Production of maleic acid, fumaric acid, or maleic anhydride from levulinic acid analogs

Abstract

A system and method for the conversion of a levulinate ester to maleic anhydride using a reducible oxide catalyst. Levulinic acid oxidation delivers maleic anhydride in good yields without viscosity and stability issues that make continuous production problematic. Due to the fact that levulinate esters are more amenable to processing, the conversion of levulinate esters to maleic anhydride represents an appropriate for the commercial production of maleic anhydride from renewable resources.

Claims

1. A method of producing maleic anhydride, comprising the step of oxidizing a quantity of methyl levulinate without forming levulinic acid to form maleic anhydride.

2. The method of claim 1, wherein the step of oxidizing the quantity of methyl levulinate to form maleic anhydride comprises the use of a reducible oxide catalyst.

3. The method of claim 2, wherein the reducible oxide catalyst is vanadium oxide (VO.sub.x) supported at monolayer loading on -Al.sub.2O.sub.3 (VO.sub.x/-Al.sub.2O.sub.3).

4. The method of claim 3, further comprising the step of producing the reducible oxide catalyst by incipient wetness impregnation of vanadium oxalate onto -Al.sub.2O.sub.3 to form a powder.

5. The method of claim 4, wherein the step of producing the reducible oxide catalyst further comprises the step of crushing the powder to achieve a uniform particle size.

6. The method of claim 5, further comprising the step of activating the powder by applying a stream of air for four hours at 723 K.

7. The method of claim 6, wherein the step of oxidizing a quantity of methyl levulinate to form maleic anhydride comprises introducing the quantity of methyl levulinate and a quantity of oxygen in a diluent of helium into a reactor having a packed bed of the reducible oxide catalyst.

8. The method of claim 7, wherein the quantity of methyl levulinate, the quantity of molecular oxygen, and the helium diluent were preheated to 403 K in a vessel field filled with quartz chips.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

(1) The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a schematic of a pathway for the formation of maleic anhydride through the oxidative cleavage of methyl levulinate;

(3) FIG. 2 is a schematic of an alternative pathway for the formation of maleic anhydride through the oxidative cleavage of methyl levulinate; and

(4) FIG. 3 is a schematic illustrating the interconversion of levulinate esters and levulinic acid with angelicalactones.

DETAILED DESCRIPTION OF THE INVENTION

(5) Referring to the figures, wherein like numerals refer to like parts throughout, there is seen in FIGS. 1 and 2, two distinct pathways for the formation of maleic anhydride (MA) through the oxidative cleavage of methyl levulinate (ML). As discussed below, preliminary data establishes that the oxidation of methyl levulinate, a representative ester of levulinic acid, may be used to form maleic anhydride. FIG. 3 illustrates the interconversion of levulinic acid and levulinate esters with all angelicalactone isomers. Because angelicalactones can interconvert with either levulinic acid and levulinate esters under reaction conditions, they can also be converted into maleic anhydride or its diacid analogs using the approach described here or, for example, in U.S. Pat. No. 9,187,399, incorporated by reference herein in its entirety. Thus, because levulinic acid and levulinate esters will reversibly form angelicalactones under the reaction conditions reported here, the present invention may be extended to produce maleic anhydride, maleic acid, or fumaric acid from various angelicalactones.

EXAMPLE

(6) The reducible oxide catalyst used in this study was a vanadium oxide (VO.sub.x) supported at monolayer loading on -Al.sub.2O.sub.3. The catalyst was prepared by incipient wetness impregnation of vanadium oxalate onto -Al.sub.2O.sub.3. A solution of oxalic acid and ammonium metavanadate at a molar ratio of 2:1 was used to wet the surface of the alumina. The resulting powder was crushed and sieved to achieve uniform particle size and was activated by a stream of air (Airgas Ultra Zero) for 4 hours at 723 K.

(7) The VO.sub.x/Al.sub.2O.sub.3 sample was then loaded into a catalytic packed bed reactor into which methyl levulinate and molecular oxygen was introduced in a helium diluent. ML was delivered into the system as a liquid using a Cole Parmer syringe pump (Model 100), while O.sub.2 (Airgas UHP) and He (Airgas UHP) were supplied by two Brooks 5850S mass flow controllers. ML, O.sub.2 and He were preheated to 403 K and mixed in a vessel field filled with quartz chips, which served to vaporize the ML. The gaseous mixture of ML, O.sub.2, and He was then preheated to reaction temperature and fed to the reactor. The effluent was kept at 473 K to avoid any product condensation and was guided to an HP 5890 gas chromatograph complete with a pair of heated gas sampling valves. Carbon oxide quantification was achieved through a TCD detector at the end of a Restek Shincarbon ST micropacked column, while the remaining product stream was quantified with a Restek Rtx-1701 column connected to an FID detector. All temperatures were monitored with type K Omega thermocouples, and the system temperature was controlled using series 16A Controllers (Love Controls).

(8) FIGS. 1 and 2 illustrate, based on product stream composition, what is believed to be two distinct pathways for the formation of MA through the oxidative cleavage of ML. In the reaction network of FIG. 1, ML forms two possible enols. Oxidative cleavage of the internal enol yields monomethyl malonate and acetic acid. Oxidative cleavage of the terminal enol yields monomethyl succinate and formic acid. The monomethyl succinate forms monomethyl maleate and/or monomethyl fumarate, through an oxidative dehydrogenation (ODH) step. Either of the above can form MA with the simultaneous release of methanol.

(9) In the pathway of FIG. 2, ML undergoes ODH to yield methyl (Z)-4-oxopent-2-enoate and/or methyl (E)-4-oxopent-2-enoate. Here, the transformation to the internal enol (forming a cumulated diene) will be much less stable than that of the terminal one (forming a conjugated diene). Methyl maleate forms upon oxidative cleavage and releases methanol to give the anhydride. Based on detailed GC-MS analysis of reaction products, there is strong evidence to support that both pathways (FIG. 1 and FIG. 2) are plausible. Should the ODH step become more facile than either enolization step, then the selectivity towards MA should be further enhanced. In the presence of methanol and water, carboxylic groups in both schemes can undergo esterification, while esters can hydrolyze to their respective carboxylic acids and we expect the presence of all those species.

(10) Using the aforementioned configuration and equipment, the data collected is presented in Table 1 below.

(11) TABLE-US-00001 TABLE 1 Reaction conditions and results Feed ML O.sub.2 rate Space partial partial Temper- Con- (umol/ Velocity pressure pressure ature version Catalyst min) (min.sup.1) (bar) (bar) (K) (%) VO.sub.x/ 37.6 0.27 0.019 0.205 588 100 -Al.sub.2O.sub.3 Internal Terminal Production rates (umol/min) MA yield cleavage cleavage Acetic (% of selectivity selectivity MA Methanol acid CO.sub.x theoretical) (%) (%) 18.9 1.0 10.1 134.2 51 35 65

(12) Preliminary data thus suggests good MA yields can be achieved from the oxidative cleavage of ML. Further optimization of catalysts and operating conditions is likely to increase MA yield. Thus, a whole family of compounds including levulinic acid, levulinic acid esters and angelicalactones can undergo oxidative cleavage, either separately or combined, at the same conditions and over the same metal oxide catalyst, to yield maleic acid, fumaric acid and MA.