Molecular sieve abstract
A method is disclosed for modifying a catalytic molecular sieve
for shape-selective hydrocarbon conversions comprises: a) selectivating
said catalytic molecular sieve by contacting with a silicon-containing
selectivating agent; and b) calcining the selectivated catalytic
molecular sieve at high temperature calcination conditions comprising
temperatures greater than 700.degree. C., which conditions are sufficient
to reduce acid activity as measured by alpha value and increase
diffusion barrier of said catalytic molecular sieve as measured
by the rate of 23-dimethylbutane uptake, as compared to the selectivated
catalyst. Catalytic molecular sieves thus prepared, such as silica-bound
ZSM-5 and their use in hydrocarbon conversion processes such as
aromatics isomerization, e.g., xylene isomerization, ethylbenzene
conversion and aromatics disproportionation, e.g., toluene disproportionation
are also disclosed.
Molecular sieve claims
It is claimed:
1. A method for modifying a catalytic molecular sieve which comprises:
a) selectivating said catalytic molecular sieve by contacting with
a silicon containing selectivating agent; and b) calcining the selectivated
catalytic molecular sieve at high temperature calcination conditions
comprising temperatures greater than 700.degree. C., which conditions
are sufficient to reduce acid activity as measured by alpha value
and increase diffusion barrier of said catalytic molecular sieve
as measured by the rate of 23-dimethylbutane uptake, as compared
to the selectivated catalytic molecular sieve.
2. A method for modifying a catalytic molecular sieve for shape-selective
hydrocarbon conversions which comprises: a) selectivating said catalytic
molecular sieve by contacting with a silicon containing selectivating
agent; and b) calcining the selectivated catalytic molecular sieve
at high temperature calcination conditions comprising temperatures
greater than 700.degree. C., which conditions are sufficient to
reduce acid activity as measured by alpha value and increase diffusion
barrier of said catalytic molecular sieve as measured by the rate
of 23-dimethylbutane uptake by at least 25%, as compared to the
selectivated catalyst.
3. The method of claim 2 wherein said catalytic molecular sieve
is selected from the group consisting of ZSM-5 ZSM-11 ZSM-12
ZSM-22 ZSM-23 ZSM-35 ZSM-48 ZSM-50 ZSM-57 ZSM-58 zeolite
beta, MCM-22 MCM-36 MCM-49 MCM-56 mordenite, MCM-58 synthetic
faujasite, natural faujasite, MCM-41 ALPO-5 VPI-5 SAPO-5 SAPO-11
SAPO-30 SAPO-31 SAPO-34 ITQ-2 ITQ-3 ITQ-12 and ITQ-13.
4. The method of claim 3 wherein said catalytic molecular sieve
is a silica-bound ZSM-5.
5. The method of claim 2 wherein said catalytic molecular sieve
comprises a metal of a group selected from Group VIIIA, Group VIIA,
Group VIA, Group VB, Group IVB, Group IIB, Group IIA, and Group
IB of the Periodic Table.
6. The method of claim 2 wherein said catalytic molecular sieve
comprises a hydrogenation metal selected from the group consisting
of platinum, palladium, iron, nickel, gallium, zinc, molybdenum,
and rhenium.
7. The method of claim 2 wherein said selectivating agent is selected
from the group consisting of polysiloxanes, siloxanes, silanes,
disilanes and alkoxysilanes.
8. The method of claim 2 wherein said selectivating is carried
out by two to six treatments with a selectivating agent.
9. The method of claim 2 wherein- said calcining is carried out
under conditions sufficient to provide a catalytic molecular sieve
having an alpha value of less than 700 and a diffusion barrier as
measured by the rate of 23-dimethylbutane uptake of less than 270
(D/(r.sup.2.times.10.sup.6 sec)).
10. The method of claim 2 wherein said calcining is carried out
under conditions sufficient to provide a catalytic molecular sieve
having an alpha value ranging from 25 to 200 and a diffusion barrier
as measured by the rate of 23-dimethylbutane uptake of less than
150 (D/(r.sup.2.times.10.sup.6 sec)).
11. The method of claim 2 wherein said calcining is carried out
under conditions sufficient to provide a catalytic molecular sieve
having an alpha value ranging from 5 to 25.
12. The method of claim 2 wherein said calcining is carried out
at temperatures ranging from greater than 700.degree. to 1200.degree.
C. for 0.1 to 12 hours.
13. The catalytic molecular sieve of claim 12 wherein said catalytic
molecular sieve is a silica-bound ZSM-5 and further comprising a
hydrogenation metal selected from the group consisting of platinum,
palladium, iron, molybdenum, and rhenium.
14. A method for shape-selective hydrocarbon conversion which comprises:
i) selectivating a catalytic molecular sieve by contacting with
a silicon-containing selectivating agent; ii) calcining the selectivated
catalytic molecular sieve at high temperature calcination conditions
comprising temperatures greater than 700.degree. C., which conditions
are sufficient to reduce acid activity as measured by alpha value
and increase diffusion barrier of said catalytic molecular sieve
as measured by the rate of 23-dimethylbutane uptake, as compared
to the selectivated catalytic molecular sieve, to provide a high
temperature calcined catalytic molecular sieve, and iii) contacting
a hydrocarbon feed under hydrocarbon conversion conditions with
said high temperature calcined catalytic molecular sieve.
15. The method of claim 14 wherein said shape-selective hydrocarbon
conversion is selected from the group consisting of catalytic cracking,
aromatics disproportionatiori, aromatics isomerization, aromatic
alkylation, catalytic dewaxing and naphtha reforming.
16. The method of claim 14 wherein said shape-selective hydrocarbon
conversion is toluene disproportionation.
17. The method of claim 14 wherein said shape-selective hydrocarbon
conversion is xylene isomerization.
18. The method of claim 1 wherein said diffusion barrier is increased
by at least 25%.
19. The method of claim 2 wherein said diffusion barrier is increased
by at least 35%.
