Cyclic catalytic hydrocarbon conversion process with reduced chloride emissions

A method is disclosed for recovering chlorine-containing species from the outlet gas of a hydrocarbon conversion process with a cyclic regeneration operation. The outlet gas from an off-stream catalyst bed in which regeneration is occurring is passed to another off-stream catalyst bed which contains spent catalyst and which is maintained at sorption conditions. The spent catalyst particles sorb the chlorine-containing species from the outlet gas. This method captures and retains within the hydrocarbon conversion process chlorine-containing species that would otherwise be scrubbed and lost from the process and that would need to be replaced by the injection of make-up chlorine-containing species. This method results in significant savings in operating costs of a cyclic regeneration process. This method is adaptable to many processes for the catalytic conversion of hydrocarbons in which deactivated catalyst are regenerated by a cyclic regeneration operation.

FIELD OF THE INVENTION 
This invention relates generally to the regeneration of hydrocarbon 
conversion catalysts in the presence of a chlorine-containing species. 
BACKGROUND OF THE INVENTION 
Although catalysts for the conversion of hydrocarbons have a tendency to 
deactivate, a catalyst's activity can usually be restored by one of a 
number of processes that are known generally as regeneration processes. 
Regeneration processes are extensively used. What specific steps comprise 
a regeneration process depends in part on the reason for the deactivation. 
For example, if the catalyst deactivated because coke deposits accumulated 
on the catalyst, regeneration usually includes removing the coke by 
burning. If the catalyst deactivated because a catalytic metal such as 
platinum became agglomerated, regeneration usually includes redispersing 
the metal by contacting the catalyst with oxygen and chlorine. If the 
catalyst deactivated because a catalytic promoter such as chloride became 
depleted, regeneration usually includes replenishing the promoter by 
contacting the catalyst with one of a number of chlorine-containing 
species, which are referred to herein as chloro-species. Operating 
conditions and methods for these regeneration processes are well known. 
Although some regeneration processes require that the catalyst be withdrawn 
from the vessel in which the hydrocarbon conversion takes place and be 
transported to a separate regeneration zone for reactivation, many 
regeneration processes can be carried out in situ. In situ regeneration is 
preferred especially for soft or brittle catalysts that attrit too readily 
when transported mechanically or pneumatically. In situ regeneration 
processes generally comprise two types of operations, a semiregenerative 
operation and a cyclic operation. In practicing the semiregenerative 
operation, the catalyst is maintained in continuous use over an extended 
period of time, say from five months to a year or more, depending on 
factors such as the quality of the catalyst and the nature of the 
feedstock. Following this extended period of operation, the reforming 
catalyst bed is taken off-stream while the catalyst is regenerated. In 
practicing the cyclic operation, the catalyst is generally regenerated 
with a greater frequency than in the semiregenerative operation. The 
cyclic operation uses multiple fixed catalyst beds arranged for serial 
flow of the feedstock in such a manner that at least one catalyst bed can 
be taken off-stream while the catalyst is regenerated. One or more 
companion catalyst beds remain on-stream, or go on-stream, to replace the 
catalyst bed that is off-stream. Subsequently, after the off-stream 
catalyst bed has had its catalyst regenerated and has again been placed 
on-stream, another catalyst bed can be taken off-stream and its catalyst 
is regenerated in like manner. A cyclic operation has the advantage over a 
semiregenerative operation of maintaining production of converted 
hydrocarbons while the catalyst is being regenerated. 
Many cyclic regeneration operations share the common feature of contacting 
the catalyst with one or more chloro-species that can restore the activity 
of the catalyst. Usually this contacting is performed by dispersing the 
chloro-species in a recycle gas stream and passing the recycle gas stream 
through a bed of catalyst. A flue gas stream containing chloro-species and 
water is withdrawn from the catalyst bed and cooled, and then a portion of 
the flue gas stream is usually rejected from the cyclic regeneration 
operation. To compensate for the rejected portion of the flue gas steam, a 
make-up stream is usually combined with the remaining portion of the flue 
gas stream, thereby forming the recycle gas stream. The recycle gas stream 
is recycled to the catalyst bed by a recycle gas compressor. Thus, the 
recycle gas stream usually contains chloro-species and water. In addition, 
the recycle gas stream comes into contact with internal parts of the 
recycle gas compressor that usually operate at a temperature below the dew 
point temperature of the recycle gas stream. Consequently, a common risk 
associated with cyclic regeneration operations is the condensation of 
corrosive hydrochloric acid within the recycle gas compressor, which can 
cause serious damage and require costly repairs or even replacement of the 
recycle gas compressor. This risk of corrosion can be decreased by two 
methods. One method is scrubbing the flue gas stream with an aqueous, 
basic solution that neutralizes the chloro-species, and the other method 
is adsorbing the chloro-species from the flue gas on an adsorbent. 
Scrubbing is the more common of the two methods, particularly in cyclic 
regeneration of reforming catalysts and of catalysts for other hydrocarbon 
conversion processes, such as dehydrogenation, isomerization, alkylation, 
and transalkylation. 
Although these two methods--scrubbing and adsorption--for decreasing the 
risk of corrosion within the recycle gas compressor of a cyclic 
regeneration operation are useful, they are also expensive and troublesome 
to operate. On the one hand, by introducing an aqueous solution into the 
flue gas, scrubbing can actually increase the risk of corrosion within the 
recycle gas compressor unless the alkalinity of the aqueous solution is 
carefully controlled. Moreover, because the aqueous solution must be 
replaced periodically, scrubbing gives rise to significant costs for 
supplying fresh solution and for disposing of the spent solution. On the 
other hand, although adsorption does not involve the introduction of an 
aqueous stream, the adsorbent also must be replaced periodically, and the 
cost of replacement of the adsorbent, including the cost of disposing of 
spent adsorbent, can far exceed the cost of replacement of the aqueous 
solution in scrubbing. 
The problem of adsorbent replacement is compounded by water in the flue gas 
stream and, as a result, traditional adsorbents are not economically 
viable for adsorbing chloro-species from flue gas streams in cyclic 
regeneration operations. In order to be economically viable, an adsorbent, 
while removing a high proportion of the chloro-species from the flue gas 
stream, must adsorb typically from 7 to 8 percent of its weight in 
chloride. In order to adsorb that much chloride, the flue gas must have a 
low water content, typically less than 0.01 mol-% water. Water competes 
with chloro-species for adsorption sites on the adsorbent, and by 
occupying sites that would otherwise be occupied by chloro-species, water 
hinders the adsorption of chloride and hastens replacement of the 
adsorbent. Thus, if the flue gas has a high water content, the adsorbent 
adsorbs too much water and is incapable of adsorbing a viable amount of 
chloride. Because water is a common by-product of coke combustion as a 
result of the hydrogen-containing compounds typically found in coke, and 
because coke combustion is one of the common cyclic regeneration steps, 
flue gas streams often do have a high water content, typically from 1 to 
10 mol-%. As a consequence, unless the flue gas is dried, an adsorbent 
will adsorb only one-third to one-half of the weight of chloride required 
for economic viability. This, in turn, doubles or triples the frequency of 
adsorbent replacement, thereby making traditional adsorbents uneconomical. 
Although in theory the adsorption of water can be mitigated by drying the 
flue gas stream prior to adsorbing the chloro-species, in fact a drier is 
costly, as well as impractical, because chloro-species such as hydrogen 
chloride tend to degrade most desiccants. 
Thus, a process is sought for removing hydrogen chloride and other 
chloro-species from the flue gas streams of cyclic catalyst regeneration 
operations without the need for aqueous solutions, adsorbents, and 
desiccants. 
SUMMARY OF THE INVENTION 
It has been discovered that a catalyst that has an alumina support and that 
is about to be, but has not yet been, regenerated can sorb 
chlorine-containing species, which are referred to herein as 
chloro-species, from an offgas stream that is emitted during a cyclic 
regeneration operation. This discovery makes possible dramatic decreases 
in both the risk of corrosion within the recycle gas compressor; as well 
as the make-up addition of chloro-species during the cyclic regeneration 
operation. The observations that led to this discovery were made while 
contacting chloro-species-containing gas streams comprising nitrogen and 
oxygen with a fresh catalyst and with a spent catalyst having coke 
deposits. Thus, this sorption phenomenon is applicable to regeneration 
processes in which the catalyst is contacted with a gas stream comprising 
chloro-species and an oxidizing agent that oxidizes either the coke 
deposits or the catalytic metal, if present, of chloride-containing 
alumina particles. In addition, it is believed that the same sorption 
phenomenon would be observed if a gas stream comprising chloro-species and 
a reducing agent such as hydrogen was contacted with a spent catalyst. 
This realization is significant because it means that this sorption 
phenomenon is applicable to regeneration processes that reduce the 
catalytic metal of metal-containing and chloride-containing alumina 
particles. In other words, this sorption phenomenon allows chloro-species 
to be sorbed not only from a combustion flue gas stream but also from a 
reduction offgas stream. 
In order to take advantage of this property of these spent catalysts to 
sorb chloride from a regeneration offgas stream, a chloride sorption step 
that can be readily integrated into existing cyclic regeneration 
operations without large capital expenditures or greatly increased 
complexity is provided. This invention is particularly applicable to 
cyclic regeneration operations that combust coke from coked, 
chloride-containing alumina particles, especially spent naphtha reforming 
catalysts and spent paraffin dehydrogenation catalysts. 
In this invention, a sorption step in combination with a cyclic 
regeneration operation retains within a hydrocarbon conversion process 
most of the chloro-species that prior art cyclic regeneration operations 
remove or otherwise reject from the process. This invention uses sorption 
to capture the chloro-species escaping from a catalyst bed that is being 
regenerated, to reuse the chloro-species in the cyclic regeneration 
operation, and to minimize the risk of condensation of hydrochloric acid 
and hence corrosion in the recycle gas compressor, if present. Unlike 
conventional caustic scrubbing methods, this invention uses sorption to 
capture chloro-species released from catalyst that is being regenerated. 
Unlike conventional adsorption methods that use a separate adsorbent which 
becomes loaded with chloro-species and then is discarded, this invention 
uses spent catalyst in a catalyst bed that is about to be regenerated to 
capture most of the chloro-species that are in the flue gas stream and to 
return the chloro-species to the cyclic regeneration operation as chloride 
on the spent catalyst. In other words, this invention uses the catalyst 
that is about to be, but has not yet been, regenerated to keep 
chloro-species within the cyclic regeneration operation and to sustain the 
chloride level on the catalyst. 
It has been discovered that, even though the spent catalyst that has not 
yet been regenerated is like traditional sorbents in that it is capable of 
sorbing up to, say, only about from 2 to 3 percent of its weight in 
chloride from a water-containing regeneration offgas stream of a cyclic 
regeneration operation, a process that uses the catalyst that is about to 
be regenerated to sorb chloro-species from the cyclic regeneration offgas 
stream is useful because of the large quantity of catalyst available for 
sorption. Accordingly, in one of its embodiments, this invention is a 
process in which spent catalyst that is about to be regenerated is 
contacted with the offgas stream in a catalyst bed that is not at either 
reaction or regeneration conditions but rather at sorption conditions. At 
sorption conditions, the spent catalyst sorbs chloro-species from the 
cyclic regeneration offgas. Because the cyclic regeneration offgas has a 
relatively high water content, the spent catalyst sorbs up to, say, only 
about from 2 to 3 percent of its weight in chloride. The spent catalyst, 
having sorbed what chloride it can, is then regenerated by contacting the 
spent catalyst with a regenerant gas at regeneration conditions. Thus, 
whatever additional chloride the spent catalyst sorbed while the catalyst 
bed was at sorption conditions is present on the catalyst at the start of 
regeneration, thereby decreasing the need to add make-up chloride to 
catalyst during regeneration. Meanwhile, as the catalyst in that catalyst 
bed is being regenerated, another catalyst bed that had been catalyzing 
hydrocarbon conversion reactions is at sorption conditions and its spent 
catalyst is being contacted with offgas from the catalyst bed that is 
undergoing regeneration. Thus, the other catalyst bed takes over the 
sorption function of the catalyst bed that is undergoing regeneration. 
