A process for the preparation of a phenolic product from 2,4-dimethylphenol / 2,5-dimethylphenol

Abstract

This invention discloses a process for preparing phenolic products from 2,4-xylenol / 2,5-xylenol. A mixture of 2,4-xylenol / 2,5-xylenol is added to a reactor containing a silica-alumina-chromium oxide and an acidic catalyst. A dealkylation reaction is carried out at 280–400°C. During the reaction, o-isopropylphenol and 2-methyl-6-ethylphenol remove propylene and ethylene, yielding a mixture of phenols and olefins containing phenol, cresol, and 2,4-xylenol / 2,5-xylenol. The mixture is then rapidly cooled and liquefied, and discharged. Olefins are extracted and distilled to obtain high-purity 2,5-xylenol / 2,4-xylenol, free from o-isopropylphenol, 2-ethyl-6-cresol, etc.; propylene is reacted with m-cresol by controlling the reaction temperature to obtain thymol, 4-isopropyl-3-cresol, etc., and ethylene is reacted with phenol to obtain o-ethylphenol and p-ethylphenol; this invention removes the ethyl group from 2-ethyl-6-cresol and the isopropyl / propyl group from o-isopropylphenol in alkylphenols at high temperature to obtain purified 2,5 / 2,4-xylenol products, producing high-purity products.

Description

Technical Field

[0001] This invention relates to a process for preparing phenolic products, specifically a process for preparing phenolic products from 2,4-xylenol / 2,5-xylenol, belonging to the field of organic synthesis and separation technology. Background Technology

[0002] Crude phenol was distilled to obtain phenol, o-cresol, tri-cresol mixture, m-p-cresol containing 55% meta-cresol, 99% m-p-cresol, and industrial xylenol. However, this process lacked proper separation. In fact, industrial xylenol can be distilled to obtain a mixture of over 80% 2,4-xylenol / 2,5-xylenol, which contains some o-isopropyl / propylphenol and 2-ethyl-6-cresol. Since 2,4-xylenol / 2,5-xylenol constitutes a relatively high proportion and quantity in xylenol, the presence of impurities such as o-isopropyl / propylphenol and 2-methyl-6-ethylphenol can affect the performance and application of 2,4-xylenol / 2,5-xylenol. Therefore, it is necessary to consider separating o-isopropylphenol / o-propylphenol and 2-ethyl-6-cresol from the 2,4-xylenol / 2,5-xylenol mixture.

[0003] The crude phenol extracted from high-temperature coal tar has a relatively high content of 2,4-xylenol / 2,5-xylenol, but very low contents of o-isopropylphenol / o-propylphenol and 2-methyl-6-ethylphenol, thus not affecting the separation and application of 2,4-xylenol / 2,5-xylenol. The crude phenol from medium- and low-temperature gasification has a low content of 2,4-xylenol / 2,5-xylenol, and low contents of o-isopropylphenol / o-propylphenol and 2-ethyl-6-xylenol, so its impact on the separation and application of 2,4-xylenol / 2,5-xylenol is not significant, although the economics of separating 2,4-xylenol / 2,5-xylenol are not very good. Medium- and low-temperature phenol-containing coal tar and coal liquefaction... The crude phenol extracted from phenol tar has a high content of 2,4-xylenol / 2,5-xylenol, as well as high contents of o-isopropylphenol / o-propylphenol and 2-methyl-6-ethylphenol, making it impossible to produce high-purity 2,4-xylenol / 2,5-xylenol products. In addition, after tert-butylation, the boiling points of 4-tert-butyl-2-methyl-6-ethylphenol and 4-tert-butyl-2,5-xylenol are close, and the boiling points of 6-tert-butyl-o-isopropylphenol and 6-tert-butyl-2,4-xylenol are close, making alkylation separation of 2,4-xylenol / 2,5-xylenol difficult and making it hard to produce 99.5% 2,4-xylenol and 2,5-xylenol products. New methods need to be developed. Summary of the Invention

[0004] The purpose of this invention is to provide a process for preparing phenolic products from 2,4-xylenol / 2,5-xylenol to solve the above-mentioned problems. This addresses the issues of traditional phenolic product extraction from phenolic coal tar, which typically involves: first, distilling the phenolic coal tar to obtain a phenolic oil fraction at 170-230℃; then, using alkaline dissolution and acid precipitation or solvent extraction to extract crude phenol and dephenolized phenolic oil; refining the crude phenol to obtain various phenolic products or mixtures; and then separating mixed phenols (a mixture of phenol and o-cresol), o-cresol fractions (containing 2,6-xylenol), m- and p-cresols, mixed xylenols, and mixed tricresols using physical or chemical methods to obtain products such as phenol, o-cresol, m-cresol, p-cresol, 2,5-xylenol, 2,4-xylenol, 3,5-xylenol, 3,4-tricresol, m-ethylphenol, and p-ethylphenol. This process is complex and economically inefficient.

[0005] This invention relates to a process for preparing phenolic products from 2,4-xylenol / 2,5-xylenol, comprising the following steps:

[0006] Step 1: Cleavage and Transposition Reactions

[0007] An acidic silica-alumina-chromium oxide solid catalyst and zirconium phosphate were loaded into a stainless steel high-pressure reactor. A mixture of 2,4-xylenol and 2,5-xylenol was added, and the reactor was sealed. The temperature was raised to 280–400°C and reacted for 3–10 hours. The pressure was gradually increased to 2.5–5.0 MPa to stop the reaction. The internal coil was cooled with programmed cooling heat transfer oil, and the temperature was rapidly reduced to 280–300°C within 1–2 hours. Then, the temperature was reduced to ≤150°C within 0.5–1 hour, and the propylene and ethylene released in the reaction were gradually discharged. The discharged gas was pressurized by a pressurizing pump and stored in a stainless steel spherical tank. After the gas was discharged, the pyrolysis reaction condensate was cooled slightly and purged with nitrogen for 0.5 hours. The pyrolysis reaction products were obtained by filtration, and the solid catalyst was reused.

[0008] Step 2: Synthesis of 2-isopropyl-5-cresol and 4-isopropyl-3-cresol and / or o- / p-isopropylphenol and / or ethylphenol, including:

[0009] 2.1 Synthesis of thymol and o-isopropylphenol;

[0010] 2.1.1 Synthesis of thymol:

[0011] Simultaneously with the cracking and transposition reactions in step one, m-cresol, an acidic catalyst, and a polymerization inhibitor are added to another stainless steel pressure vessel. Stirring is initiated, and the temperature is raised to 160–170°C. The olefins stored in a spherical tank after cooling from the cracking reaction in step one are simultaneously and slowly introduced into the stainless steel pressure vessel under reduced pressure, maintaining the vessel temperature at 170–200°C. The olefins are repeatedly introduced until the pressure inside the vessel is maintained at 2.3–2.5 MPa. When the pressure in the spherical tank drops to 2.6 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene is discharged from the vessel. Then, the olefins in the spherical tank are repeatedly introduced until the pressure inside the pressure vessel reaches 1.3–1.5 MPa. When the pressure in the spherical tank drops to 1.6 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene is discharged. The olefins are repeatedly introduced until the pressure inside the vessel reaches 0.6 MPa. When the pressure in the spherical tank drops to 0.7 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene is discharged. Unreacted ethylene; olefins are introduced to react until the pressure inside the reactor reaches 0.1 MPa. When the pressure in the spherical tank drops to 0.1 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene is discharged. The olefins are then introduced to react until the pressure in the spherical tank reaches 0.03 MPa, at which point the bubbling is stopped. The olefins are introduced for 3–12 hours, followed by 1–4 hours of heat preservation. A total of 160.7 parts of unreacted ethylene are collected. The ethylene is then pressurized and stored in the spherical tank (approximately 5 MPa) using a pressurized pump. The pressure vessel is cooled to ≤90℃ for 1–3 hours. 10–35% liquid alkali is added to the material in the vessel to neutralize it to pH 7–8. The brine layer is separated, and the material layer is added to the bottom of the distillation column. The distillation is carried out at -0.085–-0.095 MPa and a reflux ratio of 10–20 to obtain unreacted m-cresol, which is then used to obtain ≥99% 2-isopropyl-5-cresol and ≥99% high-efficiency bactericide 4-isopropyl-3-cresol.

[0012] 2.1.2 Synthesis of o-isopropylphenol:

[0013] Simultaneously with the cracking and transposition reactions in step one, phenol, an acidic catalyst, and a polymerization inhibitor are added to another stainless steel pressure vessel. Stirring is started, and the temperature is raised to 160–170°C. The olefins stored in a spherical tank after cooling from the cracking reaction in step one are simultaneously and slowly introduced into the stainless steel pressure vessel under reduced pressure, maintaining the vessel temperature at 170–200°C. The olefins are repeatedly introduced until the pressure inside the vessel is maintained at 2.3–2.5 MPa. When the pressure in the spherical tank drops to 2.6 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene in the vessel is discharged. Then, the olefins in the spherical tank are repeatedly introduced until the pressure inside the pressure vessel reaches 1.3–1.5 MPa. When the pressure in the spherical tank drops to 1.6 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene is discharged. The olefins are repeatedly introduced until the pressure inside the vessel reaches 0.6 MPa. When the pressure in the spherical tank drops to 0.7 MPa, the pressure is reduced to 0.6 MPa. When the pressure in the pressure vessel no longer decreases, unreacted ethylene is discharged. Olefins are introduced to react until the pressure inside the vessel reaches 0.1 MPa. When the pressure in the spherical tank drops to 0.1 MPa and the pressure in the pressure vessel no longer decreases, unreacted ethylene is discharged. Olefins are then introduced to react until the pressure in the spherical tank reaches 0.03 MPa, at which point the aeration is stopped. The olefin introduction time is 3–12 hours. After the aeration is completed, the reaction is maintained at a constant temperature for 2 hours. Unreacted ethylene is collected and pressurized by a pressure pump and stored in a spherical tank (approximately 5 MPa). The pressure vessel is cooled to ≤90℃ in 1–3 hours. 10–35% liquid alkali is added to the material in the vessel to neutralize it to pH 7–8. The brine layer is separated, and the material layer is added to the bottom of a distillation column. Distillation is carried out at -0.085–-0.095 MPa with a reflux ratio of 10–20 to obtain unreacted phenol, which is then used to sequentially obtain crude products of ≥99% o-isopropylphenol and ≥95% p-isopropylphenol.

