Step-wise and one-step vacuum pyrolysis of birch-derived biomass to monitor the evolution of phenols

One-step and stepwise laboratory batch vacuum pyrolysis of a mixture of birch bark (ca. 46%) and birch sapwood (ca. 54%) was carried out in the temperature range 25–550°C. The pyrolysis oil (defined as the total condensates, including water and organics) was analyzed by GC–MSD and the quantity of phenols (referred to monolignols in this paper) was determined as a function of temperature. The active zone of decomposition and the maximum recovery of phenols were found to be in the temperature range 275–350°C. Distribution of phenols, charcoal and water as a function of temperature was investigated. Stepwise and one-step pyrolysis yielded total phenols of 4.43 and 2.51 wt.% (anhydrous feed basis), respectively. The yields of pyrolysis oil (62.39 wt.%), wood charcoal (23.25 wt.%) and gas ( 14.36 wt.%) produced by both methods were approximately similar, on an anhydrous feed basis.