Molecular sieve abstract
The present invention relates to a process for catalytically dewaxing
a hydrocarbon oil feedstock by contacting the feedstock with a combination
of a catalyst comprising an intermediate pore size silicoaluminophosphate
molecular sieve and a hydrogenation component and an intermediate
pore size aluminosilicate zeolite catalyst.
Molecular sieve claims
What is claimed:
1. A process for catalytically dewaxing a hydrocarbon oil feedstock
boiling above about 350.degree. F. and containing straight chain
and slightly branched chain hydrocarbons comprising contacting said
hydrocarbon oil feedstock in the presence of added hydrogen gas
sequentially with a layered catalyst comprising a SAPO-11 SAPO-31
or SAPO-41 intermediate pore size silicoaluminophosphate molecular
sieve and a hydrogenation component, and an intermediate pore size
aluminosilicate zeolite catalyst.
2. The process of claim 1 wherein said intermediate pore size silicoaluminophosphate
molecular sieve is SAPO-11.
3. The process of claim 1 wherein said hydrogenation component
comprises a Group VIII metal.
4. The process of claim 3 wherein said Group VIII metal is platinum
or palladium.
5. The process of claim 1 wherein said silicoaluminophosphate sieve
is SAPO-11 and said hydrogenation component comprises platinum.
6. The process of claim 5 wherein said catalyst comprising said
silicoaluminophosphate molecular sieve and a hydrogenation component
further comprises an inorganic oxide matrix.
7. The process of claim 6 wherein said inorganic oxide matrix is
alumina.
8. The process of claim 1 wherein said hydrogenation component
is present in an amount of from about 0.01% to about 10% based on
the weight of said molecular sieve.
9. The process of claim 1 wherein said contacting is carried out
at a temperature of from about 200.degree. C. to 475.degree. C.,
a pressure of from 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
and a hydrogen circulation rate of from 500 to about 30000 SCF/bbl.
10. The process of claim 1 wherein said hydrocarbon oil feedstock
is a middle distillate oil.
11. The process of claim 1 wherein said feedstock is a lube oil
feedstock.
12. The process of claim 1 wherein said hydrocarbon oil feedstock
contains less than 50 ppmw organic nitrogen.
13. The process of claim 1 wherein said hydrocarbon oil feedstock
contains less than 10 ppmw organic nitrogen.
14. The process of claim 1 wherein said hydrocarbon oil feedstock
is contacted with said catalysts in one reactor.
15. The process of claim 14 wherein in said reactor said catalyst
comprising an intermediate pore size silicoaluminophosphate molecular
sieve and a hydrogenation component is layered on top of said intermediate
pore size aluminosilicate zeolite catalyst.
16. The process of claim 1 wherein said intermediate pore size
aluminosilicate zeolite has a Constraint Index measured at from
about 400.degree. C. to about 454.degree. C. of from about 4 to
about 12.
17. The process of claim 16 wherein said intermediate pore size
aluminosilicate zeolite is selected from the group consisting of
ZSM-22 ZSM-23 and ZSM-35.
18. The process of claim 1 wherein said intermediate pore size
aluminosilicate zeolite catalyst further comprises a metal selected
from the group consisting of platinum, palladium, molybdenum, nickel,
vanadium, cobalt, tungsten and zinc.
19. The process of claim 18 wherein said metal is selected from
the group consisting of platinum and palladium.
20. The process of claim 19 wherein said metal is platinum.
21. The process of claim 1 wherein the weight ratio of said intermediate
pore size silicoaluminophosphate molecular sieve to said intermediate
pore size silicoaluminophosphate zeolite molecular sieve is from
about 1:5 to about 20:1.
Molecular sieve description
BACKGROUND OF THE INVENTION
The present invention relates to a process for catalytically dewaxing
lube oils. More specifically, the invention relates to a process
for dewaxing a hydrocarbon oil feedstock wherein the feedstock is
contacted with a combination of an aluminosilicate zeolite catalyst
and an intermediate pore size silicoaluminophosphate molecular sieve
catalyst.
DESCRIPTION OF THE RELATED ART
Processes for dewaxing petroleum distillates are well known. Dewaxing
is required when highly paraffinic oils are to be used in products
which must be mobile at low temperatures, e.g., lubricating oils,
heating oils, and jet fuels. The higher molecular weight straight
chain normal and slightly branched paraffins present in such oils
are waxes which cause high pour points and high cloud points in
the oils. If adequately low pour points are to be obtained, the
waxes must be wholly or partially removed. In the past, various
solvent removal techniques were employed to remove such waxes, such
as propane dewaxing and MEK dewaxing, however, these techniques
are both costly and time consuming. Catalytic dewaxing processes
are more economical and remove the waxes by selectively cracking
the longer chain n-paraffins to produce lower molecular weight products,
some of which may be removed by distillation.
