WO2016048685A1 - Process for producing levoglucosenone using zeolite catalysts - Google Patents

Abstract

Disclosed herein are processes for producing levoglucosenone. In one embodiment, the process comprises contacting a feedstock comprising cellulose, C?6#191 sugars, starch, or mixtures thereof with a solvent in the presence of a heterogeneous catalyst comprising a H-zeolite at a temperature between about 150 °C and about 250 °C and for a reaction time sufficient to form a product mixture comprising levoglucosenone.

Description

TITLE

Process for Producing Levoglucosenone Using Zeolite Catalysts

FIELD OF DISCLOSURE

Processes for preparing levoglucosenone from cellulosic feedstocks using heterogeneous catalysts comprising a H-zeolite are provided. The feedstocks can be derived from renewable biosources.

BACKGROUND

Levoglucosenone is a highly dehydrated sugar which is useful as a chemical intermediate for the production of pharmaceuticals and industrial chemicals. A reactive α,β-unsaturated carbonyl system, protected aldehyde functionality, fixed ¹C conformation, and sterically hindered β-D-face make levoglucosenone a useful chiral synthon for the synthesis of biologically active compounds. Levoglucosenone can also be used as a feedstock for production of industrial chemicals such as 1 ,6-hexanediol, which is a useful intermediate in the industrial preparation of polyamides such as nylon 66. 1 ,6-Hexanediol can be converted by known methods to 1 ,6-hexamethylene diamine, a starting

component in nylon production.

It is increasingly desirable to obtain industrial chemicals or their precursors from materials that are not only inexpensive but also environmentally benign. Of particular interest are materials which can be obtained from renewable sources, that is, materials that are produced by a biological activity such as planting, farming, or harvesting. Biomass sources for such materials are becoming more attractive economically versus petroleum-based ones. As used herein, the terms "renewable" and "biosourced" are used interchangeably.

Methods for obtaining levoglucosenone from renewable sources have been reported. For example, Shafizadeh et al. (Carbohydrate Research, 71 , 169-191 (1979)) report the pyrolytic production of levoglucosenone from acid- treated cellulose and paper. Kawamoto et al. (J. Wood Sci (2007) 53:127-133) disclose that catalytic pyrolysis of cellulose in sulfolane containing sulfuric acid or polyphosphoric acid gave levoglucosenone, furfural, and 5-hydroxy methyl furfural. Published patent application WO 201 1/000030 A1 discloses a method of converting particulate lignocellulosic material to produce volatile organic compounds and char. One particular form of the invention provides a method of converting a lignocellulosic material, such as cellulosic bleached wood pulp, into a mixture of the volatile organic liquids, 1 (S)-6,8-dioxabicyclo[3.2.1 ]oct-2-en-4- one ((-)levoglucosenone, 2-furaldehyde (furfural) and 4-ketopentanoic acid (levulinic acid).

There is an existing need for processes to make levoglucosenone from renewable biosources. There is an existing need for improved processes to produce levoglucosenone from biomass-derived starting materials, including feedstocks comprising, cellulose, Ce sugars, starch, or mixtures thereof.

SUMMARY

In one embodiment, a process for forming a product mixture comprising levoglucosenone is provided, the process comprising: contacting a feedstock comprising cellulose, Ce sugars, starch, or mixtures thereof with a solvent in the presence of a heterogeneous catalyst comprising a H-zeolite at a temperature between about 150 °C and about 250 °C and for a reaction time sufficient to form a product mixture comprising levoglucosenone. In one embodiment, the process further comprises a step of isolation at least a portion of the levoglucosenone from the product mixture.

In one embodiment, the H-zeolite comprises H-Beta, H-Y, H-ZSM-5, H- mordenite, or mixtures thereof. In one embodiment, the H-zeolite comprises a medium pore zeolite. In one embodiment, the H-zeolite comprises a large pore zeolite.

In one embodiment, the solvent comprises sulfolane, polyethylene glycol, polyethylene glycol alkyl ether, polyethylene glycol dialkyi ether, polytrimethylene glycol, or mixtures thereof.

DETAILED DESCRIPTION

As used herein, where the indefinite article "a" or "an" is used with respect to a statement or description of the presence of a step in a process of this invention, it is to be understood, unless the statement or description explicitly provides to the contrary, that the use of such indefinite article does not limit the presence of the step in the process to one in number.

As used herein, when an amount, concentration, or other value or parameter is given as either a range, preferred range, or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.

As used herein, the terms "comprises," "comprising," "includes,"

"including," "has," "having," "contains" or "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

As used herein, the term "about" modifying the quantity of an

ingredient or reactant employed refers to variation in the numerical quantity that can occur, for example, through typical measuring and liquid handling procedures used for making concentrates or use solutions in the real world;

through inadvertent error in these procedures; through differences in the manufacture, source, or purity of the ingredients employed to make the

compositions or carry out the methods; and the like. The term "about" also encompasses amounts that differ due to different equilibrium conditions for a composition resulting from a particular initial mixture. Whether or not

modified by the term "about", the claims include equivalents to the quantities. The term "about" may mean within 10% of the reported numerical value, preferably within 5% of the reported numerical value.

