A method and system for separating m-cresol from p-cresol

Abstract

The present application belongs to the field of chemical technology, and particularly relates to a method and system for separating meta-cresol and para-cresol. The method comprises, in sequence, the steps of oxidation, neutralization, filtration, water vapor distillation and acidification. The neutralization comprises: passing in carbon dioxide until the pH of the system is 5.0-6.0. The present application selectively oxidizes para-cresol into para-hydroxybenzaldehyde, and separates the meta-cresol and para-hydroxybenzaldehyde by virtue of the difference in physical properties, thereby obtaining two products with high added value. By controlling the pH of the neutralization step to be within the range of 5.0-6.0, the yield can be improved.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology, specifically relating to a method and system for separating m-cresol and p-cresol. Background Technology

[0002] Cresol, also known as benzyl phenol, is a mixture of three isomers: o-cresol, m-cresol, and p-cresol. It is a colorless, pale yellow, pale brown, or pale red liquid with a phenolic odor.

[0003] Because m-cresol and p-cresol have similar boiling points (difference of only 0.5℃), conventional distillation methods cannot separate and purify them. Although m-cresol and p-cresol have different melting points (around 25-27℃), this temperature range falls within the eutectic region of a binary system, making it difficult for conventional crystallization techniques to separate them.

[0004] Patent document CN116535291A discloses a method for the selective oxidation of m-p-cresol from coal tar. Using m-p-cresol from coal tar as a raw material and oxygen as an oxidant, the method selectively oxidizes and synthesizes p-hydroxybenzaldehyde and m-cresol in the presence of sodium hydroxide, a main catalyst, a co-catalyst, and a solvent. In the specific operation, after the oxidation reaction is completed, water is added to cool and crystallize, followed by centrifugation. The solid obtained by centrifugation is acidified with hydrochloric acid, filtered, and the resulting filter cake is p-hydroxybenzaldehyde. The liquid obtained by centrifugation is distilled to recover methanol, then acidified with hydrochloric acid, separated, and the organic phase is purified by distillation to obtain m-cresol. This method combines the main catalyst and co-catalyst during the reaction process to selectively oxidize p-cresol, 2,6-xylenol, and o-ethylphenol in m-p-cresol from coal tar, enabling the final product purity of both p-hydroxybenzaldehyde and m-cresol to reach over 99%. However, the yield of this method is low, with the yield of p-hydroxybenzaldehyde only 68.9%-78.1% and the yield of m-cresol only 76.5%-83.8%. More importantly, after analyzing and verifying the relevant technology, the inventors found that it could not achieve the claimed technical effect at all. Specifically, 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 is completed, hydrochloric acid is used for acidification to precipitate p-hydroxybenzaldehyde first, and the filtrate after separating p-hydroxybenzaldehyde is acidified to obtain m-cresol. In actual operation, this step cannot achieve the separation of the two at all. The reason is that 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 process cannot completely separate sodium m-cresol and p-methylbenzaldehyde. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a method and system for separating m-cresol and p-cresol to improve the yield.

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

[0007] In some embodiments of this application, the present invention provides a method for separating m-cresol and p-cresol, comprising the steps of oxidation, filtration, neutralization, re-filtration, steam distillation and acidification, wherein the neutralization comprises: introducing carbon dioxide until the pH of the system is 5.0-6.0.

[0008] This invention selectively oxidizes p-cresol to p-hydroxybenzaldehyde and then separates them by utilizing the differences in their physical properties, yielding two high-value-added products. The yield can be improved by controlling the pH of the neutralization step to the range of 5.0-6.0.

[0009] In some embodiments of this application, the oxidation includes: mixing cresol to be treated, sodium hydroxide, solvent and catalyst, and introducing oxygen to carry out the oxidation reaction.

[0010] In some embodiments of this application, the temperature of the steam distillation is 80-100℃, preferably 95-100℃; the pressure of the steam distillation is 0.1-1.0MPa, preferably 0.2-0.5MPa.

[0011] In some embodiments of this application, the acidification includes adding an acidic substance to the system to adjust the pH of the system to 4.0-4.5.

[0012] This invention improves the yield of m-cresol by controlling the pH of the acidification step to the range of 4.0-4.5.

[0013] In some embodiments of this application, the acidic substance includes inorganic acids, organic acids, or combinations thereof.

[0014] In some embodiments of this application, the oxidation and neutralization process further includes decolorization and filtration steps.

[0015] In some embodiments of this application, the decolorizing agent used in the decolorization process includes activated carbon.

[0016] In some embodiments of this application, the mass ratio of the decolorizing agent to the mixed phenol is 1:200-450, preferably 1:400-450.

[0017] 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.

[0018] In some embodiments of this application, the present invention also provides a system used in the method described above, comprising:

[0019] The oxidation reactor, neutralization reactor, first solid-liquid separation mechanism, steam distillation reactor, acidification reactor, extraction phase separation reactor and concentration crystallization reactor are connected in sequence, and the oxidation reactor is equipped with a sampling port.

[0020] In some embodiments of this application, the system further includes a concentration vessel located on a connecting pipe between the first solid-liquid separation mechanism and the steam distillation vessel.

[0021] In some embodiments of this application, the system further includes: the steam distillation vessel is provided with a gas phase outlet, and the system further includes a phase separation crystallization vessel, which is connected to the gas phase outlet;

[0022] In some embodiments of this application, the system further includes a second solid-liquid separation mechanism located on the connecting pipe between the oxidation reactor and the neutralization reactor.