[0014] Add crude p-isopropylphenol and petroleum ether at 90-120°C to the reactor, start stirring, and heat to 70-90°C to completely dissolve the material. Then, first use circulating water to cool down to 30-40°C for 2-3 hours, and then use chilled brine to cool down to 0-20°C for 2-4 hours. Keep warm for 1-3 hours, filter, vacuum dry, and dry to obtain ≥99% p-isopropylphenol.

[0015] 2.1.3 Synthesis of thymol and p-isopropylphenol:

[0016] Simultaneously with the cracking and transposition reactions in step one, m-cresol, phenol, an acidic catalyst, and a polymerization inhibitor are added to another stainless steel pressure vessel. Stirring is started, and the temperature is raised to 160–170°C. The olefins discharged from the cracking reaction in step one and stored in a spherical tank are simultaneously and slowly introduced into the stainless steel pressure vessel under reduced pressure, maintaining the vessel temperature at 170–200°C. The olefins are repeatedly introduced until the pressure inside the vessel is maintained at 2.3–2.5 MPa. When the pressure in the spherical tank drops to 2.6 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene in the vessel is discharged. Then, the olefins in the spherical tank are repeatedly introduced until the pressure inside the pressure vessel reaches 1.3–1.5 MPa. When the pressure in the spherical tank drops to 1.6 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene is discharged. The olefins are repeatedly introduced until the pressure inside the vessel reaches 0.6 MPa. When the pressure in the spherical tank drops to 0.7 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene is discharged. The ethylene is reacted with olefins until the pressure inside the reactor reaches 0.1 MPa. When the pressure in the spherical tank drops to 0.1 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene is discharged. The reaction continues with olefins until the pressure in the spherical tank reaches 0.03 MPa, at which point the bubbling stops. The olefin bubbling time is 3–12 hours. After the reaction is complete, the vessel is kept at a constant temperature for 2 hours. Unreacted ethylene is collected and pressurized using a pressure pump and stored in the spherical tank. The pressure vessel is then cooled to ≤90℃ over 1–3 hours. 10-35% liquid alkali is added to the material in the reactor to neutralize to pH 7-8. The brine layer is separated, and the material layer is added to the bottom of the distillation column. The distillation is carried out at -0.085 to -0.095 MPa and a reflux ratio of 10-20 to obtain unreacted m-cresol and phenol. These are then used to obtain ≥99% o-isopropylphenol, ≥95% p-isopropylphenol, ≥99% 2-isopropyl-5-cresol, and ≥99% 4-isopropyl-3-cresol, a highly effective bactericide.

[0017] Add crude p-isopropylphenol and petroleum ether at 90-120°C to the reactor, start stirring, and heat to 70-90°C to completely dissolve the material. Then, first use circulating water to cool down to 30-40°C for 2-3 hours, and then use chilled brine to cool down to 0-20°C for 2-4 hours. Keep warm for 1-3 hours, filter, vacuum dry, and dry to obtain ≥99% p-isopropylphenol.

[0018] 2.2 Synthesis of p-ethylphenol:

[0019] While synthesizing thymol, phenol and an acidic catalyst were added to a stainless steel pressure vessel. Stirring was started, and the temperature was raised to 210–250°C. The pressurized ethylene collected in the ethylene spherical tank in step 2.1 was slowly depressurized and introduced into the stainless steel pressure vessel for reaction. The vessel temperature was maintained at 220–250°C, the pressure at 0.9–1.0 MPa, and the olefin inlet time was 4–10 hours. When the pressure in the spherical tank dropped to 1.0 MPa, gas inlet was stopped, and the pressure vessel was kept at the same temperature for 1–4 hours. The reaction was stopped when the pressure in the vessel stabilized and did not decrease. The pressure vessel was cooled to ≤90°C over 1–3 hours. 10–35% liquid alkali was added to the material in the vessel to neutralize to pH 7–8. The brine layer was separated, and the material layer was added to the bottom of a distillation column. Distillation was carried out at -0.085–-0.095 MPa and a reflux ratio of 10–20 to obtain unreacted phenol, which was then used to sequentially obtain ≥99% o-ethylphenol and ≥95% crude p-ethylphenol.

[0020] Add crude p-ethylphenol and methanol to the reactor, start stirring, and heat to 60-70℃ to completely dissolve the material. Then, first use circulating water to cool down to 30-40℃ for 2-3 hours, then use chilled brine to cool down to 0-10℃ for 2-4 hours, keep warm for 1-3 hours, filter, vacuum dry, and dry to obtain ≥99% p-ethylphenol.

[0021] Step 3: Distillation separation of pyrolysis products:

[0022] The cracking reaction product from step one was added to the bottom of a distillation column and subjected to reduced pressure distillation to obtain 99% phenol, 99% mixed cresol, ≥98% 2,5-xylenol / 2,4-xylenol (2,5-xylenol / 2,4-xylenol ≥98%, 2,5-xylenol ≥70%), mixed cresol, ≥90% crude 3,5-xylenol, and ≥90% crude 3,4-xylenol.

[0023] 99% mixed cresols can be used to distill 99.5% o-cresol and ≥98% m- and p-cresol products;

[0024] ≥98% 2,5-xylenol / 2,4-xylenol can be used for tert-butylation separation to produce 6-tert-butyl-2,4-xylenol and 4-tert-butyl-2,5-xylenol products. It can also be used to produce 2,5-xylenol by solvent crystallization. Crude 3,5-xylenol and crude 3,4-xylenol can be used to produce pure 3,5-xylenol and 3,4-xylenol by solvent crystallization or melt crystallization.

[0025] Mixed xylenols can be separated by alkylation to produce 2,4-xylenol, 2,5-xylenol, 2,3-xylenol, m-ethylphenol, p-ethylphenol, etc.

[0026] Step 4: Refining of crude cracking and distillation products:

[0027] 4.1 Add the crude 3,5-xylenol from Step 3 and the solvent into the reactor, start stirring, heat up to 60 - 90 °C to completely dissolve the materials, then first cool down to 30 - 40 °C with circulating water for 1 - 3 hours, and then cool down to 0 - 20 °C with chilled brine for 1 - 3 hours, keep warm for 1 - 2 hours, filter, drain thoroughly, and dry to obtain ≥99% 3,5-xylenol;

[0028] 4.2 Add the crude 3,4-xylenol from Step 3 and the solvent into the reactor, start stirring, heat up to 60 - 90 °C to completely dissolve the materials, then first cool down to 30 - 40 °C with circulating water for 1 - 3 hours, and then cool down to 0 - 20 °C with chilled brine for 1 - 3 hours, keep warm for 1 - 2 hours, filter, drain thoroughly, and dry to obtain ≥99% 3,4-xylenol;

[0029] 4.3 Add 500 parts of 2,5-xylenol / 2,4-xylenol from Step 3 and the solvent into the reactor, start stirring, heat up to 60 - 90 °C to completely dissolve the materials, then first cool down to 30 - 40 °C with circulating water for 1 - 3 hours, and then cool down to 0 - 20 °C with chilled brine for 1 - 3 hours, keep warm for 1 - 2 hours, filter, drain thoroughly, and dry to obtain ≥99% 2,5-xylenol;

[0030] Step 5: Separate the alkylated mixed xylenols obtained by cracking and rectification:

[0031] 5.1 Separation by octylation. Add the mixed xylenols and diisobutene obtained in Step 3 into a pressure reactor, add an acidic catalyst, stir and heat up to 100 - 150 °C for reaction for 2 - 12 hours. Take a sample for analysis. If the content of 2,3-xylenol is ≤0.5%, it is qualified. Filter, and rectify the filtrate to recover diisobutene for reuse; then successively obtain ≥95% 2,5-xylenol, 99% 3,5-xylenol; 99% antioxidant 6-isooctyl-2,4-xylenol; obtain ≥95% 6-isooctyl-2,3-xylenol; the residue in the kettle mainly contains some 6-isooctyl-m-ethylphenol, 2,6-diisooctyl-p-ethylphenol, etc.;

[0032] Add ≥95% 6-isooctyl-2,3-xylenol into a decomposition kettle, start stirring, add ≥95% sulfuric acid, heat up to 180 - 200 °C for 0.5 - 2 hours. Take a sample for analysis. If the content of 6-isooctyl-2,3-xylenol is ≤0.5%, it is qualified. After qualification, cool down to 70 - 90 °C, add 10 - 35% sodium hydroxide aqueous solution to neutralize to pH 7 - 7.5, rectify at atmospheric pressure to recover diisobutene for reuse, and then rectify under reduced pressure to obtain 99% 2,3-xylenol;

[0033] Add ≥95% 2,5-xylenol and methanol to a crystallization reactor, start stirring, and heat to 60-70℃ to completely dissolve the material. Then, first use circulating water to cool down to 30-40℃ for 1-3 hours, then use chilled brine to cool down to 0-20℃ for 1-3 hours, keep warm for 1-2 hours, filter, vacuum dry, and dry to obtain ≥99% 2,5-xylenol.

