Molecular sieve abstract
An isomerization process for lowering the normal paraffin content
of a hydrocarbon oil feedstock by contacting the feedstock with
a catalyst comprising an intermediate pore size silicoaluminophosphate
molecular sieve and at least one Group VIII metal wherein the metal
is occluded in the molecular sieve is described. The n-paraffins
in the feedstock become isomerized to isoparaffins to form liquid
range materials which contribute to a low viscosity, low pour point
product in the case of middle distillate and lube oils and high
octane in the case of gasoline.
Molecular sieve claims
What is claimed is:
1. An isomerization process of catalytically reducing the normal
paraffin content of a hydrocarbon oil feedstock containing straight
chain hydrocarbons which comprises contacting said oil feedstock
with a catalyst comprising an intermediate pore size crystalline
silicoaluminophosphate molecular sieve, and at least one platinum
or palladium metal component which metal component is occluded in
the molecular sieve and wherein said molecular sieve having resulted
from the growth of crystals of said molecular sieve from an aqueous
medium containing a water-soluble compound of said platinum or palladium
metal.
2. The method of claim 1 wherein the silicoaluminophosphate molecular
sieve has a pore size in the range of from about 5.5 to 6.2 .ANG..
3. The method of claim 1 wherein the silicoaluminophosphate molecular
sieve is selected from the group consisting of SAPO-11 and SAPO-41.
4. The method of claim 3 wherein the silicoaluminophosphate is
SAPO-11.
5. The method of claim 1 wherein the platinum or palladium is present
in the range of 0.01% to 10% based on the weight of molecular sieve.
6. The process of claim 1 wherein said process is conducted at
a temperature of from about 200.degree. C. to 475.degree. C., a
pressure of about 15 psig to about 3000 psig, a liquid hourly space
velocity of from about 0.1 hr.sup.-1 to about 20 hr.sup.-1 a hydrogen
circulation rate of from 500 to about 30000 SCF/bbl.
7. The process of claim 1 wherein the feedstock is a middle distillate
oil.
8. The process of claim 1 wherein the feedstock is a lube oil.
9. The process of claim 1 wherein the feedstock contains less than
50 ppm of nitrogen.
10. The process of claim 1 wherein the feedstock contains less
than 10 ppm of nitrogen.
Molecular sieve description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is concerned with an isomerization process for selectively
lowering the normal paraffin content of a hydrocarbon oil. In particular,
it is concerned with an isomerization process for lowering the normal
paraffin content of a hydrocarbon oil feedstock by contacting the
feedstock with a catalyst comprising an intermediate pore size silicoaluminophosphate
molecular sieve and at least one Group VIII metal wherein said metal
is occluded in the molecular sieve, i.e., the metal is added to
the molecular sieve by coprecipitation of the sieve and metal components.
2. Description of the Prior Art
Shape-selective paraffin conversion of hydrocarbon oils is well
known in the art and generally refers to the treatment of hydrocarbon
feeds to reduce the normal paraffins therein. The normal paraffin
components of hydrocarbon oils, particularly long chain normal paraffins,
impart, for-many-roses, undesirable characteristics to the oils
and hence must generally be removed, e.g., by catalytic dewaxing,
in order to produce commercially useful products. In particular,
middle-distillate and lube oil range hydrocarbon oils having high
concentrations of normal paraffins, i.e., wax, generally have higher
freeze points or pour points than oils having lower concentrations
of normal paraffins. For many purposes it is desirable to have oils
with low freeze points or pour points. Thus, for example, the lower
the freeze point of a jet fuel, the more suitable it will be for
operations under conditions of extreme cold. Thus; the fuel will
remain liquid and flow freely without external heating even at very
low temperatures. In the case of lubricating oils, it is desirable
that the pour points be low, thereby enabling the oil to pour freely
and adequately lubricate, even at low temperature.
The prior art shape-selective paraffin conversion processes, however,
have the disadvantage of having substantial cracking, and undesirably
crack some of the potentially valuable hydrocarbon feedstocks to
low value light products such as hydrocarbon gases.
