Sustainable rice straw conversion into activated carbon and nano-silica using carbonization-extraction process

Rice straw, one of the main agricultural wastes of the north of Iran, was utilized for parallel extraction of two valuable products for the first time: high surface area activated carbon (AC) and porous silica nano-particles. The positive effect of silica extraction from activated rice straw biochar on the porosity of resultant AC was determined. It was found that the performance of K2CO3 was better than KOH for producing highly porous AC (2356 m2/g) under less severe conditions (relatively low impregnation ratio = 1.5). The sensitivity analysis for several operating conditions was carried out, and the optimal conditions to reach the highest surface area, porous volume, and silica extraction yield were determined for each chemical agent using Taguchi analysis. Among the factors changed, the highest quota belongs to the impregnation ratio and activation temperature, and the other parameters were fixed at economic levels. The average production yield of activated carbon and silica from raw rice straw was calculated around 9% and 7%, respectively. The average particle size of silica powder was estimated by SEM (around 35 nm) and DLS tests (200–300 nm), and an acceptable BET surface area and pore volume of 250 m2/g and 1 cm3/g, respectively, were obtained for this product. •Rice straw conversion to value-added products by carbonization and chemical treatment.•Determination of the positive effect of Si extraction on the porosity of activated carbon.•Comparison of the overall performance of K2CO3 and KOH alkali chemical agents.•Optimization of operating conditions to achieve the best porous properties and yield.•Characterization of the optimum activated carbons and porous silica powder.