Method for separating 2, 4-xylenol and 2, 5-xylenol

Abstract

The invention relates to a method for separating 2, 4-xylenol and 2, 5-xylenol, and the method comprises the following steps: S1, mixing a xylenol mixture containing 2, 4-xylenol and 2, 5-xylenol, a heptylation reagent and an acid catalyst for a first reaction, neutralizing, washing and layering the reaction liquid obtained by the first reaction, and removing a water layer to obtain a first reaction material; and S2, carrying out rectification treatment on the first reaction material. The method disclosed by the invention is simple and easy to implement, strong in operability, multiple in product variety and high in purity, and the byproduct 6-isoheptyl-2, 4-xylenol as a polymerization inhibitor has certain economic benefits.

Description

Technical Field

[0001] The present disclosure relates to the technical field of synthesis and separation of coal chemical products, and in particular to a method for separating 2,4-dimethylphenol and 2,5-dimethylphenol. Background Art

[0002] Using crude phenol or industrial xylenol as raw material, distillation produces a certain mixed content of 2,4-xylenol and 2,5-xylenol. Since the boiling points of 2,4-xylenol and 2,5-xylenol differ by less than 1°C, traditional methods such as crystallization and distillation cannot effectively separate them. Traditional methods can react 2,4-xylenol and 2,5-xylenol with isobutylene to produce 6-tert-butyl-2,4-xylenol and 4-tert-butyl-2,5-xylenol, which have a boiling point difference of 16°C. Therefore, distillation can be used to separate them. 6-tert-butyl-2,4-xylenol and 4-tert-butyl-2,5-xylenol are heated under acidic conditions to remove isobutylene. Secondary distillation yields 99% 2,4-xylenol and 99% 2,5-xylenol, respectively, thus achieving the separation of 2,4-xylenol and 2,5-xylenol.

[0003] However, 2,4 / 2,5-xylenol extracted and refined from gasified phenol, especially medium- and low-temperature phenol-containing coal tar, generally contains impurities such as 2-ethyl-6-methylphenol, o-isopropylphenol, and 2,3-xylenol with similar boiling points. They cannot be separated by distillation, and it is also difficult to separate 2,5-xylenol and 2-ethyl-6-methylphenol by tert-butylation. CN201810102442.5 discloses a separation method for extracting 2,4-dimethylphenol and 2,5-dimethylphenol from crude phenol. This application also uses isobutylene to react with 2,4- / 2,5-dimethylphenol to produce 6-tert-butyl-2,4-dimethylphenol (boiling point 247°C) and 4-tert-butyl-2,5-dimethylphenol (boiling point 265°C), which are then distilled to obtain pure 6-tert-butyl-2,4-dimethylphenol and 4-tert-butyl-2,5-dimethylphenol; then the isobutylene is removed at a high temperature of 180-200°C under the catalysis of sulfuric acid to produce 2,4-dimethylphenol and 2,5-dimethylphenol; this method is a traditional method for separating 2,4 / 2,5-dimethylphenol, which is similar to the method for separating m-para-cresol using the isobutylene method. CN201310347375.0 discloses an asymmetric hindered phenol antioxidant and its synthesis method. This application uses boron trifluoride etherate to catalyze the reaction of excess styrene and 2,4-xylenol at 45-50°C to synthesize the hindered phenol antioxidant 2,4-dimethyl-6-phenylethylphenol, resulting in high operating costs. Existing technologies cannot directly separate vaporized phenols, particularly 2,4 / 2,5-xylenol mixtures extracted and refined from low-temperature phenol-containing coal tar, through distillation, resulting in high operating costs. Summary of the Invention

[0004] The purpose of the present disclosure is to provide a method for separating 2,4-dimethylphenol and 2,5-dimethylphenol. The method is simple and easy to operate, has strong operability, produces a variety of products with high purity, and produces a by-product polymerization inhibitor 6-isoheptyl-2,4-dimethylphenol, which has certain economic benefits.

[0005] In order to achieve the above object, the present disclosure provides a method for separating 2,4-dimethylphenol and 2,5-dimethylphenol, the method comprising the following steps: S1, mixing a xylenol mixture containing 2,4-xylenol and 2,5-xylenol, a heptylating agent and an acidic catalyst to perform a first reaction, neutralizing, washing and layering the reaction solution obtained by the first reaction, and removing the water layer to obtain a first reaction material; S2. performing rectification treatment on the first reaction material.

[0006] Optionally, the xylenol mixture further comprises one or more of 2,3-xylenol, 2-ethyl-6-methylphenol and o-isopropylphenol; Optionally, the xylenol mixture contains 70-100% by weight of mixed phenol, 0-10% by weight of 2,3-xylenol, 0-15% by weight of 2-ethyl-6-methylphenol, and 0-15% by weight of o-isopropylphenol; the mass ratio of 2,4-xylenol to 2,5-xylenol in the mixed phenol is (0.2-5):1, preferably (0.5-2):1.

[0007] Optionally, in step S1, the molar ratio of the xylenol mixture to the heptylating agent is 1:(0.8-3), preferably 1:(1-2); The mass ratio of the xylenol mixture to the acidic catalyst is 100:(1-10); The heptylating agent includes heptene, and the heptene includes one or more of 1-heptene, 2-heptene and 3-heptene; The acidic catalyst includes an inorganic acid, which includes one or more of sulfuric acid, phosphoric acid, and aminosulfonic acid; the concentration of the inorganic acid is 85-100%.

[0008] Optionally, step S1 further includes: adding a reaction aid to the first reaction, wherein the reaction aid includes 6-isoheptyl-2,4-dimethylphenol, and the mass ratio of the dimethylphenol mixture to the 6-isoheptyl-2,4-dimethylphenol is 100:(0.01~0.5).

[0009] Optionally, in step S1, the conditions of the first reaction include: temperature of 60-100° C., time of 8-12 h; In step S1, the neutralization comprises: adjusting the pH of the reaction solution obtained after the first reaction to 7-8, optionally using alkaline solution to adjust the pH; Optionally, the alkali solution includes an inorganic alkali solution, and the inorganic alkali includes one or more of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate and sodium bicarbonate.