Prior art shape-selective paraffin conversion catalysts dealing
with paraffin cracking generally comprise an aluminosilicate zeolite
having a pore size which admits the straight chain n-paraffins either
alone or with only slightly branched chain paraffins, but which
excludes more highly branched materials, cycloaliphatics and aromatics.
Zeolites such as ZSM-5 ZSM-11 ZSM-12 ZSM-23 ZSM-35 and ZSM-38
have been proposed for this purpose in shape-selective paraffin
conversion processes and their use is described in U.S. Pat. Nos.
3700585; 3894938; 4176050; 4181598; 4222855; 4229282;
4247388; 3849290; 3950241; 4032431; and 4141859.
Since shape-selective paraffin conversion processes of this kind
function by means of cracking reactions, a number of useful products
become degraded to lower molecular weight materials. For example,
waxy paraffins may be cracked down to butane, propane, ethane and
methane and so may the lighter n-paraffins which do not, in any
event, contribute to the waxy nature of the oil. Because these lighter
products are generally of lower value than the higher molecular
weight materials, it would obviously be desirable to limit the degree
of cracking which takes place during a catalytic shape-selective
conversion process.
Prior patents dealing with paraffin isomerization include U.S.
Pat. No. 3432568 which describes hydroisomerization of saturated
aliphatic and cyclic hydrocarbons by contacting with a mixed dual-functional
catalyst comprising hydrogen mordenite and a dehydrogenation component
supported on a thermally stable carrier. U.S. Pat. No. 3301917
relates to hydroisomerization of paraffinic hydrocarbons in the
presence of a mixed catalyst consisting essentially of an acid aluminosilicate
portion and a hydrogenation component of a platinum metal supported
on a thermally stable carrier. U.S. Pat. No. 3673267 describes
a process for isomerization of paraffinic hydrocarbons under isomerizing
conditions and in the presence of hydrogen with a catalyst of hydrogen
modenite having a silica to alumina mole ratio between about 20:1
and about 60:1 having associated therewith a metal of Group VIII,
Group VIB or Group IB.
U.S. Pat. No. 4419220 discloses a process wherein hydrocarbon
feedstocks are dewaxed by isomerizing the waxy component over a
zeolite beta catalyst.
In isomerization processes, a principal problem is the attainment
of high yield and selectivity of desired isomerates; and minimization
of competing reactions is a consideration. A principal undersired
competing reaction is cracking; and a common measure of effectivity
of an isomerization catalyst is its ability to maximize isomerization
while minimizing cracking.
An isomerization shape-selective paraffin conversion catalyst has
now been found which effectively removes normal paraffins from a
hydrocarbon oil feedstock by isomerizing them without substantial
cracking. By use of certain silicoaluminophosphate molecular sieve
catalysts which contain at least one Group VIII metal occluded therein,
in the shape-selective conversion process, the normal paraffin content
of hydrocarbon oil feedstocks may be effectively reduced wherein
the products obtained are of higher molecular weight than those
obtained using prior art aluminosilicate zeolites. The manner in
which the Group VIII metal is associated with the silicoaluminophosphate
is ccritical to obtaining the shape selective isomerization catalyst
of this invention. The Group VIII metal is occluded within the pores
of the silicoaluminophosphate by incorporating a water-soluble salt
of the desired metal into the forming solution of the silicoaluminophosphate
and then growing the silicoaluminophosphate crystals.
The catalyst used in the process of this invention is shape selective
in that it isomerizes normal and slightly branched paraffins and
does not essentially react with highly branched paraffins. Many
of the prior art catalysts crack both the highly branched as well
as the normal paraffins to lighter products and gases. Because these
lighter products are generally of lower value than the higher molecular
weight materials, it would obviously be desirable to limit the degree
of cracking which takes place during the process.
