Hydrothermal-mechanical conversion of lignocellulosic biomass to ethanol or other fermentation products

Abstract

A low-cost process is provided to render lignocellulosic biomass accessible to cellulase enzymes, to produce fermentable sugars. Some variations provide a process to produce ethanol from lignocellulosic biomass (such as sugarcane bagasse or corn stover), comprising introducing a lignocellulosic biomass feedstock to a single-stage digestor; exposing the feedstock to a reaction solution comprising steam or liquid hot water within the digestor, to solubilize the hemicellulose in a liquid phase and to provide a cellulose-rich solid phase; refining the cellulose-rich solid phase, together with the liquid phase, in a mechanical refiner, thereby providing a mixture of refined cellulose-rich solids and the liquid phase; enzymatically hydrolyzing the mixture in a hydrolysis reactor with cellulase enzymes, to generate fermentable sugars; and fermenting the fermentable sugars to produce ethanol. Many alternative process configurations are described. The disclosed processes may be employed for other fermentation products.

What is claimed is: 
     
         1 . A process to produce a fermentation product from lignocellulosic biomass, said process comprising:
 (a) introducing a lignocellulosic biomass feedstock to a single-stage digestor, wherein said feedstock contains cellulose, hemicellulose, and lignin;   (b) exposing said feedstock to a reaction solution comprising steam or liquid hot water within said digestor, to solubilize at least a portion of said hemicellulose in a liquid phase and to provide a cellulose-rich solid phase;   (c) refining said cellulose-rich solid phase, together with said liquid phase, in a mechanical refiner to reduce average particle size of said cellulose-rich solid phase, thereby providing a mixture comprising refined cellulose-rich solids and said liquid phase;   (d) enzymatically hydrolyzing said mixture in a hydrolysis reactor with cellulase enzymes, to generate fermentable sugars from said mixture, wherein said hydrolysis reactor includes one or more hydrolysis stages; and   (e) fermenting at least some of said fermentable sugars in a fermentor to produce a fermentation product.   
     
     
         2 . The process of  claim 1 , wherein said lignocellulosic biomass feedstock is selected from the group consisting of hardwoods, softwoods, sugarcane bagasse, sugarcane straw, energy cane, corn stover, corn cobs, corn fiber, and combinations thereof. 
     
     
         3 . The process of  claim 1 , wherein said lignocellulosic biomass feedstock is pretreated, prior to step (a), using one or more techniques selected from the group consisting of cleaning, washing, presteaming, drying, milling, particle size-classifying, and combinations thereof. 
     
     
         4 . The process of  claim 1 , wherein at least a portion of said reaction solution is introduced to said feedstock in a pre-impregnator prior to step (b). 
     
     
         5 . The process of  claim 1 , wherein step (b) includes a digestor residence time from about 2 minutes to about 4 hours. 
     
     
         6 . The process of  claim 5 , wherein said digestor residence time is about 10 minutes or less. 
     
     
         7 . The process of  claim 1 , wherein step (b) includes a digestor temperature from about 150° C. to about 220° C. 
     
     
         8 . The process of  claim 7 , wherein said digestor temperature is from about 180° C. to about 200° C. 
     
     
         9 . The process of  claim 1 , wherein step (b) is conducted at a digestor liquid-solid weight ratio from about 1 to about 4. 
     
     
         10 . The process of  claim 9 , wherein said digestor liquid-solid weight ratio is about 2 or less. 
     
     
         11 . The process of  claim 1 , wherein step (b) is conducted at a digestor pH from about 3 to about 5. 
     
     
         12 . The process of  claim 11 , wherein said digestor pH is from about 3.5 to about 4.5. 
     
     
         13 . The process of  claim 1 , wherein said reaction solution further comprises an acid. 
     
     
         14 . The process of  claim 13 , wherein said acid is acetic acid. 
     
     
         15 . The process of  claim 1 , said process employing a blow tank configured for receiving said cellulose-rich solid phase or said refined cellulose-rich solids at a pressure lower than digestor pressure. 
     
     
         16 . The process of  claim 15 , wherein said blow tank is disposed downstream of said digestor and upstream of said mechanical refiner. 
     
