An improved method for dehydrogenating dehydrogenatable hydrocarbons by contacting a gas comprising said hydrocarbons and an oxidative dehydrogenation agent at dehydrogenation conditions, the improvement which comprises contacting the hydrocarbon with an oxidative dehydrogenation agent containing a promoting amount of alkali metal and/or compounds thereof and associated with a support selected from the group consisting of alkaline earth metals and compounds thereof.

BACKGROUND OF THE INVENTION 
This invention relates to dehydrogenation of dehydrogenatable hydrocarbons. 
This invention more particularly relates to oxidative dehydrogenation 
processes. 
SUMMARY OF THE INVENTION 
It has now been found that dehydrogenation of dehydrogenatable hydrocarbons 
is improved by contacting a gas comprising said hydrocarbon at 
dehydrogenation conditions with a solid which comprises: 
(a) at least one reducible oxide of at least one metal which oxides when 
contacted with hydrocarbons at said temperature are reduced and produce 
dehydrogenated hydrocarbon products and water; 
(b) at least one promoter selected from the group consisting of alkali 
metals and compounds thereof; and 
(c) a support comprising at least one member of the group consisting of 
alkaline earth metals and compounds thereof. 
Preferably component (a) comprises at least one reducible oxide of at least 
one reducible oxide of at least one metal selected from the group 
consisting of Mn, Sn, In, Ge, Pb, Sb and Bi. Component (a) is preferably 
present in an amount within the range of about 1 to 40 wt.% based on the 
combined weight of the component (a) metal (e.g., Mn) and the support, 
more preferably within the range of about 5 to 30 wt.%, still more 
preferably within the range of about 10 to 20 wt.%. Alkali metals are 
selected from the group consisting of Li, Na, K, Rb and Cs. Preferred 
promoters are Na, K and Li. Sodium is a particularly preferred promoter. 
Particularly preferred reducible metal oxides are reducible oxides of 
manganese. Alkaline earth metals are selected from the group consisting of 
Mg, Ca, Sr and Ba. Magnesia is a particularly preferred support. 
The stability of the promoted oxidative dehydrogenation agent may be 
enhanced by incorporating a stabilizing amount of phosphorus into the 
composition. However, the agent is effective in the absence of phosphorus.

DETAILED DESCRIPTION OF THE INVENTION 
Oxidative dehydrogenation agents comprise at least one oxide of at least 
one metal, which oxides when contacted with dehydrogenatable hydrocarbons 
at dehydrogenation conditions (e.g., at a temperature selected within the 
range of about 500.degree. to 1000.degree. C.) produce dehydrogenated 
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" is used to identify those oxides of metal 
which are reduced by contacting hydrocarbon at dehydrogenation conditions 
(e.g., at temperatures selected within the range of about 
500.degree.-1000.degree. C.). The term "oxide(s) of metal(s)" includes: 
(1) one or more metal oxides (i.e., compounds described by the general 
formula M.sub.x O.sub.y wherein M is a metal and the subscripts .sub.x and 
.sub.Y designate the relative atomic proportions of metal and oxygen in 
the composition) and/or (2) one or more oxygen-containing metal compounds, 
provided that such oxides and compounds have the capability of performing 
to produce dehydrogenated hydrocarbon products as set forth herein. 
Preferred oxidative dehydrogenation agents comprise reducible oxides of 
metals selected from the group consisting of Mn, Sn, In, Ge, Sb, Pb, and 
Bi and mixtures thereof. Particularly preferred oxidative dehydrogenation 
agents comprise a reducible oxide of manganese and mixtures of a reducible 
oxide of manganese with other oxidative dehydrogenation agents. 
The promoted oxidative dehydrogenation agent of this invention contains, in 
addition to the foregoing elements, at least one alkali metal. The atomic 
ratio in which these materials are combined to form the dehydrogenation 
agent is not narrowly critical. However, the preferred atomic ratio of the 
reducible oxide component (expressed as the metal, e.g., Mn) to the alkali 
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 promoted oxidative dehydrogenation agent may also contain at least one 
phosphorus component. The amount of the phosphorus component contained in 
the dehydrogenation agent 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 oxidative dehydrogenation agent used in the process of this 
invention may be further expressed by the following empirical formula: 
EQU A.sub.a B.sub.b P.sub.c O.sub.d 
wherein A is selected from the group consisting of Mn, Sn, In, Ge, Pb, Sb, 
Bi and mixtures thereof; B is selected from the group consisting of alkali 
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. These 
components may be associated with a support material as described below. 
