WO2009021486A1 - Liquid biofuel made of esters and bound glycerides, and also process for production thereof - Google Patents

Abstract

The present invention relates to a biofuel and to a process for production thereof, which biofuel contains at least one fraction of triglycerides, a fraction of monoglycerides, a fraction of diglycerides and a fraction of alkylesters of fatty acids. The biofuel may be obtained by partial transesterification of vegetable oil or vegetable fat and is distinguished in that the mass fraction of alkylesters of fatty acids in the biofuel is smaller than the mass fraction of triglycerides. The fuel is suitable in particular as additive for conventional fuels, may be produced at high yield and can also be used at relatively low temperatures below 10°C.

Description

 Liquid biofuel of esters and bound glycerides and process for the preparation thereof

Technical application

The present invention relates to a liquid biofuel based on triglycerides, mono- and diglycerides and fatty acid alkyl esters and a process for the preparation thereof. The fuel is particularly useful as an additive to conventional fuels, e.g. Diesel, suitable. Direct use as fuel for internal combustion engines is also possible.

State of the art

Biofuels and biofuel mixtures based on vegetable oil or animal fat are described, for example, in DE 4116905 C1, WO 95/25152 A1, EP 855436 A2 or US Pat. No. 5,713,965. In particular, these publications disclose mixtures of rapeseed oils with gasoline or diesel to which an additional substance is added. In DE 4116905 Cl, this additional constituent is an alcohol, in WO 95/25152 Al an alkyl ester of a short-chain fatty acid having a chain length of at most 6 C atoms and in EP 855436 A2 an acetal.

The documents US 5713965 A, US 5480787 A and EP 1705238 Al (= WO 2005075615 Al) describe processes for the preparation of fatty acid alkyl esters by lipase-catalyzed transesterification of oils and fats. In these processes, the fatty acid Alkyl esters of bound and free glycerol separated by known methods and thus not used as a fuel fraction. The yield based on the raw material used oil or fat is due to the separation of glycerol only about 90%.

The document EP 1126011 A2 describes a process for the heterogeneously catalyzed transesterification of fats and oils under conditions in which at least one of the reactants is in the critical state. As in the case of the abovementioned publications US Pat. No. 5,713,965 A, US Pat. No. 5,480,787 A and EP 1,705,238 Al, the glycerol formed here too is separated from the fatty acid alkyl esters and not used as a fuel fraction.

The document US 5578090 A describes a biofuel consisting of fatty acid alkyl esters and bound glycerol. In contrast to the fuel described here, the bound glycerides are not in the form of mono-, di- and trialkylglycerol esters, but are present as mono-, di- and trialkylglycerol ethers. These ethers are prepared in a different from the transesterification reaction from the intermediates of the transesterification reaction.

The document US 5316927 A describes a process for the preparation of monoglycerides and fatty acid alkyl esters by lipase-catalyzed transesterification of fats and oils. After the reaction, the two products are separated and fed to different applications. Diesel fuel is a refined petroleum product, which makes up a significant part of the international fuel market. Finite resources, dramatic price increases and the current climate debate have led to increased efforts to replace, at least in part, fossil diesel fuel with renewable raw materials.

At present, vegetable oil and biodiesel (fatty acid alkyl esters) are available for this purpose. Plant oils are predominantly triglycerides, i. Esters of glycerine and three fatty acids, and too low levels of free fatty acids.

The use of pure vegetable oil as a diesel fuel is not without problems. Due to the high viscosity and the low cetane number, the combustion of the triglycerides is incomplete, which leads to deposits on valves and injection nozzles as well as to high emission values. An admixture of vegetable oil to fossil diesel is also problematic because these mixtures, especially at lower temperatures, are unstable and thus there is a risk of separation in the fuel tank.

An essential part of the problem can be circumvented by the transesterification of triglycerides with a monohydric alcohol. The resulting fatty acid alkyl esters have a diesel-like viscosity and Cetane number and can therefore be used relatively easily as a diesel substitute.

In the transesterification of vegetable or animal oils or fats, in addition to fatty acid alkyl esters (biodiesel), about 10% of free glycerm is produced. This is insoluble in biodiesel and therefore can not be used as a fuel fraction. The separated free glycerine reduces the fuel yield of the process and restores due to the required

Downstream-Processings as well as the difficult release situation for Glycerin represent a not inconsiderable cost factor.

PCT / DE2005 / 002156 describes a fuel produced by partial transesterification of triglycerides. In this case, the fuel yield is 100%, since the glycerol contained in fats and oils is not released, but is kept in the form of mono-, di- and triglycerides in solution. This mixture of bound glycerol and fatty acid alkyl esters is stable at room temperature. At lower temperatures of <10 ° C, however, crystallization processes and the precipitation of individual components occur, in particular in the case of the compositions described as particularly advantageous in PCT / DE2005 / 002156. The fuel described in PCT / DE2005 / 002156 is therefore suitable only for use at room temperature or at higher temperatures. Especially for areas with low

Temperatures, the described fuel is therefore unsuitable. The object of the present invention is to provide a biofuel and a process for the production thereof which can be prepared with high yield and can also be used at lower temperatures.

