DE102009006920A1 - Producing fatty acid alkyl ester comprises e.g. mixing fats or oils, alkyl alcohols and catalyst, separating mixture into low, ester-rich phase and heavy glycerin-rich phase, and separating fatty acid alkyl ester from low, ester-rich phase - Google Patents

Abstract

Producing fatty acid alkyl esters by transesterification of fats or oils with alkyl alcohols, comprises mixing the fats or oils and alkyl alcohols, and a catalyst in a mixing reactor (2, 5) in at least one reaction steps (1, 4); separating the resulting mixture into a low, ester-rich phase and a heavy glycerin-rich phase; separating fatty acid alkyl ester from the low, ester-rich phase; and contacting the fat or oil and/or raw alkyl ester produced by transesterification and/or biodiesel end products obtained after the separation of byproducts, with a strong organic or strong inorganic acids. Producing fatty acid alkyl esters by transesterification of fats or oils with alkyl alcohols, comprises mixing the fats or oils and alkyl alcohols, and a catalyst in a mixing reactor (2, 5) in at least one reaction steps (1, 4); separating the resulting mixture into a low, ester-rich phase and a heavy glycerin-rich phase in a separator (3, 6, 21); separating fatty acid alkyl ester from the low, ester-rich phase; and contacting the fat or oil and/or the raw alkyl ester produced by transesterification and/or biodiesel end products obtained after the separation of byproducts, with a strong organic or strong inorganic acids. Independent claims are included for: (1) agents to avoid or eliminate sterol glycoside containing precipitates in the production of fatty acid alkyl esters, where the agent is a strong organic or strong inorganic acid; and (2) a plant for the production of fatty acid alkyl esters, comprising, in at least one reaction steps, a mixing reactor for mixing the fats or oils with the alkyl alcohols and a separator in which the mixture is separated into a low, ester-rich phase and a heavy, glycerin-rich phase, and a separator (21) for separating fatty acid alkyl ester from the low, ester-rich phase, and a mixing device (26, 27, 28) for mixing the supplied fats or oil and/or raw alkyl ester produced by transesterification and/or the biodiesel end products obtained after the removal of byproducts with the agent, as ingredients.

Description

The The invention relates to the preparation of fatty acid alkyl esters by transesterification of fats and oils with alkyl alcohols in at least one reaction stage consisting of a mixing reactor, in which the fats and oils with the alkyl alcohols and a catalyst, and a separator in which the resulting mixture into a light, ester-rich phase and a heavy, glycerol-rich phase is separated, followed by from the light, ester-rich phase fatty acid alkyl esters separated.

Processes for the conversion of vegetable oils or animal fats to fuels by transesterification of the glycerol-bound fatty acids (triglycerides) with short-chain alcohols, such as, for example, methanol, are known. So will in the FR 996 608 the transesterification of palm oil with methanol or ethanol in the presence of a strong inorganic acid, such as hydrochloric acid or sulfuric acid, described as a catalyst for the purpose of fuel production.

The FR 2 560 210 describes the preparation of a methyl, ethyl, propyl or butyl ester of fatty acids from vegetable oils or animal fats and the use of the product as a diesel fuel. The light, non-polar, fatty acid ester-containing phase is separated from the heavy, polar, glycerol-containing phase. To improve the combustion properties, the product phase is treated with an adsorbent.

In the in the WO 87/07632 A1 described method, the production of biofuel starting from triglycerides in a two-stage process, where first a raw triglycerides containing substance reacts with an alkanol in the presence of a catalyst to convert the contained in the crude triglycerides border substance contained fatty acids in their alkyl esters. The product of the first process step is washed with an aqueous detergent to form a two-phase organic system, wherein the catalyst is transferred from the reaction mixture to the aqueous phase.

