Catalytic pyrolysis of pine needles with nickel doped gamma-alumina: Reaction kinetics, mechanism, thermodynamics and products analysis

Abstract

The present study aims to explore the catalytic effect of nickel doped gamma-alumina on thermal decomposition behavior of waste pine needle (PN) biomass. Effect of catalysts on pyrolysis behavior was firstly investigated through thermogravimetric (TG) analysis to determine the kinetics and mechanism of the process and then laboratory scale semi-batch reactor was used to determine the distribution and composition of the pyrolysis products. The kinetic parameters (such as activation energy (Ea) and pre-exponential parameter (A)) were evaluated using isoconversional (Ozawa Flynn Wall (OFW) and Kissinger Akahira Sunose (KAS)) methods, while reaction mechanism was elucidated using Criado plots. The results showed a significant reduction in activation energy and an improvement in reaction rate after incorporation of catalysts in the process. Comparison of experimental curves with theoretical Criado plots showed a multistep complex reaction mechanism. Thermodynamic parameters (such as Gibbs free energy, enthalpy and entropy) were also determined for the process. Pyrolysis experiments showed that catalysts addition also effected the distribution and quality of the products. Inclusion of catalysts increased the hydrocarbon and phenolic content in the bio-oil and reduced oxygen content. Ni/Al2O3 is more promising catalyst in terms of oxygen reduction potential and production of hydrocarbon and phenolic compounds as compared to Al2O3 catalyst. Catalytic pyrolysis requires less energy and produces higher quality bio-oil, which makes it a cleaner option for the sustainable utilization of harmful pine needles. The study will assist in the design, optimization and scale-up of the process at large industrial level.