U.S. patent number RE35,632 [Application Number 08/006,421] was granted by the patent office on 1997-10-14 for methane conversion process.
This patent grant is currently assigned to Atlantic Richfield Company, Phillips Petroleum Company. Invention is credited to David W. Leyshon.
United States Patent |
RE35,632 |
Leyshon |
October 14, 1997 |
Methane conversion process
Abstract
In an improved method for converting methane to at least one
higher hydrocarbon product and coproduct water which comprises
contacting a gas comprising methane and at least one added gaseous
oxidant with nonacidic solid, the improvement comprising conducting
at least a portion of said contacting in the presence of added
water.
Inventors: |
Leyshon; David W. (West
Chester, PA) |
Assignee: |
Atlantic Richfield Company (Los
Angeles, CA)
Phillips Petroleum Company (Bartlesville, OK)
|
Family
ID: |
21765293 |
Appl.
No.: |
08/006,421 |
Filed: |
January 19, 1993 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
014405 |
Feb 13, 1987 |
04801762 |
Jan 31, 1989 |
|
|
Current U.S.
Class: |
585/500; 585/415;
585/417; 585/418; 585/654; 585/656; 585/658; 585/661; 585/833;
585/905; 585/943 |
Current CPC
Class: |
C07C
2/82 (20130101); C07C 2/84 (20130101); C07C
2521/06 (20130101); C07C 2521/08 (20130101); C07C
2521/10 (20130101); C07C 2523/02 (20130101); Y10S
585/905 (20130101); Y10S 585/943 (20130101) |
Current International
Class: |
C07C
2/82 (20060101); C07C 2/84 (20060101); C07C
2/00 (20060101); C07C 002/00 () |
Field of
Search: |
;585/500,654,656,661,700,943,400,415,417,418 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Lin et al., "Oxidative Dimerization of Methane over Lanthanum
Oxide", J. Phys. Chem., vol. 90, No. 4, Feb. 1986, pp. 534-537.
.
Ito et al, "Oxidative Dimerization of Methane over a Lithium
Promoted Magnesium Oxide Catalyst", J. Am. Chem. Soc., vol. 107,
1985, pp. 5062-5068. .
Otsuka, Chem. Soc. of Japan, Chemical Letters (1986) pp. 903-906
(1986). .
Kimble, James B. et al., "Oxidative Coupling of Methane to Higher
Hydrocarbons," Amer. Inst. of Chem. Engrs. meeting in New Orleans,
Apr. 6-10, 1986..
|
Primary Examiner: Pal; Asok
Attorney, Agent or Firm: Long; William C.
Claims
What is claimed:
1. In a method for converting methane to higher hydrocarbons
wherein a gas comprising methane and a gaseous oxidant are
contacted with a nonacidic solid .Iadd.which is substantially
nonreducible under the contacting conditions .Iaddend.to produce
higher hydrocarbons and coproduct water, the improvement which
comprises conducting at least a portion of said contacting in the
presence of added water. .[.2. The method of claim 1 wherein said
solid comprises at least one reducible metal oxide of at
least one metal..].3. The method of claim 1 wherein the mole ratio
of said
added water to said methane in said gas is less than about 10. 4.
The method of claim 1 wherein the mole ratio of said added water to
said
methane in said gas is in the range of about 0.01 to about 6. 5.
The method of claim 1 wherein the mole ratio of said added water to
said
methane in said gas is in the range of about 0.05 to about 4.0. 6.
The method of claim 1 wherein the contacting is conducted at a
temperature
within the range of about 300.degree. to about 1200.degree. C. 7.
The method of claim wherein the contacting is conducted at a
temperature of
about 700.degree. to about 1200.degree. C. 8. The method of claim 1
wherein the contacting is conducted at a temperature of about
800.degree.
to about 1000.degree. C. 9. The method of claim 3 wherein the
contacting is conducted at a temperature of about 500.degree. to
about 1000.degree.
