Vapour phase esterification of free fatty acids

Abstract

A method is presented for producing biodiesel from a triglyceride feedstock. The feedstock is pretreated by thermal cracking or rapid pyrolysis to form a middle distillate fraction rich in fatty acids. The middle distillate fraction is then treated by vapour phase esterification under vacuum and in the presence of an alcohol and a solid acid catalyst to produce a biodiesel stream. The biodiesel stream can be treated with a basic solution to convert residual free fatty acids to non-foaming metallic soaps, which are separated by known means. A method is also provided for producing a biodiesel / naphtha mixture, in which a triglyceride feedstock is pretreated by thermal cracking or rapid pyrolysis to produce a middle distillate fraction, a naphtha stream and a gas stream. The naphtha stream and the middle distillate fraction are then treated by vapour phase esterification under vacuum and in the presence of an alcohol and a solid acid catalyst to produce a mixed biodiesel / naphtha stream.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a method of producing biodiesel from triglycerides combining thermal cracking and esterification.BACKGROUND OF THE INVENTION[0002]In recent years, the area of biodiesels has drawn a great deal of attention. Biodiesels are fuels produced from the esterification of biomass-derived oils with alcohol. Biodiesel can be produced from triglyceride sources such as canola, corn, soybean, palm etc.[0003]Another potential source for biodiesels are the waste triglycerides from animal rendering facilities and waste cooking oils, such as those found as restaurant trap greases. However, this potential is presently still under-explored and waste triglycerides, trap grease in particular, are most commonly dumped into landfills. Waste triglycerides often have high contaminants content, including bacteria, which must effectively be removed before processing. Furthermore, waste triglycerides tend to have a high content of free fatty acid (FFA...

AI Technical Summary

Benefits of technology

The present invention provides a method for producing biodiesel and biodiesel / naphtha mixtures from triglyceride feedstock. The method involves pretreating the feedstock by thermal cracking or rapid pyrolysis to remove contaminants and convert triglycerides to a middle distillate fraction rich in free fatty acids. The middle distillate fraction is then treated by vapor phase esterification under vacuum and in the presence of an alcohol and a solid acid catalyst to produce a mixed biodiesel / diesel stream. The mixed biodiesel / diesel stream can then be treated with a basic solution to convert residual free fatty acids to non-foaming metallic soaps, which can be separated by vacuum distillation, centrifugation, filtering or combinations therof. The technical effects of this invention include improved production of biodiesel and biodiesel / naphtha mixtures with reduced contamination levels.

Problems solved by technology

However, this potential is presently still under-explored and waste triglycerides, trap grease in particular, are most commonly dumped into landfills.

Waste triglycerides often have high contaminants content, including bacteria, which must effectively be removed before processing.

Mixtures of free fatty acids and triglycerides have been found to be very difficult to convert to useful fuels by any traditional methods.

However, the high FFA content in waste triglycerides causes undesirable soap formation in base catalyzed esterification processes, rendering this process inoperable.

Waste triglycerides are also often heavily contaminated by, for example, bacteria, detergents, silts and pesticides.

This method addresses the issue of high FFA content but does not treat or remove contaminants.

An alternate method involves performing both esterification and transesterification of triglycerides using a strong acid such as H2SO4 or sulphamic acid; however the product clean up is cumbersome and usually involves neutralization of the acidic catalyst and the removal of resulting salts.

Acid ion-exchange resins are another option, but due to possible resin degradation esterification must be carried out below the resin degradation temperature, which significantly slows down the process.

Reaction time required for typical bio-diesel production by acid esterification ranges from 10 hours to 20 hours, which makes acid esterification of fatty acids an industrially unattractive route for fuel production.

However, carrying out acid esterification at above water's boiling point diminishes alcohol solubility in the methyl-esters.

This is undesirable since, in order to bring esterification to near completion a high alcohol concentration must be maintained in the reactant mixture and this becomes difficult due to limited alcohol solubility.

Furthermore, in typical thermal cracking of clean or waste triglycerides in the presence of a catalyst, there is a tendency for coke formation to occur on the catalyst, resulting in rapid deactivation.

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