The additive advantage

2nd May, 2008

A new generation of additives is helping the industry integrate alternative fuels

To understand the critical and variable roles that additives play in realising the potential of specific natural feedstock alternatives, it is helpful to review the chemical process at the heart of biodiesel manufacture. All natural oils are glycerol esters of fatty acids, commonly known as triglycerides. In this process, the glycerol is removed and replaced with methanol, breaking up the triglyceride to create a fatty acid methyl ester (FAME).

Although the properties of FAME are more similar to diesel than triglycerides, the fatty acid chain is thermally stressed during manufacture in proportion to its level of polyunsaturation, as seen in figure 1. The more saturated natural oils, such as coconut oil, are more stable but freeze easily; the more polyunsaturated oils, such as rapeseed, offer better cold flow but exhibit less stability.

Other factors that can contribute to the low stability of natural oils include:

• The virgin or recycled nature of the feedstock
• Their lack of degradationinhibiting antioxidants
• The production process (distillation can reduce stability)
• Improper handling

Cold flow is only one of the many performance characteristics of FAMEs that needs to be enhanced with additive technology to help maintain fuel quality.

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