20. The method of claim 2 wherein said diffusion barrier is increased
by at least 50%.
Molecular sieve description
FIELD OF THE INVENTION
[0001] The present invention relates to a process for modifying
acid activity and diffusional restriction of selectivated zeolite
hydrocarbon conversion catalysts, as well as the catalysts so modified,
and their use in shape-selective hydrocarbon conversion.
BACKGROUND OF THE INVENTION
[0002] Diffusionally modified catalysts find use in many shape-selective,
hydrocarbon processing applications. The selectivity to more desirable
products (and ultimate product slate) can be modified with diffusionally
restricted catalysts. Mass transport selectivity arises from a large
difference in the diffusivity of the participating molecules in
the zeolite channels, while transition state selectivity results
from steric constraints limiting the possible transition state of
the catalytic transformation step. The advantages of diffusionally
modified catalysts are especially useful in certain petroleum/petrochemical
industry processes including catalytic dewaxing, olefin alkylation,
shape-selective cracking and aromatic conversion processes such
as aromatics disproportionation, e.g., toluene disproportionation,
aromatics isomerization, e.g., xylene isomerization, and para-selective
aromatics alkylation. The optimum level of acidity for these reactions
can vary substantially. For selective aromatics disproportionation
processes, e.g., toluene disproportionation processes, a high acid
level (700 alpha) can produce a high value product slate. Selective
ethylbenzene conversion processes are optimized by a medium acidity
level (-50-150 alpha), while dewaxing and para-selective aromatics
alkylation processes prefer lower acid activities (-5-25 alpha).
[0003] Ex-situ selectivated catalysts, such as those modified via
multiple silica treatments, are particularly attractive for these
processes because the diffusion barrier required for optimal performance
is present prior to utilization for the reaction of choice. Presently,
high acid activity zeolite catalyst can be used as a base for multiple
selectivation sequences, e.g., a 1000 alpha catalyst is used to
produce a high acid activity toluene disproportionation catalyst,
which after several selectivation treatments still has an alpha
value of about 700 while diffusionally modified catalyst for other
applications may require lower acid activity as noted above.
[0004] Steaming has been used to decrease acid activity of catalysts.
However, steaming silica-selectivated catalysts to the lower acid
activity levels required for certain applications significantly
decreases the diffusional barrier, probably resulting from migration
of the silica diffusion barrier during steaming.
[0005] Accordingly, it would be desirable to provide a method for
modifying zeolite catalyst activity, which does not decrease the
diffusion barrier of the resulting catalyst. It would further be
desirable to provide a method for modifying zeolites to provide
a diffusionally restricted catalyst having reduced acid activity
while maintaining or increasing the diffusion barrier of the modified
catalyst.
[0006] U.S. Pat. No. 5849968 to Beck et al. discloses a process
for shape-selective hydrocarbon conversion using a zeolite catalyst
selectivated with a siliceous material and treated with an aqueous
solution comprising alkaline earth metal ions under ion exchange
conditions. After selectivation, the zeolite is calcined at temperatures
greater than 200.degree. C., including temperatures below 700.degree.
C. U.S. Pat. No. 5610112 to Lago et al. discloses a process for
modifying a catalytic molecular sieve by pre-selectivation to deposit
a silicon compound on the external surface of the catalyst and then
calcined at a temperature below 600.degree. C. for one to 24 hours.
The catalyst may then be steamed at 200.degree. C. to 538.degree.
C. to provide improved selectivity. U.S. Pat. No. 5726114 to Chang
et al. discloses a method for modifying catalytic molecular sieve
to enhance shape selectivity by exposing to at least one ex situ
selectivation sequence which includes impregnation of the molecular
sieve with a selectivating agent in an aqueous emulsion and a subsequent
calcination of the impregnated molecular sieve at temperatures below
600.degree. C. U.S. Pat. No. 5384296 to Tsao discloses a thermally
stable noble metal-containing zeolite catalyst which has increased
resistance to noble metal agglomeration as a result of calcining
at at least 600.degree. C. in moist air. U.S. Pat. No. 5034362
to Chu et al. discloses a zeolite catalyst composition having improved
shaped selectivity which has been calcined at a temperature of at
least 649.degree. C. which is useful for aromatic conversion reactions.
None of these disclosures teach or suggest the use of very high
temperature calcination as a means to modify acid activity of selectivated
molecular sieves without decreasing diffusional resistance of the
modified catalyst.
SUMMARY OF THE INVENTION
[0007] The present invention relates to a method for modifying
a catalytic molecular sieve, e.g., for shape-selective hydrocarbon
conversions, which comprises:
[0008] a) selectivating said catalytic molecular sieve by contacting
with a silicon-containing selectivating agent; and
[0009] b) calcining the selectivated catalytic molecular sieve
at high temperature calcination conditions comprising temperatures
greater than 700.degree. C., which conditions are sufficient to
reduce acid activity as measured by alpha value and increase diffusion
barrier of said catalytic molecular sieve as measured by the rate
of 23-dimethylbutane uptake, as compared to the selectivated catalyst,
e.g., increasing said diffusion barrier by at least 25%, at least
35%, at least 50% or more.
[0010] In another aspect, the present invention relates to a method
for shape-selective hydrocarbon conversion which comprises:
[0011] i) selectivating a catalytic molecular sieve by contacting
with a silicon-containing selectivating agent;
[0012] ii) calcining the selectivated catalytic molecular sieve
at high temperature calcination conditions comprising temperatures
greater than 700.degree. C., which conditions are sufficient to
reduce acid activity as measured by alpha value and increase diffusion
barrier of said catalytic molecular sieve as measured by the rate
of 23-dimethylbutane uptake, as compared to the selectivated catalytic
molecular sieve, to provide a high temperature calcined catalytic
molecular sieve, and
[0013] iii) contacting a hydrocarbon feed under hydrocarbon conversion
conditions with said high temperature calcined catalytic molecular
sieve.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Further scope of applicability of the present invention
will become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the invention
will become apparent to those skilled in the art from this detailed
description.
