Molecular sieve abstract
A reactivated catalyst having optimum activity for hydrocracking
and other acid catalyzed chemical conversion processes is prepared
by contacting its deactivated counterpart, which contains a crystalline
molecular sieve, a Group VIII noble metal hydrogenation component
and carbonaceous deposits, with a gas containing molecular oxygen,
preferably air, at a temperature between 950.degree. and 1200.degree.
F., preferably between about 1050.degree. and 1150.degree. F., for
a time sufficient to remove at least a portion of the carbonaceous
deposits. When the reactivated catalyst contains a dealuminated
Y zeolite that has been ion-exchanged with both noble metal and
rare earth metal cations, its activity for hydrocracking in an ammonia-deficient
atmosphere can be further increased by a rejuvenation procedure
in which the reactivated catalyst is contacted with an aqueous ammonia
solution in which an ammonium salt has been dissolved.
Molecular sieve claims
I claim:
1. A process for reactivating a deactivated hydrocracking catalyst
produced by subjecting a fresh catalyst to hydrocracking conditions
in the presence of a hydrocarbon feedstock wherein said deactivated
catalyst comprises (1) a crystalline, dealuminated Y zeolite having
an overall silica-to-alumina mole ratio above about 6.0 said zeolite
having been ion-exchanged with rare earth-containing cations and
Group VIII noble metal-containing cations, (2) a porous, inorganic
refractory oxide and (3) carbonaceous deposits, which process comprises:
(a) contacting said deactivated catalyst with a flowing gas containing
between about 20 and about 25 volume percent molecular oxygen in
a combustion zone at a temperature between about 1025.degree. F.
and 1175.degree. F. for a time sufficient to remove at least a portion
of said carbonaceous deposits via combustion; and
(b) recovering a reactivated catalyst from said combustion zone,
said reactivated catalyst having an activity temperature for hydrocracking
less than about 48.degree. F. above the activity temperature of
said fresh catalyst.
2. A process as defined by claim 1 wherein said deactivated catalyst
contains between about 2.0 and 20 weight percent carbonaceous deposits,
calculated as carbon.
3. A process as defined by claim 1 wherein said crystalline molecular
sieve has a constraint index less than about 1.0.
4. A process as defined by claim 1 wherein said deactivated catalyst
is contacted with said flowing gas at a temperature between about
1050.degree. F. and about 1150.degree. F.
5. A process as defined by claim 1 wherein said deactivated catalyst
is contacted with said flowing gas at a temperature between about
1075.degree. F. and about 1125.degree. F.
6. A process as defined by claim 1 wherein said contacting is carried
out for a period of time between about 2.0 and about 6.0 hours.
7. A process as defined by claim 1 wherein a reactivated catalyst
is recovered from said combustion zone and has an activity temperature
at least 50.degree. F. greater than the activity temperature of
said deactivated catalyst.
8. A process as defined by claim 1 wherein said crystalline dealuminated
Y zeolite is prepared by contacting a zeolite of the Y crystal structure
and an overall silica-to-alumina mole ratio below 6.0 with an aqueous
solution of fluorosilicate salt.
9. A process as defined by claim 8 wherein said fluorosilicate
salt is ammonium hexafluorosilicate.
10. A process as defined by claim 9 wherein said crystalline dealuminated
Y zeolite is LZ-210 zeolite.
11. A process as defined by claim 1 wherein said crystalline dealuminated
Y zeolite has a composition expressed in terms of oxide mole ratios
in the anhydrous state of
wherein "M" is a cation having a valence of "n"
and "x" has a value between 6 and about 20 said Y zeolite
having an X-ray powder diffraction pattern comprising at least the
d-spacings set forth in Table I.
12. A process as defined by claim 11 wherein "x" has
a value between about 6 and 10.
13. A process as defined by claim 1 wherein said Group VIII noble
metal-containing cations comprise palladium or platinum.
14. A process as defined by claim 1 further comprising the step
of increasing the activity of said reactivated catalyst recovered
from said combustion zone by treating said recovered catalyst to
disperse said noble metal-containing cations.
15. A process as defined by claim 1 further comprising the step
of increasing the activity of said reactivated catalyst recovered
from said combustion zone by treating said recovered catalyst with
an ammonium ion-containing solution.
16. A process as defined by claim 15 wherein said ammonium ion-containing
solution is an aqueous ammonia solution containing a dissolved ammonium
salt.
17. A process as defined by claim 16 wherein said dissolved ammonium
salt is ammonium carbonate, ammonium bicarbonate, or ammonium nitrate.
18. A process as defined by claim 1 wherein said porous, inorganic
refractory oxide comprises alumina.
19. A process as defined by claim 1 wherein said reactivated catalyst
has an activity temperature for hydrocracking less than about 40.degree.
F. above the activity temperature of said fresh catalyst.
20. A process as defined by claim 1 wherein said reactivated catalyst
has an activity temperature for hydrocracking less than about 36.degree.
F. above the activity temperature of said fresh catalyst.
21. A process for reactivating a deactivated hydrocracking catalyst
produced by subjecting a fresh hydrocracking catalyst to hydrocracking
conditions in the presence of a hydrocarbon feedstock, wherein said
deactivated catalyst comprises (1) a crystalline dealuminated Y
zeolite having an overall silica-to-alumina mole ratio above about
6.0 said zeolite having been ion-exchanged with rare earth-containing
cations and Group VIII noble metal-containing cations, (2) a porous,
inorganic refractory oxide and (3) carbonaceous deposits, which
process comprises:
(a) contacting said deactivated catalyst with a flowing gas containing
between about 20 and about 25 volume percent molecular oxygen in
a combustion zone at a temperature between about 1025.degree. F.
and 1175.degree. F. for a time sufficient to remove at least a portion
of said carbonaceous deposits via combustion and thereby produce
a regenerated catalyst;
(b) contacting said regenerated catalyst with an aqueous ammonia
solution containing a dissolved ammonium salt while correlating
the contacting time with the temperature and reagent strength so
as to effect a substantial improvement in activity of said catalyst,
thereby producing a rejuvenated catalyst;
(c) separating said rejuvenated catalyst from said aqueous ammonia
solution; and
(d) drying and calcining said separated catalyst to produce a reactivated
catalyst having an activity temperature for hydrocracking less than
about 5.degree. F. above the activity temperature of said fresh
catalyst.