C. 10. The method of claim 1 wherein said solid is selected from
the group
consisting of basic metal oxides. 11. The method of claim 10
wherein said solid is selected from the group consisting of
alkaline earth oxides and
mixtures thereof. 12. The method of claim 10 wherein said solid
comprises
magnesia. 13. The method of claim 10 wherein said solid comprises
CaO.
The method of claim .[.10.]. .Iadd.1 .Iaddend.wherein said
solid
comprises titania. 15. The method of claim .[.10.]. .Iadd.1
.Iaddend.wherein said solid comprises silica. 16. The method of
claim 10 wherein said solid comprises barium. .[.17. The method of
claim 2 wherein said solid is substantially nonreducible under the
contacting
conditions..].18. The method of claim .[.11.]. .Iadd.1
.Iaddend.wherein said solid .[.further.]. comprises .Iadd.an
alkaline earth oxide together
with .Iaddend.at least one alkali metal component. 19. The method
of claim 18 wherein the alkali metal component is selected from the
group
consisting of sodium and compounds thereof. 20. The method of claim
18 wherein the alkali metal component is selected from the group
consisting
of lithium and compounds thereof. 21. The method of claim 18
whereto the alkali metal component is selected from the group
consisting of potassium
and compounds thereof. 22. The method of claim 1 wherein the
gaseous
oxidant comprises molecular oxygen. 23. The method of claim 1
wherein the
gaseous oxidant comprises oxides of nitrogen. 24. The method of
claim 23
wherein the oxides of nitrogen comprises N.sub.2 O. .[.25. In a
method for converting methane into higher hydrocarbon products and
coproduct water which comprises contacting a gas comprising methane
and an oxygen-containing gas with a solid comprising at least one
reducible metal oxide of at least one metal, which oxide when
contacted with methane at 500.degree. to 1000.degree. C. produces
higher hydrocarbons, coproduct water, and reduced metal oxide, the
improvement comprising conducting at least a portion of the
contacting in the presence of added water..]..[.26. The method of
claim 25 wherein the mole ratio of said added water to said methane
in said gas is less than about 10..]..[.27. The method of claim 25
wherein the mole ratio of said added water to said methane in said
gas is in the range of about 0.01 to about 6..]..[.28. The method
of claim 25 wherein the mole ratio of said added water to said
methane in said gas is in the range of about 0.05 to about
4.0..]..[.29. The method of claim 25 wherein the solid comprises at
least on reducible oxide of Mn..]..[.30. The method of claim 29
wherein the solid comprises at least one member of the group
consisting of alkali metals, alkaline earth metals, and
compounds and mixtures thereof..]..[.31. The method of claim 29
wherein the solid comprises at least one member of the group
consisting of boron and compounds thereof..]..[.32. The method of
claim 30 wherein the solid comprises at least one member of the
group consisting of boron and compounds thereof..]..Iadd.33. A
method for the oxidative conversion of methane to higher
hydrocarbons and coproduct water, comprising: contacting said
methane, a free oxygen-containing gas and water with at least one
solid contact material which is substantially nonreducible under
the contacting conditions selected from the group consisting of a
solid contact material consisting essentially of lanthanum oxide
and solid contact materials comprising (a) at least one promoter
comprising an alkali metal and (b) at least one base material
selected from the group consisting of magnesium oxide and calcium
oxide, under oxidative conversion conditions sufficient to convert
said methane to said higher hydrocarbons. .Iaddend..Iadd.34. A
process in accordance with claim 33, wherein said solid contact
material consists essentially of at least one lithium-containing
promoter and magnesium oxide as base material. .Iaddend .
Description
BACKGROUND OF THE INVENTION
This invention relates to the conversion of methane to higher
hydrocarbons. A particular application of this invention is a
method for converting natural gas to more readily transportable
material.
