A study of coke and char formation during pyrolysis of rice husk Mariana Santos Lemos 1 • Lidia Yokoyama 1 • Marcelo Mendes Viana 1 • Jo Dweck 1 Received: 30 September 2018 / Accepted: 15 March 2019 Ó Akade ´miai Kiado ´, Budapest, Hungary 2019 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 N 2 atmosphere. The coke formation curves, which were obtained subtracting RH TG and DTA curves in air from respective curves in N 2 , 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 instru- mental 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 m 2 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. Keywords Pyrolysis Á Rice husk Á Thermal analysis Á Adsorbents Á Methylene blue Introduction The significant increase in the consumption of fossil fuels in the last decades, consequently the emissions of green- house gases and pollutants (SO x , NO x and fine particles) as well as the inconstancy of the fossil fuels prices and depletion of their reserves, implied the search for renew- able sources of energy such as biomass [1]. It is a great energy source alternative, since according to International Energy Agency (IEA), bioenergy could provide 10% of the world’s primary energy supply by 2035, and biofuels could replace up to 27% of the world’s transportation fuel by 2050 [2]. Biomass sources include several natural materials and by-products, such as herbaceous species and wood species, wood residues, bagasse, agricultural residues as rice husks and industrial residues, paper waste, solid waste, sawdust, biosolids, food processing residues, animal waste, aquatic plants and algae [3]. The most common processes applied to biomass for its conversion in fuel and chemicals are biochemical and thermochemical conversion processes. The most well- known biochemical processes are the biochemical lique- faction and microbial gasification. The biochemical con- version processes are based on the conversion of biomass into oxygenated products by biological activity. Digestion (anaerobic and aerobic) and fermentation are typically biochemical processes used to produce methane and alco- hol. The main thermochemical processes involve pyrolysis, & Mariana Santos Lemos marianasantoslemos@yahoo.com.br 1 School of Chemistry, Rio de Janeiro Federal University, Rio de Janeiro, Brazil 123 Journal of Thermal Analysis and Calorimetry https://doi.org/10.1007/s10973-019-08196-7