WO2010102203A2 - Method for the preparation of alkyl levulinates - Google Patents

Abstract

A process for the conversion of furfuryl alcohol into levulinate esters in a single step reaction comprising addition of the product levulinate ester to the reaction mixture of an alkanol and furfuryl alcohol in the presence of a strong protic acid catalyst, wherein high yield of the levulinate ester is accompanied by low amounts of tarry residue that do not precipitate or solidify in the reaction mixture.

Description

METHOD FOR THE PREPARATION OF ALKYL LEVULINATES

This application is being filed on March 5, 2010, as a PCT International Patent application in the name of Segetis, Inc., a U.S. national corporation, applicant for the designation of all countries except the United States and Feng Jing, a citizen of the

People's Republic of China, Steven Donen, a citizen of the United States, Sergey Selifonov, a citizen of the United States, and Brian Mullen, a citizen of the United States , applicants for the designation of the U.S. only, and claims priority to U.S. Patent Application Serial Number 61/157,746, entitled "Method For The Preparation Of Alkyl Levulinates", filed on March 5, 2009, the contents of which are herein incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to methods for the preparation of levulinate esters from furfuryl alcohol.

BACKGROUND

The production of levulinic acid and levulinate esters from furfuryl alcohol is known. US Patent No. 2,738,367 discloses a process for the manufacture of levulinic acid comprising heating an aqueous solution of furfuryl alcohol in the presence of a strong acidic ion exchange resin at a temperature in the range from 3O⁰C to 100⁰C.

The cation exchange resins include AMBERLITE IR- 120 and AMBERLITE IR- 105.

Synthesis of levulinate esters was not accomplished using this technique and would require an additional step.

US Patent No. 5,175,358 discloses a process for the preparation of levulinic acid, including heating furfuryl alcohol in the presence of water and a strong protonic acid and comprising establishing a reaction medium containing water, said strong protonic acid and an amount of levulinic acid serving as the reaction solvent, and progressively introducing said furfuryl alcohol into such reaction medium. However, the only acids exemplified in the patent are hydrochloric and hydrobromic acids.

Additionally, synthesis of levulinate esters was not accomplished using this technique and would require an additional step. British Patent No. GB 1,283,185 discloses a process for the manufacture of levulinic acid comprising heating furfuryl alcohol in water with either hydrochloric or oxalic acid in the presence of a water soluble aliphatic ketone solvent. Synthesis of levulinate esters was not accomplished using this technique and would require an additional step.

Japanese Patent No. JP 0700058 IB discloses preparation of levulinic acid by heating furfuryl alcohol in a mixture OfH₂O and an organic acid (such as acetic acid) in the presence of a nonoxidizing inorganic acid (such as HCl). Synthesis of levulinate esters was not accomplished using this technique and would require an additional step.

US Patent No. 2,763,665 describes a process for the manufacture of levulinate esters, which involves the slow addition of furfuryl alcohol with a second alcohol at a temperature within the range of 64⁰C - 220⁰C under substantially anhydrous conditions in the presence hydrogen chloride or hydrogen bromide. In order to reach appreciable yield, the method requires controlling the addition rate of furfuryl alcohol such that at no time is the amount of unreacted furfuryl alcohol present in the reaction mixture greater than 2 vol% of the volume of the second alcohol. In order to maintain the desired level of furfuryl alcohol in the reaction mixture, an excess of at least 4 moles of the second alcohol per mole of furfuryl alcohol is employed. The excess alcohol must then be distilled from the reaction mixture.

US Patent No. 3,203,964 discloses a process for the manufacture of levulinate esters that is purported to be an improvement over the method US Patent No. 2,763,665 (described above). The improvement consists in carrying out the prior process in the presence of water, with the amount of water employed being more than about 0.5 percent and not substantially in excess of about 4 percent by weight of said second alcohol. The presence of water serves to avoid the formation of alkyl chlorides that otherwise form from the second alcohol when employing the anhydrous methods of US Patent No. 2,763,665. In that prior work, a significant loss of catalytic activity is lost due to the conversion of second alcohol to alkyl halide. The alkyl halide cannot be recycled in a future reaction according to the method of the invention.

US Patent No. 4,236,021 discloses a process for the purification of levulinate ester manufactured via reaction of furfuryl alcohol with an unsubstituted primary or secondary aliphatic or cycloaliphatic alcohol in the presence of a strong acid catalyst. The crude levulinate ester was collected by vacuum distillation from the admixture with at least 3 percent by volume, based on the levulinate ester, of a high-boiling solvent that (a) has a boiling point of at least 2O⁰C higher than the boiling point of the levulinate ester, (b) dissolves the by-product polymer tar and (c) is miscible with the levulinate ester. Such solvents include triacetin, dimethyl phthalate, di-n-butyl phthalate, and diethyl phthalate.

US Patent No. 7,265,239 discloses a process for the conversion of furfuryl alcohol to levulinic acid or a levulinate ester comprising contacting furfuryl alcohol and water or an alkanol with a porous heterogeneous catalyst comprising strong acid ion-exchange resin, wherein the catalyst has pores with an average pore diameter in the range of from 1 to 1000 nm.

Russian Patent No. RU 2319690 discloses a process for manufacture of levulinate esters by reacting furfuryl alcohol with aliphatic alcohols in the presence of iron acetylacetonate [Fe(acac)s] as a catalyst in carbon tetrachloride, a toxic chlorinated solvent. The components of the reaction [Fe(acac)s] : [furfuryl alcohol] :

[aliphatic alcohol] : [CCl₄] are present in a molar ratio of 1 :(50-200):(100-400):(100- 400), respectively, and the reaction is allowed to proceed for 2-5 h at the boiling point of the alcohol. Yields of levulinate esters of 80-98% are disclosed.

There is a need in the industry to provide a method of making levulinate esters from furfuryl alcohol that provides for high yield in a one-step synthesis. There is a need in the industry to provide a method of making levulinate esters from furfuryl alcohol that does not result in precipitation of tarry residues from the reaction mixture during the reaction, thereby providing for ease of synthesis and suitability for continuous methodology. There is a need in the industry to provide a method of making levulinate esters from furfuryl alcohol that avoids the use of protic acid catalysts, such as hydrochloric acid, that are corrosive to stainless steel, thereby avoiding undue costs associated with specialized equipment. There is a need in the industry to provide a method of making levulinate esters from furfuryl alcohol that utilize non-volatile protic acid catalysts, such as hydrochloric acid, for safety purposes and avoidance of corrosion due to vapor-phase acid. There is a need in the industry to provide a method of making levulinate esters from furfuryl alcohol that neither requires nor forms toxic materials such as chlorinated compounds. There is a need in the industry to provide a method of making levulinate esters from furfuryl alcohol that requires no large excesses of reagents, thereby obviating recycling and avoiding side product formation. There is a need in the industry to provide a method of making levulinate esters from furfuryl alcohol that does not require application of pressure to the reaction mixture in order to realize the above benefits. There is a need in the industry to provide a method of making levulinate esters from furfuryl alcohol that provides an industrially viable pathway to a continuous process.

SUMMARY OF THE INVENTION

The present invention discloses several embodiments of a method for synthesis of levulinate esters, including ethyl levulinate, from furfuryl alcohol in a one step process.

The methods results in high yield of the target levulinate ester. The reaction is carried out using the final product alkyl levulinate as the solvent in the reactor vessel. The reaction may be carried out using non-volatile protic acids such as sulfuric acid. The reaction may also be carried out at atmospheric pressure. The reaction may be carried out in batch or continuous mode. Purification of the levulinate ester from the reaction vessel may also be carried out in batch or continuous mode. Purification does not require any special treatment of tarry residues in order to collect the product alkyl levulinate from crude reacted mixtures, because all byproduct residues, including tarry residues, remain suspended in crude reaction mixtures. In most embodiments, the crude reaction mixtures appear to be completely homogeneous solutions. Reaction byproducts tend to remain flowing and workable even when concentrated to remove all or nearly all volatile reaction products therefrom. Thus, the methods of the invention provide for ease of synthesis and suitability for continuous methodology. The methods of the invention do not require the use of hydrochloric acid, thereby avoiding undue costs associated with specialized equipment and glass or another non-stainless steel reaction vessel, and providing for better safety and avoidance of corrosion of equipment outside the reaction vessel due to vapor-phase acid. The methods of the invention neither require nor form toxic materials such as chlorinated compounds. The methods of the invention do not require large molar excesses of reagents, and thereby obviate the need to recycle large amounts of unused reagents and further avoiding deleterious side product formation. The methods of the invention do not require application of pressure to the reaction mixture in order to realize the above benefits. The methods of the invention provide an industrially viable pathway to a continuous process.

DETAILED DESCRIPTION OF THE INVENTION The reaction according to the present invention is used to produce esters of levulinic acid (4-oxopentanoic acid) in a single reaction vessel, from furfuryl alcohol and an alkanol in the presence of an acid catalyst and the product alkyl levulinate as a solvent. For example, in production of ethyl levulinate from furfuryl alcohol and ethanol, a mixture of furfuryl alcohol and ethanol is added gradually to a mixture of ethyl levulinate, ethanol and sulfuric acid in a reaction vessel. The reaction is allowed to proceed to completion and the final product is obtained by purification of the ethyl levulinate from the other reaction constituents as well as any unwanted reaction byproducts, such as tarry residues. In some embodiments, methyl levulinate, n-propyl levulinate, isopropyl levulinate, or n-butyl levulinate are made according to the methods of the invention using methanol, n-propanol, isopropanol, n-butanol, and isobutanol, respectively, as alkanols. In some embodiments, alkanols having between 1 and 4 carbons are employed using the methods of the invention. In other embodiments, alkanols having more than 4 carbon atoms are employed in the methods of the invention.

The reaction is catalyzed by a protic acid. In embodiments, the reaction is catalyzed by a strong protic acid. "Strong protic acids" are defined, for the purposes of the invention, as protonated acids having a dissociation constant, or K_a, value of at least about 55 at 25°C/1 atm pressure. Examples of suitable strong protic acid catalysts include hydrochloric acid, hydrobromic acid, hydriodic acid, sulfuric acid, pyrosulfuric acid, perchloric acid, a phenylsulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, p-toluenesulfonic acid, 1-napthalenesulfonic acid, 2- napthalene sulfonic acid, chlorosulfonic acid, fluorosulfonic acid, and the like. In embodiments, sulfuric acid is employed as the protic acid catalyst. In other embodiments, an alkyl-aromatic sulfonic acid, an aromatic sulfonic acid, or an aliphatic sulfonic acid is employed as the protic acid catalyst. In some embodiments, the reaction is catalyzed by a weak protic acid. "Weak protic acids" are defined as protonated acids having a K₃ value of less than 55. Some examples of useful weak protic acids include phosphoric acid, pyrophosphoric acid, polyphosphoric acid, sulfamic acid, alkali metal salts of sulfuric acid such as sodium hydrogen sulfate or potassium hydrogen sulfate, chloric acid, bromic acid, perbromic acid, iodic acid, and periodic acid. While many conventional methods employ hydrochloric acid, sulfuric acid offers the advantage of being relatively noncorrosive to stainless steel reaction vessels, obviating the need for employing glass-lined vessels or more exotic metal materials of construction in order to carry out the reaction using the methods of the invention.

