Bei hydrolysis process system an improved process for the continuous hydrolysis saccharification of ligno-cellulosics in a two-stage plug-flow-reactor system

A two-stage dilute-acid hydrolysis process for the continuous saccharification of ligno-cellulosic biomass feedstock to produce hydrolysate sugars, comprising the following steps:

• (a) substantially continuously admixing, in a first-stage, a lignocellulosic biomass feedstock and a dilute mineral acid to form an aqueous preheated feedstock slurry, of about 10 to 20 wt % solids, whereas said dilute mineral acid is in a hot pressurized aqueous solution, supplied by reverse interstage transfer from a second stage, said dilute mineral acid consisting of an alpha cellulose hydrolysate and dilute mineral acid in aqueous solution;
• (b) introducing said preheated feedstock slurry into one end of a first tubular reactor and constricting the other end of said reactor so as to develop a back pressure therein;
• (c) receiving indirectly into said aqueous feedstock slurry sufficient process heat supplied-by reverse inter-stage transfer of said second-stage flash-steam to heat and maintain said slurry at a pressure ranging from about 45 to 200 psia and at a temperature ranging from about 135.degree. to 195.degree. C. saturated steam equivalent;
• (d) passing said heated feedstock slurry of step (c) into and through a reaction zone in said first tubular reactor, the length of said reaction zone and the flow rate of said heated slurry introduction being so selected as to afford an average reaction zone detention time of about 1.0 to 20 minutes;
• (e) producing hemicellulose hydrolysate sugars in said reacting slurry;
• (f) substantially continuously discharging and flashing said reacting slurry, thereby cooling by reducing the pressure and temperature of said reacting slurry, and also substantially continuously generating a first stage flashed steam supply;
• (g) thereafter separating said flashed slurry into:
• 1.) a combined hydrolysate solution, and 2.) an unhyrolyzed hemicellulose hydrolysis residue;
• (h) recovering said combined hydrolysate solution, which includes therein said hemicellulose hydrolysate sugars, said alpha cellulose hydrolyzate sugars, and said dilute-acid, thereby producing a single-solution final product of said saccharification.
• (i) admixing, within said second stage, a blend of said unhydrolyzed hemicellulose hydrolysis residue, and of a recycled up-to 50 wt % fraction of an unhydrolyzed alpha cellulose hydrolysis residue, with a fresh preheated dilute mineral acid solution, to form a partially heated aqueous alpha cellulose hydrolysis slurry, of about 10 to 20 wt % solids, whereas said dilute acid is continuingly preheated by a first stage flash steam supply;
• (j) introducing said aqueous preheated slurry into one end of a second tubular reactor and constricting the other end of said reactor so as to develop a back pressure therein;
• (k) receiving indirectly into said aqueous alpha cellulose hydrolysis slurry, suficient process heat, by way of a high temperature fresh process heat supply, to heat and maintain said aqueous slurry at a pressure ranging from about 100 to 200 psia and to a temperature ranging from about 165.degree. to 260.degree. C. saturated steam equivalent;
• (l) passing said heated slurry into and through a reaction zone in said tubular reactor, the length of said reaction zone and the flow-rate of said heated slurry introduction being so selected as to afford an average reaction zone detention time of about 0.5 to 20 minutes;
• (m) producing alpha cellulose hydrolysate sugars in said heated slurry in the presence of said dilute acid;
• (n) there after continuously discharging and flashing said reacting slurry, thereby cooling and reducing it's pressure and temperature and generating a second stage flashed steam supply.
• (o) separating said flashed slurry into:
• 1.) a hot reduced pressure alpha cellulose hydrolysate and dilute acid solution, and 2.) an unhydrolyzed alpha cellulose and lignin residue solids;
• (p) recovering said hydrolysate and dilute acid solution, whereupon continuously transferring said solution to said first stage for admixing to slurry;
• (q) recovering said unhydrolyzed alpha cellulose and lignin residue, whereupon continuously fractionating said residue, thereby an up to 50 wt % fraction is recycled within second stage and blended with said unhydrolyzed hemicellulose hydrolysis residue from said first stage, thereafter admixing said blend to said second stage slurry, whereby said remaining fraction is a unhydrolyzed alpha cellulose lignin residue and is the final solid product of said saccharification.