WO1994017027A1

WO1994017027A1 - Process for preparing lower alcohol fatty acid esters

Info

Publication number: WO1994017027A1
Application number: PCT/DE1994/000057
Authority: WO
Inventors: Manfred Gross; Gerda Tschampel
Original assignee: Chemische Und Pharmazeutische Fabriken Fahlberg-List Gmbh I.L.
Priority date: 1993-01-22
Filing date: 1994-01-19
Publication date: 1994-08-04
Also published as: HUT68284A; HU214203B; HU9402716D0; RU94042226A; DE4301686C1; EP0629185A1; PL305263A1; RU2127251C1

Abstract

A process is disclosed for preparing fatty acid esters of lower monohydric n-alcohols by transesterifying fatty acid glycerides in the presence of basic catalysts. The process is characterized in that after transesterification the ester phase is washed with glycerine, raw glycerine from glycerine preparation or the glycerine phase from a previous transesterification step, is completely separated from the last glycerine phase and is treated with bleaching earth, silicic acid or other physico-chemically similar substances. Without aqueous washing processes and without using aqueous acids for neutralizing the catalyst in the ester phases, this process, unlike known processes, allows products to be obtained from non-refined native oils having a quality which otherwise is only attainable by using purified oils and aqueous process steps.

Description

description

Process for the preparation of fatty acid esters of lower alcohols

The present invention relates to a process for the preparation of fatty acid esters of lower monohydric n-alcohols having 1 to 4 carbon atoms by transesterification of fatty acid glycerides with the corresponding alcohols in the presence of basic catalysts under special work-up conditions.

For the use of the fatty acid esters produced in this way as raw materials, in particular the methyl esters as diesel fuel, special quality parameters must be observed which make suitable manufacturing and cleaning technologies necessary.

The production of such fatty acid esters has long been known and is carried out on an industrial scale by base-catalyzed transesterification of fatty acid glycerides with lower monohydric alcohols under different reaction conditions (DE-OS 3 020 612; DE-OS 3 421 217; DE-OS 3 932 514; DE -OS 3 727 981; EP 0 391 485; WO 92/00 268). To achieve high conversion rates, it is necessary to carry out the reaction in two or more stages, to optimally design the ratio of the reactants to one another and to remove the reaction by-product glycerol from the reaction equilibrium continuously. It is also known that purified and unpurified oils and fats of natural origin and native waste oils which differ in their free fatty acid content and therefore require different amounts of catalyst can be used as starting products for the transesterification reaction. lend. An essential part of the known processes is the purification of the fatty acid esters to standards conforming to the standards, the removal of the residual amounts of glycerol and the catalyst in connection with the alcohol excess required for the complete transesterification being considered as a unit.

Significant disadvantages of the known methods exist in the purification by distillation in high energy costs as well as expensive technical equipment and in the use of water to remove residual glycerol, soaps, catalyst, excess alcohol and other water-soluble products in the accumulation and treatment of contaminated process wastewater or a glycerol phase diluted with water. When using purified native oils and fats in the transesterification process, organically contaminated washing and process water are obtained already during refining.

It was therefore an object to search for a process which avoids the disadvantages mentioned and enables the production of fatty acid esters in standard quality from triglycerides without the use of washing water and process water.

Surprisingly, it was found that the disadvantages of the known processes can be avoided if the fatty acid glycerides are mixed with a lower monohydric n-alcohol with 1 to 4 carbon atoms in a molar ratio of 1: 3 to 1: 6, in particular 1: 3.5 to 1: 5 in the presence of an alkali catalyst, in particular sodium or potassium hydroxide, dissolved in the lower alcohol in an amount of 0.01 mol to 0.05 mol, in particular 0.02 mol to 0.035 mol, based on 100 g of the fatty acid glyceride used plus the alkali - amount, which is equivalent to the acidic components contained in the fatty acid glycerides, at temperatures from ambient temperature to 70 ° C, in particular at 40 ° C to 60 ° C, after an at least two-step conversion process, after transesterification, the fatty acid ester phase to remove remaining impurities cleaning and a better phase separation with glycerin, crude glycerin from the working-up process of the glycerin or glycerin phase from the previous transesterification stage and then washing with a bleaching earth, silica or other physico-chemically similar substances, in an amount of 1% to 5%, in particular 1.5% treated up to 3% based on the fatty acid glyceride used. The amount of glycerin used for washing is dependent on the amount of impurities remaining in the ester phase, in particular dissolved glycerol, catalyst residue, soaps, excess alcohol and other substances which reduce the specific weight of the heavier glycerol phase which precipitates and on the purity and density of the used washing glycerin.

