Competitive conversion pathways of methyl palmitate to produce jet biofuel over Ni/desilicated meso-Y zeolite catalyst

Abstract

To clarify the conversion mechanism of methyl palmitate (C16:0) to produce jet biofuel over Ni/desilicated meso-Y zeolite catalyst, quantum chemistry calculation and verification experiments were conducted to evaluate three proposed competitive reaction pathways, in which hydrodecarboxylation pathway was more feasible than hydrogenolysis and decarboxylation pathways. It was found that overall enthalpy change to produce pentadecane (−130.2 kJ/mol) in hydrodecarboxylation pathway was lower than that to produce palmitic acid (−90.1 kJ/mol) in hydrogenolysis pathway and that to produce hexadecane (−68.6 kJ/mol) in decarboxylation pathway. The experimental results of hydrodeoxygenation and hydrocracking conversion of methyl palmitate into jet biofuel were consistent with quantum chemistry calculation, when conventional Y zeolite was modified into hierarchical mesoporous Y zeolite catalyst by desilication with NaOH and then loading Ni nanoparticles. The jet biofuel product selectivity reached a peak (64.8%) with reasonable composition distributions, when Ni/meso-Y zeolite was desilicated with 0.4 M NaOH to promote BET surface area (554.9 m2/g) and specific pore volume (0.340 cm3/g) with 2–10 nm mesopores. The relative content of pentadecane in liquid products was always higher than those of palmitic acid and hexadecane over Ni/meso-Y zeolite catalysts desilicated with various concentrations of NaOH. The main compositions of gas phase by-products in hydrodeoxygenation and hydrocracking conversion were CH4 with selectivity up to 25.2% and CO2 with selectivity of ∼10%, which agreed well with quantum chemistry calculation results.