JPH01249735A - Production of 1,6-hexaneidol by melt crystallization - Google Patents

Abstract

PURPOSE:To separate the subject compound of high purity, by dissolving the hydrogenated mixture prepared by oxidation of cyclohexane esterification and hydrogenation or crude diol, after distillation of the hydrogenated mixture, in a specific solvent and cooling down to crystallize out, and washing the crystals. CONSTITUTION:Cyclohexane is oxidized into carboxylic acids, esterified with alcohol and hydrogenated and the title compound which is used in the production of polyurethane or the like is separated from the reaction mixture. At this time, the hydrogenated mixture or crude diol which is obtained by distilling the mixture and containing 0.1-50wt.% of by-products melting at a temperature lower than 0 deg.C is dissolved homogeneously in at least one solvent selected form water and 3-20C organic ketones, then cooled down to the dissolving temperature to 42 deg.C to crystallize out the subject compound, which is washed whereby the by-products which could not be separated only by distillation can be removed by the process according to the present invention to give the objective compound of high purity without adverse effect on the quality, namely moisture, or AV and EV values.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention involves oxidizing cyclohexane in a liquid phase with a molecular oxygen-containing gas to produce a carboxylic acid compound, esterifying the carboxylic acid compound with an alcohol, and further, From a mixture mainly containing 1,6-hexanediol obtained by hydrogenating the esterified product, polyurethane,
The present invention relates to a method for producing highly pure 1°6-hexanediol, which has applications in unsaturated polyesters, plasticizers, medicines, agricultural chemicals, etc.

[Description of prior art]

Conventionally, various proposals have been made regarding methods for producing 1,6-hexanediol starting from liquid phase oxidation of cyclohexane with a molecular oxygen-containing gas.

For example, in German Patent No. 1206417,
The liquid-phase oxidation reaction solution of cyclohexane is extracted with water to remove most of the adipic acid from the aqueous layer, and the mother liquor is then esterified with alcohol, and this esterified product is then hydrogenated in the presence of a catalyst to give 1 A method for making 6-hexanediol is described.

US Pat. No. 3,524,892 discloses that a liquid phase oxidation reaction solution of cyclohexane is extracted with water, the aqueous layer is steam distilled, non-acidic substances such as unreacted cyclohexane, cyclohexanol, and cyclohexanone are distilled off, and the remaining A method is described for producing 1,6-hexanediol by esterifying a liquid with an alcohol and then hydrogenating the esterified product in the presence of a catalyst.

In addition, in the specification of Japanese Patent Publication No. 58-18482, (1)
To the liquid-phase oxidation reaction solution of cyclohexane using a molecular oxygen-containing gas, an aqueous solution of mirabilite having a concentration of 15% by weight to saturation is added at a ratio of 0.01 to 0.3 parts by weight per 1 part by weight of the reaction solution. step of separating into an aqueous layer and an oil layer; (2
) a step of extracting adipic acid, oxycaproic acid and their oligomers mainly contained in the aqueous layer separated in the above step with an organic solvent; (3) extracting the extract obtained in the above step with a carbon atom having 1 to 8 carbon atoms; A step of esterifying with one or more alcohols selected from the group consisting of monohydric alcohols having 2 to 8 carbon atoms and polyhydric alcohols having 2 to 8 carbon atoms;
) A step of hydrogenating the carboxylic acid ester obtained in the above step in the presence of a catalyst at a temperature of 150 to 300° C. under a hydrogen partial pressure of 150 kg/dG or more. A method for producing diols is described.

Furthermore, Japanese Patent Publication No. 53-33567 specifies that (1) an alkaline solution obtained when saponifying a liquid-phase oxidation reaction solution of cyclohexane with a molecular oxygen-containing gas with caustic soda;
A step of neutralizing with sulfuric acid to pH 3 or less, adjusting the concentration of Glauber's salt in the aqueous layer to 15% by weight or more, and separating it into an aqueous layer and an oil layer; (2) The oil layer separated in the above step is treated with an organic compound. A step of extracting with an aqueous solution of Glauber's salt having a concentration of 15% by weight or more; (3) adipine mainly contained in the aqueous layer separated in step (1) and the extract obtained in step (2); A step of extracting the acid, oxycaproic acid and its oligomer with an organic solvent; (4) The extract obtained in the above step is extracted with a monohydric alcohol having 1 to 8 carbon atoms and a polyhydric alcohol having 2 to 8 carbon atoms. A step of esterifying with one or more alcohols selected from the group consisting of alcohols; (5) The carboxylic acid ester obtained in the above step is esterified at 150 kg/d at a temperature of 150 to 300° C. in the presence of a catalyst.
A method for producing 1°6-hexanediol is described, which comprises a step of hydrogenating under a hydrogen partial pressure of G or more.