A modern process for the production of fatty acid methyl ester or fatty acid ethyl ester and glycerol by transesterification of fats or oils is in EP 0 532 767 B1 described. In this process, the reaction of the oil or fat with methanol or ethanol and an alkaline catalyst in the liquid phase to the products fatty acid methyl ester or fatty acid ethyl ester and glycerol, which are obtained separately and are value products of the process. The process works with at least two reaction stages, each reaction stage comprising a single or multistage mixing reactor and a separator for separating a light, ester-rich phase and a heavy, glycerol-rich phase. The heavy phase recovered in the separator of the second to last reaction stage is at least partially recycled to the mixing reactor of the first reaction stage. The ester products of the process after processing and purification as a so-called biodiesel represent a marketable product.

It it is known that the use of certain vegetable oils, in particular from cost-optimized oil work, in Conversion to fatty acid methyl ester or fatty acid ethyl ester (Biodiesel) to Feststoffausfällungen in the manufacturing process or during subsequent storage of the product at cold ambient temperatures can lead. This behavior is pronounced, for example. to observe when using soybean oil or palm oil. In the processing of such oils is therefore an increased Maintenance required for the production plant. In addition, the availability and thus the productivity The production facility is restricted as it is for maintenance and Elimination of Feststoffausfällungen except Operation must be taken. The precipitates can separated by mechanical methods, such as filtration or centrifugation become.

Responsible for the formation of the precipitates are so-called sterol glycosides (SG), which are widespread herbal ingredients that result from the combination of a sugar (glucose) with a phytosterol. Phytosterols are plant hormones and are components of plant cell membranes. Known representatives are stigmasterol or campesterol, whose structural forms in 1a respectively. 1b are shown. In addition, on the US 4 112 218 directed.

In the WO 2007/076163 A2 describes the addition of an adsorbent or filtration aid to separate the solid precipitates from biodiesel and its subsequent removal by filtration or centrifugation. However, this treatment is possible in a simple manner only for the finished biodiesel product. The elimination of precipitations that have already occurred in the production plant can be carried out by this measure only with great effort. From the WO 2007/076163 A2 It is also known to bring biodiesel into contact with a component which can remove sterol glycosides from the biodiesel. When Components for this are adsorbents, filter media, boric acid, soaps, sucrose, sugars, glucose, sodium chloride, citric acid, magnesium silicate, clay, silica, lecithin, proteins, carbon, cellulose, solutions with boric acid or silica hydrogel proposed. However, the proposed components are only insufficiently capable of solubilizing and eliminating precipitates caused by sterol glycosides. In addition, the above-described problem of precipitations in the production plant can not be eliminated by the treatment of the end product biodiesel.

task The present invention is in the production of biodiesel the occurrence of Feststoffausfällungen in the production plant and in the final product to avoid.

This object is achieved with the invention essentially in that the fat or oil and / or the crude alkyl ester produced by transesterification and / or a biodiesel end product obtained after removal of by-products is brought into intimate contact with a strong organic or strong inorganic acid. Surprisingly, it has been found that the treatment of precipitates formed by sterol glycosides with the proposed strong acids in contrast to those of WO 2007/076163 A2 known weak acids, such as boric acid (pK _s value = 9.28) or citric acid (pK _s value (1) = 3.14), leads to a dissolution of these precipitates. The reason for this is the ability of these strong acids to cleave the sterol glycoside molecules hydrolytically into glucose and phytosterols. This could be confirmed by the chemical detection of free glucose. The cleavage products are soluble in the non-polar phase (oil, fat or fatty acid alkyl ester = biodiesel) and thus can no longer cause precipitation.

Strong acids within the meaning of the present application have a pK _s value ≦ 3.1, preferably ≦ 1.5 and in particular ≦ 0.

Preferred agents for cleaving the sterol glycoside molecules are strong inorganic acids such as hydrochloric acid (pK _s value = -6), sulfuric acid (pK _s value = -3) or phosphoric acid (pK _s value (1) = 2.16 ). However, the use of a strong organic acid such as sulfonic acids (pK _s = 1-2) is also possible.

