Method for producing catalyst for vinyl acetate production

Abstract

Methods for producing Au-Pd catalysts suitable for the production of vinyl acetate, which may include drying the catalyst at a higher temperature (e.g., 160 °C or higher) after incorporating a promoter to reconstruct the metals and / or alloys on the catalyst. The reconstructed catalyst advantageously has increased catalytic activity and improved stability.

Description

Background Art

[0001] Vinyl acetate is produced by reacting ethylene, oxygen, and acetic acid in the presence of a catalyst (e.g., palladium and / or gold supported on a carrier). In addition, it has been shown that compounds such as sodium acetate, potassium acetate, and cesium acetate increase the yield and selectivity of the reaction to produce vinyl acetate. The acetate salts can be impregnated on a support and / or introduced into the reactor together with the feed. BRIEF DESCRIPTION OF THE DRAWINGS

[0002] The following figures are included to illustrate certain aspects of the present disclosure and should not be regarded as exclusive configurations. As will be appreciated by those skilled in the art benefiting from the present disclosure, the disclosed subject matter is capable of numerous modifications, variations, combinations, and equivalents in form and function.

[0003] Figure 1 A flowchart showing a non-limiting example method for preparing the catalyst described herein is shown.

[0004] Figure 2 A process flowchart showing an example vinyl acetate production process of the present disclosure is shown.

[0005] Figure 3 is the X-ray diffraction (XRD) data of a catalyst sample dried at 100 °C, 140 °C, or 180 °C. DETAILED DESCRIPTION

[0006] The present disclosure relates to a method for producing a catalyst suitable for vinyl acetate production. More specifically, the method described herein includes a higher drying temperature after incorporating a promoter. Without being bound by theory, it is believed that heating to 160 °C or higher after impregnation with a promoter changes the structure of the catalyst. The reconstructed catalyst advantageously has increased catalytic activity and improved stability, which reduces the time for oxygen ingress. Without being bound by theory, it is believed that the reconstruction of the catalyst involves restructuring the PdAu alloy composition into a thermodynamically more favorable PdAu alloy.

[0007] Figure 1A flow chart showing a non-limiting exemplary method for preparing the catalysts described herein is presented. Generally, the methods of the present disclosure include: impregnating a porous support 102 with a water-insoluble gold compound and a water-insoluble palladium compound 108 by precipitating a water-soluble gold compound 104 and a water-soluble palladium compound 106 in the presence of the porous support 102 to produce a precipitated support 110; washing 112 the precipitated support 110; reducing 114 the water-insoluble gold compound and the water-insoluble palladium compound on the precipitated support 110 to produce a metal-impregnated support 116; impregnating 118 the metal-impregnated support 116 with an alkali metal promoter 120 to produce a metal / promoter-impregnated support 122; and drying 124 the metal / promoter-impregnated support 122 at 160 °C or higher to produce a catalyst 126.

[0008] The porous support 102 can be impregnated 108 with the water-insoluble gold compound 104 and the water-insoluble palladium compound 106 simultaneously in the following manner: (a) mixing (or impregnating) the porous support 102 with an aqueous solution of the water-soluble gold compound 104 and the water-soluble palladium compound 106, and then (b) adding a precipitating agent to the mixture so that the water-soluble gold compound 104 and the water-soluble palladium compound 106 are precipitated onto the porous support 102 as the water-insoluble gold compound and the water-insoluble palladium compound, respectively. Alternatively, the water-insoluble gold compound 104 and the water-insoluble palladium compound 106 can be precipitated in separate steps. For example, the impregnation 108 can include: (a) mixing (or impregnating) the porous support 102 with an aqueous solution of the water-soluble palladium compound 106, (b) adding a precipitating agent to the mixture to precipitate the water-soluble palladium compound 106 as the water-insoluble palladium compound onto the porous support 102, (c) washing the porous support having the water-insoluble palladium compound thereon, (d) mixing (or impregnating) the porous support having the water-insoluble palladium compound thereon with an aqueous solution of the water-soluble gold compound 104, and (e) adding a precipitating agent (the same or different from the precipitating agent used for the water-soluble palladium compound 106) to the mixture to precipitate the water-soluble gold compound 104 as the water-insoluble gold compound, thereby producing the precipitated support 110. Alternatively, the impregnation 108 can include: (a) mixing (or impregnating) the porous support 102 with an aqueous solution of the water-soluble gold compound 104, (b) adding a precipitating agent to the mixture to precipitate the water-soluble gold compound 104 as the water-insoluble gold compound onto the porous support 102, (c) washing the porous support having the water-insoluble gold compound thereon, (d) mixing (or impregnating) the porous support having the water-insoluble gold compound thereon with an aqueous solution of the water-soluble palladium compound 106, and (e) adding a precipitating agent (the same or different from the precipitating agent used for the water-soluble gold compound 104) to the mixture to precipitate the water-soluble palladium compound 106 as the water-insoluble palladium compound, thereby producing the precipitated support 110.

