This application is a non-provisional application claiming priority from the U.S.

Provisional Patent Application No. 61/570,973, filed on December 15, 2011, entitled "DEHYDROXYLATION OF POLYHYDROXY CARBOXYLIC ACIDS TO ALIPHATIC POLYCARBOXYLIC ACIDS USING A HALOGEN-BASED CATALYST," the teachings of which are incorporated by reference herein as if reproduced in full hereinbelow.

This invention relates generally to the field of dehydroxylation of poly hydroxy carboxylic acids. More particularly, it is a process to accomplish dehydroxylation of a biorenewable material to obtain aliphatic polycarboxylic acids.

Adipic acid, also referred to as 1,6-hexanedioc acid, is an important aliphatic polycarboxylic acid and a major commodity chemical in the world today. The bulk of production, representing billions of kilograms annually, is used primarily as a precursor for the production of nylon. Other uses include as a monomer for polyurethanes and a plasticizer for polyvinyl chlorides. Small quantities of total production are also used for medical and food applications.

The most common method of producing adipic acid is via oxidation. Frequently a mixture of cyclohexanol and cyclohexanone, called ketone-alcohol oil ("KA oil"), is oxidized with nitric acid, via a multi-step pathway. Side products of the method include glutaric and succinic acids. Other processes for producing adipic acid start from cyclohexanol alone. The cyclohexanol is generally obtained by hydrogenation of phenol.

Alternative processes have been developed to include the carbonylation of butadiene. A "green" approach, producing only water as a by-product, includes the oxidation of cyclohexene with hydrogen peroxide using a tungstate-based catalyst and a phase transfer catalyst.

Other methods include, for example, WO 2010/144862 A2, which discloses production of adipic acid and its derivatives from carbohydrate-containing materials, particularly glucose. The patent discusses catalytic approaches for the conversion of glucose to glucaric acid and also conversion of glucaric acid to adipic acid, in the presence of hydrogen and a heterogeneous or homogeneous catalyst.

WO1995007996 (Al) discusses the conversion of carbohydrate sources to cis-cis muconic acid, an intermediate, which is then hydrogenated to adipic acid. US 4400468 discloses a process for the conversion of biomass to adipic acid. The biomass is hydrolyzed to form 5-hydroxymethyl furfural, which is then hydrogenated to 2,5-tetrahydrofuran dimethanol in the presence of a catalyst. The 2,5-tetrahydrofuran dimethanol is catalytically hydrogenated to 1,6-hexanediol. Oxidation of the 1,6-hexanediol is conducted in the presence of microorganisms to form adipic acid. The biomass may be a waste product of paper-making, or wood, cornstalks, or a logging residue.

In one aspect, this invention is a process for producing an aliphatic polycarboxylic acid comprising subjecting a polyhydroxy carboxylic acid to dehydroxylation conditions in the presence of a halogen-based catalyst containing at least one halogen atom, the dehydroxylation conditions including a reductive or non-reductive gas at a pressure of from 1 pound per square inch gauge (~6.89 kilopascals) to 2000 pound per square inch gauge (~ 13.79 megapascals), a temperature within a range of from 50 °C to 250 °C, a liquid reaction medium, and a ratio of moles of the polyhydroxy carboxylic acid to moles of the halogen atoms ranging from 1 : 10 to 100: 1 ; such that an aliphatic polycarboxylic acid is formed.

A particular feature of the present invention is use of a halogen-based catalyst. As defined herein, a halogen-based catalyst contains at least one halogen atom and ionizes at least partially in an aqueous solution by losing one proton. It is important to note that the definition of "halogen-based" is applied to the catalyst at the point at which it catalyzes the dehydroxylation of the crude alcohol stream. Thus, it may be formed in situ in the liquid reaction medium beginning with, for example, a molecular halogen, e.g., molecular iodine (I ₂ ), or may be introduced into the reaction as a halide acid, for example, as pre-prepared HI. Non-limiting examples include molecular iodine (I ₂ ), hydroiodic acid (HI), iodic acid (HIO ₃ ), lithium iodide (Lil), and combinations thereof. The term "catalyst" is used in the conventionally understood sense, to clarify that the halogen-based compound takes part in the reaction but is regenerated thereafter and does not become part of the final product. The halogen-based catalyst is at least partially soluble in the liquid reaction medium.