In some embodiments, the protic acid catalyst is incorporated into, or onto, or covalently bound to, a solid support material. Resin beads, membranes, porous carbon particles, zeolite materials, and other solid support materials may be functionalized with protic acid moieties that are, in embodiments, covalently bound or strongly sorbed to one or more surfaces of the solid support. In a nonlimiting example, strong cation exchange resins, such as protonated sulfonate functional crosslinked polystyrene resins, are employed to catalyze the reaction employing the method of the invention.

In employing the method of the reaction, a first mixture is charged to a reactor vessel and a second mixture is gradually added to the first mixture to facilitate the reaction. The first mixture contains alkyl levulinate, an alkanol corresponding to the ester moiety of the alkyl levulinate, the acid catalyst, and optionally a small amount of water. The second mixture contains furfuryl alcohol and an additional amount of the alkanol corresponding to the ester moiety of the alkyl levulinate.

In embodiments, the first mixture is obtained by mixing a molar ratio of alkanol to alkyl levulinate of about 1 :20 to 1 :1, about 1 :8 to 1 :2, or about 1 :6 to 1 :3. In the case of ethyl levulinate and ethanol, this ratio results in volume of ethanol of less than 5% to about 30% of the volume of the first mixture. In embodiments, the first mixture also contains the protic acid catalyst. In embodiments where sulfuric acid is employed as the protic acid catalyst, about IxIO^"4 to 2.5xlO^~2 moles, or in some embodiments about 2.5xlO^"3 to 2.5xlO^~2 moles, or in still other embodiments about 1x10 ² to 2x10 ² moles of sulfuric acid is added to the first mixture per mole of furfuryl alcohol provided in the second mixture. In some embodiments of the methods of the invention, a minor amount of water is added to the first mixture. In embodiments where water is added to the first mixture, about 1x10 ⁴ to 0.2 moles of water is added per mole of furfuryl alcohol provided in the second mixture, or about lxl O ³ to 0.1 moles of water is added per mole of furfuryl alcohol provided in the second mixture, or about lxl O ³ to 5x10 ² moles of water is added per mole of furfuryl alcohol provided in the second mixture. Even where no water is added to the reaction mixture, water is formed, in some embodiments, via the self-condensation of furfuryl alcohol or other side reactions such as Aldol condensation. In some embodiments where water is added or formed in the reaction mixture, a minor amount of levulinic acid is then formed by the reaction of furfuryl alcohol with water.

In embodiments, the second mixture is prepared by mixing furfuryl alcohol and an alkanol, in embodiments the same alkanol as employed in the first mixture, in a molar ratio of about 1 : 1.12 to 1 : 1.75 moles of furfuryl alcohol to moles of alkanol, in other embodiments about 1 : 1.20 to 1 :1.50 moles of furfuryl alcohol to moles of alkanol. In some embodiments, the number of moles of alkanol in the second mixture is selected according to the formula

D =(1+(B/A))*C

where A = moles of alkyl levulinate

B = moles of alkanol in first mixture

C = moles of furfuryl alcohol

D = moles of alkanol in second mixture.

In other embodiments, the number of moles of alkanol in the second mixture is selected to be between about (0.9D) to (D), where D is as defined above.

In embodiments, the mole ratio of reagents calculated as described above results in a homogeneous reaction mixture when the second mixture is added to the first, without, for example, precipitation of tarry residue. The mole ratio of reagents calculated as described above, in embodiments, results in a stable temperature profile when the second mixture is added gradually to the first mixture, the stable temperature profile being characterized by the lack of a sudden exotherm during the addition. The mole ratio of reagents calculated as described above results in a constant composition of the reaction mixture, that is, the mole ratio of alkanol to alkyl levulinate remains substantially within the above specified range of B/ A over the course of addition.

In embodiments such as those described above, the first mixture is heated to a target temperature prior to the addition of the second mixture. In embodiments, the target temperature is maintained during the addition of the second mixture. We have found that the target reaction temperature is, in embodiments, a higher temperature than the boiling point of the free alkanol at atmospheric pressure. The alkanol and the alkyl levulinate form a binary mixture that has a boiling point that is higher than the alkanol. This in turn allows for the unexpected benefit of higher processing target temperatures, resulting in a faster rate of reaction to form the desired alkyl levulinate.

In embodiments, the target temperature of the reaction mixture is at least about 2O⁰C higher, or at least about 4O⁰C higher, than the boiling point of the free alkanol. For example, in embodiments where ethyl levulinate is the product, the reaction is carried out at a temperature between about 95-160⁰C, or between about 110-140⁰C for production of ethyl levulinate. In some embodiments, the first mixture is heated to the temperature corresponding to the target temperature of the reaction mixture prior to addition of the second mixture.

We have found that it is preferable to maintain a reaction temperature that does not result in the vigorous reflux of the reagents during addition or during the subsequent reaction. The optimum yield of alkyl levulinate is realized, and formation of insoluble tarry materials is minimized, when the temperature is maintained for the duration of the reaction at very slightly below, to about 5⁰C below the temperature where vigorous boiling is observed. An unexpected advantage of the method of the invention is that, as noted above, the mixture of alkanol and its corresponding alkyl levulinate has a boiling point substantially higher than that of the free alkanol. This in turn enables the realization of substantially higher processing temperatures at ambient pressure when reacting alkanols having 4 or less carbons than what is available by employing conventional techniques such as, for example, addition of a high boiling solvent to the reaction mixture, or addition of pressure to the vessel. Further, in embodiments, the ratio of alkyl levulinate to alkanol employed in the reaction is selected to provide the desired reaction temperature that does not result in vigorous boiling. Addition of water to the mixture of alkanol and alkyl levulinate, where a homogeneous solution is formed, also affects the boiling point of the blend. For example, the following blends of ethanol to ethyl levulinate (with water optionally included) result in the observed boiling points (see Example 1 for experimental procedure used to measure these boiling point values): Ethanol : Ethyl Levulinate, Boiling Point of mixture, volrvol ⁰C

0.05 : 1 154.2

0.10 1 128.8

0.15 1 115.8

0.20 1 108.1

0.20 : 1 104.3 with 0.01 vol equiv. H₂O

Notably, to achieve the optimum overall yield and rate of reaction, the ratio of alkanol to alkyl levulinate should also be selected in conjunction with the ratios and calculations of reagents noted above. The second mixture is added gradually over period of time to a preheated vigorously stirred receiving solution. In some embodiments, the gradual addition of the second mixture is in the form of a divided stream of the second mixture. In some such embodiments, the divided stream is a dropwise addition. In other embodiments, the divided stream is a fine mist or spray of droplets, wherein the droplets have average droplet sizes ranging from 1 mm to submicron particle diameter. In embodiments the size of the droplet is selected to provide maximum rate of addition balanced against efficiency of mixing of the first and second mixtures. In some embodiments, the rate of addition of the second mixture to the first mixture is about 1 to 5 mole percent of furfuryl alcohol per minute based on moles of alkanol in the first mixture. In embodiments, the rapid formation of a homogeneous solution of the first and second mixtures minimizes yield loss due to tarry residue formation. For example, in some embodiments, a reaction vessel is equipped with multiple orifices or nozzles for addition of the second mixture to provide for dropwise or mist addition rather than a stream. In another example, in some embodiments, the second mixture is added to the first mixture via one or more apertures or nozzles that are not in contact with the first mixture. In such embodiments, any tarry residue that does form in the reaction mixture does not interfere with the introduction of reagents into the reaction vessel i.e. at the location point of introduction of the second mixture to the first mixture. In embodiments, the reaction mixture is reacted at ambient pressure. In embodiments, surprisingly high yields of alkyl levulinate are realized employing the methods of the invention at ambient pressure. The ability to employ ambient pressure and realize high yields is an advantageous feature of the methods of the invention for both laboratory and industrial scale processes, and for both batch and continuous reaction schemes. However, the reaction is not limited to ambient pressure conditions. In some embodiments pressure is applied to the reaction vessel in order, for example, to raise the achievable reaction temperature and thereby increase the rate of reaction. For example, in some embodiments, a pressure between atmospheric pressure and about 1 atm (1.03 kg/cm²) above atmospheric pressure is applied. In other embodiments, a pressure of about 1 atm (1.03 kg/cm²) to 10 atm (10.33 kg/cm²) above atmospheric pressure is applied. In still other embodiments, a pressure of about 10 atm (10.33 kg/cm²) to 50 atm (51.66 kg/cm²) above atmospheric pressure is applied. The reaction conditions are not limited as to the amount of pressure applied to the reaction vessel; thus, the pressure used in conjunction with the methods of the invention are selected, in various embodiments, to enable optimization of reaction parameters such as rate of addition of reagents, rate of reaction, temperature achievable, throughput of reagents or products, minimization of one or more side reactions such as tar formation, or ability to reach a targeted ratio of reagents.

At the end of a reaction according to one or more methods of the invention, and prior to purification of the reaction products thereof, a crude reacted mixture contains at least about 70 mole percent yield of alkyl levulinate based on furfuryl alcohol. In some embodiments, a crude reacted mixture contains at least about 80 mole percent of alkyl levulinate based on furfuryl alcohol. In some embodiments, the crude reacted mixture contains up to about 85 mole percent yield of alkyl levulinate based on furfuryl alcohol. In some embodiments, the crude reacted mixture contains up to about 90 mole percent yield of alkyl levulinate based on furfuryl alcohol. In some embodiments, the crude reacted mixture contains up to about 70 mole percent yield of total levulinates (i.e. alkyl levulinate plus levulinic acid) based on furfuryl alcohol. In some embodiments, the crude reacted mixture contains up to about 80 mole percent yield of total levulinates (i.e. alkyl levulinate plus levulinic acid) based on furfuryl alcohol. In some embodiments, the crude reacted mixture contains up to about 85 mole percent yield of total levulinates (i.e. alkyl levulinate plus levulinic acid) based on furfuryl alcohol. In some embodiments, the crude reacted mixture contains up to about 90 mole percent yield of total levulinates (i.e. alkyl levulinate plus levulinic acid) based on furfuryl alcohol. In some embodiments, the crude reacted mixture contains up to about 95 mole percent yield of total levulinates (i.e. alkyl levulinate plus levulinic acid) based on furfuryl alcohol. In some embodiments, soluble materials in the crude reacted mixture contain no furfuryl alcohol, only alkanol, levulinic acid, and alkyl levulinate as determined by analytical methods such as proton NMR, HPLC, or GC. In some embodiments, the crude reaction mixture includes angelicalactone. In some such embodiments, about 1% angelicalactone is observed by GC-MS. In embodiments, an observable byproduct of the reaction is a tarry residue, which is, in embodiments, about 20% or less by weight of furfuryl alcohol added. In some embodiments the tarry residue is 10% or less by weight of furfuryl alcohol added. In some embodiments the tarry residue is 5% or less by weight of furfuryl alcohol added. The content of the tarry residue is measured by evaporating alkanol and alkyl levulinate and weighing the remaining materials or an aliquot thereof from the reaction vessel.

