Oxygen enrichment process for air based gas phase oxidations which use metal oxide redox catalysts

This invention is directed towards an improved process for the selective gas phase oxidation of a organic reactant using a metal oxide redox catalyst, wherein the organic reactant and air feeds are at a substantially continuous level, the improvement comprising adding a fluctuating flow of oxygen at alternating relatively high and relatively low levels. The invention also teaches means by which a gas may be provided to a reaction process on a fluctuating basis.

FIELD OF THE INVENTION 
This invention is directed towards the use of oxygen in air based gas phase 
oxidation reactions which use metal oxide redox catalysts. More 
particularly, the invention is directed towards providing oxygen to such 
reactions on a fluctuating basis, and means for accomplishing this. 
BACKGROUND 
Air based gas phase reactions which use metal oxide redox catalysts are 
used in chemical synthesis of acrylic acid, acrylonitrile, formaldehyde, 
maleic anhydride, acrolein, isophthalonitrile, nicotinonitrile and 
phthalic anhydride. A typical redox catalyst is vanadium-phosphorus, 
though others are well known in the art. 
In the design of existing reactors both production and yield are taken into 
consideration. In this regard, it is recognized that there is a trade-off 
between production and yield such that parameters which provide a high 
level of production may, in fact, have the effect of decreasing product 
yield. For example, in order to increase production from an existing 
reactor, reactant feed rates must be increased; however, this has negative 
side-effects. Typically this procedure lowers the oxygen-to-feed ratio 
because air compressor and/or pressure drop limitations do not allow for 
an increase in the air flow rate. 
Due to this lower oxygen-to-feed ratio, the partial pressure of oxygen in 
the reactor atmosphere may become insufficient to reoxidize the metal 
oxide catalyst which then becomes over-reduced and, eventually, 
deactivated. The net result is that product yields are depressed. Redox 
catalyst over-reduction also leads to a shortening of catalyst lifetime 
because the reduced form of these catalysts is relatively unstable. 
The basic mechanism behind redox catalyst over-reduction can be understood 
by examining the following reactions which are applicable for any gas 
phase partial oxidations performed with metal oxide redox catalysts. 
1) organic reactant+oxidized catalyst.fwdarw.product +reduced catalyst 
2) reduced catalyst+oxygen.fwdarw.oxidized catalyst 
As can be seen above, as the organic reactant reacts, the catalyst is 
reduced (Reaction 1). In order for the catalyst to be returned to its 
active oxidized state, it must be re-oxidized by gas phase oxygen 
(Reaction 2). If one has too much organic reactant and not enough oxygen, 
as when there is a high reactant feed rate, too much catalyst remains in 
the reduced state, and the catalyst is considered over-reduced. 
As indicated above an over-reduced catalyst will be deactivated relative to 
the oxidized state. This deactivation is due to a combination of the 
following effects: chemical transformation of an active component into a 
less active component; reduction of active catalyst surface area through 
particle sintering, and the volatilization and loss of an active 
component. These effects are generally related to the unstable nature of a 
reduced catalyst and result in depressed reaction yield (e.g. the amount 
of desired product produced) and catalyst lifetime. 
Thus, typically, manufacturers have accepted either the lowering of yield 
and catalyst lifetime associated with operating with a low oxygen-to-feed 
ratio, or the reduction in production associated with operating with a 
high oxygen-to-feed ratio. 
One solution to this problem has been to add a continuous flow of oxygen to 
the air entering a reactor in order to maintain the oxygen-to-feed ratio 
during periods of increased production. This "oxygen enrichment" improves 
the rate of reoxidation of the catalyst, ameliorates over-reduction and 
thus allows one to maintain product yield while increasing the reactant 
feed flow to the reactor. This use of oxygen enrichment is usually only 
applicable to fluid bed reactors because these reactors are typically able 
to handle the increased heat load brought about by the increased amount of 
reaction. In this process, oxygen is typically injected into the air feed 
line of a reactor. 
