Method for producing cresol that suppresses by-product formation

Abstract

The present invention relates to a method for manufacturing cresol, which involves separating a by-product DTE generated by the method for manufacturing cresol and recycling it to the reaction step to inhibit the production of DTE. The method for manufacturing cresol according to the present invention is a process for manufacturing cresol through the reaction of halogenated toluene and an alkaline aqueous solution, and includes the following steps: separating the by-product DTE of the above process and re-introducing it into the reaction step of the above halogenated toluene and alkaline aqueous solution.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing cresol. More specifically, it relates to a method for manufacturing cresol that can increase the yield of cresol by suppressing the generation of DTE (Ditolylether) produced as a byproduct in a two-component reaction. Background Art

[0002] Cresol is used as a local anesthetic, disinfectant, fumigant, industrial solvent, herbicide, surfactant, etc. Especially in the manufacturing of synthetic resins such as semiconductor encapsulants, basic petrochemical products, pharmaceutical manufacturing, and other various pharmaceutical and chemical fields, it is also widely used as a basic raw material for organic synthesis.

[0003] Cresol is found in the form of cresylic acid in various plants (wood tar), crude oil, coal tar, etc., and is also generated during the decomposition of natural organic matter by microorganisms in soil and water.

[0004] Cresol compounds can be obtained by distilling or purifying the substances contained in the naturally occurring mixtures as described above, or can also be obtained by organic synthesis.

[0005] However, natural mixtures such as coal tar contain many substances with physicochemical properties similar to cresol, such as pyridine, methylpyridine, aniline, xylenol, etc. Therefore, it is not easy to distill, and such substances will also remain in the purified product, making it difficult to obtain high-purity cresol and not suitable for use in the above-mentioned applications. Therefore, organic synthesis is mostly used for manufacturing.

[0006] Industrially, the alkylation reaction of phenol is mostly used, and magnesium oxide-based catalysts or iron-vanadium-based catalysts are mostly used as alkylation catalysts. However, there are problems in terms of harsh reaction conditions, catalyst activity, lifespan, etc., and there are also environmental problems caused by the use of heavy metals.

[0007] In particular, the reaction process of the magnesium oxide-based catalyst is carried out at a high temperature of about 350°C or higher. Compared with the magnesium oxide-based catalyst, the iron-vanadium-based catalyst can be carried out at a relatively lower temperature, but the catalyst may be easily deactivated.

[0008] In addition, in the alkylation reaction as described above, xylenol, trimethylphenol, poly(alkyl)phenol-based polymer substances, etc. are generated as byproducts, which may hinder the reaction. As described above, the boiling points of these byproducts are similar to that of cresol, and there is a problem of difficult separation.

[0009] As a method for solving the above problems, a method of producing cresol by reacting halogenated toluene with an aqueous alkaline solution can be carried out with a high yield, thus being favored. However, such a method of producing cresol produces a large amount of DTE (ditolylether) as a by-product, and there is a problem of high cost for separating it. Summary of the Invention

[0010] The present invention provides a new manufacturing method for suppressing the generation of DTE generated by side reactions when producing cresol by reacting halogenated toluene with an aqueous alkaline solution in a reactor, thereby providing an effect of increasing the yield of cresol.

[0011] The present invention is a process for producing cresol by reacting halogenated toluene with an aqueous alkaline solution, which includes a step of separating the by-product DTE of the above process and re-introducing it into the reaction step of the above halogenated toluene and aqueous alkaline solution.

[0012] In a method for producing cresol according to an embodiment of the present invention, the method for producing cresol may include: a step of reacting halogenated toluene with an aqueous alkaline solution in a reactor; an acidification step of adding an acid; a step of adding an organic solvent to extract cresol from the water-soluble layer; and a reaction step of separating the by-product from the cresol in the extracted water-soluble layer and re-introducing the by-product into the reactor of the reaction step for reaction.

[0013] In a method for producing cresol according to an embodiment of the present invention, the acidification step is a step of adding an acid to perform acidification in the range of pH 5 to 2.5.

[0014] In a method for producing cresol according to an embodiment of the present invention, the step of reacting the above halogenated toluene with an aqueous alkaline solution may be carried out under the condition of pH 11 or higher.

[0015] In a method for producing cresol according to an embodiment of the present invention, the step of reacting the above halogenated toluene with an aqueous alkaline solution may be carried out at a temperature of 100 to 450 °C and a pressure of 100 to 500 atm.

[0016] In a method for producing cresol according to an embodiment of the present invention, the above acidification step may be carried out using an acid with a pKa value of -2 or less.

[0017] In a method for producing cresol according to an embodiment of the present invention, with respect to 100 parts by weight of the reaction product mixture containing cresol, 10 to 200 parts by weight of the above organic solvent may be used.