[0009] The porous support 102 can have any of a variety of different geometries. For example, the shape of the porous support 102 can include, but is not limited to, spheres, flakes, cylinders, fibrous, polyhedral granular, etc., and any mixtures thereof. Preferably, the porous support 102 has a diameter of from about 1 mm to about 10 mm (or from about 1 mm to about 5 mm, or from about 3 mm to about 8 mm, or from about 5 mm to about 10 mm). The diameter of the porous support 102 can be measured by light scattering techniques or microscopy techniques. Preferably, the porous support 102 is spherical and has a diameter of from about 4 mm to about 8 mm. Those skilled in the art will recognize that the shape of the porous support 102 may differ from the exact shape described. For example, the porous support 102 described as spherical has a generally spherical shape.

[0010] The surface area of the porous support 102 can be from about 10 m 2 / g to about 350 m 2 / g (or from about 10 m 2 / g to about 150 m 2 / g, or from about 100 m 2 / g to about 200 m 2 / g, or from about 150 m 2 / g to about 350 m 2 / g). The pore volume of the porous support 102 can be from about 0.1 cm 3 / g to about 2 cm 3 / g (from about 0.1 cm 3 / g to about 1 cm 3 / g, or from about 0.5 cm 3 / g to about 1.5 cm 3 / g, or from about 1 cm 3 / g to about 2 cm 3 / g). The surface area and pore volume can be measured and / or derived from measurements of BET nitrogen adsorption in accordance with ASTM D5601-96(2017).

[0011] Examples of the porous support 102 include, but are not limited to, silica, alumina, aluminosilicate, titanium dioxide, zirconia, spinel, carbon, etc., and any combination thereof. Silica is the preferred porous support 102.

[0012] Examples of the water-insoluble gold compound 104 include, but are not limited to, gold(III) chloride, tetrahydroauric(III) acid, etc., and any combination thereof.

[0013] Examples of the water-soluble palladium compound 106 include, but are not limited to, palladium(II) chloride, sodium palladium(II) chloride, alkaline earth metal tetrachloropalladate(II), palladium(II) nitrate, palladium(II) sulfate, etc., and any combination thereof.

[0014] Generally, gold is present at a lower molar concentration than palladium. The molar ratio of gold to palladium on the precipitated support 110 (and thus the metal-impregnated support 116, the metal / promoter-impregnated support 122, and the catalyst 126) can be from about 0.01:1 to about 0.7:1 (or from about 0.01:1 to about 0.1:1, or from about 0.1:1 to about 0.5:1, or from about 0.3:1 to about 0.7:1).

[0015] The total amount of metal (as gold and palladium, rather than salts) on the precipitated support 110 (and thus the metal-impregnated support 116, the metal / promoter-impregnated support 122, and the catalyst 126) can be from about 0.05 wt% to about 20 wt% (or from about 0.05 wt% to about 10 wt%, or from about 1 wt% to about 15 wt%, or from about 5 wt% to about 20 wt%).

[0016] The amount of time and temperature to which the porous support 102 is exposed to the water-soluble metal salts 104 and 106 prior to precipitation can vary. The time range can be from about 10 minutes to about 2 days (or from about 30 minutes to about 1 day, or from about 1 hour to about 6 hours). The temperature range can be from about 20 °C to about 50 °C (or from about 23 °C to about 40 °C).

[0017] The mixing (or impregnation) of the porous support 102 with the water-soluble metal salts 104 and 106 can be accomplished by optionally mixing the components together under heating and allowing time to elapse with or without additional or continuous mixing. Additionally, during the impregnation process, the water in the aqueous solution of the water-soluble metal salts 104 and 106 can optionally be allowed to evaporate such that the remaining mixture has 10 wt% or less (or 5 wt% or less, or 1 wt% or less) water. Various rotating, tumbling, or equivalent devices can be used for the mixing (or impregnation) step.

