Method of producing sugars using a combination of acids to selectively hydrolyze hemicellulosic and cellulosic materials

Abstract

A method is provided for producing sugars using a combination of acids to hydrolyze hemicellulosic and cellulosic materials in biomass, said combination of acids namely comprising a first, weak organic acid (such as acetic acid or formic acid) for providing a pentose product or stream from hydrolyzing hemicellulosic materials in the biomass on a batchwise, semi-continuous or continuous basis, and a second, strong mineral acid (such as sulfuric acid) for providing a hexose product or stream from hydrolyzing cellulosic materials in the biomass.

What is claimed is: 
     
         1 . A method of processing a lignocellulosic biomass including cellulose, hemicellulose and lignin fractions, comprising the steps of:
 applying a weak organic acid to the biomass to at least partly depolymerize the hemicellulosic and lignin materials in the biomass;   drying the weak-acid treated biomass to provide a sufficiently high solids content material as to be pelletized;   pelletizing the material from the drying step; and   shipping the pelletized material to a second location;   at the second location, recovering a cellulosic solids product from the pelletized material; and   contacting the cellulosic solids so isolated with a strong mineral acid to hydrolyze the same and provide a hexose product or stream.   
     
     
         2 . A method according to  claim 1 , wherein the cellulosic solids product is recovered from the pelletized material by solvent washing the pelletized material in one or more iterations with filtration, whereby the at least partly depolymerized hemicellulosic and lignin materials from the pelletized material are separated together from the remaining cellulosic solids. 
     
     
         3 . A method according to  claim 2 , further comprising, in one or more iterations, washing the at least partly depolymerized hemicellulosic and lignin materials with filtering to separate water-insoluble lignin solids from water-soluble hemicellulosic materials. 
     
     
         4 . A method according to  claim 1 , wherein the at least partly depolymerized hemicellulosic materials are first separated from the pelletized material by water washing the pelletized material in one or more iterations with filtration, and the lignins are subsequently separated from the cellulosic solids product by a separate solvent wash with filtration, also in one or more iterations. 
     
     
         5 . A method according to either of  claim 3  or  4 , comprising a further acid hydrolysis step conducted on the at least partly depolymerized hemicellulosic materials after the same have been separated from the lignins and cellulosic solids product. 
     
     
         6 . A method according to  claim 5 , further comprising fermenting the product of the further acid hydrolysis of the hemicellulosic materials to produce ethanol, lysine, threonine, lactic, gluconic or other organic acids, or hydrogenating and hydrotreating the product of the further acid hydrolysis step to yield a fuel additive product for transportation fuels. 
     
     
         7 . A method according to either of  claim 3  or  4 , wherein the water-insoluble lignins are subjected to ozonolysis or exposure to one or more other oxidants, or combusted as a fuel, or supplied to a coking process for making a liquid hydrocarbon product and coke, or fed to a gasifier for producing a synthesis gas. 
     
     
         8 . A method according to  claim 1 , further comprising fermenting the hexose product or stream to produce ethanol, lysine, threonine, lactic, gluconic or other organic acids. 
     
     
         9 . A method according to any of  claims 1 - 8 , wherein the lignocellulosic biomass is characterized as having an acid-detergent insoluble lignin content of 6 percent or greater by weight, on a dry weight basis. 
     
     
         10 . A method according to  claim 9 , wherein the lignocellulosic biomass is comprised of one or more of a mature grass, grain crop residue separately or contained in a grain silage, corn stover, wheat straw, barley straw,  miscanthus  specie, switchgrass, bahia grass,  Sorghum  specie, sugar cane bagasse, orchardgrass, reed canarygrass and cotton gin trash. 
     
     
         11 . A method according to  claim 10 , wherein the lignocellulosic biomass processed comprises corn stover and corn fiber. 
     
     
         12 . A method according to  claim 11 , wherein the lignocellulosic biomass processed is ensiled whole plant corn, and wherein the biomass is preprocessed before the weak organic acid is applied to isolate and remove at least one component of the ensiled whole plant corn. 
     
     
         13 . A method according to  claim 12 , wherein corn oil is recovered from the ensiled whole plant corn biomass before the same is contacted with the weak organic acid. 
     
     
         14 . A method according to  claim 12 , wherein the leaf fraction of corn stover is isolated and removed mechanically from the ensiled whole plant corn biomass before the same is contacted with the weak organic acid. 
     
