JPH0465054B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for purifying carboxylic acid, and more specifically, the present invention relates to a method for purifying carboxylic acid, and more specifically, the present invention relates to a method for purifying carboxylic acid from a crude product of carboxylic acid obtained by reacting an olefin with carbon monoxide and water, the so-called Kotsuko reaction. Regarding how to. [Prior Art and Problems to be Solved by the Invention] Various methods have been proposed in the past for purifying carboxylic acids from crude carboxylic acids.
For example, a crude carboxylic acid product is added to an aqueous alkaline solution and separated into an aqueous phase containing an alkali salt of the carboxylic acid and an oil phase containing an olefin polymer, and a mineral acid is added to the aqueous phase to precipitate the carboxylic acid and separate it. (Special Publication No. 38-11964), method of contacting crude fatty acids with an oxidizing agent and then distilling them (Special Publication No. 16897-1982)
(No. 48-23412), a method of distilling the crude product of carboxylic acid together with diethylene glycol monoethyl ether to remove the olefin polymer (Japanese Patent Publication No. 48-23412);
A method in which crude carboxylic acid is heated with water or water containing a small amount of organic acid salt or inorganic salt under liquid phase conditions at a temperature of 100 to 270°C, and then distilled.
No. 35048) is known. However, the distillation method (Special Publication No. 48-16897,
Although sulfur compounds can be removed to some extent using the Japanese Patent Publication No. 35048 (Japanese Patent Publication No. 48-35048), since the olefin polymer has a boiling point close to that of the carboxylic acid, it is difficult to separate.
This method requires an equivalent amount of alkali and acid to the carboxylic acid, and has the disadvantage that inorganic salts are mixed into the carboxylic acid, reducing the purity of the product. In addition, the method of adding diethylene glycol monoethyl ether (Japanese Patent Publication No. 48-23412) can only be applied to tertiary nonanoic acid, and it also has drawbacks such as requiring the addition of water to reuse diethylene glycol. be. [Means for Solving the Problems] As a result of extensive research in order to eliminate the above-mentioned drawbacks, the present inventor discovered that the above-mentioned objective could be achieved by extracting crude carboxylic acid with a specific extractant, The present invention was completed based on this knowledge. That is, the present invention involves extracting a crude carboxylic acid having 4 to 16 carbon atoms obtained from a Kotsuho reaction product obtained by reacting olefin with carbon monoxide and water with an aqueous methanol solution having a concentration of 20 to 90% by weight. The present invention provides a method for purifying carboxylic acid characterized by the following. The crude carboxylic acid used in the method of the present invention is a crude carboxylic acid obtained by the conventionally known Kotsuho reaction. The above Kotsuho reaction is shown by the following reaction formula. Olefin + carbon monoxide + water -------→ Sulfuric acid catalyst Carboxylic acid + olefin polymer + sulfuric ester Olefins used as raw materials for the above reaction include aliphatic olefins, alicyclic olefins, and aliphatic olefins that can be used in the Kotsuto reaction. There is no particular restriction as long as it is an alicyclic compound or an aromatic compound having a group olefin as a substituent, but it has 3 to 15 carbon atoms (C ₃ to C ₁₅ ), preferably 3 to 12 carbon atoms (C ₃ to C ₁₂ ).
It is. Such aliphatic olefins include, for example, ethylene, propylene, isobutylene, n-butene, 1-butene, pentene, hexene, heptene, octene, nonene, decene and higher alkenes. Furthermore, examples of alicyclic olefins include cyclopentene and cyclohexene, examples of alicyclic compounds having an aliphatic olefin as a substituent include vinylcyclohexane and isopropenylcyclohexene, and examples of aromatic compounds having an aliphatic olefin as a substituent include styrene. , isopropenylbenzene and the like. The above-mentioned raw material olefins may be used alone or as a mixture of two or more. The crude carboxylic acid obtained by the Kotsuto reaction using the above olefin as a raw material is a carboxylic acid with one carbon number larger than that of the raw material olefin, and the crude carboxylic acid used in the present invention is a carboxylic acid with a carbon number of 4 to 16 ( _C4 acid to C ₁₆ acid), preferably a carboxylic acid having 4 to 13 carbon atoms (C ₄ acid to C ₁₃ acid). In the method of the present invention, the above-mentioned crude carboxylic acid is made into a solution of aliphatic hydrocarbons, and then extracted with an aqueous methanol solution. The hydrogen phase is separated into a lower phase (methanol phase) consisting of a purified carboxylic acid and an aqueous methanol solution. Here, various aliphatic hydrocarbon solvents can be used, but usually n-hexane, n-