Using oxygen enrichment in the manner described above is applicable only in 
a retrofit application when market conditions make increased production 
from an existing plant desirable. Typically, such increases in production 
will only be desired for a fraction of the plant's operating life. 
Unfortunately this creates an fluctuating demand for oxygen which is 
difficult and costly to supply. 
For a fixed bed reactor, continuous oxygen enrichment can be employed to 
increase the oxygen-to-feed ratio at a fixed production level or feed flow 
rate. This oxygen enrichment improves the rate of reoxidation of the 
catalyst, ameliorates over-reduction and thus allows one to increase 
product yield while maintaining the reactant feed flow to the reactor. 
Unfortunately, continuous oxygen enrichment is generally not economical as 
the savings associated with the yield increase are not enough to pay for 
the additional oxygen required. 
For fixed bed reactors, the amount of oxygen added is usually between 1 and 
3 vol. % of the total volume of all gases in the reaction atmosphere, as 
above this level there is no longer an improvement in yield. By the term 
"reaction atmosphere" we mean the total amount of all gases entering the 
reactor. If this oxygen were added to the air stream, this addition would 
result in a total oxygen concentration of about 22-24 vol. % in the air 
stream, or 1-3 vol. % enrichment. By the terms "volume % enrichment" or "% 
enrichment" we mean the difference between the oxygen vol. % in air and 
the oxygen vol. % in the mixture that would result if all the oxygen were 
added to the air stream. 
It should noted that the oxygen concentration in the total volume of all 
the gases in the reactor is slightly less when compared to the oxygen 
concentration in the air stream-oxygen mixture, because the amount of 
oxygen is diluted by gaseous organic reactant which is present in an 
amount between 1 vol. % and 2 vol. % in fixed beds. The dilution factor is 
much greater with fluidized bed reactors as the amount of gaseous organic 
reactant is much higher. For example, the entering feed concentration, 
which includes ammonia in ammoxidation reactions, ranges from 4 vol. % for 
maleic anhydride to approximately 17 vol. % for acrylonitrile. 
Several laboratory experiments have been conducted with metal oxide systems 
that vary the oxygen-to-feed ratio by cycling the reactant feed flow 
(Saleh-Ahlamad, 1992; Fiolitakis, 1983; Silveston, 1985). The reactant 
feed flow is varied either by pulsing the reactant feed on and off or at 
relatively high and low levels. Some selectivity improvement (e.g. how 
much of actual reacted starting material produces the desired product) has 
been noted in these experiments. However, in all but one example 
(Saleh-Ahlamad, 1992) the yield is lowered because of the reduction in 
conversion (e.g. the amount of starting material that actually reacts). 
Moreover, reactant feed cycling forces periodic operation of the entire 
plant, which adds to the complexity of the plant, and may actually reduce 
the overall performance of the plant, since most process equipment is 
designed to operate continuously. 
Other laboratory experiments have alternately exposed metal oxide catalysts 
to reactant feed and to oxygen (Lang, 1989; 1991). This, in effect, is 
reactant feed and oxygen cycling. Some of these experiments have also 
included periodic flows of nitrogen to flush the catalyst. As with the 
reactant feed cycling experiments, while some selectivity increase was 
noted, product yield decreased. Further, such cycling increases the 
complexity required for plant operation. 
Contractor, in U.S. Pat. No. 4,668,802, teaches a transport bed process for 
maleic anhydride which circulates the catalyst from a reaction zone where 
it is contacted with butane, to a stripping zone where the maleic 
anhydride is removed from the catalyst, and to a regeneration zone wherein 
the catalyst is contacted with an oxygen containing gas mixture. The 
oxygen and butane are never mixed together, thus effectively creating an 
alternating flow of oxygen and reactant feed with respect to the catalyst. 
This process enables high selectivities to be obtained while keeping 
throughput high. 
However, transport bed technology is complex to design and operate and is 
not retrofitable. It is also difficult to produce the required attrition 
resistant catalyst. Finally, due to backmixing within the bed, the process 
is limited to chemicals capable of being produced in fluid beds. To date, 
the process has been applied only to maleic anhydride production. 
