A method and device for continuously producing m-cresol by coupling dehydrogenation reaction and rectification separation

Abstract

This invention discloses a method and apparatus for the continuous production of m-cresol by coupling a dehydrogenation reaction with distillation separation, relating to the field of m-cresol preparation technology. Addressing the drawbacks of traditional two-step processes—namely, their lengthy flow, high equipment investment, numerous side reactions, and the shortcomings of existing reactive distillations—such as the tendency for solid catalysts to accumulate carbon and become deactivated, the lack of a heavy component removal section, and the inability to operate continuously for extended periods—this invention employs a three-stage reactive distillation column architecture with a homogeneous acid catalytic system. 4,6-Di-tert-butyl-m-cresol enters the reaction section for catalytic dehydrogenation, producing m-cresol and isobutylene. The light m-cresol and isobutylene are drawn off from the top of the column, while the heavy component impurities descend into the stripping section. After separation, unreacted feedstock is refluxed back to the reaction section for recycling, while the heavy component impurities are discharged from the bottom of the vessel. This invention overcomes the limitations of traditional step-by-step processes, eliminates the need for external separation equipment, effectively suppresses reverse and side reactions, achieves high feedstock utilization and excellent product purity, simplifies the process flow, and enables long-term steady-state continuous production, showing broad prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of coal chemical industry, and more particularly to the field of m-cresol preparation technology, specifically to a method and apparatus for the continuous production of m-cresol by coupling dehydrocarbonization reaction and distillation separation. Background Technology

[0002] High-purity mixed m- and p-cresols can be obtained by refining crude phenols, a byproduct of coal chemical industry. m-Cresol is an important chemical raw material, serving as a crucial intermediate in the synthesis of pesticides, vitamin E, fragrances, and dyes. Compared to mixed m- and p-cresols, effective separation and purification of both would yield greater economic and application value.

[0003] In a mixture of m- and p-cresols, the boiling points of m-cresol and p-cresol differ by only 0.4°C, making efficient separation extremely difficult using conventional distillation techniques. Current research on separation technologies for mixed m- and p-cresols both domestically and internationally mainly focuses on hydrocarbonation, fractional crystallization, chemical complexation, and physical separation methods (extraction, adsorption separation, and molecular sieve membrane separation). Comparatively, hydrocarbonation offers advantages in terms of processing scale and cost, technological maturity, and product quality, and is also easier to industrialize.

[0004] The alkylation method mainly increases the boiling point difference between m- and p-cresol alkylation products through alkylation reactions, followed by distillation to obtain alkylated m- and p-cresol monomers. These monomers are then separated and purified through a high-temperature dealkylation reaction combined with further separation and purification. A typical process involves the alkylation of isobutylene with mixed m- and p-cresols under concentrated sulfuric acid catalysis to synthesize 4,6-di-tert-butyl-m-cresol and 2,6-di-tert-butyl-p-cresol. The significant boiling point difference between the two monomers allows for separation via distillation. The separated di-tert-butylcresol undergoes a two-step process: a dehydrogenation reaction under concentrated sulfuric acid catalysis to remove isobutylene and generate monocresol, followed by distillation to obtain high-purity monocresol. In the dehydrogenation and purification section, the two-step process of dehydrogenation reaction and distillation is a common process in existing literature on the separation of m- and p-cresol using the alkylation method. This process involves numerous dehydrogenation side reactions, a complex process flow, high equipment investment, and low overall efficiency.

