Biodiesel has emerged as an ideal candidate for conventional diesel replacement. Reduction in greenhouse emissions, low toxicity, biodegradability, and obtainment from renewable sources are some of its key benefits over petroleum-based diesel. However, its production still faces significant hurdles including the inability to reuse and recover the catalysts, leading to a costly purification process that generates large amounts of wastewater. In this regard, heterogeneous catalysts have become an interesting alternative to overcome these drawbacks, as they can be easily separated, recovered, and reused. Indeed, several heterogeneous catalysts for biodiesel production have been reported, such as alkaline metal oxides, zeolites, and mesoporous supported materials, e.g., silica. Nevertheless, these materials have some disadvantages, such as high cost and complex synthetic routes, in addition to the leaching of active sites. Thus, carbon-based materials have recently come to light as a promising alternative to replace these catalysts since they offer simple and inexpensive synthesis routes, possess extremely interesting physical and chemical properties, such as high surface area to volume ratios, elevated thermal stability, and metal-free composition. Moreover, the functional groups present on their surfaces can be tuned to mimic those found in homogeneous catalysts, imparting them with outstanding catalytic activity. Here we present the use of a heterogeneous carbon-based catalyst for the (trans)esterification of waste-cooking oil to produce biodiesel. We report biodiesel conversions of 98% at 90 °C, for 3 hours, using 10 wt.% catalyst loading and a 1:36 methanol to oil molar ratio. Moreover, we investigated the catalyst tolerance towards free fatty acid (FFA) content. It showed a tolerance content of up to 10 wt.%. In order to comprehend the reaction mechanism, we further characterized its surface groups to glean an understanding of surface chemistry and the role it plays in the (trans)esterification reaction. This effective and inexpensive heterogeneous catalyst proved to be a promising substitute to the commonly used homogeneous catalysts and a novel alternative to make biodiesel production more feasible.

Converting non-edible oils to biofuels using carbon-based catalysts

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