Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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WO 96/37299 r~ 96/07'746
PROCESS FOR ~7 ~ N ~ TING A HIGH 'L
TREATED ZEOLITE t-~Tl~nysT
Rll~ ND OF T~}E l~.v~ ON
The subject of the present invention is a process for
the regeneration of a hydrocarbon reforming catalyst
which has been deactivated due to buildup of
carbonaceous material on the catalyst. In particular,
the present invention relates to a process for
regenerating a high temperature treated zeolite
catalyst.
Platinum con~;n;ng catalysts are widely used in the oil
refining and petrochemical industries, and are
particularly important in a reforming process where
lS paraffins, olefins and naphthen-s are converted to
aromatic compounds. Conventional reforming catalysts
typically include one or more metals, most typically
platinum, dispersed on a base, and may also include a
b;~;ng agent for ~ing physical support to the base,
and chloride to provide an acidic function. Typically,
the catalyst base is alumina, but recently molecular
sieve based catalysts have been found to be effective
for reforming reactions.
Catalytic compositions containing zeolites are well
known in the industry and recently the use of L-zeolites
in combination with other specified catalytic components
have been found to be particularly preferred for
- reforming. The aromatic compounds produced by such a
catalytic conversion are valuable to a refiner due to
their higher octane rating, and may be recovered from
the reforming product for further processing and
reaction in the petrochemical industries. The L-zeolite
catalysts are particularly effective for converting C6
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and C~ non-aromatic hydrocarbons which normally ~oil
between 125~F and 225~F, to benzene and toluene.
In the reforming process, a hydrocarbon feedstock is
p~cc~ through a catalyst-cont~i ni ~ reactor in the
presence of h~dLo~en at an elevated temperature. In the
reactor and upon contact with the reduced or activated
catalyst, some of the paraffins, olefins and naphthenes
in the feedstock react to form a more desired, higher
octane aromatic product. In the course of typical
reforming operations, the catalysts will typically
become deactivated due to the deposition of carbonaceous
material or "coke" upon the catalyst, and/or scintering
or poisoning of the catalytic metal particles.
Reforming catalysts that have been deactivated in this
manner are typically regenerated by a method comprising
a coke burning step, a platinum redispersion step, and a
reduction step. In the coke burning step, the catalyst
~0 is contacted by an oxygen cont~; n; ng gas at elevated
t~ ~~rature to burn off coke deposits. In most cases,
the ~x;~um coke burn temperature ~ 900~F.
Platinum redispersion involves contacting the catalyst
with a halogen compound and optionally oxygen and/or
water at temperatures between 700~F and 1000~F. After
platinum redispersion, the temperature is usually
lowered and the reactor is purged with inert gas prior
to starting catalyst reduction. The catalyst is then
reduced by contacting with hydrogen.
Many variations of this method have been patented. The
following patents apply specifically to the regeneration
of reforming catalysts comprising a Group VII metal on a
zeolite support: U.S. Patent No. 3,986,982 (Crowson et
al); U.S~ Patent No. 4,359,400 (Landolt et al); U.S.
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WO 96/37299 ~ 6/07746
Patent No. 4,493,901 (Bernard et al~; U.S. Patent No.
4,810,683 (Cohn et al); U.S. Patent No. 4,914,068 (Cross
et al); U.S. Patent No. 4,92S,819 (Fung et al); U.S.
Patent No. 5,106,798 (Fung et al); U.S. Patent No.
5,155,074 (Mohr et al); and U.S. Reissue 34,250 (Van
Liersburg et al). The methods in these patents have in
common a coke burn at temperatures greater than or equal
to 800~F and platinum redispersion using a halogen
cont~ining gas.
U.S. Patent No. 5,155,075 (Innes et al) describes a
method for regeneration of a Pt-L-zeolite reforming
catalyst wherein the coke burn is done at temperatures
less than 780~F. The catalyst is then r~ c~A with
hydrogen while increasing the temperature to ~; ~t~m
between 900~F and 1000~F. Since the coke burn is done
at low temperatures, platinum redispersion is not
needed. The regeneration process is therefore halogen-
free. U.S. Patent No. 5,073,529 also describes a
halogen-free regeneration method, but does not limit the
carbon burn temperature to less than 800~F.
U.S. Patent No. 5,270,272 (Galperin) describes a
regeneration method wherein sulfur is removed from the
catalyst by treatment with ammonia in nitrogen or
hydrogen at very high temperatures. Since contacting
the catalyst with ammonia at high temperatures causes
scintering of the platinum, it is necessary to
redisperse the platinum using halogen ~.~ounds prior to
reduction.
-
R~c~tly, it has been discovered that the fouling rateof certain zeolitic reforming catalysts can be greatly
reduced by treating these catalysts in a reduced state
at temperatures ranging from 1025~F to 1275~F. One such
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high treatment ~ e is described in U.S. Patent No.
5,382,353 (Mulas~ey et al)~ As a result of the high
temperature treatment, the catalyst runs two to six
times as long before regeneration is needed.
