenol, 99% 2,4-xylenol, more than 99% 2,5-xylenol, 99% 3,5-xylenol, 98% 3,4-xylenol, m-ethylphenol, 99% p-ethylphenol and the like and corresponding extended products. After extracting the remaining materials of the above products, tri-mixed cresols, m-p-cresol, and industrial xylenol, which are by-products, are sold directly as products and can also be used to synthesize phenolic resins, insulating varnishes, and the like. At the same time, the crude phenol residue after distillation of xylenol can also collect the industrial trimethylol fraction at 226-240°C, and further extract other useful components such as 2,3,5-trimethylol, 3-methyl-5-ethylphenol, 4-ethyl-3-methylphenol, and m-p-isopropylphenol.

[0003] 2,3,5-Trimethylphenol is an important pharmaceutical intermediate for the preparation of aromatic retinoic acid, amino acid protective agent acitretin, etc. It can be separated from tar fractions, petroleum fractions and mixed phenols, but these sources are limited in quantity and purity. Therefore, it is difficult to use it as a raw material for aromatic retinoic acid, amino acid protective agents, etc.

[0004] 3-Methyl-5-ethylphenol is an important organic intermediate and is widely used in the fields of medicine, pesticides, fine chemicals, daily chemicals, etc.

[0005] The contents of 2,3,5-trimethylphenol and 3-methyl-5-ethylphenol in gasified crude phenol are approximately 0.15% and 0.25% respectively. There are approximately 30 tons and 50 tons of 2,3,5-trimethylphenol and 3-methyl-5-ethylphenol in 20,000 tons of crude phenol (taking Xinjiang Qinghua Energy's crude phenol as an example). Therefore, the quantity is relatively small. However, the market prices of 2,3,5-trimethylphenol and 3-methyl-5-ethylphenol are both above 300,000 yuan / ton. The prices are high, so there is a certain extraction value. If they are sold as phenol residues, it would be a waste of raw materials. Therefore, it is necessary to develop the extraction process of 2,3,5-trimethylphenol and 3-methyl-5-ethylphenol.

[0006] The main method for traditional synthesis of 2,3,5-trimethylphenol is to react 3,5-xylenol with methanol in a fixed bed under the catalysis of an iron-based catalyst to produce 2,3,5-trimethylphenol (Northwest Institute of Chemical Industry, Shanxi Ruicheng Foster, Shangyu Shenghui Chemical Co., Ltd., etc.), with a large amount of 2,3,5,6-tetramethylphenol as a by-product. This part of tetramethylphenol currently has no market and can only be treated as hazardous waste or fuel. It has very low value and needs to be treated. There are also methods such as the by-product 2,3,5-trimethylphenol when synthesizing 3,5-xylenol with isophorone at high temperature catalysis, and Harbin Yilan Zhongtai Chemical Co., Ltd. extracting 2,3,5-trimethylphenol from crude phenol distillation residue at 232-235°C. Currently, a relatively simple method is the 2,3,6-trimethylphenol catalytic transposition process for synthesizing 2,3,5-trimethylphenol at room temperature and pressure developed by Shangyu Shenghui Chemical Co., Ltd., with a yield of more than 92%. This process is simpler, more convenient, and has a higher yield and lower cost than the pressurized proton acid catalytic transposition reaction of 2,3,6-trimethylphenol developed by the Institute of Fine Chemicals of the Northwest Research Institute of Chemical Technology. However, this process will also produce a small amount of 2,3,5,6-tetramethylphenol as a by-product.

[0007] CN101580459A uses phenol residue as raw material, cuts into fractions, recrystallizes and centrifuges multiple times, then washes, centrifuges and dries to obtain 3-methyl-5-ethylphenol. However, since the content of 3-methyl-5-ethylphenol in crude phenol obtained by gasification of different coals varies greatly, and there are many phenols with similar boiling points, the method of direct distillation and solvent crystallization can only be applied to the residue of a small amount of crude phenol raw material distillation, and the yield is very low. The process is highly dependent on raw materials, so there is still no industrial device. Summary of the invention

[0008] The present invention is based on the inventor's discovery and understanding of the following facts and problems:

[0009] At present, there are certain amounts of phenol materials such as 2,3,5-trimethylol, 3-ethyl-5-methylol, 2-ethyl-3-methylol, 2,4,5-trimethylol, 2,3,4-trimethylol, 3-ethyl-4-methylol, and m-isopropylphenol in the residues of crude phenol refining phenol, cresol, and xylenol. The boiling points of these materials are not much different, and it is impossible to obtain pharmaceutical grade high-purity 2,3,5-trimethylol, 3-ethyl-5-methylphenol, and other products by distillation.

[0010] At present, the coking crude phenol distillation residue and the xylenol distillation residue are basically used as fuel oil, and the 2,3,5-trimethylphenol and 3-methyl-5-ethylphenol therein are not extracted. Even if 2,3,5-trimethylphenol and 3-methyl-5-ethylphenol are produced by multiple distillation, cutting and repeated crystallization as mentioned in the patent of Harbin Yilan Zhongtai Chemical Co., Ltd., the extraction rate is low and the requirements for crude phenol raw materials are high. The crude phenol must contain relatively high content of 2,3,5-trimethylphenol and 3-methyl-5-ethylphenol, and the content of meta-p-propylphenol, isopropylphenol, 3-ethyl-2-methylphenol, 4-ethyl-3-methylphenol, 2,3,4-trimethylphenol, 2,4,5-trimethylphenol and the like with similar boiling points must be very low. This is difficult to achieve in gasified crude phenol and medium and low temperature crude phenol. Therefore, it is very difficult to extract high-content 2,3,5-trimethylphenol and 3-methyl-5-ethylphenol fractions using the patented method, and in actual production, it is impossible to guarantee a large-scale supply of raw materials that meet the requirements.

[0011] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, an embodiment of the present invention provides a method for refining 3-methyl-5-ethylphenol and 2,3,5-trimethylphenol from a trimethylphenol mixture, the method utilizes that 2,3,5-trimethylphenol and 3-methyl-5-ethylphenol do not react with isobutylene, and other phenols react with isobutylene to generate corresponding tert-butylphenol, the boiling point of the tert-butylated product is significantly higher than that of 2,3,5-trimethylphenol and 3-methyl-5-ethylphenol, and crude 3-ethyl-5-methylphenol and crude 2,3,5-trimethylphenol are obtained by distillation, and then ≥99% 3-ethyl-5-methylphenol and ≥99% 2,3,5-trimethylphenol are obtained by solvent refining and melt crystallization.

[0012] A method for refining 3-methyl-5-ethylphenol and 2,3,5-trimethylphenol from a trimethylphenol mixture according to an embodiment of the present invention is characterized by comprising the following steps:

[0013] (1) subjecting the trimethylol mixture to a rectification treatment to obtain a mixed trimethylol;

[0014] (2) subjecting the mixed trimethylol, catalyst and isobutylene obtained in step (1) to a tertiary butylation reaction;

[0015] (3) washing the substance obtained in step (2) to obtain a tert-butyl reaction product, distilling the obtained tert-butyl reaction product at atmospheric pressure, and then rectifying it at reduced pressure to obtain ≥85% crude 3-methyl-5-ethylphenol, a 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction, ≥70% crude 2,3,5-tricresin, tert-butylphenol and a distillation still residue;

[0016] (4) subjecting the crude 3-methyl-5-ethylphenol with a concentration of ≥85% obtained in step (3) to crystallization and purification to obtain 3-methyl-5-ethylphenol with a concentration of ≥99%;

[0017] (5) The crude product of ≥70% 2,3,5-trimethylphenol obtained in step (3) is subjected to crystallization purification to obtain ≥99% 2,3,5-trimethylphenol.

[0018] The method for refining 3-methyl-5-ethylphenol and 2,3,5-tricresol from a trimethylol mixture according to the embodiment of the present invention has the following advantages and technical effects: 1. The method according to the embodiment of the present invention uses a tertiary butylation reaction to efficiently separate phenols with similar boiling points, has low requirements on the quality of raw materials, is easy to separate, and has significantly better separation effect and yield than traditional purely physical separation methods such as multiple distillations and multiple crystallizations. It can produce a variety of products with a large output and a high utilization rate of raw materials; 2. The method according to the embodiment of the present invention uses a trimethylol mixture with complex components, difficult to handle and low value to produce 3-methyl-5-ethylphenol and 2,3,5-tricresol, and can also produce some phenolic substances as by-products, thereby achieving the purpose of comprehensive utilization of hazardous wastes, and thus has good economic and social value.

[0019] In some embodiments, in step (1), the tri-cresol mixture comprises at least one of a xylenol post-fraction, a xylenol distillation residue, a tri-cresol fraction, or a crude phenol distillation residue;

[0020] And / or, in the step (1), the distillation treatment is carried out in a distillation tower having a theoretical plate number of not less than 100;

[0021] And / or, the composition of the mixed trimethylols includes: 0-80% of 3,4-dimethylphenol, 0-30% of 2,3,6-trimethylphenol, 1-50% of 3-methyl-5-ethylphenol, 0-30% of p-isopropylphenol, 0-50% of m-isopropylphenol, 0.1-50% of 2,3,5-trimethylphenol, 0-30% of 3-methyl-4-ethylphenol, and 0-10% of butylphenol, calculated in percentage by weight.

