Kinetic studies of upgrading pine pyrolytic oil by hydrotreatment

Abstract

The pyrolysis of biomass refers to incomplete thermal degradation resulting in char, pyrolytic oil, and gaseous products. The pyrolytic oil is a complex mixture of many components including phenolics, anhydrosugars, and polynuclear aromatics and is believed to have good potential as a liquid fuel. However, due primarily to its high oxygen content and high viscosity, the oil can currently be used only as a boiler fuel. An upgrading (hydrotreating) process is needed to improve the quality of the oil. This research used pine pyrolytic oil produced by the Tech-Air Corporation from Southern Pine sawdust and bark. The hydrotreating reactions were conducted in a trickle bed reactor system. An analytical method combining size exclusion chromatography (SEC) and high resolution gas chromatography (GC) has been developed to analyze pine pyrolytic oil and its upgraded product. Changes in product composition as a function of experimental variables (reaction temperature, hydrogen pressure, space velocity and catalyst type) were determined quantitatively by comparing SEC-GC analyses and elemental analyses of the charged stocks and products. The catalysts used in the reactions were Pt/Al2O3, CoMo/[gamma]-Al2O3, NiW/[gamma]-Al2O3 and NiMo/[gamma]-Al2O3. The reaction temperatures ranged from 623 K to 673 K, and the reaction pressures varied from 5272 kPa (750 psig) to 10443 kPa (1500 psig). Weight-hourly space velocity changed from 0.5 to 3.0 hr^-1. Two models, one for overall oxygen removal and the other for the compositional changes in hydrotreated oil, were developed. Oxygen removal was not a function of space velocity and was modeled by an empirical function of temperature and pressure. A pseudo first order reaction network was used to relate the kinetic of a lumped model composed of five fractions. The lumps were determined by used of size exclusion chromatography - gas chromatography.