EP2361150A1

EP2361150A1 - Aluminum oxide-containing adsorbents for the purification of biodiesel

Info

Publication number: EP2361150A1
Application number: EP09760491A
Authority: EP
Inventors: Ulrich Sohling
Original assignee: Sued Chemie AG
Current assignee: Sued Chemie AG
Priority date: 2008-11-21
Filing date: 2009-11-20
Publication date: 2011-08-31
Also published as: WO2010057660A1; DE102008058393A1

Abstract

The invention relates to a method for purifying biodiesel, wherein: - a crude biodiesel is provided; - the crude biodiesel is reacted with an adsorbent, which contains at least one aluminum oxide-containing component, having an aluminum portion, calculated as Al2O3, of more than 40 wt %; and - a purified biodiesel is separated from the adsorbent.

Description

Alumina-containing adsorbents for the purification of biodiesel

The invention relates to a process for the purification of biodiesel, biodiesel precursors, vegetable or animal fats and mixtures thereof.

Biodiesel, because of its origin from renewable raw materials, has a neutral combustion

Carbon dioxide balance on. Carbon dioxide is one of the greenhouse gases whose emissions are being pushed back to counteract the global warming of the climate. Biodiesel is said to play an important role as a substitute for diesel derived from fossil sources. This is also promoted by state measures. Within the European Union, for example, a share of biodiesel in diesel fuels is required by law.

Biodiesel is produced by alcoholysis of triglycerides, one mole of triglyceride reacting with three moles of alcohol to one mole of glycerol and three moles of the corresponding fatty acid ester. The reaction involves three reversible reactions whereby the triglyceride is gradually transformed into a diglyceride, a monoglyceride and finally into glycerol. In each of the steps, one mole of alcohol is consumed and one mole of a fatty acid ester is released. Alcoholysis can be carried out under both acidic and basic catalysis. In the industrial production of biodiesel, the alcoholysis is usually carried out under alkaline catalysis, since the reaction proceeds under mild conditions at a high conversion rate and therefore relatively fast. The alkaline catalysts used usually have a less corrosive effect on the synthesis reactors, so that, for example, a relatively inexpensive carbon-containing steel can be used for plant construction. In most industrial processes, the alcoholysis of the triglycerides is carried out under homogeneous alkaline catalysis. The alkoxide ion acting as a catalyst is produced by, for example, dissolving an alkali metal alcoholate in alcohol or reacting the pure alkali metal with the alcohol. In the

Methanolysis can also be a corresponding alkali metal hydroxide dissolved in methanol. Since in the alcoholysis of triglycerides phase separation by the resulting glycerol occurs relatively quickly, the major part of the alkaline catalyst is relatively quickly from the

Removed reaction mixture. The resulting fatty acid esters therefore hardly come into contact with the catalyst, so that the risk of saponification is low. Based on the oil used, the catalyst is usually used in an amount of 0.5 to 1 wt .-%. To details of

Biodiesel production is based on the monograph by M. Mittelbach, C. Remschmidt, "Biodiesel, The Comprehensive Handbook", Graz, 2004; ISBN 3-200-00249-2 is referenced.

The triglycerides used as starting materials can be obtained, for example, from vegetable or animal fat. In the case of vegetable raw materials, palm oil and soybean oil are mainly used in the worldwide production of biodiesel used. Rape oil and sunflower oil are of local importance. Other starting materials of commercial importance are animal fats, such as beef tallow, as well as used frying fats. For the future, oils from the jatropha nut as well as from algae are discussed as raw materials.

In order to ensure a uniform combustion of the biodiesel, the content of mono-, di- and triglycerides, as well as of soaps and glycerol, must be reduced as much as possible. According to DIN EN 14214, biodiesel may contain up to 0.2% by weight of monoglycerides, up to 0.8% by weight of diglycerides and up to 0.02% by weight of triglycerides. The resulting in the production of biodiesel soaps must also be removed from the biodiesel, otherwise ash can form during combustion, which can be deposited and lead to damage to the diesel engine. In order to remove soaps, as well as residual alcohol, glycerol, mono- and diglycerides from the biodiesel, a water wash is therefore usually carried out after transesterification. If the raw biodiesel contains large amounts of soaps, a stable emulsion can form, which makes the separation of the fatty acid esters considerably more difficult.

At present, most of the biodiesel is produced by alcoholysis of the triglycerides with methanol. Since the proton of the hydroxy group of the methanol is relatively acidic, methanol can be relatively easily converted by reaction with NaOH in the corresponding methanolate, which then causes the transesterification of the glyceride. However, a disadvantage of this process is the high toxicity of the methanol. Furthermore, methanol is produced petrochemically, so that only part of the biodiesel is based on renewable raw materials. As an alternative to methanolysis, methods are developed in which the triglycerides are cleaved using ethanol. This process has the advantage that both the fatty acid component and the ethanol can be obtained from renewable raw materials. Biodiesel based on fatty acid ethyl esters is therefore of particular interest for those countries in which large quantities of bioethanol are produced, for example Brazil or the USA.

Ethanol has lower acidity compared to methanol. The pKa of ethanol is 15.9 while methanol has a pKa of 15.5. Water has a pKa of 15.7. In the ethanolysis of triglycerides, therefore, in contrast to methanolysis, the saponification of glycerides by water is the preferred reaction. The reaction does not proceed completely, so that in the reaction mixture after the ethanolysis in addition to the fatty acid soaps even larger amounts of mono-, di- and triglycerides are present. Thus, the release of glycerol often results in the formation of a very stable microemulsion. This considerably impedes the separation of the glycerol. The glycerin can be separated by centrifugation or the emulsion can be broken by washing the mixture with a strong acid so that the soaps are converted to the corresponding fatty acids.