[0015] Catalysts
[0016] The catalytic molecular sieve used in the present invention
can be a zeolite, e.g., an intermediate pore-size zeolite having
a constraint index within the approximate range of 1 to 12 (e.g.,
zeolites having less than about 7 angstroms pore size, such as from
about 5 to less than 7 angstroms) having a silica to alumina mole
ratio of at least about 5 e.g., at least about 12 e.g., at least
20.
[0017] The silica to alumina mole ratio referred to may be determined
by conventional analysis. This ratio is meant to represent, as closely
as possible, the molar ratio in the rigid anionic framework of the
zeolite crystal and to exclude silicon and aluminum in the binder
or in cationic or other form within the channels.
[0018] Examples of intermediate pore size zeolites useful in this
invention include ZSM-5 (U.S. Pat. No. 3702886) and U.S. Pat.
No. Re. 29948); ZSM-11 (U.S. Pat. No. 3709979), ZSM-5/ZSM-11
intermediate (U.S. Pat. No. 3832449); ZSM-12 (U.S. Pat. No. 3832449);
ZSM-22 (U.S. Pat. No. 4556477); ZSM-23 (U.S. Pat. No. 4076842);
ZSM-35 (U.S. Pat. No. 4016245); ZSM-48 (U.S. Pat. No. 4397827);
ZSM-50 (U.S. Pat. No. 4640829; ZSM-57 (U.S. Pat. No. 5046685);
and/or ZSM-58 (U.S. Pat. No. 5417780).
[0019] Other zeolites suitable for use in some embodiments of the
present invention include zeolite beta, MCM-22 (U.S. Pat. No. 5304968),
MCM-36 (U.S. Pat. No. 5292698), MCM-49 (U.S. Pat. No. 5236575),
MCM-56 (U.S. Pat. No. 5362697), mordenite, MCM-58 (U.S. Pat. No.
5437855), synthetic and natural faujasites, and amorphous or ordered
mesoporous materials such as MCM-41 (U.S. Pat. No. 5098684).
[0020] Additional molecular sieves which find utility in conjunction
with the present invention include aluminophosphates, e.g., ALPO-5
VPI-5; silicoaluminophosphates, e.g., SAPO-5 SAPO-I;, SAPO-30
SAPO-31 SAPO-34; and other metal aluminophosphates. These are variously
described in U.S. Pat. Nos. 4440871; 4554143; 4567029; 4666875;
and 4742033.
[0021] Further additional molecular sieves which find utility in
the present invention include ITQ-2 ITQ-3 (described in U.S. Patent
No. 6500404), ITQ-12 (described in U.S. Pat. No. 6471939), and
ITQ-13 (described in U.S. Pat. No. 6471941). The structural types
and references to the synthesis of these zeolites can be found in
the "Atlas of Zeolite Framework Types" (published on behalf
of the Structure Commission of the International Zeolite Association),
by Ch. Caerlocher, W. M. Meier, and D. H. Olson, published by Elsevier,
Fifth revised edition, 2002 which is hereby incorporated by reference.
Structural types and references to the zeolites mentioned above
are available on the World Wide Web at www.iza-structure.org. Such
zeolites are commercially available from Zeolyst International,
Inc.
[0022] Alpha Value Measurement
[0023] The alpha value of a catalyst is an approximate indication
of the catalytic cracking activity of the catalyst compared to a
standard catalyst, and it gives the relative rate constant (rate
of normal hexane conversion per volume of catalyst per unit time).
It is based on the activity of the amorphous silica-alumina cracking
catalyst taken as an alpha of 1 (Rate Constant=0.016 sec.sup.-1).
The alpha test is described in U.S. Pat. No. 3354078 and in the
Journal of Catalysis, 4 522-529 (1965); 6 278 (1966); and 61
395 (1980), each incorporated herein by reference as to that description.
It is noted that intrinsic rate constants for many acid-catalyzed
reactions are proportional to the alpha value for a particular crystalline
silicate catalyst (see AThe Active Site of Acidic Aluminosilicate
Catalysts,.congruent.Nature, Vol. 309 No. 5959 589-591 (1984)).
The experimental conditions of the test used herein include a constant
temperature of 538EC. and a variable flow rate as described in detail
in the Journal of Catalysis, 61 395 (1980). The catalysts employed
in the process of the present invention can have an alpha value
less than 700 preferably 25 to 200 say, 75 to 150 5 to 25 (for
lower acid activity processes such as aromatics alkylation), and
a silica-alumina ratio less than 100 preferably 20-80. The alpha
value of the catalyst may be increased by initially treating the
catalyst with nitric acid or by mild steaming before selectivation
as discussed in U.S. Pat. No. 4326994. Generally, the present
invention relates to reducing the alpha value of catalyst as prepared
to tailor it to the specific application in which it is to be used,
without significantly reducing the diffusional barrier of the catalyst
(say, by more than 5 or 10%). Indeed, in most instances, alpha value
is reduced while actually increasing the diffusional barrier. This
represents a significant improvement in controlling catalyst selectivity
and activity inasmuch as steaming to reduce alpha value significantly
reduces the diffusional barrier.
[0024] Diffusion Barrier Measurement
[0025] As used herein, the Diffusion Parameter of a particular
porous crystalline material is defined as D/(r.sup.2.times.10.sup.6),
wherein D is the diffusion coefficient (cm.sup.2/sec) and r is the
crystal radius (cm). The required diffusion parameters can be derived
from sorption measurements provided the assumption is made that
the plane sheet model describes the diffusion process. Thus for
a given sorbate loading Q, the value Q/Q.sub..infin., where Q.sub..infin.
is the equilibrium sorbate loading, is mathematically related to
(Dt/r.sup.2).sup.1/2 where t is the time (sec) required to reach
the sorbate loading Q. Graphical solutions for the plane sheet model
are given by J. Crank in "The Mathematics of Diffusion",
Oxford University Press, Ely House, London, 1957.