In some embodiments, the reaction is allowed to proceed to completion in a batch process. In other embodiments, the reaction is carried out in a continuous process. In some embodiments, a continuous process is preferred in an industrial setting. In some such embodiments, one or more aliquots of the reaction mixture are removed periodically during the reacting, or a volume percent of the reaction mixture is removed continuously during the process of adding the second mixture to the reaction vessel, in between additions of the second mixture, or both. In embodiments where some of the reaction mixture is removed from the reaction vessel, additional amounts of alkyl levulinate, alkanol, and catalyst may be added to the reaction vessel to facilitate the continuous progress of the reaction. In such embodiments, it is preferable to adjust the rate of removal and the rate of addition to provide an approximately constant temperature profile and ratio of reagents to reaction products. For example, in some embodiments where the reaction is carried out in a continuous process, additional protic acid catalyst is added to the reaction vessel during the continuous feed of the second mixture to the first mixture, in order to compensate for the dilution of the protic acid catalyst concentration in the reaction mixture due to the gradual addition of the second mixture to the first mixture wherein the first mixture contains the original aliquot of protic acid catalyst. Preferably, in such embodiments, the additional protic acid catalyst is introduced using a separate aperture or nozzle from the aperture or nozzle employed to introduce the second mixture to the reaction vessel.

In embodiments, the methods of the invention lead to surprisingly low amounts of tarry residue formation. Formation and precipitation or solidification of tarry residue is a drawback of previously known methods of making levulinic acid and levulinate esters from furfuryl alcohol. Precipitation or solidification of the tarry residue hinders the utility of these syntheses in continuous processes, as reactor and purification systems quickly become fouled, thereby lowering the effective yield of the desired levulinate and raising the production costs thereof. In contrast to conventional methods, reactions employing the methods of the invention are characterized by a surprising and substantial lack of tarry residue precipitation or solidification within the reaction vessel. Thus, the methods of the invention provide a distinct advantage over previously known methods. In embodiments, processes employing the methods of the invention lead to less than 10 weight percent of tarry residue based on furfuryl alcohol. In other embodiments, processes employing the methods of the invention lead to about 5 weight percent or less of tarry residue based on furfuryl alcohol. In some embodiments, the tarry residue thus formed remains completely dissolved or suspended during the reaction and does not precipitate or solidify in the reaction mixture or the crude reacted mixture. In embodiments where the tarry residue remains suspended or dispersed in the crude reacted mixture, the methods of the invention are well suited for continuous processes, wherein precipitation or solidification of tarry residue would otherwise foul the reactor apparatus. Without wishing to be limited by statements of theory, we believe that the presence of alkyl levulinate as the solvent helps prevent tarry residue formation by maintaining solubility of the reagents; we further believe that the ratio of reagents in conjunction with the temperature of the reaction mixture provides a high rate of reaction of alkyl levulinate that in turn precludes the slower reactions that are responsible for tar formation.

In some embodiments, conversion of furfuryl alcohol to alkyl levulinate is substantially complete upon completion of addition of the second mixture to the first mixture. In other embodiments it is advantageous to continue heating and stirring after completion of addition of the second mixture to the first mixture. In a batch type process, conversion to alkyl levulinate is accomplished, in embodiments, in about 1 to

120 minutes, or about 60 minutes, or about 30 minutes, after completion of addition of the second mixture to the first mixture.

Levulinic acid ester final products may be recovered from the reaction mixture by methods known in the art, including distillation. Distillation of alkyl levulinate preferably is vacuum distillation, falling film distillation, wiped film distillation, or any other conventional technique commonly employed by those of skill in the art. In some embodiments, excess alkanol may be stripped from the reaction mixture by a known method and recycled prior to distillation of the alkyl levulinate. Prior to purification of alkyl levulinate, it may be desirable to neutralize the protic acid present in the reaction mixture. Neutralization is accomplished by addition of an amount of a neutralization agent to the reaction mixture in an amount sufficient to neutralize the protic acid catalyst. Alkali and alkali earth metal hydroxides, carbonates, hydrocarbonates, phosphates, tertiary amines, or carboxylates are examples of suitable neutralizing agents to neutralize the protic acid catalyst present in the reaction mixture. Buffers such as disodium hydrogen phosphate and calcium oxide are useful in some embodiments. Metal oxide neutralizing agents, such as basic alumina, further provide the feature of being insoluble in the reaction mixture and therefore easily separated from the reaction mixture after neutralization, for example by filtration, decanting, or sedimentation.

Because of the processing advantages realized by using the methods of the invention, continuous reactor designs for carrying out the methods of the invention are not particularly limited in scope. Key processing advantages include, in some embodiments, high rate of conversion, high yield, no solvent recovery steps, low to no applied pressure required, low levels of tarry residue formation, lack of tarry residue precipitation, and tarry residue that remains flowable upon partial or complete evaporation of volatile final reaction products. In embodiments, these processing advantages lead to substantial flexibility in the reactor and purification means designs that are usefully employed in conjunction with the methods of the invention. In some embodiments, a combination of equipment features are combined to provide an optimized rate of reaction and yield of alkyl levulinate based on temperature, pressure, feed compositions, mixing, addition rates, acid levels, and water levels (if any) desired. Some non- limiting examples of possible components and combinations thereof include the following: 1. Highly agitated spray nozzle addition continuous stirred tank reactor, or

CSTR, or multiple CSTR reactors in series. 2. A CSTR reactor or reactors in series followed by plug flow reactor. 3. Recycled loop type reactor or reactors in series with static mixers or in-line mechanical mixers to give improved dilution and mixing at larger scale apparatus.

4. Recycled loop type reactor or reactors in series with an expansion tank internal to the loop or between the loops to allow non-condensible gas to be removed or to add residence time.

5. Recycled loop type reactor as in any of the embodiments described above, followed by plug flow reactor(s).

6. Reactive distillation with a recycled product stream and heterogeneous catalyst to combine separations and dilution into one step.

7. Reactive distillation with a recycled product stream and homogeneous catalyst to combine separations and dilution into one step.

8. Series of recycled loops or CSTRs as in any of the embodiments described above, with continuous source(s) of fresh feeds to each stage.

In some embodiments, a finishing reactor is employed to esterify any residual levulinic acid in the crude reacted mixture to the desired alkyl levulinate. Levulinic acid is formed in some embodiments of the methods of the invention where water is added to the reaction mixture or where water is formed as a side product, as is described above. After being subjected to esterifϊcation in a finishing reactor, the reaction mixture is an esterified reacted mixture. Non- limiting examples of possible finishing reactors for either batch or continuous processes include the following:

1. A CSTR where excess alkanol is added, and water and alkanol are removed to advance the esterifϊcation. 2. Short tray distillation.

3. Reactive distillation wherein alkanol boils up from the bottom of a reactor, and contacts levulinic acid in the presence of a fixed bed of catalyst.

In some embodiments, neutralization of the acid catalyst in the crude reacted mixture or the esterified reacted mixture is carried out by employing a neutralizing agent, as is described above. In embodiments, either the reaction mixture or the esterified reacted mixture is neutralized to form a neutralized reacted mixture. Batch or continuous processing options that are useful in some embodiments to carry out the neutralization include the following: 1. Heterogeneous neutralization bed having a solid neutralizing agent, such as disodium hydrogen phosphate or calcium oxide, followed by a filter through which the reaction mixture passes before leaving the bed.

2. Addition of one or more solid neutralizing agents that are soluble in the reaction mixture to a back-mixed tank, followed by a filter to remove solids.

3. Addition of one or more liquid tertiary amines to a back-mixed tank, followed by a filter to remove solids.

4. Addition of one or more water soluble neutralizing agent, such as sodium hydroxide, to a back-mixed tank followed by a filtration or centrifugation to remove the solids or aqueous components.

In embodiments, the crude reacted mixture, esterifϊed reacted mixture, or neutralized reacted mixture contains excess alkanol, tarry residue, and the product alkyl levulinate. In some embodiments it is desirable to purify the product alkyl levulinate by removing excess alkanol, tarry residue, or both from the crude reacted mixture, esterifϊed reacted mixture, or neutralized reacted mixture. In some embodiments purification is accomplished by carrying out vacuum distillation of the crude reacted mixture, esterifϊed reacted mixture, or neutralized reacted mixture. Useful vacuum distillation apparatus includes, in embodiments, a system including a column, reboiler, condenser, and reflux path. In some embodiments a two-column design is suitably used to carry out distillation, wherein the first column runs at higher pressure to boil off some percentage of residual alkanol and the second column runs at lower pressure to remove the remaining alkanol. In some embodiments, slurry type designs or mechanical type reboilers such as a wiped film evaporator (WFE) are used to isolate the alkyl levulinate product.