[0023] In some embodiments of this application, the second solid-liquid separation mechanism is provided with a liquid outlet, and the system further includes: a first decolorizing vessel and a first phase separator connected together, the first decolorizing vessel and the first phase separator being located on a connecting pipe between the second solid-liquid separation mechanism and the neutralization vessel, the first decolorizing vessel being connected to the liquid outlet of the first solid-liquid separation mechanism, the first phase separator being provided with a liquid phase outlet, and the liquid phase outlet of the first phase separator being connected to the neutralization vessel.

[0024] In some embodiments of this application, the concentration crystallization vessel is provided with a liquid outlet, and the system further includes: a second decolorization vessel and a second phase separator connected in series, wherein the second decolorization vessel is connected to the liquid outlet of the concentration crystallization vessel. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the system for separating m-cresol and p-cresol in Example 1;

[0026] Figure 2 The flowcharts are for the methods of separating m-cresol and p-cresol in Examples 1-3;

[0027] Figure 3 This is a schematic diagram of the system for separating m-cresol and p-cresol in Example 4;

[0028] Figure 4 This is a schematic diagram of the system for separating m-cresol and p-cresol in Example 5;

[0029] Figure 5 This is a schematic diagram of the system for separating m-cresol and p-cresol in Example 6.

[0030] Figure Labels

[0031] Oxidation reactor-1;

[0032] Second solid-liquid separation mechanism - 2;

[0033] First decolorizing kettle-3;

[0034] First solid-liquid separation mechanism - 4;

[0035] Neutralization kettle-5;

[0036] Third solid-liquid separation mechanism - 6;

[0037] Concentrator-7;

[0038] Steam distillation kettle-8;

[0039] Acidification kettle-9;

[0040] Extraction phase separation vessel-10;

[0041] Concentration and Crystallization Kettle-11;

[0042] Second decolorizing kettle-12;

[0043] Second phase splitter-13;

[0044] Phase separation crystallization kettle-14. Detailed Implementation

[0045] 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.

[0046] This invention provides a method for separating m-cresol and p-cresol, comprising oxidation, filtration, neutralization, re-filtration, steam distillation and acidification in sequence.

[0047] In this application, the oxidation step includes: mixing the cresol to be treated, sodium hydroxide, solvent and catalyst, and introducing oxygen to carry out the oxidation reaction.

[0048] In this application, the term "cresol to be treated" includes m-cresol and p-cresol.

[0049] In this application, during the oxidation step, the m-cresol in the cresol to be treated can undergo a salt-forming reaction, that is, in the presence of methanol, m-cresol reacts with sodium hydroxide to produce sodium m-cresol and water, and p-cresol reacts with sodium hydroxide in the presence of methanol to produce sodium p-cresol and water.

[0050]

[0051] Next, sodium p-cresol reacts with oxygen in the presence of a catalyst to produce sodium p-aldehyde phenolate and water, while sodium m-cresol cannot undergo oxidation. Therefore, this step is a selective oxidation reaction step.

[0052]

[0053] In this application, the solvent includes, but is not limited to, alcohols, chlorinated hydrocarbons, ketones, esters, and aromatic hydrocarbons.

[0054] In this application, alcohols can be categorized as such as methanol, ethanol, n-propanol, etc.

[0055] In this application, the molar ratio of sodium hydroxide to cresol to be treated can be 1:2-5, preferably 1:3-4, in terms of the amount of sodium hydroxide used.

[0056] In this application, the catalyst, in terms of its type, includes, but is not limited to, cobalt-based catalysts.

[0057] In this application, in terms of the types of cobalt-based catalysts, cobalt-based catalysts may include substances such as cobalt acetate, cobalt oxide, cobalt hydroxide, cobalt sulfate, cobalt chloride, or their hydrates.

[0058] In this application, the mass ratio of catalyst to cresol to be treated can be 1:100-1:500.

[0059] In this application, the temperature of the oxidation reaction is 50-100°C, preferably 60-75°C.

[0060] In this application, the pressure of the oxidation reaction can be atmospheric pressure or 0.1-1.0 MPa.

[0061] In this application, regarding the extent of the oxidation reaction, the oxidation reaction continues until the mass percentage of p-cresol in the system is less than or equal to a preset threshold. The preset threshold can be set by the user, for example, it can be set to 0.5 wt%.

[0062] In this application, the neutralization step includes: introducing carbon dioxide until the pH of the system is 5.0-6.0.

[0063] In this application, during the neutralization process, the introduced carbon dioxide reacts with water in the system to produce carbonic acid, which then reacts with sodium m-cresol generated in the oxidation step to produce m-cresol. Sodium p-aldehyde phenolate generated in the oxidation step, however, does not react, allowing for the separation and purification of sodium p-aldehyde phenolate and m-cresol through subsequent filtration.

[0064]

[0065] In this application, the temperature of steam distillation can be 80-100℃, preferably 95-100℃.

[0066] In this application, the pressure of steam distillation can be 0.1-1 MPa, preferably 0.1-0.3 MPa.

[0067] In this application, the acidification step includes adding an acidic substance to the system to adjust the pH of the system to 4.0-4.5.

[0068] In this application, during the acidification process, sodium p-aldehyde phenolate can react with acidic substances such as sulfuric acid to generate p-hydroxybenzaldehyde:

[0069]

[0070] In this application, there are no restrictions on the types of acidic substances; the acidic substances can be inorganic acids, organic acids, or combinations thereof. Examples of inorganic acids include sulfuric acid and hydrochloric acid, and examples of organic acids include acetic acid.

