Membrane processes for separation of organic acids from kraft black liquors

Claim 1

A process for the recovery of a low molecular weight, aliphatic organic acid fraction from a kraft black liquor, which process comprises (a) subjecting said black liquor to ultrafiltration, thereby separating said black liquor into a concentrate enriched in the high molecular weight fraction and a permeate; (b) subjecting the permeate produced in step (a) to electrodialysis, thereby separating the permeate into a concentrate containing at least part of the inorganic acid components of the permeate and a deionate containing sodium lignin and aliphatic organic acids; (c) adding to the deionate produced in step (b) sufficient acid to reduce the pH thereof to about 4 to 5, thereby precipitating lignin solids from the deionate and leaving a solution containing inorganic acids and other materials; (d) separating the precipitate formed in step (c) from the solution produced therein; (e) raising the pH of the separated solution produced in step (d) to about 7 to about 8; and (f) subjecting the solution produced in step (e) to electrodialytic water-splitting, thereby producing a low molecular weight, aliphatic acid organic fraction and an alkaline fraction.