[0022] In some embodiments, in step (2), the catalyst includes at least one of sulfuric acid, phosphoric acid, p-toluenesulfonic acid, aminosulfonic acid, a strong acid resin, zirconium oxide or phosphotungstic acid;

[0023] And / or, the amount of the catalyst is 1 to 30 wt% of the mixed trimethylol;

[0024] And / or, the amount of isobutylene added is 20 to 300 wt % of the mixed trimethylol;

[0025] And / or, the temperature of the tert-butylation reaction is 30-150° C., and the time of the tert-butylation reaction is 2-12 hours.

[0026] In some embodiments, in step (3), the washing treatment includes water washing and alkali washing;

[0027] And / or, the vacuum distillation is carried out in a distillation kettle having a theoretical plate number of 100 to 350;

[0028] And / or, the pressure of the vacuum distillation is -0.05 to -0.1 MPa, and the reflux ratio is 15 to 25:1.

[0029] In some embodiments, in step (3), the tert-butylphenol is at least one of 6-tert-butyl-3,4-dimethylphenol, 6-tert-butyl-m-isopropylphenol, 4-tert-butyl-2,3,6-trimethylphenol, 6-tert-butyl-3-methyl-4-ethylphenol, and 2,6-di-tert-butyl-p-isopropylphenol obtained in sequence during vacuum distillation;

[0030] Preferably, concentrated sulfuric acid is added to the 6-tert-butyl-3,4-dimethylphenol, 6-tert-butyl-m-isopropylphenol, 4-tert-butyl-2,3,6-trimethylphenol, and 6-tert-butyl-3-methyl-4-ethylphenol to carry out a deisobutylene reaction, and after the reaction is completed, the temperature is lowered and an alkali solution is added to neutralize the mixture, and then the mixture is washed with water. After the separation, the layers are stratified and distilled to obtain 3,4-dimethylphenol, m-isopropylphenol, 2,3,6-trimethylphenol, and 3-methyl-4-ethylphenol.

[0031] Preferably, the amount of concentrated sulfuric acid added is 1-2 wt % of the tert-butyl phenol, the deisobutylene reaction is carried out at 160-200° C. for 2 h, and the removed isobutylene is reused.

[0032] In some embodiments, in step (4), the crystallization refining treatment comprises: adding a first solvent to a crude product of ≥85% 3-methyl-5-ethylphenol, heating to dissolve, then cooling to crystallize, then filtering to obtain a filtrate and a filter cake, and performing a melt crystallization treatment on the filter cake;

[0033] Preferably, the first solvent comprises at least one of alcohols with 1 to 4 carbon atoms, alkanes with 6 to 8 carbon atoms, petroleum ether, halogenated hydrocarbons or benzene;

[0034] and / or, the first solvent is 0.5 to 5 times the mass of ≥85% crude 3-methyl-5-ethylphenol;

[0035] And / or, the temperature of the heating dissolution is 60 to 90° C., the temperature of the cooling crystallization is -10 to 10° C., and the crystallization time is 1 to 3 hours;

[0036] And / or, the melt crystallization comprises adding the filter cake into a melt crystallizer, heating the filter cake to 57±0.5°C, then cooling the filter cake to 52±0.3°C at a rate of 0.3-0.7°C / h, and maintaining the temperature for 2-20h for crystallization, pouring out the uncrystallized solution after the crystallization is completed, heating the solid on the melt crystallizer to 53±0.2°C at a rate of 0.1-0.5°C / h, and melting the solid to obtain ≥99% of 3-methyl-5-ethylphenol; heating the remaining material on the crystallizer until it is completely melted as the rear portion.

[0037] In some embodiments, in step (5), the crystallization refining treatment comprises: adding a second solvent to a crude product of ≥70% 2,3,5-trimethylphenol, heating to dissolve the solvent, then cooling the solvent to crystallize the solvent, filtering the solvent to obtain a filtrate and a filter cake, and subjecting the filter cake to a melt crystallization treatment;

[0038] Preferably, the second solvent comprises at least one of alcohols with 1 to 4 carbon atoms, alkanes with 6 to 8 carbon atoms, petroleum ether, halogenated hydrocarbons or benzene;

[0039] and / or, the second solvent is 0.1 to 5 times the mass of ≥70% 2,3,5-trimethylphenol;

[0040] And / or, the temperature of the heating dissolution is 60-100° C., the temperature of the cooling crystallization is 0-20° C., and the time of the crystallization is 1-3 hours.

[0041] And / or, the melt crystallization comprises adding the filter cake into a melt crystallizer, heating the filter cake to 98±0.5°C, then cooling the filter cake to 93±0.3°C at a rate of 0.3-0.7°C / h, and maintaining the temperature for 3-20h for crystallization, pouring out the uncrystallized solution after the crystallization is completed, heating the solid on the melt crystallizer to 94±0.2°C at a rate of 0.1-0.5°C / h, and melting the solid to obtain ≥99% of 2,3,5-trimethylphenol; heating the remaining material on the crystallizer until it is completely melted as the rear portion.

[0042] In some embodiments, the 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction obtained in step (3), phenol, silicon-aluminum-cadmium oxide and an acidic catalyst are added to a reactor to carry out dealkylation and alkyl translocation reactions, and after the reaction is completed, the filtrate is filtered to obtain a filtrate, and the filtrate is distilled to obtain cresol, mixed xylenols, ≥95% crude 2,3,5-tricresin and 99% 2,3,5-tricresin;

[0043] Preferably, a second solvent is added to the ≥95% 2,3,5-trimethylphenol crude product, the temperature is raised to 60-90°C for dissolution, and then the temperature is lowered to 0-20°C. After keeping the temperature for 2 hours, the filtrate and filter cake are obtained by filtration, and the filter cake is dried to obtain ≥99% 2,3,5-trimethylphenol; the second solvent includes at least one of alcohols with 1 to 4 carbon atoms, alkanes with 6 to 8 carbon atoms, petroleum ether, halogenated hydrocarbons or benzene; and the second solvent is 0.1 to 5 times the mass of ≥95% 2,3,5-trimethylphenol.

[0044] In some embodiments, the mass ratio of silicon oxide, aluminum oxide and cadmium oxide in the silicon-aluminum-cadmium oxide is 0.1-10:10-0.1:0.01-0.5, and the amount of the silicon-aluminum-cadmium oxide is 0-50wt% of the mixed fraction of 3-methyl-5-ethylphenol / 2,3,5-trimethylphenol;

[0045] and / or, the acidic catalyst comprises at least one of sulfuric acid, phosphoric acid, hydrogen halide, aminosulfonic acid, benzenesulfonic acid or toluenesulfonic acid;

[0046] And / or, the acidic catalyst is used in an amount of 0.1 to 10 wt % of the 3-methyl-5-ethylphenol / 2,3,5-trimethylphenol mixed fraction;

[0047] and / or, the amount of phenol used is 0.1 to 100 wt % of the mixed phenol of 3-methyl-5-ethylphenol / 2,3,5-trimethylphenol;

[0048] And / or, the dealkylation and alkylation reactions are carried out at 350-800° C. for 1-10 hours, and then the temperature is lowered to 200-350° C. to synthesize ethylphenol, and the reaction time is 2-8 hours.

[0049] In one embodiment, the 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction obtained in step (3) is subjected to secondary distillation to obtain ≥85% crude 3-methyl-5-ethylphenol, a 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction and ≥70% crude 2,3,5-tricresin. DETAILED DESCRIPTION

[0050] Embodiments of the present invention are described in detail below. The embodiments are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0051] A method for refining 3-methyl-5-ethylphenol and 2,3,5-trimethylphenol from a trimethylphenol mixture according to an embodiment of the present invention is characterized by comprising the following steps:

[0052] (1) subjecting the trimethylol mixture to a rectification treatment to obtain a mixed trimethylol;

[0053] (2) subjecting the mixed trimethylol, catalyst and isobutylene obtained in step (1) to a tertiary butylation reaction;

[0054] (3) washing the substance obtained in step (2) to obtain a tert-butyl reaction product, distilling the obtained tert-butyl reaction product at atmospheric pressure, and then rectifying it at reduced pressure to obtain ≥85% crude 3-methyl-5-ethylphenol, a 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction, ≥70% crude 2,3,5-tricresin, tert-butylphenol and a distillation still residue;

[0055] (4) subjecting the crude 3-methyl-5-ethylphenol with a concentration of ≥85% obtained in step (3) to crystallization and purification to obtain 3-methyl-5-ethylphenol with a concentration of ≥99%;

[0056] (5) The crude product of ≥70% 2,3,5-trimethylphenol obtained in step (3) is subjected to crystallization purification to obtain ≥99% 2,3,5-trimethylphenol.