22. A process as defined by claim 21 wherein said Group VIII noble
metal-containing cations comprise platinum or palladium.
23. A process as defined by claim 21 wherein said inorganic refractory
oxide is alumina and said Group VIII noble metal-containing cations
comprise palladium.
24. A process as defined by claim 23 wherein said deactivated catalyst
is contacted in said combustion zone with flowing air at a temperature
between about 1050.degree. F. and 1150.degree. F.
25. A process as defined by claim 24 wherein said crystalline dealuminated
Y zeolite is LZ-210 zeolite.
26. A process as defined by claim 25 wherein said ammonium salt
is ammonium bicarbonate.
27. A process as defined by claim 21 wherein said Group VIII noble
metal-containing cations comprise palladium.
28. A process as defined by claim 21 wherein said porous, inorganic
refractory oxide comprises alumina.
29. A process as defined by claim 21 wherein said flowing gas comprises
air.
30. A process as defined by claim 21 wherein said deactivated catalyst
is contacted with said flowing gas at a temperature between about
1050.degree. F. and about 1150.degree. F.
31. A process as defined by claim 21 wherein said deactivated catalyst
is contacted with said flowing gas at a temperature between about
1075.degree. F. and about 1125.degree. F.
32. A process as defined by claim 21 wherein said deactivated catalyst
is contacted with said flowing gas for a period of time between
about 2.0 and about 6.0.
33. A process as defined by claim 21 wherein said reactivated catalyst
has an activity greater than the activity of said fresh catalyst.
34. A process for reactivating a deactivated hydrocracking catalyst
produced by subjecting a fresh catalyst to hydrocracking conditions
in the presence of a hydrocarbon feedstock, wherein said deactivated
catalyst comprises (1) a crystalline, dealuminated Y zeolite having
an overall silica-to-alumina mole ratio above about 6.0 said zeolite
having been ion-exchanged with rare earth-containing cations and
Group VIII noble metal-containing cations, (2) an inorganic refractory
oxide and (3) carbonaceous deposits, which process comprises:
(a) contacting said deactivated catalyst with a gas consisting
essentially of air in a combustion zone at a temperature between
about 1025.degree. F. and 1175.degree. F. for a time sufficient
to remove at least a portion of said carbonaceous deposits by combustion;
and
(b) recovering a reactivated catalyst from said combustion zone,
said reactivated catalyst having an activity temperature for hydrocracking
less than about 48.degree. F. above the activity temperature of
said fresh catalyst.
35. A process as defined by claim 34 wherein said Group VIII noble
metal-containing cations comprise platinum or palladium.
36. A process as defined by claim 35 wherein said inorganic refractory
oxide comprises alumina.
37. A process as defined by claim 34 wherein said deactivated catalyst
is contacted with said flowing gas at a temperature between about
1050.degree. F. and about 1150.degree. F.
38. A process as defined by claim 34 wherein said deactivated catalyst
is contacted with said flowing gas at a temperature between about
1075.degree. F. and about 1125.degree. F.
39. A process as defined by claim 34 further comprising the step
of increasing the activity of said reactivated catalyst recovered
from said combustion zone by treating said recovered catalyst to
disperse said noble metal-containing cations.
40. A process as defined by claim 34 further comprising the step
of increasing the activity of said reactivated catalyst recovered
from said combustion zone by treating said recovered catalyst with
an ammonium ion-containing solution.
41. A process as defined by claim 40 wherein said ammonium ion-containing
solution is an aqueous ammonia solution containing a dissolved ammonium
salt.
42. A process as defined by claim 41 wherein said treated recovered
catalyst has an activity temperature for hydrocracking less than
about 5.degree. F. above the activity temperature of said fresh
catalyst.
43. A process as defined by claim 41 wherein said treated, recovered
catalyst has an activity greater than the activity of said fresh
catalyst.
Molecular sieve description
BACKGROUND OF THE INVENTION
The invention relates to a process for reactivating deactivated
catalysts, the reactivated catalysts produced by the process, and
the use of the reactivated catalysts in acid catalyzed chemical
conversion processes, such as hydrocarbon conversion processes.
The invention is particularly concerned with reactivating deactivated
hydrocracking catalysts which comprise a crystalline molecular sieve,
a Group VIII noble metal hydrogenation component and carbonaceous
deposits, and the use of the reactivated catalysts in hydrocracking
processes, particularly hydrocracking in the substantial absence
of ammonia.
Petroleum refiners often produce desirable products, such as gasoline
and turbine fuel, by catalytically hydrocracking high boiling hydrocarbons
into product hydrocarbons of lower average molecular weight and
boiling point. Hydrocracking is generally accomplished by contacting,
in an appropriate reactor vessel, a gas oil or other hydrocarbon
feedstock with a suitable hydrocracking catalyst under appropriate
conditions, including an elevated temperature and an elevated pressure
and the presence of hydrogen, such that a hydrocarbon product is
obtained containing a substantial portion of a desired product boiling
in a specified range, as for example, a heavy gasoline boiling in
the range of 185.degree. to 420.degree. F.
Oftentimes, hydrocracking is performed in conjunction with hydrotreating,
usually by a method referred to as "integral operation."
In this process, the hydrocarbon feedstock, usually a gas oil containing
a substantial proportion of components boiling above a desired end
point, as for example, 420.degree. F. in the case of certain gasolines,
is introduced into a catalytic hydro-treating zone wherein, in the
presence of a suitable catalyst, such as a zeolite- or sieve-free,
particulate catalyst comprising a Group VIII metal component and
a Group VIB metal component on a porous, inorganic, refractory oxide
support most often composed of alumina, and under suitable conditions,
including an elevated temperature (e.g., 400.degree. to 1000.degree.
F.) and an elevated pressure (e.g., 100 to 5000 p.s.i.g.) and with
hydrogen as a reactant, the organonitrogen components and the organosulfur
components contained in the feedstock are converted to ammonia and
hydrogen sulfide, respectively. Subsequently, the entire effluent
removed from the hydro-treating zone is treated in a hydrocracking
zone maintained under suitable conditions of elevated temperature,
pressure, and hydrogen partial pressure, and containing a suitable
hydrocracking catalyst, such that a substantial conversion of high
boiling feed components to product components boiling below the
desired end point is obtained. Usually, the hydrotreating and hydrocracking
zones in integral operation are maintained in separate reactor vessels,
but, on occasion, it may be advantageous to employ a single, downflow
reactor vessel containing an upper bed of hydrotreating catalyst
particles and a lower bed of hydrocracking particles. Examples of
integral operation may be found in U.S. Pat. Nos. 3132087 3159564
3655551 and 4040944 all of which are herein incorporated by
reference in their entireties.
