Patent Application
20150041084
The present invention relates generally to processes for purifying a cellulosic material. In particular, the present invention relates to processes for extracting and recovering hemicellulose from pulp and producing a purified pulp comprising cellulose and having reduced hemicellulose content.
Cellulose is typically obtained from wood pulp and cotton and may be further modified to create derivatives including regenerated cellulose, cellulose ethers, cellulose esters and cellulose nitrate, among others. Cellulose derivatives have a variety of commercial uses. For example, cellulose acetate is the acetate ester of cellulose and is used for a variety of products, including textiles (e.g., linings, blouses, dresses, wedding and party attire, home furnishings, draperies, upholstery and slip covers), industrial uses (e.g., cigarette and other filters for tobacco products, and ink reservoirs for fiber tip pens, decking lumber), high absorbency products (e.g., diapers, sanitary napkins, and surgical products), thermoplastic products (e.g., film applications, plastic instruments, and tape), cosmetic and pharmaceutical (extended capsule/tablet release agents and encapsulating agent), medicinal (hypoallergenic surgical products) and others.
High purity α-cellulose is commonly required as a starting material to make cellulose derivatives, such as cellulose acetate. Acetate-grade pulps are specialty raw materials produced in commercial pulp processes, but the cost for such pulps is high. Commercial paper grade pulps contain less than 90% α-cellulose and are potential crude cellulosic sources for making cellulose derivatives. Paper grade pulp contains a high amount of impurities, such as hemicellulose, rendering it incompatible with certain industrial uses, such as making cellulose acetate flake or tow.
Zhou et al. discusses the use of dimethyldioxirane (DMDO), a pulp bleaching agent, to treat birch pulp and obtain acetate-grade pulp. However, currently, DMDO is not commercially available due to its instability. Therefore, it is not an ideal solvent for producing large quantities of high α-cellulose content pulp. Zhou et al. “Acetate-grade pulp from birch,” BioResources, (2010), 5(3), 1779-1778.
Studies have been done regarding the treatment of biomass to form biofuels. Specifically, it is known that various ionic liquids can be used to dissolve cellulosic material. S. Zhu et al. in Green Chem. 2006, 8, pp. 325-327, describe the possibility of dissolving cellulose in ionic liquids and recovering it by addition of suitable precipitating agents such as water, ethanol, or acetone.
Others have used ionic liquids to break down the cellulosic materials to make biofuels by way of glucose. For example, U.S. Pub. No. 2010/0112646 discloses a process for preparing glucose from a cellulose material, in which a cellulose-comprising starting material is provided and treated with a liquid treatment medium comprising an ionic liquid and an enzyme. Similarly, U.S. Pub. No. 2010/0081798 discloses a process for preparing glucose from a material containing ligno-cellulose, in which the material is first treated with an ionic liquid and then subjected to enzymatic hydrolysis. U.S. Pub. No. 2010/0081798 describes obtaining glucose by treating a material containing ligno-cellulose with an ionic liquid and subjecting same to an enzymatic hydrolysis and fermentation. However, in order to turn cellulose containing materials into glucose, the methods disclosed in these references result in breaking down the cellulose molecules, making them unsuitable for use as starting materials to make cellulose derivatives.
U.S. Pat. No. 7,828,936 describes a method for dissolving cellulose in which the cellulose based raw material is admixed with a mixture of a dipolar aprotic intercrystalline swelling agent and an ionic liquid. This method results in the complete dissolution of the cellulose and destruction of the fiber morphology of the cellulose. Although the cellulose may be regenerated using a non-solvent, the crystallinity of the regenerated cellulose is lower than the original cellulose sample.
The need exists for processes for producing high purity cellulose from lower grade starting materials without destroying the fiber morphology and other characteristics of the cellulose structure. In particular, the need exists for cost effective processes for removing and recovering hemicellulose from cellulosic materials to yield high purity cellulose that can be converted to other cellulose derivatives.
The present invention is directed to processes for purifying a cellulosic material, comprising: extracting hemicellulose from the cellulosic material with an extractant comprising a cellulose solvent and one or more co-solvents to form an extraction mixture; separating the extraction mixture to form an intermediate cellulosic material and a liquid stream containing hemicellulose; and flashing at least a portion of the liquid stream to form a vapor stream enriched in the co-solvent and a flashed liquid stream comprising the hemicellulose, the cellulose solvent, and the co-solvent. The process may further comprise combining the liquid stream with a precipitation agent in a precipitator to form a precipitation slurry, and then separating the precipitation slurry to form an intermediate hemicellulosic material and a liquid stream.
The extractant may comprise a cellulose solvent selected from the group consisting of an ionic liquid and an amine oxide; and wherein the co-solvent has a boiling point of less than 120° C., e.g., of less than 100° C. In some embodiments, the co-solvent comprises acetonitrile and/or water. The co-solvent may have an acetonitrile to water weight ratio from 6:1 to 500:1. The intermediate cellulosic material may comprise at least 10% less hemicellulose than the cellulosic material. In some embodiments, the co-solvent may be selected from the group consisting of alcohols, esters, ethers, ketones, carboxylic acids, nitriles, amine, amide, halides, hydrocarbon compounds, heterocyclic compounds, and combinations thereof. In further embodiments, the co-solvent may be selected from the group consisting of methanol, ethanol, isopropanol, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, vinyl acetate, tetrahydrofuran, acetone, acetic acid, formic acid, acetonitrile, propionitrile, butyronitrile, chloroacetonitrile, dichloromethane, chloroform, triethylamine, N,N-dimethylformamide, toluene, pyridine, water, and combinations thereof.
The cellulose solvent may comprise an ionic liquid selected from the group consisting of ammonium-based ionic substances, imidazolium-based ionic substances, phosphonium-based ionic substances, and combinations thereof. The cellulose solvent may comprise an ionic liquid selected from the group consisting of ammonium acetate, hydroxyethyl ammonium acetate, hydroxyethyl ammonium formate, tetramethylammonium acetate, tetrabutylammonium acetate, tetraethylammonium acetate, benzyltriethylammonium acetate, benzyltributylammonium acetate, benzyltriethylammonium chloride, benzyltributylammonium chloride, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, N,N-dimethylpyrrolidinium acetate, N,N-dimethylpiperidinium acetate, N,N-dimethylpyrrolidinium dimethyl phosphate, N,N-dimethylpiperidinium dimethyl phosphate, N,N-dimethylpyrrolidinium chloride, N,N-dimethylpiperidinium chloride, and combinations thereof. In some embodiments, the cellulose solvent may comprise an ionic liquid selected from the group consisting of 1-butyl-3-methylimidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate, methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate, 1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate, methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride, 1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, 1-ethyl-3-methylimidazolium dimethyl phosphate, 1-ethyl-3-methyl diethyl phosphate, 1,3-dimethylimidazolium dimethyl phosphate and combinations and complexes thereof. In some embodiments, the cellulose solvent may comprise an ionic liquid selected from the group consisting of ethyltributylphosphonium diethylphosphate, methyltributylphosphonium dimethylphosphate, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tributylmethylphosphonium methylsulfate, trihexyltetradecylphosphonium decanoate, trihexyltetradecylphosphonium dicyanamide, ethyltriphenylphosphonium acetate, ethyltributylphosphonium acetate, benzyltriethylphosphonium acetate, benzyltributylphosphonium acetate, tetrabutylphosphonium acetate, tetraethylphosphonium acetate, tetramethylphosphonium acetate, and combinations thereof. In additional embodiments, the cellulose solvent may comprise an amine oxide selected from the group consisting of compounds with chemical structure of acyclic R3N+—O−, compounds with chemical structure of N-heterocyclic compound N-oxide, and combinations thereof. In some embodiments, the cellulose solvent may comprise an amine oxide selected from the group consisting of trimethylamine N-oxide, triethylamine N-oxide, tripropylamine N-oxide, tributylamine N-oxide, methyldiethylamine N-oxide, dimethylethylamine N-oxide, methyldipropylamine N-oxide, tribenzylamine N-Oxide, benzyldimethylamine N-oxide, benzyldiethylamine N-oxide, dibenzylmethylamine N-oxide, N-methylmorpholine N-oxide (NMMO), pyridine N-oxide, 2-, 3-, or 4-picoline N-oxide, N-methylpiperidine N-oxide, N-ethylpiperidine N-oxide N-propylpiperidine N-oxide, N-isopropylpiperidine N-oxide. N-butylpiperidine N-oxide, N-hexylpiperidine N-oxide. N-methylpyrrolidine N-oxide, N-ethylpyrrolidine N-oxide N-propylpyrrolidine N-oxide, N-isopropylpyrrolidine N-oxide. N-butylpyrrolidine N-oxide, N-hexylpyrrolidine N-oxide, and combinations thereof.
The process may further comprise concentrating the intermediate cellulosic material by at least partially drying the intermediate cellulosic material and optionally washing the intermediate cellulosic material one or more times with one or more washes prior to the drying operation. The concentrated cellulosic material may be dried in a dryer to form a finished cellulosic material and may be dried to a solids content of at least 90 wt. %. The one or more washes may be selected from the group consisting of an alcohol, a ketone, a nitrile, an ether, an ester, a carboxylic acid, a halide, a hydrocarbon compound, an amine, a heterocyclic compound, water, and combinations thereof. The one or more washes may be selected from the group of water, ethylene glycol, glycerin, formamide, N,N-dimethylformamide, N-methylpyrrolidinone, N,N-dimethylacetamide, dimethyl sulfoxide (DMSO), a mixture of water and alcohol, and combinations thereof. The one or more washes may be enriched in co-solvent. The one or more washes enriched in co-solvent may comprise a condensed portion of the vapor stream of the co-solvent from the flashing. The one or more washes may comprise washing the intermediate cellulosic material with a first wash comprising greater than 90 wt % co-solvent, optionally followed with a second wash comprising greater than 90 wt % water. The one or more washes may comprise washing the intermediate cellulosic material one or more times with a first extractant stream, which comprises cellulose solvent and co-solvent, followed with a second wash containing more than 90% co-solvent, and further optionally followed with a wash containing more than 90% water. The process may further comprise separating the co-solvent from the one or more washes using distillation or a vaporizer. The precipitation agent may be selected from the group consisting of an alcohol, a ketone, a nitrile, an ether, an ester, a carboxylic acid, a halide, a hydrocarbon compound, an amine, a heterocyclic compound, water, and combinations thereof. In some embodiments, the precipitation agent is the same as the co-solvent used in the extracting. In some embodiments, acetonitrile and/or water may be used as both co-solvent and precipitation agent and the concentration of co-solvent in the precipitation slurry may be at least 1% higher than in the extractant.
