Note: Descriptions are shown in the official language in which they were submitted.
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DEWAXING PROCESS USING ZEOLITES MTT AND MTW
BACKGROUND OF THE INVENTION
This application claims the benefit of U.S. Provisional Application Serial No.
60/706,124 filed August 4, 2005.
Field of the Invention
The present invention relates to processes for dewaxing hydrocarbon
feedstocks employing a combination of zeolites MTT and MTW as a catalyst.
State of the Art
Because of their unique sieving characteristics, as well as their
catalytic properties, crystalline molecular sieves and zeolites are especially
useful in applications such as hydrocarbon conversion, including dewaxing of
hydrocarbon feedstocks. Zeolites may also be used for reducing the haze
point in feedstocks such as bright stock. (See, for example, U.S. Patent No.
6,051,129, issued April 18, 2000 to Harris et al., in which zeolite EU-1 in
combination with ZSM-48 and/or SSZ-32 is used to reduce haze in bright
stock. This patent is incorporated by reference herein in its entirety.)
Although
many different crystalline molecular sieves have been disclosed, there is a
continuing need for new zeolites with desirable properties for hydrocarbon
and chemical conversions, and other applications.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a dewaxing
process comprising contacting a hydrocarbon feedstock under dewaxing
conditions with a catalyst comprising a combination of zeolites having the
MTT and MTW framework topologies defined by the connectivity of their
tetrahedral atoms (referred to herein simply as MTT and MTW) wherein the
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MTT and MTW zeolites have a crystal size less than 0.1 micron. The MTT
and MTW zeolites are preferably predominantly in the hydrogen form.
The present invention also includes a process for improving the
viscosity index of a dewaxed product of waxy hydrocarbon feeds comprising
contacting the waxy hydrocarbon feed under isomerization dewaxing
conditions with a catalyst comprising a combination of zeolites MTT and
MTW, preferably predominantly in the hydrogen form, wherein the MTT and
MTW zeolites have a crystal size less than 0.1 micron.
The present invention further includes a process for producing a C20+
lube oil from a C20+ olefin feed comprising isomerizing said olefin feed under
isomerization conditions over a catalyst comprising at least one Group VIII
metal and a combination of zeolites MTT and MTW wherein the MTT and
MTW zeolites have a crystal size less than 0.1 micron. The zeolites may be
predominantly in the hydrogen form.
In accordance with this invention, there is also provided a process for
catalytically dewaxing a hydrocarbon oil feedstock boiling above about 350 F
and containing straight chain and slightly branched chain hydrocarbons
comprising contacting said hydrocarbon oil feedstock in the presence of
added hydrogen gas at a hydrogen pressure of about 15-3000 psi with a
catalyst comprising at least one Group VIII metal and a combination of
zeolites MTT and MTW, preferably predominantly in the hydrogen form,
wherein the MTT and MTW zeolites have a crystal size less than 0.1 micron.
Further included in this invention is a process for isomerization
dewaxing a raffinate comprising contacting said raffinate in the presence of
added hydrogen with a catalyst comprising at least one Group VIII metal and
a combination of zeolites MTT and MTW wherein the MTT and MTW zeolites
have a crystal size less than 0.1 micron. The raffinate may be bright stock,
and the zeolites may be predominantly in the hydrogen form.
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The present invention also provides a process for reducing the cloud
point of a hydrocarbon feed comprising contacting a hydrocarbon oil
feedstock which has a major portion boiiing over 1000 F with a catalyst
system comprising a combination of a zeolite having MTT topology and a
zeolite having MTW topology wherein the MTT and MTW zeolites have a
crystal size less than 0.1 micron, and wherein at least a portion of said
feedstock is converted.
DETAILED DESCRIPTION OF THE INVENTION
In hydrodewaxing, one target is to hydroconvert the longest
hydrocarbons in the feed. If these are left unconverted, they can cause haze
in the product. The haze is quantified by cloud point.
The Gibbs free energy of adsorption for n-alkanes quantifies the ability
of a particular zeolite structure for selectively absorbing and converting
n- alkanes. In order to reduce the cloud point, it is advantageous to employ
zeolites that impose a significantly lower Gibbs free energy of adsorption on
a
long as opposed to short n-alkane.
Gibbs free energies of adsorption can be determined with consistency
and accuracy. Examples of these determinations are presented in "Journal of
Physical Chemistry B" (2004), 108(33), 12301-12313. These determinations
indicate that the difference between absorbing and converting a long n-alkane
and a short n-alkane is only minimally different for MTT-type zeolites. The
MTW-type zeolites exhibit the maximum difference in Gibbs free energy of
adsorption between long and short n-alkanes. It is surprising the Gibbs free
energies of adsorption of these zeolites demonstrate such a markedly
different response to the variation in n-alkane chain length. By employing
MTW-type zeolites in addition to MTT-type zeolites, the conversion of heavy
wax (long n-alkanes) can be significantly increased, thereby lowering the
cloud point of the product.