[0018] Examples of precipitating agents include, but are not limited to, alkali metal hydroxides, alkali metal bicarbonates and / or alkali metal carbonates, alkali metal silicates, alkali metal borates, hydrazine, etc., and any combination thereof. Preferably, in cases where the water-insoluble salts of gold and / or palladium can be hydroxides and / or oxides, the precipitating agent is sodium hydroxide and / or potassium hydroxide. The precipitating agent is typically in an aqueous solution. The amount of the precipitating agent should be sufficient to ensure that all of the water-soluble salts of palladium and gold precipitate in the form of water-insoluble salts. To ensure proper precipitation, the amount of the precipitating agent present is preferably about 1 to 3 times (or 1.1 to 2 times) the total amount of anions present in the water-soluble metal salts.

[0019] Washing after precipitation can be carried out with water (such as deionized water) or other suitable solvents that do not dissolve the water-insoluble metal salts but dissolve the anions (such as chloride ions) generated during the precipitation process. Preferably, washing is carried out until there is about 1000 ppm or less of said anions in the wash effluent.

[0020] After washing 112 the precipitated support 110, the precipitated support 110 is exposed to a reducing agent. Between the washing 112 and the reduction 114, the precipitated support 110 can be dried (e.g., in an inert atmosphere such as nitrogen, argon, or air, at a temperature of about 50 °C to about 150 °C for about 30 minutes to about 3 days).

[0021] Reduction 114 can be carried out in the liquid phase or in the gas phase. For example, reduction 114 in the liquid phase can be carried out using an aqueous solution of hydrazine hydrate. The liquid phase method can be carried out at a temperature of about 20 °C to about 50 °C (or about 23 °C to about 30 °C) for a time sufficient to convert at least 95 mol% (or at least 98 mol%) of the insoluble metal salt into metal (e.g., about 1 hour to about 24 hours).

[0022] Reduction 114 in the gas phase can be carried out using, for example, hydrogen and / or a hydrocarbon (such as ethylene). Optionally, an inert carrier gas such as nitrogen or argon can be used in the gas phase method, where, for example, the concentration of hydrogen and / or hydrocarbon accumulates to about 0.1 vol% to about 10 vol% (or about 0.5 vol% to about 5 vol%) of the gas to which the precipitated support 110 is exposed. The gas phase reduction method can be carried out at a temperature of about 50 °C to about 250 °C (or about 100 °C to about 200 °C) for a time sufficient to convert at least 95 mol% (preferably at least 98 mol%) of the insoluble metal salt into metal (e.g., about 1 hour to about 24 hours).

[0023] Reduction 114 produces a metal-impregnated support 116, which is then impregnated 118 with an alkali metal promoter 120 to produce a metal / promoter-impregnated support 122. Examples of the alkali metal promoter 120 include, but are not limited to, sodium, potassium, or cesium salts of formic acid, acetic acid, propionic acid, butyric acid, etc., and any combination thereof. Potassium metal promoter is preferred. Potassium acetate is the preferred alkali metal promoter 120.

[0024] The amount of time and the temperature to which the metal-impregnated support 116 is exposed to the alkali metal promoter 120 can vary. The time range can be from about 1 minute to about 6 hours (or about 1 minute to about 1 hour, or about 30 minutes to about 1 day, or about 1 hour to about 6 hours). The temperature range can be from about 20 °C to about 50 °C (or about 23 °C to about 40 °C).

[0025] The mixing (or impregnation) of the metal-impregnated support 116 with the alkali metal promoter 120 can be carried out by optionally mixing the components together under heating and allowing time to elapse with or without additional or continuous mixing. Additionally, during the impregnation process, the water in the alkali metal promoter 120 can optionally be allowed to evaporate such that the remaining mixture has 10 wt% or less (or 5 wt% or less, or 1 wt% or less) of water. Various rotating, tumbling, or equivalent equipment can be used for the mixing (or impregnation) step.

[0026] The metal / promoter-impregnated support 122 is then dried 124 at 160 °C or higher (about 160 °C to about 250 °C, or about 160 °C to about 200 °C, or about 200 °C to about 250 °C) to produce the catalyst 126. Also, without being bound by theory, it is believed that temperatures above 160 °C will cause the catalyst to reconstruct (as shown by XRD data having a lower 2θ value at the peak intensity of 2θ between 38° and 40°). Additionally, it is believed that temperatures above 250 °C will cause the catalyst to sinter and thus cause the catalyst to begin to deactivate. Preferably, the catalyst 126 has a 2θ value at the peak XRD intensity between 38° and 40° of about 38.6° to about 39.2° (or about 38.7° to about 39.1°, or about 38.8° to about 39.1°). XRD is performed using a powder sample loaded in an in-situ cell. Unless otherwise specified, XRD measurements are performed in a nitrogen or air atmosphere and at 25 °C.