[0057] The method for refining 3-methyl-5-ethylphenol and 2,3,5-tricresol from a trimethylol mixture according to the embodiment of the present invention has the following advantages and technical effects: 1. The method according to the embodiment of the present invention uses a tertiary butylation reaction to efficiently separate phenols with similar boiling points, has low requirements on the quality of raw materials, is easy to separate, and has significantly better separation effect and yield than traditional purely physical separation methods such as multiple distillations and multiple crystallizations. It can produce a variety of products with a large output and a high utilization rate of raw materials; 2. The method according to the embodiment of the present invention uses a trimethylol mixture with complex components, difficult to handle and low value to produce 3-methyl-5-ethylphenol and 2,3,5-tricresol, and can also produce some phenolic substances as by-products, thereby achieving the purpose of comprehensive utilization of hazardous wastes, and thus has good economic and social value.

[0058] In some embodiments, preferably, in the step (1), the trimethylol mixture comprises at least one of a xylenol post-fraction, a xylenol distillation residue, a trimethylol fraction or a crude phenol distillation residue;

[0059] And / or, in the step (1), the distillation treatment is carried out in a distillation tower having a theoretical plate number of not less than 100;

[0060] And / or, the composition of the mixed trimethylols includes: 0-80% of 3,4-dimethylphenol, 0-30% of 2,3,6-trimethylphenol, 1-50% of 3-methyl-5-ethylphenol, 0-30% of p-isopropylphenol, 0-50% of m-isopropylphenol, 0.1-50% of 2,3,5-trimethylphenol, 0-30% of 3-methyl-4-ethylphenol, and 0-10% of butylphenol, calculated in percentage by weight.

[0061] Further preferably, the tricresol mixture comprises at least one of a xylenol post fraction, a xylenol distillation residue or a tricresol fraction;

[0062] The dimethylphenol post fraction comprises: p-ethylphenol 0-5%, m-ethylphenol 0-8%, 3,5-dimethylphenol 0-20%, 3,4-dimethylphenol 0-80%, 2,3,6-tricresin 0-30%, 2-ethyl-4-methylphenol 0-15%, 2-ethyl-5-methylphenol 0-10%, 3-ethyl-2-methylphenol 0-10%, 3-methyl-5-ethylphenol 0-20%, p-isopropylphenol 0-10%, m-isopropylphenol 0-15%, 2,3,5-tricresin 0-10%, calculated by mass percentage;

[0063] The dimethylphenol rectification residue and trimethylphenol fraction include: p-ethylphenol 0-2%, m-ethylphenol 0-3%, 3,5-xymethylphenol 0-5%, 3,4-xymethylphenol 0-25%, 2,3,6-trimethylphenol 0-20%, 2-ethyl-4-methylphenol 0-5%, 2-ethyl-5-methylphenol 0-5%, 3-ethyl-2-methylphenol 0-10%, 3-methyl-5-ethylphenol 2-40%, p-isopropylphenol 1-10%, m-isopropylphenol 1-15%, 2,3,5-trimethylphenol 1-30%, 3-methyl-4-ethylphenol 1-20%, 3,4,5-trimethylphenol 1-5%, tetramethylphenol 1-5%, butylphenol 1-20%, calculated by mass percentage;

[0064] The mixed trimethylol comprises 0-15% of 3,4-dimethylphenol, 0-10% of 2,3,6-trimethylphenol, 25-50% of 3-methyl-5-ethylphenol, 5-10% of p-isopropylphenol, 6-15% of m-isopropylphenol, 20-40% of 2,3,5-trimethylphenol, 10-20% of 3-methyl-4-ethylphenol and 1-5% of butylphenol;

[0065] The distillation range of the mixed trimethylols is 227-237°C.

[0066] In some embodiments, preferably, in step (2), the catalyst comprises at least one of sulfuric acid, phosphoric acid, p-toluenesulfonic acid, aminosulfonic acid, a strong acid resin, zirconium oxide or phosphotungstic acid;

[0067] And / or, the amount of the catalyst is 1 to 30 wt% of the mixed trimethylol;

[0068] And / or, the amount of isobutylene added is 20 to 300 wt % of the mixed trimethylol;

[0069] And / or, the temperature of the tert-butylation reaction is 30 to 150° C., and the time of the tert-butylation reaction is 2 to 12 hours.

[0070] Further preferably, the catalyst comprises at least one of sulfuric acid or p-toluenesulfonic acid;

[0071] And / or, the reaction temperature of the tert-butylation is 60-120°C.

[0072] In some embodiments, preferably, in the step (3), the atmospheric distillation is to distill out the front portion, which includes water, diisobutylene, oligoisobutylene and a small amount of phenol.

[0073] In some embodiments, preferably, in step (3), the washing treatment includes water washing and alkali washing;

[0074] And / or, the vacuum distillation is carried out in a distillation kettle having a theoretical plate number of 100 to 350;

[0075] And / or, the pressure of the vacuum distillation is -0.05 to -0.1 MPa, and the reflux ratio is 15 to 25:1.

[0076] More preferably, the vacuum distillation is carried out in a distillation kettle having 180 to 220 theoretical plates.

[0077] In some embodiments, preferably, in the step (3), the tert-butylphenol is obtained in sequence in a vacuum distillation process: at least one of 6-tert-butyl-3,4-dimethylphenol, 6-tert-butyl-m-isopropylphenol, 4-tert-butyl-2,3,6-trimethylphenol, 4-tert-butyl-2,3,6-trimethylphenol, 6-tert-butyl-3-methyl-4-ethylphenol, and 2,6-di-tert-butyl-p-isopropylphenol;

[0078] Preferably, concentrated sulfuric acid is added to the 6-tert-butyl-3,4-dimethylphenol, 6-tert-butyl-m-isopropylphenol, and 6-tert-butyl-3-methyl-4-ethylphenol respectively to carry out a deisobutylene reaction, and after the reaction is completed, the temperature is lowered and an alkali solution is added for neutralization, and then the mixture is washed with water, and after layering, the material layers are distilled to obtain 3,4-dimethylphenol, m-isopropylphenol, 2,3,6-trimethylphenol, and 3-methyl-4-ethylphenol;

[0079] Preferably, the amount of concentrated sulfuric acid added is 1-2 wt % of the tert-butyl phenol, the deisobutylene reaction is carried out at 160-200° C. for 1-3 h, and the removed isobutylene is reused.

[0080] Among them, tert-butylphenol is 6-tert-butyl-3,4-dimethylphenol, 6-tert-butyl-m-isopropylphenol, 4-tert-butyl-2,3,6-trimethylphenol, 6-tert-butyl-3-methyl-4-ethylphenol and 2,6-di-tert-butyl-p-isopropylphenol obtained in the process of vacuum distillation.

[0081] In some embodiments, preferably, in step (4),

[0082] The crystallization refining treatment comprises: adding a first solvent to a crude product of ≥85% 3-methyl-5-ethylphenol, heating to dissolve it, then cooling it down to crystallize it, filtering it to obtain a filtrate and a filter cake, and performing a melt crystallization treatment on the filter cake;

[0083] Preferably, the first solvent comprises at least one of alcohols with 1 to 4 carbon atoms, alkanes with 6 to 8 carbon atoms, petroleum ether, halogenated hydrocarbons or benzene;

[0084] and / or, the first solvent is 0.5 to 5 times the mass of ≥85% crude 3-methyl-5-ethylphenol;

[0085] And / or, the temperature of the heating dissolution is 60 to 90° C., the temperature of the cooling crystallization is -10 to 10° C., and the crystallization time is 1 to 3 hours;

[0086] And / or, the melt crystallization comprises adding the filter cake into a melt crystallizer, heating the filter cake to 57±0.5°C, then cooling the filter cake to 52±0.3°C at a rate of 0.3-0.7°C / h, and maintaining the temperature for 2-20h for crystallization, pouring out the uncrystallized solution after the crystallization is completed, heating the solid on the melt crystallizer to 53±0.2°C at a rate of 0.1-0.5°C / h, and melting the solid to obtain ≥99% of 3-methyl-5-ethylphenol; heating the remaining material on the crystallizer until it is completely melted as the rear portion.

[0087] Further preferably, in step (4), the first solvent comprises at least one of ethanol and petroleum ether;

[0088] and / or, the first solvent is 1 to 2 times the mass of ≥85% crude 3-methyl-5-ethylphenol;

[0089] And / or, the cooling crystallization process includes first cooling to 35° C. within 2 to 3 hours, and then cooling to -10 to 10° C. with frozen brine.

[0090] In the step (4), the uncrystallized solution and filtrate are added to a desolventizing kettle, and after the temperature is raised and the solvent is completely removed under normal pressure, the material is transported to a distillation tower for distillation to obtain crude 3-methyl-5-ethylphenol and crude 2,3,5-trimethylphenol.

