Production of Levoglucosenone

FIELD OF DISCLOSURE

Continuous processes for preparing levoglucosenone from carbohydrate sources are provided. The carbohydrate sources contain C6 sugars or the equivalent and 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 ¹ C 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; the patent application also discloses 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 in good yield and with minimum formation of undesired byproducts. There is an existing need for processes to produce levoglucosenone from biomass-derived starting materials, including carbohydrate sources such as lignocellulose, cellulose, C ₆ sugars, starch, agricultural residues, forestry waste, and paper.

SUMMARY

In one embodiment, a process for producing levoglucosenone is provided, the process comprising the steps:

a) contacting in a continuous manner a carbohydrate source, a solvent, and an acid catalyst in a continuous liquid phase reactor under reaction conditions sufficient to form a reaction mixture comprising levoglucosenone, wherein the reaction conditions include a liquid residence time in the reactor between about 0.1 minutes and about 20 minutes;

b) withdrawing a portion of the reaction mixture from the reactor to obtain a product stream comprising levoglucosenone; and

c) optionally, isolating levoglucosenone from the product stream.

In one embodiment, the carbohydrate source comprises lignocellulose, cellulose, a Ce sugar, starch, agricultural residues, forestry waste, paper, or a combination thereof. In one embodiment, the Ce sugar comprises glucose, levoglucosan, sucrose, fructose, or a mixture thereof. In one embodiment, the carbohydrate source is added to the reactor as a solid. In one embodiment, the solvent comprises an aprotic polar solvent, a polar polymeric material, or mixtures thereof.

In one embodiment, the acid catalyst comprises a mineral acid, a heteropolyacid, an organic acid, or mixtures thereof. In one embodiment, the acid catalyst is a mineral acid comprising sulfuric acid, oleum, hydrochloric acid, phosphoric acid, or a mixture thereof. In one embodiment, the acid catalyst is a heteropolyacid comprising phosphotungstic acid, molybdophosphoric acid, silicotungstic acid, or a mixture thereof. In one embodiment, the acid catalyst is an organic acid comprising a mono-carboxylic acid, a di-carboxylic acid, an alkyl sulfonic acid, an aryl sulfonic acid, a halogenated acetic acid, a halogenated alkylsulfonic acid, a halogenated aryl sulfonic acid, or a mixture thereof.

In one embodiment, the reaction conditions include a reactor temperature between about 75 °C and about 300 °C. In one embodiment, the reaction conditions include a reactor pressure between about 3 kPa and about 100 kPa.

In one embodiment, the process further comprises a step of providing a first feed and a second feed to the reactor, wherein the first feed comprises the carbohydrate source and the second feed comprises the solvent and the acid catalyst.

In one embodiment, the process further comprises a step of providing a first feed and a second feed to the reactor, wherein the first feed comprises the acid catalyst and the second feed comprises the carbohydrate source and the solvent.

In one embodiment, the process further comprises a step of providing a first feed, a second feed, and a third feed to the reactor, wherein the first feed comprises the carbohydrate source, the second feed comprises the solvent, and the third feed comprises the acid catalyst.

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, or for example 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 C _m (H ₂ O) _n , where m and n are integers, and includes Ce sugars, starch, and cellulose.

As used herein, the term "carbohydrate source" refers to any material containing at least one carbohydrate.

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 "lignocellulosic" 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 the 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).

In one embodiment, a process for producing levoglucosenone is provided, the process comprising the steps:

a) contacting in a continuous manner a carbohydrate source, a solvent, and an acid catalyst in a continuous liquid phase reactor under reaction conditions sufficient to form a reaction mixture comprising levoglucosenone, wherein the reaction conditions include a liquid residence time in the reactor between about 0.1 minutes and about 20 minutes;

b) withdrawing a portion of the reaction mixture from the reactor to obtain a product stream comprising levoglucosenone; and

c) optionally, isolating levoglucosenone from the product stream.

To be useful as a feedstock for levoglucosenone production, the carbohydrate source contains at least one carbohydrate, such as a Ce sugar or equivalent. Suitable carbohydrate sources 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 carbohydrate source is ultimately derived from biomass.

