Influences of sulfuric acid treatment on thermo-chemical properties of rice husk-pine sawdust heterogeneous briquettes

Heterogeneous briquettes made from rice husk-pine sawdust blend treated with sulfuric acid have the potential to satisfy the increasing global demand for sustainable energy. However, untreated blends are constrained by unfavorable thermochemical properties. In this study, a blend comprising 10 wt% rice husk and 90 wt% pine sawdust was subjected to H 2 SO 4 treatment at 1%, 2%, 3%, 4%, and 5% (v/v) for 1-h at ambient temperature. Briquettes were subsequently formulated, and thermochemical properties were assessed to identify treatment conditions enhancing energy and combustion performance. The briquettes were analyzed for lignocellulose using acid detergent fiber and lignin, and neutral detergent fiber; higher heating value HHV using calorimetry; and thermal efficiency and emissions using a water boiling test (WBT) coupled with a portable emission monitoring system (PEMS) 4000-series sensor. The results demonstrated that sulfuric acid treatment increased briquettes’ HHV from 18.21 ± 0.09 MJ/kg (untreated) up to 18.82 ± 0.03 MJ/kg. The 1% concentration yielded the highest thermal efficiency (71.49 ± 2.05%), accompanied by the lowest CO emissions (0.88 ± 0.03 g/MJd), meeting the ISO 19,867–1:2018 Tier 5 limits, and the lowest PM 2.5 emissions (100.67 ± 1.53 mg/MJd), within the Tier 3 limit. Overall, the optimal sulfuric acid treatment condition for effective combustion performance and energy delivery was 1%. However, cost–benefit analysis should be incorporated into future studies for practical real-world application.