[0018] In a method for producing cresol according to an embodiment of the present invention, the step of extracting with the above organic solvent may be repeated more than 2 times.

[0019] According to the method for manufacturing cresol of the present invention, cresol can be manufactured in a high yield, and DTE generated by side reactions is no longer generated due to chemical equilibrium, thus having the effect of obtaining cresol in a high yield. Detailed Description of the Invention

[0020] The present invention provides a method for manufacturing cresol having the following steps in a process of manufacturing cresol by reacting halogenated toluene with an aqueous alkaline solution: a reaction step of separating DTE generated by side reactions of the above process and re-introducing it into the reaction step of reacting the above halogenated toluene with an aqueous alkaline solution to carry out the reaction.

[0021] It has been found that the above DTE is generated as a side reactant when cresol, which is a reactant of halogenated toluene and an aqueous alkaline solution, is generated, and a certain amount of about 7 to 8 mol% is generated by the formation of cresol and equilibrium reactions in the reaction step. Therefore, these equilibrium reactions are utilized to inhibit the generation of DTE to improve the yield of cresol.

[0022] In order to inhibit the above equilibrium reaction, the inventor of the present invention found that by artificially introducing the generated DTE into the reaction solvent, the generation of DTE can be inhibited by equilibrium reactions, thereby completing the present invention.

[0023] Regarding the above DTE, by re-introducing, the DTE separated from the above reaction step is recycled to the reaction step, thereby completing the present invention.

[0024] The above reaction step of the present invention can use various types of reactors such as batch reactors, continuous reactors, or plug flow reactors, and DTE, which is a by-product generated in the reaction step, can be separated from cresol by distillation or other methods in a subsequent step and then recycled to the reactor of the reaction step.

[0025] Specifically, the manufacturing method of the present invention includes: a step of reacting halogenated toluene with an aqueous alkaline solution; a step of adding an acid for acidification; a step of adding an organic solvent to extract cresol from the water-soluble layer; and a step of separating DTE from the extracted cresol and recycling DTE to the reaction step.

[0026] According to an embodiment of the invention, the step of reacting the above halogenated toluene with an aqueous alkaline solution can preferably be carried out under the condition of pH 11 or higher.

[0027] In addition, at this time, the above reaction can preferably be carried out at a temperature of about 200 to about 450 °C and a pressure of about 100 to about 500 atm.

[0028] According to another embodiment of the invention, the above acidification step can be carried out using an acid with a pKa value of -6 or lower.

[0029] In addition, in the above acidification step, the pH can preferably be adjusted to below about 2.5.

[0030] According to another embodiment of the invention, the above organic solvent can preferably have a DI value of 20 or less.

[0031] In addition, relative to 100 parts by weight of the reaction product mixture containing cresol, about 10 parts by weight to about 200 parts by weight of the above organic solvent can preferably be included. Furthermore, the step of extracting with the above organic solvent is preferably repeated more than 2 times.

[0032] In addition, in the present invention, the separation of the above cresol and DTE can be carried out by conventional distillation, but the separation means is not limited in the present invention.

[0033] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions as long as they do not clearly indicate other meanings in the context. In this specification, terms such as "comprising / including", "having", or "possessing" should be understood as specifying the presence of the features, numbers, steps, components, or combinations thereof to be implemented, and not as precluding the presence or possibility of addition of one or more other features, numbers, steps, components, or combinations thereof.

[0034] The present invention can be subject to various changes and can have various forms. Exemplary embodiments are illustrated and described in detail below. However, this is not intended to limit the present invention to a specific disclosed form, but should be understood to include all modifications, equivalents, and substitutes included in the spirit and technical scope of the present invention.

[0035] Throughout this specification, the above-mentioned cresol includes all of ortho, meta, and para cresols.

[0036] In addition, the so-called halogenated toluene refers to a compound in which any one of the hydrogens in the benzene ring of toluene is substituted with a halogen atom including chlorine, bromine, and fluorine, and also includes all of the ortho, meta, and para forms.

[0037] Next, the present invention will be described in more detail.

[0038] First, the reaction step of halogenated toluene and an alkaline aqueous solution will be described.

[0039] In the above reaction step of the present invention, the step of reacting the above-mentioned halogenated toluene with an aqueous alkaline solution is preferably carried out under the condition of pH 11 or higher. The hydroxide ions used can preferably be from aqueous solutions of metal hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, etc., but the present invention is not necessarily limited thereto.

[0040] That is, for the reaction, during the hydrolysis reaction, hydroxide ions can be added in excess relative to the halogenated toluene. After the reaction ends, the aqueous layer can show very strong alkalinity due to the excess hydroxide ions. Therefore, the resulting cresol exists in the aqueous layer in an anionic form. Due to such a form, the equilibrium of the overall reaction is shifted towards the reactant side, thereby increasing the yield of cresol.