As used herein, the term "carbohydrate" refers to any of a large group of organic compounds having the general formula Cm(H₂O)n, where m and n are integers, and includes Ce sugars, starch, and cellulose.

As used herein, the term "biomass" refers to any cellulosic or

lignocellulosic material and includes materials comprising hemicellulose, and optionally further comprising lignin, starch, oligosaccharides and/or

monosaccharides.

As used herein, the term "cellulose" means a polysaccharide consisting of 1000-3000 or more glucose units in an unbranched, linear chain structure.

As used herein, the term "lignocellulose" means comprising both lignin and cellulose. Lignocellulosic material may also comprise hemicellulose. In some embodiments, lignocellulosic material contains glucan and xylan.

As used herein, the term "hemicellulose" means a non-cellulosic polysaccharide found in lignocellulosic biomass. Hemicellulose is a branched heteropolymer consisting of different sugar monomers. It typically comprises from 500 to 3000 sugar monomeric units.

As uses herein, the term "starch" refers to a carbohydrate consisting of a large number of glucose units joined by glycosidic bonds. Starch, also known as amylum, typically contains amylose and amylopectin. Examples of typical starches include corn starch, tapioca, wheat starch, rice starch, and potato starch.

As used herein, the term "sugar" includes monosaccharides,

disaccharides, oligosaccharides, and anhydrosugars. Monosaccharides, or "simple sugars," are aldehyde or ketone derivatives of straight-chain polyhydroxy alcohols containing at least three carbon atoms. A pentose is a monosaccharide having five carbon atoms; examples include xylose, arabinose, lyxose, and ribose. A hexose is a monosaccharide having six carbon atoms; examples include glucose and fructose. Disaccharide molecules consist of two covalently linked monosaccharide units; examples include sucrose, lactose, and maltose. Sucrose is a disaccharide composed of the monosaccharides glucose and fructose with the molecular formula C12H22O11. As used herein, "oligosaccharide" molecules consist of about 3 to about 20 covalently linked monosaccharide units. Anhydrosugars are molecules with an intramolecular ether formed by the elimination of water from reaction of two hydroxyl groups of a single

monosaccharide; examples include levoglucosenone, levoglucosan, galactosan, and mannosan. Unless indicated otherwise herein, all references to specific sugars are intended to include the D- stereoisomer, the L-stereoisomer, and mixtures of the stereoisomers.

As used herein, the term "C_n sugar" includes monosaccharides having n carbon atoms; disaccharides comprising monosaccharide units having n carbon atoms; and oligosaccharides comprising monosaccharide units having n carbon atoms. As used herein, the term "Ce sugar or equivalent" includes hexoses, disaccharides comprising hexose units, oligosaccharides comprising hexose units, and glucan.

As used herein, the abbreviation "LGone" refers to levoglucosenone, also known as 1 ,6-anhydro-3,4-dideoxy-p-D-pyranosen-2-one. The chemical structure of levoglucosenone is represented by Formula (I).

The chemical structure of levoglucosan, also known as 1 ,6-anhydro- - glucopyranose, is represented by Formula (II).

II

In one embodiment, a process for forming a product mixture comprising levoglucosenone is provided, the process comprising contacting a feedstock comprising cellulose, Ce sugars, starch, or mixtures thereof with a solvent in the presence of a heterogeneous catalyst comprising a H-zeolite at a temperature between about 150 °C and about 250 °C and for a sufficient time to form a product mixture comprising levoglucosenone.

Suitable feedstocks comprising cellulose, Ce sugars, starch, or mixtures thereof can be derived from biorenewable resources including biomass.

Biomass may be derived from a single source, or biomass can comprise a mixture derived from more than one source; for example, biomass could comprise a mixture of corn cobs and corn stover, or a mixture of grass and leaves. Biomass includes, but is not limited to, bioenergy crops, agricultural residues, municipal solid waste, industrial solid waste, sludge from paper manufacture, yard waste, wood and forestry waste or a combination thereof. Examples of biomass include, but are not limited to, corn grain, corn cobs, crop residues such as corn husks, corn stover, grasses, wheat, wheat straw, barley, barley straw, hay, rice straw, switchgrass, paper (including cardboard, kraft paper, pulp, containerboard, linerboard, corrugated container board), sugar cane bagasse, sorghum, soy, components obtained from milling of grains, trees, branches, roots, leaves, wood chips, sawdust, shrubs and bushes, vegetables, fruits, flowers, and animal manure or a combination thereof. Biomass that is useful for the present process may include biomass that has a relatively high carbohydrate value, is relatively dense, and/or is relatively easy to collect, transport, store and/or handle. In one embodiment, the feedstock is ultimately derived from biomass.

