Evaluation of Recovered Vegtable Oil as a Biodiesel Feedstock

Abstract

About 7,000 t of recovered vegetable oil (RVO) are collected in Ireland each year. The use of this material in animal feed has been banned under recent EU legislation because of food safety and animal health concerns. In order to assess its potential as a biodiesel (fatty acid methyl ester) feedstock, twenty-two 350-kg batches, with a wide range of acid values, were esterified. Ester properties were largely within specification, though variable low-temperature properties sometimes caused the material to be unsuitable for winter use. This problem could be overcome by blending with mineral diesel, but the addition of two pour-point depressants had little effect. Total glycerol concentrations in some batches were high; it could be improved by small changes in the process. Ester yields were low, due mainly to dissolution of ester in the glycerol, but also to saponification of the triglycerides. Tests of the biodiesel in vehicles showed no adverse effects on engine or lubricating oil. Specific fuel consumption was slightly higher than with mineral diesel, which would be expected with biodiesel from any feedstock. The results indicate that it is possible to produce biodiesel of acceptable quality from RVO. Where ester low-temperature properties are inadequate, the problem can be overcome by blending with mineral diesel.