JP2004339174A - Method for esterifying mixture containing carboxylic acid obtained from cyclohexane oxidation reaction liquid, and 1,6-hexanediol obtained from the ester mixture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce 1,6-hexanediol in high yield from a mixture containing a carboxylic acid and separated and recovered from a liquid-phase oxidation reaction liquid of cyclohexane, and to develop a monoalcohol esterification method for the mixture containing the carboxylic acid for the production of 1,6-hexanediol. <P>SOLUTION: The esterification of the mixture (3) containing the carboxylic acid comprises the separation of cyclohexanol and cyclohexanone from an oxidation reaction liquid obtained by the liquid-phase oxidation of the cyclohexane and the esterification of the recovered mixture containing the carboxylic acid. The esterification reaction is carried out in the presence of a strong acid solid catalyst (1) having an acid strength of ≤-3 in terms of H<SB>0</SB>(Hammett acid function) by countercurrently contacting a gaseous lower monoalcohol (2) with the mixture (3) containing the carboxylic acid. The esterified mixture obtained by the treatment is subjected to hydrocracking to obtain 1,6-hexanediol in high yield. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３２】
【発明の効果】
本発明では、シクロヘキサンの液相酸化反応液からシクロヘキサノールおよびシクロヘキサノンを分離したのち、回収されるオリゴマーを含んだカルボン酸含有混合物を強酸性固体触媒上でガス状の低級モノアルコールと向流接触させることにより一段で酸価の低いエステル化混合物に変換する方法を提供する。これによって得られるエステル化混合物は、水素化分解触媒の存在下で水素により水素化されて、１，６−ヘキサンジオールに効率的に誘導されるため、産業上有益なエステル化法となる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a method for esterifying a carboxylic acid-containing mixture containing an oligomer separated and recovered from a liquid-phase oxidation reaction solution of cyclohexane, and a method for hydrocracking the obtained esterified mixture with hydrogen to produce 1,6- The present invention relates to a method for efficiently producing hexanediol. 1,6-hexanediol is a useful compound used in polyurethane elastomers, synthetic resin additives, pharmaceutical and agricultural chemical intermediates, and the like.
[0002]
[Prior art]
The carboxylic acid-containing mixture containing the oligomer separated and recovered from the liquid-phase air oxidation reaction solution of cyclohexane is esterified, and the resulting esterified mixture is hydrocracked with hydrogen to give 1,6-hexanediol, 1,5 -Diol compounds such as pentanediol are industrially practiced.
As a method for producing a diol compound such as 1,6-hexanediol from such a carboxylic acid-containing mixture, a carboxylic acid-containing mixture is once subjected to an esterification reaction to reduce the acid value, and hydrogenolysis is performed in the presence of a catalyst. To convert to 1,6-hexanediol.
As the ester hydrocracking catalyst, a copper-based solid catalyst is generally used. This is because the catalyst is inexpensive and economical. However, since a copper-based catalyst is weak against an acid, it is necessary to use an esterification reaction solution having a small acid value as a raw material for hydrocracking. That is, the carboxylic acid-containing mixture needs to be esterified to have an acid value of, for example, 5 or less.
Therefore, there is a demand for how to suppress the acid value and find an efficient esterification method.
As this improvement method, for example, a method is disclosed in which a carboxylic acid mixture as a by-product obtained by oxidizing cyclohexane is esterified at 150 to 250 ° C. in a liquid phase and without a catalyst using 1,6-hexanediol. Have been. (See Patent Document 1)
In this method, a plurality of esterification towers are required to increase the esterification rate, that is, lower the acid value, and a reaction time of several hours requires several hours.
