A process for separating mixed cresols

Abstract

The application belongs to the technical field of chemical industry, and particularly relates to a mixed cresol separation method, which comprises selective oxidation, filtration, neutralization, secondary filtration and rectification processes in sequence. The selective oxidation comprises: adding mixed cresol, sodium hydroxide, sodium methoxide, a solvent and a catalyst into an oxidation kettle, heating, and introducing oxygen for selective oxidation. In the selective oxidation step, sodium methoxide is added, which can react with water obtained in a salification reaction step (i.e. a reaction step of sodium hydroxide and mixed cresol to generate sodium phenate and water) to generate methanol and sodium hydroxide, thereby promoting the selective oxidation reaction and improving the yield.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology, specifically relating to a method for separating mixed cresols. Background Technology

[0002] Cresol is a colorless or pale yellow liquid or crystal, slightly soluble in water, and soluble in ethanol, ether, and alkaline solutions. Cresol is a general term for a mixture of three isomers: cresol, m-cresol, and o-cresol, primarily derived from chemical synthesis or as a byproduct of coking, oil shale distillation, and city gas production. Although the uses of cresol mixtures are limited, each monomer is a widely used organic chemical intermediate. p-cresol is used in pesticides, dyes, and plastics industries, and in medicine as an anthelmintic, disinfectant, and topical anti-corrosion agent. m-cresol is used in analytical reagents and organic synthesis, and is an important raw material for synthesizing antioxidants, pesticides, vitamin E, cosmetics, and pharmaceuticals; it also has important applications in the synthesis of resins, color film developers, and adhesives. Currently, the demand for high-purity cresol monomers is increasing both domestically and internationally, while production capacity is insufficient, resulting in a supply shortage.

[0003] In actual production, because the boiling points of m-cresol and p-cresol differ by only 0.5℃, ordinary distillation techniques are insufficient to separate and purify them. Although the melting points of m-cresol and p-cresol differ by 25.5-27.5℃ (the melting point of m-cresol is approximately 8-10℃, and that of p-cresol is approximately 35.5℃), according to experimental phase diagrams, this temperature range falls within the eutectic region of this binary system, and conventional crystallization techniques also cannot achieve the separation of m-cresol and p-cresol.

[0004] Patent document CN116535291A discloses a method for selective oxidation of m-p-cresol in coal tar, comprising: weighing m-p-cresol, which by mass percentage comprises 64wt% m-cresol, 30wt% p-cresol, 1wt% 2,6-xylenol and 5wt% o-ethylphenol; and adding m-p-cresol (108g), isopropanol (200mL), sodium hydroxide (64.8g), ferric oxide (0.54g), cuprous oxide (0.54g), N-hydroxyphthalimide (0.54g), and 2,2,6,6-tetramethylpiperidine oxide (0.54g) to a reactor. The reactor temperature was set to 50°C, and stirring was started to carry out the reaction. After the reaction temperature reached the set temperature, oxygen was continuously introduced and the pressure was maintained at 0.10 MPa. The reaction was allowed to proceed for 10 hours. After the reaction was completed, water was added to cool and crystallize the product, and then centrifuged. The solid obtained by centrifugation was acidified with hydrochloric acid and filtered. The resulting filter cake was p-hydroxybenzaldehyde. The liquid obtained by centrifugation was distilled to recover methanol, then acidified with hydrochloric acid, separated, and the organic phase was distilled to obtain m-cresol (see Example 1). However, water is generated during the reaction of sodium hydroxide with mixed cresols and in the subsequent oxidation reaction, and the presence of water reduces the reaction yield. After the reaction, hydrochloric acid is used for acidification to precipitate p-hydroxybenzaldehyde first, and the filtrate after separating p-hydroxybenzaldehyde is neutralized twice to obtain m-cresol. However, this is difficult to achieve in practice because m-cresol is weaker than p-hydroxybenzaldehyde. The acidification process first generates m-cresol and then p-hydroxybenzaldehyde. Therefore, in the subsequent process, the centrifugation process cannot completely separate sodium m-methylphenol and p-hydroxybenzaldehyde. As a result, the purity cannot reach the claimed level (99.4% purity of p-hydroxybenzaldehyde and 99.1% purity of m-cresol), and the yield needs to be further improved. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for separating mixed cresols to solve the technical problems that the above method is difficult to implement in practice and that its yield needs to be further improved.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] This invention provides a method for separating mixed cresols, which includes selective oxidation, filtration, neutralization, secondary filtration and distillation steps in sequence. The selective oxidation includes adding mixed cresols, sodium hydroxide, sodium methoxide, solvent and catalyst into an oxidation reactor, and introducing oxygen to carry out selective oxidation.