[0026] The apparatus and procedures for performing static and dynamic
adsorption measurements are described in G. R. Landolt, Anal. Chem.
(1971) 43 613 and E. L. Wu, G. R. Landolt, and A. W. Chester,
"Hydrocarbon Adsorption Characterization of Some High Silica-Zeolites,"
Stud. Surf. Science & Catal. 28 p. 547. Changes in the diffuision
barrier resulting from high temperature calcination can be monitored
by observing the Diffusion Parameter as described above. The values
thereof are based on the rate of uptake of sorbate 23-dimethylbutane
(or bulkier 22-dimethylbutane for lower diffusion barriers). Equilibrium
capacity of the diffusing medium is determined according to Crank's
solution to diffusion in a porous body having flat plate geometry.
With proper adjustment, the equilibrium capacity may be estimated
from values of a more rapidly diffusing molecule, e.g., n-hexane.
The n-hexane isotherms are measured at 90.degree. C. and the amount
sorbed at 75 torr taken as sorption capacity. Nominal experimental
conditions for obtaining diffusivity measurements with 23-dimethylbutane
are 120.degree. C. and 44 torr. The weight uptake of 23-dimethylbutane
versus the square root of time is plotted from which the rate is
obtained and D/(r.sup.2.times.10.sup.6) is calculated.
[0027] Catalyst Binder
[0028] The catalysts of the present invention can optionally be
employed in combination with a support or binder material (binder).
The binder is preferably an inert, non-alumina containing material,
such as a porous inorganic oxide support or a clay binder. One such
preferred inorganic oxide is silica. Other examples of such binder
material include, but are not limited to zirconia, magnesia, titania,
thoria and boria. These materials can be utilized in the form of
a dried inorganic oxide gel or as a gelatinous precipitate. Suitable
examples of clay binder materials include, but are not limited to,
bentonite and kieselguhr. The relative proportion of catalyst to
binder material to be utilized is from about 30 wt. % to about 98
wt. %. A proportion of catalyst to binder from about 50 wt. % to
about 80 wt. % is more preferred. The bound catalyst can be in the
form of an extrudate, beads or fluidizable microspheres.
[0029] Cation Exchanged Zeolites
[0030] The catalyst may be associated with hydrogen, e.g., hydrogen-exchanged
zeolite, or the catalyst may be associated with a hydrogenation
component (hydrogenation-dehydrogenation component, e.g., hydrogenation
metal). Examples of such components include the oxide, hydroxide,
sulfide, or free metal (i.e., zero valent) forms of Group VIIA metals
(i.e., Pt, Pd, Ir, Rh, Os, Ru, Ni, Co and Fe), Group VIIA metals
(i.e., Mn, Tc, and Re), Group VIA metals (i.e., Cr, Mo, and W),
Group VB metals (i.e., Sb and Bi), Group IVB metals (i.e., Sn and
Pb), Group IIB metals (i.e., Ga and In), Group IIA metal, (e.g.,
Zn) and Group IB metals (i.e., Cu, Ag and Au). Noble metals (i.e.,
Pt, Pd, Ir, Rh, Os and Ru) are preferred hydrogenation components.
Combinations of catalytic forms of such noble or non-noble metal,
such as combinations of Pt with Sn, may be used. The metal may be
in a reduced valence state, e.g., when this component is in the
form of an oxide or hydroxide. The reduced valence state of this
metal may be attained, in situ, during the course of a reaction,
when a reducing agent, such as hydrogen, is included in the feed
to the reaction.
[0031] The hydrogenation component may be incorporated into the
catalyst by methods known in the art, such as ion exchange, impregnation
or physical admixture. For example, solutions of appropriate metal
salts may be contacted with the remaining catalyst components, either
before or after selectivation of the catalyst, under conditions
sufficient to combine the respective components. The metal-containing
salt may be water soluble. Examples of such salts include chloroplatinic
acid, tetraamineplatinum complexes, platinum chloride, tin sulfate
and tin chloride. The metal may be incorporated in the form of a
cationic, anionic or neutral complex such as Pt (NH.sub.3).sub.2.sup.2+
and cationic complexes of this type will be found convenient for
exchanging metals onto the zeolite. For example, a platinum modified
catalyst can be prepared by first adding the catalyst to a solution
of ammonium nitrate in order to convert the catalyst to the ammonium
form. The catalyst is subsequently contacted with an aqueous solution
of tetraamine platinum(II) nitrate or tetraaamine platinum(II) chloride.
Anionic complexes such as the vanadate or metatungstate ions are
also useful for impregnating metals into the zeolites. Incorporation
may be undertaken in accordance with the invention of U.S. Pat.
No. 4312790 incorporated by reference herein. After incorporation
of the metal, the catalyst can then be filtered, washed with water
and calcined at temperatures of from about 250.degree. C. to about
500.degree. C.
[0032] The amount of hydrogenation component may be that amount
which imparts or increases the catalytic ability of the overall
catalyst to catalytically hydrogenate or dehydrogenate an organic
compound under sufficient hydrogenation or dehydrogenation conditions,
e.g., hydrogenate ethylene to ethane. This amount is referred to
as a catalytic amount. The amount of the hydrogenation component
may be from 0.001 to 10 percent by weight, although this will, of
course, vary with the nature of the component, with less of the
highly active noble metals, particularly platinum, being required
than of the less active base metals.
[0033] Catalyst Selectivation
[0034] The catalyst of the present invention can be selectivated
by a vapor phase process or a liquid phase process. An example of
a liquid phase selectivation process is described herein as an ex
situ selectivation process. Examples of ex situ selectivation techniques
suitable for use in the present invention are provided in U.S. Pat.
