Biomass pretreatment
Inventors
Hennessey, Susan Marie • Friend, Julie • Elander, Richard T. • Tucker, III, Melvin P.
Assignees
Sustainable Technology Corp • US Department of Energy • Alliance for Sustainable Energy LLC
Publication Number
US-8445236-B2
Publication Date
2013-05-21
Expiration Date
2027-08-22
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Abstract
A method is provided for producing an improved pretreated biomass product for use in saccharification followed by fermentation to produce a target chemical that includes removal of saccharification and or fermentation inhibitors from the pretreated biomass product. Specifically, the pretreated biomass product derived from using the present method has fewer inhibitors of saccharification and/or fermentation without a loss in sugar content.
Core Innovation
The invention provides a method for producing an improved pretreated biomass product intended for use in saccharification followed by fermentation to produce target chemicals. Specifically, it involves pretreating biomass with an aqueous ammonia solution under controlled conditions to form a biomass-aqueous ammonia mixture where the ammonia concentration is sufficient to maintain alkaline pH but remains below about 12 weight percent relative to the dry weight of biomass. The biomass is maintained at a high solids concentration of at least about 15 weight percent relative to the mixture, forming a pretreated biomass solids product and a biomass pretreatment liquor containing saccharification or fermentation inhibitors.
The process includes removing the biomass pretreatment liquor to reduce inhibitor compounds in the pretreated biomass solids product without causing a substantial loss in sugar content. This improvement enhances the efficiency of subsequent saccharification and fermentation steps. The method may also involve adding an additional aqueous component either before, during, or after pretreatment as a wash step. The improved pretreated biomass product can then be saccharified with enzyme consortia to produce sugars, which may be fermented to generate target chemicals.
The problem addressed by this invention arises from conventional biomass pretreatment methods which release saccharification and fermentation inhibitors such as acetic acid and acetamide together with sugars into liquid fractions. Traditional approaches attempting to remove these inhibitors either are uneconomical or cause substantial sugar loss. The present invention solves this by using low concentration aqueous ammonia pretreatment at high biomass solids concentration, resulting in the release of inhibitors into a liquid fraction with insubstantial sugar release, enabling removal of inhibitors by separating this liquid fraction and thereby obtaining an improved biomass product with maximal sugar retention and minimal inhibitors.
Claims Coverage
The patent includes one independent claim encompassing the entire method of producing saccharification hydrolysate from biomass, covering pretreatment, inhibitor removal, and saccharification.
Pretreatment with low concentration aqueous ammonia at high solids concentration
The method involves contacting biomass with aqueous ammonia at a concentration sufficient to maintain alkaline pH but not exceeding 12 weight percent relative to dry biomass, with biomass at 15 weight percent solids or higher, producing a pretreated biomass solids product and a biomass pretreatment liquor containing inhibitors.
Removal of biomass pretreatment liquor containing saccharification and fermentation inhibitors
After pretreatment, the biomass pretreatment liquor containing inhibitor compounds is removed from the solids, reducing inhibitor levels without substantial sugar loss.
Saccharifying the pretreated biomass solids to form fermentable sugars
The pretreated biomass solids, after inhibitor removal, are saccharified to generate saccharification hydrolysate containing fermentable sugars usable for fermentation.
Optional addition of aqueous component before, during, or after pretreatment
An additional aqueous component such as steam, water, or buffer can be added prior to contacting biomass with ammonia, during pretreatment, or as a wash step after pretreatment to facilitate inhibitor solubilization and removal.
The independent claim covers a method comprising pretreatment of biomass with aqueous ammonia at controlled conditions and concentration, removal of inhibitor-rich pretreatment liquor, and saccharification of the resulting pretreated biomass solids, with optional aqueous component additions to improve the pretreatment.
Stated Advantages
Reduces the amount of saccharification and fermentation inhibitors in the pretreated biomass product, increasing the efficiency of saccharification and fermentation processes.
Maximizes retention of sugars in the biomass by releasing inhibitors to a separate liquid fraction, avoiding substantial sugar loss during removal of inhibitors.
The method is economical since it avoids complex and costly inhibitor removal steps such as chromatographic separations or prehydrolysate processes that reduce sugar yield.
Using aqueous ammonia during pretreatment also provides a nitrogen source for microbial growth in subsequent fermentation, potentially reducing or eliminating the need for additional nitrogen supplementation.
Documented Applications
The improved pretreated biomass product is for use in saccharification to produce fermentable sugars.
Saccharification hydrolysate derived from the pretreated biomass is used for biocatalytic fermentation to produce target chemicals including alcohols like ethanol and butanol, acids such as lactic and acetic acid, amino acids, biopolymers, pharmaceuticals, and other valuable chemicals.
The method applies to a variety of biomass sources including bioenergy crops, agricultural residues, municipal and industrial solid waste, wood and forestry waste, and mixtures thereof.
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