DE102009006920B4 - A method for preventing sterol glycoside-containing precipitates in the production of fatty acid alkyl esters - Google Patents

Abstract

A method for preventing or eliminating sterol glycoside-containing precipitates in the production 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 in at least one reaction stage with a mixing reactor and a separator in a light, ester-rich phase and separating a heavy, glycerol-rich phase and separating fatty acid alkyl esters from the light, ester-rich phase, characterized in that a strong organic or strong inorganic acid with the fat or oil prior to transesterification and / or the crude alkyl ester produced by transesterification and / or is brought into contact after removal of by-products and drying biodiesel end product and that the fats or oils glycerol is added.

Description

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 are mixed with the alkyl alcohols and a catalyst, and a separator in which the resulting mixture in a separated light phase, ester-rich phase and a heavy, glycerol-rich phase, which is then separated from the light, ester-rich phase fatty acid alkyl ester.

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 substance containing crude triglycerides reacts with an alkanol in the presence of a catalyst to convert the fatty acids contained in the crude triglycerides containing substance into 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.

The DE 10243700 A1 describes a method and an apparatus for producing biodiesel from biogenic fat- or oil-containing starting mixtures with a high proportion of free fatty acids, whereby a high flexibility is achieved with regard to the starting materials used, although the content of free and bound glycerol is far too high for some feedstocks the use as biodiesel is. To solve this problem, the esterification is divided into four sub-steps: In the first step, the free fatty acids in the presence of an acidic catalyst and glycerol as entrainer are esterified with a C1 to C4 monoalcohol. In the second step, the mixture is then purified by partially separating glycerol, acid catalyst and unreacted monoalcohol. The thus treated mixture is then reesterified in a third stage, this time using a basic catalyst. In the fourth and final step of this basic catalyst and unreacted monoalcohol and the glycerol formed in the transesterification is purified by treatment with water and subsequent drying. The respective separated components can be at least partially recovered.

The DE 102 57 215 A1 describes a process for the long-term stabilization of biodiesel in which the formation of precipitating flakes of organic nature is to be prevented. This is done by treating the formed crude methyl ester intensively with an acid or with a mixture of an acid and a complexing agent to form an emulsion. From this emulsion, the ester layer is separated, subjected to thorough washing with water and then dried.

It is known that the use of certain vegetable oils, especially from cost-optimized oil operations, in the conversion to fatty acid methyl ester or fatty acid ethyl ester (Biodiesel) can lead to Feststoffausfällungen in the manufacturing process or during subsequent storage of the product at cold ambient temperatures. This behavior is pronounced, for example, when using soybean oil or palm oil. In the processing of such oils, therefore, an increased maintenance of the production plant is required. In addition, the availability and thus the productivity of the production plant is limited because it must be taken out of service for the maintenance and elimination of Feststoffausfällungen. The precipitates may be separated by mechanical methods such as filtration or centrifugation.

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. As components for this adsorbents, filter agents, 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 are 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.

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

This object is achieved with the invention by the features of claim 1. The feedstock fat or oil and / or the crude alkyl ester produced by transesterification and / or a biodiesel end product obtained after removal of by-products are 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.

Glycerol is added to the starting material, preferably in a proportion of 1 to 10%. Free fatty acids present in the oil are reacted under these acid conditions with excess glycerol to form mono-, di- and triglycerides.

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 = -6), sulfuric acid (pK _s = -3) or phosphoric acid (pK _s = (1) = 2, 16). However, the use of a strong organic acid such as sulfonic acids (pK _s = 1-2) is also possible.

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

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.

In order to avoid cleavage of the ester, according to the invention, the acid is added to the dry ester in methanol. Under the strongly acidic anhydrous conditions, free fatty acids from the soap cleavage are converted into methyl esters in a further development of this inventive idea with an excess of methanol.

After the acid treatment, the starting material, the intermediate product and / or the biodiesel end product are preferably washed neutral with water and dried.

A plant for the production of fatty acid alkyl esters by transesterification of fats and oils with alkyl alcohols, which is suitable for carrying out the method 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 in separating a light, ester-rich phase and a heavy, glycerol-rich phase, a separation device for separating fatty acid alkyl esters from the light, ester-rich phase, and a mixer for mixing the fat or oil and / or the crude alkyl ester produced by transesterification and / or after separation obtained by-products biodiesel end product with the agent described above.

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

The mixing device has a stirring cascade with which a particularly effective mixing and treatment with the acid can be achieved.

Depending on whether the acid is used to treat the feedstock (oil, fat) of the process, the crude alkyl ester produced by transesterification or the final biodiesel product, the mixing device is placed before the mixing reactor, after the separator or after a drying stage.