In some embodiments, purification of the crude reacted mixture, esterified reacted mixture, or neutralized reacted mixture is accomplished in more than one step, in embodiments the more than one step is two steps. In some such embodiments, a first step includes evaporation of a major portion of the alkanol, resulting in a stripped reacted mixture containing principally the alkyl levulinate and tarry residue. In some such embodiments, the tarry residue remains suspended in the stripped reacted mixture. A second step includes evaporation of a portion of the alkyl levulinate from the stripped reacted mixture to yield a significant amount, for example 50 wt%, of the alkyl levulinate produced in the reaction as a purified product. In some embodiments of the reaction where simple vacuum distillation is employed to isolate the alkyl levulinate product from the stripped reacted mixture, 50 wt% to 75 wt% of the alkyl levulinate is isolated as a purified product; in other embodiments, 75 wt% to 90 wt% of the alkyl levulinate is isolated as a purified product; in other embodiments, 90 wt% to 99 wt% of the alkyl levulinate is isolated as a purified product. It is an unexpected feature of the invention that in some embodiments, the tarry residue remaining in a stripped reacted mixture is flowable and processable even as more than 50 wt% of alkyl levulinate formed is isolated and increasing weight fraction of the remaining reacted mixture is composed of the tarry residue. Where the tarry residue remains flowable, mechanically assisted evaporation techniques, such as wiped film evaporation or falling film evaporation are employed in some embodiments because they are more efficient than simple evaporation techniques for isolation of alkyl levulinate. In some such embodiments isolation of the alkyl levulinate is accomplished in two steps. The first step isolates a major portion of alkyl levulinate from the stripped reacted mixture to leave a flowable tarry residue in high solids reacted mixture. Then a second step employs a distillation apparatus that is a reboiler or evaporator designed to manage the high solids reacted mixture. In some embodiments, WFE, falling film evaporation, spray drying, high-solids managing type reboilers such as

Reactotherm®, Reasol®, Reavisc®, or Reacom® equipment sold by Buss-SMS- Canzler GmbH of Butzbach, Germany, a spray dryer, or other solids drying equipment are used as the second distillation apparatus. The second reboiler/evaporator device could also send the vapor directly to the first distillation apparatus employed in the first step; that is, two reboilers may feed the same column such that the material vaporized in the second reboiler is sent back to the first reboiler.

However, in some embodiments of the methods of the invention, further attempts to separate more than about 50 wt% the alkyl levulinate from the stripped crude product mixture by evaporation techniques as described above are problematic due to the increasing weight fraction of tarry residue, which forms a highly viscous or even solidified mass that is not suitable for the purification methods described above. In some such embodiments, it is desirable to form a plasticized tarry residue: that is, to add one or more compounds to the tarry residue that prevent solidification and/or ensure that the residue remains flowable to enable effective isolation of substantial portion of alkyl levulinate via the evaporation techniques described above. In some such embodiments, we have found that addition of biodiesel fuel to the crude reacted mixture, esterified reacted mixture, neutralized reacted mixture, or stripped reacted mixture forms a plasticized, flowable tarry residue that does not solidify during evaporation. Since the tarry residues themselves are useful for burning, i.e. for fuel value, the addition of biodiesel supplements the utility of the plasticized tarry residue remains intact, or is even increased, after substantially all alkyl levulinate is isolated. In some embodiments, the tarry residue plasticizer is 2,2,4-trimethyl-l,3-pentane-diol diisobutyrate, tridecylalcohol, a dialkyl phthalate wherein the alkyl groups independently have between 4 and 14 carbons, a dialkyl adipate wherein the alkyl groups independently have between 4 and 14 carbons, a dialkyl sebacate wherein the alkyl groups independently have between 4 and 14 carbons, a monobenzoate wherein the alkyl group has between 4 and 14 carbons, a dialkylcyclohexanoate wherein the alkyl groups independently have between 4 and 14 carbons, a trialkyl trimellitate wherein the alkyl groups independently have between 4 and 14 carbons, a trialkyl citrate wherein the alkyl groups independently have between 4 and 14 carbons, or a combination of any of these compounds. In some embodiments, the tarry residue plasticizer is substantially inert under the reaction conditions and has a higher boiling point than the alkyl levulinate, such that the tarry residue plasticizer is employed to plasticize the tarry residue during evaporation of the alkyl levulinate; the tarry residue plasticizer is then evaporated in some such embodiments to leave a solidified tarry residue, or may be burned for fuel value. In some embodiments, a minor amount of tetrahydrofurfuryl alcohol (THFA) is added to the second mixture (the mixture containing furfuryl alcohol starting material) prior to the reaction. THFA is capable, in embodiments, of reacting with furfuryl alcohol to form tetrahydrofurfuryl levulinate, which in some embodiments is a good plasticizer for the tarry residues, has low vapor pressure, and in some embodiments is burned along with the tarry residues for fuel value.

In other such embodiments, liquid/liquid extraction is employed to separate some or all of the alkyl levulinate formed in the reaction from the tarry residue.

Nonlimiting examples of solvents that are useful in extracting alkyl levulinate from tarry residues include linear, branched, or cyclic aliphatic or aromatic hydrocarbons such as hexane, toluene, and the like; petroleum ether, ethyl acetate, and biodiesel fuels. In embodiments, the invention is a process for the synthesis of alkyl levulinate, the process comprising: a. contacting a first mixture comprising i. an alkanol, ii. a protic acid catalyst, and iii. an alkyl levulinate wherein the alkyl group is the same as the alkyl group of the alkanol; with a second mixture to form a reaction mixture, the second mixture comprising i. furfuryl alcohol, and ii. an additional amount of the alkanol of the first mixture; and b. forming the alkyl levulinate in the reaction mixture wherein the alkyl group is the same as the alkyl group of the alkanol.

In embodiments, the alkyl levulinate is formed at elevated temperature. In embodiments, the second mixture is contacted with the first mixture, the first mixture maintained at an elevated temperature. In embodiments, the alkanol is methanol, ethanol, n-propanol, isopropanol, n-butanol, or isobutanol. In embodiments, the molar ratio of alkanol to alkyl levulinate in the first mixture is about 1 :20 to 1 : 1. In embodiments, the molar ratio of alkanol to alkyl levulinate in the first mixture is about 1 :8 to 1 :2. In embodiments, the molar ratio of alkanol to alkyl levulinate in the first mixture is about 1 :6 to 1 :3. In embodiments, the protic acid catalyst is sulfuric acid, a cation exchange resin comprising sulfonic acid groups, an alkyl-aromatic sulfonic acid, an aromatic sulfonic acid, or an aliphatic sulfonic acid. In embodiments, about IxIO^"4 to 2.5xlO^~2 moles of sulfuric acid is added to the first mixture per mole of furfuryl alcohol provided in the second mixture. In embodiments, about 2.5xlO^~3 to 2.5xlO^~2 moles of sulfuric acid is added to the first mixture per mole of furfuryl alcohol provided in the second mixture. In embodiments, about 1x10 ² to 2x10 ² moles of sulfuric acid is added to the first mixture based on moles of furfuryl alcohol provided in the second mixture. In embodiments, the invention further comprises adding water to the first mixture. In some such embodiments, about IxIO^"4 to 0.2 moles of water is added based on moles of furfuryl alcohol provided in the second mixture. In some such embodiments, about 1x10 ³ to 0.1 moles of water is added based on moles of furfuryl alcohol provided in the second mixture. In some such embodiments, about 1x10 ³ to 5x10 ² moles of water is added based on moles of furfuryl alcohol provided in the second mixture. In embodiments, the second mixture comprises a mole ratio of furfuryl alcohol to moles of alkanol of about 1 to 2. In embodiments, the second mixture comprises a mole ratio of furfuryl alcohol to moles of alkanol of about 1 :1.125 to 1 :1.75. In embodiments, the second mixture comprises a mole ratio of furfuryl alcohol to moles of alkanol of about 1 : 1.20 to 1 : 1.50. In embodiments, the reacting comprises heating and stirring. In some such embodiments, the alkanol is ethanol and heating comprises heating to a temperature of about 95⁰C to 16O⁰C. In embodiments, the process further comprises heating the first mixture prior to the contacting. In some such embodiments, the heating comprises raising the temperature above the boiling temperature of the alkanol. In some such embodiments, the temperature of the temperature is at least about 2O⁰C higher than the boiling point of the alkanol. In some such embodiments, the temperature is at least about 4O⁰C higher than the boiling point of the alkanol. In some such embodiments, the process is a batch process and heating is continued for about 1 to 60 minutes after addition of the second mixture to the first mixture is completed. In some such embodiments, the process is a batch process and heating is continued for about 30 minutes after addition of the second mixture to the first mixture is completed. In some embodiments, the number of moles of alkanol in the second mixture is selected according to the formula

D =(1+(B/A))*C wherein

A denotes moles of alkyl levulinate; B denotes moles of alkanol in the first mixture; C denotes moles of furfuryl alcohol; and D denotes moles of alkanol in the second mixture.

In some such embodiments, the moles of alkanol in the second mixture is selected to be in the range of about (0.9)(D) to D. In embodiments, the contacting is at a rate of about 1 to 5 mole percent of furfuryl alcohol per minute based on moles of alkanol in the first mixture. In embodiments, the contacting comprises adding the second mixture to the first mixture via one or more nozzles or apertures that are not in contact with the first mixture.

In some such embodiments, the one or more nozzles or apertures are configured to add the second mixture as a divided stream comprising a mist or fine spray of droplets. In embodiments, the process is continuous. In embodiments, the reacting comprises applying pressure. In embodiments, the applied pressure is up to about 1 atm above ambient pressure. In embodiments, the yield of alkyl levulinate after the reacting is at least about 70 mole percent based on moles of furfuryl alcohol provided in the second mixture. In embodiments, the process further comprises neutralizing the acid catalyst after the reacting. In some such embodiments, the neutralizing is accomplished by an alkali or alkali earth metal of a hydroxide, a carbonate, a hydrocarbonate, a phosphate, a tertiary amine, or a carboxylate. In embodiments, the process comprises collecting the alkyl levulinate formed. In some such embodiments, the collecting comprises evaporation of alkanol, distillation of the alkyl levulinate, decanting of soluble from insoluble reaction products, filtration of insoluble from soluble reaction products, liquid-liquid extraction, or a combination thereof. In some such embodiments, the distillation comprises applying a vacuum. In some such embodiments, the distillation comprises wiped film evaporation or falling film evaporation. In some such embodiments, the collecting is accomplished in two steps, wherein a first step comprises evaporation of alkanol and a second step comprises evaporation of alkyl levulinate; alternatively, a first step comprises evaporation of alkanol and a first portion of the alkyl levulinate, and a second step comprises removal of a second portion of alkyl levulinate. In some such embodiments, the process further comprises adding a tarry residue plasticizer to the reaction mixture between the first step and the second step. In some such embodiments, the tarry residue plasticizer is a biodiesel fuel, 2,2,4-trimethyl-l,3- pentane-diol diisobutyrate, tridecylalcohol, a dialkyl phthalate wherein the alkyl groups independently have between 4 and 14 carbons, a dialkyl adipate wherein the alkyl groups independently have between 4 and 14 carbons, a dialkyl sebacate wherein the alkyl groups independently have between 4 and 14 carbons, a monobenzoate wherein the alkyl group has between 4 and 14 carbons, a dialkylcyclohexanoate wherein the alkyl groups independently have between 4 and 14 carbons, a trialkyl trimellitate wherein the alkyl groups independently have between 4 and 14 carbons, a trialkyl citrate wherein the alkyl groups independently have between 4 and 14 carbons, or a combination thereof. In embodiments, levulinic acid is a byproduct of the process, wherein the process further comprises esterifying the levulinic acid. In some such embodiments, the combined yield of alkyl levulinate and levulinic acid after the reacting is at least about 70 mole percent based on moles of furfuryl alcohol provided in the second mixture. In embodiments, greater than 75 wt% of the alkyl levulinate formed is collected as a purified product. In embodiments, greater than 90 wt% of the alkyl levulinate formed is collected as a purified product.

