Production and characterization of sunflower stalk biochar and ash: a study on batch versus semi-batch gasifier systems

Abstract This study is the first to compare batch and semi-batch gasifier systems for turning sunflower stalks into useful products, filling an important gap in our understanding of gasification technologies that use biomass fuel. This study investigated the production and characterization of biochar and ash derived from sunflower stalks using batch and semi-batch gasifiers. The conversion process, lasting 90 min, employed the top-lit updraft mechanism to generate sunflower stalk ash and biochar under both systems. The yields of batch-based samples were 34.60 % for biochar (BSB) and 19.40 % for ash (BSA), while semi-batch samples yielded 20.80 % (SSA) and 18.55 % (SSB). Elemental analysis revealed significant carbon enrichment from 44.2 % in raw feedstock to 85.4 % in semi-batch biochar, representing a 93 % increase in carbon concentration. The biochar produced in the batch gasifier exhibited a surface area of 364.127 m 2 /g, compared to 392.508 m 2 /g for the semi-batch gasifier biochar, as determined by BET analysis. Scanning Electron Microscopy (SEM) revealed a more porous structure in the semi-batch biochar. Fourier Transform Infrared Spectroscopy (FTIR) analysis identified both similarities and differences in the functional groups between the biochar and ash samples from both systems. Thermogravimetric analysis (TGA/DTA) showed a higher mass loss in the semi-batch ash (SSA) compared to the batch sample (BSA), indicating greater thermal stability in the batch biochar. These findings showed the potential of sunflower stalk biochar and ash for diverse applications such as soil improvement, pollutant removal, and energy conversion, while also providing insights into optimizing carbonization processes for enhanced material properties.