DE4301686C1 - Fatty acid ester prodn by glyceride transesterification - using glycerol to wash ester phase - Google Patents

Abstract

Prodn. of fatty acid esters is effected by: (a) transesterifying fatty acid glycerides with a 1-4C n-alkanol in the presence of a basic catalyst; (b) washing the ester phase with glycerol, crude glycerol or the glycerol phase from a previous transesterification stage; (c) separating the ester phase from the glycerol phase; and (d) treating the ester phase with 1-5% (based on amt. of glyceride) of fuller's earth, silicic acid or a physicochemically similar substance. USE/ADVANTAGE - Methyl esters are useful as diesel fuels. The process gives high-quality prods. without the need for water or acid washing, without phase sepn. problems, and without the need to distil the prod., even when unrefined oils are used as starting materials.

Description

The present invention relates to a method for manufacturing of fatty acid esters of lower monohydric n-alcohols with 1 to 4 C atoms by transesterification of fatty acid glycerides with the ent speaking alcohols in the presence of basic catalysts special processing conditions.

For the use of the fatty acid esters produced in this way as raw material Especially the methyl esters as diesel fuel are special Maintain quality parameters, the appropriate manufacturer Make cleaning 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 Um esterification of fatty acid glycerides with lower monovalent alcohols fetch under different reaction conditions (DE-OS 3 020 612; DE-OS 34 21 217; DE-OS 39 32 514; DE-OS 37 27 981; EP 0 391 485; WO 92/00 268). It is to achieve high implementation rates required to run the reaction in two or more stages lead, the relationship of the reactants to each other optimally designed and the reaction by-product glycerol constantly removed from the reaction equilibrium. Farther is known as starting materials for the transesterification craze tion purified and unpurified oils and fats of natural origin future as well as native waste oils that are found in differ in their free fatty acid content and therefore under make different amounts of catalyst necessary. An essential The cleaning of the fatty acid is part of the known method reester to standard-compliant qualities, the removal of the Residual amounts of glycerin and the catalyst in connection with the excess alcohol required for complete transesterification it should be viewed as a unit.

Significant disadvantages of the known methods exist in the Purification by distillation in high energy costs as well expensive technical equipment and in use of water to remove residual glycerin, soaps, catalyst, excess alcohol and other water soluble products in the  Accumulation and the treatment of contaminated process wastewater or one Glycerol phase diluted with water. When using clean native oils and fats fall into the transesterification process ganically polluted washing and process water already at Raf fination.

So the task was to look for a procedure that avoids the disadvantages mentioned and the production of Fatty acid esters in standard quality from triglycerides without enables the use of washing and process water.

Surprisingly, it was found that the disadvantages of the be Known procedures can be avoided if you look at the fatty acid reglycerides with a lower monohydric n-alcohol with 1 to 4 C 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 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 amount of alkali that in the fatty acid glycerides contained acidic components is equivalent, at temperatures from ambient temperature to 70 ° C, especially at 40 ° C to 60 ° C, after an at least two-stage transesterification process implements, after the transesterification, the fatty acid ester phase Removal of remaining contaminants and a better one Phase separation with glycerin, raw glycerin from the workup process of glycerin or glycerin phase from the previous Transesterification stage and then with a bleaching earth, Silica or other physico-chemically similar substances, in an amount of 1% to 5%, in particular 1.5% to 3% gene treated for fatty acid glyceride used. The amount of Glycerin used for washing depends on the amount of impurities remaining in the ester phase in particular dissolved glycerin, catalyst residue, soaps, excess Alcohol and other substances that make up the specific weight of falling heavier glycerin phase and decrease from the pure unit and density of the washing glycerin used.  