Recently, it has been discovered that methane may be converted to
higher hydrocarbons by a process which comprises contacting methane
and an oxidative synthesizing agent at synthesizing conditions
(e.g., at a temperature selected within the range from about
500.degree. to about 1000.degree. C.) Oxidative synthesizing agents
are compositions having as a principal component at least one oxide
of at least one metal which compositions produce C.sub.2 +
hydrocarbon products, co-product water, and a composition
comprising a reduced metal oxide when contacted with methane at
synthesizing conditions. Reducible oxides of several metals have
been identified which are capable of converting methane to higher
hydrocarbons. In particular, oxides of manganese, tin, indium,
germanium, lead, antimony, bismuth, praseodymium, terbium, cerium,
iron and ruthenium are most useful. See commonly-assigned U.S. Pat.
Nos. 4,443,669 (Mn); 4,444,984 (Sn); 4,445,648 (In); 4,443,665
(Ge); 4,443,674 (Pb); 4,443,646 (Bi); 4,499,323 (Pr); 4,499,324
(Ce); and 4,593,139 (Ru), the entire contents of which are
incorporated herein by reference. See also commonly-assigned U.S.
patent application Ser. No. 666,694 (Fe) the entire content of
which is incorporated herein by reference.
Commonly-assigned U.S. Pat. No. 4,554,395 discloses and claims a
process which comprises contacting methane with an oxidative
synthesizing agent under elevated pressure (2-100 atmospheres) to
produce greater mounts of C.sub.3 + hydrocarbon products
Commonly-assigned U.S. Pat. No. 4,560,821 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 recirculate between two
physically separate zones--a methane contact zone and an oxygen
contact zone.
U.S. Pat. No. 4,499,322 discloses and claims a process for the
conversion of methane to higher hydrocarbon and comprises
contacting methane with an oxidative synthesizing agent containing
a promoting mount of alkali metal and/or compounds thereof.
U.S. Pat. No. 4,495,374 discloses and claims a process for the
conversion of methane to higher hydrocarbons which comprises
contacting methane with an oxidative synthesizing agent containing
a promoting amount of alkaline earth metal and/or compounds
thereof.
Hinsen and Baerns report studies of a continuous mode for the
oxidative coupling of methane wherein regeneration air is cofed
with methane feed. Hinsen, W. and Baerns, M., "Oxidative Koppling
von Methan zu C.sub.2 - Kohienwasserstoffen in Gegenwart
untersehiedlicher Katalsatoren", 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 degrees C., they report results of
approximately 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 studies by Hinsen and Baerns
included oxides of Bi, Sb, Sn and Mn.
U.S. Pat. No. 4,523,049, discloses and claims a process for
converting methane to higher hydrocarbons which comprises
contacting methane and an oxygen-containing gas with a solid
comprising a reducible metal oxide and an alkali/alkaline earth
metal promoter.
U.S. Pat. No. 4,523,050 discloses and claims a process for
converting methane to higher hydrocarbons which comprises
contacting methane and an oxygen-containing gas with a manganese
silicate.
Commonly-assigned U.S. patent application Ser. No. 738,110, filed
May 24, 1985, discloses and claims a method for converting methane
to higher hydrocarbons wherein methane and a gaseous oxidant are
contacted with a nonacidic solid. In a preferred embodiment, the
solid comprises an alkali metal component associated with a support
material. The application also teaches conducting the contacting in
the presence of halogen promoters when employing alk.ali-promoted
solids..
Commonly-assigned U.S. patent application Ser. No. 738,114, filed
May 24, 1985, discloses and claims a process wherein methane and a
gaseous oxidant are contacted with a nonacidic solid in the
presence of halogen promoter but in the absence of an alkali metal
promoter.
Concurrently-filed, commonly-assigned U.S. patent application Ser.
No. 07/014,406 filed 2-13-87 discloses and claims a method for
converting methane to higher hydrocarbons wherein methane and added
water are contacted in the substantial absence of added gaseous
oxidant with a solid comprising at least one reducible metal
oxide.
The reaction product of the foregoing processes are hydrocarbons,
carbon oxides, coke and water. It would be beneficial in these
processes to reduce selectivities to carbon oxides and coke and to
increase methane conversions to the desired hydrocarbon products.
