Note: Descriptions are shown in the official language in which they were submitted.
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"REGENERABLE HYDROCARBON CONVERSION PROCESS USING A
FLUORIDE-SENSITIyE CATALYST AND A FLUORIDE-FREE FEED"
FIELD OF THE INVENTIQN
The present invention relates to an improved
regenerable hydrocarbon conversion process which utilizes
a regenerable zeolite-containing catalyst to process a
hydrocarbon feed which has been treated to reduce the
fluoride content therein to below 100 ppb ~parts per
billion~.
BACKGROUND OF THE INVENTION
It is a common practice in the hydrocarbon and
petrochemical industry to treat feedstocks~ products, and
intermediates in order to purify streams or to remove
deleterious components from hydrocarbon streams.
Hydrocarbon feedstocks and intermediate process streams
are often purified to increase process efficiency. That
is, it is much more efficient to process reactant
hydrocarbons than it is to include refractor~ hydrocarbons
or hydrocarbons which lead to undesirable products in a
catalyzed hydrocarbon process. Hydrocarbon reaction
products are often purified or otherwise treated to
enhance the products value, stability, and so forth.
) Additionally, impurities in hydrocarbons being
processed in a catalytic system have been recognized as
having a negative effect on catalyst stability and
conversion. For example, cracking catalysts are poisoned
by metals such as nickel, vanadium, and sodium which
originate in the hydrocarbon feed to a cracking unit.
Treatment of such a feed to remove or passivate such
metals is well known to increase the useful life of
cracking catalysts. In another example, sulfur
accumulation on a reforming catalyst promotes undesirable
~3~41D915
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cracking reactions. The treatment of reformer feeds to
remove sulfur components is a well known method of
maintaining process efficiency and protecting catalyst
stability.
In the case of a hydrocarbon conversion process
utilizing a regenerable zeolite-containing catalyst, it is
well known that regeneration procedures which expose a
zeolite-containing catalyst to steam severely effects the
performance of the zeolite catalyst following
regeneration. This performance loss, observed even under
mild regeneration conditions, is typically not totally
recoverable. Therefore, processes and methods to suppress
zeolit~ activity loss in a hydrocarbon conversion process
employing a regenerable zeolite are quite important in
extending the useful life and thus the economic viability
of such a process.
The use of a crystalline zeolite in the catalysis
of a hydrocarbon reaction is well known in the prior art.
However, the improvement in stability of a regenerable
zeolite-containing catalyst when processing a fluorine-
deficient feed has not heretofore been recognized.
Methods for the removal of specific undesirable
components from hydrocarbon feecls prior to or following
hydrocarbon conversion process are well known. The
removal of selected components from a gas stream by
adsorption is shown in U.S. Patent 2,180,712. The
increased selectivity and surface area of molecular sieves
has caused them to predominate in the removal of inorganic
compounds from vapor streams. In Chapter 16 of The
Chemical Enqineer's Handbook, 5th Edition, McGraw-Hill
Book Co., New York, 1973, the suitability of using alumina
for drying gases and the defluorination of alkylates is
indicatad on Page 16-5. The use of fixed-bed, continuous,
and continuous countercurrent gas and liquid sorption
operations are described starting at Page 16-23. Examples
are presented using moving or fluidized beds of activated
9S
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charcoal and silica gel for gas treating operations. U.S.
Patent 3,775,310 presents a continuous ion exchange
process using countercurrent flow of the adsorbent and
trëated liquid. The removal of fluoride compounds
specifically to increase zeolite-containing hydrocarbon
conversion catalyst stability is however not disclosed in
any of these references.
U.S. Patent 4,456,527 describes a hydrocarbon
conversion process which utilizes a hydrotreating step to
reduce the sulfur content of a feed to a catalytic
reforming process. The sulfur content of the feed is
reduced to protect the stability of a catalyst comprising
a l~rge pore type zeolite containing at least one Group
VIII type metal. The intent of the '527 patent is to
protect and maintain the stability of a æeolite-containing
hydrocarbon conversion process. However, the '527 patent
discloses the advantages of feed sulfur removal and is
completely silent to the advantages of feed fluoride
removal.
Surprisingly, many prior art patents disclose the
use of a fluoride component to modify different properties
of a zeolite in a zeolite-conta:ining hydrocarbon
conversion catalyst. U.S. Patent 3,594,331 discloses a
method for increasing the thermal stability of crystalline
zeolites by treating the zeolite with a dilute solution of
a fluorine compound. The treatment with a fluorine
compound is a fluoride treatment (column 3, line 41 et.
seq.). After the fluoride treatment has been completed,
the zeolite (fluoride treated) incorporates 2 to 15 grams
of fluoride per 10,000 grams of zeolite. The patent does
note however that excess fluoride actually decreases the
thermal stability of the zeolite.
U.S. Patent 3,933,983 discloses a fluoride
treatment process similar to U.S. Patent 3,594,331 except
that an ion exchange step is added (see Claim 1).
Additionally, the removal of ~luoride-containing
13~ 95
components within a zeolite with a soluble aluminum
compound is disclosed in Canadian Patent Number 1,218,348.
The removal of fluoride components is described as being
desirable since the presence of such insoluble fluoride
compounds in physical admixture with the aluminosilicate
generally increases the rate of degradation of the
aluminosilicates due to fluoride attack on the zeolite's
lattice. Such fluorides have a tendency to cause fluxing
of inorganic materials under thermal or hydrothermal
conditions which may destroy the zeolites structure. The
prior art disclosures mentioned immediately above
emphasize the fact that fluoride has been used
advantageously to modify catalyst properties during
manufactureO The process of the instant invention, unlike
that of the '348 Canadian patent, treats fluorides in the
hydrocarbon feed by extracting them as opposed to removing
~luorides in a catalyst as a result of catalyst
manufacture.
