Complex Formation of PEO and Lignin in Prehydrolysis Liquor and its Enhancing Effect on Lignin Removal

Hemicelluloses dissolved in the pre-hydrolysis liquor (PHL) of kraftbased dissolving pulping processes can potentially be used to produce high value-added products such as fuel ethanol and xylitol. However, the isolation of lignin in PHL is a problem that remains unsolved and obstructs the utilization of those parts of hemicelluloses. Based on the principle of lignin isolation by acidification, the feasibility of using polyethylene oxide (PEO) to enhance the removal of lignin from PHL was tested in this work. The formation of lignin/PEO complexes was confirmed by means of turbidity, particle size, Fourier transform infrared spectroscopy (FTIR), and thermo-gravimetric analysis (TGA). The removal rate is affected by lignin content, chemical oxygen demand (COD), and decolorizing, and the results show that sulfuric acid acidification or PEO flocculation alone do not have an obvious effect on lignin removal from PHL. However, a much higher removal rate, compared to 2.81% (only acidification at pH 2) and 1.2% (only PEO on original PHL), of 22.75% is obtained by the sequential process of acidification and addition of PEO (pH 2 and PEO 350 mg/L in PHL).