But even after such a purification, the biodiesel still contains relatively high levels of mono-, di- and triglycerides. In many cases, the biodiesel produced in this way is still contaminated with up to 2 wt .-% monoglycerides. It does not therefore meet the specification for use as diesel fuel. Biodiesel is made from natural resources. After alcoholysis, biodiesel therefore contains, in addition to soaps, mono-, di- and triglycerides, further impurities which vary in their proportions as well as in their composition within wide limits. These contaminants can also lead to difficulties in the production or use of biodiesel. If biodiesel is cooled down to room temperature after production or even when stored for a prolonged period of time, for example, small amounts of a fine, slightly soluble substance often fall

Precipitation out. This fine precipitate can then cause, for example, the clogging of filters. Often the fine precipitate consists of glycosides. In biodiesel, which is made from vegetable material, the precipitate often consists of steryl glycosides. Sterols are cholesterol-derived glycosides that only have a hydroxy group at C ₃ , but no other functional groups. Most of them have a double bond in 5/6 position, more rarely in 7/8 or 8/9 position. They are formally alcohols and are therefore often referred to as sterols. Naturally occurring steryl glycosides often include, in addition to the glycosidically linked steryl radical, a fatty acid with which the primary hydroxyl group of the sugar is acylated. They are therefore very well soluble in vegetable or animal fats. It is also believed that during the alcoholysis of the triglycerides, the acyl group on the primary hydroxy group of the steryl glycosides is cleaved to give an unacylated steryl glycoside. These non-acylated steryl glycosides are almost insoluble in biodiesel. They are therefore considered very fine

Suspended particles, for example, can act as nuclei for the crystallization of other compounds. Non-acylated steryl glycosides can already be found in very low levels Concentrations cause the precipitation of solid aggregates of biodiesel. Even concentrations in the double-digit ppm range can lead to the formation of turbidity in biodiesel at room temperature. Non-acylated steryl glycosides have a very high melting point of about 24O ⁰ C. Turbidity or precipitation caused by non-acylated steryl glycosides can therefore not be resolved by heating the biodiesel to a higher temperature. If there are already deposits on a filter, this clogs in the presence of non-acylated

Steryl glycosides in biodiesel complete relatively quickly.

After the production process, the biodiesel is subjected to a final inspection. If it is found that the test for blocking filters is not passed because the finished biodiesel still contains very small amounts of non-acylated steryl glycosides, this biodiesel can not be released.

A known from the prior art method for the separation of ingredients, such as steryl glycosides, from biodiesel based on the fact that the crude biodiesel is cooled to low temperatures and then filtered. However, this method is extremely expensive in its execution.

WO 2007/076163 A describes a process for the treatment of biodiesel with adsorbents and the like for the removal of steryl glycosides. Various adsorbents are described, with glucose, diatomaceous earth, clays and in particular magnesium silicate being used as the adsorbent in the examples. WO 2008/055676 A describes a process for purifying a crude biodiesel, wherein the adsorbent used is a clay material having a specific surface area of more than 120 m ² / g, a cumulative pore volume of 0.35 ml / g and a SiO ₂ Content of more than 60 wt .-% is used.

In US 2005/0188607 Al a process for the purification of crude biodiesel is described, wherein in particular methanol is removed. The plant for the production of biodiesel comprises a first section in which a crude biodiesel is prepared by reacting the oil used as starting material with methanol in the presence of a catalyst. In a second section, excess methanol is recovered from the crude biodiesel. For this purpose, a portion of the methanol is first distilled off from the crude biodiesel. For shares still present in the biodiesel

To remove methanol, the pre-purified biodiesel is then mixed with an adsorbent, such as magnesium silicate. The adsorbent is left in the biodiesel for about 10 to 15 minutes and then the purified biodiesel is separated from the adsorbent by filtration.

WO 2007/143803 A1 describes a process for the transesterification of vegetable or animal fats under base catalysis. The catalysts used are strong bases which contain no metal ions. As a result, no soaps are to be formed in the transesterification, whereby the formation of emulsions can be avoided when washing the crude biodiesel with water. As the base for the transesterification Guanidinhydroxyde are used, which have a pK _a in the range of 13.6 to 13.9, and quaternary ammonium hydroxides or alkoxides of guanidine. Of the

Catalyst can be used both in homogeneous phase and in heterogeneous phase can be used. The catalysts are useful for the alcoholysis of triglycerides using both methanol and ethanol.

In WO 2005/037969 A2, a process for the purification of biodiesel is described, wherein the crude biodiesel is reacted with magnesium silicate as an adsorbent.

As already stated above, the use of ethanol in the alcoholysis of triglycerides offers the possibility of producing a biodiesel whose starting materials can be obtained from renewable raw materials. A disadvantage of the process, however, is that the resulting biodiesel still contains relatively large amounts of impurities, in particular mono-, di- and triglycerides, soaps and glycosides, so that such ethylbiodiesel often does not yet meet the specifications, for example, for use in internal combustion engines are predetermined.

The invention therefore an object of the invention to provide a method for the purification of biodiesel, which allows efficient removal of impurities from crude biodiesel and which is particularly suitable for the purification of crude Ethylbiodiesel.

This object is achieved by a method having the features of patent claim 1. Preferred embodiments of the method according to the invention are the subject of the dependent subclaims.

According to the invention, it has been found that by using an adsorbent which contains a high proportion of aluminum oxide, it is possible to very efficiently remove impurities from crude biodiesel. The method can be used for Use purification of crude biodiesel, as it is obtained immediately after the alcoholysis, in particular after separation of the glycerol phase. The method can also be used for the post-purification of biodiesel, which still contains small amounts of impurities and, for example, does not meet a specific specification. The process according to the invention can also be used routinely as a final purification stage for the further refinement of an already prepurified biodiesel.

According to the invention, therefore, a method for purifying biodiesel is provided, wherein

a raw biodiesel is provided; the crude biodiesel is reacted with an adsorbent which contains at least one alumina-containing component which has an aluminum content, calculated as Al ₂ O ₃ , of more than 40% by weight; and a purified biodiesel is separated from the adsorbent.

In the method according to the invention, a raw biodiesel is first provided.

By "biodiesel" is meant a mixture of fatty acid alkyl esters commonly obtained in the alcoholysis of natural fats and oils. Alcoholysis may have been carried out under both acidic and alkaline catalysis. As alcohols can be used for the

Production of biodiesel conventional alcohols are used, for example, methanol, ethanol or propanol. As natural fats and oils, such fats and oils can be used as they usually are in the production be used by biodiesel. If reference is made to "fats" below, oils should also be included. Likewise, fats should also be recorded when referring to oils.

