Synergetic effect of steam and activated tyre char on the selective production of levoglucosan-rich bio-oil from catalytic pyrolysis of wood chips

The catalysts used in the pyrolytic bio-oil upgrading process are either expensive or not efficient enough. This research aims to investigate and improve the catalytic capability of tyre char (TC), an otherwise low-value waste, as an effective catalyst for upgrading bio-oil derived from the pyrolysis of eucalyptus wood chips. Efforts were specifically made to tailor the TC properties to improve the selectivity of levoglucosan (LGA), a value-added bio-chemical in bio-oil. Experiments were carried out in a two-stage fixed-bed reactor in the absence and presence of steam (30 vol%) at different heating rates (10 °C/min and 110 °C/min). By using 3-Flex, SEM-EDX, XRD, XRF, CHNS, and synchrotron XAS analyses, it was found that zinc and sulphur added during the tyre manufacturing process were mainly present in the form of ZnS nanoparticles with a crystallite size less than 1 nm in the TC matrix. An overall deoxygenation extent of 31.7 wt% was achieved with original TC catalyst and slow heating rate of 10 °C/min. However, this number was increased to 49.2 wt% with steam activated TC and fast heating rate of 110 °C/min, and adding steam to the reactor at the optimum temperature of 500 °C. More specifically, the introduction of steam and activated TC to the pyrolysis reactor enhanced the transformation of heavy hydrocarbons to light species and value-added chemicals such as LGA and furfural, reaching 34.9 wt% and 11.3 wt% on the mass basis of bio-oil, respectively. The high catalytic performance can be attributed to the large porosity and better exposure of ZnS nanoparticles on the surface of the activated TC, and the influence of steam in shifting the reactions toward more selective production of light hydrocarbons.