In Further development of the invention, the acid is the starting material (Oil, fat), the crude alkyl ester and / or the biodiesel end product as a concentrated acid or anhydrous solution with an acid content of 0.1 to 30 wt .-% added wherein treatment temperatures of 70 to 150 ° C are preferred become. According to the invention, the starting material, Intermediate (crude alkyl ester) or biodiesel end product 2 to 15% by volume (acid content) of concentrated acid or aqueous acid solution.

The best results for the removal of the substances causing the precipitation are achieved if the starting oil or fat and / or the trans-esterified crude alkyl esters and / or the biodiesel end product are multiply batchwise, for example in a mixing zone having a plurality of mixing zones, or continuously be treated in countercurrent with the acid. In a further development of this inventive concept, the mixture is carried out in an intensive mixer, for example. As from EP 0 513 709 B2 known in a turbomixer or ultrasonic mixer.

According to one preferred embodiment of the invention, the feedstock glycerol, preferably added in a proportion of 1 to 10%. In the oil Existing free fatty acids are under these acidic conditions with excess glycerol to mono-, di- and triglycerides implemented.

Around to avoid cleavage of the ester, the acid according to the invention is the dry esters in methanol. Among the strongly acidic anhydrous Conditions are in further development of this inventive concept with an excess of methanol-free fatty acids converted from the soap cleavage to methyl esters.

To the acid treatment becomes the feedstock, the intermediate and / or the biodiesel end product, preferably neutral with water washed and dried.

The The invention also includes a means for avoidance or elimination of solid precipitates in the production of fatty acid alkyl esters by transesterification of fats and oils with alkyl alcohols, wherein the agent is a strong organic or strong inorganic Acid is, preferably hydrochloric acid, sulfuric acid, Phosphoric acid or a sulfonic acid.

An inventive plant for the production of fatty acid alkyl esters by transesterification of Fet alcohols and alkyl alcohols suitable for carrying out the process described above comprises at least one reaction stage with a mixing reactor for mixing the fats and oils with the alkyl alcohols and a separator in which the mixture is in a light, ester-rich phase and a heavy, separating a glycerol-rich phase, a separating device for separating fatty acid alkyl esters from the light, ester-rich phase, and a mixing device for mixing the fat or oil and / or the crude alkyl ester produced by transesterification and / or obtained after removal of by-products Biodiesel end product with the above described means.

The Mixing device is preferably a turbomixer or an ultrasonic mixer.

In Further development of the invention, the mixing device has a stirring cascade on, with which a particularly effective mixing and Treatment with the acid can be achieved.

ever after that, if the acid is used to treat the starting materials (Oil, grease) of the process of transesterification Rough alkyl ester or the final biodiesel product is used the mixing device according to the invention before the mixing reactor, arranged after the separator or after a drying stage.

Around after mixing with the acid, the solid precipitates It is preferable to remove causative compounds from the process following each, at least the last mixing device a wash column for neutral washing of the mixture, preferably with water intended. Especially if the neutral laundry after a Washing column for the separation of glycerol, according to the invention is a drying step downstream of a dried (largely anhydrous) biodiesel end product to obtain.

Further developments, Advantages and applications of the invention result also from the following description of exemplary embodiments and the drawing. All are described and / or illustrated illustrated features alone or in any combination the subject of the invention, regardless of its summary in the claims or their dependency.

It demonstrate:

1a the structural formula of stigmasterol as an example of a sterol glycoside,

1b the structural formula of campesterol as an example of a sterol glycoside and

2 schematically a plant for carrying out the method according to the invention.

In the 2 schematically illustrated plant for the production of fatty acid alkyl esters by transesterification of fats and oils with alkyl alcohols has two reaction steps. In the illustrated embodiment, methanol is used as the alcohol, but the process can be carried out in the same way with ethanol to produce ethyl ester.