[0005] In existing technologies, there are technical solutions that couple the dehydrogenation reaction of alkylphenols with distillation separation in the same column. For example, CN104474731B discloses a method for reactive distillation pyrolysis of alkylphenols, which uses a reactive distillation column packed with a solid molecular sieve catalyst to integrate the thermal dehydrogenation and distillation separation of alkylphenols into the same column, thereby simplifying the process and reducing equipment investment. However, this technology uses solid bed catalysis, which has problems such as easy carbon deposition and deactivation of the catalyst, difficulty in in-situ regeneration, and insufficient stability for long-term continuous operation. In addition, its reactive distillation column only has a reaction section and a rectification section, lacking a section for the removal of heavy components, which leads to the easy accumulation of high-boiling impurities and tar at the bottom of the column, requiring periodic slag removal and affecting the efficiency of continuous operation. Summary of the Invention

[0006] The technical problem this invention aims to solve is as follows: Addressing the issues of numerous dehydrogenation side reactions, complex process flow, high equipment investment, thermodynamic equilibrium limitations, and low raw material conversion rates in two-step processes, as well as the shortcomings of solid molecular sieve catalysis such as easy catalyst carbon buildup and deactivation, difficulty in in-situ regeneration, poor continuous operation stability, and the lack of continuous removal of heavy components in reactive distillation columns leading to tar accumulation and the need for periodic slag discharge, this invention provides a method for the continuous production of m-cresol by coupling dehydrogenation reaction and distillation separation. This method overcomes the technical prejudice that concentrated sulfuric acid cannot be used for continuous reactive distillation. It employs a three-stage column structure + homogeneous catalysis with low-concentration concentrated sulfuric acid + rapid vacuum separation + refined reflux to achieve simultaneous coupling of 4,6-di-tert-butyl-m-cresol dehydrogenation and distillation. This solves the problems of low conversion rate, numerous side reactions, intermittent operation, easy catalyst deactivation, tar accumulation, and product loss in traditional processes, resulting in high-purity m-cresol and long-term stable operation.

[0007] The technical solution adopted by the present invention to solve its technical problem is: a method for continuous production of m-cresol by coupling dehydrocarbonization reaction and distillation separation, wherein the method is carried out in the same reactive distillation column; The reactive distillation column is provided with a rectification section, a reaction section and a stripping section from top to bottom; The 4,6-di-tert-butyl-m-cresol feedstock enters the reaction section of the reactive distillation column, where it undergoes a dehydrocarbonization reaction under the catalysis of an acidic catalyst to generate m-cresol and isobutylene in the gaseous phase. The generated m-cresol rises into the rectification section for purification and concentration, and the m-cresol and isobutylene are drawn out from the top of the reactive distillation column; The heavy component impurities generated in the reaction section flow downward into the stripping section, where the unreacted raw materials (including incompletely reacted light intermediate products) are separated and returned to the reaction section, thus realizing the continuous conversion of raw materials. The heavy component impurities (including acid catalysts) are discharged from the bottom of the reactive distillation column.

[0008] This scheme adopts a three-stage tower structure to simultaneously complete the reaction, distillation, and removal of heavy components, simplifying the process and reducing equipment investment. The stripping section can continuously remove heavy component impurities, avoiding tar accumulation and achieving long-term stable operation. Unreacted raw materials can be returned to the reaction section to continue the reaction, improving raw material utilization and conversion rate. Products are removed from the reaction zone in real time to suppress reverse and side reactions, improving product purity and production efficiency. Acid-phase catalysis is used to avoid carbon buildup and deactivation of solid catalysts, resulting in stronger stability during continuous operation.

[0009] In some embodiments, the gaseous m-cresol and isobutylene discharged from the top of the reactive distillation column are partially condensed by a condenser to obtain a high-purity m-cresol liquid phase. The liquid phase is refluxed and the product is collected by adjusting the reflux ratio. The uncondensed gaseous phase is isobutylene and enters the isobutylene recovery and utilization system under vacuum.

[0010] Efficient gas-liquid phase separation is achieved through partial condensation at the top of the column, eliminating the need for an external gas-liquid separator, further simplifying the process and reducing equipment investment. A portion of the high-purity m-cresol in liquid phase is refluxed to the reactive distillation column, ensuring stable purity of the top product (≥99.5%), which can be directly used as an intermediate feedstock for downstream product synthesis. The remaining liquid phase is directly collected as the product, resulting in a simple, continuous, and stable process. The uncondensed gaseous m-butene enters the isobutene recovery and utilization system through vacuum, achieving efficient isobutene recovery and resource utilization, improving economic efficiency. The reflux ratio (i.e., the ratio of the product flow rate returning to the reactive distillation column to the product flow rate exiting the reactive distillation column) is preferably controlled at 2~4.