In some embodiments, the feedstock comprises cellulose, Ce sugars, starch, or mixtures thereof. In some embodiments, the feedstock comprises cellulose. In some embodiments, the feedstock comprises a Ce sugar. In some embodiments, the feedstock comprises a C₆ sugar selected from the group consisting of glucose, levoglucosan, sucrose, starch, and mixtures thereof. In some embodiments, the feedstock comprises glucose. In some embodiments, the feedstock comprises levoglucosan. In some embodiments, the feedstock comprises sucrose. In some embodiments, the feedstock comprises starch.

Optionally, energy may be applied to the feedstock to reduce the size, increase the exposed surface area, and/or increase the availability of C₆ sugars, cellulose and/or oligosaccharides to the catalyst and to the solvent used in the contacting step. Energy means useful for reducing the size, increasing the exposed surface area, and/or increasing the availability of Ce sugars, cellulose and/or oligosaccharides present in the feedstock include, but are not limited to, milling, crushing, grinding, shredding, chopping, disc refining, ultrasound, and microwave. In some embodiments, the feedstock can have an average particle size below about 5 mm, for example below about 1 mm.

The feedstock may be used directly as obtained from the source or may be dried to reduce the amount of moisture contained therein. In some

embodiments, the feedstock has a moisture content of less than about 15 weight percent, for example less than about 10 weight percent, or for example less than about 5 weight percent.

The process is conducted in the presence of a solvent, or solvent mixture, which may serve to reduce the viscosity of the system to improve fluidity of the mixture of the feedstock and the heterogeneous catalyst in the reaction vessel, and / or to remove the heat of reaction and improve the performance of the process. Suitable solvents typically have boiling points in the range of 150°C to 500°C, for example in the range of 150 °C to 300 °C, and are substantially inert under the reaction conditions of the contacting step. In one embodiment, the solvent comprises an aprotic polar solvent, a polar polymeric material, or mixtures thereof. As used herein, the term "mixtures thereof encompasses both mixtures within and mixtures between the solvent classes, for example mixtures aprotic polar solvents, and also mixtures between aprotic polar solvents and polar polymeric materials.

In one embodiment, the solvent comprises an aprotic solvent. Examples of suitable aprotic polar solvents include sulfolane, dimethylformamide, N-methyl- 2-pyrrolidone, and dimethyl sulfoxide. In one embodiment, the aprotic solvent comprises sulfolane. Sulfolane is also referred to as tetrahydrothiophene 1 ,1 - dioxide, or as 2,3,4,5-tetrahydrothiophene-1 ,1 -dioxide. In one embodiment, the aprotic solvent comprises dimethylformamide. In one embodiment, the aprotic solvent comprises N-methyl-2-pyrrolidone. In one embodiment, the aprotic solvent comprises dimethyl sulfoxide.

In one embodiment, the solvent comprises a polar polymeric material. Examples of suitable polar polymer materials include polyethylene glycol, polyethylene glycol alkyl ether, polyethylene glycol dialkyi ether, polytrimethylene glycol, and mixtures thereof. In one embodiment, the solvent comprises polyethylene glycol. In one embodiment, the solvent comprises polyethylene glycol alkyl ether, wherein the alkyl groups are selected from methyl or ethyl. In one embodiment, the solvent comprises polyethylene glycol monomethyl ether. In one embodiment, the solvent comprises polyethylene glycol monoethyl ether. In one embodiment, the solvent comprises polyethylene glycol dialkyi ether, wherein the alkyl groups are selected from methyl or ethyl . In one embodiment, the solvent comprises polyethylene glycol dimethyl ether. In one embodiment, the solvent comprises polyethylene glycol diethyl ether. In one embodiment, the solvent comprises polytrimethylene glycol.

Suitable polyethylene glycols, polyethylene glycol alkyl ethers,

polyethylene glycol dialkyi ethers, and polytrimethylene glycols have molecular weights between about 300 daltons and 10,000 daltons. In some embodiments, the number average molecular weight of the polyethylene glycols, the

polyethylene glycol alkyl ethers, the polyethylene glycol dialkyi ethers, and/or the polytrimethylene glycols is between and optionally includes any two of the following values: 300 daltons, 500 daltons, 1000 daltons, 1500 daltons, 2000 daltons, 2500 daltons, 3000 daltons, 3500 daltons, 4000 daltons, 5000 daltons, 6000 daltons, 7000 daltons, 8000 daltons, 9000 daltons, and 10,000 daltons. In some embodiments, the molecular weight is between 300 daltons and 1500 daltons. In some embodiments, the molecular weight is between1000 and 10,000 daltons. In some embodiments, the molecular weight is between 500 daltons and 5000 daltons.

In some embodiments, the solvent has a water content of about 5 weight percent or less. In some embodiments, the solvent has a water content of about 2 weight percent or less, for example about 1 weight percent or less. In some embodiments, the solvent is anhydrous.

Suitable solvents are typically available commercially from various sources, such as Sigma-Aldrich (St. Louis, MO), in various grades, many of which may be suitable for use in the processes disclosed herein. Technical grades of a solvent can contain a mixture of compounds, including the desired component and higher and lower molecular weight components or isomers.

