CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a PCT International application which claims the benefit of and priority to U.S. Provisional Application Ser. No. 62/213,396 filed September 2, 2015 and U.S. Application Serial No. 15/243,281 filed August 22, 2016, entitled "Process for Oxidation Reactions," both of which are hereby incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR

DEVELOPMENT

[0002] None.

FIELD OF THE INVENTION

[0003] A process for oxidation reactions.

BACKGROUND OF THE INVENTION

[0004] One-pot direct conversion of paraffins to oxygenates or olefins is difficult to obtain. For example, the activation of methane and reaction with oxygen to directly produce methanol in a commercial-scale continuous process is not currently feasible.

[0005] For example, to obtain methanol from methane, one would typically convert methane to syngas (H ₂ +CO) which is then converted to methanol in a separate reaction step. Others have attempted to utilize a-oxygen species to oxidize methane to methanol. However, such a process faces significant hurdles, for example the pulsed nature of methane and the oxidant means that the process is not continuous and the low α-oxygen capacity of the catalyst material means that the single pass conversion of methane to methanol is very low.

[0006] Others have attempted to achieve this solution but have required the addition of steam to the anode feedstock thereby increasing the cost and complexity of the system. Such a system would also require a low operating temperature (below 250°C) which would cause CO poisoning and rapidly deactivate the anode catalyst.

[0007] There exists a need for a selective and continuous one-pot partial oxidation of organic compounds such as hydrocarbons or heteroatom-containing hydrocarbons. BRIEF SUMMARY OF THE DISCLOSURE

[0008] The current embodiment describes a process of flowing an oxidant species over the reducing side of an oxygen transport membrane. O ^2" anions are then continuously transported from the reducing side through the oxygen transport membrane to the oxidizing side where an organic compound is partially oxidized.

[0009] In an alternate embodiment a process is described where air is flowed over the reducing side of a solid oxide cell. The air is reduced to produce oxygen-deficient air and O ^2" anions. Only the O ^2" anions are continuously transported from the reducing side of the solid oxide cell to the oxidizing side. On the oxidizing side of the cell the O ^2" anions then react with methane and a catalyst layer to produce methanol.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A more complete understanding of the present invention and benefits thereof may be acquired by referring to the follow description taken in conjunction with the accompanying drawings in which:

[0011] Figure 1 depicts a planar structure of an oxygen transport membrane.

[0012] Figure 2 depicts a tubular structure of an oxygen transport membrane.

[0013] Figure 3 depicts a variation of Figure 1 with a bilayer system.

[0014] Figure 4 depicts a gas chromatogram of air saturated with methanol.

[0015] Figure 5 depicts a gas chromatogram of air.

[0016] Figure 6 depicts a gas chromatogram of Sample 1.

[0017] Figure 7 depicts a gas chromatogram of Sample 2.

DETAILED DESCRIPTION

[0018] Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow.

[0019] The current embodiment describes a process of flowing an oxidant species over the reducing side of an oxygen transport membrane. The oxidant species is then reduced to generate O ^2" anions. O ^2" anions are then continuously transported from the reducing side through the oxygen transport membrane to the oxidizing side. An organic compound is then converted to a partially oxidized organic compound on the oxidizing side.

[0020] Typically, the oxygen transport membrane is a solid oxide cell or other electrochemical cell that is constructed of at least three layers. The arrangement of these three layers can be in any known configuration for solid oxide fuel cells (SOFC), solid oxide electrolysis cells (SOEC), solid electrolyte oxygen separators, or other solid oxide electrochemical cells. Two embodiments of such configurations include planar (Figure 1) or tubular (Figure 2) structures. Both Figure 1 and Figure 2 depict a middle layer being a cell electrolyte or oxygen transport membrane 2. Also, in both Figure 1 and Figure 2, the other two layers are the reducing side or the cathode 6 and the oxidizing side or the anode 4. Both the anode and cathode in these embodiments can be connected together in an electrical circuit. Figure 1 depicts one embodiment wherein the oxygen transport membrane is connected to an electrical circuit 8. The electrical circuit can be a conventional external electrical circuit, or an internal electrical circuit, depending on the nature of the materials used and the operation conditions.

[0021] In both the planar and tubular versions of the oxygen transport membrane the cathode facilitates a reduction reaction while the anode facilitates an oxidation reaction. More specifically, the cathode is exposed to an oxidant species such as an oxygen source like air. The cathode uses electrons from the electrical circuit to activate the oxidant species. When using air as an oxidant species, an oxygen anion (O ^2" ) is formed and is transported through the electrolyte layer to the anode or oxidizing side.