For example, in one non-limiting embodiment where HI is selected as the halogen- based catalyst, it may be prepared as it is frequently prepared industrially, i.e., via the reaction of I ₂ with hydrazine, which also yields nitrogen gas, as shown in the following equation.

2 I ₂ + N ₂ H ₄ → 4 HI + N ₂

[Equation 1] When performed in water, the HI must be distilled. Alternatively, HI may be distilled from a solution of Nal or another alkali iodide in concentrated hypophosphorous acid. Another way to prepare HI is by bubbling hydrogen sulfide steam through an aqueous solution of iodine, forming hydroiodic acid (which must then be distilled) and elemental sulfur (which is typically filtered).

H ₂ S + I ₂ → 2 HI + S

[Equation 2]

Additionally, HI can be prepared by simply combining H ₂ and I ₂ . This method is usually employed to generate high purity samples.

H ₂ + I ₂ → 2 HI

[Equation 3]

Those skilled in the art will be able to easily identify process parameters and additional methods to prepare HI and/or other reagents falling within the scope of the invention. It is noted that sulfuric acid will not generally work for preparing HI as it will tend to oxidize the iodide to form elemental iodine.

As used herein the term "polyhydroxy carboxylic acid" is used to define a compound having any number of carbon atoms as a main chain, preferably from 4 to 20 carbon atoms, more preferably from 4 to 12, still more preferably from 4 to 8, and most preferably from 5 to 6 carbon atoms. These compounds have at least one carboxyl (COOH) functional group, and in many cases are diacids, i.e., they contain two COOH groups. Non- limiting examples may include glucaric acid (also called saccharic acid), mucic acid (also called galactaric acid), xylaric acid (also called trihydroxy glutaric acid), and combinations thereof. Isomers of the above are also examples of polyhydroxy carboxylic acids. Collectively, these materials are alternatively referred to herein as the "starting material." A particular advantage of the present invention is that the starting material may be glucaric acid, which may be obtained by a simple oxidation of glucose. Because glucose is a biorenewable material, the invention offers convenient sourcing as well as relatively mild conditions. Oxidation of glucose to glucaric acid may be carried out by, for example, oxidizing glucose by reacting it with nitric acid.

In practicing the present invention the starting material and the catalyst are desirably proportioned for optimized conversion of the starting material to at least one desired aliphatic polycarboxylic acid product. Those skilled in the art will be aware without further instruction as to how to determine such proportions, but generally a ratio of moles of starting material to moles of halogen atoms ranging from 1:10 to 100:1 is preferred. More preferred is a molar ratio ranging from 1:1 to 100: 1; still more preferably from 4:1 to 27:1; and most preferably from 4:1 to 8:1. Alteration of the proportion of the catalyst to starting material will alter conversion of starting material to the corresponding aliphatic polycarboxylic acid(s), which may be, for example, a diacid. By "corresponding" is meant that the aliphatic polycarboxylic acid has the same carbon atom number as the starting polyhydroxy carboxylic acid.

Temperature parameters employed in the invention may vary within a range of from 50 °C to 250 °C, but are preferably from 100 °C to 210 °C. Those skilled in the art will be aware that certain temperatures may be preferably combined with certain molar ratios of material and catalyst to obtain optimized olefin yield. For example, a temperature of at least 180 °C combined with a molar ratio of starting material to halogen atoms of 6: 1 may result, in some embodiments, in particularly desirable yields. Other combinations of temperature and ratio of moles of starting material to moles of halogen atoms may also yield desirable conversions. For example, with an excess of HI, temperature may be varied especially within the preferred range of 100 °C to 210 °C, to obtain a range of conversion at a fixed time, e.g., 3 hours. Those skilled in the art will be aware that alteration of any parameter or combination of parameters may affect yields, and that routine experimentation to identify optimized parameters will be, as is typical, necessary prior to advancing to commercial production.

In certain particular embodiments the conditions may also include a reaction time, typically within a range of from 1 hour to 10 hours. While a time longer than 10 hours may be selected, such may tend to favor formation of intermediates or of less stable aliphatic polycarboxylic acid products, neither of which is usually desirable. Intermediates formation may be more prevalent in a batch reactor than in a continuous process. Conversely, a time shorter than 1 hour may reduce overall product yield.

