CS253633B1 - Method of metacrylic acid's 2-hydroxyethylester continuous refining - Google Patents

Abstract

A method of continuously refining 2-hydroxyethyl ester methacrylic acid from the reaction mixtures prepared by re-esterification with methyl or methacrylic acid ethyl esters with ethylene glycol under catalytic agitation alkali metal alcoholates, in particular methylate or sodium glycolate, optionally quaternary ammonium swamps. that the water-diluted reaction mixture is subjected to countercurrent continuous organic extraction solvent-type alkanes with temperature boiling point 40 to 120 ° C, preferably hexane or heptane under vibration motion, wherein the diluted reaction mixture is dispersed in drops into said alkane solvents.

Description

(54)

Process for the continuous refining of 2-hydroxyethyl methacrylic acid ester

A process for the continuous refining of 2-hydroxyethyl methacrylic ester from a reaction mixture prepared by re-esterification of methyl or ethyl methacrylic esters with ethylene glycol to catalyze the alkali metal alcoholates, especially sodium methylate or glycolate or quaternary ammonium bases, is to be subjected to continuous water dilution. an organic solvent of the alkane type having a boiling point of 40 to 120 ° C, preferably hexane or heptane, under the action of a vibration movement, wherein the diluted reaction mixture is dispersed into drops into said alkane solvent.

253 633

253 633

The invention relates to a process for the continuous refining of 2-hydroxyethyl methacrylic acid ester of the formula I

CH-C-COOCH 2 CH-OH (I)

CH from the reaction mixture. Compound 1 is a basic monomer that is converted by polymerization to hydrophilic polymers used in the field of medical orthotics, eg as a substitute for body organs, in the production of contact lenses, etc., and also for some industrial purposes, eg to consolidate granulated sorbents columns, etc.

On an industrial scale, a compound of formula I is produced primarily in two ways:

(a) From methacrylic acid which is condensed with ethylene oxide under the catalytic action of metal oxides such as copper, chromium or zinc. The 2-hydroxyethyl ester thus produced contains unreacted starting methyl methacrylic acid, undesired diglycol methacrylate and other reaction by-products in relatively high amounts and needs to be carefully refined, especially when used for medical prosthetics.

b) Reesterification of methacrylic acid methyl ester with ethylene glycol under the catalytic action of alkali metal alcoholates, preferably sodium methylate, sodium glycolate or quaternary ammonium bases. The product obtained in this way always contains a substance resulting from the double re-esterification of ethylene glycol with methyl methacrylate (hereinafter referred to as diester) of the formula II

CH

AND

CH ₂ = C-COOCH ₂ -CH ₂ 00 C-C = CH ₂ (II),

253 633 which is produced in an amount of up to 7 wt. %, further contains unreacted methylmethacrylates and glycol and finally methanol. Of the monomer of the formula I, which in particular contains the diester of the formula II in an amount above 1 wt. Some types of contact lenses cannot be produced at all because the polymer is not mechanically satisfactory, especially during machining. The advantage of this preparation method is that the reaction mixture never contains unreacted methyl methacrylic acid. Numerous experiments have shown that the diester of formula II cannot be removed by fractional distillation or by modification of the reaction conditions of said reesterification.

The only known refining process is based on the liquid extraction described in the description of the invention to the U.S. Pat. The extraction is carried out by repeatedly dispersing the reaction mixture, which is diluted 2: 1 with water into an organic phase, such as petroleum ether or alkanes. Extraction is performed by rotary movement and subsequent settling of the liquid phases.

It has now been found that 1: 4 aqueous raffinate to organic solvent is best dosed each time. In this way unreacted methyl methacrylic acid methyl ester and diester of formula II are extracted, while the 2-hydroxyethyl ester of formula I remains in the aqueous phase to which sodium chloride is added in a 1: 1 weight ratio based on the ester. Extraction of the methacrylic acid ester is then carried out again by repeatedly dispersing the aqueous phase into ether in a 4: 1 weight ratio.

In both cases the pure solvent is always used for repeated scattering and settling.

The method described has several drawbacks. First of all, it is batch-wise, which brings about a rapid increase in the volume of equipment with an increase in production capacity and a significant proportion of manual skilled labor.

Furthermore, only one-time contact with the solvent is envisaged, which leads to a large consumption of solvent and high energy consumption during its regeneration. Another major disadvantage of the described process is the release of the ester of formula I from the aqueous phase by salting out, causing corrosion of the equipment and contamination of the aqueous solution of unreacted glycol with sodium chloride, thereby preventing subsequent use of ethylene glycol and finally resulting in large losses of up to 5%

