Effects of Raw Materials and Production Practices on Biodiesel Quality and Performance

Abstract

The demand for transportation fuels is increasing around the world, especially the demand for petroleum-based fuels. To cope with rising demand and dwindling petroleum reserves, alternative motor fuels such as biodiesel are at the forefront of commercialization. Biodiesel is an environmental renewable clean burning fuel. Biodiesel is a replacement for diesel in compression-ignition engines. Biodiesel is composed of mono-alkyl esters of long chain fatty acids. These esters are produced when virgin vegetable oils, i.e., soy, canola, palm and rapeseed oil, animal fats from tallow, poultry offal and fish oils or used cooking oils and trap grease from restaurants are reacted with an alcohol. The major chemical components of vegetable oils, fats and greases are triacylglycerols. The chemical reaction of converting triacylglycerols into methyl esters is termed transesterification. A stochiometric excess of alcohol and a catalyst is required for the effective transesterification of triacylglycerols into alkyl esters. The transesterification reaction is depicted in Figure 1. The alcohol used for producing biodesel is usually methanol. Methanol is the least expensive alcohol and therefore the alcohol of choice. The catalyst can be an acid or a base depending on the amount of free fatty acids present. The catalyst bases most commonly used are NaOH or KOH. The acid catalyst is usually H2SO4. In order to be commercially available in the United States and Canada, biodiesel must meet the specifications in ASTM D6751, Standard Specification for Biodiesel Fuel (B100) Blend Stock for Distillate Fuels. In Europe they follow the requirements and test methods for fatty acid methyl esters (FAME). The requirements are specified in EN 14214. The requirements for these two standards are given in Table 1. These specifications are designed to meet the requirements necessary for the proper performance of compression-ignited engines. Feedstock, feedstock quality and production practices can influence the quality of the biodiesel and therefore, the performance and commercial approval of the final product.