Development in hydrotreating process of bio-oil

This paper reviews catalytic the hydrotreatment upgrading technology of biomass-derived oil. It provides an overview of the reaction mechanism and the condition of the operation, then summarizes the process of bio-oil hydrogenation at home and abroad. Detailed comparison of various technological processes such as multi-stage hydrogenation, hydrogenation-esterification, in-situ hydrogenation, etc. are made. Multi-stage hydrogenation, which separates the hydroprocessing into two stages (mild hydrotreating and deep hydrotreating), can improve the selectivity of products, moreover avoiding an economic penalty by using less hydrogen. Hydrogenation-esterification combines hydrogenation and esterfication to establish a new upgrading method. Through the method, unstable compounds of biomass-derived oil can be converted more effectively. In-situ hydrogenation, which leads to reducing the cost and enhancing the safety, uses other reagents as resources of hydrogen, simultaneously generating hydrogen and hydrotreating in one reaction system to replace transporting hydrogen from outside. The reasonable optimization of the process routes benefits improving product quality. Research in this area is expected to become a main research direction for bio-oil hydrotreatment. Experimental data were collected about various model compounds including cresol, phenol, guaiacol, acetone, aldehyde, etc. and bio-oil from the literature in the field of this study. Also, a test is reviewed about a range of catalysts including the conventional and novel types of supported noble metal and transition metal catalytic materials and their performance in bio-oil hydroprocessing. Conventional catalysts, such as NiMo and CoMo, have economic advantages; the reaction using noble metal catalysts have better reactivity; amorphous catalysts have both advantages of these two types of catalysts, but amorphous catalysts have terrible thermal stability, and can only be used below 473 K; then, zeolite catalysts and mesoporous catalysts exhibit magnificent effects on reducing oxygen content and moisture content in bio-oil, but still can't avoid coking in the reaction. Unfortunately, researchers have not found any catalyst's hydrothermal stability good enough to improve the effect of reaction continuously (more than seven days), Deactivation and coking of catalysts are still main problems. Obviously, further study is required to prepare these catalysts which have better durability. Finally, this article gives information about the problems which researchers may meet, including equipment plugging, catalyst deactivation, and high operation costs etc., and predicts that the future research directions of this technology is to optimize the hydrogenation process, and to develop new types of composite catalysts which exhibit excellent activity at low temperature and anti-coking performance. The technology development is still on the way but can play a significant role in supplying increasingly expensive petroleum.