The first implementation stage 1 has a mixing reactor 2 and a subsequent gravitational separator 3 on. Accordingly, also the second implementation stage 4 a mixed reactor 5 and a gravity separator 6 on. The oil or fat to be treated flows through a pipe 7 in the mixing reactor 2 , The reactor 2 one leads further by a line 8th largely anhydrous methanol and a catalyst and through the line 9 the heavy, glycerol-containing phase from the second reaction stage 4 to. The catalyst is passed through the line 10 introduced and mixed with the methanol. In the reactor 2 Intensive mixing takes place with the aid of at least one stirring device 11 , The mixing reactor 2 may comprise a plurality of cascaded mixing chambers in a known manner.

The temperatures in the mixing reactor 2 are usually in the range of 40 ° C to the boiling point of the mixture. When working at atmospheric pressure, temperatures up to 68 ° C. have proven to be expedient. At higher pressures, temperatures up to 90 ° C make sense. Between the mixing reactor 2 and the separator 3 a cooling not shown here may be provided to the separation in the separator 3 to facilitate. As a gravity separator is preferably used fiber bed, known per se and, for example. In "Filtration and Separation", September / October 1990, pages 360 to 363 are described.

In the separator 3 Draw a light, methyl ester-rich phase, which is passed through the line 12 to the mixing reactor 5 the second implementation stage 4 leads. The in the line 13 withdrawn heavy, gly cerinreiche phase is combined with the wash water from a wash column 21 After pH adjustment to 1.5-2.0 in a collecting line 23 for rectification of a column 14 given up. In the known rectification column 14 you win over head largely anhydrous methanol, which is in the line 15 withdraws and the methanol of the line 8th admits. From the bottom of the column 14 you go through a pipe 16 a glycerol / water / fatty substance mixture which is supplied to a gravitational separator at temperatures of 50 ° C to 90 ° C for the separation of the fatty acid and methyl ester constituents dispersed in the glycerol water. As a light phase, the fatty substance forms ("Fatty Matter") and is withdrawn continuously. The heavy water-glycerol phase becomes an evaporator 17 fed and the water separated. The crude glycerol with a water content of 2 to max. 10% is over a line 18 fed to a cleaning, not shown.

The second implementation stage 4 one leads next to the light, methyl ester-rich phase from the separator 3 over a line 19 a mixture of methanol and catalyst. Before entering the mixing reactor 5 can the temperature of the methyl ester-rich phase of the line 12 lowered or raised in a heat exchanger, not shown. In the mixed reactor 5 , in which again intensive mixing takes place, the temperature is about the same as in the mixing reactor 2 , In front of the separator 6 In turn, a cooling, not shown, may be provided.

The heavy, glycerol-rich phase, in the separator 6 accumulates and contains 90% of the added catalyst and unused methanol is passed through the line 9 to the mixing reactor 2 recycled. The light, methyl ester-rich phase (crude ester) passes through the line 20 after neutralization of the catalyst residues in the ester by admixing 1% of a 3% HCl solution in an intensive mixer and phase separation in a separator to a wash column 21 , the one over the line 22 that in the evaporator 17 supplied water feeds. The water absorbs the water-soluble Substan zen, especially methanol, glycerol, salts and the excess salts of the upstream catalyst neutralization on. The aqueous phase, which contains methanol and glycerol and is virtually free of methyl ester, is passed over the line 23 the glycerol-rich phase of the line 13 which are admixed after separation of the fatty substance of the rectification column 14 gives up.

On the other hand, from the wash column 21 over the line 24 Deducted fatty acid methyl ester, which can be used as biodiesel. Since the water content in the biodiesel for end use is still too high, it must by heating in a heat exchanger, not shown, and subsequent drying, eg. Vacuum drying, in a drying step 25 be reduced. This gives a largely dried (anhydrous) product with a biodiesel specification corresponding to the maximum water content of 0.05%, which is then freed of impurities in a filter unit and stored in a product tank.