Nos. 5367099; 5404800; and 5365004. The ex situ selectivation
treatment may result in the deposition of at least 1 wt. % of siliceous
material on the zeolite. The treatment deposits siliceous material
on the catalyst by contacting the catalyst with a silicon-containing
selectivating agent. Subsequent to treatment with the selectivating
agent, the catalyst may be conventionally calcined at temperatures,
below, say, 600.degree. C. or less, under conditions sufficient
to remove organic material therefrom while leaving the siliceous
material on the zeolite, preferably without reducing the crystallinity
of the zeolite.
[0035] The catalyst may be ex situ selectivated by single or multiple
treatments with a liquid organosilicon compound in a liquid carrier.
Each treatment can be followed by calcination of the treated material
in an oxygen-containing atmosphere, e.g., air.
[0036] In accordance with the multiple impregnation ex situ selectivation
method, the zeolite is treated at least twice, e.g., from 2 to 6
times, with a liquid medium comprising a liquid carrier and at least
one liquid organosilicon compound. The organosilicon compound may
be present in the form of a solute dissolved in the liquid carrier
or in the form of emulsified droplets in the liquid carrier. For
the purposes of the present disclosure, it will be understood that
a normally solid organosilicon compound will be considered to be
a liquid (i.e., in the liquid state) when it is dissolved or emulsified
in a liquid medium. The liquid carrier may be water, an organic
liquid or a combination of water and an organic liquid. Particularly
when the liquid medium comprises an emulsion of the organosilicon
compound in water, the liquid medium may also comprise an emulsifying
agent, such as a surfactant. Stable aqueous emulsions of organosilicon
compounds (e.g., silicone oil) suitable for use in the present invention
are described in U.S. Pat. No. 5726114 to Chang et al. These emulsions
are generated by mixing the organosilicon oil and an aqueous component
in the presence of a surfactant or surfactant mixture. Useful surfactants
include any of a large variety of surfactants, including ionic and
non-ionic surfactants. Preferred surfactants include non-nitrogenous,
non-ionic surfactants such as alcohol, alkylphenol, and polyalkoxyalkanol
derivatives, glycerol esters, polyoxyethylene esters, anhydrosorbitol
esters, ethoxylated anhydrosorbitol esters, natural fats, oils,
waxes and ethoxylated esters thereof, glycol esters, polyalkylene
oxide block co-polymer surfactants, poly(oxyethylene-co-oxypropylene)
non-ionic surfactants, and mixtures thereof. More preferred surfactants
include octoxynols such as Octoxynol-9. Such preferred surfactants
include the TRITON.RTM. X series, such as TRITON.RTM. X-100 and
TRITON.RTM. X-305 available from Rohm & Haas Co., Philadelphia,
Pa., and the Igepal.RTM. Calif series from GAF Corp., New York,
N.Y. Emulsions formulated using such surfactants are effective for
selectivating zeolites such as ZSM-5 to enhance shape selectivity,
and to passivate surface acidity detrimental to product selectivity
in certain regioselective catalytic applications such as the disproportionation
of alkylbenzenes. Organosilicon compounds useful herein are water
soluble and may be described as organopolysiloxanes. The preferred
compounds are polyalkylene oxide modified organopolysiloxanes. The
organopolysiloxanes are preferably larger than the pores of the
catalyst and do not enter the pores.
[0037] The organosiliocon compound selectivating agent may be,
for example, a silicone, a siloxane, a silane or mixtures thereof.
These organosilicon compounds may have at least 2 silicon atoms
per molecule. These organosilicon compounds may be solids in pure
form, provided that they are soluble or otherwise convertible to
the liquid form upon combination with the liquid carrier medium.
The molecular weight of the silicone, siloxane or silane compound
employed as a preselectivating agent may be between about 80 and
about 20000 and preferably within the approximate range of 150
to 10000. Suitable silicon-containing selectivating agent is selected
from the group consisting of polysiloxanes, siloxanes, silanes,
disilanes and alkoxysilanes. Representative ex situ selectivation
silicone compounds include dimethyl silicone, diethyl silicone,
phenylmethyl silicone, methylhydrogen silicone, ethylhydrogen silicone,
phenylhydrogen silicone, methylethyl silicone, phenylethylsilicone,
diphenyl silicone, methyltrifluoropropyl silicone, ethyltrifluoropropyl
silicone, polydimethyl silicone, tetrachlorophenylmethyl silicone,
tetrachlorophenylethyl silicone, tetrachlorophenylhydrogen silicone,
tetrachlorophenyl silicone, methylvinyl silicone, and ethylvinyl
silicone. The ex situ selectivating silicone, siloxane or silane
compound need not be linear, but may be cyclic, for example, hexamethyl
cyclotrisiloxane, octamethyl cyclotetrasiloxane, hexaphenyl cyclotrisiloxane
and octaphenyl cyclotetrasiloxane. Mixtures of these compounds may
also be used as liquid ex situ selectivating agents, as may silicones
with other functional groups.
[0038] Preferred silicon-containing selectivating agents, particularly
when the ex situ selectivating agent is dissolved in an organic
carrier or emulsified in an aqueous carrier, include dimethylphenylmethylpolysilo-
xane (e.g., Dow-550.RTM.) and phenylmethyl polysiloxane (e.g., Dow-710.RTM.).
Dow-550.RTM. and Dow-710.RTM. are available from Dow Chemical Company,
Midland, Mich.
[0039] Water soluble organosilicon compounds are commercially available
as, for example, SAG-5300.RTM., manufactured by Union Carbide, Danbury
Conn., conventionally used as an anti-foam, and SF 1188.RTM. manufactured
by General Electric, Pittsfield, Mass.
[0040] When the organosilicon ex situ selectivating agent is present
in the form of a water soluble compound in an aqueous solution,
the organosilicon may be substituted with one or more hydrophilic
functional groups or moieties, which serve to promote the overall
water solubility of the organosilicon compound. These hydrophilic
functional groups may include one or more organoamine groups, such
as --N(CH.sub.3).sub.3 --N(C.sub.2H.sub.5).sub.3 and --N(C.sub.3H.sub.7).sub.3.