In embodiments, the process of the invention is a process for synthesis of alkyl levulinate, the process comprising: a. forming a first mixture comprising i. an alkanol, ii. sulfuric acid, and iii. an alkyl levulinate wherein the alkyl group is the same as the alkyl group of the alkanol; b. heating the first mixture to a temperature of at least about 2O⁰C higher than the boiling point of the alkanol; c. contacting the first mixture with a second mixture at ambient pressure to form a reaction mixture, the second mixture comprising i. furfuryl alcohol, and ii. an alkanol that is the alkanol from the first mixture, wherein the mole ratio of furfuryl alcohol to alkanol is about 1 : 1.125 to 1:1.75; d. reacting the reaction mixture at ambient pressure and at a temperature between about 95⁰C and 160⁰C to form alkyl levulinate wherein the alkyl group is the same as the alkyl group of the alkanol; and e. collecting the alkyl levulinate, wherein about 0.01 to 2 mole percent of sulfuric acid is added to the first mixture based on moles of furfuryl alcohol in the second mixture, and wherein the number of moles of alkanol in the second mixture is selected to be between 0.9D and D wherein

D is defined according to the formula

D =(1+(B/A))*C wherein

A denotes moles of alkyl levulinate, B denotes moles of alkanol in the first mixture,

C denotes moles of furfuryl alcohol, and D denotes moles of alkanol in the second mixture. In embodiments, the alkanol is methanol, ethanol, isopropanol, n-propanol, n-butanol, or isobutanol. In some such embodiments, the alkanol is ethanol. In some embodiments, the process further comprises neutralizing the sulfuric acid prior to the collecting.

EXPERIMENTAL

The following examples are illustrative of the invention.

Example 1

A 250 mL three-neck flask equipped with a magnetic stir bar, thermocouple, condenser, and rubber septum was charged with 100 mL ethyl levulinate (obtained from the Langfang Triple Well Chemicals Company, Ltd. of Langfang City, HeBei, China) and 5 mL ethanol (100%, obtained from Sigma-Aldrich, St. Louis, MO). The flask was heated to reflux with a heating mantle. The boiling point stabilized at 154.2 ⁰C within 25 minutes. At 10 minute intervals, three consecutive 5 mL aliquots of ethanol were added to the flask through the rubber septum using a syringe, and the boiling point was recorded. Finally, 1 mL of de-ionized water was added to the flask through the rubber septum. The boiling point was recorded after 10 minutes. Table 1 shows the recorded boiling points of the mixtures.

Table 1. Boiling points of ethanol/ethyl levulinate mixtures.

Example 2 A 500 mL three-neck flask was equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple. The flask was charged with 100.06g (0.694 mol) ethyl levulinate (obtained from the Langfang Triple Well Chemicals Company, Ltd. of Langfang City, HeBei, China) 11.48g (0.249mol) ethanol (99.5+%, obtained from Acros Organics of Geel, Belgium), and a sulfuric acid solution made by mixing 0.575 mL cone, sulfuric acid in 1.463 mL deionized water. The mixture was stirred and heated to reflux at 107.0⁰C in a 120⁰C oil bath. A mixture of 49.23g (0.497 mol) furfuryl alcohol (99%, obtained from Acros Organics) and 31.5Og (0.684 mol) ethanol was added to the reaction mixture dropwise over 108 minutes. The reaction was refluxed for additional 1 h after addition was completed. The reaction flask was taken out of the oil bath and allowed to cool to ambient temperature.

A sample of the crude reaction mixture was removed for analysis. The crude reaction product was dissolved in MTBE, which resulted in the precipitation of a small amount of tarry residue, and was subjected to GC-MS. A large peak was determined to be 98.9% ethyl levulinate; a small peak was determined to be angelicalactone. GC-MS did not detect the presence of ethanol due to its volatility.

A solution of sodium hydroxide, made by mixing 0.884g sodium hydroxide in 1 mL de-ionized water and 9 mL ethanol, was added to the reaction mixture with stirring. The mixture was distilled by vacuum distillation at 2-3 Torr to give a distilled reaction product. An undistillable residue of about 8.49g was left at the end of the distillation. The undistillable solid contained about 1.53g sodium sulfate and about 6.96 g. of a tarry residue. The amount of tarry residue was 14.1 weight percent based on the weight of furfuryl alcohol charged to the reaction. A GC-MS trace of the distilled reaction product resulted in the measurement of 99% ethyl levulinate as a percent of peak area.

Example 3

A 500 mL three-neck flask equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple was charged with 100.2 Ig (0.695mol) ethyl levulinate (obtained from the Langfang Triple Well Chemicals Company, Ltd. of Langfang City, HeBei, China), 7.6Og (0.165 mol) ethanol (99.5+%, obtained from Acros Organics of Geel, Belgium), and a sulfuric acid solution made by mixing 0.575 mL cone, sulfuric acid in 1.463 mL deionized water. The mixture was refluxed at 116.3°C in a 135°C oil bath. A mixture of 49.12g (0.496mol) furfuryl alcohol (99%, obtained from Acros Organics) and 28.72g (0.624 mol) ethanol was added to the reaction mixture dropwise over 115 minutes. The reaction was reflux for additional 1 h after addition was complete. Then the reaction flask was taken out of the oil bath and allowed to cool to room temperature. About 50.445 g of the reaction mixture was transferred to a 250 rnL flask and distilled using a Kugelrohr apparatus at about 7-10 Torr and an air bath temperature of up to 18O⁰C. After distillation, total amount of undistillable tarry solid left in the flask was 1.622 g, which contained sulfuric acid 0.290 g and tar 1.332 g. The amount of tar formed in the reaction to the amount of furfuryl alcohol added was 9.8% by weight.

GC-MS analysis of the crude reaction product was carried out as for Example 1 and showed that ethyl levulinate was present at 98.6%.

Comparative Example 4 A 500 mL three-neck flask equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple was charged with 62.24g (1.351mol) ethanol (200 proof, obtained from Acros Organics of Geel, Belgium), and a sulfuric acid solution made by mixing 0.575 mL cone, sulfuric acid in 1.463 mL deionized water. The mixture was refluxed at 76 ⁰C in a 100 ⁰C oil bath. About 49 mL of furfuryl alcohol (99%, obtained from Acros Organics) was added to the dropping funnel. An initial aliquot of about 2 mL furfuryl alcohol was added to the reaction mixture dropwise from the dropping funnel. During the addition, significant amount of solid tar was observed to build up in the flask. Due to the solid tar buildup, the remainder of the furfuryl alcohol from the dropping funnel could not be added. The reaction flask was taken out of the oil bath and allowed to cool to room temperature.

Example 5

The procedure of Example 1 was repeated with n-butyl levulinate (obtained from the Langfang Triple Well Chemicals Company, Ltd. of Langfang City, HeBei, China) and n-butanol (99.9%, obtained from the Sigma-Aldrich Company of St.

Louis, MO). Table 2 shows the recorded boiling points of the mixtures.

Table 2. Boiling points of n-butanol/n-butyl levulinate mixtures.

A 500 rnL three-neck flask equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple was charged with 100.04g (0.581mol) n- butyl levulinate (obtained from the Langfang Triple Well Chemicals Company, Ltd. of Langfang City, HeBei, China), 20.84g (0.281 mol) n-butanol (99.9%, obtained from the Sigma-Aldrich Company of St. Louis, MO), 1.463 mL deionized water, and 0.575 mL cone, sulfuric acid. The mixture was heated with a heating mantle to a temperature of 130⁰C. A mixture of 49.07g (0.495 mol) furfuryl alcohol (99%, obtained from Acros Organics of Geel, Belgium) and 55.0Og (0.742 mol) n-butanol was added to the reaction mixture dropwise over about 65 minutes. The reaction temperature was maintained at 130⁰C for additional 1 hour after addition was complete. Then the reaction flask was allowed to cool to room temperature. The crude reaction mixture appeared to be homogeneous, with no insoluble or phase- separated material observed. About 50.1O g of the reaction mixture was transferred to a 250 mL flask and distilled using a Kugelrohr apparatus at about 7-10 Torr and an air bath temperature of up to 181⁰C.

After distillation, total amount of undistillable solid left in the flask was 1.43 g, which contained 0.23 g sulfuric acid and 1.20 g of a tarry residue. The ratio of the amount of tarry residue to the amount of furfuryl alcohol added was measured to be 11.1 wt%. GC-MS analysis of the crude reaction product was carried out as for Example 2 and showed that n-butyl levulinate was present at 98.0% based on peak area.

Comparative Example 6

A 500 mL four-neck flask equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple was charged with 100.16g (1.35 lmol) n- butanol (redistilled from 99.4% n-butanol obtained from Acros Organics of Geel, Belgium), and a sulfuric acid solution made by mixing 0.575 mL cone, sulfuric acid in 1.463 mL deionized water. The mixture was refluxed at 95 ⁰C in a 120 ⁰C oil bath. 49.38g (0.498mol) furfuryl alcohol (99%, obtained from Acros Organics) was added to the reaction mixture dropwise over 110 minutes. During the addition, solid tarry material was observed to build up in the flask. The reaction was reflux for additional 1 h after addition was complete. Then the reaction flask was taken out of the oil bath and allowed to cool to room temperature. Total weight of the crude reaction mixture was 149.22 g. Total mass loss after the reaction was 2.84 g.

Example 7

A 2 L two-neck flask equipped with a magnetic stir bar, a Dean-Stark trap, and a thermocouple was charged with 232.52g (2.002mol) levulinic acid (obtained from the Langfang Triple Well Chemicals Company, Ltd. of Langfang City, HeBei, China), 241.52g (4.019 mol) n-propanol (>99.8%, obtained from the Sigma-Aldrich Company of St. Louis, MO), 600 mL toluene, and 2 mL cone, sulfuric acid. The reaction was heated on a heating mantle to reflux. After refluxing overnight, total amount of 42.7 mL of water was collected and removed from the Dean-Stark trap. The reaction flask was allowed to cool to room temperature. Then 100 g basic alumina (obtained from the Sigma-Aldrich Company of St. Louis, MO) was added to the reaction solution and stirred for about 80 minutes. The solids were then filtered off, and the filtrate was concentrated on a rotary evaporator with the filtrate in a flask immersed in an oil bath set to 75⁰C and 15 Torr vacuum to remove toluene and n- propanol. The residue was distilled on the rotary evaporator in a flask immersed in an oil bath set to 110°-120°C and 15 Torr vacuum to yield 284.48 g colorless liquid in the catch flask. The product was determined by GC-MS to be 99.51% n-propyl levulinate.

