Multiple biogenic waste valorization via pyrolysis technologies in palm oil industry: economic and environmental multi-objective optimization for sustainable energy system

Agricultural biomass is one of the major wastes in the world. Most of these wastes end up in landfills and incineration, causing significant environmental problems that are detrimental to human health and other species on the Earth. Thermochemical conversion can solve this issue by utilizing the energy embedded inside the biomass, mainly organic matter, into high-grade fuels and chemicals. Fast pyrolysis is one of the technologies that can convert biomass waste to a high yield of bio-oil, which can then be used as biofuels in vehicles. In this study, palm oil biomass wastes are valorized to generate bio-oil sustainably via several pyrolysis technologies such as conventional pyrolysis, microwave pyrolysis, and thermo-catalytic pyrolysis in a multi-objective optimization framework. The formulated multi-objective mixed-integer linear programming problems are solved using the ɛ-constraint method. The Pareto-optimal solutions have illustrated a clear trade-off between two conflicting objectives: total annualized profit and the global warming potential. The most profitable solution economically has an annualized profit of $237 per ton of biomass with an emission of 628 kg CO₂ equivalent per ton of biomass. On the other hand, the most environmentally sustainable solution, while still generating positive income, has an annualized profit of $122 per ton of biomass with an emission of 132 kg CO₂ equivalent per ton of biomass. A second scenario with a case study presented on the palm oil industry in Malaysia has also demonstrated the selection of biomass during feedstock blending when a constraint on biomass feedstock availability is pre-defined. The proposed model is robust for planning bioenergy complex, especially those involving multiple biomass feedstocks. In fact, this study has addressed the research gap in comparison of multiple distinctive pyrolysis processes with respect to multiple palm biomass feedstocks.