This invention relates to the synthesis of hydrocarbons from a methane source. A particular application of this invention is a method for convert¬ ing natural gas to more readily transportable material.

A major source of methane is natural gas. Other sources of methane have been considered for fuel supply, e.g., the methane present in coal deposits or formed during mining operations. Relatively small amounts of methane are also produced in various petro¬ leum processes.

The composition of natural gas at the well¬ head varies but the major hydrocarbon present is meth¬ ane. For example, the methane content of natural gas may vary within the range from about 40 to about 95 volume percent. Other constituents of natural gas include ethane, propane, butanes, pentane (and heavier hydrocarbons), hydrogen sulfide, carbon dioxide, helium and nitrogen.

Natural gas is classified as dry or wet depending upon the amount of condensable hydrocarbons contained in it. Condensable hydrocarbons generally comprise C3+ hydrocarbons carbons although some ethane may be included. Gas conditioning is required to alter the composition of wellhead gas, processing facilities usually being located in or near the pro¬ duction fields. Conventional processing of wellhead natural gas yields processed natural gas containing at least a major amount of methane.

Large scale use of natural gas often re¬ quires a sophisticated and extensive pipeline system. Liquefaction has also been employed as a transportation means, but processes for liquefying, transporting, and revaporizing natural gas are complex, energy-intensive and require extensive safety precautions. Transport of natural gas has been a continuing problem in the

exploitation of natural gas resources. It would be extremely valuable to be able to convert methane (e.g., natural gas) to more readily handleable or transport¬ able products. Moreover, direct conversion of olefins such as ethylene or propylene would be extremely valuable to the chemical industry.

Recently, it has been discovered that methane may be converted to higher hydrocarbons (e.g., ethane, ethylene and higher homologs) by contacting methane with a reducible metal oxide as a selective oxygen source. As the methane is converted to hydrocarbon products and co-product water, the active oxygen of the metal oxide is depleted, resulting in a reduced metal oxide. The reduced metal oxide is relatively inactive for the oxidative conversion of methane but active oxygen may be replaced by regenerating a reducible metal oxide. Such regeneration is accomplished by reoxidation of the reduced metal oxide.

Reducible oxides of several metals have been identified which are capable of converting methane to higher hydrocarbons. Oxides of manganese, tin, indium, germanium, lead, antimony and bismuth are particularly useful. See U.S. Patent Numbers 4,443,649? 4,444,984? 4,443,648; 4,443,645? 4,443,647? 4,443,644? and 4,443, 646, the entire contents of each being incorporated herein by reference.

Commonly-assigned ^' U.S. Patent Application Serial Number 522,935, filed August 12, 1983, discloses and claims a process which comprises contacting methane with an oxidative synthesizing agent under elevated pressure (e.g., 2-100 atmospheres) to produce greater amounts of C3+hydrocarbon products.

Commonly-assigned U.S. Patent Application Serial Number 522,938, filed August 12, 1983, discloses and claims a process for the conversion of methane to higher hydrocarbons which comprises contacting methane with particles comprising an oxidative synthesizing

agent which particles continuously recirculate between two physically separate zones—a methane contact zone and an oxygen contact zone.

U.S. Patent 4,499,322 discloses and claims a process for the conversion of methane to higher hydro¬ carbons which comprises contacting methane with an oxidative synthesizing agent containing a promoting amount of alkali metal and/or compounds thereof. The entire content of this patent is incorporated herein by reference.

U.S. Patent 4,495,374 discloses and claims a process for the conversion of methane to higher hydro¬ carbons which comprises contacting methane with an oxidative synthesizing agent containing a promoting amount of alkaline earth metal and/or compounds thereof. The entire content of this patent is incorporated herein by reference.

U.S. Patent 4,499,323 discloses and claims a process for the conversion of methane to higher hydro¬ carbons which comprises contacting methane with a con¬ tact solid comprising a reducible oxide of praseodymium and at least one member of the group consisting of alkali metals, alkaline earth metals, and compounds thereof. The entire content of this patent is incor¬ porated herein by reference.

Commonly-assigned U.S. Patent Application Serial Number 06/600,918 discloses and claims a process for the conversion of methane to higher hydrocarbons which comprises contacting methane with a contact solid comprising a reducible oxide of terbium and at least one member of the group consisting of alkali metals, alkaline earth metals, and compounds thereof. The entire content of this application is incorporated herein by reference.