Zeolite-containing catalyst regeneration methods
are also well known in the prior art. Typically, the
regeneration methods emphasize l:he importance of
performing the zeolite catalyst regeneration procedure at
low levels of moisture to reduce steam deactivation of the
zeolite during regeneration procedures. Examples of such
processes and methods include removing combustion moisture
with a water-lean adsorbent as is done in u.S~ Patent
3,756,961, or by removing a portion of water containing
gas from the system as is described in U.S. Patent
4,480,144. Many other methods of regenerating zeolite
catalyst to prevent thermal degradation of the zeolite by
steam are disclosed. None have disclosed the advantages
of regenerating a zeolite-containing catalyst accrued by
processing only hydrocarbon feed containing less than 100
ppb fluoride.
The prior art discloses various aspects of the
instant invention such as fluoride removal methods,
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zeolite catalyst treating methods and catalyst
regeneration methods. However, no prior art disclosure
describes a hydrocarbon conversion process such as
described herein where a regenerable zeolitic catalyst's
stability is improved by reacting it with hydrocarbon
feeds which have been treated so they contain only minute
amounts of fluorides.
It has now been surprisingly found that if a
hydrocarbon feed is first treated to reduce its fluoride
content to below 100 ppb that the use of such a
hydrocarbon feed in a hydrocarbon conversion process
utilizing a regenerable zeolite will result in a higher
retention of catalyst activity of the regenerated
catalyst. The improvement being longer catalyst life
expectancy because of the zeolite-containing catalysts
greater resistance to activity loss during catalyst
regeneration.
SUMMARY OF THE INVENTION
A principal object of the present invention is to
provide an improved hydrocarbon conversion process which
overcomes prior art zeolite-containing hydrocarbon
conversion catalyst stability problems by recognizing the
high sensitivity of zeolite catalysts to fluorine
compounds by controlling the fluoride concentration of
hydrocarbon feeds to such zeolite catalyzed processes to
less than 100 ppb, calculated as wt. elemental fluorine~
Using such a feed in a process which employs a regenerable
zeolite-containing catalyst results in an extension of the
useful life of the zeolite-containing catalyst.
Accordingly, a broad embodiment of the process of the
present invention is directed toward an improvement in a
hydrocarbon conversion process for catalytically
converting a hydrocarbon- and fluoride-containing feed
having a fluoride concentration substantially greater than
~304~)95
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100 ppb in the presence of a regenerable catalyst
comprising a crystalline zeolite at hydrocarbon conversion
conditions wherein the improvement requires treating the
feed prior to contact with the catalyst for removal of
fluoride to produce a treated feed containing less than
100 ppb fluoride calculated as wt. of elemental fluorine.
In another embodiment, a regenerable hydrocarbon
conversion process is provided which utilizes the steps
of: (a) subjecting a C~ 0 hydrocarbon feed to a
fluorine compound removal step to reduce the feed fluorine
content to below 100 ppb; (b) catalytically converting the
resulting fluorine-free C1-C10 hydrocarbon feedstock in
the presence of a regenerable crystalline zeolite-
containing hydrocarbon conversion catalyst where the
crystalline zeolite has a silica to alumina ratio greater
than 2; and, (c) regenerating the crystalline zeolite-
containing hydrocarbon conversion which has become
deactivated by the deposition of carbon in the form of
coke upon the catalyst by exposing the deactivated
catalyst to an OXygen-ContainincJ gas stream at conditions
sufficient to combust the coke and restore catalyst
activity. The process describecl above is useful in the
conversion of Cl to C10 aliphatic hydrocarbon containing
feedstocks in hydrocarbon conversion processes such as
paraffin dehydrogenation, oligomerization, alkylation,
aromatization, dehydrocyclodimerization, and the like.
In a preferred embodiment, the present invention is
directed to an improved process for the
dehydrocyclodimerization of a hydrocarbon feedstock
comprising C2 to C6 aliphatic components in the presPnce
of a regenerable ZSM-type zeolite catalyst. The
hydrocarbon feedstock initially undergoes a fluoride
compound removal step to reduce the concentration of
fluoride in the feed to below 100 ppb, calculated as wt.
of elemental fluorine. The feedstock thusly treated is
catalytically dehydrocyclodimerized in the presence of a
130~95
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regenerable dehydrocyclodimerization catalyst comprised of
a ZSM-type srystalline zeolite. When deactivat~d by the
accumulation of carbonaceous deposits known as coke on the
catalyst, the catalyst is regenerated by exposing it to an
oxygen-containing gas at conditions sufficient to combust
the coke on the catalyst. Besides comprising a ZSM-type
zeolite component, the dehydrocyclodimerization catalyst
preferably comprises a gallium component, a phosphorus-
containing alumina component, and a refractory inorganic
oxide component.
DESCRIPTION OF THE DRAWING
The drawing presents C3 feed conversion results of
pilot plant testing performed on fresh and regenerated
dehydrocyclodimerization catalysts as a function of hours-
on-stream. The testing was performed using hydrocarbon
feedstocks containing 13,000 ppb, 500 ppb, and O ppb
levels of fluoride which were charged to a conversion zone
containing a zeolite-containing catalyst. The test
involved a number of regeneration cycles.
DETAILED DESCRIPTION
In its broadest aspect, the present invention
consists of reacting a hydrocarbon containing feedstock of
exceedingly low fluorine content (less than 100 wt. ppb
calculated on a ~luorine basis) over a zeolite-containing
hydrocarbon conversion catalyst where the æeolite-
containing catalyst is regenerable. It has been found,
surprisingly and unexpectedly, that a zeolite catalyst
employed in the instant process exhibits a higher level of
activity upon regeneration than a zeolite catalyst of the
prior art. This results in a catalytic process with a
longer catalyst life expectancy. This improved retention
of catalytic activity after one or more regeneration
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procedures increases the attractiveness of such a process
by allowing the catalyst of the instant invention to be
regenerated more times before ~eolite catalyst replacement
is required.
In accordance with the present invention, the
process disclosed herein involves in part a hydrocarbon
feed pretreatment step to reduce the level of fluoride
components in a hydrocarbon feedstock to below 500 ppb,
and preferably to below lOO ppb based upon the weight of
elemental fluorine in the treated hydrocarbon. The
hydrocarbon is pretreated before it is exposed to a
regenerable zeolite-containing hydrocarbon conversion
catalyst at hydrocarbon conversion conditions.
