DE869947C - Process for the continuous production of carboxylic acid esters. - Google Patents

Description

It is known that carboxylic acid esters with higher boiling points than those used for esterification can be used Alcohols, transesterified kano. The transesterification

R ₁ -COO-R ₂ + R ₈ -OH ^ R ₁ -COO-R ₃ + R ₂ -OH is an equilibrium reaction and is incomplete in the presence of the reaction products. It has therefore been suggested that the alcohol produced should be carried through. To remove distillation continuously in order to shift the equilibrium in the sense of the desired implementation. But it is not possible in this way, continuously and directly

Obtain pure esters because these are continuous through dlie Addition of starting materials are constantly contaminated again.

It has now been found that carboxylic acid ^ esters particularly simple and in pure form in continuous Operation can be established by transesterification, if one is in the upper part of a distillation column the mixture of an ester with a higher-boiling alcohol than that used for esterification was used, allowed to flow in and the column heated in such a way that the alcohol formed from the The reaction zone is continuously distilled off and

the "^ ntetandenie" ester at the bottom of the column, liquid, withdrawn! can be.

The process is suitable for the transesterification of esters, a: - and polybasic carboxylic acids of various kinds, e.g. B. of, aliphatic mono and ¹ Polycarbonsäuiren, such as butyric acid ', Laurini-. acid, oleic acid or stearic acid, oxalic acid, adipic acid, ketopimelic acid or sebacic acid, or of aromatic mono- and! Polycarboxylic acids,

ίο z. B. benzoic acid, salicylic acid or phthalic acid.

As alcohols both for the starting ester and

also come primarily for transesterification monohydric alcohols such as methanol, ethanol, prim., sec. and tert. Butanol, dodecyl alcohol, free oxy groups containing ethers and esters of polyhydric alcohols, e.g. B. glycol monoethers, and alcohol mixtures, z. B. initial fatty alcohol, the alcohol mixtures formed in the carbon dioxide lowering as well as' through reduction, through the accumulation of Carbon oxide and hydrogen on olefin mixtures resulting, aldehydes obtainable alcohols, into consideration. Also polyhydric alcohols, e.g. B. Ethylene glycol, polyethylene glycol, thiodiglycol, 1,3- and 1,4-butylene glycol, 1,6-hexanediol, hexanetriol, Trimethylol ethane and propane or pentaerythritol are suitable as starting materials.

The reaction is effected in such a way that a mixture of the ester with the alcohol, expediently in an equivalent ratio at the upper part of the column. It is useful Mixture preheated, as it flows through the column, the transesterification takes place. It is expedient to work at normal pressure, but it is also possible to work at reduced pressure, if the alcohol released during the transesterification has a relatively high boiling point.

The temperature of the column is chosen so

that the resulting ester is liquid at the bottom of the column can be drawn off and the alcohol released is continuously distilled off at the top.

To accelerate the transesterification, it is advisable to use esterification catalysts in the presence to work. For example, the starting mixture flowing in at the upper part of the column can be used add small amounts of mineral acid

or the column with a transesterification Fill favorable material, e.g. B. with silica

, gel, or other acidic catalysts, e.g. B.

Boron phosphate or solid hydrogen ion exchangers.

In order to be able to maintain the temperatures required for the process in the column. the column is equipped with special heating devices. It is expedient to surround it with an outer heating jacket and at the same time ensure that it can also be heated from the inside ¹ . For this purpose, the column can be designed, for example, in such a way that it is subdivided several times by a number of horizontal, perforated trays, on which the catalyst is arranged at a certain height of the layer. Between: a Katälysätorschicht and the underside of the floor above it _kai ™ <one each install a radiator, z. B. a heating coil. Depending on the boiling point ¹ of the substances flowing through the column, heating is either only done from the outside or only from the inside or with both heating devices.

Instead of only carrying out the conversion in the column, you can also proceed in such a way that you do it in two stages. For example · you can the reaction mixture in one of the column upstream Vessel, expediently in the presence of a catalyst, such as small amounts of concentrated sulfuric acid, as long as for the Reaction heat up the most suitable temperature until the equilibrium between the reaction part - takers has partially or completely discontinued, and then the reaction in the column with removal of the alcohol released from the reaction zone to the end.

In this way it is possible to transesterify carboxylic acid esters with alcohols higher than those which were used for the esterification, very quickly with excellent yields and conversions perform. According to the present process, the implementation is complete.

'■ Example · 1

Every hour, 600 cm ^{3 of} a mixture of 174.1 parts by weight of dimethyl adipate and 61312.71 parts by weight of decyl alcohol are added dropwise to the upper part of a column which is 2 m long and 30 mm in diameter. The column is filled with a coradensation product made from phenol, sodium sulfate and formaldehyde, hardened with concentrated sulfuric acid and washed out with water. This catalyst is treated with dilute hydrochloric acid, washed with distilled water and dried before use. The upper part of the colony. is set to 13 (01 to 135 °, the center of i-5Pi ° -. heated and the column foot at 170 to 175 ⁰ The liberated methanol distilled from the upper part of the column The Adipinisäuredecylester is withdrawn at the column foot by a siphon He.. is very pure and has the theoretically required saponification number.

Example 2

In the column described in Example 1, which is filled with boron phosphate, 4 (0O cm ³ per hour of a mixture of 1212, 1 part by weight of dimethyl phthalate and 1 and 1 parts by weight of hexamethylene glycol) are allowed to flow in. The upper part of the column is adjusted to 14p ⁰ ', the middle is ^{heated to 170I 01} and the column ^{foot to 190 0.} The methanol released distills over at the top of the column. The resulting ester of phthalic acid and hexamethylene glycol, a pale yellow, viscous liquid with the theoretically required saponification number, winds at the column foot withdrawn through a siphon.

Claims (1)

PATENT CLAIM: Process for continuous production . of carboxylic acid esters by transesterification of Carboxylic acid esters with higher boiling alcohols than those. Used for esterification were, appropriately in the presence of, esterification catalysts with continuous distillation of the resulting alcohol ·, d & dlurch characterized in that a mixture of the ester is placed in the upper part of a distillation column with the alcohol or a corresponding one up to a maximum of equilibrium. flow in the transesterified mixture, let and the column is heated in such a way that the alcohol formed continuously from the reaction zone! distilled off wind andi the resulting ester can be drawn off in liquid form at the base of the column. Referred publications:
U.S. Patents No. 2 oSu 322,227410.61; British Patent No. 346,486. I 5764 2.53