Waste materials for production of biodiesel catalysts: Technological status and prospects

Consequent to the escalations in global energy consumption, the biomass-to-fuel processes are increasingly becoming important areas to the energy industry and policy makers. In this perspective, the valorization of oils and fats via transesterification/esterification reaction is an attractive method for producing biodiesel with qualities suitable for the diesel engines. Owing to its numerous advantages, the global consumption of biodiesel had increased from 0.25 billion gallons in 2006 to similar to 2.0 billion gallons in 2018, and the trend has also been projected to be linear in the future years. Although several catalytic systems have been evaluated for its production, the recent interest indicated a shift to industrial wastes as another approach for escalating the process eco-scientific efficiencies. The review therefore comprehensively explored the role of utilizing red mud, tailings, slags, other geothermal wastes, carbide slag (CS) and fly-ash-derived zeolites as catalytic systems for biodiesel production. The influence of waste compositions, modifications and reaction/calcination conditions in achieving optimum activity were discussed. The paper further documented progress in terms of process mechanism, active sites identification and strategies adopted for promoting catalyst stability, recovery and reuse. Key perspective areas for further research studies were carefully identified and discussed. (C) 2020 Elsevier Ltd. All rights reserved.