DE1057595B - Process for the preparation of dimethyl isophthalate - Google Patents

Description

GERMAN

The uncatalyzed esterification of isophthalic acid is known from British patent specification 695 566. According to the examples, the esterification at elevated pressure with an excess of alcohol and carried out at a temperature of over 150 ° C.

It is also known from British patent specification 728 997, solid aromatic dicarboxylic acids with superheated vaporous alcohols in the presence of non-volatile esterification catalysts implement and then withdraw the ester obtained in vapor form. The byproducts Ether then have to be separated off in a special way.

In the process according to the invention, the esterification is carried out in a known manner in the liquid phase performed. The esterification mixture is then cooled and the diester which has crystallized out is separated off in a known manner, e.g. B. by filtration, from. A considerable amount of mother liquor is obtained as the filtrate, which consists mainly of alcohol, and only small amounts of water, diesters and half-esters contains. In order to ensure an economical process, it is necessary to add the mother liquor attributed to the esterification.

Before the alcoholic mother liquor was returned to the esterification, it was previously considered necessary considers to rid them of water by single or multiple distillation. Especially when the esterification was carried out with methanol or ethanol, it was necessary to use large amounts of alcohol to fractionate in order to obtain the alcohol in a sufficiently anhydrous state. The presence that is, water has hitherto been viewed as very harmful to esterification.

It has now been found, surprisingly, that it is not necessary in the esterification of To completely separate isophthalic acid in the mother liquor before reusing it, if according to the invention the isophthalic acid with methanol in excess and in the absence of one Catalyst heated at elevated pressure and a temperature of over 150 ° C in the liquid phase, the on cooling separates off the crystallizing ester, and the alcoholic mother liquor obtained in this way directly or, after only partial removal of the water, is fed back to the esterification.

This procedure is of great advantage in the esterification of isophthalic acid with methanol which is often a 20 to 40 fold molar excess of alcohol is used.

The elimination of the dewatering of the mother liquor has a significant advantage. Also at an only partial separation of the water reduces the distillation costs compared to the previous one Operation considerably reduced. Low in the process for the production of dimethyl isophthalate

Applicant:

N. V. De Bataafsche Petroleum Maatschappij, The Hague

Representative: Dr.-Ing. F. Wuesthoff, Dipl.-Ing. G. Pulse and Dipl.-Chem. Dr. rer. nat. E. Frhr. v. Bad luck man,

Patent Attorneys, Munich .9, Schweigerstr. 2

Claimed priority: The Netherlands, January 6, 1956

Christiaan Pieter van Dijk, Jacobus Bastiaan de Jonge

and Nikolaas Max,

Amsterdam, Netherlands),

have been named as inventors

Amounts of monoester present in mother liquor are returned to the esterification stage without being isolated transferred into the diester.

The recycling of the mother liquor can of course be repeated several times before the process becomes unfavorable because of the excess water content. Since the water content of the esterification mixture the more often the esterification process is repeated, the more it increases, it gradually becomes less Obtain diesters and more monoesters.

Under no circumstances should the water content in the mother liquor exceed 30 percent by weight, because then further reuse of the mother liquor is not possible. Has this limit been reached? or slightly exceeded, it is necessary to start over using fresh alcohol or to separate all or part of the water from the mother liquor. This can be done in usual Way to be carried out. A particularly preferred process is the so-called expansion distillation (flash distillation) of the still hot Reaction mixture immediately after it has left the reaction vessel. The advantage of this procedure is that very little or even

909 527/430>

1,057,695

no heat has to be added. and that. the reaction mixture also cools down rapidly.

It is not necessary to take the water out. remove all of the mother liquor and then recycle the latter; it is sufficient if the water is separated from only part of the mother liquor ¹ .

The process according to the invention is illustrated in more detail by the following examples.

For example

83 g of isophthalic acid were mixed with 640 g of practically anhydrous methanol (water content approx 0.1 percent by weight) heated to 225 ° C for 3 hours in a 2 liter rotary autoclave, then the esterification mixture is cooled to 0 ° C, the crude diester is suctioned off and this with the

5. Washed amount of methanol, which is theoretically necessary 'to' esterify a further 83 g of isophthalic acid. This second part of isophthalic acid was then added to the mother liquor obtained in this way and this Mix in the same way as described above

ίο esterified. The esterification was a total of six times performed. The results obtained are shown in Table 1.

Amount of raw,
sucked off,
washed and
dried
Dimethyl ester
(ing) Together
Rea
(in(
mono-
methylestcr Tabel 1 In the mother liquor
after implementation
available water
(in percent by weight) Yield of the isolated
Diesters based on
the ever esterification
added isophthalic
acid
(in mole percent) No.
of the attempt 65 2.0 ab
ction product
Weight process
Dimethyl- '
ester sucked
it
It)
Isophthalic
acid 2.5 65.7 1 92 2.0 98.0 0 4.9 93.0 2 92 2.1 98.0 0 7.3 92.8 3 93 3.1 97.9 0 9.5 93.0 4th 94 3.5 96.9 0 11.5 93.4 5 96 8.0 96.5 0 13.4 91.0 6th 92.0 0

After six esterifications, 498 g (3 mol) of isophthalic acid became 513.4 g (2.65 mol) of diester and 18.6 g (0.10MoI) monoester obtained. The yield of diester and the monoester, calculated on the amount of isophthalic acid charged, was 88 and 3.3 mole percent, respectively.

Example 2

In order to determine the permissible amount of water, a series of further tests were carried out in the example 1 carried out autoclave described, wherein the temperature was 200 ° C and the residence time was 5 hours, while by adding known amounts of water, the selected methanol-water ratio at the beginning each attempt was different. In all experiments it was found that after a reaction time of 5 hours, with the reaction conditions maintained, the composition of the reaction product remained unchanged.

Table 2

The results of these tests are shown in Table 2.

Amount of water
in the mother liquor
(in percent by weight)

0
5

10
20th

Isophthalic

composition

of the reaction product

(in mole percent)

0
0
1
2

Monomethyl ester

4th
12th
17th
31

Dimethyl

96
88
82
67

Claims (3)

Patent claims: 1. Process for the production of isophthalic acid dimethyl esters, by esterification of isophthalic acid with methanol in excess in the absence a catalyst, at elevated pressure and a temperature of over 150 ° C in liquid phase, characterized in that the aqueous alcoholic mother liquor directly or after partial separation of the water formed during the esterification for re-esterification used. 2. The method according to claim 1, characterized in that the mother liquor in so long the reaction vessel is returned until the water content does not exceed 30 percent by weight. 3. The method according to claim 1 and 2, characterized in that there is as much water from the Separates mother liquor or part of the mother liquor, so that the water content is 30 percent by weight does not exceed. Considered publications:
British Patent No. 728 997. © 909 527/430 5.59