Formation of non-oxygenated phase of bio-oil produced by copyrolysis of corn cobs and polypropylene plastic using zeolite catalysts at low heating rate

Abstract

Thermal co-pyrolysis of corn cobs and polypropylene (PP) at low heating rate (thermal slow co-pyrolysis) has succeeded in separating bio-oil produced between oxygenated and non-oxygenated phases spontaneously. In co-pyrolysis, PP can sequester oxygen from bio-oil to convert part of bio-oil to non-oxygenated phase and can contribute partly non-oxygenated phase by PP carbon chain cracking. Catalytic fast co-pyrolysis has been commonly used to improve bio-oil yield and to improve non-oxygenated fraction of bio-oil. However, the catalytic fast co-pyrolysis is unable to obtain separate non-oxygenated fraction of bio-oil. In present work, zeolite catalyst was introduced in co-pyrolysis of corn cobs and PP at low heating rate to undertake catalytic slow co-pyrolysis in order to obtain synergistic effect of non-oxygenated fraction of bio-oil while obtaining separate non-oxygenated fraction of bio-oil. The present co-pyrolysis work was carried out in a stirred tank reactor at heating rate of 5 °C/min and maximum temperature of 500 °C. The composition of feed was varied at 0, 50 and 100%PP in the mixture of corn cob particles and PP granules. The experiment involved 3 catalytic configurations, i.e., no catalyst, ZSM5-38 and ZSM5-70, in which 38 and 70 represents the mole ratio of SI/Al in the catalysts. The results show that in slow co-pyrolysis of biomass-PP, the use of zeolite catalyst with high acidity suppressed the pyrolysis of PP to form wax and reduced bio-oil yield, and the synergistic effect was obtained as the co-pyrolysis used no catalyst and zeolite catalyst of ZSM5-70, while that using zeolite catalyst of ZSM5-38 reached negative synergistic effect. Utilization of catalyst generated high amount of aliphatic moieties, i.e. methyl, methine and methylene. With ZSM5 catalyst utilization, production of allyl decreased. Most of non-polar bio-oil fractions have similar or slightly higher heating values (HHVs) compared to those of commercial fuels. Branching index (BI) values of non-polar phase of bio-oil generated straight carbon chain with higher branches compared to those commercial fuels.