[0041] According to an embodiment of the reaction, the step of reacting the above-mentioned halogenated toluene with an aqueous alkaline solution is preferably carried out under temperature conditions of about 200 to about 450 °C and pressure conditions of about 100 to about 500 atm.

[0042] When the reaction temperature during the hydrolysis reaction is too low, problems such as a decrease in the conversion rate of halogenated toluene, the selectivity and yield of cresol may occur. When the temperature is too high, the operating cost for high-temperature operation increases, and problems such as a decrease in the economy for cresol production may occur.

[0043] In addition, when the reaction pressure is too low, the conversion rate of halogenated toluene, the selectivity and yield of cresol decrease. When the pressure is too high, there is a problem of an increase in equipment costs associated with setting up high-pressure equipment.

[0044] The product during the hydrolysis reaction of the present invention contains cresol and 7 to 8 mol% of ditolylether (DTE) generated by a chemical equilibrium reaction to form reactants. The present inventors recognized that the above-mentioned DTE is inevitably generated by an equilibrium reaction. When the DTE generated in the reaction is re-introduced into the hydrolysis reaction step together with the raw materials, the amount introduced exists in the reaction solvent, inducing the equilibrium from cresol towards DTE formation towards cresol, so that DTE is no longer generated, increasing the yield of cresol, and significantly reducing the amount of DTE generated as a by-product to be discarded or that should be discarded, and an economical and environmentally friendly manufacturing method can be provided.

[0045] On the other hand, most of the cresol isomers as the product after the reaction exist in the aqueous layer in the form of cresol anions. Cresol cannot be commercialized in a state dissolved in the aqueous layer, so it needs to be extracted from the aqueous layer.

[0046] Therefore, in the present invention, the above substitution reaction is followed by a step of acidification by adding an acid.

[0047] According to an embodiment of the invention, the acidification step may preferably utilize a strong acid with a pKa value of about -6 or less. Specifically, for example, hydrochloric acid, chloric acid, chlorous acid, bromic acid, nitric acid, dilute sulfuric acid, etc. can be cited, but the invention is not necessarily limited thereto. Any strong acid that can provide sufficient hydrogen atoms to cresol anions or cresol to facilitate easy dissolution into the oil-soluble layer can be used without particular limitation.

[0048] In addition, according to another embodiment of the invention, the pH in the acidification step can be adjusted to about 2.5 or less, preferably, it can be adjusted to about -5 to about 2.5, and more preferably, it can be adjusted to about -5 to about 1.5. When the pH deviates from the above range, a considerable amount of the generated cresol compound remains in the water-soluble layer, which may cause environmental problems during the treatment of reaction waste.

[0049] As described above, cresol converted into an oil-soluble form by acid treatment and DTE as a by-product can be extracted from the water-soluble layer by adding an organic solvent and obtained in a state dissolved in the organic solvent layer.

[0050] As the organic solvent that can be used at this time, any organic solvent that can fractionate cresol in the water-soluble layer can be used, and an organic solvent with a DI value of about 20 or less can be preferably used.

[0051] Specifically, for example, benzene, toluene, methyl tert-butyl ether (MTBE), methyl isobutyl ketone (MIBK), isobutyl acetate (iBA), or a mixture thereof. In addition, hexane, heptane, cyclohexane, xylene, etc., which are commonly used organic solvents in the technical field to which the present invention pertains, can be used without particular limitation.

[0052] In addition, according to another example of the present invention, relative to 100 parts by weight of the reaction product mixture containing cresol, about 10 to about 200 parts by weight of the above organic solvent can be preferably used.

[0053] When using less than 10 parts by weight of the organic solvent relative to the reaction product mixture containing cresol, the cresol in the water-soluble layer is not easily separated, the water-soluble layer contains an excessive amount of cresol, which may cause environmental problems, and the cresol contains inorganic hydroxide ions, resulting in a problem of decreased purity of cresol.

[0054] In addition, when the organic solvent is more than 200 parts by weight relative to the reaction product mixture containing cresol, the content of the organic solvent in cresol after the extraction process is high, and an additional process is required to separate the organic solvent, resulting in a decrease in economy.

[0055] In addition, according to another embodiment of the invention, the step of extracting with the above organic solvent can be preferably repeated more than 2 times or about 2 to about 5 times.

[0056] Cresol is a toxic compound. Even in trace amounts, it can be absorbed through the skin or mucous membranes, etc., and concentrated and distributed in organs such as the blood, liver, brain, lungs, and kidneys, thus showing human toxicity. Therefore, in terms of the environment and safety, it is important to more thoroughly remove the residual cresol in the water-soluble layer.