Accordingly, an object of this invention is to provide an improved
process for converting methane to higher hydrocarbons. More
particular aspects, objects and the several advantages of this
invention will become apparent to those skilled in the an upon
reading this disclosure and the appended claims.
SUMMARY OF THE INVENTION
It has been found that processes for producing higher hydrocarbons
wherein methane and a gaseous oxidant are contacted with a
nonacidic solid are improved when the contacting is conducted in
the presence of added water. This added water is separate and apart
from the coproduct water produced from methane conversion during
the contacting. However, such coproduct water (or a portion
thereof) may be separated from the other products and introduced
into the contacting zone as the added water.
In processes conducted according to this invention, methane is
converted to higher hydrocarbons with improved efficiency, e.g.,
increased selectivity to higher hydrocarbon products.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are plots respectively of the effect of steam partial
pressure vs C.sub.2 + hydrocarbon selectivity and steam partial
pressure vs. CO.sub.x formation rate from the tests described in
Example 7.
DETAILED DESCRIPTION OF THE INVENTION
In addition to methane the methane feedstock, employed in the
method of this invention may contain other hydrocarbon or
non-hydrocarbon components. The methane content of the hydrocarbon
portion 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 gaseous oxidant cofed with methane to the contacting zone
preferably comprises a gas containing molecular oxygen (e.g., air).
However, oxides of nitrogen, esp. N.sub.2 O, have also been found
to be effective gaseous oxidants. See U.S. Pat. No. 4,547,610, the
entire content of which is incorporated herein by reference.
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.
Preferably, the ratio is maintained within the range of about
0.1-300:1, more preferably within the range of about 1-150:1.
Methane/air feed mixtures containing about 30 to 90 volume %
methane have been found to comprise a desirable feedstream. Further
dilution of the feedstream with gases such as nitrogen may be
beneficial for improved temperature control.
The amount of added water present during at least a portion of the
methane/solid contacting may vary over a wide range. Preferably,
the mole ratio of added water to methane in the gas to be contacted
is less than about 10. More preferably, this mole ratio is in the
range of about 0.01 to about 6, still more preferably about 0.05 to
about 4.0. The added water may be combined with the
methane-containing gas and/or the oxygen-containing gas prior to
the contacting the nonacidic solid. For example, the
methane-containing gas or the oxygen-containing gas may be
contacted with water so that the gas "picks-up" a predetermined,
controlled amount of added water prior to the methane/solid
contacting. Alternately, a predetermined, controlled amount of
water e.g., steam, can be injected into the methane-containing gas
and/or the oxygen-containing gas and/or directly into the
methane/solid contacting zone or zones.
The solids useful in the present invention are characterized as
"nonacidic". This descriptor is meant to refer to the main,
predominant surface properties of the non-acidic solids. For
example some solid bases are known to have acidic properties to
some extent. See Tanabe, K., "Solid Acid and Base Catalysts."In:
Catalysis Science & Technology, vol. 2 (New York,
Springer-Verlag Berlin Heidelberg, 1981). Currently preferred
nonacidic solids used in the present process are characterized by
negligible acidity (less than about 0.01 meg/gm) in the H.sub.o
range less than about 3.3, preferably less than about 6.8, H.sub.o
is the Haminert acidity parameter described on pp. 234-241 of
Tanable.
A further characteristic of preferred nonacidic solids for the
present process is a relatively low surface area. Nonacidic solids
having surface areas less than about 50 cm.sup.2 /gm are suitable,
but the surface areas of preferred solids are within the range of
about 0.1-10 m.sup.2 /gm.
In one distinct embodiment of this invention, methane and a gaseous
oxidant are contacted with a nonacidic solid characterized by the
substantial absence of reducible metal oxides. Characteristics of
nonacidic acids preferred for this embodiment are that they be
stable and substantially nonreducible under process conditions.