In some embodiments, the carbohydrate source comprises lignocellulose, cellulose, a Ce sugar, starch, agricultural residues, forestry waste, paper, or a combination thereof. In some embodiments, the carbohydrate source comprises lignocellulose. In some embodiments, the carbohydrate source comprises cellulose. In some embodiments, the carbohydrate source comprises starch. In some embodiments, the carbohydrate source comprises agricultural residues. In some embodiments, the carbohydrate source comprises forestry waste. In some embodiments, the carbohydrate source comprises paper. In some embodiments, the carbohydrate source comprises a Ce sugar. In some embodiments, the carbohydrate source is a Ce sugar comprising glucose, levoglucosan, sucrose, fructose, or mixtures thereof. In some embodiments, the carbohydrate source comprises glucose. In some embodiments, the carbohydrate source comprises levoglucosan. In some embodiments, the carbohydrate source comprises sucrose.

Optionally, energy may be applied to the carbohydrate source to reduce the size, increase the exposed surface area, and/or increase the availability of Ce sugars or equivalents present in the carbohydrate source to the acid 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 or equivalents present in the carbohydrate source include, but are not limited to, milling, crushing, grinding, shredding, chopping, disc refining, ultrasound, and microwave. The carbohydrate source may be used directly as obtained from the source or may be dried to reduce the amount of moisture contained therein.

The present 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 carbohydrate source and the acid catalyst in the reaction vessel and / or to remove the heat of reaction and improve the performance of the process.

Solvents suitable for use in the present processes typically have boiling points in the range of 150°C to 500°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, for example. 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 polar solvent comprises sulfolane, dimethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, or mixtures thereof. In one

embodiment, the 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 solvent comprises dimethylformamide. In one

embodiment, the solvent comprises N-methyl-2-pyrrolidone. In one embodiment, the solvent comprises dimethyl sulfoxide. In one embodiment, the solvent comprises a polar polymeric material. Examples of suitable polar polymeric materials include polyethylene glycol, polyethylene glycol dimethyl ether, and mixtures thereof. In one embodiment, the solvent comprises polyethylene glycol. In one embodiment, the solvent comprises polyethylene glycol dimethyl ether.

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 solvent may be present in the reaction mixture in a range from about 50 wt% to about 99 wt% based on the weight of the total reaction mixture. For example, the solvent may be from about 60% to about 99%, or from about 70 wt% to about 99 wt%, or from about 80 wt% to about 99 wt%, of the total reaction mixture.

The acid catalyst comprises a mineral acid, a heteropolyacid, an organic acid, or mixtures thereof. In one embodiment, the acid catalyst is a mineral acid comprising sulfuric acid, oleum, hydrochloric acid, phosphoric acid, or a mixture thereof. As used herein, the term "oleum" refers to solutions of sulfur trioxide in sulfuric acid. As used herein, the term "phosphoric acid" refers to

orthophosphoric acid, H ₃ PO ₄ , and can include, unless otherwise specified, polyphosphoric acids derived from condensation of orthophosphoric acid molecules and having the general formula HO(PO ₂ OH) _x H, where x is the number of phosphoric units in the molecule. In one embodiment, the acid catalyst comprises sulfuric acid. In one embodiment, the acid catalyst comprises oleum. In one embodiment, the acid catalyst comprises hydrochloric acid. In one embodiment, the acid catalyst comprises phosphoric acid. In one embodiment, the acid catalyst is a heteropolyacid comprising phosphotungstic acid,

molybdophosphoric acid, silicotungstic acid, or a mixture thereof. In one embodiment, the acid catalyst comprises phosphotungstic acid. In one

embodiment, the acid catalyst comprises molybdophosphoric acid. In one embodiment, the acid catalyst comprises silicotungstic acid. In one embodiment, the acid catalyst is an organic acid comprising a mono-carboxylic acid, a di- carboxylic acid, an alkyl sulfonic acid, an aryl sulfonic acid, a halogenated acetic acid, a halogenated alkylsulfonic acid, a halogenated aryl sulfonic acid, or a mixture thereof. Suitable monocarboxylic acids include formic acid and acetic acid. Suitable dicarboxylic acids include oxalic acid, malonic acid, and citric acid. An example of a suitable alkyl sulfonic acid is methane sulfonic acid. An example of a suitable aryl sulfonic acid is toluenesulfonic acid. An example of a suitable halogenated acetic acid is trifluoroacetic acid. An example of a suitable halogenated alkylsulfonic acid is trifluoromethane sulfonic acid. An example of a suitable halogenated aryl sulfonic acid is fluorobenzenesulfonic acid.