[0011] In some embodiments, the refluxed high-purity m-cresol is fed into the upper part of the reaction section to gently regulate the reaction environment.

[0012] When high-purity m-cresol reflux enters the upper part of the reaction section, it comes into contact with the rising gas and liquid phases. Its temperature is lower than the reaction temperature of the section, which slightly cools the upper part and suppresses side reactions caused by localized high temperatures. Simultaneously, the small amount of m-cresol entering the reaction section creates a local equilibrium in the acidic environment, preventing the reaction section from being completely devoid of products, thus preventing runaway reaction rates and a surge in side reactions, and making the dehydrocarbonization reaction more stable and controllable. The main function of reflux is to allow m-cresol to undergo sufficient gas-liquid equilibrium conversion, thereby increasing its purity.

[0013] In some embodiments, the reactive distillation column employs reduced pressure distillation, with the top operating pressure being 10 kPa to 40 kPa, to rapidly remove and remove m-cresol and isobutylene generated in the dehydrocarbonization reaction from the reaction zone.

[0014] A higher vacuum level (i.e., a lower operating pressure at the top of the column) can reduce the reaction temperature and distillation temperature, enabling rapid distillation separation of the product m-cresol and rapid removal of isobutylene, reducing the reverse reaction of m-cresol alkylation and the side reaction of isobutylene self-polymerization. However, the vacuum level should not be too high, as an excessively high vacuum level will lead to the loss of raw materials and products due to untimely condensation.

[0015] In some embodiments, the acid catalyst is concentrated sulfuric acid, and the amount of concentrated sulfuric acid added accounts for 0.5% to 5% of the total mass of the raw materials and the acid catalyst, preferably 1% to 3%.

[0016] Concentrated sulfuric acid is selected as a homogeneous acid catalyst, which has high catalytic activity, does not require regeneration or replacement of solid catalyst, avoids the problem of carbon deposition and deactivation of solid catalyst, and is suitable for continuous long-term operation of reactive distillation. The amount of concentrated sulfuric acid added is limited to 0.5% to 5% of the total mass of raw materials and acid solution, which can ensure sufficient catalytic activity for dehydrocarbonization reaction and avoid excessive acid consumption that would aggravate equipment corrosion and increase side reactions.

[0017] It should be noted that concentrated sulfuric acid is a high-boiling-point heavy component and will be discharged from the bottom of the column along with heavy component impurities.

[0018] In some embodiments, the dehydrogenation reaction temperature of the reaction section is controlled between 120 °C and 155 °C. This temperature range matches the dehydrogenation reaction of 4,6-di-tert-butyl-m-cresol catalyzed by concentrated sulfuric acid.

[0019] In some embodiments, the reaction temperature in the reaction section is 120℃~155℃, preferably 130℃~150℃, and can be controlled by the vacuum degree at the top of the reactive distillation column and the heating temperature of the reboiler. The temperature of the reboiler (stripping section) is 135℃~165℃, preferably 145℃~160℃.

[0020] An apparatus for the continuous production of m-cresol by coupling a dehydrocarbonization reaction with distillation separation includes a reactive distillation column, a reaction section, and a stripping section arranged sequentially from top to bottom, a condenser, and... The feed line is connected to the reaction section of the reactive distillation column and is used to add 4,6-di-tert-butyl-m-cresol and acid catalyst to the reaction section. The top discharge pipeline is connected to the top of the rectification section of the reactive distillation column. The condenser is installed on the top discharge pipeline and is used to extract the reacted m-cresol and isobutylene from the top of the column and send them into the condenser for partial condensation. A reflux line, one end of which is connected to the outlet side of the condenser on the top discharge line of the tower, and the other end is connected to the reaction section, for refluxing a portion of the high-purity m-cresol in liquid phase to the upper part of the reaction section, and discharging the other portion from the top discharge line of the tower; A vacuum recovery pipeline is connected to the outlet side of the condenser on the top discharge pipeline of the tower and the isobutylene recovery and utilization system, and is used to transport the condensed gaseous isobutylene using vacuum. The bottom discharge pipeline of the column is connected to the bottom of the stripping section of the reactive distillation column and is used for the discharge of heavy component impurities.