Accordingly, every time a catalyst bed is switched from sorbing 
chloro-species to being regenerated, that catalyst bed is replaced by 
another catalyst bed that is switched from converting hydrocarbons to 
sorbing chloro-species. Thus, there is a continual progression of catalyst 
beds containing spent catalyst that is capable of being made available for 
sorption purposes and that is more than sufficient to compensate for the 
fact that the spent catalyst sorbs only up to about 2 to 3 percent of its 
weight in chloride. In short, in this invention an abundant quantity of 
catalyst that is available for sorption more than compensates for what 
persons skilled in the art would consider a small and uneconomical amount 
of chloride sorbed by the catalyst. The benefits of this invention for the 
cyclic regeneration operation include a decrease in the concentration of 
chloro-species in the offgas, a decrease in the rate of addition, if any, 
of make-up chloro-species to the recycle gas, and a decrease in the rate 
of usage and subsequent disposal of aqueous solution, if any, that is used 
for scrubbing. 
In cyclic regeneration operations as currently commercially practiced, the 
flue gas from a zone in which coke is combusted from chlorided platinum 
alumina catalysts typically contains from 10 to 500 mol-ppm chlorine and 
from 500 to 10000 mol-ppm hydrogen chloride. By practicing this invention 
in which a high proportion of the chlorine and hydrogen chloride in the 
flue gas is sorbed on the coked catalyst prior to the combustion of the 
coke, the chlorine concentration in the flue gas may be reduced to the 
range of from 1 to 10 mol-ppm and the hydrogen chloride concentration may 
be reduced to the range of from 10 to 1000 mol-ppm. The method of this 
invention can be used to supplement or replace conventional means for 
removing chlorine and hydrogen chloride from flue gas streams, such as 
scrubbing or adsorption. In either case, this invention significantly 
lowers the substantial costs of building and operating the conventional 
means of chloro-species removal. In addition, this invention reduces 
significantly the requirements for adding make-up chloride to the cyclic 
regeneration operation, because this invention returns to the cyclic 
regeneration operation a large portion of the chlorine or hydrogen 
chloride that would otherwise be removed from the process by conventional 
means of chloro-species removal, such as flue gas scrubbing. Thus, the 
method of this invention can eliminate or drastically reduce the problems 
and costs associated with cyclic regeneration operations in which catalyst 
that is being regenerated emits a flue gas stream containing hydrogen 
chloride or chlorine. 
This invention is applicable to numerous hydrocarbon conversion processes 
and to their associated cyclic catalyst regeneration operations. A basic 
requirement for using this invention is a catalyst bed that contains 
catalyst that is regenerated in the presence of chloride which is carried 
out of the zone in the form of a chloro-species by an outlet stream. 
Examples of chloro-species that are released from the zone and are 
susceptible to recovery by the method of this invention include Cl.sub.2 
and HCl. Another basic requirement for using this invention is a catalyst 
that has sorption capacity for the chloro-species. This invention is not 
limited to any particular type of catalyst; any catalysts with the 
necessary capacity may be used. Preferably, the catalyst will recover 50 
wt-% and, more preferably, more than 90 wt-%, of the chloro-species in the 
outlet stream. The typical catalysts suitable for use in this invention 
comprise alumina, including alumina, activated aluminas, silica alumina, 
molecular sieves, and alumino-silicate clays such as kaolin, attapulgite, 
sepiolite, polygarskite, bentonite, and montmorillonite, particularly when 
the clays have not been washed by acid to remove substantial quantities of 
alumina. Reference is made to Zeolitic Molecular Sieves, by Donald W. 
Breck (John Wiley & Sons, 1974), which describes the use and selection of 
zeolite adsorbents and which is incorporated herein by reference. 
The sorption and removal capacity of the catalyst for the chloro-species 
must exist under a reasonable range of conditions. With respect to the 
removal capacity, the capability for chloride to be removed from the 
catalyst during regeneration is a necessary feature of the cyclic catalyst 
regeneration operation to which the invention is applied. In other words, 
the conditions at which the cyclic regeneration occurs are conditions that 
are sufficient to remove chloride from the catalyst. As a practical 
matter, however, this requirement does not limit the scope of this 
invention in any significant way. With respect to the capacity of the 
catalyst to sorb chloro-species, preferably the process conditions of the 
offgas will complement the sorption requirements of the catalyst. In a 
surprising aspect of this invention, the sorption of chloro-species is 
favored by a decrease rather than an increase in the pressure of sorption. 
Although persons of ordinary skill in the art of sorption processes would 
have expected that a decrease in pressure would not have been beneficial 
for the sorption of gaseous chloro-species onto the catalyst, it has been 
discovered that the opposite is true in the presence of water and at the 
temperatures of the sorption. It has been discovered that although a 
decrease in pressure causes the sorption of water from the offgas onto the 
catalyst to decrease, the sorption of chloro-species does not decrease, 
even at the temperatures of the sorption. Therefore, a decrease in 
pressure selectively favors the sorption of chloro-species relative to 
that of water. Consequently, a preferred embodiment of this invention 
includes operating the catalyst bed in which sorption is occurring at a 
pressure that is less than the pressure of the catalyst bed in which 
regeneration is occurring. This embodiment may be well suited for those 
prior art cyclic regeneration operations that employ a recycle gas 
compressor to circulate a recycle gas stream through catalyst beds and 
where the suction pressure of the recycle gas compressor is less than the 
discharge pressure. In such prior art processes, it is somewhat beneficial 
to perform the sorption of the chloro-species on the catalyst at or near 
the relatively low pressure of the recycle gas compressor suction and the 
regeneration at or near the relatively high pressure of the recycle gas 
compressor discharge. All other factors being the same, however, the 
favorable increase in sorption that occurs as a result of a decrease in 
pressure diminishes as the total pressure of the catalyst beds increases. 
Thus, because cyclic regeneration operations generally operate at an 
elevated pressure and because the difference between the suction and 
discharge pressures of the recycle gas compressor is generally relatively 
small, the benefit of a lower pressure for the sorption zone, although 
present, may not be substantial. 
This invention is not limited to the recovery and reuse of a single 
chloro-species in a cyclic regeneration process, but may include 
arrangements for the recovery of two or more chloro-species. Preferably, 
the catalyst in a single catalyst bed will sorb all of the various 
chloro-species that are present in the offgas stream. Where necessary, 
multiple catalyst beds operating at different sorption conditions may be 
used to recover the various chloro-species from the offgas stream. 
Thus, this invention uses a sorption step in combination with a 
regeneration step in a cyclic catalyst regeneration operation of a 
hydrocarbon conversion process that results in the recovery and return of 
chloro-species to the process. This invention is compatible with a wide 
variety of existing cyclic catalyst regeneration operations and typical 
cyclic regeneration conditions. 
It is an object of this invention to improve processes for cyclic 
regeneration of hydrocarbon conversion catalysts that use chloro-species. 
It is another object of this invention to recover chloro-species that are 
present during cyclic catalyst regeneration. 
A further object of this invention is to decrease the costs that are 
incurred in removing chloro-species from cyclic catalyst regeneration 
processes. 
Accordingly, this invention is in one embodiment a sorptive method for 
recovering chloro-species from an outlet stream of a cyclic regeneration 
operation of a hydrocarbon conversion process. The hydrocarbon conversion 
process has at least three catalyst beds. In a first catalyst bed, 
hydrocarbons are contacted with a catalyst in order to convert 
hydrocarbons. At least a portion of an outlet stream comprising a 
chloro-species is passed to a second catalyst bed containing the catalyst. 
At least a portion of the chloro-species is sorbed on the catalyst in the 
second catalyst bed at sorption conditions. An effluent stream having a 
decreased concentration of the chloro-species relative to the portion of 
the outlet stream is withdrawn from the second catalyst bed. In a third 
catalyst bed, the catalyst containing chloride is at least partially 
regenerated and at least a portion of the chloride is removed from the 
catalyst at regeneration conditions. The outlet stream is withdrawn from 
the third catalyst bed. Periodically, the functions of the first, second 
and third catalyst beds are shifted. The first catalyst bed is operated to 
function as the second catalyst bed, the second catalyst bed is operated 
to function as the third catalyst bed, and the third catalyst bed is 
operated to function as the first catalyst bed. 
In a more limited embodiment, this invention is a sorptive method for 
recovering chlorine or hydrogen chloride from the flue gas of a cyclic 
regeneration operation of a hydrocarbon reforming process. The hydrocarbon 
reforming process has at least three reforming catalyst beds. A feed 
stream comprising hydrocarbons having a boiling range of from 180 to 
400.degree. F. is passed to a first reforming catalyst bed containing 
reforming catalyst. The reforming catalyst comprises alumina, platinum 
metal, and chloride. In the first reforming catalyst bed, the hydrocarbons 
are reformed at reforming conditions sufficient to deposit coke on the 
reforming catalyst. An exit stream is withdrawn from the first reforming 
catalyst bed and passed to a first separation zone. A product stream 
comprising reformed hydrocarbons is recovered from the first separation 
zone. A regenerant stream comprising nitrogen, oxygen, and at least one of 
hydrogen chloride and chlorine is passed to a second reforming catalyst 
bed. The second reforming catalyst bed contains the reforming catalyst 
comprising chloride and having coke deposited thereon. At regeneration 
conditions, at least a portion of the coke and the chloride is removed 
from the reforming catalyst in the second reforming catalyst bed. A flue 
gas stream comprising nitrogen and at least one of chlorine and hydrogen 
chloride is withdrawn from the second reforming catalyst bed. The flue gas 
stream is cooled to produce a cooled flue gas stream that is passed to a 
third reforming catalyst bed. The third reforming catalyst bed contains 
the reforming catalyst having coke deposited thereon. A portion of at 
least one of chlorine and hydrogen chloride is removed from the cooled 
flue gas stream by sorption on the reforming catalyst in the third 
reforming catalyst bed. An effluent stream comprising nitrogen and having 
a decreased concentration of chlorine or hydrogen chloride relative to the 
cooled flue gas stream is withdrawn from the third reforming catalyst bed. 
Periodically, the functions of the first, second and third reforming 
catalyst beds are shifted. The first reforming catalyst bed is operated to 
function as the second reforming catalyst bed, the second reforming 
catalyst bed is operated to function as the third reforming catalyst bed, 
and the third reforming catalyst bed is operated to function as the first 
reforming catalyst bed. 
Other objects, embodiments and details of this invention are presented in 
the following detailed description of the invention. 
INFORMATION DISCLOSURE 
U.S. Pat. No. 2,773,014 (Snuggs et al.) discloses a reforming process with 
cyclic catalyst regeneration in which an alternate off-stream catalyst bed 
can take the place of any one of three on-stream catalyst beds by an 
arrangement of valves and connections. 
U.S. Pat. No. 5,336,834 (Zarchy et al.) discloses an adsorption zone in 
combination with a catalytic hydrocarbon conversion process that keeps 
chlorine-containing compounds in the catalyst bed and prevents 
contamination of product streams with chlorine-containing compounds.

DETAILED DESCRIPTION OF THE INVENTION 
This invention can be used to recover halogen-containing species in an 
outlet stream of a cyclic regeneration operation of a catalytic 
hydrocarbon conversion process that uses a catalyst that can sorb 
halogen-containing species and from which halogens can be removed. 
Although halogens may include fluorine, bromine, and iodine, the preferred 
halogen is chlorine. Accordingly, this invention is particularly 
applicable to decreasing the concentration of chloro-species in the outlet 
stream of a cyclic regeneration operation. The term "chloro-species" 
herein refers to any molecule that contains chlorine, other than the 
chloride component or chloride entities that exist on the catalyst. For 
example, chloro-species include chlorine, hydrogen chloride, chlorinated 
hydrocarbons with or without oxygen, and compounds containing chlorine and 
a metal. The term "chlorine" herein refers to elemental chlorine, which 
exists as a diatomic molecule at standard conditions. The term "chloride" 
when used alone herein refers to the chloride component or chloride 
entities that exist on the catalyst. Chloride on the catalyst is believed 
to exist as various compounds depending on the composition and conditions 
of the catalyst. For example, if the catalyst contains alumina then the 
chloride may exist on the catalyst as an entity consisting of chlorine, 
oxygen, hydrogen, and aluminum atoms. 