[0027] Drying 124 can be carried out in an inert atmosphere such as nitrogen, argon, or air for about 10 minutes to about 1 day (or about 10 minutes to about 3 hours, or about 30 minutes to about 8 hours, or about 6 hours to about 1 day). Drying 124 can be carried out in any suitable system, including but not limited to a fluidized bed dryer, a belt dryer, or any other drying vessel.

[0028] Based on the dry weight, the alkali metal promoter 120 can be present in the catalyst 126 at about 0.1 wt% to about 10 wt% (about 0.1 wt% to about 5 wt%, or about 1 wt% to about 7 wt%, or about 5 wt% to about 10 wt%).

[0029] Thus, the catalysts of the present disclosure can comprise: (a) gold, palladium, and / or a gold-palladium alloy, (b) an alkali metal promoter, and (c) a porous support, wherein the catalyst has a 2θ value at the peak x-ray diffraction intensity between 38° and 40° of about 38.6° to about 39.2°.

[0030] The catalysts of the present disclosure can be used for the synthesis of vinyl acetate from ethylene, oxygen, and acetic acid in the gas phase. For example, the method can include: reacting ethylene, oxygen, and acetic acid in the presence of the catalysts of the present disclosure to produce vinyl acetate.

[0031] The catalysts prepared by the methods described herein can be used in a variety of vinyl acetate synthesis methods and systems, including fluidized bed reactors, gas phase reactors, or stirred tank reactor methods and systems. Examples of vinyl acetate synthesis methods and systems are described in U.S. Patent Nos. 5,731,457, 5,968,860, 6,107,514, 6,420,595, 8,822,717, and U.S. Patent Application No. 2010 / 0125148, each of which is incorporated herein by reference.

[0032] By way of non-limiting example, Figure 2 FIG. 200 is a process flow diagram of an exemplary vinyl acetate production process in which the catalysts of the present disclosure can be implemented. Components can be added to and modified in process 200 without changing the scope of the invention. Further, as will be appreciated by those skilled in the art, the description of process 200 and the associated systems uses flows to describe the fluids passing through the various pipelines. For each flow, whether explicitly described or not, the associated system has a corresponding pipeline (e.g., a pipe or other path through which the corresponding fluid or other material can easily pass) and optionally valves, pumps, compressors, heat exchangers, or other equipment to ensure the proper operation of the system.

[0033] Further, the descriptors used for the various flows do not limit the composition of the flows to that consisting of the descriptors. For example, an ethylene flow does not necessarily consist only of ethylene. Instead, an ethylene flow can contain ethylene and a diluent gas (e.g., an inert gas). Alternatively, an ethylene flow can consist solely of ethylene. Alternatively, an ethylene flow can contain ethylene, another reactant, and optionally an inert component.

[0034] In the illustrated process 200, an acetic acid stream 202 and an ethylene stream 204 are introduced into vaporizer 206. Optionally, ethane can also be added to vaporizer 206. Further, one or more recycle streams (shown as recycle streams 208 and 210) can also be introduced into vaporizer 206. Although recycle streams 208 and 210 are shown as being introduced directly into vaporizer 206, the recycle streams or other recycle streams can be combined with acetic acid stream 202 (not shown) prior to introduction into vaporizer 206.

[0035] The temperature and pressure of vaporizer 206 can vary over a wide range. Vaporizer 206 is preferably operated at a temperature from 100°C to 250°C, or from 100°C to 200°C, or from 120°C to 150°C. The operating pressure of vaporizer 206 is preferably from 0.1 MPa to 2 MPa, or 0.25 MPa to 1.75 MPa, or 0.5 MPa to 1.5 MPa. Vaporizer 206 produces a vaporized feed stream 212. The vaporized feed stream 212 exits vaporizer 206 and is combined with an oxygen stream 214 prior to feeding into vinyl acetate reactor 218 to produce a combined feed stream 216.

[0036] Regarding the general operating conditions of the vinyl acetate reactor 218, when producing vinyl acetate in the vinyl acetate reactor 218, the molar ratio of ethylene to oxygen is preferably less than 20:1 (for example, 1:1 to 20:1, or 1:1 to 10:1, or 1.5:1 to 5:1, or 2:1 to 4:1). In addition, the molar ratio of acetic acid to oxygen in the vinyl acetate reactor 218 is preferably less than 10:1 (for example, 0.5:1 to 10:1, 0.5:1 to 5:1, or 0.5:1 to 3:1). The molar ratio of ethylene to acetic acid in the vinyl acetate reactor 218 is preferably less than 10:1 (for example, 1:1 to 10:1, or 1:1 to 5:1, or 2:1 to 3:1). Thus, the combined feed stream 216 can contain ethylene, oxygen, and acetic acid in the stated molar ratios.