As can be seen from the above discussion, under current processes one must 
accept either lower yields, lower production, or increased capital costs. 
OBJECTS OF THE INVENTION 
It is therefore an object of the invention to provide an improved method 
for gas phase oxidations which use metal oxide redox catalysts. 
It is a further object of the invention to provide a method which allows 
for both increased production and increased yield. 
It is a still further object of the invention to provide a method for gas 
phase oxidations in which oxygen is provided in alternating relatively 
high and relatively low amounts such that the benefits of increased 
production, increased yield and longer catalyst life are realized and the 
cost of the additional oxygen required is offset. 
It is another object of the invention to provide methods by which oxygen 
can be provided to the gas phase oxidation process of the invention. 
SUMMARY OF THE INVENTION 
This invention teaches an improved process for the selective gas phase 
oxidation of an organic reactant using a metal oxide redox catalyst, 
wherein the organic reactant and air feeds are at a substantially 
continuous level, the improvement comprising adding oxygen to the gas 
phase in alternating relatively high and relatively low amounts. 
In a preferred embodiment the oxidation takes place in a fixed-bed reactor 
or a fluidized-bed reactor. 
In other embodiments, the relatively low amount is preferably greater than 
or equal to 0% enrichment, more preferably 0% enrichment, and is less than 
the relatively high amount. 
In still other embodiments, the relatively high amount of oxygen is 
preferably less than or equal to 9%, more preferably 1-3% enrichment, and 
is greater than the relatively low amount. 
The invention also includes processes by which oxygen may be provided in 
relatively high and relatively low amounts to a reaction. 
In preferred embodiments, these processes include the use of a manifold or 
a baffle in a fixed-bed reactor to provide oxygen to the catalyst 
containing tubes therein, on an individual or grouped basis. 
In another preferred embodiment, oxygen is provided to various regions of 
either a fixed-bed or fluid-bed reactor through the use of injector ports 
located in these regions. 
In another preferred embodiment, oxygen is provided through means of a 
single adsorption bed connected directly to the reaction. 
In another preferred embodiment, a flow of oxygen is cycled between 
reactors in a multiple parallel reactor production system. 
In still another preferred embodiment, an accumulator is provided between 
the oxygen source and the reactor such that while a continuous flow is 
provided to the accumulator, an alternating relatively high and relatively 
low flow is withdrawn and provided to the reactor.

DETAILED DESCRIPTION OF THE INVENTION 
Our invention has been derived from observations associated with continuous 
oxygen enrichment processes in redox catalyst driven gas phase oxidations. 
While not wishing to be bound by any theory, the explanation below 
discloses what we believe to be the mechanism behind our invention. 
During reaction, the catalyst continuously undergoes reduction and 
oxidation. The rate of reduction and the rate of oxidation balance to 
produce a catalyst with a certain overall state of oxidation. When 
additional oxygen is added, the relative rates of oxidation and reduction 
change and a new equilibrium is obtained. If the catalyst is normally 
operated in an over-reduced state, this new balance is associated with a 
different overall state of oxidation. Since more oxygen has been added, 
this new state of oxidation will be a higher state than the previous one 
(if such a state is possible). This higher oxidation state roughly 
corresponds to an increase in yield, which like oxidation state, has a 
maximum value which may be achieved. This is graphically represented in 
FIG. 1, which shows oxidation state and yield for a continuous enrichment 
process. 
Similarly, when the additional oxygen is withdrawn, the rates of oxidation 
and reduction will balance once again to produce the original state of 
oxidation. This state of oxidation is lower than that obtained with the 
additional oxygen. In each of the above cases, there is a finite time 
associated with the transition from the lower to higher and higher to 
lower oxidation states, respectively. 
If operating without the addition of oxygen results in an over-reduced 
catalyst and operating with the additional oxygen ameliorates this over 
reduction, the transition from one oxidation state to another will be 
accompanied by variations in yield. If the time it takes to transform from 
the lower oxidation state to the higher oxidation state is smaller than 
the time to transform from the higher state to the lower, then one may use 
a fluctuating supply of oxygen to produce an average yield increase 
greater than that obtained if the same absolute amount of oxygen was added 
continuously. 
