Optimization of fast pyrolysis parameters of biomass and effects of catalysts on products

Because of its abundance and low emissions biomass has become a promising alternative energy source that can replace fossil fuels that will soon be depleted. Fast pyrolysis, one of the thermochemical conversion technologies, is one of the important methods of converting biomass into valuable products such as bio oil. In this study, Pearl Millet (Millet) and Sida cordifolia (Sida), which are abundant in Niger but used less, were used as biomass. Thermogravimetric analysis (TGA) was performed for both biomasses in five different heating rates (10, 20, 30, 40, 50 oC/min) and under atmospheric pressure, representing pyrolysis and combustion processes. Kinetic and thermodynamic parameters were determined by the iso-conversion models of Flynn-Wall-Ozawa (FWO) and Kissenger-Akahira-Sunose (KAS). Then, optimization of process parameters such as particle size (PS), reaction temperature (RT), and nitrogen gas flowrate (NGF) to obtain maximum bio-oil yield (BY) from the fast pyrolysis of Millet and Sida was carried out by using the Response Surface Methodology (RSM) with the Central Composite Design (CCD) approach. The most effective factor of each experimental design response was identified and an empirical model in terms of factors was obtained with the ANOVA method. In order to relate parameters with BV, the quadratic polynomial equation has been developed. To investigate the effects of catalysts on product distribution and bio-oil quality in fast pyrolysis experiments using optimized process parameter values, catalytic fast pyrolysis (CFP) of Millet and Sida was performed by using five different catalysts such as zeolite socony mobil-5 (ZSM-5), cerium oxide (CeO2), zirconium oxide (ZrO2), zinc oxide (ZnO), and sodium carbonate (Na2CO3). The activation energy (Ea) calculated by FWO and KAS models using TGA data obtained from pyrolysis of Millet and Sida was 89.63 and 83.89, 80.74 and 74.74 kJ/mol, respectively. Similarly, Ea calculated by FWO and KAS models using TGA data obtained from combustion of Millet and Sida was 57.27 and 49.47, 58.91 and 51.08 kJ / mol, respectively. Kinetic and thermodynamic parameters such as Ea, enthalpy change (ΔH), anthropy change (ΔS), and Gibbs free energy change (ΔG) obtained by using FWO and KAS showed that Millet and Sida are remarkable biomasses for bioenergy production through pyrolysis and combustion methods. In the optimization process, cubic and quadratic models represented the best the data of Millet and Sida, respectively. Maximum BY of Millet (48.27%) and Sida (48.00%) were obtained at optimum parameter values of 1.5 mm, 400oC, and 200 mL/min for both biomasses. During CFP experiments using optimized process parameter values, BY decreased independently of the type of catalyst and biomass, but the yields of biochar and gas mixtures did not show a certain trend, i.e. sometimes decreased, sometimes increased. Among all the catalysts CeO2 was found to be the most suitable for producing acids and alkanes from CFP of Millet but acids, ketones, and aromatics from CFP of Sida. High amounts of ketones from Millet but alkanes from Sida were obtained with Na2CO3 catalyst. High amount of aromatic with ZrO2 but alcohols, amines, and other chemicals with ZSM-5 in bio oil of Millet were observed. In general, CFP of Millet and Sida by using optimized parameter values appear to be suitable for producing fuel (bio-oil) or value added chemicals. KEYWORDS: Catalyst, Fast Pyrolysis, Optimization, Pearl Millet, Renewable Energy Sida cordifolia.