Optimization of Slow Pyrolysis Process for Avocado peel and Cashew Nutshell Biochar Production: Physicochemical Properties and Stability for Carbon Sequestration

Atchara Chaiya; Ackapon Morgkhad; Apichaya Kemudorn; Chutithanyakan Siri; Penwarat Panphattharachai

doi:10.55003/ETH.430108

Authors

Atchara Chaiya Rajamangala University of Technology Lanna, Thailand
Ackapon Morgkhad Rajamangala University of Technology Lanna, Thailand
Apichaya Kemudorn Rajamangala University of Technology Lanna, Thailand
Chutithanyakan Siri Rajamangala University of Technology Lanna, Thailand
Penwarat Panphattharachai Interdisciplinary and Technology College, Rajamangala University of Technology Lanna, Thailand

DOI:

https://doi.org/10.55003/ETH.430108

Keywords:

Biochar, Slow pyrolysis, Carbon sequestration, Avocado peel, Cashew nutshell

Abstract

This study examined the slow pyrolysis of avocado peel (AP) and cashew nutshell (CNS) to produce biochar for adsorption, solid fuel, and carbon sequestration. Experiments were conducted at 400–600°C with residence times of 30–120 min, with process optimization via Response Surface Methodology (RSM). A central finding was a “physicochemical decoupling” effect, whereby conditions maximizing yield and adsorption capacity differ fundamentally from those required for carbon stability and energy densification. RSM models predicted maximum yield for both feedstocks at 400°C and 30 min, while peak iodine adsorption was achieved at 600°C — at 30 min for AP (530.19 mg/g) and 120 min for CNS (552.95 mg/g). SEM and elemental analyses confirmed that higher temperatures promoted well-developed porous networks and elevated carbon content, with Higher Heating Value (HHV) reaching 26.82 MJ/kg for AP and 32.20 MJ/kg for CNS, comparable to commercial biomass fuel benchmarks. Notably, CNS biochar at 600°C and 120 min achieved an O/C ratio of 0.055, classifying it as IBI Class 1 with a predicted carbon sequestration half-life exceeding 1,000 years. These results establish a condition-selection framework: 400°C for adsorbent production and 600°C for solid fuel and long-term carbon sequestration.

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