In practice, we have observed in benzene-based maleic anhydride production 
that the yield increase associated with using continuous oxygen enrichment 
to increase the oxygen-to-feed ratio lingers for sometime after it was 
withdrawn. Additionally, no delay was noted for the onset of the yield 
increase. Thus, the transition from the over-reduced to the more oxidized 
state was very quick. Together, these observations suggest that for this 
system under these conditions, the transition from the higher to lower 
oxidation state upon removal of the additional oxygen takes longer than 
the transition from the lower oxidation state to the higher oxidation 
state. 
The above observations support our conclusion that a relatively high 
average yield increase need not require that oxygen be provided in a 
continuous flow. Rather, the same advantage could be obtained for metal 
oxide redox systems by providing a fluctuating source of oxygen while 
maintaining a continuous air and reactant feed flow. This inventive 
process offers several advantages over conventional processes. 
As compared to continuous oxygen enrichment, by using an oxygen on a 
fluctuating and/or intermittent basis, oxygen requirements are reduced and 
the economics of oxygen addition are improved. 
In addition, providing oxygen on a fluctuating and/or intermittent basis is 
better than reactant feed cycling, alternating reactant feed and oxygen, 
and transport bed technologies not only because of increased yields, but 
also due to its ease of installation and operation. Finally, unlike 
reactant feed cycling and the alternating of oxygen and reactant feed, 
fluctuating and/or intermittent oxygen enrichment improves yield without 
sacrificing production. 
Two preferred methods of the invention are disclosed below. These are meant 
to be illustrative, and are not intended to limit the scope of the 
invention. 
The first method is shown in FIG. 2a. In this figure the initial yield is 
that which is obtained in an air based reaction. A yield increase is 
obtained by adding oxygen to the reaction. After a maximum yield is 
attained, the oxygen continues to run for a short time, then turned off. 
By continuing to supply oxygen even after a maximum yield is attained, one 
is able to more completely reoxidize the catalyst in the system. As noted 
on the figure, the yield remains at an elevated level for a period after 
the oxygen is shut off. At this point the yield and oxidation states 
slowly return to their original values. Upon reaching this value, oxygen 
is again added and the cycle begins again. As can be seen the average 
yield may be increased due to the inventive process. When compared to FIG. 
1, the disclosed example attains 70% of the yield benefit associated with 
a conventional oxygen enrichment process is obtained using only 50% of the 
oxygen required for that process. 
It should be noted that the amount of time that the oxygen flow is 
maintained after a maximum yield is achieved is subject to optimization 
and design criteria. Clearly, if more or less oxygen use is desired then 
the oxygen may be cycled for longer or shorter periods of time with a 
concomitant effect upon average yield. In any event, the invention is 
based upon a recognition that a constant supply of oxygen is not required 
to maintain an elevated yield or oxidation state for the reasons set forth 
above. 
A second alternative is illustrated in FIG. 2b. In this method, the 
increased yield is kept constant by regulating the oxygen supply such that 
oxygen is provided until a desired elevated yield is obtained, then is 
shut off. At a point immediately before the yield decreases, the oxygen is 
again turned on. In this way, the yield remains constant at 100% of what 
would have been achieved through continuous oxygen enrichment while using 
only 50% of the oxygen required in that process. 
Note that in each of the above examples, air, reactant and catalyst feed 
are kept constant, while only the flow rate of oxygen is adjusted. This 
offers simplified operation over the conventional systems discussed 
previously. 
There are seven variables to consider in the inventive process: location of 
oxygen injector site or sites, high oxygen flow rate, low oxygen flow 
rate, duration of the high oxygen flow rate regime, duration of low oxygen 
flow regime, and the profile of ramp-up from low flow rate to high flow 
rate, and ramp-down from high flow rate to low flow rate. These may be 
optimized depending upon the particular gas phase oxidation process used. 
What follows are some general considerations to take into account. 