Alternatively, the increased resistance to fouling makes
it possible to operate at higher throughputs and/or
lower hyd~o~en to hydrocarbon ratios. It also allows
heavier feedstocks to be processed. Each of these
process i~L ~ve~cnts has a substantial economic benefit.
Unfortunately, the regeneration processes of the prior
art do not fully restore the fouling resistance of the
high temperature treated catalyst. It has also been
found that repeating the original high temperature
treatment prior to the second reaction period usually
leads to lower activity and a higher start of run
temperature. The economic benefit of the high
temperature treatment has thus far been mostly limited
to the first cycle. A process which offers a successful
and practical solution to the problem of regenerating
such catalysts without substantial loss in activity or
stability would be of great value to the reforming
industry.
Accordingly, it is an object of the present invention to
provide a process for regenerating a high temperature
treated zeolite catalyst.
Another object of the present invention is to provide a
process which can efficiently and effectively regenerate
a high temperature treated zeolite without sacrificing
catalytic activity or stability.
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These and other ob~ects of the present i~.v~Lion will
become apparent upon a review of the following
specification and the claims app~n~ thereto.
S~MMARY OF T~E l~.v~ ON
In accordance with the foregoing objectives, the present
invention provides a process for regenerating a high
temperature treated reforming catalyst, which has been
deactivated due to coke deposition, and which catalyst
comprises at least one Group VIII metal supported on a
zeolite base. For the purpose of this invention, a high
temperature treated catalyst is defined as a catalyst
that has been treated in an inert gas or reducing
atmosphere at a temperature greater than or equal to
1025~F.
The process comprises the steps of
(a) contacting the catalyst with an oxygen
con~;n;ng gas at temperature and for a time
sufficient to remove at least part of the coke
deposited on the catalyst; then
(b) reducing the catalyst with a hydrogen
containing gas; and
(c) treating the catalyst in an inert-gas or
reducing atmosphere at temperatures in the
range of 975~F to 1150CF.
It is preferred that the high treatment step be
conducted in manner which limits the water concentration
in the effluent gas to 200 ppmv or less.
The process of the present invention regenerates high
temperature treated catalysts with a ~in;~l-~ loss of
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WO 96/37299 1 _lIU_3~07~46
activity or run length. A ~ other factors, the
present invention recognizes that regeneration is
different from activation. The ~o~r~ature treatment is
different in the regeneration than in the activation.
Temperature treatments of 1150~F and above have been
found to be exL~ -ly detrimental if the catalyst has
been previously subjected to a treatment at temperatures
of above 1025~F, and thus the treatment range for the
final step of the present process is much lower than
when treating fresh catalyst. The present invention
permits one to run a reforming process for many cycles
while utilizing a zeolite catalyst which was originally
activated by a method comprising treatment with an inert
gas or hydrogen containing gas in the temperature range
of from 1025~F to 1275~F. The regeneration process of
the present invention avoids any substantial lowering in
the catalytic activity or stability of the high
temperature treated catalyst. Such high temperature
treated catalysts exhibit i~y~o~ed activity and a longer
run life. The process of the present invention permits
one to utilize these catalysts and take advantage of
their i~ oved activity and longer run life for numerous
cycles.
BRIEF DESCRIPTION OF T}IE DRAWING
FIG. 1 of the Drawing is a plot of average catalyst
temperature versus time representing the run of ~x~ple
6.
FIG. 2 of the Drawing is a plot of average catalyst
temperature versus time representing the initial run of
Example 7.
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WO 96/37299 1 ~ . /07'746
FIG. 3 of the Drawing is a plot of average catalyst
temperature versus time representing the s~o~ run of
Example 7.
FIG. 4 of the Drawing is a plot of average catalyst
temperature versus time representing the run of ~mple
8.
DET~T.~n DESCR~P~ION OF ~XE PREFERRED EMBOD~
The catalyst regenerated in the process of the present
invention has been deactivated due to coke deposition in
the reforming process. The catalyst has also been
previously subjected to a high temperature treatment at
a temperature of at least 1025~F. Preferably, this
previous high temperature treatment comprised treating
the catalyst at a temperature in the range of from
1025~F to 1275~F, while maint~in;ng the water level of
the effluent gas below 200 ppmv.
More specifically, the catalyst is a large-pore zeolite
charged with at least one Group VIII metal. The
preferred Group VIII metal is platinum, which is more
selective for dehydrocyclization and which is more
stable under reforming reaction conditions than other
Group VIII metals. The catalyst should contain between
0.1% and 5% platinum based on the weight of the
catalyst, more preferably from 0.1% to 2.0%, and most
preferably from about 1.0 to 1.5 wt %, e.g., about 1.2
wt %. The use of at least 1.0 wt % platinum is
considered preferred as it helps the activity and
stability of the catalyst in working with the naphtha
feedstocks cont~in;ng more than 5.0 wt ~ Cg+
hydrocarbons.
