Processes for the esterification of free fatty acids and the production of biodiesel

Abstract

The effluent from an acid esterification of free fatty acid with alkanol to produce alkyl ester of fatty acid is contacted with glycerin to remove water and alkanol. The alkanol separated with the glycerin can be recycled to the acid esterification by contacting the glycerin with fatty acid-containing feed being passed to the acid esterification.

Description

FIELD OF THE INVENTION[0001]This invention pertains to processes for making alkyl esters, especially biodiesel, from feeds containing free fatty acids and to the esterification by acid catalysis of free fatty acids with lower alkanol.BACKGROUND TO THE INVENTION[0002]Biodiesel is being used as an alternative or supplement to petroleum-derived diesel fuel. Biodiesel is a mixture of alkyl esters which can be made from various bio-generated oils and fats from vegetable and animal sources.[0003]One process for making biodiesel involves the transesterification of triglycerides in the oils or fats with a lower alkanol in the presence of a base catalyst to produce alkyl ester and a glycerin co-product. Unfortunately, most oils and fats useful as triglyceride-containing feeds for transesterification also contain free fatty acids which are not converted under typical transesterification conditions to biodiesel. Moreover, biodiesel must meet demanding product specifications. See, for instance,...

AI Technical Summary

Benefits of technology

[0012]This invention provides improved processes for the esterification of feeds containing free fatty acids especially glycerides feeds containing free fatty acids wherein the glycerides in the feed are suitable to be transesterified with alkanol to produce biodiesel. The esterification of the free fatty acids is conducted with a stoichiometric excess of alkanol to provide an esterification effluent containing alkyl esters, unreacted alkanol and water. In accordance with processes of this invention, at least a portion of the esterification effluent is contacted with glycerin to reduce the concentration of water and alkanol in the esterification effluent containing alkyl esters, and the glycerin is separated by phase separation.

[0013]In one broad aspect of the processes of this invention, a feed containing free fatty acid is subjected to acidic esterification conditions in the presence of a stoichiometric excess of alkanol to provide an esterification effluent containing alkyl ester, water and unreacted alkanol. The esterification effluent is contacted with glycerin to form a two phase mixture. Water and alkanol are extracted into the glycerin phase which can be phase separated from the oil phase comprising alkyl ester. The processes of this aspect of the invention are particularly useful in conjunction with facilities to produce biodiesel from glycerides by transesterification as glycerin is available as a co-product of the transesterification. Additionally, where the acid catalyst is contained in the esterification effluent, the glycerin phase can remove the acid catalyst from the esterification effluent.

Problems solved by technology

Unfortunately, most oils and fats useful as triglyceride-containing feeds for transesterification also contain free fatty acids which are not converted under typical transesterification conditions to biodiesel.

These specifications, among other requirements, limit the amount of free fatty acid that can be contained in biodiesel.

They caution that acid esterification should only be used if disposal of the fatty acids or soaps thereof is not economic or possible or the feed used generates a lot of fatty acids.

They note that acid esterification increases capital and production costs, and that sulfuric acid creates sulfates which increase the removal cost from glycerin.

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