Around in the production of fatty acid alkyl esters described above the formation of precipitates based on sterol glycosides to avoid or already formed such precipitates dissolve the feedstocks (oil, fat), the intermediate (crude alkyl esters produced by transesterification) and / or the biodiesel end product with a strong inorganic or organic Acid, for example hydrochloric acid, sulfuric acid, Phosphoric acid or sulfonic acids, brought into contact. Particularly preferred is a 0.1-30 wt .-% anhydrous Mineral acid used. The treatment temperature is between 40 and 180 ° C, depending on which Place of the process carried out the acid treatment becomes.

• a) Behandlung des Pflanzenöls oder -fettes vor der ersten Umsetzungsstufe;
• b) Behandlung des Rohesters nach dem Abscheider der letzten (meist der zweiten) Umsetzungsstufe;
• c) Behandlung des getrockneten Fettsäuremethylesters.

The following patented embodiments are possible:

• a) treatment of the vegetable oil or fat prior to the first stage of the reaction;
• b) treatment of the crude ester after the separator of the last (usually the second) reaction stage;
• c) Treatment of the dried fatty acid methyl ester.

• (a) Die Säure wird zusammen mit Glycerin einer vor der ersten Umsetzungsstufe 1 angeordneten ersten Mischeinrichtung 26 zugeführt, in welcher bei Verweilzeiten von 15 bis 180 min und Temperaturen zwischen 40 und 180°C, vorzugsweise zwischen 50 und 65°C, eine innige Vermischung mit dem Einsatzstoff (Öl, Fett) des Prozesses erfolgt. Temperaturen über 65°C, vorzugsweise zwischen 100 und 150°C, haben den Vorteil einer kurzen Reaktionszeit von 1 bis 15 min zur Spaltung der Sterolglycoside. Soll aus dem Öl oder Fett Methylester nach einem üblichen drucklosen Biodieselherstellungsverfahren produziert werden, muss das Reaktionsgut für die Umsetzung mit Methanol auf Temperaturen < 65°C abgekühlt werden.

Each of these treatments requires special conditions, which are explained below.

• (a) The acid is combined with glycerol one before the first reaction step 1 arranged first mixing device 26 fed, in which at residence times of 15 to 180 minutes and temperatures between 40 and 180 ° C, preferably between 50 and 65 ° C, an intimate mixing with the feedstock (oil, fat) of the process takes place. Temperatures above 65 ° C, preferably between 100 and 150 ° C, have the advantage of a short reaction time of 1 to 15 min to cleave the sterol glycosides. If methyl ester is to be produced from the oil or fat by a conventional pressureless biodiesel production process, the reaction mixture must be cooled to temperatures <65 ° C. for the reaction with methanol.

The glycerol is added to avoid that in addition to the sterol glycoside not even the Fatty acid glycerides are cleaved to fatty acids, wherein the glycerol content is between 1 and 10% of the starting material (oil, fat).

One Advantage of the treatment of the oil / fat before transesterification is that also fatty acid-containing oils / fats with a fatty acid content of up to 5% used as feedstock can be, because under these conditions the fatty acids acid catalyzed to react with glycerides.

To The acid treatment can be carried out in a downstream separator the acidic glycerol are separated, then again for sterol cleavage can be used.

• (b) Nach einer anderen bevorzugten Ausführungsvariante wird die Säure in eine zweite Mischeinrichtung 27 eingebracht, die unmittelbar nach dem Abscheider der letzten Reaktionsstufe angeordnet ist, um mit dem durch Umesterung erzeugten Rohalkylester innig vermischt zu werden.

The remaining oil / fat phase must be neutralized. This can be done most simply by a correspondingly higher dosage of the basic catalyst or by pre-addition of alkalis or alkaline earths.

• (b) According to another preferred embodiment variant, the acid is introduced into a second mixing device 27 introduced, which is located immediately after the separator of the last reaction stage to be intimately mixed with the crude alkyl ester produced by transesterification.

in the conventional biodiesel production process is after the transesterification of the alkaline crude ester in a mixer with dilute treated aqueous hydrochloric acid. In the following Separator falls part of the dissolved in the crude ester Sterol glycosides as finely divided particles.

