The present invention involves a biorefinery process for pressure cooking woody or fibrous biomass (i.e., non-food plant biomass such as wood chips, plant stubble, food processing waste or other sources) in water to yield fermentable saccharides, commercial chemicals, and other useful lignocellulosic derivatives, and also to yield woody or fibrous solids that are significantly improved for manufacture of pulp and paper, fuel pellets, fiberboard, and other useful products.
Various processes have been proposed for recovery of purified chemical compounds from plant biomass, e.g., wood chips or agricultural residues. Typically these fall into three categories: chemical hydrolysis, enzymatic hydrolysis, or hydrothermal hydrolysis in combination with a chemical and/or enzymatic treatment. The general goal of these processes is depolymerization of cellulose (the structural portion of the biomass) into fermentable sugars and other biomass component chemicals, and/or directly targeting the end-product of ethanol.
Chemical hydrolysis relies on using (primarily) an acidic (i.e., low pH) or (less frequently) an alkaline (i.e., high-pH) solution to break down the structure of the biomass, and/or extract component chemicals from the fibrous or chipped plant material. For example, Lightner Published Application US 2003/0154975 discusses of a method of hydrolyzing biomass, to produce a sugar phase and an aqueous acidic solution phase. The process involves removing sugars from a hydrolysate. The hydrolysate is formed into a phase containing sugars and a phase containing concentrated acid. The separated sugar phase may be subjected to additional processing. Similarly, O'Connor et al. Published Application US 2009/0176286, Foody et al. Published Application US 2009/0023187, Zhang Published Application US 2009/0229599, Torget U.S. Pat. No. 6,228,177, and Tsao et al. U.S. Pat. No. 4,281,063 treat lignocellulosic biomass with an acid solution for varying temperatures and times.
Enzymatic depolymerization systems are generally deployed in conjunction with, or following, hydrothermal fiberization (steam explosion) or physical comminution (grinding) of lignocellulosic biomass. Ahring et al. U.S. Pat. No. 6,555,350, and Ahring et al. Published Application US 2009/0178671 present a process for converting lignocellulosic biomass to ethanol while utilizing only a low volume of clean water. Brink U.S. Pat. No. 5,628,830 enzymatically treats finely ground lignocellulosic biomass to disassemble cellulose into its component glucose sugars for fermentation to ethanol. Noriyuki et al. Japan Publication number 207-074992, and Japan Publication number 2007-074993 utilize a combination of enzymatic and hydrothermal/peroxide-aided treatment for the purpose of saccharifying cellulose. Lynd et al. U.S. Pat. No. 5,258,293 provide an improvement to “Direct Microbial Conversion” combined with “Simultaneous Saccharification and Fermentation” in which a single microbial system produces a cellulose disassembly enzyme, and subsequently also produces ethanol as a fermentation product in a single bioreactor at high volumetric productivity rates.
Hydrothermal only treatments are presented by Schmidt et al. U.S. Pat. No. 6,692,578 wherein corn fiber is heated in water to 110° C. to separate and hydrolyze hemicellulose into monosaccharides. Dahlman Published International Application WO 2009/068525 utilizes wood hydrolysis, subjecting the wood to an aqueous hydrothermal treatment for hydrolyzing and saccharifying the cellulose contained in the biomass, and separating it into fractions for production of polymers and monomers. Lignin is decomposed by enzyme action, and removed.
None of these previously proposed systems specifically address removal of acetic acid or other fermentation inhibitive chemicals from the extractant liquor, and consequently it is not likely that the processes isolate highly fermentable sugars from the lignocellulosic material. Similarly, none of the previously proposed systems separate and recover the wide array of commercially valuable, naturally occurring chemicals contained in lignocellulosic biomass. Lastly, these prior systems tend to attack the structural component of the woody biomass, and therefore none of these prior systems recognize the manufacturing benefits available from keeping the fibrous solids largely intact during and after removal of the hemicellulosic and other wood-derived compounds.