The terms "fluoride", "fluoride component", and/or
"fluoride-containing'l are used herein to describe any
chemical formulation containing elemental fluorine alone
or within its molecular structure. This includes fluorine
in its elemental and diatomic form and compounds
containing fluorine atoms and atoms of other elements.
The hydrocarbon-containing process streams from which
these materials are removed may be characterized as fluid
streams as they may be both gas~eous and liquid~ In a
refinery situation, it is anticipated that fluoride-
containing components may originate from fluoride-
containing catalysts such as boron trifluoride or aluminumfluoride, hydrogen fluoride, and the like, from a reactant
used in a fluorination step, or from by-products of a
hydrogen conversion reaction such as alkylfluorides
produced as a by~product of an HF alkylation reaction.
The previous description of potential sources of and types
of fluoride components in the hydrocarbon feed of the
present invention is not meant to restrict the instant
process. It is anticipated that hydrocarbon feedstocks
can become contaminated with fluoride components in a
refinery in a myriad of methods. The method that a
feedstock may become contaminated is not as important to
13~gS
this invention as is ~he treatment and processing of such
a contaminated feedstock.
A variety of methods are known in the art to remove
fluoride components from gaseous and liquid hydrocarbon
streams. One of the most common methods of removing these
fluoride-containing chemicals is to pass the fluid stream
through a bed of selective adsorbent such as alumina,
bauxite, silica gel, or activated charcoal. This is
normally accomplished using a fixed bed of the adsorbent,
but moving beds have also been utilized. For instance,
alumina is used to remove alkylfluorides from a liquid
hydrocarbon stream. Such fixed bed adsorbent systems are
commonly referred to as "guard beds" as their purpose as a
fixed "bed" of adsorbent is to "guard" a reactor full of
expensive catalyst from being contaminated with a catalyst
deactivator such as suifur or, as in this case, fluoride
components. It is anticipated that guard beds that are
useful in removing fluorides from hydrocarbon feedstocks
of the present invention could contain any compound, in
solid, gel, or liquid that is known to scavenge fluoride
compounds. It is also anticipated that such a guard bed
could manifest itself in any useful flowscheme known in
the prior art. As mentioned above, some useful adsorbants
including alumina, activated charcoal, and silica gel are
all known to be useful guard bed adsorbents. In addition,
zeolites, amorphous silica aluminas, crystalline silica,
and the like could all be usefully utilized in the instant
process. It is anticipated that for ease of operation, a
guard bed system would consist of two parallel guard bed
vessels, each containing a similar fluoride adsorptive
material. Having two guard bed vessels will enable one
guard bed vessel to be in operation while the other is
not. In this way, a continuous process can be maintained.
It is also possible that distinct beds of two or more
adsorbents or intimate mixtures of two or more fluoride-
scavenging adsorbents can be utilized in a fluoride guard
~30~095
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bed of the instant invention. Msthods of using liquids to
remove halogen components, including fluoride components
from hydrocarbon feeds are also well known and documented.
A basic aqueous solution works well in removing most
halogen-containing chemicals. U.S. Patent 3,917,733
describes a continuous process for treating a gaseous and
a liquid halogen-containing hydrocarbon stream
simultaneously and continuously to reduce said halogen
content of the hydrocarbon streams to low levels. The
treatment described in the '733 patent is accomplished
with alumina which becomes spent and is replaced on a
continuous basis. Such a process also is capable of
employing other fluoride-scavenging adsorbents besides
alumina. A continuous process as described in the '733
patent or similar, or other continuous adsorbent processes
known in the prior art would be particularly advantageous
as the fluoride removal step of the instant process as a
ontinuous fluoride removal step would result in a more
efficient overall process.
In summary, any process utilizing an adsorbent,
liquid, or some other known method to remove fluoride or
fluoride-containing components from a gaseous or liquid
hydrocarbon feed may be success~Eully employed as a portion
of the instant process. In fact, it is anticipated that a
two-bed zeolite catalyst containing hydrocarbon conversion
process could be successfully employed to remove fluorides
from a fluoride-containing hydrocarbon feed. Such a
process would utiliæe the crystalline aluminosilicate
zeolite in the ~irst reactor as a sacrificial catalyst
bed. The first reactor products could be separated to
recover reactants or sent in entirety to a second or
subsequent reactor containing a crystalline
aluminosilicate catalyst for further processing. The type
of process would be characterized in that the fluoride
content of the feed would be reduced to below 100 ppb in
the first zeolite catalyst containing reactor and
13a~4~9~i
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processed in subsequent zeolite catalyst containing
reactors. Whatever process is employed to remove
~luorides from a fluoride containing hydrocarbon feed must
however be capable of reducing the fluoride content of the
said hydrocarbon to below 500 ppb and preferably to a
level below 100 ppb.
The fluoride removal step can be useful on any
hydrocarbon feeds containing more than 100 ppb fluorides.
However, due to the erection and operational costs o~ a
fluoride removal system, it is anticipated that such a
system will be most useful for removing fluorides from
fluoride-containing hydrocarbon feeds containing greater
than 500 ppb fluorides.
The hydrocarbon conversion process disclosed as the
process of the presant invention comprises all hydrocarbon
conversion processes which employ a regenerable zeolite-
containing catalyst to accomplish a desired hydrocarbon
conversion reaction. Examples of such hydrocarbon
conversion processes which have been disclosed as
employing a regenerable zeolite--containing catalyst
include among others, catalytic cracking, catalytic
reforming, catalytic hydrotreating, alkylation of aromatic
and aliphatic hydrocarbons, dehydrocyclodimerization,
oligomerization, dehydrogenation, and so fortht It is
anticipated that the desired hydrocarbon conversion
reaction can take place in the presence of a regenerable
zeolite-containing catalyst in a reactor system comprising
a fixed bed system, a moving bed system, a fluidized bed
system, or in a batch-type operation; however, in view of
the fact that attrition losses o~ the valuable regenerable
zeolite-containing catalyst should be minimized and of the
well-known operation advantages, it is pre~erred to use
either a fixed bed catalytic system, or a dense phase
moving bed system such as is shown in U.S. Patent
3,725,249. It is also anticipated that the catalytic
system may comprise a single regenerable catalyst which
~3(~Q~5
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has been formulated with a zeolite or a mixture of two or
more unique re~enerable catalysts of which at least one
has been formulated with a zeolite component.
