Hydrothermal processing of pine wood: effect of process variables on bio-oil quality and yield

Abstract

Hydrothermal liquefaction processes (HTL) comprise complex chemical and physical transformations of biomass under the conditions of high temperature and pressure, commonly near- or supercritical water. During this processes, the components of biomass undergo various complicated chemical reactions strongly influenced by process variables. In this study, lignocellulosic biomass (pine wood) has been converted via liquefaction in subcritical water to bio-oil, water-soluble organics, gas and solid products. The process parameters (i.e. temperature and time processing) affecting the bio-oil yields and composition were comparatively studied. The chemical composition of resulting bio-oils was analyzed by means of mid-infrared spectroscopy, gel permeation chromatography, gas chromatography coupled to mass spectrometry and elemental analysis. The maximum bio-oil yield (38.35 wt.%) was obtained at 350 ºC for 10 min. The HHV of the obtained resultant bio-oils varied in the range of 24-28 MJ kg-1. Bio-oils from HTL of pine wood are complex mixtures of aromatic and cyclic compounds with numerous hydroxyl and carboxyl functional groups. The experiments exhibited that the increase in the temperature results in adeeper decomposition of biomass manifested by the higher yield of bio-oil and its gradual deoxygenation. In fact, the obtained oil products are promising, valuable intermediates, which may act as a source of many valueadded chemicals.