SUMMARY OF THE INVENTION
In accordance with the present invention, there has been discovered
an isomerization process for catalytically reducing the normal paraffin
content of a hydrocarbon oil feedstock containing straight chain
hydrocarbons which comprises contacting said oil feedstock with
a catalyst comprising an intermediate pore size crystalline silicoaluminophosphate
molecular sieve, and at least one Group VIII metal component which
metal component is occluded in the molecular sieve and wherein said
molecular sieve having resulted from the growth of crystals of said
molecular sieve from an aqueous medium containing a water-soluble
compound of said Group VIII metal.
Examples of the silicoaluminophosphate molecular sieves of the
type used in the process of this invention are described in U.S.
Pat. No. 4440871 which is incorporated totally herein by reference.
It has been found that the present process provides selective conversion
of n-paraffins to branched paraffins. During processing the normal
paraffins undergo isomerization reactions to yield iso-paraffin
products with minor cracking reactions occurring. The n-paraffins
become isomerized to iso-paraffins to form liquid range materials
which contribute to a low viscosity, low pour point product in the
case of middle distillate and lube oils, and high octane in the
case of gasoline.
Because of the selectivity of the catalyst used in the process
of this invention, cracking reactions which tend to increase gas
yield are reduced, thereby preserving the economic value of the
feedstock.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a ternary diagram showing the compositional parameters
of the silicoaluminophosphates of U.S. Pat. No. 4440871 in terms
of mole fractions of silicon, aluminum and phosphorus.
FIG. 2 is a ternary diagram showing the preferred compositional
parameters of the silicoaluminophosphates of mole fractions of silicon,
aluminum and phosphorus.
DESCRIPTION OF SPECIFIC EMBODIMENTS
Feedstock
The present process may be used to reduce the normal paraffin content
of a variety of feedstocks ranging from relatively light distillate
fractions up to high boiling stocks such as whole crude petroleum,
reduced crudes, vacuum tower residua, cycle oils, synthetic crudes
(e.g., shale oils, tar sand oil, etc.), gas oils, vacuum gas oils,
foots oils, and other heavy oils. The process is particularly useful
with waxy distillate stocks such as middle distillate stocks including
gas oils, kerosenes, and jet fuels, lubricating oil stocks, heating
oils and other distillate fractions whose pour point and viscosity
need to be maintained within certain specification limits, and with
lighter distillates containing normal paraffins such as straight
run gasoline or gasoline range fractions from hydrocracking or reforming
whose octanes need to be within certain limits. Hydrocracked stocks
are a convenient source of lubricating oil stocks and also of other
distillate fractions since they normally contain significant amounts
of waxy n-paraffins. The feedstock of the present process will normally
be a C.sub.5 + feedstock containing paraffins, olefins, naphthenes,
aromatics and heterocyclic compounds and with a substantial proportion
of n-paraffins. During the processing, the n-paraffins undergo isomerization
to iso-paraffins which are liquid range materials. The small degree
of cracking which occurs is, however, limited so that the gas yield
is reduced, thereby preserving the economic value of the feedstock.
While the process herein can be practiced with utility when the
feed contains organic nitrogen (nitrogen-containing impurities),
it is preferred that the organic nitrogen content of the feed be
less than 50 more preferably less than 10 ppmw. Especially good
results, in terms of activity and length of catalyst cycle (period
between successive regenerations or start-up and first regeneration),
are experienced when the feed contains less than 10 ppmw of organic
nitrogen.
SILICOALUMINOPHOSPHATE CATALYSTS COMPOSITIONS (SAPOs)
Silicoaluminophosphate molecular sieves (SAPOs) suitable for use
in the instant process comprise any molecular sieve having a silicoaluminophosphate
molecular framework which has an intermediate pore size and which
comprises a molecular framework of corner-sharing [SiO.sub.2 ] tetrahedra,
[AlO.sub.2 ] tetrahedra and [PO.sub.2 ] tetrahedra, [i.e., (Si.sub.x
Al.sub.y P)O.sub.2 tetrahedral units], and which functions to convert
at effective process conditions the aforementioned feedstock to
products of reduced normal paraffin content and includes those silicoaluminophosphate
molecular sieves described in U.S. Pat. No. 4440871 which is incorporated
herein by reference.