[0071] In some embodiments of this application, a decolorization step is included after filtering and before neutralization.

[0072] In this application, the decolorizing agent used in the decolorization process includes activated carbon, as per the decolorization step.

[0073] In this application, the mass ratio of the decolorizing agent to sodium hydroxide is 1:200-450, with regard to the amount of activated carbon used.

[0074] In some embodiments of this application, a distillation step is included after neutralization and before steam distillation to recover the solvent.

[0075] In this application, the distillation temperature can be 60-100℃, preferably 60-80℃.

[0076] In this application, the distillation pressure can be 10-100 kPa, preferably 50-100 kPa.

[0077] The present invention also provides a system for the method described above, comprising:

[0078] The oxidation reactor, the first solid-liquid separation mechanism, the neutralization vessel, the second solid-liquid separation mechanism, the steam distillation vessel, the acidification vessel, the extraction and phase separation vessel, and the concentration and crystallization vessel are connected in sequence. The oxidation reactor is equipped with a sampling port.

[0079] In some embodiments of this application, the system further includes a concentration vessel located on a connecting pipe between the second solid-liquid separation mechanism and the steam distillation vessel.

[0080] In some embodiments of this application, the steam distillation vessel is provided with a gas phase outlet, and the system also includes a phase separation crystallization vessel connected to the gas phase outlet of the steam distillation vessel.

[0081] In some embodiments of this application, the first solid-liquid separation mechanism is provided with a liquid outlet. The system further includes: a first decolorizing vessel and a first phase separator connected together. The first decolorizing vessel and the first phase separator are located on a connecting pipe between the first solid-liquid separation mechanism and the neutralization vessel. The first decolorizing vessel is connected to the liquid outlet of the first solid-liquid separation mechanism. The first phase separator is provided with a liquid phase outlet, and the liquid phase outlet of the first phase separator is connected to the neutralization vessel.

[0082] In some embodiments of this application, the concentration crystallization vessel is provided with a liquid outlet, and the system further includes: a second decolorization vessel and a second phase separator connected in series, wherein the second decolorization vessel is connected to the liquid outlet of the concentration crystallization vessel.

[0083] 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.

[0084] Example 1

[0085] like Figure 1 The system shown is for separating m-cresol and p-cresol. The system includes an oxidation reactor 1, a second solid-liquid separation mechanism 2, a first decolorization reactor 3, a first phase separator 4, a neutralization reactor 5, a first solid-liquid separation mechanism 6, a concentration reactor 7, a steam distillation reactor 8, an acidification reactor 9, an extraction phase separator 10, a concentration crystallization reactor 11, a second decolorization reactor 12, and a second phase separator 13, all connected in sequence.

[0086] Please continue reading. Figure 1The oxidation reactor 1 is equipped with a raw material inlet (not shown), an oxygen inlet (not shown), a discharge port (not shown), a temperature control component (not shown), a pressure gauge (not shown if necessary), and a sampling port (not shown). Oxidation reactor 1 is existing technology and will not be described in detail here. Oxidation reactor 1 serves as a mixing place for the cresol to be treated (a mixture of o-cresol and p-cresol), sodium hydroxide (the molar ratio of sodium hydroxide to the cresol to be treated can be 1:2-5), a catalyst (e.g., cobalt acetate, cobalt oxide, cobalt hydroxide, cobalt sulfate, cobalt chloride, or their hydrates, etc., with a mass ratio of catalyst to the cresol to be treated of 1:100-1:500), and a solvent (e.g., methanol, ethanol, isopropanol, etc.). In oxidation reactor 1, m-cresol in the cresol to be treated reacts with sodium hydroxide in the presence of solvents such as methanol to produce sodium m-cresol and water, and p-cresol reacts with sodium hydroxide in the presence of methanol to produce sodium p-cresol and water.

[0087] (Methanol is used as an example solvent here);

[0088] Subsequently, sodium p-cresol reacts with oxygen introduced into oxidation reactor 1 under the action of a catalyst to produce sodium p-aldehyde phenolate and water, while sodium m-cresol does not undergo oxidation:

[0089] (Methanol is used as an example solvent here);

[0090] Please continue reading. Figure 1 The second solid-liquid separation unit 2 is used to separate the reaction products obtained in the oxidation reactor 1 into solid and liquid phases to recover the catalyst in the system. The second solid-liquid separation unit 2 is equipped with a feed inlet (not shown), a solid phase outlet (not shown), and a liquid phase outlet (not shown). The feed inlet of the second solid-liquid separation unit 2 is connected to the discharge outlet of the oxidation reactor 1. The second solid-liquid separation unit 2 employs an automatic phase separator or a solid-liquid separation centrifuge. Automatic phase separators or solid-liquid separation centrifuges are existing technologies and will not be described in detail here.

[0091] Specifically, this embodiment adds a second solid-liquid separation mechanism on the connecting pipe between the oxidation reactor and the neutralization reactor, which enables the recovery of the catalyst in the reaction system in the oxidation reactor for reuse, thereby reducing production costs.