The inventive process may be carried out as either a reductive dehydroxylation or a non-reductive dehydroxylation. In the case of a reductive dehydroxylation, gaseous hydrogen may be employed in essentially pure form as the reductant, but also may be included in mixtures further comprising, for example, carbon dioxide, carbon monoxide, nitrogen, methane, and any combination of hydrogen with one or more the above. The hydrogen itself may therefore be present in the atmosphere, generally a gas stream, in an amount ranging from 1 weight percent (wt ) to 100 wt . Where a non-reductive dehydroxylation is desired, the atmosphere/gas stream is desirably substantially or, preferably, completely hydrogen-free. In this case other gases, including but not limited to nitrogen, carbon dioxide, carbon monoxide, methane, and combinations thereof, may be employed. Any constituent therefore may be present in amounts ranging from 1 wt to 100 wt , but the total atmosphere is desirably at least 98 wt , preferably 99 wt , and more preferably 100 wt , hydrogen-free.

The hydrogen-containing (reductive) or non-reductive atmosphere is useful in the present invention at a gas pressure sufficient to promote conversion of, for example, molecular halogen to halide, for example, I ₂ to an iodide, preferably hydroiodic acid (HI, also known as "hydrogen iodide"). The pressure is desirably from 1 psig (—6.89 KPa) to 2000 psig (-13.79 MPa), and preferably from 50 psig (-344.5 KPa) to 200 psig (-1.38 MPa). A gas pressure within the above ranges, especially the preferred range, is often favorable for efficient conversion of molecular halide to the corresponding acid iodide. In many embodiments gas pressures in excess of 2000 psig (—13.79 MPa) provide little or no discernible benefit and may simply increase cost of the process.

The conversion to an aliphatic polycarboxylic acid, e.g., to adipic acid, glutaric acid, tartaric acid, or a combination thereof, may be accomplished using many of the equipment and overall processing parameter selections that are generally known to those skilled in the art. Depending in part upon other processing parameters selected as discussed hereinabove, it may be desirable or necessary to include a liquid reaction medium. The starting material may function as both the compound(s) to be converted and the liquid reaction medium wherein the conversion will take place, or if desired, an additional solvent such as water, acetic acid, or another organic may be included. Acetic acid may help to dissolve the halogen formed as part of the catalytic cycle and act as a leaving group, thereby facilitating the cycle. Organic solvents may be helpful in removing any water accumulated during the course of the reaction. Dialkyl ethers may also be selected.

EXAMPLE

General experimental procedure:

Conduct the reaction in a Parr 300 milliliter (mL) High Pressure Hastelloy-C 276

Reactor, with a glass insert. Charge 90 mL of acetic acid (C2H4O2) into the reactor. Add a known amount of mucic acid (CeHioOs) to the acetic acid. Add HI 4 mL (55 % aqueous solution) to the reactor. Close the reactor and mount it on the reactor stand. Flush the reactor void space twice with nitrogen (200 psig,—1.38 megapascals, MPa) and release. Feed hydrogen to the reactor up to a pressure of 500 psig (~3.45 MPa), and heat under stirring (1000 revolutions per minute, rpm) to a temperature of 210 °C. Note reactor pressure on attaining the temperature and then increase up to 1000 psig (~6.89 MPa). Reaction commences as seen from a drop in the pressure of the reactor, and monitor against time. Continue the reaction in this fashion for a period of 3 hours. Fill with hydrogen intermittently to make up for the consumption of hydrogen in the reactor.

Example 1

Using the above general experimental procedure, conduct the reductive dehydroxylation reaction of 0.07 moles of glucaric acid and 0.06 moles of HI in acetic acid solvent at a temperature of 210 °C for 3 hours. During the course of the reaction, observe a drop in the reactor pressure, which is indicative of the consumption of hydrogen. Analyze the liquid sample using nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography-mass spectroscopy (LC-MS). The LC-MS peak (mass-to-charge ratio based on negative ion) at 145 shows the presence of adipic acid (weight average molecular weight M _w 146) in the product. Calculate the conversion of the reaction using ^] H NMR. Use the acetic acid -CH ₃ protons as an internal standard. After 3 hours, estimate the conversion to adipic acid at 40 %.