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Co-production of organic oil phase (OP) and adsorption biochar from cashew nut shells: modeling and optimization of intermediate pyrolysis process
(Springer Science and Business Media LLC, 2023) Kazawadi, D.; Ntalikwa, J; Kombe, G.
Cashew nut shells (CNS) are an underutilized agricultural residue generated in large quantities. The study aimed at modeling and optimizing of intermediate pyrolysis (IP) process using response surface methodology of Box-Bohnken method (RSM-BB). Batch experiments were conducted in a fixed-bed reactor to pyrolyze CNS at various particle sizes (1–10 mm), residence times (20–60 min), heating rates (1–10 °C/min), and temperatures (400–600 °C). Ten responses were modeled and optimized to co-produce adsorption carbon and OP as fuel. Co-production occurred at 1–1.7-mm particle size, 22-min residence time, 2.03 °C/min heating rate, and 470 °C temperature. The above optimal parameters gave the yields of biochar, bio-oil, OP, and gas to be 36.52%, 40.9%, 27.8%, and 22.6%, respectively. The analysis of OP revealed that it exhibited pH of 4.65, moisture content of 2.68%, heating value of 26.7 MJ/kg, and density of 1.09 g/cc which were not in the range of values of fossil diesel. Adsorption biochar produced had gold adsorption capacity of 1.86 mgAu/g which was lower than that commercial activated carbon (3–15 mgAu/g). The study demonstrated that IP has potential for valorizing CNS into value-added biochar and OP.