Because of their selectivity, prior art dewaxing catalysts 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 dewaxing processes. Their use is described in U.S.
Pat. Nos. 3700585; 3894938; 4176050; 4181598; 4222855;
4229282 and 4247388.
Since dewaxing 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 contribute to the waxy nature of the oil.
Because these lighter products are generally of lower value than
the higher molecular weight materials, it is desirable to limit
the degree of cracking which takes place during a catalytic dewaxing
process.
European Patent Application No. 225053 discloses a process for
producing lubricant oils by partially dewaxing a lubricant base
stock by isomerization dewaxing followed by a selective dewaxing
step. The isomerization dewaxing step is carried out using a large
pore, high silica zeolite dewaxing catalyst such as high silica
Y or zeolite beta which isomerizes the waxy components of the base
stock to less waxy branched chain isoparaffins. The selective dewaxing
step may be either a solvent, e.g., MEK dewaxing operation or a
catalytic dewaxing, preferably using a highly shape zeolite such
as ZSM-22 or ZSM-23.
U.S. Pat. No. 4437976 discloses a two-stage hydrocarbon dewaxing
hydrotreating process wherein the pour point of a hydrocarbon charge
stock boiling from 400.degree. F. to 1050.degree. F. is reduced
by catalytically dewaxing the charge stock in the presence of a
zeolite catalyst and subsequently subjecting at least the liquid
portion thereof to hydrogenation in the presence of a hydrotreating
catalyst comprising a hydrogenating component and a siliceous porous
crystalline material from the class of ZSM-5 ZSM-11ZSM-23 and ZSM-35
zeolites.
U.S. Pat. No. 4575416 to Chester et al. discloses a hydrodewaxing
process with a first zeolitic catalyst having a Constraint Index
not less than 1 a second catalytic component of specified characteristics
and a hydrogenation component.
As set forth in co-pending application Ser. No. 07/351532 applicant
previously discovered a dewaxing catalyst which provides superior
selectivity with respect to the nature of the products obtained
in a dewaxing process. Applicant discovered that by using an intermediate
pore size silicoaluminophosphate molecular sieve catalyst in the
dewaxing process, hydrocarbon oil feedstocks can be effectively
dewaxed and the products obtained thereby are of higher molecular
weight than those obtained using the prior art aluminosilicate zeolites.
The products obtained from the dewaxing process have better viscosities
and viscosity indexes at a given pour point as compared to the above-described
prior art process using aluminosilicate zeolites.
SUMMARY OF THE INVENTION
The present invention overcomes the problems and disadvantages
of the prior art by providing a process for catalytically dewaxing
a hydrocarbon oil feedstock which produces a lube oil having an
improved viscosity index and superior yield.
It is an object of the invention to provide a process for dewaxing
a lube oil which produces a yield and viscosity index improvement
which in combination is greater than the viscosity index or yield
achievable with either an intermediate pore size silicoaluminophosphate
molecular sieve catalyst or a shape selective catalyst such as an
intermediate pore size aluminosilicate zeolite catalyst.
Additional objects and advantages of the invention will be set
forth in part in the description which follows, and in part will
be obvious from the description, or may be learned by practice of
the invention. The objects and advantages of the invention will
be realized and attained by means of the instrumentalities and combinations,
particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the
invention, as embodied and broadly described herein, the invention
provides a process for catalytically dewaxing a hydrocarbon oil
feedstock boiling above 350.degree. F. and containing straight chain
and slightly branched chain hydrocarbons comprising contacting the
hydrocarbon oil feedstock with an intermediate pore size aluminosilicate
zeolite catalyst and a catalyst comprising an intermediate pore
size silicoaluminophosphate molecular sieve and a hydrogenation
component.
The combination of the catalysts produces a greater yield of lube
oil than achieved when dewaxing is carried out with either catalyst
alone. Since lube oil is valuable, maximization of the yield is
commercially important.
The catalyst comprising an intermediate pore size silicoaluminophosphate
molecular sieve and a hydrogenation component is employed in the
process of the invention to reduce the pour point of the hydrocarbon
oil feedstock to an intermediate value, i.e., of from about 30.degree.
