Method for separating mixed cresols

Abstract

The present invention belongs to the technical field of chemical engineering, and specifically relates to a method for separating mixed cresols. The method for separating mixed cresols comprises the successive steps of selective oxidation, filtration, neutralization, secondary filtration and rectification, wherein the selective oxidation comprises: adding mixed cresols, sodium hydroxide, sodium methoxide, a solvent and a catalyst to an oxidizing kettle, heating same, and introducing oxygen into the oxidizing kettle to perform selective oxidation. In the present invention, sodium methoxide is added in the step of selective oxidation; and sodium methoxide can react with water obtained in the step of a salt forming reaction (i.e., the reaction step of reacting sodium hydroxide with mixed cresols to generate sodium phenolate and water) to generate methanol and sodium hydroxide, thereby promoting the progression of a selective oxidation reaction and increasing the yield.

Description

A method for separating mixed cresols Technical Field

[0001] The invention belongs to the technical field of chemical industry, and particularly relates to a method for separating mixed cresols. Background Art

[0002] Cresol is a colorless or pale yellow liquid or crystal, slightly soluble in water, but soluble in ethanol, ether, and alkali. Cresol is a general term for a mixture of three isomers: p-cresol, m-cresol, and o-cresol. It primarily originates from chemical synthesis or as a byproduct of coking, oil shale retorting, and city gas. While the uses of cresol mixtures are limited, the individual monomers are widely used organic chemical intermediates. p-cresol is used in pesticides, dyes, plastics, and other industrial applications, and in medicine as an anthelmintic, disinfectant, and topical anticorrosive. m-cresol is used in analytical reagents and organic synthesis, and is an important raw material for the synthesis of antioxidants, pesticides, vitamin E, cosmetics, and pharmaceuticals. It also has important applications in synthetic resins, color film developers, and adhesives. Currently, demand for high-purity cresol monomers is increasing both domestically and internationally, but insufficient production capacity has resulted in a supply shortage.

[0003] In actual production, conventional distillation techniques are difficult to separate and purify m-cresol from p-cresol, as their boiling points differ by only 0.5°C. Although the melting points of m-cresol and p-cresol differ by 25.5-27.5°C (m-cresol's melting point is approximately 8-10°C, and p-cresol's melting point is approximately 35.5°C), experimental phase diagrams indicate that this temperature range falls within the eutectic region of the binary system, making conventional crystallization techniques incapable of separating m-cresol from p-cresol.

[0004] Patent document CN116535291A discloses a method for selective oxidation of m-cresol in coal tar, comprising: weighing m-cresol, which comprises, by mass percentage, 64 wt% of m-cresol, 30 wt% of p-cresol, 1 wt% of 2,6-dimethylphenol, and 5 wt% of o-ethylphenol; and adding m-cresol (108 g), isopropyl alcohol (200 mL), sodium hydroxide (64.8 g), ferric oxide (0.54 g), cuprous oxide (0.54 g), N-hydroxyphthalimide (0.54 g), and 2,2,6,6-tetramethylpiperidinyl oxide (0.54 g) into a reactor. The reactor temperature was set to 50°C, stirring was started, and the reaction was carried out. After the reaction temperature reached the set temperature, oxygen was continuously introduced, the pressure was maintained at 0.10 MPa, and the reaction was fully reacted for 10 hours. After the reaction was completed, water was added to cool and crystallize, and centrifugation was performed. The solid obtained by centrifugation was acidified with hydrochloric acid and filtered to obtain a filter cake of p-hydroxybenzaldehyde. The liquid obtained by centrifugation was distilled to recover methanol, and 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 and mixed cresols and during the subsequent oxidation reaction, and the presence of water reduces the reaction yield. After the reaction is completed, hydrochloric acid is used for acidification to first precipitate p-hydroxybenzaldehyde, and the filtrate after separating p-hydroxybenzaldehyde is secondary neutralized to obtain m-cresol. However, this is difficult to achieve in actual operation because the acidity of m-cresol is weaker than that of p-hydroxybenzaldehyde. The acidification process first generates m-cresol and then p-hydroxybenzaldehyde. Therefore, in the subsequent process, the centrifugation step cannot completely separate sodium m-cresol and p-hydroxybenzaldehyde. Therefore, the purity cannot reach the claimed level (the purity of p-hydroxybenzaldehyde is 99.4%, and the purity of m-cresol is 99.1%), and the yield needs to be further improved.

[0005] Summary of the Invention

[0006] In view of this, the object 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 actual operation and its yield needs to be further improved.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] The invention provides a method for separating mixed cresols, which sequentially comprises the steps of selective oxidation, filtration, neutralization, secondary filtration and rectification. The selective oxidation comprises: adding mixed cresols, sodium hydroxide, sodium methoxide, a solvent and a catalyst into an oxidation kettle, and introducing oxygen for selective oxidation.