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WO ~6137~g9 ~ r07746
The term "large-pore zeolite" is defined as a zeolite
ha~ing an effective pore diameter of from 6 to 15
L~ c. The preferred pore diameter is from 6.5 to
10 ~yaL~ums~ Type L zeolite, zeolite X, and zeolite Y,
zeolite beta and synthetic zeolites with the mazzite
structure are suitable large-pore zeolites for this
operation. Zeolites with non-intersecting large pores
such as zeolite-L and mazzite are thought to benefit
most from the high temperature treatment. Type L
zeolite is described in U.S. Patent No. 3,216,78~.
Zeolite X is described in U.S. Patent No. 2,882,244.
Zeolite beta is described in U.S. Patent No. 3,308,069.
ZSM-4, described in U.S. Patent No. 4,021,447, is an
example of a zeolite with the mazzite structure.
Zeolite Y is described in U.S. Patent No. 3,130,007.
U.S. Patent Nos. 3,216,789; 2,882,244; 3,130,007;
3,308,069; and 4,021,447 are hereby incorporated by
reference to show zeolites useful in the present
invention. The preferred zeolite is a type L zeolite.
Type L zeolites are synthesized largely in the potassium
form. These potassium cations, however, are
exchangeable, so that other type L zeolites can be
obtained by ion ~xch~ging the type L zeolite in
appropriate solutions. It is difficult to exchange all
of the original catior.s, sir.ce som~ ~f tnese cations are
in sites which are difficult to reach. It may also be
desirable at times to only partially ~rhAnge the
potassium cations. The potassium may be ion ~hAnged,
fully or partially, with an alkali or alkaline earth
metal, such as sodium, cesium, lithium, rubidium,
barium, strontium, or calcium. Preferably, in an
~yçhAnger the total amount of alkali or AlkAline earth
metal ions should be enough to satisfy the cation
~ch~nge sites of the zeolite or be slightly in eY
CA 0222068~ 1997-11-10
WO 96137299 1 ~ J~C~
It is preferred that the zeolite ~ contain ~Y~h~geable
cations, at least 90% of which are selected from the
group consisting of Li, Na, K, Rb, Cs, Ba and Sr ions or
mixtures thereof.
An inorganic oxide can be used as a carrier to bind the
large-pore zeolite. This carrier can be natural,
synthetically produced, or a combination of the two.
Preferred loadings of inorganic oxide are from S% to 50%
of the weight of the catalyst. Useful carriers include
silica, alumina, aluminosilicates, and clays.
The original high temperature treatment of the catalyst
may occur at any time in the life of the catalyst. It
is preferred that this treatment be carried out with
fresh catalyst before use in the reforming process.
Preferably, the high temperature treatment used on the
fresh catalyst occurs in the presence of a reducing gas
such as hydrogen, as described in U.S. Patent No.
5,382,353, issued January 17, 1995, which is hereby
expressly incorporated by reference in its entirety.
Generally, the contacting occurs at a pressure of from 0
to 3aO psig and a temperature of from 1025~F to 1275~F
for from 1 hour to 120 hours, more preferably for at
least 2 hours, and most preferably at least 4-48 hours.
More preferably, the temperature is from 1050~F to
lZ50~F. In general, the length of time for the
pretreatment will be somewhat dependent upon the final
treatment temperature, with the higher the final
temperature the shorter the treatment time that is
needed.
In another ~rho~; ~nt, the catalyst can be treated using
an inert gaseous environment in the temperature range of
from 1025-1275~F, as described in cop~n~ing U.S. Serial
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CA 02220685 lsg7-ll-lo
Wos6~72ss PCT~S~6/077~6
~.
~o 08/450,~97 (~0 96/37298), which is hereby
expressly incorporated by reference in its entirety.
The preferred inert gas used is nitrogen, for reasons of
availability and cost. Other inert gases, however, can
be used, such as helium, argon and krypton, or mixtures
thereof. The use of purely an inert gas atmosphere for
the high temperature treatment allows one to avoid the
problems inherent in using a reducing gas such as
hydrogen.
The feed to the reforming process is typically a naphtha
that contains primarily paraffins, olefins and
naphthenes, generally having normal boiling points in
the range of 100-400~F, and more preferably 160-350~F.
This ~eed should be substantially free of sulfur,
nitrogen, metals and other known poisons. These poisons
can be removed by first using conventional hydrofining
techniques, then using sorbents to remove the remaining
sulfur compounds and water.
Because the catalyst of the present invention has been
pretreated as previously described, it exhibits a longer
run life with heavier feedstocks, e.g., containing at
least 5 wt % C9+ hydrocarbons, than similar catalysts
having been subjected to a di~ferent treatment. The
catalyst obtained via the treatment of the present
invention, therefore, makes it quite practical to
process feedstocks containing at least 5 wt % Cg+
hydrocarbons, and for example at least 10 wt % C9+
hydrocarbons, with from 10-20 wt % C9+ hydrocarbons being
preferred.
AMENDED SHEET
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WO 96/37299 ~ 07'746
In the reforming ~r o~ess, the feed is contacted with the
catalyst in either a fixed bed system, a moving bed
system, a fluidized system, or a batch system. Either a
fixed bed system or a moving bed system is preferred.