Under sufficient reaction conditions, the acid catalyst catalyzes conversion of the C6 sugars or equivalents contained in the carbohydrate source to levoglucosenone. The concentration of the acid catalyst in the reaction mixture can be selected to provide acceptable rates of feed conversion while minimizing unwanted side reactions, such as char formation. In some embodiments, the reaction mixture has an acid catalyst concentration between about 0.01 weight percent and about 10 weight percent, based on the total weight of the reaction mixture. In some embodiments, the acid catalyst concentration in the reaction mixture is between and optionally includes any two of the following values: 0.01 wt%, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.15 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%, 1 .5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, and 10 wt%. The acid catalyst may be obtained from commercial sources or prepared according to known methods.

In the step of contacting in a continuous manner the carbohydrate source, the solvent, and the acid catalyst, the ratio of the carbohydrate source to the sum of the solvent and the acid catalyst can be between about 1 :100 and about 1 :2 on a mass basis. In some embodiments, the ratio on a mass basis of the carbohydrate source to the sum of the solvent and the acid catalyst is between and optionally includes any two of the following values: 1 :100, 1 :90, 1 :80, 1 :70, 1 :60, 1 :50, 1 :40, 1 :30, 1 :25, 1 :20, 1 :15, 1 :10; 1 :9, 1 :8, 1 :7, 1 :6, 1 :5, 1 :4, 1 :3, and 1 :2. The ratio employed can depend upon conditions such as temperature, the acid catalyst, and the content of Ce sugars or equivalent in the carbohydrate source.

In the reactor, contacting the carbohydrate source, solvent, and acid catalyst may be performed at a temperature between about 75 °C and about 300 °C. In some embodiments, the temperature is between and optionally includes any two of the following values: 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, 105 °C, 1 10 °C, 1 15 °C, 120 °C, 125 °C, 130 °C, 135 °C, 140 °C, 145 °C, 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, 250 °C, 255 °C, 260 °C, 265 °C, 270 °C, 275 °C, 280 °C, 285 °C, 290 °C, 295 °C, and 300 °C. In some embodiments, the temperature is between about 100 °C and about 300 °C. In some embodiments, the temperature is between about 150 °C and about 250 °C. In some embodiments, the temperature is between about 180 °C and about 220 °C. During the contacting step, the temperature may be kept constant or varied. Higher contacting temperatures may permit use of shorter liquid residence times in the reactor, and lower contacting temperatures may permit use of longer liquid residence times.

Contacting the carbohydrate source, solvent, and acid catalyst may be performed at or below atmospheric pressure. The use of reduced pressure may facilitate water removal from the liquid phase of the reaction mixture and inhibit side reactions. In some embodiments, the reactor pressure is between about 3 kPa and about 100 kPa , and optionally includes any two of the following values: 3 kPa, 10 kPa, 20 kPa , 30 kPa, 40 kPa, 50 kPa, 60 kPa, 70 kPa, 80 kPa, 90 kPa, and 100 kPa. In some embodiments, the pressure is between about 20 kPa and about 100 kPa, for example between about 20 kPa and about 80 kPa, or between about 20 kPa and about 50 kPa. In some embodiments, the pressure is between about 3 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 may be influenced by economic considerations and/or ease of operation.

In one embodiment, the acid catalyst comprises sulfuric acid and the reaction conditions include a reactor temperature between about 180 °C and about 220 °C, and a reactor pressure between about 10 kPa and about 50 kPa. In one embodiment, the acid catalyst comprises sulfuric acid and the reaction mixture has a sulfuric acid concentration between about 0.05 weight percent and about 0.2 weight percent.