[0010] Optionally, the distillation treatment includes: S21, subjecting the first reaction material to a first stage distillation treatment to separate unreacted heptylating agent and 2,5-dimethylphenol; S22. The material obtained by the first distillation treatment is subjected to a second distillation treatment to obtain a 6-isoheptyl-2,4-dimethylphenol logistics, a first dimethylphenol mixture, a 6-isoheptyl-2,3-dimethylphenol logistics, a second dimethylphenol mixture, a 4-isoheptyl-2-ethyl-6-methylphenol logistics and a 4,6-diisoheptyl-2-isopropylphenol logistics.

[0011] Optionally, the conditions of the first stage distillation treatment include: the number of theoretical plates of the distillation tower is 100 to 300, the pressure is -0.07 MPa to -0.09 MPa, and the reflux ratio is 2 to 10:1; The conditions of the second stage distillation treatment include: the number of theoretical plates of the distillation tower is 100-300, the pressure is 200 Pa to 20 Pa, and the reflux ratio is 5-25:1.

[0012] Optionally, the method further includes: contacting the 6-isoheptyl-2,3-xylenol stream with an inorganic acid for a second reaction, neutralizing the resulting second reaction solution and subjecting it to a third distillation treatment to obtain a regenerated heptylating agent and a 2,3-xylenol product; and / or, contacting the 4-isoheptyl-2-ethyl-6-methylphenol stream with an inorganic acid for a second reaction, neutralizing the resulting second reaction solution and subjecting it to a third distillation treatment to obtain a regenerated heptylating agent and a 2-ethyl-6-methylphenol product; and / or, The 4,6-diisoheptyl-2-isopropylphenol flow is contacted with an inorganic acid to perform a second reaction, and the obtained second reaction liquid is neutralized and subjected to a third rectification treatment to obtain a regenerated heptylating agent and an o-isopropylphenol product.

[0013] Optionally, the mass ratio of the 6-isoheptyl-2,3-dimethylphenol stream to the inorganic acid is 100:(0.5-3); and / or, The mass ratio of the 4-isoheptyl-2-ethyl-6-methylphenol stream to the inorganic acid is 100:(0.5-3); and / or, The mass ratio of the 4,6-diisoheptyl-2-isopropylphenol stream to the inorganic acid is 100:(0.5-3); The inorganic acid includes one or more of sulfuric acid, phosphoric acid, and aminosulfonic acid; The conditions of the second reaction include: temperature of 160-200°C and time of 1-4 hours; The conditions for the third distillation treatment include: the number of theoretical plates of the distillation tower is 100-300, the pressure is -0.085 to -0.098 MPa, and the reflux ratio is 5-10:1.

[0014] Optionally, the method further comprises: distilling the first xylenol mixture to obtain 6-isoheptyl-2,4-xylenol and 6-isoheptyl-2,3-xylenol; and / or, The second xylenol mixture is subjected to distillation treatment to obtain 6-isoheptyl-2,3-xylenol and 4-isoheptyl-2-ethyl-6-methylphenol.

[0015] Through the above technical solution, the present invention uses a heptylating agent to react with 2,4-xylenol under certain conditions to generate a highly efficient polymerization inhibitor 6-isoheptyl-2,4-xylenol, while the heptylating agent does not react with 2,5-xylenol. The boiling point difference between 6-isoheptyl-2,4-xylenol and 2,5-xylenol is large. 6-isoheptyl-2,4-xylenol and 2,5-xylenol with high purity are obtained by distillation separation, thereby achieving the separation of 2,4-xylenol and 2,5-xylenol. In addition, for industrial xylenol containing 2,4-xylenol and 2,5-xylenol, the heptylating agent is used to cause the impurities therein to undergo a heptylation reaction. The boiling points of the heptylating products are greatly different. Further, the impurities in the industrial xylenol mixture can be separated in sequence by combining distillation, deheptylation, and re-distillation. The method disclosed herein is simple and easy to implement, has strong operability, produces a wide variety of products with high purity, and has certain economic benefits. In addition, the method disclosed herein produces the polymerization inhibitor 6-isoheptyl-2,4-dimethylphenol as a by-product. Compared with using the higher-purity 2,4-dimethylphenol alone to prepare 6-isoheptyl-2,4-dimethylphenol, the method disclosed herein has low raw material costs and high product purity, thereby significantly reducing raw material costs.

[0016] Other features and advantages of the present disclosure will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0017] The following describes the specific embodiments of the present disclosure in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0018] The present disclosure provides a method for separating 2,4-dimethylphenol and 2,5-dimethylphenol, the method comprising the following steps: S1, mixing a xylenol mixture containing 2,4-xylenol and 2,5-xylenol, a heptylating agent and an acidic catalyst to perform a first reaction, neutralizing, washing and layering the reaction solution obtained by the first reaction, and removing the water layer to obtain a first reaction material; S2. performing rectification treatment on the first reaction material.

[0019] The present invention uses a heptylating agent to react with 2,4-xylenol under certain conditions to generate a high-efficiency polymerization inhibitor, 6-isoheptyl-2,4-xylenol. The heptylating agent does not react with 2,5-xylenol, and the boiling point difference between 6-isoheptyl-2,4-xylenol and 2,5-xylenol is large. 6-isoheptyl-2,4-xylenol and 2,5-xylenol with higher purity are obtained by distillation separation, thereby achieving the separation of 2,4-xylenol and 2,5-xylenol. In addition, for industrial xylenol containing 2,4-xylenol and 2,5-xylenol, the heptylating agent is used to cause impurities in the mixture of 2,4-xylenol and 2,5-xylenol to undergo a heptylation reaction. The boiling points of the heptylating products are greatly different. The impurities in the industrial xylenol mixture are separated in sequence by further combining distillation, deheptylation, and re-distillation. The method disclosed herein is simple and easy to implement, has strong operability, produces a wide variety of products with high purity, and has certain economic benefits. In addition, the method disclosed herein produces the polymerization inhibitor 6-isoheptyl-2,4-dimethylphenol as a by-product. Compared with using the higher-purity 2,4-dimethylphenol alone to prepare 6-isoheptyl-2,4-dimethylphenol, the method disclosed herein has low raw material costs and high product purity, thereby significantly reducing raw material costs.

