WO2001080988A2

WO2001080988A2 - Catalyst and process for gas phase reactions

Info

Publication number: WO2001080988A2
Application number: PCT/US2001/013325
Authority: WO
Inventors: Theodore Augur Koch; David J. Bueker; Karl R. Krause; Sourav K. Shengupta
Original assignee: E.I. Dupont De Nemours And Company
Priority date: 2000-04-25
Filing date: 2001-04-25
Publication date: 2001-11-01
Also published as: WO2001080988A3; AU2001255670A1

Abstract

A process for conducting gas-phase catalytic reactions, such as the production of hydrogen cyanide, with a grain stabilized platinum-group metal component is disclosed. For example, the catalyst is grain-stabilized with a Group IIIB or Group IVB metal oxide, thereby providing a higher hardness and creep resistance at elevated temperature, longer catalyst life and higher conversion efficiency.

Description

TITLE CATALYST AND PROCESS FOR GAS PHASE REACTIONS

Technical Field This invention relates to a process for conducting high temperature gas-phase reactions, such as the production of hydrogen cyanide, in the presence of a catalyst.

Background Art High temperature gas-phase catalytic reactions, such as the production of hydrogen cyanide are well-known processes and have been refined over many years. Hydrogen cyanide (HCN) is produced when compounds containing hydrogen, nitrogen, and carbon are brought together at high temperatures, with or without a catalyst. HCN is an important chemical with many uses in the chemical and mining industries. For example, HCN is a raw material for the manufacture of adiponitrile for use in the production of nylon. It is also used for the conversion of acetone cyanohydrin to methyl methacrylate, for use in making acrylic plastics. HCN is further used to make sodium cyanide for use in gold recovery. Moreover, it can be used as an intermediate in the manufacture of pesticides, agricultural products, chelating agents, and animal feed.

HCN is most commonly produced industrially by the Andrussow process and to a lesser extent by the Degussa process. Other catalytic processes for making HCN that have not been significantly exploited commercially, include direct reaction between methane and ammonia using microwave or induction heating, formamide dehydration, and methanol ammonolysis.

The Andrussow process involves catalytic oxidative dehydrogenation of methane and ammonia according to Equation 1.

CH₄ + NH₃ + 1.50₂ → HCN + 3H₂O (1)

The reaction proceeds at temperatures of about 1,100°C over precious metal catalysts, typically platinum (Pt), platinum-rhodium (Pt/Rh) or platinum-iridium alloy, in gauze form at about atmospheric pressure. A description is provided, for example, in the Encyclopedia of Chemical Technology (Fourth Edition, Volume 7, pages 753 to 782) edited by Kirk-Othmer. The Degussa process involves the endothermic reaction of methane and ammonia according to Equation 2.

CH₄ + NH₃ → HCN + 3H₂ (2)

In this process, methane and ammonia are reacted in the absence of oxygen at temperatures above about 1200°C. The reaction is performed in externally heated sintered alumina (ceramic) tubes within a furnace, the tubes being lined with platinum. Liquefied hydrocarbons, methanol, or ethanol can be used as starting materials if methane is limited in supply.

Koch et al, in U.S. Patents 5,470,541 and 5,529,669, provide an apparatus and a process for the improved small scale production (termed "on-site generation") of HCN, disclosing a process and apparatus for preparation of HCN from the reaction of ammonia vapor and a hydrocarbon gas over a platinum group metal catalyst while providing heat using single mode microwave irradiation. Substantial heat is required to provide the high process temperature and satisfy the endothermic character of the process.

WO 95/21126 provides a further advance over microwave irradiation processes to heat catalysts for production of HCN, disclosing a process for the preparation of HCN by reacting ammonia and a hydrocarbon gas in the presence of a platinum group metal catalyst while heating the catalyst by induction, using a frequency of 0.5 to 30 MHz.

M. Fathi et al., Catal. Today, 42, 205-209 (1998) disclose the catalytic partial oxidation of methane over Pt, Pt/Rh, Pt/lr and Pd gauze catalysts at contact times of 0.00021 to 0.00033 seconds. Pt, Pt/5%Rh and Pt/10% Rh gauzes were tested under the same conditions at 700°C to 1100°C. The best results were obtained at 1100°C using the Pt/10% Rh gauze catalyst. The CH₄ conversion was about 30%; the O₂ conversation was about 60%; the CO selectivity was about 95%; and the H₂ selectivity was about 30%.