U.S. Patent 4,499,324 discloses and claims a process for the conversion of methane to higher hydro¬ carbons which comprises contacting methane with a

contact solid comprising a reducible oxide of cerium and at least one member of the group consisting of alkali metals, alkaline earth metals, and compounds thereof. The entire content of this patent is incor¬ porated herein by reference.

Commonly-assigned U.S. Patent Application Serial Number 06/600,730 discloses and claims a process for the conversion of methane to higher hydrocarbons which comprises contacting methane with a contact solid comprising a reducible oxide of iron and at least one member of the group consisting of alkali metals, alkaline earth metals, and compounds thereof. The entire content of this application is incorporated herein by reference.

U.S. Patent 4,489,215 discloses and claims a process for the conversion of methane to higher hydro¬ carbons which comprises contacting methane with a con¬ tact solid comprising a reducible oxide of ruthenium and at least one member of the group consisting of alkali metals, alkaline earth metals, and compounds thereof. The entire content of this patent is incor¬ porated herein by reference.

In a typical application of the foregoing processes for the oxidative conversion of methane, methane feed is contacted with a reducible metal oxide and regeneration is accomplished separately by contact¬ ing the reduced metal oxide with an oxygen-containing gas (e.g., air). Thus, a cyclic redox process results in which methane reaction and reoxidation of the metal oxide "reagent" are performed separately and repeatedly for a continuous process.

Such a procedure presents several disadvan¬ tages for large scale continuous operation. One dis¬ advantage is the large quantity of solid cycling between methane reaction and reoxidation in such a way that the methane and oxygen are not mixed. Another disadvantage is the necessity of developing a com-

position that is resistant to mechanical attrition and repeated exposure to reductive and oxidative environ¬ ments.

Hinsen and Baerns recently reported studies of a continuous mode for the oxidative coupling of methane wherein regenerating air is cofed with the methane feed. Hinsen, . and Beams, M. , "Oxidative Kopplung von Methan zu C2~Kohlenwasserstoffen in Gegenwart unterschiedlicher Katalysatoren", Chemiker- Zeitung, Vol. 107, No. 718, pp. 223-226 (1983). Using a catalyst based on lead oxide and gamma-alumina in a fixed bed reactor operated at 1 atmosphere total pressure and 600-750°C, they report results of approxi¬ mately 53% selectivity to ethane and ethylene at 8% methane conversion for a feed consisting of about 50% methane, 25% air and 25% nitrogen. Other metal oxides studied by Hinsen and Baerns included oxides of Bi, Sb, Sn and Mn. SUMMARY OF THE INVENTION

It has now been found that the conversion of methane to higher hydrocarbons in the presence of oxygen is improved by contacting a first, hydrocarbon gas comprising methane and a second, oxygen-containing gas with a promoted contact solid which comprises: (a) at least one reducible oxide of at least one metal which oxide(s) when contacted with methane at methane conversion conditions (preferably at a temperature within the range of about 500 to 1000°C) are reduced and produce higher hydrocarbon products and water and (b) a promoting amount of at least one promoter selected from the group cons-isting of alkali metals, alkaline earth metals, and compounds thereof. Pre¬ ferred reducible oxides include oxides of metals se¬ lected from the group consisting of Mn, Sn, In, Ge, Pb, Sb and Bi. Preferred reducible oxides also include oxides of metals selected from the group consisting of Pr, Tb and Ce. More preferably, reducible oxides are

oxides of Mn, Pr and/or Tb. Reducible oxides of Mn are, currently, particularly preferred. Alkali metals are selected from the group consisting of Li, Na, K, Rb and Cs. Alkaline earth metals are selected from the group consisting of Mg, Ca, Sr, and Ba. A currently preferred alkaline earth metal is Ca. How¬ ever, alkali metals are preferred promoters. More preferred promoters are lithium and sodium. Sodium is a particularly preferred promoter.

The stability of the promoted contact solid is further enhanced by incorporating a stabilizing amount of phosphorus into the composition.

The improved process of the present invention produces higher methane conversion at similar hydro¬ carbon selectivity or increased hydrocarbon selectivity at similar methane conversion, as compared to prior methods such as that taught by Hinsen and Baerns, supra. DETAILED DESCRIPTION OF THE INVENTION

In addition to methane the hydrocarbon feed¬ stock employed in the method of this invention may contain other hydrocarbon or non-hydrocarbon components, The methane content of the feedstock, however, will typically be within the range of about 40 to 100 vol. %, preferably within the range of about 80 to 100 vol. %, more preferably within the range of about 90 to 100 vol. %.