[0008] Optionally, the molar ratio of the mixed cresol to sodium hydroxide is 2.0-5.0:1, preferably 3.0-5.0:1.

[0009] Optionally, the molar ratio of the mixed cresol to sodium methoxide is 1:1.0-2.0, preferably 1:1.2-2.0.

[0010] Optionally, the catalyst includes a cobalt-based catalyst.

[0011] Optionally, the cobalt-based catalyst includes at least one of cobalt acetate, cobalt oxide, cobalt hydroxide, cobalt sulfate, cobalt chloride, hydrated cobalt acetate, hydrated cobalt oxide, hydrated cobalt sulfate, and hydrated cobalt chloride.

[0012] Optionally, the solvent includes one or more of methanol, ethanol, n-propanol, and isopropanol.

[0013] Optionally, the mass ratio of the mixed cresol to the catalyst is 100:1-500:1, preferably 300:1-500:1.

[0014] Optionally, the temperature of the selective oxidation is 50-100℃, preferably 60-75℃; the pressure of the selective oxidation is atmospheric pressure or 0.1-1.0MPa.

[0015] Optionally, oxygen can be introduced for selective oxidation until the p-cresol content is ≤0.5 wt%.

[0016] Optionally, after filtering and before neutralization, a decolorization step is also included.

[0017] Optionally, the neutralization includes: introducing carbon dioxide into the system until the pH of the system is 3.0-4.0, preferably 3.0-3.5.

[0018] Optionally, the distillation temperature is 140-200℃, preferably 160-180℃; the distillation pressure is 5kPa-1kPa, preferably 2kPa-1kPa.

[0019] As described above, the method for separating mixed cresols of the present invention has the following beneficial effects:

[0020] In this invention, sodium methoxide is added to the selective oxidation step. Sodium methoxide can react with the salt formation reaction step (i.e., the reaction step in which sodium hydroxide reacts with mixed cresol to produce sodium phenolate and water) and the water produced in the selective oxidation step of p-cresol to produce methanol and sodium hydroxide, thereby promoting the selective oxidation reaction and improving the yield.

[0021] This invention selectively oxidizes cresol to p-hydroxybenzaldehyde using pressurized carbon dioxide acidification, without producing inorganic salts such as sodium chloride or sodium sulfate as byproducts. Furthermore, it utilizes the boiling point difference between m-cresol and p-hydroxybenzaldehyde for separation, achieving high yields of two high-purity products with high added value.

[0022] Compared with traditional methods, the method of the present invention produces less waste, lower production costs, and higher product added value, and has good prospects for industrialization. Detailed Implementation

[0023] The present invention will be further illustrated below through specific examples. However, it should be noted that the specific material ratios, process conditions, and results described in the embodiments of the present invention are only for illustrative purposes and should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention. It should be noted that, unless otherwise specified, "wt%" in the present invention refers to mass percentage.

[0024] This invention provides a method for separating mixed cresols, which includes selective oxidation, filtration, decolorization, neutralization, secondary filtration and distillation steps in sequence;

[0025] Selective oxidation includes: adding mixed cresol, sodium hydroxide, sodium methoxide, solvent, and catalyst to an oxidation reactor; the molar ratio of mixed cresol to sodium hydroxide is 2.0-5.0:1, the molar ratio of mixed cresol to sodium methoxide is 1:1.0-2.0, and the mass ratio of mixed cresol to catalyst is 100:1-500:1; the solvent includes one or more of methanol, ethanol, n-propanol, and isopropanol; the catalyst is a cobalt-based catalyst, including at least one of cobalt acetate, cobalt oxide, cobalt hydroxide, cobalt sulfate, cobalt chloride, hydrated cobalt acetate, hydrated cobalt oxide, hydrated cobalt sulfate, and hydrated cobalt chloride; and selectively oxidizing the cresol to ≤0.5wt% by introducing oxygen at 50-100℃ and atmospheric pressure or 0.1-1.0MPa.