The promoted oxidative dehydrogenation agent of this invention is 
associated with a support comprising at least one member of the group 
consisting alkaline earth metals and compounds thereof. Preferred support 
materials comprise MgO, CaO, BaO and mixtures thereof. MgO is a 
particularly preferred support. 
The promoted oxidative dehydrogenation agent can be prepared by any 
suitable method. Conventional methods such as precipitation, 
co-precipitation, impregnation, or dry mixing can be used. Supported 
solids may be prepared by methods such as adsorption, impregnation, 
precipitation, co-precipitation, and dry-mixing. Thus, a compound of Mn, 
Sn, In, Ge, Pb, Sb and/or Bi; a compound of an alkali metal; and 
optionally a compound of phosphorus can be combined in any suitable way. 
When phosphorus is incorporated in the agent, it is desirable to provide 
it in the form of a phosphate of an alkali metal. Substantially any 
compound of these elements can be employed in the preparation of the 
promoted dehydrogenation agent. 
A suitable method of preparation is to impregnate a support with solutions 
of compounds of the desired metals. Suitable compounds useful for 
impregnation include the acetates, acetylacetonates, oxides, carbides, 
carbonates, hydroxides, formates, oxalates, nitrates, phosphates, 
sulfates, sulfides, tartrates, fluorides, chlorides, bromides, or iodides. 
After impregnation the preparation is dried in an oven to remove solvent 
and the dried solid is prepared for use by calcining, preferably in air at 
a temperature selected within the range of about 300.degree. to 
1200.degree. C. Particular calcination temperatures will vary depending 
upon the particular metal compound or compounds employed. 
If phosphorus is used, the alkali metal and phosphorus are preferably added 
to the composition as compounds containing both P and alkali metals. 
Examples are the orthophosphates, metaphosphates, and pyrophosphates of 
alkali metals. Pyrophosphates have been found to give desirable results. 
Sodium pyrophosphate is particularly preferred. The alkali metal and the 
phosphorus can be incorporated into the promoted dehydrogenation agent as 
separate compounds. Suitable phosphorus compounds useful for preparing the 
compositions include orthophosphoric acid, ammonium phosphates and 
ammonium hydrogenphosphates. 
Regardless of how the components are combined, the resulting composite 
generally will be dried and calcined at elevated temperatures prior to use 
in the process of this invention. 
One class of preferred compositions is characterized by the substantial 
absence of catalytically effective Ni and the noble metals (e.g., Rh, Pd, 
Ag, Os, Ir, Pt and Au) and compounds thereof, to minimize the deleterious 
catalytic effects of such metals and compounds thereof. For example, at 
the conditions (e.g., temperatures) under which the present compositions 
are used, these metals tend to promote coke formation and oxides of these 
metals tend to promote formation of combustion products (CO.sub.x) rather 
than the desired hydrocarbons. The term "catalytically effective" is used 
to identify that quantity of one or more of nickel and the noble metals 
and compounds thereof which, when present, substantially changes the 
distribution of products obtained when employing the compositions of this 
invention. 
The dehydrogenatable hydrocarbon feedstock employed in the method of this 
invention is intended to include a wide variety of hydrocarbons: e.g., 
C.sub.2 + alkanes, cycloalkanes, olefins, alkylaromatic, etc. The 
dehydrogenated product will of course depend in part on the feed stock 
selected. For example, alkanes may be dehydrogenated to form olefins, 
diolefins, alkynes, etc., and olefins may be dehydrogenated to form 
diolefins, alkynes, etc. Thus, potential uses for the present process 
include the following conversions: 
(1) ethane.fwdarw.ethylene.fwdarw.acetylene; 
(2) propane.fwdarw.propylene; 
(3) butane.fwdarw.butene.fwdarw.butadiene; 
(4) 2-methylbutane.fwdarw.2-methylbutenes.fwdarw.isoprene; and 
(5) toluene.fwdarw.stilbene. 
One preferred class of feedstocks comprises C.sub.2 -C.sub.5 alkanes. 
Operating temperatures for the contacting of hydrocarbon-containing gas and 
the promoted oxidative dehydrogenation agent are selected within the range 
of about 500.degree. to 1000.degree. C., the particular temperature 
selected depending upon the particular reducible metal oxide(s) employed. 
