Metal compounds to eliminate nonproductive enzyme adsorption and enhance enzymatic saccharification of lignocellulose
Inventors
Liu, Hao • ZHU JUNYONG, null • Zhu, Junyoug
Assignees
US Department of Agriculture USDA • Wisconsin Alumni Research Foundation
Publication Number
US-8815561-B2
Publication Date
2014-08-26
Expiration Date
2031-08-23
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Abstract
Methods and composition for biofuel processing are provided. For example, in certain aspects methods for using metal compounds to enhance cellulose enzymatic hydrolysis are described. Furthermore, the invention provides integrated processes with fewer lignin removal steps to improve efficiency.
Core Innovation
The invention provides methods and compositions that use metal compounds, particularly divalent metals like calcium and magnesium, to enhance enzymatic hydrolysis of lignocellulose biomass. This approach involves forming lignin-metal complexes that reduce or eliminate nonproductive adsorption of enzymes onto lignin, thereby increasing enzymatic cellulose saccharification efficiency. The invention also enables integrated processes with fewer lignin removal steps, improving process efficiency and reducing water and energy consumption.
The problem addressed relates to the inhibitory effects of lignin, both bound and unbound, in lignocellulosic biomass on enzymatic hydrolysis. Lignin nonproductively adsorbs cellulase enzymes, reducing their availability and activity. Conventional removal of lignin involves washing steps that consume large amounts of water and energy, increasing costs and environmental impacts. Existing methods using proteins or surfactants to block lignin adsorption are limited by cost or process complications such as foaming.
The invention overcomes these limitations by applying divalent metal compounds that bind lignin, including sulfonated lignin such as lignosulfonate, to form lignin-metal complexes. This complexation deactivates enzyme adsorption sites on lignin, freeing enzymes for cellulose hydrolysis. The method allows elimination or substantial reduction of washing steps, saving water and energy, and enables simultaneous saccharification and fermentation processes with unwashed biomass, thus simplifying biomass-to-biofuel processing.
Claims Coverage
The patent contains one independent composition claim and one independent method claim encompassing the use of divalent metals to enhance enzymatic cellulose hydrolysis of lignocellulosic biomass.
Lignocellulose-containing composition with divalent metal ions
A composition comprising an unwashed pretreated biomass containing free lignin and at least 10% solid lignocellulose, an aqueous solution with a divalent cation (calcium or magnesium) at 1 to 10 mol per kilogram solid lignocellulose that enhances enzymatic hydrolysis compared to absence of the cation, and a cellulase enzyme.
Metal ion forms and aqueous solution pH
The calcium or magnesium may be present as CaCl2, CaCO3, CaSO4, MgSO4, Ca(OH)2, CaO, or combinations thereof. The aqueous solution has a pH ranging from 2 to 8, preferably 4 to 7.
Method for cellulose hydrolysis using metal ions without washing
A method comprising pretreating an unwashed biomass with free lignin and at least 10% solid lignocellulose, mixing with an aqueous solution comprising calcium or magnesium ions at 1 to 10 mol per kilogram solid lignocellulose and cellulase, and treating the mixture to hydrolyze cellulose.
Pretreatment and biomass feedstock specifications
The biomass can be pretreated with sulfite or bisulfite and can include grasses, agricultural residues, municipal solid waste, waste paper, softwood, and hardwood materials.
Optional size reduction and separation steps
The method may further include reducing biomass size and separating the unwashed pretreated biomass into solid and liquid portions.
Fermentation integration
The method may include fermenting the treated mixture to produce biofuels in the same or separate reactors, and hydrolyzing hemicellulose if present in the mixture.
The claims cover compositions and methods using divalent calcium or magnesium compounds to reduce lignin inhibition on enzymatic hydrolysis of unwashed pretreated lignocellulosic biomass, enabling enhanced cellulose hydrolysis and integration with fermentation for biofuel production.
Stated Advantages
Enhanced enzymatic cellulose hydrolysis through reduction or elimination of enzyme adsorption on lignin via lignin-metal complexation.
Reduction or elimination of washing steps reduces water and energy use, lowering operational costs and environmental impact.
Allows integration of simultaneous saccharification and fermentation processes, simplifying biofuel production.
Use of inexpensive metal salts such as calcium and magnesium compounds makes the process economically viable at commercial scale.
Documented Applications
Use in biofuel production by enzymatic hydrolysis of lignocellulosic biomass to produce fermentable sugars followed by fermentation to ethanol and other biofuels.
Integrated biomass biorefining processes including SPORL sulfite pretreatment combined with metal ion treatment to enhance saccharification of woody and non-woody biomass.
Simultaneous saccharification and combined fermentation (SSCombF) of cellulose solid substrates with hemicellulose sugar streams containing dissolved lignosulfonate.
Reduction of enzyme inhibition by unbound and bound lignin in biomass processing without costly washing and detoxification steps.
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