The zeolite component of the regenerable zeolite~
containing hydrocarbon conversion catalyst may be any
natural or synthetic zeolite known. Zeolitic materials
are typically ordered, porous crystalline aluminosilicates
having a definite crystalline structure as datermined by
X-ray diffraction, within which there are a large number
of smaller cavities which may be interconnected by a
number of still smaller channels or pores. These cavities
and pores are uniform in size within a specific zeolitic
material. Since the dimensions o~ these pores are such as
to accept for adsorption molecules of certain dimensions
while rejecting those of larger dimensions, these
materials have come to be known as "molecular sieves" and
are utilized in a variety of ways to take advantage of
these properties. Zeolites may be represented by the
empirical formula:
MnO2/n A12O3 xSio2 yH2O
in which n is the valence of M which is generally an
element of Group I or II, in paxticular, sodium,
potassium, magnesium, calcium, strontium, or barium and x
is generally equal to or greater than 2.
Prior art techniques have resulted in the formation
o~ a great variety of synthetic zeolites~ The zeolites
have come to be designated by letter or other convenient
symbols, as illustrated by zeolite A (U.S. Patent
2,882,243), zeolite X (U.S. Patent 2,882,244), zeolite Y
30 (U.S. Patent 3,110,007), zeolite ZK 5 (U.S. Patent
3,247,195), zeolite ZK-4 (U.S. Patent 3,314,752), zeolite
ZSM-5 (U.S. Patent 3,702,886), zeolite ZSM-ll (U.S. Patent
3,709,979), zeolite ZSM-12 (U.S. Patent 3,832,449),
zeolite ZSM-20 (U.S. Patent 3,972,983), zeolite ZSM-35
~3~41~9~;i
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(U.S. Patent 4,016,245), zeolite ZSM-38 (U.S. Patent
4,046,859), and zeolite ZSM-23 (U.S. Patent 4,076,842), to
name but a few.
The SiO2/Al2O3 ratio of a given zeolite i6 often
variable. For example, zeolite X can be synthesized with
SiO2/Al2O3 ratios of from 2 to 3; zeolite Y, from 3 to
about 6. In some zeolites, the upper limit of the
SiO2/Al2O3 ratio is unbounded. ZSM-5 is one such example
wherein the SiO2/A1203 ratio is at least 5 and up to
infinity. U.S. Patent 3,941,871 ~Re. No. 29,948~
discloses a porous crystalline silicate made from a
reactivn mixture containing no deliberately added alumina
in the recipe and exhibiting the X-ray diffraction pattern
charactPristic of ZSM-5 type zeolites. U.S. Patents
4,061,724, 4,073,865, and 4,104,294 describe crystalline
silicates or organosilicates of varying alumina and metal
content.
In a preferred embodiment, the zeolite-containing
catalyst of the present invention exhibits a silican to
alumina molar ratio of 2 or more. The æeolites disclosed
hereinabove as well as other known synthetic and naturally
occurring zeolites which have a silican to alumina molar
ratio greater than 2 are all candidates as the preferred
zeolitic component of the regenerable zeolite-containing
hydrocarbon conversion catalyst of the instant invention.
It is an important aspect of the instant invention
that the zeolite-containing hydrocarbon conversion
catalyst be regenerable by the oxidation or burning of
catalyst deactivating carbonaceous deposits with oxygen or
an oxygen~containing gas. By "regenerable", it is meant
that at least a portion of the zeolite-containing
catalyst's initial activity can be recovered by combusting
the coke deposits on the catalyst with oxygen or an
oxygen-containing gas. The prior art is replete with
zeolite catalyst regeneration techniques. Some of these
regeneration techniques involve chemical methods of
~ ~.3~ 9~
-14-
increasing the activity of deactivated zeolites. Others
are related to processes or methods for regenerating
carbon (also known as coke~ deactivated zeolites by
combustion of the coke with an oxygen-containing gas
stream. For example, U.S. Patent 2,391,327 (~ekler)
discloses the regeneration of catalysts contaminated with
carbonaceous deposits with a cyclic flow of regeneration
gases. U.S. Patent 3,755,961 relates to the regeneration
of coke-containing crystalline zeolite molecular sieves
which have been employed in an absorptive hydrocarbon
separation process. The process involves the continuous
circulation of an inert gas containing a quantity of
oxygen in a closed loop arrangement through the bed of
molecular sieves. U.S. Patent 4,~0,144 relates to the
use of a circulating gas to regenerate a coke deactivated
zeolite-containing catalyst. The circulating gas is
maintained at a low moisture level by purging wet gases
from the loop while simultaneously introducing dry gases
to the loop. The conditions and methods at which a
zeolite-containing catalyst may be regenerated by coke
combustion with oxygen vary. It is typically desired to
perform the coke combustion at conditions of temperature,
pressure, gas space velocity, etc. which are least
damaging thermally to the catalyst being regenerated. It
is also desired to perform the regeneration in a timely
manner to reduce process down-time in the case of a fixed
bed reactor system or equipment size in the case of a
continuous regeneration process.
Optimum regeneration conditions and methods are
those typically disclosed in the prior art as mentioned
hereinbefore. To reiterate, zeolite regeneration is
typically accomplished at conditions including a
temperature range of from 315C to 500C or higher, a
pressure range of from atmospheric to 20 atmospheres, and
a regeneration gas oxygen content of from 0.1 to 23.0 mole
percent. The oxygen content of the regeneration gas is
~30~1~9S
typically increased during the course of a catalyst
regeneration procedure based on catalyst bed outlet
temperatures in order to regenerate the catalyst as
quickly as possible while avoiding catalyst-damaging
process conditions.
The regeneration of zeolite catalysts is preferably
conducted in two steps, a main burn and a clean-up burn.