Elevated temperature, gas-phase reactions using one or more platinum group metals in the gauze form suffer from lower catalyst life due to higher pressure drop due to rapid restructuring of the gauze as observed in Andrussow processes. Also, platinum group metal gauze catalysts are prone to higher wire breakage. Wire breakage could also have a catastrophic effect on any induction-heating process. East German Patent No. 136,825 ('825 patent) discloses a process for the production of HCN from methane and ammonia in the presence of a platinum metal or platinum metal alloy catalyst in the form of packed nets, wherein at least one net is coated with a fire-resistant oxide or salt of a platinum metal. The platinum metal or platinum metal alloy nets are coated by immersing the net into an aqueous solution of compounds such as aluminum, silicium, gallium, germanium, titanium, zirconium, boron or a colloidal solution of the oxides and hydroxides thereof. The oxide coating is impregnated with platinum metal salts and then subjected to reduction by heating the impregnated net in a flowing reducing gas at a temperature ranging from 250°C to 1200°C. This process creates a coated catalyst, which is modified on a macroscopic level. However, since the '825 patent only addresses the initial activities of the catalyst, there is no evidence of the characteristics of the catalyst over a longer period of time. Therefore, there is no indication that a catalyst as described by the '825 patent will maintain its activity and strength, or extended period of time on stream. Despite the refinements to the high temperature gas-phase catalytic reactions for the production of hydrogen cyanide, there has been a need for a process for the production hydrogen cyanide, which employs a catalyst having a longer life and provides a higher conversion efficiency over a longer period of time and provides less downtime as compared to the prior art processes. As disclosed herein, the present invention addresses this need by providing a process utilizing an optimized platinum group metal catalyst, which has a higher hardness and creep resistance at elevated temperatures than prior art catalysts.

Disclosure of Invention This invention relates to the use of a catalyst in a process for conducting gas- phase catalytic reactions, for example, the production of hydrogen cyanide at temperatures of greater than about 500°C. The catalyst is composed of one or more platinum group metals, grain-stabilized with at least one Group IIIB or IVB metal oxide, nitride, carbide, or sulfide, wherein the grain-stabilization is conferred by a fine particle dispersion rather than a post treatment coating or impregnation. The catalyst (e.g. zirconia-grain stabilized Pt or Pt/Rh alloys) displays properties superior to conventional catalysts such as greater strength, hardness and creep resistance at elevated temperature. In the catalyst of the invention, the metal grains of the platinum group metal are separated by the stabilizing agent, e.g., zirconia.

In one embodiment, the invention is directed to a process for the production of hydrogen cyanide comprising contacting in a vapor-phase, a hydrocarbon, ammonia and oxygen in the presence of a catalyst comprising at least one platinum-group metal component, which is grain-stabilized with at least one metal oxide, nitride, carbide, and/or sulfide selected from Group IIIB or Group IVB metals or combinations thereof.

In another embodiment, the present invention is directed to a process for the production of hydrogen cyanide, which provides a high production capacity, safe operation and superior and prolonged catalyst performance.

These and other embodiments of the present invention will become apparent upon a review of the following specification and the claims appended thereto.

Mode(s) for Carrying Out the Invention The present invention relates to a process utilizing a catalyst found to be particularly suited for high temperature catalytic reactions. While the invention is applicable for high temperature, gas-phase, catalytic reactions, in which refractory metal oxide grain-stabilized Pt group metal catalysts could be employed, the invention will be described in the context of an exemplary process of HCN synthesis, wherein a hydrocarbon, ammonia, and oxygen or oxygen-containing gas are contacted in the vapor-phase and in the presence of a Pt or Pt/Rh alloy catalyst grain-stabilized with at least one metal oxide, nitride, carbide, or sulfide at a temperature of about 500°C or more, preferably about 1000°C or more. The preferred temperature range is between about 800°C to about 1350°C.

Hydrocarbons suitable for use in making HCN include aliphatic, cycloaliphatic, and aromatic hydrocarbons of which a few examples are disclosed in U.S. Patent No. 1,934,838. Methane or a methane-containing gas, such as natural gas, is a preferred hydrocarbon. Ammonia used in the process is preferably substantially pure, for example, about 90% by volume, preferably about 95%) by volume. Suitable oxygen- containing gases include pure oxygen, air, enriched air, and oxygen-containing inert gases.

The catalyst used in the present invention comprises one of the platinum-group metals or alloys thereof, grain-stabilized with at least one grain-stabilizing metal oxide, carbide, nitride, or sulfide. The grain-stabilizing metal is selected from a Group IIIB or Group IVB metal or combinations thereof. For example, Group IIIB and Group IVB metals suitable as the grain-stabilizing metal include cerium, scandium, yttrium, lanthanum, titanium, zirconium, and hafnium. The grain-stabilizing metal is dispersed throughout, not merely on the surface, of the platinum-group metals or alloys in the form of an oxide, carbide, nitride, or sulfide. Preferably, the grain-stabilizing metal is dispersed in the platinum-group metals or alloys as an oxide. More preferably, the dispersed metal oxide is zirconia and/or yttria.