Examples of suitable nonacidic solids include those solid bases
described in Table 2 on p. 233 of Tanabe. supra. However, presently
preferred nonacidic solids are metal oxides and mixed oxides.
Alkaline earth oxides are particularly preferred, especially MgO
and CaO. Other suitable metal oxides are SiO.sub.2, alpha-Al.sub.2
O.sub.3, La.sub.2 O.sub.3, ThO.sub.2, TiO.sub.2, and ZrO.sub.2.
Such materials are relatively stable under the conditions of the
present process.
Alkali metal-promoted alkaline earth oxides are preferred nonacidic
solids for this embodiment. Such solids are described and
exemplified in commonly-assigned U.S. patent application Ser. No.
738,110, filed May 24, 1985, the entire content of which is
incorporated herein by reference. Halogen promoters may be
employed, but in such event, the use of alkali metal promoters is
not preferred. See commonly-assigned U.S. patent application Ser.
No. 738,114, filed May 24, 1985, the entire content of which is
incorporated herein by reference.
In another distinct embodiment of this invention, methane and a
gaseous oxidant are contacted with solid comprising a reducible
metal oxide. While such solids are sometimes referred to as
"catalysts" it will be understood that, under conditions of use,
nonacidic solids comprising a reducible metal oxide act as
selective oxidants, and, therefore, take on the characteristics of
a reactant during use. Thus, for example, the term "Mn-containing
oxides" is meant to embrace both reducible oxides of Mn and reduced
oxides of Mn, it being understood reducible oxides comprise the
principal active component of the compositions.
In their active state, such catalysts comprise at lease one
reducible oxide of at least one metal, which oxide when contacted
with methane at synthesizing conditions (e.g., at a temperature
within the range of about 500.degree. to 1000.degree. C.) produces
higher hydrocarbon products, coproduct water, and a reduced metal
oxide. The term "reducible" is used to identify those oxides of
metals which are reduced under the aforesaid conditions. The term
"reducible oxides of metals" includes: (1) compounds described by
the general formula M.sub.x O.sub.y wherein M is a metal and x and
y designate the relative atomic proportions of metal and oxygen in
the composition and/or (2) one or more oxygen-containing metal
compounds (i.e., compounds containing elements in addition to the
metal and O), provided that such oxides and compounds have the
capability of producing higher hydrocarbon products from methane as
described 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. See U.S. Pat. Nos. 4,443,649; 4,444,984; 4,443,648;
4,443,645; 4,443,647; 4,443,644; and 4,443,646. Reducible oxides of
manganese are particularly preferred catalyst components.
Reducible oxides of cerium, praseodymium, and terbium have also
been found to be effective for the conversion of methane to higher
hydrocarbons, particularly associated with an alkali metal
component and/or an alkaline earth metal component. See U.S. Pat.
Nos. 4,499,324 (Ce) and 4,499,323 (Pt) and also see
commonly-assigned U.S. patent application Set. No. 06/600,918
(Tb).
Reducible oxides of iron and ruthenium are also effective,
particularly when associated with an alkali or alkaline earth
component. See commonly-assigned U.S. patent application Ser. No.
06/600,730 (Fe) and U.S. Pat. Nos. 4,489,215 and 4,593,139
(Ru).
Alkali and alkaline earth metals and compounds thereof have been
found to improve the hydrocarbon product selectivity of reducible
metal oxides. The further incorporation of phosphorus into solids
promoted by alkali or alkaline earth components enhances catalyst
stability. See commonly-assigned U.S. Pat. Nos. 4,499,322 and
4,495,374, the entire content of which are incorporated herein by
reference. Alkali metals are selected from the group consisting of
lithium, sodium, potassium, rubidium and cesium. Lithium, sodium
and potassium, and especially lithium and sodium, are preferred
alkali metals. Alkaline earth metals are selected from the group
consisting of magnesium, calcium, strontium and barium. Presently
preferred members of this group are magnesium and calcium.