[0021] This device uses a three-stage reactive distillation column, along with supporting pipelines, condensers, and vacuum systems, to complete the dehydrocarbonization reaction, m-cresol purification, isobutylene removal, and discharge of heavy component impurities within the same unit. This eliminates the need for multiple units connected in series, significantly simplifying the device configuration and reducing equipment investment and floor space requirements.

[0022] The beneficial effects of this invention are: (1) This invention integrates the dehydrocarbonization reaction, product distillation and purification, and removal of heavy component impurities into the same three-stage reactive distillation column and performs them simultaneously. It uses concentrated sulfuric acid homogeneous catalysis to replace the existing solid molecular sieve catalysis route, breaking the traditional two-step process of first dehydrocarbonization and then purification and separation. It is also different from the simple coupling mode in the prior art, which only sets up a distillation section and a reaction section without the special removal of heavy components. (2) By matching and optimizing the pressure and reflux ratio at the top of the column, this invention achieves rapid collection of m-cresol and immediate removal and separation of isobutylene, which greatly shortens the residence time of the product in the high temperature environment and concentrated sulfuric acid catalytic system. Compared with the conventional approach of only controlling the reaction temperature and the amount of catalyst, this invention suppresses the reverse reaction and side reactions such as isobutylene self-polymerization from the perspective of immediate removal of the product, effectively promoting the continuous positive progress of the dehydrocarbonization reaction, and achieving the reaction conversion rate and selectivity improvement effect that cannot be achieved by conventional process control methods. (3) Based on the three-stage tower structure adapted to the vacuum distillation and the top part of the tower condensation ratio design, the present invention can directly obtain high-purity m-cresol with a purity of ≥99.5% at the top of the tower without the need for an additional external gas-liquid separator, while ensuring efficient recovery of isobutylene. While simplifying the process flow and reducing equipment configuration and engineering investment, it simultaneously achieves multiple improvements in product quality, raw material utilization rate and by-product resource utilization benefits. It breaks through the inherent industry convention that existing reactive distillation processes must be equipped with external separation equipment, and generates comprehensive industrial benefits that exceed the expectations of existing technologies. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Figure 1 This is a schematic diagram of the structure of the device of the present invention.

[0025] Figure 2 This is a flowchart illustrating the method of the present invention.

[0026] In the diagram: 1. Feed line; 2. Reactive distillation column; 3. Condenser; 4. Top discharge line; 5. Reflux line; 6. Vacuum recovery line; 7. Bottom discharge line. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0028] For ease of understanding, the inventive concept will be described in its entirety before a detailed description of the embodiments of the present invention: Addressing the pain points of existing alkylphenol dehydrocarbonization to m-cresol processes and comparative reactive distillation technologies, such as catalyst deactivation due to carbon buildup, continuous removal of non-heavy components, lengthy processes requiring external separation equipment, numerous side reactions, and limited conversion rates, this paper focuses particularly on the stringent requirements of long-term stable, high-purity, and low-cost operation for continuous industrial production. It achieves this through a three-stage reactive distillation column integrating dehydrocarbonization-distillation-removal coupling, homogeneous catalysis with concentrated sulfuric acid replacing solid-state catalysis, rapid product removal by matching the column top pressure and reflux ratio under reduced pressure, and recovery of unreacted feedstock and continuous removal of heavy components in the stripping section. This effectively suppresses reverse and side reactions, precisely ensuring high purity of the m-cresol product. Overcoming the technical limitations of traditional processes and comparative documents, this paper achieves multiple advantages for m-cresol production: integrated coupling, long operating cycle, high product purity, simplified process flow, low equipment investment, and strong industrial adaptability.