The amount of solvent used in the contacting step can vary, depending for example on the viscosity of the mixture of feedstock, solvent, and catalyst.

Typically, the solvent may be present in the contacting step in an amount ranging from about 75 weight percent to about 98 weight percent, based on the weight of the feedstock, catalyst, and solvent. For example, the solvent may comprise from about 80 weight percent to about 98 weight percent, or from about 85 weight percent to about 98 weight percent, or from about 90 weight percent to about 98 weight percent, of the total weight. The amount of solvent may be adjusted to obtain the desired viscosity.

In the processes disclosed herein, a feedstock comprising cellulose, Ce sugar, starch, or mixtures thereof is contacted with a solvent in the presence of a heterogeneous catalyst comprising a H-zeolite under reaction conditions sufficient to form a product mixture comprising levoglucosenone. As used herein, the term "heterogeneous catalyst" refers to a solid catalyst which does not dissolve in the reaction medium under reaction conditions. As used herein, the prefix "H-", when used with "zeolite" or a zeolite structure type, refers to the hydrogen-exchanged form of the zeolite or the zeolite structure type, where the original cations have been exchanged for protons, and indicates that the zeolite or zeolite structure type contains an acid site. For example, "H-mordenite" refers to a mordenite structure type zeolite in which the original cations have been exchanged for protons. As used herein, the prefix "Na-", when used with "zeolite" or a zeolite structure type, refers to the sodium-exchanged form of the zeolite or the zeolite structure type, where the original cations have been exchanged for sodium cations. As used herein, the prefix "NH -", when used with "zeolite" or a zeolite structure type, refers to the ammonium-exchanged form of the zeolite or the zeolite structure type, where the original cations have been exchanged for ammonium cations.

Zeolites can be generically described as complex aluminosilicates characterized by a three-dimensional framework structure enclosing cavities occupied by ions and water molecules. In commercially useful zeolites, the water molecules can be removed from or replaced within the framework without destroying its geometry. Zeolites can be represented by the following formula: M2/_nO-Al2O3-xSiO2-yH₂O, wherein M is a cation of valence n, x is greater than or equal to 2, and y is a number determined by the porosity and the hydration state of the zeolite, generally from 2 to 8. In naturally-occurring zeolites, M is principally represented by Na, Ca, K, Mg and Ba in proportions usually reflecting their approximate geochemical abundance. The cations M are loosely bound to the structure and can frequently be completely or partially replaced with other cations by conventional ion exchange.

The zeolite structure consists of corner-linked tetrahedra with Al or Si atoms at centers of tetrahedra and oxygen atoms at corners. Such tetrahedra are combined in a well-defined repeating structure comprising various

combinations of 4-, 6-, 8-, 10-, and 12-membered rings. The resulting framework consists of regular channels and cages, which impart a useful pore structure for separation or catalysis. Pore dimensions are determined by the geometry of the aluminosilicate tetrahedra forming the zeolite channels or cages, with nominal openings of about 0.26 nm for 6-member rings, about 0.40 nm for 8-member rings, about 0.55 nm for 10-member rings, and about 0.74 nm for 12-member rings (these numbers assume ionic radii for oxygen). Zeolites with the largest pores, being the 8-member rings, 10-member rings, and 12-member rings, are considered small, medium, and large pore zeolites, respectively. Pore dimensions are critical to the performance of these materials in catalytic and separation applications since this characteristic determines whether molecules of a certain size can enter and exit the zeolite framework. In practice, it has been observed that very slight decreases in ring dimensions can effectively hinder or block movement of particular molecular species through the zeolite structure.

The effective pore dimensions that control access to the interior of the zeolites are determined not only by the geometric dimensions of the tetrahedra forming the pore opening, but also by the presence or absence of ions in or near the pore. For example, in the case of zeolite type A, access can be restricted by monovalent ions such as Na⁺ or K⁺ that may be situated in or near the openings of a 6-member or 8-member ring. Conversely, access can be enhanced by divalent ions, such as Ca²⁺, that may be situated in or near 6-member ring openings. Thus, the potassium and sodium salts of zeolite A exhibit effective pore openings of about 0.3 nm and about 0.4 nm, respectively, whereas the calcium salt of zeolite A has an effective pore opening of about 0.5 nm. The presence or absence of ions in or near the pores, channels and/or cages can also significantly modify the accessible pore volume of the zeolite for sorbing materials.

Representative examples of medium pore zeolites include zeolites H- ZSM-5 (MFI), H-ZSM-1 1 (MEL), H-ZSM-57 (MFS), H-ZSM-23 (MTT), H-SSZ-44 (SFF), H-SSZ-58 (SFG), and H-SSZ-35 (STF). Representative examples of large pore zeolites include zeolites H-Y (FAU), H-ZSM-20 (EMT), H-beta (BEA), H-mordenite (MOR), H-offretite (OFF), H-ZSM-18 (MEI), H-ZSM-12 (MTW), and H-ZSM-10 (MOZ). The letters in parentheses give the framework structure type of the zeolite as approved by the International Zeolite Association. Small pore zeolites may also be effective catalysts if the surface area of the zeolites provides sufficient number of active sites.