Compositions derived from magnesia have been found to be
particularly effective catalytic materials. Boron and compounds
thereof are also desirably present in the reducible metal oxide
catalyst employed in the process of this invention. See
commonly-assigned U.S. patent application Ser. No. 06/877,574,
entire content of which is incorporated herein by reference. One
class of boron-promoted compositions useful in the process of this
invention comprises:
(1) at least one reducible metal oxide,
(2) at least one member of the group consisting of boron and
compounds thereof, and
(3) at least one member of the group consisting of oxides of
alkaline earth metals.
A related class of catalyst compositions further comprises at least
one alkali metal or compound thereof. Sodium and lithium are
preferred alkali metal components.
One further, special class of catalyst compositions useful in the
process of this invention are mixed oxides of sodium, magnesium,
manganese and boron characterized by the presence of the
crystalline compound NaB.sub.2 Mg.sub.4 Mn.sub.2 O.sub.x wherein x
is the number of oxygen atoms required by the valence states of the
other elements, said compound having a distinguishing x-ray
diffraction pattern. In its most active form, the compound is
believed to correspond to the formula NaB.sub.2 Mg.sub.4 Mn.sub.2
O.sub.11. While this crystalline compound has been found to be
associated with highly effective oxidant compositions, it has
further been found that still better results are obtained when the
oxidant is characterized by both: (1) the presence of crystalline
compound NaB.sub.2 Mg.sub.4 Mn.sub.2 O.sub.x and (2) a
stoichiometric excess of of Mn relative to at least one of the
other elements of the crystalline compound. In currently preferred
oxidants of this type, a stoichiometric excess of Mn relative to B
is provided. In a still more specific preferred embodiment excess
amounts of Na and Mg, as well as Mn, are present in the mixed oxide
composition relative to the amounts required by the amount of boron
present to satisfy the stoichiometry of the compound NaB.sub.2
Mg.sub.4 Mn.sub.2 O.sub.x.
Further examples of components which may be present in the
catalysts used in the process of this invention are halogen and
chalcogen components. Such components may be added either during
preparation of the catalysts or during use. Methane conversion
processes employing halogen-promoted reducible metal oxides are
disclosed in U.S. Pat. No. 1,544,784. Methane conversion processes
employing chalcogen-promoted, reducible metal oxides are disclosed
in U.S. Pat. No. 4,544,785.
The reducible metal oxides compositions may be supported by or
diluted with support materials such as silica, alumina, titania,
zirconia and the like, and combinations thereof. When supports are
employed, alkaline earth oxides, especially magnesia, are
preferred.
The catalysts are conveniently prepared by any of the methods
associated with similar compositions known in the art. Thus, such
methods as precipitation, co-precipitation, impregnating,
granulation, spray drying or dry-mixing can be used. Supported
solids may be prepared by methods such as adsorption, impregnation,
precipitation co-precipitation, and dry-mixing. For example,
compounds of Mn,Sn,In,Ge,Pb,Sb,Bi,Pr,Tb,Ce,Fe and or Ru may be
combined with compounds of other components in any suitable way.
Substantially any compound of the components can be employed.
Compounds typically used would be oxides or organic or inorganic
salts of the recited components.
To illustrate, when preparing a catalyst containing: (1) a
reducible metal oxide component (e.g., Mn). (2) an alkali metal
component, (3) a boron component and (4) an alkaline earth
component; one suitable method of preparation is to impregnate
compounds of the fourth component of the composition with solutions
of compounds of Mn, alkali metals, and/or boron. Suitable compounds
for impregnation include the acetates, acetyl acetonates, oxides,
carbides, 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 at a temperature
selected within the range of about 300.degree. to 1200.degree. C.
Particular calcination temperatures will vary depending on the
compounds employed. Preferably, the alkaline earth component is
provided as the oxide. Preferably, the alkali metal component is
provided as a basic composition of the alkali metal(s). Examples
are sodium hydroxide, sodium acetate, lithium hydroxide, lithium
acetate, etc. When P is employed as an additive, it has been found
desirable to add the alkali metal and P to the composition as
compounds such as the orthophosphates, metaphosphates, and
pyrophosphates of alkali metals. Pyrophosphates are preferred.