[0022] In one embodiment, the anode uses the oxygen species from the electrolyte to facilitate the oxidation of a hydrocarbon, for example, forming methanol from methane, and producing electrons that are sent to the electrical circuit. The resulting oxygenate may optionally be converted to a second oxygenate or an olefin within the same device by the anode catalyst. For example, the device might be configured to produce dimethyl ether from methane, rather than methanol.

[0023] In one embodiment the anode and cathode can be connected with an external electrical circuit. The external circuit can contain a power supply in order to supply electrical energy to the system for an endothermic overall reaction or an electrical load (resistance or power sink) to extract electrical energy from the system in the case of an exergonic overall reaction. In order to prevent the cell from shorting, the electrical conductivity of the electrolyte in this configuration must be minimized.

[0024] In another embodiment the anode and cathode may be connected with an internal electrical circuit. In this design the device design is simplified and may allow the device to be constructed at significantly lower cost. In this embodiment the electrolyte provides electrical connection of the anode and cathode and the electrolyte must therefore have significant electrical conductivity in addition to oxygen anion conductivity. This type of electrolyte is often referred to as a mixed ionic-electronic conductor (MIEC).

[0025] In yet another embodiment the anode and cathode layers may be omitted. In this embodiment, the electrolyte material would be composed of a mixed ionic-electronic conductor that also provides sufficient activity for the reduction of oxygen molecules to oxygen anions as well as for the oxidation of the alkane to the desired oxygenated product.

[0026] In each embodiment it is necessary to utilize a solid oxide electrolyte, which functions as an oxygen transport membrane. In one embodiment, the oxygen transport membrane would be a thin layer of non-porous oxide with appreciable oxygen ionic conductivity at operation temperature. Other embodiments that are possible include having the electrolyte layer be composed of a mixed ionic-electronic conductor if operating with an internal circuit configuration or if omitting the electrocatalyst layers. In another embodiment the electrolyte layer could be a mixture of several different materials. One example would be a composite of several different layers of materials such as a layer of mixed ionic-electronic conductor with high ionic conductivity and high electronic conductivity, combined with a layer of a different oxide material with high ionic conductivity but low electronic conductivity, such that the electrolyte as a whole would have high ionic conductivity and low electronic conductivity. In yet another embodiment, the electrolyte layer could comprise a thick layer of highly porous oxide support material with a thin layer of a dense oxygen transport membrane material.

[0027] Any commonly known solid oxide materials could be used for the electrolyte layer. Some of these materials include yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), ceria, gadolinium-doped ceria (GDC), samarium-doped ceria (SDC), calcium-doped ceria (CDC), ceria-carbonate composites (such as CDC/Na ₂ C0 ₃ ), lanthanum strontium gallate magnesite (LSGM) such as Lao _.9 Sr _0. iGao _.8 Mgo _.2 0 ₃ -5, lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium gallium magnesium oxide, lanthanum chromium vanadium oxide, lanthanum strontium chromium vanadium oxide, lanthanum chromium vanadium oxide doped with a transition metal, bismuth oxide, erbium bismuth oxide, niobium cerium oxide, bismuth molybdenum vanadium oxide, lanthanum strontium iron chromium oxide, strontium magnesium manganese molybdenum oxide, barium-zirconium-cerium-yttrium oxides, such as Ba(Zr _0. iCe ₀ .7Yo.2)0 ₃ _5, barium-cerium-yttrium oxides, such as Ba(Ce ₀ .8Yo.2)0 ₃ , Zr0 ₂ or any mixtures or layers of these or other oxygen transport membrane candidate materials. Other commonly known materials that can be used that are hereby incorporated by reference can be found: such as "Solid electrolyte membrane reactors: Status and trends" (conference paper). Catalysis Today, Vol. 104, Issue 2-4, 30 June 2005, pages 158-199 and "Solid-Electrolyte Membrane Reactors: Current Experience and Future Outlook" Catalysis Reviews - Science and Engineering, Vol. 42, Issue 1-2, February 2000, Pages 1-70.