The process may further comprise concentrating the intermediate hemicellulosic material by at least partially drying the intermediate hemicellulosic material, and optionally washing the intermediate hemicellulosic material one or more times with one or more washes prior to the drying. The intermediate hemicellulosic material may be dried in a dryer to form a finished hemicellulose material and may be dried to a solids content of at least 90 wt. %. The one or more washes may be selected from the group consisting of an alcohol, a ketone, a nitrile, an ether, an ester, a carboxylic acid, a halide, a hydrocarbon compound, an amine, a heterocyclic compound, water, and combinations thereof. In some embodiments, the one or more washes may be selected from the group of water, ethylene glycol, glycerin, formamide, N,N-dimethylformamide, N-methylpyrrolidinone, N,N-dimethylacetamide, DMSO, a mixture of water and alcohol, and combinations thereof. The one or more washes may comprise a stream enriched in co-solvent. The stream enriched in co-solvent may comprise a condensed portion of the vapor stream of the co-solvent from the flashing. The one or more washes may comprise a stream enriched in the precipitation agent. The one or more washes may comprise washing the intermediate hemicellulosic material one or more times with a first wash comprising greater than 90 wt % co-solvent, optionally followed with a second wash comprising greater than 90 wt % water. The one or more washes may comprise washing the intermediate hemicellulosic material one or more times with a first wash containing more than 90% precipitation agent, followed with a second wash containing more than 90% co-solvent, and further optionally followed with a third wash containing more than 90% water. The process may further comprise separating co-solvent from the wash using distillation and/or evaporation. The process may further comprise separating precipitation agent from the extractant using distillation and/or evaporation. The extracting may be conducted at a pressure at least 3% higher than the pressure of the flashing. The extracting may be conducted at a pressure from 20 to 20,000 kPa and at a temperature from 20° C. to 150° C. The separating may comprise filtering, wherein the filtering may be conducted at a pressure from 20 to 20,000 kPa and at a temperature from 10° C. to 150° C. The flashing may be conducted at a pressure from 1 to 10,000 kPa and at a temperature from 0° C. to 300° C. The extractant may comprise at least 15 wt. % co-solvent. The extractant may comprise from 1 to 85 wt. % ionic liquid and/or amine oxide. In some embodiments, the extractant may comprise from 0.1 to 50 wt. % ionic liquid and from 50 to 99.9 wt. % co-solvent. The mass ratio of extractant to the cellulosic material may be from 5:1 to 500:1. The extracting and/or washing may be conducted one or more times in counter-current and/or co-current equipment in a continuous, semi-batch, or batch process.
In a second embodiment, the present invention is directed to a process for purifying a cellulosic material, comprising: extracting hemicellulose from the cellulosic material with an extractant at a pressure from 20 to 20,000 kPa to form an extraction mixture; filtering the extraction mixture to form an extraction filtrate and an intermediate cellulosic material comprising at least 10% less hemicellulose than the cellulosic material; and concentrating the intermediate cellulosic material to form a concentrated cellulosic material having an increased solids content; wherein the liquid extractant comprises an ionic liquid, a co-solvent comprising acetonitrile, and a secondary co-solvent.
In a third embodiment, the present invention is directed to a process for purifying a cellulosic material, comprising: extracting hemicellulose from the cellulosic material with an extractant to form an extraction mixture; filtering the extraction mixture to form an extraction filtrate and an intermediate cellulosic material comprising at least 10% less hemicellulose than the cellulosic material; and concentrating the intermediate cellulosic material to form a concentrated cellulosic material having an increased solids content; wherein the liquid extractant comprises an amine oxide and a co-solvent comprising acetonitrile.
The present invention will be better understood in view of the appended non-limiting figures, in which:
The present invention relates to processes for purifying a cellulosic material, comprising separating, e.g., extracting, hemicellulose and other cellulosic impurities (e.g., dichloromethane (DCM) extractables and degraded cellulose) from the cellulosic material with an extractant to form an extraction mixture; separating the extraction mixture to form an intermediate cellulosic material and an extraction filtrate; and flashing the extraction filtrate. The process thereby beneficially involves the removal of hemicellulose from a cellulosic material to increase its purity. As used herein, the term “hemicellulose” refers to several heteropolymers, e.g., polysaccharides, separately or collectively, that are present in plant cell walls. Hemicellulose can include, for example, one or more of xylan, glucuronoxylan, arabinoxylan, glucomannan, galactomannan, and xyloglucan.
The extractant used in the separating step comprises a cellulose solvent and one or more cellulose co-solvents. The flashing step forms a vapor stream enriched in the co-solvent and a liquid stream enriched in the cellulose solvent, and preferably is conducted at a pressure lower than the extracting step, such as at most 95%, at most 85% or at most 70% of the pressure of the extracting step. The cellulose solvent may or (more preferably) may not fully dissolve α-cellulose, but preferably dissolves at least hemicellulose and degraded cellulose. The cellulose solvent preferably is selected from the group consisting of an ionic liquid, an amine oxide and combinations thereof, and the cellulose co-solvent preferably is selected from the group consisting of acetonitrile, acetone, methanol, ethanol, isopropanol, methyl acetate, ethyl acetate, vinyl acetate, propionitrile, dichloromethane, chloroform, butyronitrile, chloracetonitrile, water, and combinations thereof. In some embodiments, the cellulose solvent is an ionic liquid. The cellulose co-solvent may be a low-boiling point co-solvent, e.g., a co-solvent with a boiling point less than 120° C. or less than 100° C. In some embodiments, the co-solvent comprises a combination of acetonitrile and water and may be present in a weight ratio of acetonitrile to water from 6:1 to 500:1, e.g., from 10:1 to 200:1 or from 30:1 to 100:1. The intermediate cellulosic material may be further concentrated, e.g., washed and/or dried, to form a finished cellulosic product.
The processes of the invention are particularly suitable for separating and removing impurities, such as hemicellulose and/or degraded cellulose, from a cellulosic material to form a finished cellulosic product, the purity of which may vary widely depending largely on the composition of the starting cellulosic material, the composition of the extractant used, and extraction conditions. In some embodiments, the finished cellulose product comprises higher grade cellulose, e.g. acetate grade cellulose.
During extraction, hemicellulose and preferably degraded cellulose are separated from the extraction mixture to form an extraction filtrate comprising extractant and extracted hemicellulose, and may also comprise extracted degraded cellulose. As a result, the intermediate cellulosic material and the ultimately formed cellulosic product comprise less hemicellulose, and preferably less degraded cellulose, than the starting cellulosic material, e.g., at least 10% less, at least 20% less, at least 30%, or at least 50% less hemicellulose than the starting cellulosic material and at least 5% less, at least 10% less or at least 20% less degraded cellulose than the starting cellulosic material. During extraction, and throughout the cellulose purification and hemicellulose recovery process, the generation of side products or by-products, e.g. mono-, di-, and oligo-saccharide, may be limited. However, if side products and/or by-products are generated, they may be removed from the process according to conventional means. This removal may be preferred if the process is continuous, so as to prevent build-up of side products and/or by-products.
The intermediate cellulosic material formed in the extraction mixture separation step may initially comprise a minor amount of residual extractant, residual hemicellulose and/or residual degraded cellulose, and may be washed with one or more extractant washes to remove one or more of these materials. Depending on the extraction wash, the washing may occur at a temperature from its melting point to its boiling point, conveniently, from 0 to 95° C., e.g., from 30 to 95° C. or from 75 to 95° C. In some embodiments, the extractant wash may be selected from the group consisting of an alcohol, a ketone, a nitrile, an ether, an ester, a carboxylic acid, a halide, a hydrocarbon compound, an amine, a heterocyclic compound, water, and combinations thereof. In other embodiments, the extractant wash may be selected from the group consisting of acetonitrile, acetone, methanol, ethanol, isopropanol, methyl acetate, ethyl acetate, vinyl acetate, propionitrile, dichloromethane, chloroform, butyronitrile, chloroacetonitrile, water, and combinations thereof. In yet other embodiments, the extractant wash may be selected from the group consisting of water, ethylene glycol, glycerin, formamide, N,N-dimethylformamide, N-methylpyrrolidinone, N,N-dimethylacetamide, DMSO, a mixture of water and alcohol, and combinations thereof. The extractant wash may be enriched in co-solvent and may comprise a condensed portion of the vapor stream of the co-solvent from the flashing step. After washing, the intermediate cellulosic material preferably comprises less than 5 wt. % extractant, e.g., less than 1 wt. %, or less than 0.1 wt. % extractant, based on the total weight of the intermediate cellulosic material (including any residual extractant). The washing step may be repeated, as necessary, to remove residual extractant to a desired level.
The processes of the invention also involve the separation and recycle of various process streams, e.g., extractant, extractant wash streams, precipitation agent, and precipitant wash streams, used in the cellulose and hemicellulose purification processes. For example, after the washing step, the resulting filtrate containing extractant wash may be subjected to a separation step, e.g., in one or more flashers and/or distillation columns, to separate extractant wash from the extractant. The recovered extractant may be recycled to the extraction step, and the recovered extractant wash may be recycled to the washing step. As described above, any side products and/or by-products that are generated in the extraction process may be removed out from the system using appropriate separating technology, e.g., membrane/ion exchange or other technologies known to one of ordinary skill in the art.
Various embodiments described herein include the separation and recovery of hemicellulose from a starting cellulosic material. In this process, it is implicit that separation of hemicellulose may include separation of other undesirable components such as degraded cellulose and other extractables, the content of which may need to be reduced to reach desired treated cellulose quality.
The process may also comprise recovering hemicellulose from the extraction filtrate. Hemicellulose recovery may be achieved by flashing the extraction filtrate in a flasher to separate the co-solvent from the cellulose solvent and hemicellulose. The vapor stream exiting the flasher, which may be enriched in co-solvent, may be advantageously recycled to the extractor or be employed as a washing agent, e.g., extractant wash, for the cellulosic product, while the liquid stream comprising cellulose solvent and hemicellulose as well as co-solvent may be directed to a precipitator, to which a precipitation agent is added to form a precipitation slurry. The precipitation slurry may then be filtered and optionally washed with a precipitant wash, e.g., water, to form a precipitation agent filtrate and recovered solid hemicellulose. The precipitation agent filtrate may be separated, e.g., in a distillation column, to form a second recovered extractant, recovered precipitation agent and optionally recovered precipitant wash. The recovered precipitation agent may be recycled to the precipitator, optionally after being combined with additional precipitation agent. The second recovered extractant may be recycled to the extractor, optionally after being combined with additional extractant. The optional recovered precipitant wash may be recycled to the precipitant wash step, optionally after being combined with additional precipitant wash. The recovered solid hemicellulose may then be dried, optionally with either or both heat and/or mechanical means, e.g., squeeze rolls and/or centrifugation, to form a finished hemicellulose product.
The present invention is broadly applicable to the treatment of natural cellulosic materials, including plant and plant-derived materials. As used herein, the term “cellulosic material” refers to any material comprising cellulose, such as a pulp, and which may contain, for example, α-cellulose, hemicellulose and degraded cellulose. In preferred embodiments, the cellulosic material comprises wood pulp, e.g., paper grade wood pulp. When the cellulosic material is paper grade wood pulp, the processes described herein may be advantageously used to produce acetate grade wood pulp from the paper grade wood pulp, although the processes of the invention are not limited to the use of paper grade wood pulp as the starting cellulosic material.
In some embodiments, the cellulosic material may comprise a cellulosic raw material, which may include, without limitation, plant derived biomass, corn stover, sugar cane stalk, bagasse and cane residues, rice and wheat straw, agricultural grasses, hard wood, hardwood pulp, soft wood, softwood pulp, herbs, recycled paper, waste paper, wood chips, pulp and paper wastes, waste wood, thinned wood, cornstalk, chaff, and other forms of wood, bamboo, soyhull, bast fibers, such as kenaf, hemp, jute and flax, agricultural residual products, agricultural wastes, excretions of livestock, microbial, algal cellulose, and all other materials proximately or ultimately derived from plants. Such cellulosic raw materials are preferably processed in pellet, chip, clip, sheet, attritioned fiber, powder form, or other form rendering them suitable for extraction with the extractant.