The oxygen-containing gas generally comprises molecular oxygen: other gases such as nitrogen and car¬ bon oxides may be present. A preferred oxygen- containing gas is air.

The ratio of hydrocarbon feedstock to oxygen- containing gas is not narrowly critical to the present invention. Generally, it is desirable to control the hydrocarbon/oxygen molar ratio to avoid the formation of gaseous mixtures within the flammable region. It is preferred to maintain the volume ratio of hydrocarbon/

oxygen within the range of about 0.1-100:1, more pre¬ ferably within the range of about 1-50:1. Methane/air feed mixtures containing about 50 to 90 volume % meth¬ ane have been found to comprise a desirable feedstream. Further dilution of the feedstream with gases such as nitrogen is not necessary.

The contact solid which is contacted with methane in the first stage of the present process has heretofore been generally referred to as a promoted oxidative synthesizing agent. Oxidative synthesizing agents comprise at least one oxide of at least one metal, which oxides when contacted with methane at temperatures selected within the range of about 500 to 1000°C produce higher hydrocarbon products, co-product water and a reduced metal oxide. The composition thus contains at least one reducible oxide of at least one metal. The term "reducible" identifies those oxides of metals which are reduced by the methane contact. The term "oxide(s) of metal(s)" includes: (1) one or more metal oxides (i.e., compounds described by the general formula M _x O _v wherein M is a metal and the subscripts x and y designate the relative atomic proportions of metal and oxide in the composition) and/or (2) one or more oxygen-containing metal compounds, provided that such oxides and compounds have the capability of per¬ forming to produce higher hydrocarbon products as set forth herein.

Effective agents for the conversion of methane to higher hydrocarbons have previously been found to comprise reducible oxides of metals selected from the group consisting of manganese, tin, indium, germanium, antimony, lead, bismuth and mixtures thereof.

Reducible oxides of cerium, praseodymium, and terbium have also been found to be effective for the conversion of methane to higher hydrocarbons when the rare earth component is associated with an alkali metal component (i.e., lithium, sodium, potassium, rubidium.

cesium and compounds thereof) and/or an alkaline earth metal component (i.e., magnesium, calcium, strontium, barium, and compounds thereof).

The contact solid employed in the process of the present invention contains, in addition to the reducible metal oxide component, at least one alkali or alkaline earth metal. The atomic ratio in which these materials are combined to form the contact solid is not narrowly critical. However, the preferred atomic ratio of the reducible oxide component (expressed as the metal, e.g., Mn) to the alkali/ alkaline earth metal component (expressed as the metal, e.g., Na) is within the range of about 0.1-100:1, more preferably within the range of about 0.3-10:1.

The contact solid may optionally contain at least one phosphorus component. The amount of phos¬ phorus contained in the contact solid is again not narrowly critical. The atomic ratio of phosphorus to the reducible oxide component (expressed as the metal, e.g., Mn) is preferably less than about 2:1. More preferably, this ratio is within the range of about 0.1-0.5:1.

A preferred contact solid used in the process of this invention may be further expressed by the following empirical formula:

A _a B _b P _c O _d wherein A is selected from the group consisting of Mn, Sn, In, Ge, Pb, Sb, Bi, Pr, Tb, Ce and mixtures thereof _? B is selected from the group consisting of alkali and alkaline earth metals including mixtures thereof _? a to d indicate the atomic ratio of each component _? and when a is 10, b is within the range of about 1-33, c is within the range of about 0-20, and d has a value which is determined by the valence and proportions of the other elements present.

The metal components may be associated with support materials such as silica, alumina, titania.

magnesia, zirconia and the like and combinations there¬ of. When employing agents containing rare earth com¬ ponents-oxides of Ce, Pr, and Tb—the rare earth oxides preferably serve as supports.

Reducible oxides of manganese have been found to be particularly desirable for methane conversion according to the method of the present invention when associated with an alkali metal (preferably sodium). Particularly preferred agents comprise silica- and/or magnesia-supported solids containing oxides of man¬ ganese and sodium.

The solid contacted with methane and an oxygen-containing gas can be prepared by any suitable method. Conventional methods such as precipitation, coprecipitation, impregnation or dry mixing can be used. Supported solids may be prepared by methods such as adsorption, impregnation, precipitation, coprecipi¬ tation, and dry mixing. hen phosphorus is incorpor¬ ated into the agent, it is desirable to provide it in the form of a phosphate of an alkaline metal or alka¬ line earth metal.