Other specific terminology is used herein to refer to the catalyst as it 
progresses through the various stages of the method of this invention. The 
term "spent catalyst" refers to catalyst that has become deactivated or 
otherwise manifests a decline in hydrocarbon conversion performance 
usually as a result of reactions that take place in the hydrocarbon 
conversion catalyst bed. Spent catalyst is catalyst that has not been used 
to sorb chloro-species from the outlet stream and has not been 
regenerated. The term "chlorided catalyst" refers to spent catalyst that 
has sorbed chloro-species from the outlet stream. Like spent catalyst, 
chlorided catalyst has not been regenerated. The term "regenerated 
catalyst" refers to catalyst that has undergone one or more steps of 
cyclic regeneration and has been at least partially regenerated. The term 
"combusted catalyst" refers to spent catalyst or chlorided catalyst that 
has had at least a portion of its coke removed by combustion, one of the 
cyclic regeneration steps. The coke content of combusted catalyst may be 
0.01% by weight of the catalyst weight or less, but generally it is 
0.2-0.5% by weight. 
Terms used herein that refer to the streams that pass through the various 
zones of this invention are as follows. The terms "regenerant stream" and 
"regenerant gas stream" refer to a stream comprising a regeneration agent 
such as oxygen or chlorine that is passed to a catalyst bed in which 
regeneration is occurring. The term "outlet stream" refers to a stream 
comprising chloro-species that is withdrawn from a catalyst bed in which 
regeneration is occurring. The terms "offgas stream," "flue stream" and 
"flue gas stream" refer to particular kinds of outlet streams. The terms 
"effluent stream" and "effluent gas stream" refer to a stream having a 
reduced concentration of chloro-species relative to either the flue stream 
or the flue gas stream and which is withdrawn from a catalyst bed in which 
sorption is occurring. The terms "recycle stream" or "recycle gas stream" 
refer to a particular kind of regenerant stream or regenerant gas stream 
in which at least a portion of either the effluent stream or effluent gas 
stream forms or provides a portion of the regenerant stream or regenerant 
gas stream. 
Generally, the catalysts that can sorb and desorb chloro-species comprise 
inorganic oxides, preferably alumina. The alumina may be present alone or 
it may be combined with a porous inorganic oxide diluent as a binder 
material. Alumina that has a high surface area is preferred. The alumina 
may be present in any of its solid phases, but gamma-alumina is preferred. 
The alumina may also be present as a chemical combination with other 
elements, such as in silica-aluminas or alumino-silicate clays. The 
catalyst may also be comprised of one or more metals in addition to the 
metal, if any, that comprises the inorganic oxide. Depending on the 
catalyst, this additional metal can comprise a transition metal such as a 
Group VIII noble metal (e.g., platinum). Because many hydrocarbon 
conversion catalysts comprise alumina, the hydrocarbon conversion 
catalysts that may be used with this invention are numerous. They include 
catalysts for reforming, dehydrogenation, isomerization, alkylation, 
transalkylation, and other catalytic conversion processes. These catalysts 
are well known. See, for example, U.S. Pat. Nos. 2,479,110 and 5,128,300 
(reforming); U.S. Pat. Nos. 4,430,517 and 4,886,928 (dehydrogenation); 
U.S. Pat. Nos. 2,999,074 and 5,017,541 (isomerization); U.S. Pat. Nos. 
5,310,713 and 5,391,527 (alkylation); and U.S. Pat. No. 3,410,921 
(transalkylation). The teachings of these patents are incorporated herein 
by reference. 
It is believed that the most widely-practiced processes with cyclic 
catalyst regeneration operations that produce offgas streams containing 
chloro-species and that also employ alumina-containing catalyst are cyclic 
catalytic hydrocarbon conversion processes. The most widely practiced 
cyclic hydrocarbon conversion process to which the present invention is 
applicable is cyclic catalytic reforming. Therefore the discussion of the 
invention herein will refer to its application to a cyclic catalytic 
reforming reaction system. It is not intended that this limit the scope of 
the invention as set forth in the claims. 
Catalytic reforming is a well-established hydrocarbon conversion process 
employed in the petroleum refining industry for improving the octane 
quality of hydrocarbon feedstocks, the primary product of reforming being 
motor gasoline. The art of catalytic reforming is well known and does not 
require detailed description herein. 
Briefly, in catalytic reforming, a feedstock is admixed with a recycle 
stream comprising hydrogen and contacted with catalyst in a catalyst bed. 
The usual feedstock for catalytic reforming is a petroleum fraction known 
as naphtha and having an initial boiling point of about 180.degree. F. 
(80.degree. C.) and an end boiling point of about 400.degree. F. 
(205.degree. C.). The catalytic reforming process is particularly 
applicable to the treatment of straight run gasolines comprised of 
relatively large concentrations of naphthenic and substantially straight 
chain paraffinic hydrocarbons, which are subject to aromatization through 
dehydrogenation and/or cyclization reactions. 
Reforming may be defined as the total effect produced by dehydrogenation of 
cyclohexanes and dehydroisomerization of alkylcyclopentanes to yield 
aromatics, dehydrogenation of paraffins to yield olefins, 
dehydrocyclization of paraffins and olefins to yield aromatics, 
isomerization of n-paraffins, isomerization of alkylcycloparaffins to 
yield cyclohexanes, isomerization of substituted aromatics, and 
hydrocracking of paraffins. Further information on reforming processes may 
be found in, for example, U.S. Pat. No. 4,119,526 (Peters et al.); U.S. 
Pat. No. 4,409,095 (Peters); and U.S. Pat. No. 4,440,626 (Winter et al.). 
A catalytic reforming reaction is normally effected in the presence of 
catalyst particles comprised of one or more Group VIII noble metals (e.g., 
platinum, iridium, rhodium, palladium) and a halogen combined with a 
porous carrier, such as a refractory inorganic oxide. The halogen is 
normally chloride. Alumina is a commonly used carrier. The preferred 
alumina materials are known as the gamma, eta and theta alumina with gamma 
and eta alumina giving the best results. An important property related to 
the performance of the catalyst is the surface area of the carrier. 
Preferably, the carrier will have a surface area of from 100 to about 500 
m.sup.2 /g. It has been discovered that the greater the surface area of 
the carrier, the greater is the capacity of the catalyst to sorb chloride 
according to the method of this invention. Catalyst particles are usually 
cylindrical or spheroidal, having a diameter of from about 1/16th to about 
1/8th inch (1.5-3.1 mm), though they may be as large as 1/4th inch (6.35 
mm). When cylindrical, the catalyst particles have a length of from about 
1/8th to about 1/4th inch (3.1-6.35 mm). In a particular catalyst bed, 
however, it is desirable to use catalyst particles which fall in a 
relatively narrow size range. A preferred catalyst particle diameter is 
1/16th inch (3.1 mm). During the course of a reforming reaction, catalyst 
particles become deactivated as a result of mechanisms such as the 
deposition of coke on the particles; that is, after a period of time in 
use, the ability of catalyst particles to promote reforming reactions 
decreases to the point that the catalyst is no longer useful. The catalyst 
must be regenerated before it can be reused in a reforming process. 
In a common form, a catalytic reforming process with cyclic catalyst 
regeneration will employ four catalyst beds. The catalyst beds can be any 
of the well-known arrangements for contacting solid catalyst particles 
with a hydrocarbon gas stream and performing reforming reactions. Although 
a catalyst bed can comprise a fluidized, ebuliated, or bubbling bed of 
catalyst, the most common catalyst bed for cyclic reforming comprises a 
fixed bed of catalyst. Typically, at any given time three catalyst beds 
are on-stream and employed in catalyzing reforming reactions while one 
catalyst bed is off-stream, meaning that it is either being prepared for 
regeneration, undergoing regeneration, or being prepared for a return to 
reforming. Periodically, after regeneration of the off-stream catalyst bed 
has been completed, the off-stream catalyst bed is placed on-stream, 
replacing one of the on-stream catalyst beds which is itself then 
regenerated. Catalyst is generally not withdrawn from or transported to 
any catalyst bed, but instead remains as a fixed bed inside each catalyst 
bed both when it is catalyzing reforming reactions and when it is being 
regenerated. When a catalyst bed is being regenerated, the catalyst 
therein undergoes a multi-step regeneration process that is used to 
regenerate the catalyst to restore its full reaction promoting ability. 
The inlets and outlets of the catalyst beds are connected to each other by 
conduits or pipelines, which contain valves or blinds. These valves or 
blinds can be opened in order to allow individual streams to flow to and 
from any particular catalyst bed, and they can be closed in order to block 
in or isolate a particular catalyst bed from any individual stream or 
streams. For example, for a catalyst bed containing catalyst that has 
completed the various regeneration steps, the valves in the inlets and 
outlets lines that connect the catalyst bed with regenerant gas streams 
and regeneration equipment are closed. At the same time, or shortly 
thereafter, the valves that connect the catalyst bed with the hydrocarbon 
streams and reforming equipment are opened. The reverse of these steps is 
performed for a catalyst bed containing catalyst that has become 
deactivated and is about to be regenerated. 
Although reforming of hydrocarbons is undergoing continuously, it is often 
referred to as cyclic. By cyclic it is meant that each individual catalyst 
bed cycles back and forth between reforming and regeneration, or that the 
repeated taking off-stream of spent catalyst beds and repeated placing 
on-stream of regenerated catalyst beds is practiced in a cyclical pattern. 
For example, although a catalyst bed may be regenerated every 12 or 24 
hours, any particular catalyst bed is typically regenerated less 
frequently, such as every 48, 72, 96 or more hours. The frequency at which 
any particular catalyst bed is regenerated depends on many factors, 
including the quantity of catalyst and on the rate of deactivation of the 
catalyst in the catalyst bed. 
This invention is applicable to many of the individual regeneration steps 
that typically comprise a cyclic reforming catalyst regeneration 
operation. Generally, these steps involve contacting the catalyst in an 
off-stream, fixed bed catalyst bed with a recycle gas stream containing a 
regeneration agent, and withdrawing from the catalyst bed an offgas stream 
that contains chloro-species, and recycling a portion of the offgas stream 
to the catalyst bed. In the prior art, these steps also involve scrubbing 
or otherwise removing chloro-species from the offgas or recycle gas. One 
common example of such a step is coke combustion. If the recycle gas 
stream contains a low concentration of oxygen of typically from 0.5 to 1.5 
vol-%, coke which could have accumulated on surfaces of the catalyst 
because of the reforming reactions can be removed by combustion. Coke is 
comprised primarily of carbon but is also comprised of a relatively small 
quantity of hydrogen, generally from 0.5 to 10 wt-% of the coke. The 
mechanism of coke removal includes oxidation to carbon monoxide, carbon 
dioxide, and water. The coke content of spent catalyst may be as much as 
20% by weight of the catalyst weight, but 5-7% is a more typical amount. 
Coke is usually oxidized at temperatures ranging from 900 to 100.degree. 
F. (482 to 538.degree. C.), but temperatures in localized regions may 
reach 1100.degree. F. (593.degree. C.) or more. Because of these high 
temperatures and also because of high water concentrations, catalyst 
chloride is quite readily removed from the catalyst during coke 
combustion. Although the presence of chloro-species in the combustion 
recycle gas is not a requirement, the supplemental injection of 
chloro-species into the combustion recycle gas can help prevent too much 
catalyst chloride from being stripped away, and can also help prevent the 
catalyst metal from agglomerating. Coke combustion consumes oxygen, so a 
small stream of make-up gas is added to the flue gas to replace the 
consumed oxygen, and a small amount of flue gas is vented off to allow for 
the addition of the make-up gas. The steady addition of make-up gas, the 
venting of flue gas and, if used, scrubbing of the flue gas establishes a 
steady state condition during most of the coke combustion step that 
produces a nearly constant concentration of chloro-species, as well as of 
water and oxygen, in the recycle gas and in the flue gas. 