[0092] Please continue reading. Figure 1 The first decolorizing vessel 3 is used to decolorize the liquid phase obtained after solid-liquid separation, thereby improving the quality of the final product. The first decolorizing vessel 3 is equipped with a liquid inlet (not shown), a discharge outlet (not shown), and a decolorizing agent inlet (not shown). The liquid inlet of the first decolorizing vessel is connected to the liquid phase outlet of the second solid-liquid separation mechanism 2, and the first decolorizing agent inlet is used to add a decolorizing agent (e.g., activated carbon) to the first decolorizing vessel 3.

[0093] Please continue reading. Figure 1 The first phase separator 4 is used to perform solid-liquid separation in the decolorized mixture (containing decolorizing agents such as activated carbon) to recover the decolorizing agent. The first phase separator 4 is equipped with a feed inlet (not shown), a solid phase outlet (not shown), and a liquid phase outlet (not shown). The feed inlet of the first phase separator 4 is connected to the discharge outlet of the first decolorizing vessel 3. The first phase separator 4 can be an automatic phase separator or a solid-liquid separation centrifuge. Automatic phase separators or solid-liquid separation centrifuges are existing technologies and will not be described in detail here.

[0094] Specifically, this embodiment adds a first decolorizing vessel 3 and a first phase separator 4 to the connecting pipe between the oxidation reactor 1 and the neutralization vessel 5, which can decolorize the reaction system in the oxidation reactor and recover the decolorizing agent, thereby improving the quality of the separated product.

[0095] Please continue reading. Figure 1 The neutralization vessel 5 is equipped with a liquid inlet (not shown), a liquid outlet (not shown), a gas inlet (not shown), and a temperature control component (not shown). The liquid inlet of the neutralization vessel 5 is connected to the liquid phase outlet of the first phase separator 4. The gas inlet of the neutralization vessel 5 is used to introduce carbon dioxide gas into the neutralization vessel 5. The introduced carbon dioxide reacts with the water obtained from the oxidation reactor 1 to produce carbonic acid. The carbonic acid reacts with the sodium m-cresol produced in the oxidation reactor 1 to produce m-cresol, while the sodium p-aldehyde phenolate produced in the oxidation reactor 1 does not react. This allows for the separation and purification of sodium p-aldehyde phenolate and m-cresol through subsequent solid-liquid separation.

[0096]

[0097] Please continue reading. Figure 1 The first solid-liquid separation unit 6 is used to perform solid-liquid separation on the mixture treated by the neutralization vessel 5, so as to separate the sodium bicarbonate obtained from the reaction in the neutralization vessel. The first solid-liquid separation unit 6 is provided with a feed inlet (not shown), a solid phase outlet (not shown), and a liquid phase outlet (not shown). The feed inlet of the first solid-liquid separation unit 6 is connected to the liquid outlet of the neutralization vessel 5. The first solid-liquid separation unit 6 employs an automatic phase separator or a solid-liquid separation centrifuge. Automatic phase separators or solid-liquid separation centrifuges are existing technologies and will not be described in detail here.

[0098] Please continue reading. Figure 1 The concentration vessel 7 is used to distill the solvent in the system to recover the solvent. The concentration vessel 7 is provided with a liquid inlet (not shown), a liquid outlet (not shown), and a gas outlet (not shown). The liquid inlet of the concentration vessel 7 is connected to the solid phase outlet of the first solid-liquid separation mechanism 6.

[0099] Specifically, this embodiment adds a concentration vessel 7 on the connecting pipe between the first solid-liquid separation mechanism 6 and the steam distillation vessel 8, which can recover the solvent added in the oxidation step and reduce production costs.

[0100] Please continue reading. Figure 1 The steam distillation vessel 8 is used to perform steam distillation on the liquid treated by the concentration vessel 7. The steam distillation vessel 8 is equipped with a liquid inlet (not shown), a water inlet (not shown), a liquid outlet (not shown), a vapor outlet (not shown), and a temperature control component (not shown). The liquid inlet of the steam distillation vessel 8 is connected to the liquid outlet of the concentration vessel 7, and the water inlet of the steam distillation vessel 8 is used to introduce water into the steam distillation vessel 8.

[0101] Please continue reading. Figure 1 Acidification vessel 9 is used to acidify the liquid obtained after treatment by steam distillation vessel 8 to adjust the pH of the system to 4.0-4.5. In acidification vessel 9, sodium p-aldehyde phenolate reacts with acidic substances (such as sulfuric acid, hydrochloric acid, acetic acid) added to acidification vessel 9 to produce p-hydroxybenzaldehyde.

[0102] (Using sulfuric acid as an example here);

[0103] The acidification vessel 9 is equipped with a feed inlet (not shown), an acid inlet (not shown), and a discharge outlet (not shown). The feed inlet of the acidification vessel 9 is connected to the liquid outlet of the steam distillation vessel 8, and the acid inlet is used to add acidic substances to the acidification vessel 9 (the amount used is to adjust the pH of the system to 4.0-4.5).

[0104] Please continue reading. Figure 1 The extraction phase separation vessel 10 is used to extract the liquid treated by the acidification vessel 9 to separate the inorganic and organic phases. The extraction phase separation vessel 10 is equipped with a liquid inlet (not shown), an extraction solvent inlet (not shown), an inorganic phase outlet (not shown), and an organic phase outlet (not shown). The liquid inlet of the extraction phase separation vessel 10 is connected to the outlet of the acidification vessel 9, and the extraction solvent inlet is used to add the extraction solvent (e.g., dichloromethane) into the extraction phase separation vessel 10. The extraction phase separation vessel 10 can be an extraction vessel, which is existing technology and will not be described in detail here.

