Biodiesel from Second-Generation Feedstock:

Ever-increasing energy demand, spiralling fossil fuel prices, and global warming due to unwarranted exploitation of fossil fuels have resulted in the emerge of biodiesel as a promising eco-friendly and renewable substitute for fossil-based fuels. Chemically, biodiesel stands for fatty acid alkyl (usually ethyl or methyl) esters, which are prepared via transesterification of vegetable oils and animal fats. Biodiesel has many advantages over petro-based diesel fuel, as it is free of harmful hydrocarbons, and causes lower emissions of harmful greenhouse gases, particulate matter, and sulphur compounds. Despite its many benefits, biodiesel has not attracted the interest and popularity in the commercial sector in India due to the high production cost coupled with the deficiency of sufficient feedstock. In a country like India, which imports a significant portion of its edible oil, the use of second-generation feedstock (non-edible oils, waste cooking oil, and animal fat) could be advantageous to avoid a food versus fuel conflict. However, such feedstock usually has high free fatty acid contents, and thus, conventionally used homogeneous alkali catalysts could not be employed here for transesterification. Heterogeneous catalysts offer a wide range of advantages over homogeneous counterparts, viz. ease of catalyst separation, regeneration, and reuse. In the recent past, diverse solid catalysts have been extensively explored for biodiesel (BD) production utilizing second-generation feedstock. In this context, mesoporous silica offers attractive properties, such as ease of surface modification via impregnation or grafting of catalytically active species, high thermal stability, variable pore size, and high surface area. In this chapter, properties of second-generation feedstock and its application for biodiesel production in the presence of various heterogeneous catalysts is reviewed.