Generally, cellulosic material may be derived from lignin-containing materials, where lignin has been removed therefrom. In cellulosic materials, hemicellulose is linked to cellulose by hydrogen bonds. Overall, the cellulose material has a linear shape of fiber morphology, which is surrounded by hemicellulose via hydrogen bonds. These bonds between cellulose and hemicellulose may become weakened by treating the cellulosic material with an extractant to selectively dissolve the hemicellulose while maintaining the fiber morphology of the cellulose material, e.g., leaving the fiber morphology unchanged.
In one embodiment of the invention, the cellulosic material is a paper grade pulp provided in forms such as, but not limited to, rolls, sheets, or bales. Preferably, the paper grade pulp comprises at least 70 wt. % α-cellulose, e.g., at least 80 wt. % α-cellulose or at least 85 wt. % α-cellulose. Paper grade pulp typically also comprises at least 5 wt. % hemicellulose, at least 10 wt. % hemicellulose or at least 15 wt. % hemicellulose. In another embodiment, the cellulosic material may be another α-cellulose containing pulp, such as viscose grade pulp, rayon grade pulp, semi-bleached pulp, unbleached pulp, bleached pulp, Kraft pulp, sulfide pulp, absorbent pulp, dissolving pulp, or fluff. While these cellulosic materials comprise various concentrations of α-cellulose, the inventive processes may advantageously treat them, based on optimized process design, to produce higher purity α-cellulose products.
Cellulose is a straight chain polymer and is derived from D-glucose units, which condense through β-1,4-glycosidic bonds. This linkage motif contrasts with that for α-1,4-glycosidic bonds present in starch, glycogen, and other carbohydrates. Unlike starch, there is no coiling or branching in cellulose and cellulose adopts an extended and rather stiff rod-like confirmation, which is aided by the equatorial confirmation of the glucose residues. The multiple hydroxyl groups on the glucose from one chain form hydrogen bonds with oxygen atoms on the same or on a neighboring chain, holding the chains firmly together side-by-side and forming microfibrils with high tensile strength, which then overlay to form the macrostructure of a cellulose fiber. In preferred embodiments of the invention, the finished cellulosic product retains its fiber structure throughout and after the extraction step.
As indicated above, the term “hemicellulose” refers to several heteropolymers, e.g., polysaccharides, separately or collectively, that are present in plant cell walls. Hemicellulose can include, for example, one or more of xylan, glucuronoxylan, arabinoxylan, glucomannan, galactomannan, and xyloglucan. These polysaccharides contain many different sugar monomers and can be hydrolyzed to invert sugars, such as xylose, mannose, galactose, rhamnose and arabinose. Xylose is typically the primary sugar present in hard woods and mannose is the primary sugar present in softwoods.
The processes of the present invention are particularly beneficial in that they are effective for use with paper grade wood pulp that is derived from softwoods and hardwoods. The processes of the present invention provide a technique for upgrading paper grade pulp produced from softwood species, which are generally more abundant, and faster growing, than most hardwood species.
Softwood is a generic term typically used in reference to wood from conifers (i.e., needle-bearing trees from the order Pinales). Softwood-producing trees include pine, spruce, cedar, fir, larch, douglas-fir, hemlock, cypress, redwood and yew. Conversely, the term hardwood is typically used in reference to wood from broad-leaved or angiosperm trees. The terms “softwood” and “hardwood” do not necessarily describe the actual hardness of the wood. While, on average, hardwood is of higher density and hardness than softwood, there is considerable variation in actual wood hardness in both groups, and some softwood trees can actually produce wood that is harder than wood from hardwood trees. One feature separating hardwoods from softwoods is the presence of pores, or vessels, in hardwood trees, which are absent in softwood trees. On a microscopic level, softwood contains two types of cells, longitudinal wood fibers (or tracheids) and transverse ray cells. In softwood, water transport within the tree is via the tracheids rather than the pores of hardwoods.
As described above, hemicellulose and optionally degraded cellulose is extracted from the cellulosic material using an extractant. The extractant comprises a cellulose solvent and one or more co-solvents. The cellulose solvent is selected from the group consisting of an ionic liquid, an amine oxide and mixtures thereof, examples of which are described below. The cellulose solvent may or (more preferably) may not fully dissolve α-cellulose, but preferably dissolves at least hemicellulose and degraded cellulose. α-cellulose preferably is less soluble in the co-solvent than in the cellulose solvent.
a. Ionic Liquid
Ionic liquids are organic salts with low melting points, preferably less than 200° C., less than 150° C., or less than 100° C., many of which are consequently liquid at room temperature. Specific features that make ionic liquids suitable for use in the present invention are their general lack of vapor pressure, their ability to dissolve a wide range of organic compounds and the versatility of their chemical and physical properties. In addition, ionic liquids are non-flammable making them particularly suitable for use in industrial applications. In some embodiments, the cellulose solvent comprises one or more ionic liquids.
It has been found that, in addition to these beneficial properties, when contacted with cellulosic materials, including plant matter and plant matter derivatives, the ionic liquids are capable of acting as a cellulose solvent, dissolving the hemicellulose and cellulose contained therein. In addition, with the appropriate choice of treatment conditions (for example, duration of contact, temperature, and co-solvent composition), ionic liquids penetrate the structure of the cellulose-containing material to break down the material and extract organic species therein. In particular when used in combination with one or more co-solvents, α-cellulosic components remaining in the cellulosic material are preserved and the fiber morphology is advantageously retained.
Ionic liquids, in pure form, generally are comprised of ions and do not necessitate a separate solvent for ion formation. Ionic liquids existing in a liquid phase at room temperature are called room temperature ionic liquids. Generally, ionic liquids are formed of large-sized cations and a smaller-sized anion. Cations of ionic liquids may comprise nitrogen, phosphorous, sulfur, or carbon. Because of the disparity in size between the cation and anion, the lattice energy of the compound is decreased resulting in a less crystalline structure with a low melting point.
Exemplary ionic liquids include the compounds expressed by the following Formula (1):
[A]+[B]− (1)
In one embodiment, the ionic liquid is selected from the group consisting of substituted or unsubstituted imidazolium salts, pyridinium salts, ammonium salts, triazolium salts, pyrazolium salt, pyrrolidinium salt, piperidium salt, and phosphonium salts. In preferred embodiments, [A]+ is selected from the group consisting of:
wherein, R1, R2, R3, R4, R5, R6 and R7 are each independently selected from the group consisting of hydrogen, C1-C15 alkyls, C2-C15 aryls, and C2-C20 alkenes, and the alkyl, aryl or alkene may be substituted by a substituent selected from the group consisting of sulfone, sulfoxide, thioester, ether, amide, hydroxyl and amine. [B]− is preferably selected from the group consisting of Cl−, Br−, 1, OH−, NO3−, SO42−, CF3CO2−, CF3SO3−, BF4−, PF6−, CH3COO−, (CF4SO2)2N−, AlCl4−, HCOO−, CH3SO4−, (CH3)2PO4−, (C2H5)2PO4− and CH3HPO4−.
Examples of ionic liquids include tetrabutylammonium hydroxide 30 hydrate (TBAOH.30H2O), benzyltriethylammonium acetate (BnTEAAc), tetraethylammonium acetate tetrahydrate (TEAAc.4H2O), benzyltrimethylammonium hydroxide (BnTMAOH), ammonium acetate, hydroxyethylammonium acetate, hydroxyethylammonium formate, tetramethylammonium acetate, tetramethylammonium hydroxide (TMAOH), tetraethylammonium acetate, tetrabutylammonium acetate, tetrabutylammonium hydroxide, 1-butyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate, methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate, 1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate, methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride, 1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, and mixtures or complexes thereof, but the disclosed concept of utilizing ionic liquids is not limited to the disclosed species.
In some embodiments, the ionic liquid is selected from the group consisting of ammonium-based ionic substances, imidazolium-based ionic substances, phoshonium-based ionic substances, and mixtures thereof. The ammonium-based ionic liquid may be selected from the group consisting of ammonium acetate, hydroxyethylammonium acetate, hydroxyethylammonium formate, tetramethylammonium acetate, tetrabutylammonium acetate, tetraethylammonium acetate, benzyltriethylammonium acetate, benzyltributyl ammonium acetate and combinations thereof. The imidazolium-based ionic liquid may be selected from the group consisting of 1-butyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate, methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate, 1-ethyl-3-ethyl imidazolium acetate, 1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate, methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride, 1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, 1-ethyl-3-methylimidazolium dimethyl phosphate, 1-ethyl-3-methyl diethyl phosphate (EMIMDEP), 1,3-dimethylimidazolium dimethyl phosphate (DMIMDMP) and mixtures or complexes thereof. The ionic liquid may also be selected from the group consisting of N,N-dimethylpyrrolidinium acetate, N,N-dimethylpiperidinium acetate, N,N-dimethylpyrrolidinium dimethyl phosphate, N,N-dimethylpiperidinium dimethyl phosphate, N,N-dimethylpyrrolidinium chloride, N,N-dimethylpiperidinium chloride, and combinations thereof.
In still other embodiments, the ionic liquid may be selected from the group consisting of 1-butyl-3-methylimidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidazolium tetrachloroaluminate, 1-ethyl-3-methyl imidalzolium hydrogensulfate, 1-butyl-3-methyl imidazolium hydrogensulfate, methylimidazolium chloride, 1-ethyl-3-methyl imidazolium acetate, 1,3-diethylimidazolium acetate (EEIM Ac), 1-butyl-3-methyl imidazolium acetate, tris-2(hydroxyl ethyl)methylammonium methylsulfate, 1-ethyl-3-methyl imidazolium ethylsulfate, 1-ethyl-3-methyl imidazolium methanesulfonate, methyl-tri-n-butylammonium methylsulfate, 1-butyl-3-methyl imidazolium chloride, 1-ethyl-3-methyl imidasolium chloride, 1-ethyl-3-methyl imidazolium thiocyanate, 1-butyl-3-methyl imidazolium thiocyanate, 1-aryl-3-methyl imidazolium chloride, 1-ethyl-3-methylimidazolium dimethyl phosphate, 1-ethyl-3-methyl diethyl phosphate, 1,3-dimethylimidazolium dimethyl phosphate and combinations and complexes thereof.
In further embodiments, the ionic liquid may be selected from the group consisting of ethyltributylphosphonium diethylphosphate, methyltributylphosphonium dimethylphosphate, tetrabutylphosphonium bromide, tetrabutylphosphonium chloride, tributylmethylphosphonium methylsulfate, trihexyltetradecylphosphonium decanoate, trihexyltetradecylphosphonium dicyanamide, ethyltriphenylphosphonium acetate, ethyltributylphosphonium acetate, benzyltriethylphosphonium acetate, benzyltributylphosphonium acetate, tetrabutylphosphonium acetate, tetraethylphosphonium acetate, tetramethylphosphonium acetate, and combinations thereof.
The ionic liquid may be commercially available, and may include Basionic™ AC 01, Basionic™ AC 09, Basionic™ AC 25, Basionic™ AC 28, Basionic™ AC 75, Basionic™ BC 01, Basionic™ BC 02, Basionic™ FS 01, Basionic™ LQ 01, Basionic™ ST 35, Basionic™ ST 62, Basionic™ ST 70, Basionic™ ST 80, Basionic™ VS 01, and Basionic™ VS 02, but the invention is not limited to use of these species.
