In this work, poly ethylene oxide (PEO) with various molecular weights (MW)s was employed to separate the lignin of prehydrolysis liquor (PHL) of a kraft-based dissolving pulp process. The results revealed that, the higher the MW and concentration of PEO in the PHL at pH 2, the higher are the removals of lignin and chemical oxygen demand (COD) but with a marginal removal of sugars. Alternatively, poly aluminum chloride (PAC) (200 mg/L) and PEO (8 MDa MW) (200 mg/L) were employed in a dual polymer system to extract the lignin, and the PAC/PEO system (MWs of 2 kDa/8 MDa) was more effective than the PEO/PEO system (MWs of 0.1 MDa/8 MDa) in removing lignin and COD of PHL. The maximum lignin, sugar, and COD removals were 46%, 18.8%, and 32%, respectively, under the conditions of 400 mg/g PEO (with a MW of 8 MDa) at pH 2 and room temperature in a singular PEO system.