[0028] At the cathode side of the oxygen transport membrane the cathode is exposed to an oxidant species and catalyzes a reduction half-reaction. The cathode uses electrons from the electrical circuit to activate the oxidant species and form an oxygen anion, which is transported through the solid electrolyte layer to the anode. In another embodiment, this reduction half- reaction can be facilitated directly by the electrolyte without the use of a separate cathode electrocatalyst. While air may be the most common choice, in principle any species capable of producing O ^2" anions can be used as the oxidant species. The general form of the reaction carried out at the cathode is:

(Oxidant species) + (2x)e- - xO ^2" + (Reduced species)

[0029] In this equation the value of x will depend on the nature of the oxidant species.

[0030] Examples of oxidant species, and the reduced form of the oxidant, that can be used include: air, which is reduced to oxygen-deficient air (air with less than 21% 0 ₂ ); 0 ₂ , which reacts completely to form O ^2" and leaves no other reduced species; H ₂ 0 which is reduced to H ₂ ; C0 ₂ which is reduced to CO or C; N ₂ 0 which is reduced to N ₂ or NO; NO which is reduced to N ₂ ; H ₂ 0 ₂ which is reduced to H ₂ 0 or H ₂ ; and S0 ₂ which is reduced to S.

[0031] The cathode catalyst itself, if used, may be any electrically conductive oxide species that can activate the oxidant species and produce an oxygen anion species in the electrolyte. It is theorized but not required that the cathode material is selected to improve the oxygen ion conductivity of the cathode. For example, any material used as a solid oxide fuel cell cathode may be a good choice. Examples of cathode material include gadolinium-doped ceria (GDC), gadolinium strontium manganate (GSM), lanthanum strontium manganite (LSM), lanthanum strontium gallate magnesite (LSGM), lanthanum strontium ferrite (LSF), lanthanum strontium cobalt oxide (LSC), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium manganese cobalt oxide (LSMC), lanthanum strontium manganate chromate (LSMC), lanthanum calcium manganate (LCM), lanthanum nickel ferrite (LNF) or strontium samarium cobalt oxide (SSC). The cathode may also be composed of a mixture or layers of such materials. For example the cathode can be a bilayer, trilayer or multilayer cathode.

[0032] In another embodiment, the cathode could be selected from materials that include yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (ScSZ), ceria, gadolinium-doped ceria (GDC), samarium-doped ceria (SDC), calcium-doped ceria (CDC), ceria-carbonate composites (such as CDC/Na ₂ C0 ₃ ), lanthanum strontium gallate magnesite (LSGM) such as Lao _. 9Sr _0. iGao _. 8Mgo _.2 0 ₃ -5, lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium gallium magnesium oxide, lanthanum chromium vanadium oxide, lanthanum strontium chromium vanadium oxide, lanthanum chromium vanadium oxide doped with a transition metal, bismuth oxide, erbium bismuth oxide, niobium cerium oxide, bismuth molybdenum vanadium oxide, lanthanum strontium iron chromium oxide, strontium magnesium manganese molybdenum oxide, barium-zirconium-cerium-yttrium oxides, such as Ba(Zr _0. iCeo _.7 Yo _.2 )0 ₃ _5, barium-cerium-yttrium oxides, such as Ba(Ce _0.8 Yo _.2 )0 ₃ , Zr0 ₂ or any mixtures or layers of these or other oxygen transport membrane candidate materials.

[0033] At the anode side of the oxygen transport membrane the anode uses the oxygen species from the electrolyte to facilitate the oxidation of a hydrocarbon. The resulting oxygenate may optionally be converted to a second oxygenate or an olefin within the same device by the anode. Both reactions may be carried out by a single anode material or, to facilitate the desired series of reactions, the anode may comprise a mixture or layers of catalyst and/or electrocatalyst materials. The anode material may also be omitted if the electrolyte itself can facilitate the desired oxidation reaction. As shown, Figure 3 depicts a variation of Figure 1 wherein the anode contains a bilayer system with layer 4 and layer 10 providing different or complimentary functionality. Examples of anode materials include metal-doped perovskites, yttria-stabilized zirconia, scandia-stabilized zirconia, gadolinium-doped ceria (GDC), samarium doped ceria, ceria, iron manganese cerium oxide, gadolinium strontium manganate (GSM), lanthanum strontium manganite (LSM), lanthanum strontium gallate magnesite (LSGM), lanthanum strontium ferrite (LSF), lanthanum strontium cobalt oxide (LSC), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium manganese cobalt oxide (LSMC), lanthanum strontium chromate (LSCr), lanthanum strontium manganate chromate (LSMCr), lanthanum strontium iron chromium oxide, lanthanum strontium titanium oxide, strontium magnesium manganese molybdenum oxide, lanthanum calcium manganate (LCM), lanthanum nickel ferrite (L F), lanthanum chromium vanadium oxide, lanthanum strontium chromium vanadium oxide, lanthanum chromium vanadium oxide doped with a transition metal, bismuth oxide, erbium bismuth oxide, niobium cerium oxide, bismuth molybdenum vanadium oxide, nickel, nickel oxide cermet, copper, copper oxide, zeolites such as ZSM-5, and metal-doped zeolites such as copper-doped ZSM-5, iron-doped ZSM-5, copper- and iron-doped ZSM-5. The anode may also be composed of a mixture or layers of such materials.

