Method of increasing the oxidation stability of biodiesel

Abstract

The invention relates to a method of increasing the oxidation stability of biodiesel, which comprises adding a primary antioxidant having a melting point of less than or equal to 40° C. to the biodiesel to be stabilized in an amount of from 10 to 20 000 ppm (w / w), where the primary antioxidant comprises at least one compound having the structure where: R1, R2=hydrogen, a linear alkyl group having from 1 to 20 carbon atoms or where * is a carbon atom of the aromatic ring system, R3, R5=hydrogen, a linear alkyl group having from 1 to 20 carbon atoms, R4=hydrogen, a linear alkyl group having from 1 to 40 carbon atoms, where both the substituents of the type R1 and R2 and those of the type R3 and R5 are in each case identical or different.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The invention relates to a method of increasing the oxidation stability of biodiesel. The invention also includes the oxidation-stabilized produced thereby. [0003] 2. Description of the Background [0004] An alternative to conventional diesel fuel which is being used to an increasing extent today is biodiesel, which comprises monoalkyl esters of vegetable oils, animal fats and also used cooking fats. Biodiesel is obtained by transesterification of oils, for example rapeseed oil, soybean oil or sunflower oil and also used cooking oils, with an alcohol in the presence of a catalyst. [0005] Since the importance of biodiesel as an alternative diesel fuel for passenger cars has been continually increasing in importance in recent times, the production of biodiesel has also increased to a corresponding extent in recent years. Biodiesel has a high content of unsaturated fatty acid esters which can easily be oxidized by atmos...

AI Technical Summary

Benefits of technology

[0009] It is an object of the present invention to provide an improved method of increasing the oxidation stability of biodiesel. In particular, it is an object of the invention to improve the processability of the primary antioxidant in biodiesel and thus improve the economics or the use of primary antioxidants in biodiesel.

[0010] It has surprisingly been found that the addition of a liquid primary antioxidant based on substituted alkylphenols having the structure I to biodiesel makes it possible to improve the handleability of the primary antioxidants in biodiesel. The primary antioxidant used in the method of the invention has a low melting point, i.e. a melting point of less than or equal to 40° C. Owing to its low melting point, this primary antioxidant can, in the method of the invention, be mixed as liquid directly into the biodiesel without this primary antioxidant firstly having to be dissolved in a solvent, for example alcohol, or in biodiesel. Thus, the preparation of a masterbatch of this primary antioxidant in biodiesel can be dispensed with. The masterbatches are generally prepared using the biodiesel for which the masterbatch is ready to be used. In the case of large distances between biodiesel and antioxidant manufacturers in particular, this leads to high costs for storage and transport in the case of primary antioxidants according to the prior art. The primary antioxidant used in the method of the invention thus leads to low production costs for the oxidation-stabilized biodiesel, since, firstly, the preparation of solutions or masterbatches comprising the active ingredient primary antioxidant can be dispensed with and, secondly, the present method shows that a product mixture from the manufacturing process of substituted alkylphenols can be used without complicated separation and purification steps. A further advantage of the method of the invention is that the production of the oxidation-stabilized biodiesel can be carried out at low temperatures and within a relatively short time. The method of the invention thus makes it possible to improve the economics of the production of oxidation-stabilized biodiesel. The active content of the liquid primary antioxidant used according to the present invention is 100% compared to 20% of the liquid primary antioxidants according to the prior art, since the liquid generally contains only about 20% by weight of the active ingredient antioxidant. The use of a liquid primary antioxidant according to the method of the invention likewise enables transport and storage costs to be saved as a result of the high active content of primary antioxidant per liter. The use of a liquid primary antioxidant according to the method of the invention also leads to reduced crystallization of the primary antioxidant in the biodiesel or in plant components at low temperatures.

[0018] R4=hydrogen, a linear alkyl group having from 1 to 40 carbon atoms, where both the substituents of the type R1 and R2 and those of the type R3 and R5 are in each case identical or different, for increasing the oxidation stability of biodiesel.

Problems solved by technology

In the case of large distances between biodiesel and antioxidant manufacturers in particular, this leads to high costs for storage and transport in the case of primary antioxidants according to the prior art.

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