Progress in waste oil to sustainable energy, with emphasis on pyrolysis techniques

This paper begins with a review on the current techniques used for the treatment and recovery of waste oil, which is then followed by an extensive review of the recent achievements in the sustainable development and utilization of pyrolysis techniques in energy recovery from waste oils. The advantages and limitations shown by the use of pyrolysis technique and other current techniques were discussed along with the future research that can be performed on the pyrolysis of waste oil. It was revealed that the current techniques (transesterification, hydrotreating, gasification, solvent extraction, and membrane technology) are yet to be sustainable or completely feasible for waste oil treatment and recovery. It was established that pyrolysis techniques offer a number of advantages over other existing techniques in recovering both the energetic and chemical value of waste oil by generating potentially useful pyrolysis products suitable for future reuse. In particular, microwave pyrolysis shows a distinct advantage in providing a rapid and energy-efficient heating compared to conventional pyrolysis techniques, and thus facilitating increased production rates. It was found that microwave pyrolysis of waste oil showed good performance with respect to product yield, reaction time, energy consumption, and product quality, and thus showing exceptional promise as a sustainable means for energy recovery from waste oils. Nevertheless, it was revealed that some important characteristics of the pyrolysis process have yet to be fully investigated. It was thus concluded that more studies are needed to extend existing understanding in the optimal reaction and process parameters in order to develop the pyrolysis technology to be a sustainable and commercially viable route for energy recovery from problematic waste oils. (C) 2015 Elsevier Ltd. All rights reserved.