Optimization of process parameters for waste motor oil pyrolysis towards sustainable waste-to-energy utilizing a combinatorial approach of response surface methodology and desirability criteria

Sustainable management of hazardous waste and alternate energy generation needs to occur concurrently. Therefore, the objective of the present study is to investigate the optimum operating conditions for the pyrolysis of waste motor oil in a semi-batch scale robust pyrolyzer to generate transport grade fuels. Process parameter optimization was done using the Box-Behnken design and the desirability criteria to maximize the pyro-oil yield. Reactor temperature, holding time, and heating rate affected the pyro-oil yield the most. A maximum pyro-oil yield of 92.55 % with a desirability of 0.843 was obtained for 477 degrees C, and 10 degrees C/min of reactor temperature, holding time, and heating rate, respectively, at a constant nitrogen flowrate of 0.6 LPM. The confirmation and validation of the optimized condition were also performed. The paraffinic groups were abundantly found in the optimized pyro-oil, methylene possessing the highest fraction, followed by methyl and methine paraffinic groups. Besides, the (H/C)eff ratio surged from 1.85 to 1.95, whereas the O/C ratio noticeably decreased from 0.69 to 0.02 after the pyrolysis indicating improvement in the igniting characteristics and oxidative stability of the pyrooil. Further, the decline in kinematic viscosity and density was also observed. Furthermore, a considerable improvement in the physiochemical properties of the generated pyro-oil with reduced moisture and enrichment in higher heating value was also observed. Altogether, the generated pyro-oil could be used as transport-grade fuel.