The procedure of Example 1 was used to generate a profile of boiling points using n-propanol and n-propyl levulinate. The measured boiling points are shown in Table 3.

Table 3. Boiling points of n-propanol/n-propyl levulinate mixtures. A 500 niL four-neck flask was equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple. The flask was charged with 100.02g (0.632mol) n-propyl levulinate (synthesized from levulinic acid as described above), 16.48g (0.274mol) n-propanol, 1.463 mL deionized water, and 0.575 mL cone, sulfuric acid. The mixture was heated with a heating mantle to a temperature at 120⁰C. A mixture of 49.07g (0.495mol) furfuryl alcohol (99%, obtained from Acros Organics of Geel, Belgium) and 43.06g (0.716 mol) n-propanol was added to the reaction mixture dropwise over about 117 minutes. The reaction was refluxed for additional 1 hour after addition was complete. Then the reaction flask was allowed to cool to room temperature. The crude reaction mixture appeared to be homogeneous, with no insoluble or phase-separated material observed. About 50.1O g of the reaction mixture was transferred to a 250 mL flask and distilled using a Kugelrohr apparatus at about 4-8 Torr and an air bath temperature of up to about 179⁰C.

After distillation, total amount of undistillable solid left in the flask was 1.16 g, which contained 0.25 g sulfuric acid and 0.91 g of a tarry residue. Ratio of the amount of tarry residue formed in the reaction to the amount of furfuryl alcohol added was 7.8%. GC-MS analysis of the crude reaction product was carried out as for Example 2 and showed that n-propyl levulinate was present at 99.1%.

Example 8

A 2 L three-neck flask equipped with a magnetic stir bar, a Dean-Stark trap, and a thermocouple was charged with 232.35g (2.00 lmol) levulinic acid (obtained from the Langfang Triple Well Chemicals Company, Ltd. of Langfang City, HeBei,

China), 310 mL (4.049 mol) isopropanol (obtained from Thermo Fisher Scientific of Waltham, MA), 600 mL toluene (obtained from Thermo Fisher Scientific), and 2 mL cone, sulfuric acid. The reaction was heated on a heating mantle to reflux. After refluxing overnight, about 31 mL of water was collected and removed from the Dean- Stark trap. The reaction flask was allowed to cool to room temperature. Then 100 g basic alumina (obtained from the Sigma- Aldrich Company of St. Louis, MO) was added to the reaction solution and stirred for 2 h. The solid was filtered off, then the filtrate was concentrated in a on a rotary evaporator by immersing the flask containing the filtrate in an oil bath set to a temperature of 70⁰C and applying a vacuum at 20 Torr to remove toluene and isopropanol. The residue was distilled on the rotary evaporator at an oil bath temperature of 100 ⁰C and 8-10 Torr vacuum to give 270.26 g colorless liquid in a catch flask. The product was determined by GC to be 99.98% isopropyl levulinate.

The procedure of Example 1 was used to generate a profile of boiling points using isopropanol and isopropyl levulinate. The measured boiling points are shown in Table 4. A 500 mL three-neck flask equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple was charged with 100.0 Ig (0.632mol) isopropyl levulinate, 16.08g (0.268 mol) isopropanol (certified, obtained from Thermo Fisher

Table 4. Boiling points of isopropanol/isopropyl levulinate mixtures.

Scientific of Waltham, MA), 1.463 mL deionized water, and 0.575 mL cone, sulfuric acid. The mixture was heated to gently reflux at 110⁰C in a heating mantle. A mixture of 49.13g (0.496mol) furfuryl alcohol (99%, obtained from Acros Organics of Geel, Belgium) and 42.76g (0.711 mol) isopropanol was added to the reaction mixture dropwise over 170 minutes. The reaction was re fluxed for additional 1 h after addition was complete. Then the reaction flask was allowed to cool to room temperature. The crude reaction mixture appeared to be homogeneous, with no insoluble or phase-separated material observed. About 50.07 g of the reaction mixture was transferred to a 250 mL flask and distilled using a Kugelrohr apparatus at about 5-6 Torr and air bath temperature of up to about 18O⁰C.

After distillation, total amount of undistillable solid left in the flask was 1.74 g, which contained 0.26 g sulfuric acid and 1.48 g of a tarry residue. Ratio of the amount of tarry residue formed in the reaction to the amount of furfuryl alcohol added was 12.3%. GC-MS analysis of the crude reaction product was carried out as for Example 2 and showed that isopropyl levulinate was present at 97.0%.

Example 9

A 2 L two-neck flask equipped with a magnetic stir bar, a Dean-Stark trap, and a thermocouple was charged with 232.67g (2.004mol) levulinic acid (obtained from the Langfang Triple Well Chemicals Company, Ltd. of Langfang City, HeBei, China), 192.47g (6.007 mol) methanol (obtained from VWR International of West Chester, PA), 600 mL toluene, and 2 mL cone, sulfuric acid. The reaction was heated on a heating mantle to reflux. After refluxing overnight, the reaction flask was allowed to cool to room temperature. The reaction mixture separated into two layers. The reaction mixture was transferred to a 1 L separatory funnel. The bottom layer, which contained about 5OmL of liquid, was drained from the separatory funnel. The top layer was collected in a 1 L flask. To the flask was added about 1O g basic alumina (obtained from the Sigma-Aldrich Company of St. Louis, MO), and the mixture was stirred for 2 h at room temperature. The solid was filtered off and the filtrate was concentrated on a rotary evaporator by placing the flask with the filtrate in an oil bath set to 80⁰C and applying a vacuum at 27 Torr to remove toluene and methanol. The residue was distilled on a Kugelrohr apparatus at 95°C air bath temperature and 10-15 Torr vacuum to yield 186.73 g of a colorless liquid. The product was determined by GC-MS to be 99.80% methyl levulinate.

The procedure of Example 1 was used to generate a profile of boiling points using methanol and methyl levulinate. The measured boiling points are shown in Table 5.

Table 5. Boiling points of methanol/methyl levulinate mixtures. A 500 niL four-neck flask equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple was charged with 100.04g (0.769mol) methyl levulinate, 7.52g (0.235mol) methanol (obtained from VWR International of West Chester, PA), 1.463 mL deionized water, and 0.575 mL cone, sulfuric acid. The mixture was heated to a gentle reflux at 102⁰C using a heating mantle. A mixture of

49.04g (0.495mol) furfuryl alcohol (99%, obtained from Acros Organics of Geel, Belgium) and 20.94g (0.654 mol) methanol was added to the reaction mixture dropwise over 83 minutes. The reaction was refluxed for additional 1 h after addition was complete. Then the reaction flask was allowed to cool to room temperature. The crude reaction mixture appeared to be substantially homogeneous, with a very small amount of insoluble or phase-separated material observed on a portion of the side of the reaction flask at the liquid-air interface. About 50.02 g of the reaction mixture was transferred to a 250 mL flask and distilled using a Kugelrohr apparatus at about 176⁰C air temperature and 7-10 Torr. After distillation, the total amount of undistillable solid left in the flask was

4.46 g, which contained 0.30 g sulfuric acid and 4.16 g of a tarry residue. Ratio of the amount of tarry residue formed in the reaction to the amount of furfuryl alcohol added was 30.0%. GC-MS analysis of the crude reaction product was carried out as for Example 2 and showed that methyl levulinate was present at 98.3%.

Example 10

A 500 mL four-neck flask was equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple. The whole setup was protected under positive nitrogen pressure to prevent moisture buildup. The flask was charged with 100.05 g (0.691 mol) ethyl levulinate (obtained from the Langfang Triple Well

Chemicals Company, Ltd. of Langfang City, HeBei, China), 7.60 g (0.165 mol) ethanol (100%, obtained from Sigma-Aldrich, St. Louis, MO), 0.575 mL (0.0106 mol) sulfuric acid (95-98%, obtained from Sigma-Aldrich, St. Louis, MO). The mixture was stirred at room temperature, and an aliquot was withdrawn for analysis. The mixture was heated to 118-120⁰C using a heating mantle. After the temperature reached 118 ⁰C, an aliquot was withdrawn for analysis. A mixture of 49.18 g (0.491 mol) furfuryl alcohol (98%, obtained from Sigma-Aldrich of St. Louis, MO) and 28.70 g (0.623 mol) ethanol (200 proof, obtained from Sigma-Aldrich, St. Louis, MO) was added to the reaction mixture dropwise over 99 minutes. Two aliquots were withdrawn during the addition. The reaction was heated for additional 30 minutes after the addition was complete. During the reaction, the reaction mixture was completely homogenous and free of observable tarry residue, and only gentle refluxing was observed. The reaction temperature profile and HPLC results of ethyl levulinate and levulinic acid are shown in Table 6.

Table 6. Reaction profile and HPLC results on ethyl levulinate and levulinic acid concentrations.

Based on the ethyl levulinate and levulinic acid concentrations measured in the final reaction solution, the yield of ethyl levulinate from furfuryl alcohol was calculated:

W₁

Levulinic acid yield = levulinic -acid {final ) -x 100% (2)

W ¹ M^V1 W ^γr levulinic -acid furfuryl -alcohol

MW furfuryl- alcohol

where:

Wethyi-ievuiinate(fmai) is the ethyl levulinate weight (ethyl levulinate concentration times total reaction weight) in the final reaction mixture

Wethyi-ievuiinate(mitiai) is the ethyl levulinate weight added to the reaction, accounting for the measured purity of ethyl levulinate Wievuiinic-acidCfinai) is the levulinic acid weight in final reaction mixture

Wfor&ryi-aicohoi is the weight of furfuryl alcohol added to the reaction, accounting for the measured purity of the furfuryl alcohol

MWethyi-ievuimate is the molecular weight of ethyl levulinate MWforfuryi-aicohoi is the molecular weight of furfuryl alcohol, and MWievuimic-acid is the molecular weight of levulinic acid

Based on equations (1) and (2), the final conversion from furfuryl alcohol to ethyl levulinate was 84.29 mol%, and the conversion from furfuryl alcohol to levulinic acid was 6.41 mol%. Overall conversion of furfuryl alcohol to levulinate species was 90.70 mol%.