The main burn constitutes the principal portion of the
regeneration process. With the molecular oxygen level
maintained below about 1.0 mole percent during this main
burn, the burning of the coke consumes a major portion of
the oxygen so that molecular oxygen in amounts less than
that found at the reactor inlet is detected in the gaseous
stream at the outlet of the reactor vessel. Near the end
of the main burn, oxygen consumption across the catalyst
bed will start to decrease producing an increasing
concentration of molecular oxygen at the exit of the
reactor. This point in the main burn is referred to as
the oxygen breakthrough and essentially marks the end of
the main burn. At this point, the clean-up burn portion
of the regeneration is initiated by gradually increasing
the molecular oxygen concentration in the gas introduced
to the catalyst bed. The oxygen concentration can usually
be slowly increased to about 7.0 mole percent or greater
until the end of the clean-up burn which is indicated by a
gradual decline in the temperature at the exit of the
catalyst bed until the inlPt and outlet temperatures of
the catalyst bed merge, i.e. there is essentially no
temperature rise across the bed.
U.S. Patent 4,645,751 discloses a specific method
of regenerating a noble metal containing zeolite catalyst.
The method disclosed involves a first coke-burning step
followed by a second noble metal redispersing step. It is
anticipated that reactivation techniques such as the noble
metal redispersing technique taught in the '751 patent may
be an aspect of the regeneration technique utilized in the
~.30~95
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practice of the present invention. Such reactivation
techniques are utilized to restore catalytic activity
beyond that gained through zeolite catalyst coke
co~bustion methods alone. ~nother example of zeolitic
catalyst activity reactivation techniques disclosed in the
prior art is found in U.S. Patent 4,649,127 which
describes the use of a hydrogen contacting step followed
by a polar solvent contacting to reactivate nitrogen
poisoned catalysts. The regenerable zeolite hydrocarbon
conversion catalyst utilized in the instant invention must
exhibit catalyst activity recovery following a coke
burning regeneration step. In addition to the coke
burning step, other methods of zeolite reactivation known
in the prior art may be employed in the regeneration of
the zeolite-containing catalyst of the present invention
to further enhance the activity of the regenerated
catalyst.
It is a preferred embodiment of the hydrocarbon
conversion process of the present invention that the
hydrocarbon feedstock employed in the process is comprised
of C1-C10 aliphatic and aromatic: hydrocarbons. The
hydrocarbon feedstock may contain minor amounts of larger
carbon number hydrocarbons and/or hydrocarbon feedstock
diluents such as, but not limited to, hydrogen, nitrogen,
oxygen, carbon dioxide, steam, and so forth. It is also
an aspect of the preferred process that the Cl-C10
aliphatic and aromatic hydrocarbon feedstock may comprise
a pure component selected from the Cl-C10 aliphatic and
aromatic hydrocarbons, a mixture of two pure components
such as ethane and ethylene and so forth up to and
including a feedstock containing a mixture of many to all
Cl-C10 aliphatic and aromatic hydrocarbons. That is to
say, a C1-C10 aliphatic and aromatic hydrocarbon feedstock
may contain one or more Cl-ClO aliphatic and aromatic
hydrocarbon components. Cl-C10 aliphatic and aromatic
hydrocarbons were chosen as the preferred feedstock for
4~5
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the instant process for a variety of reasons. It was felt
that Cl-C10 hydrocarbons were the most likely to contain
deleterious amounts of fluoride components in the form of
alkylfluorides. It was also felt that processes employing
such Cl-C10 hydrocarbon feedstocks such as catalytic
reforming, dehydrocyclodimerization, hydrogenation, and
the like are typically operated at reaction conditions
which can cause zeolite-containing catalysts to deactivate
quickly by coke accumulation th~reon resulting in freguent
catalyst regeneration requirements. Therefore, the
process of this invention is particularly suited to
extending the viability of regenerable zeolite catalysts
employed in hydrocarbon conversion processes utilizing a
Cl-C10 aliphatic and aromatic hydrocarbon feedstock.
In preferred embodiments of the present invention,
the desired hydrocarbon conversion processes of the
present invention are dehydrogenation, oligomerization,
alkylation, and dehydrocyclodimeri-zation.
Dehydrogenation is a well-known hydrocarbon
conversion process. Dehydrogenation may be effected by
reacting dehydrogenatable hydrocar-bons in a
dehydrogenation process at dehydrogenation conditions in
the presence of certain zeolite-containing catalytic
compositions of matter. The particular dehydrogenation
catalysts which are employed are well known in the art and
comprise such compounds as nickel, and iron, and the like
composited on a solid zeolite-containing support. Some
dehydrogenation processes have employed, in addition to
the dehydrogenation catalysts, an oxidation catalyst in
the reaction process. The presence of the oxidation
catalyst is precipitated by the fact that it is
advantageous to oxidize the hydrogen which is produced by
contact with an oxygen-containing gas in order to maintain
the desired reaction temperature and reaction e~uilibrium.
For example, styrene, which is an important chemical
compound utilized for the preparation of polystyrene,
~;~04~9~5
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plastics, resins or synthetic elastomers such as styrene-
butadiene rubber, etc., may be prepared from the
dehydrogenation of ethylbenzene. A variety of
dehydrogenatable hydrocarbons are also Cl-C10 aliphatic
and aromatic hydrocarbons. Examples of such hydrocarbons
which are susceptible to dehydrogenation in a
dehydrogenation process utilizing known zeolite-containing
dehydrogenation catalysts include lower alkyl-substituted
aromatic hydrocarbons such as ethylbenzenel
diethylbenzene, isopropylbenzene, o-ethyltoluene,
m-ethyltoluene, p-ethyltoluene, o-isopropyltoluene,
m-isopropyltoluene, p-isopropyltoluene, ethylnaphthalene,
propylnaphthalene, isopropylnaphthalene,
diethylnaphthalene, etc.; paraffins such as ethane,
propane, n-butane, isobutane, n-pentane, isopentane,
n-hexane, n-heptane, n-octane, n-nonane, n-decane, and
branched chain isomers thereof; cycloparaffins such as
cyclobutane, cyclopentane, cyclohexane,
methylcyclopentane, methylcyclohexane, ethylcyclopentane;
olefins such as ethylene, propylene, 1-butene, 2-butene,
l-pentene, 2-pentene, 1-hexene, 2-hexene, 3-hexene, and
branched chain derivatives thereo~, etc. It is intended
to include any zeolite-containing dehydrogenation catalyst
disclosed in the prior art as a regenerable zeolite-
2~ containing catalyst of a preferred dehydrogenationconversion process of the present invention. The
dehydrogenation of dehydrogenatable hydrocarbons such as,
for example, ethylbenzene, propane, or ethane is effected
by contacting the desired dehydrogenatable hydrocarbon
with the aforesaid regenerable zeolite-containing
hydrocarbon conversion catalyst. Dehydrogenation
conversion conditions typically are in the range of from
350C to about 750C and at reaction pressures ranging
from about 0O1 to about 20 atmospheres. The exact
dehydrogenation conditions are, however, a function of the
particular hydrocarbon undergoing dehydrogenation. Other
~L30~
--19--
reaction conditions will include a Liquid Hourly Space
Velocity based on the hydrocarbon charge of from about 0.1
to about 20 hr 1. Diluents such as steam, hydrogen,
oxygen, nitrogen, and the like may he added to the feed or
at any point in the reactor. The number of reactors or
catalyst beds utilized in the dehydrogenation reaction
zone may be one or more than one, and as previously
mentioned, the dehydrogenation catalyst may be employed in
conjunction with an oxidation catalyst to increase process
efficiency. The above description of dehydrogenation
processing conditions and methods is meant to be exemplary
in nature and is not meant to restrict the possible
dehydrogenation process schemes able to be practicad
within the scope of this invention.
