DE19514930A1 - Purification of synthetic carboxylic acid ester(s) - Google Patents

Abstract

Purification of synthetic carboxylic acid esters comprises treating the acid esters with one or more bases, ion exchange resins, adsorbing materials based on silica gel or an aluminosilicate, opt. scrubbing with water and removing the water, and opt. drying with a drying agent.

Description

Field of the Invention

The invention relates to a method for cleaning synthetic Carboxylic acid esters by neutralization, treatment with a Ion exchanger and treatment with a silicate adsorption material and their use for refrigeration oils.

State of the art

Synthetic carboxylic acid esters are an important class of technical compounds which is produced by esterification from alcohols and carboxylic acids. To The esterification often requires the products to be cleaned in order to unreacted starting materials, by-products or catalyst residues remove. A number of methods can be used, e.g. B. the Distillation, washing with cleaning liquids, such as aqueous bases, or treatment with solid adsorbents, e.g. B. bleaching earths.

The use of adsorbents based on silica gel or bleaching earth has in the chemical technology found widespread. The products are  often for cleaning gases and liquids, e.g. B. to decolorize Cooking oil used.

Certain classes of synthetic carboxylic acid esters are special high purity requirements. If e.g. B. for refrigerator oils synthetic carboxylic acid esters should be used, DIN 51 503, which relates to refrigeration oils based on mineral oils, be used. This standard prescribes a number of specifications including an acid number of <0.08 and a particularly low one Ash content of less than 0.01%.

Such particularly low key figures can be achieved using the Achieve prior art only with difficulty. At a Wet neutralization, for example, is particularly low acid numbers difficult to reach. The removal of catalyst residues can also be large To cause difficulties. The European patent EP-A1 449 406 suggests Adsorption process to achieve the key figures for refrigeration oils, and cites treatment with a zeolite as an example.

The object of the invention was to provide a method that allows synthetic carboxylic acid esters with particularly low To provide acid numbers and particularly low ash contents.

Surprisingly, it was found that synthetic carboxylic acid esters with low Acid numbers and low ash levels are available when initially using a base are neutralized, then an ion exchange treatment undergo and then for the removal of trace elements and color impurities of a treatment with a silicate Adsorption material are subjected.  

Description of the invention

The invention relates to a method for cleaning synthetic Carboxylic acid esters by taking the carboxylic acid esters in sequence

• - with one or more bases,
• - ion exchange resins
• - Adsorbent materials based on silica gel or aluminosilicate treated,
• - if necessary, wash with water and then separate the water and
• - if desired, dries with a drying agent.

Another object of the invention is the use of the purified esters as refrigeration oils.

Synthetic carboxylic acid esters are esters of carboxylic acids and alcohols.

Linear or branched monocarboxylic acids with 2 to 4 come as carboxylic acids 24 carbon atoms, preferably 4 to 18 carbon atoms. Furthermore come Di- or Polycarboxylic acids with 2 to 54 carbon atoms, preferably 2 to 18 carbon atoms in Consideration. Provide the dimer and / or trimer fatty acids and carbonic acid also represent polycarboxylic acids in the sense of the invention. Also aromatic Polycarboxylic acids such as B. the isomers of phthalic acid, trimellitic acid and the trimesic acid are carboxylic acids in the sense of the invention.

Linear or branched monofunctional alcohols with 1 to come as alcohols 22 carbon atoms into consideration. Polyfunctional alcohols with 2 to 8 also come  OH groups into consideration. Examples of diols are difunctional alcohols with 2 to 12 carbon atoms, e.g. B. 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 2-methyl-1,4-butanediol, 2,2- Dimethyl-1,3-propanediol, 1,6-hexanediol, 1,10-decanediol and 1,4-dihydroxymethyl cyclohexane. Examples of polyols are glycerol, trimethylolethane, Trimethylolpropane, pentaerythritol, ditrimethylolpropane, dipentaerythritol and Tripentaerythritol.

In the case of esters of polyols, all or at least one hydroxyl group can be used Carboxylic acids are esterified.

Both simple esters, i.e. H. Ester from a monofunctional alcohol with mono- or polyfunctional carboxylic acids or a monofunctional carboxylic acid and a mono- or polyfunctional alcohol as well as complex esters come into consideration as synthetic carboxylic acid esters.

