Energy & Fuels, Vol.30, No.1, 326-333, 2016
Upgraded Biofuel Diesel Production by Thermal Cracking of Castor Biodiesel
The continual growth in commercial diesel fuel and more strict environmental legislations have led to immense interest in developing green diesel fuels from renewable biomass. Thermal cracking of vegetable oil, as a method to produce green fuel, is gaining worldwide attention and significance because it is a low-cost process. This study was performed to evaluate the use of transesterified vegetable oil (famous to biodiesel) as feedstock in thermal cracking to overcome limitations of crude vegetable oil thermal cracking, namely, a low biofuel production yield with a high amount of water content. The central composite method was used to design the experiments with reaction temperature and feed flow rate as parameters. Experiments were conducted in a continuous cracking reactor system using castor methyl ester as feedstock. Pre-transesterification improved thermal cracking of vegetable oil by increasing the yield of the desirable liquid cracking product (up to 94%) and decreasing the water content to a negligible amount. The diesel fraction separated from primary liquid crackate, as the main product of this study, contained very low high-molecular-weight (MW) fatty acid methyl esters (FAMEs) compared to original feedstock, which contained nearly 100% FAME. Thus, the diesel fraction produced by this method showed a similar distillation curve to typical petrol diesel, unlike biodiesel feedstock. Properties of the diesel product, including heating value, kinematic viscosity, cetane index, cloud point, and pour point, were compatible with standard diesel No. 2 according to ASTM D975. Thermal cracking may lead to an attractive process to produce bio-based diesel. Moreover, thermal cracking could be used to upgrade biodiesel by improving the heating value, viscosity, and cold properties.