In addition, the fatty acid sterol glycoside esters (acylated sterol glycosides or "ASG") contained in the oil / fat, which also have good solubility in biodiesel, are hydrolysed to sterol glycosides and free fatty acids by the aqueous acid. Examinations of the SG and ASG content from different biodiesel process stages have shown that the highest SG contents in the acidic crude ester occur after neutralization before entering the wash column: Implementation of palm oil (Palmetta, WALTER RAU Neusser Öl and Fett AG) SG [ppm] oil output <50 Ester after transesterification before HCl wash 140 Ester at the end of the HCl wash 157 Wash water HCl wash not definable Ester before wash column 154 Wash columns wash water not definable Ester by wash column (removal of SG sludge) 77 Ester after centrifugation 17 Ester after drying 21

The conventional treatment of crude ester with diluted aqueous acid does not lead to cleavage the sterol glycosides. The SG particles then collect in the following Washing column in the column head as sludge between the lower water phase and the upper crude ester phase.

Surprisingly It was found that the crude ester treatment with anhydrous acid leads to cleavage of the contained sterol glycosides.

The Addition of 3% sulfuric acid to the crude ester caused one Temperature of 55 ° C and a residence time of 30 min next a complete neutralization of the basic catalyst a decrease in the SG content in the crude ester of originally 160 to 14 ppm.

The Formation of a sludge layer in the washing column head at the boundary layer between water and ester phase was not found.

• c) Schließlich kann eine dritte Mischeinrichtung 28 nach der Trocknungsstufe 25 angeordnet werden, um die Säure mit dem Biodiesel-Endprodukt innig zu vermischen. Die wasserfreie Säure wird hierbei dem trockenen Ester vorzugsweise in Methanol zugegeben, um eine Esterspaltung zu verhindern. Gleichzeitig werden freie Fettsäuren aus der Seifenspaltung zu Methylestern umgesetzt.

The dried methyl ester showed no sedimentation even after prolonged storage.

• c) Finally, a third mixing device 28 after the drying step 25 be arranged to to intimately mix the acid with the biodiesel end product. The anhydrous acid is added to the dry ester, preferably in methanol, to prevent ester cleavage. At the same time, free fatty acids from the soap cleavage are converted to methyl esters.

The first to third mixing devices 26 to 28 can be provided individually or in any combination.

Following at least the last mixing device 26 . 27 and or 28 can each have washing facilities 29 . 30 respectively. 31 be provided to wash the mixture neutral with water. The washed-out acid components can be removed and, if necessary, reused after treatment. After the last wash column 31 is a second drying step 32 designed to remove the water from the biodiesel end product and reach a dry end product.

By the cleavage of the sterol glycoside molecules with the help of Strong organic or inorganic acid is the formation reliably avoided by SG solid precipitation. If the acid is added, if already precipitates occurred, they can be resolved. By the final washing and drying is a specification-compliant and storage-stable biodiesel end product receive

1

first conversion stage

2

mixing reactor

3

separators

4

second conversion stage

5

mixing reactor

6

separators

7

management

8th

management

9

management

10

management

11

agitator

12

management

13

management

14

column

15

management

16

management

17

Evaporator

18

management

19

management

20

management

21

washing column

22

management

23

management

24

management

25

drying stage

26-28

mixers

29-31

Laundry facilities

32

second drying stage

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• FR 996608 [0002]
• - FR 2560210 [0003]
• WO 87/07632 A1 [0004]
• - EP 0532767 B1 [0005]
• - US 4112218 [0007]
• - WO 2007/076163 A2 [0008, 0008, 0010]
• - EP 0513709 B2 [0014]

Cited non-patent literature

• - "Filtration and Separation", September / October 1990, pages 360 to 363 [0031]

Claims (26)