[0003]
Further, a process has been proposed in which a carboxylic acid mixture separated from an oxidation reaction solution of cyclohexane is esterified, adipic acid ester therein is converted into 1,6-hexanediol, and oxycaproic acid ester is converted into caprolactone. . (See Patent Document 2)
That is, a complicated process has been proposed in which a carboxylic acid mixture from an oxidation reaction solution of cyclohexane is esterified with a low-molecular alcohol, and 1,6-hexanediol and caprolactone are produced together through an ester separation / separation step. Although this method is a co-production method, the yield of 1,6-hexanediol is low. The carboxylic acid-containing mixture contains oxycaproic acid and caprolactone in addition to adipic acid as active ingredients that can be converted to 1,6-hexanediol. In addition, oligomers also exist in a large amount as active ingredients that can be converted into 1,6-hexanediol, but this is not a process for converting these active ingredients into 1,6-hexanediol with high yield.
[0004]
Further, a method is disclosed in which an organic substance obtained as a by-product in a cyclohexane oxidation step is subjected to nitric acid oxidation, and the esterified ester is converted into a valuable substance. (See Patent Document 3)
This method shows that the yield of dicarboxylic acid is increased by oxidizing by-product organic matter with nitric acid. In the esterification, a two-stage liquid phase esterification reaction using alkyl alcohol having 1 to 4 carbon atoms is proposed. are doing. However, the experimental examples also show that high esterification rates were not necessarily achieved. When the esterified product is converted to diol or the like by hydrogen reduction in the presence of a catalyst, efficient conversion to diol is difficult unless the esterified solution has a low acid value. Therefore, in this invention, after the esterification reaction, the esterified product is separated and recovered by a distillation step.
[0005]
[Patent Document 1]
JP-B-49-27164 [Patent Document 2]
JP 2000-506134 A [Patent Document 3]
JP 2003-0555303 A
Generally, as a general method for obtaining an esterified product from a carboxylic acid and a monoalcohol, a method using an acid catalyst such as sulfuric acid or paratoluenesulfonic acid is widely known. In this esterification method, it is known that the esterification proceeds smoothly at a low temperature if the produced water is removed. By using such a liquid acid catalyst, it is possible to esterify the carboxylic acid mixture separated from the liquid oxidation reaction liquid of cyclohexane with a monoalcohol. However, since the ester coexists with an acid catalyst, the hydrogenolysis reaction is difficult in the presence of a copper catalyst. Copper is eluted, and not only a great deal of labor is required for the treatment of the reaction solution, but also the deterioration of the copper catalyst, which is considered to be caused by acid, occurs, and a high yield of 1,6-hexanediol cannot be obtained. In addition, the ester has a high boiling point and is difficult to separate from the catalyst by distillation.
[0007]
As described above, the esterification method of the carboxylic acid mixture separated from the cyclohexane oxidation reaction solution is esterification with 1,6-hexanediol or the like in the liquid phase, and esterification with methanol in the liquid phase. It is only known that In the latter, sulfuric acid, paratoluenesulfonic acid and the like are used as catalysts. However, the reactivity is not sufficient when hydrogenating the esterified solution to obtain 1,6-hexanediol. This indicates that there is a problem in the conventional esterification method of a carboxylic acid-containing mixture from a cyclohexane oxidation reaction solution.
[0008]
[Problems to be solved by the invention]
The present invention provides a method for monoalcohol esterification of a carboxylic acid-containing mixture in order to obtain 1,6-hexanediol in a high yield from a carboxylic acid-containing mixture separated and recovered from the liquid-phase oxidation reaction solution of cyclohexane as a raw material. It is intended for development.
[0009]
[Means for Solving the Problems]
An object of the present invention is to separate cyclohexanol and cyclohexanone from an oxidation reaction solution obtained by subjecting cyclohexane to liquid phase oxidation, and subjecting the recovered carboxylic acid-containing mixture to an esterification reaction.
(1) In the presence of a strongly acidic solid catalyst having an acid strength of H ₀ (Hammet's acidity function) of −3 or less,
(2) gaseous lower monoalcohol;
(3) bringing the above-mentioned carboxylic acid-containing mixture into countercurrent contact;
It is an object of the present invention to provide a 1,6-hexanediol which is solved by a method for esterifying a carboxylic acid-containing mixture, and which is derived from hydrocracking an esterified mixture obtained by the method.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The carboxylic acid-containing mixture used in the present invention is a mixture containing a carboxylic acid recovered after separating cyclohexanol and cyclohexanone from a liquid-phase oxidation reaction solution of cyclohexane for the production of cyclohexanol and cyclohexanone.