Fats and oils are generally understood to mean triglycerides of long-chain fatty acids. The fatty acids preferably comprise more than 10 carbon atoms and preferably comprise 15 to 40 carbon atoms. The alkyl chain of the fatty acids is preferably straight-chain. It may be fully hydrogenated or may comprise one or more double bonds. Suitable starting materials are vegetable fats, such as rapeseed oil, sunflower oil, soybean oil or palm oil. However, other vegetable fats can be used, such as jatropha oil or oils derived from algae. These oils are not suitable for human consumption. In addition, agricultural land not suitable for the production of food can be used for the production of these crops. For example, the jatropha nut can also be cultivated on very barren soils that are not suitable for grain production. Furthermore, animal fats can be used, such as beef tallow. It is also possible to use used fats, such as frying fats. It can be used both oils and fats, which go back to only one source. But it is also possible to use mixtures of fats or oils. The fats or oils are preferably purified prior to alcoholysis in a known manner and, for example, degummed and / or deodorized. According to a preferred embodiment, fats or oils having a lecithin content of less than 10% by weight, in particular less than 5% by weight, more preferably less than 10 ppm, in particular less than 5 ppm, are used for the alcoholysis. These fats and oils are usually cleaved by alcoholysis into glycerol and fatty acid esters. The alcoholysis is preferably carried out under alkaline catalysis. Alcohols which can be used in the production of biodiesel are customary alcohols, such as methanol, ethanol or propanol. The use of other alcohols is also possible.

In the context of the present invention, the term "biodiesel" may in particular also refer to any mixture of fatty acid alkyl esters. The alkyl radical of the

For example, fatty acid alkyl ester may be straight-chain or branched and may comprise 1 to 28 carbon atoms. In particular, the fatty acid alkyl ester may be, for example, a methyl, ethyl, propyl, butyl, pentyl or hexyl ester of a fatty acid. Preferably, the mixture of fatty acid alkyl esters comprises a content of at least 70 wt .-%, preferably of at least 85 wt .-%, preferably of at least 95 wt .-%, particularly preferably of at least 98 wt .-% of fatty acid alkyl esters, each based on the Total weight of the organic components of the mixture.

Biodiesel mixtures may contain any amount of mono-, di- and / or triglycerides. Preferably, the biodiesel has a low content of mono-, di- and / or triglycerides. For example, the biodiesel may have a maximum content of 2% by weight, preferably of at most 0.8% by weight for monoglycerides, a maximum content of 2% by weight, preferably at most 0.2% by weight, of diglycerides, and / or a maximum content of 2% by weight, preferably of not more than 0.2% by weight, of triglycerides, determined in accordance with the standard DIN EN 14214. The mixture obtained in the alcoholysis of fats and oils is worked up in a conventional manner. Thus, for example, the glycerol phase can be separated from the crude biodiesel or the crude biodiesel can also be washed once or several times with water. But it is also possible that at the

Alcoholysis obtained crude biodiesel first to clean with the help of an adsorbent.

A crude biodiesel is understood as meaning any biodiesel which has a higher content of impurities than a biodiesel which has been purified by the process according to the invention. Accordingly, a "purified biodiesel" is understood to mean a biodiesel that has a lower impurity content than crude biodiesel. Exemplary impurities that may be present in a crude biodiesel are mono-, di- or triglycerides, soaps or even glycosides, such as steryl glycosides.

A crude biodiesel can therefore be a biodiesel, as it is obtained immediately after the alcoholysis of the fats and / or oils, for example immediately after separation of the glycerol phase. However, a raw biodiesel can also be a biodiesel which has already undergone purification stages after alcoholysis but, for example, still has too high a glycoside content, in particular too high a content of steryl glycosides, mono-, di- or

Triglycerides or soaps, so it does not meet a specific specification and must be cleaned.

The crude biodiesel is added according to the invention with a special adsorbent. The adsorbent can be incorporated in any desired form into the raw biodiesel to be purified. For example, it is possible to stir the adsorbent in ground form into the biodiesel.

If the adsorbent in the form of a powder or granules is introduced into the crude biodiesel and suspended in this embodiment, the crude biodiesel is preferably moved during the purification, for example with the aid of a stirrer, so that the adsorbent intimately with the biodiesel is mixed and does not settle.

The amount of adsorbent added to the biodiesel depends on the amount of impurities contained in the crude biodiesel. If a raw biodiesel is used, as it is immediately after alcoholysis

Triglycerides is obtained, it makes sense to use larger amounts of the adsorbent. If, on the other hand, the process according to the invention is used for the post-purification of an already prepurified crude biodiesel which only contains small amounts of impurities, the amount of adsorbent added can correspondingly be kept low.

The treatment time during which the crude biodiesel is contacted with the adsorbent is intrinsically dependent on the relative amounts of crude biodiesel and adsorbent, as well as the amount of impurities contained in the crude biodiesel. However, it has been found that the adsorbent used in the process according to the invention has a relatively fast kinetics. Preferably, the contact time between raw biodiesel and adsorbent is longer than 5 minutes, preferably longer than 10 and according to a selected further embodiment longer than 15 minutes. According to one embodiment, the treatment time is shorter than 120 minutes, according to another embodiment, shorter than 60 minutes and, according to another embodiment, shorter than 30 minutes.

The process according to the invention is preferably carried out at room temperature or, more preferably, at temperatures above room temperature. The crude biodiesel therefore preferably has a temperature in the range of more than 15 ^° C. during the treatment with the adsorbent, more than 30 ^° C. in accordance with a further embodiment and more than 40 ^° C. according to a further embodiment. In most cases, it is not necessary to heat the biodiesel to a high temperature. According to one embodiment, the temperature is less than 100 ⁰ C, according to another embodiment, less than 90 ⁰ C and, according to one embodiment, less than 80 ⁰ C.

The cleaning, in particular a fine cleaning of the biodiesel, is preferably carried out at a temperature above room temperature. A fine cleaning is understood to be a post-purification of an already prepurified biodiesel, the crude biodiesel containing only small amounts of impurities. Such a fine cleaning can be carried out, for example, if the crude biodiesel is already less than 2.0% by weight, preferably less than 1.0% by weight, monoglycerides or less than 2% by weight, preferably less than 1% by weight. % Diglycerides or less than 1% by weight, preferably less than 0.5% by weight, of triglycerides, but does not fulfill a given specification and contains, for example, more than 0.2% by weight of monoglycerides, or more than 0, Contains 8 wt .-% diglycerides or more than 0.02 wt .-% triglycerides. After the fine cleaning with the inventive method, the purified biodiesel then meets the specification, ie it contains less than 0.2 wt .-% monoglycerides, less than 0.8 wt .-% diglycerides and less than 0.02 wt .-% triglycerides ,

If the purification of the crude biodiesel is carried out at elevated temperature, in particular the solubility of impurities, which are present in solid form in the biodiesel, is known to be better. By heating the crude biodiesel, such impurities present in solid form, which have precipitated, for example, after cooling of the biodiesel, can be brought back into solution. Working at elevated temperature also ensures that these solid impurities are depleted after adsorption on the adsorbent after re-dissolution and not just a filtration. This is of particular importance when the adsorbent is provided in the form of a column packing for the purification of the biodiesel. The formation of precipitates would clog the column and make it difficult to regenerate a column.