In a fixed bed system, the preheated feed is passed into
at least one reactor that contains a fixed bed of the
catalyst. The flow of the feed can be either upward,
downward, or r~;Al. The pressure is from about 1
atmosphere to about 500 psig, with the preferred
pressure being from abut 50 psig to about 200 psig. The
preferred temperature is from about 800~F to about
1025~F. The liquid hourly space velocity (LHSV) is from
about 0.1 hr~l to about
10 hrs~l, with a preferred LHSV of from about 0.3 hr~~ to
about 5 hrs~~. Enough hydrogen is used to insure a H2/HC
ratio of up to about 20:1. The preferred H2/HC ratio is
from about 1:1 to about 6:1. Reforming produces
hydrogen. Thus, additional hy~yen is not needed
except when the catalyst is reduced and when the feed is
first il-L~od~ced. Once reforming is underway, part of
the hydrogen that is produced is recycled over the
catalyst.
During the reforming reaction, the gradual ac~ lation
of coke and other deactivating carbonaceous deposits on
the catalyst will eventually reduce the activity of the
catalyst and selectivity of the aromatization process.
Typically, catalyst regeneration h~o~c desirable when
from about 0.5 to about 3.0 weight percent or more of
carbonaceous deposits are laid down upon the catalyst.
At this point, it is typically n~c~c~y to take the
hydrocarbon feed stream out of contact with the catalyst
and purge the hydrocarbon conversion zone with a
suitable gas stream. The catalyst regeneration method
of the present invention is then performed either by
CA 0222068~ 1997-11-10
P~ 07746
WO 96/37299
unloading the catalyst from the conversion zone and
regenerating in a separate vessel or facility, or
performing regeneration in-si~. Alternatively, the
catalyst may be continuously withdrawn from the reactor
for regeneration in a separate vessel, to be returned to
the reactor as in a continuous catalytic reformer.
According to the catalyst regeneration process of the
present invention, the initial step involves treating
the catalyst with an oxygen containing gas to burn off
coke deposits. It is preferred that the coke is burned
from the catalyst by maintaining the catalyst at a
temperature less than 800~F, and preferably less than
750~F. The burn step is preferably effected by
contacting the deactivated catalyst with a gaseous
mixture of oxygen and an inert gas. The oxygen is
typically derived from air and an inert gas serves as a
diluent, such that the oxygen concentration ranges from
about 21 mole percent oxygen to a lower limit which for
the practice of the present invention may be as low as
0.1 mole percent oxygen. The burn step is not limited
to the use of air, however, and a higher level of oxygen
may used in methods where oxygen is supplied in a more
pure form such as from cylinders or other containing
25 ~~n~. Typical inert gases useful in the low
temperature coke burn step may include nitrogen, helium,
carbon dioxide and like gases or any mixture thereof.
Nitrogen is the preferred inert gas, however.
The regeneration gases should be substantially sulfur
free as they enter they reactor, and preferably contain
less than 100 parts per million by volume water.
Because the oxygen content determines the rate of burn,
it is desirable to keep the oxygen content low so as not
to damage the catalyst by overheating and causing metal
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wo 96/3729g 1~ n7746
agglomeration. It has been found desirable to keep the
oxygen level in the inlet to the regeneration vessel
between 0.2 to 4.0 mole percent during the coke burn
step to avoid thermal damage to the catalyst, and still
allow for the regeneration process to be accomplished in
a r~con~hle . ~.L of time.
Other conditions present during the coke burn step
include a pressure sufficient to maintain the flow of
the gaseous oxygen containing mixture through the
catalyst zone such as a pressure of between 1.0-50.0
atmospheres and preferably from about 2 to about 15
atmospheres, and a gas hourly space velocity of about
100 to about 10,000 per hour, with a preferred value of
about 500 to about 5,000 per hour.
It is also preferred that the burn step is conducted in
a halogen free environment. By halogen free is meant
that chlorine, fluorine, bromine or iodine, or their
compounds including for example hydrogen chloride, are
not ~ at any time during the catalyst regeneration
process. In general, the coke burn step can follow
along the lines of the low temperature regeneration
process described in U.S. Patent No. 5,155,075, which is
incorporated by reference expressly herein in its
entirety.
Coke removal may also be done at temperatures above
800~F. In which case, a platinum redispension step
using halogens will be required prior to reduction.
After the coke burnoff, the catalyst is reduced by
contacting the catalyst with a reducing gas in the
temperature range of from 300~F to 700~F. The
temperature is then raised in a stepwise or ramping
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Wos6~7299 ~ 5-ro~
fashion to complete reduction and drying. The reducing
gas is preferably l.~droyen, although other reducing
gases can also be used. The hydrogen is generally mixed
with an inert gas such as niL~o~ , with the amount of
hydrogen in the mixture generally ranging from 1 to 99%
by volume. Preferred conditions for the initial
reduction include a temperature in the range of about
400~F to about 600~F for a period of from about 0.1 to
10 hours. The pressure and gas rates utilized in the
reduction step are preferably very similar to those
described above with regard to the coke burn step.