The catalyst of the invention further comprises at least one platinum-group metal. Preferred platinum-group metals include platinum, rhodium, iridium, palladium, osmium, ruthenium, alloys of two or more thereof, and mixtures of two or more thereof. Most preferably, the catalyst of the invention is a zirconia-grain stabilized Pt or Pt/Rh alloy containing about 0 to about 20% by weight of Rh.

The basic grain-stabilizing process using the metal oxide, carbide, sulfide, or nitride, for application to Pt and Pt/Rh alloys is known in the art. For example, such stabilization processes are described by Selman, G.L., Day, J.G., and Bourne, A.A. Platinum Metals Rev., 1974, 18(s), 46, and Selman, G.L. and Bourne, A.A. Platinum Metals Rev., 1976, 20(3), 46. Pt and Pt/Rh zirconia grain-stabilized materials are extensively used in the glass industry due to their high strength and rigidity even at extremely high operating temperatures. It has been found that the zirconia-grain stabilized Pt group metals and alloys are compatible in the chemical environment for synthesizing, for example, hydrogen cyanide.

The catalyst of the present invention can be prepared by spray dispersion methods for making dispersion strengthened metals, such as described in U.S. Pat. No. 3,696,502. The spray dispersion process creates a dispersion strengthened catalyst having a fine grain size about the size of the sprayed particles, wherein the metal oxide, nitride, or carbide particles are dispersed throughout the platinum-group catalyst matrix. The dispersed phase resides at the grain boundaries of the platinum and confers superior mechanical strength to the substrate metal or alloy. As a result of the grain stabilization, the volume expansion of the catalyst, caused by the restructuring of the wires, is much lower than that of the standard Pt or Pt/Rh catalysts. Moreover, as a result of this process, the catalyst of the present invention has dispersed throughout it, a Group IIIB or IVB metal oxide, nitride, carbide, or sulfide. This is in direct contrast to other catalysts, which are merely coated with a metal oxide on the surface of the catalyst. Thus, this fine dispersion throughout the catalyst of the present invention allows the use of the catalyst for over a month without any or substantially any loss of activity and increased pressure drop.

In general, methods of making the dispersion strengthened metals alloys may be conducted by mixing metal or alloy powders with fine refractory particles and then consolidating the particular mixture by known powder metallurgical techniques.

In addition, U.S. Patent No. 3,696,502 describes an exemplary method used to make a catalyst used in the present process. In particular, a metallic starting material is made by combining a platinum-metal group metallic host material and a relatively minor concentration of a "reactive" metal, which is more reactive than the host material. The "reactive" metal is at least one group IIIB or IVB metal. This mixture of the platinum-group host and reactive metal is then sprayed in finely divided molten particles of the starting mixture in the form of a jet on to a cooled target or mold. The atmosphere in which the particles pass serves to convert the reactive metal into the oxide, carbide, nitride, or sulfide form of the group IIIB or IVB metal. As the metallic mixture is sprayed onto the cooled target or mold, an ingot is built up. The ingot is then removed from the target or mold and worked up into a rod, wire, sheet, bar or other shape.

Another method of making the dispersion strengthened material involves melting a large bath of a platinum-metal group metallic host metal or alloy, which contains a small proportion of the reactive constituent, at least one group IIIB or IVB metal, required for the final dispersant. The bath is melted first under inert or reducing conditions in, for example, an induction furnace, which promotes violent stirring.

Atmospheric conditions are then adjusted so that the reactive metal oxidizes while the basic metal or alloy is unaffected and finally, the melt containing a fine dispersion of oxide is cast into an ingot, which can be worked by conventional methods.

The catalyst of the present invention may be employed in a variety of forms such as sheets, wires, turnings, and gauze. Preferably, the catalyst is in the form of one or more layers of fine wire gauze through which the reactant gases are passed. Such a gauze is usually woven or knitted and, for example, may be prepared from wire of 0.00762 cm (0.003 inch) diameter having about 40 to about 80 meshes to the linear inch.

The reaction may be carried out over a wide range of pressures. The process of making HCN may be operated at pressures from about 101 kPa to about 3000 kPa. In large-scale operations, atmospheric or super-atmospheric pressures may be used. The reaction is preferably carried out in super-atmospheric pressures.

The process of making HCN may be operated at temperatures of between about 500°C to about 1350°C, preferably from about 1000°C to about 1200°C. One or more of the reacting gases are preferably preheated before contact with the catalyst to from about 50°C to about 700°C.