[0057] As shown in an example of the present invention, when the step of extraction with an organic solvent is repeated more than 2 times or about 2 to about 5 times, the cresol present in the water-soluble layer can be reduced to about 500 ppm or less, more preferably about 100 ppm or less, and most preferably about 10 ppm or less, which is the limit detectable by liquid chromatography. Therefore, it is very environmentally beneficial.

[0058] The subsequent steps are: separating the cresol extracted with the organic layer from DTE, recycling the separated DTE to the reaction step, and shifting the equilibrium towards the cresol side in a manner that inhibits the formation of DTE. When the amount of recycled DTE is increased such that it reaches 7 to 8 mol% of the generated cresol, no more DTE by-products are generated from the reactants, and only cresol is produced. Therefore, it can have great economic benefits in terms of the side reaction of DTE formation and the cost of disposing of it.

[0059] The separation of the above-mentioned cresol and DTE can be carried out by distillation. As a specific example, the distillation column for separation can have a total of 100 trays, and can be fractionated by a DWC (Dividing wall column) with a top temperature of 140.7 °C, a top pressure of 0.1 barg, a bottom temperature of 206.6 °C, and a bottom pressure of 0.14 barg, but it is not limited thereto.

[0060] Next, the functions and effects of the invention will be described in more detail through specific examples of the invention. However, such examples are only presented as illustrations of the invention, and the scope of the invention claimed is not limited thereto.

[0061] <Example 1>

[0062] In a continuous reactor, NaOH (10 wt%): chlorotoluene: DTE were charged in a molar ratio of 2.5:1:0.08, and the conditions of 400 °C and 300 atm were maintained for 30 minutes, thereby carrying out the reaction under alkaline conditions.

[0063] After the above reaction, 28 g of hydrochloric acid was added to 100 g of the product, and the pH was adjusted to 1.

[0064] An organic solvent was added and stirred for 30 minutes to mix uniformly, and then the product, i.e., cresol, was separated from the water-soluble layer. After phase separation, the content of cresol in the water-soluble layer was analyzed by liquid chromatography. As a result, the ratio of cresol to the DTE product was 92 mol%:8 mol%. It was found that no additional DTE was generated other than the amount of DTE produced as a side reaction product.

[0065] <Comparative Example 1>

[0066] In a continuous reactor, NaOH (10 wt%) and chlorotoluene were introduced in a molar ratio of 2.5:1, and the conditions of 400 °C and 300 atm were maintained for 30 minutes to carry out the reaction under alkaline conditions. Otherwise, it was carried out in the same manner as in Example 1. The contents of cresol and DTE in the produced water-soluble layer were measured. As a result, it was found that DTE was produced in a molar ratio of 92.3:7.7.

[0067] <Example 2>

[0068] In Example 1, 4 mol% of the recycled DTE was introduced relative to chlorotoluene, and otherwise, it was carried out in the same manner. As a result, it was found that the content of DTE as a by-product was 7.8 mol%, indicating that 3.7 mol% more was produced than the introduced amount.

[0069] From the above examples and comparative examples, it can be seen that by introducing the recycled DTE into the reaction step, DTE is no longer generated. By this method, the generation of unwanted DTE is suppressed, and thus a new and economical method for manufacturing cresol with excellent environmental performance can be provided.

Claims

1. A method for manufacturing cresol, which is a process for manufacturing cresol by the reaction of halogenated toluene and an alkaline aqueous solution, comprising the following steps: A step of separating 7 mol% to 8 mol% of DTE, which is a by-product of the above process, and recycling it to the reaction step of the halogenated toluene and the alkaline aqueous solution.

2. The production method of cresol according to claim 1, wherein, The method for manufacturing cresol includes the following steps: a step of reacting halogenated toluene and an alkaline aqueous solution in a reactor; An acidification step of adding an acid; A step of adding an organic solvent to extract cresol from the water-soluble layer; and A reaction step of separating the by-product from the cresol in the extracted water-soluble layer, recycling the by-product to the reactor in the reaction step, and performing the reaction.

3. The method for producing cresol according to claim 2, wherein, The acidification step is a step of adding an acid to perform acidification in the range of pH 5 to 2.

5.

4. The method for producing cresol according to claim 1, wherein, The step of reacting the halogenated toluene and the alkaline aqueous solution is carried out under the condition of pH 11 or higher.

5. The method for producing cresol according to claim 1, wherein, The step of reacting the halogenated toluene and the alkaline aqueous solution is carried out at a temperature of 100 to 450 °C and a pressure of 100 to 500 atm.

6. The method for producing cresol according to claim 2, wherein, The acidification step is carried out using an acid with a pKa value of -2 or less.

7. The method for producing cresol according to claim 2, wherein, Relative to 100 parts by weight of the reaction product mixture containing cresol, 10 to 200 parts by weight of the organic solvent is used.

8. The method for producing cresol according to claim 2, wherein, The step of extracting with the organic solvent is repeated more than 2 times.