A suitable method of preparation is to impregnate a support with solutions of the desired metals. Suitable compounds useful for impregnation include the acetates, acetylacetonates, oxides, car¬ bides, carbonates, hydroxides, formates, oxalates, nitrates, phosphates, sulfates, sulfides, tartrates, fluorides, chlorides, bromides, or iodides. After impregnation the preparation is dried to remove solvent and the dried solid is calcined, preferably in air, at a temperature within the range of about 300 to 1200°C. Particular calcination temperatures will vary depending upon the particular metal compound or compounds employed.

Regardless of how the components of the agent are combined, the composite will be dried and calcined at elevated temperatures prior to use of the process of

this invention.

Preferably, methane and oxygen are contacted with the agent in the substantial absence of catalytic- ally effective nickel, noble metals and compounds thereof, (i.e., nickel, rhodium, palladium, silver, osmium, iridium, platinum and gold) to minimize the deleterious catalytic effects thereof. These metals, when contacted with methane at the temperatures em¬ ployed in the first step of the present invention, tend to promote coke formation, and the metal oxides tend to promote the formation of combustion products rather than the desired hydrocarbons. The term "catalytically effective" is used herein to identify that quantity of one or more of nickel and of the noble metals and compounds thereof which substantially changes the distribution of products obtained in the method of this invention relative to such contacting in the absence of such metals and compounds thereof.

Operating temperatures for the method of this invention are generally within the range of about 300 to 1200°C, more preferably within the range of about 5Q0 to 1000°C. Best results for contact solids con¬ taining manganese have been found at operating temper¬ atures within the range of about 800 to 900°C. If reducible oxides of metals such as In, Ge or Bi are present in the solid, the particular temperature selected may depend, in part, on the particular reduc¬ ible metal oxide(s) employed. Thus, reducible oxides of certain metals may require operating temperatures below the upper part of the recited range to minimize sublimation or volatilization of the metals (or com¬ pounds thereof) during methane contact. Examples are: (1) reducible oxides of indium, (operating temperatures will preferably not exceed about 850°C) _? (2) reducible oxides of germanium (operating temperatures will pre¬ ferably not exceed about 850°C) _? and (3) reducible oxides of bismuth (operating temperatures will prefer-

ably not exceed about 850°C).

Operating pressures for the methane contact¬ ing step are not critical to the presently claimed invention. However, both general system pressure and partial pressures of methane and oxygen have been found to effect overall results. Preferred operating pressures are within the range of about 0.1 to 30 atmospheres.

The space velocity of the gaseous reaction streams are similarly not critical to the presently claimed invention, but have been found to effect over¬ all results. Preferred total gas hourly space veloc¬ ities are within the range of about 10 to 100,000 hr."l, more preferably within the range of about 600 to 40,000 hr." ¹ .

Contacting methane and a reducible metal oxide to form higher hydrocarbons from methane also produces co-product water and reduces the metal oxide. The exact nature of the reduced metal oxides are un¬ known, and so are referred to as "reduced metal oxides". Regeneration of reducible ^" metal oxides in the method of the present invention occurs "in situ"—by contact of the reduced metal oxide with the oxygen cofed with methane to the contact zone.

The contact solids may be maintained in the contact zone as fixed, moving, or fluidized beds of solids. A fixed bed of solids is currently preferred for the method of this invention.

The effluent from the contact zone contains higher hydrocarbon products (e.g., ethylene, ethane and other light hydrocarbons), carbon oxides, water, un- reacted hydrocarbon (e.g., methane) and oxygen, and other gases present in the oxygen-containing gas fed to the contact zone. Higher hydrocarbons may be re¬ covered from the effluent and, if desired, subjected to further processing using techniques known to those skilled in the art.

_U nreacted methane may be recovered and recycled to the contact zone.

The invention is further illustrated by refer¬ ence to the following examples.

EXAMPLE 1

A contact solid consisting of 10 wt. % Mn/5 wt. % a4P2θ on silica was prepared by impregnating the silica support with appropriate amounts of sodium pyrophoshate and manganese (as manganese acetate). The impregnated solid was dried for 2 hours at 110°C and then calcined in air for 16 hours at 850°C. A quartz tube reactor (12 mm. inside diameter) was charged with 10 ml. of the calcined solids and the reactor was heated to 700°C with a heated stream of nitrogen. Results obtained when methane/air mixtures were con¬ tacted with the calcined solid are shown below in Table 1. Also shown in Table 1 are results obtained when methane and air were cyclically introduced to the reactor.