A preferred water soluble organosilicon preselectivating agent is
an n-propylamine silane, available as Hydrosil 2627.RTM. from Creanova
(formerly Huls America), Somerset, N.J.
[0041] The organosilicon compound can be preferably dissolved in
an aqueous solution in an organosilicon compound/H.sub.2O weight
ratio of from about 1/100 to about 1/1.
[0042] A "solution" is intended to mean a uniformly dispersed
mixture of one or more substances at the molecular or ionic level.
The skilled artisan will recognize that solutions, both ideal and
colloidal, differ from emulsions.
[0043] The catalyst can be contacted with a substantially aqueous
solution of the organosilicon compound at a catalyst/organosilicon
compound weight ratio of from about 100 to about 1 at a temperature
of about 10.degree. C. to about 150.degree. C., at a pressure of
about 0 psig to about 200 psig, for a time of about 0.1 hour to
about 24 hours, the water is preferably removed, e.g., by distillation,
or evaporation with or without vacuum, and the catalyst is calcined.
[0044] Additional suitable ex situ selectivating agents for the
present invention are disclosed in U.S. Pat. No. 5849968 to Beck
et al.
[0045] Selectivation is carried out on the catalyst, e.g., by conventional
ex situ treatments of the catalyst before loading into a hydrocarbon
conversion reactor. Multiple ex situ treatments, say, 2 to 6 treatments,
preferably 2 to 4 treatments, have been found especially useful
to selectivate the catalyst. When the zeolite is ex situ selectivated
by a single or multiple impregnation technique, the zeolite is calcined
after each impregnation to remove the carrier and to convert the
liquid organosilicon compound to a solid residue material thereof.
This solid residue material is referred to herein as a siliceous
solid material, insofar as this material is believed to be a polymeric
species having a high content of silicon atoms in the various structures
thereof, resulting from the residue of the organo portion of the
organosilicon compound used to impregnate the catalyst.
[0046] Following each impregnation, the zeolite may be calcined
at a rate of from about 0.2.degree. C./minute to about 5.degree.
C./minute to a temperature greater than 200.degree. C., but below
the temperature at which the crystallinity of the zeolite is adversely
affected. This conventional calcination temperature is below 700.degree.
C., e.g., within the approximate range of 350.degree. C. to 550.degree.
C. The duration of calcination at the calcination temperature may
be from 1 to 24 hours, e.g., from 2 to 6 hours.
[0047] The impregnated zeolite may be calcined in an inert or oxidizing
atmosphere. An example of such an inert atmosphere is a nitrogen,
i.e., N.sub.2 atmosphere. An example of an oxidizing atmosphere
is an oxygen containing atmosphere, such as air. Calcination may
take place initially in an inert, e.g., N.sub.2 atmosphere, followed
by calcination in an oxygen containing atmosphere, such as air or
a mixture of air and N.sub.2. Calcination should be performed in
an atmosphere substantially free of water vapor to avoid undesirable
uncontrolled steaming of the zeolite. The zeolite may be calcined
once or more than once following each impregnation. The various
conventional calcinations following each impregnation need not be
identical, but may vary with respect to the temperature, the rate
of temperature rise, the atmosphere and the duration of calcination.
[0048] The amount of siliceous residue material which is deposited
on the zeolite or bound zeolite is dependent upon a number of factors
including the temperatures of the impregnation and calcination steps,
the concentration of the organosilicon compound in the carrying
medium, the degree to which the catalyst has been dried prior to
contact with the organosilicon compound, the atmosphere used in
the calcination and duration of the calcination.
[0049] High Temperature Calcination
[0050] Subsequent to the selectivating procedure(s) and any conventional
calcination associated therewith, the selectivated catalyst of the
present invention is subjected to a severe, high temperature, calcination
treatment. Crystallinity can be measured by hexane uptake (percent
crystallinity for hexane uptake calculated as hexane uptake of sample
divided by hexane uptake of uncalcined sample). Crystallinity can
also be measured by X-ray diffraction.
[0051] The high temperature calcining step can be carried out under
conditions sufficient to provide a catalyst having an alpha value
of less than 700 preferably less than 250 say, from 75 to 150
or 5 to 25 depending on the catalyst application, a crystallinity
as measured by X-ray diffraction of no less than 85%, preferably
no less than 95%, and a diffusion barrier of the catalytic molecular
sieve as measured by the rate of 23-dimethylbutane or 22-dimethylbutane
uptake of less than 270 preferably less than 150 (D/(r.sup.2.times.10.sup.6
sec)).
[0052] The high temperature calcining step can be carried out at
temperatures ranging from greater than 700.degree. C. to 1200.degree.
C. for 0.1 to 12 hours, e.g., from 750.degree. C. to 1000.degree.
C. for 0.3 to 2 hours, preferably from 750.degree. C. to 1000.degree.
C. for 0.5 to 1 hours.
[0053] The selectivated zeolite may be high temperature calcined
in an inert atmosphere, an oxidizing atmosphere, or a mixture of
both. An example of such an inert atmosphere is nitrogen, i.e.,
N.sub.2. An example of an oxidizing atmosphere is an oxygen containing
atmosphere, such as air. Alternatively, calcination may take place
initially in an inert, e.g., N.sub.2 atmosphere, followed by calcination
in an oxygen containing atmosphere, such as air or a mixture of
air and N.sub.2 or vice versa. Calcination should be performed
in an atmosphere substantially free of water vapor to avoid undesirable
uncontrolled steaming of the zeolite. Thus, the high temperature
calcining step is preferably carried out in the absence of intentionally
added steam.
