Synergistic effects on properties of biofuel and biochar produced through co-feed pyrolysis of Erythrina indica and Azadirachta indica biomass

Co-feed pyrolysis is a thermochemical conversion process that entails the simultaneous or sequential decomposition of various feedstock in an oxygen-free environment, concurrently improving the quality of the end products. The technique is widely used to produce a range of valuable products, including biofuels, chemicals and biochar, capitalizing on the synergies between various feedstock. The current study focuses on the synergistic effects of co-feed pyrolysis of Erythrina indica (EI) and Azadirachta indica (AI) biomass at different co-feed ratios (EI:AI) of 1:4, 1:3, 1:2, 1:1, 2:1, 3:1 and 4:1 on weight basis. The reactions were carried out at a temperature of 600 °C under a pressure of 1 bar using nitrogen as inert atmosphere. The bio-oil yield produced through the co-feed pyrolysis reactions ranged from 29.51 to 32.40 % by weight, while the biochar and non-condensable gases yields ranged from 38.25 to 42.48 % and 26.90 to 30.73 % by weight, respectively. Positive synergistic effects of co-feed pyrolysis led to a notable enhancement in physicochemical properties of the fuel phase, especially by virtue of calorific value, density and presence of low mol. wt. components when compared to their individual counterparts. Specifically, the fuel phase obtained at 1:1 co-feed ratio exhibited the peak calorific value of 36.80 MJ/kg along with lowest density of 0.82 g/ml and pH of 3.58 which is the pinnacle accomplishment of this work; and comparable with commercial gasoline. Gas chromatography and mass spectroscopy of biofuels revealed alkanes, alkenes, alcohols, aromatics, esters, nitro compounds and organosilicons as their main compounds. Specific compounds, including cyclopentane, methyl-, 1-cyclohexyl-2-propen-1-ol and 1-pentene, 3-methyl, are the most significant compounds at co-feed ratio of 1:1. Biochar produced at co-feed ratio of 1:1 also depicted excellent physiochemical properties with the highest elemental carbon of 79.23 wt % and lowest oxygen and hydrogen contents of 18.49 wt % and 2.28 wt %, respectively with a maximum calorific value of 29.23 MJ/kg; which can be utilized as solid fuels. The biochar produced from the co-feed pyrolysis reactions also possesses highly porous structure which can be useful as a soil conditioner, carbon sequestration water filtration or wastewater treatment. Additionally, non-condensable gases composed of 7.45 vol % hydrogen, 34.26 vol % carbon monoxide, 21.32 vol % methane and 36.97 vol % carbon dioxide when co-feed ratio is 1:1.