Unveiling the reactor effect: a comprehensive characterization of biochar derived from rubber seed shell via pyrolysis and in-house reactor

Abstract

Utilization of agricultural waste to produce biochar has already proven to be an efficient method for transforming waste into valuable resources. In this study, rubber seed shell (RSS) was utilized to prepare two biochar samples via an in-house built reactor (RSSBC-1) and a pyrolysis reactor (RSSBC-2) under identical conditions (600 °C for 3 h at a heating rate of 10 °C per min). A comprehensive characterization of the prepared biochar samples was carried out to reveal the reactor effect on the biochar properties. For this, proximate and ultimate analyses were carried out which estimated the carbon stability, polarity, and aromaticity of the biochar samples. For RSSBC-1, C and N content were higher, whereas H and O content were higher for RSSBC-2, as found from elemental, EDX, and XPS analyses. Point of zero charge (PZC) values of 7.65 and 6.14 for RSSBC-1 and RSSBC-2, respectively, emphasized the importance of pH in the removal of ionic contaminants. Furthermore, the superiority of RSSBC-1 in terms of specific surface area of 336.02 m² g⁻¹ compared to 299.09 m² g⁻¹ of RSSBC-2 was articulated by BET analysis. XPS and FESEM analyses revealed the chemical state of surface elements and surface morphology, respectively of the biochar samples. XRD patterns assured the amorphous nature of biochar samples, and functional groups were well depicted by FTIR analysis. DLS showed a larger average hydrodynamic diameter for RSSBC-2 (248.68 nm) with a zeta potential of −14.91 mV compared to RSSBC-1 (115.23 nm) with a heterogeneous charge distribution (−16.72 mV and +37.61 mV). TGA analysis revealed the thermal stability of both biochar samples. Overall, the results explicitly depict a distinction in the properties of biochar samples prepared in two different reactors, where RSSBC-1, with its superior properties suggests the in-house built reactor as a promising alternative to expensive pyrolytic reactors for waste valorization.