[0029] Example 1: like Figure 1 The diagram shows an embodiment 1 of the present invention, an apparatus for the continuous production of m-cresol by coupling a dehydrocarbonization reaction with distillation separation, comprising a feed line 1, a reactive distillation column 2, a condenser 3, a top discharge line 4, a reflux line 5, a vacuum recovery line 6, and a bottom discharge line 7. The reactive distillation column 2 has a three-section structure, consisting of a rectification section, a reaction section, and a stripping section from top to bottom.

[0030] The feed line 1 connects to the reaction section of the reactive distillation column 2, and is used to add 4,6-di-tert-butyl-m-cresol and acid catalyst to the reaction section. The top discharge line 4 connects to the top of the rectification section of the reactive distillation column 2. The condenser 3 is installed on the top discharge line 4 and is used to extract the reacted m-cresol and isobutylene from the top of the column and send them to the condenser 3 for partial condensation. One end of the reflux line 5 connects to the outlet side of the condenser 3 on the top discharge line 4, and the other end connects to the reaction section. It is used to reflux a portion of the high-purity m-cresol in liquid phase to the upper part of the reaction section, and the other portion of the high-purity m-cresol in liquid phase that is not refluxed is discharged through the top discharge line 4. The vacuum recovery line 6 connects the outlet side of the condenser 3 on the top discharge line 4 and the isobutylene recovery system, and is used to transport the vapor phase isobutylene after condensation using vacuum. The bottom discharge line 7 connects to the bottom of the stripping section of the reactive distillation column 2 and is used to discharge heavy component impurities.

[0031] In this embodiment, the reactive distillation column 2 is provided with 13 trays arranged sequentially from top to bottom. The trays are numbered from top to bottom according to industry conventions, from tray 1 to tray 13. The outlet end of the feed line 1 is connected to the fifth tray of the reactive distillation column 2. The 4,6-di-tert-butyl-m-cresol feedstock and the acid catalyst are precisely fed into the reactive distillation column 2 from the fifth tray through the feed line 1.

[0032] The first to fourth trays constitute the rectification section of the reactive distillation column 2, used to purify and concentrate the rising m-cresol vapor from the top of the column; the fifth tray serves as the feed tray and is also located at the beginning of the reaction section, where the feed (4,6-di-tert-butyl-m-cresol) and acid catalyst enter the reactive distillation column 2 and flow downwards through subsequent trays to participate in the dehydrocarbonization reaction; the fifth to tenth trays constitute the reaction section, providing sufficient residence contact space for the dehydrocarbonization reaction; the eleventh to thirteenth trays constitute the stripping section, used to separate and recover unreacted feed, enrich and remove heavy component impurities.

[0033] In this embodiment, the stripping section can adopt a gas-liquid countercurrent stripping separation method. The rising gas phase in the reactive distillation column 2 performs mass transfer stripping on the descending liquid phase (containing acid catalyst, unreacted raw materials, and high-boiling heavy component impurities). The unreacted raw materials entrained in the liquid phase are vaporized and rise back to the reaction section to participate in the reaction, while the heavy component impurities and acid catalyst remain in the liquid phase, accumulate downwards, and are discharged from the bottom of the column.

[0034] In the embodiments, the reaction section, upper rectification section and lower stripping section of the reactive distillation column 2 can be selected as packed columns to achieve full contact and mixing, thereby enhancing the chemical reaction and distillation process.

[0035] In this embodiment, the reactive distillation is vacuum distillation, with the top operating pressure being 10 kPa to 40 kPa, preferably 10 kPa to 20 kPa. A higher vacuum level (i.e., a lower top operating pressure) can reduce the reaction temperature and distillation temperature, enabling rapid distillation separation of the product m-cresol and rapid removal of isobutylene, reducing the reverse reaction of m-cresol alkylation and the side reaction of isobutylene self-polymerization. However, the vacuum level should not be too high, as excessively high vacuum levels can lead to losses due to untimely condensation and removal of raw materials and products.