Subsequent to reduction, the reduced catalyst is then
treated at a temperature in the range of from about
975~F to less than 1150~F, and most preferably in the
range of from 1000~F to about 1100~F. It is also most
preferred that the water level of the effluent gas
during the treatment of the catalyst at the high
temperature is maintained below 200 ppmv, for otherwise
the activity of the catalyst may be detrimentally
effected.
It is also important that the temperature of this
treatment not ~c~ 1150~F, and preferably 1100~F. For
it has been discovered that when the temperature during
this treatment reaches or exceeds 1150~F, catalyst
activity is severely sacrificed. This high temperature
treatment is not the same as the original high
temperature treatment conducted on fresh catalyst, and
therefore a different temperature profile must be
observed and followed.
Treatment of the catalyst in the temperature range of
from 975~F to less than 1150~F can be conducted in the
presence of a reducing gas, such as hydrogen, or an
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inert gas atmosphere. The preferred reducing gas is
that of hydrogen, with the hydrogen generally being
mixed with an inert gas, such as nitrogen. When an
inert gas atmosphere is used, it is preferred that
nitrogen be the inert gas, although other inert gases
such as helium, argon or krypton, or mixtures of inert
gases, can also be used.
The temperature for the final treatment is generally
achieved by raising the temperature from the reducing
step at a rate of between 5~F and 50~F per hour until
the final treatment temperature is reached. More
preferably, it is preferred that the temperature is
increased at a rate of between 10~F and 25~F per hour.
The temperature can be increased in a stepwise or
ramping fashion. It is most preferred, particularly
when the treatment range of 975~F is approached, that
the temperature program and gas flow rates be selected
to limit water vapor levels in the reactor to less than
200 ppmv, and preferably, less than 100 ppmv. This is
particularly desirable when the catalyst bed temperature
~YC~ 1000~F.
During the final temperature treatment of the catalyst,
it is preferred that the gas flow through the catalyst
bed (G~SV) exceed 500 volumes per volume of catalyst per
hour, where the gas volume is measured at standard
conditions of one atmosphere and 60~F. From the
standpoint of catalyst performance, the higher the gas
velocity the better. GHSVs between 600 and 2000 h-l are
most preferred from a practical point of view.
To aid in maintaining the water level of the effluent
gas below 200 ppmv in the final treatment of the
catalyst, the inert or reducing gas entering the reactor
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16
should contain less than loO ppmv water. It is
preferred that the gas contain less than 10 ppmv water.
The effluent gas, may be passed through a drier
cont~ining a desiccant or sorbent such as 4 A mo~
sieves. The dried gas can then be recycled to the
reactor.
The length of the final treatment step can vary
depending upon gas velocity, temperature, and catalyst
particle size. Generally, however, the final treatment
in the regeneration process will range from about 1 hour
to about 120 hours, more preferably, for at least 2
hours, and most preferably in the range of from about 4
to 48 hours. In general, the length of time for the
final treatment will be dependent upon the final
treatment temperature. The higher the final temperature
the shorter the time at final temperature needed.
However, it is important that the temperature not reach
1150~F in the final treatment for otherwise catalyst
activity and stability will be severely sacrificed. It
is also important that the temperature be high enough
and be maintained for a sufficient length of time to
achieve an activity and stability approaching that of
the original catalyst. Thus, the temperature range of
from 1000~F to 1100~F is most preferred for the final
treatment.
The invention will be illustrated in greater detail by
the following specific examples. It is understood that
these examples are given by way of illustration and are
not meant to limit the disclosure or the claims to
follow. All water measurements are in parts per million
by volume (ppmv).
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WO 96137299 ~ U~96/07746
E~NPLE S
A highly stable catalyst was ob~i n~ using the
following activation procedure with fresh catalyst. A
catalyst comprising 0.64% platinum on silica-bound,
barium-~Ych~nged, L-zeolite 1/16" diameter extrudates
was charged to a pilot plant reactor. The catalyst was
dried by circulating nitrogen at 70 psig and 1000 h-
G~S~ through the catalyst bed and a molecular sieve
drier while heating the reactor to 500~F. Nitrogen
circulation was continued until the water level in the
reactor effluent dropped below 100 ppmv.
The catalyst was reduced by adding hydrogen to the
recycle gas stream and increasing the total pressure to
100 psig. Thereafter, hydrogen was added to maintain
pressure. The temperature was held at 500~F until the
water concentration in the reactor effluent dropped
below 100 ppmv. The catalyst then was heated at a rate
of 10~F/h to 900~F. The temperature was held at 900~F
until water in the reactor effluent fell again fell
below 20 ppmv. The temperature was raised at a rate of
10~F/h to 1100~F. Above 900~F, the water concentration
in the reactor was then less than 50 ppmv. The
temperature was held for three hours at 1100~F before
cooling to reaction temperature.
The catalyst thus activated was used under a variety of
- conditions for the conversion of naphtha to aromatics.