Another example of a cyclic catalyst regeneration step to which this 
invention is applicable is redispersion of the catalyst metal. The 
redispersion recycle gas generally contains a higher concentration of 
oxygen than for coke combustion, usually from 2 to 21 vol-%. The 
redispersion recycle gas also generally contains either chlorine or 
another chloro-species that can be converted to chlorine at the 
redispersion conditions. The chlorine or chloro-species is generally 
introduced in a stream of carrier gas that is added to the redispersion 
recycle gas, and so a portion of the flue gas is vented off to allow for 
the addition of the carrier gas. The volumetric flow rates of the carrier 
gas stream and of the portion of the flue gas steam that is vented are 
relatively small in comparison to the volumetric flow rates of the 
redispersion recycle gas stream and the total flue gas stream. The steady 
addition of carrier gas, the venting of flue gas and, if used, scrubbing 
of the flue gas establishes a steady state condition that produces a 
nearly constant concentration of chlorine or chloro-species in the 
redispersion recycle gas and in the flue gas. Although the actual 
mechanism by which chlorine redisperses catalyst metal such as platinum is 
the subject of a variety of theories, it is generally recognized that the 
metal may be redispersed without increasing the catalyst chloride content. 
In other words, although the presence of chlorine is a requirement for 
metal redispersion to occur, once the metal has been redispersed it is 
generally recognized that it is not necessary that the catalyst chloride 
content be maintained above that of the catalyst prior to redispersion. 
Thus, the agglomerated metal of a catalyst can be redispersed without a 
net increase in the overall chloride content of the catalyst. 
A third example of a cyclic regeneration step to which this invention is 
applicable is rechloriding of the catalyst. Although the rechloriding 
recycle gas must contain a chloro-species, the rechloriding recycle gas 
generally does not require the presence of oxygen unless it is needed to 
decompose the chloro-species in order to deposit chloride on the catalyst. 
The chloro-species is generally introduced in a relatively small stream of 
carrier gas that is added to the rechloriding recycle gas, and so a small 
amount of flue gas is vented off to allow for the addition of the carrier 
gas. Like coke combustion and metal redispersion, rechloriding that adds 
carrier gas and vents flue gas establishes steady state concentrations of 
chlorine or chloro-species in the recycle gas and in the flue gas. 
A fourth example of a cyclic regeneration step to which this invention is 
applicable is reduction of the catalyst. The recycle gas must contain a 
reducing agent, which is usually hydrogen which oxidizes to water as the 
oxidation state of the catalyst metal reduces, usually to zero. At typical 
reduction conditions some of the water of reduction occupies catalyst 
surface sites and displaces chloride, which appears as hydrogen chloride 
in the outlet gas that is withdrawn from the cyclic catalyst bed. Although 
the presence of chloro-species in the recycle gas during reduction is not 
a requirement, a supplemental injection of chloro-species can help prevent 
an excessive amount of catalyst chloride from being stripped from the 
catalyst. In any event, recycling of hydrogen through the cyclic catalyst 
beds during reduction establishes steady state concentrations of water and 
chlorine or chloro-species in the recycle gas and in the outlet gas. 
When applied to cyclic regeneration steps such as those just described and 
while one catalyst bed is off-stream for regeneration, this invention 
employs an additional catalyst bed off-stream for sorption of the 
chloro-species in the flue gas that is withdrawn from the catalyst bed 
that is being regenerated. So, unlike a typical cyclic reforming process 
where at any given time only one catalyst bed is off-stream, this 
invention employs at least two catalyst beds off-stream. Accordingly, when 
a catalyst bed is taken off-stream in order for its catalyst bed to be 
regenerated, the first event that occurs is not regeneration of the spent 
catalyst. Rather, the catalyst bed is contacted first with the 
regeneration flue gas in order to sorb chloro-species and only thereafter 
is the catalyst bed regenerated. Consequently, in the cyclic regeneration 
process of this invention, each catalyst bed continually undergoes a 
three-step cycle consisting of on-stream reforming which produces spent 
catalyst, then off-stream sorption which produces chlorided catalyst, and 
finally off-stream regeneration which produces regenerated catalyst. After 
regeneration, the catalyst bed containing regenerated catalyst is placed 
back on-stream to promote more reforming reactions, thereby completing one 
cycle and starting the next. 
The majority of the description of the embodiments of this invention is 
presented in terms of combusting coke in an off-stream catalyst bed of a 
reforming process with cyclic catalyst regeneration, because this is 
believed to be the most common application of this invention. However, 
this description is not intended to limit the scope of this invention as 
set forth in the claims. 
Generally, the make-up gas during the combustion step of a cyclic 
regeneration of a reforming catalyst comprises air and most of the oxygen 
in the make-up air is consumed in the combustion of coke. Therefore, the 
flue gas generally contains from 70 to 80 mol-% nitrogen, from 10 to 20 
mol-% carbon oxides, which is mainly carbon dioxide with trace amounts of 
carbon monoxide, and from 0.2 to 2.0 mol-% oxygen. Oxygen might, however, 
not be present in the flue gas stream if all of the oxygen in the 
regenerant gas stream is consumed in the combustion of coke. While 
nitrogen, carbon oxides, and oxygen are typical but not required 
components of the gas stream that is passed to the catalyst bed in which 
sorption is occurring, the gas stream must contain a chloro-species, such 
as hydrogen chloride or chlorine. The concentration of hydrogen chloride 
in the flue gas stream to the catalyst bed during sorption is generally 
from 500 to 10000 mol-ppm, and preferably from 1000 to 5000 mol-ppm. The 
concentration of chlorine in the flue gas stream to the catalyst bed 
during sorption is generally from 10 to 500 mol-ppm, and preferably from 
25 to 100 mol-ppm. Water may also be present in the flue gas stream. The 
concentration of water in the flue gas stream to the catalyst bed during 
sorption is generally form 1 to 20 vol-%, and preferably from 2 to 5 vol-% 
because water competes with chloro-species for sorption on the catalyst 
particles. The flue gas stream may also contain trace amounts of other 
volatile chloro-species such as chlorinated hydrocarbons and chlorinated 
metals. 
Sulfur, in the form of sulfur oxides such as sulfur dioxide and sulfur 
trioxide, is often present in the flue gas streams of the combustion step 
of cyclic catalyst regeneration processes. Hydrocarbon feedstocks are 
often contaminated with low concentrations of sulfur, some of which can 
sorb or deposit on the catalyst in the catalyst bed during reforming. 
Generally, when spent catalyst containing sulfur is contacted with oxygen 
during the combustion step of a cyclic catalyst regeneration process, the 
sulfur is typically converted to sulfur dioxide and trace amounts of 
sulfur trioxide, which appear in the flue gas from the catalyst bed that 
is being regenerated. These sulfur oxides can harm the performance of the 
catalyst by forming sulfates on the catalyst or by agglomerating the 
platinum metal. In order to avoid these harmful effects, it is preferred 
that the sulfur concentration of the hydrocarbon feedstock be maintained 
as low as possible in order to minimize the presence of the sulfur oxides 
in the flue gas. 
The catalyst particles in a catalyst bed of a cyclic regeneration process 
are typically contained in an elongated bed having two elongated sides. In 
one common arrangement, the two elongated sides are open for transverse 
gas flow through the catalyst bed. In another common arrangement, the 
elongated bed has two ends, which are generally perpendicular to the 
elongated sides and which are open for axial gas flow through the bed. 
When the regenerant gas contacts the coked catalyst in the catalyst bed, 
the coke begins to burn. Generally, the flow rate, temperature, and oxygen 
concentration of the regenerant gas are controlled in order to produce a 
combustion front within the catalyst bed and to prevent the temperature of 
the combustion front from exceeding about 1050.degree. F. (566.degree. 
C.). Combusting coke in this manner is well known in the art of 
hydrocarbon processing. The combustion front passes slowly from the inlet 
to the outlet of the catalyst bed. The intensity of coke burning and the 
rate of progression of the combustion front through the catalyst bed can 
be controlled by monitoring the temperature at various locations within 
the bed or the bulk temperature of the flue gas stream leaving the bed. 
When using the method of this invention to remove chloro-species from the 
flue gas, a portion of the flue gas stream is passed to an off-stream 
catalyst bed that contains spent catalyst that has not yet been combusted. 
Unlike prior art processes, the method of this invention does not use a 
separate adsorbent or caustic scrubbing to remove the chloro-species from 
the flue gas stream, but instead this invention uses the catalyst itself 
for the sorption. Catalyst is generally not withdrawn from or transported 
to the catalyst bed that is used for sorption, but preferably remains 
within the catalyst bed as a fixed bed, as when it is catalyzing reforming 
reactions and being regenerated. The direction of the flue gas flow 
through the catalyst bed is preferably cocurrent relative to the 
directions of the flow of the hydrocarbon combined feed and of the 
regenerant gas stream, but the flue gas direction can also be 
countercurrent, crosscurrent, or a combination of cocurrent, 
countercurrent, and crosscurrent. 
The catalyst bed in which chloro-species are sorbed is operated at sorption 
conditions that are effective to sorb at least a portion of the 
chloro-species from the flue gas stream. Sorption conditions include a gas 
hourly space velocity of generally less than 100000 hr.sup.-1 and 
preferably less than 50000.sup.-1. The chloride content of the spent 
catalyst prior to sorption may be as much as 5% by weight of the catalyst 
weight, but from 0.1 to 2.0% is a more typical amount. Although the spent 
catalyst particles that sorb chloro-species have a higher coke content 
than fresh catalyst particles, it has been discovered that spent catalyst 
particles have surprisingly similar capabilities for chloride retention as 
fresh catalyst particles. Accordingly, it is believed that spent catalyst 
particles have similar capabilities for chloride retention as oxidized 
catalyst particles. Thus, in order for sorption of chloro-species to occur 
in the off-stream catalyst bed through which the flue gas is passing, the 
operating conditions in that catalyst bed must be more favorable for 
sorption of chloro-species than the operating conditions of the catalyst 
bed in which the coke is being combusted. Generally, these more favorable 
conditions for sorption include a decreased temperature, a decreased 
pressure, or a decreased water content of the gas that contacts the 
catalyst. Preferably, the catalyst bed in which sorption occurs operates 
at a decreased temperature relative to the catalyst bed in which coke 
combustion occurs. 
A cooler temperature in the catalyst bed in which sorption occurs relative 
to the catalyst bed in which combustion occurs can achieved in a variety 
of ways. Although either the spent catalyst in the catalyst bed in which 
sorption occurs can be cooled prior to beginning sorption or the catalyst 
bed may be equipped with cooling means to cool the flue gas or catalyst 
within the catalyst bed in which sorption occurs, the preferred method of 
maintaining a cooler temperature in the catalyst bed in which sorption 
occurs is by cooling the flue gas after leaving the catalyst bed in which 
combustion occurs and prior to entering the catalyst bed for sorption. The 
flue gas can be cooled by any suitable cooler, but an air-cooled 
shell-and-tube heat exchanger having the flue gas within the tubes is 
preferred. The temperature of the flue gas is generally from 150 to 
900.degree. F. (66 to 482.degree. C.) and preferably from 300 to 
500.degree. F. (150 to 260.degree. C.). In order to maximize heat 
integration and energy efficiency between the catalyst beds in which 
sorption and combustion are occurring, the flue gas leaving the catalyst 
bed in which combustion is occurring can be cooled by exchanging heat with 
the regenerant gas entering the catalyst bed in which combustion is 
occurring. Thus, a large portion of the required duty to heat the 
regenerant gas to combustion temperatures can be supplied by the flue gas. 
If, even after heat exchanging, the temperature of the flue gas is still 
higher than the desired temperature for passing to the catalyst bed in 
which sorption is occurring, then a trim flue gas cooler may be employed. 
Likewise, if the regenerant gas has not been sufficiently heated then a 
trim regenerant gas heater may be used to achieve the desired inlet 
temperature for the catalyst bed in which combustion is occurring. 