[0009] Optionally, the molar ratio of the mixed cresols to sodium hydroxide is 2.0-5.0:1, preferably 3.0-5.0:1.

[0010] Optionally, the molar ratio of the mixed cresols to sodium methoxide is 1:1.0-2.0, preferably 1:1.2-2.0.

[0011] Optionally, the catalyst comprises a cobalt-based catalyst.

[0012] 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.

[0013] Optionally, the solvent includes one or more of methanol, ethanol, n-propanol, and isopropanol.

[0014] Optionally, the mass ratio of the mixed cresol to the catalyst is 100:1-500:1, preferably 300:1-500:1.

[0015] Optionally, the temperature of the selective oxidation is 50-100° C., preferably 60-75° C.; the pressure of the selective oxidation is normal pressure or 0.1-1.0 MPa.

[0016] Optionally, oxygen is introduced to perform selective oxidation until the content of p-cresol is ≤0.5 wt %.

[0017] Optionally, a decolorization step is further included after the filtration and before the neutralization.

[0018] Optionally, the neutralization comprises: introducing carbon dioxide into the system until the pH value of the system is 3.0-4.0, preferably 3.0-3.5.

[0019] Optionally, the distillation temperature is 140-200° C., preferably 160-180° C.; the distillation pressure is 5 kPa-1 kPa, preferably 2 kPa-1 kPa.

[0020] As described above, the separation method of mixed cresols of the present invention has the following beneficial effects:

[0021] In the present invention, sodium methoxide is added in the selective oxidation step, and the sodium methoxide can react with water produced in the salt-forming reaction step (i.e., the reaction step in which sodium hydroxide reacts with mixed cresols to produce sodium phenolate and water) and the p-cresol selective oxidation step to produce methanol and sodium hydroxide, thereby promoting the selective oxidation reaction and improving the yield.

[0022] The present invention selectively oxidizes cresol to p-hydroxybenzaldehyde using carbon dioxide pressurized acidification, without producing inorganic salts such as sodium chloride or sodium sulfate. Furthermore, the difference in boiling points between m-cresol and p-hydroxybenzaldehyde is utilized for separation, yielding two high-value, high-purity products in high yield.

[0023] Compared with traditional methods, the method of the present invention has less three wastes, low production cost, high product added value, and good industrialization prospects. DETAILED DESCRIPTION

[0024] The present invention is further illustrated below by means of specific examples. However, it should be noted that the specific material ratios, process conditions, and results described in the examples of the present invention are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be included within the scope of protection of the present invention. It should be noted that, unless otherwise specified, "wt%" herein refers to the percentage by mass.

[0025] The present invention provides a method for separating mixed cresols, which comprises the steps of selective oxidation, filtration, decolorization, neutralization, secondary filtration and rectification in sequence;

[0026] The selective oxidation comprises the following steps: adding mixed cresol, sodium hydroxide, sodium methoxide, a solvent and a catalyst into an oxidation kettle, wherein the molar ratio of the mixed cresol to the sodium hydroxide is 2.0-5.0:1, the molar ratio of the mixed cresol to the sodium methoxide is 1:1.0-2.0, and the mass ratio of the mixed cresol to the catalyst is 100:1-500:1; the solvent comprises one or more of methanol, ethanol, n-propanol and isopropanol; the catalyst is a cobalt-based catalyst, and the cobalt-based catalyst comprises 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 introducing oxygen to carry out selective oxidation at 50-100°C and normal pressure or 0.1-1.0 MPa until the content of p-cresol is less than or equal to 0.5wt%.

[0027] Neutralization includes: introducing carbon dioxide into the system until the pH value of the system is 3.0-4.0.

[0028] The distillation temperature is 140-200°C, and the distillation pressure is 5kPa-1kPa.

[0029] The present invention is described in detail below by way of specific examples. It should also be understood that the following examples are only used to specifically illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the scope of protection of the present invention. The specific process parameters and the like in the following examples are only examples within a suitable range, and those skilled in the art can make selections within a suitable range through the description herein, and are not to be limited to the specific numerical values ​​exemplified below.

[0030] Example 1

[0031] A method for separating mixed cresols, comprising the following steps:

[0032] S1: 3000mL of methanol, 444.5g of solid sodium hydroxide (purity 99%, 11mol), 491g of sodium methoxide (purity 99%, 9mol), 648g of mixed cresols (containing 60wt% of m-cresol and 40wt% of p-cresol, a total of 6mol) and 1.5g of cobalt oxide were put into an autoclave, oxygen was continuously introduced and the reaction was carried out at a temperature of 75°C and a pressure of 0.1MPa. Sampling and analysis were performed every 1h. After 5h, the p-cresol content was 0.18wt% (analyzed by gas chromatography GC, 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 (50mL×3, i.e., washed three times with 50mL of methanol each time). After the washing solution and the filtrate were combined, 2.5g of activated carbon was added, and the mixture was heated to reflux for 1h. The activated carbon was removed by hot filtration to obtain a decolorized solution.