The production of the HCN may involve the reaction of ammonia and methane from natural gas in the presence of air, enriched air, other oxygen-containing gas, or oxygen. In a preferred process of the present invention, the air/enriched air and natural gas is preheated prior to being mixed with the ammonia and fed into the converter. Such preheating is described in detail in U.S. Pat. No. 3,104,945 to Jenks et al. and U.S. Pat. No. 5,882,618 to Bhatia et al. When preheating is employed, the gases are usually heated to temperatures between about 50°C to about 700°C, preferably between about 300°C to about 500°C, and most preferably between about 450°C to about 490°C. The initial air to natural gas ratio is maintained in the range of about 4.5:1 to about 5.5:1, this ratio may be adjusted by increasing or decreasing natural gas to achieve maximum production.

The air to ammonia ratio is set between about 3.0:1 to about 9.0:1, preferably between about 3.0: 1 to about 6.0: 1. If preheating is employed, the range will usually be between about 3.3 : 1 to about 5.0: 1. The air to ammonia ratio is first fixed at a selected setting and then constantly maintained at this ratio. The air to natural gas ratio is then varied to obtain the maximum HCN production.

The off-gas from the converter may be analyzed by on-line gas chromatography, mass spectrometry, or infrared spectroscopy or a combination thereof to determine the volume percent of all the components in the effluent gas stream.

Yield of HCN and conversions of methane and ammonia are calculated to determine the performance of the converter. The HCN made using the catalytic process of the present invention may be used in many different applications. For example, it may be used to produce adiponitrile, which is used in nylon applications, to convert acetone cyanohydrin to methyl methacrylate for acrylic plastics, or make sodium cyanide for use in gold recovery. HCN can also be used as an intermediate in the manufacture of pesticides, agricultural products, chelating agents, and animal feeds. Preferably, the HCN produced by the present invention is used in the production of adiponitrile and in the production of nylons.

In the production of nylons, HCN may be reacted with butadiene to produce a mixture of pentenenitrile (3-pentenenitrile and 2-methyl-3-butenenitrile). This particular reaction may be catalyzed by known catalysts, such as nickel phosphite catalysts as described in, e.g., U.S. Patent Nos. 3,496,215 and 5,821,378. The branched 2-methyl-3-butenenitrile is then isomerized to produce linear 3- pentenenitrile, as disclosed in e.g. U.S. Patent No. 3,536,748. Thereafter, hydrocyanation of the pentenenitrile produces adiponitrile as catalyzed by a nickel catalyst and a promoter (see, e.g, U.S. Patent Nos. 3,676,481 and 5,512,696). Suitable nickel catalysts are described in U.S. Patent Nos. 3,496,215 and 5,821,378, and the promoter may be any promoter suitable to effectuate the catalytic activity of the nickel catalyst. For example, a suitable promoter is a Lewis acid such as triarylborane. The adiponitrile can then be hydrogenated to produce hexamethylenediamine (HMD). For example, the adiponitrile may be hydrogenated in the presence of an iron catalyst, such as described in U.S. Patent No. 3,986,985, at high temperatures, such as 150°C, and pressure, such as 34.47 MPa (5000 psig). Alternatively, adiponitrile may be hydrogenated in the presence of a Raney nickel catalyst or Raney cobalt catalyst at low temperature, such as 75°C, and pressure of about 3.4 MPa (500 psig). The resulting HMD may be condensed with adipic acid to produce nylon 6,6. Such a hydrogenation process is described, for example, in Tolman, C. et al. , Advances in Catalysis, 11 :1 -46 (1985).

The metal-grain stabilized Pt group metal catalyst of the present invention, which is described in detail above for the synthesis of HCN from methane, ammonia, and air/oxygen, is also applicable to elevated temperature gas-phase catalytic reactions in general. Examples of such elevated temperature gas-phase catalytic reactions include the preparation of synthesis gas from methane by steam reforming according to Equation 3; dry reforming according to Equation 4; preparation of synthesis gas from methane according to Equation 5; cracking reactions of hydrocarbons for instance in refining processes; cracking of halocarbons, such as the preparation of tetrafluoroethylene from octafluorocyclobutane according to Equation 6; or the environmentally safe destruction of volatile organic chemicals (VOC), for instance chlorofluorocarbons according to Equation 1, 8 or 9. Accordingly, the present invention is further directed to the production of other gases, such as carbon monoxide, hydride, and tetrafluoroethylene gases, as well as the safe conversion of chlorofluorocarbons. One of skill in the art is capable of determining the desired operating pressures and times for these reactions.