[0034] 5.2 Isohexylation Separation: The mixed xylenol and 6-isohexyl-2,4-xylenol obtained in step 3 were added to a pressure vessel, along with a strong acid resin. The mixture was stirred and heated to 100–150°C. Vaporized isohexene was introduced until the pressure in the reaction vessel reached 0.6 MPa. When the pressure inside the vessel decreased to 0.1 MPa, vaporized isohexene was introduced again until the pressure reached 0.6 MPa. This reaction was repeated multiple times. When the pressure inside the vessel decreased slowly, a sample was taken for analysis. The 2,3-xylenol content was ≤0.5%, which was considered acceptable. The reaction time was 4–12 hours. After the reaction was complete, the mixture was cooled to 70–90°C and filtered. The filtrate was distilled under reduced pressure to obtain ≥98% 2,5-xylenol, ≥99% 3,5-xylenol, 99% 6-isohexyl-2,4-xylenol, and 95% 6-isohexyl-2,3-xylenol.

[0035] Add 6-isohexyl-2,3-dimethylphenol to a decomposition vessel, start stirring, add sulfuric acid, heat to 180-200℃ and keep the temperature for 0.5-3 hours to remove isohexene, and distill to obtain 99% 2,3-dimethylphenol. The isohexene is reused.

[0036] Add ≤99% 2,5-xylenol and methanol to the reactor, start stirring, and heat to 65℃ to completely dissolve the material. Then, first use circulating water to cool down to 30-40℃ for 2-4 hours, and then use frozen brine to cool down to -10-10℃ for 2-4 hours. Keep warm for 1-3 hours, filter, vacuum dry, and dry to obtain 99.5% 2,5-xylenol.

[0037] Step Six: Alkylation Separation of 2,5-Xylenol / 2,4-Xylenol:

[0038] Add the ≥98% 2,5-xylenol / 2,4-xylenol and 6-isononyl-2,4-xylenol obtained in step 3 to a pressure vessel, add strong acid resin, stir and heat to 100-180℃, add isononene dropwise for 4-12 hours, and maintain the reaction temperature for 1-4 hours after the addition is complete. Take a sample for analysis. If 2,4-xylenol ≤0.3% is qualified, determine the amount of isononene used, and after the reaction is complete, cool to 70-100℃ and filter. Distill the filtrate under reduced pressure (-0.09 to -0.1 MPa, reflux ratio 10-30:1) to obtain ≥99.5% 2,5-xylenol and ≥99% antioxidant 6-isononyl-2,4-xylenol.

[0039] Preferably, in step one, a mixture of 2,4-xylenol and 2,5-xylenol is added, wherein the ratio of 2,4-xylenol to 2,5-xylenol in the mixture is 0.5 to 2:1, and the 2,4-xylenol / 2,5-xylenol content is 50 to 97%, preferably 70 to 90%; wherein the ratio of o-isopropylphenol to o-propylphenol in the mixture is 1 to 30%, preferably 5 to 20%; and 2-ethyl-6-cresol is 0 to 30%, preferably 1 to 20%.

[0040] Preferably, in step one, an acidic silica-alumina-chromium oxide solid catalyst is loaded into a stainless steel high-pressure reactor (with an external stainless steel condenser and an internal coil). The silica-alumina-chromium oxide consists of silicon dioxide, acidic alumina, and chromium oxide, wherein the mass ratio of silicon dioxide to acidic alumina is 0.1–10:10–0.1, preferably 0.2–5:5–0.2, and the amount of chromium oxide is 0.01–0.2% of the mass of silicon dioxide; the amount of the silica-alumina-chromium oxide is 5–30% of the weight of the 2,4 / 2,5-xylenol mixture.

[0041] Preferably, in step one, the temperature of the heat transfer oil is gradually and slowly reduced from a high temperature to 80°C, where the high temperature is 50-100°C lower than the temperature of the pyrolysis and transposition reaction.

[0042] Preferably, in step one, the filtration yields a pyrolysis reaction product [a mixture of phenols composed of 2,5-xylenol / 2,4-xylenol (mainly 2,5-xylenol), other xylenols (mainly 3,5-xylenol), and some phenols and cresols (mainly m-cresol), etc.], wherein the cresol is a mixture of m-cresol, p-cresol, o-cresol, o-ethylphenol, etc., with m-cresol being the main component; the ratio of 2,4-xylenol to 2,5-xylenol in the 2,4-xylenol / 2,5-xylenol ratio is 1:2 to 5; the other xylenols are 3,5-xylenol, 2,3-xylenol, 3,4-xylenol, a small amount of m- and p-ethylphenol, etc., with 3,5-xylenol being the main component.

[0043] Preferably, in step 2.1, the acidic catalyst is at least one of sulfuric acid, phosphoric acid, p-toluenesulfonic acid, benzenesulfonic acid, solid acid catalyst, acidic resin, zirconium oxide, acidic alumina, and silicon oxide, preferably a mixture of sulfuric acid and phosphoric acid; the amount of the mixed acid is 0.5-5% of the mass of m-cresol or phenol or a mixture of m-cresol and phenol, wherein the mass ratio of sulfuric acid to phosphoric acid is 5-7:5-3.

[0044] Preferably, in step 2.2, the acidic catalyst is at least one of sulfuric acid, phosphoric acid, p-toluenesulfonic acid, benzenesulfonic acid, solid acid catalyst, acidic resin, zirconium oxide, acidic alumina, silicon oxide, etc., preferably a mixture of sulfuric acid and phosphoric acid; the amount of the mixed acid is 1 to 5% of the mass of phenol, wherein the mass ratio of sulfuric acid to phosphoric acid is 9 to 7: 1 to 3.

[0045] Preferably, the polymerization inhibitor in step 2.1 is hydroquinone, 2-methylhydroquinone, 2-tert-butylhydroquinone, 6-tert-butyl-2,4-dimethylphenol, p-methoxyphenol, etc., with 2-methylhydroquinone being the most preferred.

[0046] Preferably, in step 2.1.3, m-cresol and phenol are added to another stainless steel pressure vessel, wherein the mass ratio of m-cresol to phenol is 1:0.5 to 2.

[0047] Preferably, in step three, the mixed xylenol is composed of two or more of the following: 2,4-xylenol, 2,5-xylenol, 2,3-xylenol, 3,5-xylenol, and a small amount of m-p-ethylphenol, with 2,3-xylenol being the main component and its content generally not less than 50%.

[0048] Preferably, the solvents used in steps 4.1, 4.2, and 4.3 are alcohols (methanol, ethanol, etc.), alkanes (including petroleum ether), ethers, esters, ketones, etc., with methanol and petroleum ether being the most preferred.

[0049] Preferably, in step five, an acidic catalyst is added. The acidic catalyst is an inorganic acid such as sulfuric acid or phosphoric acid, an organic acid such as aminosulfonic acid, benzenesulfonic acid, or toluenesulfonic acid, a solid acid containing antimony acid, or a strong acidic resin, preferably a strong acidic resin.

[0050] Beneficial effects:

[0051] 1. This invention removes the ethyl group from 2-ethyl-6-methylphenol and the isopropyl / propyl group from o-isopropylphenol / o-propylphenol in alkylphenols at high temperature to obtain purified 2,5 / 2,4-dimethylphenol products, producing high-purity products.

[0052] 2. This invention removes isopropyl / propyl groups from alkylphenols at high temperature, then selectively reacts excess m-cresol with isopropyl groups under acidic catalysis, and distills to obtain 2-isopropyl-5-cresol and 4-isopropyl-3-cresol products, with petrochemical-grade m-cresol as a byproduct.

[0053] 3. This invention removes isopropyl / propyl groups from alkylphenols at high temperature, then selectively reacts excess phenol with isopropyl groups under acidic catalysis, and distills to obtain petrochemical-grade o-isopropylphenol and p-isopropylphenol products, with petrochemical-grade phenol products as a byproduct.

[0054] 4. This invention removes the ethyl group from alkylphenols at high temperature, then selectively reacts excess phenol with the ethyl group under acidic catalysis, and distills to obtain petrochemical-grade o-ethylphenol and p-ethylphenol products, with petrochemical-grade phenol products as a byproduct.

[0055] 5. This invention achieves the transfer of other cresols to m-cresol, other xylenols to 3,5-xylenol and 2,5-xylenol, and other ethylphenols to m-ethylphenol through high-temperature dealkylation and medium-low-temperature alkyl transposition reactions in alkylphenols. Since the market value of m-cresol, m-ethylphenol, 3,5-xylenol, etc. is significantly higher than that of o-cresol, p-cresol, 2,4-xylenol, and o-ethylphenol after dealkylation and before transposition, the value of phenolic products is greatly increased.

[0056] 6. The present invention alkylates a mixture of 2,5 / 2,4-dimethylphenol with isononene to obtain high-purity 2,5-dimethylphenol, a highly efficient polymerization inhibitor and antioxidant 6-isononyl-2,4-dimethylphenol, while effectively separating 2,5 / 2,4-dimethylphenol.

[0057] 7. The present invention can also use diisobutylene, isohexene, etc. to separate mixed xylenol by alkylation method with xylenol, and produce byproducts such as 3,5-xylenol, 3,4-xylenol, and 2,3-xylenol.