[0105] Please continue reading. Figure 1 The concentration crystallization vessel 11 is used to recover the extraction solvent in the organic phase obtained by the extraction phase separation vessel 10, so as to recover the extraction solvent in the system. The concentration crystallization vessel 11 is provided with a liquid inlet (not shown), a liquid outlet (not shown), and a gas outlet (not shown). The liquid inlet of the concentration crystallization vessel 11 is connected to the organic phase liquid outlet of the extraction phase separation vessel 10.

[0106] Specifically, this embodiment adds a concentration crystallization vessel 11 on the connecting pipe between the extraction phase separation vessel 10 and the second phase separator 13, which can recover the extraction solvent added during the extraction phase separation process and reduce production costs.

[0107] Please continue reading. Figure 1 The second decolorizing vessel 12 is used to decolorize the liquid obtained after treatment in the concentration and crystallization vessel 11, thereby improving the quality of the final product. The second decolorizing vessel 12 is equipped with a liquid inlet (not shown), a discharge outlet (not shown), and a decolorizing agent inlet (not shown). The liquid inlet of the second decolorizing vessel 12 is connected to the discharge end of the concentration and crystallization vessel 11, and the decolorizing agent inlet is used to add a decolorizing agent (e.g., activated carbon) to the first decolorizing vessel.

[0108] Please continue reading. Figure 1 The second phase separator 13 is used to perform solid-liquid separation on the mixture after decolorization treatment by the second decolorization vessel 12 to recover the decolorizing agent. The second phase separator 13 is provided with a feed inlet (not shown), a solid phase outlet (not shown), and a liquid phase outlet (not shown). The feed inlet of the second phase separator 13 is connected to the discharge outlet of the second decolorization vessel 12. The second phase separator 13 can be an automatic phase separator or a solid-liquid separation centrifuge. Automatic phase separators or solid-liquid separation centrifuges are existing technologies and will not be described in detail here.

[0109] Specifically, this embodiment adds a second decolorizing vessel 12 and a second phase separator 13, and connects the second decolorizing vessel 12 to the concentration crystallization vessel 11, which can decolorize the system, improve the quality of the obtained p-hydroxybenzaldehyde, and recover the decolorizing agent, thereby reducing production costs.

[0110] Please continue reading. Figure 1 The system in this embodiment also includes a phase separation crystallizer 14, which is connected to the gas phase outlet of the steam distillation vessel 8. The phase separation crystallizer 14 is used to crystallize the distilled phase (containing m-cresol and water) obtained after treatment by the steam distillation vessel 8 to remove moisture.

[0111] It should be noted that all connecting pipes are equipped with on / off valves and centrifugal pumps.

[0112] The principle of the system in this embodiment is as follows: By adding a neutralization vessel 5, carbon dioxide can be introduced into the neutralization vessel 5. The carbon dioxide reacts with water in the system to generate carbonic acid. The carbonic acid reacts with sodium m-cresol generated in the oxidation step (sodium m-cresol in the cresol to be treated can undergo a salt formation reaction, that is, it reacts with sodium hydroxide in the presence of methanol to generate sodium m-cresol and water, and sodium p-cresol can react with sodium hydroxide in the presence of methanol to generate sodium p-cresol and water. Then, in the oxidation vessel, sodium p-cresol reacts with oxygen in the presence of a catalyst to generate sodium p-aldehyde phenolate and water, while sodium m-cresol does not undergo an oxidation reaction) to generate m-cresol, while sodium p-aldehyde phenolate generated in the oxidation step does not react. By adding an acidification vessel 9, acidic substances such as sulfuric acid, hydrochloric acid, and acetic acid can be added to the acidification vessel 9. These acidic substances react with sodium p-aldehyde phenolate generated in the neutralization vessel 5 to generate p-hydroxybenzaldehyde, thereby recovering p-hydroxybenzaldehyde and improving the yield. In this embodiment, p-cresol is selectively oxidized to p-hydroxybenzaldehyde, and the physical properties of m-cresol and p-hydroxybenzaldehyde are used for separation, thereby improving the yield.

[0113] like Figure 2 As shown, the specific steps for separating m-cresol and p-cresol using this system are as follows:

[0114] 3000 mL of methanol solvent, 848 g of 99% pure solid sodium hydroxide (21 mol), 648 g (6 mol) of cresol to be treated containing 64 wt% m-cresol and 36 wt% p-cresol, and 2 g of cobalt hydroxide were added to oxidation reactor 1 through the raw material inlet. The temperature of oxidation reactor 1 was controlled at 70℃ and the pressure at 0.1 MPa. In oxidation reactor 1, m-cresol in the cresol to be treated reacted with sodium hydroxide in the presence of solvents such as methanol to produce sodium m-cresol and water, and p-cresol reacted with sodium hydroxide in the presence of methanol to produce sodium p-cresol and water.

[0115]

[0116] Subsequently, sodium p-cresol reacts with oxygen introduced into oxidation reactor 1 under the action of a catalyst to produce sodium p-aldehyde phenolate and water, while sodium m-cresol does not undergo oxidation:

[0117]

[0118] Every hour, samples were taken through the sampling port and analyzed using gas chromatography (specifically, the area normalization method). After 15 hours, the p-cresol content was 0.13%.