For example, 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) during 
hydrocarbon 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 850.degree. C.). 
Operating pressures for the hydrocarbon contacting step are not critical to 
the presently claimed invention. Contacting dehydrogenatable hydrocarbons 
and a promoted oxidative dehydrogenation agent to form dehydrogenated 
hydrocarbons also produces a reduced metal oxide and co-product water. The 
exact nature of the reduced metals oxides are unknown, and so are referred 
to herein as "reduced metal oxides". Regeneration of a reducible metal 
oxide is readily accomplished by contacting such reduced materials with 
oxygen (e.g., an oxygen-containing gas such as air) at elevated 
temperatures, preferably at a temperature selected within the range of 
about 300.degree. to 1200.degree. C., the particular temperature selected 
depending on the metal(s) included in the promoted oxidative synthesizing 
agent. 
In carrying out the present process, a single reactor apparatus containing 
a fixed bed of solids may be used with intermittent or pulsed flow of a 
first gas comprising hydrocarbon and a second gas comprising oxygen (e.g., 
oxygen, oxygen diluted with an inert gas, or air, preferably air). The 
hydrocarbon contacting step and the oxygen contacting step may also be 
performed in physically separate zones with solids recirculating between 
the two zones. 
Thus, a suitable method for dehydrogenating dehydrogenatable hydrocarbons 
comprises: (a) contacting a gas comprising said hydrocarbon and particles 
comprising a promoted oxidative dehydrogenation agent to form 
dehydrogenated hydrocarbon products, co-product water, and reduced metal 
oxide; (b) removing particles comprising reduced metal oxide from the 
first zone and contacting the reduced particles in a second zone with an 
oxygen-containing gas to form particles comprising a promoted oxidative 
dehydrogenation agent; and (c) returning the particles produced in the 
second zone to the first zone. The steps are preferably repeated at least 
periodically, and more preferably the steps are continuous. In the more 
preferred embodiment solids are continuously circulated between at least 
one hydrocarbon-contact zone and at least one oxygen contact zone. 
Particles comprising a promoted oxidative dehydrogenation agent which are 
contacted with hydrocarbon may be maintained as fluidized, ebullating, or 
entrained beds of solids. Preferably hydrocarbon is contacted with a 
fluidized bed of solids. 
Similarly, particles comprising reduced metal oxide which are contacted 
with oxygen may be maintained as fluidized, ebullating or entrained beds 
of solids. Preferably oxygen is contacted with a fluidized bed of solids. 
In the more preferred embodiment of the present invention, hydrocarbon 
feedstock and particles comprising a promoted oxidative dehydrogenation 
agent are continuously introduced into a hydrocarbon contact zone 
maintained at dehydrogenation conditions. Dehydrogenation conditions 
include the temperatures and pressures described above. Gaseous reaction 
products from the hydrocarbon contact zone (separated from entrained 
solids) are further processed--e.g., they are passed through a 
fractionating system wherein the desired hydrocarbon products are 
separated from unconverted hydrocarbon and combustion products. 
Unconverted hydrocarbon may be recovered and recycled to the hydrocarbon 
contact zone. 
Particles comprising reduced metal oxide are contacted with oxygen in an 
oxygen contact zone for a time sufficient to oxidize at least a portion of 
the reduced oxide to produce a reducible metal oxide and to remove, i.e., 
combust, at least a portion of any carbonaceous deposit which may form on 
the particles in the methane contact zone. The conditions of the oxygen 
contact zone will preferably include a temperature selected within the 
range of about 300.degree. to 1200.degree. C., pressures of up to about 30 
atmospheres, and average particle contact time within the range of about 1 
to 120 minutes. Sufficient oxygen is preferably provided to oxidize all 
reduced metal oxide to produce a reducible oxide and to completely combust 
any carbonaceous deposit material deposited on the particles. At least a 
portion of the particles comprising promoted oxidative synthesizing agent 
which are produced in the oxygen contact zone are returned to the 
hydrocarbon contact zone. 
The rate of solids withdrawal from the hydrocarbon contact zone is 
desirably balanced with the rate of solids passing from the oxygen contact 
zone to the hydrocarbon contact zone so as to maintain a substantially 
constant inventory of particles in the hydrocarbon contact zone, thereby 
enabling steady state operation of dehydrogenation synthesizing system.