     
         17 . The process of  claim 15 , wherein said blow tank is disposed downstream of said digestor and downstream of said mechanical refiner. 
     
     
         18 . The process of  claim 15 , wherein vapor is separated from said blow tank. 
     
     
         19 . The process of  claim 18 , wherein heat is recovered from at least some of said vapor. 
     
     
         20 . The process of  claim 18 , wherein at least some of said vapor is condensed or compressed and returned to said digestor. 
     
     
         21 . The process of  claim 1 , wherein a first blow tank is disposed upstream of said mechanical refiner and a second blow tank is disposed downstream of said mechanical refiner. 
     
     
         22 . The process of  claim 1 , wherein said mechanical refiner is selected from the group consisting of a hot-blow refiner, a hot-stock refiner, a blow-line refiner, a disk refiner, a conical refiner, a cylindrical refiner, an in-line defibrator, an extruder, a homogenizer, and combinations thereof. 
     
     
         23 . The process of  claim 1 , wherein said mechanical refiner is operated at a refining pressure selected from about 1 bar to about 20 bar. 
     
     
         24 . The process of  claim 23 , wherein said refining pressure is about 3 bar or less. 
     
     
         25 . The process of  claim 24 , wherein said mechanical refiner is operated at or about at atmospheric pressure. 
     
     
         25 . The process of  claim 1 , wherein said mechanical refiner operates at an electrical load from about 2 kW to about 50 kW refining power per ton of said cellulose-rich solid phase. 
     
     
         26 . The process of  claim 25 , wherein said mechanical refiner operates at an electrical load from about 5 kW to about 20 kW refining power per ton of said cellulose-rich solid phase. 
     
     
         27 . The process of  claim 1 , wherein said mechanical refiner transfers up to about 500 kW-hr refining energy per ton of said cellulose-rich solid phase. 
     
     
         28 . The process of  claim 27 , wherein said mechanical refiner transfers from about 50 kW-hr to about 200 kW-hr refining energy per ton of said cellulose-rich solid phase. 
     
     
         29 . The process of  claim 1 , said process comprising utilizing multiple mechanical refiners at different parts of said process. 
     
     
         30 . The process of  claim 29 , said process comprising, between steps (c) and (d), conveying at least a portion of said mixture to a second mechanical refiner operated at a lower refining pressure compared to that of said mechanical refiner in step (c). 
     
     
         31 . The process of  claim 30 , wherein said mechanical refiner in step (c) is a pressurized refiner and said second mechanical refiner is an atmospheric refiner. 
     
     
         32 . The process of  claim 1 , wherein step (d) utilizes multiple enzymatic-hydrolysis reactors. 
     
     
         33 . The process of  claim 1 , wherein step (d) utilizes single-stage enzymatic hydrolysis configured for cellulose liquefaction and saccharification, wherein said single-stage enzymatic hydrolysis includes one or more tanks or vessels. 
     
     
         34 . The process of  claim 1 , wherein step (d) utilizes multiple-stage enzymatic hydrolysis configured for cellulose liquefaction followed by saccharification, wherein each stage includes one or more tanks or vessels. 
     
     
         35 . The process of  claim 34 , said process further comprising additional mechanical refining of said mixture, or a partially hydrolyzed form thereof, following at least a first stage of enzymatic hydrolysis. 
     
     
         36 . The process of  claim 34 , said process further comprising:
 introducing said mixture to a first enzymatic-hydrolysis reactor under effective hydrolysis conditions to produce a liquid hydrolysate comprising sugars from said refined cellulose-rich solids and optionally from said hemicellulose, and a residual cellulose-rich solid phase;   optionally separating at least some of said liquid hydrolysate from said residual cellulose-rich solid phase;   conveying said residual cellulose-rich solid phase through an additional mechanical refiner and/or recycling said residual cellulose-rich solid phase through said mechanical refiner, to generate refined residual cellulose-rich solids; and   introducing said refined residual cellulose-rich solids to a second enzymatic-hydrolysis reactor under effective hydrolysis conditions, to produce additional sugars.   
     