[0020] 2,5-Dimethylphenol (CAS#95874): Boiling point 211.2°C, melting point 75°C. It is an organic pharmaceutical and dye intermediate used in the synthesis of lipid-lowering drug gemfibrozil and vitamin E intermediate 2,3,6-trimethylphenol.

[0021] 2,4-Dimethylphenol (CAS#105679): Boiling point 211°C, it is an organic pharmaceutical intermediate used in the synthesis of high-efficiency polymerization inhibitors and pharmaceutical intermediates 6-tert-butyl-2,4-dimethylphenol, 6-phenylethyl-2,4-dimethylphenol, and the pesticide dimethylamine glufosinate intermediate 2,4-dimethyl-6-nitrophenol; it also has important applications in pesticides, plastics, rubber, etc.

[0022] According to one embodiment of the present disclosure, the xylenol mixture comprises 23% to 77% by weight of 2,4-xylenol and 23% to 77% by weight of 2,5-xylenol. For example, the weight content of 2,4-xylenol may be 23%, 30%, 33%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 67%, 70%, 75%, 77%, or a value in a range consisting of any two thereof, and is preferably 33% to 67%; the weight content of 2,5-xylenol may be 23%, 30%, 33%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 67%, 70%, 75%, 77%, or a value in a range consisting of any two thereof, and is preferably 33% to 67%; the weight ratio of 2,4-xylenol to 2,5-xylenol is not particularly limited, and may be, for example, (0.2 to 5):1, and is preferably (0.5 to 2:1).

[0023] According to one embodiment of the present disclosure, in step S1, the molar ratio of the xylenol mixture to the heptylating agent is 1:(0.8-3), for example, 1:0.8, 1:1, 1:1.6, 1:2, 1:2.3, 1:2.5, 1:3, or a value within a range consisting of any two thereof; preferably, 1:(1-2). This embodiment facilitates the heptylation reaction, thereby effectively separating 2,4-xylenol and 2,5-xylenol, and removing impurities from the mixture.

[0024] According to one embodiment of the present disclosure, in step S1, the heptylating agent includes heptene, and the heptene includes one or more of 1-heptene, 2-heptene, and 3-heptene. This embodiment facilitates the heptylation reaction of 2,4-xylenol and impurities in the mixture, thereby effectively separating 2,4-xylenol and 2,5-xylenol, and separating impurities in the mixture.

[0025] According to one embodiment of the present disclosure, in step S1, the mass ratio of the xylenol mixture to the acidic catalyst is 100:(1-10); for example, it can be 100:1, 100:3, 100:5, 100:7, 100:10, or a value within a range consisting of any two thereof, preferably 100:(3-5). This embodiment facilitates the heptylation reaction of 2,4-xylenol and impurities in the mixture, thereby effectively separating 2,4-xylenol from 2,5-xylenol and impurities in the mixture. According to one embodiment of the present disclosure, in step S1, the acidic catalyst comprises an inorganic acid, including one or more of sulfuric acid, phosphoric acid, and sulfamic acid; the concentration of the inorganic acid is 85-100%. This embodiment facilitates the heptylation reaction of 2,4-xylenol and impurities in the mixture, thereby effectively separating 2,4-xylenol from 2,5-xylenol and impurities in the mixture.

[0026] According to one embodiment of the present disclosure, step S1 further comprises: adding a reaction aid to the first reaction, wherein the reaction aid comprises a polymerization inhibitor. The above embodiment is conducive to reducing the dimerization and polymerization reactions of the heptylating agent such as heptene, and improving the utilization efficiency of the heptylating agent.

[0027] According to one embodiment of the present disclosure, the reaction aid is preferably 6-isoheptyl-2,4-dimethylphenol, and the mass ratio of the dimethylphenol mixture to the 6-isoheptyl-2,4-dimethylphenol is 100:(0.01-0.5), for example, 100:0.01, 100:0.03, 100:0.07, 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5, or a value within a range consisting of any two thereof. The above embodiment is beneficial for reducing the dimerization and polymerization reactions of heptylating agents such as heptene, improving the utilization efficiency of the heptylating agents, while not introducing new impurities and reducing production costs.

[0028] According to one embodiment of the present disclosure, in step S1, the conditions of the first reaction include: a temperature of 60-100°C and a time of 8-12 hours; for example, the temperature can be 60°C, 70, 80°C, 90°C, 100°C, or a value in the range of any two thereof, preferably 80-100°C, and the first reaction can be 8h, 9h, 11h, 12h, or a value in the range of any two thereof, preferably 8-10h. The above embodiment is conducive to the heptylation reaction, thereby effectively separating 2,4-dimethylphenol and 2,5-dimethylphenol and impurities in the mixture.

[0029] According to one embodiment of the present disclosure, in step S1, the standard for analyzing the completion of the first reaction can be to detect that the mass content of 2,4-dimethylphenol is less than 0.5 wt % by gas chromatography analysis.

[0030] According to one embodiment of the present disclosure, in step S1, the neutralization includes: adjusting the pH of the reaction solution obtained after the first reaction to 7-8, optionally, using an alkali solution to adjust the pH; optionally, the alkali solution includes an inorganic alkali solution, and the inorganic alkali includes one or more of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate and sodium bicarbonate.

[0031] According to one embodiment of the present disclosure, in step S1, the distillation treatment includes: S2a, subjecting the first reaction material to a first stage distillation treatment to separate unreacted heptylating agent and 2,5-dimethylphenol; S2b, the material obtained from the first distillation treatment is subjected to a second distillation treatment to obtain a 6-isoheptyl-2,4-dimethylphenol stream. The above embodiment is conducive to separating 2,5-dimethylphenol and the heptylation product, and is also conducive to recovering the heptylation reagent.

