The assignee for this patent application is
Reporters 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
In addition to obtaining background information on this patent application, NewsRx editors 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) contacting the feedstock with sulfur dioxide, water, and optionally a solvent for lignin, wherein the sulfur dioxide is present at a first concentration, to produce intermediate solids;
"© contacting the intermediate solids with sulfur dioxide, water, and a solvent for lignin, wherein the sulfur dioxide is present at a second concentration that is different than the first concentration, to produce cellulose-rich solids and a liquid phase comprising hemicelluloses and lignin;
"(d) recovering the cellulose-rich solids;
"(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.
"In some embodiments, the first concentration of sulfur dioxide is higher than the second concentration of sulfur dioxide. In other embodiments, the first concentration of sulfur dioxide is lower than the second concentration of sulfur dioxide. It may be desirable to vary the SO.sub.2 concentration in the different stages--optionally in conjunction with varying temperature, residence time, liquor/solids ratio, or other factors--to enhance the removal of hemicellulose versus lignin, or vice-versa. Process flexibility can be improved.
"In some embodiments, the first concentration of sulfur dioxide is selected from about 0.1 wt % to about 12 wt % SO.sub.2. In these or other embodiments, the second concentration of sulfur dioxide is selected from about 8 wt % to about 30 wt % SO.sub.2.
"In some embodiments, step (b) includes a solvent for lignin. The concentration of solvent, if employed, in step (b) may be different than the concentration of solvent in step ©. The concentration in step (b) may be lower, for example, if the step is targeting hemicellulose removal over lignin removal. Or, the solvent concentration in step (b) may be higher, for example, if the step is targeting lignin removal.
"In some embodiments, step (e) is conducted in the presence of heat and optionally a hydrolysis catalyst, such as 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 hydrolysis catalyst includes lignosulfonic acid derived from the first liquid phase and/or the second liquid phase.
"The cellulose-rich solids from step (d) may contain, on a dry basis, about 5 wt % or less hemicellulose content, such as about 4 wt %, about 3 wt %, about 2 wt %, or less hemicellulose content. The cellulose-rich solids from step (d) may contain, on a dry basis, about 4 wt % or less lignin content, such as about 3 wt %, about 2 wt %, about 1 wt %, or less lignin content. In certain embodiments, the cellulose-rich solids from step (d) contain, on a dry basis, about 2 wt % or less hemicellulose content and about 2 wt % or less lignin content.
"Some variations provide a process for fractionating lignocellulosic biomass, the process comprising:
"(a) providing a feedstock comprising lignocellulosic biomass;
"(b) in a first digestor stage, contacting the feedstock with sulfur dioxide, water, and optionally a first solvent for lignin, wherein the sulfur dioxide is present at a first concentration, to produce intermediate solids and a first liquid phase comprising hemicelluloses and lignin;
"© in a second digestor stage, contacting the intermediate solids with sulfur dioxide, water, and a second solvent for lignin, wherein the sulfur dioxide is present at a second concentration that is different than the first concentration, to produce cellulose-rich solids and a second liquid phase comprising hemicelluloses and lignin;
"(d) separating and recovering the cellulose-rich solids from the liquid phase;
"(e) hydrolyzing the hemicelluloses to produce monomeric sugars; and
"(f) recovering the monomeric sugars.
"The first digestor stage and the second digestor stage may be physically separate reactors or separated zones in a single reactor, for example. In some embodiments, the first liquid phase is removed, at least in part, prior to the second digestor stage.
"The process may further include bleaching the intermediate solids and/or the cellulose-rich solids. The process may further include hydrolyzing the cellulose-rich solids using an acid catalyst or cellulase enzymes to produce glucose. The process may further include recovering or further treating the cellulose-rich solids as a cellulose product or precursor material.
"Apparatus may be configured for carrying out the disclosed processes, as further discussed below. Products produced by these processes are further described in the detailed description.
BRIEF DESCRIPTION OF THE FIGURE
"FIG. 1 is an exemplary block-flow diagram of some embodiments of the invention to fractionate biomass into cellulose, hemicellulose, and lignin using multiple digestor stages with different SO.sub.2 concentrations."
For more information, see this patent application: RETSINA, Theodora; PYLKKANEN, Vesa. Biomass Fractionation Processes Employing Sulfur Dioxide. Filed
Keywords for this news article include: Alcohols, Chemicals, Chemistry, Chalcogens, Ethanolamines, Sulfur Oxides, Sulfuric Acid, Sulfur Dioxide, Sodium Hydroxide, Enzymes and Coenzymes,
Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC
Most Popular Stories
- What Hamas and Israel Hope to Gain in Gaza
- Homeowners More Satisfied With Mortgage Servicers
- House Shelves Immigration Bill, Goes on Vacation
- NASA Plans to Make Oxygen on Mars
- Why Samsung Shares Plunged in the April-June Quarter
- House GOP Leaders Abandon Immigrant Bill
- Notorious RBG Tells All in Couric Interview
- Wisconsin Supreme Court: Voter IDs Must Be Free
- Ford Tremor: Easy to Park, Hard to Pay For
- Market Loses All of July's Gains in One Day