     
         37 . The process of  claim 1 , wherein a self-cleaning filter is configured downstream of said hydrolysis reactor to remove cellulosic fiber strands. 
     
     
         38 . The process of  claim 37 , wherein said cellulosic fiber strands are recycled back to said hydrolysis reactor. 
     
     
         39 . The process of  claim 1 , wherein cellulase enzymes are introduced directly to said mechanical refiner or to said cellulose-rich solid phase prior to step (c). 
     
     
         40 . The process of  claim 39 , wherein said mechanical refiner is operated at a maximum temperature of 75° C. or less to maintain effective hydrolysis conditions. 
     
     
         41 . The process of  claim 1 , wherein step (d) includes enzymatic hydrolysis of hemicellulose oligomers to generate fermentable monomer sugars. 
     
     
         42 . The process of  claim 1 , wherein step (e) includes enzymatic hydrolysis of hemicellulose oligomers to generate fermentable monomer sugars within said fermentor. 
     
     
         43 . The process of  claim 42 , wherein at least a portion of said fermentable monomer sugars are also fermented to produce said fermentation product. 
     
     
         44 . The process of  claim 1 , said process further comprising removal of one or more fermentation inhibitors. 
     
     
         45 . The process of  claim 1 , said process further comprising concentrating said fermentation product by distillation. 
     
     
         46 . The process of  claim 45 , wherein said distillation generates a distillation bottoms stream, and wherein said distillation bottoms stream is evaporated in a distillation bottoms evaporator that is a mechanical vapor compression evaporator or is integrated in a multiple-effect evaporator train. 
     
     
         47 . The process of  claim 1 , wherein said fermentation product is selected from the group consisting of ethanol, isopropanol, acetone, n-butanol, isobutanol, 1,4-butanediol, succinic acid, lactic acid, and combinations thereof. 
     
     
         48 . The process of  claim 47 , wherein said fermentation product is ethanol. 
     
     
         49 . A process to produce a fermentation product from lignocellulosic biomass, said process comprising:
 (a) introducing a lignocellulosic biomass feedstock to a digestor, wherein said feedstock contains cellulose, hemicellulose, and lignin;   (b) exposing said feedstock to a reaction solution comprising steam or liquid hot water within said digestor, to solubilize at least a portion of said hemicellulose in a liquid phase and to provide a cellulose-rich solid phase;   (c) separating at least a portion of said liquid phase from said cellulose-rich solid phase;   (d) mechanically refining said cellulose-rich solid phase to reduce average particle size, thereby providing refined cellulose-rich solids;   (e) enzymatically hydrolyzing said refined cellulose-rich solids in a hydrolysis reactor with cellulase enzymes, to generate fermentable sugars;   (f) hydrolyzing said hemicellulose in said liquid phase, separately from step (e), to generate fermentable hemicellulose sugars; and   (g) fermenting at least some of said fermentable sugars, and optionally at least some of said fermentable hemicellulose sugars, in a fermentor to produce a fermentation product.   
     
     
         50 . A process to produce a fermentation product from lignocellulosic biomass, said process comprising:
 (a) introducing a lignocellulosic biomass feedstock to a digestor, wherein said feedstock contains cellulose, hemicellulose, and lignin;   (b) exposing said feedstock to a reaction solution comprising steam or liquid hot water within said digestor, to solubilize at least a portion of said hemicellulose in a liquid phase and to provide a cellulose-rich solid phase;   (c) mechanically refining said cellulose-rich solid phase to reduce average particle size, thereby providing refined cellulose-rich solids mixed with said liquid phase;   (d) separating at least a portion of said liquid phase from said refined cellulose-rich solids;   (e) enzymatically hydrolyzing said refined cellulose-rich solids in a hydrolysis reactor with cellulase enzymes, to generate fermentable sugars;   (f) hydrolyzing said hemicellulose in said liquid phase, separately from step (e), to generate fermentable hemicellulose sugars; and   (g) fermenting at least some of said fermentable sugars, and optionally at least some of said fermentable hemicellulose sugars, in a fermentor to produce a fermentation product.