FIGS. 3a and 3b illustrate the possible alternatives for where oxygen may 
be injected into the process with respect to a fixed bed reactor 1 or 
fluidized bed reactor 7, respectively. 
As is recognized in the art, and shown in FIG. 3a, a fixed bed reactor 
operates in such a manner that an air feed 2 and a reactant feed 3 are 
combined into a single mixture feed 4 outside the reactor. It is the 
mixture feed which passes into the reactor, the interior of which is shown 
in FIG. 4a. 
Inside the reactor 1, this feed is passed through a plurality of tubes 12, 
each of which contain a redox catalyst, and wherein the reactant is 
oxidized to form product. 
In the fixed bed process, oxygen may be injected into the air line 2 via 
line 5a, the reactant feed line 3 via line 5b, the combined air-feed 
mixture 4 via line 5c, or directly into the reactor 1 via manifold 6. Each 
of these locations are discussed below. 
In fixed bed processes, since the feed and reactant are premixed, there is 
no difference in the effect of the oxygen whether it is injected into the 
air, the reactant or the mixed stream. From a safety and ease of operation 
perspective, injection into the air line 2 is preferred. It may also be 
desirable to inject the oxygen directly into the reactor via manifold 6. A 
more detailed explanation of the latter process may be understood with 
reference to FIGS. 4a-4d which show the interior of a fixed bed reactor. 
As explained above, fixed bed reactors 1 are composed of many separate 
tubes 12 each filled with a redox catalyst. Therefore, an oxygen manifold 
6 could be used to inject oxygen directly into the individual tubes as in 
FIG. 4a or into groups of tubes as in FIG. 4b. This manifold could also be 
used to cycle oxygen from one set of tubes to another through valves 13. 
Since these reactors contain a very large number of tubes (about 10,000), 
such a manifold would be complicated. 
Another alternative is set forth in FIG. 4c, wherein a baffle 14 is used to 
section the reactor into groups of individual tubes 12, and manifold 6 is 
used to provide oxygen to each of these sections. 
A final alternative is shown in FIG. 4d. In this alternative, oxygen flow 
is alternated between different regions of the reactor by injecting oxygen 
at different injector locations 15. 
In any of the above embodiments set forth in FIGS. 4a-4d, the gas flow to 
each tube, groups of tubes or regions of the reactor may be controlled 
separately, as exemplified in FIG. 4a, through the use of flow meters 16, 
pressure gauges 17 and valves 13. The timing may be controlled by a timer 
18 and solenoid valves 19. The timer and solenoid valves are supplied with 
power from a source 20 and are connected to that power source by a switch 
21. One skilled in the art may run this system in a completely automated 
mode. 
FIG. 3b shows the alternatives for injection of oxygen in a fluid bed 
reactor process. A fluid bed process differs from a fixed bed process, as 
shown in FIG. 3b, in that there is a separate air feed 8 and reactant feed 
9 which pass directly into the reactor 7. There is no prior mixing of 
reactant and air. In a fluid bed process, catalyst circulates freely 
within the reactor. 
Injection of oxygen into the air line 8 of a fluid bed via line 10a is 
simple, safe, and the generally preferred embodiment. However, there are 
advantages associated with injection of oxygen into the feed line 9 via 
line 10b or directly into the reactor via line 11 in the fluid bed 
alternative. Note that in this last option, oxygen may be injected into 
the reactor at different injector locations, in a similar fashion as was 
discussed above with respect to fixed-bed reactors. 
Injection into the reactant feed line of a fluidized-bed reactor may 
minimize the oxygen requirement because oxygen is injected directly into a 
localized zone of over-reduced catalyst within the bed. This form of 
direct injection is disclosed in commonly assigned U.S. patent application 
Nos. 08/519,003 and 08/519,011, the contents of which are herein 
incorporated by reference. 
However, injecting oxygen into the reactant feed line may increase the risk 
of feed and oxygen forming a dangerous flammable mixture within the oxygen 
piping. This could be avoided by providing a reduced flow of oxygen rather 
than turning off the oxygen altogether. 