A second preferred hydrocarbon conversion process
of the instant invention is oligomerization. The
oligomerization process is well known in the prior art.
In a brief description, the oligomerization process
comprises uniting hydrocarbon olefins into larger olefinic
hydrocarbon molecules consisting of multiples of the
original molecules. Therefore, the oligomerization of,
for example, ethylene (C2=) wou]d produce C4, C6l and
perhaps C8 ol~fins or dimers, trimers, and tetramers of
the original ethylene feed molecule. In the case of a
mixed light olefin feed, combinations of dimers, trimers,
and perhaps tetramers and more highly substituted
molecules comprising a mixture of the mixed feed olefins
would be produced. In general, the feedstock to an
oligomerization reactor might comprise one or a mixture of
two or more olefins containing from 2 to 10 carbon atoms,
and preferably containing from 2 to about 6 carbon atoms
such as ethylene, propylene, butene-l, butene-2,
pentene-1, pentene-2, and pentene-3. Oligomerization may
then be effected by reacting the olefin in the presence of
a zeolite-containing catalyst at oligomerization
conditions which includes a temperature in the range of
~30~0~S
~20-
from about -20C to about 120C, the preferred range being
from about 30C to about 80C, and a pressure in the range
of from about 5 to about 68 atmospheres. The pressure
which is utilized may be the autogenous pressure provided
for by the feedstock, if in gaseous phase, or, the
feedstock may supply only a partial pressure, the
remainder of such pressure being provided by the
introduction of an inert gas such as nitrogen, helium,
argon, etc. into the reaction zone. As stated
hereinabove, the products of the oligomerization reaction
comprise mainly dimers, trimers, and tetramers of the
original olefinic reactant or reactants. Such
oligomerization products are useful in further processing
such as in the production of linear alkylbenzenes, and as
a motor fuel constituent among other uses. It is of
course an important aspect of the present invention that
the oligomerization reaction take place in the presence of
a regenerable zeolite-containing catalyst utilizing a feed
that has been pretreated to reduce the fluoride content
therein to below 100 ppb. It is also an aspect of the
preferred oligomerization process that the zeolite have a
silicon to aluminum molar ratio of 2 or more and that the
zeolite-containing catalyst is regenerable by combustion
of coke thereon with an oxygen-containing gas at
regeneration conditions.
Alkylation is a third preferred hydrocarbon
conversion process of the instant invention. Motor fuel
alkylation and aromatic alkylation utilizing a zeolite
catalyst comprise some of the various types of alkylation
processes which can be accomplished utilizing a Cl-C10
aliphatic and aromatic hydrocarbon feedstock which has
been first treated to reduce the fluoride content therein
to less than 100 ppb. Motor fuel alkylation is achieved
as a result of the reaction between an isoparaffin and an
olefin. The motor fuel alkylate product is particularly
useful as a high octane blending stock in gasoline. The
~30~0~S
use of a crystalline aluminosilicate was disclosed in U~S.
Patent 3,251,902 among others as an effective motor fuel
alkylation catalyst. The alkylation of aromatics such as
benzene with olefins such as ethylene, propylene, and so
forth is also well known in the prior art for producing
such useful aromatic products as ethylbenzene and cumene
to mention but a few. Such products are useful as plastic
precursors, as feedstock for other petrochemical processes
and so forth. Processing schemes and conditions useful in
various alkylation reactions vary widely depending upon
feedstock, catalyst, whether the reaction is gas phase or
liquid phase, and so on. The use of a zeolite-containing
regenerable alkylation catalyst in a process for the
alkylation of an olefin with a paraffin while not common
is disclosed in the prior art such as in U.S. Patent
3,778,489. Conditions suitable for the alkylation of such
a feedstock in the presence of a zeolite-containing
catalyst include a temperature of from -60C to 100C, a
pressure of from 1 to 20 atmospheres, an olefin to
paraffin molar feed ratio of from 1:1 to 1:20, and a
liquid hourly space velocity of from 0.1 to 20.
The use of zeolite-containing catalysts in the
alkylation of aromatic hydrocarbons is well known and
documented such as in U.S. Patent 4,185,040 which
describes a crystalline aluminosilicate zeolite catalyst
and its usefulness in the alkylation of an aromatic with a
c2-C4 olefin. Process conditions sufficient to promote
the alkylation of an aromatic such as benzene with a C2-C4
olefin in the presence of a regenerable zeolite-containing
cataly~t include a temperature of from 80C to 400C, a
pressure of from 1 to 40 atmosphares, an aromatic to
olefin mole ratio of from l:1 to 20:1, and a liquid hourly
space velocity of from 0.1 to 20. Process flow schemes,
process combinations, the use of cofeeds, etc. are all
applicable to the aromatic alkylation conversion process
of the present invention. It is therefore an aspect of
~;~04~9S
-22-
the preferred alkylation conversion process of the instant
invention that the alkylation reaction be performed at any
conditions and usinq any method disclosed in the prior art
which utilizes a regenerable zeolite-containing catalyst.