After the treatment, the biodiesel is separated again from the adsorbent. For this purpose, usual methods can be used. For example, the adsorbent can be sedimented and the supernatant purified biodiesel decanted off. But it is also possible to separate the adsorbent, for example by filtration from the purified biodiesel.

The aluminum oxide-containing component used as adsorbent in the process according to the invention preferably has a very high specific surface area of more than 100 mVg. According to a preferred embodiment, the alumina-containing component has a specific surface area in the range of 100 to 750 m ² / g, more preferably 120 to 700 m ² / g, particularly preferably 140 to 650 m ² / g. The specific surface area is determined by the BET method.

According to a further preferred embodiment, the aluminum oxide-containing component of the adsorbent used in the process according to the invention preferably has a high pore volume. The alumina-containing component preferably has a pore volume of more than 0.3 ml / g, more preferably a pore volume of more than 0.45 ml / g, particularly preferably more than 0.50 ml / g. The pore volume is determined to be cumulative pore volume according to BJH (I.P. Barret, L.J. Joiner, P.P. Haienda, J. Am. Chem. Soc., 73, 1991, 373) for pores having a diameter of 1.7 to 300 nm. According to one embodiment, the alumina-containing

Component has a pore volume of less than 1.4 ml / g. According to a further embodiment of the method, the pore volume of the alumina-containing component is less than 1.3 ml / g and in another embodiment less than 1.2 ml / g.

On the one hand, the high specific surface area and the high pore volume enable a high adsorption capacity for the impurities contained in the crude biodiesel and a rapid kinetics of the adsorption, so that the process is particularly suitable for industrial use.

In the process according to the invention, an adsorbent is used which contains an aluminum oxide-containing component which has an aluminum content, calculated as Al ₂ O ₃ , of more than 40% by weight, it being particularly preferred that the aluminum content (calculated as Al ₂ O ₃ ) at more than 45% by weight, more preferably more than 50% by weight, more preferably more than 60% by weight, more preferably more than 70% by weight and most preferably more than 75% by weight. But it is also possible that the alumina-containing component contains the aluminum in the form of, for example, a mixed oxide. In addition to aluminum, at least one further metal may be present in the alumina-containing component, such as silicon, titanium, magnesium, calcium and / or zirconium.

It has surprisingly been found that by using an adsorbent according to the invention which has a high proportion of aluminum oxide, it is also possible to remove impurities from crude biodiesel efficiently even when using small amounts of the adsorbent. Thus, the use of the adsorbent with a high alumina content allows the removal of mono-, di- and triglycerides from crude biodiesel and with appropriate reaction, it is possible, for example, after the alcoholysis of the triglycerides and the separation of the glycerol phase to dispense with a step in the the raw biodiesel is washed with water. The crude biodiesel can be reacted directly with the adsorbent, removing impurities of the biodiesel from the adsorbent from the crude biodiesel. This is particularly advantageous when the crude biodiesel comprises a high proportion of fatty acid soaps, which can lead to the formation of a stable emulsion in a water wash.

As the alumina-containing component, aluminum oxides, aluminum hydroxides, boehmite or aluminosilicates are preferably used. These compounds may be mentioned in pure form or else in the form of mixtures of the abovementioned

Connections are used. As aluminum oxide can both α-, γ ~ and S-Al ₂ O ₃ are used. In a preferred embodiment, aluminum oxides are used, with more preference being given to y-Al ₂ O ₃ . The aluminas can be used in pure form or as a mixture of two or three of said phases. It is possible to use aluminum hydroxides of different composition, which may also have a different degree of dehydration or polymerization. Boehmite is AlOOH.

The alumina-containing component can be degraded from a natural source, so be a natural mineral. Preferably, however, synthetic compounds are used. These can be produced under controlled conditions and therefore lead to reproducible properties and results in the process according to the invention. The adsorbent is preferably predominantly of the alumina-containing component. It is possible that the adsorbent in addition to the alumina-containing component, for example, contains a binder, wherein the binder is preferably selected from the group consisting of at least one clay mineral, at least one water glass and at least one organic polymer and mixtures thereof. The proportion of the binder on the adsorbent is preferably in a range of 0.01 to 10 wt%, more preferably 0.05 to 5 wt%, and most preferably 0.1 to 1 wt%. Preferably, the proportion of the alumina-containing component in the adsorbent is more than 60 wt .-%, preferably more than 80 wt .-%, more preferably more than 90 wt .-%. The difference to 100% could for example be formed in each case by a proportion of a binder, with which the alumina-containing component is bound to an adsorbent particle. According to In a particularly preferred embodiment, the adsorbent consists only of the alumina-containing component.

For example, aluminas and their hydrates can be prepared by neutralizing basic aluminate solutions by the addition of acid. The precipitation of

Aluminum hydroxides or their hydrates can be assisted by the addition of crystallization nuclei. It is also possible to precipitate hydrated aluminum hydroxides from acidic solutions of aluminum salts by adding bases or by combining basic solutions of aluminates with acidic solutions of aluminum salts. The hydrated aluminas separated from the aqueous phase can then be converted to aluminas by annealing.

A suitable process for producing hydrated aluminas is described, for example, in WO 01/02297.

The aluminas and their hydrates can also be prepared via a sol-gel process. For example, aluminum alkoxides can be hydrolyzed for this purpose. The hydrolysis can generally be carried out in a temperature range from 30 to 150 ^° C. The solid alumina hydrate is separated from the aqueous alcohol phase. For example, the obtained crystals may be aged under hydrothermal conditions.

A suitable method is described for example in WO 00/09445. According to another preferred embodiment, the alumina-containing component is a synthetic aluminosilicate.