[0091] In some embodiments, preferably, in the step (5), the crystallization refining treatment comprises: adding a second solvent to a crude product of ≥70% 2,3,5-trimethylphenol, heating to dissolve the solvent, then cooling the solvent to crystallize the solvent, filtering the solvent to obtain a filtrate and a filter cake, and subjecting the filter cake to a melt crystallization treatment;

[0092] Preferably, the second solvent comprises at least one of alcohols with 1 to 4 carbon atoms, alkanes with 6 to 8 carbon atoms, petroleum ether, halogenated hydrocarbons or benzene;

[0093] and / or, the second solvent is 0.1 to 5 times the mass of ≥70% 2,3,5-trimethylphenol;

[0094] And / or, the temperature of the heating dissolution is 60-100° C., the temperature of the cooling crystallization is 0-20° C., and the time of the crystallization is 1-3 hours.

[0095] And / or, the melt crystallization comprises adding the filter cake into a melt crystallizer, heating the filter cake to 98±0.5°C, then cooling the filter cake to 93±0.3°C at a rate of 0.3-0.7°C / h, and maintaining the temperature for 3-20h for crystallization, pouring out the uncrystallized solution after the crystallization is completed, heating the solid on the melt crystallizer to 94±0.2°C at a rate of 0.1-0.5°C / h, and melting the solid to obtain ≥99% of 2,3,5-trimethylphenol; heating the remaining material on the crystallizer until it is completely melted as the rear portion.

[0096] Further preferably, in step (5), the second solvent comprises at least one of methanol or n-hexane;

[0097] and / or, the second solvent is 0.5 to 3 times the mass of ≥70% 2,3,5-trimethylphenol;

[0098] And / or, the cooling crystallization process includes first cooling the temperature to 35° C. within 2 to 3 hours using jacket cold water, and then cooling the temperature to 0 to 20° C. using frozen brine.

[0099] In the step (5), the uncrystallized solution and filtrate are added to a desolventizing kettle, and after the temperature is raised and the solvent is completely removed under normal pressure, the material is transported to a distillation tower for distillation to obtain crude 3-methyl-5-ethylphenol and crude 2,3,5-trimethylphenol.

[0100] In some embodiments, preferably, the 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction obtained in step (3), phenol, silicon-aluminum-cadmium oxide and acidic catalyst are added to a reactor to carry out dealkylation and alkyl translocation reactions, and after the reaction is completed, the filtrate is filtered to obtain a filtrate, and the filtrate is distilled to obtain cresol, mixed xylenols, ≥95% crude 2,3,5-tricresin and 99% 2,3,5-tricresin;

[0101] Preferably, a second solvent is added to the ≥95% crude 2,3,5-trimethylphenol, the temperature is raised to 60-90°C for dissolution, and then the temperature is lowered to 0-20°C. After keeping the temperature for 1-3 hours, the filtrate and filter cake are obtained by filtering, and the filter cake is dried to obtain ≥99% 2,3,5-trimethylphenol, and the second solvent includes at least one of alcohols with 1 to 4 carbon atoms, alkanes with 6 to 8 carbon atoms, petroleum ether, halogenated hydrocarbons or benzenes.

[0102] More preferably, the filtrate produced during the crystallization and purification of ≥95% crude 2,3,5-tricresol is used instead of the second solvent for the crystallization and purification of ≥70% crude 2,3,5-tricresol. If the filtrate is insufficient, the second solvent can be used to make up the difference.

[0103] In the embodiment of the present invention, since the boiling points of 3-methyl-5-ethylphenol and 2,3,5-tricresin are close, although the relative volatility difference can be used to obtain the crude products of each, and then the pure product can be obtained by solvent refining and melt crystallization, the yield is low and the production cost of repeated distillation and crystallization is high. In the presence of a catalyst, the 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction is subjected to dealkylation and alkyl transposition reaction to remove the ethyl group in the 3-methyl-5-ethylphenol to obtain m-cresol, and the removed ethyl group is converted into m-cresol. The methyl group reacts with phenol to obtain stable ethylphenol, while 2,3,5-trimethylphenol is relatively stable, and most of it still exists as 2,3,5-trimethylphenol, with only a small amount of methyl falling off, thereby obtaining a mixed phenol mainly composed of cresol (mainly m-cresol), ethylphenol (mainly m-ethylphenol) and 2,3,5-trimethylphenol. The mixed phenol can be distilled to obtain a crude 2,3,5-trimethylphenol with a purity of more than 95%, and then a high-purity 2,3,5-trimethylphenol is obtained by a crystallization method, which greatly improves the extraction rate of 2,3,5-trimethylphenol.

[0104] Further preferably, the second solvent comprises at least one of methanol or n-hexane; and the second solvent is 0.5 to 3 times the mass of ≥95% 2,3,5-trimethylphenol.

[0105] The refined mother liquor of ≥95% crude 2,3,5-trimethylphenol can be used as the second solvent to purify the crude 2,3,5-trimethylphenol of ≥70%, or it can be added to the desolventizing kettle, and the material after heating and removing the solvent is returned to the distillation tower for distillation to obtain crude 3-ethyl-5-methylphenol and crude 2,3,5-trimethylphenol.

[0106] In some embodiments, preferably, the mass ratio of silicon oxide, aluminum oxide and cadmium oxide in the silicon-aluminum-cadmium series oxide is 0.1-10:10-0.1:0.01-0.5, and the amount of the silicon-aluminum-cadmium series oxide is 0-50wt% of the mixed fraction of 3-methyl-5-ethylphenol / 2,3,5-trimethylphenol;

[0107] and / or, the acidic catalyst comprises at least one of sulfuric acid, phosphoric acid, hydrogen halide, aminosulfonic acid, benzenesulfonic acid or toluenesulfonic acid;

[0108] And / or, the acidic catalyst is used in an amount of 0.1 to 10 wt % of the 3-methyl-5-ethylphenol / 2,3,5-trimethylphenol mixed fraction;

[0109] and / or, the amount of phenol used is 0.1 to 100 wt % of the mixed phenol of 2,3,5-trimethylphenol / 3-methyl-5-ethylphenol;

[0110] And / or, the dealkylation and alkylation reactions are carried out at 350-800° C. for 1-10 hours, and then the temperature is lowered to 200-350° C. to synthesize ethylphenol, and the reaction time is 2-8 hours.

[0111] Further preferably, the mass ratio of silicon oxide, aluminum oxide and cadmium oxide in the silicon-aluminum-cadmium oxide is 0.2-5:5-0.2:0.02-0.1;

[0112] and / or, the acidic catalyst comprises sulfuric acid;

[0113] And / or, the amount of phenol used is 20-50 wt % of the mixed phenol of 2,3,5-trimethylphenol / 3-methyl-5-ethylphenol.

[0114] In one embodiment, preferably, the 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction obtained in step (2) is subjected to secondary distillation to obtain ≥85% crude 3-methyl-5-ethylphenol, a 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction and ≥70% crude 2,3,5-tricresin.

[0115] In some embodiments, preferably, in step (3), the distillation still residue comprises 2,6-di-tert-butyl-p-isopropylphenol and tri-tert-butylphenol. Further preferably, concentrated sulfuric acid is added to the distillation still residue and the temperature is raised to 160-200°C for reaction for 1-3h to remove isobutylene, then the temperature is lowered to below 100°C and 30% alkali solution is added for neutralization, water washing is performed, and a material layer is obtained after stratification, and the material layer is distilled to obtain 98% p-isopropylphenol and ≥99% phenol; the amount of concentrated sulfuric acid added is 1-2wt% of the distillation still residue.

[0116] The technical solution of the present invention is described in detail below in conjunction with specific embodiments.

[0117] Example 1

[0118] The distillation residue of xylenol was analyzed and its composition is shown in Table 1. The content of each component is expressed in mass percentage.

[0119] Table 1 Chromatographic analysis report of distillation residue

[0120] Material Name content,% Material Name content,% 3,5-Dimethylphenol 1.22 p-Ethylphenol 0.28 m-Ethylphenol 0.33 3,4-Dimethylphenol 2.15 2-Ethyl-4-methylphenol 1.20 3-Ethyl-2-methylphenol 4.81 Propylphenol 5.24 Isopropylphenol 6.38 3-Methyl-5-ethylphenol 28.33 2,3,5-Trimethylphenol 15.63 3-Methyl-4-ethylphenol 15.28 Other trimethylols 7.30 Tetramethylphenol 2.21 Various butylphenols 6.25 other 3.39

[0121] Step 1: Distillation and purification

[0122] 4800 parts of the above-mentioned xylenol distillation residue were added into the bottom of a distillation tower with a theoretical plate number of 250, and distilled under reduced pressure (vacuum degree -0.088MPa, reflux ratio 10-15:1) to obtain 2552.6 parts of mixed trimethylols (composition: 3,4-xylenol 0.82%, p-isopropyl phenol 5.72%, m-isopropyl phenol 6.96%, 2,3,5-trimethylol 27.92%, 3-methyl-5-ethyl phenol 38.28%, 3-methyl-4-ethyl phenol 15.85%, butyl phenol 3.98%, and others 0.45%).

