Transformation of bio-oil during pyrolysis and reforming

Abstract

The pyrolysis of biomass is a very effective means of energy densification. With the bio-char returned to the field as a soil conditioner and for carbon bio-sequestration, bio-oil can be used in many ways, including being upgraded into liquid transport biofuels or being used as a feedstock for gasifiers or conventional boilers. However, a number of technical challenges exist during bio-oil applications, such as formation of tar and coke. The fundamental understanding on the transformation of bio-oil under various thermal chemical conversion conditions is essential for the development of novel technologies for the clean utilisation of bio-oil.Thermal decomposition (pyrolysis) is always the first step in all thermal chemical processes involving bio-oil. The pyrolysis of bio-oil and its separated fractions was carried out in a novel two-stage fluidised-bed/fixed-bed quartz reactor. The results indicated that bio-oil was exceedingly reactive and underwent drastic changes when it was further heated. The evolution of various complex aromatic ring systems was tightly related to the formation of coke and tar. The interactions among the different chemical groups of the bio-oil constituted a unique thermal behaviour of bio-oil.The behaviour of bio-oil during reforming was studied. The non-catalytic/catalytic steam reforming of above feedstock was conducted respectively. Without catalysts, extra steam supply showed limited effects on tar reforming. Char-supported iron catalyst showed good performance on the reforming of tars produced from the thermal cracking of the bio-oil and its components with steam. The catalytic steam reforming showed obvious effects on the conversion of non-aromatics (e.g. sugars), particularly the large molecules at low temperatures (< 700 °C). With increasing temperature, the catalyst showed good performance on the reforming of aromatic ring systems. The interactions among the species degraded from lignin and cellulose/hemicellulose obviously affected the evolution of aromatic structures during the catalytic steam reforming of bio-oil. The main possible role played by cellulose/hemicellulose-derived species was the provision of additional radicals during the reforming of bio-oil.