The contacting of the carbohydrate source, solvent, and acid catalyst is performed in a continuous manner under reaction conditions sufficient to form a reaction mixture comprising levoglucosenone, wherein the reaction conditions include a liquid residence time in the reactor between about 0.1 minutes and about 20 minutes. Residence time is defined as the average length of time a portion of material spends in the reactor. For a continuous reactor, liquid residence time is calculated by dividing the volume of material in the reactor by the total volumetric flow rate of material fed to the reactor. Typically, the liquid residence time in the reactor is between about 0.1 minutes and about 20 minutes. In some embodiments, the reaction conditions include a liquid residence time in the reactor between and optionally including any two of the following values: 0.1 minutes (min), 0.2 min, 0.25 min, 0.3 min, 0.4 min, 0.5 min, 0.6 min, 0.7 min, 0.8 min, 0.9 min, 1 min, 1 .25 min, 1 .5 min, 1 .75 min, 2 min, 2.25 min, 2.5 min, 2.75 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, 5.5 min, 6 min, 6.5 min, 7 min, 7.5 min, 8 min, 8.5 min, 9 min, 9.5 min, 10 min, 10.5 min, 1 1 min,

1 1 .5 min, 12 min, 12.5 min, 13 min, 13.5 min, 14 min, 14.5 min, 15 min, 15.5 min, 16 min, 16.5 min, 17 min, 17.5 min, 18 min, 18.5 min, 19 min, 19.5 min and 20 min. In some embodiments, the liquid residence time is between 0.1 minutes and 3 minutes. In some embodiments, the liquid residence time is between 0.1 minutes and 15 minutes, for example between about 0.1 minutes and about 10 minutes, or between about 0.1 minutes and about 6 minutes. The liquid residence time can vary, depending upon conditions such as temperature, pressure, acid catalyst, concentration of the acid catalyst in the reactor, carbohydrate content of the carbohydrate source, loading of the carbohydrate source in the reactor, and particle size of the carbohydrate source. Typically, a suitable liquid residence time allows for conversion of at least a portion of the carbohydrate source to levoglucosenone while minimizing the production of undesired side products, such as char formation.

The reaction mixture formed during the contacting step comprises levoglucosenone. The reaction mixture further comprises solvent and acid catalyst. In some embodiments, the reaction mixture additionally further comprises unreacted carbohydrate source. In some embodiments, the reaction mixture may contain from about 1 weight percent to about 43 weight percent levoglucosenone, for example from about 1 weight percent to about 5 weight percent, of from about 1 weight percent to about 10 weight percent, or from about 1 weight percent to about 20 weight percent, or from about 1 weight percent to about 30 weight percent, or from about 1 weight percent to about 40 weight percent, or from about 5 to about 40 weight percent levoglucosenone.

After the contacting step, a portion of the reaction mixture is withdrawn from the reactor to obtain a product stream comprising levoglucosenone. In one embodiment, the product stream comprising levoglucosenone is a liquid stream. In one embodiment, the product stream comprising levoglucosenone comprises both liquid and gas phases. In some embodiments, the product stream may contain the same concentration of levoglucosenone as contained in the reaction mixture within in the reactor. Optionally, at least a portion of the

levoglucosenone may be isolated from the product stream using techniques known in the art, for example by distillation or liquid-liquid extraction.

The processes disclosed herein can be performed in any suitable continuous liquid phase reactor. Optionally, the reactor may be equipped with a means, such as impellers, for agitating the carbohydrate source, solvent, and acid catalyst. Contacting the carbohydrate source with a solvent and an acid catalyst may be performed in a 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. In some embodiments, the continuous liquid phase reactor is selected from the group consisting of continuous stirred tank reactors, plug flow tubular flow reactors, and slurry bubble column reactors. In one embodiment, the continuous liquid phase reactor is a stirred tank reactor. In one embodiment, the continuous liquid phase reactor is a plug flow tubular flow reactor. In one embodiment, the continuous liquid phase reactor is a slurry bubble column reactor.

In some embodiments, the carbohydrate source is added to the reactor as a solid.

In some embodiments, the processes disclosed herein further comprise a step of providing a first feed and a second feed to the reactor, wherein the first feed comprises the carbohydrate source and the second feed comprises the solvent and the acid catalyst.