The aluminosilicates preferably have a silicon content, calculated as SiO ₂ , of less than 60% by weight, preferably less than 55% by weight, more preferably less than 50% by weight. According to one embodiment, the silicon content of the aluminosilicate, calculated as SiO ₂ , is more than 0.5% by weight, according to a further embodiment more than 0.75% by weight.

Aluminosilicates can be prepared, for example, by hydrolyzing organic aluminum compounds under acidic conditions and then aged together with silicic acid or silicic acid compounds under hydrothermal conditions. Suitable organic aluminum compounds are, for example, aluminum alcoholates,

Aluminum hydroxyalcoholates, Aluminiumacetylacetonate, aluminum alkyl chlorides or aluminum carboxylates. A suitable method is described for example in US 6,245,310 Bl.

In order to obtain particularly pure aluminosilicates, it is also possible to use hydrolyzable organosilicon compounds instead of silica, the hydrolysis of the organosilicon compounds and of the hydrolyzable aluminum compounds being carried out together. Such a method is described for example in EP 0 931 017 Bl.

Particular preference is given to using aluminosilicates which contain only SiO ₂ and Al ₂ O ₃ as constituents. Of the Proportion of further metals, calculated as the most stable oxide, is preferably chosen to be less than 1% by weight.

The adsorbent may be provided, for example, in the form of a powder. An adsorbent in the form of a powder is suitable, for example, when the adsorbent is stirred into the crude biodiesel, that is in the form of a suspension.

The particle size of the powder is generally adjusted so that the adsorbent can be readily separated from the purified biodiesel within a suitable period of time by a suitable method, such as filtration. When a powder is used which is suspended in the crude biodiesel, the dry sieving residue of the adsorbent on a sieve having a mesh of 63 μm is preferably more than 25% by weight and is preferably in a range of 30 to 50% by weight. The dry sieve residue on a sieve with a mesh size of 25 μm is preferably more than 80% by weight and is preferably in a range of 85 to 88% by weight. Furthermore, the dry sieve residue on a sieve with a mesh size of 45 μm is preferably more than 35% by weight, particularly preferably more than 45% by weight.

In particular, for an application of the adsorbent in the form of a column packing but also larger particle sizes are suitable. For this purpose, the adsorbent is preferably used in the form of granules. In particular, for the production of column packings, a granulate is preferably used which has a particle size of more than 0.1 mm. Preferably, the granules have a particle size in the range of 0.2 to 5 mm, particularly preferably 0.3 to 2 mm. The grain size can be adjusted, for example, by sieving.

The granules can be prepared by conventional methods, for example, by applying a finely ground adsorbent with a granulating agent, for example water, and then granulated in a conventional granulating in a mechanically generated fluidized bed. However, other methods can be used to prepare the granules. Thus, the powdered adsorbent can be formed for example by compaction to a granulate.

The adsorbent may also be provided as shaped articles, which may be obtained, for example, by extrusion of a plastic mass. For this purpose, from the alumina-containing component and optionally further

Components, such as a binder, prepared by adding a liquid, preferably water, a paste. This paste is then extruded and the extrudate comminuted, for example by cutting the extruded strand into short cylindrical pieces, and then drying the resulting shaped articles. Besides massive cylinders, in this way e.g. also hollow cylinder can be produced.

After shaping, the granules or the shaped bodies can still be heat-treated and sintered, for example, by heating. As a result, the stability of the granules or the shaped bodies can be increased. For the heat treatment, the shaped body or the granules are preferably at a temperature of more than 300 ⁰ C, according to another embodiment, to a temperature of more than 400 ⁰ C, and heated according to yet another embodiment to a temperature of more than 500 ⁰ C. According to one embodiment, the temperature is less than 1200 ⁰ C, chosen according to another temperature lower than 1000 ⁰ C.

In order to obtain stable shaped bodies, the heat treatment is preferably selected for a duration of at least 30 minutes, according to a further embodiment for a duration of at least 60 minutes. According to one embodiment, the duration of treatment is chosen to be less than 5 hours.

As already explained, the adsorbent can be added directly to the crude biodiesel, wherein the biodiesel is preferably stirred. The amount of the adsorbent is preferably selected in a range of 0.05 to 5 wt .-%, particularly preferably 0.1 to 2 wt .-%. The percentages of the adsorbent are based on the weight of the crude biodiesel.

According to another embodiment, the adsorbent is provided in the form of a column packing. The raw biodiesel can then be passed through the column packing. The column packing may be provided, for example, in the form of a cartridge. In practice, the crude biodiesel can then be passed through the cartridge until the adsorption capacity of the adsorbent contained in the cartridge is exhausted. The cartridge can then be easily replaced with a new cartridge. The cartridge may then be discarded or, as far as the separated contaminants are to be reused or the cartridge reused, the compounds bound on the adsorbent may also be eluted with a suitable eluent. When the adsorbent is provided in the form of a column packing, the adsorbent is provided in the form of larger granules to prevent excessive pressure drop across the column packing.

In this embodiment, therefore, the adsorbent is preferably used in the form of a granule having a particle diameter of more than 0.1 mm, particularly preferably a particle diameter in the range of 0.2 to 5 mm.

To avoid clogging of the column, the crude biodiesel is preferably heated to a temperature above room temperature before being added to the column.

The use of the adsorbent in the form of a column also enables regeneration of the column, e.g. with solvents, whereby the column packing can be used several times. Suitable regenerants are, for example, alcohols, mixtures of alcohols and alkanes or chlorinated hydrocarbons or aqueous surfactant-containing solutions. Optionally, the regeneration may also be carried out in a gradient wherein the biodiesel is first washed with a relatively nonpolar solvent from the column and then transferred to a more polar solvent, for example an alcohol such as methanol or ethanol, around the impurities bound to the adsorbent , in particular sterylglycosides, to elute from the column.

The adsorbents used in the process according to the invention preferably react neutral to slightly alkaline. A suspension of 10 wt .-% of the adsorbent in water has preferably has a pH in the range from 5 to 9, more preferably 6 to 8.5, and most preferably in the range of 6.5 to 8. The pH is determined by means of a pH electrode according to DIN ISO 7879.

