DE1793441C3 - - Google Patents

Description

3 4

the excess crotonaldehyde, possibly after free from tonaldehyde. While on line 10 every hour

Fractionation, recovered in pure form, and 136 parts by weight of crotonaldehyde are obtained

246 parts by weight of one per hour are fed back to the reaction via line 10 via line 11

can. raw, crotonaldehyde-free, catalyst-containing poly-

The catalyst-containing 5 esters obtained via line 11 and fed to the stirred tank 13 are crotonaldehyde-free reaction product (polyester). The latter is fed a total of 492 parts by weight of its further reactor 13, where parts of 30% strength aqueous hydrochloric acid are added per hour. The thereby obtained hot mixture of hydrochloric weight parts via line 18 and 21 are fed to acid and crude sorbic acid is fed via line 14 to a io The Rührkesseltemperatur is 70 ⁰ C. According to a cooler 15 and from there via line 16 to a centrifugal average residence time of The joint 17 is fed for 1 hour. The hydrochloric acid is circulated via line 18, consisting of crude sorbic acid, and a partial flow via line 14 to scraped surface cooler 15, via line 14, to a distillation device 20 for purification. The cooled (18 ° C.) is fed in via line 16. While 15 high-boiling conversion mixture is fed to the centrifuge 17 via line 22. Where impurities are obtained, the hydrochloric acid is separated from the crude sorbic acid via line. 21 hydrochloric acid or hydrogen chloride. The former, which is still salt, is circulated via line 18, acid-containing crude sorbic acid is continuously fed via line 19 to the washer 24 to the washer 24. In this, a thin-film evaporator 20 is fed, the crude sorbic acid is washed free of hydrochloric acid with water which is fed in via line 25 ″ via line 22 high-boiling impurities, and the water is drawn off, while raw sorbic acid is drawn off via line 21, while raw sorbic acid is fenced in via line 27 The acid-containing water is discharged every hour 265 parts by weight of crude sorbin via line 26. The acid obtained during the washing, which still contains 14.7% hydrochloric acid, and the resulting loss of hydrochloric acid is due Addition * 5 is fed to the scrubber 24. There, the raw sorbin fresh hydrochloric acid is replenished via line 12. Acid with 1325 parts by weight of water every hour

The obtained by the process of the invention are fed via line 25, free from hydrochloric acid.

Crude sorbic acid yields wash after crystallization from water. Via line 26 are hourly ^; ch 1327 Ge

or from water-solvent mixtures (for example, parts by weight of water containing hydrochloric acid are discharged and

wise water-acetone) a stable, colored and 3 ° via line 27 per hour 263 parts by weight eini

odorless pure sorbic acid. 80% raw sorbhic acid with a residual moisture of

With the method according to the invention it is possible to obtain 14.7%.

to produce sorbic acid in an economical way, it is obtained by crystallization from water

with good yields of sorbic acid with 197 parts by weight of a colorless and odorless one per hour

times process engineering and low expenditure on 35 pure sorbic acid, corresponding to a yield of

Energy and auxiliary materials can be achieved. 87.9% based on ketene.

Example 1 Example 2

298 7 parts by weight of a mixture consisting of 246 parts by weight of polyester, which were prepared according to the information 8 7 parts by weight of tetra-n-butyl titanate and 290 Ge 4o of Example 1, with 500 parts by weight of crotonaldehyde, the 0.1 weight percent by weight 20.2 % hydrochloric acid is added and contains 3 hours-2 6 ^ di-tertiary-butyl-p-cresol, are stirred ^{at 90 ° C. every hour.} The upper end of the column charged with Raschig rings is then cooled to 18 ° C., filtered off with suction and the crude sorbic acid obtained is fed to column 2 via line 1. The lower part is washed free of hydrochloric acid with a little cold water. The effluent from the end of the column is continuously 45 285.5 parts by weight of crude sorbic acid are fed into the reactor 4 from below via line 3, residual moisture of 21% being obtained. From this, 195 parts by weight of color weighted ketene are introduced into the simultaneously 84 Ge / hour recrystallization from water via line *. The reactive and odorless pure sorbic acid, corresponding to a tion temperature, is kept at 40 ° C. While the yield of 87% based on ketene.
Reactor exhaust gas escaping via line 6 in 5 ° Example 3
lower part of the Raschigrir.gkolonne 2 is initiated, .._ .. ,,. ... is with the help of the overflow 7, the ongoing procedure as indicated in Example 1, but a reaction mixture (crotonaldehyde and catalyst at a reaction temperature of 6O ⁰ C in the reactor 4, containing polyester) one working at 20 Torr. Thus, during the work-up of the conversion mixture, the still system 8 is fed. The colorless and odorless sorbic acid in a failed reactor exhaust gas via line 9 55 is practically ketene and crochet of 72.5%, based on ketene.