By injecting oxygen directly into the reactor via injector 11, one may be 
able to deliver the oxygen directly to the localized zone of over-reduced 
catalyst without incurring the safety concerns associated with injection 
into the reactant feed line. However, this requires adding an oxygen 
injector directly into the reactor, which is a costly operation. 
As indicated above, oxygen flow rates are another factor which must be 
considered. The amount of oxygen injected into the reaction is determined 
by oxygen flow rates. In accordance with the invention, these rates are 
regulated at relatively high and relatively low levels. The higher the 
flow rate, the more oxygen is injected. 
As indicated above, oxygen may be injected into several alternative 
locations in a reactor system. A similar flow rate results in a similar 
amount of oxygen added to the system, notwithstanding where in the system 
the oxygen is added. 
In a preferred embodiment, oxygen is injected directly into the air feed 
line of a reactor. One may determine the volume percentage of oxygen in 
this combined air-oxygen mixture by adding the oxygen in air (21 vol. %) 
to the oxygen added, and dividing by the total volume of air plus oxygen. 
In a simple case, if 1.28 mole/hr of oxygen is added to a 100 mole/hr air 
stream, then there is (21+1.28)/(100+1.28) or 22 vol. % oxygen in the air 
feed. This amount of oxygen addition is typically referred to as 1% 
enrichment since the oxygen percentage is one percentage point greater 
than the amount of oxygen in the air stream. 
However, this is not the volume % oxygen in the reactor, because in that 
case one must also take into account the amount of gaseous hydrocarbon 
reactant (HC) in the system. For example, in a fixed bed reactor a typical 
hydrocarbon volume % is 1-2% of the reaction atmosphere. Therefore, if the 
hydrocarbon percentage is 1% and the air flow is 100 mole/hr, the 
hydrocarbon flow will be 1.01 mole/hr (1.01/(1.01+100)=1 vol. percent. In 
order to determine the volume of oxygen percentage in the reactor when 1% 
oxygen enrichment is added the air feed, one must divide the volume of 
oxygen in enriched air stream by the volume of the enriched air stream 
plus the volume of the hydrocarbon stream. Therefore, if the standard 
hydrocarbon percentage without the addition of oxygen is one percent, and 
the hydrocarbon and air feeds are unaltered when the oxygen is added to 
the air stream there is (21+1.28)/(100+1.28+1.01) or 21.8 vol. % oxygen in 
the reactor. In this case, the oxygen concentration in the reactor is 
effectively diluted relative to the oxygen concentration in the air stream 
by the HC feed. It should be noted that in a fluidized bed reactor, 
reactant feed concentration, which includes ammonia in the ammoxidation 
reactions, ranges from 4% vol. % of the reaction atmosphere for maleic 
anhydride to 17 vol. % of the reaction atmosphere for acrylonitrile. 
Again, it should be noted that the actual amount of oxygen added would be 
the same, notwithstanding the location, because the oxygen addition flow 
rate would be the same at each location. The oxygen vol. % differs only 
depending upon where in the system it is measured. 
In terms of the amount of oxygen added, a preferred relatively low amount 
of oxygen is 0 vol. % (0% enrichment). However, the relatively low amount 
is limited only in that it must be less than the relatively high amount. 
With respect to the relatively high amount, a preferred amount is 9 vol. % 
(9% enrichment) of the air feed or a resultant total of 29.5-29.7 vol. % 
oxygen in the reaction atmosphere of a fixed bed reactor assuming that 
there is no change in the original air and hydrocarbon flow rates 
(25.4-28.9 vol. % oxygen in a fluidized bed reactor). A more preferred 
amount is 1-3 vol. % (1-3% enrichment) of the air feed or a resultant 
total of 21.6-23.8 vol. % oxygen in the reaction atmosphere of a fixed bed 
reactor (18.3-23.1 vol. % oxygen in a fluidized bed reactor). However, the 
relatively high amount is limited only in that it must be greater than the 
relatively low amount. 