Heptane is preferred. The methanol aqueous solution used has a concentration of 20 to 90% by weight, preferably 60 to 88% by weight. If the methanol concentration is less than 20% by weight, the carboxylic acid concentration in the methanol aqueous solution phase will be extremely reduced, and if it exceeds 90% by weight, it will not be possible to separate the aliphatic hydrocarbon phase and the methanol phase, which is not preferable. Next, an extraction example of the present invention will be explained. The crude reaction product obtained by diluting the Kotsuho reaction product with n-hexane as a solvent was partially stripped, and 1 volume of an 80% by weight methanol aqueous solution was added to 2 volumes of the crude carboxylic acid, which was concentrated to a concentration of about 50%. Extract with a separatory funnel. The upper phase (n-hexane phase) contains impurities such as olefin polymers, and the lower phase (methanol aqueous solution phase) extracts only carboxylic acid according to partition equilibrium. Another 80% by weight methanol aqueous solution is added to the n-hexane phase and the extraction is repeated. There is no particular limit to the number of extractions.
This may be continued until the desired carboxylic acid is sufficiently extracted. Next, the method for purifying carboxylic acid of the present invention will be explained with reference to the drawings. FIG. 1 is a process flow sheet illustrating one embodiment of the present invention. An 80% by weight aqueous methanol solution was added to the carboxylic acid extraction tower 4 from the top, and a crude carboxylic acid solvent (50%
% hexane) solution is fed and countercurrently contacted. In the carboxylic acid extraction tower 4, the olefin polymer in the crude carboxylic acid is not extracted into the methanol aqueous solution, but remains as a hexane solution from the top of the carboxylic acid extraction tower 4 to the pipe 5.
It is supplied to the hexane recovery tower 7 through. In the hexane recovery tower 7, the olefin polymer is separated from the bottom of the tower, and hexane is supplied from the top of the tower via a pipe 8 to the carboxylic acid extraction tower 4 again. On the other hand, the carboxylic acid extracted into the methanol aqueous solution in the carboxylic acid extraction tower 4 is supplied to the methanol recovery tower 10 from the bottom of the tower via a pipe 6. In the methanol recovery column 10, an aqueous methanol solution is recovered from the top of the column and is again supplied to the carboxylic acid extraction column 4 via a pipe 11. On the other hand, the carboxylic acid (purified carboxylic acid) in the methanol recovery column 10 is supplied from the bottom of the column through a pipe 12 to a carboxylic acid distillation column 13, where it is separated into fractions of each carbon number. [Effects of the Invention] According to the purification method of the present invention, it is possible to completely remove the olefin polymer having a boiling point close to that of the carboxylic acid, and at the same time, it is also possible to remove the sulfuric acid ester, making it possible to isolate highly pure carboxylic acids. can. Further, the purification method of the present invention can be carried out at normal temperature and pressure, and does not require the use of large amounts of inorganic chemicals, so it is an economical and industrially superior method. Therefore, the method of the present invention is very useful as a method for purifying carboxylic acids. [Example] Next, the present invention will be explained in detail with reference to Examples. Example 1 Crude pivalic acid (purity 73%) containing olefins ( _C11 - _C12 ) with close boiling points as impurities
500 ml of n-hexane and 500 ml of 80% by weight methanol aqueous solution were added to 500 ml (420 g), shaken in a separatory funnel, and then allowed to stand. Next, the lower phase methanol aqueous solution phase was separated, and the upper phase was further extracted using 500 ml of fresh 80% methanol aqueous solution.
Repeated times. The recovery rate of pivalic acid was determined by analyzing the n-hexane phase after a total of three extractions using gas chromatography. In addition, after combining the lower methanol aqueous solution phase,
