Catalyzing a New Alternative

Heterogeneous catalyst could offer new recipe for biodiesel production
By Bryan Sims | August 16, 2011

Typically, biodiesel is produced via a transesterification reaction in a homogenous phase, meaning the raw materials, such as soybean oil and methanol and a catalyst are in the same liquid phase. But this route can be cost-prohibitive for producers as conventional catalysts used today, such as sodium or potassium methoxide, cannot be reused or regenerated since the catalyst is consumed in reaction. Researchers at the Autonomous Meritorious University of Puebla in Mexico believe they’ve discovered an alternative to this conventional route, however, by employing hydrated lime, or calcium hydroxide, in a heterogeneous process that enables easier separation, higher activity, selectivity and longer catalyst life.

According to Manuel Sanchez-Cantu, lead researcher on the project at the school’s chemical engineering department, he and his team purchased 24-kilogram sacks of hydrated lime from a seller in Perote, Mexico, and soybean oil that they bought from a local grocery store. They then added methanol and lime to the used soybean oil. After two hours at reaction temperatures of around 60 degrees Celsius, the process yielded conversion rates that approached 100 percent. Sanchez-Cantu notes that the hydrated lime was reused twice with full conversion of the used soybean oil and methanol to produce biodiesel and the catalyst was not consumed or dissolved in the reaction, which allowed for separation from the products via centrifugation.

“The advantage that hydrated lime has over other catalysts is that hydrated lime represents an inexpensive option compared to other catalysts for obtaining biodiesel since it’s produced in large amounts and it’s readily available,” Sanchez-Cantu says, adding that hydrated lime is also commonly used for industrial applications such as food preparation (to make tortillas in Mexico), water treatment and petroleum refining. Previous studies have indicated that a different type of lime, calcium oxide, has also shown to efficiently catalyze the transesterification process.

That hydrated lime could also potentially be used for a long period allowing the generation of technology adjusted for continuous processing, which would improve the economics of biodiesel production, Sanchez-Cantu says, adding, "though a lot of work and research should be done."

Sanchez-Cantu says castor oil will also be examined using hydrated lime as a catalyst, but more work is being carried out to optimize the process with soybean oil. “We’re performing tests on the catalyst’s stability and investigating ways to increase it,” he says. “Also, research is underway on the shaping process of the catalyst employing distinct binders in order to carry out continuous production of biodiesel.”

—Bryan Sims

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