By Ron Kotrba | May 01, 2012

For anyone who thinks the biodiesel production process is a simple, cut-and-dried, cookie-cutter procedure, consider this.

There are multitudes of feedstocks, for starters, each of which may require pretreatment options in one form or another. Free fatty acids on the frontend can be handled in one of many ways, including acid esterification, glycerolysis or simple removal for sale in other markets, to name a few. Or, in the case of some newer production technologies, the free fatty acids can simply be mixed with the triglycerides for single-step esterification/transesterification.

Scores of main conversion options are available, including the most common approach, homogeneous base chemical catalysis with sodium or potassium methoxide. Then there is also heterogeneous powder catalysis to consider, such as that offered by Catilin, and solid catalyst methods. Just recently, enzymatic conversion routes have surfaced by companies such as Piedmont, which is working with Novozymes, and Biodiesel Experts International, which is working with Isreal-based Transbiodiesel.

On the backend, there are several fuel purification options, including water and caustic water washing, dry washing using various media or ion exchange resins, and now enzymatic polishing. For problematic feedstocks, the final treatment that works every time, while expensive to build and operate, is distillation.

Over the years, the biodiesel fuel quality specification has evolved as a result of issues in the marketplace, concerns from oil companies and states being required to blend biodiesel, the introduction of alternative feedstocks, and the forethought of dedicated biodiesel industry personnel. With tighter specifications come improved production and purification processes. For instance, the introduction of the cold soak filtration test in the quality specification has led to some producers chilling down their fuel and warming it back up again to remove any impurities such as sterols, which, if not removed, would lead to a failed CSFT and, if that fuel entered the marketplace, clogged filters.

In this issue, we bring you features and columns focused on biodiesel purification, including some of the latest developments in enzymatic polishing. Enjoy the content and let us know what you think.

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