The methanol aqueous solution was removed by distillation, and the residue was further rectified to obtain 302 g of pivalic acid. The purity and recovery rate of the obtained pivalic acid are shown in Table 1. Example 2 Crude nonanoic acid (purity 80.9%) 100 containing olefins (C ₁₆ ) with close boiling points as impurities
ml (90.3 g) were added with 100 ml of n-hexane and 100 ml of 80% by weight aqueous methanol solution, and after shaking in a separatory funnel, the mixture was allowed to stand still. The operation of separating the lower methanol aqueous solution phase and extracting the upper phase using 100 ml of fresh 80% methanol aqueous solution was repeated 6 times. The recovery rate of nonanoic acid was determined by analyzing the n-hexane phase after a total of seven extractions using gas chromatography. Further, after combining the lower methanol aqueous solution phases, the methanol aqueous solution was distilled off, and the residue was further rectified to obtain 71 g of nonanoic acid. Table 1 shows the purity and recovery rate of the obtained nonanoic acid. Example 3 In Example 2, the concentration of methanol aqueous solution was 70
Total weight percentage and number of extractions
Extraction was carried out in the same manner as in Example 2 except that the number of extractions was 13 times. After a total of 13 extractions, 97.5% by weight of the initial nonanoic acid had been extracted. Note that the nonanoic acid purity of the n-hexane phase was 9.7%. By distilling off the methanol aqueous solution from 1310 ml of the combined methanol aqueous extract, 72.2 g of nonanoic acid was obtained. Table 1 shows the purity and recovery rate of the obtained nonanoic acid. Example 4 Extraction was carried out in the same manner as in Example 2 except that n-pentane was used instead of n-hexane and the number of extractions was 6 times in total. After a total of six extractions, nonanoic acid had been almost completely extracted. Further, after distilling off n-pentane from 28 ml of the n-pentane phase, 7.7 g of a liquid mixture was obtained.
The composition of the liquid mixture was analyzed by gas chromatography and found to be 92.2% olefin polymer and 7.8% nonanoic acid. 77.9 g of a liquid mixture was obtained by distilling off the methanol aqueous solution from 605 ml of the combined methanol aqueous solution phase at normal pressure. The composition of the liquid mixture was analyzed by gas chromatography and found to be 4.8% olefin polymer and 95.2% nonanoic acid.
The purity and recovery rate of nonanoic acid are shown in Table 1. Comparative Example 1 Crude pivalic acid containing olefins (C ₁₁ - _{C 12} ) with close boiling points as impurities (purity 73%)
500 ml (430 g) was distilled using a precision distillation apparatus with 100 theoretical plates to obtain 390 g of a fraction at 163 to 164°C.
Table 1 shows the analysis results of the obtained fraction by gas chromatography. As is clear from Table 1, olefins could hardly be removed. Comparative Example 2 Crude nonanoic acid (purity 80.9%) 500 containing olefins (C ₁₆ ) with close boiling points as impurities
ml (452 g) was distilled under reduced pressure using a 30 cm Widmer column to obtain 405 g of an 85-93°C/1 mmHg fraction. Table 1 shows the analysis results of the obtained fraction by gas chromatography. As is clear from Table 1, olefins could hardly be removed. Comparative Example 3 To 500 ml of the same crude pivalic acid as in Example 1, 500 ml of n-hexane and 500 ml of a 95% methanol aqueous solution were added.
ml was added, shaken in a separatory funnel, and left to stand.
The phase became homogeneous and the n-hexane phase and methanol aqueous solution phase could not be separated. The results are shown in Table 1. Comparative Example 4 To 100 ml of the same crude nonanoic acid as in Example 2, 100 ml of n-hexane and 100 ml of 95% methanol aqueous solution were added.
was added, shaken in a separatory funnel, and then allowed to stand, but the resulting mixture became a homogeneous phase, and it was not possible to separate the n-hexane phase and the methanol aqueous solution phase. The results are shown in Table 1. Example 5 Kotsuho reaction crude product liquid containing unreacted olefin polymer as an impurity (olefin polymer 13.2
wt%, _C5 acid 7.5wt%, _C6 acid 2.8wt%, _C7 acid 3.5wt%
wt%, _C9 acid 45.6 wt%, C10 ₊ acid 27.4 wt% (analysis by gas chromatography)) 100ml (86.7wt%)
100 ml of n-hexane and 100 ml of 80% by weight aqueous methanol solution were added to g), and after shaking with a separatory funnel, the mixture was allowed to stand still. The lower phase methanol aqueous solution was separated, and the upper n-hexane phase was further extracted with 100 ml of a fresh 80% methanol aqueous solution six times. After a total of seven extractions, the n-hexane phase was analyzed by gas chromatography to determine the recovery rate of carboxylic acid. Next, n-hexane was distilled off from the n-hexane phase to obtain 13.7 g of a liquid mixture. As a result of analyzing the composition of the liquid mixture by gas chromatography, it was found that 69.6% by weight of olefin polymer;
