Hydrothermal Conversion of Lignin and Black Liquor for Phenolics with the Aids of Alkali and Hydrogen Donor

Abstract The potentials of phenolic productions from lignin and black liquor (BL) via hydrothermal technology with the aids of alkalis and hydrogen donors were investigated, by conducting batch experiments in micro-tube reactors with 300 °C sub-critical water as the solvent. The results showed that all the employed alkalis improved lignin degradation and thus phenolics production, and the strong alkalis additionally manifested deoxygenation to produce more phenolics free of methoxyl group(s). Relatively, hydrogen donors more visibly facilitated phenolics formation. Combination of strong alkali and hydrogen donors exhibited synergistically positive effects on producing phenolics (their total yield reaching 22 wt.%) with high selectivities to phenolics, among which the yields of catechol and cresols respectively peaked 16 and 3.5 wt.%. BL could be hydrothermally converted into phenolics at high yields (approaching 10 wt.% with the yields of catechol and cresols of about 4 and 2 wt.%, respectively) with the aids of its inherent alkali and hydrogen donors, justifying its cascade utilization.