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Abstract

There is provided a process for recovery of lignin from black liquor that contains either soluble or dispersed lignin, generating a “liquid-lignin” at high yield. Lignin at elevated pH is precipitated by reducing the pH of the black liquor stream with carbon dioxide, at elevated temperature and pressure, creating two bulk fluid phases: a dense liquid-lignin phase and a light lignin-depleted phase. The dense liquid-lignin phase is separated and washed with a strong acid to displace metal cations from the lignin, creating a low-salt, randomly shaped lignin. If needed, especially for lignin recovered from kraft papermaking black-liquor streams, an oxidation step is included to eliminate negative odor for high value green chemistry applications.

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