The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "Biomass refining (or biorefining) is becoming more prevalent in industry. Cellulose fibers and sugars, hemicellulose sugars, lignin, syngas, and derivatives of these intermediates are being used by many companies for chemical and fuel production. Indeed, we now are observing the commercialization of integrated biorefineries that are capable of processing incoming biomass much the same as petroleum refineries now process crude oil. Underutilized lignocellulosic biomass feedstocks have the potential to be much cheaper than petroleum, on a carbon basis, as well as much better from an environmental life-cycle standpoint.
"Lignocellulosic biomass is the most abundant renewable material on the planet and has long been recognized as a potential feedstock for producing chemicals, fuels, and materials. Lignocellulosic biomass normally comprises primarily cellulose, hemicellulose, and lignin. Cellulose and hemicellulose are natural polymers of sugars, and lignin is an aromatic/aliphatic hydrocarbon polymer reinforcing the entire biomass network. Some forms of biomass (e.g., recycled materials) do not contain hemicellulose.
"There are many reasons why it would be beneficial to process biomass in a way that effectively separates the major fractions (cellulose, hemicellulose, and lignin) from each other. Cellulose from biomass can be used in industrial cellulose applications directly, such as to make paper or other pulp-derived products. The cellulose can also be subjected to further processing to either modify the cellulose in some way or convert it into glucose. Hemicellulose sugars can be fermented to a variety of products, such as ethanol, or converted to other chemicals. Lignin from biomass has value as a solid fuel and also as an energy feedstock to produce liquid fuels, synthesis gas, or hydrogen; and as an intermediate to make a variety of polymeric compounds. Additionally, minor components such as proteins or rare sugars can be extracted and purified for specialty applications.
"In light of this objective, a major shortcoming of previous process technologies is that one or two of the major components can be economically recovered in high yields, but not all three. Either the third component is sacrificially degraded in an effort to produce the other two components, or incomplete fractionation is accomplished. An important example is traditional biomass pulping (to produce paper and related goods). Cellulose is recovered in high yields, but lignin is primarily consumed by oxidation and hemicellulose sugars are mostly degraded. Approximately half of the starting biomass is essentially wasted in this manufacturing process. State-of-the-art biomass-pretreatment approaches typically can produce high yields of hemicellulose sugars but suffer from moderate cellulose and lignin yields.
"There are several possible pathways to convert biomass into intermediates. One thermochemical pathway converts the feedstock into syngas (CO and H.sub.2) through gasification or partial oxidation. Another thermochemical pathway converts biomass into liquid bio-oils through pyrolysis and separation. These are both high-temperature processes that intentionally destroy sugars in biomass.
"Sugars (e.g., glucose and xylose) are desirable platform molecules because they can be fermented to a wide variety of fuels and chemicals, used to grow organisms or produce enzymes, converted catalytically to chemicals, or recovered and sold to the market. To recover sugars from biomass, the cellulose and/or the hemicellulose in the biomass must be hydrolyzed into sugars. This is a difficult task because lignin and hemicelluloses are bound to each other by covalent bonds, and the three components are arranged inside the fiber wall in a complex manner. This recalcitrance explains the natural resistance of woody biomass to decomposition, and explains the difficulty to convert biomass to sugars at high yields.
"Fractionation of biomass into its principle components (cellulose, hemicellulose, and lignin) has several advantages. Fractionation of lignocellulosics leads to release of cellulosic fibers and opens the cell wall structure by dissolution of lignin and hemicellulose between the cellulose microfibrils. The fibers become more accessible for hydrolysis by enzymes. When the sugars in lignocellulosics are used as feedstock for fermentation, the process to open up the cell wall structure is often called 'pretreatment.' Pretreatment can significantly impact the production cost of lignocellulosic ethanol.
