Upgrading of biofuel by the catalytic deoxygenation of biomass

Biomass can be used to produce biofuels, such as bio-oil and bio-diesel, by a range of methods. Biofuels, however, have a high oxygen content, which deteriorates the biofuel quality. Therefore, the upgrading of biofuels via catalytic deoxygenation is necessary. This paper reviews the recent advances of the catalytic deoxygenation of biomass. Catalytic cracking of bio-oil is a promising method to enhance the quality of bio-oil. Microporous zeolites, mesoporous zeolites and metal oxide catalysts have been investigated for the catalytic cracking of biomass. On the other hand, it is important to develop methods to reduce catalyst coking and enhance the lifetime of the catalyst. In addition, an examination of the effects of the process parameters is very important for optimizing the composition of the product. The catalytic upgrading of triglycerides to hydrocarbon-based fuels is carried out in two ways. Hydrodeoxygenation (HDO) was introduced to remove oxygen atoms from the triglycerides in the form of H₂O by hydrogenation. HDO produced hydrogenated biodiesel because the catalysts and process were based mainly on well-established technology, hydrodesulfurization. Many refineries and companies have attempted to develop and commercialize the HDO process. On the other hand, the consumption of huge amounts of hydrogen is a major problem hindering the wide-spread use of HDO process. To solve the hydrogen problem, deoxygenation with the minimum use of hydrogen was recently proposed. Precious metal-based catalysts showed reasonable activity for the deoxygenation of reagent-grade fatty acids with a batch-mode reaction. On the other hand, the continuous production of hydrocarbon in a fixed-bed showed that the initial catalytic activity decreases gradually due to coke deposition. The catalytic activity for deoxygenation needs to be maintained to achieve the widespread production of hydrocarbon-based fuels with a biological origin.