[0058] 8. This invention is particularly applicable to the green extraction of crude phenol from phenolic coal tar using a medium-low temperature solvent method, and the separation of a mixture of 2,4 / 2,5-dimethylphenol with high o-isopropylphenol / o-propylphenol and 2-ethyl-6-methylphenol content obtained from the crude phenol purification. No relevant literature or patent reports have been found for this part, which is a completely new research topic with good economic and social benefits. Detailed Implementation

[0059] Example 1

[0060] A process for preparing phenolic products from 2,4-xylenol / 2,5-xylenol includes the following steps: Step 1: Cleavage and transposition reaction.

[0061] In a stainless steel high-pressure reactor equipped with an external stainless steel condenser and an internal coil, 750 parts of acidic silica-alumina-chromium oxide solid catalyst (silicon-alumina-chromium ratio 1:2:0.2), 50 parts of zirconium phosphate, and 5000 parts of a 2,4-xylenol / 2,5-xylenol mixture (containing 15 parts of m-p-cresol, 1875 parts of 2,4-xylenol, 1375 parts of 2,5-xylenol, 750 parts of o-isopropylphenol / o-propylphenol, 920 parts of 2-ethyl-6-cresol, and 63 parts of 2,3-xylenol) were added. The reactor was sealed and heated to 340°C for 4 hours, with the pressure gradually increased to 3.8–3.9 MPa. The reaction was then stopped. The internal coil was cooled using programmed cooling heat transfer oil (the heat transfer oil temperature was gradually and slowly reduced from high temperature to 80°C), and the temperature was lowered to 280°C in 0.5 hours. The material temperature was then further reduced over 40 minutes. The temperature was lowered to 150℃, and the propylene and ethylene released during the reaction were gradually discharged. The discharged gas was pressurized by a pressure pump and stored in a stainless steel spherical tank (approximately 5 MPa). After the gas was discharged, the pyrolysis reaction condensate was cooled slightly and purged with nitrogen for 0.5 hours. After filtration, 4506.9 parts of pyrolysis reaction products were obtained (containing 694.8 parts of cresol, 9.8 parts of 6-ethyl-2-cresol, 497.8 parts of phenol, 431.3 parts of 2,4-xylenol, 1784.2 parts of 2,5-xylenol, 651.3 parts of 3,5-xylenol, 224.6 parts of 3,4-xylenol, 165.3 parts of 2,3-xylenol, 3.2 parts of o-ethylphenol, 6.5 parts of m-p-ethylphenol, and 38.1 parts of others). Solid catalyst was reused (it is necessary to supplement with some silicon-aluminum oxidant, about 5% silicon-aluminum oxide, and zirconium phosphate).

[0062] Step 2: Synthesis of 2-isopropyl-5-cresol, 4-isopropyl-3-cresol, and ethylphenol

[0063] 2.1 Synthesis of thymol, etc.

[0064] Simultaneously with the cracking and transposition reactions in step one, 953 parts of m-cresol and 30 parts of a sulfuric acid / phosphoric acid mixture (m-cresol being 1.6 times the molar mass of o-isopropylphenol / propylphenol, 98% sulfuric acid: 85% phosphoric acid mass ratio 7:3) were added to another stainless steel pressure vessel. Stirring was started, and the temperature was raised to 180°C. The olefins discharged from the cracking reaction in step one and stored in a spherical tank were simultaneously and slowly introduced into the stainless steel pressure vessel under reduced pressure, maintaining the vessel temperature at 180–190°C. The olefins were introduced until the pressure inside the vessel reached 2.3–2.5 MPa. When the pressure in the spherical tank dropped to 2.6 MPa and the pressure in the pressure vessel no longer decreased, unreacted ethylene was discharged. Then, the olefins were introduced until the pressure inside the vessel reached 1.3–1.5 MPa. When the pressure in the spherical tank dropped to 1.6 MPa and the pressure in the pressure vessel no longer decreased, unreacted ethylene was discharged. The olefins were introduced until the pressure inside the vessel reached 0.6 MPa. When the pressure in the spherical tank dropped to 0.7 MPa, the pressure... Unreacted ethylene was discharged when the pressure in the reactor stopped decreasing; olefins were introduced to react until the pressure inside the reactor reached 0.1 MPa. When the pressure in the spherical tank dropped to 0.1 MPa and the reactor pressure stopped decreasing, unreacted ethylene was discharged; olefins were then introduced to react until the pressure in the spherical tank reached 0.03 MPa, at which point the buoyancy was stopped. The olefin introduction time was 10 hours, followed by a 2-hour heat preservation reaction. A total of 160.7 parts of unreacted ethylene were collected. The ethylene was pressurized and stored in the spherical tank (approximately 5 MPa) using a pressure pump; 90 parts of 30% liquid alkali were added to the internal material to neutralize it to pH 7.5. The brine layer was separated, and the material layer was added to the bottom of a distillation column (theoretical plate number 200). Distillation was carried out at -0.095 MPa and a reflux ratio of 15-20 to obtain 344.5 parts of unreacted m-cresol, which was then reused to obtain 488.5 parts of 99.5% 2-isopropyl-5-cresol (thymol) and 279.9 parts of 99.6% high-efficiency bactericide 4-isopropyl-3-cresol.

[0065] 2.2 Synthesis of p-ethylphenol, etc.

[0066] Concurrently with the synthesis of thymol, 800 parts of phenol and 25 parts of sulfuric acid / phosphoric acid (phenol being 1.26 times the molar mass of 2-ethyl-6-cresol, and the mass ratio of 98% sulfuric acid to 85% phosphoric acid being 8-9:2-1) were added to a stainless steel pressure vessel. Stirring was started, and the temperature was raised to 240°C. The pressurized ethylene collected in the ethylene spherical tank in step 2.1 was slowly introduced into the stainless steel pressure vessel under reduced pressure for reaction. The vessel temperature was maintained at 230-240°C, the pressure at 0.9-1.0 MPa, and the olefin was introduced for 6 hours. Gas introduction was stopped when the pressure in the spherical tank dropped to 1.3 MPa. The reaction was carried out in a pressure vessel for 3 hours. The reaction was stopped when the pressure dropped to 0.6 MPa or did not drop. 70 parts of 30% liquid alkali were added to the material in the vessel to neutralize it to pH 7.5. The brine layer was separated, and the material layer was added to the bottom of a distillation column (theoretical plate number 200). Distillation was carried out at -0.09 MPa and a reflux ratio of 10 to 15 to obtain 391.8 parts of unreacted phenol, which was then reused. Then, 176.6 parts of 99.6% o-ethylphenol and 319.8 parts of 96.37% crude p-ethylphenol were obtained in sequence (308.2 parts of p-ethylphenol, 11.3 parts of m-ethylphenol, and 0.3 parts of other compounds).

[0067] 319.8 parts of crude p-ethylphenol (96.37%) and 300 parts of methanol were added to the reactor. The mixture was stirred and heated to 65°C to completely dissolve the material. Then, the mixture was cooled to 35°C in a cold water bath for 2 hours, followed by a cooling to 0°C in an ice water bath for 3 hours. The mixture was kept at this temperature for 2 hours, filtered, dried under vacuum, and then dried to obtain 292.4 parts of 99.71% p-ethylphenol, with a purification yield of 94.6%.

[0068] Step 3: Distillation separation of pyrolysis products

[0069] 4506.9 parts of the cracking reaction product from step one were added to the bottom of a distillation column (the bottom of the column already contained 100 parts of dimethyl diphenyl ether, a high-boiling-point solvent). The column was then subjected to vacuum distillation (vacuum degree -0.088 MPa, reflux ratio 15-25:1) to obtain 457.5 parts of 99.23% phenol, 647.1 parts of 99.1% cresol (232.9 parts of o-cresol, 116.7 parts of p-cresol, 291.8 parts of m-cresol, and 3.1 parts of o-ethylphenol), and 2141.8 parts of 98.73% 2,4 / 2,5-xylenol (409.6 parts of 2,4-xylenol, 1705.1 parts of 2,5-xylenol, 9.8 parts of m-p-cresol, 15.2 parts of 2,3-xylenol, and 2.1 parts of other compounds). 79.61% xylenol), 209.2 parts of mixed xylenol (12.4 parts of 2,4-xylenol, 41.3 parts of 2,5-xylenol, 139.2 parts of 2,3-xylenol, 12.3 parts of 3,5-xylenol, 4 parts of m-p-ethylphenol, 66.54% xylenol), 638.7 parts of crude 96.4% 3,5-xylenol (6.5 parts of 2,3-xylenol, 615.8 parts of 3,5-xylenol, 14.6 parts of 3,4-xylenol, 1.8 parts of m-p-ethylphenol), and 216.1 parts of crude 93.61% 3,4-xylenol (1.1 parts of 2,3-xylenol, 10.2 parts of 3,5-xylenol, 202.3 parts of 3,4-xylenol);

[0070] 647.1 parts of 99.1% cresol (232.8 parts of o-cresol, 116.7 parts of p-cresol, 291.8 parts of m-cresol, and 3.2 parts of o-ethylphenol) can be used for distillation of 99.5% o-cresol and 99% m-p-cresol products.

[0071] 98.73% 2,4 / 2,5-dimethylphenol (2,5-dimethylphenol content 79.61%) can be used for tert-butylation separation to produce 6-tert-butyl-2,4-dimethylphenol and 4-tert-butyl-2,5-dimethylphenol products. It can also be used to produce 2,5-dimethylphenol by solvent crystallization. 96.4% crude 3,5-dimethylphenol and 93.61% crude 3,4-dimethylphenol can be used to produce pure 3,5-dimethylphenol and 3,4-dimethylphenol by solvent crystallization or melt crystallization.