[0037] The vinyl acetate reactor 218 can be a shell-and-tube reactor capable of absorbing the heat generated by the exothermic reaction through a heat exchange medium and controlling the temperature therein within a temperature range of 100°C to 250°C, or 110°C to 200°C, or 120°C to 180°C. The pressure in the vinyl acetate reactor 218 can be maintained at 0.5 MPa to 2.5 MPa, or 0.5 MPa to 2 MPa.

[0038] In addition, the vinyl acetate reactor 218 can be a fixed-bed reactor or a fluidized-bed reactor, preferably a fixed-bed reactor containing a catalyst prepared by the methods disclosed herein.

[0039] The vinyl acetate reaction in the reactor 218 produces a crude vinyl acetate stream 220. Depending on the conversion rate and reaction conditions, the crude vinyl acetate stream 220 can contain 5 wt% to 30 wt% vinyl acetate, 5 wt% to 40 wt% acetic acid, 0.1 wt% to 10 wt% water, 10 wt% to 80 wt% ethylene, 1 wt% to 40 wt% carbon dioxide, 0.1 wt% to 50 wt% alkanes (such as methane, ethane, or a mixture thereof), and 0.1 wt% to 15 wt% oxygen. Optionally, the crude vinyl acetate stream 220 can also contain 0.01 wt% to 10 wt% ethyl acetate. The crude vinyl acetate stream 220 can contain other compounds such as methyl acetate, acetaldehyde, acrolein, propane, and inert gases such as nitrogen or argon. Generally, except for inert gases, these other compounds are present in very low amounts.

[0040] The crude vinyl acetate stream 220 passes through a heat exchanger 222 to reduce the temperature of the crude vinyl acetate stream 220. Preferably, the crude vinyl acetate stream 220 is cooled to a temperature of 80°C to 145°C, or 90°C to 135°C.

[0041] The systems and methods described herein measure the concentration of one or more metal components in the crude vinyl acetate stream 220 or a downstream stream thereof. As described above, the concentration of the metal components can be used to evaluate, inter alia, the operating condition of the system and / or the condition of the catalyst.

[0042] The crude vinyl acetate stream 220 can then be fed to a separator 226 (e.g., a distillation column). Preferably, the liquefiable components are hardly condensed, and the cooled crude vinyl acetate stream 220 (post heat exchanger 222) is introduced into the separator 226 as a gas.

[0043] The energy for separating the components in the crude vinyl acetate stream 220 can be provided by the heat of reaction in the reactor 218. In some embodiments, an optional reboiler (not shown) may be present, dedicated to increasing the separation energy within the separator 226.

[0044] The separator 226 separates the crude vinyl acetate stream 220 into at least two streams: an overhead stream 228 and a bottoms stream 230. The overhead stream 228 can contain ethylene, carbon dioxide, water, alkanes (e.g., methane, ethane, propane, or mixtures thereof), oxygen, and vinyl acetate. The bottoms stream 230 can contain vinyl acetate, acetic acid, water, and possibly ethylene, carbon dioxide, and alkanes.

[0045] The overhead stream 228 can be further processed 232 (e.g., for further separation and / or enrichment of gases such as ethylene and / or methane) to ultimately produce a recycle stream 210. Similarly, it is optional for the recycle stream 210 to be used as feed to the vaporizer 206 (as is or pre-mixed with another stream).

[0046] The bottoms stream 230 can be further processed 234 (e.g., for further purification and separation) to ultimately produce a vinyl acetate product stream 236 and a recycle stream 208. Similarly, it is optional for the recycle stream 208 to be used as feed to the vaporizer 206 (as is or pre-mixed with another stream).