Presentation of the invention

The object is achieved with the biofuel according to claim 1 and the method according to claim 13. Advantageous compositions of the biofuel and embodiments of the method for producing the same are the subject of the dependent claims or can be taken from the following description and the exemplary embodiments.

The biofuel according to the invention contains at least one fraction of triglycerides, in particular vegetable oil or vegetable fat, and at least one fraction of monoglycerides and at least one fraction of diglycerides and additionally contains at least one fraction of fatty acid alkyl esters.

Surprisingly, it has been found that there is a defined range of compositions from the said fractions, in which it succeeds, despite reducing the viscosity and increasing the cetane number by partial transesterification of all contained in the oil glycerol in the form of mono-, di- and triglycerides in the fuel to keep in solution and to achieve a storage even under 10 ⁰ C without segregation or crystallization. This segregation remains even after a mixture of the biofuel according to the invention with diesel fuel, although by the mixture with Diesel the polarity of the mixture is changed. Mixtures of the biofuel of the invention with diesel therefore remain clear and single-phase even in winter conditions.

The decisive factor for the optimized solubility of glycerides in fatty acid alkyl esters (FSAE) even at lower temperatures shows that the proportion of FSAE in the fuel must be smaller than the proportion of triglycerides. A particularly good solubility of glycerides even at temperatures below 10 ⁰ C is achieved if the triglyceride content is greater than 29 Mass .-% is selected, advantageously greater than 40 mass%, and the FSAE content greater than 14 Mass .-% and less than 36 mass%.

Another factor to increase the solubility of glycerides in FSAE-containing fuels is the ratio of monoglycerides to diglycerides.

At a ratio of diglycerides to monoglycerides, which falls below the value of 2, there is a particularly rapid precipitation of particles.

A particularly advantageous mixture of mono-, di-, triglycerides with FSAE for cold storage contains the following composition:

A mixture which contained 20-25% by mass of FSAE, 50-55% by weight,% of triglycerides, 20% by weight of diglycerides and 5% by weight of monoglycerides proved to be particularly cold-stable. A further improvement in cold stability can be achieved by adding up to 2% by weight of ethanol.

The biofuel can be mixed in any ratio with fossil fuel, biodiesel or BTL fuel, thereby diluted and used as fuel for internal combustion engines. It is also possible to achieve a dilution of the fuel according to the invention in that diesel fuel or biodiesel is already added before the partial transesterification of the triglycerides.

It is also appropriate to use mono- and diglycerides in biofuel derived from another reaction, e.g. in the transesterification of

Vegetable oil are formed to fatty acid alkyl esters. However, it is also possible and possibly advantageous to use mono-, di- and triglycerides which originate from another, possibly animal source or are of synthetic origin. Thus, mono- and diglycerides can be used in biofuel containing fatty acids with less than 10 carbon atoms. One possible method of production of the proposed biofuel is based on a partial transesterification of triglycerides. For this purpose, triglycerides are mixed with an alcohol and through

Adding a catalyst or bringing it into contact with a catalyst. The triglycerides used may be a raw material of vegetable, animal or synthetic origin as well as mixtures of triglycerides of various origin.

The alcohol used is preferably a monohydric alcohol of any chain length. Both organic and inorganic compounds as well as enzymes and microorganisms can be used as the catalyst. The reaction can be carried out both by homogeneous and heterogeneous catalysis. In an economically particularly advantageous embodiment used as raw material source used cooking oils.

About the residence time, the type and amount of the catalyst and the amount of alcohol used, the composition of the biofuel, in particular the ratio of the proportions by weight of fatty acid alkyl esters and triglycerides and / or the mass fractions of diglycerides to monoglycerides, can be adjusted. By residence time is meant the period of time during which the catalyst and the added alcohol are in contact with the triglycerides. Particularly advantageous is the use of carrier-bound sn-1,3 regiospecific lipases as a catalyst. It shows that a gradual addition of enzymes over several discontinuous production cycles leads to a particularly good yield. In each production cycle, the enzyme of the previous production cycle is used, with a small amount of unused enzyme being additionally added for a particularly good yield.

In addition, it has been shown that a substoichiometric alcohol addition in several steps or a continuous alcohol addition is particularly advantageous. If possible, the gradual or continuous addition of alcohol should be designed such that an alcohol concentration of 4% by mass is not exceeded. Particularly advantageous for a high enzyme stability and thus a long service life of the enzyme was a maximum alcohol concentration of 3% by mass.