However, the liquid-phase oxidation reaction solution of cyclohexane using molecular oxygen-containing gas contains unreacted cyclohexane, non-acidic substances such as cyclohexanol, cyclohexanone, and cyclohexyl hydroperoxide, and dibasic substances such as adipic acid, glutaric acid, and succinic acid. Acids, monobasic acids such as caproic acid, valeric acid, butyric acid, oxycaproic acid,
oxyacids such as oxyvaleric acid and oligomers of these;
It contains esters of the above acids, aldehydes, alcohols, and various other unknown substances.

Therefore, if a liquid-phase oxidation reaction solution of cyclohexane containing a variety of compositions using a molecular oxygen-containing gas is used to perform the saponification, esterification, and hydrogenation reactions for the synthesis of 1,6-hexanediol, , adipic acid, oxycaproic acid, and oligomers thereof for the synthesis of 1,6-hexanediol, as well as a reaction solution containing homologs and isomers from the coexisting acids.

Incidentally, in the methods described in any of the above patent specifications, a distillation operation is used to separate and purify 1,6-hexanediol from this reaction solution.

However, 1,6- obtained by distilling this reaction solution
The hexanediol fraction contains monoalcohols with close boiling points, diol homologs and isomers, as well as high-boiling substances produced during the reaction, and 1,6-hexanediol can be extracted from these fractions. Selective separation by distillation is difficult as an economic separation and purification method.

Therefore, according to the conventional method of purifying the reaction liquid obtained from the liquid-phase oxidation reaction liquid of cyclohexane using a molecular oxygen-containing gas through an esterification process and a hydrogenation process by distillation, water (wt% ), AV value (acid value, which refers to the number of potassium hydroxide required to neutralize the acidic substance contained in 1 g of the product), EV value (ester value, which refers to the number of potassium hydroxide required to neutralize the acidic substance contained in 1 g of the product), (This refers to the number of potassium hydroxides required to completely saponify the ester.) However, it had the disadvantage of low purity.

[Problem to be solved by the invention]

As described above, the method of purifying the reaction liquid obtained from the liquid-phase oxidation reaction liquid of cyclohexane using a molecular oxygen-containing gas through the esterification process and the hydrogenation process by distillation is as follows. 1 obtained by distillation
, the 6-hexanediol fraction contains monoalcohols with close boiling points, diol homologues and isomers, and high-boiling compounds produced during the reaction, and 1,6-hexanediol is distilled from such a fraction. It is economically difficult to selectively separate it, and there are problems in that the purity is low.

The object of the present invention is to esterify a liquid-phase oxidation reaction liquid of cyclohexane with a molecular oxygen-containing gas and then hydrogenate the reaction liquid, or to obtain 1,6-hexane by further distilling this reaction liquid. In the process of purifying the diol fraction, by-products that cannot be separated and purified by distillation alone are removed, and compared to conventional production methods, water and A
High purity 1,6 without reducing quality such as V value and EV value.
- To provide a method for producing hexanediol.

[Means to solve the problem]

That is, this invention includes: (A) a step of oxidizing cyclohexane to produce a carboxylic acid compound; (B) a step of esterifying the carboxylic acid compound produced in step (A) with alcohol; (C) the step of esterifying the carboxylic acid compound produced in step (A); (B) Hydrogenating the esterified product obtained in step (C) to produce a mixture (hydrogenated solution) mainly containing 1,6-hexanediol; (D) or a 1,6-hexanediol distillate containing 0.1 to 50% by weight of by-products obtained by once distilling this hydrogenated solution. ) and one or more solvents selected from the group consisting of water or organic ketones having 3 to 20 carbon atoms, and heating the mixture to uniformly dissolve it; ( E) Cool the solution obtained in step (D) above to a temperature of 42°C or lower and below the melting temperature in step (D) to form crystals of 1,6-hexanediol. The present invention relates to a method for producing 1,6-hexanediol, comprising the following steps: precipitating the crystals, separating the crystals, and washing the crystals.

[Detailed explanation of each requirement of the present invention]

Next, each step of the method of the present invention will be specifically explained.

Steps (A) to (C) These steps involve 1. using cyclohexane as a starting material.
A conventionally known process for obtaining a product mixture containing mainly 6-hexanediol.

For example, the methods described in the above-mentioned German Patent No. 1206417 Al and Japanese Patent Publication No. 53-33567 are employed.