[0123] Step 2: Tert-butylation Separation

[0124] Into an enamel kettle, add 2552.6 parts of the mixed trimethylols and 60 parts of p-toluenesulfonic acid obtained in the first step, start stirring, raise the temperature to 110°C, introduce 602 parts of isobutylene for reaction, keep the reaction warm for 8 hours, take samples for analysis, 0.18% of 2-tert-butyl isopropyl phenol is qualified, add a mixed solution of 57 parts of caustic soda and 150 parts of water for neutralization, and then perform vacuum distillation (vacuum degree -0.095MPa, reflux ratio 25:1, theoretical plate number of distillation kettle is 250) to obtain 934.1 parts of crude 3-methyl-5-ethylphenol with a content of 85.12%, 22 parts of 3-methyl-5-ethylphenol / 2,3,5-trimethylphenol mixed fraction 8.4 parts (59.54% 3-methyl-5-ethylphenol, 39.8% 2,3,5-trimethylphenol, 0.45% 2,4,5-trimethylphenol, 0.21% others), 654.8 parts of 73.6% crude 2,3,5-trimethylphenol, 29 parts of 96.8% 6-tert-butyl-3,4-dimethylphenol, 514.4 parts of 97.8% 6-tert-butyl-3-methyl-4-ethylphenol, 204.6 parts of 99% 2,6-di-tert-butyl-p-isopropyl phenol (antioxidant), 419.8 parts of kettle residue (including 250.6 parts of 4,6-di-tert-butyl-m-isopropyl phenol and 87.7 parts of tri-tert-butyl phenol).

[0125] Step 3: Deisobutylene and distillation

[0126] (1) Add 145 parts (5 batches combined) of 96.8% 6-tert-butyl-3,4-xylenol from the second step into a 316L stainless steel kettle, add 2 parts of concentrated sulfuric acid, heat to 185°C and maintain for 2 hours, stop the reaction when the content of 6-tert-butyl-3,4-xylenol is 0.38% by gas spectrum detection, cool to less than 100°C, and neutralize to neutrality with 5.5 parts of 30% liquid alkali, transfer the material into the kettle of a distillation tower after stratification, and perform vacuum distillation to obtain 90.9 parts of 99.3% 3,4-xylenol, and recover 42.4 parts of isobutylene for use.

[0127] (2) 514.4 parts of 6-tert-butyl-3-methyl-4-ethylphenol obtained in the second step were added to a 316L stainless steel kettle, 10 parts of concentrated sulfuric acid were added, the temperature was raised to 190° C. and maintained for 1.5 hours, and the reaction was stopped when the content of 6-tert-butyl-3-methyl-4-ethylphenol was 0.16% by gas spectrum detection. The temperature was lowered to less than 100° C. and neutralized to neutrality with 28 parts of 30% liquid alkali. After stratification, the material was transferred to a distillation tower kettle and subjected to vacuum distillation to obtain 335.8 parts of 99.1% 3-methyl-4-ethylphenol with a yield of 93.4%, and 139.5 parts of isobutylene were recovered for use.

[0128] (3) Add 2099 parts of the kettle residue from the second step into a 316L stainless steel kettle, add 20 parts of concentrated sulfuric acid, raise the temperature to 200° C. and maintain for 2 hours. Stop the reaction when the content of tert-butylphenol is 0.22% by gas spectrum detection. Cool to less than 100° C. and neutralize with 55.5 parts of 30% liquid alkali to neutrality. After stratification, transfer the material into the kettle of a distillation tower and perform vacuum distillation to obtain 227.3 parts of 99.8% phenol, 790.6 parts of 99.2% m-isopropyl phenol, and 856.7 parts of isobutylene for recycling.

[0129] Step 4: Refining of crude 3-methyl-5-ethylphenol

[0130] (4) Add 934.1 parts of 85.12% crude 3-methyl-5-ethylphenol and 1750 parts of ethanol to a stainless steel crystallization kettle, start stirring, heat the mixture to 60°C in a water bath to completely dissolve the materials, then cool the mixture to 25°C in a cold water bath, and then cool the mixture to 0°C in a salt water bath for 2 hours, keep the mixture at room temperature for 1 hour, filter, drain, and air-dry to obtain 712.3 parts of 96.2% 3-methyl-5-ethylphenol filter cake and 1947.5 parts of filtrate.

[0131] (5) 90 parts of 96.2% 3-methyl-5-ethyl phenol were added to a melt crystallizer, heated to 57° C. to dissolve the phenol, then slowly cooled to 52° C. at 0.5° C. / h, and kept warm for 3 hours to fully crystallize the phenol, and then 1.7 parts of uncrystallized solution were discharged; then the temperature was raised to 53° C. at 0.2° C. / h and kept warm for 2 hours to melt part of the material, and 79.2 parts of a colorless 3-methyl-5-ethyl phenol product with a content of 99.7% was collected, which was a white solid after cooling, with a primary melt crystallization yield of 91.2%; the remaining material was quickly heated and melted, and 8.2 parts of 3-methyl-5-ethyl phenol with a content of 87.8% was obtained after all the material was dissolved, and was incorporated into the next batch of 3-methyl-5-ethyl phenol crude product.

[0132] (6) 1947.5 parts of the filtrate were added to an enameled distillation kettle with a condenser, and the temperature was raised to recover 1712.4 parts of the solvent for reuse. After evaporation to dryness, 216.1 parts of material (including 58.3% of 3-methyl-5-ethylphenol, 39.62% of 2,3,5-trimethylphenol, and 1.8% of 2,4,5-trimethylphenol) were obtained. This part of the material was used for dealkylation reaction to produce 2,3,5-trimethylphenol, and it can also be incorporated into the tert-butylation product of the second step to distill the crude products of 3-methyl-5-ethylphenol and 2,3,5-trimethylphenol.

[0133] Step 5: Refining of crude 2,3,5-trimethylphenol

[0134] (7) Add 654.8 parts of 73.6% crude 2,3,5-trimethylphenol and 1218 parts of 90-120°C petroleum ether to a stainless steel crystallization kettle, start stirring, heat the water bath to 90°C to completely dissolve the materials, then cool to 50°C in a cold water bath, then cool naturally to room temperature, and finally cool to 15°C in an ice water bath, keep warm for 2 hours, filter, drain, and air-dry to obtain 418.4 parts of 95.8% 2,3,5-trimethylphenol filter cake and 1401.3 parts of filtrate.

[0135] (8) 90.3 parts of 95.8% 2,3,5-trimethylphenol were added to the melt crystallizer, the oil bath was heated to 98°C to dissolve it, and then the temperature was slowly lowered to 93°C at a rate of 0.5°C / h and kept at this temperature for 5 hours to allow the 2,3,5-trimethylphenol to fully crystallize. Then 8.6 parts of the uncrystallized solution (including 33.8% 3-methyl-5-ethylphenol and 64.7% 2,3,5-trimethylphenol) were discharged, and the uncrystallized solution was incorporated into the tert-butylated product of the second step and distilled together with 3-methyl- The crude products of 5-ethylphenol and 2,3,5-trimethylphenol were prepared; the temperature was then raised to 94°C at a rate of 0.2°C / h and kept at this temperature for 2 hours to melt part of the material, and 78.1 parts of 2,3,5-trimethylphenol product with a content of 99.5% were collected, which was a white solid after cooling, and the yield of one melt crystallization was 89.8%; the remaining material was quickly heated and melted, and 3.2 parts of 2,3,5-trimethylphenol with a content of 90.6% were obtained after all of them were dissolved, which were added to the next batch of crude 2,3,5-trimethylphenol for solvent crystallization.

[0136] (9) 1401.3 parts of the filtrate was added to an enameled still equipped with a condenser, and the temperature was raised to recover 1078 parts of the solvent, which was evaporated to dryness to obtain 225.8 parts of material (including 63.8% of 3-methyl-5-ethylphenol and 34.5% of 2,3,5-trimethylphenol). This material was incorporated into the tert-butylation product of the second step to distill the crude products of 3-methyl-5-ethylphenol and 2,3,5-trimethylphenol.

[0137] In the sixth step, the 3-methyl-5-ethylphenol / 2,3,5-trimethylphenol mixed fraction obtained in the second step is used for secondary distillation of crude 2,3,5-trimethylphenol and crude 3-ethyl-5-methylphenol.

[0138] The embodiment of the present invention produces: 99.3% 3,4-dimethylphenol, 99.1% 3-methyl-4-ethylphenol, 99.8% phenol, 99.2% m-isopropylphenol, 99% 2,6-di-tert-butyl-p-isopropylphenol (sold as an antioxidant), 99.7% 3-methyl-5-ethylphenol and 99.5% 2,3,5-trimethylphenol products.