The presence of aluminum atoms in the framework of a zeolite results in hydrophilic sites. On removal of these framework aluminum atoms, water adsorption is seen to decrease and the material becomes more hydrophobic and generally more organophilic. Hydrophobic zeolites generally have Si/AI ratios greater than or equal to about 5, and the hydrophobicity generally increases with increasing Si/AI ratios. It is also possible to make any zeolite hydrophobic by treating it with a hydrophobic reagent such as an organosilane.

Acid forms of zeolites, H-zeolites, can be prepared by a variety of techniques including ammonium exchange followed by calcination, direct exchange of alkali ions for protons using mineral acids or ion exchangers, and by introduction of polyvalent ions. Ammonium exchange is typically performed under conditions which can provide complete exchange of ammonium cations for protons, but partial ammonium exchange may also be performed. The acid sites produced are generally believed to be of the Bronsted (proton donating) type or of the Lewis (electron pair accepting) type. Bronsted sites are generally produced by deammoniation at low temperatures, exchange with protons, or hydrolysis of polyvalent cations. Lewis sites are believed to arise from

dehydroxylation of the H-zeolites or from the presence of polyvalent ions.

The zeolites can be used as powders or as shaped particles having any shape or mixture of shapes, for example spherical, rod-like, or irregular. The zeolites may be obtained from commercial sources or prepared synthetically using known methods.

In one embodiment, the heterogeneous catalyst comprises a H-zeolite. In one embodiment, the H-zeolite comprises H-Beta, H-Y, H-ZSM-5, H-mordenite, or mixtures thereof. In one embodiment, the zeolite comprises H-Beta. In one embodiment, the zeolite comprises H-ZSM-5. In one embodiment, the zeolite comprises H-mordenite. In one embodiment, the zeolite comprises H-Y. In one embodiment, the heterogeneous catalyst comprises a H-zeolite comprising a medium pore zeolite. In one embodiment, the heterogeneous catalyst comprises a H-zeolite comprising a large pore zeolite.

In one embodiment, the heterogeneous catalyst comprises a H-zeolite, and further comprises a NH -zeolite. In some cases, reaction conditions sufficient to form a product mixture comprising levoglucosenone may also be sufficient to convert at least a portion of a NH₄-zeolite catalyst to the H-zeolite form, thus generating an acid form zeolite which can catalyze the production of levoglucosenone.

Under sufficient reaction conditions, the heterogeneous catalyst catalyzes conversion of the cellulose, Ce sugar, starch, or mixtures thereof in the feedstock to levoglucosenone. The amount of the catalyst used in the reaction mixture can be selected to provide acceptable rates of feedstock conversion while minimizing unwanted side reactions, such as char formation and production of furfural and/or formaldehyde. In some embodiments, the amount of the catalyst used in the contacting step can be between about 0.1 weight percent and about 80 weight percent (wt%), based on the weight of the feedstock. In some embodiments, the amount of the catalyst used is between and optionally includes any two of the following values: 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt% and 80 wt%, based on the weight of the feedstock. The amount employed can depend on conditions such as temperature, the specific catalyst used, and the feedstock.

In one embodiment, the use of a heterogeneous catalyst comprising a H- zeolite may provide levoglucosenone yields comparable to those obtained by processes utilizing a homogeneous acid catalyst. In one embodiment, the use of a heterogeneous catalyst may provide levoglucosenone yields which are improved over those obtained by processes utilizing a homogeneous acid catalyst.

Contacting the feedstock with the solvent in the presence of the

heterogeneous catalyst may be performed at a temperature between about 150 °C and about 250 °C. In some embodiments, the temperature is between and optionally includes any two of the following values: 150 °C, 155 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C, 200 °C, 205 °C, 210 °C, 215 °C, 220 °C, 225 °C, 230 °C, 235 °C, 240 °C, 245 °C, and 250 °C. In some embodiments, the temperature is between about 170 °C and about 230 °C. In some embodiments, the temperature is between about 180 °C and about 225 °C. In some embodiments, the temperature is between about 100 °C and about 200 °C. In some embodiments, the temperature is between about 200 °C and about 250 °C. During the contacting step, the temperature may be kept constant or varied. Higher contacting temperatures may permit use of shorter reaction times, and lower contacting temperatures may permit use of longer reaction times.

Contacting the feedstock with the solvent in the presence of the

heterogeneous catalyst may be performed below atmospheric pressure, at atmospheric pressure, or above atmospheric pressure. In some embodiments, the reactor pressure is between about 0.25 kPa and about 40 kPa , and optionally includes any two of the following values: 0.25 kPa, 0.5 kPa, 1 kPa, 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa, 10 kPa, 15 kPa, 20 kPa , 25 kPa, 30 kPa, 35 kPa, and 40 kPa. In some embodiments, the pressure is between about 1 kPa and about 40 kPa, for example between about 10 kPa and about 40 kPa, or between about 20 kPa and about 40 kPa. In some

embodiments, the pressure is between about 1 kPa and about 20 kPa. In some embodiments, the contacting is done under autogenous pressure. Optionally, the contacting may be performed under an inert gas such as nitrogen or argon. The choice of operating pressure may be related to the temperature of the contacting step and is often influenced by economic considerations and/or ease of operation.

