Production of biodiesel via catalytic upgrading and refining of sustainable oleagineous feedstocks

Depletion of world crude oil reserves has been predicted to occur in less than 10 decades, and despite new discoveries, the use of these fossil fuel resources is not compatible with the challenge of restricting global temperature rises to <2°C. Alternative sources of renewable or low-carbon sustainable energy will thus be essential to meet the demands of a growing population and developing nations. First-generation of biodiesel from edible crops has brought many disputes over land and crops rivalry; however, second-generation biodiesel from nonedible crops has sought to address this problem. Biodiesel, which is ordinarily obtained from vegetable oils or animal fats by transesterification, still has an important role to play in the renewable energy arena. However, current processes whereby the triglycerides react with a short chain alcohol in the presence of a homogeneous catalyst, such as sodium hydroxide, has various drawbacks including saponification, difficulty in isolation, purification, and separation of the catalyst from the fatty acid methyl esters, as well as immiscibility of the catalyst with the reactants and incomplete transesterification. The aim of this review is to give an overview on the current status of biodiesel production using heterogeneous solid acid and base catalysts, which can offer significant process advantages of improved product separation, decreased waste, and also opportunities to work in continuous operation. A particular focus of the review will be on recent robust technology that seeks to overcome mass transfer limitation in bulky oil by designing tailored hierarchical macroporous–mesoporous frameworks and also tuning surface hydrophobicity will be discussed.