[0032] According to one embodiment of the present disclosure, in step S2a, the conditions for the first distillation treatment include: a distillation tower with a theoretical plate number of 100 to 300, preferably 150 to 250; a pressure of -0.07 MPa to -0.09 MPa, preferably -0.08 MPa to -0.085 MPa; and a reflux ratio of 2 to 10:1, preferably 3 to 5:1. This embodiment is beneficial for improving the recovery rate of the heptylating agent, while simultaneously isolating 2,5-dimethylphenol, thereby increasing the purity and yield of 2,5-dimethylphenol.

[0033] According to one embodiment of the present disclosure, in step S2b, the conditions for the second distillation treatment include: a distillation tower with a theoretical plate number of 100 to 300, preferably 150 to 250; a pressure of 200 Pa to 20 Pa, preferably 100 Pa to 50 Pa; and a reflux ratio of 5 to 25:1, preferably 10 to 20:1. This embodiment facilitates the production of a high-efficiency polymerization inhibitor as a byproduct, improving product purity and yield.

[0034] According to one embodiment of the present disclosure, the xylenol mixture is industrial xylenol; the xylenol mixture further comprises one or more of 2,3-xylenol, 2-ethyl-6-methylphenol and o-isopropylphenol.

[0035] o-Isopropylphenol: CAS#88-69-7, oily liquid or crystalline solid, melting point 15-16°C, boiling point 212-213°C, used as an intermediate for plasticizers, surfactants, and fragrances. In pesticides, it is mainly used in the production of isoprocarb and leafhopper powder.

[0036] 2-Ethyl-6-methylphenol: CAS#1687-64-5, boiling point 209.8°C, melting point 45-46°C. 2-Ethyl-6-methylphenol has insecticidal and fungicidal properties. It is a raw material for the production of the important pesticide herbicide butachlor, dyes, and the pharmaceutical intermediate 2-ethyl-6-methylaniline. It can also be used in other organic syntheses.

[0037] 2,3-Dimethylphenol: CAS#526-75-0, boiling point 217°C, mainly used in the manufacture of phenolic resins, plasticizers, dyes, flotation agents, insecticides, fungicides, mold adhesives, wood preservatives, antioxidants, lubricant additives, etc. It can also be used to synthesize 2,3,6-trimethylphenol, an intermediate for vitamin E, and 2,3-dimethylaniline, an intermediate for pesticides.

[0038] According to one embodiment of the present disclosure, the xylenol mixture further contains other cresols / xylenols or other phenolic compound impurities, such as industrial xylenol extracted from medium- and low-temperature phenol-containing coal tar. The contents of 2,4-xylenol and 2,5-xylenol in the xylenol mixture can vary within a certain range, for example, the weight content of 2,4-xylenol can be 35-65%, and the weight content of 2,5-xylenol can be 23-50%; in a further embodiment, the xylenol mixture contains 70-100% by weight of mixed phenol, 0-10% by weight of 2,3-xylenol, 0-15% by weight of 2-ethyl-6-methylphenol, and 0-15% by weight of o-isopropylphenol; the mass ratio of 2,4-xylenol to 2,5-xylenol in the mixed phenol is (1-2):1.

[0039] Industrial xylenol generally contains impurities such as 2-ethyl-6-methylphenol, o-isopropylphenol, and 2,3-xylenol with similar boiling points. They cannot be separated by distillation, and it is difficult to separate 2,5-xylenol and 2-ethyl-6-methylphenol by tert-butylation. The inventors of the present application have found that 2,5-xylenol does not react with a heptylating agent, while 2,4-xylenol can react with a heptylating agent to produce 6-isoheptyl-2,4-xylenol. The impurity 2-ethyl-6-methylphenol can react with a heptylating agent to produce 4-isoheptyl-2-ethyl-6-methylphenol, and o-isopropylphenol can react with a heptylating agent to produce 4,6-diisoheptyl-2-isopropylphenol. 2,3-Xylenol can react with a heptylating agent to produce 6-isoheptyl-2,3-xylenol. At the same time, since the boiling point of 4,6-diisoheptyl-2-isopropylphenol is more than 15°C higher than that of 4-isoheptyl-2-ethyl-6-methylphenol, the boiling point of 4-isoheptyl-2-ethyl-6-methylphenol is about 20°C higher than that of 6-isoheptyl-2,4-xylenol, and the boiling point of 4-isoheptyl-2-ethyl-6-methylphenol is about 15°C higher than that of 6-isoheptyl-2,3-xylenol, 2,5-xylenol, 2,4-xylenol, 2,3-xylenol, o-isopropylphenol, and 2-ethyl-6-methylphenol can be separated through isoheptylation reaction, distillation, deheptylation, and secondary distillation.

[0040] According to an embodiment in which the mixed xylenol further comprises other phenolic compounds, in step S1, the distillation treatment comprises: S21, subjecting the first reaction material to a first stage distillation treatment to separate unreacted heptylating agent and 2,5-dimethylphenol; S22. The material obtained from the first distillation treatment is subjected to a second distillation treatment to obtain a 6-isoheptyl-2,4-xylenol stream, a first xylenol mixture, a 6-isoheptyl-2,3-xylenol stream, a second xylenol mixture, a 4-isoheptyl-2-ethyl-6-methylphenol stream, and a 4,6-diisoheptyl-2-isopropylphenol stream. The above embodiment is conducive to separating 2,5-xylenol and heptyl products.

[0041] According to one embodiment of the present disclosure, in step S21, the conditions for the first distillation treatment include: a distillation tower with a theoretical plate number of 100 to 300, preferably 150 to 250; a pressure of -0.07 MPa to -0.09 MPa, preferably -0.08 MPa to -0.085 MPa; and a reflux ratio of 2 to 10:1, preferably 3 to 5:1. This embodiment is beneficial for improving the recovery rate of the heptylating agent and increasing the purity and yield of 2,5-dimethylphenol.