An advantage of operating at a pressure below atmospheric pressure is that any water formed in the contacting step can be removed in a vapor stream. Removing the water reduces its concentration in the product mixture and thus minimizes furfural formation. In one embodiment, the step of contacting the feedstock with a solvent in the presence of a heterogeneous catalyst comprising a H-zeolite to form a product mixture comprising levoglucosenone is performed as a reactive distillation, wherein at least a portion of the water and at least a portion of the levoglucosenone are removed from the product mixture under reduced pressure. In one embodiment, the water content of the product mixture comprising levoglucosenone is less than about 15 weight percent. In some embodiments, the heterogeneous catalyst comprises H- mordenite and the solvent comprises sulfolane. In some embodiments, the heterogeneous catalyst comprises H-mordenite and the temperature is between about 200 °C and about 250 °C. In some embodiments, the heterogeneous catalyst comprises H-mordenite and the feedstock comprises cellulose.

The contacting of the feedstock with a solvent in the presence of the heterogeneous catalyst comprising a H-zeolite is performed at a temperature between about 150 °C and about 250 °C and for a reaction time sufficient to form a product mixture comprising levoglucosenone. In some embodiments, the reaction time can be between about 1 minute and about 20 minutes. In some embodiments, the reaction time can be between and optionally include any two of the following values: 1 minute, 1 .5 minutes, 2 minutes, 2.5 minutes, 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 1 1 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, and 20 minutes. The reaction time can vary, depending upon conditions such as temperature, pressure, the catalyst, amount of heterogeneous catalyst used, feedstock, and particle size of the feedstock. Typically, a sufficient reaction time allows for conversion of at least a portion of the cellulose, Ce sugar, and/or starch of the feedstock to levoglucosenone while minimizing production of undesired side products, such as furfural and char.

The product mixture formed from the contacting step comprises

levoglucosenone. The product mixture further comprises solvent and water. In some embodiments, the product mixture may further comprise one or more of levoglucosan, 1 ,6-anhydro-beta-D-glucofuranose, furfural, hydroxymethylfurfural, or formaldehyde,. In some embodiments, the product mixture may contain from about 0.1 weight percent to about 8 weight percent levoglucosenone, for example from about 0.1 weight percent to about 6 weight percent, or from about 0.1 weight percent to about 5 weight percent, or from about 0.1 weight percent to about 3 weight percent levoglucosenone, based on the total weight of the product mixture. The processes disclosed herein may optionally further comprise a step of isolating at least a portion of the levoglucosenone from the product mixture. Levoglucosenone may be isolated from the product mixture using techniques known in the art, for example by distillation or by liquid-liquid extraction. In one embodiment, the step of isolating the levoglucosenone is by distillation. In one embodiment, the step of isolating the levoglucosenone is by liquid-liquid extraction. In one embodiment, isolating at least a portion of the

levoglucosenone from the product mixture can be performed at the same time as levoglucosenone is formed by contacting the feedstock with a solvent in the presence of the heterogeneous catalyst, for example by using reactive distillation.

The processes disclosed herein can be performed in any suitable reactor. Optionally, the reactor may be equipped with a means, such as impellers, for agitating the feedstock, solvent, and catalyst. Contacting the feedstock with a solvent and the heterogeneous catalyst may be performed in a batch,

continuous, or semi-continuous manner. The contacting step may be performed in one reactor, or in a series of reactors. Suitable reactor types may include, for example, continuous stirred-tank reactors, plug flow tubular flow reactors, and slurry bubble column reactors. Reactor design is well-known and is disclosed in engineering handbooks.

The processes disclosed herein offer several advantages over other methods for obtaining levoglucosenone. Unlike traditional pyrolysis processes, the use of a solvent can help to control unwanted secondary reactions, minimize char formation, and minimize polymerization of reactive compounds. In addition, the continuous removal of water via distillation under reduced pressure can limit the water-catalyzed degradation of levoglucosenone to furfural and provide higher yields of levoglucosenone. Use of a heterogeneous catalyst comprising a H-zeolite instead of a homogeneous acid catalyst can simplify separation of the catalyst from the reaction mixture, and recycle of the catalyst to the process.

EXAMPLES The processes described herein are illustrated in the following examples. From the above discussion and these examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications to adapt it to various uses and conditions.

The following abbreviations are used in the examples: "°C" means degrees Celsius; "wt%" means weight percent; "g" means gram(s); "min" means minute(s); "μηη" means micrometer(s); "μί" means microliter(s); "ml_" means milliliter(s); "mm" means millimeter(s); "GC" means gas chromatography;

"LGone" means "levoglucosenone"; "ID" means "identification"; "Ex" means Example; "Comp Ex" means Comparative Example.

