A study of coke and char formation during pyrolysis of rice husk

Abstract

The present study about pyrolysis of the rice husk (RH) was carried out to evaluate indicated operating conditions to obtain chars with adsorbent properties. Initially, thermogravimetry (TG), derivative thermogravimetry (DTG) and differential thermal analysis (DTA) were performed in order to obtain the TG and DTA RH coke formation curves and to evaluate the formed products (chars) at different selected pyrolysis temperatures. For the thermal analyses, 10 mg samples were used at a heating rate of 10 °C min−1, from ambient temperature to 1000 °C, in alumina crucibles, under air and N2 atmosphere. The coke formation curves, which were obtained subtracting RH TG and DTA curves in air from respective curves in N2, show that there are two types of coke formation, being the second the most stable and more suitable for adsorption, with maximum formation at 500 °C. Then, pyrolysis products obtained at selected temperatures of 400, 500 and 600 °C, respectively, named RHC400, RHC500 and RHC600, were characterized by thermal analysis in air and by other instrumental analyses in order to evaluate their chemical composition and adsorbing properties. The results of char TG and DTG curves, based on the original rice husk initial mass, allow to estimate and to compare contents of residual organic components during pyrolysis. The characterization by XRF, SEM and BET showed that RH and RHCs have silica in greater quantity in their chemical composition, with mainly carbon, silicon, calcium and oxygen distributed on their surfaces, which present a low surface area (16–26 m2 g−1). The analyzed chars show, by proximate analysis, a progressive concentration of fixed carbon from 400 to 600 °C. BET data show that they are mesoporous and potential adsorbents for large molecules as dyes, being RHC600 the most suitable for this purpose, as shown by preliminary results of blue methylene adsorption.