[0119] Open the switch valve and centrifugal pump on the connecting pipe between oxidation reactor 1 and the second solid-liquid separation mechanism 2. The centrifugal pump sends the reaction system in oxidation reactor 1 into the second solid-liquid separation mechanism 2. The second solid-liquid separation mechanism 2 performs solid-liquid separation on the reaction products obtained in oxidation reactor 1 to recover the catalyst in the system.

[0120] Open the switch valve and centrifugal pump on the connecting pipe between the second solid-liquid separation mechanism 2 and the first decolorizing kettle 3. The centrifugal pump sends the liquid phase obtained after being processed by the second solid-liquid separation mechanism 2 into the first decolorizing kettle 3. Add 2.5g of decolorizing agent activated carbon into the first decolorizing kettle 3 through the decolorizing agent inlet. The activated carbon removes the color from the system.

[0121] Open the switch valve and centrifugal pump on the connecting pipe between the first decolorizing kettle 3 and the first phase separator 4. The centrifugal pump sends the mixture obtained after being processed by the first decolorizing kettle 3 into the first phase separator 4. The first phase separator 4 performs solid-liquid separation on the decolorized mixture to recover the decolorizing agent activated carbon.

[0122] Open the switch valve and centrifugal pump on the connecting pipe between the first phase separator 4 and the neutralization vessel 5 (i.e., the primary neutralization vessel). The centrifugal pump sends the liquid obtained after treatment by the first phase separator 4 into the neutralization vessel 5. Carbon dioxide gas is introduced into the neutralization vessel 5 through the inlet until the system pH reaches 5.0. Then, the carbon dioxide introduction is stopped, and the temperature of the neutralization vessel is controlled at 50°C. The introduced carbon dioxide reacts with the water obtained from the oxidation reactor 1 to produce carbonic acid. The carbonic acid reacts with the sodium m-cresol produced in the oxidation reactor 1 to produce m-cresol, while the sodium p-aldehyde phenolate produced in the oxidation reactor 1 does not react. This allows for the separation and purification of sodium p-aldehyde phenolate and m-cresol through subsequent solid-liquid separation.

[0123]

[0124] Open the switch valve and centrifugal pump on the connecting pipe between the neutralization vessel 5 and the first solid-liquid separation mechanism 6. The centrifugal pump sends the mixture obtained after being processed by the neutralization vessel 5 into the first solid-liquid separation mechanism 6. The first solid-liquid separation mechanism 6 performs solid-liquid separation on the mixture processed by the neutralization vessel 5 to separate out the sodium bicarbonate obtained from the reaction in the neutralization vessel.

[0125] Open the switch valve and centrifugal pump on the connecting pipe between the first solid-liquid separation mechanism 6 and the concentration vessel 7. The centrifugal pump sends the liquid phase obtained after being processed by the first solid-liquid separation mechanism 6 into the concentration vessel 7. Under the conditions of 70°C and 100kPa, the concentration vessel 7 processes the solvent in the liquid phase system to recover the solvent in the system.

[0126] Open the switch valve and centrifugal pump on the connecting pipe between the concentration vessel 7 and the steam distillation vessel 8. The centrifugal pump sends the liquid obtained after treatment by the concentration vessel 7 into the steam distillation vessel 8. Add 1000mL of water into the steam distillation vessel 8 through the water inlet. The steam distillation vessel 8 performs steam distillation treatment on the liquid after treatment by the concentration vessel 7 at a temperature of 95℃.

[0127] Open the valve and centrifugal pump on the connecting pipe between the steam distillation kettle 8 and the acidification kettle 9 (i.e., the secondary acidification kettle). The centrifugal pump sends the liquid obtained after treatment in the steam distillation kettle 8 into the acidification kettle 9. Add sulfuric acid to the acidification kettle 9 to adjust the pH of the system to 4.0. In the acidification kettle 9, sodium p-aldehyde phenolate reacts with the sulfuric acid added to the acidification kettle 9 to produce p-hydroxybenzaldehyde.

[0128]

[0129] Open the switch valve and centrifugal pump on the connecting pipe between acidification vessel 9 and extraction phase separation vessel 10. The centrifugal pump sends the liquid obtained after treatment in acidification vessel 9 into extraction phase separation vessel 10. Add the extraction solvent dichloromethane to extraction phase separation vessel 10 through the extraction solvent inlet (a total of three times, each time 500mL, i.e., 500mL×3). The extraction solvent extracts the liquid after treatment in acidification vessel 9 to separate the inorganic phase and organic phase, and combine the extracts.

[0130] Open the switch valve and centrifugal pump on the connecting pipe between the extraction phase separation vessel 10 and the concentration crystallization vessel 11. The centrifugal pump sends the organic phase obtained after treatment by the extraction phase separation vessel 10 into the concentration crystallization vessel 11. The concentration crystallization vessel 11 recovers the extraction solvent in the organic phase obtained after treatment by the extraction phase separation vessel 10 in order to recover the solvent in the system.

[0131] Open the switch valve and centrifugal pump on the connecting pipe between the concentration crystallization kettle 11 and the second decolorization kettle 12. The centrifugal pump sends the liquid obtained after treatment in the concentration crystallization kettle 11 into the second decolorization kettle 12. Add decolorizing agent activated carbon into the second decolorization kettle 12 through the decolorizing agent inlet. The activated carbon removes the color from the system.

