Effects of Torrefaction Severity and Acid Pretreatment on the Quality of Fast Pyrolysis Bio-Oil from Rice Straw

Rice straw is one of the most abundant secondary agricultural residues in the US and other rice-growing countries, which can be converted to a liquid fuel through the fast pyrolysis reaction. Fast pyrolysis is a thermal degradation process where biomass feedstocks are directly converted to a crude liquid fuel at the temperature range of 500-600°C, high heating rate, and in the absence of oxygen. On the other hand, the torrefaction process has been applied to improve the quality of biomass for combustion, gasification and pyrolysis, where this process operates at a temperature range of 200-300°C, low heating rate, and in the absence of oxygen. To this end, the effects of torrefaction severity on the quality of fast pyrolysis bio-oil from rice straw with several conditions were investigated. Torrefaction of rice straw was firstly conducted at a temperature of 250, 275, and 300 °C with the resident time of 30 minutes. After that, fast pyrolysis of torrefied rice straw was carried out at a temperature of 450, 500, and 550 °C with a high heating rate of 1,000 °C s^-1. The experiments were performed in the micropyrolysis reactor (CDS analytical model 5200HP pyroprobe). The results of bio-oil quality and product distributions of bio-oil, char, and gas from the fast pyrolysis of torrefied rice straw were compared with those results obtained from only fast pyrolysis of rice straw. Meanwhile, the effects of minerals content in rice straw on the bio-oil product distribution were investigated, in which rice straw sample with and without acid pretreatment (0.1 M HCl) were performed at identical pyrolysis condition after pyrolysis experiment trials complete. From the preliminary results, the optimum condition for fast pyrolysis of rice straw was found at the temperature of 550 °C, the product distributions of bio-oil, char, gas, and water of 50%, 34%, 14%, and 2%, respectively, were obtained at this condition.