Method to separate lignin-rich solid phase from acidic biomass suspension at an acidic pH

A method for treating lignocellulosic biomass comprising:

• treating the lignocellulosic biomass with an extractant to extract a suspension comprising soluble components having colloidal material and primarily lignin containing particles from the lignocellulosic biomass, yielding a residual biomass and the suspension having a pH less than about 4;
• separating the suspension from the residual biomass;
• adding a flocculating agent to the suspension to form a flocculated suspension, wherein the flocculating agent comprises polyethylene oxide (PEO) in an amount sufficient to achieve a 99.5% reduction in turbidity after separation;
• adding to the suspension a precipitated calcium carbonate to raise the pH between about 5 and 7.5;
• and
• separating a flocculated portion of the flocculated suspension from a non-flocculated portion of the flocculated suspension to produce a fermentable solution from the lignocellulosic biomass.

A method of separating a lignin-rich solid phase from a suspension comprising:

• dividing a lignocellulosic biomass into a residual lignocellulosic biomass and a suspension comprising soluble components having colloidal material and primarily lignin containing particles, the suspension having a pH less than about 4, using a pretreatment fluid;
• treating the suspension with a polymer flocculating agent comprising a sufficient amount of polyethylene oxide (PEO) and precipitated calcium carbonate to raise the pH to between about 5 and 7.5 and said polymer flocculating agent, being substantially without additional cofactors;
• and
• separating the flocculated suspension to remove agglomerates to achieve a reduction in turbidity of about 99.5%.