Fast pyrolysis of the waste lignocellulosic phloem fraction of Quercus cerris bark in a twin-screw reactor

Tree bark is among the most important lignocellulosic waste materials with high ash, extractive, and lignin contents. These wastes may be valorized through thermochemical methods. The thermochemical conversion of tree bark via fast pyrolysis is usually not economic due to low bio-oil yields and the challenge to valorize biochar in current industrial installations. However, screw-reactor-based fast pyrolysis is a particularly suitable method for producing bio-oils from high ash-containing and heterogeneous lignocellulosic feedstocks. The lower carrier gas requirement and the efficient recovery of biochar make this method economically attractive for the bark of Turkey oak (Quercus cerris) which is composed largely of phloem tissues. Here we showed that the phloem of Q. cerris can be converted to value-added bio-oils and biochars using the screw reactor without operational problems. The yields of marketable organic liquids and biochars were 32% and 21%, respectively. A process modeling was developed with ASPEN plus software to evaluate the available excess process heat of the fast pyrolysis unit for integration into phloem separation or cork processing units. From an assumed feedstock capacity of 25 MW phloem, 6.8 MW excess heat and 1.5 MW power are supplied in addition to the produced bio-oil. This excess heat can be integrated into bark separation or cork processing operations to save energy and reduce CO₂ emissions.