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Zeolites having the MTT framework topology are known. For example,
the zeolite designated "SSZ-32" and methods for making it are disclosed in
U.S. Patent No. 5,053,373, issued October 1, 1991 to Zones. This patent
discloses the preparation of zeolite SSZ-32 using an N-lower alkyl-N'-
isopropylimidazolium cation as an organic structure directing agent (SDA),
sometimes called a templating agent. U.S. Patent No. 4,076,842, issued
February 28, 1978 to Plank et al., discloses the preparation of the zeolite
designated "ZSM-23", a zeolite with a structure similar to SSZ-32, using a
cation derived from pyrrolidine as the SDA. Zeolites SSZ-32 and ZSM-23 are
commonly referred to as having the MTT framework topology. Both of the
aforementioned patents are incorporated herein by reference in their entirety.
In addition, R. Szostak, Handbook of Molecular Sieves, 1992 lists zeolites
designated ISI-4 and KZ-1 as having the MTT topology. The zeolite
designated EU-13 is described in C. Baerlocher et al., Atlas of Zeolite
Framework Types, 5 th Revised Edition, 2001, International Zeolite Association
as having the MTT topology.
Dewaxing processes using MTT zeolites are known. For example, U.
S. Patent No. 4,222,855, issued September 16, 1980 to Pelrine et al.,
discloses a dewaxing process using ZSM-23 or ZSM-35. Likewise,
U. S. Patent No. 5,376,260, issued December 27, 1994 to Santilli et al.,
discloses a dewaxing process using a catalyst containing SSZ-32. U. S.
Patent No. 6,663,768, issued December 16, 2003 to Miller, also discloses a
dewaxing process which uses ZSM-23 or SSZ-32 in the catalyst. U. S. Patent
No. 4,601,993, issued July 22, 1986 to Chu et al., discloses a dewaxing
process using a combination of ZSM-23 and zeolite Beta. ZSM-12 (MTW) is
mentioned as a possible catalyst, but the combination of ZSM-23 and ZSM-1 2
is not disclosed.
Zeolites having the MTW topology are also known. For example, the
zeolite designated ZSM-12, disclosed in U. S. Patent No. 3,832,449 issued
August 27, 1974 to Rosinski et al. (incorporated by reference herein in its
entirety), has the MTW topology and is said to be useful in catalysts for a
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variety of hydrocarbon conversion reactions. Likewise, the zeolites designated
CZH-5 (disclosed in UK 2,079,735) and TEA-Silicate (disclosed in U. S.
Patent No. 4,104,294) and Theta-3 (disclosed in EP 162,719) have the MTW
framework topology. U. S. Patent No. 4,360,419, issued November 23, 1982
to Miller, discloses a dewaxing process using CZH-5.
U. S. Patent No. 4,575,416, issued March 11, 1986, discloses a
dewaxing process using a combination of two catalysts. ZSM-23 (MTT) and
ZSM-12 (MTW) are included in a list of zeolites that can be employed, but the
combination of ZSM-23 and ZSM-12 is not disclosed.
U. S. Patent No. 4,599,162, issued July 8, 1986 to Yen, discloses a
dual catalyst cascade dewaxing process. In Examples 2-8, the first stage of
the cascade process uses a combination of ZSM-12 and ZSM-23 in admixture
as the catalyst. However, there is no disclosure of a ZSM-12/ZSM-23
combination in which the crystal size of the zeolites is less than 0.1 micron.
The MTT and MTW zeolites are used in the present invention in
combination. As used herein, the term "combination" includes mixtures of the
zeolites, layers of the zeolites, or any other configuration in which the feed
comes in contact with both zeolites. For example, the combination may be a
graduated mixture in which the feed initially contacts a portion of the
mixture
which comprises essentially all one of the zeolites. The concentration of the
second zeolite can be gradually increased, and the concentration of the first
zeolite gradually decreased, in successive portions of the mixture until the
mixture becomes essentially all second zeolite. Depending on the feed,
reaction conditions, and desired product, the combination may be such that
the feed initially contacts the MTT zeolite first or the MTW zeolite first.
The combination of MTT and MTW zeolites may also be used in layers.
The use of catalyst layers is disclosed in U. S. Patent No. 5,149,421, issued
September 22, 1992 to Miller, which is incorporated by reference herein in its
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entirety. The order of the layers may be MTT in a first layer and MTW in a
subsequent layer, or vice versa.
Depending upon the nature of the feed and the desired products, the
MTT and MTW zeolites can be employed over a wide range of
concentrations. The catalyst combination may comprise 1-99 weight percent
MTT zeolite and 99-1 weight percent MTW zeolite.