A further increase in the activity of the adsorbent can be achieved according to one embodiment when the adsorbent is pre-dried. According to one embodiment of the invention, the adsorbent has a water content of less than 5 wt .-%, according to another embodiment has a water content of less than 3 wt .-% and according to another embodiment has a water content of less than 2 wt .-%.

It may also be advantageous to heat the adsorbent to a higher temperature to remove physically bound water. For this purpose, according to one embodiment, the

Adsorbent be heated to a temperature of more than 600 ⁰ C. According to one embodiment, the temperature is chosen lower than 1000 ⁰ C. By means of such a treatment, for example, boehmite can first be used to remove the superficially bound water and to convert the hydrate into an oxide phase.

The inventive method is also particularly suitable for the removal of glycosides from biodiesel. As already explained, the method is suitable in particular for the post-purification of already prepurified biodiesel. With the method according to the invention, glycosides can be removed from the biodiesel if they are present in the biodiesel in only very small amounts. In this embodiment, a biodiesel that is already very pure is subjected to a post-purification. According to a preferred Thus, the crude biodiesel has a glycoside content of less than 5,000 ppmw, more preferably less than 2,000 ppmw, most preferably less than 500 ppmw. The inventive method is particularly suitable for the removal of very small amounts of glycosides, especially Sterylglykosiden. Therefore, according to a preferred embodiment, the crude biodiesel has a glycoside content of less than 100 ppmw, more preferably less than 80 ppmw, most preferably less than 50 ppmw. According to one embodiment, the crude biodiesel has a glycoside content of more than 10 ppmw, according to another embodiment more than 20 ppmw.

Glycosides are generally understood to mean compounds of carbohydrates and aglycones. As carbohydrates, both mono- and oligosaccharides in the

Be included glycosides. As aglycones, all compounds which can react with the carbohydrate to form a glycosidic bond can in themselves act. The aglycone can be bound both α- and β-glycosidic. As carbohydrates both aldoses and ketoses may be included, which may be present both as 5- and as 6-rings, ie as furanosides or pyranosides.

In particular, the process according to the invention is suitable for the separation of steryl glycosides from crude biodiesel.

Steryl glycosides are glycosides which include sterols as aglycone. Sterols are nitrogen-free, polycyclic, hydroaromatic compounds, in particular derivatives of guanan or of perhydro-1H-cyclopenta- [α] -phenanthrene. Examples of sterol glycosides are stiosteryl, stigmasterol or campesterol-β-glycoside. The steryl glycosides are preferably in the form of a glycoside.

The glycosides, in particular steryl glycosides, are preferably present in non-acylated form. Due to the polar hydroxyl groups of the saccharide, the glycosides, in particular steryl glycosides, have a very poor solubility in the biodiesel. They therefore very easily form a sparingly soluble precipitate in the biodiesel. As already explained, the method according to the invention is particularly suitable for the purification of biodiesel, which still has low levels of contamination by glycosides, in particular steryl glycosides. These are present as a very fine precipitate.

According to one embodiment of the method, the crude biodiesel therefore comprises the at least one glycoside, in particular sterol glycoside, in the form of a finely divided precipitate, the mean particle size of the precipitate (D50) being less than 200 μm, preferably less than 100 μm, according to one embodiment. Preferably, the particle size of the precipitate is in the range of 10 to 100 microns, more preferably in the range of 10 to 20 microns. The average particle size is determined at room temperature (20 ^° C.), for example by laser diffraction.

The glycoside, in particular Sterylglykosid, precipitates in the form of crystal agglomerates, wherein the agglomerates at

View under the microscope an amorphous structure of gelly loosely interconnected crystallites. These agglomerates usually do not consist of pure glycoside, in particular steryl glycoside, but also contain fatty acid esters which are adsorbed on the precipitate. The adsorbents according to the invention are also suitable for the administration of glycosides of animal origin which are still present in the biodiesel. Impurities due to glycosides of animal origin are found in biodiesel when animal fats are used as raw material. These animal fats contain cholesterylglycerides, which can lead to biodiesel problems similar to those described for the sterylglycosides of plant origin.

The adsorbent used in the process according to the invention has a high adsorption capacity, in particular for mono-, di- and triglycerides, as well as fatty acid soaps and glycosides. If the process is used for a post-purification of a biodiesel containing only small amounts of impurities, it is sufficient if only a small amount of the adsorbent is added to the crude biodiesel. The adsorbent can be easily separated after treatment, for example by filtration, again from the purified biodiesel. In one embodiment, the adsorbent is added in a proportion of less than 5% by weight, based on the crude biodiesel. According to a further embodiment, the adsorbent is added in an amount of less than 3 wt .-%, according to another embodiment in a proportion of less than 2 wt .-%. In order to achieve a sufficient cleaning effect, according to one embodiment, the adsorbent is added to the crude biodiesel in a proportion of more than 0.2 wt .-%, according to another embodiment in a proportion of more than 0.5 wt .-%.

As already explained above, the crude biodiesel still contains relatively large amounts of impurities after the alcoholysis when the transesterification is carried out using ethanol. Because of the high binding capacity of the inventive Method used adsorbent, this is therefore particularly suitable for a biodiesel, which is composed essentially of fatty acid ethyl esters.

The invention will be further illustrated by way of examples and with reference to the accompanying drawings. Showing:

Fig. 1: a graphic representation of the monoglyceride content of a biodiesel which has been purified with various adsorbents; and

Fig. 2: a graphic representation of the monoglyceride content of a biodiesel which has been purified with various pre-dried adsorbents.

The physical properties of the adsorbent were determined by the following methods:

BET surface area / pore volume after BJH and BET:

The surface area and the pore volume were determined with a fully automatic nitrogen porosimeter from Micromeritics type ASAP 2010.

The sample is cooled in a high vacuum to the temperature of liquid nitrogen. Subsequently, it becomes continuous

Nitrogen dosed into the sample chambers. By detecting the adsorbed amount of gas as a function of pressure, an adsorption isotherm is determined at a constant temperature. In a pressure equalization, the analysis gas is gradually removed and a desorption isotherm is recorded. To determine the specific surface area and the porosity according to the BET theory, the data are evaluated in accordance with DIN 66131.