In some embodiments, the ionic liquid compound, as shown below, may be 1-ethyl-3-methyl imidazolium acetate (EMIM Ac) of the structural formula (2), 1-butyl-3-methyl imidazolium acetate (BMIMAc) of the structural formula (3), 1-ethyl-3-methyl imidazolium dimethylphosphate of structural formula (4), 1-ethyl-3-methyl imidazolium formate of the structural formula (5), tetrabutylammonium acetate (TBAAc) of the structural formula (6), 1-allyl-3-methyl imidazolium chloride of the structural formula (7), or 1-n-butyl-3-methyl imidazolium chloride of the structural formula (8):
b. Amine Oxide
Amine oxides are chemical compounds that contain the functional group R3N+—O−, which represents an N—O bond with three additional hydrogen and/or hydrocarbon side chains. Amine oxides are also known as tertiary amines, N-oxides, amine-N-oxide and tertiary amine N-oxides. In one embodiment, amine oxides that are stable in water may be used.
In some embodiments, the amine oxide may be selected from the group consisting of compounds with chemical structure of acyclic R3N+—O−, compounds with chemical structure of N-heterocyclic compound N-oxide, and combinations thereof. In further embodiments, the amine oxide may be an acyclic amine oxide compound with structure of R1R2R3N+—O−, wherein R1, R2 and R3 are alkyl or aryl chains, the same or different, with chain length from 1 to 18, e.g. trimethylamine N-oxide, triethylamine N-oxide, tripropylamine N-oxide, tributylamine N-oxide, methyldiethylamine N-oxide, dimethylethylamine N-oxide, methyldipropylamine N-oxide, tribenzylamine N-Oxide, benzyldimethylamine N-oxide, benzyldiethylamine N-oxide, dibenzylmethylamine N-oxide. In some embodiments, the amine oxide may be a cyclic amine oxide compound including the structures such as pyridine, pyrrole, piperidine, pyrrolidine and other N-heterocyclic compounds, e.g. N-methylmorpholine N-oxide (NMMO), pyridine N-oxide, 2-, 3-, or 4-picoline N-oxide, N-methylpiperidine N-oxide, N-ethylpiperidine N-oxide N-propylpiperidine N-oxide, N-isopropylpiperidine N-oxide. N-butylpiperidine N-oxide, N-hexylpiperidine N-oxide. N-methylpyrrolidine N-oxide, N-ethylpyrrolidine N-oxide N-propylpyrrolidine N-oxide, N-isopropylpyrrolidine N-oxide. N-butylpyrrolidine N-oxide, N-hexylpyrrolidine N-oxide. In some embodiments, the amine oxide may be the combination of the above mentioned acyclic and/or cyclic amine oxides.
In specific embodiments, the amine oxide may be selected from the group consisting of trimethylamine N-oxide, triethylamine N-oxide, tripropylamine N-oxide, tributylamine N-oxide, methyldiethylamine N-oxide, dimethylethylamine N-oxide, methyldipropylamine N-oxide, tribenzylamine N-Oxide, benzyldimethylamine N-oxide, benzyldiethylamine N-oxide, dibenzylmethylamine N-oxide, N-methylmorpholine N-oxide (NMMO), pyridine N-oxide, 2-, 3-, or 4-picoline N-oxide, N-methylpiperidine N-oxide, N-ethylpiperidine N-oxide N-propylpiperidine N-oxide, N-isopropylpiperidine N-oxide. N-butylpiperidine N-oxide, N-hexylpiperidine N-oxide. N-methylpyrrolidine N-oxide, N-ethylpyrrolidine N-oxide N-propylpyrrolidine N-oxide, N-isopropylpyrrolidine N-oxide. N-butylpyrrolidine N-oxide, N-hexylpyrrolidine N-oxide, and combinations thereof.
Cellulose is insoluble in most solvents because of its strong and highly structured intermolecular hydrogen bonding network. Without being bound by theory, NMMO is able to break the hydrogen bonding network that keeps cellulose insoluble in most solvents. Therefore, the use of NMMO alone would destroy the fiber morphology of cellulose. It has now been discovered that by using the proper ratio of an amine oxide, such as NMMO, with a co-solvent, α-cellulosic components in the cellulosic material may be beneficially preserved and the fiber morphology retained. NMMO is typically stored in 50 to 70 vol. %, e.g., 60 vol. %, aqueous solution as pure NMMO tends toward oxygen separation. See, e.g., U.S. Pat. No. 4,748,241, the entirety of which is incorporated herein by reference. Further contaminants in commercial NMMO product, e.g., N-methylmorpholine, peroxides, and acid components, tend to degrade the storage stability. In other words, further application of NMMO needs to address all stability concerns. For example, developed stabilizers like propyl gallate may be added.
c. Co-Solvent
As stated above, the extractant also comprises a co-solvent. Co-solvents in the context of this invention include solvents that do not have the ability to readily dissolve α-cellulose. The co-solvent may be selected to be miscible with the cellulose solvent. In exemplary embodiments, the co-solvent is selected from the group consisting of alcohols, esters, ketones, carboxylic acids, nitriles, amines, halides, hydrocarbon compounds, heterocyclic compounds, and combinations thereof. In other exemplary embodiments, the co-solvent is selected from the group consisting of methanol, ethanol, iso-propanol, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, vinyl acetate, tetrahydrofuran, acetone, acetic acid, formic acid, acetonitrile, propionitrile, butyronitrile, chloroacetonitrile, dichloromethane, chloroform, triethylamine, N,N-dimethylformamide, toluene, pyridine, water, and combinations thereof. In some embodiments, the extractant comprise greater than 15 wt. % co-solvent, e.g., greater than 25 wt. % or greater than 40 wt. %. In one embodiment, the co-solvent may comprise a combination of acetonitrile and water. The acetonitrile and water may be present in a weight ratio from 6:1 to 500:1, e.g., from 10:1 to 200:1 or from 30:1 to 100:1.
In some embodiments, the co-solvent has a boiling point of less than 120° C., or of less than 100° C. Additional co-solvents having a boiling point of less than 120° C. include acetic acid, alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, halogenated solvents, e.g. carbon tetrachloride, dichloroethane or chlorobenzene, ethers, e.g. tetrahydrofuran, diethyl ether, methyl tert-butyl ether, esters, e.g. dimethyl carbonate, and mixtures thereof.
Since the boiling points of the above listed co-solvents vary, the efficient purification processes associated with each co-solvent may not be exactly the same. The co-solvent may be chosen in view of its boiling point, to allow for maximized separation of the cellulose solvent from the co-solvent in the flashing step. For example, in order to maximize flash separation efficiency, the decrease of pressure in flashing step may vaporize at least 3% of the co-solvent, e.g., at least 10%, or at least 30% of the co-solvent. Additionally, the extractant wash and precipitant wash agents used in the cellulose and hemicellulose purification processes may be chosen based on the boiling point of the co-solvent chosen. For example, the difference in boiling point between the extractant wash agent or precipitant wash agent solvent and the co-solvent may be greater than 10° C., greater than 20° C. or greater than 30° C.
In one embodiment, a second co-solvent may be used in conjunction with the first co-solvent and the cellulose solvent, e.g., amine oxide or ionic liquid, as described above. In one embodiment, the second co-solvent decreases the viscosity of the extractant. The second co-solvent may have a viscosity, for example, of less than 10 mPa·s, e.g., less than 5 mPa·s or less than 3 mPa·s at 25° C., or in terms of ranges from 0.1 to 10 mPa·s, from 0.15 to 5 mPa·s, or from 0.2 to 3 mPa·s. In some embodiments, the second co-solvent is selected from the group consisting of formamide, DMF, dimethylacetamide, N-methylpyrrolidone, propylene carbonate, acetonitrile and mixtures thereof. Without being bound by theory, it is postulated that by using a low viscosity second co-solvent in the extractant, the extraction rate is enhanced and a smaller amount of ionic liquid is needed to extract the hemicellulose in the cellulosic material.
Without being bound by theory, the insolubility of the α-cellulose in the co-solvent and the resulting extractant maintains the cellulose fiber morphology, e.g., leaving the fiber morphology unchanged, while the extractant penetrates the cellulosic material, dissolves and extracts the hemicellulose and preferably degraded cellulose from the cellulosic material. Depending on the specific co-solvent used in the extractant, the weight percentage of the cellulose solvent and the co-solvent in the extractant may vary widely.
d. Extractant Compositions
The specific formulation of the extractant employed may vary widely, depending, for example, on the hemicellulose and degraded cellulose content of the starting cellulosic material, and the processing scheme employed. In one embodiment, the extractant optionally comprises at least 0.1 wt. % amine oxide, e.g., at least 2 wt. % or at least 4 wt. %. In terms of upper limits, the extractant optionally comprises at most 85 wt. % amine oxide, e.g., at most 75 wt. %, or at most 70 wt. % amine oxide. In terms of ranges, the extractant optionally comprises from 0.1 wt. % to 85 wt. % amine oxide, e.g., from 2 wt. % to 75 wt. %, or from 4 wt. % to 70 wt. %. The extractant optionally comprises at least 0.1 wt. % co-solvent, e.g., at least 1 wt. %, or at least 3 wt. % co-solvent. In terms of upper limits, the extractant optionally comprises at most 99.9 wt. %, at most 98 wt. %, or at most 97 wt. % co-solvent. In terms of ranges, the extractant optionally comprises from 0.1 wt. % to 99.9 wt. % co-solvent, e.g., from 1 wt. % to 98 wt. %, or from 3 wt. % to 97 wt. % co-solvent.
In one embodiment, the extractant comprises an aqueous co-solvent, e.g., water, and an amine oxide. For example, the extractant optionally comprises at least 40 wt. % amine oxide, e.g., at least 50 wt. % or at least 60 wt. %. In terms of upper limits, the extractant optionally comprises at most 90 wt. % amine oxide, e.g., at most 85 wt. %, or at most 80 wt. % amine oxide. In terms of ranges, the extractant optionally comprises from 40 wt. % to 90 wt. % amine oxide, e.g., from 50 wt. % to 85 wt. %, or from 60 wt. % to 80 wt. % amine oxide. The extractant optionally comprises at least 1 wt. % aqueous co-solvent, e.g., at least 5 wt. %, or at least 10 wt. % aqueous co-solvent. In terms of upper limits, the extractant optionally comprises at most 50 wt. % aqueous co-solvent, at most 40 wt. %, or at most 30 wt. %. In terms of ranges, the extractant optionally comprises from 1 wt. % to 50 wt. % aqueous co-solvent, e.g., from 5 wt. % to 40 wt. %, or from 10 wt. % to 30 wt. %.
In one embodiment, the extractant comprises an organic co-solvent and an amine oxide. In this aspect, the extractant optionally comprises at least 0.1 wt. % amine oxide, e.g., at least 1 wt. % or at least 2 wt. % amine oxide. In terms of upper limits, the extractant optionally comprises at most 85 wt. % amine oxide, e.g., at most 80 wt. %, or at most 70 wt. %. In terms of ranges, the extractant optionally comprises from 0.1 wt. % to 85 wt. % amine oxide, e.g., from 1 wt. % to 80 wt. %, or from 2 wt. % to 70 wt. %. In this aspect, the extractant optionally comprises at least 15 wt. % organic co-solvent, e.g., at least 20 wt. %, or at least 30 wt. %. In terms of upper limits, the extractant optionally comprises at most 99.9 wt. % organic co-solvent, at most 98 wt. %, or at most 97 wt. %. In terms of ranges, the extractant optionally comprises from 15 wt. % to 99.9 wt. % organic co-solvent, e.g., from 20 wt. % to 98 wt. %, or from 30 wt. % to 97 wt. %. In one embodiment, the organic co-solvent is acetonitrile.