In some integral operation refining processes, and especially those
designed to produce gasoline from the heavier gas oils, a relatively
high proportion of the product hydrocarbons obtained from integral
operation will have a boiling point above the desired end point.
For example, in the production of a gasoline product boiling in
the C.sub.4 to 420.degree. F. range from a gas oil boiling entirely
above 570.degree. F., it may often be the case that as much as 30
to 60 percent by volume of the products obtained from integral operation
boil above 420.degree. F. To convert these high boiling components
to hydrocarbon components boiling below 420.degree. F.,+ the petroleum
refiner separates the 420.degree. F.+ high boiling components from
the other products obtained in integral operation, usually after
first removing ammonia by a water washing operation, a hydrogen-containing
recycle gas by high pressure separation, and an H.sub.2 S-containing,
C.sub.1 to C.sub.3 low BTU gas by low pressure separation. This
420.degree. F.+ boiling bottom fraction is then subjected to further
hydrocracking, either by recycle to the hydrocracking reactor in
single stage operation or by introduction into a second hydrocracking
zone wherein yet more conversion to the desired C.sub.4 to 420.degree.
F. product takes place.
In the foregoing two-stage process, the two hydrocracking reaction
zones can contain hydrocracking catalysts of the same or different
composition. One catalyst suitable for use in both reaction zones
is disclosed as Catalyst A in Example 16 of U.S. Pat. Nos. 3897327
and 3929672 both of which are herein incorporated by reference
in their entireties, which catalyst is comprised of a palladium-exchanged,
steam-stabilized Y zeolite hydrocracking component. But although
the catalysts used in the two hydrocracking reaction zones may have
the same composition and the same catalytic properties, the hydrocracking
conditions required in the second hydrocracking reaction zone are
less severe than those required in the first. The reason for this
is that ammonia is not present in the second hydrocracking reaction
zone (due to water washing) whereas a significant amount of ammonia
is present in the first hydrocracking zone. To account for the difference
in operating conditions, it is believed that ammonia neutralizes
or otherwise interferes with the acidity of the zeolite in the catalyst
of the first reaction zone, thereby forcing the refiner to employ
relatively severe conditions for operation, as for example, increased
temperature. On the other hand, in the ammonia-deficient atmosphere
of the second hydrocracking reaction zone, high conversions to the
desired product are obtainable under relatively moderate conditions,
often with an operating temperature about 100. to 210.degree. F.
lower than that required in the first hydrocracking reaction zone.
Further description of two-stage hydrocracking operations may be
found in U.S. Pat. Nos. 4429053 and 4857169 herein incorporated
by reference in their entireties, which patents provide process
flow sheets for typical two-stage hydrocracking processes.
Although hydrocracking catalysts containing noble metal-exchanged
zeolites are effective for use in single stage hydrocracking as
discussed above or in either the first or second stage of the two-stage
process discussed above, the activity of such catalysts is diminished
during the course of hydrocracking as coke materials deposit on
the catalyst particles and interfere with the activity of the catalyst.
It is thus necessary to periodically regenerate the catalyst by
combusting these carbonaceous deposits, usually at temperatures
between 700.degree. and 925.degree. F. It has been found, however,
that, after regeneration at temperatures in this range, the catalyst
used in the second hydrocracking reaction zone loses substantial
activity for hydrocracking under the relatively moderate conditions
employed therein.
Many attempts have been made to overcome the detrimental effects
associated with regenerating hydrocracking catalysts for use in
the ammonia-deficient environments of the second hydrocracking zone,
in particularly with respect to catalysts containing noble metal-exchanged
zeolites. These attempts have largely focused on methods for restoring
some or all of the catalytic activity lost through regeneration
by treating the regenerated catalyst with an ammonium salt, ammonium
hydroxide, gaseous ammonia, or mixtures thereof, thereby rejuvenating
the catalyst. The general theory behind these methods is that the
activity losses of catalysts used in hydrocracking environments
are caused by the agglomeration of the otherwise dispersed noble
metal hydrogenation component, and the ammoniation treatments redisperse
the noble metal component.
Although the above-discussed methods of regeneration and rejuvenation
of catalysts containing noble metal-exchanged zeolites have met
with some success, the results have not been consistent. For example,
in various instances regeneration has resulted in "reactivated"
catalysts that range from about 60.degree. to 110.degree. F. less
active than the fresh catalyst for hydrocracking under second stage
conditions, i.e., hydrocracking in an ammonia-deficient atmosphere.
Furthermore, for catalysts which can withstand rejuvenation utilizing
ammonia or ammonium ion treatments without collapse of the zeolitic
crystal structure, regeneration followed by rejuvenation has resulted
in reactivated catalysts that are between 10.degree. F. and 35.degree.
F. less active than the fresh catalyst for hydrocracking under second
stage conditions.
Accordingly, it should be clear that new methods for reactivating
deactivated noble metal-exchanged zeolitic catalysts, particularly
hydrocracking catalysts, are needed so that their catalytic activity
is substantially restored to the activity of the fresh catalyst
prior to deactivation.
SUMMARY OF THE INVENTION
In accordance with the invention, it has now been surprisingly
found that the activity of a reactivated catalyst comprising a crystalline
molecular sieve and a Group VIII noble metal component is sensitive
to the temperature at which its deactivated counterpart is regenerated
and that optimum activity of the reactivated catalyst is not obtained
unless the regeneration temperature is above about 950.degree. F.,
usually above about 1000.degree. F. Accordingly, the invention is
directed to a process for reactivating a deactivated catalyst, and
the reactivated catalyst resulting therefrom, by contacting the
deactivated catalyst, which comprises a crystalline molecular sieve,
a Group VIII noble metal component and carbonaceous deposits, with
a gas containing molecular oxygen in a combustion zone at a temperature
between 950.degree. F. and about 1200.degree. F. for a time sufficient
to remove at least a portion of the carbonaceous deposits via combustion.