Example 11

A 500 mL four-neck flask was equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple. The whole setup was protected under slightly positive nitrogen pressure to prevent moisture buildup. The flask was charged with 100.04 g (0.690 mol) ethyl levulinate (obtained from the Langfang Triple Well Chemicals Company, Ltd. of Langfang City, HeBei, China), 7.6O g (0.165 mol) ethanol (100%, obtained from Sigma- Aldrich of St. Louis, MO), 0.36 g (0.0200 mol) de-ionized water, 0.575 mL (0.0106 mol) sulfuric acid (95-98%, obtained from Sigma- Aldrich of St. Louis, MO). The mixture was stirred at room temperature, and an aliquot was withdrawn for analysis. The mixture was heated to 115 ⁰C using a heating mantle. After the temperature reached 115°C, an aliquot was withdrawn for analysis. A mixture of 49.10 g (0.491 mol) furfuryl alcohol (98%, obtained from Sigma- Aldrich) and 28.48 g (0.618 mol) ethanol (200 proof, obtained from Sigma- Aldrich) was then added to the reaction mixture dropwise over 93 minutes. Two aliquots were withdrawn during the addition. The reaction was heated for additional 30 minutes after addition was complete. During the reaction, the reaction mixture was completely homogenous and free of tarry residue, and only gentle refluxing was observed. The reaction temperature profile and HPLC results of ethyl levulinate and levulinic acid are shown in Table 7.

Table 7. Reaction profile and HPLC results on ethyl levulinate and levulinic acid concentrations.

Using equations 1 and 2 as in Example 10, the conversion from furfuryl alcohol to ethyl levulinate was calculated to be 83.45 mol%, and the conversion from furfuryl alcohol to levulinic acid was calculated to be 8.19 mol%. Overall conversion of furfuryl alcohol to levulinic species was 91.64 mol%.

Example 12

A 500 mL four-neck flask was equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple. The whole setup was protected under positive nitrogen pressure to prevent moisture buildup. The flask was charged with 100.07 g (0.691 mol) ethyl levulinate (obtained from the Langfang Triple Well Chemicals Company, Ltd. of Langfang City, HeBei, China), 7.60 g (0.165 mol) ethanol (100%, obtained from Sigma-Aldrich of St. Louis, MO), 1.46 g (0.0812 mol) water, 0.575 mL (0.0106 mol) sulfuric acid (95-98%, obtained from Sigma-Aldrich). The mixture was stirred at room temperature, and an aliquot was withdrawn for analysis. The mixture was heated to 108⁰C with a heating mantle. After the temperature reached 108⁰C, an aliquot was withdrawn for analysis. A mixture of

49.10 g (0.491 mol) furfuryl alcohol (98%, obtained from Sigma-Aldrich) and 28.54 g (0.619 mol) ethanol (200 proof, obtained from Sigma-Aldrich) was then added to the reaction mixture dropwise over 125 minutes. Two aliquots were withdrawn during the addition. The reaction was heated for additional 30 minutes after addition was complete. During the reaction, the reaction mixture was completely homogenous and free of tarry residue, and only gentle refluxing was observed at later stage. The reaction temperature profile and HPLC results of ethyl levulinate and levulinic acid are shown in Table 8.

Table 8. Reaction profile and HPLC results on ethyl levulinate and levulinic acid concentrations.

Using equations 1 and 2 as in Example 10, the conversion from furfuryl alcohol to ethyl levulinate was calculated to be 78.73 mol%; conversion from furfuryl alcohol to levulinic acid was calculated to be 12.22 mol%. Overall conversion to levulinic species was 90.95 mol%.

Example 13

A 2 L four-neck flask was equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple. The whole setup was protected under positive nitrogen pressure to prevent moisture buildup. The flask was charged with 600.10 g (4.142 mol) ethyl levulinate (obtained from the Langfang Triple Well Chemicals Company, Ltd. of Langfang City, HeBei, China), 46.36 g (1.006 mol) ethanol (100%, obtained from the Sigma- Aldrich Company of St. Louis, MO), 3.45 mL (0.0647 mol) sulfuric acid (95-98%, obtained from Sigma- Aldrich). The mixture was heated to 118°C using a heating mantle. After the temperature reached 118°C, a mixture of 299.93 g (2.996 mol) furfuryl alcohol (98%, obtained from Sigma- Aldrich) and 171.68 g (3.727 mol) ethanol (200 proof, obtained from Sigma- Aldrich) was added to the reaction mixture dropwise over 169 minutes. The reaction was heated for additional 30 minutes after addition was complete. During the reaction, the reaction mixture was completely homogenous and free of tarry residue, and only gentle refluxing was observed. The reaction temperature profile is shown in Table 9. Total weight of the crude reaction mixture was 1122.40 g. Mass loss after the reaction was 2.02 g; 0.71 g of the mixture was removed for analysis.

Table 9. Reaction temperature profile.

To the mixture in the reaction flask was added 112.5 g disodium hydrogen phosphate (obtained from Thermo Fisher Scientific of Waltham, MA). The mixture was stirred at 90⁰C for 30 min, then allowed to cool to room temperature. Solids were removed by suction filtration. Total amount of 1074.37 g of filtrate was recovered.

The filtrate was transferred to a 2 L 4-neck roundbottom flask. The total weight of transferred filtrate was 1072.25 g. The filtrate was distilled over about 3 hours from a flask set in an oil bath having a temperature set to 90⁰C and an applied vacuum of about 32 Torr. The weight of a first distillate was 84.83 g. The first distillate was 2.5 wt% ethyl levulinate, remainder ethanol, as determined by GC-FID. The residue in the roundbottom flask was then distilled under vacuum (4-7 Torr) over about 2.5 hours employing a short-path distillation setup and an oil bath heated to 120⁰C to 154°C. A total of 920.18 g of a second distillate was collected. Total weight of a black, tarry residue remaining was 48.65g. Mass lost after distillation was 18.59g. By acid titration and GC-FID, the second distillate contained 97.6 wt% ethyl levulinate and 0.7 wt% levulinic acid.

Based on the amounts of ethyl levulinate in the combined first and second distillates, and employing equations 1 and 2 as in Example 10, percent conversion from furfuryl alcohol to ethyl levulinate was calculated to be 70.6 mol%. Example 14

A 2 L four-neck flask was equipped with a magnetic stir bar, a dropping funnel, a condenser, and a thermocouple. The whole setup was protected under positive nitrogen pressure to prevent moisture buildup. The flask was charged with

600.09 g (4.142 mol) ethyl levulinate (obtained from the Langfang Triple Well Chemicals Company, Ltd. of Langfang City, HeBei, China), 46.35 g (1.006 mol) ethanol (100%, obtained from the Sigma- Aldrich Company of St. Louis, MO), and 3.45 mL (0.0647 mol) sulfuric acid (95-98%, obtained from Sigma- Aldrich). The mixture was heated to 118°C using a heating mantle. After the temperature reached

118°C, a mixture of 300.59 g (3.003 mol) furfuryl alcohol (98%, obtained from Sigma- Aldrich) and 171.76 g (3.728 mol) ethanol (200 proof, obtained from Sigma- Aldrich) was added to the reaction mixture dropwise over 150 minutes. The reaction was heated for additional 30 minutes after addition was complete. During the reaction, the reaction mixture was completely homogenous and free of tarry residue, and only gentle refluxing was observed. The reaction temperature profile is shown in Table 10. The total weight of the crude reaction mixture was 1125.14g. Mass loss after the reaction was 2.44 g.

A portion of the crude reaction mixture (574.62 g) was transferred to a dropping funnel. The dropping funnel was assembled with a 250 mL 3-neck roundbottom flask. The flask was equipped with a stir bar, an anti-splash adapter, a stillhead adapter, and a receiving flask. The flask was heated in an oil bath having a temperature set to 150⁰C. The solution in the dropping funnel was added dropwise into the roundbottom flask. The flask was heated with a heating mantle and a first distillate was collected at a head temperature of 110-115°C at 10-15 Torr. After a total of 6 hours, 45 minutes, the addition and distillation were complete. The total weight of the first distillate was 508.31 g. A tarry residue remained in the flask that was found to weigh 23.69 g. Mass loss after distillation was 42.62 g. Based on titration and GC-FID results, the distillate was 97.2 wt% ethyl levulinate and 1.0 wt% levulinic acid.

Table 10. Reaction temperature profile.

Employing the calculations shown in Example 10, the yield of ethyl levulinate was determined to be 84.9 mol%.

To the reaction mixture left in the reaction flask (547.03 g) was added 55 g disodium hydrogen phosphate (obtained from Thermo Fisher Scientific of Waltham, MA) and 2Og anhydrous sodium sulfate (obtained from Sigma-Aldrich). The mixture was stirred at 90⁰C for 30 min, and was allowed to cool to room temperature. Solids were removed by suction filtration. A total of 519.77 g of filtrate was recovered. The filtrate was transferred to a dropping funnel. The dropping funnel was assembled with a 250 mL 3-neck roundbottom flask. The flask was equipped with a stir bar, an anti-splash adapter, a stillhead adapter, and a receiving flask. The flask was heated in a 150 ⁰C oil bath. The solution in the dropping funnel was added dropwise into the round-bottom flask. A second distillate was collected at a head temperature of about

105 ⁰C under aboutlO Torr vacuum. After 6 h 14 min, the addition and distillation were complete. The weight of the second distillate was 462.05 g. A tarry residue remained in the flask and was determined to weigh 20.34 g. The total mass loss after distillation was 36.99 g. Based on titration and GC-FID results, the second distillate contained 96.4 wt% ethyl levulinate and 1.5 wt% levulinic acid.

Using the calculations employed in Example 10, the yield of ethyl levulinate was determined to be 73.3 mol%. Example 15

A l L, three-neck roundbottom flask was equipped with an overhead stirrer, a condenser and liquid trap, and a thermocouple. The whole setup was protected under positive nitrogen pressure to prevent moisture buildup. The flask was charged with 501.8 g (4.395 mol) ethyl levulinate (obtained from the Langfang Triple Well

Chemicals Company, Ltd. of Langfang City, HeBei, China), 53.0 g (1.150 mol) ethanol (100%, obtained from Sigma-Aldrich, St. Louis, MO), and 2.95 g (0.0301 mol) sulfuric acid (95-98%, obtained from Sigma-Aldrich, St. Louis, MO). The mixture was heated to 118 ⁰C using a heating mantle. After the temperature reached 118 ⁰C, a mixture of 252.1 g (2.518 mol) furfuryl alcohol (98%, obtained from

Sigma-Aldrich) and 148.6 g (3.226 mol) ethanol (200 proof, obtained from Sigma- Aldrich) was added through a HPLC pump at a rate of 4 mL/min to the reaction mixture over about 100 minutes. The reaction was heated at 118°C for additional 30 minutes after the addition was complete. During the heating, about 5Og of a condensate was collected. The reaction mixture appeared completely homogenous and free of observable tarry residue. The final sample weight was 895.7 g. Total mass loss after the reaction was 62.75 g. The crude reaction mixture was a black liquid. HPLC of the crude reaction mixture showed the composition contained 84.2 wt% ethyl levulinate and 3.3 wt% levulinic acid. About 100 g of the crude reaction mixture was placed in a rotary evaporator under 100 Torr vacuum. The heat was slowly increased, and the bulk of the sample was distilled over after the oil bath temperature reached 181°C. The final weight of the residual material in the flask was 9.7 g. The residual material was a viscous, tar- like material that flowed slowly at room temperature. The distillate was a water-like liquid.