From the oxidation reaction solution obtained by oxidizing cyclohexane, cyclohexanone and cyclohexanol were separated mainly by distillation, and the recovered carboxylic acid-containing mixture, which may be used as it is, was extracted with water or with an organic solvent. Preferably, one is used. Alternatively, an alkaline extraction may be performed once, followed by neutralization, followed by water extraction or organic solvent extraction.
The carboxylic acid-containing mixture obtained in this manner is adipic acid, dibasic acids such as glutaric acid and succinic acid, and oxyacids such as oxycaproic acid, caprolactone, oligomers thereof, and various other oxidation products. It contains. Not only free monomers such as adipic acid, oxycaproic acid and caprolactone in the carboxylic acid-containing mixture, but also oligomers are sources of 1,6-hexanediol.
The content ratio of these components is not particularly limited, but is usually 5 to 20% by weight of adipic acid.
Oxycaproic acid 1-10% by weight
Caprolactone 0.05-3% by weight
Oligomer 30 to 70% by weight is used.
[0011]
The strongly acidic solid catalyst used in the present invention are those as acid strength H ₀ function -3 represented by (Hammett acidity function), preferably -6 or less, more preferably, -9 or less, More preferably, it is -10 or less.
A solid catalyst having an acid strength greater than -3 is not preferable because the esterification reaction becomes insufficient.
Specific examples of the strongly acidic solid catalyst used in the present invention include the following.
ZrO ₂ —SO ₄ , TiO ₂ —SO ₄ , Fe ₂ O ₃ —SO ₄ , SiO ₂ —ZrO ₂ , SiO ₂ —Ga ₂ O ₃ , TiO ₂ —Al ₂ O ₃ , TiO ₂ —ZrO ₂ , SiO ₂ -al ₂ O _3, zeolites, kaolin, montmorillonite, heteropoly _{acid, TiO 2 -SnO 2, ZrO 2} -WO 3, SiO 2 -WO 3, TiO 2 -WO 3, SiO 2 -TiO 2, SiO 2 supported fluorinated Examples include a sulfonated resin, supported antimony fluoride, supported boron fluoride, supported aluminum chloride, niobate, and metal sulfate.
Preferred are ZrO ₂ —SO _4, SiO ₂ —Al ₂ O ₃ , montmorillonite, and a supported fluorinated sulfonated resin catalyst.
[0012]
The lower monoalcohol for esterification used in the present invention is not particularly limited, but is preferably an aliphatic monoalcohol having 6 or less carbon atoms. More preferably, it is an aliphatic monoalcohol having 4 or less carbon atoms.
Specific examples include methanol, ethanol, n-propanol, iso-propanol, n-butanol s-butanol and t-butanol, n-pentanol, n-hexanol and cyclohexanol.
Preferred are methanol, ethanol, propanol and butanol.
These lower alcohols may be used in the reaction without any problem, but are preferably gaseous and used in the reaction. Examples of the method of gasification include a method of vaporizing by heating, and a method of vaporizing by accompanying an inert gas.
[0013]
In the esterification method of the present invention, the method of bringing the lower monoalcohol and the carboxylic acid-containing mixture into countercurrent contact is not particularly limited, but as an example, filling the above-mentioned strongly acidic solid catalyst in a vertical fixed-bed reactor, A one-pass system in which the liquid carboxylic acid-containing mixture is supplied from the top of the reactor and gaseous lower monoalcohol is supplied from the bottom of the reactor.
That is, an esterification mixture is obtained at the bottom of the reactor, and gaseous product water and gaseous unreacted alcohol are recovered from the reactor top.
The reaction conditions are selected so that the acid value of the esterification mixture obtained at the bottom of the reactor is preferably 5 or less, more preferably 3 or less, still more preferably 2 or less.