Sodium pyrophosphate is particularly preferred. Preferably, the
boron component is provided as boric acid, boric oxide (or
anhydride), alkali metal borates, boranes, borohydrides, etc.,
especially boric acid or oxide.
Formation of the crystalline compound NaB.sub.2 Mg.sub.4 Mn.sub.2
O.sub.x may be accomplished by reacting active compounds of the
substituent elements. A suitable mixture of the reactive compounds
is formed and heated for a time sufficient to form the crystalline
material. Typically, a temperature of about 850.degree. to about
950.degree. C. is sufficient. When preparing mixed oxide
compositions characterized by the presence of other crystalline
compound, the composition is desirably incorporated with binders or
matrix materials such as silica, alumina, titania, zirconia,
magnesia and the like.
Regardless of which particular catalyst is prepared or how the
components are combined, the resulting composite will generally be
dried and calcined at elevated temperatures prior to use.
Calcination can be done under air, H.sub.2, carbon oxides, steam,
and/or inert gases such as N.sub.2 and the noble gases.
Preferably, methane is contacted with reducible metal oxides in the
presence of added water and in the substantial absence of
catalytically 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 employed in the methane contacting 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 the quantity of one or more of nickel and
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.
Regardless of which class of contacting solid is selected (i.e.,
reducible or nonreducible solid), operating temperatures are
generally within the range of about 300.degree. to about
1200.degree. C.
If nonacidic solids are employed without the presence of reducible
metal oxides, operating temperature are preferably within the range
of about 700.degree. to about 1200.degree. C., more preferably
about 800.degree. to about 1000.degree. C.
If reducible metal oxides are employed, the temperature selected
may depend in part on the particular reducible metal oxide(s)
employed. Best results for contact solids containing manganese have
been found at operating temperatures within the range of about 800
degrees to 900 degrees C. 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
compounds thereof) durin methane contact. Examples are: (1)
reducible oxides of indium, (operating temperatures will preferably
not exceed about 850.degree. C.); (2) reducible oxides of germanium
(operating temperatures will preferably not exceed about
850.degree. C.); and (3) reducible oxides of bismuth (operating
temperatures will preferably not exceed about 800.degree. C.).
Operating pressures are not critical to the presently claimed
invention. However, both general syste pressure and partial
pressures of methane and water have have been found to effect
overall results. Preferred general system 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 overall results. Preferred total gas hourly space
velocities ar within the range of about 100 to 300,000 hr..sup.-1,
more preferably within the range of about 600 to 100,000
hr..sup.-1.
Contacting methane and a reducible metal oxide to form higher
hydrocarbons from methane also produces coproduct water and reduces
the metal oxide. The exact nature of the reduced metal oxides are
unknown, 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 solids may be maintained in the contact zone as fixed, moving,
or fluidized beds of solids. A fixed bed of contact 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 lighter hydrocarbons),
carbon oxides, water and unreacted hydrocarbons (e.g., methane).
Higher hydrocarbons may be recovered from the effluent and, if
desired, subjected to further processing using techniques known to
those skilled in the art. Unreacted methane may be recovered and
recycled to the contact zone.
The invention is further illustrated by reference to the following
examples.
COMPARATIVE EXAMPLE A AND EXAMPLES 1-2
A gaseous feedstream of air/methane and, in Example 1 steam, was
contacted with solid MgO (suppied by Kaiser Chemicals) which was
impregnated with lithium to contain 0.36% by weight of lithium,
calculated as elemental metal. Results are shown in Table I.