The crystal size of the MTT and MTW zeolites is less than 0.1 micron,
i.e., the longest dimension of the crystal is less than 0.1 micron.
The crystalline MTT and MTW can be used as-synthesized, but
preferably will be thermally treated (calcined). Usually, it is desirable to
remove the alkali metal cation by ion exchange and replace it with hydrogen,
ammonium, or any desired metal ion. The zeolite can be leached with
chelating agents, e.g., EDTA or dilute acid solutions, to increase the silica
to
alumina mole ratio. The zeolite can also be steamed; steaming helps stabilize
the crystalline lattice to attack from acids.
The zeolite can be used in intimate combination with hydrogenating
components, such as tungsten, vanadium, molybdenum, rhenium, nickel,
cobalt, chromium, manganese or a noble metal, such as palladium or
platinum.
Metals may also be introduced into the zeolite by replacing some of the
cations in the zeolite with metal cations via standard ion exchange techniques
(see, for example, U.S. Patent Nos. 3,140,249 issued July 7, 1964 to Plank et
al.; 3,140,251 issued July 7, 1964 to Plank et al.; and 3,140,253 issued
July 7, 1964 to Plank et al.). Typical replacing cations can include metal
cations, e.g., rare earth, Group IA, Group IIA and Group VIII metals, as well
as their mixtures. Of the replacing metallic cations, cations of metals such
as
rare earth, Mn, Ca, Mg, Zn, Cd, Pt, Pd, Ni, Co, Ti, Al, Sn and Fe are
particularly preferred.
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The hydrogen, ammonium and metal components can be ion-
exchanged into the zeolites. The zeolites can also be impregnated with the
metals, or the metals can be physically and intimately admixed with the
zeolites using standard methods known to the art.
Typical ion-exchange techniques involve contacting the zeolites with a
solution containing a salt of the desired replacing cation or cations.
Although a
wide variety of salts can be employed, chlorides and other halides, acetates,
nitrates and sulfates are particularly preferred. The zeolites are usually
calcined prior to the ion-exchange procedure to remove the organic matter in
the channels and on the surface, since this result in a more effective ion
exchange. Representative ion exchange techniques are disclosed in a wide
variety of patents including U.S. Patent Nos. 3,140,249 issued July 7, 1964 to
Plank et al.; 3,140,251 issued July 7, 1964 to Plank et al. and 3,140,253
issued on July 7, 1964 to Plank et al.
Following contact with the salt solution of the desired replacing cation,
the zeolites are typically washed with water and dried at temperatures ranging
from 65 C to about 200 C. After washing, the zeolites can be calcined in air
or
inert gas at temperatures ranging from about 200 C to about 800 C for
periods of time ranging from 1 to 48 hours, or more, to produce a
catalytically
active product especially useful in hydrocarbon conversion processes.
The zeolites can be formed into a wide variety of physical shapes.
Generally speaking, the zeolite can be in the form of a powder, a granule or a
molded product, such as extrudate having a particle size sufficient to pass
through a 2-mesh (Tyler) screen and be retained on a 400-mesh (Tyler)
screen. In cases where the catalyst is molded, such as by extrusion with an
organic binder, the zeolite can be extruded before drying, or dried or
partially
dried and then extruded.
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The zeolites can be composited with other materials resistant to the
temperatures and other conditions employed in organic conversion
processes. 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. Examples of such materials and the manner in
which they can be used are disclosed in U.S. Patent No. 4,910,006, issued
May 20, 1990 to Zones et al. and U.S. Patent No. 5,316,753, issued
May 31, 1994 to Nakagawa, both of which are incorporated by reference
herein in their entirety.
The MTT and MTW zeolites are used in dewaxing hydrocarbonaceous
feedstocks. Hydrocarbonaceous feedstocks contain carbon compounds and
can be from many different sources, such as virgin petroleum fractions,
recycle petroleum fractions, shale oil, liquefied coal, tar sand oil,
synthetic
paraffins from NAO, recycled plastic feedstocks, bright stock, Fischer-Tropsch
waxes (i.e., synthetic waxes derived from a Fischer Tropsch process,
preferably an oxygenate-containing Fischer Tropsch process, boiling below
about 700 F) and, in general, can be any carbon containing feedstock
susceptible to zeolitic catalytic dewaxing reactions. Depending on the type of
processing the hydrocarbonaceous feed is to undergo, the feed can contain
metal or be free of metals. It can also have high or low nitrogen or sulfur
impurities. It can be appreciated, however, that in general processing will be
more efficient (and the catalyst more active) the lower the metal, nitrogen,
and
sulfur content of the feedstock. Preferably, after treating the feedstock in
accordance with the present invention, the cloud point of the feedstock
(depending on its original composition) is reduced to not more than 10 C.