[0132] Open the switch valve and centrifugal pump on the connecting pipe between the second decolorizing kettle 12 and the second phase separator 13. After the centrifugal pump recovers the decolorizing agent through the second decolorizing kettle 12, the mixture is sent into the second phase separator 13. The second phase separator 13 performs oil-water phase separation on the mixture after the decolorizing agent is recovered through the second decolorizing kettle 12. After the oil phase is concentrated and crystallized, p-hydroxybenzaldehyde is obtained.

[0133] Open the switch valve and centrifugal pump on the connecting pipe between the phase separation crystallizer 14 and the steam distillation vessel 8. The centrifugal pump sends the distilled phase (containing m-cresol and water) obtained after treatment by the steam distillation vessel 8 into the phase separation crystallizer 14. The phase separation crystallizer 14 crystallizes the distilled phase (containing m-cresol and water) obtained after treatment by the steam distillation vessel 8 at 20℃ and 100kPa to remove moisture and obtain m-cresol.

[0134] Example 2

[0135] In this embodiment, the cresol to be treated is a mixture of o-cresol and p-cresol in a mass ratio of 60:40. The amount of cresol to be treated is 537.5 g (5 mol), the amount of sodium hydroxide (purity of 99%) is 808 g (20 mol), the catalyst is cobalt oxide with an amount of 1.2 g, the solvent is methanol with an amount of 2500 mL, the temperature of the oxidation reactor is controlled at 50°C, the pressure is 0.5 MPa, and after 6 h, the p-cresol content in the system is 0.25 wt%.

[0136] 1.0g of decolorizing agent activated carbon was added to the first decolorizing kettle 3 through the decolorizing agent inlet, and the mixture was heated under reflux for 1 hour.

[0137] The temperature of neutralization vessel 5 is controlled at 55℃. Carbon dioxide gas is introduced into neutralization vessel 5 through the gas inlet until the pH of the system reaches 6.0, and then the introduction of carbon dioxide is stopped.

[0138] The solvent in the liquid phase system was distilled in the concentration vessel 7 at 72℃ and 100kPa to recover the solvent in the system;

[0139] 1000 mL of water is added to the steam distillation vessel 8 through the water inlet, and the liquid after being treated by the concentration vessel is steam distilled in the steam distillation vessel 8 at a temperature of 100°C.

[0140] Sulfuric acid was added to acidification reactor 9 to adjust the pH of the system to 4.5;

[0141] Dichloromethane, the extraction solvent, is added to the extraction phase separation vessel 10 through the extraction solvent inlet (a total of three times, each time with a volume of 500 mL, i.e., 500 mL × 3) to separate the inorganic phase and the organic phase, and the extracts are combined.

[0142] 2.0g of decolorizing agent activated carbon is added to the second decolorizing kettle 12 through the decolorizing agent inlet; the decolorized material is subjected to solid-liquid separation to recover the decolorizing agent, and the filtrate is concentrated and crystallized to obtain p-hydroxybenzaldehyde;

[0143] The phase-separation crystallization vessel 14 at 22℃ and 100kPa crystallizes the distilled phase (containing m-cresol and water) obtained after treatment by steam distillation vessel 8 to remove moisture and obtain m-cresol.

[0144] Example 3

[0145] In this embodiment, the cresol to be treated is a mixture of o-cresol and p-cresol in a mass ratio of 60:40, 537.5 g (5 mol), sodium hydroxide (purity of 99%) is used in an amount of 808 g (20 mol), cobalt oxide is used as the catalyst, the amount of catalyst is 1.2 g, methanol is used as the solvent, the amount of solvent is 2500 mL, the temperature of the oxidation reactor is controlled at 100℃, the pressure is 1.0 MPa, and after 10 h, the p-cresol content in the system is 0.19 wt%.

[0146] 1g of decolorizing agent activated carbon was added to the first decolorizing kettle 3 through the decolorizing agent inlet, and the mixture was heated and refluxed for 2 hours.

[0147] The temperature of neutralization vessel 5 is controlled at 60℃. Carbon dioxide gas is introduced into neutralization vessel 5 through the gas inlet until the pH of the system reaches 5.5, and then the introduction of carbon dioxide is stopped.

[0148] The solvent in the liquid phase system was distilled in the concentration vessel 7 at 75℃ and 100kPa to recover the solvent in the system;

[0149] 1000 mL of water is added to the steam distillation vessel 8 through the water inlet, and the liquid treated by the concentration vessel is steam distilled in the steam distillation vessel 8 at a temperature of 95°C.

[0150] Sulfuric acid was added to acidification reactor 9 to adjust the pH of the system to 4.2;

[0151] Dichloromethane, the extraction solvent, is added to the extraction phase separation vessel 10 through the extraction solvent inlet (a total of three times, each time with a volume of 500 mL, i.e., 500 mL × 3) to separate the inorganic phase and the organic phase, and the extracts are combined.

[0152] 2g of decolorizing agent activated carbon is added to the second decolorizing kettle 12 through the decolorizing agent inlet; the decolorized material is subjected to solid-liquid separation to recover the decolorizing agent, and the filtrate is concentrated and crystallized to obtain p-hydroxybenzaldehyde;

[0153] The distilled phase (containing m-cresol and water) obtained after treatment by steam distillation vessel 8 was crystallized in phase separation crystallizer 14 at 25℃ and 100kPa to remove water and obtain high-purity m-cresol with high yield.

[0154] Example 4

[0155] like Figure 3 As shown, the difference between this embodiment and embodiment 1 is that the first decolorizing kettle 3 and the first phase separator 4 are not included.

