Continuous process for the production of ethanol from lignocellulosic biomass

A continuous process for converting carbohydrates from lignocellulosic biomass to ethanol, comprising the steps of:

• a) cutting said lignocellulosic biomass to a prescribed size to obtain sized biomass;
• b) steaming said sized biomass from step a) at atmospheric pressure for 10 to 60 minutes to obtain steamed biomass;
• c) squeezing said steamed biomass from step b) to remove a first liquid stream and generating squeezed biomass, wherein said steamed biomass is compressed up to 6-1;
• d) adding mineral or organic acid to said squeezed biomass from step c) in an amount of 0.5% to 0.9% w/w on an incoming biomass dry matter basis, and presteaming said squeezed biomass for 5 to 90 minutes to obtain acidified biomass;
• e) adjusting a moisture content of said acidified biomass from step d) to 50% to 80% w/w water, to obtain moisture adjusted acidified biomass;
• f) pretreating said moisture adjusted acidified biomass from step e) in a continuous treatment vessel by steam treatment under pressure at a preselected pretreatment temperature for a preselected pretreatment time and at a preselected pretreatment pressure, wherein said preselected temperature is 130° C. to 180° C., said preselected pretreatment time is 30 minutes to 4 hours, said preselected pretreatment pressure is 35-110 psi;
• g) continuously purging under pressure from said continuous treatment vessel of step f) volatile components generated by the pressurized steam treatment and liquid condensate formed in the vessel and containing soluble biomass components;
• h) submitting to explosive decompression said biomass exiting said continuous treatment vessel of step g) prior to or after the washing step to obtain pre-treated biomass;
• i) extracting said pre-treated biomass from step h) with water to recover a cellulose rich solids stream and a liquid stream, wherein said cellulose rich solids stream contains 4% to 8% w/w xylose from remaining xylose, xylooligosaccharides and xylans in said pre-treated biomass;
• j) heating the said liquid stream from step i) to simultaneously concentrate said liquid stream and remove inhibitory compounds by evaporation of volatile components, to obtain a concentrated liquid stream containing at most 6 g/L acetic acid, said evaporation being carried out at pressure and temperature conditions selected from the group consisting of:
• atmospheric pressure at a temperature of 90° C. to 100° C.;
• under vacuum of 50 mbar to 250 mbar at a temperature of 70° C. to 85° C., under pressure of 5 psig to 35 psig, and combinations thereof;
• k) hydrolyzing xylooligosaccharides in said liquid stream from step i) before, during or after the concentrating step of step j);
• l) hydrolyzing said cellulose rich solids stream from step i) with a mixture of cellulase and hemicellulose to obtain a hydrolyzed solid stream;
• m) combining said hydrolyzed solids stream from step l) with said concentrated liquid stream to obtain a combined hydrolysate stream comprising hexose and pentose sugars;
• n) co-fermenting said hexose and pentose sugars in said combined hydrolysate stream from step m) in a fermentation broth to produce ethanol;
• o) distilling said ethanol from said fermentation broth from step n) to recover ethanol and a de-ethanolized slurry.