[0139] Example 2

[0140] Step 1: Distillation of post-distillation fraction of xylenol

[0141] 25,000 portions of the dimethyl phenol fraction produced in the workshop (10.07% of 3,5-dimethylphenol, 2.31% of p-ethylphenol, 2.71% of m-ethylphenol, 43.64% of 3,4-dimethylphenol, 6.5% of 2,3,6-trimethylphenol, 2.77% of 2,3,5-trimethylphenol, 11.84% of 3-methyl-5-ethylphenol, 5.81% of p-isopropylphenol, 8.35% of m-isopropylphenol, 2.49% of 3-methyl-4-ethylphenol) were added into the kettle of a distillation tower with a theoretical plate number of 250, and vacuum distillation (vacuum degree -0.088MPa, reflux ratio 20-25:1) was performed to obtain 3,4-dimethylphenol / 2,3,6-trimethylphenol 7480.9 parts of mixed cresols (75.66% 3,4-dimethylphenol, 12.95% 2,3,6-trimethylphenol, 3.24% p-isopropylphenol, 5.31% m-isopropylphenol, 1.11% 3-ethyl-5-methylphenol, 0.12% 2,3,5-trimethylphenol, 1.61% others), 6967 parts of mixed trimethylphenols (composition: 7.32% 3,4-dimethylphenol, 17.37% p-isopropylphenol, 22.68% m-isopropylphenol, 8.9% 2,3,5-trimethylphenol, 0.79% 2-ethyl-3-methylphenol, 40.62% 3-methyl-5-ethylphenol, 2.32% 2,3,6-trimethylphenol).

[0142] Step 2: Tert-butylation and distillation of mixed tricresol

[0143] In an enamel reactor, add 6967 parts of mixed trimethylols (510 parts of 3,4-xylenol, 1210.2 parts of p-isopropylphenol, 1580.1 parts of m-isopropylphenol, 620 parts of 2,3,5-trimethylphenol, 55.1 parts of 2-ethyl-3-methylphenol, 2830 parts of 3-methyl-5-ethylphenol, 161.6 parts of 2,3,6-trimethylphenol) and 200 parts of sulfuric acid, start stirring, raise the temperature to 60°C, introduce 2900 parts of isobutylene for reaction, seal and keep warm for 12 hours, take samples for analysis, 0.11% of 2-tert-butyl-p-isopropylphenol is qualified, add 161 parts of caustic soda flakes and 373 parts of water for mixture. The mixture was neutralized with the liquid and then distilled under reduced pressure (pressure of -0.095, reflux ratio of 20 to 25:1, theoretical plate number of the distillation tower of 250) to obtain 2790.8 parts of crude 3-methyl-5-ethylphenol with a content of 95.78% (2673.1 parts of 3-methyl-5-ethylphenol and 117.7 parts of 2,3,5-trimethylphenol), 268.8 parts of a mixed fraction of 3-methyl-5-ethylphenol / 2,3,5-trimethylphenol (148.6 parts of 3-methyl-5-ethylphenol, 112.1 parts of 2,3,5-trimethylphenol and 7.6 parts of 2,4,5-trimethylphenol), and 73.46% 2,3,5-trimethylphenol. 519.2 parts of crude cresol (133.2 parts of 3-ethyl-5-methylphenol, 380.9 parts of 2,3,5-trimethylphenol, 5.1 parts of 6-tert-butyl-3,4-dimethylphenol), 713.6 parts of 90.81% 6-tert-butyl-3,4-dimethylphenol (648 parts of 6-tert-butyl-3,4-dimethylphenol, 65.6 parts of 6-tert-butyl-m-isopropylphenol), 2243.8 parts of 95.33% 6-tert-butyl-m-isopropylphenol (82.1 parts of 6-tert-butyl-3,4-dimethylphenol, 2139.1 parts of 6-tert-butyl-m-isopropylphenol, 22.6 parts of 4-tert-butyl-2,3,6-trimethylphenol) 95.32% 4-tert-butyl-2,3,6-trimethylphenol 213.1 parts (6-tert-butyl-m-isopropyl phenol 3.7 parts, 4-tert-butyl-2,3,6-trimethylphenol 203.2 parts, 2,6-di-tert-butyl-p-isopropyl phenol 6.2 parts), 99.52% antioxidant 2,6-di-tert-butyl-p-isopropyl phenol 2183.4 parts (4,6-di-tert-butyl-2-ethyl-3-methylphenol 10.5 parts), kettle residue 112.9 parts (including 4,6-di-tert-butyl-2-ethyl-3-methylphenol 89 parts, 2,6-di-tert-butyl-p-isopropyl phenol 5.6 parts, sodium sulfate 18.3 parts).

[0144] Step 3: Deisobutylene and distillation

[0145] (1) 713.6 parts of 90.81% 6-tert-butyl-3,4-xylenol obtained in the second step are added to a 316L stainless steel reactor, 10 parts of concentrated sulfuric acid are added, the temperature is raised to 195° C. and maintained for 2 hours, and the reaction is stopped when the content of 6-tert-butyl-3,4-xylenol is 0.15% by gas spectrum detection, the temperature is lowered to less than 100° C., and 27.5 parts of 30% liquid alkali are used to neutralize the mixture to neutrality. After stratification, the material is transferred to a distillation tower kettle for vacuum distillation to obtain 441.2 parts of 96.64% 3,4-xylenol, and 216.3 parts of isobutylene are recovered for use.

[0146] 441.2 parts of crude 3,4-dimethylphenol and 200 parts of methanol were added to an enameled crystallization kettle, and the temperature was raised to 70°C while stirring to completely dissolve the materials. The circulating water was cooled to 30°C, and then cooled to 0°C within 3 hours with frozen brine, kept warm for 1 hour, filtered, rinsed with 20 parts of 0°C methanol, drained, and the materials were dried to obtain 401.6 parts of 99.6% 3,4-dimethylphenol and a crystallization yield of 93.8%.

[0147] (2) Add 2243.8 parts of 95.33% 6-tert-butyl meta-isopropyl phenol obtained in the second step into a 316L stainless steel reactor, add 30 parts of concentrated sulfuric acid, raise the temperature to 190°C and maintain for 2 hours, cool to 60°C and neutralize with 84 parts of 30% liquid alkali to neutrality, and after stratification, transfer the material into the reactor of a distillation tower and perform vacuum distillation to obtain 1362.6 parts of 99.3% meta-isopropyl phenol, and recover 636.6 parts of isobutylene for use.

[0148] (3) 213.1 parts of 95.32% 4-tert-butyl-2,3,6-trimethylphenol obtained in the second step were added to a 316L stainless steel reactor, 4 parts of concentrated sulfuric acid were added, the temperature was raised to 200°C and maintained for 1.5 hours, the temperature was lowered to less than 80°C, and 11 parts of 30% liquid alkali were used to neutralize the mixture to neutrality. After stratification, the material was transferred to the reactor of a distillation tower and subjected to vacuum distillation to obtain 140.1 parts of 98.6% 2,3,6-trimethylphenol, and 61.3 parts of isobutylene were recovered for use.

[0149] 140.1 parts of 98.6% 2,3,6-trimethylphenol and 300 parts of 90-120°C petroleum ether were added into a stainless steel crystallization kettle, heated to a slight boil with stirring to completely dissolve the materials, cooled to 40°C with circulating water, and then cooled to 10°C within 3 hours with frozen brine, kept warm for 2 hours, filtered, rinsed with 10 parts of 90-120°C petroleum ether, pressed dry, and dried to obtain 131.7 parts of 99.7% 2,3,6-trimethylphenol with a crystallization yield of 95.1%.

[0150] (4) 112.9 parts of the still residue were added to a 316L stainless steel reactor, 2 parts of concentrated sulfuric acid were added, the temperature was raised to 200° C. and maintained for 2 hours, the temperature was lowered to less than 80° C. and neutralized to neutrality with 5.5 parts of 30% liquid caustic soda, and after stratification, the material was transferred to the still of a distillation tower (dimethyl anisole with a boiling point of 290° C. was added to the still), and vacuum distillation was performed to obtain 47.8 parts of 95.1% 2-ethyl-3-methylphenol, and 41.4 parts of isobutylene were recovered for use.

[0151] 47.8 parts of 95.1% 2-ethyl-3-methylphenol and 100 parts of 90-120°C petroleum ether were added into a stainless steel crystallization kettle, heated to a slight boil with stirring to completely dissolve the materials, cooled to 40°C with circulating water, and then cooled to 0°C within 3 hours with frozen brine, kept warm for 2 hours, filtered, rinsed with 10 parts of 90-120°C petroleum ether, pressed dry, and dried to obtain 40.6 parts of 99.1% 2-ethyl-3-methylphenol with a crystallization yield of 88.6%.

[0152] (5) Add 1000 parts of 99.52% 2,6-di-tert-butyl-p-isopropylphenol into a 316L stainless steel reactor, add 20 parts of concentrated sulfuric acid, raise the temperature to 200°C and maintain for 2 hours, cool to 80°C and neutralize with 56 parts of 30% liquid alkali to neutrality, transfer the material into the reactor of a distillation tower after stratification, and perform vacuum distillation to obtain 535.9 parts of 99.7% p-isopropylphenol, and recover 438 parts of isobutylene for use.

[0153] Step 4: Refining of crude 3-methyl-5-ethylphenol

[0154] (6) Add 2790.8 parts of 95.78% crude 3-methyl-5-ethylphenol and 2000 parts of methanol into an enameled crystallization kettle, start stirring, heat the mixture in a water bath to a slight boil (65° C.) to completely dissolve the materials, then cool the mixture to 35° C. in a cold water bath and then to 0° C. in a salt water bath for 3 hours, keep the mixture warm for 2 hours, filter, drain, and air-dry to obtain 2549.8 parts of 99.5% 3-methyl-5-ethylphenol, with a yield of 94.91%. Recover the solvent and materials from the filtrate in the same manner as in Example 1.