The temperature in the catalyst bed in which sorption occurs and in any 
coolers and heat exchangers if present is preferably maintained above the 
dew point temperature of the flue gas in order to minimize the possibility 
of condensing corrosive acidic liquid in any equipment. The temperature of 
the cooled flue gas is generally from 150 to 900.degree. F. (66 to 
482.degree. C.) and preferably from 300 to 500.degree. F. (150 to 
260.degree. C.). The temperature of the spent catalyst prior to the 
passage of the cooled flue gas to the catalyst bed for sorption is 
generally from 150 to 900.degree. F. (66 to 482.degree. C.) and preferably 
from 300 to 500.degree. F. (150 to 260.degree. C.). Although in principle 
the heat of sorption of the chloro-species on the spent catalyst also 
influences the temperature of the catalyst bed in which sorption occurs, 
it is believed that the heat of sorption is not a significant factor 
relative to the flow rates and temperatures of the streams entering and 
leaving the catalyst bed for sorption. 
A lower pressure in the catalyst bed in which sorption is occurring 
relative to the catalyst bed in which combustion is occurring can be 
achieved by various methods. The simplest method is using a 
pressure-reducing valve in the flue gas conduit between the outlet of the 
catalyst bed in which combustion is occurring and the inlet of the 
catalyst bed in which chloro-species are being sorbed. The pressure of the 
catalyst bed in which chloro-species are sorbed is generally form 0 to 500 
psi (0 to 3447 kPa) absolute and preferably from 15 to 100 psi (103 to 689 
kPa). The pressure of the catalyst bed in which sorption is occurring is 
generally from 5 to 100 psi (34 t 689 kPa), and preferably from 15 to 50 
psi (103 to 344 kPa) less than the pressure of the catalyst bed in which 
combustion is occurring. Another method is especially adaptable to many 
existing cyclic regeneration processes that employ a recycle compressor to 
circulate regenerant gases through the catalyst bed in which combustion is 
occurring. In this method, the recycle compressor takes suction from the 
catalyst bed in which sorption is occurring and discharges to the catalyst 
bed in which combustion is occurring. This method of decreasing the 
pressure of the catalyst bed in which sorption is occurring be 
advantageously combined with cooling the flue gas. By passing the flue gas 
stream through a cooler that cools and at the same time causes a pressure 
drop in the flue gas stream, both the temperature and the pressure of the 
catalyst bed in which sorption is occurring can be decreased. 
A decrease in the water content of the flue gas that contacts the spent 
catalyst promotes sorption of chloro-species by decreasing the water that 
is present and capable of competing with the chloro-species for sorption 
on the spent catalyst particles. Although not necessary, drying the flue 
gas stream prior to its entering the catalyst bed in which sorption is 
occurring is a preferred method of performing this invention. The water in 
the flue gas can be removed by passing the flue gas stream through an 
adsorbent such as silica gel that preferentially adsorbs water but not 
chloro-species. Although silica gel deteriorates over time in the presence 
of water and some chloro-species, a bed of silica gel can be used or 
sacrificed to remove water from the flue gas until the silica gel becomes 
unusable. 
The ability of the catalyst to sorb chloro-species during sorption can also 
be enhanced by drying the spent catalyst prior to its use for sorption. 
Water that is already sorbed on the spent catalyst before the catalyst is 
used for sorption occupies sites that would otherwise be available for 
sorption of chloro-species. Thus, as with drying the flue gas, drying the 
spent catalyst is a preferred but not necessary method of performing this 
invention. This drying step can comprise contacting the spent catalyst 
with a hot, dry gas such as nitrogen. The water content of the spent 
catalyst is generally less than 1 wt-% and preferably less than 0.1 wt-%. 
For a typical spent hydrocarbon conversion catalyst, however, the water 
content is usually less than 0.1 wt-% and is therefore neither a 
significant factor nor an important variable for chloride sorption. 
This invention is not limited to cyclic regeneration operations in which 
the regeneration and sorption steps occur in the gas phase. Rather, it is 
believed that the regeneration conditions can include conditions in which 
the regenerant stream, the flue stream, or both are at least partially in 
the liquid phase. Likewise, it is believed that the sorption conditions 
can include conditions in which the flue stream, the effluent stream, or 
both are at least partially in a liquid phase. Nevertheless, gas phase 
conditions are very common for cyclic regeneration operation in the 
hydrocarbon processing industry and are preferred. 
It is not a necessary element of this invention that any portion of the 
effluent gas stream form the regenerant gas stream or provide any portion 
of the regenerant gas stream. In other words, the benefit of this 
invention can be achieved regardless of whether any portion of the 
effluent gas stream is recycled, directly or indirectly, from the catalyst 
bed in which sorption is occurring to the catalyst bed in which 
regeneration is occurring. The benefit of this invention is achieved when 
chloro-species are removed from the flue gas stream of a catalyst bed in 
which regeneration is occurring by sorption on catalyst that has not yet 
been regenerated. This benefit is achieved even if none of the effluent 
gas stream from the catalyst bed in which sorption is occurring is 
recycled to the catalyst bed in which regeneration is occurring. The 
benefit is the decrease in the concentration of chloro-species of the flue 
gas stream, without regard for the purpose to which the effluent gas 
stream having the decreased concentration of chloro-species is 
subsequently employed. Of course, in many commercial cyclic regeneration 
operations, generally more than 50% and often more than 90% of the gas 
that passes through catalyst beds in which regeneration is occurring is 
gas that is recycled by a recycle compressor. In processes such as these, 
this invention can be used to remove chloro-species from the flue gas 
stream in order that the gas stream that is recycled by the recycle 
compressor has a decreased concentration of chloro-species relative to the 
flue gas and poses a minimal risk of damage to the recycle compressor. 
The make-up gas that enters a cyclic regeneration operation during 
combustion contains oxygen. There are some advantages to raising the 
concentration of oxygen in the make-up gas stream. The concentration of 
oxygen in the catalyst bed which is undergoing coke combustion depends on 
the amount of oxygen added to the combustion zone. By increasing the 
concentration of oxygen in the make-up gas, the volumetric flow rate of 
make-up gas that must be added to the cyclic regeneration process in order 
to maintain a given oxygen concentration in the combustion zone is 
decreased. One consequence of the addition of less make-up gas is a 
decrease in the volumetric flow rate of gas vented from the cyclic 
regeneration process. Thus, if the gas stream that is vented from the 
process is passed to a supplemental means of removal of chloro-species in 
order to further remove chloro-species from the vent gas stream, this 
decrease in flow rate of the vent gas stream generally decreases the 
capital and operating expense of that supplemental means. Accordingly, a 
preferred embodiment of this invention uses an oxygen-enriched air stream 
for the make-up gas during combustion. A number of processes are known for 
enriching air streams with oxygen. These processes can use selective 
adsorbents, gas permeable membranes or a combination of both to generate 
such streams. One such process that uses a gas permeable membrane to 
enrich an oxygen stream and produce a non-permeate stream with an 
increased nitrogen concentration is shown in U.S. Pat. No. 4,787,919, the 
teachings of which are herein incorporated by reference. Additional 
diffusion membranes for the separation of gases are also shown in U.S. 
Pat. No. 3,830,733, the teachings of which are incorporated by reference. 
These and other commercially available processes can economically produce 
oxygen-enriched gas streams having concentrations of 39 mole percent. Air 
separation processes are beneficial since they provide oxygen-enriched 
streams that can be used in the combustion step of a cyclic regeneration 
operation. Nevertheless, this invention does not require the use of any 
particular source of oxygen-enriched gas streams for use in the combustion 
step. 
FIGS. 1A and 1B illustrate a cyclic reforming process that uses the 
reforming catalyst contained in an off-stream catalyst bed to remove 
chloro-species from the flue gas stream leaving another off-stream 
catalyst bed containing reforming catalyst that is being regenerated. 
Starting with the flow of hydrocarbons, a naphtha feedstock is charged to 
the process through line 10. The feedstock combines with 
hydrogen-containing recycle gas that is flowing through line 158 to 
provide a combined feed stream flowing through line 12. The combined feed 
stream is heated and at least partially vaporized in heat exchanger 14 by 
heat transferred from the catalyst bed effluent stream flowing through 
line 142. The combined feed stream passes through line 16 to heater 18, 
where the combined feed stream is heated further to reaction temperature. 
The combined feed stream passes through lines 20 and 30 to catalyst bed 
40, valve 28 being open and valves 32 and 36 being closed. Details of the 
contacting beds and other internals of catalyst bed 40 and the other four 
catalyst beds, 42, 44, 46, and 48, are well known to those skilled in the 
art of hydrocarbon processing. Catalyst bed 40 contains reforming catalyst 
that has previously been brought to reaction temperature and pressure by 
means that are not shown but are well known in the art, such as by 
circulating hot hydrogen or hot hydrocarbons through the catalyst bed. The 
combined feed is introduced to catalyst bed 40. Partially converted 
combined feed is withdrawn from catalyst bed 40 at a temperature lower 
than the inlet temperature of the combined feed because the reforming 
reactions are endothermic. Valve 52 is open and valves 56, 60, 210, and 
270 are closed, and hence the partially converted combined feed passes 
through lines 50 and 66 to interheater 68 wherein it is reheated to 
reaction temperature. The partially converted combined feed passes through 
lines 70 and 72 to catalyst bed 42, valve 74 being open and valves 82 and 
88 being closed. Catalyst bed 42 also contains reforming catalyst at 
reaction temperature and pressure. The partially converted combined feed 
is introduced to catalyst bed 42 wherein endothermic reforming reactions 
occur. Partially converted combined feed is withdrawn from catalyst bed 42 
and passes through lines 92 and 106 to interheater 108 wherein it is again 
reheated to reaction temperature. Valve 94 is open and valves 96, 100, 
204, and 264 are closed. After reheating, the partially converted combined 
feed passes through lines 110 and 112 to catalyst bed 44, valve 114 being 
open and valves 124 and 128 being closed. It is introduced to catalyst bed 
44 which also contains reforming catalyst which is also at reaction 
temperature and pressure and which promotes more reforming reactions to 
occur. With valve 132 being open and valves 134 and 136 being closed, the 
catalyst bed effluent stream withdrawn from catalyst bed 44 passes through 
lines 130 and 142 to heat exchanger 14, wherein the catalyst bed effluent 
stream is cooled by transferring heat to the combined feed stream, as 
described previously. The cooled catalyst bed effluent passes through line 
144 to the gas separation and product fractionation system 146. 
Numerous systems that are suitable for use as system 146 are known to 
persons of ordinary skill in the art. In system 146, the cooled catalyst 
bed effluent is separated into a gas containing hydrogen and C.sub.5 and 
lighter hydrocarbons and condensed liquids containing some C.sub.1 
-C.sub.4 hydrocarbons but mainly C.sub.5 and heavier hydrocarbons. The gas 
stream is divided into a net gas stream withdrawn through line 148 and a 
recycle gas stream withdrawn through line 154. The recycle gas stream 
passes through line 154 to compressor 156, which discharges the recycle 
gas through line 158 to combine with the naphtha feedstock as described 
previously. The condensed liquids are fractionated to produce a liquid 
C.sub.1 -C.sub.4 hydrocarbon stream withdrawn through line 150 and a 
liquid C.sub.5 +reformed naphtha product stream withdrawn through line 
152. The particular details of the gas separation and product 
fractionation system 146 need not be described in further detail herein 
because they are not an essential part of this invention and are well 
known to persons of ordinary skill in the art of reforming processes. 
After the catalyst beds 40, 42, and 44 have been on-stream for several 
days, the activity or selectivity of the reforming catalyst in the 
catalyst beds declines, especially in the last catalyst bed 44. This 
decline in the ability of the catalyst to reform is usually reflected in a 
decline in the octane number of the reformed naphtha product. Although 
this decline in octane can be minimized by increasing the catalyst bed 
inlet temperature, or by decreasing the charge rate, to one or more of the 
catalyst beds, the decline is usually corrected by periodically 
regenerating the catalyst. The final catalyst bed may require regeneration 
more frequently than the first catalyst bed, and the system in FIGS. 1A 
and 1B is one in which the alternate, off-stream catalyst beds 46 and 48 
can take the place of any one of the on-stream catalyst beds 40, 42, and 
44 by an arrangement of valves and connections. See U.S. Pat. No. 