[0034] In one example of a multilayer or mixed anode system, one material may be used to provide electrical conductivity of the electrode (this material may be a conventional fuel cell electrode material) while a second material is added to catalyze the conversion of the paraffin to an oxygenate and a third material is added to convert the resulting oxygenate into an olefin.

[0035] Some possible organic reactants and their possible products include (but are not limited to):

[0036] If a cell with external circuit configuration is used, at least one anode material should be electrically conductive to serve as the electrode for connection of the external circuit. For example, a common formulation for the anode could be a 50/50 physical mixture (by weight) of lanthanum strontium manganite and Fe-modified ZSM-5 or a layered structure of the same two components. The anode may also be composed of any SOFC electrode material combined with any zeolite material (optionally doped/modified with a transition metal).

[0037] If a cell with an internal circuit configuration is used the anode material may not need to be conductive since the electrolyte may provide sufficient conductivity.

[0038] The construction of the oxygen transport membrane can be done in a variety of different ways by those skilled in the art. Specifically, one should be able to produce the oxygen transport membrane using any known manufacturing technique known for producing solid oxide fuel cells or other solid oxide cells.

[0039] In one embodiment the oxygen transport membrane is used to generate electricity.

[0040] As discussed above, the oxidation of the alkanes takes place at the anode and reduction of the oxidant to the oxygen ion species occurs at the cathode. For the oxygen ions to diffuse through the electrolyte at an operable rate, the ionic conductivity of the oxygen transport membrane must be sufficiently high. The relative rate of oxygen ion transport depends strongly on the chosen electrolyte. Another factor is the operating temperature, as the ionic conductivity of each membrane material depends on the operating temperature. As such, the optimum temperature will be the lowest temperature that gives sufficient rates of oxygen transport through the membrane. For example, the oxygen ion conductivity of yttria-stabilized zirconia (YSZ) is sufficient when the operating temperature is higher than 750°C. In another example the oxygen ion conductivity of lanthanum strontium gallate magnesite (LSGM) is sufficient when the operating temperature is higher than 600°C. In other embodiments the operating temperature of the oxygen transport membrane is from about 300 °C to about 800 °C or even from about 450 °C to about 700 °C.

[0041] The following examples of certain embodiments of the invention are given. Each example is provided by way of explanation of the invention, one of many embodiments of the invention, and the following examples should not be read to limit, or define, the scope of the invention. Example 1

[0042] [ H ₄ ][ZSM-5] (Si0 ₂ /Al ₂ 0 ₃ = 50) catalyst was crushed to a size of 20-40 mesh. The catalyst was calcined in a muffle furnace at 550°C to convert the ammonium form to the acidic form, H-ZSM-5. Samples were heated to 150°C at 2°C/min, maintained at 150°C for 2 hours, heated to 450°C at 4°C/min, maintained at 450°C for 12 hours, then heated to 550°C at 4°C/min and held 550°C for 6 hours. Following calcination, the catalyst was cooled to ambient temperature.

[0043] The resulting H-ZSM-5 powder was sieved to a particle size of <140 mesh and suspended in terpineol such that the resulting suspension was 35% H-ZSM-5 by weight. The H- ZSM-5/terpineol suspension was then mixed with an equal weight of lanthanum strontium manganite (LSM) electrode ink.

[0044] The experiment used an electrolyte-supported button cell with total active electrode area of 0.71 cm ² . The electrolyte material was scandia-stabilized zirconia (ScSZ). The cathode side of the electrolyte was coated with LSM electrode ink using a screen printing procedure and then dried.

[0045] The anode side of the electrolyte was coated with the ZSM-5/LSM mixture described above using a screen printing procedure and then dried. Ag mesh and Ag wires were then attached to each side of the cell using an Ag/Pd conductive paste and the assembly was dried in air at 125°C for 30 minutes.