[0047] Example embodiment

[0048] A first non-limiting exemplary embodiment of the present disclosure is a method that includes: impregnating a porous support with a water-insoluble gold compound and a water-insoluble palladium compound by precipitating a water-soluble gold compound and a water-soluble palladium compound in the presence of the porous support to produce a precipitated support; washing the precipitated support; reducing the water-insoluble gold compound and the water-insoluble palladium compound on the precipitated support to produce a metal-impregnated support; impregnating the metal-impregnated support with an alkali metal promoter to produce a metal / promoter-impregnated support; and drying the metal / promoter-impregnated support at 160 °C or higher to produce a catalyst. The first non-limiting exemplary embodiment may further include one or more of the following: Element 1: wherein the impregnation of the porous support is carried out in multiple steps, the steps including: impregnating the porous support with a first water-soluble compound, the first water-soluble compound being the water-insoluble gold compound or the water-insoluble palladium compound; precipitating the first water-soluble compound in the presence of the porous support; impregnating the porous support with a second water-soluble compound, the second water-soluble compound being the water-insoluble gold compound or the water-insoluble palladium compound, wherein the first and second water-soluble compounds are different; and precipitating the second water-soluble compound in the presence of the porous support; Element 2: wherein the molar ratio of gold to palladium in the catalyst is from about 0.01:1 to about 0.7:1; Element 3: wherein, based on dry weight, the alkali metal in the alkali metal promoter is present in the catalyst in an amount of about 0.1 wt% to about 10 wt%; Element 4: wherein the alkali metal promoter is selected from the group consisting of sodium, potassium or cesium salts of formic acid, acetic acid, propionic acid, butyric acid, and any combination thereof; Element 5: wherein the drying of the metal / promoter-impregnated support is carried out in the presence of a gas comprising nitrogen, argon and / or air; Element 6: wherein the catalyst has a 2θ value of the peak x-ray diffraction intensity between 38° and 40° of about 38.6° to about 39.2°; Element 7: wherein the reduction is carried out in a gas phase comprising hydrogen and / or a hydrocarbon; Element 8: Element 7, and wherein the hydrocarbon is ethylene; Element 9: Element 7, and wherein the gas phase further comprises an inert carrier gas; Element 10: Element 7, and wherein the reduction is carried out at about 50 °C to about 250 °C for about 1 hour to about 24 hours; Element 11: wherein the reduction is carried out in a liquid phase using hydrazine hydrate; Element 12: Element 11, and wherein the reduction is carried out at about 20 °C to about 50 °C for about 1 hour to about 24 hours; Element 13: wherein the drying of the metal / promoter-impregnated support is at about 160 °C to about 250 °C; and Element 14: Element 13, and wherein the drying of the metal / promoter-impregnated support lasts for about 10 minutes to about 1 day.Examples of combinations include, but are not limited to, combinations of element 11 (and optionally element 12) with one or more of elements 1-10; combinations of element 13 (and optionally element 14) with one or more of elements 1-10; combinations of element 7 with one or more of elements 8-10; combinations of element 1 with one or more of elements 2-10; combinations of element 2 with one or more of elements 3-10; combinations of element 3 with one or more of elements 4-10; combinations of element 4 with one or more of elements 5-10; and combinations of element 5 with one or more of elements 6-10.

[0049] A second non-limiting exemplary embodiment is a catalyst produced by the method of the first non-limiting exemplary embodiment (optionally including one or more of elements 1-14).

[0050] A third non-limiting exemplary embodiment is a catalyst comprising: (a) gold, palladium, and / or a gold-palladium alloy, (b) an alkali metal promoter, and (c) a porous support, wherein the catalyst has a peak x-ray diffraction intensity between 38° and 40° with a 2θ value of from about 38.6° to about 39.2°. The third non-limiting exemplary embodiment may further include one or more of the following: Element 15: wherein the molar ratio of the gold and the palladium as elemental metals and alloys in the catalyst is from about 0.01:1 to about 0.7:1; Element 16: wherein, based on dry weight, the alkali metal in the alkali metal promoter is present in the catalyst at about 0.1 wt% to about 10 wt%; Element 17: wherein the alkali metal promoter is selected from the group consisting of sodium, potassium, or cesium salts of formic acid, acetic acid, propionic acid, butyric acid, and any combination thereof; and Element 18: wherein the porous support is selected from the group consisting of silica, alumina, aluminosilicate, titanium dioxide, zirconia, spinel, carbon, and any combination thereof. Examples of combinations include, but are not limited to, combinations of Element 15 with one or more of Elements 16-18; combinations of Element 16 with one or both of Elements 17-18; and combinations of Elements 17 and 18.