2,773,014. Thus, after catalyst beds 40, 42, and 44 have been on-stream 
for one or two days, the fresh catalyst in off-stream catalyst bed 48 may 
be brought to reforming reaction temperature and pressure as described 
previously. Then, reheated partially converted combined feed flowing 
through line 110 is introduced to catalyst bed 48 by opening valves 128 
and 136 and by closing valve 114. Immediately prior to closing valve 114, 
catalyst beds 44 and 48 are operating in parallel, both receiving 
partially converted combined feed from line 110 and both discharging to 
line 142. Immediately after closing valve 114 and prior to closing valve 
132, catalyst bed 44 may be purged of hydrocarbon by introducing hot 
hydrogen-containing gas to catalyst bed 44 by means not shown in FIGS. 1A 
and 1B. When purging is complete, valve 132 is closed. Thus, the partially 
converted combined feed flowing through line 110 passes to catalyst bed 48 
through lines 118, 126 and 90. The catalyst bed effluent stream to the 
heat exchanger 14 no longer comes from catalyst bed 44 but instead from 
catalyst bed 48 through lines 116, 138, 140, and 142, with valves 60, 100, 
132, 134, 222, and 284 being closed and valve 136 being open. 
It should be pointed out that after the catalyst beds 40, 42, and 44 had 
been on-stream for several days, off-stream catalyst bed 48 could have 
taken the place of either on-stream catalyst beds 40 and 42 instead of 
on-stream catalyst bed 44. Thus, in a manner similar to that described for 
replacing on-stream catalyst bed 44 with catalyst bed 48, off-stream 
catalyst bed 48 could have taken the place of on-stream catalyst bed 42 by 
opening valves 88 and 100 and closing valves 74 and 94. In that case, the 
partially converted combined feed flowing through line 70 would have 
passed to catalyst bed 48 through lines 78, 86, and 90, and the partially 
converted combined feed that then would have been withdrawn from catalyst 
bed 48 would have passed to heater 108 through lines 116, 102, 104, and 
106. Alternatively, off-stream catalyst bed 48 could have taken the place 
of on-stream catalyst bed 40 by opening valves by opening valves 36 and 60 
and closing valves 28 and 52. In that case, the combined feed flowing 
through line 20 would have passed to catalyst bed 48 through lines 24, 26, 
38, and 90, and the partially converted combined feed that then would have 
been withdrawn from catalyst bed 48 would have passed to heater 68 through 
lines 116, 58, 62, 64 and 66. 
After the catalyst beds 40, 42, and 48 have been on-stream for several 
days, off-stream catalyst bed 46 can take the place of catalyst bed 42 by 
opening valves 82 and 96 and closing valves 74 and 94. This leaves 
catalyst beds 40, 46, and 48 on-stream and catalyst beds 42 and 44 
off-stream. Thus, the partially converted combined feed stream from 
interheater 68 is not passing to catalyst bed 42 but instead to catalyst 
bed 46 through lines 70, 78, 80 and 84, with valve 74 and 88 being closed 
and valve 82 being open. Also, the partially converted combined feed 
stream to interheater 108 is now not coming from catalyst bed 42 but 
instead from catalyst bed 46 through lines 76, 98, 104, and 106, with 
valves 56, 94, 100, 134, 216, and 276 being closed and valve 96 being 
open. In a similar manner to that described previously for catalyst bed 
48, off-stream catalyst bed 46 could have taken the place of either 
on-stream catalyst beds 40 or 48 instead of on-stream catalyst bed 42. 
Thus, off-stream catalyst bed 46 could have taken the place of on-stream 
catalyst bed 40 by opening valves 32 and 56 and closing valves 28 and 52. 
In that case, the combined feed flowing through line 20 would have passed 
to catalyst bed 46 through lines 24, 34 and 84, and the partially 
converted combined feed that then would have been withdrawn from catalyst 
bed 46 would have passed to heater 68 through lines 76, 54, 64 and 66. 
Alternatively, off-stream catalyst bed 46 could have taken the place of 
on-stream catalyst bed 48 by opening valves 124 and 134 and closing valves 
128 and 136. In that case, the partially converted combined feed flowing 
through line 110 would have passed to catalyst bed 46 through lines 118, 
120, and 84, and the partially converted combined feed that then would 
have been withdrawn from catalyst bed 46 would have passed to heat 
exchanger 14 through lines 76, 135, 140, and 142. 
Referring next to the regeneration of off-stream catalyst beds, the process 
in FIGS. 1A and 1B provides four connections per catalyst bed for each of 
four gas streams that are associated with regeneration. All five catalyst 
beds are provided with these gas connections in order that each on-stream 
catalyst bed can be replaced with an off-stream catalyst bed, taken 
off-stream, and regenerated. The four gas streams are the regenerant gas 
stream, the flue gas stream containing chloro-species, the cooled flue gas 
stream, and the effluent gas stream which has a lower concentration of 
chloro-species relative to the flue gas stream. 
For the regenerant gas, the outlet of regeneration heater 170 is equipped 
with connections to provide regenerant gas through line 172 to any of the 
five catalyst beds. Thus, regenerant gas from heater 170 can flow to 
catalyst bed 48 through lines 172 and 174 and valve 176; to catalyst bed 
46 through lines 172, 178, and 180 and valve 182; to catalyst bed 40 
through lines 172, 178, 184, and 186, and valve 188; to catalyst bed 42 
through lines 172, 178, 184, 190, and 192, and valve 194; and to catalyst 
bed 44 through lines 172, 178, 184, 190, and 196, and valve 198. 
For the flue gas, heat exchanger 166 is equipped with connections in accord 
with this invention to collect flue gas through line 226 from all five 
catalyst beds. Thus, flue gas to exchanger 166 can flow from catalyst bed 
48 through lines 224 and 226 and valve 222; from catalyst bed 46 through 
lines 218, 220, and 226 and valve 216; from catalyst bed 40 through lines 
212, 214, 220, and 226 and valve 210; from catalyst bed 42 through lines 
206, 208, 214, 220, and 226, and valve 204; and from catalyst bed 44 
through lines 202, 208, 214, 220, and 226, and valve 200. 
For the cooled flue gas stream, flue gas cooler 230 is equipped with 
connections in accord with this invention to provide cooled flue gas 
through line 232 to all five catalyst beds. Thus, cooled flue gas from 
flue gas cooler 230 can flow to catalyst bed 48 through lines 232 and 234 
and valve 236; to catalyst bed 46 through lines 232, 238, and 240 and 
valve 242; to catalyst bed 40 through lines 232, 238, 244, 246, and valve 
248; to catalyst bed 42 through lines 232, 238, 244, 250, and 252, and 
valve 254; and to catalyst bed 44 through lines 232, 238, 244, 250, and 
256, and valve 258. 
Lastly, for the effluent gas, effluent gas heat exchanger 292 is equipped 
with connections in accord with this invention to collect effluent gas 
through lines 288 and 290 from all five catalyst beds. Thus, effluent gas 
to exchanger 292 can flow from catalyst bed 48 through lines 286, 288, and 
290 and valve 284; from catalyst bed 46 through lines 280, 282, 288, and 
290, and valve 276; from catalyst bed 40 through lines 272, 274, 282, 288, 
and 290, and valve 270; from catalyst bed 42 through lines 266, 268, 274, 
282, 288, and 290, and valve 264; and from catalyst bed 44 through lines 
262, 268, 274, 282, 288, and 290, and valve 260. 
The description that follows describes the case where catalyst beds 42 and 
44 are off-stream, with catalyst bed 44 undergoing regeneration by coke 
combustion and with catalyst bed 42 sorbing chloro-species from the cooled 
flue gas leaving catalyst bed 44. From the preceding description, however, 
it should be clear that connections are provided so that catalyst bed 46 
or 48 could be regenerated in the place of catalyst bed 44. Likewise, it 
should be evident that catalyst bed 46 or 48 could take the place of 
catalyst bed 42 and sorb chloro-species from the cooled flue gas leaving 
the catalyst bed being regenerated, which is catalyst bed 44 in the 
description that follows. Thus, it is not intended that this description 
limit the scope of the invention as set forth in the claims. 
Make-up gas for coke combustion is typically ambient air which is supplied 
to the process through line 160 from a source not shown that typically 
comprises an air compressor and an air drier. In a preferred embodiment, 
the make-up gas flowing in line 160 is an oxygen-enriched gas which is 
produced from dried ambient air by a gas separation system. Generally, the 
make-up gas stream is added to the process at a rate of addition generally 
equal to the rate of the gas venting from line 300. The make-up air 
combines with the circulating gases flowing in line 302 to form a recycle 
gas stream, which passes to recycle compressor 164 through line 162. From 
compressor 164, the recycle gas stream flows through line 165 to heat 
exchanger 166 wherein the recycle gas stream is heated by heat transferred 
from the circulating flue gas stream flowing through line 226. The recycle 
gas stream passes through line 168 to heater 170, where the recycle gas 
stream is heated further to a catalyst bed inlet temperature for coke 
combustion, which is at a temperature of typically from 700 to 
1000.degree. F. (371 to 538.degree. C.) and preferably from 750 to 
900.degree. F. (399 to 482.degree. C.) and at a pressure of typically from 
14.7 to 155 psi (101 to 1069 kPa) absolute. The concentration of oxygen in 
the inlet recycle gas stream is typically 0.3 to 5.0 mol-% oxygen, which 
can be measured by an oxygen analyzer not shown at the outlet of heater 
170 and which is usually controlled by regulating the flow rate of make-up 
air through line 160. The heated recycle gas stream flows from heater 170 
and is introduced to catalyst bed 44 through lines 172, 178, 184, 190 and 
196, valve 198 being open, and valves 176, 182, 188, and 194 being closed. 
When the heated regenerant gas contacts the coke on the catalyst within 
catalyst bed 44, the coke begins to bum. The flue gas produced is 
withdrawn from catalyst bed 44 through line 202, valve 200 being open and 
valves 132 and 260 being closed. In the embodiment of the invention shown 
in FIGS. 1A and 1B, the flue gas stream is cooled prior to passage of the 
flue gas stream to another off-stream catalyst bed for sorption of the 
chloro-species. Although the flue gas stream is cooled, the temperature in 
any coolers and heat exchangers if present and in the off-stream catalyst 
bed in which sorption occurs is preferably maintained above the dew point 
temperature of the flue gas in order to minimize the possibility of 
condensing corrosive acidic liquid in any equipment. Accordingly, the flue 
gas in line 202 passes to heat exchanger 166 through lines 208, 214, 220 
and 226, valves 204, 210, 216 and 222 being closed. By transferring heat 
from the flue gas to the recycle gas, heat exchanger 166 cools the flue 
gas to a temperature of generally from 500 to 900.degree. F. (260 to 
482.degree. C.) and preferably from 500 to 700.degree. F. (260 to 
371.degree. C.). Next, the flue gas passes through line 228 to a 
water-cooled shell-and-tube heat exchanger 230, which transfers additional 
heat from the flue gas to cooling water in order to further cool the flue 
gas to an inlet temperature of catalyst bed 42 in which chloro-species are 
sorbed from the flue gas. Suitable inlet temperatures of the cooled flue 
gas to catalyst bed 42 are generally from 150 to 900.degree. F. (66 to 
482.degree. C.) and preferably from 300 to 500.degree. F. (150 to 
260.degree. C.). In the cooled flue gas stream, the concentration of 
hydrogen chloride can be from 100 to 100000 mol-ppm, and preferably from 
500 to 3000 mol-ppm. The concentration of chlorine in the cooled flue gas 
stream can be from 1 to 1000 mol-ppm, and preferably from 10 to 300 
mol-ppm. These ranges of concentrations of hydrogen chloride and chlorine 
in the cooled flue gas stream are exemplary and do not limit the scope of 
applicability of this invention. The increase in chloride content of a 
catalyst that is sorbing hydrogen chloride and chlorine depends not only 
on the composition of the cooled flue gas stream but also on the gas 
hourly space velocity, the elapsed time during which the catalyst is 
exposed to the cooled flue gas stream, and other sorption conditions. 