Dehydrocyclodimerization is the final preferred
process of the present invention.
Dehydrocyclodimerization is a process utilizing reactants
comprising paraffins and olefins, containing from 2 to 6
carbon atoms per molecule. These reactants are reacted
over a catalyst to produce primarily aromatics, H2 and
light ends as by-products. Typically, the
dehydrocyclodimerization reaction is carried out at
temperatures in excess of 260C using dual functional
catalysts containing acidic and dehydrogenation
components. These catalysts include crystalline
aluminosilicate zeolite~ which have been success-fully
employed as catalyst components for the
dehydrocyclodimerization reaction.
Many regenerable zeolite-containing catalysts have
been disclosed in the prior art as useful for the
dehydrocyclodimerization of C2-C6 aliphatic hydrocarbons.
These catalysts as well as processe~ employing such
catalysts are disclosed as potential catalysts and
processing schemes of the preferred
dehydrocyclodimerization process of the present invention.
It is most preferred that the hydrocarbon
conversion process of the instant invention comprise first
subjecting a C2~C6 aliphatic hydrocarbon feedstock to a
~luoride removal step to reduce the concentration of
fluoride in said feed to below 100 ppb. The treated feed
is then contacted with a ZSM-type zeolite-containing
catalyst in a dehydrocyclodimerization reaction zone at
dehydrocyclodimerization conditions followed by
regeneration of the coke deactivated zeolite catalyst in
the presence of an oxyyen-containing gas. The ZSM zeolite
component of the preferred dehydrocyclodimerization
~l304C19~
-23-
catalyst is preferably ZSM-5. The
dehydrocyclodimerization catalyst preferably contains, in
addition to a ZSM-5 zeolite component, from 0.1 to 5 wt.%
of a gallium component, and from 30 to 70 wt.% of a
phosphorus-containing alumina component. It is also
preferred that the phosphorus to alumina ratio of the
phosphorus-containing alumina ranges from 1:1 to 1:100.
U.S. Patent 4,636,483 describes the preferred
dehydrocyclodi-merization catalyst.
It has not been intended through the description of
the four preferred hydrocarbon conversion processes
hereinabove to limit the hydrocarbon conversion aspect of
the process of the present invention. As previously
stated, the instan~ process will be useful in hydrocarbon
conversion processes which utilize a regenerable æeolite
to maintain regenerated zeolite-containing catalyst
activity by first treating said hydrocarbon feed to reduce
the fluoride content therein to below 500 ppb and
preferably below 100 ppb. Additionally, it is nct
intended to limit the scope of the preferred hydrocarbon
conversion processes useful in the instant process by the
generic description of said processes given above. The
only limitation placed on said processes is that the
feedstock useful in such preferred processes must be
limited at most to C1-C10 aliphatic and aromatic
hydrocarbons, that catalysts useful in said processes must
be regenerable by coke combustion and that the catalyst
must contain a zeolite with a silicon to alumina molar
ratio greater than 2. It is left up to the prior art to
limit the scope of hydrocarbon conversion processes useful
in the instant invention based upon the limitations set
forth herein.
It is an aspect of this invention that the
hydrocarbon conversion process be a complete process.
That is to say, the hydrocarbon conversion process will
,..
.~
13~9~;
-~4-
comprise a reaction section and other sections such as gas
recycle, liquid recycle, product rPcovery, and the like
such that the process is viable and efficient. Examples
of some of the product recovery techniques that could be
employed alone or in combination in the product~recovery
zone of a hydrocarbon conversion process are:
distillation including vacuum, atmospheric, and
superatmospheric distillation; extraction techniques
including, for example, liquid/liquid extractions,
vapor/liquid extractions, supercritical extractions and
others; absorption techniques, adsorption techniques, and
any other known mass transfer techniques which can achieve
the recovery of the desired products.
The following examples will serve to illustrate
certain specific embodiments of the herein disclosed
invention. The examples should not, however, be construed
as limiting the scope of the invention as set forth in the
claims as there are many variations which may be made
thereon without departing from the spirit of the
invention, as those of skill in the art will recognize.
EXAMPLE I:
This example introduces methods used for preparing
and/or determining th~ fluoride content of fluoride-
containing light hydrocarbon feedstocks. Three propane
feedstocks prepared and/or evaluated utilizing the method
as set forth herein below were subsequently tested in
Example II.
The first propane feedstock was analyzed directly
and determined to contain 13 ppm (13,000 ppb) fluoride
therein. A spectrophotometric analysis was used to
determine the propane fluoride content. The method used
consisted of first burning a known weight of propane feed
with a stainless steel burner in a Wickbold quartz-tube
oxy-hydrogen combustion apparatus. The combustion
~3~4~9~i
-25-
products were absorbed in a 25 ml solution of 2% boric
acid that had been subsequently diluted with water from an
apparatus cleaning step. The solution was then treated
wi~h 5 ml of formaldehyde to remove excess peroxides and
heated until 70 ml of solution remain. The 70 ml of
fluoride-containing solution was then diluted to 100 ml.
It was necessary to determine the proper aliquot
empirically from a dilution of the diluted absorber
solution containing no fluoride reagent. 40 ml of water
and 10 ml of a fluoride reagent prepared by mixing equal
volumes of a solution of 2.87 g SPADNS Eastman Kodak 7309
(4-5-dihydroxy-3-(p~sulophenylazo)-2,7-naphthalene-
disulfonic acid, trisodium salt) in 500 ml water and a
zirconyl chloride solution comprising 0.133 g zirconyl
chloride, 350 ml conc HCl diluted to 500 ml were added to
a 100-ml volumetric flask~ Using a Mohr pipet, 0.2 ml of
the diluted absorber solution was transferred to the flask
containing water and fluoride reagent and the degree of
bleaching of the fluoride xeagent was noted. Diluted
absorber solution was added to the reagent flask in 0.2 ml
increments until a suitable degree of bleaching was
obtained. The final solution was diluted to the 100 ml
mark with water, mixed well, ancl the fluoride
concentration was determined from a prepared calibration
curve based upon the volume of absorber solution used.