F. to about 60.degree. F. Selective conversion of waxy n-paraffins
to non-waxy paraffins occurs during processing. The waxy paraffins
undergo mild cracking reactions to yield non-waxy products of higher
molecular weight than compared to products obtained using the prior
art zeolitic catalysts. At the same time, a measure of isomerization
takes place, so that not only is the pour point reduced by reason
of the cracking reactions described above, but in addition, the
n-paraffins become isomerized to iso-paraffins to form liquid range
materials which contribute to a low viscosity, low pour point product.
Due to the selectivity of the catalyst employed in the process of
this invention, the gas yield is reduced, thereby preserving the
economic value of the feedstock. Further, hydrogen consumption is
less compared to prior art processes using conventional dewaxing
catalysts because isomerization does not consume hydrogen and cracking
to liquid range products consumes less hydrogen than cracking to
gas.
The intermediate pore size aluminosilicate zeolite catalyst is
employed in the process of the invention to further reduce the pour
point to a desired level. Suitable aluminosilicate zeolite catalysts
for use in the process of the invention are those catalysts that
are very selective for cracking out the remaining amount of waxy
paraffins left in the hydrocarbon oil feedstock following the isomerization
step of the process. Zeolites that are very selective for cracking
out the remaining amount of waxy paraffins are those aluminosilicate
zeolite catalysts having a Constraint Index measured at from 400.degree.
C. to about 454.degree. C. of from about 4 to about 12. Such catalysts
are described in U.S. Pat. No 4658079 the pertinent disclosure
of which is incorporated herein by reference.
The accompanying drawings, which are incorporated in and constitute
a part of this specification, illustrate several exemplary embodiments
of this invention and together with the description, serve to explain
the principles of the invention.
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 in terms
of silicon, aluminum and phosphorus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the preferred embodiments
of applicant's invention.
Feedstock
The process of the invention may be used to dewax 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 feedstock will normally be a C.sub.10
+ feedstock generally boiling above about 350.degree. F. since lighter
oils will usually be free of significant quantities of waxy components.
However, 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. Lubricating oil stocks will generally
boil above 230.degree. C. (450.degree. F.), more usually above 315.degree.
C. (600.degree. F.). Hydroprocessed stocks are a convenient source
of stocks of this kind 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.10 + feedstock
containing paraffins, olefins, naphthenes, aromatics and heterocyclic
compounds and a substantial proportion of higher molecular weight
n-paraffins and slightly branched paraffins which contribute to
the waxy nature of the feedstock. During processing, the n-paraffins
and slightly branched paraffins undergo some cracking or hydrocracking
to form liquid range materials which contribute to a low viscosity
product. The degree of cracking which occurs is, however, limited
so that the gas yield is reduced, thereby preserving the economic
value of the feedstock. Typical feedstocks include light gas oils,
heavy gas oils and reduced crudes boiling above 350.degree. F.
While the process of the invention 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 ppmw, more preferably less than 10 ppmw. Particularly
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 Molecular Sieve Catalvst Compositions (SAPOs)
The catalyst employed in the process of the invention has an acidic
component and a hydrogenation component. The acidic component comprises
an intermediate pore size silicoaluminophosphate molecular sieve
which is described in U.S. Pat. No. 4440871 the pertinent disclosure
of which is incorporated herein by reference.