In order to remove from the process, after the mixture with the acid, the compounds causing the solid precipitations, a washing column for neutral washing of the mixture, preferably with water, is preferably provided after each, in each case the last, mixing device. In particular, when the neutral washing is carried out after a scrubbing column for the separation of glycerol, a drying step is followed according to the invention to obtain a dried (largely anhydrous) biodiesel end product.

Further developments, advantages and applications of the invention will become apparent from the following description of exemplary embodiments and the drawings. All described and / or illustrated features alone or in any combination form the subject matter of the invention, regardless of their combination in the claims or their dependency.

Show it:

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, which are known per se and, for example, in "Filtration and Separation", September / October 1990, page 360 to 363 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, glycerol-rich 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 substances, 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.

In order to avoid the formation of precipitates based on sterol glycosides or to dissolve already formed precipitates in the production of fatty acid alkyl esters described above, the starting materials (oil, fat), the intermediate product (trans-esterified crude alkyl esters) 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 where in the process the acid treatment is carried out.

• 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).

An advantage of the treatment of the oil / fat before the transesterification is that even fatty acid-containing oils / fats with a fatty acid content of up to 5% can be used as starting material, since under these conditions the fatty acids react acid catalyzed to glycerides.

After the acid treatment, the acidic glycerol can be separated in a downstream separator, which can then be used again for sterol cleavage.

• (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, after the transesterification, the alkaline raw ester is treated in a mixer with dilute aqueous hydrochloric acid. In the following separator, some of the sterol glycosides dissolved in the crude ester precipitate out 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 the crude ester with dilute aqueous acid does not lead to cleavage of the sterol glycosides. The SG particles then collect in the subsequent wash column in the column head as sludge between the lower water phase and the upper crude ester phase.

Surprisingly, it has been found that the crude ester treatment with anhydrous acid leads to cleavage of the sterol glycosides contained.

The addition of 3% sulfuric acid to the crude ester caused at a temperature of 55 ° C and a residence time of 30 min in addition to a complete neutralization of the basic catalyst, a lowering of the SG content in the crude ester of originally 160 to 14 ppm.

The formation of a sludge layer in the wash column head at the boundary layer between water and ester phase was not observed.

• 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 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.

The cleavage of the sterol glycoside molecules with the aid of the strong organic or inorganic acid reliably avoids the formation of SG solid precipitates. If the acid is added, if already precipitations have occurred, they can be dissolved. The final washing and drying gives a specification-compliant and storage-stable biodiesel end product.

LIST OF REFERENCE NUMBERS

1

first implementation stage

2

mixing reactor

3

separators

4

second implementation 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

Claims (14)

A method for preventing or eliminating sterol glycoside-containing precipitates in the production 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 in at least one reaction stage with a mixing reactor and a separator in a light, ester-rich phase and a heavy, glycerol-rich phase are separated, and wherein one separated from the light, esterreichen phase fatty acid alkyl esters, characterized in that a strong organic or strong inorganic acid with the fat or oil prior to the transesterification, and / or the Rohalkylester produced by transesterification and / or is brought into contact after removal of by-products and drying biodiesel end product and that the fats or oils glycerol is added. A method according to claim 1, characterized in that hydrochloric acid, sulfuric acid, phosphoric acid is used as the acid. A method according to claim 1, characterized in that a sulfonic acid is used as the acid. Method according to one of the preceding claims, characterized in that the acid is added to the feedstock, the crude alkyl ester and / or the biodiesel end product as a concentrated acid or anhydrous solution having an acid content of 0.1 to 30 wt .-%. Method according to one of the preceding claims, characterized in that the acid is added to the starting material, the crude alkyl ester and / or the biodiesel end product with a volume fraction of 2 to 15 vol .-%. Method according to one of the preceding claims, characterized in that the treatment with the acid takes place at a temperature of 70 to 150 ° C. Method according to one of the preceding claims, characterized in that the treatment with the acid takes place in one or more mixing zones in countercurrent. Method according to one of the preceding claims, characterized in that the treatment with the acid is batchwise or continuously. Method according to one of the preceding claims, characterized in that the glycerol content is between 1 and 10% of the starting material. Method according to one of the preceding claims, characterized in that existing in the oil free fatty acids are reacted with excess glycerol to mono-, di- and triglycerides. Method according to one of the preceding claims, characterized in that the acid is added to the dry ester in methanol. A method according to claim 12, characterized in that are reacted with an excess of methanol-free fatty acids 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 the acid treatment is washed neutral with water and dried. Use of a strong organic or strong inorganic acid in the preparation of fatty acid alkyl esters from fats or oils to prevent or eliminate sterol glycoside-containing precipitates, wherein glycerol is added to the fats or oils.

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