[0033] S2: introducing the decolorizing solution into an autoclave, maintaining the temperature at 55°C, and introducing carbon dioxide gas into the autoclave for neutralization reaction until the pH of the system reaches 3.0. At this time, the aeration is stopped, and the system is cooled to room temperature. The obtained solid is filtered and dried to obtain sodium bicarbonate solid;

[0034] S3: The liquid obtained by filtration in step S2 is cooled to 70°C at normal pressure to recover methanol, and then distilled under reduced pressure at 4 kPa and 146-150°C to obtain 359.3 g of m-cresol, and distilled under reduced pressure at 1 kPa and 175-180°C to obtain 269.9 g of p-hydroxybenzaldehyde.

[0035] The purity of the meta-cresol obtained in this example, the yield of the meta-cresol, the purity of the p-hydroxybenzaldehyde, and the yield of the p-hydroxybenzaldehyde were tested, and the results are shown in Table 1.

[0036] The purity of m-cresol was detected by gas chromatography using an α-DET 120 cyclodextrin column (30 m×0.25 mm×0.25 μm). The chromatographic conditions were as follows: column temperature: initial temperature 150°C, dwell time 15 min, heating to 180°C at a rate of 10°C / min, and constant temperature maintained at 180°C for 5.3 min; carrier gas was high-purity nitrogen, column head pressure was 6.5 pisa, column flow rate was 12.6 cm / s, and the purity was calculated according to the following formula:

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

[0038] The purity of p-hydroxybenzaldehyde was detected by high performance liquid chromatography (HPLC), wherein the chromatographic conditions were: ODS column Φ2*300 mm, eluent composed of methanol and water in a volume ratio of 1:2, flow rate of 1.0 mL / min, ultraviolet detection wavelength of 254 nm, and calculated according to the following formula:

[0039] The yield of p-hydroxybenzaldehyde is calculated according to the following formula:

[0040] Example 2

[0041] A method for separating mixed cresols, comprising the following steps:

[0042] S1: 2500mL of methanol, 404g of solid sodium hydroxide (purity 99%, 10.0mol), 545g of sodium methoxide (purity 99%, 10.0mol), 540g of mixed cresols (containing 60wt% of m-cresol and 40wt% of p-cresol, 5mol in total) and 5.4g of cobalt hydroxide were put into an autoclave, oxygen was continuously introduced and the reaction was carried out at a temperature of 50°C and a pressure of 1.0MPa. Sampling and analysis were performed every 1h. After 5h, the p-cresol content was 0.23wt% (analyzed by gas chromatography GC, area normalization method). The catalyst cobalt oxide was recovered by filtration while hot. The solid obtained by filtration was the catalyst and washed with methanol (50mL×3, i.e., three times with 50mL of methanol each time). After the washing solution and the filtrate were combined, 3g of activated carbon was added, and the mixture was heated to reflux for 1h. The activated carbon was removed by filtration while hot to obtain a decolorized solution.

[0043] S2: introducing the decolorizing solution into an autoclave, maintaining the temperature at 50°C, and introducing carbon dioxide gas into the autoclave for neutralization reaction until the pH of the system reaches 3.0. At this time, the aeration is stopped, and the system is cooled to room temperature. The obtained solid is filtered and dried to obtain sodium bicarbonate solid;

[0044] S3: The liquid filtered in step S2 was distilled at 70°C under atmospheric pressure to recover methanol. 301.9 g of m-cresol was distilled under reduced pressure at 5 kPa and 155°C. 232.4 g of p-hydroxybenzaldehyde was distilled under reduced pressure at 1 kPa and 180°C. The purity of m-cresol, the yield of m-cresol, the purity of p-hydroxybenzaldehyde, and the yield of p-hydroxybenzaldehyde obtained in this example were tested, and the results are shown in Table 1.

[0045] Example 3

[0046] A method for separating mixed cresols, comprising the following steps:

[0047] 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 cresols (containing 60 wt % of m-cresol and 40 wt % of p-cresol, a total of 5 mol) and 1.1 g of cobalt oxide were placed in an autoclave, oxygen was continuously introduced and the reaction was carried out at a temperature of 100° C. and normal pressure. Sampling and analysis were performed every 1 h. After 10 h, the p-cresol content was 0.38 wt % (analyzed by gas chromatography (GC) using an 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 times with 50 mL of methanol each time). The washing solution and the filtrate were combined and 3 g of activated carbon was added. The mixture was heated to reflux for 1 h and the activated carbon was removed by hot filtration to obtain a decolorized solution.