[0155] Step 5: Refining of crude 2,3,5-trimethylphenol

[0156] (7) Add 519.2 parts of 73.46% crude 2,3,5-trimethylphenol and 1150 parts of 90-120°C petroleum ether to a stainless steel crystallization kettle, start stirring, heat the mixture to 90°C in a water bath to completely dissolve the materials, then cool the mixture to 50°C in a cold water bath, naturally cool the mixture to room temperature, and finally cool the mixture to 20°C in an ice water bath. Keep the temperature for 2 hours, filter, drain, and air-dry to obtain 317.0 parts of 97.2% 2,3,5-trimethylphenol filter cake. The filtrate is used to recover the solvent and materials in the same manner as in Example 1.

[0157] (8) 100 parts of 97.2% 2,3,5-trimethylphenol filter cake were added to a stainless steel melt crystallizer, the temperature was raised to 98°C to dissolve it, and then the temperature was slowly lowered to 93°C at a rate of 0.5°C / h and kept at this temperature for 5 hours to allow the 2,3,5-trimethylphenol to fully crystallize. Then, 7.1 parts of the first part that did not crystallize (including 30.1% 3-methyl-5-ethylphenol and 68.3% 2,3,5-trimethylphenol) were discharged and this part of the material was incorporated into the alkylation product of the second step to distill 3-methyl- The crude products of 5-ethylphenol and 2,3,5-trimethylphenol were prepared; the temperature was then raised to 94°C at a rate of 0.2°C / h and kept at this temperature for 2 hours to melt part of the material, and 89.1 parts of 2,3,5-trimethylphenol product with a content of 99.8% were collected, which was a white solid after cooling, and the yield of one melt crystallization was 91.3%; the remaining material was quickly heated and melted, and 3.3 parts of 2,3,5-trimethylphenol with a content of 91.5% were obtained after all of them were dissolved, which were added to the next batch of crude 2,3,5-trimethylphenol for solvent crystallization.

[0158] The embodiment of the present invention produces: 99.64% and 99.6% 3,4-dimethylphenol, 99.3% m-isopropylphenol, 99.7% 2,3,6-trimethylphenol, 99.1% 2-ethyl-3-methylphenol, 99.7% p-isopropylphenol, 99.5% 3-methyl-5-ethylphenol, 99.8% 2,3,5-trimethylphenol, and 99.52% antioxidant 2,6-di-tert-butyl-p-isopropylphenol.

[0159] Example 3

[0160] Dealkylation and alkylation reactions of 3-ethyl-5-methylphenol / 2,3,5-trimethylphenol mixed fractions

[0161] (1) The raw materials are 228.4 parts of 3-ethyl-5-methylphenol / 2,3,5-trimethylphenol in the second step of Example 1 (136 parts of 3-ethyl-5-methylphenol, 90.9 parts of 2,3,5-trimethylphenol, and 1.0 part of 2,4,5-trimethylphenol), 216.1 parts of the solvent crystallization mother liquor desolvation residue of the crude 3-ethyl-5-methylphenol in the fourth step (125.9 parts of 3-ethyl-5-methylphenol, 85.6 parts of 2,3,5-trimethylphenol, and 3.9 parts of 2,4,5-trimethylphenol), 268.8 parts of 3-ethyl-5-methylphenol / 2,3,5-trimethylphenol obtained in the second step of Example 2 (148.6 parts of 3-ethyl-5-methylphenol, 112.1 parts of 2,3,5-trimethylphenol, and 7.6 parts of 2,4,5-trimethylphenol), and 350 parts of phenol.

[0162] In a stainless steel high-pressure reactor with an external stainless steel condenser and an inner coil, 650 parts of acidic silicon-aluminum-cadmium oxide solid catalyst (silicon-aluminum-cadmium ratio of 1:2:0.02) were loaded, 713.3 parts of the 3-ethyl-5-methylphenol / 2,3,5-trimethylphenol mixture obtained in the second step (410.5 parts of 3-ethyl-5-methylphenol, 288.6 parts of 2,3,5-trimethylphenol, 12.5 parts of 2,4,5-trimethylphenol, and 1.7 parts of others) and 350 parts of phenol were added, 10 parts of sulfuric acid were added, the reactor was sealed, 10 parts of hydrogen was introduced, the temperature was raised to 500°C, the reaction was reacted for 6 hours, 3-methyl-5-ethylphenol was sampled and detected to be 1.83%, the reaction was terminated, and the inner coil was filled with a process The temperature of the heat transfer oil was cooled by programmed cooling (the temperature of the heat transfer oil was gradually reduced from high temperature to 250°C), and the temperature was reduced to 250°C in 1 hour, and the reaction was continued for 2 hours; the temperature of the inner coil was continued to be cooled by programmed cooling of the heat transfer oil, and the temperature was reduced to 180°C in 1 hour, and a small amount of ethylene and other gases remaining after the reaction were slowly discharged, and the pressure was reduced to normal pressure, and the temperature was continued to be reduced to 90°C, and 1058.8 parts of products were obtained by filtration (containing sulfuric acid and its reaction products, 57.1 parts of phenol, 329.3 parts of cresol, 346.3 parts of ethylphenol, 20.1 parts of 3-ethyl-5-methylphenol, 267.2 parts of 2,3,5-trimethylphenol, 2.2 parts of 2,4,5-trimethylphenol, 25.5 parts of xylenol, and 1.1 parts of others).

[0163] (2) Distillation

[0164] 1058.8 parts of the dealkylation and alkylation products of 3-ethyl-5-cresol / 2,3,5-trimethylphenol were added to the kettle of the distillation tower (100 parts of high-boiling dimethyl diphenyl ether were previously added to the kettle), and vacuum distillation (vacuum degree -0.088 MPa, reflux ratio 20-25:1) was performed to obtain 54.1 parts of 99.5% phenol, 326 parts of 99.3% cresol (89.1% of m-cresol, 8.3% of p-cresol, 1.8% of o-cresol, 0.5% of o-ethylphenol, and 0.3% of others), 8.6 parts of mixed xylenols, and 364.9 parts of 99.5% phenol. 9.48% 3,5-dimethylphenol / m-p-ethylphenol / 3,4-dimethylphenol (93.94% m-p-ethylphenol, 4.16% 3,5-dimethylphenol, 1.38% 3,4-dimethylphenol, 0.52% others), 45.1 parts of a mixed fraction of 3-ethyl-5-methylphenol / 2,3,5-trimethylphenol (37.47% 3-ethyl-5-methylphenol, 61.86% 2,3,5-trimethylphenol, 0.67% others), 167.1 parts of 98.2% 2,3,5-trimethylphenol, and 72.6 parts of 99.68% 2,3,5-trimethylphenol.

[0165] (3) Refining of 2,3,5-trimethylphenol

[0166] Add 167.1 parts of 98.2% 2,3,5-trimethylphenol and 500 parts of 90-120°C petroleum ether into the reactor, start stirring, heat to 75°C to completely dissolve the materials, then cool to 35°C with a cold water bath, then cool to 20°C with an ice water bath, keep warm for 2 hours, filter, drain, and dry to obtain 155.7 parts of 99.63% 2,3,5-trimethylphenol, with a refining yield of 94.53%. The refined mother liquor (containing petroleum ether and 2,3,5-trimethylphenol, 3-ethyl-5-methylphenol, etc.) is analyzed for the content of phenolic substances (after deducting petroleum ether, the content of 2,3,5-trimethylphenol is 78.7%), and used as a partial refining solvent for ≥70% 2,3,5-trimethylphenol crude product.

[0167] The embodiment of the present invention produces: 99.5% phenol, 99.3% cresol, 99.48% 3,5-dimethylphenol / m-p-ethylphenol / 3,4-dimethylphenol, 99.68% 2,3,5-trimethylphenol, and 99.63% 2,3,5-trimethylphenol.

[0168] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0169] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within the scope of protection of the present invention.

Claims

1. A method for refining 3-methyl-5-ethylphenol and 2,3,5-tricresol from a trimethylol mixture, characterized in that: The following steps are involved: (1) subjecting the trimethylol mixture to a rectification treatment to obtain a mixed trimethylol; (2) subjecting the mixed trimethylol, catalyst and isobutylene obtained in step (1) to a tertiary butylation reaction; (3) washing the substance obtained in step (2) to obtain a tert-butyl reaction product, distilling the obtained tert-butyl reaction product at atmospheric pressure, and then rectifying it at reduced pressure to obtain ≥85% crude 3-methyl-5-ethylphenol, a 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction, ≥70% crude 2,3,5-tricresin, tert-butylphenol and a distillation still residue; (4) subjecting the crude 3-methyl-5-ethylphenol with a concentration of ≥85% obtained in step (3) to crystallization and purification to obtain 3-methyl-5-ethylphenol with a concentration of ≥99%; (5) The crude product of ≥70% 2,3,5-trimethylphenol obtained in step (3) is subjected to crystallization purification to obtain ≥99% 2,3,5-trimethylphenol.