[0156] Example 5

[0157] like Figure 4 As shown, the difference between this embodiment and embodiment 1 is that the second decolorizing kettle 12 and the second phase separator 13 are not included.

[0158] Example 6

[0159] like Figure 5 As shown, the difference between this embodiment and embodiment 1 is that the second solid-liquid separation mechanism 2 is not included.

[0160] Comparative Example 1

[0161] The difference between this comparative example and Example 1 is that the temperature of the neutralization vessel 5 is controlled at 50°C, and carbon dioxide gas is introduced into the neutralization vessel 5 through the gas inlet until the pH of the system reaches 4.5, at which point the introduction of carbon dioxide is stopped.

[0162] Comparative Example 2

[0163] The difference between this comparative example and Example 1 is that the temperature of the neutralization vessel 5 is controlled at 50°C, and carbon dioxide gas is introduced into the neutralization vessel 5 through the gas inlet until the pH of the system reaches 6.5, at which point the introduction of carbon dioxide is stopped.

[0164] Comparative Example 3

[0165] The difference between this comparative example and Example 1 is that sulfuric acid was added to the acidification vessel 9 to adjust the pH of the system to 3.5.

[0166] Comparative Example 4

[0167] The difference between this comparative example and Example 1 is that sulfuric acid was added to the acidification vessel 9 to adjust the pH of the system to 5.0.

[0168] Detection

[0169] The purity, moisture content and yield of m-cresol obtained in Examples 1-3 and Comparative Examples 1-4 were tested, and the results are shown in Table 1.

[0170] The purity and yield of p-hydroxybenzaldehyde obtained in Examples 1-3 and Comparative Examples 1-4 were tested, and the results are shown in Table 1.

[0171] The purity of m-cresol was determined using gas chromatography. The column used was a 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 psi; column flow rate was 12.6 cm / s. The results were calculated using the following formula:

[0172]

[0173] The yield of m-cresol is calculated according to the following formula:

[0174]

[0175] The moisture content in m-cresol was determined using the Karl Fischer method.

[0176] 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:

[0177]

[0178] The yield of p-hydroxybenzaldehyde is calculated according to the following formula:

[0179]

[0180] Table 1 Test Results

[0181] Example 1 99.1％ 93.8％ 0.15％ 99.2％ 91.1％ Example 2 99.0％ 92.5％ 0.11％ 99.0％ 91.5％ Example 3 99.3％ 90.8％ 0.20％ 98.8％ 90.6％ Comparative Example 1 98.5％ 88.5％ 0.24％ 98.5％ 85.7％ Comparative Example 2 99.0％ 84.3％ 0.38％ 97.5％ 89.8％ Comparative Example 3 99.1％ 91.1％ 0.18％ 96.8％ 86.5％ Comparative Example 4 99.0％ 90.1％ 0.25％ 96.0％ 83.9％

[0182] As shown in Table 1, the yields of m-cresol and p-hydroxybenzaldehyde obtained in Examples 1-3 reached 93.8% and 91.5%, respectively. These results demonstrate that the method of the present invention significantly improves the yield.

[0183] As shown in Table 1, the yields of m-cresol obtained in Comparative Example 1 (pH not within the range of 5.0-6.0 in the neutralization step, specifically 4.5) and Comparative Example 2 (pH not within the range of 5.0-6.0 in the neutralization step, specifically 6.5) were 88.5% and 84.3%, respectively, while the yield of m-cresol obtained in Example 1 (pH within the range of 5.0-6.0 in the neutralization step) was 93.8%. That is, compared with Comparative Examples 1 and 2, the method of Example 1 significantly increased the yield of m-cresol. This result indicates that the present invention can improve the yield and content of m-cresol by controlling the pH of the neutralization step to the range of 5.0-6.0.

[0184] As shown in Table 1, the yields of m-hydroxybenzaldehyde obtained in Comparative Example 3 (pH not within the range of 4.0-4.5, specifically 3.5) and Comparative Example 4 (pH not within the range of 4.0-4.5, specifically 5.0) were 86.5% and 83.9%, respectively, while the yield of m-cresol obtained in Example 1 (pH within the range of 4.0-4.5) was 93.8%. That is, compared with Comparative Examples 3 and 4, the yield of m-cresol obtained by the method in Example 1 was significantly increased. This result indicates that the present invention can improve the yield and content of p-hydroxybenzaldehyde by controlling the pH of the acidification step to the range of 4.0-4.5.

[0185] 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 m-cresol and p-cresol, characterized in that, The process includes the following steps in sequence: oxidation, neutralization, filtration, steam distillation, and acidification. The neutralization step includes: introducing carbon dioxide until the pH of the system is 5.0-6.

0. The steam distillation temperature is 80-100℃ and the steam distillation pressure is 0.1-1MPa. The acidification includes adding an acidic substance to the system to adjust the pH of the system to 4.0-4.

5.

2. The method as described in claim 1, characterized in that, The oxidation process includes mixing cresol, sodium hydroxide, solvent, and catalyst, and then introducing oxygen to carry out the oxidation reaction.

3. The method as described in claim 1, characterized in that, The oxidation process, followed by neutralization, also includes decolorization and filtration.

4. The method as described in claim 3, characterized in that, The decolorizing agent used in the decolorization process includes activated carbon; And / or, the mass ratio of the decolorizing agent to the mixed phenol is 1:200-500; And / or, the acidic substance includes inorganic acids, organic acids, or combinations thereof.

Images