The pore volume is further determined from the measurement data using the BJH method (I.P. Barret, L.G.Joiner, P.P. Haienda, J.Am.Chem.Soc.73, 1991, 373). This procedure also takes into account effects of capillary condensation. Pore volumes of certain volume size ranges are determined by summing up incremental pore volumes obtained from the evaluation of the BJH adsorption isotherm. The total pore volume by BJH method refers to pores with a diameter of 1.7 to 300 nm.

water content

The water content of the products at 105 ⁰ C is determined using the method DIN / ISO-787/2.

loss on ignition

In an annealed weighed porcelain crucible with lid, about 1 g of dried sample is weighed to the nearest 0.1 mg and annealed for 2 hours at 1000 ^° C. in a muffle furnace. Thereafter, the crucible is cooled in a desiccator and weighed.

Determination of dry residue

About 50 g of the air-dry clay material to be examined are weighed out on a sieve of the corresponding mesh size. The strainer is connected to a vacuum cleaner which, through a suction slot rotating under the bottom of the sieve, passes through the sieve all the parts which are finer than the sieve sucks. The strainer is covered with a plastic lid and the vacuum cleaner is switched on. After 5 minutes, the vacuum cleaner is switched off and the amount of remaining on the screen coarser fractions determined by differential weighing.

Determination of bulk density

A graduated cylinder cut off at the 1000 ml mark is weighed. Then, the sample to be examined is filled by means of a Pulvertrichters so in a train in the measuring cylinder that above the conclusion of the

Measuring cylinder forms a Schüttkegel. The pour cone is removed by means of a ruler, which is led over the opening of the measuring cylinder, and the filled measuring cylinder is weighed again. The difference corresponds to the bulk density.

Determination of glycerol and glycerides in biodiesel

The determination of the content of glycerol and glycerides in biodiesel was carried out according to DIN EN 14105.

Determination of steryl glycosides by GC-MS

For the determination of the steryl glycosides, a GC-MS method developed by ASG Analytik-Service Gesellschaft mbH, Trentiner Ring 30, 86356 Neusäß was used. The procedure was as follows:

1. Enrichment of Sterylglucoside

To enrich the Sterylglycoside was according to the

IP 387/97 Filter Blocking Tendency (FBT test) a defined The amount of raw biodiesel to be analyzed is filtered through a 1.6 μm glass fiber filter. For a complete test, about 300 mL biodiesel is needed.

The filter was then first extracted with 4 mL of hexane and then the steryl glycosides washed with 1 mL of pyridine from the filter. To the sample are added 100 μL of MSTFA (N-methyl-N- (trimethylsilyl) trifluoroacetamide) as the silylation reagent and 50 μL of tricaprine (71.3 mg of tricaprin per 10 mL of pyridine). The mixture was allowed to stand for 20 min at 60 ⁰ C and then added 7 mL of hexane. The mixture is filtered through a 0.45 μm syringe filter. For the measurements, 1 μL each of the solution was injected into the GC / MS system.

2. Calibration standards

The quantification of sterylglucosides was carried out by comparison with a calibration curve.

For this purpose, a stock solution of a pure Sterylglucosidmischung was prepared in pyridine, the concentration was set in the range of about 50 mg / 10 mL. Defined volumes of the stock solution were measured and mixed with 100 μL MSTFA and 50 μL tricaprin solution. The mixture was allowed to stand for 20 minutes at 60 ⁰ C and filtered after addition of 8 mL of hexane through a 0.45 micron syringe filter. For the measurements, 1 μL each of the solution was injected into the GC / MS system. From the intensities of the MS signals, a calibration curve was created as a function of the injected sample quantity.

3. Measurement on GC / MS 3.1 Conditions GC

Guard column: Zebron Guard Column; 10 m; 0.32 mm ID column: Zebron-5HT Inferno; 15 m; 0.32 mm ID; 0.25 μm injection: on column carrier gas: helium flow: 1.5 mL / min

Oven: 60 ⁰ C for 1 min, with 15 ° C / min to 375 ⁰ C, hold for 3 min temperature

3.2 Conditions MS segment 1: 0-2 min hexane, cut off segment 2: 2 - 25 min EI (auto), 40 - 650 m / z

Scan Time: 0.50 scans / sec

Multiplier Offset: 0 V Emission Current: 40 μA

Count Threshold: 1 counts

Target TIC: 10000 counts

Prescan Ionization Time 100 μsec

Max. Ionization Time: 5000 μsec Background Mass: 50 m / z

RF dump value: 650 m / z

4. Evaluation

The amount of sterylglucosides contained in the samples was determined by comparing the intensity of the MS signals with the calibration curve.

Adsorbents used

For the purification of crude biodiesel, various commercially available aluminosilicates were used. These are under the names Siral ^® 5, Siral ^® 30, Siral ^® 40 available. Furthermore, a boehmite was tested, which is sold under the name Pural ^® SCC 150. As a further adsorbent aluminas were used, which are offered under the name Puralox ^® . These adsorbents were manufactured by Sasol Germany GmbH,

Ankelmannsplatz 1, 20537 Hamburg, DE, related. As a comparison, a commercially available calcium bentonite was (calcigel ^®, Süd-Chemie AG, Munich, DE), as well as a commercially available synthetic magnesium silicate (Magnesol ^®, The Dallas Corp., Dallas, USA).

For the investigated adsorbents, the following designations are chosen below:

Adsorbent 1: Siral 5 ^®

Adsorbent 2: Siral ^® 30

Adsorbent 3: Siral ^® 40

Adsorbent 4: Puralox® ^® KR-160

Adsorbent 5: Pural ^® SCC 150

Adsorbent 6: Puralox ^® SCCa-150/230

The properties of the adsorbents are summarized in Table 1: Stolmar Scheele & Partner - 35/48 - 20 November 2009 34561-SOUTH-P-WO

Table 1: Physical properties of the adsorbents (according to Herstellerilerangaben) compared to a calcium bentonite

ul

Stolmar Scheele & Partner - 36/48 - 20. November 2009 34561-SOUTH P-WO

Example 1: Removal of sterol glycosides from soyabiodiesel

For the investigations, a biodiesel (methyl ester) made from soybean oil was used. The crude biodiesel had a non-acylated steryl glycoside content of 49 ppm.

To each about 500 to 800 g of the crude biodiesel 1 wt .-% adsorbent was added with stirring. The sample was stirred for 20 minutes at room temperature and then the adsorbent was separated by filtration through a paper filter. The filtrate was used directly for the quantification of the steryl glycosides.

