Co-hydrotreating of used engine oil and the low-boiling fraction of bio-oil blends for the production of liquid fuel

• Co-hydrotreating can effectively improve properties of UEO and LBF blends.
• Pt/C and Rh/C exhibited the highest performance for the removal of heteroatoms.
• The UEO/LBF ratio significantly affected the properties of the upgraded oil.
• A positive synergistic effect occurred during the co-hydrotreating process.
• The upgraded oil can potentially be used for energy and heat generation.

The low-boiling fraction (LBF) of bio-oil produced from the hydrothermal liquefaction of peanut straw and used engine oil (UEO) blends were co-hydrotreated. The effects of the catalyst type on the yields of the product fractions resulting from the co-hydrotreating of the LBF with UEO and on the properties of the upgraded oil were first examined. The results revealed that noble metals with one electron in the outermost shell demonstrated high performance in the removal of heteroatoms. Of all of the noble metals tested, Pt/C and Rh/C exhibited the highest performance in the overall removal of heteroatoms from the feedstock mixture. With Rh/C as the catalyst, the effects of the catalyst loading (0–0.3 kgcatalyst/kgfeed), UEO/LBF mass ratio (3:0–0:3), and temperature (350–430 °C) were further examined. A positive synergistic effect occurred during the co-hydrotreating process at a UEO/LBF mass ratio of 2.5:0.5. The UEO/LBF mass ratio significantly affected the product yields and the properties of the upgraded oil. The presence of UEO suppressed char formation. The energy density of the vast majority of the upgraded oils was higher than that of petroleum diesel. This study suggested that UEO is a good solvent for the hydrotreating of bio-oil derived from the hydrothermal liquefaction of peanut straw.

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