It has been unexpectedly found that, to obtain optimum activity
upon reactivation, the temperature of the catalyst during the combustion
step should usually be in a range around about 1100.degree. F.,
and therefore it is generally preferred that the deactivated catalyst
be contacted with the gas containing molecular oxygen so that the
temperature of the catalyst is maintained in a range between about
1025.degree. F. and 1175.degree. F., more preferably between 1050.degree.
F. and 1150.degree. F., and most preferably between 1075.degree.
F. and 1125.degree. F.
It has been found that the activity of certain types of catalysts
that have been reactivated in accordance with the embodiment of
the invention described above, when used in particular applications,
can be further improved by subjecting the regenerated catalyst to
rejuvenation procedures to disperse the noble metal components,
usually by treating the regenerated catalyst with an aqueous ammonia
solution containing a dissolved ammonium salt. For example, it has
been found that the activity of a regenerated catalyst that contains
a dealuminated Y zeolite having an overall silica-to-alumina mole
ratio above about 6.0 which Y zeolite has been exchanged with both
noble metal-containing cations and rare earth-containing cations,
can be significantly improved for second stage hydrocracking under
ammonia-deficient conditions by treating the regenerated catalyst
with an aqueous ammonia solution containing dissolved ammonium bicarbonate.
In fact, it has been surprisingly found that, when optimum regeneration
temperatures are used to produce a reactivated catalyst from its
deactivated counterpart, rejuvenation of the reactivated catalyst
results in a second stage activity that is higher than the second
stage activity of the fresh catalyst.
The reactivated catalysts of the invention have been found to have
catalytic activity with respect to a variety of acid catalyzed chemical
conversion reactions and are therefore useful in a variety of hydrocarbon
conversion processes including hydrocracking processes, with particular
use being found in hydrocracking processes employing an ammonia-deficient
environment. For example, a reactivated catalyst of the invention
can be employed in the second hydrocracking zone of a petroleum
refining process wherein a hydrocarbon feedstock is first treated
employing an integral hydrotreating-hydrocracking operation followed
by further hydrocracking of unconverted components in a second hydrocracking
zone wherein an ammonia-deficient environment exists.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a plot which shows that the activity for second
stag hydrocracking under ammonia-deficient conditions of a catalyst
reactivated in accordance with the process of the invention is at
an optimum when the regeneration temperature is between about 1050.degree.
and 1150.degree. F.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a process for reactivating
a catalyst comprising a molecular sieve and a Group VIII noble metal
hydrogenation component, which catalyst has been deactivated by
the formation thereon of carbonaceous deposits during use of the
catalyst in a catalytic conversion process. The invention is also
directed to the reactivated catalyst produced by this process and
the use of such a reactivated catalyst in acid catalyzed chemical
conversion processes, particularly hydrocracking processes. The
present invention is particularly directed to reactivating a noble
metal-exchanged, zeolitic hydrocracking catalyst by combusting the
carbonaceous deposits contained thereon in the presence of a gas-containing
molecular oxygen at a temperature between 950.degree. F. and about
1200.degree. F., and then reusing the regenerated catalyst to hydrocrack
hydrocarbon feeds. The invention is also directed to rejuvenating
the regenerated catalyst by dispersing the Group VIII noble metal
components, and then reusing the rejuvenated catalyst to hydrocrack
a hydrocarbon feedstock in the substantial absence of ammonia, i.e.,
in an atmosphere containing less than about 200 ppmv ammonia, preferably
less than about 20 ppmv.
Deactivated catalysts which may be reactivated in accordance with
the invention usually comprise at least one Group VIII noble metal
component supported on a mixture of a crystalline molecular sieve
and a porous, inorganic refractory oxide component. These deactivated
catalysts also contain carbonaceous deposits which reduce their
effective surface area and pore volume, thereby substantially decreasing
their activity compared to that of their fresh counterparts.
The crystalline molecular sieve component of the deactivated and
reactivated catalysts may be a nonzeolitic or a zeolitic molecular
sieve having cracking activity in its activated form and is present
in the deactivated and reacted catalysts in amounts that typically
range from 10 to 90 weight percent, based on the weight of their
fresh counterparts, frequently between about 70 and 90 weight percent.
The term "molecular sieve" as used herein refers to any
material capable of separating atoms or molecules based on their
respective dimensions. The term "pore size as used herein refers
to the diameter of the largest molecule that can be sorbed by the
particular molecular sieve in question. The measurement of such
diameters and pore sizes is discussed more fully in Chapter 8 of
the book entitled "Zeolite Molecular Sieves" written by
D. W. Breck and published by John Wiley & Sons in 1974 the
disclosure of which book is hereby incorporated by reference in
its entirety. The term "nonzeolitic" as used herein refers
to molecular sieves whose frameworks are not formed of substantially
only silicon and aluminum atoms in tetrahedral coordination with
oxygen atoms whereas the term "zeolitic" as used herein
refers to molecular sieves whose frameworks are formed of substantially
only silicon and aluminum atoms in tetrahedral coordination with
oxygen atoms, such as the frameworks present in ZSM-5 zeolites,
zeolite beta, zeolite L, zeolite omega, Y zeolites and X zeolites.
Preferably, the molecular sieve used in the catalyst support is
a large pore sieve having a pore size greater than about 7.0 angstroms.
Thus, the sieve will generally have a low constraint index, typically
below 1.0 preferably below 0.75 and usually below 0.5.
Examples of nonzeolitic crystalline molecular sieves which may
be a component of both the deactivated catalyst and its reactivated
counterpart include silico-aluminophosphates, aluminophosphates,
ferrosilicates, galliosilicates, borosilicates, chromosilicates,
titanium aluminosilicates, titanium silicates, titanium aluminophosphates,
gallioaluminosilicates and crystalline silicas. Several of these
nonzeolitic molecular sieves are discussed in more detail in U.S.
Pat. Nos. 4867861 and 4829040 the disclosures of which are
hereby incorporated by reference in their entireties. It will be
understood that, although the reactivated catalysts of the invention
may include a nonzeolitic molecular sieve as discussed above, catalysts
which are essentially free of such sieves, including galliosilicates
and the other specific nonzeolitic molecular sieves mentioned above,
are within the scope of the invention.