The content of steryl glycosides determined after purification is summarized in Table 2 for the experiments carried out.

Table 2: Sterylglykosidgehalt in biodiesel (soybean oil) after purification with various adsorbents (1 wt .-%, based on the biodiesel)

With the adsorbents 1-6 used according to the invention, the sterol glycoside content could be lowered below the detection limit. With boehmite a significant depletion of the crude biodiesel of steryl glycosides succeeds. Thus, the method according to the invention shows the same performance as the magnesium silicate used already in the art as an adsorbent (Magnesol ^®). By contrast, the calcium bentonite used as a comparison shows only a low performance.

To further characterize the effectiveness of the adsorbents for the removal of sterylglycosides, their

Concentration gradually lowered. As a comparison was cleaned a sample of the raw biodiesel with Magnesol ^® . The adsorbent was added in an amount of 0.5% by weight, 0.2% by weight and 0.04% by weight, respectively. The purification was carried out as described above. The results are summarized in Table 3.

Table 3: Steryl glycoside content in biodiesel (soybean oil) after purification with various adsorbents at various concentrations

Adsorbent 0, 5 wt% 0.2 wt% 0.04 wt%

Magnesol ^® <5 <5 46

3 <5 <5 26

4 <5 8 n.d.

5 10 24 n.d.

6 14 25 n.d.

With an amount of 0.5 wt .-% adsorbent is achieved with all adsorbents a significant reduction in Sterylglycosidkonzentration. If the added amount is reduced to 0.04 wt .-%, with the adsorbent 3 is still a significant reduction in Sterylglycosidkonzentration achieved, while Magnesol ¹⁵ no significant reduction is observed. Example 2: Removal of Monoglycerides from Ethyl Biodiesel

For the investigation, an ethylbiodiesel obtained from soybean oil was used, which had a monoglyceride content of 1.92% by weight, determined in accordance with DIN EN 14105. This was treated because of the high monoglyceride content with 7 wt .-% adsorbent. For comparison, the cleaning was carried out using magnesium silicate (Magnesol ^®) and calcium bentonite.

100 ml of biodiesel were heated to 55 ° C, in each case with 7% by weight of the adsorbent added and for 45 minutes at this

Temperature stirred with a magnetic stirrer. The sample was then filtered through a syringe prefilter. The content of monoglycerides in the filtrate was determined according to DIN EN 14105.

In a first series of experiments, the adsorbents were used without predrying. The results are shown in Table 3 and FIG.

Table 3: Content of monoglycerides in ethylbiodiesel samples after treatment with 7% by weight of adsorbent

When using alumina adsorbents a significant reduction in monoglyceride content is achieved. This exceeds the performance of Magnesol ^® and Calciumbentonite.

Example 3: Removal of Monoglycerides from Ethyl Biodiesel with Pre-Dried Adsorbents

Example 2 was repeated, but the adsorbents were previously dried for 45 minutes at 55 ⁰ C in a drying oven. The water content after drying was less than 2% by weight for all adsorbents. Subsequently, the ethyl biodiesel sample with the dried adsorbents in the treated as described above. The content of monoglycerides determined in the filtrate is summarized in Table 4 and shown graphically in FIG.

Table 4: Content of monoglycerides in ethylbiodiesel after treatment with 7% by weight pre-dried adsorbent

By predrying the adsorbents, a further improvement of the adsorption performance can be achieved. The SiO ₂ - containing aluminas from Siraltyp (adsorbent 1, 2 and 3) show the highest efficiency thereby. If the bound amount of monoglyceride is converted into a binding capacity, the result is 16.7% by weight of monoglyceride for adsorbent 3. The adsorbents can thus be used very well for removing monoglycerides from biodiesel.

Claims

claims

A process for purifying biodiesel to provide a crude biodiesel; the crude biodiesel is reacted with an adsorbent containing at least one alumina-containing component having an aluminum content, calculated as A12O3, greater than 40% by weight; and a purified biodiesel is separated from the adsorbent.

2. The method according to claim 1, characterized in that the synthetic alumina-containing component has a specific surface area of more than 100 m ² / g.

3. The method according to claim 1 or 2, characterized in that the synthetic alumina-containing component has a pore volume of more than 0.3 ml / g, determined as a cumulative pore volume after BJH for pores having a diameter of 1.7 to 300 nm.

4. The method according to any one of the preceding claims wherein the aluminum oxide-containing component in addition to aluminum nor at least one further metal selected from the group consisting of silicon, titanium, magnesium, calcium, zirconium and mixtures thereof.

5. The method according to any one of the preceding claims, characterized in that the alumina-containing component is a synthetic aluminosilicate.

6. The method of claim 5, wherein the aluminosilicate has a silicon content, calculated as SiO2, of less than 60% by weight.

7. The method of claim 5 or 6, wherein the aluminosilicate is composed essentially of Si and Al oxides and the proportion of other metals, calculated as the most stable oxide, less than 1 wt .-% is.

8. The method according to any one of claims 1 to 4, characterized in that the alumina-containing component is an aluminum oxide.

9. The method according to claim 8, characterized in that the aluminum oxide is selected from γ ~, δ-, θ- and α-

Alumina.

10. The method according to any one of claims 1 to 4, characterized in that the alumina-containing component is a boehmite.

11. The method according to any one of the preceding claims, characterized in that the crude biodiesel contains at least one glycoside in a proportion of more than 10 ppm.

12. The method according to claim 11, characterized in that the at least one glycoside is a Sterylglykosid or a Cholesterylglykosid.

13. The method according to any one of claims 11 or 12, characterized in that the glycoside forms a fine precipitate in the crude biodiesel, which is a has mean particle size D50 of less than 200 microns.

14. The method according to any one of the preceding claims, characterized in that the reaction of the crude biodiesel is carried out with the adsorbent at a temperature of more than 50 ⁰ C.

15. The method according to any one of the preceding claims, wherein the adsorbent, based on the crude biodiesel, in a

Proportion of less than 5 wt .-% is added.

16. The method according to any one of the preceding claims, characterized in that the biodiesel is composed essentially of fatty acid ethyl esters.

17. The method according to any one of the preceding claims, characterized in that the adsorbent has a water content of less than 5 wt .-%.

18. The method according to any one of the preceding claims, characterized in that the adsorbent is provided in the form of a column packing, which is repeatedly regenerated and used several times.