2. The method for refining 3-methyl-5-ethylphenol and 2,3,5-tricresol from a trimethylol mixture according to claim 1, characterized in that: In the step (1), the tricresol mixture comprises at least one of a xylenol fraction, a xylenol distillation residue, a tricresol fraction or a crude phenol distillation residue; And / or, in the step (1), the distillation treatment is carried out in a distillation tower having a theoretical plate number of not less than 100; And / or, the composition of the mixed trimethylols includes: 0-80% of 3,4-dimethylphenol, 0-30% of 2,3,6-trimethylphenol, 1-50% of 3-methyl-5-ethylphenol, 0-30% of p-isopropylphenol, 0-50% of m-isopropylphenol, 0.1-50% of 2,3,5-trimethylphenol, 0-30% of 3-methyl-4-ethylphenol, and 0-10% of butylphenol, calculated in percentage by weight.

3. The method for refining 3-methyl-5-ethylphenol and 2,3,5-tricresol from a trimethylol mixture according to claim 1, characterized in that: In the step (2), the catalyst includes at least one of sulfuric acid, phosphoric acid, p-toluenesulfonic acid, aminosulfonic acid, strong acid resin, zirconium oxide or phosphotungstic acid; And / or, the amount of the catalyst is 1 to 30 wt% of the mixed trimethylol; And / or, the amount of isobutylene added is 20 to 300 wt % of the mixed trimethylol; And / or, the temperature of the tert-butylation reaction is 30 to 150° C., and the time of the tert-butylation reaction is 2 to 12 hours.

4. The method for refining 3-methyl-5-ethylphenol and 2,3,5-tricresol from a trimethylol mixture according to claim 1, characterized in that: In the step (3), the washing treatment includes water washing and alkali washing; And / or, the vacuum distillation is carried out in a distillation kettle having a theoretical plate number of 100 to 350; And / or, the pressure of the vacuum distillation is -0.05 to -0.1 MPa, and the reflux ratio is 15 to 25:

1.

5. The method for refining 3-methyl-5-ethylphenol and 2,3,5-tricresol from a trimethylol mixture according to claim 1, characterized in that: In the step (3), the tert-butylphenol is at least one of 6-tert-butyl-3,4-dimethylphenol, 6-tert-butyl-m-isopropylphenol, 4-tert-butyl-2,3,6-trimethylphenol, 6-tert-butyl-3-methyl-4-ethylphenol and 2,6-di-tert-butyl-p-isopropylphenol obtained in sequence in a vacuum distillation process; Preferably, concentrated sulfuric acid is added to the 6-tert-butyl-3,4-dimethylphenol, 6-tert-butyl-m-isopropylphenol, 4-tert-butyl-2,3,6-trimethylphenol, and 6-tert-butyl-3-methyl-4-ethylphenol to carry out a deisobutylene reaction, and after the reaction is completed, the temperature is lowered and an alkali solution is added to neutralize the mixture, and then the mixture is washed with water. After the separation, the layers are stratified and distilled to obtain 3,4-dimethylphenol, m-isopropylphenol, 2,3,6-trimethylphenol, and 3-methyl-4-ethylphenol. Preferably, the amount of concentrated sulfuric acid added is 1 to 2 wt % of the tert-butyl phenol, the deisobutylene reaction is carried out at 160 to 200° C. for 1 to 3 h, and the removed isobutylene is reused.

6. The method for refining 3-methyl-5-ethylphenol and 2,3,5-tricresol from a trimethylol mixture according to claim 1, characterized in that: In the step (4), the crystallization refining treatment comprises: adding a first solvent to a crude product of ≥85% 3-methyl-5-ethylphenol, heating to dissolve it, then cooling it down to crystallize it, then filtering to obtain a filtrate and a filter cake, and performing a melt crystallization treatment on the filter cake; Preferably, the first solvent comprises at least one of alcohols with 1 to 4 carbon atoms, alkanes with 6 to 8 carbon atoms, petroleum ether, halogenated hydrocarbons or benzene; and / or, the first solvent is 0.5 to 5 times the mass of ≥85% crude 3-methyl-5-ethylphenol; And / or, the temperature of the heating dissolution is 60 to 90° C., the temperature of the cooling crystallization is -10 to 10° C., and the crystallization time is 1 to 3 hours; And / or, the melt crystallization comprises adding the filter cake into a melt crystallizer, heating the filter cake to 57±0.5°C, then cooling the filter cake to 52±0.3°C at a rate of 0.3-0.7°C / h, and maintaining the temperature for 2-20h for crystallization, pouring out the uncrystallized solution after the crystallization is completed, heating the solid on the melt crystallizer to 53±0.2°C at a rate of 0.1-0.5°C / h, and melting the solid to obtain ≥99% of 3-methyl-5-ethylphenol; heating the remaining material on the crystallizer until it is completely melted as the rear portion.

7. The method for refining 3-methyl-5-ethylphenol and 2,3,5-tricresol from a trimethylol mixture according to claim 1, characterized in that: In the step (5), the crystallization refining treatment comprises: adding a second solvent to a crude product of ≥70% 2,3,5-trimethylphenol, heating to dissolve the solvent, then cooling the solvent to crystallize the solvent, filtering the solvent to obtain a filtrate and a filter cake, and subjecting the filter cake to a melt crystallization treatment; Preferably, the second solvent comprises at least one of alcohols with 1 to 4 carbon atoms, alkanes with 6 to 8 carbon atoms, petroleum ether, halogenated hydrocarbons or benzene; and / or, the second solvent is 0.1 to 5 times the mass of ≥70% 2,3,5-trimethylphenol; And / or, the temperature of the heating dissolution is 60-100° C., the temperature of the cooling crystallization is 0-20° C., and the time of the crystallization is 1-3 hours. And / or, the melt crystallization includes adding the filter cake into a melt crystallizer, heating it to 98±0.5°C, then cooling it to 93±0.3°C at a rate of 0.3-0.7°C / h, and keeping it warm for 3-20h for crystallization, pouring out the uncrystallized solution after the crystallization is completed, heating the solid on the melt crystallizer to 94±0.2°C at a rate of 0.1-0.5°C / h, melting it to obtain ≥99% of 2,3,5-trimethylphenol; heating until the remaining material on the crystallizer is completely melted as the rear portion.

8. The method for refining 3-methyl-5-ethylphenol and 2,3,5-tricresol from a trimethylol mixture according to claim 1, characterized in that: The 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction obtained in step (3), phenol, silicon-aluminum-cadmium oxide and an acidic catalyst are added to a reactor to carry out dealkylation and alkyl translocation reactions, and after the reaction is completed, the filtrate is filtered to obtain a filtrate, and the filtrate is distilled to obtain cresol, mixed xylenols, ≥95% crude 2,3,5-tricresin and 99% 2,3,5-tricresin; Preferably, a second solvent is added to the ≥95% 2,3,5-trimethylphenol crude product, the temperature is raised to 60-90°C for dissolution, and then the temperature is lowered to 0-20°C. After keeping the temperature for 2 hours, the filtrate and filter cake are obtained by filtration, and the filter cake is dried to obtain ≥99% 2,3,5-trimethylphenol; the second solvent includes at least one of alcohols with 1 to 4 carbon atoms, alkanes with 6 to 8 carbon atoms, petroleum ether, halogenated hydrocarbons or benzene; and the second solvent is 0.1 to 5 times the mass of ≥95% 2,3,5-trimethylphenol.

9. The method for refining 3-methyl-5-ethylphenol and 2,3,5-tricresol from a trimethylol mixture according to claim 8, characterized in that: The mass ratio of silicon oxide, aluminum oxide and cadmium oxide in the silicon-aluminum-cadmium oxide is 0.1-10:10-0.1:0.01-0.5, and the amount of the silicon-aluminum-cadmium oxide is 0-50wt% of the mixed fraction of 3-methyl-5-ethylphenol / 2,3,5-trimethylphenol; and / or, the acidic catalyst comprises at least one of sulfuric acid, phosphoric acid, hydrogen halide, aminosulfonic acid, benzenesulfonic acid or toluenesulfonic acid; And / or, the acidic catalyst is used in an amount of 0.1 to 10 wt % of the 3-methyl-5-ethylphenol / 2,3,5-trimethylphenol mixed fraction; and / or, the amount of phenol used is 0.1 to 100 wt % of the mixed phenol of 3-methyl-5-ethylphenol / 2,3,5-trimethylphenol; And / or, the dealkylation and alkylation reactions are carried out at 350-800° C. for 1-10 hours, and then the temperature is lowered to 200-350° C. to synthesize ethylphenol, and the reaction time is 2-8 hours.

10. The method for refining 3-methyl-5-ethylphenol and 2,3,5-tricresol from a trimethylol mixture according to claim 1, characterized in that: The 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction obtained in step (3) is subjected to secondary distillation to obtain ≥85% of crude 3-methyl-5-ethylphenol, a 3-methyl-5-ethylphenol / 2,3,5-tricresin mixed fraction and ≥70% of crude 2,3,5-tricresin.