The term "unit empirical formula" is used herein according
to its common meaning to designate the simplest formula which gives
the relative number of atoms of silicon, aluminum and phosphorus
which form a [PO.sub.2 ], [AlO.sub.2 ] and [SiO.sub.2 ] tetrahedral
unit within a silicoaluminophosphate molecular sieve and which forms
the molecular framework of the SAPO composition(s). The unit empirical
formula is given in terms of silicon, aluminum and phosphorus as
shown in Formula (1), above, and does not include other compounds,
cations or anions which may be present as a result of the SAPO's
preparation or the existence of other impurities or materials in
the bulk composition not containing the aforementioned tetrahedral
unit as the molecular framework. The amount of template R is reported
as part of the composition when the assynthesized unit empirical
formula is given, and water may also be reported unless such is
defined as the anhydrous form. For convenience, coefficient "m"
for template "R" is reported as a value that is normalized
by dividing the number of moles of R by the total number of moles
of silicon, phosphorus and aluminum. When moles of water are reported
the moles of water relative to the mole fractions of silicon, aluminum
and phosphorus is reported as a value that is normalized by dividing
the number of moles of water by the total moles of silicon, phosphorus
and aluminum. The values of x, y and z are determined by dividing
the number of moles of silicon, aluminum and phosphorus individually
by the total number of moles of silicon, aluminum and phosphorus.
The unit empirical formula for a SAPO may be given on an "as-synthesized"
basis or may be given after an "as-synthesized" SAPO composition
has been subjected to some post treatment process, e.g., calcined.
The term "as-synthesized" herein shall be used to refer
to the SAPO composition(s) formed as a result of the hydrothermal
crystallization but before the SAPO composition has been subjected
to post treatment to remove any volatile components present therein.
The actual value of "m" for a post-treated SAPO will depend
on several factors (including: the particular SAPO, template, severity
of the post-treatment in terms of its ability to remove the template
from the SAPO, the proposed application of the SAPO composition,
and etc.) and the value for "m" can be within the range
of values as defined for the as-synthesized SAPO compositions although
such is generally less than the as-synthesized SAPO unless such
post-treatment process adds template to the SAPO so treated. A SAPO
composition which is in the calcined or other post-treated form
generally has an empirical formula represented by Formula (1), except
that the value of "m" is generally less than about 0.02.
Under sufficiently severe post-treatment conditions, e.g., roasting
in air at high temperature for long periods (over 1 hr.), the value
of "m" may be zero (0) or, in any event, the template,
R, is undetectable by normal analytical procedures.
The above silicoaluminophosphates are generally synthesized by
hydrothermal crystallization from a reaction mixture comprising
reactive sources of silicon, aluminum and phosphorus, and one or
more organic templating agents. Optionally, alkali metal(s) may
be present in the reaction mixture. The reaction mixture is placed
in a sealed pressure vessel, preferably lined with an inert plastic
material, such as polytetrafluoroethylene, and heated, preferably
under autogenous pressure at a temperature of at least about 100.degree.
C., and preferably between 100.degree. C. and 250.degree. C., until
crystals of the silicoaluminophosphate product are obtained, usually
for a period of from 2 hours to 2 weeks. While not essential to
the synthesis of SAPO compositions, it has been found that in general
stirring or other moderate agitation of the reaction mixture and/or
seeding the reaction mixture with seed crystals of either the SAPO
to be produced, or a topologically similar composition, facilitates
the crystallization procedure. The product is recovered by any convenient
method such as centrifugation or filtration.
After crystallization the SAPO may be isolated and washed with
water and dried in air. As a result of the hydrothermal crystallization,
the as-synthesized SAPO contains within its intracrystalline pore
system at least one form of the template employed in its formation.
Generally, the template is a molecular species, but it is possible,
steric considerations permitting, that at least some of the template
is present as a charge-balancing cation. Generally the template
is too large to move freely through the intracrystalline pore system
of the formed SAPO and may be removed by a post-treatment process,
such as by calcining the SAPO at temperatures of between about 200.degree.