(D) Step In this step, a mixture (hydrogenated liquid) containing mainly 1゜6-hexanediol produced in the above (C) step, or a mixture obtained from the hydrogenated liquid by the method described below. A crude diol solution is supplied.

The purpose of this step and the next step (E) is to
Solubility of 1,6-hexanediol in water or organic ketones at the heating dissolution temperature of the hydrogenated solution obtained in the step or the crude diol solution obtained in this step and water or organic ketones as a solvent and the solubility of 1,6-hexanediol in water or organic ketones at the temperature after cooling the heated solution.

The objective is to precipitate crystals of 6-hexanediol.

The solubility of 1,6-hexanediol in water or organic ketones tends to increase as the temperature increases;
In the range close to 2°C, its solubility approaches infinity (.

Therefore, in this step, first, the hydrogenated liquid obtained in the above step (C) or the crude diol liquid obtained in this step,
At least one solvent selected from the group consisting of water or organic ketones having 3 to 20 carbon atoms, and 0.01 to 0.01 parts by weight of the solvent per 1 part by weight of the hydrogenated solution or crude diol solution.
2 parts by weight, preferably 0.1 to 1 part by weight,
Preferably, it is heated to 42° C. or higher to uniformly dissolve it.

Therefore, in view of the purpose of this step and the next step (E) described above, it is important in the present invention to first select the solvent to be used.

Industrially employable solvents are those that have low solubility in 1,6-hexanediol at low temperatures, and that contain the aforementioned by-products (monoalcohols with boiling points close to E6-hexanediol, diol homologues, isomers, etc.) Solvents with a high solubility of are suitable, as mentioned above, saturated aliphatic ketones or cycloaliphatic ketones having from 3 to 20 carbon atoms, preferably from 4 to 15 carbon atoms.

Specifically, organic ketones that satisfy these conditions include methyl isobutyl ketone, methyl ethyl ketone,
Saturated aliphatic ketones such as methyl propyl ketone, diethyl ketone, methyl butyl ketone, cyclohexanone,
Examples include alicyclic ketones such as methylcyclohexanone, and mixtures thereof.

In addition, among polar solvents, water has a relatively high solubility for 1,6-hexanediol at low temperatures (and is effective because it does not require recovery and circulation equipment compared to the case of the ketone solvents mentioned above). It can be a useful solvent.

By the way, as mentioned above, the solubility of 1.6-hexanediol in the above solvent is close to infinity in a range close to 42°C, which is the melting point of 1.6-hexanediol, so heating dissolution is It is sufficient to simply add the solvent to the hydrogenated solution or crude diol solution and heat it to at least 42°C or higher, but preferably, this operation is performed while stirring with a stirrer in order to obtain a more uniform solution. It's good.

Next, a method for producing the crude diol liquid supplied to this process will be described.

The mixture (hydrogenated liquid) mainly containing 1,6-hexanediol produced by the hydrogenation reaction of the esterified product in step (C) is distilled to contain 0.1 to 50% by weight of by-products. A 1,6-hexanediol distillate (crude diol liquid) is obtained.

Distillation of the hydrogenated solution is carried out in two stages.

That is, the mixture (hydrogenated liquid) mainly containing 1,6-hexanediol is heated at 21° C. in a preheater, for example.
It is preheated to 0°C or higher and supplied to the first distillation column, and the reflux ratio is 1:
1, distilled under normal pressure and at a temperature of 120 to 230°C,
Water and monohydric alcohol M (middle oil) are distilled out from the top, and the bottom liquid is led to the second distillation column.

In the bottom liquid of the first distillation column, which has removed water and medium oil,
Unreacted ester remains. Among these esters, there are high-boiling esters and low-boiling esters that become diols when hydrogenated. In the 2M distillation column, for example, vacuum distillation is performed under the reduced pressure of 40 plates HH at a temperature of 170 to 230°C, and from the top, 0.1 to 50% by weight of by-products (with a boiling point close to that of E6-hexanediol) are extracted from the top. A 1,6-hexanediol distillate (crude diol liquid) containing monoalcohols, diol homologs, isomers, etc. ) process].

The type of distillation column used is a packed column or a bubble column.

(E) Step The hydrogenated liquid obtained in the above step (C) or the above (D)
A heated solution of the crude diol liquid obtained in the step and a solvent such as water or an organic ketone is cooled to a temperature of 42° C. or below and below the above-mentioned dissolution temperature, and 1. 6
- Utilizing the temperature-dependent difference in solubility of hexanediol in the water or organic ketone solvent, 1,
After precipitating crystals of 6-hexanediol and separating the crystals, the same solvent used for the heating dissolution was added to 5 to 3
0% by weight, preferably 10-20% by weight for cleaning.