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

In contrast to the known methods in which the separators Last glycerin phase alone, or together with washing water because of the time-consuming phase separation or emulsion education is problematic occur after the invention Process a good washing and cleaning effect of the ester phase but no phase separation problems, and the ester phase can can be separated after a short time, which also the Space-time yield of the process is significantly improved. In addition, no contaminated wastewater or one with water falls diluted glycerol phase. Surprisingly, the Glycerol wash neither the reaction equilibrium of the transesterification reaction delayed, nor the concentration of free or ge bound glycerin increased in the final product. The complete Ab separation of the heavier glycerol phase can be done if necessary the use of a coalescence separator or separator be accelerated or improved.

Another disadvantage of the known methods is their use aqueous organic or inorganic acids, acid salts or of ion exchangers to neutralize the alkalinity of the Ester phase. However, fatty acids are still present Salted the acids released, causing an increase in acidity Number of the final product leads, since the free fatty acids are water in the ester phase than in an aqueous glycerol phase.

The residual alkalinity of the Ester phase by treatment with bleaching earth, silica or other physico-chemically similar substances removed. To  the ester phase with such a substance in a Amount of 1% to 5%, in particular 1.5% to 3% based on used fatty acid glyceride treated at process temperature. This process is not identical to the known bleaching earth treatment in the refining of vegetable oils. The treatment can be used 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 through filters or centrifuges and is not a problem. The use of Bleaching earth or similar adsorbents still has the Advantage that other hydro remaining in the ester phase phile impurities such as B. glycerin, glycerides or oil soluble phytonutrients are also removed. When using raw crude fatty acid glycerides or virgin waste oils This process step is material for the transesterification process of great advantage and leads to good quality parameters of the End product, especially with native waste oils with spe special sorbent systems can 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) while 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 10 ml of crude glycerol (D. 1.260 g / cm ³ (20 ° C.)) are added and the mixture is 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.

(Glycerides content <0.1%; free glycerin <0.001%; acid number 0.23; pH 5.6. The pH was in the aqueous phase Distribution of rapeseed methyl ester with the same volume de still water measured.)

Example 2

Reaction control analogous to Example 1 using 6 g Kie silica for treatment at process temperature and simultaneously Removal of volatile components. 265 g are obtained Rapeseed methyl ester conforming to standards.

(Glycerides content <0.1%; free glycerin <0.01%; acid number 0.15; pH 5.8.)

Example 3

Reaction procedure 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 control analogous to Example 3 using deep fryer waste oil (acid number 1.8) as a starting product and a potassium 5.2 g of hydroxide.

First glycerol phase: 49 ml, D. 1.057 g / cm ³ (20 ° C)
Second glycerin 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 sodium are dissolved in 22 g ethanol (96%) and 85% this solution to 100 g of rapeseed oil refinery with stirring in the room temperature added. The mixture is then heated to 45 ° C. and Stirred at this temperature for 30 min. The mixture remains Stand overnight and the heavy phase is removed by centrifugation Cut. (For better phase separation, the Reak tion mixture of the first transesterification stage treated with glycerol The remaining amount of the Added sodium alcoholate solution. The mixture is at 30 min Stirred at 40 ° C, then mixed with 5 ml glycerol, more Stirred for 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 (content of glycerides <0.1%; free Glycerin <0.001%; Acid number 0.15; pH value 5.7.)

Example 6

Reaction control analogous to Example 5 using 25 g n-propanol and a reaction time of 4 hours at 70 ° C. Man receives 62 g rapeseed oil n-propyl ester (content of glycerides <0.1%; free glycerin <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. 82 g of rapeseed oil n-butyl ester are obtained (content of glycerides <0.15%; free glycerol <0.001%; acid number 0.21; pH 6.1 ) .

Claims (4)

1. A process for the preparation of lower fatty acid esters of 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 followed, the ester phase with glycerol, crude glycerol or glycerol phase Wash the previous transesterification stage, 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 Add wash glycerin before separating the last one Glycerin phase takes place. 3. The method according to claim 1, characterized in that the Amount of bleaching earth, silica or others used 1.5% to 3% related to physico-chemically similar substances on fatty acid glyceride used. 4. The method according to claim 1 and 2, characterized in that the density of the glycerol phase to be separated does not fall below 1.03 g / cm ³ (20 ° C).