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Thermal degradation of rise husks: Structure, morphology, thermal and kinetics characteristics

Sevdalina Chr.Turmanova, Svetlana D.Genieva, Lyubomir T.Vlaev

Rice husks are an important by-product of rice milling process and are major waste product of the agricultural industry. They have now become a great source as a raw biomass material for manufacturing value-added silicon composite products, including silicon carbide, silicon nitride, silicon tetrachloride, magnesiumsilicide, pure silicon, zeolite, fillers of rubber and plastic composites, adsorbent and support of heterogeneous catalysts. The bulk and true densities of rawrice husks (RRH)with differentmoisture and sizes were determined. The rice husk was subjected to pyrolysis in fluidized-bed reactor in air or nitrogen atmosphere. The controlled thermal degradation of the rice husks in air or nitrogen leads to production of white rice husks ash (WRHA) and black rice husks ash (BRHA) respectively. The products obtained were characterized by X-ray powder and thermogravimetric analysis, IR-spectroscopy, scanning electronmicroscopy and nitrogen adsorption. WRHA contains almost pure (95mass %) silica in a hydrated amorphous form, similar to silica gel, with high porosity and reactive surface OH groups. BRHA contains different amounts of carbon and silica in amorphous form with high specific surface area and porosity. On the basis of non-isothermal heating of raw rice husks in air or nitrogen media was established, that the kinetics of the pyrolysis process were best described by the equation of Ginstling-Brounshtein, valid for diffusioncontrolled reactions, starting on the exterior of spherical particles with uniformradius. The values of activation energy, frequency factor inArrhenius equation, changes of entropy, enthalpy and Gibbs free energy were calculated for the formation of the activated complex fromthe reagent. The aimof the present microreview is to presented our investigations of the study and characterization of rawrice husks and the obtained fromthemthermal degradation black and white rice husk ash.