In this case, the heated solution may be cooled directly by an internal condenser tube or other internal cooling device installed in the crystallizer, or by an external jacket or other external cooling device, or by evaporating the solvent under reduced pressure to remove its latent heat of vaporization. (If the solvent is water, this method is particularly advantageous as it eliminates the need for recovery and circulation equipment.), and other cooling methods commonly used in industry. It will be done.

Further, for separation after crystallization of 1,6-hexanediol, a centrifuge may be used, filtration separation using a filter may be performed, or any other method that can easily separate the crystals may be used. Any method is fine.

After crystal separation, the by-products contained in the hydrogenated solution or crude diol solution move to the mother liquor side, so the produced crystals are removed using the same solvent used for the heating and dissolution. After washing the adhering mother liquor, the solvent adhering to the crystals is further removed by, for example, heating under reduced pressure.

In addition, in washing this 1,6-hexanediol crystal with the above-mentioned solvent, 1,6-hexanediol itself also migrates to the mother liquor side in an amount corresponding to its solubility.
It is also necessary to recover 1,6-hexanediol contained in the mother liquor.

Therefore, this invention has been able to invent a solvent with such a large effect that it can be used to convert cyclohexane into a liquid-phase oxidation reaction solution using a molecular oxygen-containing gas. - In order to extract the active ingredients for hexanediol synthesis, these acids are extracted and separated under economical extraction conditions, and the active ingredients are obtained at a stage of low purity, and then crystallized after going through the diol synthesis process. Highly purified 1.6
- A method for producing hexanediol has been established.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 A carboxylic acid compound obtained from an alkaline waste liquid obtained by liquid-phase oxidation of cyclohexane with a molecular oxygen-containing gas and then saponification treatment with an aqueous caustic soda solution is esterified with alcohol through a neutralization and solvent extraction process. After that, the esterified product was hydrogenated to obtain 60% by weight of 1,6-hexanediol (melting point: 42°C), 9% by weight of 1,5-bentanediol (melting point: 18°C), and n- A hydrogenated solution containing 1% by weight of butyl alcohol (melting point: 90.2°C), 1% by weight of n-amyl alcohol (melting point: 79°C), etc. was obtained.

Add an equal weight of methyl isobutyl ketone to this hydrogenated solution, heat it to 60°C, dissolve it, and slowly cool the solution.
Crystals begin to precipitate at 0°C, so after that, it is further slowly cooled and maintained at 15°C, and in order to separate the crystals, it is filtered with filter paper, and further, in order to remove the mother liquor that adheres to the surface of the separated crystals, After washing with the solvent in an amount equivalent to 10% of the crystal weight, the solvent still attached to the crystals is removed under a vacuum of 40%.
rxIi) removed at 1g and 120°C, purified 1
．． 6-hexanediol was obtained.

The recovery rate of 1,6-hexanediol was 85%. In addition, the effect of purity is that the value of 60% before purification is 99% after purification.
%, and the purification effect of removing impurities was obtained.

Example 2 1,6-hexanediol was produced in the same manner as in Example 1, except that an equal weight of methyl ethyl ketone was added to the hydrogenated solution obtained in Example 1 instead of methyl isobutyl ketone.

The recovery rate of 1,6-hexene diol was 60%,
A purity of 99% was obtained.

Example 3 1,6-hexanediol was produced in the same manner as in Example 1, except that crystal separation was performed using a centrifuge instead of filtration using a filter paper.

The recovery rate of 1.6-hexanediol was 90%,
A purity of 99% was obtained. In addition, the KZ value (E6
- It is determined from the consumption amount of the reducing substance in hexanediol reacted with potassium permanganate under an acidic sulfuric acid aqueous solution, and is expressed as the number i of consumption of N/10KMnOa solution per 1 kg of 1,6-hexanediol. . )teeth,
The M-product value was 350 d/kg, but after purification, a product with a value of 10 d/kg was obtained.

Example 4 The following were added to the hydrogenated solution obtained in Example 1, except that 0.2 times the amount (weight ratio) of water was added instead of methisobutyl ketone.
1,6-hexanediol was produced in the same manner as in Example 1.

The recovery rate of 1.6-hexanediol was 70%,
A purity of 94% was obtained.