[0054] Shape Selective Conversions
[0055] Zeolites modified in accordance with the invention are generally
useful as catalysts in shape selective hydrocarbon conversion processes
including cracking reactions, including those involving dewaxing
of hydrocarbon feedstocks; isomerization of alkylaromatics, e.g.,
xylene isomerization; oligomerization of olefins to form gasoline,
distillate, lube oils or chemicals; alkylation of aromatics; transalkylation
of aromatics, e.g. toluene disproportionation; conversion of oxygenates
to hydrocarbons; rearrangement of oxygenates; and conversion of
light paraffins and olefins to aromatics, e.g., naphtha reforming.
Non-limiting examples include: cracking hydrocarbons with reaction
conditions including a temperature of from-about 300.degree. C.
to about 700.degree. C., a pressure of from about 0.1 atmosphere
(bar) to about 30 atmospheres and weight hourly space velocity of
from about 0.1 hr.sup.-1 to about 20 hr.sup.-1; dehydrogenating
hydrocarbon compounds with reaction conditions including a temperature
of from about 300.degree. C. to about 700.degree. C., a pressure
of from about 0.1 atmosphere (bar) to about 10 atmospheres and weight
hourly space velocity of from about 0.1 hr.sup.-1 to about 20 hr.sup.-1;
converting paraffins to aromatics with reaction conditions including
from about 300.degree. C. to about 700.degree. C., a pressure of
from about 0.1 atmosphere (bar) to about 60 atmospheres and weight
hourly space velocity of from about 0.5 hr.sup.-1 to about 400 hr.sup.-1
and a hydrogen/hydrocarbon mole ratio of from about 0 to about 20;
converting olefins to aromatics, e.g., benzene, toluene and xylene,
with reaction conditions including a temperature from about 100.degree.
C. to about 700.degree. C., a pressure of from about 0.1 atmosphere
(bar) to about 60 atmospheres, weight hourly space velocity of from
about 0.5 hr.sup.-1 to about 400 hr.sup.-1 and a hydrogen/hydrocarbon
mole ratio of from about 0 to about 20; converting alcohols, e.g.,
methanol, or ethers, e.g., dimethylether, or mixtures thereof to
hydrocarbons, including olefins and/or aromatics with reaction conditions
including a temperature from about 275.degree. C. to about 600.degree.
C., a pressure of from about 0.5 atmosphere (bar) to about 50 atmospheres,
weight hourly space velocity of from about 0.5 hr.sup.-1 to about
100 hr.sup.-1; isomerizing xylene feedstock components with reaction
conditions including a temperature from about 230.degree. C. to
about 510.degree. C., a pressure of from about 3 atmosphere (bar)
to about 35 atmospheres, weight hourly space velocity of from about
0.1 hr.sup.-1 to about 200 hr.sup.-1 and a hydrogen/hydrocarbon
mole ratio of from about 0 to about 100; disproportionating toluene
with reaction conditions including a temperature from about 200.degree.
C. to about 760.degree. C., a pressure of from about atmospheric
to about 60 atmospheres, weight hourly space velocity of from about
0.08 hr.sup.-1 to about 20 hr.sup.-1; alkylating aromatic hydrocarbons,
e.g., benzene and alkylbenzenes in the presence of an alkylating
agent, e.g., olefins, formaldehyde, alkyl halides and alcohols,
with reaction conditions including a temperature from about 250.degree.
C. to about 500.degree. C., a pressure of from about atmospheric
to about 200 atmospheres, weight hourly space velocity of from about
2 hr.sup.-1 to about 2000 hr.sup.-1 and an aromatic hydrocarbon/alkylating
agent mole ratio of from about 1/1 to about 20/1; and transalkylating
aromatic hydrocarbons in the presence of polyalkylaromatic hydrocarbons
with reaction conditions including a temperature from about 340.degree.
C. to about 500.degree. C., a pressure of from about atmospheric
to about 200 atmospheres, weight hourly space velocity of from about
10 hr.sup.-1 to about 1000 hr.sup.-1 and an aromatic hydrocarbon/polyalkylaromatic
hydrocarbon mole ratio of from about 1/1 to about 16/1. Additional
conditions for using selectivated catalysts are set out in U.S.
Pat. No. 5455213 to Chang et al.
[0056] In general, therefore, catalytic conversion conditions over
a catalyst comprising the modified zeolite prepared by the present
method include a temperature from about 100.degree. C. to about
760.degree. C., a pressure of from about 0.1 atmosphere (bar) to
about 200 atmospheres (bar), weight hourly space velocity of from
about 0.08 hr.sup.-1 to about 2000 hr.sup.-1 and a hydrogen/organic,
e.g., hydrocarbon compound, molar ratio of from about 0 to about
100.
[0057] All of the foregoing U.S. patents are incorporated herein
by reference.
[0058] The following examples will serve to further illustrate
processes and some advantages of the present invention.
EXAMPLE 1
Silicone Selectivation Treatment of ZSM-5 Catalysts
[0059] High activity ZSM-5 65 wt. %/35 wt. % silica bound were
selectivated by four consecutive silicone selectivation treatments.
To this catalyst, 0.1 wt. % Pt was added via incipient wetness impregnation
with Pt(NH.sub.3).sub.4(NO.sub.3).sub.2 followed by calcination.
[0060] The selectivated catalysts exhibited the following characteristics:
alpha=610; 23-DMB (.times.10.sup.-6 sec.sup.-1)=248 and crystallinity
based on n-hexane sorption of 99.8%.
EXAMPLE 2
High Temperature Calcination of Silicone-Selectivated ZSM-5
[0061] High temperature calcinations of a selectivated product
of Example 1 were performed in a horizontal tube furnace. A quartz
tube was placed in the furnace, whose length extended a few inches
beyond the furnace itself, to both hold the catalyst sample boat
and to allow for controlling the atmosphere in the catalyst bed
during treatment. Air, predried over CaCl.sub.2 and activated sieves,
was flowed through the tube during calcination at about 0.5 liter
air/minute. The catalyst was placed in a quartz boat, which contained
an internal thermowell for monitoring the actual catalyst bed temperature,
then placed within the quartz tube to initiate the high temperature
treatment. Treatment time is defined as follows: start time is when
catalyst temperature is within 5.6.degree. C. (10.degree. F.) of
stated temperature. Following calcination treatment, the quartz
boat was removed from the furnace and allowed to cool to room temperature
quickly. The results are set out in Table 1 below.