Catalyst CH₄ + H₂0 → CO + 3H₂ (3)

(ΔH = +206 kJ/mol)

Catalyst CH₄ + C0₂ → 2 CO + 2H₂ (4)

(ΔH - +247 kJ/mol)

Catalyst CH₄ + V₂0₂ → CO + 2H₂ (5)

(ΔH = -36 kJ/mol)

Catalyst C₍F₂- jF₂→2CF₂ = CF₂ (6)

CF₂-CF₂

(ΔH = +212kJ/mol)

Catalyst CC1₂F₂ → C + Cl₂ + F₂ (7)

(ΔH = +491 kJ/mol)

Catalyst 2CHF₂C1 → C₂F₄ + 2HC1 (8)

(ΔH = +120kJ/mol)

Catalyst 3CHF₂C1 → C₃F₆ + 3HC1 (9)

(ΔH = 89 kJ/mol) The invention is now illustrated by the following examples, which are intended to illustrate, but not to limit the invention.

EXAMPLES In the examples, the reactants, mixed in pre-determined stoichiometric proportions, were passed through the catalyst bed, at a total flow rate of about 5 SLM at a pressure of 34.47 kPa (5 psig). The feed composition was controlled by mass flow controllers and the reactor pressure was set by a forward pressure regulator. Most of the lines were 0.635 cm ( inch) diameter with laminar flow and a linear velocity of 2.6 m/s. Mixing of the feed was enhanced by turbulent flow through 1.22 m (4 foot) of thick wall (0.0889 cm; i.e., 0.035 inch wall thickness) 0.318 cm (1/8 inch) tubing.

The reactor itself was about 0.95 cm (3/8 inch) ID and 1.9 cm (% inch) OD quartz tube pressure tested up to 5,520 kPa (800 psig) at room temperature. A 137 kPa (20 psig) rupture disk was used to protect against reactor overpressure. The residence time of the gas in the quartz tube was less than half of a second, less than 5 milliseconds of which was spent traveling through the catalyst pack. A thick polycarbonate shield was placed in front of the quartz reactor and the hood enclosure doors were closed during operation.

A flame arrestor was positioned immediately prior to the reactor to prevent any flames from propagating from the reactor back up to the gas cylinders. The 15.24 cm (6 inch) piece of thick walled 0.318 cm (1/8 inch) tubing had an ID of 1.4 cm (0.55 inch), less than half of the quenching diameter required to extinguish a methane or ammonia flame (0.33 cm; i.e., 0.13 inch). A startup-heater was used to light off the HCN synthesis reaction. After the light off, the heater would be turned off, and the reaction would be sustained by its own heat of reaction.

All lines after the reactor were electrically heat-traced to at least 105°C to prevent water condensation and avoid plugging due to HCN polymer formation. The total volume in the lines after the reactor was about 55 cm³ and it required less than 1 second for gas to travel from the reactor to the burner or vent. A small portion of the off-gas from the reactor was fed to a gas chromatograph for quantitative analysis of the reaction products. A number of safety interlocks and pressure switches were installed to safeguard the system from overpressure, undesired changes in the feed composition which could cause an explosion, accidental breakage of the quartz reactor, power and hood failure. The heat tapes and startup heater were protected by independent over-temperature thermocouples, which would turn off power to the affected heater but not automatically interlock the process.

In examples 1-3 either a catalyst pack comprising 9 or 10 layers of 80 mesh, 0.00762 cm (0.003 inch) wire diameter grain-stabilized Pt/Rh or Pt gauze catalyst or a catalyst pack comprising 9 or 10 layers of 80 mesh, 0.00762 cm (0.003 inch) wire diameter Pt/Rh or Pt gauge catalyst was sandwiched between two 1.27 cm (^lA inch) pieces of porous (76.2 pores per cm; 30 ppi) ceramic foam. These catalysts are commercially available and were obtained from Johnson-Matthey. The ceramic foam was used as a catalyst support and as radiation shield to reduce heat loss from the system during operation. Other useful supports can be formed from fiberglass or alumina. A type of S (Pt/Pt-10% Rh) thermocouple housed in a sealed ceramic sheath was used to measure temperature immediately below the ceramic foam. The reaction zone of the quartz reactor was surrounded by a 10.16 cm (4 inch) by 10.16 cm (4 inch) by 15.24 cm (6 inch) high steel box packed with insulation. This allowed the system to operate almost adiabatically (about 50-100°C lower than adiabatic temperature is expected) and provided an extra measure of protection in case the quartz reactor accidentally shattered.

HCN synthesis experiments were carried out using 4 different catalyst packs namely 90/10 Pt/Rh (90 weight % platinum; 10 weight % rhodium), 90/10 Pt/Rh zirconia grain stabilized (ZGS), 95/5 Pt/Rh ZGS, and 100/0 Pt/Rh ZGS gauze catalysts. Pure methane, ammonia, and air were used. At the onset of each experimental run, the methane to air and ammonia to air ratios were set by modifying the flow rates of the air, ammonia, and methane. The gases were premixed in the mixing chamber and fed to the reactor without preheating. The methane to air and ammonia to air ratios were maintained for 48 hours to ensure steady-state operation and then methane to air ratio were varied keeping constant ammonia to air ratio.