TABLE I ______________________________________ Comparative Example
Example A Example 1 2* ______________________________________
Temperature, .degree.C. 909 884 897 Methane GHSV hr..sup.-1 23,700
25,000 25,000 Total Pressure, Psia 19.7 34.7 19.7 O.sub.2 Partial
Pressure, Psi 0.55 0.52 0.52 CH.sub.4 Partial Pressure, Psi 7.56
7.97 7.96 H.sub.2 O Partial Pressure, Psi 0 15.0 0 CH.sub.4
Conversion, % 1.44 10.1 3.76 O.sub.2 Conversion, % 8.36 58.0 21.3
C.sub.2 + Selectivity, % 86.9 93.5 91.5
______________________________________ *Note: Steam was excluded
from the feed to the contacting zone for 45 minutes before the
Example 2 sample was collected.
These Examples were run one after the other in the order shown.
These results demonstrate certain of the substantial benefits of
the present invention. For example, the presence of water during
the contacting provides for increased methane conversion, oxygen
conversion and selectivity to the valuable C.sub.2 + hydrocarbons.
In addition, comparing Example 2 to Example 1 and Comparative
Example A suggests that certain of the beneficial effects of added
water may last after water addition is complete. Thus, it is
possible to obtain at least a portion of the benefits of water
addition by periodic, rather than continuous, addition of
water.
EXAMPLES 3-6 and COMPARATIVE EXAMPLES B-C
A contact solid consisting of 15% by weight manganese (calculated
as elemental metal) and 5% by weight Na.sub.4 P.sub.2 O.sub.7 on
silica was prepared by impregnating the silica support with
appropriate amounts of sodium pyrophosphate and manganese (as
manganese acetate). The impregnated solid was dried and then
calcined in air.
A quartz tube reactor was charged with the calcined solids. A
series of experiments were run at one atmosphere total pressure
using a gaseous mixture of 10% by volume of air in methane to
contact these calcined solids. When steam was added it equaled 14%
of the total number of moles of methane and air fed to the
reactor
Results are shown in Table II.
TABLE II ______________________________________ EXAMPLE B C 3 4 5 6
______________________________________ Temperature, 900 900 900 899
900 900 .degree.C. CH.sub.4 GHSV, 15000 15000 15000 15000 15000
15000 hr..sup.-1 Steam Added No No Yes Yes Yes Yes CH.sub.4 Conver-
2.8 2.7 3.5 3.1 3.1 3.7 sion, % O.sub.2 Conver- 83.5 81.6 -- 68.6
66.9 74.2 sion, % C.sub.2 = Selec- 21.9 20.3 30.6 28.4 29.3 33.5
tivity, % C.sub.2 Selec- 40.1 40.4 44.7 43.8 46.6 40.5 tivity, %
C.sub.3 Selec- 1.6 1.4 2.6 2.7 2.2 3.7 tivity, % >C.sub.4 Selec-
0 0 0.2 0.2 0 0.3 tivity, % C.sub.2 + Selec- 63.7 62.0 78.1 75.1
78.1 77.9 tivity, % ______________________________________
These results demonstrate certain of the benefits of the present
invention. For example, the presence of steam during the
methane/air/contact solids contacting does provide for generally
high selectivity to valuable C.sub.2 + hydrocarbons.
EXAMPLE 7
A series of runs were made using the Li/MgO described in
Comparative Example A and Examples 1-2. Partial pressure of methane
ranged from about 7.5 to 8.0 psia and that of oxygen from about 0.5
to 0.62 psia. Partial pressure of steam ranged from about 0.5 to 15
psia. Methane GHSV ranged from about 23,700 to 25,000 hr..sup.-1
and temperature from about 884.degree. to 909.degree. C.
The results achieved are depicted graphically in attached FIGS. 1
and 2. Referring to FIG. 1, it can be seen that the addition of
steam to the feed mixture has a substantial effect on the
selectivity of the reaction to the desired C.sub.2 .sup.+
hydrocarbon products.
As shown in FIG. 2, the reaction rate is increased by a very
significant extent by the addition of steam to the feed.
While this invention has been described with respect to various
specific examples and embodiments, it is to be understood that the
invention is not limited thereto and that it can be variously
practiced within the scope of the following claims.
* * * * *