By the end of the run, the catalyst activity loss
corresponded to about a 70~F increase in the reaction
temperature. When testing was completed, the catalyst
was stripped of hydrocarbons with hydrogen and the
reactor was purged with nitrogen and cooled to room
temperature. The deactivated catalyst was ground into
- - :
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~ WO 96/3729g 1 ~ 96107'746
18
20-40 mesh granules and thoroughly ;YO~. Portions of
this catalyst were then regenerated in a microreactor to
study the effects of carbon burn temperature and high
temperature treatment temperature.
Each experiment was carried out as follows. A catalyst
sample was heated to 500~F in nitrogen flowing at 50
psig and 8000 h-~ GHSV. A carbon burn was initiated by
replacing the nitrogen with a 1.0 % oxygen in a nitrogen
blend. The catalyst was heated 25~F/h to a final burn
temperature between 700 and 800~F. The oxygen/nitrogen
flow continued at this temperature for 20 hours to
complete the carbon burn. The reactor was then cooled to
500~F.
The catalyst was then reduced with dry (< 10 ppmv water)
hyd~oyen at 500~F, 50 psig, and 8000 h-l G~SV. Hydrogen
flow continued as the catalyst was heated 10~F/h to a
final temperature between 900 and 1150~F. At
temperatures above 975~F, the water concentration in
reactor effluent was less than 100 ppmv. The catalyst
was held at the final temperature for 20 hours and then
cooled to reaction temperature.
Each regenerated catalyst sample was tested for the
conversion of a light naphtha to benzene and toluene.
Table 1 shows how the final carbon burn and hydrogen
treatment temperatures affected catalyst performance.
When the hydrogen treatment temperature was limited to
975~F or less, the catalyst deactivated at a much faster
rate than when the hydrogen treatment was 1000~F or
higher. The best results were ob~i no~ when the final
carbon burn temperature was 700~F and the final hydrogen
treatment ~ompo~ature was 1000~F. A 750~F carbon burn
was acceptable, but an 800~F burn temperature caused
CA 02220685 1997-ll-lO
Wog6~7~s P~llU~g6/077
significant catalyst deactivation. Surprisingly, the
regenerated catalyst samples did not require as high a
hyd~o~en treatment temperature as a fresh catalyst to
produce a beneficial effect on catalyst stability.
Table 1. Ef~ect of Regeneration Temperatures on
Catalyst Performance
Final F~al Wt ~ YicldWt ~ Yi~ld
0 r,.~ ~ydrog~n Aro~tics Aromatics
Bur~ Tr~atment ~fter Two~fter Eisht
~mp., F Temp., F Dars Days
700 900 30 25
700 975 35 30
15 700 1000 36 36
750 1000 30 30
800 1000 24 20
700 1025 32 30
700 lOS0 31 30
20 700 1100 29 30
700 llS0 29 30
Run Conditions: light naphtha feed, lOWHSV, 50 psig,
950~F, 5.0 hydrogenJnaphtha feed molar
ratio
.
EgaMPLE 2
An eighty cubic-centimeter portion of a catalyst
comprising 0.64% platinum on silica-bound, barium-
exchanged, 1/16-inch, L-zeolite extrudates was charged
to a one-inch diameter tubular reactor. The catalyst
was dried as in Example 1. The catalyst reduction and
high temperature treatment were done with once-through
hydrogen ~lowing at 2000 h-l G~SV and 70 psig. The
catalyst was reduced initially at 500~F, the catalyst
temperature was raised lOF/h to 1100~F. The water
concentration in the reactor e~fluent at temperatures
above 900~F was less than 70 ppmv. Above 975~F, the
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water concentration was less than 50 pp~v. The
t~mp~ature was held at 1100~F for three hours before
cooling to reaction temperature.
This catalyst was tested for the conversion of a light
naphtha to benzene, toluene, ethylbenzene, and xylenes.
The naphtha feed rate was 128 mL/h, the hydrogen to
naphtha feed molar ratio was 3.0, and the reaction
pressure was 100 psig. The reaction temperature was
adjusted to maintain a 51.5 wt % aromatics concentration
in the debutanized liquid product. The start-of-run
average catalyst temperature for the target aromatics
level was 847~F and the fouling rate was 0.010~F/h. By
way of comparison, a catalyst activated with hydrogen at
500-900~F had a start of run temperature of 847~F and a
fouling rate of 0.025~F. At the end of the run, the
naphtha feed was stopped and the catalyst stripped of
hydrocarbons with hydrogen. The catalyst was then
purged with nitrogen and cooled to room temperature.
ExaMpLE 3
The catalyst from Example 2 was regenerated as follows.
The catalyst was heated to 500~F as nitrogen was
recirculated at 70 psig pressure through the reactor and
recycle-gas drier. At 500~F, air was added to the
recycle gas stream to initiate the carbon burn. The air
feed rate was adjusted to maintain a 0.5~ oxygen
concentration at the reactor inlet. When oxygen
appeared in the reactor effluent, the temperature was
raised 25~F/h to 700~F. Upon reaching 700~F, the oxygen
concentration was raised from 0.5 % to 1.0 %. After 24
hours the air feed was stopped. Nitrogen circulation
continued while the reactor cooled to 500~F. At 500~F,
the ~O~L essor was stopped and once-through nitrogen
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flow started. The reactor pressure was 50 psig and the
G~SV was 1000 h-l.