It is advantageous to choose the amount and quality of the washing glycerol in such a way that a density of 1.03 g / cm ³ (20 ° C.) in the glycerol phase to be separated is not undercut. The washing process can be carried out with stirring using the technological systems customary for this after the transesterification has taken place and before or after the separation of the last glycerol phase in multi-stage procedures, although it is not necessary to separate the last glycerol phase before adding the washing glycerol.

In contrast to the known methods in which the separation of the last glycerol phase alone, or together with washing water is problematic because of the time-consuming phase separation or emulsion formation, the process according to the invention gives a good washing and cleaning effect of the ester phase but no phase separation problems, and the ester phase can be separated after a short time, which also means that space-time Yield of the process is significantly improved. In addition, there is no contaminated waste water or a glycerol phase diluted with water. Surprisingly, the glycerol wash neither delays the reaction equilibrium of the transesterification reaction, nor increases the concentration of free or bound glycerol in the end product. The complete separation of the heavier glycerol phase can optionally be accelerated or improved by using a coalescence separator or separator.

Another disadvantage of the known processes is the use of aqueous organic or inorganic acids, acid salts or of ion exchangers for neutralizing the alkalinity of the ester phase. However, the acids are released from the fatty acid salts still present, which leads to an increase in the acid number of the end product, since the free fatty acids dissolve better in the ester phase than in an aqueous glycerol phase.

According to the method according to the invention, the residual alkalinity of the ester phase is removed by treatment with bleaching earth, silica or other physico-chemically similar substances. For this purpose, the ester phase with such a substance, in particular in an amount of 1% to 5% 1.5% to 3% based on the fatty acid glyceride used at process temperature delt. This process is not identical to the known bleaching earth treatment in the refining of vegetable oils. The treatment can be carried out separately or in conjunction with the removal of the volatile components from the ester phase. The separation of the contaminated bleaching earth from the ester phase is carried out using filters or centrifuges and is unproblematic. The use of bleaching earth or similar adsorbents has the further advantage that other hydrophilic impurities such as e.g. B. glycerol, glycerides or oil-soluble plant ingredients are removed with. When using unpurified fatty acid glycerides or native waste oils as raw materials for the transesterification process, this process step is of great advantage and leads to good quality parameters of the end product, and in particular with native waste oils with special impurities, special sorbent systems can also be used for cleaning.

The invention is illustrated by the following examples:

example 1

4.5 g of potassium hydroxide are dissolved in 47.5 g of methanol and 55 ml of this solution are added to 300 g of unpurified rapeseed oil (acid number 1.2) with stirring at room temperature. The mixture is then heated to 60 ° C. and stirred at this temperature for 30 min. After one hour, the heavy glycerol phase is separated off (46 ml; D. 1.085 g / cm ³ (20 ° C.)). The remaining amount (7 ml) of the methanolic potassium hydroxide solution is added to the ester phase. The mixture is stirred at 40 ° C. for 30 min, then with 10 ml of crude glycerol (D. 1.260 g / cm ³ (20 ° C)) and stirred for a further 30 min. After two hours, the glycerol phase (20 ml; D. 1.127 g / cm ³ (20 ° C)) is completely separated. After treatment with 6 g of bleaching earth at process temperature and simultaneous removal of the volatile components, after suctioning off the contaminated bleaching earth, 270 g of light yellow standard-compliant rapeseed methyl ester are obtained. (Content of glycerides <0.1%; free glycerin <0.001%; acid number 0.23; pH value 5.6. The pH value was measured in the aqueous phase when rapeseed methyl ester was poured out with the same volume of distilled water .)

