Single and Co-Feed Pyrolysis of Erythrina Indica and Azadirachta Indica: Analysis of Products, Kinetics and Thermodynamics

Abstract

Growing concerns over fossil fuel utilization and their impending scarcity have spurred a transition towards renewable energy sources. Biomass has gained remarkable traction due to its widespread availability and adaptability. Pyrolysis, amid various biomass conversion routes, boasts advantages like moderate operating conditions, facile handling and efficient product distribution. However, commercialization faces hurdles due to the large fraction of non-fuel phase in pyrolytic bio-oil. This thesis focusses on the fuel phase extraction of bio-oil obtained from pyrolytic conversion of Erythrina indica (EI) and Azadirachta indica (AI) biomass using dichloromethane and n-hexane at four vol.% (10, 20, 30 and 40%) of solvent relative to the volume of pyrolytic raw bio-oil. Average yields of bio-oil, biochar and non-condensable gases from EI biomass pyrolysis were 26.873 wt.%, 42.870 wt.% and 30.257 wt.%, respectively; for AI biomass, the values were 27.286 wt.%, 41.053 wt.% and 31.662 wt.%. n-hexane proved superior for isolating fuel phases, showing improved properties in terms of density, viscosity and calorific value compared to dichloromethane and without using any solvent for separating the fuel phases. Fuel phases extracted using 30 vol.% and 40 vol.% n-hexane depicted properties similar to conventional gasoline. The average calorific values of biochar from EI and AI biomass were 28.030 MJ/kg and 28.500 MJ/kg, respectively, and for non-condensable gases, the respective values were 14.486 MJ/Nm³ and 14.882 MJ/Nm³. EI and AI biochar exhibited physiochemical properties, flowability and combustion indices comparable to conventional coal. In the non-condensable gases obtained from EI and AI biomass pyrolysis, approximately 50-65% (by volume) of the gases were constituted by combustible gases including H2, CO and CH4. Co-feed pyrolysis of EI and AI biomass yielded bio-oil, biochar and non-condensable gases in the range of 29.512-32.399 wt.%, 38.249-42.480 wt.% and 26.901-30.730 wt.%, respectively. The 1:1 co-feed ratio showed optimal outcomes, with a maximum calorific value of 36.798 MJ/kg for the fuel phase (extracted using 10 vol.% of n-hexane) and 29.233 MJ/kg for biochar and 13.761 MJ/Nm3 for non-condensable gases. Economic analysis for setting a 10-ton batch-type pyrolysis plant indicated viable projects with positive net present values by the end of the project. Payback periods were 3.90 years for EI, 6.46 years for AI and 4.05 years for their 1:1 co-feed ratio.