[0026] Neutralization involves introducing carbon dioxide into the system until the pH value of the system is 3.0-4.0.

[0027] The distillation temperature is 140-200℃, and the distillation pressure is 5kPa-1kPa.

[0028] The present invention will be described in detail below through specific examples and embodiments. It should also be understood that the following embodiments are only for specific illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0029] Example 1

[0030] A method for separating mixed cresols, the specific steps of which are as follows:

[0031] S1: 3000 mL of methanol, 444.5 g of solid sodium hydroxide (99% purity, 11 mol), 491 g of sodium methoxide (99% purity, 9 mol), 648 g of mixed cresol (containing 60 wt% m-cresol and 40 wt% p-cresol, totaling 6 mol), and 1.5 g of cobalt oxide were added to a high-pressure reactor. Oxygen was continuously introduced and the reaction was carried out at a temperature of 75℃ and a pressure of 0.1 MPa. Samples were taken for analysis every 1 hour. After 5 hours, the p-cresol content was 0.18 wt% (analyzed by gas chromatography, area normalization method). The catalyst cobalt oxide was recovered by hot filtration. The solid obtained by filtration, i.e., the catalyst cobalt oxide, was washed with methanol (50 mL × 3, i.e., three washes, each time using 50 mL of methanol). The washing liquid and filtrate were combined and 2.5 g of activated carbon was added. The mixture was heated under reflux for 1 hour and then filtered while hot to remove the activated carbon, resulting in a decolorized solution.

[0032] S2: The decolorizing solution is introduced into a high-pressure reactor and the temperature is maintained at 55°C. Carbon dioxide gas is introduced into the high-pressure reactor to carry out a neutralization reaction until the pH of the system is 3.0. At this point, the gas is stopped, the mixture is cooled to room temperature, filtered, and the resulting solid is dried to obtain sodium bicarbonate solid.

[0033] S3: The liquid obtained by filtration in step S2 is subjected to atmospheric pressure and 70℃ to recover methanol, and vacuum distilled at 4kPa and 146-150℃ to obtain 359.3g of m-cresol, and vacuum distilled at 1kPa and 175-180℃ to obtain 269.9g of p-hydroxybenzaldehyde.

[0034] The purity, yield, purity, and yield of m-cresol, p-hydroxybenzaldehyde, and p-hydroxybenzaldehyde obtained in this embodiment were tested, and the results are shown in Table 1.

[0035] The purity of m-cresol was determined by gas chromatography using an α-DET 120 cyclodextrin column (30m × 0.25mm × 0.25μm). The chromatographic conditions were as follows: column temperature: initial temperature 150℃, hold for 15 min, then increase to 180℃ at a rate of 10℃ / min, and hold at 180℃ for 5.3 min; carrier gas was high-purity nitrogen, column inlet pressure was 6.5 pisa, and column flow rate was 12.6 cm / s. The results were calculated using the following formula:

[0036]

[0037] The yield of m-cresol is calculated according to the following formula:

[0038]

[0039] The purity of p-hydroxybenzaldehyde was determined by high-performance liquid chromatography (HPLC). The chromatographic conditions were as follows: ODS column Φ2*300mm, eluent composed of methanol and water in a volume ratio of 1:2, flow rate 1.0mL / min, and UV detection wavelength 254nm. The purity was calculated using the following formula:

[0040]

[0041] The yield of p-hydroxybenzaldehyde is calculated according to the following formula:

[0042]

[0043] Example 2

[0044] A method for separating mixed cresols, the specific steps of which are as follows:

[0045] S1: 2500 mL of methanol, 404 solid sodium hydroxide (99% purity, 10.0 mol), 545 g of sodium methoxide (99% purity, 10.0 mol), 540 g of mixed cresol (containing 60 wt% m-cresol and 40 wt% p-cresol, totaling 5 mol), and 5.4 g of cobalt hydroxide were added to a high-pressure reactor. Oxygen was continuously introduced and the reaction was carried out at a temperature of 50℃ and a pressure of 1.0 MPa. Samples were taken for analysis every 1 hour. After 5 hours, the p-cresol content was 0.23 wt% (analyzed by gas chromatography using the area normalization method). The catalyst, cobalt oxide, was recovered by hot filtration. The solid obtained by filtration was the catalyst. It was washed with methanol (50 mL × 3, i.e., three washes, each using 50 mL of methanol). The washing liquid and filtrate were combined and 3 g of activated carbon was added. The mixture was heated under reflux for 1 hour and then filtered while hot to remove the activated carbon, resulting in a decolorized solution.

[0046] S2: The decolorizing solution is introduced into a high-pressure reactor and the temperature is maintained at 50°C. Carbon dioxide gas is introduced into the high-pressure reactor to carry out a neutralization reaction until the pH of the system is 3.0. At this point, the gas is stopped, the mixture is cooled to room temperature, filtered, and the resulting solid is dried to obtain sodium bicarbonate solid.

[0047] S3: The liquid obtained from filtration in step S2 was distilled at atmospheric pressure at 70°C to recover methanol. Then, it was distilled under reduced pressure at 155°C and 5 kPa to obtain 301.9 g of m-cresol. Finally, 232.4 g of p-hydroxybenzaldehyde was distilled under reduced pressure at 180°C and 1 kPa. The purity, yield, and purity and yield of p-hydroxybenzaldehyde obtained in this example were determined, and the results are shown in Table 1.

[0048] Example 3

[0049] A method for separating mixed cresols, the specific steps of which are as follows:

[0050] S1: 2500 mL of methanol, 606 g of solid sodium hydroxide (99% purity, 15 mol), 54.5 g of sodium methoxide (99% purity, 1 mol), 540 g of mixed cresol (containing 60 wt% m-cresol and 40 wt% p-cresol, totaling 5 mol), and 1.1 g of cobalt oxide were added to a high-pressure reactor. Oxygen was continuously introduced and the reaction was carried out at 100℃ and atmospheric pressure. Samples were taken for analysis every 1 hour. After 10 hours, the p-cresol content was 0.38 wt% (analyzed by gas chromatography, area normalization method). The cobalt oxide catalyst was recovered by hot filtration. The solid obtained by filtration was the cobalt oxide catalyst. It was washed with methanol (50 mL × 3, i.e., three washes, each time using 50 mL of methanol). The washing liquid and filtrate were combined and 3 g of activated carbon was added. The mixture was heated under reflux for 1 hour and then filtered while hot to remove the activated carbon, resulting in a decolorized solution.

[0051] S2: The decolorizing solution is introduced into a high-pressure reactor and the temperature is maintained at 60°C. Carbon dioxide gas is introduced into the high-pressure reactor to carry out a neutralization reaction until the pH of the system is 4.0. At this point, the gas is stopped, the system is cooled to room temperature, filtered, and the resulting solid is dried to obtain sodium bicarbonate solid.

[0052] S3: The liquid obtained from filtration in step S2 was distilled at atmospheric pressure at 70°C to recover methanol. Then, it was distilled under reduced pressure at 150°C and 5 kPa to obtain 294.6 g of m-cresol. Finally, it was distilled under reduced pressure at 175°C and 1 kPa to obtain 225.4 g of p-hydroxybenzaldehyde. The purity, yield, and purity of m-cresol and p-hydroxybenzaldehyde obtained in this example were determined, and the results are shown in Table 1.

[0053] The purity, yield, purity, and yield of m-cresol, p-hydroxybenzaldehyde, and p-hydroxybenzaldehyde obtained in this embodiment were tested, and the results are shown in Table 1.

