Eco-innovation in energy: Solid degradation kinetics of rejected red macroalgae (Kappaphycopsis cottonii) for bio-oil and biochar production

Abstract

In the pursuit of renewable energy sources, biomass conversion into biofuels has garnered attention as a sustainable alternative to fossil fuels. This research focuses on the pyrolytic conversion of red macroalgae, specifically rejected Kappaphycus cottonii, an underutilized biomass in Indonesia, into valuable bio-energy carriers, while analyzing the solid degradation kinetics involved. The dried K. cottonii underwent slow pyrolysis at varying temperatures (400–600 °C) and time intervals (10–50 min). The impact of these variables on the yield of bio-oil and biochar, alongside the thermogravimetric profiles indicating mass loss, was thoroughly assessed. The study also explores the chemical kinetics of the decomposition process, utilizing the first-order reaction model to analyze the solid biomass conversion rate, activation energy, and frequency factor. Key findings demonstrate that the optimal pyrolysis temperature for maximizing bio-oil yield was precisely 500 °C, beyond which thermal cracking led to yield reductions. Reaction times also greatly affect yield, highlighting the importance of optimized pyrolysis conditions. The determined activation energy and frequency factor, based on the Arrhenius equation, highlighted K. cottonii's lower decomposition energy barrier relative to terrestrial biomass. This distinction is largely ascribed to its unique chemical makeup, notably a lower lignin content, positioning K. cottonii as an advantageous feedstock for biofuel production through pyrolysis.