In one embodiment, the extractant includes an amine oxide, a first co-solvent and a second co-solvent. In one embodiment, the extractant includes an amine oxide, an aqueous co-solvent, e.g., water, and an organic co-solvent, e.g., acetonitrile. In this aspect, the amine oxide concentration may range, for example, from 1 wt. % to 85 wt. %, the water concentration may range from 1 wt. % to 35 wt. %, and the organic co-solvent, e.g., acetonitrile, concentration may range from 1 wt. % to 98 wt. %.
In other embodiments, the cellulose solvent used in the extractant comprises one or more ionic liquids. For example, the extractant optionally comprises at least 0.1 wt. % ionic liquid, e.g., at least 1 wt. % or at least 2 wt. %. In terms of upper limits, the extractant optionally comprises at most 95 wt. % ionic liquid, e.g., at most 90 wt. %, or at most 85 wt. %. In terms of ranges, the extractant optionally comprises from 0.1 wt. % to 95 wt. % ionic liquid, e.g., from 1 wt. % to 90 wt. %, or from 2 wt. % to 85 wt. %. The extractant optionally comprises at least 5 wt. % co-solvent, e.g., at least 10 wt. %, at least 15 wt. %, at least 20 wt. % or at least 50 wt. %. In terms of upper limits, the extractant optionally comprises at most 99.9 wt. % co-solvent, at most 99 wt. %, or at most 98 wt. %. In terms of ranges, the extractant optionally comprises from 5 wt. % to 99.9 wt. % co-solvent, e.g., from 10 wt. % to 99 wt. %, or from 20 wt. % to 98 wt. %.
In one embodiment, the cellulose solvent comprises one or more ionic liquids and the co-solvent comprises an aqueous co-solvent, e.g., water. In this aspect, the extractant preferably comprises at least 50 wt. % ionic liquid, e.g., at least 65 wt. % or at least 80 wt. %. In terms of upper limits, the extractant optionally comprises at most 95 wt. % ionic liquid, e.g., at most 90 wt. %, or at most 85 wt. %. In terms of ranges, the extractant optionally comprises from 50 wt. % to 95 wt. % ionic liquid, e.g., from 65 wt. % to 90 wt. %, or from 70 wt. % to 85 wt. %. The extractant optionally comprises at least 5 wt. % aqueous co-solvent, e.g., at least 10 wt. %, at least 15 wt. %, at least 20 wt. % or at least 50 wt. %. In terms of upper limits, the extractant optionally comprises at most 50 wt. % aqueous co-solvent, e.g., at most 35 wt. %, or at most 20 wt. % aqueous co-solvent. In terms of ranges, the extractant may comprise from 5 wt. % to 50 wt. % aqueous co-solvent, e.g., from 10 wt. % to 35 wt. %, or from 15 wt. % to 20 wt. %.
In one embodiment, when the extractant comprises one or more ionic liquids as cellulose solvent and an organic co-solvent, the extractant preferably comprises at least 0.1 wt. % ionic liquid, e.g., at least 1 wt. % or at least 2 wt. %. In terms of upper limits, the extractant optionally comprises at most 50 wt. % ionic liquid, e.g., at most 40 wt. %, or at most 30 wt. %. In terms of ranges, the extractant may comprise from 0.1 wt. % to 50 wt. % ionic liquid, e.g., from 1 wt. % to 40 wt. %, from 2 wt. % to 30 wt. % or from 10 to 30 wt. %. The extractant optionally comprises at least 50 wt. % organic co-solvent, e.g., at least 60 wt. %, or at least 70 wt. %. In terms of upper limits, the extractant may comprise at most 99.9 wt. % organic co-solvent, e.g., at most 98 wt. %, or at most 97 wt. %. In terms of ranges, the extractant optionally comprises from 50 wt. % to 99.9 wt. % organic co-solvent, e.g., from 60 wt. % to 98 wt. %, or from 70 wt. % to 97 wt. %. In one embodiment, the organic co-solvent is acetonitrile.
In one embodiment, the extractant includes a cellulose solvent, e.g., amine oxide or ionic liquid, a first co-solvent and a second co-solvent. In this aspect, the weight ratio of first co-solvent to second co-solvent is preferably from 10:1 to 500:1, e.g. from 10:1 to 100:1 or from 10:1 to 50:1. Since current production costs of ionic liquids are generally higher than those of co-solvents, the use of a large amount of the second co-solvent beneficially reduces the cost of purifying the cellulosic material.
In one embodiment, the extractant includes an ionic liquid, a first co-solvent and a second co-solvent. In one embodiment, the extractant includes an ionic liquid, an aqueous co-solvent, e.g., water, and an organic co-solvent, e.g., acetonitrile. In the tertiary extractant system, the extractant may include at most 85 wt. % ionic liquid, e.g., at most 75 wt. %, or at most 50 wt. %. In terms of lower limit, the extractant may include at least 0.1 wt. % ionic liquid, e.g., at least 5 wt. % or at least 10 wt. %. In terms of ranges, the extractant may include from 0.1 wt. % to 85 wt. % ionic liquid, e.g., from 5 wt. % to 75 wt. %, from 10 wt. % to 50 wt. % or from 20 to 30 wt. %. In some embodiments, the extractant may include at most 20 wt. % the first co-solvent, i.e., at most 16 wt. %, or 10 wt. %. In terms of ranges the extractant may include from 0.1 wt. % to 20 wt. % the first co-solvent, e.g., from 0.5 wt. % to 16 wt. % or from 1 wt. % to 10 wt. %. In one embodiment, water is the first co-solvent. In one embodiment, acetonitrile is the second co-solvent. Without being bound by theory, it is postulated that the decrease in viscosity in the extractant by using the second co-solvent beneficially enhances the extraction rate and increases the amount of hemicellulose extracted from the cellulosic material when operated at the same extraction conditions.
In one embodiment, the extractant comprises an aqueous co-solvent, an ionic liquid and an amine oxide. In this aspect, the co-solvent concentration may range, for example, from 5 wt. % to 50 wt. %, the ionic liquid concentration may range from 0.1 wt. % to 50 wt. %, and the amine oxide concentration may range from 0.1 wt. % to 80 wt. %.
In one embodiment, the extractant comprises an organic co-solvent, an ionic liquid and an amine oxide. In one aspect, the co-solvent concentration may be up to 50 wt. %, the amine oxide concentration may be up to 90 wt. %, and the ionic liquid concentration may be up to 50 wt. %. In another aspect, the co-solvent concentration may, for example, range from 5 wt. % to 99 wt. %, the ionic liquid concentration may range from 0.1 wt. % to 50 wt. %, and the amine oxide concentration may range from 0.1 wt. % to 80 wt. %. In one aspect, the co-solvent may be water, the ionic liquid may be EMIM Ac, and the amine oxide may be NMMO.
As described herein, cellulosic material may be purified through an inventive extraction process that removes hemicellulose and preferably degraded cellulose.
Extractant 104 for extracting cellulosic material 103 may be any extractant capable of dissolving preferably at least 50% of the hemicellulose, more preferably at least 75% or at least 90% of the hemicellulose, in cellulosic material 103, as determined by UV absorbance analysis of the concentration of hemicellulose, e.g. xylan, and mass measurements of the feed, cellulosic product, and hemicellulose product. Extractant 104 comprises a cellulose solvent and co-solvent in relative amounts that do not overly degrade the cellulose. For example, in one embodiment, the extractant dissolves less than 15% of the α-cellulose in cellulosic material 103, e.g., less than 10%, or less than 5%, as determined similarly by UV absorbance analysis and mass measurements.
As described above, amine oxides and ionic liquids may tend to dissolve α-cellulose. The extractant preferably comprises sufficient co-solvent to reduce α-cellulose solubility in the overall extractant to a point that the α-cellulose does not readily dissolve therein. Preferably, the α-cellulose is substantially insoluble in the co-solvent. Extractant 104, in accordance with the present invention, therefore has the property of selectively dissolving the hemicellulose and preferably degraded cellulose that is in cellulosic material 103.
Exemplary compositions for the cellulosic material and extractant fed to the extractor, and for the resulting extraction mixture are provided in Table 1.
The treatment of cellulosic material 103 with extractant 104 may be conducted at an elevated temperature, and preferably occurs at atmospheric pressure or slightly above atmospheric pressure. Preferably, the contacting is conducted at a temperature from 20° C. to 150° C., e.g., from 40° C. to 140° C., or from 80° C. to 130° C. In terms of upper limits, the treatment of cellulosic material 103 may be conducted at a temperature of less than 150° C., e.g., less than 140° C., or less than 130° C. In terms of lower limit, the treatment of cellulosic material 103 may be conducted at a temperature of greater than 20° C., e.g., greater than 40° C., or greater than 80° C. The pressure (absolute, unless otherwise indicated) is in the range from 20 kPa to 20,000 kPa, preferably from 40 kPa to 10,000 kPa, more preferably from 100 kPa to 5000 kPa. In some embodiments, the pressure may be optimized, e.g., reduced below 20 kPa, in order to maintain a liquid phase for the extraction process.
Cellulosic material 103 may contact extractant 104 (or have a residence time in extractor 105 for continuous processes) between 5 minutes to 1000 minutes, e.g., between 20 minutes to 500 minutes, or from 40 minutes to 200 minutes. In terms of lower limits, the treatment of cellulosic material 103 may be for at least 5 minutes, e.g., at least 20 minutes or at least 40 minutes. In terms of upper limits, the treatment of cellulosic material 103 may be for at most 1000 minutes, e.g., at most 500 minutes, or at most 200 minutes.
The extraction process may be conducted in a batch, a semi-batch or a continuous process with material flowing either co-current or counter-current in relation to one another. In a continuous process, cellulosic material 103 contacts extractant 104 in one or more extraction vessels. In one embodiment, extractant 104 may be heated to the desired temperature before contacting cellulosic material 103. In one embodiment, the extraction vessel(s) may be heated by any suitable means to the desired temperature. Additionally, an inert gas (not shown), e.g., nitrogen or CO2, may be supplied to the extractor to improve turbulence in the extractor and thus improving heat and mass transfers. The flow rate of inert gas will be controlled not to cause hydrodynamic problem, e.g. flooding. When the size and concentration of solid materials along with the flow rate of inert gas are well controlled, the addition of an inert gas may cause the solids in extractor 105 to float on the surface of the extraction mixture allowing for the solids to be skimmed off the surface of the liquid phase contained in extractor 105.
In the extraction step, the mass ratio of extractant to cellulosic material may range from 5:1 to 500:1, e.g., from 7:1 to 300:1, or from 10:1 to 100:1. The solid:liquid volume ratio may range from 0.005:1 to 0.17:1, e.g., from 0.01:1 to 0.15:1 or from 0.02:1 to 0.1:1, depending on the extraction apparatus and set-up. In one embodiment, a solid:liquid ratio of from 0.01:1 to 0.02:1 or about 0.0125:1 may be used to facilitate the filtration operation in a batch process. In another embodiment, a solid:liquid ratio of 0.1:1 to 0.17:1 can be used, in particular for extractors employing countercurrent extraction. The amount of extractant employed has a significant impact on process economics. Counter-current extraction may achieve greater extraction efficiency while maintaining reasonable extractant usage. Counter-current extraction of solubles from pulp can be accomplished in a variety of commercial equipment such as, but not limited to, a series of agitated tanks, hydrapulpers, continuous belt extractors, and screw extractors. Twin-screw extractors are generally more efficient than single-screw extractors. After extraction, the separation of solid and liquid phases can be completed in suitable commercial equipment, which includes filters, centrifuges, and the like.