The present invention may suitably comprise, consist of, or consist essentially of, any of the disclosed or recited elements. The invention illustratively disclosed herein can be suitably practiced in the absence of any element which is not specifically disclosed herein. The various embodiments described above are provided by way of illustration only and should not be construed to limit the claims attached hereto. It will be recognized that various modifications and changes may be made without following the example embodiments and applications illustrated and described herein, and without departing from the true spirit and scope of the following claims.

Claims

We claim:

1. A process for the synthesis of an alkyl levulinate, the process comprising: a. contacting a first mixture comprising i. an alkanol, ii. a protic acid catalyst, and iii. an alkyl levulinate wherein the alkyl group is the same as the alkyl group of the alkanol; with a second mixture to form a reaction mixture, the second mixture comprising j. furfuryl alcohol, and iii. an additional amount of the alkanol of the first mixture; and b. forming the alkyl levulinate in the reaction mixture wherein the alkyl group is the same as the alkyl group of the alkanol.

2. The process of claim 1 wherein the alkyl levulinate is formed at elevated temperature.

3. The process of claim 2 wherein the second mixture is contacted with the first mixture, the first mixture maintained at an elevated temperature.

4. The process of claim 1 wherein the alkanol is methanol, ethanol, n- propanol, isopropanol, n-butanol, or isobutanol.

5. The process of claim 1 wherein the molar ratio of alkanol to alkyl levulinate in the first mixture is about 1 :20 to 1 :1.

6. The process of claim 4 wherein the molar ratio of alkanol to alkyl levulinate in the first mixture is about 1 :8 to 1 :2.

7. The process of claim 4 wherein the molar ratio of alkanol to alkyl levulinate in the first mixture is about 1 :6 to 1 :3.

8. The process of claim 1 wherein the protic acid catalyst is sulfuric acid, a cation exchange resin comprising sulfonic acid groups, an alkyl-aromatic sulfonic acid, an aromatic sulfonic acid, or an aliphatic sulfonic acid.

9. The process of claim 8 wherein about IxIO^"4 to 2.5xlO^~2 moles of sulfuric acid is added to the first mixture per mole of furfuryl alcohol provided in the second mixture.

10. The process of claim 8 wherein about 2.5x10-3 to 2.5xlO^~2 moles of sulfuric acid is added to the first mixture per mole of furfuryl alcohol provided in the second mixture.

11. The process of claim 8 wherein about 1x10 ² to 2x10 ² moles of sulfuric acid is added to the first mixture per mole of furfuryl alcohol provided in the second mixture.

12. The process of claim 1 wherein the first mixture additionally comprises water.

13. The process of claim 12 wherein about IxIO^"4 to 0.2 moles of water is present per mole of furfuryl alcohol provided in the second mixture.

14. The process of claim 12 wherein about 1x10 ³ to 0.1 moles of water is present per mole of furfuryl alcohol provided in the second mixture.

15. The process of claim 12 wherein about 1x10 ³ to 5x10 ² moles of water is present per mole of furfuryl alcohol provided in the second mixture.

16. The process of claim 1 wherein the second mixture comprises a mole ratio of furfuryl alcohol to moles of alkanol of about 1 to 2.

17. The process of claim 1 wherein the second mixture comprises a mole ratio of furfuryl alcohol to moles of alkanol of about 1 : 1.125 to 1 : 1.75.

18. The process of claim 1 wherein the second mixture comprises a mole ratio of furfuryl alcohol to moles of alkanol of about 1 : 1.20 to 1 :1.50.

19. The process of claim 3 wherein the reaction mixture is stirred at an elevated temperature.

20. The process of claim 19 wherein the alkanol is ethanol and the elevated temperature is about 95°C to 160⁰C.

21. The process of claim 20 further comprising heating the first mixture prior to the contacting.

22. The process of claim 21 wherein the heating comprises raising the temperature above the boiling point of the alkanol.

23. The process of claim 22 wherein the temperature is at least about 20⁰C higher than the boiling point of the alkanol.

24. The process of claim 22 wherein the temperature is at least about 40⁰C higher than the boiling point of the alkanol.

25. The process of claim 2 wherein the process is a batch process and the elevated temperature is maintained for about 1 to 60 minutes after contacting of the second mixture with the first mixture is completed.

26. The process of claim 2 wherein the process is a batch process and the elevated temperature is maintained for about 30 minutes after contacting of the second mixture with the first mixture is completed.

27. The process of claim 1 wherein the number of moles of alkanol in the second mixture is selected according to the formula

D = (1+ (B/A))*C wherein

A denotes moles of alkyl levulinate;

B denotes moles of alkanol in the first mixture;

C denotes moles of furfuryl alcohol; and

D denotes moles of alkanol in the second mixture.

28. The process of claim 27 wherein the moles of alkanol in the second mixture is selected to be in the range of about (0.9)(D) to D.

29. The process of claim 1 wherein furfuryl alcohol is contacted with alkanol in the reaction mixture at a rate of about 1 to 5 mole percent per minute per mole of alkanol in the first mixture.

30. The process of claim 1 wherein the contacting comprises adding the second mixture to the first mixture via an aperture, the aperture not in contact with the first mixture.

31. The process of claim 30 wherein the aperture comprises a spray nozzle configured to contact the second mixture as a divided stream comprising a mist or fine spray of droplets to the surface of the first mixture.

32. The process of claim 1 wherein the process is continuous.

33. The process of claim 1 wherein the reaction mixture is maintained at elevated pressure.

34. The process of claim 33 wherein the elevated pressure is between greater than ambient to about 1 atmosphere above ambient.

35. The process of claim 1 wherein the yield of alkyl levulinate is at least about 70 mole percent based on moles of furfuryl alcohol in the second mixture.

36. The process of claim 1 further comprising neutralizing the acid catalyst after the forming alkyl levulinate.

37. The process of claim 36 wherein the neutralizing is accomplished by an alkali or alkali earth metal of a hydroxide, a carbonate, a hydrocarbonate, a phosphate, a tertiary amine, or a carboxylate.

38. The process of claim 1 further comprising collecting the alkyl levulinate formed.

39. The process of claim 38 wherein the collecting comprises evaporation of alkanol, distillation of the alkyl levulinate, decanting of soluble from insoluble reaction products, filtration of insoluble from soluble reaction products, liquid-liquid extraction, or a combination thereof.

40. The process of claim 39 wherein the distillation comprises vacuum disatillation.

41. The process of claim 39 wherein the distillation comprises wiped film evaporation or falling film evaporation.

42. The process of claim 38 wherein the collecting is accomplished in two steps.

43. The process of claim 42 wherein the two steps comprise a first step comprising evaporation of alkanol and a second step comprising evaporation of alkyl levulinate.

44. The process of claim 42 wherein a first step comprises evaporation of alkanol and a first portion of the alkyl levulinate, and a second step comprises removal of a second portion of alkyl levulinate.

45. The process of claim 42 further comprising adding a tarry residue plasticizer to the reaction mixture between the first step and the second step.

46. The process of claim 45 wherein the tarry residue plasticizer is a biodiesel fuel, 2,2,4-trimethyl-l,3-pentane-diol diisobutyrate, tridecylalcohol, a dialkyl phthalate wherein the alkyl groups independently have between 4 and 14 carbons, a dialkyl adipate wherein the alkyl groups independently have between 4 and 14 carbons, a dialkyl sebacate wherein the alkyl groups independently have between 4 and 14 carbons, a monobenzoate wherein the alkyl group has between 4 and 14 carbons, a dialkylcyclohexanoate wherein the alkyl groups independently have between 4 and 14 carbons, a trialkyl trimellitate wherein the alkyl groups independently have between 4 and 14 carbons, a trialkyl citrate wherein the alkyl groups independently have between 4 and 14 carbons, or a combination thereof.

47. The process of claim 1 wherein a byproduct comprising levulinic acid is esterifϊed to form alkyl levulinate.

48. The process of claim 1 wherein the combined yield of alkyl levulinate and levulinic acid after forming is at least about 70 mole percent based on moles of furfuryl alcohol provided in the second mixture.

49. The process of claim 38 wherein greater than 75 wt% of the alkyl levulinate formed is collected as a purified product.

50. The process of claim 38 wherein greater than 90 wt% of the alkyl levulinate formed is collected as a purified product.

51. A process for synthesis of alkyl levulinate, the process comprising: a. forming a first mixture comprising i. an alkanol, ii. sulfuric acid, and iii. an alkyl levulinate wherein the alkyl group is the same as the alkyl group of the alkanol; b. heating the first mixture to a temperature of at least about 20⁰C higher than the boiling point of the alkanol; c. contacting the first mixture with a second mixture at ambient pressure to form a reaction mixture, the second mixture comprising i. furfuryl alcohol, and ii. an alkanol that is the alkanol from the first mixture, wherein the mole ratio of furfuryl alcohol to alkanol is about 1 :1.125 to 1 :1.75; and d. reacting the reaction mixture at ambient pressure and at a temperature between about 95°C and 160⁰C to form alkyl levulinate wherein the alkyl group is the same as the alkyl group of the alkanol; and e. recovering the alkyl levulinate, wherein about 0.01 to 2 mole percent of sulfuric acid is added to the first mixture based on moles of furfuryl alcohol in the second mixture, and wherein the number of moles of alkanol in the second mixture is selected to be between 0.9D and D wherein D is defined according to the formula

D =(1+(B/A))*C wherein

A denotes moles of alkyl levulinate,

B denotes moles of alkanol in the first mixture,

C denotes moles of furfuryl alcohol, and

D denotes moles of alkanol in the second mixture.

52. The process of claim 51 wherein the alkanol is methanol, ethanol, isopropanol, n-propanol, n-butanol, or isobutanol.

53. The process of claim 51 wherein the alkanol is ethanol.

54. The process of claim 51 further comprising neutralizing the sulfuric acid prior to the collecting.