[0042] According to one embodiment of the present disclosure, in step S22, the conditions for the second distillation treatment include: a distillation tower with a theoretical plate number of 100 to 300, preferably 150 to 250; a pressure of 200 Pa to 20 Pa, preferably 100 Pa to 50 Pa; and a reflux ratio of 5 to 25:1, preferably 10 to 20:1. This embodiment facilitates the production of high-efficiency polymerization inhibitors and other heptylation products of phenolic compounds, improving product variety, purity, and yield.

[0043] According to one embodiment of the present disclosure, the method further includes: contacting the 6-isoheptyl-2,3-xylenol stream with an inorganic acid for a second reaction, neutralizing the resulting second reaction liquid and performing a third distillation treatment to obtain a regenerated heptylating agent and a 2,3-xylenol product. The above embodiment is conducive to the deheptylation reaction, separating 2,4-xylenol and 2,5-xylenol, and separating impurities in the mixture, while recovering the heptylating agent. In the above embodiment, the standard for analyzing the end of the second reaction can be that the mass content of 6-isoheptyl-2,3-xylenol can be less than 0.5% by gas spectroscopy.

[0044] According to one embodiment of the present disclosure, the mass ratio of the 6-isoheptyl-2,3-dimethylphenol stream to the inorganic acid is 100:(0.5-3), for example, 100:0.5, 100:0.8, 100:1, 100:1.6, 100:2.1, 100:3, or a value within a range consisting of any two thereof, preferably 100:(1-2). This embodiment facilitates the deheptylation reaction of the 6-isoheptyl-2,3-dimethylphenol stream, the separation of 2,4-dimethylphenol and 2,5-dimethylphenol, and the separation of impurities in the mixture.

[0045] According to one embodiment of the present disclosure, the method further includes: contacting the 4-isoheptyl-2-ethyl-6-methylphenol logistics with an inorganic acid for a second reaction, neutralizing the resulting second reaction liquid and performing a third rectification treatment to obtain a regenerated heptylating agent and a 2-ethyl-6-methylphenol product. The above embodiment is conducive to the deheptylation reaction of the 4-isoheptyl-2-ethyl-6-methylphenol logistics, separating 2,4-dimethylphenol and 2,5-dimethylphenol, and separating impurities in the mixture, while recovering the heptylating agent. In the above embodiment, the standard for analyzing the end of the second reaction can be that the mass content of 4-isoheptyl-2-ethyl-6-methylphenol can be less than 0.5% by gas spectroscopy.

[0046] According to one embodiment of the present disclosure, the mass ratio of the 4-isoheptyl-2-ethyl-6-methylphenol stream to the inorganic acid is 100:(0.5-3), for example, 100:0.5, 100:0.8, 100:1, 100:1.6, 100:2.1, 100:3, or a value within a range consisting of any two thereof, preferably 100:(1-2). This embodiment facilitates the deheptylation reaction of 4-isoheptyl-2-ethyl-6-methylphenol, the separation of 2,4-dimethylphenol and 2,5-dimethylphenol, and the separation of impurities in the mixture.

[0047] According to one embodiment of the present disclosure, the method further includes: contacting the 4,6-diisoheptyl-2-isopropylphenol logistics with an inorganic acid for a second reaction, neutralizing the resulting second reaction liquid and performing a third rectification treatment to obtain a regenerated heptylating agent and an o-isopropylphenol product. The above embodiment is conducive to the deheptylation reaction of 4,6-diisoheptyl-2-isopropylphenol, separating 2,4-dimethylphenol and 2,5-dimethylphenol, and separating impurities in the mixture, while recovering the heptylating agent. In the above embodiment, the standard for analyzing the end of the second reaction can be that the mass content of 6-isoheptyl-2-isopropylphenol can be less than 0.5% by gas spectroscopy detection.

[0048] According to one embodiment of the present disclosure, the mass ratio of the 4,6-diisoheptyl-2-isopropylphenol stream to the inorganic acid is 100:(0.5-3), for example, 100:0.5, 100:0.8, 100:1, 100:1.6, 100:2.1, 100:3, or a value within a range consisting of any two thereof, preferably 100:(1-2). This embodiment facilitates the deheptylation reaction of 4,6-diisoheptyl-2-isopropylphenol, the separation of 2,4-dimethylphenol and 2,5-dimethylphenol, and the separation of impurities in the mixture.

[0049] According to one embodiment of the present disclosure, the inorganic acid includes one or more of sulfuric acid, phosphoric acid, and sulfamic acid, and the concentration of the inorganic acid can be 85% to 100%. The above embodiment is conducive to the deheptylation reaction of the heptyl product and the separation of impurities in the xylenol mixture.

[0050] According to one embodiment of the present disclosure, the conditions for the second reaction include: a temperature of 160-200°C and a time of 1-4 hours. For example, the temperature can be 160°C, 180°C, 190°C, 200°C, or a value within a range consisting of any two thereof, preferably 180-195°C, and the time can be 1 hour, 2 hours, 3 hours, or 4 hours, preferably 2-3 hours. The above embodiment is conducive to the deheptylation reaction of the heptyl product and the separation of impurities in the xylenol mixture.

[0051] According to one embodiment of the present disclosure, the conditions for the third distillation process include: the number of theoretical plates of the distillation tower is 100 to 300, preferably 150 to 250, the pressure is -0.085 to -0.098 MPa, preferably -0.085 to -0.09 MPa, and the reflux ratio is 3 to 10:1, for example, 5:1, 6:1, 8:1, 10:1, or a value within the range of any two thereof, preferably 5 to 8:1. The above embodiment is conducive to separating impurities from the xylenol mixture and improving product yield and purity.

[0052] According to one embodiment of the present disclosure, the method further comprises: distilling the first xylenol mixture to obtain 6-isoheptyl-2,4-xylenol and 6-isoheptyl-2,3-xylenol. The above embodiment is conducive to improving product yield.