The preferred intermediate pore size silicoaluminophosphate molecular
sieves (SAPOs) are characterized as comprising a three-dimensional
micro-porous crystal framework structure of [SiO.sub.2 ], [AlO.sub.2
] and [PO.sub.2 ] tetrahedral units which have a unit empirical
formula on an anhydrous basis of:
wherein "R" represents at least one organic templating
agent (hereinafter also referred to as "template") present
in the intracrystalline pore system; "m" represents the
moles of "R" present per mole of (Si.sub.x Al.sub.y P.sub.z)O.sub.2
and has a value of from zero to about 0.3 with the maximum value
of "m" being related at least in part to the molecular
dimensions of the template and the void volume of the intracrystalline
pore system of the particular SAPO; "x", "y"
and "z" represent the mole fractions of silicon, aluminum
and phosphorus, respectively, present as tetrahedral oxide units,
said mole fractions being within the pentagonal compositional area
defined by points A, B, C, D and E of the ternary compositional
diagram depicted by FIG. 1 wherein points A, B, C, D and E are represented
by the following values for "x", "y" and "z":
______________________________________ Mole Fraction Point x y
z ______________________________________ A 0.01 0.47 0.52 B 0.94
0.01 0.05 C 0.98 0.01 0.01 D 0.39 0.60 0.01 E 0.01 0.60 0.39 ______________________________________
A preferred sub-class of the SAPOs of formula (I), have a minimum
value of "m" of 0.02 in the as-synthesized form and have
values of "x", "y", and "z" within
the pentagonal compositional area defined by points a, b, c, d,
and e of the ternary diagram of FIG. 2 wherein points a, b, c, d,
and e are represented by the following values of "x",
"y" and "z":
______________________________________ Mole Fraction Point x y
z ______________________________________ a 0.02 0.49 0.49 b 0.25
0.37 0.38 c 0.25 0.48 0.27 d 0.13 0.60 0.27 e 0.02 0.60 0.28 ______________________________________
The term "unit empirioal formula" as used herein means
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 form the molecular framework of the SAPO
composition(s). The unit empirical formula is given in terms of
silicon, aluminum and phosphorus as set forth in formula (I) and
does not include other compounds, cations or anions which may be
present as a result of the SAPO's preparation or 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 as-synthesized unit empirical formula is given, and water may
also be reported unless such is defined as the anhydrous form. For
convenience, the coefficient "m" for the 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, and template,
severity of the post-treatment in terms of its ability to remove
the template from the SAPO, and the proposed application of the
SAPO composition) 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 the formula
(I), 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., preferably between 100.degree. C. and 250.degree. C., until
crystals of the silicoaluminophosphate product are obtained, usually
for a period of from about 2 hours to about 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
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 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
are carried out in the case of zeolites.
The SAPOs are preferably formed from a reaction mixture having
a mole fraction of alkali metal cation that is sufficiently low
to not interfere with the formation of the SAPO composition. Although
the SAPO compositions will form if alkali metal cations are present,
reaction mixtures having the following bulk composition are 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 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.
Although the presence of alkali metal cations is not preferred,
when 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, preferably nitrogen, phosphorus, arsenic
and/or antimony, more preferably nitrogen or phosphorus, 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. 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 triamines, 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 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. 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),
135-trimethylbenzene (7.5), 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 intermediate pore size molecular sieve is used in admixture
with at least one Group VIII metal. Preferably, the Group VIII metal
is selected from the group consisting of at least one of platinum
and palladium, and optionally, other catalytically active metals
such as molybdenum, nickel, vanadium, cobalt, tungsten, zinc, and
mixtures thereof. More preferably, the Group VIII metal is selected
from the group consisting of at least one of platinum and palladium.
The amount of metal ranges from about 0.01% to about 10% by weight
of the molecular sieve, preferably from about 0.2% to about 5% by
weight of the molecular sieve. The techniques of introducing catalytically
active metals into a molecular sieve are disclosed in the literature,
and pre-existing metal incorporation techniques and treatment of
the molecular sieve to form an active catalyst such as ion exchange,
impregnation or occlusion during sieve preparation are suitable
for use in the present process. Such techniques are disclosed in
U.S. Pat. Nos. 3236761; 3226339; 3236762; 3620960; 3373109;
4202996; 4440781 and 4710485 which are incorporated herein
by reference.
The term "metal" or "active metal" as used
herein means one or more metals in the elemental state or in some
form such as sulfide, oxide and mixtures thereof. Regardless of
the state in which the metallic component actually exists, the concentrations
are computed as if they existed in the elemental state.
The physical form of the silicoaluminophosphate molecular sieve
and the aluminosilicate zeolite catalysts depend 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.
The intermediate pore size molecular sieve can be manufactured
into a wide variety of physical forms. The molecular sieve can be
in the form of a powder, a granule, or a molded product, such as
an extrudate having a particle size sufficient to pass through a
2-mesh (Tyler) screen and be retained on a 40-mesh (Tyler) screen.
In cases wherein 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.
In a preferred embodiment, the final catalyst will be a composite
and includes an intermediate pore size silicoaluminophosphate molecular
sieve, a platinum or palladium hydrogenation metal component and
an inorganic oxide matrix. The most preferred silicoaluminophosphate
is SAPO-11 the most preferred metal component is platinum, and
the most preferred support is alumina.
PROCESS CONDITIONS
The catalytic isomerization step of the invention may be conducted
by contacting the feed to be dewaxed 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 employed depend on the feed
used and the desired pour point. Generally, the temperature is from
about 200.degree. C. and about 475.degree. C., preferably between
about 250.degree. C. and about 450.degree. C. The pressure is typically
from about 15 psig and about 3000 psig, preferably between about
200 psig and 3000 psig. The liquid hourly space velocity (LHSV)
preferably will be from 0.1 to 20 preferably between about 0.2
and 10.
