Process for treating lignin

摘要

A process for recovery of lignin from black liquor that contains either soluble or dispersed lignin by generating a “liquid lignin” at high yield is disclosed. Soluble lignin at a high pH is precipitated by reducing the pH of the black liquor stream by countercurrent reaction with carbon dioxide, at elevated temperature and pressure, creating a heavy lignin-rich phase and a light lignin-depleted phase. The heavy lignin-rich phase is separated and washed countercurrently with a non-sulfur containing acid, such as acetic acid, to displace metal cations from the lignin, creating a low-salt lignin, which is then formed into a low-dust, high-bulk density lignin fuel pellet. If desired, an oxidation step may be used to eliminate odor for lignins having high value green chemistry applications.

主权项

1. A process for recovering lignin from paper making black liquor comprising:
(a) carbonizing said black liquor at a temperature between 80° C. and 200° C. and a pressure between about 50 psig and about 200 psig with and about of carbon dioxide to reduce the pH to between 9.0 and 10.5; (b) subjecting said carbonated black liquor to a phase separation wherein a dense liquid-lignin phase is formed and a lignin-depleted liquid phase is formed, and NaOH and other basic components are neutralized; (c) recovering said lignin-depleted liquid phase; (d) removing said dense liquid-lignin phase and neutralized NaOH and other basic components and acidifying said dense liquid-lignin phase with a acetic acid to neutralize residual NaOH and other basic components, thereby generating an acidified granular lignin; and (e) recovering lignin from said acidified granular lignin to remove residual acid and ash content, thereby generating purified lignin.