DE1793441A1 - Process for the production of sorbic acid - Google Patents

Description

WACKER CHEMISTRY GMBH

Munich, September 16, 1968 IX / Pat.Abt. Dr.

Addition to P 15 93 709.4-42

Int.No. Wa 6823

Process for the production of sorbic acid

In the patent application P 1b 93 709.4, DBP ........ a Process for the preparation of sorbic acid described by reacting ketene with preferably stoichiometrically excess Crotonaldehyde in the presence of catalysts and conversion of the resulting polyester by saponification or thermal cleavage into sorbic acid, the process is thereby characterized that one ICeten with crotonaldehyde, the given

- 2 -

209818/1177

^8AD

if 0.01 to 1 fo, based on the grotonaldehyde used, contains a sterically hindered phenol as a stabilizing agent, in the presence of tetraalkyl titanates, the alkyl groups of which are straight-chain or branched-chain and contain 2 to 18 carbon atoms, or their condensation products, at temperatures of 70 up to 110 ° C, especially 80 to 102 ° G.

The polyester obtained can be saponified or by thermal Cleavage to be worked up. The alkaline saponification requires large amounts of alkali lye and mineral acid, which are lost in the form of the corresponding alkali salts. In the case of thermal cleavage (distillation) lower yields achieved. In addition, technical difficulties arise when the process is carried out continuously,

When using acidic saponification, which is an economical work-up method due to the low consumption of auxiliary substances and the ease with which it can be carried out, the sorbic acid yield is below b0 $.

- 3 - 209818/1177

A process has now been found for the production of Sorbic acid by reacting ketene with preferably stoichiometrically excess crotonaldehyde, which if necessary a sterically hindered phenol contains, in the presence of tetraalkyl titanates, their alkyl groups. are straight or branched chain and have 2 to 18 carbon atoms contain, or their condensation products and conversion of the resulting polyester by saponification in sorbic acid according to patent application P 1b 93 709.4-42, DBP ........ The process is characterized in that the reaction of ketene with crotonaldehyde at temperatures below 70 C, preferably at 3 !? up to 4b ° 0 and the resulting, catalyst-containing, excess Crotonaldehyde-free polyester with at least 20.2% color Treated aqueous hydrochloric acid at temperatures from bO to 100 ° C.

It is advantageous to use crotonaldehyde, which may be stabilized with small amounts of a sterically hindered phenol is to be used in excess. This creates too high a toughness of the reaction product avoided during the reaction and a Trouble-free reaction process ensured. The crotonaldehyde excess can be different according to the reaction temperature

- 4 209818/1177

and is generally about $ 200 of theory. By this measure is given a quantitative ketene turnover. It succeeds due to the advantageous properties of the used Catalysts the excess crotonaidehyde practically recover quantitatively.

Keten can be used in a technically pure form (approx. 90 $). However, a ketene is particularly suitable which, according to the information provided by Deutsche Patentschriit 1 079 623 or according to the German Auslegeschrift 1 203 248 is obtained.

When using hydrochloric acid, it proves to be particularly advantageous if its concentration is at least 20.2 ⁰ Jo . If the hydrochloric acid has a concentration of less than $ 20.2, additional amounts of water must be removed by distillation when cleaning it. If a more highly concentrated hydrochloric acid is used, the formation of vaporous hydrogen chloride increases with increasing temperature during the acidic treatment of the polyester.

In general, small additions of hydrochloric acid are sufficient. In order to facilitate the continuous processing, it is , however,

209818/1177

“AD

beneficial that the weight ratio hydrochloric acid: polyester set to 1: 1 "to 10: 1.

The saponification temperature is inversely proportional to the residence time. Both sizes can be different within the broadest limits. To be favoured but high saponification temperatures, for example ™ 70 to 80 ° and short dwell times, e.g. 0,!? up to 1 hour.

The process can be carried out batchwise or continuously.

The continuous operation is carried out as follows:

Technically pure ketene is introduced into the lower part of the reactor 4 (see FIG.) Via line b. Catalyst-containing crotonaldehyde is fed to this at the same time m from below via line 3. The exhaust gas escaping from the reactor 4 via the degassing pipe 6 is fed to the catalyst-containing prischerotonaldehyde fed in via line 1 in a Raschig ring column 2 connected downstream of the reactor 4. While a ketene- and crotonaldehyde-free exhaust gas escapes at the upper end of column 2 via line 9, the discharge from column 2 is via line

- 6 -209818/1177 _eAD ORIGINAL

The reactor residence time can be adjusted via the overflow 7. This can vary within wide limits. Residence times of 2 to 6 hours have proven to be advantageous.

read reaction product obtained via line 7 is, for example continuously subjected to vacuum distillation in a thin-film evaporator 8, the excess crotonaldehyde, optionally after fractionation, can be recovered in pure form and fed back to the reaction via line 10.