[0036] Example 2: like Figure 2The diagram shows Embodiment 2 of the present invention. Based on Embodiment 1, it describes a method for the continuous production of m-cresol by coupling a dehydrogenation reaction with distillation separation. 4,6-Di-tert-butyl-m-cresol feedstock and concentrated sulfuric acid are mixed and fed into the reaction section of a reactive distillation column 2 via feed line 1. The amount of concentrated sulfuric acid added is 2%. In the reaction section, under the catalysis of concentrated sulfuric acid, a dehydrogenation reaction occurs within the reaction temperature range, producing m-cresol. The reaction temperature range of the reaction section is 132 ℃~142 ℃, and the bottom temperature is 150 ℃. The product m-cresol is rapidly purified and concentrated in the distillation section. The operating pressure at the top of the column is 20 kPa. After partial condensation of the gaseous components (m-cresol and isobutylene) by the top condenser 3, the condensate (high-purity m-cresol liquid) is controlled at a reflux ratio of 3. The reflux portion is returned to the reactive distillation column via reflux line 5, and the non-reflux portion is discharged through the top discharge line 4 to obtain high-purity m-cresol. The uncondensed gaseous phase mainly consists of isobutylene removed by the dehydrocarbonization reaction, which is transported to the isobutylene recovery system via vacuum recovery line 6. The liquid phase flowing down from the reaction section to the stripping section contains heavy component impurities (including concentrated sulfuric acid), as well as unreacted raw materials and their light intermediate products. The unreacted raw materials and their light intermediate products are separated from the heavy component impurities and returned to the reaction section. The heavy component impurities are transported to the wastewater treatment system via the bottom discharge line 7.

[0037] It should be noted that the rapid purification and concentration of m-cresol through the rectification section refers to the following: through multi-stage "partial condensation and gas-liquid countercurrent", the upward vapor (m-cresol and isobutylene in the gas phase) continuously releases the non-volatile heavy impurities to the downward liquid phase in the stripping section, while obtaining more volatile light components of m-cresol from the liquid, thereby achieving the stepwise purification and concentration of m-cresol.

[0038] Example 3: A method for the continuous production of m-cresol by coupling a dehydrocarbonization reaction with distillation separation, wherein the bottom temperature of the column is 140 ℃, the reaction temperature range of the reaction section is 130 ℃~135 ℃, and other conditions are the same as in Example 2.

[0039] Example 4: A method for the continuous production of m-cresol by coupling a dehydrocarbonization reaction with distillation separation, wherein the reflux ratio is controlled at 4 and other conditions are the same as in Example 2.

[0040] Comparative Example 1: A method for the continuous production of m-cresol by coupling a dehydrocarbonization reaction with distillation separation, wherein the top operating pressure of the column is 2 kPa, the bottom temperature is 145 ℃, the reaction temperature range of the reaction section is 125 ℃~135 ℃, and other conditions are the same as in Example 2.

[0041] Compared with Example 2, Comparative Example 1 mainly reduced the operating pressure at the top of the column (i.e., increased the vacuum level), and the temperature of the column bottom and reaction section changed accordingly. The other conditions were the same as in Example 2.

[0042] Comparative Example 2: A method for the continuous production of m-cresol by coupling a dehydrocarbonization reaction with distillation separation, wherein the top operating pressure of the column is 70 kPa, the bottom temperature is 160 ℃, the reaction temperature range of the reaction section is 133 ℃~143 ℃, and other conditions are the same as in Example 2.

[0043] Compared with Example 2, Comparative Example 2 mainly increased the operating pressure at the top of the column (i.e., reduced the vacuum level), and the temperature of the column bottom and reaction section changed accordingly. The other conditions were the same as in Example 2.