C. and to about 700.degree. C. so as to thermally degrade the template
or by employing some other post-treatment process for removal of
at least part of the template from the SAPO. In some instances the
pores of the SAPO are sufficiently large to permit transport of
the template, and, accordingly, complete or partial removal thereof
can be accomplished by conventional desorption procedures such as
carried out in the case of zeolites.
The SAPOs are preferably formed from a reaction mixture having
a mole fraction of alkali metal cation which is sufficiently low
that it does not interfere with the formation of the SAPO composition.
Although the SAPO compositions will form if alkali metal cation
are present, such reaction mixtures are not generally preferred.
A reaction mixture, expressed in terms of molar oxide ratios, having
the following bulk composition is preferred:
wherein "R" is a template; "a" has a value
great enough to constitute an effective concentration of "R"
and is within the range of from greater than zero (0) to about 3;
"b" has a value of from zero to 500; "x", "y"
and "z" represent the mole fractions, respectively of
silicon, aluminum and phosphorus wherein x, y and z each have a
value of at least 0.01. The reaction mixture is preferably formed
by combining at least a portion of the reactive aluminum and phosphorus
sources in the substantial absence of the silicon source and thereafter
combining the resulting reaction mixture comprising the aluminum
and phosphorus sources with the silicon source. When the SAPOs are
synthesized by this method the value of "m" in Formula
(1) is generally above about 0.02.
Though the presence of alkali metal cations are not preferred,
when they are present in the reaction mixture it is preferred to
first admix at least a portion of each of the aluminum and phosphorus
sources in the substantial absence of the silicon source. This procedure
avoids adding the phosphorus source to a highly basic reaction mixture
containing the silicon and aluminum source.
The reaction mixture from which these SAPOs are formed contain
one or more organic templating agents (templates) which can be most
any of those heretofore proposed for use in the synthesis of aluminosilicates.
The template preferably contains at least one element of Group VA
of the Periodic Table, particularly nitrogen, phosphorus, arsenic
and/or antimony, more preferably nitrogen or phosphorus and most
preferably nitrogen. The template contains at least one alkyl, aryl,
araalkyl, or alkylaryl group. The template preferably contains from
1 to 8 carbon atoms, although more than eight carbon atoms may be
present in the template. Nitrogen-containing templates are preferred,
including amines and quaternary ammonium compounds, the latter being
represented generally by the formula R'.sub.4 N+ wherein each R'
is an alkyl, aryl, alkylaryl, or araalkyl group; wherein R' preferably
contains from 1 to 8 carbon atoms or higher when R' is alkyl and
greater than 6 carbon atoms when R' is otherwise, as hereinbefore
discussed. Polymeric quaternary ammonium salts such as [(C.sub.14
H.sub.32 N.sub.2)(OH).sub.2 ].sub.x wherein "x" has a
value of at least 2 may also be employed. The mono-, di- and tri-amines,
including mixed amines, may also be employed as templates either
alone or in combination with a quaternary ammonium compound or another
template.
Representative templates, phosphorus, aluminum and silicon sources
as well as detailed process conditions are more fully described
in U.S. Pat. No. 4440871 which is incorporated totally herein
by reference.
By "intermediate pore size", as used herein, is meant
an effective pore aperture in the range of about 5.3 to 6.5 Angstroms
when the molecular sieve is in the calcined form. Molecular sieves
having pore apertures in this range tend to have unique molecular
sieving characteristics. Unlike small pore zeolites such as erionite
and chabazite, they will allow hydrocarbons having some branching
into the molecular sieve void spaces. Unlike larger pore zeolites
such as the faujasites and mordenites, they can differentiate between
n-alkanes and slightly branched alkanes on the one hand and larger
branched alkanes having, for example, quaternary carbon atoms.
The effective pore size of the molecular sieves can be measured
using standard adsorption techniques and hydrocarbonaceous compounds
of known minimum kinetic diameters. See Breck, Zeolite Molecular
Sieves, 1974 (especially Chapter 8); Anderson et al., J. Catalysis
58 114 (1979); and U.S. Pat. No. 4440871 all of which are incorporated
herein by reference.