The first three runs shown in Table 1 used a cyclic process in which methane was passed over the solid for 2 minutes followed by a 10 minute N2 purge, a 20 minute air reoxidation, a 15 minute 2 purge, and then repeating the cycle. Also see Run 8. Runs 4-7, 9 and 10 used a mixed feed containing 90 vol. % methane and 10 vol. % air. Runs 11-15 used a mixed feed con¬ taining 50 vol. % methane and 50 vol. % air. The total gas hourly space velocity (GHSV) of all of the runs shown in Table I was 600 hr."---. The experimental results presented in Table 1 include methane conver¬ sions and product selectivities calculated on a molar basis. Results are based on gas chromatographic analysis of total reactor effluent collected over the run time. Changes in feed composition for the methane/ air runs and changes in flow rate and temperature were accomplished by diverting the feed stream from the reactor for a short period of time to adjust the oper-

ating variable and then reintroducing the feed to the reactor at the various operating conditions shown in Table 1.

^• TABLE 1 Methane/Air Mixtures Over 10% Mn/5% Na _A P-?θ7/Silica

(total GHSV = 600 hr. ^"1 ) Run No.

(time Feed Rxn CH4 % Selectivity to: in min) (%) Temp. % Conv. C~+ CO CO- Coke

1(2) CH4 700°C 4.4 59.0 15.9 20.4 4.5 2(2) CH ₄ 800 12.0 61.7 5.0 29.1 4.1 3(2) CH ₄ 800 13.9 68.3 5.7 23.0 2.9

4(10) CH ₄ (90), 600 1.5 6.7 93.3

AIR(IO)

5(10) CH ₄ (90), 700 3.0 53.0 47.0

AIR(IO)

6(10) CH ₄ (90), 750 5.6 66.0 7.1 26.8

AIR(IO) (10) CH ₄ (90) 800 6.9 70.3 7.2 22.4

AIR(IO) (30) CH ₄ 800 1.6 89.8 10.2 (30) CH ₄ (90), 800 4.4 68.3 9.0 22.6

AIR(IO) 0(60) CH ₄ (90), 800 3.9 67.7 10.3 21.9

AIR(IO) 1(30) CH ₄ (50) 600 5.6 — 100

AIR(50) 2(30) CH ₄ (50) 700 15.3 15.1 5.9 78.9

AIR(50) 3(30) CH ₄ (50), 750 20.1 35.8 6.3 57.8

AIR(50) 4(30) CH ₄ (50), 800 22.6 46.9 7.9 45.1

AIR(50) 5(60) CH ₄ (50) 850 22.8 49.6 12.2 38.1

AIR(50)

Run 7 demonstrates that improved hydrocarbon selec¬ tivity can be obtained using the method of this inven¬ tion at conversion levels similar to those reported by Hinsen and Baerns. Run 15 demonstrates that substan¬ tial increases in methane conversion can be realized while maintaining hydrocarbon selectivities comparable to those reported by Hinsen and Baerns. The data also demonstrates that use of higher operating temperatures offers improved process results.

EXAMPLE 2 This example was carried out in the same manner as Example 1 using the same contact solid and shows the effect of increasing space velocity on con¬ version and selectivity. A 50% methane, 50% air feed mixture was studied at 800°C and various total feed flow rates. The results are shown in Table 2. Runs 1-7 indicate that as the space velocity is increased there is little or no change in methane conversion with a maximum in hydrocarbon selectivity at a gas hourly space velocity (GHSV) of 2400 hr.-*--. As the GHSV is increased above 9600 both conversion and selectivity decrease. Table 2 also includes data for % O2 conver¬ sion and methane weight hourly space velocity (CH ₄ WHSV: weight of methane fed per hour per weight of contact solid in the reactor) .

TABLE 2

1: 1, Methane Air Mixtures Over 10% Mn, 5% Na ₄ P ₂ 0 ₇ on Silica at 800°C

Run No. Total CH ₄ %

(time GHSV WHSV CH ₄ % Selectivity tc >: % 0 ₂ in min) (hr ^-1 ) (hr ^{^1} ) Conv. C ₂ + CO co ₂ Conver.