Examples of zeolitic, crystalline molecular sieves which may be
a component of the deactivated catalyst and its reactivated counterpart
include Y zeolites, X zeolites, zeolite beta, zeolite L, zeolite
omega, mordenite, and modifications of such zeolites. However, the
preferred zeolitic molecular sieves are Y zeolites and modified
Y zeolites which possess cracking activity. U.S. Pat. No. 3130007
the disclosure of which is hereby incorporated by reference in its
entirety, describes Y-type zeolites having framework silica-to-alumina
mole ratios between 3.0 and 6.0 with a typical Y zeolite having
a framework silica-to-alumina mole ratio of about 5.0.
The modified Y zeolites which may be a component of the deactivated
catalyst and its reactivated counterpart are generally derived from
Y zeolites by treatment which results in a significant modification
of the Y zeolite framework structure, usually an increase in the
framework silica-to-alumina mole ratio to a value typically above
6.0 and/or a reduction in unit cell size. It will be understood,
however, that, in converting a Y zeolite starting material to a
modified Y zeolite, the resulting modified Y zeolite may not have
exactly the same X-ray powder diffraction pattern for Y zeolites
as is disclosed in U.S. Pat. No. 3130007. The d-spacings may be
shifted somewhat due to a shrinkage in the unit cell size caused
by an increase in the framework silica-to-alumina mole ratio. The
essential crystal structure of the Y zeolite will, however, be retained
so that the essential X-ray powder diffraction pattern of the modified
zeolite will be consistent with that of either Y zeolite itself
or a Y zeolite of reduced unit cell size. Examples of modified Y
zeolites which may be a component of the deactivated catalyst and
its reactivated counterpart include steam-stabilized Y zeolites,
dealuminated Y zeolites, and ultrahydrophobic Y zeolites.
Ultrahydrophobic zeolites are modified Y zeolites having a unit
cell size between about 24.20 and about 24.45 angstroms, preferably
between about 24.20 and 24.39 angstroms, most preferably between
about 24.20 and 24.35 angstroms, and a sorptive capacity for water
vapor less than about 5 weight percent, preferably less than about
4 weight percent, of the zeolite at 25.degree. C. and a p/p. value
of 0.10. The zeolites are the same or similar to the UHP-Y zeolites
disclosed in U.S. Pat. No. 4401556 and U.K. Patent 2014970 published
on Jun. 29 1982 the disclosures of which patents are hereby incorporated
by reference in their entireties. According to these references,
a UHP-Y zeolite is defined as a zeolite having a silica-to-alumina
mole ratio of from 4.5 to 35 the essential X-ray powder diffraction
pattern of zeolite Y, an ion exchange capacity of not greater than
0.070 a unit cell size from 24.20 to 24.45 angstroms, a surface
area of at least 350 square meters per gram (BET), a sorptive capacity
for water vapor less than 5 weight percent at 25 C. and a p/p. value
of 0.10 and a Residual Butanol Test Value of not more than 0.4
weight percent. The Residual Butanol Test is a measure of the adsorptive
selectivity of zeolite adsorbents for relatively nonpolar organic
molecules under conditions in which there is active competition
between water and less polar molecules for adsorption on the zeolite.
The test procedure is described in detail in the above-identified
patents. As used herein, "p/p." represent the water vapor
partial pressure to which the zeolite is exposed divided by the
water vapor partial pressure at 25.degree. C.
Preferably, the ultrahydrophobic zeolite has a silica-to-alumina
mole ratio between about 4.5 and 9 the essential X-ray powder diffraction
pattern of zeolite Y, an ion exchange capacity of not greater than
0.70 and a Residual Butanol Test Value of not more than 0.4 weight
percent. More preferably, the ultrahydrophobic zeolite is LZ-10
zeolite, a modified Y zeolite having a silica-to-alumina mole ratio
between about 4.5 and about 6.0 a surface area between about 500
and 700 square meters per gram, a unit cell size between about 24.20
and 24.35 angstroms, and a sorptive capacity for water vapor less
than about 5 percent by weight of the zeolite at 25.degree. C. and
a p/p. value of 0.10.
Steam-stabilized Y zeolites are Y zeolites which have been hydrothermally
treated to increase their framework silica-to-alumina mole ratio
but not their overall silica-to-alumina mole ratio. Steam stabilization
normally involves calcination of the ammonium or hydrogen form of
the Y zeolite starting material at relatively high temperatures,
typically above about 900.degree. F., in the presence of steam.
This treatment results in the expulsion of tetrahedral aluminum
from the framework into non-framework positions, but normally does
not remove the aluminum from the zeolite and therefore does not
increase the overall silica-to-alumina mole ratio of the starting
Y zeolite.
Preferred steam-stabilized Y zeolite which may be a component of
the deactivated catalyst and its reactivated counterpart are disclosed
in U.S. Pat. No. 3929672 herein incorporated by reference in its
entirety. These zeolites preferably have a unit cell size above
24.45 angstroms and a water vapor sorptive capacity greater than
15 weight percent at 25.degree. C. and a p/p. value of 0.10 and
are, in essence, produced by a three-step procedure in which a sodium
Y zeolite usually containing between about 10 and 14 weight percent
sodium, calculated as Na.sub.2 O, and having a unit cell size above
about 24.65 angstroms, usually between 24.65 and 24.75 angstroms,
is (1) cation exchanged with ammonium ions to decrease its sodium
content to between about 0.6 and 5.0 weight percent, calculated
as Na20 (2) calcined at a temperature between about 600.degree.
F. and 1650.degree. F., preferably between about 900.degree. F.
and 1300.degree. F., in the presence of steam at a water vapor partial
pressure of at least 0.2 psia to reduce the unit cell size of the
ammonium-exchanged zeolite to a value in the range between about
24.40 and 24.64 angstroms, preferably between about 24.48 and 24.58
angstroms, and (3) exchanged with ammonium cations to replace at
least about 25 weight percent of the residual sodium cations and
obtain a zeolite product containing less than about 1.0 weight percent
sodium, preferably less than about 0.6 weight percent sodium, calculated
as Na.sub.2 O. The resultant ammonium-exchanged, steam-calcined
zeolite may optionally, in a fourth step, be subjected to a further
calcination in a dry atmosphere, i.e., in essentially water- and
steam-free air, at a temperature usually between about 800.degree.