In one embodiment, the cellulosic material is subjected to repeated extraction steps. For example, the cellulosic material may be treated with the extractant in an initial extraction step followed by one or more additional extraction steps, in the same or multiple extractors, to further extract residual hemicellulose and/or degraded cellulose. In one embodiment, the cellulosic product may be subjected to an initial extraction step, followed by an extraction wash step (discussed below), followed by a second extraction step. In some embodiments, the cellulosic product may be subjected to a third or fourth extraction step. When multiple extraction steps are employed, the extractant in each extraction step may be the same or varied to account for the different concentrations of hemicellulose and degraded cellulose in intermediate cellulosic materials between extraction steps. For example, a first extraction may use an extractant comprising an ionic liquid and a co-solvent and a second extraction may use an extractant comprising another ionic liquid and another co-solvent at different concentrations from the first extractant, or vice versa, optionally with one or more extractant wash steps and/or de-liquoring steps between and/or after the second extraction step. Similar configurations can be designed and optimized based upon the general chemical engineering principles and process design theory.
In another embodiment (not shown), the process may further include enzymatic digestion of hemicellulose, extraction and/or isolation of digested hemicellulose and recovery of a cellulosic product with reduced hemicellulose content. Without being bound by theory, by treating the cellulosic material first with the extractant, enzymes may be better able to penetrate the cellulosic material to hydrolyze residual hemicellulose and/or degraded cellulose contained therein. On the contrary, experimental data has shown that less hemicellulose may be removed from the cellulosic material if it is first treated with an enzyme cocktail under optimum enzyme hydrolysis conditions, followed by an extraction step. For enzymes to be effective in hydrolyzing hemicellulose, a pretreatment step (e.g., prehydrolysis) is preferred in order to make the cellulosic materials amenable to enzymatic hydrolysis. The pretreatment step preferably comprises treating the cellulosic material with high pressure steam, optionally at low or high acid concentrations, or ammonia treatment. Some modification to the process flow scheme may be desired since the enzyme treatment would likely necessitate increased residence time to complete enzymatic hydrolysis. In addition, acidity (pH), temperature and ionic strength would likely need to be adjusted for effective enzymatic treatment.
In this embodiment, after the extraction step, the cellulosic material may be treated with an enzyme, preferably a hemicellulase, to break down residual hemicellulose contained in the cellulosic material. The hemicellulase includes one or more enzymes that hydrolyze hemicellulose to form simpler sugars, ultimately yielding monosaccharides, such as glucose, hexoses and pentoses. Suitable hemicellulase include one or more of xyloglucanase, β-xylosidase, endoxylanase, α-L-arabinofuranosidase, α-glucuronidase, mannanase, and acetyl xylan esterase. Preferably, the enzymes include a combination of both endo-enzymes (i.e., enzymes hydrolyzing internal polysaccharide bonds to form smaller poly- and oligosaccharides) and exo-enzymes (i.e., enzymes hydrolyzing terminal and/or near-terminal polysaccharide bonds) to facilitate the rapid hydrolysis of large polysaccharide molecules. Suitable commercial hemicellulase include SHEARZYME (available from Novozymes A/S, Bagsvaerd, Denmark), PULPZYME (available from Novozymes A/S, Bagsvaerd, Denmark), FRIMASE B210 (available from Puratos, Groot-Bijgaarden, Belgium), FRIMASE B218 (available from Puratos, Groot-Bijgaarden, Belgium), GRINDAMYL (available from Danisco, Copenhagen, Denmark), ECOPULP TX200A (available from AB Enzymes, Darmstadt, Germany), MULTIFECT Xylanase (available from Genencor/Danisco, Palo Alto, USA), PENTOPAN Mono BG (available from Novozymes, Bagsvaerd, Denmark), and PENTOPAN 500 BG (available from Novozymes, Bagsvaerd, Denmark).
The enzymes generally can be used in amounts that are not particularly limited. For example, hemicellulase can be used in amounts ranging from about 0.001 mg/g to about 500 mg/g (e.g., about 0.05 mg/g to about 200 mg/g, about 0.1 mg/g to about 100 mg/g, about 0.2 mg/g to about 50 mg/g, or about 0.3 mg/g to about 40 mg/g). The concentration units are milligrams of enzyme per gram of cellulosic material to be treated.
After the desired contacting time, an extraction mixture is removed from extractor 105 via line 106. The extraction mixture 106 comprises extractant, dissolved hemicellulose, dissolved degraded cellulose, side products, e.g. mono-, di-, and oligo-saccharide, and an intermediate cellulosic material having reduced hemicellulose content and preferably reduced degraded cellulose content. As shown, extraction mixture 106 is fed to filter 110 to remove extractant, dissolved hemicellulose, and dissolved degraded cellulose as well as dissolved side products. Removal of the extractant in the filtering step reduces the amount of residual hemicellulose that must be further processed with the intermediate cellulosic material. It also reduces the amount of extractant that must be separated from the intermediate cellulose in subsequent steps. Filter 110 may comprise solid-liquid separation equipment, including but not limited to, for example, rotary vacuum drums, belt filters, centrifuge, and screw presses. Filter 110 may be operated at a pressure from 20 kPa to 20,000 kPa, from 40 kPa to 10,000 kPa, or from 100 kPa to 5,000 kPa and a temperature from 10° C. to 150° C., from 15° C. to 140° C., or from 20° C. to 130° C. In some embodiments, the pressure on the filtrate side may be reduced to below 100 kPa, e.g. from 1 to 99 kPa for enhanced filtering process rate. Filter 110 forms an intermediate cellulosic material 112 and an extraction filtrate 111.
After exiting filter 110 and optional de-liquoring steps, intermediate cellulosic material 112 may be directed to washer 115 where it is washed with extractant wash 118 to further reduce the amount of extractant remaining in the intermediate cellulosic product. The washing may be conducted in a batch, a semi-batch or a continuous process with material flowing either co-current or counter-current in relation to one another. In some embodiments, only one washing step is used. In other embodiments, as shown, the intermediate cellulosic material may be washed more than once in separate washers 115 and 120. When more than one washing step is used, the composition of the extractant wash may vary in the different washing steps. For example, a first washing step may use co-solvent, e.g. acetonitrile as extractant wash 118 to remove residual cellulose solvent and residual hemicellulose and a second washing step may use water as extractant wash 124 to remove residual acetonitrile. A similar configuration can be designed and optimized based upon the general chemical engineering principles and process design theory and it is understood that multiple washing steps, optionally with de-liquoring and/or drying steps in between, may be used. The washing step may be conducted at a higher temperature in order to enhance mass transfer and to increase the solubility. The temperature may be from 10° C. to 100° C., e.g., from 15° C. to 90° C., or from 20° C. to 80° C.
Extractant wash 118 preferably comprises a co-solvent, which dissolves residual cellulose solvent and residual hemicellulose and/or degraded cellulose from the cellulosic material, but may preferably be substantially free of cellulose solvent. Extractant wash 124 preferably comprise a co-solvent, which can be used to wash away the residual of the first co-solvent in the cellulose material and can be further separated conventionally from the cellulose material. In one embodiment, the extractant wash is selected from the group consisting of acetonitrile, acetone, methanol, ethanol, iso-propanol, methyl acetate, ethyl acetate, vinyl acetate, propionitrile, dichloromethane, chloroform, butyronitrile, chloroacetonitrile, water, and combinations thereof. In another embodiment, the extractant wash is a combination of acetonitrile and an alcohol, e.g. ethanol or methanol. In other embodiments, the extract wash is selected from the group consisting of water, ethylene glycol, glycerin, formamide, N,N-dimethylformamide, N-methylpyrrolidinone, N,N-dimethylacetamide, DMSO, a mixture of water and alcohol, and combinations thereof. In some embodiments, first extractant wash 118 may comprise greater than 85 wt. % acetonitrile, e.g., greater than 90 wt. % or greater than 95 wt. %; and second extractant wash 124 may comprise greater than 90 wt. % washing solvent, preferably water, e.g., greater than 95 wt. % water, greater than 99 wt. % water or greater than 99.5 wt. % water. It should be understood that, depending on the amount of residual hemicellulose contained in the cellulosic material, the amount of extractant wash may be minimized to reduce capital cost and energy requirements for subsequent separation and recycle, described below.
The extractant wash may further comprise one or more washing aids that improve the removal of extractant from the cellulosic material, improve operability, or otherwise improve the physical properties of the intermediate cellulose material. The washing aids may include, for example, defoamers, surfactants, and mixtures thereof. The amount of washing agent can vary widely based upon the amount of residual extractant, quality requirement for cellulosic product, and process operability.
The first extractant wash may then be removed via line 117 and the second extractant wash may be removed via line 121, e.g., as used extractant wash filtrates. In some embodiments, used extractant wash filtrate 117 may be returned to extractor 105, either directly to extractor 105 or combined with solvent 104. Used extractant wash filtrate 121 may be used in hemicellulose recovery zone 102. The intermediate cellulosic material exits filter 110 and washer 115 and washer 120 via line 122. Washed intermediate cellulosic material 122 has reduced hemicellulose content and preferably reduced degraded cellulose content. Washed intermediate cellulosic material 122 may comprise less than 6 wt. % extractant, e.g., less than 5 wt. % or less than 4 wt. % extractant. In some embodiments, washed intermediate cellulosic material 122 may comprise less than 0.5 wt. % cellulose solvent (ionic liquid and/or amine oxide), e.g., less than 0.05 wt. %, less than 0.005 wt. %, or less than 0.001 wt %. Washed intermediate cellulosic material 122 may comprise from 9.9 to 99% solids, e.g., from 19 to 90% or from 28 to 85%.
As shown in
Exemplary compositions using acetonitrile as the co-solvent, acetonitrile as the first extractant wash and water as the second extractant wash for the intermediate cellulosic material are provided in Table 2. When acetonitrile is used as the co-solvent and first extractant wash 118, and water is used as second extractant wash 124, at least 90% or at least 95% of the cellulose in cellulosic material 103 is maintained in washed intermediate cellulosic material 122, as described herein. If no further processing is required, washed intermediate cellulosic material 122 may be referred to as finished cellulosic material.
As shown in
As shown in
In some embodiments (not shown), washed intermediate cellulosic material 122 or 116 may then be further de-liquored, e.g., mechanically concentrated in a concentrator to form a concentrated cellulosic material having an increased solids content, e.g., from 10 to 99 wt %, from 20 to 90 wt % or from 30 to 85 wt %. In some embodiments, the solids content is at least 90 wt. %. The concentrator may include squeeze rolls, rotating rolls, and/or ringer rolls as well as optional heat exchangers to vaporize the liquids. Additional water removal methods may be used to concentrate the cellulosic material, depending on the desired solids content and available energy supply. The concentrated cellulosic material may comprise from 2 to 99 wt. % cellulose (e.g., from 3 to 95 wt. % cellulose), from 1 to 60 wt. % water (e.g., from 1 to 50 wt. % water), and from 0.01 to 20 wt. % hemicellulose (e.g., from 0.5 to 10 wt. % hemicellulose). The concentrated cellulosic material may then be further dried in a dryer (not shown). The dryer may function to remove residual extractant wash. Exemplary dryers include disintegrator dryers, flash dryers, apron dryers, rotary dryers, heated rolls, infrared dryers, ovens and vacuums. Without being bound by theory, the disintegrator dryer may be used to further open the cellulosic material, which may be advantageous for subsequent processing, e.g., in the formation of cellulose acetate, and derivatives thereof. In another embodiment, a dryer may be designed to comprise heated rolls which may be used to form baled sheets or product rolls of cellulosic material.
