Valorization of biodiesel-derived glycerol into fuel additives: advances in esterification, etherification, and ketalization using sulfonated catalysts

Over the past two decades, the rising global energy demand, coupled with increasing concerns regarding environmental sustainability and fossil resource depletion, has driven a significant expansion in biodiesel production and consumption, firmly establishing the fuel within the market. As a result, glycerol production has also increased, as it is a byproduct of biodiesel. However, demand has not kept pace, leading to an excess of glycerol in the global market and a subsequent decline in its value. To address economic challenges and manage the surplus of glycerol, it is essential to explore alternative approaches for utilizing crude glycerol. The valorization of glycerol through chemical processes represents a promising strategy for converting this byproduct into higher-value compounds, thereby optimizing profitability across the biodiesel production chain. Esterification, etherification, and ketalization reactions emerge as viable alternatives for producing fuel additives, enhancing the performance of diesel and gasoline when incorporated into blends. This review examines various aspects related to the production of fuel additives derived from glycerol, beginning with an updated analysis of the global market and trends in biodiesel and glycerol production. Subsequently, it explores the specific characteristics of each valorization route, considering operational and economic variables, with an emphasis on the incorporation of sulfonated catalysts to optimize the investigated reactions. As a result, this review provides an assessment of the technical and economic feasibility of these routes, highlighting their potential in the context of glycerol valorization.