The off-gas from the reactor was analyzed by on-line Hewlett-Packard 6890 gas chromatograph to determine the volume percent of all the components in the effluent gas stream. Conversation and yield of HCN, based on methane and ammonia, were determined using the HCN in the effluent and methane and ammonia in the feed and off-gas. Yield of HCN (based on ammonia or methane) and conversion of ammonia (or methane) have been defined as:

Product HCN

Conversation of NH₃ = NH₃ in Influent and

Product HCN HCN Yield 1 = Yield of HCN (based on NH₃) =

NH₃ in Influent - NH₃ in Effluent

Product HCN HCN Yield 2 = Yield of HCN (based on CH ₄)

(CH₄ in Influent - CH₄ in Effluent)

Similarly, one can define conversion of methane and yield of HCN based on methane.

Comparative Example Control experiments were performed with 9 layers (0.87 gm) of 90/10 Pt/Rh gauze catalysts. Conversion and yield of tfCN, based on methane and ammonia, were obtained as a function of methane to air ratio and are presented in Table 1.

Example 1 In a manner analogous to that of the Comparative Example , a second run was performed under analogous conditions, except that 9 layers (0.80 gm) of 90/10 Pt/Rh ZGS catalyst was used instead of 90/10 Pt/Rh catalyst pack. Conversion and yield of HCN, based on methane and ammonia, were obtained as a function of methane to air ratio and have been presented in Table 2.

Example 2 Again, in a manner analogous to that of the Comparative Example, a third run was performed under analogous conditions, except that 9 layers (0.76 gm) of 95/5 Pt/Rh ZGS catalyst was used instead of 90/10 Pt/Rh catalyst pack. Conversion and yield of HCN, based on methane and ammonia, were obtained as a function of methane to air ratio and have been presented in Table 3. Example 3 Again, in a manner analogous to that of the Comparative Example, a fourth run was performed under analogous conditions, except that 10 layers (0.80 gm) of 100/0 Pt/Rh ZGS catalyst was used instead of 90/10 Pt/Rh catalyst pack. Conversion and yield of HCN, based on methane and ammonia, were obtained as a function of methane to air ratio and have been presented in Table 4.

TABLE 1 COMPARATIVE EXAMPLE

Methane/ Air HCN Yield 1 NH₃ HCN Yield 2 CH₄

Ratio (%) Conversion (%) Conversion (%) (%)

0.172 52.3+0.1 50.1+0.2 61.5+0.2 61.5+0.2

0.182 59.6+0.8 56.5+0.7 65.2+0.8 65.2+0.8

0.193 64.1+0.6 58.0+0.6 66.1+0.6 63.3+0.7

0.202 68.2+0.6 62.1+0.7 67.1+0.5 64.7+0.7

0.213 67.4+0.7 55.6+0.8 64.8+0.6 55.0+0.8

0.223 63.7+1.0 49.3+0.8 59.4+0.9 46.7+0.8

0.232 61.0+0.9 45.2+0.4 57.0+1.6 40.9+0.3

TABLE 2 (EXAMPLE 1)

Methane/ Air HCN Yield 1 NH₃ HCN Yield 2 CH₄

Ratio (%) Conversion (%) Conversion (%) (%)

0.172 51.9+0.3 50.1+0.3 61.5+0.4 61.5+0.4

0.183 59.6+0.3 56.3+0.2 65.1+0.3 65.1+0.3

0.193 64.2+0.9 57.2+1.3 64.6+1.2 63.2+1.4

0.202 70.5+0.8 63.0+1.2 68.2+0.9 65.7+1,3

0.213 68.9+0.7 55.7+1.1 63.0+0.6 55.1+1.1

0.223 68.2+1.0 51.0+1.1 60.0+0.9 48.2+1.0

0.232 66.3+0.8 47.0+0.9 56.3+0.8 42.6+0.8 TABLE 3 (EXAMPLE 2)

Methane/Air HCN Yield 1 NH₃ HCN Yield 2 CH₄

Ratio (%) Conversion (%) Conversion (%) (%)

0.172 52.5+0.6 47.4+0.6 61.0+0.8 58.2+0.7

0.182 58.5+0.5 51.1+0.5 62.7+0.6 59.1+0.5

0.193 60.8+0.6 49.2+0.5 60.1+0.6 53.8+0.5

0.202 65.1+0.8 52.8+1.2 61.3+1.0 55.0+1.3

0.213 60.6+0.7 44.6+0.5 55.0+0.4 44.2+0.5

0.223 60.0+0.7 42.0+0.5 52.3+0.7 39.7+0.5

0.232 59.8+0.4 40.2+0.5 49.4+0.2 36.4+0.4

TABLE 4 (EXAMPLE 3)

