Treating black liquor with bio-oil acids for lignin recovery

The present invention describes a method intended for lignin recovery, said method comprising:- a first step of mixing a stream of black liquor with an acidic biomass stream for providing a mixed heterogenous stream;wherein the acidic biomass stream is an acidic biomass liquid comprising at least one fraction of pyrolysis oil and having a total acid number in a range of 47 - 210 mg KOH/g;and wherein the first step involves mixing a stream of black liquor with an acidic biomass stream from a ratio of 1:0.2 on black liquor : acidic biomass at a total acid number of 210 mg KOH/g of the acidic biomass to a ratio of 1 :2 on black liquor : acidic biomass at a total acid number of 47 mg KOH/g of the acidic biomass;and said method also comprising- a second step of separating the mixed heterogenous stream in a separation unit for providing one aqueous light phase stream and one lignin-containing heavy phase stream.