"One of the most challenging technical obstacles for cellulose has been its recalcitrance towards hydrolysis for glucose production. Because of the high quantity of enzymes typically required, the enzyme cost can be a tremendous burden on the overall cost to turn cellulose into glucose for fermentation. Cellulose can be made to be reactive by subjecting biomass to severe chemistry, but that would jeopardize not only its integrity for other potential uses but also the yields of hemicellulose and lignin.
"Many types of pretreatment have been studied. A common chemical pretreatment process employs a dilute acid, usually sulfuric acid, to hydrolyze and extract hemicellulose sugars and some lignin. A common physical pretreatment process employs steam explosion to mechanically disrupt the cellulose fibers and promote some separation of hemicellulose and lignin. Combinations of chemical and physical pretreatments are possible, such as acid pretreatment coupled with mechanical refining. It is difficult to avoid degradation of sugars. In some cases, severe pretreatments (i.e., high temperature and/or low pH) intentionally dehydrate sugars to furfural, levulinic acid, and related chemicals. Also, in common acidic pretreatment approaches, lignin handling is very problematic because acid-condensed lignin precipitates and forms deposits on surfaces throughout the process.
"One type of pretreatment that can overcome many of these disadvantages is called 'organosolv' pretreatment. Organosolv refers to the presence of an organic solvent for lignin, which allows the lignin to remain soluble for better lignin handling. Traditionally, organosolv pretreatment or pulping has employed ethanol-water solutions to extract most of the lignin but leave much of the hemicellulose attached to the cellulose. For some market pulps, it is acceptable or desirable to have high hemicellulose content in the pulp. When high sugar yields are desired, however, there is a problem. Traditional ethanol/water pulping cannot give high yields of hemicellulose sugars because the timescale for sufficient hydrolysis of hemicellulose to monomers causes soluble-lignin polymerization and then precipitation back onto cellulose, which negatively impacts both pulp quality as well as cellulose enzymatic digestibility.
"An acid catalyst can be introduced into organosolv pretreatment to attempt to hydrolyze hemicellulose into monomers while still obtaining the solvent benefit. Conventional organosolv wisdom dictates that high delignification can be achieved, but that a substantial fraction of hemicellulose must be left in the solids because any catalyst added to hydrolyze the hemicellulose will necessarily degrade the sugars (e.g., to furfural) during extraction of residual lignin.
"Contrary to the conventional wisdom, it has been found that fractionation with a solution of ethanol (or another solvent for lignin), water, and sulfur dioxide (SO.sub.2) can simultaneously achieve several important objectives. The fractionation can be achieved at modest temperatures (e.g., 120-160.degree. C.). The SO.sub.2 can be easily recovered and reused. This process is able to effectively fractionation many biomass species, including softwoods, hardwoods, agricultural residues, and waste biomass. The SO.sub.2 hydrolyzes the hemicelluloses and reduces or eliminates troublesome lignin-based precipitates. The presence of ethanol leads to rapid impregnation of the biomass, so that neither a separate impregnation stage nor size reduction smaller than wood chips are needed, thereby avoiding electricity-consuming sizing operations. The dissolved hemicelluloses are neither dehydrated nor oxidized (Iakovlev, 'SO.sub.2-ethanol-water fractionation of lignocellulosics,' Ph.D. Thesis, Aalto Univ., Espoo,
"Commercial sulfite pulping has been practiced since 1874. The focus of sulfite pulping is the preservation of cellulose. In an effort to do that, industrial variants of sulfite pulping take 6-10 hours to dissolve hemicelluloses and lignin, producing a low yield of fermentable sugars. Stronger acidic cooking conditions that hydrolyze the hemicellulose to produce a high yield of fermentable sugars also hydrolyze the cellulose, and therefore the cellulose is not preserved.
"The dominant pulping process today is the Kraft process. Kraft pulping does not fractionate lignocellulosic material into its primary components. Instead, hemicellulose is degraded in a strong solution of sodium hydroxide with or without sodium sulfide. The cellulose pulp produced by the Kraft process is high quality, essentially at the expense of both hemicellulose and lignin.