In some embodiments, as described herein, when the process comprises more than one washing step, a concentrator may be utilized between washing steps or after all washing steps in order to improve washing efficiency for the cellulose solvent and co-solvent, as well as to maximize separation of any remaining hemicellulose, thereby reducing total washing agent quantity required and associated energy and disposal costs.
Depending on the purity of the starting cellulosic material, in accordance to preferred embodiments of the present invention, high purity α-cellulose product may be produced. In preferred embodiments, the finished cellulose product comprises high purity α-cellulose products such as high purity dissolving grade pulps with less than 5 wt. % hemicellulose, e.g., less than 2 wt. % hemicellulose or less than 1 wt. % hemicellulose. In one embodiment, the cellulosic product has a UV absorbance of less than 2.0 at 277 nm, e.g., less than 1.6 at 277 nm, or less than 1.2 at 277 nm. Paper grade pulp typically has an UV absorbance of greater than 4.7 at 277 nm, as determined by standard UV absorbance measurements. Conveniently and accurately, purity of the α-cellulose product may be indicated by a lower absorbance at a certain wavelength.
In addition to retaining the fiber morphology of the cellulosic product, the high purity α-cellulose grade pulp product also may advantageously retain other beneficial characteristics such as intrinsic viscosity and brightness. The high purity α-cellulose grade pulp product may be further processed to make cellulose derivatives, such as cellulose ether, cellulose esters, cellulose nitrate, other derivatives of cellulose, or regenerated cellulose fiber, such as viscose, lyocell, rayon, etc. Preferably, the high purity α-cellulose grade pulp may be used to make cellulose acetate.
In a preferred embodiment, extractant filtrate 111 is sent to a flasher 130 to form a vapor stream enriched in co-solvent 132 and a liquid stream enriched in cellulose solvent 131. Without being bound by theory, it is believed that the flashing step form the vapor stream enriched in co-solvent 132 and the liquid stream enriched in cellulose solvent 131 due to the low to negligible vapor pressure of cellulose solvent and the significant higher vapor pressure of co-solvent. Vapor stream 132 may be condensed in condenser 133. At least a portion of the condensed vapor stream may be employed as the first extractant wash 118 via line 138 and at least a portion of the condensed vapor stream may be employed as the hemicellulose precipitant wash 158, discussed herein, via line 134. Either a pressure drop from filter 110 to flasher 130 or additional energy supply can drive the separation of the cellulose solvent from the co-solvent in the flasher. Flasher 130 may be operated at a pressure from 1 to 10,000 kPa, e.g., from 10 to 5,000 kPa, or from 100 to 1,000 kPa and at a temperature from 0° C. to 300° C., e.g., from 20° C. to 200° C., or from 80° C. to 160° C. In some embodiments, the extracting step is conducted at a higher pressure than the flashing step, e.g., a pressure at least 3% higher, e.g., at least 10% higher, at least 20% higher, or at least 30% higher. In other embodiments, the flashing step is conducted at a pressure lower than the extracting step, e.g., a pressure at most 97% of the pressure of the extracting step, e.g., at most 90% or at most 80%. Exemplary compositions for liquid stream 131 and vapor stream 132 are provided in Table 3.
In embodiments where only very small amount of water exists in the liquid stream 131 from the flash separation step, the liquid stream 131 may then be fed directly to precipitator 145 to precipitate hemicellulose therefrom at temperature from 0° C. to 100° C. using a precipitation agent other than water, as shown in
As shown in
Precipitator 145 may comprise one or more stirred tanks or other agitation equipment, and may be either batch or continuous. It may utilize electrostatic charge to facilitate precipitation. Precipitation agent 129 may be selected from the group consisting of an alcohol, e.g. methanol, ethanol, iso-propanol, and butanol; ketone, e.g. acetone, 2-butanone; ninitrile, e.g. acetonitrile, propionitrile, butyronitrile, chloroacetonitrile; ether, e.g. tetrahydrofuran, diethyl ether, dibutyl ether; ester, e.g. methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, vinyl acetate, propylene carbonate; carboxylic acid, e.g. acetic acid, formic acid; amide, e.g formamide; halide, e.g. dichloromethane, chloroform, 1-chlorobutane, 1,2-dichlorethane; hydrogencarbon compound; e.g. hexane, 2,2,4-trimethylpentane, benzene, toluene; amine, e.g. ethylamine, butylamine, ethyldiamine; heterocyclic compound, e.g. pyridine, pyrrole, pyrrolidine, piperidine; water, and combinations thereof. Precipitation agent 129 may also comprise a mixture of an alcohol and water, optionally at an alcohol:water mass ratio from 1:1 to 20:1 or from 2:1 to 15:1. In some embodiments, precipitation agent 129 is the same as the co-solvent, e.g., acetonitrile. When acetonitrile and/or water are used as both the co-solvent and the precipitation agent, the concentration of co-solvent in the precipitation slurry is at least 1% higher than the concentration of co-solvent in the extractant, e.g., at least 2% higher or at least 5% higher. Precipitation slurry 146 may comprise, for example, from 0.001 to 3 wt. % cellulose, from 0.001 to 15 wt. % hemicellulose, from 1 to 10 wt. % water, from 0.05 to 50 wt. % solvent, from 0.05 to 50 wt. % co-solvent, and from 10 to 60 wt. % precipitation agent.
In another embodiment, the precipitator may comprise a crystallizer and/or precipitation agent 129 may be fed at a lower temperature, e.g. from 10° C. to 60° C. as long as the hemicellulose solubility is sensitive to solvent temperature. In this aspect, the reduced temperature may cause the hemicellulose to precipitate as solids from the solution.
In yet another embodiment, a gas, optionally an inert gas, e.g. nitrogen, may be fed to precipitator 145. In some embodiments, the inert gas is carbon dioxide, optionally supercritical carbon dioxide. In this embodiment, the supercritical carbon dioxide may lead to the formation of a carbon dioxide phase, a solvent phase and a hemicellulose phase. In this aspect, hemicellulose are automatically separated out as a solids rich stream. The carbon dioxide may be flashed under low pressure, recovered using a compressor, and returned to precipitator 145. Some or all of the co-solvent may be flashed at reduced pressure and recycled (not shown). This type of concentrating process for hemicellulose may advantageously reduce the downstream washing requirements and associated energy costs (described below).
As shown, precipitation slurry 146 may then be sent to filter 150 which separates a precipitation agent filtrate 151 from filtered intermediate hemicellulose 152. Filter 150 may comprise solid-liquid separation equipment, including but not limited to rotary vacuum drums, belt filters, centrifuge, and screw presses. Without being bound by theory, it is believed that the pressure difference between precipitation slurry 146 and filtrate stream 151 may serve as the driving force for filtration. The pressure difference may vary from 1 to 10,000 kPa, e.g., from 10 to 5,000 kPa, or from 100 to 1,000 kPa. Precipitation agent filtrate 151 may be directed to a distillation column 165 to form a distillate 166 comprising precipitation agent and a residue 167 comprising cellulose solvent and co-solvent. In one embodiment, distillate 166 may comprise from 0.1 to 25 wt. % water, from 5 to 40 wt. % co-solvent, from 45 to 90 wt. % precipitation agent and less than 0.0001 cellulose solvent (e.g., substantially free of cellulose solvent). Distillate 166 may be directed to precipitator 145. Residue 167 may comprise from 20 to 70 wt. % cellulose solvent and from 20 to 80 wt. % co-solvent. Residue 167 may be returned directly to extractor 105 via line 104 or may be combined with fresh extractant and then directed to extractor 105 via line 104. Column 165 may be operated at a temperature from 0° C. to 300° C., e.g., from 10° C. to 200° C. or from 25° C. to 150° C. and at a pressure (absolute) from 1 to 10,000 kPa, e.g., from 5 to 4,000 kPa, or from 3 to 1,000 kPa.
As shown in
Precipitant washes 158 or 187″ and 168 or 186″ may preferably be substantially free of the cellulose solvent. Further, precipitant wash 158 or 187″ preferably has high solubility to cellulose solvent but low solubility to mono-, di-, and oligo-saccharide and other side products. In one embodiment, precipitant wash 158 or 187″ is selected from, but not limited to, the group of alcohol, e.g. methanol, ethanol, iso-propanol, and butanol; ketone, e.g. acetone, 2-butanone; ninitrile, e.g. acetonitrile, propionitrile, butyronitrile, chloroacetonitrile; ether, e.g. tetrahydrofuran, diethyl ether, dibutyl ether; ester, e.g. methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, vinyl acetate, propylene carbonate; carboxylic acid, e.g. acetic acid, formic acid; amide, e.g formamide; halide, e.g. dichloromethane, chloroform, 1-chlorobutane, 1,2-dichlorethane; hydrogencarbon compound; e.g. hexane, 2,2,4-trimethylpentane, benzene, toluene; amine, e.g. ethylamine, butylamine, ethyldiamine; heterocyclic compound, e.g. pyridine, pyrrole, pyrrolidine, piperidine; water, and combinations thereof. The precipitant wash may be enriched in co-solvent and may comprise a condensed portion of the vapor stream of the co-solvent from the flashing step. In another embodiment, the precipitant wash may comprise a stream enriched in precipitation agent.
On the other hand, when high purity hemicellulose material 162 is used, precipitant wash 168 or 186″ preferably has the high solubility to side products and is selected from, but not limited to, the group of water, ethylene glycol, glycerin, formamide, N,N-dimethylformamide, N-methylpyrrolidinone, N,N-dimethylacetamide, DMSO, mixture of water and alcohol, and/or their combinations. Accordingly, the side products, e.g. mono-, di-, and oligo-saccharide, are dissolved in used precipitant wash 164 and may be removed out using extra operation (not shown) so that their concentrations in precipitant wash 168 are lower than those in stream 164. In one embodiment, used precipitant wash 164 may be combined with used extractant wash 121 and directed to separator 185 via line 188. In some aspects, precipitant wash 158 is the same as extractant wash 118 and precipitant wash 168 is the same as extractant wash 124. As shown in
Exemplary compositions using ethanol as precipitating agent 129 or 166, acetonitrile as precipitant wash 158 or 187″ and water as precipitant wash 168 or 186″ are provided in Table 4. When acetonitrile is used as the co-solvent and first extractant wash 118 or a combination of lines 132 and 187′, and water is used as second extractant wash 124 or 186′, at least 90% of the cellulose in cellulosic material 103 is maintained in washed intermediate cellulosic material 122, as described herein. If no further processing is required, washed hemicellulose 162 may be referred to as a finished hemicellulose product in which the ratio of hemicellulose concentration to cellulose concentration is at least 5 times higher than in feed stream 103.
