The present invention generally provides methods of improving
lignin separation during lignocellulosic
biorefining, comprising the steps of (i) catalyzing
fractionation or
hydrolysis with an acid to release sugars into an acidified solution containing
lignin, (ii) neutralizing the acidified solution with a base to form a salt in a neutralized solution; (iii) in a separation unit, separating the salt and the
lignin, each in free or combined form, from the neutralized solution; and then (iv) recycling a portion of the salt and optionally a portion of the lignin to step (i) to combine, physically or chemically, with the lignin, to improve lignin separation in the separation unit. In certain embodiments, the acid is a
sulfur-containing acid and the base is
lime, forming
gypsum which is then recycled, in part, to the
hydrolysis reactor.