[0062] All dynamic measurements were obtained with a High Resolution
Thermogravimetric Analyzer (TA Instruments Model 2950) equipped
with an evolved gas furnace, a gas switching accessory and an automatic
sample changer. A hydrocarbon sparging system consisting of mass
flow controllers heating mantle, condenser, and circulating bath
delivered the sorbates. During the sorption experiment a helium
purge gas entered the balance head and blended with a sorbate carried
by helium which entered through the furnace inlet tube. The carrier
gas sparged through the sorbate which was maintained at a specified
temperature. The flow rate of the two gas streams were controlled
by mass flow controllers and were adjusted to achieve the desired
partial pressures.
[0063] All static measurements were performed on a sorption system
from VTI Corp. (Model MB 300). This PC controlled system consisted
of an integrated microbalance from Cahn (Model D200), furnace, constant
temperature bath, vacuum system and gas manifold. Adsorption isotherms
were obtained by selecting a starting point of the isotherm pressure
step, maximum pressure, equilibrium criteria and experimental temperature.
The program provided for automatic outgassing of the sample followed
by sorption of organic vapor, i.e., n-hexane.
1TABLE 1 % Crystallinity Calc. Temp Time 23-D/r.sup.2 (hexane
(.degree. F.) (Hours) Alpha (.times.10.sup.-6 sec.sup.-1) sorption)
None None 610 248 100 1400 1 256 215 100 1500 1 167 122 99 1600
1 110 95 98 1700 1 65 41 96 1800 0.5 43 17 95
[0064] The results presented in Table 1 show that high temperature
treatment of diffusionally modified catalysts can decrease acid
activity, as measure by alpha, as well as substantially increase
diffusional resistance (lower D/r.sup.2 represents an increase in
diffusional resistance). Thus, calcination at 1600.degree. F. (871.degree.
C.) for one hour decreases alpha (from 610 to 110), but increases
the diffusional resistance over two-fold. This contrasts with the
results presented in Table 2 below for steam treatment, in which
a similar decrease in alpha results in a net decrease in diffusional
resistance. Note that the diffusional resistance of the 1800.degree.
F. (982.degree. C.) calcined sample has increased fifteen-fold,
a very significant increase in diffusional resistance over the untreated
catalyst.
EXAMPLE 3
Preparation of Steamed, Uncalcined ZSM-5 (Comparative)
[0065] Steam treatments of a selectivated product of Example 1
were preformed in the same furnace setup as in the previous Example.
The atmosphere through the quartz tube was steam, generated by boiling
water. Steaming temperature. steam time, and alpha values and 23-dimethylbutane
diffusivity measurements taken according to the above-described
procedures are set out below in Table 2. The results show that steam
treatment can be used to decrease acid activity, as measured by
alpha. However, the steam treatment also decreases the diffusional
resistance (higher D/r.sup.2 values represent a decreased diffusional
resistance).
2TABLE 2 23-DMB D/r.sup.2 Steaming T (.degree. F.) Steam Time
(hours) Alpha (.times.10.sup.-6 sec.sup.-1) None None 737 195 800
20 270 415 800 26 151 620
EXAMPLE 4
Comparison ofHigh Temperature Calcination Treatment Versus Steam
Treatmentfor Modifying 4.times. Selectivated Catalysts
[0066] The data from Examples 2 and 3 are plotted in the Figure.
They clearly show that high temperature calcination results in an
increase in diffusional resistance (lower D/r.sup.2) with lower
acidity (as measured by alpha). In contrast, when steaming, which
is a standard method for decreasing acidity (as measured by alpha),
is applied to the catalyst, the diffusional resistance decreases
(higher D/r.sup.2). This clearly shows both the difference in these
two treatments for modifying acidity, as well as the utility of
this invention--that more diffusionally resistant catalysts can
be produced using the high temperature calcination method.
EXAMPLE 5
Hydrocarbon Conversion Process Using High Temperature Calcined,
Selectivated ZSM-5 and Steamed ZSM-5
[0067] Two catalysts were prepared for this example in accordance
with the previous Examples. The first was prepared. by high temperature
calcination of a 3.times. selectivated catalyst at 1700.degree.
F., while the second (Comparative) was prepared by steaming a 4.times.
selectivated catalyst for 3 hours at 990.degree. F. These catalysts
were then used to convert ethylbenzene in a xylene isomerization
reactor. The feed is a xylene-containing feed, with 10% ethylbenzene,
1% para-xylene, 64% meta-xylene, and 25% ortho-xylene. The catalysts
were first reduced in hydrogen, then lined out for 24 hours using
this feed. The catalysts were then evaluated at temperatures of
820.degree.-760.degree. F. in 20.degree. F. increments, at 20 WHSV,
10 WHSV and 5 WHSV using a 1/1 hydrogen/hydrocarbon ratio at 200
psig. The results are shown in Table 3 below.
3 TABLE 3 High Temperature Steamed Catalyst Calcined Catalyst Catalyst
Yields (wt. %) C.sub.5.sub..sup.- 1.9 2.0 Benzene 5.4 5.6 Toluene
0.5 1.1 Ethylbenzene 1.2 1.1 Para Xylene 1.8 2.6 Meta Xylene 63.2
62.7 Ortho Xylene 26.0 25.1 Heavies (C.sub.9+) 0.0 0.0 Ethylbenzene
Conversion 87.6 88.9 Xylene Loss 0.2 0.8 Para Approach (PATE) 3.0
7.6
[0068] These data show that the high temperature calcined catalyst
effectively converts ethylbenzene. They also show that the xylene
loss afforded over the high temperature calcined catalyst is lower
than that afforded over the steamed catalyst. |