1 sheet of drawings

Claims (1)

1 2 temperatures below 70 ° C, preferably at 35 to claims: 45 ° C and the resulting, catalysis-containing, freed from excess crotonaldehyde 1. Process for the production of sorbic acid polyester with at least 20.2% strength aqueous Saizdurch Implementation of ketene with excess 5 acid in a manner known per se to sorbic acid ver-crotonaldehyde in the presence of tetraalkyltita soap. It is advantageous to use crotonaldehyde, the given if necessary in the presence of a sterically hindered phenol, if stabilized with small amounts of a sterically hindered phenol as stabilizing agent and conversion, phenol should be used in excess, the resulting polyester by saponification in io Avoided product during the reaction and a marked that the implementation ensures trouble-free course of the reaction. The Crovon ketene with crotonaldehyde at a temperature tonaldehydüberschuß, the reac-below performs according to 7O ⁰ C and the catalyst-tion temperature is different, and in allgehaitigen, excess crotonaldehyde loading 15 my about 200% of theory. This measure gives free polyester with at least 20.2% aqueous ketene conversion. In doing so, hydrochloric acid is saponified in a manner known per se for sorbent due to the advantageous properties of the acid. used catalysts, the excess cro- 2. The method according to claim 1, characterized by recovering tonaldehyde practically quantitatively, shows that the reaction of ketene with Cro- ao ketene can be in technically pure form (about 90%) tonaldehyde can be used at temperatures of 35 to 45 ° C. However, a ketene is particularly suitable. is carried out. according to the information in the German patent specification 1 079 623 or according to those of the German interpretation 1 203 248 is received. 35 It turns out to be the case with the use of hydrochloric acid as particularly beneficial when their concentration In German patent 1,293,752, a process is at least 20.2%. The hydrochloric acid knows described for the production of sorbic acid, by concentration of less than 20.2%, so must Implementation of ketene with preferably stoichiome- additional amounts of water during their purification trisch excess crotonaldehyde in the presence of 30 distillation separated. Will a higher conv Using catalysts and converting the resulting centered hydrochloric acid, it increases with polyester by saponification or thermal cleavage of increasing temperature in the acidic treatment in sorbic acid. The process is characterized by the fact that polyester draws the accumulation of vaporous chlorine, that one ketene with crotonaldehyde, the hydrogen. optionally 0.01 to 1%, based on the amount used. In general, small additions of salts are sufficient Crotonaldehyde, a sterically hindered phenolic acid. In order to facilitate the continuous work-up as Contains stabilizing agents, in the presence of tern, but it is advantageous that the weight-T ^ raalkyltuanaten, their straight-chain alkyl groups have a hydrochloric acid to polyester ratio of 1: 1 to 10: 1 or are branched and adjusts 2 to 18 carbon. atoms or condensation products thereof, 40 The saponification is the residence time to ^b e "temperatures ^{of 70 to uo} ° ^c> especially 80 to inversely proportional and lies between 50 and 100 ° C. 102 C. Both sizes can be different within the broadest limits. The polyester obtained may be by saponification or by. However, high saponification rates are preferred thermal cleavage are worked up. Da- temperature ^ for example 70 to 80 ° C, and short at the alkaline saponification requires large amounts 45 residence times, z. B. 0.5 to 1 hour, of alkali lye and mineral acid, which are in the form of the ent- The process can be batchwise or continuously speaking alkali salts are lost. Be carried out at the ther- mixing cleavage (distillation) will result in lower output The continuous operation is as follows prey achieved. In addition, the following occur during the continuous: Technically pure ketene is in the lower part of the process on. Reactor 4 (see FIG.) Introduced via line 5. Hei application of the acidic saponification, which as a result of this is fed simultaneously from below via line 3 of the low consumption of auxiliaries and the simple, catalyst-containing crotonaldehyde. ! The feasibility of an economic work-up of the reactor 4 via the degassing tube 6 escaping Tfh ™ ° / ^{tellt> cherishes the Sorbinsäureausbeute under} - ⁵⁵ exhaust gas in a reactor 4 downstream half 50 / _0th Raschigring column 2 fed in via line 1 A process has now been found for the preparation of fresh crotonaldehyde containing catalysts to counteract the gelation of sorbic acid by reacting ketene with leads. WS H rend at the upper end of column 2 via preferably stoichiometrically excess croton line 9 in ketene and crotonaldehyde-free exhaust gas aldehyde, which optionally escapes a sterically hindered 6 °, the outflow of column 2 contains lei-phenol, in the presence of Tetraa .Ikyltitanaten, device 3 fed to the reactor 4 as described, the alkyl groups of which are straight or branched chain. Through the overflow 7, the reactor residence time and 2 to 18 carbon atoms can be set, or can be adjusted. This can vary within wide limits condensation products and transfer of the ent. An advantageous residence times prove standenen polyester by saponification in sorbic acid ⁶ 5 of 2 to 5 hours. according to the process of the German patent. The reaction product obtained via line 7 1 293 752, which is characterized in that one is, for example, in a thin-film evaporator 8 the reaction of ketene with crotonaldehyde is continuously subjected to vacuum distillation, with