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Abstract

The method is for separation of lignin from original black liquor (BL_IN) that has a first precipitation stage (PR) for precipitation of lignin by a first acidification using acidifier AC₁, preferably using CO₂, at alkaline conditions, then separating a lignin cake with subsequent suspension of the lignin cake in a strong acid in order to leach our metals from the lignin followed by dewatering and obtaining a clean lignin product LP. The process further is improved by intensified hydrolysis of lignin cake such that most of the carbohydrates are broken down to dissolvable monomers that could be separated from the lignin in the filtrate from a filtering stage subsequent to the hydrolysis. The improved hydrolysis could reduce as much as 90% of the carbohydrate content using a moderately increased temperature and increased charge of acidifier while avoiding any larger lignin yield losses.

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First Claim