253 B33

The process for the continuous refining of 2-hydroxyethyl methacrylic acid 2-hydroxyethyl ester according to the present invention is characterized in that the reaction product diluted with water at a weight ratio of 12 is continuously fed in close countercurrent contact with a water immiscible organic alkane solvent boiling at 0 to 120 ° C. by dispersing the aqueous phase in the droplets into the organic solvent by means of a vibration motion. The droplets of the water phase sink downwards because they have a specific gravity higher than the organic solvent. The solvent saturated with unreacted methacrylic acid methyl ester and diester of formula II is treated by distillation refining, while the aqueous phase containing 2-hydroxyethyl methacrylate and unreacted ethylene glycol is again fed continuously in close contact with the organic solvent with a water immiscible ether, for example diethyl ether. The aqueous phase is dispersed into drops into an organic solvent, such as diethyl ether, or the solvent is dispersed into drops into the aqueous phase by means of a vibrational movement. The aqueous phase containing ethylene glycol is returned to the reaction after concentration or is useful as an antifreeze. The ether phase is fed to a continuous film evaporator where the ether is separated from the refined 2-hydroxyethyl methacrylic acid ester of formula I.

The operating temperature during contacting is maintained between 15 and 50 ° C, preferably 20 ° C. The process of continuous refining 2-hydroxyethyl methacrylic acid ester from the reaction mixture after re-esterification of the methacrylic acid methyl ester with ethylene glycol according to the present invention allows far to overcome the disadvantages of the prior art methods of removing unreacted feedstocks. contacting the product-containing aqueous phase droplets with an ether solvent using a vibration motion ensures a high degree of refining of 2-hydroxyethyl methacrylic acid ester with minimal solvent consumption, human skilled labor and minimal equipment volume, with product losses not exceeding 12%. It also removes the disadvantageous salting out of the ester of the formula I from the aqueous phase during the extraction with ether. The process according to the invention has been verified in laboratory and pilot plant and has been found to provide high purity products with a diester content of formula II of less than 0.5 wt.

- For these purposes, this degree of purity is sufficient. ^{253 633}

The details of the method according to the invention are described in more detail in the following examples, but the method is not limited thereto.

Example 1 liters of the reaction mixture after re-esterification containing 48% by weight of the compound of formula I, 7.0% by weight. % diester of formula II, 5 > % methyl methacrylate, 26.3 wt. ethylene glycol was diluted with 3 liters of water and cooled to 20 ° C. Thereafter, the reaction mixture was subjected to hexane extraction with hexane at a flow rate of 1: 1.2. The obtained aqueous raffinate contained less than 0.05 wt. % diester of formula II, 18.7 wt. % of the ester of formula I and 10.4 wt. ethylene glycol. Further, the raffinate thus obtained was extracted with ethyl ether at a flow rate ratio of 1: 1.5. The extract obtained was concentrated on a vacuum film evaporator. The resulting 2-hydroxyethyl methacrylate ester contained 0.25 wt. % diester of formula II and 3.1 wt. ethylene glycol. Both extractions were performed on a countercurrent column with vibrating trays ·

Example 2 liters of the reaction mixture after re-esterification having the same composition as in Example 1 was diluted with 3 liters of water and cooled to 20 ° C. The reaction mixture treated in this way was subjected to extraction with petroleum ether in a flow ratio of 1: 1.3. The obtained aqueous raffinate contained 0.07% by weight of diester of formula II,

17.3% wt. % of the ester of formula I and 9.6 wt. ethylene glycol. This raffinate was subjected to extraction with diisopropyl ether at a flow rate ratio of 1: 1.7. The obtained extract was stripped of solvent on a vacuum film evaporator. The resulting methacrylic acid 2-hydroxyethyl ester product contained 0.23% by weight of diester of formula II and 2.9% by weight of ethylene glycol · The yield of ester of formula I based on the ester content of the reaction mixture was 89% · Both extractions were performed on a countercurrent column with vibrating patry ·

Claims (5)

SUBJECT OF THE INVENTION 253 R33 Process for continuously refining methacrylic acid 2-hydroxyethyl ester from a reaction mixture prepared by re-esterifying methyl or ethyl methacrylic esters with ethylene glycol under the catalytic action of alkali metal alcoholates, in particular sodium methylate or glycolate or quaternary ammonium bases, characterized by subjecting the water-diluted reaction mixture to countercurrent continuous extraction with an alkane-type organic solvent having a boiling point of 40 to 120 ° C, preferably with hexane or heptane under the effect of a vibration movement, the diluted reaction mixture being dispersed into drops into said alkane solvent · Process according to claim 1, characterized in that the extraction is carried out at temperatures of 5 to 35 ° C, preferably 20 ° C. 3. A process according to claim 1, wherein the ratio of the volumetric flow rates of the aqueous solution and said alkane solvent is between 11 and 14, preferably 11, Process according to any one of claims 1 to 3, characterized in that the reaction mixture is subjected to a subsequent countercurrent continuous extraction with an ether solvent, preferably diethyl ether, under a vibration motion, dispersing the reaction mixture into the ether solvent or dispersing it as droplets. to reaction mixture · 5. The method according to claim 4, wherein the ratio of the volume flow rates of the aqueous solution and said ether solvent is 1 to 4, preferably 1.5 to 1.5.