F. and 1000.degree. F.
The steam calcination step described above is usually carried out
in the presence of at least about 2.0 psia water vapor, preferably
at least 5.0 psia water vapor, and more preferably still between
5 and about 15 psia water vapor, and most preferably of all, in
an atmosphere consisting essentially of or consisting of steam.
The preferred steam-stabilized Y zeolites, whether produced by
the three- or four-step process described above or steam stabilized
via a different route, have (1) a unit cell size or dimension a.sub.o
greater than about 24.45 angstroms, preferably between about 24.46
and 24.61 angstroms, and most preferably between about 24.52 and
24.59 angstroms and (2) a sorptive capacity for water vapor greater
than about 15 weight percent at 25. C. and a p/p. value of 0.10
preferably greater than 18 weight percent, and usually between about
18 and 25 weight percent. The overall silica-to-alumina mole ratio
of these modified Y zeolites generally ranges between 5.1 and 6.0
typically between about 5.4 and 5.9. Examples of preferred steam-stabilized
Y zeolites include LZY-82 or Y-82 zeolite and LZY-84 or Y-84 zeolite
sold by UOP, CP300-56 zeolite sold by the PQ Corporation and CBV-530
CBV-531 CBV-705 CBV-712 and CBV-720 zeolites sold by Conteka-BV.
LZ-210 zeolites are conveniently prepared from a Y zeolite starting
material in silica-to-alumina mole ratios between about 6.0 and
about 20 although higher ratios are possible. Typically, the unit
cell size is at or below 24.63 angstroms and will normally range
between about 24.40 and about 24.63 angstroms, preferably between
about 24.47 and 24.62 angstroms. LZ-210 zeolites having a silica-to-alumina
mole ratio below 20 generally have a sorptive capacity for water
vapor at 25.degree. C. and 4.6 mm mercury water vapor partial pressure
of at least 20 weight percent based on the anhydrous weight of the
zeolite. Normally, the oxygen sorptive capacity at 100 mm mercury
and -183.degree. C. will be at least 25 weight percent.
In general, LZ-210 zeolites may be prepared by contacting a conventional
Y zeolite having an overall silica-to-alumina mole ratio less than
about 6.0 with an aqueous solution of a fluorosilicate salt, preferably
a solution of ammonium hexafluorosilicate to extract aluminum from
the framework structure while incorporating silicon from the solution
therein. The dealumination and silicon incorporation is accomplished
by placing an ammonium-exchanged Y zeolite into an aqueous reaction
medium such as an aqueous solution of ammonium acetate, and slowly
adding an aqueous solution of ammonium hexafluorosilicate. After
allowing the reaction to proceed, a zeolite having an increased
silica-to-alumina mole ratio is produced. The magnitude of the increase
is dependent at least in part on the amount of fluorosilicate solution
contacted with the zeolite and on the reaction time allowed. Normally,
a reaction time of between about 10 and about 24 hours is sufficient
for equilibrium to be achieved. The resulting solid product, which
may be separated from the aqueous reaction medium by conventional
filtration techniques, is a form of LZ-210 zeolite. In order to
provide greater activity and crystalline stability, this product
may be subjected to a steam calcination by contacting the product
with water vapor at a partial pressure of at least 0.2 p.s.i.a.
for a period of between about 1/4 to about 3 hours at a temperature
between about 900.degree. F. and about 1500.degree. F.
Catalysts to be reactivated in accordance with the invention and
their reactivated counterparts contain, in addition to the above-discussed
crystalline molecular sieves, a Group VIII noble metal hydrogenation
component, which is usually ion exchanged into the zeolite before
it is composited with the inorganic refractory oxide component of
the catalyst. The Group VIII noble metals which can be used in the
hydrogenation component include platinum, palladium, rhodium, iridium,
ruthenium and osmium. The preferred noble metal component comprises
platinum or palladium with palladium being most preferred. Typically,
the deactivated catalyst and its reactivated counterpart contain
at least 0.1 preferably between about 0.2 and about 8.0 and more
preferably between about 0.4 and 2.0 weight percent of the noble
metal component, calculated as the metal, and based on the weight
of their fresh counterparts.
Examples of the inorganic refractory oxide component of the deactivated
catalyst and its reactivated counterpart include alumina, silica-alumina,
silica-magnesia, clay such as kaolin, as well as combinations of
these and other materials. Such a component is usually present in
the deactivated and reactivated catalysts in an amount between about
10 and 90 weight percent, frequently between about 10 and 40 weight
percent, based on the weight of their fresh counterparts. The crystalline
molecular sieve and the porous, inorganic refractory oxide component
are physically integrated into particles which may have various
cross sectional sizes and shapes, e.g., a circle, trilobal clover-leaf,
quadrolobal clover-leaf, etc., and are usually between about 1/16
and 3/4 of an inch in length. Preferably, the catalyst particles
are in the shape of cylinders but, as mentioned above, other cross
sectional shapes are possible as is shown, for example, in FIGS.
8 and 10 respectively, in U.S. Pat. No. 4028227 herein incorporated
by reference in its entirety. Although the catalyst particles are
normally in the form of extrudates, they may also be in the shape
of tablets, granules, spheres and pellets. It will be understood,
of course, in the foregoing description that the porous, inorganic
refractory oxide is used a binder material for the crystalline molecular
sieve, and accordingly, if desired, other materials may be present
in the catalyst including, for example, inorganic refractory oxide
diluents which may or may not possess some type of catalytic activity.
Examples of such diluents include clays, alumina, silica-alumina,
and a heterogeneous dispersion of finely divided silica-alumina
in an alumina matrix, which dispersion is described in detail in
U.S. Pat. Nos. 4097365 and 4419271 the disclosures of which
are herein incorporated by reference in their entireties.
In some instances, the deactivated catalyst and its reactivated
counterpart may contain rare earth metal cations in addition to
the noble metal hydrogenation component. These rare earth metal
cations are normally ion exchanged into the molecular sieve from
rare earth metal solutions derived from ores such as bastnaesite
and monazite. Such rare earth solutions typically contain a mixture
of rare earth cations including lanthanum, cerium, praseodymium,
neodymium, samarium, europium, gadolinium, terbium, dysprosium,
holmium, erbium, thulium, ytterbium and lutetium. In general, if
the deactivated and reactivated catalysts do contain rare earth
metals, they are present in amounts between about 2 and 10 weight
percent, calculated as RE.sub.2 O.sub.3 and based on the weight
of their fresh counterparts. Catalysts comprising a dealuminated
Y zeolite which has been ion exchanged with both noble metal and
rare earth-containing cations, and methods of making such catalysts,
are described in detail in U.S. Pat. Nos. 4429053; 4604373 and
4857169 the disclosures of which are herein incorporated by reference
in their entireties.
