Co-pyrolysis of biomass with oxygen-lean polymer waste is a promising way to improve both quantity and quality of the derived oil. However, the release of sulfur contaminants causes serious adverse effects on the utilization of the derived oil. In order to promote the efficient and economic utilization of the derived products, the high-temperature desulfurization was conducted in this study using a ternary molten carbonates (Li2CO3-Na2CO3-K2CO3). And the effects of added Ca2+ or Cl-/SO42- on the desulfurization were estimated. The results demonstrated that the molten carbonates showed high efficiency in the removal of H2S/COS/SO2 at 500 degrees C. Alkali metals competitively reacted with H2S/COS to form various sulfides and sulfur species in the cooled products were probably determined by the crystallization processes. Besides, H2S removal was stimulated by adding CaCO3 and the formed CaS was precipitated from the molten salts. The addition of Cl-/SO42- changed the ion distribution characteristics of the molten salts and had slightly adverse effects on the removal of H2S. In contrast, SO2 removal was hardly affected while COS removal efficiency was decreased after adding Ca2+ or Cl-/SO42-. Anyway, the added Ca2+ favored the recovery of sulfur as well as the regeneration of spent molten carbonates. (c) 2019 Elsevier Ltd. All rights reserved.