Activity of solid acid catalysts for biodiesel production: A critical review

• Selectivity is promoted by hydrophobic surface on solid acid catalysts.
• Hydrophobic surface also minimizes deactivation by polar species like water and glycerol.
• Interconnected system of large pores minimizes diffusion problems.
• Appreciable reaction rates are favored by moderate to high concentration of strong acidic sites.
• Prevailing reaction conditions determine the activity of the catalyst.

Homogeneous acid catalysts received wide acceptability because of their fast reaction rates. However, postproduction costs incurred from aqueous quenching, wastewater and loss of catalysts led to the search for alternatives. Until recently, heterogeneous base catalyzed-biodiesel production also gained the attention of most researchers. This was because the process minimized the problems of homogeneous catalysis in terms of catalyst regeneration and recycling in continuous processes. However, despite these advances, the ultimate aim of producing biodiesel at affordable cost is yet to be realized. Further, the process requires refined feedstocks which account for as high as 88% of the final production costs. Thus, the focus of many research efforts is towards the rational design and development of solid acid catalysts aimed at reducing biodiesel production costs. Therefore, this study reviewed current literature on the activities and advantages of solid acid catalysts used in biodiesel production. It discussed in details how the preparation method and prevailing reaction conditions affect the catalytic activity of the catalyst. The review concluded by suggesting way forward from the traditional trial-and-error method to a rational means of determining catalytic activities.

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