[0053] According to one embodiment of the present disclosure, the method further comprises: distilling the second xylenol mixture to obtain 6-isoheptyl-2,3-xylenol and 4-isoheptyl-2-ethyl-6-methylphenol. The above embodiment is conducive to improving product variety and yield.

[0054] According to one embodiment of the present disclosure, the method further includes: mixing the 4-isoheptyl-2-ethyl-6-methylphenol obtained by distillation with the corresponding stream obtained by the second distillation treatment in step S22, and performing the second reaction and the third distillation treatment. This embodiment is conducive to improving product yield and economic benefits.

[0055] According to one embodiment of the present disclosure, the method further includes: mixing the 6-isoheptyl-2,3-dimethylphenol obtained by distillation with the corresponding stream obtained by the second distillation treatment in step S22 to perform the second reaction and the third distillation treatment. This embodiment is conducive to improving product yield and economic benefits.

[0056] The present disclosure is further described in detail below through examples, but is not limited to the present disclosure.

[0057] In the following examples, the calculation method of yield is: Yield of 2,5-xylenol = (weight percentage of product × mass percentage) / weight percentage of 2,5-xylenol in raw material × 100%; Yield of antioxidant 6-isoheptyl-2,4-dimethylphenol = (weight fraction of product × mass percentage) / theoretical yield × 100%; Yield of 2,3-xylenol = (weight percentage of product × mass percentage) / weight percentage of 2,3-xylenol in raw material × 100%; Yield of 2-ethyl-6-methylphenol = (weight percentage of product × mass percentage) / weight percentage of 2-ethyl-6-methylphenol in raw material × 100%; The yield of o-isopropylphenol = (weight percentage of product × mass percentage) / weight percentage of o-isopropylphenol in raw material × 100%.

[0058] Example 1 S1. Add 400 parts by weight of a mixture of 2,4-xylenol and 2,5-xylenol (containing 61.5 wt% of 2,4-xylenol and 38.5 wt% of 2,5-xylenol, with a mass ratio of 2,4-xylenol to 2,5-xylenol of 1.6:1), 525 parts by weight of 1-heptene (the molar ratio of the xylenol mixture to heptene is 1:1.64), 2 parts by weight of 6-isoheptyl-2,4-xylenol (the molar ratio of the xylenol mixture to 6-isoheptyl-2,4-xylenol) into the reactor. The mixture was stirred at 100 ° C. and kept for 7 hours for sampling and analysis. The weight content of 2,4-dimethylphenol was 0.29% by weight, and the reaction was qualified by gas chromatography. 77.7 parts by weight of 31% liquid alkali (sodium hydroxide aqueous solution) and 200 parts by weight of water were added to neutralize the mixture to pH 7.5, and the mixture was separated. The material layer was washed once with 100 parts by weight of water, and the water was separated to obtain a first reaction material. S2. The first reaction material was added to a distillation tower (theoretical plate number is 150), and vacuum distillation was carried out at a pressure of -0.08 MPa and a reflux ratio of 5:1 to obtain 311 parts by weight of unreacted 1-heptene and 147.8 parts by weight of 2,5-dimethylphenol with a content of 99.5%, with a yield of 95.5%; The vacuum degree was then increased to 100 Pa and the reflux ratio was 5:1, and distillation was performed to obtain 416.4 parts by weight of 99.6% antioxidant 6-isoheptyl-2,4-dimethylphenol, with a yield of 93.5%.

[0059] 99.6% antioxidant 6-isoheptyl-2,4-dimethylphenol and 99.5% 2,5-dimethylphenol are sold as products.

[0060] Example 2 S1. Add 1000 parts by weight of a mixture of 2,4-xylenol and 2,5-xylenol (containing 40.4 wt% of 2,4-xylenol, 33.7 wt% of 2,5-xylenol, 7.1 wt% of 2,3-xylenol, 8.6 wt% of 2-ethyl-6-methylphenol, 10.2 wt% of o-isopropylphenol, and a mass ratio of 2,4-xylenol to 2,5-xylenol of 1.2:1), 1413 parts by weight of 2-heptene (the molar ratio of the xylenol mixture to heptene is 1:1.79), 5 parts by weight of 6-isoheptene) into the reactor. -2,4-xylenol (the mass ratio of the xylenol mixture to 6-isoheptyl-2,4-xylenol is 100:0.5), 75 parts by weight of concentrated sulfuric acid (the mass ratio of the xylenol mixture to sulfuric acid is 100:7.5), start stirring, heat to 80°C and keep reacting for 10 hours, take samples for analysis, the 2,4-xylenol content is 0.18wt% and the reaction is qualified, add 194 parts by weight of 31% liquid alkali (sodium hydroxide aqueous solution) and 400 parts by weight of water to neutralize to pH 8, separate the layers, add 200 parts by weight of water to wash once, separate the water, and obtain a first reaction material; S2. The first reaction material was added to a distillation tower (theoretical plate number is 200), and vacuum distilled at a pressure of -0.080 MPa and a reflux ratio of 5:1 to obtain 780.5 parts by weight of 2-heptene and 317.8 parts by weight of 2,5-dimethylphenol with a content of 99.7%, with a yield of 94.0%; Then the vacuum degree was increased to 100 Pa, and the reflux ratio was 20:1, and the distillation was carried out to obtain 439.9 parts by weight of 99.3% antioxidant 6-isoheptyl-2,4-dimethylphenol, with a primary distillation yield of 60%; 328.3 parts by weight of a mixture of 6-isoheptyl-2,4-dimethylphenol and 6-isoheptyl-2,3-dimethylphenol (276.9 parts by weight of 6-isoheptyl-2,4-dimethylphenol, 51.4 parts by weight of 6-isoheptyl-2,3-dimethylphenol), 67.2 parts by weight of 99.1% 6-isoheptyl-2,3-dimethylphenol The following ingredients were prepared from 1,2-dimethyl-2,4-diisoheptyl-2,6-dimethylphenol (13.5 parts by weight of a mixture of 6-isoheptyl-2,3-xymethylphenol and 4-isoheptyl-2-ethyl-6-methylphenol, 124.8 parts by weight of 99.3% 4-isoheptyl-2-ethyl-6-methylphenol (83.7% yield in one distillation), and 242.7 parts by weight of the still residue (241.5 parts by weight of 4,6-diisoheptyl-2-isopropylphenol).