Hydrogen is preferably present in the reaction zone during the
catalytic isomerization process. The hydrogen to feed ratio is typically
between about 500 and about 30000 SCF/bbl (standard cubic feet
per barrel), preferably from about 1000 to about 20000 SCF/bbl.
Generally, hydrogen will be separated from the product and recycled
to the reaction zone.
The molecular sieve can be composited with other materials resistant
to the temperatures and other conditions employed in the dewaxing
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 dewaxing process so that products can be obtained economically
without employing other means for controlling the rate of reaction.
The silicoaluminophosphates 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
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 silicoaluminophosphates
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 other 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 the zeolites can
also be composited in a porous inorganic matrix.
The intermediate pore size silicoaluminophosphate molecular sieve
catalyst is employed in the process of the invention to convert
the waxy components to non-waxy components and reduce their pour
point to from about 30.degree. F. to about 60.degree. F. The amount
of catalyst employed is dependent on the reaction conditions.
The intermediate pore size aluminosilicate zeolite catalyst may
be used in the same reactor as the silicoaluminophosphate molecular
sieve catalyst, or may be used in a separate reactor. When both
catalysts are used in the same reactor, the silicoaluminophosphate
molecular sieve catalyst is layered on top of the aluminosilicate
zeolite catalyst.
The aluminosilicate zeolite catalyst preferably contains a Group
VIII metal, such as platinum, palladium, molybdenum, nickel, vanadium,
cobalt, tungsten, zinc, and mixtures thereof. More preferably, the
intermediate pore size aluminosilicate zeolite catalyst contains
at least one Group VIII metal selected from the group consisting
of platinum and palladium. Most preferably, the intermediate pore
size aluminosilicate zeolite catalyst contains platinum.
The amount of metal ranges from about 0.01% to about 10% by weight
of the molecular sieve, preferably from about 0.2% to about 5% by
weight of the molecular sieve. The techniques of introducing catalytically
active metals to a molecular sieve are disclosed in the literature,
and pre-existing metal incorporation techniques and treatment of
the molecular sieve to form an active catalyst such as ion exchange,
impregnation or occlusion during sieve preparation are suitable
for use in the present process. Such techniques are disclosed in
U.S. Pat. Nos. 3236761; 3226339; 3236762; 3620960; 3373109;
4202996; 4440781 and 4710485 which are incorporated herein
by reference.
Exemplary suitable aluminosilicate zeolite catalysts for use in
the process of the invention include ZSM-22 ZSM-23 and ZSM-35.
The silicoaluminophosphate molecular sieve catalyst and the aluminosilicate
zeolite catalyst are employed in the process of the invention in
a weight ratio of the intermediate pore size silicoaluminophosphate
molecular sieve to the intermediate pore size aluminosilicate zeolite
molecular sieve of from about 1:5 to about 20:1.
When the catalysts are used in the same reactor, a fixed fluidized
bed must be employed. When the catalysts are used in separate reactors,
a transport bed must be employed.
It is often desirable to use mild hydrogenation referred to as
hydrofinishing to produce more stable lubricating oils. The hydrofinishing
step can be performed after the isomerization step. Hydrofinishing
is typically conducted at temperatures ranging from about 190.degree.
C. to about 340.degree. C., at pressures of from about 400 psig
to about 3000 psig, at space velocities (LHSV) of from about 0.1
to about 20 and hydrogen recycle rates of from about 400 to about
1500 SCF/bbl. The hydrogenation catalyst employed must be active
enough not only to hydrogenate the olefins, diolefins and color
bodies within the lube oil fractions, but also to reduce the content
of any aromatics present. The hydrofinishing step is beneficial
in preparing an acceptably stable lubricating oil since unhydrofinished
lubricant oils tend to be unstable in air and light and tend to
spontaneously and quickly form sludges.
Suitable hydrogenation catalysts include conventional, metallic
hydrogenation catalysts, particularly the Group VIII metals such
as cobalt, nickel, palladium and platinum. The metals are typically
associated with carriers such as bauxite, alumina, silica gel, silica-alumina
composites, and crystalline aluminosilicate zeolites. Palladium
is a particularly preferred hydrogenation metal. If desired, non-noble
Group VIII metals can be used with molybdates. Metal oxides or sulfides
can be used. Suitable catalysts are disclosed in U.S. Pat. Nos.
3852207; 4157294; 3904513 and 4673487 which are incorporated
herein by reference. |