The _C9 acid was 8.0% by weight and the C10 ₊ acid was 22.4% by weight. The methanol aqueous solution was distilled off from 780 ml of the combined methanol aqueous solution extracts to obtain 58.1 g of a liquid mixture. Table 2 shows the analysis results (purified product composition) of the liquid mixture by gas chromatography and the recovery rate of the carboxylic acid. Example 6 One volume of Kotsuho reaction crude product liquid having the same composition as in Example 5 was diluted with one volume of n-hexane. Extraction tower (helipack packed bed: inner diameter 4.5cm, height
47cm, void volume ^233cm3 ; upper stationary layer: inner diameter 4.5cm,
Height 7.0cm, volume 35cm ³ ; Lower stationary layer: inner diameter 4.5cm,
Height 11.5cm, volume 58cm ³ ; Total internal volume of extraction tower 326cm ³ )
Add 80% methanol aqueous solution from the top using
An n-hexane solution of the Kotsuho reaction crude product solution was passed from the bottom at a rate of 180 ml/hour, respectively, to bring about countercurrent contact. After 5 hours, the raffinate from the top of the column was 58
ml/h, and an extract was obtained from the bottom of the column at a rate of 302 ml/h. After n-hexane and a small amount of methanol were distilled off from the raffinate, analysis by gas chromatography revealed that the content was 49.9% by weight of olefin polymer, 7.2% by weight of _C9 acid, and 42.9% by weight of C10 ₊ acid. Furthermore, the above extract was analyzed by gas chromatography. Table 2 shows the analysis results (excluding methanol and a small amount of n-hexane) and the recovery rate of each fraction of acid. Example 7 100ml of Kotsuho reaction crude product liquid with the same composition as Example 5
(88.2 g) were added with 100 ml of n-pentane and 100 ml of 80% by weight aqueous methanol solution, and after shaking in a separatory funnel, the mixture was allowed to stand still. The lower methanol aqueous solution phase was separated, and the upper phase was further extracted with 100 ml of a fresh 80% methanol aqueous solution six times. After a total of seven extractions, the n-pentane phase was analyzed by gas chromatography to determine the recovery rate of carboxylic acid. Next, from 30 ml of n-pentane phase to n-
Pentane was distilled off to obtain 10.3 g of a liquid mixture. As a result of analyzing the composition of the liquid mixture by gas chromatography, it was found that 87.9% by weight of olefin polymer;
The _C9 acid was 3.1% by weight and the C10 ₊ acid was 9.0% by weight. Further, an aqueous methanol solution was distilled at normal pressure from 793 ml of the combined extracts to obtain 66.4 g of a liquid mixture. Table 2 shows the analysis results of the liquid mixture by gas chromatography and the carboxylic acid recovery rate. Comparative Example 5 Kotsuho reaction crude product containing olefin polymer (C ₇ - _{C 25} ) as an impurity (analysis result by gas chromatography: olefin polymer 5.6%,
_C5 acid 10.4%, _C6 acid 2.1%, _C7 acid 1.9%, _C9 acid 57.2%,
1000g of C10 ₊ acid (22.8%) was vacuum distilled using a 70cm Widmer column at a pressure of 10mmHg. The boiling point, yield and olefin polymer content of each fraction are shown in Table 3.

【table】

【table】

【table】

[Table] As is clear from Table 3, carboxylic acid and olefin polymer were mixed in each fraction, and it was not possible to purify the carboxylic acid. Comparative Example 6 Countercurrent contact was carried out in the same manner as in Example 6, except that the methanol aqueous solution concentration was 95% by weight. A homogeneous phase was formed, and the n-hexane phase and methanol aqueous solution phase could not be separated.

[Brief explanation of the drawing]

The drawing is a flow sheet showing one embodiment of the invention. 1...Aliphatic alcohol aqueous solution supply port, 2...
Crude carboxylic acid supply port, 3...Solvent supply port, 4...
Carboxylic acid extraction tower, 7... Solvent recovery tower, 10...
Aliphatic alcohol recovery column, 13... Carboxylic acid distillation column, 5, 6, 8, 9, 11, 12... Pipe line.

Claims (1)

[Claims] 1 A crude carboxylic acid having 4 to 16 carbon atoms obtained from a Kotsuho reaction product obtained by reacting olefin with carbon monoxide and water is extracted with an aqueous methanol solution having a concentration of 20 to 90% by weight. Method for purifying carboxylic acid.