1(30) 600 0.38 22.6 47 8 45 93

2(30) 800 0.51 22.7 49 9 42 87

3(30) 1000 0.64 22.7 51 9 40 85

4(30) 1200 0.76 22.4 52 10 38 85

5 (30) 2400 1.53 24.1 57 10 33 87

6(30) 4800 2.92 23.2 55 11 34 85

7(30) 9600 5.78 22.4 55 11 34 84

8(15) 28800 17.53 10.4 48 13 39 42

9(15) 38400 23.03 7.0 45 14 40 27

EXAMPLE 3

A series of experiments similar to Examples 1 and 2 showed that by changing the composition of the contact solid to 15 wt. % Mn/4 wt. % Na ₄ P2θ7 on silica, further improvements in methane conversion and hydrocarbon selectivity could be obtained. This example also shows that as the percentage of air in the feed is increased for a given set of conditions, the methane conversion increases and the hydrocarbon selec¬ tivity decreases. Table 3 summarized the results for this example. By comparing run 6 in Table 2 with run 12 in Table 3 one can see the improvement in using 15 wt. % Mn/4 wt. % Na P2θ7 on silica as the contact solid.

TABLE 3 . Methane/Air Mixtures Over 15% Mn, 4% Na^P-**^ on Silica Run No. Total CH %

(time GHSV WHSV Feed CH ₄ Temp % Selectivity to: in min) (hr ^-1 ) (hr ^"1 ) (%) Conv. °C C ₂ + CO C0 ₂ 1(4)* 600 0.70 CH ₄ (100) 6.9 700 65.4 — 28.8 2(4) 600 0.70 CH ₄ (100) 17 800 56.6 7.1 35.0 3(30) 1200 1.26 CH ₄ (90), 2.8 700 56.0 — 44.0

AIR(IO) 4(30) 1200 1.26 CH ₄ (90), 2.5 750 48.0 — 52.0

AIR(IO) 5(30) 1200 1.26 CH ₄ (90), 3.2 800 65.3 9.4 25.2

AIR(IO) 6(30) 1200 1.26 CH (90), 4.7 800 67.2 8.5 24.3

AIR(10) 7(30) 1200 1.12 CH ₄ (80), 6.7 800 64.3 7.4 28.2

AIR(20) 8(30) 1200 0.98 CH ₄ (70), 11 800 60.5 8.1 31.3

AIR(30) 9(30) 1200 0.98 CH ₄ (70), 12 850 66.6 10.1 23.2

AIR(30) 10(30) 2400 1.96 CH ₄ (70), 13 850 69.1 10.3 20.6

AIR(30) 11(30) 2400 2.24 CH (80) 8.3 850 74.5 9.1 16.5

AIR(20) 12(30) 4800 2.81 CH (50), 25 800 60.0 11.1 28.8

AIR(50) 13(30) 2400 1.4 CH ₄ (50), 24 800 56.0 10.0 34.0

AIR(50) 14(4) 1200 1.4 CH ₄ (100), 9.8 800 81.3 6.5 12.3 * Coke selectivity was 5.8% for this inital run.

EXAMPLE 4 Feeds containing more than 50% air were studied in this example which used a contact solid consisting of 15 wt. % Mn/4 wt. % Na ₄ P2θ7 on silica. Feeds containing 70, 75 and 80% air were studied at temperatures of 600 to 800°C and a constant total gas hourly space velocity (GHSV) of 2400 hr." ¹ . Large exotherms were observed. The results, shown in Table 4, show that large amounts of air in the feed (greater than 50%) produced relatively inferior hydrocarbon selectivities. The duration of each run shown was 30 minutes.

TABLE 4 CH ₄ Run Temp. WHSV Feed % O2 % CH ₄ % Selectivity to; No. % (hr ^-1 ) (%) Conv. Conv. c _? + CO CO?