A process for the preparation of fatty acid alkyl esters by transesterification of fats or oils with alkyl alcohols, wherein the fats or oils and the alkyl alcohols and a catalyst are separated in at least one reaction stage with a mixing reactor and a separator in a light, high-ester phase and a heavy, glycerol-rich phase, and separating fatty acid alkyl esters from the light, ester-rich phase, characterized in that the fat or oil and / or the crude alkyl ester produced by transesterification and / or a biodiesel end product obtained after removal of by-products and drying are in contact with a strong organic or strong inorganic Acid is brought. Method according to claim 1, characterized in that hydrochloric acid, sulfuric acid, Phosphoric acid is used. Method according to claim 1, characterized in that that a sulfonic acid is used as the acid. Method according to one of the preceding claims, characterized in that the acid is the feedstock, the crude alkyl ester and / or the biodiesel end product as concentrated Acid or as an anhydrous solution with an acid content from 0.1 to 30 wt .-% is added. Method according to one of the preceding claims, characterized in that the acid is the feedstock, the crude alkyl ester and / or the biodiesel end product with a volume fraction from 2 to 15% by volume is added. Method according to one of the preceding claims, characterized in that the treatment with the acid at a temperature of 70 to 150 ° C. Method according to one of the preceding claims, characterized in that the treatment with the acid in one or more mixing zones in countercurrent. Method according to one of the preceding claims, characterized in that the treatment with the acid in sets or continuously. Method according to one of the preceding claims, characterized in that added to the feedstock glycerol becomes. Method according to claim 9, characterized in that that the glycerol content is between 1 and 10% of the starting material. Method according to claim 9 or 10, characterized that in the oil existing free fatty acids with excess glycerol be converted to mono-, di- and triglycerides. Method according to one of the preceding claims, characterized in that the acid is the dry ester is added in methanol. Method according to claim 12, characterized in that that with an excess of methanol free fatty acids be converted from the soap cleavage to methyl esters. Method according to one of the preceding claims, characterized in that the starting material, the crude alkyl ester and / or the biodiesel end product after acid treatment washed neutral with water and dried. Means for preventing or eliminating sterol glycosides containing precipitates in the production of fatty acid alkyl esters by transesterification of fats or oils with alkyl alcohols, characterized in that the agent is a strong organic or strong inorganic acid is. Agent according to claim 15, characterized that the acid hydrochloric acid, sulfuric acid, Phosphoric acid or a sulfonic acid. Use of an agent according to claim 15 or 16 in the production of fatty acid alkyl esters from fats or oils. Use according to claim 17, characterized Glycerol is added to the fats or oils. Plant for the preparation of fatty acid alkyl esters by transesterification of fats or oils with alkyl alcohols, with at least one reaction stage ( 1 . 4 ) with a mixing reactor ( 2 . 5 ) for mixing the fats or oils with the alkyl alcohols and a separator ( 3 . 6 ), in which the mixture is separated into a light, ester-rich phase and a heavy, glycerol-rich phase, and a separating device ( 21 ) for the separation of fatty acid alkyl esters from the light, ester-rich phase, characterized by a mixing device ( 26 . 27 . 28 ) for mixing the feedstock or grease and / or the crude alkyl ester produced by transesterification and / or a biodiesel end product obtained after removal of by-products with an agent according to claim 15 or 16. Plant according to claim 19, characterized in that the mixing device ( 26 . 27 . 28 ) is a turbomixer. Plant according to claim 19, characterized in that the mixing device ( 26 . 27 . 28 ) is an ultrasonic mixer. Installation according to one of claims 19 to 21, characterized in that the mixing device ( 26 . 27 . 28 ) has a stirring cascade. Installation according to one of claims 19 to 22, characterized in that the mixing device ( 26 ) in front of the mixing reactor ( 2 ) is arranged. Installation according to one of claims 19 to 23, characterized in that the mixing device ( 27 ) after the separator ( 3 . 6 ) is arranged. Installation according to one of claims 19 to 24, characterized in that the mixing device ( 28 ) after a drying step ( 25 ) is arranged. Installation according to one of claims 19 to 25, characterized in that after the mixing device ( 26 . 27 . 28 ) a washing device ( 29 . 30 . 31 ) and a second drying stage ( 32 ) are provided.