The fluoride contents of the propane feeds
containing 500 ppb and essentially o ppb fluorides were
determined in a different manner. In both cases, the
propane feed was pretreated by passing the feed across a
guard bed containing a gamma-alumina adsorbent at 230C
and at from 13.6 to 17.0 atmospheres. The guard bed was
replaced and the alumina analyzed for fluorides until, in
the case of the second feedstock, a trace of fluoride was
found on the guard bed alumina and, in the case of the
third feedstock, no fluorides were detected on the
alumina. The second and third feedstocks were then
~l3at~ s
-26-
processed in the pilot plant per the procedure established
in Example II and a representative sample of the spent
catalyst from Example II was then analyzed for fluoride.
From the spent catalyst fluoride analysis, and based upon
the weight of feed processed, it was determined that the
feedstock prepared for the second series of tests
contained at least 500 ppb fluoride and the feedstock
prepared for the third series of tests was essentially
fluoride-free.
EXAMPLE II:
In order to demonstrate the retention of catalytic
activity of a regenerable zeolite-containing catalyst when
processing a feedstock containing less than 100 ppb of
fluoride, a hydrocarbon conversion catalyst disclosed in
lS U.S. Patent 4,636,483 was prepared by the method set forth
below. A first solution was prepared by adding phosphoric
acid to an aqueous solution of hexamethylenetetramine
(HMT~ in an amount to yield a phosphorus content of the
finished catalyst equal to about 11 wt.~. A second
solution was prepared by adding a ZSM-5 type zeolite to
anough alumina sol, prepared by digesting metallic
aluminum in hydrochloric acid, to yield a zeolite content
in the finished catalyst equal to about 67 wt.~. These
two solutions were commingled to achieve a homogeneous
admixturP of HMT, phosphorus, alumina sol, and zeolite.
This admixture was dispersed as droplets into an oil bath
maintained at about 93C. The droplets remained in the
oil bath until they set and formed hydrogel spheres.
These spheres were removed from the oil hath, water
~0 washed, air dried, and calcined at a temperature of about
482C. A solution of gallium nitrate was utilized to
impregnate the spheres to achieve a gallium content on the
finished catalyst aqual to about 1 wt.%. After
~ 30~L C99S
-27-
impregnation, the spheres were calcined a second time, in
the presence of steam, at a temperature of about 649C.
The hydrocarbon conversion catalyst as prepared
above was utilized in a dehydrocyclodimerization pilot
plant to convert a propane feed into aromaticsO Three
series of tests were performed. Each series was performed
with a feedstock containing different amounts of fluoride.
Each cycle consisted of a pilot plant conversion run
lasting about 100 hours, followed by a catalyst
regeneration step. The amounts of fluoride in the feed
were 13,000 ppb, 500 ppb, and essentially 0 ppb for s~ries
1, 2, and 3, respectively. The zeolite-containing
catalyst was exposed to the propane feedstock and tested
for dehydrocyclodimerization performance in identically
the same manner in all series and cycles using a flow
reactor processing a feed comprising 100% propane and
varying levels of fluoride. The operating conditions used
in the performance test comprised a reactor pressure of 1
atmosphere, a liquid hourly space velocity of 0.8 hr~l,
and a reaction zone inlet temperature of about 538C. The
change in the conversion of the feed over ~00 hours of
processing was monitored.
Following each pilot plalnt run, the sa~e catalyst
was regenerated and rerun for approximately 100 hours
while processing a feedstock with the same level of
fluoride. This testing was repeated for four or five
times for each test series, with each pilot plant run of
the catalyst comprising one cycle in the series.
The catalyst regeneration method was similar in all
cases. ~he procedure consisted of placing the coke
deactivated zeolite-containing catalyst in a 0.28 meter
(ll-inch) bed and establishing an inert gas flow across
the catalyst bed at a gas hourly space velocity of 4800
hr~1. The corresponding superficial veloeity was 0.5
m/sec (1.6 ft/sec) and the regeneration was performed at
atmospheric pressure. The regeneration temperature and
13~)40~5
-28-
oxygen content were varied over the 7-hour regeneration
based upon the schedule below:
Hours Temp. (C~ 2-~ mole %
0-1 490
1-2 490 2
2-3 490 5
3-4 490 20
4-5 490-540 20
5-7 540 20
After regeneration, the catalyst was cooled and then
reloaded into the dehydrocyclodimerization pilot plant for
another cycle of testing. Each cycle is counted upon the
completion of a pilot plant run. Thus, the pilot plant
testing of the fresh catalyst would be cycle number 1. A
four-cycle catalyst will have undergone three
regenerations.
The surprising pilot plant results of the series of
tests can be found in the attached Figure. The Figure is
a plot of C3 conversion over time in the pilot plant.
First and last cycle pilot plant conversion results are
plotted for each of the series of three tests. Before
discussinq the results, it should be noted that the
initial cycle results using a fresh catalyst in each of
the three series were essentially identical. ~his result
indicates that the pilot plant test results are
reproducible. The first series utilized a C3 feedstock
containing 13 ppm of fluoride. After four cycles in which
three catalyst regeneration steps had been performed, the
catalyst lost 12% of its original C3 conversion ability.
The second series utilized a C3 feedstock containing 500
ppb fluoride. After five cycles in which four catalyst
regenerati~n steps had been performed, the catalyst lost
about 6% of its original C3 conversion ability. The final
series, series 3, utilizing an essentially fluoride-free
13~4~9~;
-29-
C3 feed exhibited no loss of C3 conversion over five
cycles of testing including four regenerations.
It can be readily seen from these results that the
removal of fluoride compounds from a hydrocarbon feedstock
and the processing of such a feedstock containing very low
levels of fluoride is highly desirable in maintaining the
activity of a zeolite-containing regenerable hydrocarbon
conversion catalyst. The presence of even small amounts
~500 ppb) of fluorides caused appreciable catalyst
activity loss after only four regenerations, thus
providing the impetus for removing as much detrimental
fluorides from the feed as possible.
,:. , , :
