Methods for separating and refining lignin from black liquor and compositions thereof

The invention relates methods and processes for the separation and refining of lignin from spent cooking liquor， called black liquor， present in industrial chemical plants， and compositions thereof. A process is provided for separating black liquor into at least two， three， or four streams selected from: (i) a gaseous stream comprising volatile sulfur compounds; (ii) a lignin-comprising stream produced by extracting lignin into a limited solubility solvent S 1; (iii) a salt stream， comprising solid sodium and sulfate salts; and (iv) a salt-depleted and lignin-depleted aqueous stream comprising hydrocarbons.