[0061] 242.7 parts by weight of the kettle residue were added to the decomposition kettle, and 3 parts by weight of 98% sulfuric acid was added (the mass ratio of 4,6-diisoheptyl-2-isopropylphenol stream to sulfuric acid was 100:1.23). The temperature was raised to 190° C. and maintained for 2.5 hours under stirring. The gas spectrum detection showed that the content of 6-isoheptyl-2-isopropylphenol was 0.23%, and the reaction was stopped. The temperature was cooled to 90° C. and neutralized with 7.8 parts by weight of 31% sodium hydroxide aqueous solution to a pH of 7.5. The mixture was subjected to vacuum distillation (the number of theoretical plates of the distillation tower was 200, the pressure was -0.085 MPa, and the reflux ratio was 8:1) to obtain 95.9 parts of 99.6% o-isopropyl phenol, the deoctyl reaction yield was 96.5%, and 140.4 parts by weight of regenerated 2-heptene were recovered and used.

[0062] 124.8 parts by weight of 99.3% 4-isoheptyl-2-ethyl-6-methylphenol were added to a decomposition kettle, and 1.5 parts by weight of 98% sulfuric acid was added (the mass ratio of 4-isoheptyl-2-ethyl-6-methylphenol to sulfuric acid was 100:1.2). The temperature was raised to 195° C. with stirring and maintained for 2 hours. Gas chromatography detection showed that the weight content of 4-isoheptyl-2-ethyl-6-methylphenol was 0.15%, and the reaction was stopped. The temperature was lowered to 90° C. and neutralized with 3.9 parts by weight of 31% aqueous sodium hydroxide solution to a pH of 7.5. The mixture was subjected to vacuum distillation (distillation tower with 200 theoretical plates, pressure of -0.085 MPa, reflux ratio of 10:1) to obtain 69.9 parts by weight of 99.6% 2-ethyl-6-methylphenol. The deoctylation reaction yield was 96.7%, and 51.2 parts by weight of regenerated 2-heptene were recovered and used.

[0063] 67.2 parts by weight of 99.1% 6-isoheptyl-2,3-dimethylphenol were added to a decomposition kettle, and 1.5 parts by weight of 98% sulfuric acid was added (the mass ratio of 6-isoheptyl-2,3-dimethylphenol to sulfuric acid was 100:2.2). The temperature was raised to 200° C. and maintained for 1 hour under stirring. The weight content of 6-isoheptyl-2,3-dimethylphenol was 0.12% by gas spectroscopy detection, and the reaction was stopped. The temperature was lowered to 90° C. and neutralized with 3.9 parts by weight of 31% aqueous sodium hydroxide solution to a pH of 7.5. The mixture was subjected to vacuum distillation (the number of theoretical plates of the distillation tower was 200, the pressure was -0.085 MPa, and the reflux ratio was 5:1) to obtain 35.8 parts by weight of 99.4% 2,3-dimethylphenol. The deoctyl reaction yield was 96.3%, and 29.3 parts by weight of 2-heptene were recovered for use.

[0064] 99.3% of 2,5-dimethylphenol, 99.3% of the antioxidant 6-isoheptyl-2,4-dimethylphenol, 99.5% of o-isopropylphenol, 99.6% of 2-ethyl-6-methylphenol, and 99.4% of 2,3-dimethylphenol are sold as products.

[0065] Example 3 The method of this embodiment is the same as that of Example 1, except that the conditions of the first reaction are different. The specific reaction is as follows: Add 400 parts by weight of a mixture of 2,4-xylenol and 2,5-xylenol (containing 61.5 wt% of 2,4-xylenol, 38.5 wt% of 2,5-xylenol, and a mass ratio of 2,4-xylenol to 2,5-xylenol of 1.6:1), 525 parts by weight of 1-heptene (the molar ratio of the xylenol mixture to heptene is 1:1.64), 2 parts by weight of 6-isoheptyl-2,4-xylenol (the mass ratio of the xylenol mixture to 6-isoheptyl-2,4-xylenol is 100:0.5), and 30 parts by weight of concentrated sulfuric acid (the mass ratio of the xylenol mixture to sulfuric acid is 100:7.5) into the reactor, start stirring, heat to 50°C, and react for 10 hours. Sample analysis shows that the weight content of 2,4-xylenol is 1.22%, and the reaction is unqualified. , and then continue the reaction for 5 hours. After sampling and analysis, the weight content of 2,4-dimethylphenol was 0.61%, and the reaction was unqualified. 77.7 parts of 31% liquid alkali (sodium hydroxide aqueous solution) and 200 parts by weight of water were added to neutralize to pH 7.5, and the layers were separated. The material layer was washed once with 100 parts by weight of water, and the water was removed to obtain a first reaction material; the first reaction material was added to a distillation tower (theoretical plate number is 150), and the pressure was -0.09 MPa and the reflux ratio was 5:1. The vacuum distillation was performed to obtain 319 parts by weight of unreacted 1-heptene and 146.9 parts by weight of 2,5-dimethylphenol with a content of 98.4%, with a yield of 93.9%. The vacuum degree was then increased to 100 Pa and distilled to obtain 410 parts by weight of 99.1% antioxidant 6-isoheptyl-2,4-dimethylphenol, with a yield of 91.6%.