600 0.41 CH ₄ (30) 7 3.2 0 0 0 0 1 10001 0 AIR(70)

700 0.41 CH ₄ (30) 49 19 1 1..22 4 4..44 9 944. .44 AIR(70)

800 0.41 CH ₄ (30) 93 34 1 199..22 3 3..11 7 777., .77 AIR(70)

700 ^a 0.41 CH ₄ (30) 60 22 3.5 4.2 92, .4 AIR(70)

800 ^a 0.41 CH ₄ (30) 92 39 34.1 6.4 59. .6 AIR(70)

800 ^a 0.34 CH ₄ (25) 93 47 30.7 6.0 63. .3 AIR(75)

880 ^b 0.34 CH ₄ (25) 93 48 32.8 7.8 59. ,5 AIR(75)

800 ^a 0.27 CH ₄ (20) 93 56 27.3 5.5 67. ,2 AIR(80)

The temperature shown is the initial reaction temperature . The subsequent axothe:rm was allowed to occur in these runs without the te pe:rature controller :responding. b. The temperature shown is thei initial reaction

temperature. The temperature controller respond¬ ed during the run to maintain reaction temper¬ atures close to the initial temperature shown.

EXAMPLE 5 A contact solid consisting of 10 wt. % Sn/2 wt. % Na on silica was prepared by impregnating the silica support with appropriate amounts of sodium (as sodium acetate) and tin (provided as 7% solution of tin tartrate in hydrochloric acid) . The impregnated solid was dried for 2 hours at 110°C and then calcined in air for 16 hours at 850°C. Using the procedure described above in Example 1, a number of methane/air runs were performed over this solid at varying feed compositions operating temperatures and space velocities. Results are shown below in Table 5. The duration of each run shown was 30 minutes.

TABLE 5 CHa/Air Mixtures Over 10% Sn/2% Na on Silica Run Feed Rxn Total CH ₄ % % Selectivity to: No. (%) Temp. GHSV Conv. C~+ CO CO

1 CH ₄ (90) 600°C 1200hr ^"1 0.1 0 0 100 AIR(IO)

2 CH ₄ (90) 700 1200 2.9 76.9 17.0 6.1 AIR(IO)

3 CH ₄ (90) 800 1200 3.0 51.8 22.6 25.6 AIR(IO)

4 CH ₄ (80) 800 1200 4.7 37.8 18.6 44.0 AIR(20)

5 CH ₄ (70) 800 1200 7.8 32.0 12.4 55.7 AIR(30)

6 CH ₄ 60), 800 1200 10.6 28.8 10.6 60.5 AIR(40)

7 CH ₄ (80) 800 2400 4.4 39.4 13.8 46.9 AIR(20)

EXAMPLE 6 A contact solid consisting of 50 wt. % Mn on silica was prepared by impregnating the silica support with appropriate amounts of manganese (provided as a solution of manganese acetate). The impregnated solid was dried for 2 hours at 110°C and then calcined in air for 16 hours at 850°C. Using the procedure described above in Example 1, a number of methane/air runs were performed over this solid at varying feed compositions operating temperatures and space velocities. Results are shown below in Table 6. The duration of each run shown was 30 minutes.

TABLE 6

CHd/A: Lr Mixtures Over 50% Mn on Silica

Run Feed Rxn Total CH % % Selectivil :y to:

No. (%) Temp. GHSV Conv. C2± CO CO?

1 CH ₄ (45) 750°C lδOOhr ^"1 17.1 7.98 14.5 77.4 AIR(55)

2 CH ₄ (70) 750 1800 7.9 15.35 30.2 54.4 AIR(30)

3 CH ₄ (70) 750 3600 7.55 14.44 28.3 57.2

AIR(30)

4 CH ₄ (70) 750 5400 7.75 16.76 29.2 53.8

AIR(30) 30

EXAMPLE 7

A contact solid consisting of 5 wt. % Mn on silica was prepared by impregnating the silica support with appropriate amounts of an aqueous solution of manganese acetate. The impregnated solid was dried for 2 hours at 110°C and then calcined in air for 16 hours at 850°C. Using the procedure described above in Example 1, a number of methane/air runs were performed over this solid at varying feed compositions operating temperatures and space velocities. Results are shown below in Table 7. The duration of each run shown was 30 minutes.

TABLE 7

CH_ _t /Air Mixtures Over 5% Mn on Silica Run Feed Rxn Total CH % % Selectivity to: No. (%) Temp. GHSV Conv. Cp+ CO CO?

1 CH ₄ (95.2) 650°C 600hr ^-1 1.13 2.54 44.9 52.4

AIR(4.8)

2 CH (95.2) 700 600 1.23 4.28 52.8 42.8

AIR(4.8)

3 CH ₄ (95.2) 750 600 1.22 7.9 5.0.0 42.1

AIR(4.8)

4 CH ₄ (95.2) 800 600 1.32 15.4 51.5 32.0

AIR(4.8)