Microwave vacuum co-pyrolysis of waste plastic and seaweeds for enhanced crude bio-oil recovery: Experimental and feasibility study towards industrialization

Abstract Waste-to-energy is a promising approach to tackle the energy shortage and reduce the environmental pollution. The present study aimed to evaluate the technical and economic feasibility of microwave vacuum co-pyrolysis of seaweeds and low-density polyethylene (LDPE). Although the three studied seaweeds namely; Ulva intestinalis, Sargassum polycystum, and Hypnea valentiae showed similar thermal weight loss profile, U. intestinalis showed the highest biomass and bio-oil yields which resulted in superior bio-oil areal productivity of 30.1 g m−2. Therefore, it was selected for co-pyrolysis with LDPE at different blend ratios. Compared to individual pyrolysis of U. intestinalis, the increase inLDPE ratio enhanced the crude bio-oil production with simultaneous reduction in bio-char yield. The experimental bio-oil yields from co-pyrolysis showed higher values than the corresponding theoretical values, confirming a synergistic effect between the two feedstocks. The bio-oil produced from co-pyrolysis at 75% LDPE blend ratio showed better characteristics compared to the individual pyrolysis. Van Krevelen plot suggested that LDPE produces hydrogen radicals during co-pyrolysis reactions, which increased the H/C ratio and reduced the O/C ratio. GC/MS analysis confirmed that the increase in LDPE stimulates hydrocarbons proportion up to 51.2% at 75% blend ratio with significant reduction in N-containing compounds, carboxylic acids, furans, aldehydes/ketones, saccharides, and phenols. The economic feasibility analysis at a feedstock feeding rate of 11.4 ton h−1 using Aspen Plus showed estimated net profit of 23.17 million US$ for a 20-years life time plant. The present study provides a potential approach for sustainable energy recovery from waste plastic/seaweeds blend using microwave vacuum co-pyrolysis.