During the course of processing a hydrocarbon-containing oil, fresh
catalysts comprising a crystalline molecular sieve and a Group VIII
noble metal component become deactivated as carbonaceous deposits
or coke accumulate thereon, thereby reducing their total available
surface area and plugging their pores. The resultant deactivated
or spent catalysts normally contain more than about 0.5 weight percent
carbonaceous deposits, calculated as carbon, typically between about
2.0 and 20 weight percent, and frequently between 5 and 15 weight
percent. These catalysts also may contain small amounts, i.e., less
than about 1.0 weight percent calculated as the element, of sulfur
and nitrogen components. Typically, these deactivated catalysts
lose, compared to their fresh counterparts, at least about 50 percent,
normally at least about 80 percent, and frequently over 100 percent,
of their catalytic activity at the end of the processing cycle.
It has been surprisingly found that, when such deactivated catalysts
are reactivated via regeneration, i.e., by removing the coke by
oxidation to carbon monoxide, carbon dioxide and water, the activity
of the regenerated catalyst is sensitive to the regeneration temperature.
If the deactivated catalyst is subjected to a temperature which
is too low or too high during regeneration, the activity of the
regenerated catalyst will not be at an optimum. It has been found
that for the regenerated catalyst to have an optimum activity, the
catalyst must reach a temperature between 950.degree. F. and 1200.degree.
F. during regeneration. Thus, the deactivated catalyst is typically
regenerated or reactivated by contacting it with a gas containing
molecular oxygen under conditions such that the catalyst is subjected
to a temperature in this range while at least a portion of the carbonaceous
deposits are burned off.
Prior to subjecting the deactivated catalyst to regeneration, it
is contacted with a flowing gas such as air, nitrogen or the like
at temperatures below that at which combustion of the carbonaceous
deposits occurs, typically at temperatures between about 350.degree.
and 450.degree. F., to remove volatile components such as free water
and light hydrocarbons. After this low temperature treatment, the
deactivated catalyst is then contacted with a flowing gas containing
molecular oxygen under conditions such that the temperature of the
deactivated catalyst is raised to between 950.degree. and 1200.degree.
F. as at least a portion of the carbonaceous deposits are combusted.
Also, small amounts of other materials subject to oxidation, such
as nitrogen and sulfur components, will be removed. It has been
found that the activity of the resulting regenerated catalyst reaches
an optimum when the combustion temperature is near about 1100 F.
Thus, it is normally preferred that the catalyst reach a temperature
in the combustion zone between about 1025.degree. F. and 1175.degree.
F., more preferably between about 1050.degree. F. and 1150.degree.
F., and most preferably between about 1075.degree. F. and 1125.degree.
F. Typically, the combustion of the carbonaceous material is continued
until less than about 1.0 weight percent carbonaceous material,
calculated as carbon, remains on the catalyst, frequently less than
about 0.5 weight percent.
The oxygen-containing gas used to combust the carbonaceous deposits
may be any inert gas which contains oxygen and is free of other
reactive compounds such as water and chlorine. It is important that
the gas be substantially free of water and steam since these substances
will cause the noble metal components to agglomerate at high temperatures
and thereby reduce the activity of the regenerated catalyst. Normally,
the oxygen content of the gas will range between about 0.5 and 50
volume percent, typically between 5 and 25 volume percent. Generally,
air, which contains about 20 volume percent oxygen, is the preferred
gas. The deactivated catalyst is normally contacted with air or
other gas containing molecular oxygen for a time sufficient to remove
the desired amount of carbonaceous material. The contacting time
will normally range between 5 minutes and 10 hours, usually between
2 and 6 hours and frequently between 3 and 5 hours.
The deactivated catalyst can be regenerated or reactivated in the
reactor in which it became deactivated or it can be removed from
the reactor and then regenerated. If the regeneration is carried
out in the reactor, i.e., in-situ, the catalyst is first stripped
with nitrogen or other inert gas to remove light hydrocarbons, free
water and other volatiles and then contacted in a fixed bed with
a gas containing molecular oxygen, which gas is passed downwardly
through the fixed bed at pressures sufficient to force the gas uniformly
through the deactivated catalyst, usually pressures between about
50 and 200 psia. The oxygen content of the downflowing gas is typically
controlled so that the peak combustion temperature is kept below
the temperature at which the noble metal-components agglomerate
If, on the other hand, the deactivated catalyst is first removed
from the reactor and then regenerated, i.e. ex-situ, the carbonaceous
deposits are normally removed, after volatiles have been driven
off, by combustion at atmospheric pressure in a belt-type regenerator,
a direct or indirect fired, rotary-type dryer/calciner, such as
a Roto-Louvre dryer, or in similar equipment. Such equipment will
be familiar to those skilled in the art. In these types of commercial
dryers/calciners, the catalyst bed does not move vertically, but
instead is passed in nonuniform thickness either horizontally, such
as in belt-type regenerators, or at an incline either up or down
from the horizontal in rotary type dryers/calciners. Regardless
of whether the catalyst is regenerated in-situ in a fixed bed or
ex-situ in a moving, non-vertical bed, the catalyst bed is not normally
confined by gas permeable sidewalls such as retention screens.
It should be emphasized that the regeneration temperatures referred
to above are the temperatures on the surface of the deactivated
catalyst even though the surrounding temperature of the oxygen-containing
gas atmosphere may be somewhat different. Typically, the temperature
on the surface of the catalyst is determined by catalyst bed temperature
sensing devices, such as in-bed thermocouples or infrared pyrometers.
During regeneration, the surface temperature of the deactivated
catalyst must be controlled to prevent excessive agglomeration of
the catalytically active noble metal components which, in turn,
causes diminished restoration of catalytic activity.
