529 / 2019-01-10 14:33:06

Hydrotreatment of low boiling-point fraction of bio-oil in hydrogen donor solvent for production of trace-sulfur liquid fuel

Soybean straw; crude bio-oil; vacuum distillation; low boiling-point distillate; hydrotreatment; hydrogen donor solvent

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The low boiling-point distillate (LBD) separated from vacuum distillation of bio-oil produced from hydrothermal liquefaction of soybean straw was hydrotreated, aiming to produce ultra-low sulfur liquid fuel. Effects of five hydrogen donors(HDSs) such as cyclohexene (CCH), cyclohexane (CYH), decahydronaphthalene (DHN), tetrahydronaphthalene (THN), and indane (IND) on the heteroatom’s removal efficiency were first examined at 350 °C for 2 h with added 6 MPa H2 and 5 wt.% Pt/C. The LBD to HDS mass ratio was set at 1:1. The presence of HDS not only can reduce the yields of solid and gas and increase the yield of the upgraded oil but also can favor the denitrogenation, desulfurization, and deoxygenation. The DHN showed the best performance for denitrogenation and the THN was the most suitable catalyst for deoxygenation and desulfurization. With employing the mixture of DHN and THN mixture (1:1), effects of temperature (300-450°C), time (1-6 h), hydrogen pressure(1atm-10MPa), and Pt/C loading (0-20 wt.%) on the product distribution and quality of the upgraded oil produced from hydrotreatment of the LBD were examined. The upgraded oil was always the dominant fraction under all examined reaction conditions, which varied between 76.7 and 87.3 wt.%. Positive synergistic effect was observed for the removal of N, O, and S as the LBD was hydrotreated in the mixture of DHN and THN than that in the DHN or THN alone. The HDS mainly acted as a hydrogen transfer agent in the LBF hydrotreatment process, during which HDS mainly provided the hydrogen for the hydrogenation reaction and this consumed hydrogen was recharged by the external hydrogen source. The N is the most difficult heteroatom to remove followed by O and S. Catalyst loading is the most influential factor affecting the N, O, and S removal efficiency. Under optimal reaction conditions, 93% of N, 95% of O, and 99% of S in the blend of LBO and HDS were removed, which correspond to concentrations of 0.05 wt%, 0.42 wt%, and 21 ppm of the upgraded oil, respectively. The upgraded oil consisted mainly of saturated alkanes, unsaturated alkanes and aromatics, which is close to the properties of Gasoline (93#).