[0072] 209.2 parts of mixed xylenol (12.4 parts of 2,4-xylenol, 41.3 parts of 2,5-xylenol, 139.2 parts of 2,3-xylenol, 12.3 parts of 3,5-xylenol, 4 parts of m- and p-ethylphenol, and 66.54% of 2,3-xylenol) can be alkylated to produce 2,4-xylenol, 2,5-xylenol, 2,3-xylenol, m- and p-ethylphenol, etc.

[0073] Step 4: Refining the crude product obtained from cracking and distillation

[0074] 4.1 Add 638.7 parts of crude 96.4% 3,5-xylenol from step 3 and 500 parts of methanol to the reactor, start stirring, and heat to 60°C to completely dissolve the material. Then, first use circulating water to cool down to 35°C for 2 hours, then use chilled brine to cool down to 0°C for 2 hours, keep warm for 2 hours, filter, vacuum dry, and dry to obtain 584.7 parts of 99.82% 3,5-xylenol, with a purification yield of 94.8%.

[0075] 4.2 Add 216.1 parts of the crude 93.61% 3,4-xylenol from step 3 and 600 parts of petroleum ether at 90-120℃ to the reactor, start stirring, and heat to 70℃ to completely dissolve the material. Then, first use circulating water to cool down to 33℃ for 2.5 hours, then use chilled brine to cool down to 20℃ for 2 hours, keep warm for 2 hours, filter, vacuum dry, and dry to obtain 178.2 parts of 99.64% 3,4-xylenol, with a purification yield of 87.8%.

[0076] 4.3 Add 500 parts (79.61%) of 98.73% 2,4 / 2,5-xylenol from step 3 and 300 parts of methanol to the reactor, start stirring, and heat to 60°C to completely dissolve the material. Then, first use circulating water to cool down to 35°C for 2 hours, then use frozen brine to cool down to -10°C for 3 hours, keep warm for 2 hours, filter, vacuum dry, and dry to obtain 261.5 parts of 99.85% 2,5-xylenol, with a purification yield of 65.6%.

[0077] Step 5: Separation of the mixed xylenol octylated product obtained from cracking distillation

[0078] 209.2 parts of the mixed xylenol obtained in step three (12.4 parts of 2,4-xylenol, 41.3 parts of 2,5-xylenol, 139.2 parts of 2,3-xylenol, 12.3 parts of 3,5-xylenol, and 4 parts of m-p-ethylphenol) and 600 parts of diisobutylene were added to a reaction vessel, along with 100 parts of strong acid resin. The mixture was stirred and heated to 110°C for 10 hours. Analysis showed that 4-isooctyl-p-ethylphenol was 0.01%, which was within acceptable limits. The mixture was filtered, and the filtrate was distilled to recover 435 parts of diisobutylene for reuse. Then, the mixture was distilled under reduced pressure (-0.09). At 5 MPa and a reflux ratio of 25–30:1, 38.2 parts of 98.32% 2,5-xylenol and 10.3 parts of 99.13% 3,5-xylenol were obtained sequentially, with yields of 90.9% and 83.2%, respectively; 19.5 parts of 99.23% 6-isooctyl-2,4-xylenol (antioxidant) were obtained, with a yield of 81.2%; and 207.9 parts of 97.35% 6-isooctyl-2,3-xylenol were obtained, with a yield of 75.8%. The residue in the reactor mainly contained some 2-isooctyl-5-ethylphenol and 2,6-diisooctyl-4-ethylphenol.

[0079] 207.9 parts of 97.35% 6-isooctyl-2,3-xylenol were added to a decomposition vessel, stirred, and 5 parts of sulfuric acid were added. The temperature was raised to 200℃ for 1.5 hours, and the product was distilled to obtain 103.3 parts of 99.38% 2,3-xylenol, with a yield of 94.7%; (high-boiling-point dimethyl diphenyl ether was added to the distillation column bottom beforehand).

[0080] 38.2 parts of 98.32% 2,5-xylenol and 24 parts of methanol were added to the reactor. The mixture was stirred and heated to 60°C to completely dissolve the material. Then, the mixture was cooled to 35°C in a cold water bath and then cooled to -10°C in an ice water bath. The mixture was kept at this temperature for 2 hours, filtered, dried under vacuum, and then dried to obtain 36.2 parts of 99.53% 2,5-xylenol with a purification yield of 95.9%.

[0081] Step Six: Alkylation Separation of 2,5 / 2,4-Xylenol (Crude 2,5-Xylenol)

[0082] 1000 parts of 98.73% 2,4 / 2,5-xylenol obtained in step three (191.2 parts of 2,4-xylenol, 796.1 parts of 2,5-xylenol, 4.6 parts of m-p-cresol, 7.1 parts of 2,3-xylenol, and 1 part of other compounds) and 1 part of 6-isononyl-2,4-xylenol were added to a pressure vessel, along with 200 parts of strong acid resin. The mixture was stirred and heated to 120°C for reaction. Isononene was then added dropwise over 6 hours. After the addition was complete, the equipment was sealed, and the temperature was raised to 160°C for 1 hour. The sample analysis showed that 0.11% of 2,4-xylenol was within acceptable limits. 241 parts of isononene were used (the amount of isononene was 1.22 times the molar amount of 2,4-xylenol in the 2,5 / 2,4-xylenol mixture). After the reaction was complete, the mixture was cooled to 90℃ and filtered. The filtrate was then distilled under reduced pressure (-0.098 MPa, reflux ratio 20-25:1) to obtain 756.9 parts of 99.5% 2,5-xylenol, with a yield of 94.6%; and 349 parts of 99.0% 9-isononyl-2,4-xylenol, with a yield of 88.9%.

[0083] Example 2

[0084] Step 1: Pyrolysis reaction

[0085] In a stainless steel high-pressure reactor equipped with an external stainless steel condenser and an internal coil, 1000 parts of acidic silica-alumina-chromium oxide solid catalyst (silicon-alumina-chromium ratio 1:2:0.1), 30 parts of zirconium phosphate, and 4908 parts of a 2,4-xylenol / 2,5-xylenol mixture (containing 2361.6 parts of 2,4-xylenol, 1586.4 parts of 2,5-xylenol, and 960 parts of o-isopropylphenol / o-propylphenol) were added. The reactor was sealed and heated to 300℃ for 6 hours. The pressure was gradually increased to 2.8–2.9 MPa, and the reaction was terminated. The internal coil was then rapidly cooled using programmed cooling heat transfer oil (the temperature of the heat transfer oil was gradually and slowly decreased from a high temperature). The temperature was lowered to 80℃. When the material temperature dropped to 150℃, the propylene removed after the reaction was discharged. The cooling time was about 1 hour. The discharged gas was pressurized by a pressure pump and stored in a stainless steel spherical tank (about 5MPa). After the gas was discharged, it was cooled slightly and purged with nitrogen for 0.5 hours. After filtration, 4606 parts of cracking reaction products were obtained (15.2 parts of o-isopropylphenol, 23.2 parts of m-p-isopropylphenol, 624.4 parts of phenol, 628 parts of 2,4-xylenol, 2431.2 parts of 2,5-xylenol, 578.4 parts of 3,5-xylenol, 138.4 parts of 3,4-xylenol, 92.8 parts of 2,3-xylenol, and 74.4 parts of others).

[0086] Step 2: Synthesis of o-isopropylphenol and p-isopropylphenol

[0087] Add 1525 parts of phenol and 50 parts of 98% sulfuric acid (phenol is twice the molar mass of o-isopropyl / propylphenol) to a stainless steel pressure vessel. Start stirring and heat to 160°C. Simultaneously introduce propylene stored in a stainless steel spherical tank after cooling from the cracking reaction in step one into the stainless steel pressure vessel for reaction. Maintain the vessel temperature at 160–170°C and the pressure at 0.8–0.9 MPa. Introduce propylene for 5 hours, followed by a 3-hour heat treatment after propylene introduction. The contents of the vessel... 133.5 parts of 30% liquid alkali were added to the feed to neutralize it to pH 7.0. The brine layer was separated, and the feed layer was added to the bottom of a distillation column (theoretical plate number 200). Distillation was carried out at -0.09 MPa and a reflux ratio of 15-20 to obtain 871.6 parts of unreacted phenol, which was then reused. Subsequently, 537.6 parts of 99.1% o-isopropylphenol and 336.2 parts of 96.6% crude p-isopropylphenol (325.8 parts of p-isopropylphenol and 10.4 parts of m-isopropylphenol) were obtained.

[0088] Add 336.2 parts of 96.6% crude p-isopropylphenol and 1000 parts of petroleum ether at 90-120℃ to the reactor, start stirring, and heat to 70℃ to completely dissolve the materials. Then, first cool down to 35℃ in a cold water bath for 3 hours, then cool down to 20℃ in an ice water bath for 3 hours, keep warm for 1 hour, filter, vacuum dry, and dry to obtain 304.5 parts of 99.7% p-isopropylphenol, with a purification yield of 93.2%.