The reactivated catalysts produced by regeneration in accordance
with the process of the invention normally contain less than about
1.0 preferably between about 0.1 and 0.5 weight percent carbonaceous
deposits, calculated as carbon. The high temperature regeneration
or combustion step also removes hydrogen, sulfur and nitrogen components
associated with the deactivated catalysts so that the regenerated
catalysts contain less than about 0.2 weight percent of these components,
calculated as hydrogen, sulfur, and nitrogen, respectively. The
reactivated catalysts typically have a surface area ranging between
about 400 and 750 frequently between 500 and 700 square meters
per gram. In general, the surface area of the reactivated catalysts
is between 20 and 150 frequently between 60 and 125 square meters
per gram less than their fresh counterparts.
Catalysts regenerated in accordance with the process of the invention
typically have an activity that is at least 50 percent that of the
original activity of the fresh catalyst, preferably at least 75
percent, and more preferably at least about 90 percent. The actual
percentage of activity restoration will depend primarily on the
particular use intended for the regenerated catalyst when it is
returned to service. For example, when the regenerated catalyst
is a hydrocracking catalyst and is returned to service in ammonia-rich
first stage hydrocracking, i.e. hydrocracking in the presence of
greater than 2000 ppmv ammonia, the activity of the catalyst is
normally restored to about 99 percent of its fresh activity. In
general, catalysts regenerated in accordance with the invention
are at least 25.degree. F. more active than the deactivated catalyst,
frequently at least 50.degree. F. more active, and quite frequently
at least 70.degree. F. more active.
With respect to certain uses, the regenerated catalyst of the invention
may not exhibit the desired activity in relation to the fresh catalyst.
For example, regenerated catalysts containing dealuminated Y zeolites
that have been exchanged with rare earth and noble metal-containing
cations may have less than 50 percent the activity of their fresh
counterparts when used in ammonia-deficient second stage hydrocracking.
It is believed that this failure to reclaim substantially all of
the activity of the fresh catalyst upon regeneration is due to the
agglomeration of the Group VIII noble metal constituents and the
failure of the regeneration procedure to adequately redistribute
or redisperse the agglomerated constituents.
It has now been surprisingly found that the activity of such catalysts
regenerated in accordance with the process of the invention can
be further increased to a level above that of their fresh counterparts
by treating the regenerated catalysts with gaseous ammonia or an
ammonium-ion containing solution such as an aqueous ammonia solution
containing a dissolved ammonia salt. It is believed that this further
treatment, which is referred to as rejuvenation, restores the activity
of the catalysts to a level near or above that of their fresh counterparts
by dispersing the agglomerated noble metal-containing cations.
One method of carrying out the rejuvenation is described in U.S.
Pat. No. 3899441 the disclosure of which is hereby incorporated
by reference in its entirety, and involves first steam treating
the regenerated catalyst to fill its pores with water, treating
the water saturated catalyst with ammonia vapor, stripping the catalyst
with an inert gas such as nitrogen and then drying and calcining
the catalyst. Another rejuvenation technique involves steam-treating
the regenerated catalyst followed by a gaseous ammonia treatment,
a contacting with an aqueous solution of an ammonium salt such as
ammonium nitrate, drying and calcining. This procedure is described
in more detail in U S. Pat. Nos. 3692692 and 3835028 the disclosures
of which are hereby incorporated by reference in their entireties.
A preferred method for carrying out the rejuvenation is described
in U.S. Pat. No. 3849293 the disclosure of which is hereby incorporated
by reference in its entirety. This procedure involves treating the
regenerated catalyst with an aqueous ammonia solution in which an
ammonium salt, such as ammonium nitrate, ammonium carbonate, or
ammonium bicarbonate, is dissolved. This technique is typically
carried out by placing the regenerated catalyst in a closeable vessel,
adding water to the vessel to a level just above that of the catalyst,
and then adding an aqueous ammonia solution containing an ammonium
salt. The contents of the vessel are then heated to a temperature
below the boiling point of water, usually between about 50.degree.
and 80.degree. C., as the aqueous ammonia solution containing the
ammonium salt is circulated through the catalyst bed. The catalyst
is then separated from the solution, washed with deionized water,
dried at a temperature between about 90.degree. and 120.degree.
C. and then calcined between about 400.degree. and 600.degree. C.
The resultant rejuvenated catalyst, especially one containing a
dealuminated Y zeolite having an overall silica-to-alumina mole
ratio greater than 6.0 that has been ion exchanged with noble metal
and rare earth-containing cations, has been found to have an activity
for second stage hydrocracking that is equal to or better than that
of its fresh counterpart. It is believed that this complete restoration
of activity is due to the deactivated catalyst being regenerated
in the critical temperature range between 950.degree. and 1200.degree.
F.
Other methods for carrying out the rejuvenation are described in
U.S. Pat. Nos. 3943051; 4190553; 4002575; 4107031 and 4139433.
The disclosures of these five patents are hereby incorporated by
reference in their entireties.
Catalysts of the invention, which have been reactivated either
by the regeneration process of the invention or regeneration followed
by rejuvenation, can be used for converting hydrocarbons and other
organic compounds into more valuable reaction products by acid catalyzed
reactions such as isomerization, reforming, hydrogenation, hydrocracking
and the like. Normally, however, the reactivated catalysts of the
invention are used as hydrocracking catalysts in the conversion
of a wide variety of hydrocarbon feedstocks to a hydrocarbon product
of lower average boiling point and/or molecular weight. Before such
use, however, the noble metal components of the reactivated catalysts
are typically reduced to their active form by contacting the catalyst
at an elevated temperature, e.g., 300.degree. to 700.degree. F.,
with hydrogen gas.
The feedstocks that may be subjected to hydrocracking using the
reactivated catalysts of the invention include all mineral oils
and synthetic oils (e.g., shale oil, tar sand products, etc.) and
fractions thereof. Illustrative feedstocks include straight run
gas oils, vacuum gas oils, coker gas oils, and catcracker distillates.
The typical hydrocracking feedstock, however, contains a substantial
proportion of components, usually at least 50 percent by volume,
often at least 75 percent by volume, boiling above the desired end
point of the product, which end point, in the case of gasoline,
will generally be in the range of about 380.degree. to 420.degree.
F., and in the case of middle distillates, will typically be in
the range of 650.degree. to 700.degree. F. Usually, the feedstock
will also contain gas oil components boiling above 550.degree. F.,
with highly useful results being achievable with feeds containing
at least 30 percent by volume of components boiling between 600.
and 1100 F. |