[0014]
In the present invention, as a specific example, the above-mentioned strongly acidic solid catalyst is filled in a vertical fixed bed reactor, and a carboxylic acid-containing mixture and a gaseous lower monoalcohol are brought into countercurrent contact on the catalyst. There is no particular limitation, and the esterification mixed solution having an acid value of 5 or less is usually adjusted by adjusting the LHSV (liquid space supply rate) of the carboxylic acid mixture to be supplied. In the embodiment of the present invention, it is preferable that the LHSV of the carboxylic acid mixture based on the amount of the catalyst is 0.01 to 10 / hr.
[0015]
If the carboxylic acid-containing mixture to be supplied to the esterification reactor is liquid, it may be supplied as it is or may be diluted with a solvent without any problem. When a solvent is used, a compound that does not participate in the reaction may be used, or a monoalcohol may be used. In the latter case, the monoalcohol solvent may participate in the esterification reaction.
Examples of the solvent that does not participate in the reaction include ethers.
Examples of the monoalcohol include ordinary aliphatic monoalcohols, and the above-mentioned lower monoalcohols are preferable in consideration of the separation operation after the esterification reaction.
[0016]
Usually, the ratio of the gaseous lower monoalcohol supplied from the lower part and the carboxylic acid-containing mixture supplied from the upper part is 1 or more in the ratio of the number of moles of the lower alcohol to the number of moles of the carboxylic acid-containing mixture in terms of carboxylic acid groups. There is no particular problem. In consideration of controlling the acid value to 5 or less and the post-treatment of the esterification reaction, the range of 1 to 100 is preferable.
[0017]
The reaction temperature in the present invention may be adjusted so as to obtain an esterification mixed liquid having an acid value of 5 or less, but is preferably 70 to 180 ° C. More preferably, it is 100 to 160 ° C. If the reaction temperature is too high, a part of the obtained esterification mixture becomes gaseous and scatters to the top of the reactor, which is not preferable because the active ingredient tends to decrease. There is no problem with the pressure as long as the lower monoalcohol can be introduced into the reactor in a gasified state, but the pressure is usually 0.1 to 5 MPa, preferably 0.1 to 1 MPa.
[0018]
As described above, the present invention is to convert a carboxylic acid-containing mixture separated from a cyclohexane oxidation reaction solution into a low acid value ester solution. By being subjected to the decomposition reaction, 1,6-hexanediol is derived in high yield.
[0019]
The esterification reaction solution obtained from the above carboxylic acid mixture is usually hydrocracked in the presence of a copper catalyst to be converted to 1,6-hexanediol.
The reaction method of hydrocracking is not particularly limited, and may be a liquid phase suspension bed reaction method or a fixed bed flow method.
The copper _{catalyst, CuO · Cr 2 O 3,} CuO · ZnO, CuO · SiO 2, known Cu-containing catalyst which express activity such as hydrogenation reaction CuO · ZrO ₂ and their catalysts suitably mainly Used.
In this hydrocracking reaction, the reaction temperature is 150 to 300 ° C, preferably 200 to 300 ° C, and the hydrogen pressure is 5 to 30 MPa, preferably 15 to 30 MPa.
The charged esterification mixture may be used as it is, or a solvent that does not affect the reaction, such as alcohol, may be coexisted.
Moisture and acidic substances in the reaction solution cause deterioration of the copper catalyst, and therefore it is necessary to use those having a small content thereof.
In particular, it is preferable to use an esterification mixture having an acid value of 5 or less. More preferably, the reaction solution contains an esterification mixture whose acid value is adjusted to 2 or less.
Since the esterification reaction according to the present invention provides an esterification mixture containing little water and having an acid value as low as 5 or less, 1,6-hexanediol can be obtained in a high yield by the hydrogenolysis reaction.
[0020]
Hereinafter, the present invention will be described by way of examples, but the present invention is not limited to these examples.
Incidentally, the Hammett acidity function H ₀ of the catalyst in the examples were determined by the indicator method. The basic measurement principle is described in (Non-Patent Document 1).