[0089] Step 3: Distillation of pyrolysis reaction products

[0090] 4606 parts of the cracking reaction product from step one were added to the bottom of a distillation column (the bottom of the column already contained 100 parts of dimethyl diphenyl ether, a high-boiling-point solvent). The column was then subjected to vacuum distillation (vacuum degree -0.088 MPa, reflux ratio 10–30:1) to obtain 591.6 parts of 99.5% phenol, 2928.4 parts of 99.36% 2,5 / 2,4-xylenol (595.2 parts of 2,4-xylenol, 2314.4 parts of 2,5-xylenol, 10 parts of o-isopropylphenol, and 79.03% of 2,5-xylenol), and 122.4 parts of mixed xylenol (5.2 parts of 2,4-xylenol, 21.2 parts of 2,5-xylenol, 80.8 parts of 2,3-xylenol, and 3,5-xylenol). - Xylenol 14.4 parts, others 0.8 parts, 2,3-xylenol 66.01%), 93.91% crude 3,5-xylenol 584.4 parts (2,3-xylenol 9.2 parts, 3,5-xylenol 548.8 parts, 3,4-xylenol 24.8 parts), 92.57% crude 3,4-xylenol 118.4 parts (2,3-xylenol 1.2 parts, 3,5-xylenol 7.6 parts, 3,4-xylenol 109.6 parts), 87.02% m-p-isopropylphenol 26.2 parts (m-p-isopropylphenol 22.8 parts, 3,4-xylenol 0.3 parts, others 3.1 parts, m-isopropylphenol:p-isopropylphenol ratio 1.98:1);

[0091] 99.36% 2,5 / 2,4-xylenol can be separated by tert-butylation to produce 6-tert-butyl-2,4-xylenol and 4-tert-butyl-2,5-xylenol, and 2,5-xylenol can also be produced by solvent crystallization; 93.91% crude 3,5-xylenol and 92.93% crude 3,4-xylenol can be produced by solvent crystallization or melt crystallization to produce pure 3,5-xylenol and 3,4-xylenol, respectively.

[0092] 87.02% m-p-isopropylphenol (22.8 parts m-p-isopropylphenol, 0.3 parts 3,4-xylenol, and 3.1 parts others, with a m-p-isopropylphenol:p-isopropylphenol ratio of 1.98:1) can be used as a raw material for enameled wire varnish, flame retardant plasticizer, and photoresist; it can also be used for alkylation separation of m-p-isopropylphenol.

[0093] Step 4: Refining of Crude Products from Cracking and Distillation

[0094] 4.1 Add 584.4 parts of crude 3,5-xylenol (93.91%) and 500 parts of petroleum ether (90-120℃) obtained in step 3 to the reactor, start stirring, and heat to 75℃ to completely dissolve the materials. Then, first use circulating water to cool down to 40℃ for 2.5 hours, then use chilled brine to cool down to 20℃ for 2 hours, keep warm for 2 hours, filter, vacuum dry, and dry to obtain 497.6 parts of 99.36% 3,5-xylenol, with a purification yield of 90.1%.

[0095] 4.2 Add 118.4 parts of the crude 92.57% 3,4-xylenol obtained in step 3 and 100 parts of petroleum ether at 90-120℃ to the reactor, start stirring, heat to 70℃ to completely dissolve the material, then cool down to 35℃ with circulating water for 2.5 hours, then cool down to 15℃ with chilled brine for 2 hours, keep warm for 2 hours, filter, vacuum dry, and dry to obtain 97.6 parts of 99.12% 3,4-xylenol, with a purification yield of 88.3%;

[0096] 4.3 Add 200 parts (79.03%) of 99.36% 2,5 / 2,4-xylenol obtained in step 3 and 100 parts of methanol to the reactor. Start stirring and heat to 60°C to completely dissolve the material. Then, first use circulating water to cool down to 35°C for 2 hours, and then use frozen brine to cool down to -10°C for 3 hours. Keep warm for 2 hours, filter, vacuum dry, and dry to obtain 113 parts of 99.55% 2,5-xylenol with a purification yield of 71.2%.

[0097] Step 5: Separation of the mixed xylenol octylated product obtained from cracking distillation

[0098] Add 122.4 parts of the mixed xylenol obtained in step three (5.2 parts of 2,4-xylenol, 21.2 parts of 2,5-xylenol, 80.8 parts of 2,3-xylenol, 14.4 parts of 3,5-xylenol, and 0.8 parts of other compounds, with 2,3-xylenol accounting for 66.01%) and 400 parts of diisobutylene to a reaction vessel, along with 100 parts of strong acid resin. Stir and heat to 110°C for 10 hours. Sample analysis shows that 0.05% of 4-isooctyl-4-ethylphenol is within acceptable limits. Filter the solution. Diisobutylene 322.3 parts were recovered by distillation and reused; then, vacuum distillation (-0.095 MPa, reflux ratio 25-30:1) was used to obtain 19.2 parts of 98.22% 2,5-xylenol and 11.7 parts of 99.33% 3,5-xylenol, with yields of 89.0% and 81.2%, respectively; 8.1 parts of 99.05% 6-isooctyl-2,4-xylenol, an antioxidant, with a yield of 80.3%; and 120.2 parts of 98.26% 6-isooctyl-2,3-xylenol, with a yield of 78.9%.

[0099] 120.2 parts of 98.26% 6-isooctyl-2,3-dimethylphenol were added to a decomposition vessel, stirred, and 1.5 parts of sulfuric acid were added. The temperature was raised to 190℃ for 2 hours, and then distilled (-0.09MPa, reflux ratio 25-30:1) to obtain 62.1 parts of 99.61% 2,3-dimethylphenol, with a yield of 95.3% (high-boiling-point dimethyl diphenyl ether was pre-added to the distillation column).

[0100] 19.2 parts of 98.22% 2,5-xylenol and 15 parts of methanol were added to the reactor. The mixture was stirred and heated to 65°C to completely dissolve the material. Then, the mixture was cooled to 37°C in a cold water bath for 2 hours, followed by cooling to 0°C in a chilled brine bath for 2 hours. The mixture was kept at this temperature for 2 hours, filtered, dried under vacuum, and then dried to obtain 17.8 parts of 99.75% 2,5-xylenol, with a purification yield of 94.2%.

[0101] Step Six: Alkylation Separation of 2,5-xylenol / 2,4-xylenol (Crude 2,5-xylenol)

[0102] 1000 parts of 99.36% 2,5-xylenol / 2,4-xylenol obtained in step three (203.3 parts of 2,4-xylenol, 790.3 parts of 2,5-xylenol, and 3.4 parts of o-isopropylphenol) and 1 part of 6-isononyl-2,4-xylenol were added to a pressure vessel, along with 200 parts of strong acid resin. The mixture was stirred and heated to 140°C for reaction. Isononene was added dropwise over 6 hours. After the addition was complete, the reaction was maintained at this temperature for 2 hours, and a sample of 0.0 mmol of 2,4-xylenol was taken for analysis. The 7% standard was achieved. 250 parts of isononene were used (the amount of isononene was 1.19 times the molar amount of 2,4-xylenol in 2,5 / 2,4-xylenol). After the reaction was complete, the mixture was cooled to 90℃ and filtered. The filtrate was then distilled under reduced pressure (-0.098 MPa, reflux ratio 10-20:1) to obtain 755.4 parts of 99.6% 2,5-xylenol (yield 95.2%) and 386.5 parts of 99.3% 6-isononyl-2,4-xylenol (yield 92.9%).

[0103] Example 3

[0104] Step 1: Cleavage and Transposition Reactions

[0105] In a stainless steel high-pressure reactor equipped with an external stainless steel condenser and an internal coil, 2000 parts of acidic silica-alumina-chromium oxide solid catalyst (silicon-alumina-chromium ratio 1:2:0.2), 200 parts of zirconium phosphate, and 10000 parts of a 2,4 / 2,5-xylenol mixture (extracted and refined from low-temperature phenolic coal tar, containing 4318 parts of 2,4-xylenol, 3635 parts of 2,5-xylenol, 1204 parts of o-isopropylphenol / o-propylphenol, 521 parts of 2-ethyl-6-cresol, 306 parts of 2,3-xylenol, and 16 parts of other components) were added. The reactor was sealed and heated to 280℃ for 10 hours, with the pressure gradually increased to 2.5–2.6 MPa. The reaction was then stopped. The internal coil was cooled using programmed cooling heat transfer oil (the temperature of the heat transfer oil was gradually and slowly decreased from a high temperature). The temperature was lowered to 80℃, then reduced to 250℃ within 10 minutes, and then the material temperature was lowered to about 150℃ in about 0.5 hours. Propylene and ethylene released during the reaction were gradually discharged. The discharged gas was pressurized by a pressure pump and stored in a stainless steel spherical tank (about 5MPa). After the gas was discharged, the condensate of the cracking reaction was cooled slightly and replaced with nitrogen for 0.5 hours. After filtration, 9790.2 parts of cracking reaction products were obtained (containing 422.1 parts of cresol, 815.6 parts of phenol, 1164.8 parts of 2,4-xylenol, 4484.6 parts of 2,5-xylenol, 1799.8 parts of 3,5-xylenol, 612 parts of 3,4-xylenol, 450.1 parts of 2,3-xylenol, and 41.2 parts of others). Solid catalyst was reused (some silicon aluminum oxide needs to be added).

[0106] Step 2: Synthesis of 2-isopropyl-5-cresol, 4-isopropyl-3-cresol, ethylphenol, etc.

[0107] 2.1 Synthesis of thymol, etc.