[0044] Comparative Example 3: 4,6-Di-tert-butyl-m-cresol and concentrated sulfuric acid were mixed in a dehydrocarbonation reactor for a dehydrocarbonation reaction. The reaction temperature range was 132 ℃ to 142 ℃. The reactor was connected to a vacuum system, which was used to create negative pressure inside the reactor, maintaining a constant negative pressure of 20 kPa throughout the entire dehydrocarbonation reaction system. After the reaction was complete (no more isobutylene was released), the reactor feed was transferred to a distillation column for distillation separation. The bottom temperature of the distillation column was 150 ℃, the reaction temperature range in the reaction section was 132 ℃ to 142 ℃, the operating pressure at the top of the column was 20 kPa, and the reflux ratio was controlled at 3.

[0045] Compared with Example 2, Comparative Example 3 mainly adopts a two-step process, namely, the dehydrogenation reaction and the distillation process are carried out in separate steps, and the dehydrogenation reaction conditions and distillation conditions are the same as those in Example 2.

[0046] The purity of the m-cresol discharged from the top of the column, the composition of the non-condensed gas at the top of the column, and the composition of the heavy components in the bottom of the column in Examples 2-4 and Comparative Examples 1-3 were analyzed and summarized, and Table 1 was obtained.

[0047] Table 1. Results of the reactive distillation process for 4,6-di-tert-butyl-m-cresol

[0048] As shown in Table 1, in Examples 2-4, the purity of the m-cresol discharged from the top of the column was ≥99.5%, meeting the product quality requirements. The composition of the non-condensable gas at the top of the column (which does not participate in condensation and liquefaction) consisted only of isobutylene removed in the dehydrogenation reaction, with no other components being extracted or lost. The components discharged from the bottom of the column did not contain the raw material (4,6-di-tert-butyl-m-cresol) or mono-tert-butyl-m-cresol (mono-tert-butyl-m-cresol is an intermediate product of the dehydrogenation reaction, which continues to participate in subsequent dehydrogenation reactions, ultimately generating the target product m-cresol, which can be returned to the reaction section together with 4,6-di-tert-butyl-m-cresol in the stripping section). This indicates that the dehydrogenation reaction was complete with few side reactions, and the distillation separation met the requirements, demonstrating the effectiveness of this method.

[0049] As shown in Table 1, comparing Comparative Example 1 and Example 2, the main difference lies in the significantly increased vacuum level of Comparative Example 1. While this had no significant impact on the purity of the m-cresol product and the reaction efficiency, the excessively high vacuum level resulted in the presence of m-cresol in the non-condensable gas composition at the top of the column, leading to some condensate not being promptly removed and lost. Comparing Comparative Example 2 and Example 2, the main difference lies in the significantly decreased vacuum level of Comparative Example 2. This decrease in vacuum level significantly affected the purity of the m-cresol product and the reaction efficiency. The m-cresol product could not be quickly separated, and isobutylene could not be rapidly removed, increasing the reverse alkylation reaction of m-cresol and the self-polymerization side reaction of isobutylene. This resulted in lower purity of the m-cresol output (most impurities were trimerisobutylene), and the bottom column composition contained 4,6-di-tert-butyl-m-cresol and mono-tert-butyl-m-cresol, leading to a significant decrease in reaction efficiency. Therefore, a suitable high vacuum level is necessary for the effective operation of this method.

[0050] As shown in Table 1, the main difference between Comparative Example 3 and Example 2 is that Comparative Example 3 employs a two-step process, where the dehydrogenation reaction and distillation are carried out separately. Because the products are not separated in a timely manner in the two-step process, numerous side reactions result in a more complex composition of the liquid phase after the dehydrogenation reaction. Under the same distillation conditions, high-purity m-cresol cannot be obtained, requiring more stringent distillation conditions (more trays, higher reflux ratio, etc.).