Returning to washed hemicellulose 162 or 157, the stream may then be mechanically de-liquored (not shown), e.g., concentrated in a concentrator to form concentrated hemicellulose material. The solids content in concentrated hemicellulose material may be from 10 to 99 wt. %, e.g., from 20 to 90 wt. % or from 30 to 85 wt. %. In some embodiments, the solids content is greater than 90 wt. %. The concentrator may include squeeze rolls, rotating rolls, and/or wringer rolls. It should be understood that additional water removal methods may be used to concentrate the hemicellulose, depending on the desired solids content and available energy supply.
In some embodiments, the concentrated hemicellulose material may then be further dried in a dryer. The dryer may function to remove residual precipitant wash, e.g., water. Exemplary dryers may include disintegrator dryers, flash dryers, apron dryers, rotary dryers, heated rolls, infrared dryers, ovens and vacuums. The finished hemicellulose product, as well as any hemicellulose rich stream, e.g. stream 131, has a broad application to generate high value chemicals. Some, but not all, examples are described briefly here. Firstly, it may be advantageously used as an intermediate in furfural, methyl furfural, or valerolactone production. Secondly, the finished hemicellulose product may also be used as a feedstock to produce ethanol and/or as a fuel to a recovery boiler. Thirdly, hemicellulose can be used as a starting material to produce functional chemicals, such as adhesives and sweeteners. Fourthly, it can be recycled back to paper mill to make papers with special features.
While the above invention is applicable to processes in which mono-, di-, and oligo-saccharide and/or other side products may be generated in the extraction process, flashing process, and/or other operating steps, several other technologies can also be chosen to remove them from the system in order to maintain continuous operation. In some embodiments, evaporation, membrane, ion exchange, activated carbon bed, simulated moving bed chromatographic separation, flocculant, e.g. polydiallyldimethylammonium chloride (polyDADMAC), and/or their combinations may be employed to separate mono-, di-, and oligo-saccharide from the liquid stream. In other embodiments, polymer-bound boronic acid has been demonstrated to be able to form complex with sugars so that the sugars are separated from the liquid stream. In yet other embodiments, the small sugars may be converted by either enzymatic treatment or acid-catalytic process into furfural, ethanol, acetic acid, and/or other products which can be further separated out from the system. In still other embodiments, mono-, di-, and oligo-saccharide and other side products can be removed in one or more operations, which are located before the separation of the extraction filtrate, after precipitation step, in the hemicellulose wash steps, and/or in other steps. The operating conditions are also determined by the stability of the extractant. Without being bound by theory, it is believed that this allows for the minimization of degradation products of the extractant. For a continuous operation, degradation products may be removed by directly purging a degradation products stream. Additionally, distillation may be used to purge degradation products from a column as a distillate or a residue, depending on the boiling point(s) of the degradation product(s). In some embodiments, combinations of these degradation product removal strategies may be employed.
Similarly, accumulated dissolved and/or suspended solids may be removed from the system in order to maintain continuous operation. In some embodiments, evaporation, membrane filtration, ion exchange, activated carbon bed, simulated moving bed chromatographic separation, flocculant, e.g. polydiallyldimethylammonium chloride (polyDADMAC), and/or their combinations may be employed to separate the accumulated dissolved and/or suspended solids from the system.
It is understood that the processes described herein may be further modified based upon the extraction capability, stability, and costs of ionic liquid and co-solvent.
The present invention will be better understood in view of the following non-limiting experiment examples and process simulation completed by using commercial Aspen™ software.
The functionality of ionic liquid and co-solvent, e.g. acetonitrile, was demonstrated by purifying pulp according to the following process and conditions. All the extractions were conducted at no more than 95° C. in a 50 ml glass via using water bath for 1 hr. The solid loading for all the experiment was set to 5 wt % solid to liquid (S/L) ratio. After the extraction, the pulp was separated from extraction solution via centrifuge-filtration. The pulp was washed with fresh extractant 1 or 2 times. The pulp was then washed with water 4 times and separated from the wash solution via centrifuge-filtration. The pulp was dispersed in acetone and filtered under vacuum to form a loose mat. The pulp mat was left in a chemical hood for overnight drying at room temperature. The pulp was then subjected to standard UV absorbance measurement for pulp purity characterization. Specifically, the UV absorbance measurement follows the procedure below.
Pulp (approximately 0.11 g) was dried on a moisture balance twice. The moisture and final weight of pulp were recorded. The dry pulp was placed in a glass tube and hydrolyzed with 72% sulfuric acid (1 ml) at 30° C. for 1 h, then diluted with 5 ml of water. This procedure converted hemicellulose, e.g., xylan to furfural while cellulose was not affected due to the difference in sugar dehydration rates. UV absorbance from 600 to 210 nm was measured and the peak value at 277 nm was recorded. Qualitatively, for the lower hemicellulose concentration in the solid, the lower UV intensity was at 277 nm. Quantitatively, for comparison, a high-grade acetylation grade (AG) pulp used as a comparative sample with a lower hemicellulose concentration of 1.5-2.0 wt % was measured for UV absorbance to be from 0.6 to 0.9 at 277 nm.
The following table shows the UV absorbance of a paper grade hardwood (PGHW) pulp extracted by an EMIM Ac and acetonitrile system (e.g., purified pulp) with different concentration of EMIM Ac in acetonitrile. The highest extraction of hemicellulose was achieved when EMIM Ac concentration in acetonitrile was from approximately 23 wt. % to approximately 25 wt. %.
The same procedures as described in Example 1 were followed, except that a paper grade softwood (PGSW) pulp was extracted by an EMIM Ac and acetonitrile extractant system with different concentrations of EMIM Ac in acetonitrile at 95° C. for 1 hr. The extraction of hemicellulose was changed significantly when EMIM Ac was varied from 0 wt. % to 15 wt. %, as shown in the table below.
The same procedures as described in Example 1 were followed, except that the PGSW pulp was extracted by EMIM Ac-acetonitrile-H2O extractant system with different concentration of H2O in EMIM Ac/Acetonitrile (25/75 w/w) at 95° C. for 1 hr. The extent of hemicellulose extraction changed with the variation of water concentration, as shown in the table below along with the UV measurement for standard high-grade AG pulp sample for comparison.
The same procedures as described in Example 1 were followed, except that the PGSW pulp and the PGHW pulp were extracted using different ionic liquid under different experimental conditions. The EMIM Ac/acetonitrile system achieved the highest hemicellulose extraction yield, as shown in the table below along with the UV measurement for standard high-grade AG pulp sample for comparison.
The same procedures as described in Example 1 were followed, except that the PGHW pulp and the PGSW pulp were extracted by an NMMO H2O/acetonitrile system with different concentrations of NMMO H2O in acetonitrile. The extent of hemicellulose extracted changed when NMMO concentration varied, as shown in the table below along with the UV absorbance measurement of high-grade AG pulp sample for comparison.
The process shown in
The extraction filtrate was then flashed in a flasher to form a vapor stream comprising 91.2 wt. % acetonitrile, due to the low water concentration in the extraction filtrate. The vapor was condensed and used as the washing agent for the intermediate cellulose material and for the filtered hemicellulose. The liquid stream from the flasher comprised 41.4 wt. % acetonitrile, 50.2 wt. % EMIM Ac and 4.8 wt. % hemicellulose. The liquid stream was sent to a precipitator where it was combined with ethanol to form a precipitation slurry comprising 37.5 wt. % acetonitrile, 18.9 wt. % EMIM Ac, 34.2 wt. % ethanol, 1.7 wt. % hemicellulose and 0.2 wt. % cellulose. The precipitation slurry was filtered to form a filtered intermediate hemicellulose comprising 5.5 wt. % water, 25.6 wt. % hemicellulose, 27.6 wt. % acetonitrile, 25.2 wt. % ethanol and 13.9 wt. % EMIM Ac, and a precipitation filtrate comprising 38.2 wt. %, acetonitrile, 34.9 wt. % ethanol and 19.3 wt. % EMIM Ac. The filtered hemicellulose was washed with acetonitrile and then with water to form a washed hemicellulose comprising 44.5 wt. % hemicellulose, 4.0 wt. % cellulose and 51.6 wt. % water. The precipitation filtrate was separated in a distillation column to return a distillate comprising precipitation agent to the precipitator and a residue comprising solvent and co-solvent to the extractor.
As indicated above, the weight percentage of degraded cellulose was included in that of hemicellulose. The following table shows the information of each stream in
The process shown in
Returning to the extraction filtrate, the extraction filtrate was directed to a flasher and flashed to form a liquid stream and a vapor stream comprising 98.8 wt. % acetonitrile and 1.2 wt. % water, due to the low water concentration in the extraction filtrate. The vapor was condensed and used as a portion of the washing agent for the intermediate cellulose material. The liquid stream from the flasher comprised 35.7 wt. % acetonitrile, 58.8 wt. % EMIM Ac, 4.8 wt. % hemicellulose, 0.4 wt. % cellulose and 0.3 wt. % water. The liquid stream was sent to a distillation column to produce a distillate comprising 9.8 wt. % water, 90.1 wt. % acetonitrile, and less than 0.1 wt. % ethanol (which was present due to recycle streams) and a residue comprising 34.1 wt. % acetonitrile, 60.5 wt. % EMIM Ac, 04 wt. % cellulose, 5.0 wt. % hemicellulose. The residue was sent to a precipitator where it was combined with a precipitation agent stream comprising 4.3 wt. % water, 15.2 wt. % acetonitrile and 80.5 wt. % ethanol to form a precipitation slurry comprising 11.8 wt. % water, 28.9 wt. % acetonitrile, 43.8 wt. % EMIM Ac, 22.3 wt. % ethanol, 36.1 wt. % hemicellulose and 3.7 wt. % cellulose. The precipitation slurry was filtered to form a filtered intermediate hemicellulose comprising 0.7 wt. % water, 41.3 wt. % hemicellulose, 3.7 wt. % cellulose, 16.6 wt. % acetonitrile, 12.8 wt. % ethanol and 25.1 wt. % EMIM Ac, and a precipitation filtrate comprising 1.2 wt. % water, 15.2 wt. % acetonitrile, 45.6 wt. % EMIM Ac, and 23.2 wt. % ethanol. The filtered hemicellulose was washed with an acetonitrile wash to form a washed filtered hemicellulose comprising 19.3 wt. % hemicellulose, 1.7 wt. % cellulose, 78.7 wt. % acetonitrile and 0.3 wt. % water, and a used acetonitrile wash comprising 96.2 wt. % acetonitrile, 1.3 wt. % ethanol and 2.5 wt. % EMIM Ac. The used acetonitrile wash and the precipitation filtrate were directed to a distillation column to form a distillate which was used as the precipitation agent stream, and a residue which was used as the extractant. The washed filtered hemicellulose was then washed with water to form a hemicellulose product 48.7 wt. % water, 47.1 wt. % hemicellulose and 4.2 wt. % cellulose, and a used water wash comprising 69.5 wt. % water and 30.5 wt. % acetonitrile.
As indicated above, the weight percentage of degraded cellulose was included in that of hemicellulose. The following table shows the information of each stream in
While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to those of skill in the art. It should be understood that aspects of the invention and portions of various embodiments and various features recited above and/or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the various embodiments, those embodiments which refer to another embodiment may be appropriately combined with other embodiments as will be appreciated by one of ordinary skill in the art. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention.
This application claims priority to U.S. Application No. 61/862,914, filed Aug. 6, 2013 and to U.S. Application No. 61/933,203, filed Jan. 29, 2014, the entireties of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61862914 | Aug 2013 | US | |
| 61933203 | Jan 2014 | US |