It proves to be particularly advantageous for the same purpose to dissolve the alcohol in a largely freed from lipases reaction mixture and bring after the complete dissolution of the alcohol with the lipases again in contact. In this case, lipase-free product is removed from the reaction vessel several times during the production cycle in order to dissolve the alcohol required for the reaction. Contact of high alcohol concentrations with the enzyme is thereby avoided. It has been found that the alcohol concentration in the said reaction mixture before Jerk mixing with the lipase should not exceed 5%.

The process temperature depends on the catalyst used and the triglyceride used, in particular its melting temperature. The residence time depends on the catalyst used, the amount of catalyst, the alcohol used and the triglyceride used.

embodiment

In 100g of rapeseed oil, 2.0 g of ethanol are completely dissolved. The transesterification reaction is started by adding 1.0 g of an immobilized S _n -I, 3 regiospecific lipase. The mixture is mixed for 3 hours at the temperature with the highest lipase activity.

After 3 hours 5OmL lipase-free intermediate are removed from the reaction vessel. 2.0 g of ethanol are completely dissolved in the withdrawn reaction medium. Subsequently, the product-ethanol solution is returned to the reaction vessel. This is repeated after a further 3 hours dwell time.

After a total of 10 hours, the lipase is separated from the reaction product to obtain a clear, single-phase liquid consisting of 30% by mass of fatty acid ethyl ester, 24% by mass of diglycerides,

9 mass% monoglycerides and 36 mass% triglycerides and about 1 mass% ethanol. The separated enzyme can be reused in a second production cycle. This is carried out identically to that described above. At the start of the reaction, 0.1 g of fresh enzyme is added to the enzyme used in the first production cycle.

Claims

claims 1. biofuel containing at least one fraction of triglycerides, a fraction of monoglycerides, a fraction of diglycerides and a fraction of fatty acid alkyl esters, characterized in that the mass fraction of fatty acid alkyl ester in the biofuel is less than the mass fraction of triglycerides. 2. biofuel according to claim 1, characterized in that the ratio of the mass fractions of diglycerides to monoglycerides ≥ 2. 3. biofuel according to claim 1 or 2, characterized in that the mass fraction of fatty acid alkyl ester amounts to a minimum of 15% and a maximum of 35%. 4. biofuel according to one of claims 1 to 3, characterized in that the mass fraction of triglycerides amounts to at least 30%. 5. biofuel according to claim 4, characterized in that the mass fraction of triglycerides is greater than 40%. 6. biofuel according to claim 4 or 5, characterized in that the mass fraction of triglycerides a maximum of 65 ^! amounts. 7. Biofuel according to one of claims 1 to 6, characterized in that the mass fraction of monoglycerides is between 0.1% and 10%. 8. biofuel according to any one of claims 1 to 7, characterized in that the mass fraction of diglycerides is between 4% and 30%. 9. biofuel according to claim 1, characterized in that the mass fraction of fatty acid alkyl ester between 20% and 25%, the mass fraction of triglycerides between 50% and 55%, the Mass fraction of diglycerides at 20% and the mass fraction of monoglycerides is 5%. 10. biofuel according to any one of claims 1 to 9, characterized in that the biofuel contains an addition of ethanol in a mass fraction of up to 2%. 11. Biofuel according to any one of claims 1 to 10, which is fossil fuel, biodiesel or BTL Fuel is mixed. 12. Use of the biofuel according to one of the preceding claims as fuel for internal combustion engines. 13. A method for producing the biofuel according to any one of claims 1 to 11 by partial transesterification of triglycerides, wherein at least one fraction of triglycerides, a fraction of monoglycerides, a fraction of diglycerides and a fraction of fatty acid alkyl ester is obtained, characterized in that the partial transesterification is carried out so that the mass fraction of fatty acid alkyl ester in the biofuel is less than the mass fraction of triglycerides 14. The method according to claim 13, characterized in that the partial transesterification is carried out so that the ratio of the mass fractions of diglycerides to monoglycerides ≥ 2. 15. The method according to claim 13 or 14, characterized in that as catalyst for the partial transesterification bound sn-1,3 regiospecific lipases are used. 16. The method according to claim 15, characterized in that the partial transesterification over several discontinuous production cycles with stepped wise addition of enzymes. 17. The method according to any one of claims 13 to 16, characterized in that an addition of alcohol for the transesterification is carried out stoichiometrically. 18. The method according to claim 17, characterized in that the addition of alcohol takes place continuously or in several steps during the transesterification. 19. The method according to claim 18, characterized in that upon addition of the alcohol in several steps, an alcohol concentration of 3% by mass is not exceeded. 20. The method according to any one of claims 13 to 16, characterized in that in the transesterification first alcohol in a largely freed from lipases, the reaction mixture containing triglycerides dissolved and the reaction mixture is brought into contact only after the complete dissolution of the alcohol with lipases as a catalyst , 21. The method according to claim 20, characterized in that in the reaction mixture before contact with the lipases, an alcohol concentration of ≤ 5% by mass is set. 22. The method according to any one of claims 13 to 21, characterized in that the partial transesterification takes place with vegetable oil or vegetable fat as triglycerides.