Catalyst reduction was initiated at 500~F by slowly
replacing nitrogen with hydrogen until the stream
consisted entirely of hydrogen. The temperature was
then increased from 500 to 1150~F at rate of lOF/h. The
catalyst temperature was main~ e~ at 1150~F for three
hours and then allowed to cool to reaction temperature.
The regenerated catalyst was tested in the same way as
the fresh high temperature treated catalyst in
Example 2. Compared to the first cycle, the start-of-
run temperature was 875~F versus 847~F and the fouling
rate was 0.009~F/h versus 0.010~F/h. The 1150~F
treatment caused the catalyst to loose a significant
amount of activity (28~F), but the catalyst still
exhibited excellent stability.
E~AMPLE ~
The catalyst from Example 2 was regenerated a second
time after completing the catalyst test in ~Y~mple 3.
This time the ~Y;~llm temperature during the high
temperature treatment step was 1000~F instead of 1150~F.
After the second regeneration, the start of run
temperature was 872~F compared to 875~F for the previous
cycle and the fouling rate was unchanged. Thus, a
1000~F treatment maintained a low fouling rate without
causing a further loss of start-of-run activity.
EXAMPLE 5
Eighty milliliters of a Pt-Ba-L-zeolite catalyst of the
same type used in Examples one through four were
charged to l.0-inch diameter pilot plant reactor. The
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catalyst was dried by heating to 500~F in flowing
nitrogen. The reactor was at atmospheric pressure and
the flow-rate was 3.0 ft3/h. The nitrogen flow continued
at 500~F until the water cn~c~ntration in the reactor
effluent was less 100 ppmv. The catalyst was then
r~r~A at 500~F by changing the gas to dry hydrogen and
increasing the reactor pressure to 50 psig. The G~SV
was adjusted to 4500 h-l. After the water level in the
reactor effluent again dropped below 100 ppmv, the
temperature was increased from 500~F to 1100~F at a rate
of 10~F/h. After holding ~or three hours at 1100~F, the
reactor was cooled to reaction temperature.
The catalyst was tested for the conversion of a C6-~
naphtha feed to benzene and toluene. The start-of-run
temperature was 852~F and the fouling rate was
0.003~F/h. This compares to 847~F and 0.020~F/h for
the same catalyst and feed when the catalyst is
activated with hydrogen at 500-900~F. When the run was
completed, the catalyst was stripped of hydrocarbons
with hydrogen. The reactor was then purged with
nitrogen and cooled to room temperature.
Later the catalyst was heated to 500~F in nitrogen
flowing at rate of 3 SCF/min. At 500~F, air was added
to the nitrogen at rate sufficient to give a reactor
inlet oxygen concentration of 0.5%. After oxygen
breakthrough, the temperature was raised 25~F/h to
700~F. The carbon burn was continued at 700~F with 1.0%
oxygen for 24 hours. After the carbon burn, the
catalyst was reduced at 500~F and heated to 1100~F in
hydrogen following the same procedure used in the first
cycle. The reforming process was then resumed under the
original conditions.
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The start-of-run temperature for the second cycle was
857~F and the fouling rate was 0.013~F/h. The 1100~F
treatment resulted in only a 5~F loss in start-of-run
activity ~mp~ed to the first cycle. The fouling rate
in the s~co~ cycle was better than achieved when the
hydrogen treatment t~p~rature is limited to 900~F, but
was not as low as in the first cycle.
EXAMPLE 6
Eighty cubic centimeters of a catalyst comprising 1.2%
platinum on K-Ba L-zeolite 1/16 inch extrudates were
charged to a one-inch diameter reactor. The catalyst
was dried by circulating nitrogen at 60 psig and 1000
hr-l GHS~ through the catalyst bed and a mol~c~ ~ sieve
drier downstream of the catalyst bed. With the nitrogen
gas recirculating, the reactor temperature was increased
to 500~F at 25~F/hr. On reaching 500~F, nitrogen
recirculation was continued until the concentration of
water in the recirculating gas had decreased to 100
ppmv. The catalyst was then reduced by adding hydrogen
to the recycle gas while maint~;n;ng 60 psig, and a
recirculation rate of 1000 hr-l GHSV. The reactor
temperature was held at 500~F during the hydrogen
addition until the recirculation gas had changed from
100% nitrogen to 95% + hydrogen. During the hydrogen
addition~ reactor pressure was held at 60 psig by
excessing under pressure control some of the recycle gas
(nitrogen+hydrogen). In addition, to prevent against
sudden increases in water concentrations in the recycle
gas, hydrogen addition was stopped at any time that the
concentration of water in the recycle gas increased to
400 ppmv. When the water concentration decreased to
less than 400 ppmv, hydrogen addition was resumed. Once
the nitrogen had been completely replaced with hydrogen
and the water content of the recycle gas had decreased
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24
to 100 ppmv, the reactor temperature was increased at
lOF/hr to a tomr~ature of 1100~F. On r~hing 1100~F,
this condition was held for 3 hours before cooling the
reactor to reaction temperature.
s
A C6-Cg naphtha conl ~;n;ng 13.29% Ca9+ hydrocarbon was
p~cs~ over the catalyst at 75 psig, 1.0 L~SV and a 5/1
H2/HC mole ratio. The specific components of the feed
are described in Table 2 below.