The cooled flue gas stream passes from heat exchanger 230 through lines 
232, 238, 244, 250 and 252 to catalyst bed 42, valve 254 being open and 
valves 236, 242, 248, and 258 being closed. When the cooled flue gas 
contacts the catalyst within catalyst bed 42, the chloro-species are 
sorbed on the catalyst and an effluent gas stream is produced. The 
temperature of the catalyst within catalyst bed 42 during sorption is 
generally from 150 to 900.degree. F. (66 to 482.degree. C.) and preferably 
from 300 to 500.degree. F. (150 to 260.degree. C.). Although other factors 
may influence the temperature at which sorption of the chloro-species on 
the catalyst occurs, preferably the temperature of the catalyst in 
catalyst bed 42 is controlled by the inlet temperature of the cooled flue 
gas stream. The factors that can influence the temperature within the 
catalyst bed during sorption include not only the temperature of the 
cooled flue gas stream, but also the thermal mass flow rate of the cooled 
flue gas stream, the thermal mass of the catalyst, the temperature of the 
catalyst, the elapsed time of contacting between the cooled flue gas 
stream and the catalyst, and heat losses from the catalyst bed. A cooling 
step can be used prior to the sorption step in order to cool the catalyst 
from the reforming reaction temperature to the desired sorption 
temperature. Such a cooling step can immediately follow after the 
previously described purge step that is conducted when a catalyst bed is 
taken off-stream in order to purge hydrocarbons from the catalyst. Thus, 
although initially the inlet temperature of the hydrogen-containing purge 
gas will usually be relatively high in order to ensure that hydrocarbons 
are purged from the catalyst, after a sufficient quantity of hydrocarbon 
is purged from the catalyst bed the temperature of the hydrogen-containing 
purge gas can be reduced in order to cool the catalyst in the catalyst bed 
prior to the sorption step. Although this cooling step is not necessary, 
it is preferred in order to maximize the sorption of chloro-species onto 
the catalyst once the cooled flue gas stream begins to contact the 
catalyst. 
The effluent gas stream is withdrawn from catalyst bed 42 through line 266, 
valve 264 being open and valves 94 and 204 being closed. The effluent gas 
then passes to heat exchanger 292 through lines 268, 274, 282, 288, and 
290, valves 260, 270, 276 and 284 being closed. Prior to entering heat 
exchanger 292, the effluent gas stream flowing in line 288 is contacted 
with an aqueous caustic stream containing sodium hydroxide. The aqueous 
caustic stream flows through a line 320 and is dispersed in the effluent 
gas stream. The combined stream of effluent gas and aqueous caustic 
solution flows through line 290 and into the heat exchanger 292. Heat 
exchanger 292 cools the combined stream to a suitable suction temperature 
for recycle compressor 164, which is generally from 40 to 150.degree. F. 
(4 to 66.degree. C.) and preferably from 60 to 100.degree. F. (16 to 
38.degree. C.). The aqueous caustic stream cools the effluent gas stream 
somewhat. But more importantly the aqueous caustic solution neutralizes 
hydrogen chloride and chlorine present in the effluent gas stream, thereby 
minimizing the possibility of hydrochloric acid corrosion in lines 290 and 
heat exchanger 292. After cooling in heat exchanger 292, the combined 
stream of effluent gas and aqueous caustic solution passes through line 
294 and into gas-liquid separator 296. An aqueous caustic stream 
comprising sodium chloride salt leaves the separator 296 through line 304. 
A spent aqueous stream can be withdrawn through line 306 in order to 
reject the sodium chloride salt from the process. A make-up aqueous 
caustic stream containing sodium hydroxide can be added to the stream in 
line 308 through line 310. Make-up water can be added to the stream in 
line 312 through line 314. The aqueous caustic stream passes through line 
316 to pump 318, which recirculates the aqueous caustic stream through 
line 320. The aqueous caustic stream combines with the effluent gas in 
line 288, as described previously. 
A gas stream exits the separator 296 through line 298. Because most of the 
hydrogen chloride and chlorine that was originally in the flue gas stream 
leaving catalyst bed 44 has been removed by sorption in catalyst bed 42 
and by caustic scrubbing in line 290, exchanger 292, and line 294, the gas 
stream flowing through line 298 contains low concentrations of chlorine 
and hydrogen chloride. With caustic scrubbing, the gas stream flowing 
through line 298 typically contains less than 10 mol-ppm hydrogen chloride 
and less than 0.1 mol-ppm chlorine. This gas stream is also depleted in 
oxygen because the combustion of coke in catalyst bed 44 consumed oxygen. 
In order to replenish the oxygen, a portion of the gas stream flowing 
through line 298 is vented through line 300, and make-up air is added 
through line 160 to the remainder of the gas stream that flows through 
line 302. This forms the recycle gas stream that passes through line 162 
to compressor 164, as described previously. The recycle gas typically 
contains from 1 to 100 mol-ppm hydrogen chloride and less than 10 mol-ppm 
chlorine. If higher concentrations of chlorine or hydrogen chloride in the 
recycle gas are desired, then a chloro-species, such as chlorine, hydrogen 
chloride, or a chloro-hydrocarbon which can decompose at the conditions in 
line 168 or 172 to form chlorine or hydrogen chloride, such as 1,1,1 
trichloroethane, can be injected into the recycle gas stream into line 168 
or 172. 
Caustic scrubbing of the effluent gas stream flowing through line 288 
serves at least three purposes. First, caustic scrubbing helps to minimize 
corrosion by liquids that contain hydrochloric acid and that might 
condense in heat exchanger 292, separator 296, and their associated 
equipment. Second, caustic scrubbing reduces the quantities of hydrogen 
chloride and chlorine that are released from the process with the gas 
stream that is vented through line 300. Third, caustic scrubbing decreases 
the likelihood of damage that chlorine and hydrogen chloride in the 
regeneration stream passing line 162 might cause to the internal working 
parts of recycle compressor 164. Although caustic scrubbing serves these 
three purposes, it is believed that certain situations can permit a 
process such as that shown in FIGS. 1A and 1B to operate without the need 
to contact the effluent gas stream flowing through line 288 with a 
neutralizing caustic stream. For example, if the heat exchanger 292, 
separator 296, and recycle compressor 164 can withstand the corrosive 
effects of the relatively low concentrations of chlorine and hydrogen 
chloride in the effluent gas stream, and if the quantities of chorine and 
hydrogen chloride that are vented from the process through line 300 are 
not excessive, then caustic scrubbing may not be necessary. The greater 
the extent that chloro-species are sorbed from the cooled flue gas stream 
in line 232 according to the method of this invention, the lower is the 
concentration of chloro-species in the effluent gas stream in line 288 and 
the less likely is the need for caustic scrubbing. Persons of ordinary 
skill in the art can determine whether it is desirable to employ caustic 
scrubbing as shown in FIGS. 1A and 1B and, if so, can design and build a 
suitable caustic scrubbing system. 
When coke combustion in catalyst bed 44 is complete, other cyclic 
regeneration steps of the catalyst in catalyst bed 44 may take place. To 
the extent that these other steps result in the release of chloro-species 
from the catalyst in catalyst bed 44 and the presence of these 
chloro-species in the gas stream that is withdrawn from catalyst bed 44, 
catalyst bed 42 may be employed generally to continue to sorb these 
chloro-species in the manner described previously during the coke 
combustion step. However, the use of catalyst bed 42 for sorption during 
other cyclic regeneration steps is subject to at least two limitations. 
First, for a given spent catalyst and given sorption conditions, it is 
believed that there is an upper limit on the chloride content that the 
spent catalyst can sorb. Accordingly, as the content of chloride of the 
catalyst in catalyst bed 42 approaches that upper limit, the capacity of 
the catalyst to sorb more chloride becomes limited. The factors that are 
believed to set the upper limit on chloride content of the catalyst are 
the support material, surface area, pore volume, metals content, coke 
content, water content, and the sulfur content of the catalyst, as well as 
the temperature, pressure, water content, and chloro-species content of 
the flue gas. Second, the conditions that promote sorption of chloride on 
the catalyst in catalyst bed 42 generally should not cause serious or 
irreversible damage to the catalyst in catalyst bed 42. For example, the 
spent catalyst in catalyst bed 42 typically contains from 5 to 10% by 
weight carbon of the catalyst weight and, even though redispersion can be 
effected at lower oxygen concentrations, the redispersion step of a cyclic 
regeneration operation typically employs a redispersion recycle gas that 
contains from 5 to 10 mol-% oxygen. Thus, if a relatively high 
temperature, such as more than about from 600 to 700.degree. F. (316 to 
371.degree. C.), is employed for sorption, the conditions within catalyst 
bed 42, the oxidation of the carbon on the spent catalyst in catalyst bed 
42 can occur and temperatures in localized regions within the catalyst bed 
in catalyst bed 42 may reach 1100.degree. F. (593.degree. C.) or more. One 
problem associated with localized regions of intense coke combustion is 
catalyst deactivation. The combination of temperature, water vapor, and 
exposure time determine the useful life of the catalyst. Exposure of high 
surface area catalyst to high temperatures for prolonged periods of time 
will create a more amorphous material having a reduced surface area which 
in turn lowers the activity of the catalyst until it reaches a level where 
it is considered deactivated. Deactivation of this type is permanent, 
thereby rendering the catalyst unusable. When moisture is present--water 
is a by-product of the coke combustion--the deactivating effects of high 
temperature exposure are compounded. Accordingly, to the extent that at 
sorption conditions the flue gas causes undesirable damage to the spent 
catalyst in catalyst bed 42, then the use of catalyst bed 42 for sorption 
may be limited. A jump-over line (not shown) from line 232 to line 288 may 
be used to route the flue gas around catalyst bed 42 during steps in which 
damage to the catalyst in catalyst bed 42 would otherwise occur. 
In any event, when the regeneration of the catalyst in catalyst bed 44 is 
complete, the catalyst in catalyst bed 44 is once again capable of 
performing reforming reactions and can be returned to an on-stream 
position, taking the place of one of on-stream catalyst beds 46 or 48. In 
the description that follows, catalyst bed 44 is placed on-stream taking 
the place of catalyst bed 48, catalyst bed 48 is taken off-stream and 
takes the place of catalyst bed 42 the catalyst of which is loaded with 
sorbed chloride, and catalyst bed 42 remains off-stream and takes the 
place of catalyst bed 44 in order to undergo regeneration. This step-wise 
switching of the position of the catalyst beds in the process flow can be 
conducted in a number of ways. The first step of a preferred method of 
switching catalyst beds involves routing the recycle gas stream from 
entering catalyst bed 44 to entering catalyst bed 42 and temporarily 
stopping flow of the flue gas stream and of the cooled flue gas stream. 
This is achieved by closing valves 198, 200, and 254 and opening valve 
194. Thus, the regenerant gas flows from heater 170 through lines 172, 
178, 184, 190, and 192 and through valve 194 to catalyst bed 42. The flue 
gas stream that exits catalyst bed 42 follows the flow path of the 
effluent gas stream described previously, flowing through line 266, valve 
264 having been kept open, and through lines 268, 274, 282, 288, and 290. 
The gas stream then passes through exchanger 292, separator 296, 
compressor 164, exchanger 166, and heater 170, and is recycled as recycle 
gas to catalyst bed 42. The second step consists of replacing on-stream 
catalyst bed 48 with off-stream catalyst bed 44 in a reversal of the 
manner described previously for replacing on-stream catalyst bed 44 with 
off-stream catalyst bed 48. Thus, this second step is accomplished by 
opening valves 114 and 132 and closing valves 128 and 136. The third and 
final step consists of reestablishing the flows of the flue gas stream and 
of the cooled flue gas stream through catalyst beds 42 and 48. This third 
step is performed by opening valves 204, 236, and 284 and closing valve 
264. Thus, when all three steps are complete, the three on-stream catalyst 
beds are catalyst beds 40, 46, and 44 as the first, second, and third 
reforming catalyst beds, respectively. Catalyst beds 42 and 48 are 
off-stream, with catalyst bed 42 undergoing regeneration and with catalyst 
bed 48 adsorbing chlorine and hydrogen chloride from the cooled flue gas 
stream of catalyst bed 42. 