[0066] 99.1% of the antioxidant 6-isoheptyl-2,4-xylenol is sold as a product, and 98.4% of the 2,5-xylenol still needs secondary refining to obtain a 99% grade product. The method disclosed herein is simple and easy to implement, has strong operability, can effectively separate 2,4-xylenol and 2,5-xylenol mixture, and the by-product polymerization inhibitor 6-isoheptyl-2,4-xylenol has high yield and high purity, and has certain economic benefits. By comparing Example 1 with Example 3, it can be seen that within the condition range of the preferred first reaction of the present disclosure, the heptyl reaction is more sufficient, the yield and purity of 2,5-xylenol are higher, and the purity and yield of the polymerization inhibitor are higher.

[0067] The preferred embodiments of the present disclosure are described in detail above. However, the present disclosure is not limited to the specific details of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0068] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0069] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for separating 2,4-dimethylphenol and 2,5-dimethylphenol, characterized in that: The method comprises the following steps: S1, mixing a xylenol mixture containing 2,4-xylenol and 2,5-xylenol, a heptylating agent and an acidic catalyst to perform a first reaction, neutralizing, washing and layering the reaction solution obtained by the first reaction, and removing the water layer to obtain a first reaction material; S2. performing rectification treatment on the first reaction material.

2. The method according to claim 1, wherein The xylenol mixture further comprises one or more of 2,3-xylenol, 2-ethyl-6-methylphenol and o-isopropylphenol; Optionally, the xylenol mixture contains 70-100% by weight of mixed phenol, 0-10% by weight of 2,3-xylenol, 0-15% by weight of 2-ethyl-6-methylphenol, and 0-15% by weight of o-isopropylphenol; the mass ratio of 2,4-xylenol to 2,5-xylenol in the mixed phenol is (0.2-5):1, preferably (0.5-2):

1.

3. The method according to claim 1, wherein In step S1, the molar ratio of the xylenol mixture to the heptylating agent is 1:(0.8-3), preferably 1:(1-2); The mass ratio of the xylenol mixture to the acidic catalyst is 100:(1-10); The heptylating agent includes heptene, and the heptene includes one or more of 1-heptene, 2-heptene and 3-heptene; The acidic catalyst includes an inorganic acid, which includes one or more of sulfuric acid, phosphoric acid, and aminosulfonic acid; the concentration of the inorganic acid is 85-100%.

4. The method according to claim 1, wherein Step S1 further includes: adding a reaction aid to the first reaction, wherein the reaction aid includes 6-isoheptyl-2,4-dimethylphenol, and the mass ratio of the dimethylphenol mixture to the 6-isoheptyl-2,4-dimethylphenol is 100:(0.01~0.5).

5. The method according to claim 1, wherein In step S1, the conditions of the first reaction include: temperature of 60-100°C and time of 8-12 hours; In step S1, the neutralization comprises: adjusting the pH of the reaction solution obtained after the first reaction to 7-8, optionally using alkaline solution to adjust the pH; Optionally, the alkali solution includes an inorganic alkali solution, and the inorganic alkali includes one or more of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate and sodium bicarbonate.

6. The method according to claim 2, wherein: The distillation treatment comprises: S21, subjecting the first reaction material to a first stage distillation treatment to separate unreacted heptylating agent and 2,5-dimethylphenol; S22. The material obtained by the first distillation treatment is subjected to a second distillation treatment to obtain a 6-isoheptyl-2,4-dimethylphenol logistics, a first dimethylphenol mixture, a 6-isoheptyl-2,3-dimethylphenol logistics, a second dimethylphenol mixture, a 4-isoheptyl-2-ethyl-6-methylphenol logistics and a 4,6-diisoheptyl-2-isopropylphenol logistics.

7. The method according to claim 6, wherein: The conditions of the first stage distillation treatment include: the number of theoretical plates of the distillation tower is 100 to 300, the pressure is -0.07 MPa to -0.09 MPa, and the reflux ratio is 2 to 10:1; The conditions of the second stage distillation treatment include: the number of theoretical plates of the distillation tower is 100-300, the pressure is 200 Pa to 20 Pa, and the reflux ratio is 5-25:

1.

8. The method according to claim 6, wherein: The method further comprises: contacting the 6-isoheptyl-2,3-xylenol stream with an inorganic acid for a second reaction, neutralizing the resulting second reaction solution and subjecting it to a third distillation treatment to obtain a regenerated heptylating agent and a 2,3-xylenol product; and / or, contacting the 4-isoheptyl-2-ethyl-6-methylphenol stream with an inorganic acid for a second reaction, neutralizing the resulting second reaction solution and subjecting it to a third distillation treatment to obtain a regenerated heptylating agent and a 2-ethyl-6-methylphenol product; and / or, The 4,6-diisoheptyl-2-isopropylphenol flow is contacted with an inorganic acid to perform a second reaction, and the obtained second reaction liquid is neutralized and subjected to a third rectification treatment to obtain a regenerated heptylating agent and an o-isopropylphenol product.

9. The method according to claim 8, wherein The mass ratio of the 6-isoheptyl-2,3-dimethylphenol stream to the inorganic acid is 100:(0.5-3); and / or, The mass ratio of the 4-isoheptyl-2-ethyl-6-methylphenol stream to the inorganic acid is 100:(0.5-3); and / or, The mass ratio of the 4,6-diisoheptyl-2-isopropylphenol stream to the inorganic acid is 100:(0.5-3); The inorganic acid includes one or more of sulfuric acid, phosphoric acid, and aminosulfonic acid; The conditions of the second reaction include: temperature of 160-200°C and time of 1-4 hours; The conditions for the third distillation treatment include: the number of theoretical plates of the distillation tower is 100-300, the pressure is -0.085 to -0.098 MPa, and the reflux ratio is 5-10:

1.

10. The method according to claim 6, wherein: The method further comprises: distilling the first xylenol mixture to obtain 6-isoheptyl-2,4-xylenol and 6-isoheptyl-2,3-xylenol; and / or, The second xylenol mixture is subjected to distillation treatment to obtain 6-isoheptyl-2,3-xylenol and 4-isoheptyl-2-ethyl-6-methylphenol.