TABLE 2
Feed Description
ASTM - D86, ~F
LV%, St 145
184
198
219
243
go 262
EP 295
gravity, API 65.8
Carbon No. distribution - wt~
Cs 1.82
C6 27.72
~ 22.77
C8 33.77
Cg 13.29
ClO 0.72
PNA - wt %
P (n+i) 72.32
naphthenes 17.67
aromatics 9,37
unknown O.64
Total 100.00
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Feed was hydrofined to reduce sulfur content to
acceptable levels.
The operating temperature was selected to achieve 83.5
wt% aromatics in the C5+ liquid. After the fresh
catalyst had stabilized, the fouling rate was calculated
to be 0.016~F/hr with an average start-of-run
temperature of 864~F. The plot of average catalyst
temperature versus time is shown in Figure 1.
After about 900 hours on stream, the naphtha feed was
stopped and the catalyst was readied for regeneration.
EXAMPLE 7
The catalyst of Example 6 was regenerated by burning off
the carbon deposited on the catalyst as described in
~Y~rle 3 with the following exceptions. The reactor
pressure was 85 psig. The reactor was heated up to
700~F at a 10~F/hr rate. On reaching 700~F and with the
oxygen concentration at 0.5% to the reactor inlet, this
condition was held for four hours. Following this step,
the oxygen content was increased to 1%. After 24 hours
at 700~F and 1% oxygen, the air feed was discontinued,
the reactor was purged with nitrogen and cooled to
500~F.
The catalyst was then reduced in hydrogen as described
in Example 6 except that the pressure was held at 60
psig and the catalyst was heated at 10~F/hr to a final
temperature of 1050~F as compared to 1100~F in ~mple
6. Following the three hour hold at 1050~F, the
catalyst temperature was reduced to reaction
temperature.
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WO g6137299
The same C6-~ naphtha ~s used in Example 6 was rAc
over the regenerated catalyst at the same operating
conditions as in Example 6. After the catalyst had
stabilized, the fouling rate was 0.012~F/hr and the
average start-of-run temperature was 867~F. The plot of
the average catalyst temperature versus time is shown in
Figure 2. The fouling rate of the regenerated high
temperature hydrogen-treated catalyst was significantly
lower than that obtained when the catalyst was fresh,
namely 0.016~F/hr. In addition, the start-of-run
temperature is only 3~F higher than with the fresh
catalyst. In other words, the regenerated catalyst lost
only 3~F of activity as a result of the regeneration and
high temperature hydLoyen treatment. Thus,
~u~ ~r isingly, the regenerated catalyst does not reguire
as high a hydrogen treatment temperature as the fresh
catalyst to e~ual or ~c~ the fresh catalyst
stability.
At about 1000 hours on stream in the second cycle, the
C6-~ naphtha feed was discontinued and replaced with a
C6-~ naphtha. After 900 hours on stream with this new
feed, the catalyst fouling rate was calculated to be
0.004~FJhr The start-of-run temperature with this feed
was estimated to be about 845~F. The plot of the
average catalyst temperature versus time is shown in
Figure 3.
EXAMPLE 8
The catalyst of Example 7 was regenerated for a second
time by burning off the carbon deposited on the
catalyst. The regeneration was carried out as described
in Examples 3 and 7. Following the ~ -val of the
deposited carbon, the catalyst was reduced in hydrogen
and high temperature treated in hydrogen as described in
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Example 7. In par~ ~, as in Example 7, the final
treatment temperature was 1050~F.
After cooling the reactor/catalyst to reaction
~Dmr~rature, the C6-~ naphtha used in Example 7 was
r~cc~A over the catalyst. After 1000 hours on stream,
the catalyst fouling rate was calculated to be
0.005~F/hr with a start-of-run average catalyst
temperature of 855~F. The plot of average catalyst
temperature versus time is shown in Figure 4. Thus, the
second regeneration and the third high temperature
hydrogen treatment resulted in a 10~F loss in initial
catalyst activity relative to the second cycle and a
slightly higher fouling rate than obtained in the second
cycle, i.e., 0.005 versus 0.004~F/hr. Again, this shows
that for the third cycle good catalyst perform~nc~ was
achieved without having to subject the catalyst to the
same high hydrogen treatment temperature as the fresh
catalyst.
While the invention has been described with preferred
~mhoA; m~nts, it is to be understood that variations and
modifications may be resorted to as will be apparent to
those skilled in the art. Such variations and
modifications are to be considered within the purview
and the scope of the claims appended hereto.
