A process for isolating lignin of pre-hydrolysis liquor of kraft pulping process based on surfactant and calcium oxide treatments

Hemicelluloses present in the pre-hydrolysis liquor (PHL) of the kraft-based dissolving pulp production process can potentially be converted into value-added products such as ethanol and xylitol. However, the lignin present in the PHL is an inhibitor of fermentation processes, and thus should be isolated from the PHL prior to fermentation. In this study, a new process was proposed for isolating the lignin of PHL by overliming and surfactant treatment. The fundamentals associated with the interactions of lignin, surfactants and calcium hydroxide were discussed. In the experimental part of this work, three different cationic surfactants were applied to industrially produced PHL, and the most effective one, dodecyltrimethyl ammonium chloride (DTAC), was selected for further analysis. The optimum dosage of 0.3% DTAC/PHL was identified via turbidity and particle size analyses. Additionally, overliming via CaO treatment resulted in removing 36.1% lignin and 23% hemicelluloses. Overliming followed by the DTAC treatment was more effective than the DTAC treatment followed by overliming in removing lignin. In the former, the maximum removals of 43.6% lignin and 27% hemicelluloses were obtained. The formation of lignocelluloses/surfactant complexes was confirmed by means of a Fourier transform infrared spectroscopy (FTIR) and thermo gravimetric analyzer (TGA).

► A new process for isolating lignin of pre-hydrolysis liquor was proposed.
► Pre-hydrolysis liquor was treated with surfactant and acid/lime under different sequences/conditions.
► The maximum lignin removal was obtained via overliming and surfactant treatments.
► The isolated lignocelluloses were evaluated by FTIR, TGA, and particle size analyser.