Catalytic pyrolysis of rice husk with SnCl2, Al2O3.4SiO2.H2O, and MoS2 for improving the chemical composition of pyrolysis oil and gas

Pyrolysis of Indian variety rice husk was carried out in a semi-batch reactor in the presence of SnCl2, Al2O3.4SiO2.H2O, and MoS2 catalysts at a fixed temperature (550 °C), heating rate (50 °C min−1), and N2 flow rate (0.3 L min−1). The yield of pyrolysis oil increased in the presence of Al2O3.4SiO2.H2O catalyst but deteriorated in presence of SnCl2, and MoS2 catalyst. At 550 °C, the maximum pyrolysis oil yield from non-catalytic pyrolysis (NCP) was 37.46 wt% and with Al2O3.4SiO2.H2O catalyst it was 38.41 wt%. The yield of H2 (7.27 mol %) in pyrolysis-gas after catalytic pyrolysis (CP) was 0.72 mol% higher than NCP (6.55 mol %). The gross calorific value (GCV) of pyrolysis-gas after CP increased to 5.99 MJ m−3 from 3.84 MJ m−3 (NCP). High lignin contained in rice husk gave a better CH4 yield of 10.13 mol. %. Reduction in water content (3.07–5.77 wt %) of pyrolysis oil after CP elevated the high heating value (HHV) to 28.61 from 22.41 MJ kg−1. A 3.0–4.58 mol. % reductions in the acidic compound content after CP impacted the pH and TAN of pyrolysis oils. The Al2O3.4SiO2.H2O catalyst elevated the area percentage of naphthenic (0.54 mol. %), olefinic (1.98 mol. %), aromatic (4.18 mol. %), and paraffinic (4.42 mol. %) compounds in pyrolysis oil. A 3.86 mol. % increase in the phenolic compounds was observed in presence of MoS2 catalyst. Approximately, 22 wt% loss in oxygen with 21 and 2.65 wt% increases in the carbon and hydrogen content of biochar elevated the HHV to 30.60 MJ kg−1 after CP.