In some embodiments, the processes disclosed herein further comprise a step of providing a first feed and a second feed to the reactor, wherein the first feed comprises the acid catalyst and the second feed comprises the

carbohydrate source and the solvent.

In some embodiments, the processes disclosed herein further comprise a step of providing a first feed, a second feed, and a third feed to the reactor, wherein the first feed comprises the carbohydrate source, the second feed comprises the solvent, and the third feed comprises the acid catalyst.

The processes disclosed herein offer several advantages over pyrolysis methods, which are typically performed at high temperatures without any solvent. In the processes disclosed herein, the carbohydrate source can be fed directly to the reactor as a solid, without any pretreatment step, and the solvent can be at reaction temperature when the solid carbohydrate source is added to the reactor. This contrasts with processes in which the carbohydrate source is first mixed with the solvent, then the mixture is heated to the reaction temperature, which can give time for undesired side reactions to occur. By adding the carbohydrate source to the solvent at temperature, levoglucosenone can be obtained in higher yield and purity. Also, using direct solid feed in a continuous process can enable high heating rates of the solid feed as well as precise control of the solvent residence time and temperature, which are important in maximizing yield. The continuous processes disclosed herein also can provide operational flexibility, in that the acid can be added to the reactor together with the solvent, or by itself. Lower operating temperatures could also provide cost savings in process heating, as well as enabling the use of less expensive materials of construction for the reactor.

EXAMPLES

The processes described herein are illustrated in the following exampl 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); "wt%" means weight percent; "ml_" means m ill il iter(s); "mL/min" means milliliter(s) per minute; "GC" means gas chromatography; "LG" means "levoglucosenone"; "Temp" means temperature; "Ex" means Example, "Comp Ex" means Comparative Example.

Materials

All commercial materials were used as received unless stated otherwise. Pure microcrystalline powdered cellulose (Avicel PH-101 ) was purchased from Fluka Analytical (LOT# BCBJ8498V). Sulfolane (99%) was purchased from Alfa Aesar (LOT# E02Z031 ). Sulfuric acid (98% by weight) was purchased from EMD (LOT# 52277). Glucose was purchased from Sigma Aldrich (LOT# SLBC4983V). Levoglucosan (99%) was purchased from Slovak Academy of Sciences.

Switchgrass was obtained from University of Tennessee. Levoglucosenone (99%) for GC calibration was purchased from MVS Chemical.

Analytical Methods

Product stream solutions were analyzed by GC-FID using standard GC and GC/MS equipment.

Yields were calculated as follows: During a typical reaction, after steady state conditions were obtained the liquid effluent from the reactor was collected in a sampling flask over a 5 min period. The total moles of levoglucosenone in the liquid effluent sample was determined by GC-FID. The yield of

levoglucosenone was calculated by dividing the moles of levoglucosenone by the moles of C6 sugar contained in the carbohydrate source fed to the reactor during the 5 minute sampling period. Cellulose, levoglucosan, and glucose were considered to be 100% C6 sugar by weight. The switchgrass used in Example 14 contained 36 weight percent C ₆ sugars as determined by the procedure described in the National Renewable Energy Lab NREL/TP-510-42618 technical report. Prior to reaction the switchgrass was hammer milled and screened to a particle size of 0.5-1 mm.

EXAMPLES 1 -14

In each of Examples 1 -14 the conversion of carbohydrate-containing feedstock to levoglucosenone was conducted in a 50 mL glass stirred tank reactor according to the following procedure. At the beginning of a run the reactor was initially filled with 25 mL of sulfolane containing sulfuric acid at a concentration as shown in Table I. The reactor outlet was opened and the pressure was reduced to 20 kPa using a vacuum pump. The reactor was then heated to the reaction temperature shown in Table I using a molten metal bath. Upon reaching reaction temperature, a preheated solution of sulfuric acid in sulfolane was pumped into the reactor through a sub-surface dip leg. The flowrate of the solution of sulfuric acid in sulfolane was set to obtain the desired residence time shown in Table I. At the same time, preheated nitrogen purge gas was fed to the reactor at a flow rate of 200 mL min ^"1 through another subsurface dip leg. The liquid level in the reactor was maintained at 25 mL during the reaction by use of a dip tube at the reactor outlet. During the run, liquid effluent from the reactor flowed through a two way valve to one of two 1000 mL sample collection flasks. The valve allowed one flask to be filled while the other was isolated from the system and emptied. The outlets of the sample collection flasks were connected to a vacuum pump to maintain the desired system pressure.