That is, 10 mg of the pulverized strongly acidic solid catalyst was suspended in 10 ml of benzene, and a few drops of an appropriate 2% ethanol solution of 2% Hammett indicator were added thereto, and the color change was visually observed with stirring. From the color of observations using various Hammett indicator, it decided in width in the H ₀ of the strongly acidic catalyst.
The Hammett indicators used are p-nitrotoluene, anthraquinone, benzylideneacetophenone, disinnamylideneacetone, 4- (phenylazo) diphenylamine.
[0021]
[Non-patent document 1]
"Catalyst Course Vol. 3" (edited by the Catalysis Society of Japan, published by Kodansha, 1985) p. 220
[0022]
The acid value (AV) in the examples is mg of KOH required to neutralize the sample unit amount (1 gr), and was determined by titration.
The components of each carboxylic acid contained in the carboxylic acid-containing mixture were determined by gas chromatography analysis, liquid chromatography analysis, and gel permeation chromatography analysis.
In addition, 1,6-hexanediol produced by hydrogenolysis of the esterified solution was determined by gas chromatography analysis and liquid chromatography analysis.
[0023]
Example 1
(Carboxylic acid-containing mixture)
A carboxylic acid-containing mixture obtained by removing cyclohexanol and cyclohexanone from an oxidation reaction solution obtained by a liquid phase oxidation reaction of cyclohexane was used. That is, the liquid-phase air oxidation reaction solution of cyclohexane was washed with an aqueous sodium hydroxide solution, the washed solution was neutralized with dilute sulfuric acid, extracted with methyl isobutyl ketone and concentrated, and 9.8% by weight of adipic acid was added. Contains 3.0% by weight of caproic acid, 0.1% by weight of caprolactone, 0.8% by weight of glutaric acid, 1.2% by weight of succinic acid, and> 48% by weight of oligomers from adipic acid and oxycaproic acid A carboxylic acid-containing mixture was obtained. The carboxylic acid mixture contained about 58% by weight of an active ingredient, including oligomers, which could be converted to 1,6-hexanediol, and had an acid value (AV) of 366 mg-KOH / gr.
(Esterification)
The esterification reaction was continuously performed by a countercurrent reaction by filling a vertical reaction tube with a fixed bed catalyst. That is, two ports were attached to the upper part of the catalyst layer of the SUS vertical reaction tube having an inner diameter of 10 mm and a length of 700 mm, and two ports were also attached to the lower part. One upper port was a supply port for the liquid carboxylic acid-containing mixture as a raw material, and the other port was a gas outlet. One port at the bottom was a supply port for gaseous methanol as a raw material, and the other port was an outlet for the esterification reaction solution.
The reaction tube was filled with 40 ml of a montmorillonite-based solid acid catalyst (KP-10 manufactured by Sudohemie Catalyst Co., Ltd.). Acid strength of the catalyst was <-10.5 at _{H 0.} The temperature of the catalyst layer was set to 150 ° C., the pressure in the reaction tube was set to 0.5 MPa, and the above-mentioned carboxylic acid-containing mixture was diluted with methanol and fed at a rate of 0.1 gr / min from the raw material supply port at the top of the reaction tube. Then, a nitrogen gas containing 80 vol% of methanol gas was supplied at a rate of 175 ml / min from a methanol supply port at a lower portion of the reaction tube. Water vapor, methanol gas, nitrogen gas, etc. were collected from the gas outlet at the top of the reaction tube. The esterification mixture obtained by the esterification reaction was cooled and collected from the reaction solution outlet at the lower part of the reaction tube. The collected reaction solution contained various esters, methanol, and the like, and had an acid value of 2.7 mg-KOH / gr.
(Hydrocracking)
100 g of the mixture obtained by the esterification and 3 gr of a powdery CuO-ZnO-based catalyst (UHP manufactured by Ube Industries, Ltd.) were charged into an autoclave, and a hydrogen decomposition reaction was performed at 250 ° C. for 5 hours under a pressure of 25 MPa of hydrogen. As a result, the ester conversion was 95%, and the yield of 1,6-hexanediol was about 93 mol% based on the active ingredient in the esterification liquid.