While the above amounts of oxygen are generally applicable to all injection 
locations for fixed and fluid bed processes, certain considerations must 
be taken into account. For example, if injecting oxygen directly into the 
reactor, both high and low oxygen flow would be determined by process and 
safety considerations. If injecting oxygen into the reactant feed, the 
high oxygen flow would be limited by the upper flammability limit of the 
mixture so as to insure that the combined oxygen-feed mixture is not 
flammable. The low oxygen feed flow should be at least great enough so as 
to prevent the backstreaming of reactant feed into the oxygen piping. 
As can be seen from FIGS. 2a and 2b, the cycle time may be in the range of 
seconds to days depending upon the particular oxidation reaction, 
catalyst, reactant and air feed rates. The exact cycle time is a function 
of optimization. 
From an oxygen supply viewpoint, it is desirable to provide a continuous 
flow of oxygen rather than a fluctuating flow. However, if the consumption 
of oxygen is periodic as in the instant invention, significant amounts of 
oxygen will be vented and wasted if the oxygen supply is periodic. There 
are four methods by which a continuous flow of oxygen can be used to 
achieve fluctuating enrichment. These are, in order of preference, 1) 
direct flow from a single adsorption bed, 2) cycling between parallel 
reactor trains, 3) using an accumulator and 4) cycling within a single 
reactor. 
A single adsorption bed arrangement is shown in FIG. 5. A single adsorption 
bed 22 produces oxygen in a periodic way and is typically attached to an 
accumulator in order to produce a continuous flow. If the cycle time of 
the adsorption bed is the same as the cycle time required by the process, 
then the single adsorption bed could be coupled directly to the reactor 1 
or 7 without using an accumulator. 
Chemical plants often employ multiple parallel reactor trains, as shown in 
FIG. 6. For the purposes of the instant invention, oxygen can be 
alternated between two or more reactors 1a or 7a, 1b or 7b and/or 1c or 7c 
in such a manner that while one or more, but not all of the reactors 
receive a flow of oxygen in a relatively high amount, the remaining 
reactor or reactors receive a flow of oxygen in a relatively low amount. 
Note that this embodiment is not available if the plant only employs a 
single reactor. 
If the cycle time is on the order of one hour or less, an accumulator could 
be placed in the oxygen supply line as illustrated in FIG. 7. The oxygen 
supply source would continuously feed the accumulator 23, while the oxygen 
is periodically withdrawn to the reactor 1 or 7. This is similar to how a 
continuous flow is provided in a conventional adsorption bed set up. As 
implied above, this option is unavailable for cycle periods which are 
greater than on the order of one hour. This is because the required 
accumulator and compression equipment would simply be too expensive. 
As discussed above, and shown in FIGS. 4a-4d fixed bed reactors are 
composed of many separate tubes 12 each filled with redox catalyst. An 
oxygen manifold could be used to inject oxygen directly into these tubes. 
The manifold could either inject oxygen individually into each tube or 
into a series of tubes via valves 13. The manifold would be used to cycle 
oxygen from one set of tubes to another within the reactor. Specifically, 
the fixed bed reactors would comprise at least two sets of tubes having 
catalyst therein, each set comprising one or more, but not all of said 
tubes, and wherein the oxygen flow to each set of tubes is regulated via a 
manifold such that a flow of oxygen is alternated between each set, and 
when oxygen is injected into a first set or sets in said relatively high 
amount, oxygen is injected into a second set or sets in said relatively 
low amount. 
As suggested above, a baffle 14 could also be used in this capacity. Note 
that the manifold and baffle options are unavailable for fluid bed 
reactors, as they are not divided into individual sections. Further, the 
reactor head must be able to accommodate the manifold or baffle. 
Also as suggested above, different injectors 15 could be used to inject 
oxygen into different regions of the reactor. 
It should be noted that any of the above methods could be used to supply a 
gas to any manufacturing process where a fluctuating supply of that gas is 
desired. 
Specific features of the invention are shown in one or more of the drawings 
for convenience only, as each feature may be combined with other features 
in accordance with the invention. Alternative embodiments will be 
recognized by those skilled in the art and are intended to be included 
within the scope of the claims.