Elsevier

Fuel Processing Technology

Volume 86, Issue 10, 25 June 2005, Pages 1097-1107
Fuel Processing Technology

Biodiesel processing and production

https://doi.org/10.1016/j.fuproc.2004.11.005Get rights and content

Abstract

Biodiesel is an alternative diesel fuel that is produced from vegetable oils and animal fats. It consists of the monoalkyl esters formed by a catalyzed reaction of the triglycerides in the oil or fat with a simple monohydric alcohol. The reaction conditions generally involve a trade-off between reaction time and temperature as reaction completeness is the most critical fuel quality parameter. Much of the process complexity originates from contaminants in the feedstock, such as water and free fatty acids, or impurities in the final product, such as methanol, free glycerol, and soap. Processes have been developed to produce biodiesel from high free fatty acid feedstocks, such as recycled restaurant grease, animal fats, and soapstock.

Introduction

Biodiesel is an alternative fuel for diesel engines that is produced by chemically reacting a vegetable oil or animal fat with an alcohol such as methanol. The reaction requires a catalyst, usually a strong base, such as sodium or potassium hydroxide, and produces new chemical compounds called methyl esters. It is these esters that have come to be known as biodiesel.

Because its primary feedstock is a vegetable oil or animal fat, biodiesel is generally considered to be renewable. Since the carbon in the oil or fat originated mostly from carbon dioxide in the air, biodiesel is considered to contribute much less to global warming than fossil fuels. Diesel engines operated on biodiesel have lower emissions of carbon monoxide, unburned hydrocarbons, particulate matter, and air toxics than when operated on petroleum-based diesel fuel.

The objective of this paper is to describe the processing and production of biodiesel. The emphasis will be on processing as it is conducted in the United States, where most biodiesel is produced by reacting soybean oil or used cooking oils with methanol.

Section snippets

Background

At current production levels, biodiesel requires a subsidy to compete directly with petroleum-based fuels. However, federal and state governments are providing incentives that encourage the rapid growth of the biodiesel industry. Current production levels are 20–25 million gallons/year, but achieving current European levels of 500 million to 1 billion gallons/year should be feasible.

The combined vegetable oil and animal fat production in the United States totals about 35.3 billion pounds per

Conclusions

Biodiesel is an important new alternative transportation fuel. It can be produced from many vegetable oil or animal fat feedstocks. Conventional processing involves an alkali-catalyzed process, but this is unsatisfactory for lower cost high free fatty acid feedstocks due to soap formation. Pretreatment processes using strong acid catalysts have been shown to provide good conversion yields and high-quality final products. These techniques have even been extended to allow biodiesel production

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