After stable reactor temperature, flow rates, and reactor pressure were achieved (circa 5 min), the solid carbohydrate-containing feed was introduced to the reactor by an auger type solid feeder located at the top of the reactor. After an amount of time equal to 5 times the residence time, the two way valve was switched and liquid effluent was diverted to an empty product collection flask to collect a steady-state sample of the reaction mixture from the reactor. After collecting a sufficient amount of sample for analysis, the valve was switched again, and the steady state sample flask was removed from the system. The amount of levoglucosenone in the liquid sample was analyzed by GC-FID. The steady state molar yield of levoglucosenone was then calculated and is reported in Table I.

COMPARATIVE EXAMPLE A

Comparative Example A was performed following the procedure of Examples 1 -14 with reaction conditions as indicated in Table 1 , except that the carbohydrate-containing feed was pre-treated with acid before use and there was no continuous addition of acid solution to the reactor. The cellulose was impregnated with acid according to the following method. Equal parts by weight of aqueous 0.1 wt% sulfuric acid and cellulose were mixed to form a slurry. The water was then removed from the slurry by holding the sample in a 50° C vacuum oven overnight. The dried, acid-impregnated cellulose obtained in this manner contained 0.1 wt% acid based on total weight of the cellulose and acid. The acid concentration in sulfolane in the reactor calculated from the flow rate of acid and sulfolane to the reactor was 0.007 wt%.

Table 1 . Reaction Conditions and Levoglucosenone Yield for Examples 1 -14 and Comparative Example A

The results in Table I demonstrate production of levoglucosenone from cellulose, levoglucosan, glucose, and switchgrass as carbohydrate sources using the processes disclosed herein. Higher yields of levoglucosenone were obtained at higher temperature, as seen by the comparison of Examples 6 and 12, which used cellulose as feed, and also the series of Examples 7, 8, 9, 10, and 1 1 which used levoglucosan as feed. Examples 1 1 , 12, 13, and 14 demonstrated the best levoglucosenone yields, above 40 mole%, under reaction conditions which included higher temperature (215 °C) and lower residence time (3.3 - 3.8 minutes). The results for Example 4 and Example 5 demonstrated levoglucosenone yields comparable to that of Comparative Example A, which was performed under similar reaction conditions but using cellulose which had been pre-treated with acid and at an acid concentration in the reactor equivalent to 0.007 weight percent sulfuric acid in sulfolane.

EXAMPLE 15

The conversion of cellulose to levoglucosenone was conducted in batch mode in a 50 ml_ glass stirred tank reactor according to the following procedure. At the beginning of the run the reactor was filled with 50 ml_ of solution containing 0.12 weight percent sulfuric acid in sulfolane. The reactor outlet was opened and the pressure was reduced to 20 kPa using a vacuum pump. The reactor was then heated to 190° C using a molten metal bath. Preheated nitrogen purge gas was fed to the reactor at a flow rate of 200 ml_ min ^"1 through a sub-surface dip leg.

After stable reactor temperature and reactor pressure were achieved (circa 5 min), 1 .0 g of cellulose was quickly introduced to the reactor in a few seconds by an auger-type solid feeder located at the top of the reactor.

Samples (1 ml_) of the liquid reaction mixture were taken through a septum port with a syringe immediately after introducing the cellulose ( at 0 min of reaction time) and at 2, 4, 6, 8, 10, 15 min after the cellulose was fed to the reactor. The amount of levoglucosenone in the liquid samples was analyzed by GC-FID. The molar yield of levoglucosenone at the different reaction times was then calculated and is reported in Table 2.

Table 2. Reactor Liquid Residence Time and Levoglucosenone Yield for Example 15

The data in Table 2 show the effect of reactor residence time on the yield of levoglucosenone. At these reaction conditions, a residence time of 4 minutes was found to maximize the levoglucosenone yield. After 6 minutes the yield of levoglucosenone had decreased.