Methane/Air HCN Yield 1 NH₃ HCN Yield 2 CH₄

Ratio (%) Conversion (%) Conversion (%) (%)

0.172 42.9+1.4 35.7+1.2 46.2+1.6 43.8+1.4

0.182 51.2+0.7 40.7+0.4 50.1+0.7 46.9+0.5

0.193 65.3+0.4 53.9+0.8 62.3+0.9 58.9+1.0

0.202 60.5+0.5 44.1+0.5 50.6+0.6 45.9+0.6

0.213 67.3+0.6 49.2+0.4 54.9+0.4 48.7+0.4

0.223 61.0+1.6 40.5+1.7 45.7+1.8 38.3+1.7

0.232 58.1+0.9 34.7+1.1 39.5+0.6 31.4+1.0

It was expected that the presence of the zirconia would substantially decrease the activity of the catalyst to catalyze the production of HCN. This is because zirconia in the catalyst for example, the Pt or Pt/Rh ZGS catalyst of the invention resides on the grain boundary, thereby, perhaps blocking the active sites (Pt) and acting as a product inhibitor (since zirconia does not catalyze the HCN synthesis reaction). Surprisingly, that was found not to be true. However, as can be seen from the above Tables 1-4, the catalyst of the present invention was useful in converting the methane and ammonia to HCN. The presence of the zirconia did not substantially decrease the activity of the catalyst.

Another advantage of the catalysts of the present invention was the unexpected, improved and extended life of the catalyst. In particular, the catalyst pack of the comparative example is subjected to a drop in pressure over the course of its life. It was unexpectedly found that the volume expansion of the wires in the woven gauze due to the introduction of zirconia in the Pt/Rh metal alloy matrix was less than the alloy itself during the high temperature HCN synthesis process. As a result, the catalyst packs of the present invention did not suffer from the pressure drop since the dispersion of zirconia therein apparently slowed down the catalyst restructuring with little or no adverse effect or the activity of the catalyst. Therefore, the catalyst packs of the present invention had an extended life relative to the comparative example catalysts.

Example 4 In a manner analogous to that of Example 1 , experiments are performed essentially under identical conditions, except that 10 layers of yttria-stabilized Pt gauze catalyst is used instead of 90/10 Pt/Rh gauze catalyst pack. The effect of methane to air ratio on the conversion of methane and ammonia to HCN and the yield of HCN are evaluated. Example 5

In a manner analogous to that of Example 1, experiments are performed essentially under identical conditions, except that 10 layers of yttria-stabilized 90/10 (volume ratio) Pt/Rh gauze catalyst is used instead of 90/10 Pt/Rh gauze catalyst pack. The effect of methane to air ratio on the conversion of methane and ammonia to HCN and the yield of HCN are evaluated.

Example 6 In a manner analogous to that of Example 1, experiments are performed essentially under identical conditions, except that 10 layers of yttria-stabilized 85/15 (volume ratio) Pt/Rh gauze catalyst is used instead of 90/10 Pt/Rh gauze catalyst pack. The effect of methane to air ratio on the conversion of methane and ammonia to HCN and the yield of HCN are evaluated. Example 7 In a manner analogous to that of Example 1 , experiments are performed essentially under identical conditions, except that 10 layers of ceria-stabilized Pt gauze catalyst is used instead of 90/10 Pt/Rh gauze catalyst pack. The effect of methane to air ratio on the conversion of methane and ammonia to HCN and the yield of HCN are evaluated.

Example 8 In a manner analogous to that of Example 1, experiments are performed essentially under identical conditions, except that 10 layers of ceria-stabilized 90/10 (volume ratio) Pt/Ir gauze catalyst is used instead of 90/10 Pt/Rh gauze catalyst pack. The effect of methane to air ratio on the conversion of methane and ammonia to HCN and the yield of HCN are evaluated.

Example 9 In a manner analogous to that of Example 1 , experiments are performed essentially under identical conditions, except that 10 layers of ceria-stabilized 85/15 (volume ratio) Pt/Ir gauze catalyst is used instead of 90/10 Pt/Rh gauze catalyst pack. The effect of methane to air ratio on the conversion of methane and ammonia to HCN and the yield of HCN are evaluated.