The catalyst-containing, crotonaldehyde-free obtained via line 11 Reaction product (polyester) is fed to a further reactor 13 and there with hydrochloric acid with stirring at elevated temperature treated. The resulting hot mixture of hydrochloric acid and crude sorbic acid is fed via line 14 to a cooler 1b and from there supplied via line 16 to a centrifuge 17. The hydrochloric acid is circulated via line 18, with a partial stream is fed via line 19 to a distillation device 20 for cleaning. While over line 22 high boiling Impurities are obtained, hydrochloric acid falls through line 21 or hydrogen chloride. The still hydrochloric acid-containing raw sorbin

- 7 -209818/1177

acid is continuously fed to the scrubber 24 via line 23. In this, the crude sorbic acid is washed free of hydrochloric acid with water, which is fed in via line 2b, and the water-moist crude sorbic acid is fed via line 27 to the crystallization. The water containing hydrochloric acid is discharged via line 26. The loss of hydrochloric acid resulting from washing is made up by adding fresh hydrochloric acid via line 12.

The crude sorbic acid obtained by the process of the invention is obtained after crystallization from water or from water / solvent mixtures (e.g. water / acetone) a stable, colorless and odorless pure sorbic acid.

The process according to the invention is economical Way to produce sorbic acid, with good yields of sorbic acid with a simple process technology and little effort of energy and auxiliary materials.

2098 1.8 / .1177

example 1

298.7 parts by weight of a mixture consisting of 8.7 parts by weight of tetra ~ n-butyl titanate and 290 parts by weight of crotonaldehyde, which contains 0.1 percent by weight of 2,6-di-tertiary-butyl-p-cresol, are added every hour to the upper end of the with Raschig rings fed to column 2 via line 1. The effluent occurring at the lower end of the column is continuously fed via line 3 from below to reactor 4, into which S4 parts by weight of ketene are simultaneously introduced via line t> hourly. The reaction temperature is maintained at 4-O ⁰ O. While the reactor exhaust gas escaping via line 6 is introduced into the lower part of the Raschig ring column 2, the continuously occurring reaction mixture (crotonaldehyde and catalyst-containing polyester) is fed to a distillation plant 8 operating at 20 Torr with the help of the overflow 7. The reactor exhaust gas obtained via line 9 is practically free of ketene and crotonaldehyde. While 136 parts by weight of crotonaldehyde are obtained per hour via line 10, 246 parts by weight of a crotonaldehyde-free, catalyst-containing polyester are obtained per hour via line 11 and are fed to the stirred tank 13. The latter will be total

- 9 -209818/1177 8AD OWGlNAL

492 parts by weight of 30 sequence aqueous hydrochloric acid were added per hour, 59 parts by weight being fed in via line 12 and 4b3 parts by weight via lines 18 and 21, respectively. The stirred tank temperature is 70 ° C. After an average dwell time of 1 hour, the hot mixture, consisting of crude sorbic acid and hydrochloric acid, is fed to the scraped surface cooler 1b via line 14-. The cooled (18 G) conversion mixture is fed to the centrifuge 17 via line 16. There the hydrochloric acid is separated from the crude sorbic acid. The former is circulated via line 18 »A partial stream is fed via line 19 to a thin-film evaporator 20 for cleaning. High-boiling impurities are removed via line, while pure hydrochloric acid or hydrogen chloride are obtained via line 21». Via line 23, 26b parts by weight of crude sorbic acid, which still contains 14.7% hydrochloric acid, are obtained every hour and fed to the scrubber 24. There the crude sorbic acid is washed hourly with 132b parts by weight of water, which are fed in via line 2b, with hydrochloric acid free of charge. Reconciliation 26 1327 parts by weight of hydrochloric acid containing water per hour are discharged and received over circuit 27 hour 263 parts by weight of a 80 follow crude sorbic acid with a residual moisture content of 14.7 $>.

- 10 209818/1177

- ίο -

By crystallization from water, 197 parts by weight per hour of a colorless and odorless rexsorbic acid are obtained, corresponding to a yield of 87 »9 ° / °, based on ketene.

Example 2

246 parts by weight of polyester, which were produced according to the details of Example 1, are mixed with 100 parts by weight of 20.2% hydrochloric acid and the mixture is stirred at 90 ° C. for 3 hours. It is then cooled to 180, filtered off with suction and the crude sorbic acid obtained is washed free of hydrochloric acid with a little cold water. 28b, b parts by weight of crude sorbic acid with a residual moisture content of 21 f are obtained. After recrystallization from water, 191? Parts by weight of colorless and odorless pure sorbic acid, corresponding to a yield of $ 87, based on ketene.

11 -

209818/1177

Claims (2)

Patent claims: 1. Process for the preparation of sorbic acid by reacting ketene with preferably stoichiometrically excess crotonaldehyde, which optionally contains a sterically hindered phenol, in the presence of tetraalkyl titanates, the alicyl groups of which are straight or branched and contain 2 to 18 carbon atoms, or their condensation products and conversion of the resulting polyester by saponification in sorbic acid according to patent application P 1b 93 YOy.4, DBP ....... characterized in that the reaction of ketene with crotonaldehyde at temperatures below 70 ° C, preferably at 3t? " his 4 b C performs and the resulting catalyst-containing treated excess crotonaldehyde liberated polyester with at least 20.2 <fo strength wiißriger hydrochloric acid at temperatures of HO to 100 ° C. • AD 209818/1177 2. The method according to claim 1, · thereby geicenn draws that a weight ratio hydrochloric acid to polyester from 1: 1 "to 10: 1. 2098-18 / 1 177