     
         15 . A method according to  claim 12 , wherein one or more components which are higher in sulfur, nitrogen or ash content are mechanically isolated and removed from the ensiled whole plant corn biomass is contacted with the weak organic acid. 
     
     
         16 . A method according to any of  claims 1 - 15 , wherein the weak organic acid is applied in the vapor phase at an elevated temperature of 50 degrees Celsius or greater. 
     
     
         17 . A method according to  claim 16 , wherein the weak organic acid is acetic acid or formic acid, and the acid is applied at a temperature of from 50 degrees Celsius to 160 degrees Celsius, a pressure of from atmospheric pressure to 3.5 MPa, gauge, and for a time period of 30 minutes and more. 
     
     
         18 . A method according to any of  claims 1 - 17 , wherein the weak organic acid or acids are applied to the lignocellulosic biomass at a concentration of at least 50 percent of such acid or acids in water. 
     
     
         19 . A method according to  claim 18 , wherein the weak organic acid or acids are applied to the biomass at a concentration of 70 percent or more of such acid or acids in water. 
     
     
         20 . A method according to any of  claims 1 - 19 , wherein the weak acid-treated biomass is dried to a moisture content of 10 percent or less by weight. 
     
     
         21 . A method according to  claim 20 , wherein the dried biomass is pelletized without the addition of a further binder. 
     
     
         22 . A method according to any of  claims 1 - 21 , wherein the weak acid treatment, drying and pelletizing steps are applied at a plurality of locations for shipment of pelletized material to a common second location. 
     
     
         23 . A method according to  claim 22 , wherein the plurality of sites are on average a distance of 50 or more kilometers from the common second location. 
     
     
         24 . A method according to  claim 23 , wherein the plurality of sites are on average a distance of 80 or more kilometers from the common second location. 
     
     
         25 . A method according to  claim 20 , wherein the weak acid hydrolysis, drying and pelletizing steps are applied to produce a pelletized material at a location that is at least 50 kilometers from the second location. 
     
     
         26 . A method according to  claim 1 , further comprising preprocessing the biomass before contact with the weak organic acid to isolate and remove at least one component of the biomass that is higher in protein and suitable for use in or for an animal feed, or that has a higher than desired sulfur, nitrogen or ash content. 
     
     
         27 . A method of processing a lignocellulosic biomass including cellulose, hemicellulose and lignin fractions, comprising the steps of:
 applying a weak organic acid to the biomass to hydrolyze hemicellulosic and lignin materials in the biomass;   in one or more iterations, washing the weak acid-treated material with a solvent or solvent mixture and filtering to separate hemicellulosic and lignin materials in the filtrate and cellulosic materials as a solid residue;   drying the solid residue to provide a sufficiently high solids content material as to be pelletized;   pelletizing the material from the drying step;   shipping the pelletized material to a second location; and   at the second location, contacting the cellulosic materials so isolated with a strong mineral acid to hydrolyze the same and provide a hexose product or stream.   
     
     
         28 . A method of processing a lignocellulosic biomass including cellulose, hemicellulose and lignin fractions, comprising the steps of:
 applying a weak organic acid to the biomass to hydrolyze hemicellulosic and lignin materials in the biomass;   in one or more iterations, washing the weak organic acid-treated material with a solvent or solvent mixture and filtering to separate hemicellulosic and lignin materials in the filtrate and cellulosic materials as a solid residue; and   contacting the cellulosic materials so isolated with a strong mineral acid to hydrolyze the same and provide a hexose product or stream.   
     
     
         29 . A method according to either of  claim 27  or  28 , wherein the weak organic acid is applied in the vapor phase at an elevated temperature of 50 degrees Celsius and greater. 
     
     
         30 . A method according to  claim 29 , wherein the weak organic acid is acetic acid or formic acid, and the acid is applied at a temperature of from 50 degrees Celsius to 160 degrees Celsius, a pressure of from atmospheric pressure to 3.5 MPa, gauge, and for a time period of 30 minutes and more. 
     
     
         31 . A method according to  claim 30 , wherein the weak organic acid or acids are applied to the lignocellulosic biomass at a concentration of at least 50 percent of such acid or acids in water. 
     
     
         32 . A method according to  claim 31 , wherein the weak organic acid or acids are applied to the biomass at a concentration of 70 percent or more of such acid or acids in water.