Example 10 To carry out tests on the partial oxidation of methane, a reactor suitable for laboratory investigation of the catalyst of the preferred embodiments is used. This reactor resembles a reactor suitable for industrial catalysis, but is scaled down in size. The partial oxidation reactions are carried out with a 19 mm O.D. x 13 mm I.D. quartz reactor with ten rhodium gauze (12 mm O.D.) catalyst pack held between two 5 mm x 12 mm and 101.6 pores per cm (40 ppi) alpha-alumina foam disks, which serves as radiation shields. The inlet radiation shield also aids in uniform distribution of the feed gases. The gauze and the disks are wrapped with an alumina cloth to obtain a single cylinder 13 mm diameter. The catalyst is tightly forced inside the reactor to minimize gas by-pass. Two band heaters are fitted around the quartz reactor. The band heaters are used to supply thermal energy to light off the reaction and to preheat the feed gases. After light off, the band heaters are turned off and the reaction proceeds autothermally. Two Type S thermocouples, one at each end of the gauze stack, are used to monitor the reaction temperature.

Control experiments are performed with 10 layers of Rh gauze catalysts. The effects of pressure, preheat temperature, and gas hourly space velocity (GHSV) on the conversion of methane, and selectivties to carbon monoxide and hydrogen are determined.

Example 11 In a manner analogous to that of Example 10, experiments are performed essentially under identical conditions, except that 10 layers of zirconia-stabilized Rh gauze catalyst is used instead of Rh gauze catalyst pack. The effects of pressure, preheat temperature, and gas hourly space velocity (GHSV) on the conversion of methane, and selectivties to carbon monoxide and hydrogen are determined.

Claims

WHAT IS CLAIMED IS:

1. A process for conducting a gas-phase catalytic reaction comprising contacting one or more reactant gases in the presence of a catalyst comprising at least one platinum-group metal component grain-stabilized with particles of at least one metal oxide, nitride, carbide, or sulfide, wherein the grain-stabilizing metal is selected from Group IIIB or Group IVB metal, or combinations thereof.

2. The process of claim 1, wherein the gas-phase catalytic reaction is conducted at a temperature of about 500°C or higher.

3. The process of claim 1 , wherein the grain-stabilizing particles are dispersed throughout the platinum-group metal component by spray dispersion.

4. The process of claim 1, wherein the process catalyzes the production of hydrogen cyanide.

5. The process of claim 4, wherein the reactant gases are a hydrocarbon, ammonia, and oxygen or an oxygen containing gas.

6. The process of claim 1 , wherein the platinum-group metal component is selected from the group consisting of platinum, rhodium, iridium, palladium, osmium, ruthenium, an alloy of two or more thereof, or mixtures thereof.

7. The process of claim 6, wherein the platinum-group metal component is selected from the group consisting of platinum, rhodium, and mixtures thereof.

8. The process of claim 1 , wherein the metal oxide is present and is selected from the group consisting of ceria, scandia, yttria, lanthana, titania, zirconia, or hafnia.

9. The process of claim 1 , wherein the metal oxide is present and is zirconia or yttria.

10. The process of claim 1 , wherein the metal oxide is present and is dispersed throughout the platinum-group metal component, while the platinum-group metal component is molten.

11. The process of claim 1 , wherein the platinum-group metal component is in a form of a gauze through which a gas may pass.

12. The process of claim 1, wherein the platinum-group metal component is in a form of interwoven wire, randomly oriented wire, knitted wire, mesh, perforated sheet, unperforated sheet, or corrugated sheet.

13. The process of claim 1 , wherein the catalyst comprises a pack of a plurality of platinum-group metal components placed next to each other.

14. The process of claim 1 , wherein the catalyst is in the form of a pack and comprises a catalyst support or a radiation shield.

15. The process of claim 1 , wherein the catalyst is in the form of a gauze comprising a platinum/rhodium alloy grain-stabilized with zirconia.

16. A process for the production of hydrogen cyanide comprising contacting in a vapor-phase, a hydrocarbon, ammonia and oxygen or oxygen - containing gas in the presence of a catalyst comprising at least one platinum-group metal component, which is grain stabilized with at least one metal oxide selected from Group IIIB or Group IVB metal oxides or both, wherein the platinum-group metal component is platinum, rhodium, iridium, palladium, osmium, ruthenium, a mixture or an alloy thereof, or a combination thereof, and wherein the metal oxide is dispersed throughout the platinum-group metal component.

17. The process of claim 16, wherein the metal oxide is zirconia.

18. The process of claim 16, further comprises using the hydrogen cyanide to produce nylon.

19. The process of claim 16, wherein the catalyst is in the form of a gauze . comprising a platinum rhodium alloy grain-stabilized with zirconia.

20. The process of claim 19, wherein the platinum is present in the alloy in an amount of from about 90 to about 100% and the rhodium is present in an amount of from about 0 to about 10%.