[0046] The cell was then affixed to a button cell testing apparatus and placed within a tube furnace. Flowing air was provided to both sides of the cell at ambient pressure and a flow rate of 50 standard cubic centimeters per minute (seem). The apparatus was heated to an internal temperature of 800°C at a rate of l°C/min.

[0047] After finishing the initial temperature ramp, the anode and cathode voltage leads were connected to a potentiostat. The flow of air to the anode was ceased and the anode was swept with 50 seem (standard cubic centimeters per minute) N ₂ to flush out 0 ₂ to avoid flammability issues when CH ₄ was later added. After 30 minutes of N ₂ sweep, the flow of N ₂ to the anode was ceased, and 50 seem CH ₄ was supplied. The potentiostat was used to supply a constant current of 50 mA through the cell. After operation for approximately 1600 seconds, a gas phase sample (Sample 1) was collected using a plastic syringe from the anode effluent. [0048] A sample of air saturated with methanol vapor was analyzed to determine the retention time of methanol and act as a standard for the detection of methanol. Figure 4 depicts a gas chromatogram of the methanol-in-air standard sample.

[0049] After this methanol standard, ambient air was analyzed in the gas chromatograph to ensure there were not large amounts of holdover methanol vapors from injection of the standard sample. Figure 5 depicts a gas chromatogram sample of air.

[0050] Sample 1 described above was then analyzed; the methanol peak area observed for Sample 1 was similar to that of the methanol standard, suggesting that Sample 1 was nearly saturated with methanol vapors. Significant quantities of CO and C0 ₂ were not observed in Sample 1. A gas chromatograph of Sample 1 is shown in Figure 6. Following the analysis of Sample 1, another pure air sample was analyzed and did not show a large methanol peak.

[0051] Gas flow to the cell cathode was then changed to pure N ₂ (50 seem). Without 0 ₂ at the cathode, it is should not be possible to transport O ^2" anions across the electrolyte; therefore, methanol production at the anode should not be observed.

[0052] Sample 2 was collected from the anode effluent during N ₂ flow to the cathode and gas chromatograph analysis indeed did not seem to indicate the conversion of methane to methanol in significant quantities. A gas chromatogram of Sample 2 is shown in Figure 7.

Example 2

[0053] Strontium chloride (267 mg), lanthanum nitrate (1300 mg), and manganese sulfate (845 mg) were dissolved in distilled water (2 mL). This solution was added dropwise to ZSM-5 (4g) with mechanical stir bar mixing. This wet powder was calcined in air to generate the oxide (500 C, 30 minutes).

[0054] One gram of the resulting dark powder oxide was combined with one gram of terpineol. This slurry was combined with 2 grams of commercially available lanthanum strontium manganite (LSM). A portion of this mixture was then deposited uniformly in a 1 cm diameter circle onto a 1 inch diameter electrolyte disc. This deposition was carried out by screen printing. The cell was heated to 125°C for 30 min to remove the terpineol solvent.

[0055] An identical screen-printed deposition, this time of the pure commercial LSM, was carried out on the opposite face of the electrolyte disc, overlapping as exactly as possible with the deposition on the original side, sandwiching the electrolyte disc in between. The cell was heated to 125°C for 30 minutes to remove the solvent. Two silver wire meshes, attached to silver electrical leads, were adhered to the LSM-containing deposits (one mesh on each face of the cell), using a metallic palladium and silver based conductive paste. The paste was then air dried at room temperature for 1 hour. The entire cell was then sealed to the mouth of a 1 inch diameter alumina tube with a high temperature adhesive. The ZSM-5 containing face was pointed toward the interior of the tube.

[0056] The apparatus was heated at 1°C per minute from ambient to a reaction temperature of 800 C. The internal side of the 1-inch tube was then purged with nitrogen by flowing through a smaller, concentric tube at 100 seem for 15 minutes, following a 50/50 nitrogen/methane mixture flowed through it at 200 seem (100 seem N ₂ and 100 seem CH ₄ ). A dry ice cooled condenser was attached to the exhaust, to trap any liquid products. Outside the tube, air was flowed over the exterior face of the cell at a rate of 100 seem. The silver electrodes inside and outside the tube were short-circuited to each other through a potentiostat (for current measurement) for a total of 4 hours. Following this period, the dry ice trap was sealed off at each end, it was heated to room temperature to vaporize the liquid that was collected in the trap, and its contents were injected into a mass spectrometer for characterization. Methanol was observed at a mass-to-charge ratio (m/z) of 31.

[0057] In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as an additional embodiment of the present invention.

[0058] Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.