Example 5 A carboxylic acid compound obtained through a neutralization/solvent extraction process is esterified with alcohol from an alkaline waste liquid obtained by liquid-phase oxidation of cyclohexane with a molecular oxygen-containing gas and then saponification treatment with an aqueous caustic soda solution. After that, the esterified product was hydrogenated to obtain 1,6-hexanediol (as the main component) by distillation from a mixture containing mainly 1,6-hexanediol (hydrogenated liquid).
1.6-hexanediol containing 12% by weight of 1.5-bentanediol (melting point: 18°C), 1.2% by weight of n-amyl alcohol (melting point: 79°C), etc. A distillate (crude diol liquid) was obtained.

Add an equal weight of methyl isobutyl ketone to this crude diol solution, heat it to 60°C, dissolve it, and then slowly cool the solution.
Crystals begin to precipitate at 30°C, so after that, it is further slowly cooled and maintained at 15°C, and in order to separate the crystals, it is filtered with filter paper, and further, in order to remove the mother liquor that adheres to the separated crystal surface, After washing with the solvent in an amount equivalent to 10% of the crystal weight, the solvent still attached to the crystals is removed at a vacuum level of 4.
Removed at 0 mmHg and 170°C, purified 1°6
-Hexanediol was obtained.

The recovery rate of 1,6-hexanediol was 85%. In addition, the effect of purity is that the value of 72% before purification is 98% after purification.
．． 5% was obtained, and the purification effect of removing impurities was obtained.

Example 6 1,6-hexanediol was added in the same manner as in Example 5, except that an equal weight of methyl ethyl ketone was added to the 1,6-hexanediol distillate obtained in Example 5 instead of methyl isobutyl ketone. Manufactured.

The recovery rate of 1.6-hexanediol was 85%,
A purity of 98% was obtained.

Example 7 1,6-hexanediol was produced in the same manner as in Example 5, except that crystal separation was performed using a centrifuge instead of using a filter.

The recovery rate of 1.6-hexanediol was 90%,
A purity of 98.5% was obtained. Further, the KZ value indicating potassium permanganate consumption 1, which is an index of impurities, was 350 d/kg before purification and 10 d/kg after purification.

Example 8 1.6-hexanediol was prepared in the same manner as in Example 5, except that 0.2 times the amount (weight ratio) of water was added to the crude diol solution obtained in Example 5 instead of methyl isobutyl ketone. was manufactured.

The recovery rate of 1.6-hexanediol was 70%,
A purity of 96% was obtained.

[Explanation of effects]

As described above, the production method of the present invention involves separating a carboxylic acid compound from a liquid-phase oxidation reaction liquid of cyclohexane using a molecular oxygen-containing gas, esterifying it, and then hydrogenating the reaction liquid, or a reaction liquid thereof. The 1,6-hexanediol distillate obtained by distilling 1,6-hexanediol contains monoalcohols with similar boiling points, diol homologues and isomers, and high-boiling substances produced during the reaction. It is difficult to selectively and economically separate and purify 1,6-hexanediol from such reaction liquids or distillates, and this method has the problem of low purity. A solvent such as water or organic ketones is added to the reaction solution obtained by hydrogenation or the 1,6-hexanediol distillate obtained by distillation of this reaction solution, dissolved by heating, and then cooled to crystallize. By performing analysis and crystal washing, it is possible to remove the above-mentioned by-products that cannot be produced by distillation alone, and compared to conventional distillation operations, it is possible to obtain high-purity products without degrading the quality of moisture, AV value, EV value, etc. 1.6
- It has the effect of providing a method for producing hexanediol.

Patent distributor: Ube Industries Co., Ltd.

Claims (2)

[Claims] (1) (A) Step of oxidizing cyclohexane to produce a carboxylic acid compound; (B) Step of esterifying the carboxylic acid compound produced in step (A) with alcohol; (C) Step (B) of above; A step of hydrogenating the esterified product obtained in the step to produce a mixture (hydrogenated solution) mainly containing 1,6-hexanediol; (D) Hydrogenation produced in the step (C) A step of mixing the treatment liquid and at least one solvent selected from the group consisting of water or organic ketones having 3 to 20 carbon atoms, and heating the mixture to uniformly dissolve it; (E) The solution obtained in the step (D) is cooled to a temperature of 42° C. or lower and lower than the dissolution temperature in the step (D) to precipitate crystals of 1,6-hexanediol, A method for producing 1,6-hexanediol, comprising the steps of separating and washing the crystals. (2) In step (D), the hydrogenated solution obtained in step (C) is distilled to produce a 1,6-hexanediol distillate ( A crude diol solution) is obtained, the crude diol solution is mixed with water or at least one solvent selected from the group consisting of organic ketones having 3 to 20 carbon atoms, and the mixed solution is heated. 2. The method according to claim 1, wherein the method is characterized in that the method is made to dissolve uniformly.