Intermediate pore size molecular sieves will typically admit molecules
having kinetic diameters of 5.3 to 6.5 Angstroms with little hindrance.
Examples of such compounds (and their kinetic diameters in Angstroms)
are: n-hexane (4.3), 3-methylpentane (5.5), benzene (5.85), and
toluene (5.8). Compounds having kinetic diameters of about 6 to
6.5 Angstroms can be admitted into the pores, depending on the particular
sieve, but do not penetrate as quickly and in some cases are effectively
excluded. Compounds having kinetic diameters in the range of 6 to
6.5 Angstroms include: cyclohexane (6.0), 23-dimethylbutane (6.1),
and m-xylene (6.1). Generally, compounds having kinetic diameters
of greater than about 6.5 Angstroms do not penetrate the pore apertures
and thus are not absorbed into the interior of the molecular sieve
lattice. Examples of such larger compounds include: o-xylene (6.8),
hexamethylbenzene (7.1), and tributylamine (8.1).
The preferred effective pore size range is from about 5.5 to about
6.2 Angstroms.
In performing adsorption measurements to determine pore size, standard
techniques are used. It is convenient to consider a particular molecule
as excluded if it does not reach at least 95% of its equilibrium
adsorption value on the molecular sieve in less than about 10 minutes
(p/po=0.5; 25.degree. C.).
The preferred intermediate pore size silico-aluminophosphate molecular
sieves which are useful in the process of this invention include
SAPO-11 SAPO-31 and SAPO-41 and are described in U.S. Pat. No.
4440871 which is incorporated herein by reference.
Introduction of the metal compound to the molecular sieve-forming
reaction mixture may be made by the addition of such compound to
one of the reactants used in preparation of the forming mixture.
Alternatively, the metal compound may be introduced by addition
to the already formed molecular sieve reaction mixture, either before
or after precipitation of the amorphous slurry. It is, however,
essential that the metal compound be present in the reaction mixture
before crystallization of the molecular sieve takes place in order
that crystals of the molecular sieve may grow in the presence of
the metal compound. It is contemplated that the specific reagents,
amounts and concentrations for the aluminous, phosphorus and siliceous
salts and other reagents used in preparation of the crystalline
silicoaluminophosphate molecular sieve employed herein are the same
as those heretofore conventionally employed for the preparation
of the above-described molecular sieves in the absence of a metal
compound. Likewise, the conditions for inducing crystallization
of the resulting initially formed amorphous precipitate are contemplated
to be the same as those heretofore employed for preparation of the
crystalline molecular sieve in the absence of metal compound.
The preferred Group VIII metal is a metal of the platinum series,
e.g., platinum, palladium, iridium, rhodium, ruthenium, or osmium.
Of this group platinum and palladium are accorded preference. Each
of the Group VIII metals may occur in a variety of compounds. The
compounds of the useful platinum metals may be subdivided into compounds
in which the metal is present in the neutral state, compounds in
which the metal is present in the cation of the compound and compounds
in which it is present in the anion of the compound. All of the
foregoing types of compounds, that is types which contain the metal
in the neutral, cationic or anionic state may be used. It is, however,
a preferred aspect of the method of the invention to employ ionizable
platinum metal compounds in which the metal is in the cationic state,
i.e., in the form of a cation or cation complex, since the catalyst
products prepared with the use of such compounds and particularly
compounds in which platinum metal is present in divalent cationic
form, exhibited marked catalytic selectivity. Thus, suitable metal
compounds of the platinum series include:
[Pt(NH.sub.3).sub.6 ]Cl.sub.4; [Pt(NH.sub.3).sub.5 Cl]Cl.sub.3;
[Pt(NH.sub.3).sub.4 Cl.sub.2 ]Cl.sub.2; [Pt(NH.sub.3).sub.3 Cl.sub.3
]Cl; [Pt(NH.sub.3).sub.2 Cl.sub.4 ]; [Pt(NH.sub.3).sub.4 ]Cl.sub.2;
[Pt(NH.sub.3).sub.2 Cl.sub.2 ]; [Pt(NH.sub.3).sub.4 ](OH).sub.2;
[Pt(C.sub.2 H.sub.5 OH).sub.2 Cl.sub.4 ]; [Pt(C.sub.6 H.sub.5 CN).sub.2
Cl.sub.4 ]; [Pt(NH.sub.3).sub.2 ]CN.sub.2; [Pt(NH.sub.2 -CH.sub.2
-CH.sub.2 -NH.sub.2).sub.2 ]Cl.sub.2; [Pd(NH.sub.3).sub.2 (NO.sub.2).sub.2
]; [Pd)NH.sub.3).sub.2 (C.sub.2 O.sub.4)]; [PtCl.sub.2 . CO]; [OsCl.sub.2.3CO].