Esters of neopentyl glycol or polyols and monocarboxylic acids are preferred with 4 to 7 carbon atoms and complex esters made of neopentyl glycol or polyols, Monocarboxylic acids with 4 to 7 carbon atoms and dicarboxylic acids with 4 to 8 carbon atoms Atoms.

When carrying out the method according to the invention, the remaining acid groups in the synthetic carboxylic acid ester from unreacted Neutralized carboxylic acid or catalyst with the help of bases. Preferred Bases are the hydroxides of the alkali and / or alkaline earth metals, namely preferably in the form of their aqueous solution.

The bases are used in amounts of up to 5%, preferably from 0.1 to 2% by weight. Active ingredient based on the synthetic carboxylic acid ester added, in any case but so much that all acid groups in the synthetic carboxylic acid ester can be neutralized.  

The neutralization is preferably carried out so that the synthetic carboxylic acid ester and the aqueous bases are mixed intensively by stirring. After the door tion of the organic and aqueous phase, the aqueous phase is separated. If instead of neutralization with an aqueous solution with bases in their is neutralized in the solid form, the solid is stirred intensively in the synthetic carboxylic acid esters and then by a Separation operation, preferably a filtration, separated.

The organic phase is also used in the process according to the invention Ion exchangers cleaned. Cations and are used as ion exchangers Anion exchangers or so-called mixed bed exchangers are Mixtures of cation and anion exchangers, in question. The application Mixed bed ion exchangers are preferred, but they can be used for cleaning Systems are also used in which the anionic and the cationic exchange components are separated. When using such The resins can be immobilized in separate systems, for example packed columns or in a movable form, for example in fluid beds are used.

The treatment with the ion exchange resins can also be carried out so that the Ion exchangers in amounts of 1 to 10 wt .-%, based on synthetic Carboxylic acid esters are added. Become cation and anion exchangers used separately, one of the two is first used in any order Types of exchangers added to the synthetic carboxylic acid ester, stirred and then filtered off.

If a mixed bed ion exchanger is used, only a single addition and Separation operation required. It is stirred and then the solid Ion exchange resin by a separation step, preferably a filtration severed.

After treatment with the ion exchangers, treatment is carried out with adsorbent materials based on silicate.  

For example, bleaching earths based on natural aluminosilicates can be used Use come such. B. bentonite, montmorrillonite, kaolinite or clay, the optionally activated by thermal and / or acid treatment could be.

Also alkali or alkaline earth alumosilicates, e.g. B. amorphous magnesium silicates in particular zeolites or the so-called molecular sieves can be used will.

Silica gel is preferably used. Silica gel or silica gel represents one water-containing to almost water-free amorphous colloidal silica, which has a porous structure with a surface area of up to 500 m² / g. It can from aqueous solution in the form of precipitated silica or by gas phase Reaction can be obtained as pyrogenic silica. Silica gels are still obtainable by hydrolysis or solvolysis of halogen and / or alkoxysilanes. Both wide-pore and narrow-pore gels are suitable.

A natural form of amorphous silica, which is also part of the Er can be used, the so-called diatomaceous earth, which represents consists mainly of deposits of fossil diatoms.

In the context of the invention, silica gels can also be used which are characterized by a Modification of the silica gel with organic substances were obtained. Organic acids are preferably used to modify the silica gel. The use of a keel is particularly preferred in the context of the invention selgels obtained by modification with citric acid. Such one The product is commercially available under the name Trisyl® 300 (Grace).

In addition, amorphous magnesium silicates are suitable, which have a MgO: SiO₂ ratio from 1: 3 to 1: 4.  

Treatment with adsorbent materials can be done simply by that after esterification to the synthetic carboxylic acid ester are given. The amounts can be between 0.1 and 5% by weight, preferably 0.5 up to 2% by weight, based on the synthetic carboxylic acid ester. The mixture of esters and adsorbent materials is expedient over a period of about 30 minutes to 5 hours at temperatures of stirred about 20 to 100 ° C. Then the adsorbent materials separated by filtration.

The solids content can be separated off by pressure filtration temperatures of the reaction mixture are particularly suitable above 50 ° C and in particular working temperatures in the range of about 70 to 90 ° C.

Another method according to the invention for the treatment of synthetic Carboxylic acid ester with adsorbent materials is that to fill adsorbent materials in a column and the material to be treated synthetic carboxylic acid ester with one of the column dimensions flow rate over the column.