The dewaxing of hydrocarbonaceous feeds can take place in any
convenient mode, for example, in fluidized bed, moving bed, or fixed bed
reactors depending on the types of process desired. The formulation of the
catalyst particles will vary depending on the conversion process and method
of operation.
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Typical dewaxing reaction conditions which may be employed when
using catalysts comprising a combination of zeolites MTT and MTW in the
dewaxing reactions of this invention include a temperature of about
200-475 C, preferably about 250-450 C, a pressure of about 15-3000 psig,
preferably about 200-3000 psig, and a LHSV of about 0.1-20, preferably
0.2-10.
The MTT and MTW combination, preferably predominantly in the
hydrogen form, can be used to dewax hydrocarbonaceous feeds by
selectively removing straight chain paraffins. Typically, the viscosity index
of
the dewaxed product is improved (compared to the waxy feed) when the waxy
feed is contacted with a combination of zeolites MTT and MTW under
isomerization dewaxing conditions.
The catalytic dewaxing conditions are dependent in large measure on
the feed used and upon the desired pour point. Hydrogen is preferably
present in the reaction zone during the catalytic dewaxing process. The
hydrogen to feed ratio is typically between about 500 and about
30,000 SCF/bbl (standard cubic feet per barrel), preferably about 1000 to
about 20,000 SCF/bbl. Generally, hydrogen will be separated from the
product and recycled to the reaction zone. Typical feedstocks include light
gas
oil, heavy gas oils and reduced crudes boiling above about 350 F.
A typical dewaxing process is the catalytic dewaxing of a hydrocarbon
oil feedstock boiling above about 350 F and containing straight chain and
slightly branched chain hydrocarbons by contacting the hydrocarbon oil
feedstock in the presence of added hydrogen gas at a hydrogen pressure of
about 15-3000 psi with a catalyst comprising a combination of zeolites MTT
and MTW and at least one Group VIII metal.
The hydrodewaxing catalyst may optionally contain a hydrogenation
component of the type commonly employed in dewaxing catalysts. See the
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aforementioned U.S. Patent No. 4,910,006 and U.S. Patent No. 5,316,753 for
examples of these hydrogenation components.
The hydrogenation component is present in an effective amount to
provide an effective hydrodewaxing and hydroisomerization catalyst
preferably in the range of from about 0.05 to 5% by weight. The catalyst may
be run in such a mode to increase isodewaxing at the expense of cracking
reactions.
The feed may be hydrocracked, followed by dewaxing. This type of two
stage process and typical hydrocracking conditions are described in U.S.
Patent No. 4,921,594, issued May 1, 1990 to Miller, which is incorporated
herein by reference in its entirety.
The combination of MTT and MTW may also be used to dewax
raffinates, including bright stock, under conditions such as those disclosed
in
U. S. Patent No. 4,181,598, issued January 1, 1980 to Gillespie et al., which
is incorporated by reference herein in its entirety.
It is often desirable to use mild hydrogenation (sometimes referred to
as hydrofinishing) to produce more stable dewaxed products. The
hydrofinishing step can be performed either before or after the dewaxing step,
and preferably after. Hydrofinishing is typically conducted at temperatures
ranging from about 190 C to about 340 C at pressures from about 400 psig to
about 3000 psig at space velocities (LHSV) between about 0.1 and 20 and a
hydrogen recycle rate of about 400 to 1500 SCF/bbl. The hydrogenation
catalyst employed must be active enough not only to hydrogenate the olefins,
diolefins and color bodies which may be present, but also to reduce the
aromatic content. Suitable hydrogenation catalyst are disclosed in U. S.
Patent No. 4,921,594, issued May 1, 1990 to Miller, which is incorporated by
reference herein in its entirety. The hydrofinishing step is beneficiai in
preparing an acceptably stable product (e.g., a lubricating oil) since dewaxed
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products prepared from hydrocracked stocks tend to be unstable to air and
light and tend to form sludges spontaneously and quickly.
Lube oil may be prepared using a combination of zeolites MTT and
MTW. For example, a C20+ lube oil may be made by isomerizing a C20+ olefin
feed over a catalyst comprising a combination of zeolites MTT and MTW,
preferably predominantly in the hydrogen form, and at least one Group VIII
metal. Alternatively, the lubricating oil may be made by hydrocracking in a
hydrocracking zone a hydrocarbonaceous feedstock to obtain an effluent
comprising a hydrocracked oil, and catalytically dewaxing the effluent at a
temperature of at least about 400 F and at a pressure of from about 15 psig to
about 3000 psig in the presence of added hydrogen gas with a catalyst
comprising a combination of zeolites MTT and MTW, preferably
predominantly in the hydrogen form, and at least one Group VIII metal.
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