[0024]
Example 2
(Esterification)
In the esterification reaction, methyl esterification was carried out by the same raw materials and method as in Example 1, except that the catalyst was changed to a Nafion-based catalyst (NEC Cat Cat SAC-13) and the reaction temperature was set to 120 ° C. Was. Acid strength of the catalyst was <-10.5 at _{H 0.} A liquid containing a carboxylic acid mixture methyl ester and the like was cooled and collected from a reaction liquid outlet at a lower portion of the reaction tube. The collected esterified solution contained esters, methanol, and the like, and had an acid value of 1.0 mg-KOH / gr.
(Hydrocracking)
100 g of the obtained esterified solution and 3 g of a CuO-ZnO-based catalyst (UHP manufactured by Ube Industries, Ltd.) were charged into an autoclave, and a hydrogenolysis reaction was performed at 250 ° C. for 5 hours under a pressure of 25 MPa of hydrogen. As a result, the yield of 1,6-hexanediol was 95 mol% based on the active ingredient in the esterification liquid.
[0025]
Example 3
(Esterification)
A methyl esterification reaction was carried out using the same raw materials and method as in Example 1, except that the catalyst was changed to SiO ₂ —Al ₂ O ₃ (Al ₂ O ₃ content: 15% by weight). The acid strength of this catalyst was −8.2 <H ₀ <−5.6. A liquid containing a carboxylic acid mixture methyl ester and the like was cooled and collected from a reaction liquid outlet at a lower portion of the reaction tube. The collected reaction solution contained esters, methanol, and the like, and had an acid value of 2.8 mg-KOH / gr.
(Hydrocracking)
The hydrocracking reaction using the obtained esterified liquid as a raw material was performed under the same conditions as in Example 1. As a result, the yield of 1,6-hexanediol was about 92 mol% based on the active ingredient in the esterification liquid.
[0026]
Example 4
(Esterification)
A methyl esterification reaction was performed using the same raw materials and method as in Example 1, except that the catalyst was changed to SiO ₂ —Al ₂ O ₃ (Al ₂ O ₃ content: 40% by weight) in the esterification reaction. The acid strength of this catalyst was −5.6 <H ₀ <−3.0. A liquid containing a carboxylic acid mixture methyl ester and the like was cooled and collected from a reaction liquid outlet at a lower portion of the reaction tube. The collected reaction solution contained ester, methanol, and the like, and had an acid value of 3.5 mg-KOH / gr.
(Hydrocracking)
A hydrocracking reaction using the obtained esterified liquid as a raw material was performed under the same conditions as in Example 1. As a result, the yield of 1,6-hexanediol was about 88 mol% based on the active ingredient in the esterification liquid.
[0027]
Example 5
(Esterification)
In the esterification reaction, except that the catalyst was changed to a sulfated zirconia catalyst (acid strength was <-10.5 at H ₀ ) and the reaction temperature was changed to 160 ° C., methyl esterification was performed by the same raw material and method as in Example 1. Then, a liquid material containing a methyl ester of the carboxylic acid mixture and the like was cooled and collected from a reaction liquid outlet at a lower portion of the reaction tube. The collected esterified solution contained esters, methanol and the like, and had an acid value of 3.0 mg-KOH / gr.
(Hydrocracking)
100 g of the obtained esterified solution and 3 g of a CuO-ZnO-based catalyst (UHP manufactured by Ube Industries, Ltd.) were charged into an autoclave, and a hydrogenolysis reaction was performed at 250 ° C. for 5 hours under a pressure of 25 MPa of hydrogen. As a result, the yield of 1,6-hexanediol was 90 mol% based on the active ingredient in the esterification liquid.