[0054] Comparative Example 1

[0055] Except for the following conditions, the mixed cresols were separated and purified in the same manner as in Example 1:

[0056] S1: 3000 mL of methanol, 444.5 g of solid sodium hydroxide (99% purity, 11 mol), 648 g of mixed cresol (containing 60 wt% m-cresol and 40 wt% p-cresol, totaling 6 mol), and 1.5 g of cobalt oxide were added to a high-pressure reactor. Oxygen was continuously introduced, and the reaction was carried out at a temperature of 75℃ and a pressure of 0.1 MPa. Samples were taken for analysis every 1 hour. After 5 hours, the p-cresol content was 0.12 wt% (analyzed by gas chromatography, area normalization method). The catalyst cobalt oxide was recovered by hot filtration. The solid obtained by filtration, i.e., the catalyst cobalt oxide, was washed with methanol (50 mL × 3, i.e., three washes, each time using 50 mL of methanol). The washing liquid and filtrate were combined, and 2.5 g of activated carbon was added. The mixture was heated under reflux for 1 hour, and the activated carbon was removed by hot filtration to obtain a decolorized solution.

[0057] The purity and yield of m-cresol, the purity and yield of p-hydroxybenzaldehyde obtained in this comparative example were determined, and the results are shown in Table 1.

[0058] Detection

[0059] Table 1 Test Results

[0060] Group Purity of m-cresol yield of m-cresol Purity of p-hydroxybenzaldehyde Yield of p-hydroxybenzaldehyde Example 1 99.0％ 91.5％ 98.5％ 90.8％ Example 2 99.2％ 92.4％ 99.0％ 94.3％ Example 3 98.9％ 89.9％ 99.1％ 91.5％ Comparative Example 1 95.7％ 82.4％ 98.6％ 78.1％

[0061] As shown in Table 1, the yields of m-cresol and p-hydroxybenzaldehyde obtained in Examples 1-3 reached 92.4% and 94.3%, respectively. These results demonstrate that the separation method of the present invention significantly improves the yield.

[0062] As shown in Table 1, the yield of m-cresol obtained in Comparative Example 1 (without sodium methoxide in the selective oxidation step) was 82.4%, and the yield of p-hydroxybenzaldehyde was 78.1%, while the yield of m-cresol obtained in Example 1 (with sodium methoxide in the selective oxidation step) was 91.5%, and the yield of p-hydroxybenzaldehyde was 90.8%. That is, compared with Comparative Example 1, the yields of m-cresol and p-hydroxybenzaldehyde obtained by the separation method in Example 1 were significantly increased. This result indicates that the addition of sodium methoxide in the selective oxidation step of this invention, where sodium methoxide reacts with the water obtained in the salt formation reaction step (i.e., the reaction step where sodium hydroxide reacts with mixed phenols to produce water) and the selective oxidation step of p-cresol to produce methanol and sodium hydroxide, promotes the selective oxidation reaction and thus improves the yield.

[0063] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for separating mixed cresols, characterized in that, The process includes selective oxidation, filtration, neutralization, secondary filtration, and distillation. The selective oxidation involves adding a mixture of cresol, sodium hydroxide, sodium methoxide, solvent, and catalyst to an oxidation reactor, introducing oxygen to selectively oxidize until the cresol content is ≤0.5 wt%. The selective oxidation temperature is 50-100℃, and the selective oxidation pressure is atmospheric pressure or 0.1-1.0 MPa. The molar ratio of the mixed cresol to sodium methoxide is 1:1.0-2.0, and the molar ratio of the mixed cresol to sodium hydroxide is 2.0-5.0:

1. The catalyst includes a cobalt-based catalyst, comprising at least one of cobalt acetate, cobalt oxide, cobalt hydroxide, cobalt sulfate, cobalt chloride, hydrated cobalt acetate, hydrated cobalt oxide, hydrated cobalt sulfate, and hydrated cobalt chloride. The mass ratio of the mixed cresol to the catalyst is 100:1-500:

1. The neutralization includes: introducing carbon dioxide into the system until the pH of the system is 3.0-4.0; The distillation temperature is 140-200℃, and the distillation pressure is 5kPa-1kPa. The process includes a decolorization step after filtration and before neutralization.

Images