[0108] Simultaneously with the cracking and transposition reactions in step one, 907 parts of 99.3% coking m-cresol (containing 28 ppm nitrogen oxides and 19 ppm sulfur oxides), 790 parts of 99% coking phenol (containing 1080 ppm nitrogen oxides and 462 ppm sulfur oxides), and 50 parts of a sulfuric acid / phosphoric acid mixture (the amount of m-cresol and phenol is 1.9 times the molar mass of o-isopropyl / propylphenol, and the mass ratio of 98% sulfuric acid to 85% phosphoric acid is 7:3) were added to another stainless steel pressure vessel. Stirring was started, and the temperature was raised to 190°C. The olefins discharged after cooling from the cracking reaction in step one and stored in a spherical tank were simultaneously and slowly depressurized. The reaction is introduced into a stainless steel pressure vessel, maintaining the vessel temperature at 190–200°C. Olefins are introduced until the pressure inside the vessel reaches 2.3–2.5 MPa. Unreacted ethylene is discharged when the pressure in the spherical tank drops to 2.6 MPa and the pressure in the pressure vessel no longer decreases. Then, olefins are introduced until the pressure inside the vessel reaches 1.3–1.5 MPa. Unreacted ethylene is discharged when the pressure in the spherical tank drops to 1.6 MPa and the pressure in the pressure vessel no longer decreases. Olefins are introduced until the pressure inside the vessel reaches 0.6 MPa. Unreacted ethylene is discharged when the pressure in the spherical tank drops to 0.7 MPa and the pressure in the pressure vessel no longer decreases. The reaction is repeated until the pressure inside the vessel reaches 0... At a pressure of 0.1 MPa, unreacted ethylene was discharged when the pressure in the spherical tank dropped to 0.1 MPa and the pressure in the pressure vessel no longer decreased. The olefin reaction continued until the pressure in the spherical tank reached 0.03 MPa, at which point the olefin reaction was stopped. The olefin reaction lasted for 10 hours, followed by a 2-hour heat preservation reaction. A total of 106.2 parts of unreacted ethylene were collected. The ethylene was pressurized and stored in the spherical tank (approximately 5 MPa) using a pressurized pump. 150 parts of 30% liquid alkali were added to the material in the vessel to neutralize it to pH 7.5. The brine layer was separated, and the material layer was added to the bottom of a distillation column (theoretical plate number 250). Distillation was performed at -0.095 MPa and a reflux ratio of 25–30 to obtain… 271.6 parts of 99.9% petrochemical grade phenol (containing 1.8 ppm nitrogen oxides and 3.2 ppm sulfur oxides), 528.4 parts of 99.8% petrochemical grade m-cresol (containing 0.7 ppm nitrogen oxides and 0.9 ppm sulfur oxides) were then successively used to obtain 418.1 parts of 99.6% o-isopropylphenol, 263 parts of 96.5% crude p-isopropylphenol (253.8 parts p-isopropylphenol and 9.2 parts m-isopropylphenol), 299.5 parts of 99.6% 2-isopropyl-5-cresol (thymol), and 168.2 parts of 99.5% high-efficiency bactericide 4-isopropyl-3-cresol;

[0109] 263 parts of crude p-isopropylphenol (96.5%) and 200 parts of methanol were added to the reactor. The mixture was stirred and heated to 65°C to completely dissolve the material. Then, the temperature was lowered to 35°C by circulating water for 2.5 hours, followed by cooling to 0°C by chilled brine for 3 hours. The temperature was maintained for 2 hours, filtered, dried under vacuum, and then dried to obtain 241.3 parts of 99.6% p-isopropylphenol, with a purification yield of 94.7%.

[0110] 2.2 Synthesis of p-ethylphenol, etc.

[0111] Simultaneously with the synthesis of thymol, 685 parts of 99% coking phenol (containing 1080 ppm of nitrogen oxides and 462 ppm of sulfur oxides) and 25 parts of sulfuric acid / phosphoric acid (phenol being 1.9 times the molar mass of 2-ethyl-6-cresol, and the mass ratio of 98% sulfuric acid to 85% phosphoric acid being 9:1) were added to a stainless steel pressure vessel. Stirring was started, and the temperature was raised to 220°C. The pressurized ethylene collected in the ethylene spherical tank in step 2.1 was slowly reduced in pressure and introduced into the stainless steel pressure vessel for reaction. The vessel temperature was maintained at 220–230°C, the pressure at 0.9–1.0 MPa, and the olefin was introduced for 8 hours. Gas introduction was stopped when the pressure in the spherical tank dropped to 1.2 MPa. The reaction was carried out in a pressure vessel for 3 hours. The reaction was stopped when the pressure dropped to 0.6 MPa or did not drop. 70 parts of 30% liquid alkali were added to the material in the vessel to neutralize it to pH 7.5. The brine layer was separated, and the material layer was added to the bottom of a distillation column (theoretical plate number 200). Distillation was carried out at -0.09 MPa and a reflux ratio of 10 to 15 to obtain 407.6 parts of petrochemical grade 99.9% phenol (containing 1.1 ppm of nitrogen oxides and 1.9 ppm of sulfur oxides). Then, 129.2 parts of 99.7% o-ethylphenol and 206 parts of 96.46% crude p-ethylphenol (p-ethylphenol 198.7 parts, m-ethylphenol 7.1 parts, and other 0.2 parts) were obtained in sequence.

[0112] 206 parts of crude p-ethylphenol (96.46%) and 120 parts of methanol were added to the reactor. The mixture was stirred and heated to 65°C to completely dissolve the material. Then, the mixture was cooled to 35°C in a cold water bath for 2 hours, and then cooled to 0°C in an ice water bath for 3 hours. The mixture was kept at this temperature for 2 hours, filtered, dried under vacuum, and then dried to obtain 190.6 parts of 99.53% p-ethylphenol, with a purification yield of 95.5%.

[0113] Step 3: Distillation separation of pyrolysis products

[0114] 9790.2 parts of the pyrolysis reaction product from step one (containing 422.1 parts cresol, 815.6 parts phenol, 1164.8 parts 2,4-xylenol, 4484.6 parts 2,5-xylenol, 1799.8 parts 3,5-xylenol, 612 parts 3,4-xylenol, 450.1 parts 2,3-xylenol, and 41.2 parts other components) were added to the bottom of a distillation column (the bottom of the column already contained 100 parts of high-boiling-point dimethyl diphenyl ether solvent) and subjected to vacuum distillation (vacuum degree -0.08). At 8 MPa and a reflux ratio of 15–25:1, 171.1 parts of 99.1% phenol were obtained (to be applied to step two), 635.6 parts of petrochemical-grade 99.8% phenol (containing 0.9 ppm nitrogen oxides and 1.1 ppm sulfur oxides), and 411.6 parts of 99.2% petrochemical-grade cresol (containing 2.0 parts phenol, 146.8 parts o-cresol, 74.7 parts p-cresol, 186.8 parts m-cresol, and 1.3 parts o-ethylphenol, containing 0.6 ppm nitrogen oxides and 0.8 ppm sulfur oxides). ppm), 99.12% 2,5 / 2,4-xylenol 5502.4 parts (2,4-xylenol 1119.3 parts, 2,5-xylenol 4334.7 parts, m-p-cresol 6.6 parts, 2,3-xylenol 41.8 parts, 2,5-xylenol 78.78%), mixed xylenol 557.2 parts (2,4-xylenol 33.8 parts, 2,5-xylenol 105 parts, 2,3-xylenol 382.9 parts, 3,5-xylenol 34.3 parts), 1.2 parts of m-p-ethylphenol, 68.72% of 2,3-xylenol; 1776.4 parts of crude 96.76% 3,5-xylenol (17.8 parts of 2,3-xylenol, 1718.9 parts of 3,5-xylenol, 39.2 parts of 3,4-xylenol, 0.5 parts of m-p-ethylphenol); 577.3 parts of crude 94.53% 3,4-xylenol (3.1 parts of 2,3-xylenol, 28.5 parts of 3,5-xylenol, 545.7 parts of 3,4-xylenol);

[0115] 99.2% petrochemical grade cresol can be used to distill 99.5% o-cresol and 99% m-p-cresol products, and is mainly used to prepare cresol phenolic resin for photoresists, flame retardant plasticizers, etc.

[0116] 99.12% 2,5 / 2,4-dimethylphenol (2,5-dimethylphenol content 78.78%) can be used for tert-butylation separation to produce 6-tert-butyl-2,4-dimethylphenol and 4-tert-butyl-2,5-dimethylphenol products. It can also be used to produce 2,5-dimethylphenol by solvent crystallization. 96.76% crude 3,5-dimethylphenol and 94.53% crude 3,4-dimethylphenol can be used to produce pure 3,5-dimethylphenol and 3,4-dimethylphenol by solvent crystallization or melt crystallization.

[0117] Step 4: Refining of Crude Products from Cracking and Distillation

[0118] 4.1 Add 1776.4 parts of crude 96.76% 3,5-xylenol from step 3 and 1500 parts of methanol to the reactor, start stirring, and heat to 60°C to completely dissolve the material. Then, first use circulating water to cool down to 33°C for 3 hours, then use frozen brine to cool down to -10°C for 3 hours, keep warm for 2 hours, filter, vacuum dry, and dry to obtain 1643.2 parts of 99.58% 3,5-xylenol, with a purification yield of 95.2%.

[0119] 4.2 Add 577.3 parts of the crude 94.53% 3,4-xylenol from step 3 and 1800 parts of petroleum ether at 90-120℃ to the reactor, start stirring, and heat to 80℃ to completely dissolve the materials. Then, first use circulating water to cool down to 38℃ for 3.5 hours, then use chilled brine to cool down to 15℃ for 4 hours, keep warm for 2 hours, filter, vacuum dry, and dry to obtain 494.1 parts of 99.52% 3,4-xylenol, with a purification yield of 90.1%.