"Sulfite pulping produces spent cooking liquor termed sulfite liquor. Fermentation of sulfite liquor to hemicellulosic ethanol has been practiced primarily to reduce the environmental impact of the discharges from sulfite mills since 1909. However, ethanol yields do not exceed one-third of the original hemicellulose component. Ethanol yield is low due to the incomplete hydrolysis of the hemicelluloses to fermentable sugars and further compounded by sulfite pulping side products, such as furfural, methanol, acetic acid, and others fermentation inhibitors.
"Solvent cooking chemicals have been attempted as an alternative to Kraft or sulfite pulping. The original solvent process is described in U.S. Pat. No. 1,856,567 by Kleinert et al. Groombridge et al. in U.S. Pat. No. 2,060,068 showed that an aqueous solvent with sulfur dioxide is a potent delignifying system to produce cellulose from lignocellulosic material. Three demonstration facilities for ethanol-water (Alcell), alkaline sulfite with anthraquinone and methanol (ASAM), and ethanol-water-sodium hydroxide (Organocell) were operated briefly in the 1990s.
"In view of the state of the art, what is desired is to efficiently fractionate any lignocellulosic-based biomass (including, in particular, softwoods) into its primary components so that each can be used in potentially distinct processes. While not all commercial products require pure forms of cellulose, hemicellulose, or lignin, a platform biorefinery technology that enables processing flexibility in downstream optimization of product mix, is particularly desirable. An especially flexible fractionation technique would not only separate most of the hemicellulose and lignin from the cellulose, but also render the cellulose highly reactive to cellulase enzymes for the manufacture of fermentable glucose.
"The AVAP.RTM. fractionation process developed by
As a supplement to the background information on this patent application, NewsRx correspondents also obtained the inventors' summary information for this patent application: "The present invention addresses the aforementioned needs in the art.
"In some variations, the invention provides a process for fractionating lignocellulosic biomass, the process comprising: (a) providing a feedstock comprising lignocellulosic biomass; (b) extracting hemicelluloses from the feedstock in the presence of steam or hot water, and optionally a first hydrolysis catalyst, thereby generating a first solids stream and a first liquid stream; © contacting the first solids stream with an acid or acid precursor, water, and a solvent for lignin, to produce a second liquid stream containing cellulose-rich solids and lignin; (d) recovering the cellulose-rich solids from the second liquid stream; (e) hydrolyzing the hemicelluloses to produce monomeric sugars; and (f) recovering the monomeric sugars.
"In some embodiments, the process further comprises hydrolyzing the cellulose-rich solids using an acid catalyst or cellulase enzymes to produce glucose. In some embodiments, the process further comprises recovering or further treating the cellulose-rich solids as pulp, a cellulose product, or a cellulose derivative.
"The first hydrolysis catalyst of step (b), in some embodiments, includes an acid selected from the group consisting of acetic acid, formic acid, uronic acids, levulinic acid, sulfur dioxide, sulfurous acid, sulfuric acid, lignosulfonic acid, carbon dioxide, carbonic acid, and combinations thereof.
"The acid or acid precursor in step © may be selected from the group consisting of sulfur dioxide, sulfurous acid, sulfur trioxide, sulfuric acid, lignosulfonic acid, and combinations, salts, or derivatives thereof. In particular embodiments, the acid or acid precursor is sulfur dioxide.
"When the second liquid stream contains hemicellulose oligomers, the process may further include hydrolyzing the hemicellulose oligomers to monomers in the presence of heat and optionally a second hydrolysis catalyst. In some embodiments, the second hydrolysis catalyst is present and includes hemicellulase enzymes or an acid selected from the group consisting of acetic acid, formic acid, uronic acids, levulinic acid, sulfur dioxide, sulfurous acid, sulfuric acid, lignosulfonic acid, carbon dioxide, carbonic acid, and combinations thereof.
"In certain embodiments, the hemicelluloses from step (e) and the hemicellulose oligomers (in the second liquid stream) are combined and hydrolyzed in a single reactor.