Materials

All commercial materials were used as received unless stated otherwise. All reagents were obtained from Sigma-Aldrich (St. Louis, MO) unless stated otherwise. Levoglucosenone (90% purity) was obtained from TimTec LLC (Newark, DE). Sulfuric acid (98 wt%) was obtained from EMD Chemicals

(Gibbstown, NJ). Zeolites were obtained from Zeolyst International

(Conshohocken, PA), PQ (Conshohocken, PA), and Conteka (the Netherlands) as indicated in Table 1 , and were activated as described in the notes following Table 1 . After activation, the zeolites were stored at room temperature in air-tight containers for varying time periods before use.

Cellulose was used as received from Sigma-Aldrich. Switchgrass was obtained from Genera.

GC Analysis Method

To a weighed aliquot of the sample to be analyzed was added a standard solution of 3.5 wt% diethylene glycol diethyl ether in isopropanol. The sample was mixed thoroughly, then 1 mL was filtered through a 0.2 μιτι filter (GHP Acrodisc® 13 mm syringe filter, PALL Life Sciences, Port Washington, NY) into an auto sampler vial. GC analysis of the sample was performed with an Agilent 5890 gas chromatograph with 7673 auto sampler. The column was an Agilent RTX Stabilwax® column (30 m x 0.25 mm x 0.5 μηη). The injector was

maintained at 250 °C and the injection volume was 1 μΙ_ with a split ratio of 20:1 . The carrier gas was helium at 1 mL/min and a FID detector at 250 °C was used. Concentrations of levoglucosenone and furfural were determined from a standard calibration curve developed for each of the analytes with diethylene glycol diethyl ether.

Description of Experimental Apparatus for Levoglucosenone Production

A 4-necked round-bottom flask (250 ml_) was equipped with each of the following items attached to one of the necks: a short path distillation apparatus, a glass solid addition tube, a glass dip-tube filled with mineral oil for internal temperature monitoring, and an adapter containing a metal tube used for nitrogen purge. A round-bottom flask was attached as a distillation receiver to the end of the condenser of the short path distillation unit to collect any volatiles that distilled over; the distillation receiver was cooled with a dry ice/acetone bath. Vacuum was introduced to the system using a diaphragm vacuum pump. House nitrogen supply was used as the nitrogen source. The vacuum and nitrogen flow were controlled with Swagelok® needle valves. The internal pot temperature and the short path distillation head temperature were monitored using digital Fluke 5211 thermocouples. The 4-necked round-bottom flask and its contents were heated with an oil bath, and aluminum foil was used to insulate the exposed sections of the apparatus which were not immersed in the oil bath. General Procedure for Evaluation of Catalysts for Levoglucosenone Production A weighed quantity of cellulose (2.5 g) was loaded into a solid addition tube. A magnetic stir bar, sulfolane (100 mL), and the appropriate amount of catalyst for the desired catalyst loading were placed into the reaction flask. In the case of Examples 1 -16, 1 .3 g of zeolite was used to give a catalyst loading of 52 weight percent relative to the cellulose feedstock, corresponding to about 1 weight percent catalyst relative to the solvent. The rest of the apparatus was assembled as described above.

Once fully assembled, the system was placed under a vacuum of about 13.3 kPa (-99.6 Torr). Subsurface nitrogen purging (-327 mL/min) was initiated once the vacuum had stabilized. Heating was begun once both the nitrogen and vacuum pressure were equilibrated. The internal temperature of the flask contents was monitored and upon reaching -200 °C, the cellulose in the solid addition tube was dispensed into the catalyst/sulfolane mixture over about 3 minutes. The reaction mixture was subsequently heated at -200-210 °C for a reaction time of 10 minutes. After the desired reaction time, the reaction mixture was allowed to cool to room temperature.

Once cooled, the reaction mixture was filtered to separate the solids and obtain a filtrate. The solids were washed well with water and dried. Any liquid remaining in the short path condenser, which had not fully distilled over into the distillation receiver, was rinsed from the condenser with methylene chloride and collected. The filtrate, the material from the condenser, and the contents of the distillation receiver were analyzed separately by GC for levoglucosenone; the amounts were summed and reported in Table 2 as total yield of

levoglucosenone. In all the Examples, the majority of the levoglucosenone was found in the filtrate.

Yields of levoglucosenone were calculated by dividing the actual yield of levoglucosenone (in g) by the theoretical yield of levoglucosenone (in g) expected from 2.5 g cellulose, and multiplying by 100. It was assumed that the cellulose was 100 % Ce sugar.

EXAMPLES 1 -17

Several different types of H-zeolite catalysts with a range of Si/AI molar ratios were screened according to the general procedure provided herein above for conversion of cellulose to levoglucosenone. Information about the zeolites and the levoglucosenone yields for each Example are shown in Table 1 . Furfural was observed in the product mixture for all Examples; its yield was determined to be less than 1 mole% except in Example 15, in which furfural was obtained in 1 mole% yield.

