Study on chemical kinetics and characterization of nanosilica from rice husk and rice straw in the fixed-bed pyrolysis process

Abstract

Rice husk (RH) and rice straw (RS) are important by-products from the rice industry. When RH and RS are subjected to pyrolysis, the products include char, tar, and a gaseous mixture containing syngas. In this study, silica was obtained by subjecting char to alkaline extraction. The obtained silica was modified to fit sophisticated industrial applications by adding alcohol and water during extraction in an optimized silicate:alcohol:water ratio. Methanol (MeOH), ethanol (EtOH), and propanol (PrOH) were used as particle size modifiers. The silica obtained were characterized through methods such as Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), Brunauer-Emmett-Teller (BET), and field emission scanning electron microscope (FESEM). The obtained silica had an average particle size of 20–170 nm, a high average BET-specific surface area of 328 m2/g, and a high purity of 98.26%, which enhanced its favorability in the pharmaceutical and food-packaging sectors. FTIR analysis confirmed the presence of Si–O–Si, Si–OH, and Si–O bonds in the silica. A higher purity of silica was obtained from RS than from RH. To obtain high-purity silica, nitrogen should be used as the pyrolyzing agent and acid leaching of the extracted silica should be conducted. To facilitate the design, operation, and economic study of industrial process plant, the clear understanding on kinetics of RH and RS plays a very important role. The kinetic parameters for RH and RS char were estimated through Gaussian distribution of the activation energy model (DAEM).