[0051] A fourth non-limiting exemplary embodiment is a method that includes reacting ethylene, oxygen, and acetic acid in the presence of a catalyst of the present disclosure to produce vinyl acetate. The fourth non-limiting exemplary embodiment may further include one or more of the following: Element 19: wherein the molar ratio of ethylene to oxygen is less than about 20:1; Element 20: wherein the molar ratio of acetic acid to oxygen is less than about 10:1; Element 21: wherein the molar ratio of ethylene to acetic acid is less than about 10:1; Element 22: wherein the reaction is at from about 100 °C to about 250 °C; Element 23: wherein the reaction is at from about 0.5 MPa to about 2.5 MPa; Element 24: wherein the reaction produces 5 wt% to 30 wt% vinyl acetate, 5 wt% to 40 wt% acetic acid, 0.1 wt% to 10 wt% water, 10 wt% to 80 wt% ethylene, 1 wt% to 40 wt% carbon dioxide, 0.1 wt% to 50 wt% alkanes, 0.1 wt% to 15 wt% oxygen, and optionally 0.01 wt% to 10 wt% ethyl acetate; and Element 25: Element 24, and the method further includes separating at least a portion of the vinyl acetate from the other products. Examples of combinations include, but are not limited to, combinations of two or more of Elements 19-21; combinations of Element 22 and Element 23; combinations of Element 22 and / or Element 23 with one or more of Elements 19-21; and combinations of Element 24 (and optionally Element 25) with one or more of Elements 19-23.

[0052] Unless otherwise indicated, all numerical values expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and the like used in the specification and the related claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the embodiments of the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0053] One or more illustrative embodiments incorporating one or more elements of the present invention are presented herein. For clarity, not all features of a physical implementation are described or shown in this application. It should be understood that in developing a physical embodiment incorporating one or more elements of the present invention, numerous implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related, business-related, government-related, and other constraints, which vary by implementation and over time. While such efforts may be time-consuming, such efforts would be routine tasks for those of ordinary skill in the art that would benefit from the present disclosure.

[0054] While these compositions and methods are described herein using the transitional phrase "comprising" various components or steps, the compositions and methods can also "consist essentially of" or "consist of" these various components and steps.

[0055] To facilitate a better understanding of the embodiments of the present invention, examples of the following preferred or representative embodiments are given. The following examples should in no way be construed as limiting, or defining the scope of, the present invention.

[0056] Instance

[0057] Catalyst samples were prepared by using Na2PdCl4 and NaAuCl4 as water-soluble metal salts, NaOH as a precipitant, KA-160 (a silica / alumina support material available from Sud Chemie) as a porous support, and potassium acetate (KOAc) as an alkali metal promoter to prepare Pd / Au / KOAc-impregnated KA-160 mother material. After impregnation with KOAc, the samples were loaded into an in-situ cell for XRD analysis. Under a nitrogen-containing atmosphere, the samples in the XRD were ramped to a specified drying temperature of 100 °C, 140 °C, or 180 °C. XRD data for 2θ between 36° and 52° were continuously collected with a Cu K-α source at a step size of 0.06°. Phases were determined by peak matching with a crystallographic database such as the ICDD database.

[0058] Figure 3 are the XRD data of the samples at 100 °C, 140 °C, or 180 °C. The XRD spectra show that increasing the temperature changes the structure of the catalyst, because the peak between 38° and 40° for the sample at 180 °C is at a lower 2θ value compared to the samples at 100 °C and 140 °C. More specifically, the 2θ values corresponding to the maximum signal between 38° and 40° for the samples at 100 °C, 140 °C, or 180 °C are 39.4°, 39.5°, and 38.9°, respectively. After cooling to room temperature, the 2θ value corresponding to the maximum signal between 38° and 40° remains unchanged. Additionally, this 2θ value corresponding to the maximum signal between 38° and 40° was observed in other samples that were dried to the same maximum temperature in other apparatuses (such as an oven) and then cooled to room temperature.

[0059] This example shows that the structure in the final catalyst changes when heated to a higher temperature. Without being bound by theory, it is believed that after impregnation with the alkali metal promoter, drying at 160 °C and higher is required to see this structural change.

[0060] Accordingly, the present invention is well suited to attain the ends and advantages mentioned as well as those inherent therein. The specific examples and configurations disclosed above are merely illustrative, as it will be apparent to those skilled in the art who have benefited from the teachings herein that the present invention can be modified and practiced in different but equivalent ways. Additionally, no limitation is intended as to the details of the construction or design shown herein other than as described in the following claims. Thus, it is evident that the specific illustrative examples disclosed above can be varied, combined, or modified, and all such variations are considered to be within the scope and spirit of the present invention. The present invention disclosed illustratively herein can be suitably practiced in the absence of any element not specifically disclosed herein and / or any optional element disclosed herein. While these compositions and methods are described with the transitional terms "comprising," "containing," or "including" various components or steps, these compositions and methods can also "consist essentially of these various components and steps" or "consist of these various components and steps." All numerical values and ranges disclosed above can vary to some extent. Whenever a numerical range with a lower and upper limit is disclosed, any numerical value and any included range falling within that range are specifically disclosed. In particular, each range of values disclosed herein (of the form "from about a to about b," or equivalently, "from approximately a to b," or equivalently, "from approximately a - b") should be understood to set forth every numerical value and range subsumed within the broader value range. Additionally, the terms in the claims have their plain and ordinary meaning unless the patentee has otherwise defined them clearly and explicitly. Further, the indefinite articles "a" or "an" as used in the claims are defined herein to mean one or more than one of the elements they introduce.