[0048] S2: introducing the decolorizing solution into an autoclave, maintaining the temperature at 60°C, and introducing carbon dioxide gas into the autoclave for neutralization reaction until the pH of the system reaches 4.0. At this time, the aeration is stopped, and the system is cooled to room temperature. The obtained solid is filtered and dried to obtain sodium bicarbonate solid;

[0049] S3: The liquid filtered in step S2 was distilled at 70°C under atmospheric pressure to recover methanol. Reduced pressure distillation at 5 kPa and 150°C was then performed to obtain 294.6 g of m-cresol. Reduced pressure distillation at 1 kPa and 175°C was then performed to obtain 225.4 g of p-hydroxybenzaldehyde. The purity of the m-cresol, the yield of m-cresol, and the purity and yield of p-hydroxybenzaldehyde obtained in this example were tested, and the results are shown in Table 1.

[0050] The purity of the meta-cresol obtained in this example, the yield of the meta-cresol, the purity of the p-hydroxybenzaldehyde, and the yield of the p-hydroxybenzaldehyde were tested, and the results are shown in Table 1.

[0051] Comparative Example 1

[0052] The mixed cresols were separated and purified in the same manner as in Example 1 except for the following conditions:

[0053] S1: 3000mL of methanol, 444.5g of solid sodium hydroxide (purity 99%, 11mol), 648g of mixed cresols (containing 60wt% of m-cresol and 40wt% of p-cresol, a total of 6mol) and 1.5g of cobalt oxide were put into an autoclave, oxygen was continuously introduced and the reaction was carried out at a temperature of 75°C and a pressure of 0.1Mpa. Sampling and analysis were performed every 1h. After 5h, the p-cresol content was 0.12wt% (analyzed by gas chromatography GC, 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 (50mL×3, i.e., washed three times, each time with 50mL of methanol). After the washing solution and the filtrate were combined, 2.5g of activated carbon was added, and the mixture was heated to reflux for 1h. The activated carbon was removed by hot filtration to obtain a decolorized solution.

[0054] The purity of the meta-cresol obtained in this comparative example, the yield of the meta-cresol, the purity of the p-hydroxybenzaldehyde and the yield of the p-hydroxybenzaldehyde were tested, and the results are shown in Table 1.

[0055] Detection

[0056] Table 1 Test results

[0057] As shown in Table 1, the yield of m-cresol obtained in Examples 1-3 can reach 92.4%, and the yield of p-hydroxybenzaldehyde can reach 94.3%. This result shows that the separation method of the present invention significantly improves the yield.

[0058] As shown in Table 1, the yield of meta-cresol obtained in Comparative Example 1 (sodium methoxide was not added in the selective oxidation step) was 82.4%, and the yield of p-hydroxybenzaldehyde was 78.1%, while the yield of meta-cresol obtained in Example 1 (sodium methoxide was added 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 yield of meta-cresol and p-hydroxybenzaldehyde obtained by the separation method of Example 1 was significantly increased. This result shows that the present invention adds sodium methoxide in the selective oxidation step, and sodium methoxide can react with the water obtained in the salt-forming reaction step (i.e., the reaction step in which sodium hydroxide and mixed phenol react to generate water) and the p-cresol selective oxidation step to generate methanol and sodium hydroxide, thereby promoting the selective oxidation reaction, thereby improving the yield.

[0059] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may 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 one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for separating mixed cresols, characterized in that: The method comprises the steps of selective oxidation, filtration, neutralization, secondary filtration and rectification in sequence. The selective oxidation comprises: adding mixed cresol, sodium hydroxide, sodium methoxide, solvent and catalyst into an oxidation kettle, and introducing oxygen for selective oxidation.

2. The separation method according to claim 1, characterized in that The molar ratio of the mixed cresol to sodium hydroxide is 2.0-5.0:

1.

3. The separation method according to claim 1, characterized in that The molar ratio of the mixed cresol to sodium methoxide is 1:1.0-2.

0.

4. The separation method according to claim 1, characterized in that The catalyst includes a cobalt-based catalyst.

5. The separation method according to claim 4, characterized in that 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.

6. The separation method according to claim 1, characterized in that The mass ratio of the mixed cresol to the catalyst is 100:1-500:1; And / or, after the filtration and before the neutralization, a decolorization step is also included.

7. The separation method according to claim 1, characterized in that The temperature of the selective oxidation is 50-100° C., and the pressure of the selective oxidation is normal pressure or 0.1-1.0 MPa.

8. The separation method according to claim 1, characterized in that Oxygen is introduced to carry out selective oxidation until the content of p-cresol is ≤0.5wt%.

9. The separation method according to claim 1, characterized in that The neutralization comprises: introducing carbon dioxide into the system until the pH value of the system is 3.0-4.

0.

10. The separation method according to claim 1, characterized in that The distillation temperature is 140-200° C., and the distillation pressure is 5 kPa-1 kPa.

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