[0120] 4.3 Add 1000 parts of 99.12% 2,5 / 2,4-xylenol (78.78% 2,5-xylenol) and 500 parts of methanol from step 3 to the reactor, start stirring, and heat to 65°C to completely dissolve the material. Then, first use circulating water to cool down to 36°C for 2 hours, and then use frozen brine to cool down to -10°C for 3 hours. Keep warm for 2 hours, filter, vacuum dry, and dry to obtain 544.3 parts of 99.68% 2,5-xylenol, with a purification yield of 68.9%.

[0121] Step 5: Separation of the mixed xylenols obtained from cracking distillation by isohexylation

[0122] Add 557.2 parts of the mixed xylenol obtained in step three (33.8 parts of 2,4-xylenol, 105 parts of 2,5-xylenol, 382.9 parts of 2,3-xylenol, 34.3 parts of 3,5-xylenol, and 1.2 parts of m-p-ethylphenol) and 1 part of 6-isohexyl-2,4-xylenol to a pressure vessel, along with 110 parts of strong acid resin. Stir and heat to 110°C to react. Introduce vaporized isohexene until the pressure in the reaction vessel reaches 0.6 MPa. When the pressure inside the vessel decreases to 0.1 MPa, introduce isohexene again until the pressure reaches 0.6 MPa. Repeat this reaction multiple times. When the pressure inside the vessel decreases slowly, take a sample for analysis. If the 2,3-xylenol content is 0.32%, the reaction is considered complete. The reaction took 9 hours, with 342 parts of isohexene (the amount of isohexene was 1.19 times the molar amount of 2,4 / 2,3-xylenol in the mixed xylenol). After the reaction was complete, the mixture was cooled to 80°C and filtered. The filtrate was then distilled under reduced pressure (-0.095 MPa, reflux ratio 25-30:1) to obtain 94.9 parts of 98.68% 2,5-xylenol and 28.5 parts of 99.33% 3,5-xylenol, with yields of 89.2% and 82.6%, respectively; 47.7 parts of 99.09% 6-isohexyl-2,4-xylenol (antioxidant), with a yield of 82.8%; and 590.6 parts of 96.97% 6-isohexyl-2,3-xylenol, with a yield of 88.6%.

[0123] 590.6 parts of 96.97% 6-isohexyl-2,3-dimethylphenol were added to a decomposition vessel, stirred, and 5 parts of sulfuric acid were added. The mixture was heated to 190℃ for 2 hours to remove isohexene. The product was then distilled (at -0.09 MPa and a reflux ratio of 25–30:1) to obtain 342.1 parts of 99.15% 2,3-dimethylphenol, with a yield of 93.3%. 237.8 parts of isohexene were recovered and reused by adding high-boiling-point dimethyl diphenyl ether to the distillation column bottom.

[0124] 94.9 parts of 98.68% 2,5-xylenol and 60 parts of methanol were added to the reactor. The mixture was stirred and heated to 65°C to completely dissolve the material. Then, the temperature was lowered to 34°C by circulating water for 2 hours, followed by cooling to -10°C by chilled brine for 3 hours. The temperature was maintained for 2 hours, filtered, dried under vacuum, and then dried to obtain 87.1 parts of 99.83% 2,5-xylenol with a purification yield of 93.8%.

[0125] Step Six: Alkylation Separation of 2,5-xylenol / 2,4-xylenol (Crude 2,5-xylenol)

[0126] 2000 parts of 99.12% 2,5 / 2,4-xylenol obtained in step three (406.8 parts of 2,4-xylenol, 1575.6 parts of 2,5-xylenol, 2.4 parts of m-p-cresol, and 15.2 parts of 2,3-xylenol) and 2 parts of 6-isononyl-2,4-xylenol were added to a pressure vessel, along with 300 parts of strong acid resin. The mixture was stirred and heated to 130°C. Isononene was added dropwise over 8 hours. After the addition was complete, the reaction was maintained at this temperature for 2 hours. A sample of 2,4-xylenol was taken for analysis. The 15% standard was achieved. 480 parts of isononene were used (the amount of isononene was 1.14 times the molar amount of 2,4-xylenol in 2,5 / 2,4-xylenol). After the reaction was complete, the mixture was cooled to 80℃ and filtered. The filtrate was then distilled under reduced pressure (-0.095 MPa, reflux ratio 25-30:1) to obtain 1488.7 parts of 99.7% 2,5-xylenol (yield 94.2%) and 763.5 parts of 99.2% 9-isononyl-2,4-xylenol (yield 91.6%).

[0127] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0128] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A process for preparing phenolic products from 2,4-xylenol / 2,5-xylenol, characterized in that, Includes the following steps: Step 1: Cleavage and Transposition Reactions An acidic silica-alumina-chromium oxide solid catalyst and zirconium phosphate are loaded into a stainless steel high-pressure reactor. The acidic silica-alumina-chromium oxide consists of silica, acidic alumina, and chromium oxide. A mixture of 2,4-xylenol and 2,5-xylenol is added, wherein the mass ratio of 2,4-xylenol to 2,5-xylenol in the mixture is 0.5–2:1, and the 2,4-xylenol / 2,5-xylenol accounts for 50–97% of the total content. The content of o-isopropylphenol / o-propylphenol in the mixture is 1–30%. 2-ethyl... The 6-cresol content is 0-30%, sealed, and heated to 280-400℃ for 3-10 hours. The pressure is gradually increased to 2.5-5.0 MPa to stop the reaction. The internal coil is cooled with programmed cooling heat transfer oil, rapidly cooled to 280-300℃ within 1-2 hours, and then the temperature is reduced to ≤150℃ within 0.5-1 hour. Propylene and ethylene released in the reaction are gradually discharged. The discharged gas is pressurized by a pressure pump and stored in a stainless steel spherical tank. After the gas is discharged, the condensate from the cracking reaction is cooled slightly and purged with nitrogen for 0.5 hours. The cracking reaction products are obtained by filtration, and the solid catalyst is reused. Step 2: Synthesize thymol: Simultaneously with the cracking and transposition reactions in step one, m-cresol, an acidic catalyst, and a polymerization inhibitor are added to another stainless steel pressure vessel. The acidic catalyst is a mixture of sulfuric acid and phosphoric acid. Stirring is started, and the temperature is raised to 160–170°C. The olefins discharged from the cracking reaction in step one, stored in a spherical tank, are simultaneously and slowly introduced into the stainless steel pressure vessel under reduced pressure, maintaining the vessel temperature at 170–200°C. The olefins are repeatedly introduced until the pressure inside the vessel is maintained at 2.3–2.5 MPa. When the pressure in the spherical tank drops to 2.6 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene in the vessel is discharged. Then, the olefins in the spherical tank are repeatedly introduced until the pressure inside the pressure vessel reaches 1.3–1.5 MPa. When the pressure in the spherical tank drops to 1.6 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene is discharged. The olefins are repeatedly introduced until the pressure inside the vessel reaches 0.6 MPa. When the pressure in the spherical tank drops to 0.7 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene is discharged. The olefin reaction is continued until the pressure inside the vessel reaches 0.1 MPa. When the pressure in the spherical tank drops to 0.1 MPa and the pressure in the pressure vessel no longer decreases, the unreacted ethylene is discharged. The olefin reaction continues until the pressure in the spherical tank reaches 0.03 MPa, at which point the bubbling is stopped. The olefin reaction time is 3–12 hours. After the bubbling is completed, the reaction is kept at a constant temperature for 1–4 hours. A total of 160.7 parts of unreacted ethylene are collected. The ethylene is pressurized and stored in the spherical tank using a pressurized pump. The pressure vessel is cooled to ≤90℃ in 1–3 hours. 10–35% liquid alkali is added to the material in the vessel to neutralize it to pH 7–8. The brine layer is separated, and the material layer is added to the bottom of the distillation column. At -0.085–-0.095 MPa and a reflux ratio of 10–20, the unreacted m-cresol is obtained and reused, and then thymol is obtained.

2. The process for preparing phenolic products from 2,4-xylenol / 2,5-xylenol according to claim 1, characterized in that, The mass ratio of silicon dioxide to acidic alumina is 0.1-10:10-0.1, the amount of chromium oxide is 0.01-0.2% of the mass of silicon dioxide, and the amount of acidic silicon aluminum chromium oxide is 5-50% of the weight of the 2,4-xylenol / 2,5-xylenol mixture.

3. The process for preparing phenolic products from 2,4-xylenol / 2,5-xylenol according to claim 1, characterized in that, In step one, the temperature of the heat transfer oil is gradually and slowly reduced from a high temperature to 80°C. The high temperature is 50-100°C lower than the temperature of the pyrolysis and transposition reaction.

4. The process for preparing phenolic products from 2,4-xylenol / 2,5-xylenol according to claim 1, characterized in that, In step one, the pyrolysis reaction product is obtained by filtration. The reaction product is a mixed phenol composed of 2,5-xylenol / 2,4-xylenol, other xylenols, and some phenols and cresols. The cresols are a mixture of m-cresol, p-cresol, and o-cresols. The other xylenols are 3,5-xylenol, 2,3-xylenol, and 3,4-xylenol.

5. The process for preparing phenolic products from 2,4-xylenol / 2,5-xylenol according to claim 1, characterized in that, The amount of the mixed acid used is 0.5-5% of the mass of m-cresol, wherein the mass ratio of sulfuric acid to phosphoric acid is 5-7:5-3.

6. The process for preparing phenolic products from 2,4-xylenol / 2,5-xylenol according to claim 1, characterized in that, The polymerization inhibitors are hydroquinone, 2-methylhydroquinone, 2-tert-butylhydroquinone, 6-tert-butyl-2,4-dimethylphenol, and p-methoxyphenol.