Claims

1. A method for preparing a catalyst, which comprises: impregnating a porous support with a water-insoluble gold compound and a water-insoluble palladium compound by precipitating a water-soluble gold compound and a water-soluble palladium compound in the presence of the porous support to produce a precipitated support; washing the precipitated support; reducing the water-insoluble gold compound and the water-insoluble palladium compound on the precipitated support to produce a metal-impregnated support; impregnating the metal-impregnated support with an alkali metal promoter to produce a metal / promoter-impregnated support; and drying the metal / promoter-impregnated support in an inert atmosphere at a temperature of 160 °C to 250 °C to produce a catalyst.

2. The method according to claim 1, wherein The impregnation of the porous support is carried out in a plurality of steps, which include: impregnating the porous support with a first water-soluble compound, which is the water-insoluble gold compound or the water-insoluble palladium compound; precipitating the first water-soluble compound in the presence of the porous support; impregnating the porous support with a second water-soluble compound, which is the water-insoluble gold compound or the water-insoluble palladium compound, wherein the first and second water-soluble compounds are different; and precipitating the second water-soluble compound in the presence of the porous support.

3. The method according to claim 1 or 2, wherein The molar ratio of gold to palladium in the catalyst is from 0.01:1 to 0.7:

1.

4. The method according to claim 1 or 2, wherein Based on the dry weight, the alkali metal in the alkali metal promoter is present in the catalyst in an amount of 0.1 wt% to 10 wt%.

5. The method according to claim 1 or 2, wherein The alkali metal promoter is selected from the group consisting of the sodium salts, potassium salts or cesium salts of formic acid, acetic acid, propionic acid, butyric acid, and any combination thereof.

6. The method according to claim 1 or 2, wherein The reduction is carried out in a gas phase containing hydrogen and / or a hydrocarbon.

7. The method according to claim 6, wherein The hydrocarbon is ethylene.

8. The method according to claim 6, wherein, The gas phase further contains an inert carrier gas.

9. The method according to claim 6, wherein, The reduction is carried out at 50 °C to 250 °C for 1 hour to 24 hours.

10. The method according to claim 1 or 2, wherein The reduction is carried out in a liquid phase using hydrazine hydrate.

11. The method according to claim 6, wherein, The reduction is carried out at 20 °C to 50 °C for 1 hour to 24 hours.

12. The method according to claim 1, wherein the drying of the metal / promoter-impregnated support lasts for 10 minutes to 1 day.

13. The method according to claim 1 or 2, wherein The inert gas includes nitrogen, argon and / or air.

14. The method according to claim 1 or 2, wherein, The catalyst has a 2θ value of the peak x-ray diffraction intensity between 38° and 40° in the range of 38.6° to 39.2°.

15. A catalyst prepared by the method according to claim 1, which comprises: (a) gold, palladium and / or a gold-palladium alloy, (b) an alkali metal promoter and (c) a porous support, wherein the catalyst has a 2θ value of the peak x-ray diffraction intensity between 38° and 40° in the range of 38.6° to 39.2°.

16. The catalyst according to claim 15, wherein, The molar ratio of gold to palladium in the catalyst, cumulatively in the form of elemental metal and alloy, is from 0.01:1 to 0.7:

1.

17. The catalyst according to claim 15 or 16, wherein, Based on the dry weight, the alkali metal in the alkali metal promoter is present in the catalyst in an amount of 0.1 wt% to 10 wt%.

18. The catalyst according to claim 15 or 16, wherein, The alkali metal promoter is selected from the group consisting of: sodium salts, potassium salts or cesium salts of formic acid, acetic acid, propionic acid, butyric acid, and any combination thereof.

19. The catalyst according to claim 15 or 16, wherein, The porous support is selected from the group consisting of: silica, alumina, aluminosilicate, titanium dioxide, zirconia, spinel, carbon, and any combination thereof.

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