An Overview of Bio-oil Upgrading with High Hydrogen-containing Feedstocks to Produce Transportation Fuels: Chemistry, Catalysts, and Engineering

As an alternative to increasingly depleted traditional petroleum fuel, bio-oil has many advantages: high energy density, flexibility, easy storage and transportation. Nevertheless, bio-oil also presents some unwanted characteristics such as high viscosity, acidity, oxygen content and chemical instability. The process of bio-oil upgrading is necessary before utilization as transportation fuels. In addition, the bio-oil has low effective hydrogen/ carbon molar ratio (H/Ceff) which may lead to coke formation and hence deactivation of the catalyst during the upgrading process. Therefore, it seemed that co-refining of biooil with other higher hydrogen-containing feedstocks is necessary. This paper provides a broad review of the bio-oil upgrading with high hydrogen-containing feedstocks to produce transportation fuels: chemistry, catalyst, and engineering research aspects were discussed. The different thermochemical conversion routes to produce bio-oil and its physical-chemical properties are discussed firstly. Then the bio-oil upgrading research using traditional technologies and common catalysts that emerged in recent years are briefly reviewed. Furthermore, the applications of high H/Ceff feedstock to produce high-quality of bio-oil are also discussed. Moreover, the emphasis is placed on co-refining technologies to produce transportation fuels. The processes of co-refining bio-oil and vacuum gas oil in fluid catalytic cracking (FCC) unit for transportation fuels from laboratory scale to pilot scale are also covered in this review. Co-refining technology makes it possible for commercial applications of bio-oil. Finally, some suggestions and prospects are put forward.