Valorization of Rejected Macroalgae Kappaphycopsis cottonii for Bio-Oil and Bio-Char Production via Slow Pyrolysis

Abstract

Kappaphycopsis cottonii, a prominent macroalgaespecies cultivated in an Indonesian marine culture, yieldssignificant biomass, a portion of which is often rejected byindustry. This study explores the potential valorization of rejectedK. cottonii biomass through slow pyrolysis for bio-oil and biocharproduction, presenting an alternative and sustainable utilizationpathway. The study utilizes a batch reactor setup for the thermaldecomposition of K. cottonii, conducted at temperatures between400 and 600 °C and varying time intervals between 10 and 50 min.The study elucidates the temperature-dependent behavior of K.cottonii during slow pyrolysis, emphasizing its impact on productdistributions. The results suggest that there is a rise in bio-oilproduction when the pyrolysis temperature is raised from 400 to 500 °C. This uptick is believed to be due to improved dehydrationand greater thermal breakdown of the algal biomass. Conversely, at 600 °C, bio-oil yield diminishes, indicating secondary cracking ofliquid products and the generation of noncondensable gases. Chemical analysis of bio-oils reveals substantial quantities of furanderivatives, aliphatic hydrocarbons, and carboxylic acids. Biochar exhibits calorific values within the range of 17.52−19.46 MJ kg−1,and slow pyrolysis enhances its specific surface area, accompanied by the observation of carbon nanostructures. The study not onlyinvestigates product yields but also deduces plausible reaction routes for the generation of certain substances throughout the processof slow pyrolysis. Overall, the slow pyrolysis of rejected K. cottonii presents an opportunity to obtain valuable chemicals and biochar.These products hold promise for applications such as biofuels and diverse uses in wastewater treatment, catalysis, and adsorption,contributing to both environmental mitigation and the circular economy.