[0051] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for the continuous production of m-cresol by coupling a dehydrocarbonization reaction with distillation separation, characterized in that: The method is carried out in a reactive distillation column (1) which is provided with a rectification section, a reaction section and a stripping section from top to bottom; The raw material 4,6-di-tert-butyl-m-cresol enters the reaction section and undergoes a dehydrocarbonization reaction under the catalysis of an acid catalyst to produce m-cresol and isobutylene; The generated m-cresol ascends into the rectification section for purification and concentration, and the m-cresol and isobutylene are discharged from the top of the reactive distillation column (1) and partially condensed. The heavy component impurities generated in the reaction section flow downward into the stripping section, where the unreacted raw materials are separated and returned to the reaction section, and the heavy component impurities are discharged from the bottom of the reactive distillation column (1).

2. The method for continuous production of m-cresol by coupling dehydrocarbonization reaction and distillation separation according to claim 1, characterized in that: The m-cresol and isobutylene discharged from the top of the reactive distillation column (1) are partially condensed by the condenser (3) to obtain liquid and gas phases; The liquid phase is high-purity m-cresol; The gas phase is isobutylene.

3. The method for continuous production of m-cresol by coupling dehydrocarbonization reaction and distillation separation according to claim 1, characterized in that: The high-purity m-cresol obtained from partial condensation is partially refluxed to the upper part of the reaction section.

4. The method for continuous production of m-cresol by coupling dehydrocarbonization reaction and distillation separation according to claim 1, characterized in that: The reactive distillation column (1) adopts reduced pressure distillation, and the operating pressure at the top of the column is 10 kPa to 40 kPa.

5. The method for continuous production of m-cresol by coupling dehydrocarbonization reaction and distillation separation according to claim 3, characterized in that: The ratio of the reflux flow rate to the non-reflux flow rate of the high-purity m-cresol in liquid phase is 2-4.

6. The method for continuous production of m-cresol by coupling dehydrocarbonization reaction and distillation separation according to claim 1, characterized in that: The reaction temperature of the reaction section is 120 ℃~155 ℃, and the bottom temperature of the reactive distillation column (1) is 135 ℃~165 ℃.

7. The method for continuous production of m-cresol by coupling dehydrocarbonization reaction and distillation separation according to claim 1, characterized in that: The acid catalyst is concentrated sulfuric acid. The amount of concentrated sulfuric acid added is 0.5% to 5% of the total mass of the raw materials and acid catalyst.

8. The method for continuous production of m-cresol by coupling dehydrocarbonization reaction and distillation separation according to claim 1, characterized in that: The acid catalyst is mixed with the raw material and then fed into the reaction section of the reactive distillation column (1).

9. The method for continuous production of m-cresol by coupling dehydrocarbonization reaction and distillation separation according to claim 1, characterized in that: The heavy component impurities include an acid catalyst.

10. An apparatus for the continuous production of m-cresol by coupling a dehydrocarbonization reaction with distillation separation according to any one of claims 1-9, characterized in that: Also includes Feed line (1), the feed line (1) is connected to the reaction section of the reactive distillation column (2) and is used to add 4,6-di-tert-butyl-m-cresol and acid catalyst to the reaction section; The top discharge pipeline (4) is connected to the top of the rectification section of the reactive distillation column (2). The condenser (3) is installed on the top discharge pipeline (4) and is used to extract the reacted m-cresol and isobutylene from the top of the column under high vacuum and send them into the condenser (3) for partial condensation. The reflux line (5) is connected at one end to the outlet side of the condenser (3) on the top discharge line (4) of the tower, and at the other end to the reaction section, for refluxing high-purity m-cresol in liquid phase to the upper part of the reaction section in proportion; Vacuum recovery pipeline (6), the vacuum recovery pipeline (6) is connected to the outlet side of the condenser (3) on the top discharge pipeline (4) of the tower and the isobutylene recovery and utilization system, and is used to transport the gaseous isobutylene after condensation by vacuum to the isobutylene recovery and utilization system. The bottom discharge pipeline (7) is connected to the bottom of the stripping section of the reactive distillation column (2) and is used to discharge heavy component impurities containing acid catalyst.

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