"Embodiments of the process can produce cellulose-rich solids having low hemicellulose content, such as about 5 wt %, 4 wt %, 3 wt %, 2 wt % hemicellulose content or less. In certain embodiments, the cellulose-rich solids from step (d) contain, on a dry basis, about 2 wt % or less hemicellulose content.
"Other variations of the invention provide a process for fractionating lignocellulosic biomass, the process comprising: (a) providing a feedstock comprising lignocellulosic biomass; (b) contacting the feedstock with an acid or acid precursor, water, and a solvent for lignin, to produce a first liquid stream containing cellulose-rich solids and lignin; © separating a first solids stream comprising the cellulose-rich solids from the first liquid stream; (d) extracting hemicelluloses from the cellulose-rich solids in the presence of steam or hot water, and a hydrolysis catalyst, thereby generating a second solids stream and a second liquid stream; (e) hydrolyzing the hemicelluloses to produce monomeric sugars; (f) recovering the monomeric sugars; and (g) recovering cellulose solids from the second solids stream.
"In some embodiments, the process further comprises hydrolyzing the cellulose solids using an acid catalyst or cellulase enzymes to produce glucose. In these or other embodiments, the process further comprises recovering or further treating the cellulose solids as pulp, a cellulose product, or a cellulose derivative.
"The acid or acid precursor is selected from the group consisting of sulfur dioxide, sulfurous acid, sulfur trioxide, sulfuric acid, lignosulfonic acid, and combinations, salts, or derivatives thereof. A preferred acid or acid precursor is sulfur dioxide.
"The hydrolysis catalyst may include hemicellulase enzymes or an acid selected from the group consisting of acetic acid, formic acid, uronic acids, levulinic acid, sulfur dioxide, sulfurous acid, sulfuric acid, lignosulfonic acid, carbon dioxide, carbonic acid, and combinations thereof.
"When the first liquid stream contains hemicellulose oligomers, the process may further comprise hydrolyzing the hemicellulose oligomers to monomers in the presence of heat and optionally a hydrolysis catalyst. The optional hydrolysis catalyst may includes hemicellulase enzymes or an acid selected from the group consisting of acetic acid, formic acid, uronic acids, levulinic acid, sulfur dioxide, sulfurous acid, sulfuric acid, lignosulfonic acid, carbon dioxide, carbonic acid, and combinations thereof.
"In some embodiments, the hemicelluloses from step (e) and the hemicellulose oligomers are combined and hydrolyzed in a single reactor.
"Embodiments of the process can produce cellulose solids having low hemicellulose content, such as about 5 wt %, 4 wt %, 3 wt %, 2 wt % hemicellulose content or less. In certain embodiments, the cellulose solids from step (g) contain, on a dry basis, about 2 wt % or less hemicellulose content.
BRIEF DESCRIPTION OF THE FIGURES
"FIG. 1 is an exemplary block-flow diagram of some embodiments of the invention to fractionate biomass into cellulose, hemicellulose, and lignin, comprising hot-water extraction followed by digestion with an acid and solvent for lignin.
"FIG. 2 is an exemplary block-flow diagram of some embodiments of the invention to fractionate biomass into cellulose, hemicellulose, and lignin, comprising digestion with an acid and solvent for lignin followed by hot-water extraction."
For additional information on this patent application, see: RETSINA, Theodora; PYLKKANEN, Vesa. Biomass Fractionation Processes, Apparatus, and Products Produced Therefrom. Filed
Keywords for this news article include: Alcohols, Chemicals, Chemistry, Cellulases, Chalcogens, Keto Acids, Acetic Acids, Formic Acids, Sulfur Acids, Acyclic Acids, Carbonic Acid, Ethanolamines, Sulfur Oxides, Carbon Dioxide, Sulfur Dioxide, Sulfuric Acids, Sulfurous Acid, Levulinic Acids, Sodium Hydroxide, Noncarboxylic Acids, Enzymes and Coenzymes.
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