COMPARATIVE EXAMPLE A A Na-mordenite zeolite having a silicon to aluminum molar ratio of 5 was tested for conversion of cellulose to levoglucosenone according to the general procedure. Under the reaction conditions used, no levoglucosenone was observed. Results are included in Table 1 . COMPARATIVE EXAMPLE B.

Comparative Example B was performed according to the general procedure except that no heterogeneous catalyst was used; instead, sulfuric acid was used as a homogeneous catalyst. For Comparative Example B, 0.13 g of 98 wt% H₂SO₄ was used to give a catalyst loading of 5 weight percent relative to the cellulose feedstock, corresponding to 0.1 weight percent catalyst relative to the solvent. Levoglucosenone was obtained in 43% molar yield. Results are also shown in Table 1 .

Table 1 . Levoglucosenone Yield Obtained and Catalyst Used for Examples 1 -17 and Comparative Examples A and B

Notes:

¹ As-received zeolite was heated from room temperature to 525 °C at 10°C/min, then from 525 °C to 540 °C at 2 °C/min, then from 540 °C to 550 °C at 1 °C/min, followed by an 8 hour hold at 550 °C before cooling to 1 10 °C.

² As-received zeolite was heated from room temperature to 525 °C at 10°C/min, then from 525 °C to 550 °C at 2 °C/min, followed by an 8 hour hold at 550 °C before cooling to 1 10 °C.

-Mordenite (CBV-30A) calcined by Zeolyst

The results in Table 1 show that a variety of medium and large pore H- zeolites were useful in converting cellulose to levoglucosenone under the reaction conditions employed. Zeolite types H-Beta, H-ZSM-5, and H- mordenite generally provided levoglucosenone in higher yields than did H-Y zeolite. The highest yield of levoglucosenone (55%) was observed using a H- mordenite zeolite. Example 8, in which a NH -zeolite was used, gave 3 mole% yield of levoglucosenone. In contrast, the use of a Na-mordenite in Comparative Example A produced no levoglucosenone. Levoglucosenone yields for Examples 15 and 16, which used H-mordenite zeolites, were higher than or comparable to the yield of Comparative Example B, in which the catalyst was homogeneous sulfuric acid.

Comparative Example C

A H-ZSM-5 catalyst (CBV-5524G) was evaluated for conversion of a lignocellulosic feedstock to levoglucosenone following the General Procedure given herein above, except that switchgrass that had been milled to -1 -3 mm particle size was used in place of cellulose. The switchgrass had

approximately 8-10 weight percent moisture content after drying at 105 °C for 24 hours. No levoglucosenone was observed by GC analysis.

Claims

What is claimed is: 1 . A process comprising:

contacting a feedstock comprising cellulose, C6 sugars, starch, or mixtures thereof with a solvent in the presence of a heterogeneous catalyst comprising a H-zeolite at a temperature between about 150 °C and about 250 °C and for a reaction time sufficient to form a product mixture comprising levoglucosenone.

2. The process of claim 1 , wherein the H-zeolite comprises H-Beta, H-Y, H-ZSM-5, H-mordenite, or mixtures thereof.

3. The process of claim 2, wherein the zeolite comprises H-ZSM-5.

4. The process of claim 2, wherein the zeolite comprises H-mordenite.

5. The process of claim 2, wherein the zeolite comprises H-Beta.

6. The process of claim 2, wherein the zeolite comprises H-Y.

7. The process of claim 1 , wherein the H-zeolite comprises a medium pore zeolite.

8. The process of claim 1 , wherein the H-zeolite comprises a large pore zeolite.

9. The process of claim 1 , wherein the heterogeneous catalyst further comprises a NH₄-zeolite.

10. The process of claim 1 , wherein the solvent comprises sulfolane, polyethylene glycol, polyethylene glycol alkyl ether, polyethylene glycol dialkyi ether, polytrimethylene glycol, or mixtures thereof.

1 1 . The process of claim 10, wherein the solvent comprises sulfolane.

12. The process of claim 1 , wherein the contacting is performed at a pressure between about 0.25 kPa and about 40 kPa.

13. The process of claim 1 , wherein the contacting is performed in a batch manner.

14. The process of claim 1 , wherein the contacting is performed in a continuous manner.

15. The process of claim 1 , wherein the feedstock comprises cellulose.

16. The process of claim 1 , wherein the amount of heterogeneous catalyst in the contacting step is between 0.1 weight percent and 80 weight percent, based on the weight of the feedstock.

17. The process of claim 1 , further comprising a step of isolating at least a portion of the levoglucosenone from the product mixture.

18. The process of claim 17, wherein the step of isolating is by distillation.

19. The process of claim 2, wherein the H-zeolite comprises H-mordenite and the solvent comprises sulfolane.

20. The process of claim 2, wherein the H-zeolite comprises H-mordenite and the temperature is between about 200 °C and about 250 °C.

21 . The process of claim 2, wherein the H-zeolite comprises H-mordenite and the feedstock comprises cellulose.