Analytical fast pyrolysis of P. Juliflora: A thermal and catalytic study

Abstract

Thermal and catalytic fast pyrolysis of Prosopis juliflora (P.juliflora), fractions namely wood, seed pods, leaves and their mixtures (wood: seeds: leaves at 80:10:10, and seeds: leaves at 50:50) were investigated. Fast pyrolysis tests were performed in a py-GC/MS to study the product distribution at 450, 500 and 550 °C. Further catalytic tests at 500 °C, used HZSM-5, 1 wt.% Ni-HZSM-5 and 5 wt.% Ni-HZSM-5, and the wood fraction as feedstock. For all the non-catalytic thermal tests, significant proportions of acids, ketones, aldehydes, sugars, alcohols, phenols, nitrogenous compounds (NITs) and other oxygenates were observed. Out of the three Prosopis fractions studied, the wood at 500 °C yielded the highest amount of ketones, aldehydes and phenolics (78.67%), whilst the mixture (wood: seeds: leaves at 80:10:10), yielded 83.04%. This suggests that Prosopis feedstock can be processed as a mixture thus eliminating the need for pre-separation. The catalytic tests were completed at 500 °C with catalyst: biomass ratios (C/B) of 3:1, 6:1 and 9:1. The use of zeolite-based catalysts, improved the product distribution by forming aromatic hydrocarbons (monocyclic) and polycyclic aromatic hydrocarbons (PAHs) thus reducing the proportion of oxygenates detected in the thermal tests. The addition of nickel to the zeolite catalyst (9:1 C/B ratio; 5 wt.% Ni-HZSM-5), resulted in aromatics and polyaromatic hydrocarbons (PAHs) yields of 60.28% and 27.50%, respectively. Overall, the tests using Ni-loaded zeolites showed selectivity towards aromatics, as higher proportions were obtained when compared to PAHs. Our results correlated the influence of specific components in the individual fractions of Prosopis (wood, seeds, and leaves) on the pyrolysis products. We established the potential of using an invasive plant to yield aromatics, which are main components for biofuels production, thus proposing a sustainable pathway to manage its spread and to yield a high-value product.