It is contemplated that water will ordinarily be the solvent for
the metal compound used. The concentration of the metal compound
in the solution employed may vary widely depending upon the amount
of metal and/or metal ions desired in the final composition and
on the conditions under which crystallization is effected. An amount
of metal compound introduced into the molecular sieve-forming mixture,
however, is generally such that the ultimate crystalline molecular
sieve contain therein an amount of metal and/or metal ions, expressed
in terms of metal, from about 0.01 percent to about 10 percent by
weight, and more usually between about 0.1 percent and about 5 percent
by weight.
After the contact period, the resulting crystalline molecular sieve
containing metal and/or metal ions therein is removed from the forming
solution and washed with water. The resulting material is then dried,
generally in air, to remove substantially all of the water therefrom.
The dried material may be desirably subjected to an activating
treatment to render the final composition catalytically active.
Such treatment involves heating the dried material at a temperature
in the approximate range of 250.degree. F. to 1100.degree. F. to
effect at least partial conversion of the metal content to a catalytically
active state. In a preferred aspect of the invention, the dried
material is subjected to treatment in an atmosphere containing free
oxygen, such as air, at a temperature within the approximate range
of 250.degree. F. to 1100.degree. F. for from about 1/4 hour to
24 hours and thereafter in an atmosphere of hydrogen at a temperature
within the above range to effect at least partial reduction of metal-containing
ion to free metal.
The Group VIII metal utilized in the process of this invention
can mean one or more of the metals in its elemental state or in
some form such as the sulfide or oxide and mixtures thereof. As
is customary in the art of catalysis, when referring to the active
metal or metals it is intended to encompass the existence of such
metal in the elemental state or in some form such as the oxide or
sulfide as mentioned above, and regardless of the state in which
the metallic component actually exists the concentrations are computed
as if they existed in the elemental state.
Also, any alkali metal cations which may be present in the as synthesized
molecular sieve hereby prepared can be replaced, if desired, in
accordance with techniques well known in the art, at least in part,
by ion exchange with other cations. Preferred replacing cations
include metal ions, ammonium ions, hydrogen ions and mixtures thereof.
Particularly preferred cations include hydrogen and metals of Groups
IIA, IVA, IB, IIB, IIIB, VIB and VIIB of the Periodic Table.
Of the replacing metallic cations, particular preference is given
to cations of metals such as, for example, rare earth, Mn, Ca, Mg,
Zn, Cd, Cu, Sn, and Ag.
Typical ion exchange technique would be to contact the zeolite
with a salt of the desired replacing cation or cations. Although
a wide variety of salts can be employed, particular preference is
given to chlorides, nitrates and sulfates.
Representative ion exchange techniques are disclosed in a wide
variety of patents including U.S. Pat. Nos. 3140249; 3140251;
and 3140253.
The physical form of the silicoaluminophosphate catalyst depends
on the type of catalytic reactor being employed and may be in the
form of a granule or powder, and is desirably compacted into a more
readily usable form (e.g., larger agglomerates), usually with a
silica or alumina binder for fluidized bed reaction, or pills, prills,
spheres, extrudates, or other shapes of controlled size to accord
adequate catalyst-reactant contact. The catalyst may be employed
either as a fluidized catalyst, or in a fixed or moving bed, and
in one or more reaction stages.
