Resource recovery from synthetic polymers via microwave pyrolysis using different susceptors

In this study, microwave assisted pyrolysis of polypropylene (PP) was conducted, and the effects of microwave power, susceptor type, and PP to susceptor ratio on (i) temperature and heating rate profiles, (ii) overall oil, gas and char yields, (iii) composition of oil and gas, and (iv) heating value of oil, were evaluated. Pyrolysis experiments were carried out in a multimode microwave reactor equipped with accurate temperature monitoring system. The individual constituents in oil and gaseous fractions were analyzed using gas chromatograph equipped with mass spectrometer and flame ionization detectors. Six different microwave susceptors such as graphite, aluminum, silicon carbide, activated carbon, lignin and fly ash were utilized. At optimal conditions of 450 W microwave power and 100:1 wt./wt. of PP (5 g):graphite, nearly 48 wt.% of oil with heating value of 44.45 MJ kg−1 was obtained along with 50 wt.% of C3-C6 gaseous hydrocarbons. The scalability of the process was evaluated by pyrolyzing 50 g of PP under the above conditions, which resulted in 83% energy recovery in the oil. While alkenes and cycloalkanes constituted a major fraction in the oil, their relative yields varied significantly with different susceptors suggesting that the susceptors also acted as catalysts and interacted with the polymer besides transferring the incident microwave energy. The applicability of the technique was also demonstrated for pyrolysis of commercial polyethylenes and polyisoprene.