[0028]
Comparative Example 1 COA Carboxylic Acid-Containing Mixture and Methanol in Cocurrent Downflow Reaction (Esterification)
The same carboxylic acid-containing mixture as in Example 1 was used as a raw material in a cocurrent flow reaction in the presence of a solid strong acid catalyst. The solid strong acid catalyst is sulfated zirconia catalyst (acid strength <-10.5 in _{H 0)} were filled with 40ml used in the reaction tube is. The temperature of the catalyst layer was set to 160 ° C., a carboxylic acid-containing mixture was supplied at a rate of 0.05 gr / min and methanol at a rate of 0.45 gr / min from the upper part of the reaction tube, and the reaction product was extracted from the lower part of the reaction tube and collected. did. The collected liquid contained diester and monoester esters, as well as unreacted adipic acid, water, methanol and the like. The acid value was 58 mg-KOH / gr.
(Hydrocracking)
The hydrocracking reaction using the obtained esterified liquid as a raw material was performed under the same conditions as in Example 1. As a result, elution of copper as a catalyst component occurred during the hydrocracking reaction, and the reaction hardly proceeded. That is, the yield of 1,6-hexanediol was small.
[0029]
Comparative Example 2
(Esterification)
In Example 1, the esterification reaction was carried out by changing the esterifying agent from methanol to ethylene glycol and setting the reaction temperature to 180 ° C.
The acid value of the esterification reaction liquid collected from the lower outlet of the reaction tube was 5.5 mg-KOH / gr.
(Hydrocracking)
A hydrocracking reaction using the obtained esterified liquid as a raw material was performed under the same conditions as in Example 1. As a result, the yield of 1,6-hexanediol was about 67 mol% based on the active ingredient in the esterification liquid.
[0030]
Comparative Example 3
(Esterification)
It was replaced catalyze the _{MgO-Al 2 O 3 (Al} 2 O 3 content of 70 wt%), the same raw material as in Example 1, was subjected to methylation esterification reaction in the process. The acid strength of this catalyst was −3.0 <H ₀ <+1.5. A liquid containing a carboxylic acid mixture methyl ester and the like was cooled and collected from a reaction liquid outlet at a lower portion of the reaction tube. The collected reaction solution contained esters, methanol, and the like, and had an acid value of 87 mg-KOH / gr.
(Hydrocracking)
The hydrocracking reaction using the obtained esterified liquid as a raw material was performed under the same conditions as in Example 1. As a result, elution of copper as a catalyst component occurred during the hydrogenolysis reaction, the reaction hardly proceeded, and the yield of 1,6-hexanediol was small.
[0031]
Tables 1 collectively show Examples 1 to 5 and Comparative Examples 1 to 3.
[Table 1]

[0032]
【The invention's effect】
In the present invention, after separating cyclohexanol and cyclohexanone from a liquid-phase oxidation reaction solution of cyclohexane, a carboxylic acid-containing mixture containing the recovered oligomer is brought into countercurrent contact with a gaseous lower monoalcohol on a strongly acidic solid catalyst. Thereby, a method for converting into an esterified mixture having a low acid value in one step is provided. The resulting esterification mixture is hydrogenated with hydrogen in the presence of a hydrocracking catalyst and is efficiently derived into 1,6-hexanediol, making it an industrially useful esterification method.

Claims (4)

When cyclohexanol and cyclohexanone are separated from an oxidation reaction solution obtained by performing liquid phase oxidation of cyclohexane, and the collected carboxylic acid-containing mixture is subjected to an esterification reaction,
(1) In the presence of a strongly acidic solid catalyst having an acid strength of H ₀ (Hammet's acidity function) of −3 or less,
(2) gaseous lower monoalcohol;
(3) bringing the above-mentioned carboxylic acid-containing mixture into countercurrent contact;
A method for esterifying a carboxylic acid-containing mixture. (2) The lower mono alcohol is
The esterification method according to claim 1, wherein the esterification is methanol. The esterification method according to claim 2, wherein the esterification reaction is performed at a reaction temperature of 70 to 180C and a reaction pressure of 0.1 to 5 MPa. A 1,6-hexanediol obtained from the esterification mixture obtained by the esterification method according to claim 1.