Solvated liquid-lignin fractions from a Kraft black liquor

A softwood Kraft black liquor was acidified with carbon dioxide at 115 °C and 6.2 bar over a pH range of 13.6–9.5, resulting in the precipitation of liquefied-lignin fractions as a separate phase. Seven such “liquid-lignin” fractions were produced, with each fraction being phase-separated within a narrow pH band of 0.5 units. The fractions were found to be highly hydrated phases, containing 32.3–48.2 wt.% water; as a result, their measured melting points were quite low, 90.7–110.5 °C. In contrast, no melting point was detected up to 375 °C for any of the lignin fractions after drying. Significant reductions in metals content were observed for the lignin fractions compared to the original black-liquor feed.