Renewable aviation fuel by advanced hydroprocessing of biomass: Challenges and perspective

Present-day, commercial airlines are getting into the use of bio-jet fuel, by blending vegetable oil derived bio-jet fuel with fossil jet fuel in maximum up to 50%, which is ASTM-certified. In order to reduce the dependency on fossil jet fuel, recent research trend shows that most of the renewable aviation fuel or bio-jet fuel were derived from the complex liquid biomass via hydroprocessing technology. Hence there is a necessity to have an insight into the production technology, typically the hydroprocessing technology. Generally, hydroprocessing technology for the liquid biomass conversion into bio-jet fuel involved multi intermediate steps, such as deoxygenation, cracking and isomerization. This conventional process is further upgraded and simplified into single step reaction, which minimizes the post-treatment effort to be done in every reaction step, and thus reduces the production cost. Moreover, other economic factors such as catalyst price, hydrogen production cost and plant size will also consider as major impacts towards biofuel production scale and cost. Therefore, this paper aims to review the bio-jet fuel conversion technologies in a different perspective, by comparing the hydroprocessing technology of bio-jet fuel (i.e. three-step process, two-step process, single step process), and the effect of reaction variables (i.e. feedstock, catalyst, and reacting gas). The details of outputs for different hydroprocessing technology are also discussed herein. In summary, most research works have achieved positive findings in single step process, by adapting hydrodeoxygenation process in majority. However, there are some limitation and challenges that can be further improved in the single step process, such as exploration on potential feedstock, development of catalyst and optimization of reacting parameters. The energy, environmental and economic analysis on the advanced hydroprocessing of bio-jet fuel are yet to be conducted, in order to compare their merits.