Following treatment with silicate adsorbers, the synthetic one Carboxylic acid esters can be washed with water if desired. For this will the ester with water, preferably demineralized water, in amounts of 5 to 200 % By weight, based on synthetic carboxylic acid esters, and Temperatures below 30 ° C stirred for up to 1 hour. You leave the phases separate and separate the aqueous phase.

The organic phase, which is the synthetic carboxylic acid ester, is optionally dried in vacuo to remove residual water. If if desired, the carboxylic acid ester can subsequently be mixed with a drying agent, e.g. B. treated with a molecular sieve. The amount of desiccant is between  1 and 30 wt .-%, preferably between 5 and 10 wt .-%, based on the synthetic carboxylic acid ester.

The synthetic cleaned by the inventive method Carboxylic acid esters can be used as lubricants, for cosmetic purposes and are preferably used as refrigerator oils.

Examples

All percentages in the examples are understood, unless otherwise indicated, in percent by weight.

Raw materials

A complex ester was made from
505.1 grams of isovaleric acid (4.95 mol; 72.16% by weight),
161.8 grams of pentaerythritol (1.19 mol; 23.12% by weight) and
4.72 grams of adipic acid (0.23 mol; 4.72% by weight).

The mixture of isovaleric acid adipic acid and pentaerythritol was 0.1 % By weight of tin oxalate and with stirring in an esterification apparatus Water separator heated to a temperature of 180 to 250 ° C. That through the Water of reaction formed was continuously separated off. With excess isovaleric acid distilled off the water after the Water is separated, can be returned to the reaction circuit. As soon as no more water was separated off, the esterification was complete. In this way you get a raw complex ester that is on way is cleaned according to the invention.

Amberlit MB1 is a mixed bed ion exchanger.

Trisyl® 300, a silica gel modified with citric acid, was developed by Grace based.  

example 1

2 kg of the complex ester of isovaleric acid, pentaerythritol and adipic acid were mixed in a stirred vessel with 40 ml of 10% sodium hydroxide solution. After 10 The stirrer was switched off for minutes. After phase separation the aqueous phase separated. The organic phase was treated with 200 g of amberlite MB1 added and heated to 60 ° C with stirring for one hour. Subsequently the mixed bed ion exchanger was separated off by filtration.

The resulting complex ester was mixed with 66 g of Trisyl® 300 (3rd % By weight based on the monometer) and heated to 80 ° C. with stirring. After 30 minutes the absorbent material was filtered off and the organic Phase washed with demineralized water, then the Residual water in the ester is removed by drying in vacuo. It resulted in one complex ester with an acid number of 0.03 and an ash content of <0.05%.

The complex ester produced according to Example 1 had a tin content of 0 ppm and a sodium content of 1 ppm. One for comparison to conventional Type of complex ester produced by neutralization with aqueous sodium hydroxide solution has a tin content of 247 ppm and a sodium content of 1100 ppm.

Claims (8)

1. Process for purifying synthetic carboxylic acid esters by sequentially removing the carboxylic acid esters

• - with one or more bases,
• - ion exchange resins
• - Treated adsorbent materials based on silica gel or an aluminosilicate,
• - if necessary, washes with water and then separates the water and
• - if desired, dries with a drying agent.

2. The method according to claim 1, characterized in that as bases aqueous solutions of alkali and / or alkaline earth metal hydroxides be used. 3. The method according to claims 1 or 2, characterized in that mixed bed ion exchange resins used as ion exchange resins will. 4. The method according to claims 1 to 3, characterized in that as Silica gels treated with organic acids be used. 5. The method according to claims 1 to 4, characterized in that the organic acid represents citric acid.   6. The method according to claims 1 to 5, characterized in that the esters with the adsorbent materials according to claims 1 to 3 in amounts of 0.1 to 5 wt .-% - based on the carboxylic acid ester - mixes at temperatures from 20 to 100 ° C for a period of 30 Minutes to 5 hours and then the adsorbent materials separated by filtration. 7. The method according to claims 1 to 6, characterized in that one into the adsorbent materials according to claims 1 to 3 Column layers and the esters at temperatures of 20 to 100 ° C. a flow rate adapted to the column dimensions the column sends. 8. Use of synthetic carboxylic acid esters, prepared according to a Method of claims 1 to 7, as refrigerating machine oils.