After the regeneration of catalyst bed 42 is complete, then of the three 
original on-stream catalyst beds only catalyst bed 40 remains 
unregenerated. In order to regenerate catalyst bed 40, three more 
step-wise shifts of catalyst bed positions are necessary. In the first 
switch, catalyst bed 42 is placed on-stream taking the place of catalyst 
bed 46, catalyst bed 46 is taken off-stream and takes the place of 
catalyst bed 48 the catalyst of which is loaded with sorbed chloride, and 
catalyst bed 48 remains off-stream and takes the place of catalyst bed 44 
in order to undergo regeneration. First, the regenerant gas stream is 
routed from the inlet of catalyst bed 42 to the inlet of catalyst bed 48 
and the flows of the flue gas stream and of the cooled flue gas stream are 
stopped temporarily. This is achieved by closing valves 194, 204, and 236 
and opening valve 176, so that the regenerant gas flows from heater 170 
through lines 172 and 174, and through valve 176 to catalyst bed 48. The 
flue gas stream that exits catalyst bed 48 flows through line 286, valve 
284 having been kept open, and through lines 288 and 290. The gas stream 
then passes through exchanger 292, separator 296, compressor 164, 
exchanger 166, and heater 170, and is recycled as regenerant gas to 
catalyst bed 48. The second step consists of replacing on-stream catalyst 
bed 46 with off-stream catalyst bed 42 by opening valves 74 and 94 and 
closing valves 82 and 96. The final step consists of opening valves 222, 
242, and 276 and closing valve 284. Thus, when all three steps are 
complete, the three on-stream catalyst beds are catalyst beds 40, 42, and 
44 as the first, second, and third reforming catalyst beds, respectively, 
and the two off-stream catalyst beds are catalyst bed 48, which is 
undergoing regeneration, and catalyst bed 46, which is sorbing chlorine 
and hydrogen chloride from the cooled flue gas stream. With the method of 
switching catalyst beds having now been described in sufficient detail to 
enable a person of ordinary skill in the art to practice the invention, in 
the interest of brevity the last two steps of switching catalyst beds are 
described only briefly. In the second switch, catalyst bed 48 is placed 
on-stream taking the place of catalyst bed 40, catalyst bed 40 is taken 
off-stream and takes the place of catalyst bed 46 in sorbing 
chloro-species, and catalyst bed 46 remains off-stream and takes the place 
of catalyst bed 48 in being regenerated. In the third and final switch, 
catalyst bed 46 is placed on-stream taking the place of catalyst bed 44, 
catalyst bed 44 is taken off-stream and takes the place of catalyst bed 40 
in sorbing chloro-species, and catalyst bed 40 remains off-stream and 
takes the place of catalyst bed 46 in being regenerated. Thus, when all 
three switches are complete, the three on-stream catalyst beds are 
catalyst beds 48, 42, and 46 as the first, second, and third reforming 
catalyst beds, respectively and the two off-stream catalyst beds are 
catalyst bed 40 which is being regenerated and catalyst bed 44 which is 
sorbing chlorine and hydrogen chloride. Once catalyst bed 40 is 
regenerated, one more switch of catalyst bed positions returns catalyst 
bed 40 to an on-stream position. 
The method of switching catalyst bed positions that is described in the two 
previous paragraphs involves in its first step temporarily stopping the 
flows of the flue gas stream and the cooled flue gas stream and in the 
third and final step reestablishing the flows of these two streams. During 
this temporary stoppage of flow, flue gas does not flow from either of the 
off-stream catalyst beds through line 226 exchanger 166, line 228, and 
exchanger 230, and cooled flue gas does not flow from line 232 to either 
of the off-stream catalyst beds. Thus, during this temporary flow stoppage 
the head that is required of compressor 164 to circulate gas will decrease 
because there are no pressure losses associated with the exchangers and 
piping of the flue gas circuit because the compressor 164 is not 
circulating gas through this flue gas circuit. Accordingly, the throughput 
of compressor 164 may have to be temporarily reduced in order to prevent 
compressor 164 from surging. Persons of ordinary skill in the art of gas 
compression are able to adjust the operation of the compressor 164 in a 
manner that compensates for the temporary decrease in required head of 
compressor 164. Alternatively, the throughput of compressor 164 may be 
kept the same, provided that the recycle compressor 164 is equipped with a 
spill back circuit through which any excess gas throughput can be recycled 
from the discharge to the suction of the recycle gas compressor 164. 
Although FIGS. 1A and 1B depicts a process that employs five catalyst beds 
with three catalyst beds on-stream and two catalyst beds off-stream, it 
should be understood that in other embodiments of this invention the 
number of catalyst beds can vary. At a minimum, however, there must be at 
least three catalyst beds. Where there are only three catalyst beds, one 
catalyst bed is on-stream and catalyzing reforming reactions, the second 
catalyst bed is off-stream and being regenerated, and the third catalyst 
bed is off-stream and sorbing chloro-species. Where there are more than 
three catalyst beds, various combinations of on-stream and off-stream 
catalyst beds are possible. For example, two or more on-stream catalyst 
beds can be used, and it is common in reforming processes to use three, 
four, or five on-stream catalyst beds. Similarly, three or more off-stream 
catalyst beds can be used. Although it is usually not economical to keep 
too many catalyst beds off-stream, it may be advantageous in some 
situations to simultaneously regenerate two or more catalyst beds or to 
simultaneously sorb chloro-species in two or more catalyst beds. 
Simultaneously sorbing chloro-species in more than one off-stream catalyst 
bed allows each off-stream catalyst bed to operate at different sorption 
conditions. Thus, the sorption conditions may be chosen to maximize the 
sorption of one chloro-species in one catalyst bed and of another 
chloro-species in another catalyst bed. For example, two off-stream 
catalyst beds can be arranged series sorption, with the flue gas first 
contacting a catalyst bed that sorbs chloro-species at a relatively high 
temperature and then passing to the second catalyst bed that sorbs the 
remainder of the chloro-species at a relatively low temperature. 
EXAMPLES 
Unless noted otherwise in the description of the examples that follows, 
each catalyst chloride result was obtained by analyzing one or more 
samples of catalyst on an as-received basis. In addition, the molar ratio 
of water per hydrogen chloride and the hydrogen chloride content of each 
gas mixture were computed by considering all chloro-species in the gas 
mixture as hydrogen chloride. 
Three reforming catalysts were tested for chloride sorption. Catalysts 1, 2 
and 3 had nominal compositions of about 0.38 wt-% platinum (volatile free) 
and 0.3 wt-% tin (volatile free) on a gamma alumina support. Catalysts 1 
and 2 were fresh catalysts and had a nominal loss on ignition at 
900.degree. C. (1652.degree. F.) of 0.5--1.5 wt-% and a nominal coke 
content of less than 0.1 wt-% (as received). Catalyst 1 had a surface area 
of 186 m.sup.2 /gram and a chloride content of 0.99 wt-%. Catalyst 2 had a 
surface area of 210 m.sup.2 /gram and a nominal chloride content of about 
1.15 wt-%. Catalyst 3 was withdrawn from a commercial reforming process 
with a continuous regeneration section and had a loss on ignition at 
900.degree. C. (1652.degree. F.) of 6.1 wt-%, a coke content of about 5 
wt-%, a surface area of 113 m.sup.2 /gram, and a chloride content of 0.97 
wt-%. 
Example 1 
Samples of Catalysts 1 and 3 were contacted with a gas mixture containing 
nitrogen, water, and hydrogen chloride. The gas mixture was prepared by 
vaporizing an aqueous hydrogen chloride solution and injecting it into a 
gas stream containing more than 99.9 mol-% nitrogen so that the gas 
mixture contained 10 mol-% water, had a molar ratio of water per hydrogen 
chloride of 12.5, and contained 800 mol-ppm hydrogen chloride. The 
sorption conditions included a temperature of 302.degree. F. (150.degree. 
C.), a pressure of 14.7 psi (101 kPa), and a superficial contact time of 
the gas mixture with the catalyst of 10 seconds. These sorption conditions 
were maintained for twelve hours. After twelve hours, the chloride content 
was 2.42 wt-% for the sample of Catalyst 1 and 1.87 wt-% for Catalyst 3. 
Example 2 
Samples of Catalysts 1 and 2 were contacted at the same sorption conditions 
as Example 1, except that the gas mixture contained carbon dioxide in 
addition to nitrogen, water, and hydrogen chloride. The gas mixture was 
prepared by vaporizing an aqueous hydrogen chloride solution and injecting 
it into a gas stream containing about 86 mol-% nitrogen and about 14 mol-% 
carbon dioxide so that the gas mixture contained 10 mol-% water, had a 
molar ratio of water per hydrogen chloride of 12.5, and contained 800 
mol-ppm hydrogen chloride. After twelve hours of contacting, the sample of 
Catalyst 1 had a chloride content of 2.42 wt-%, which is the same as the 
chloride content of the sample of Catalyst 1 after contacting with 
nitrogen in Example 1. After twelve hours of contacting, the sample of 
Catalyst 2 had a chloride content of 2.57 wt-%. 
Example 3 
Samples of Catalysts 1 and 2 were contacted at the same sorption conditions 
as Example 1, except that the gas mixture had a molar ratio of water per 
hydrogen chloride of 24 instead of 12.5 and contained 417 mol-ppm hydrogen 
chloride instead of 800 mol-ppm. The gas mixture was prepared by 
vaporizing an aqueous hydrogen chloride solution, which was less 
concentrated in hydrogen chloride than the solution used in Example 1, and 
injecting it into a gas stream containing more than 99.9 mol-% nitrogen so 
that the gas mixture contained 10 mol-% water, had a molar ratio of water 
per hydrogen chloride of 24, and contained 417 mol-ppm hydrogen chloride. 
After twelve hours of contacting, the sample of Catalyst 1 had a chloride 
content of 2.24 wt-% which is 0.18 wt-% lower than the chloride content of 
the sample of Catalyst 1 after contacting in Example 1. After twelve hours 
of contacting, the sample of Catalyst 2 had a chloride content of 2.43 
wt-%. 
Example 4 
Samples of Catalysts 1 and 2 were contacted at the same sorption conditions 
as Example 1, except that the sorption temperature was 572.degree. F. 
(300.degree. C.) instead of 302.degree. F. (150.degree. C.). After twelve 
hours of contacting, the sample of Catalyst 1 had a chloride content of 
1.80 wt-%, which is 0.62 wt-% lower than the chloride content of the 
sample of Catalyst 1 after contacting in Example 1. After twelve hours of 
contacting, the sample of Catalyst 2 had a chloride content of 1.97 wt-%. 
Example 5 
A sample of Catalyst 1 was contacted with a pretreating gas containing air, 
water, and hydrogen chloride. The pretreating gas was prepared by 
vaporizing a 0.6 M aqueous hydrogen chloride solution and injecting it 
into an air stream. The hydrogen chloride solution was injected at a 
liquid volumetric rate of 45 cc/hour into the air stream that was flowing 
at a gas volumetric rate of 3 liter/minute. The pretreatment conditions 
included a temperature of 977.degree. F. (525.degree. C.) and were 
maintained for two hours. After two hours, the chloride content of the 
sample of Catalyst 1 was 0.85 wt-%. 
After pretreatment, the sample of Catalyst 1 was contacted at the same 
sorption conditions as Example 1, except that the gas mixture contained 5 
mol-% water, the gas mixture had a molar ratio of water per hydrogen 
chloride of 300, the gas mixture contained 167 mol-ppm hydrogen chloride, 
and the sorption temperature was 482.degree. F. (250.degree. C.). After 
about four days of contacting, the sample of Catalyst 1 had a chloride 
content of 1.25 wt-%.