Methods for producing sugars from biomass

A method for producing a sugar mixture solution from a solid biomass feedstock comprising hemicellulose, cellulose, and lignin using a counter current extraction apparatus, wherein said counter current extraction apparatus comprises:

• a tube having a proximal end and a distal end, wherein:
• said proximal end comprises a proximal inlet port and a proximal outlet port;
• and
• said distal end comprises distal inlet port and a distal outlet port;
• and
• at least one material-transporting element within said tube such that a first material introduced in said proximal inlet port is transported towards said distal outlet port and a second material introduced in said distal inlet port is transported towards said proximal outlet port, and wherein said material-transporting element intimately mixes the first material and the second material within said counter current extraction apparatus;
• said method comprising:
• introducing a solid biomass feedstock comprising hemicellulose, cellulose, and lignin into said proximal inlet port of said counter current extraction apparatus and transporting the solid biomass feedstock towards said distal outlet port;
• introducing an acidic solution comprising a primary solvent and a miscible bulking agent into said distal inlet port and transporting the acidic solution towards said proximal outlet port;
• contacting the solid biomass feedstock with the acidic solution within said counter current extraction apparatus under conditions sufficient to produce a solution extract comprising a mixture of lignin and sugar from the solid biomass feedstock, wherein said step of contacting the solid biomass feedstock with the acidic solution fluidizes the solid biomass feedstock as the solid biomass feedstock is transported from said proximal inlet port to said distal outlet port of said counter current extraction apparatus such that the total amount of solid recovered from said distal outlet port is about 20% or less of the total solid biomass feedstock introduced into said proximal inlet port;
• recovering the solution extract through said proximal outlet port of said counter current extraction apparatus;
• and
• separating lignin from the solution extract to produce a concentrated sugar solution that is substantially free of lignin.