Example 2

Reaction control analogous to Example 1 using 6 g of silica for treatment at process temperature and simultaneous removal of the volatile components. 265 g of rape methyl ester conforming to standards are obtained. (Glycerides content <0.1%; free glycerin <0.01%; acid number 0.15; pH 5.8.)

Example 3

Reaction control analogous to Example 1 using 20 ml glycerol phase from the first esterification stage (D. 1.075 g / cm ³ (20 ° C)) as a washing medium. 30 ml of second glycerol phase with a density of 1.059 g / cm ³ (20 ° C.) and 272 g of rapeseed methyl ester conforming to standards are obtained. (Glycerides content <0.1%; free glycerin <0.001%; acid number 0.25; pH 5.4.) Example 4

Reaction procedure analogous to Example 3 using deep-frying oil (acid number 1.8) as the starting product and an amount of potassium hydroxide of 5.2 g. First glycerol phase: 49 ml, D. 1.057 g / cm ³ (20 ° C) Second glycerol phase: 30.5 ml, D. 1.030 g / cm ³ (20 ° C) Waste oil methyl ester: 262 g; Glycerides content <0.2%; free glycerin <0.01%; Acid number 0.4; pH 5.8.

Example 5

0.72 g of sodium are dissolved in 22 g of ethanol (96%) and 85% of this solution is added to 100 g of rapeseed oil refinery with stirring at room temperature. The mixture is then heated to 45 ° C. and stirred at this temperature for 30 min. The mixture remains overnight and the heavy phase is separated by centrifugation. (For better phase separation, the reaction mixture of the first transesterification stage can already be treated with glycerol.) The remaining amount of the sodium alcoholate solution is added to the ester phase. The mixture is stirred at 40 ° C. for 30 min, then 5 ml of glycerol are added, the mixture is stirred for a further 20 min and completely separated from the glycerol phase. After treatment with 2 g of bleaching earth analogous to Example 1, 54.2 g of rapeseed oil ethyl ester are obtained (content of glycerides <0.1%; free glycerol <0.001%; acid number 0.15; pH value 5.7).

Example 6

Reaction control analogous to Example 5 using 25 g of n-propanol and a reaction time of 4 hours at 70 ° C. 62 g of rapeseed oil n-propyl ester are obtained (content of glycerides <0.1%; free glycerol <0.001%; acid number 0.18; pH 5.9).

Example 7

Reaction control analogous to Example 5 using 31 g of n-butanol and a reaction time of 4 hours at 70 ° C. This gives 82 g of rapeseed oil n-butyl ester (content of glycerides <0.15%; free glycerol <0.001%; acid number 0.21; pH 6.1).

Claims

1. Process for the preparation of fatty acid esters of lower monohydric n-alcohols having 1 to 4 carbon atoms by transesterification of fatty acid glycerides with the lower alcohols in the presence of basic catalysts, characterized in that after the transesterification, the ester phase with glycerol, crude glycerol or Glycerol phase of a previous transesterification stage is washed, completely separated from the last glycerol phase and treated with bleaching earth, silica or other physico-chemically similar substances in an amount of 1% to 5%, based on the fatty acid glyceride used.

2. The method according to claim 1, characterized in that the addition of the washing glycerol takes place before the separation of the last glycerol phase.

3. The method according to claim 1, characterized gekennzeich¬ net that the amount of bleaching earth, silica or other physico-chemically similar substances used is 1.5% to 3% based on the fatty acid glyceride used.

4. The method according to claim 1 and 2, characterized gekenn¬ characterized in that the density of the glycerol phase to be separated 1.03 g / cm ³ (20 ° C) does not undercut.