Process Conditions
The isomerization step of this invention may be conducted by contacting
the feed to be isomerized with a fixed stationary bed of catalyst,
with a fixed fluidized bed, or with a transport bed, as desired.
A simple and therefore preferred configuration is a trickle-bed
operation in which the feed is allowed to trickle through a stationary
fixed bed, preferably in the presence of hydrogen. The catalytic
isomerization conditions are dependent in large measure on the feed
used and upon the desired product properties. Generally, the temperature
will be between about 200.degree. C. and about 475.degree. C., preferably
between about 250.degree. C. and about 450.degree. C. The pressure
is typically between about 15 psig and about 3000 psig, preferably
between about 200 psig and 3000 psig. The liquid hourly space velocity
(LHSV) preferably will be form 0.1 to 20 preferably between about
0.2 and about 10.
Hydrogen is preferably present in the reaction zone during the
isomerization process. The hydrogen to feed ratios is typically
between about 500 and about 30000 SCF/bbl (standard cubic feet
per barrel), preferably about 1000 to about 20000 SCF/bbl. Generally,
hydrogen will be separated from the product and recycled to the
reaction zone.
The silicoaluminophosphate molecular sieve catalyst can be manufactured
into a wide variety of physical forms. Generally speaking, the molecular
sieve catalyst can be in the form of a powder, a granule, or a molded
product, such as extrudate having particle size sufficient to pass
through a 2-mesh (Tyler) screen and be retained on a 40-mesh (Tyler)
screen. In cases where the catalyst is molded, such as by extrusion
with a binder, the silicoaluminophosphate can be extruded before
drying, or, dried or partially dried and then extruded.
The molecular sieve catalyst can be composited with other materials
resistant to the temperatures and other conditions employed in the
isomerization process. Such matrix materials include active and
inactive materials and synthetic or naturally occurring zeolites
as well as inorganic materials such as clays, silica and metal oxides.
The latter may be either naturally occurring or in the form of gelatinous
precipitates, sols or gels including mixtures of silica and metal
oxides. Inactive materials suitably serve as diluents to control
the amount of conversion in the isomerization process so that products
can be obtained economically without employing other means for controlling
the rate of reaction. The silicoaluminophosphate catalyst may be
incorporated into naturally occurring clays, e.g., bentonite and
kaolin. These materials, i.e., clays, oxides, etc., function, in
part, as binders for the catalyst. It is desirable to provide a
catalyst having good crush strength, because in petroleum refining
the catalyst is often subjected to rough handling. This tends to
break the catalyst down into powder-like materials which cause problems
in processing.
Naturally occurring clays which can be composited with the silicoaluminophosphate
catalyst include the montmorillonite and kaolin families, which
families include the sub-bentonites, and the kaolins commonly known
as Dixie, McNamee, Georgia and Florida clays or others in which
the main mineral constituent is halloysite, kaolinite, dickite,
nacrite, or anauxite. Fibrous clays such as halloysite, sepiolite
and attapulgite can also be used as supports. Such clays can be
used in the raw state as originally mined or initially subjected
to calcination, acid treatment or chemical modification.
In addition to the foregoing materials, the silicoaluminophosphate
catalyst can be composited with porous matrix materials and mixtures
of matrix materials such as silica, alumina, titania, magnesia,
silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,
silica-beryllia, silica-titania, titania-zirconia as well as ternary
compositions such as silica-alumina-thoria, silica-alumina-titania,
silica-alumina-magnesia and silica-magnesia-zirconia. The matrix
can be in the form of a cogel.
The silicoaluminophosphate catalysts used in the process of this
invention can also be composited with zeolites such as synthetic
and natural faujasites, (e.g., X and Y) erionites, and mordenites.
They can also be composited with purely synthetic zeolites such
as those of the ZSM series. The combination of zeolites can also
be composited in a porous inorganic matrix.
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