Note: Descriptions are shown in the official language in which they were submitted.
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ISOMERIZATION CATALYST AND PROCESSES
BACKGROUND OF THE INVENTION
[0001] This invention relates to an improved catalytic composite and process
for the
conversion of hydrocarbons, and more specifically for the selective upgrading
of a paraffinic
feedstock by isomerization.
[0002] The widespread removal of lead antiknock additive from gasoline and the
rising fuel-
quality demands of high-performance internal-combustion engines have
cornpelled petroleum
refiners to install new and modified processes for increased "octane," or
knock resistance, in the
gasoline pool. Refiners have relied on a variety of options to upgrade the
gasoline pool, including
higher-severity catalytic reforming, higher FCC (fluid catalytic cracking)
gasoline octane,
isomerization of light naphtha and the use of oxygenated compounds. Such key
options as
increased reforming severity and higher FCC gasoline octane result in a higher
aromatics content
of the gasoline pool at the expense of low-octane heavy paraffins.
[0003] Refiners are also faced with supplying reformulated gasoline to rrieet
tightened
automotive emission standards. Reformulated gasoline differs from the
traditional product in
having a lower vapor pressure, lower final boiling point, increased content of
oxygenates, and
lower content of olefins, benzene and aromatics. Benzene content generally is
being restricted to
1% or lower, and is limited to 0.8% in U.S. reformulated gasoline. Gasoline
aromatics content is
likely to be lowered, particularly as distillation end points (usually
characterized as the 90%
distillation temperature) are lowered, since the high-boiling portion of the
gasoline which thereby
would be eliminated usually is an aromatics concentrate. Since aromatics have
been the principal
source of increased gasoline octanes during the recent lead-reduction program,
severe restriction
of the benzene/aromatics content and high-boiling portion will present
refiners with processing
problems. These problems have been addressed through such technology as
isomerization of light
naphtha to increase its octane number, isomerization of butanes as alkylation
feedstock, and
generation of additional light olefins as feedstock for alkylation and
production of oxygenates
using FCC and dehydrogenation. This issue often has been addressed by raising
the cut point
between light and heavy naphtha, increasing the relative quantity of naphtha
to an isomerization
unit.
- [0004] Additionally, instead of reforming, the isomerization of longer chain
hydrocarbons
such as C7 and C8 hydrocarbons into branched hydrocarbons of higher octane
could be used to
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increase the octane number of fuels without increasing the amount of
aromatics. However, many
isomerization catalysts suffer significant disadvantages when applied to the
longer chain
hydrocarbons. A principal problem is the generation of byproducts such as
cracked hydrocarbon
materials. The cracking decreases the amount of long chain paraffins available
for isomerization
and reduces the ultimate yield.
[0005] Several catalysts for isomerization are known, and a family of
tungstated zirconia
catalysts have been used. For example, US 5,510,309 B1, US 5,780,382 B1, US
5,854,170, and
US 6,124,232 B 1 teach methods of making an acidic solid having a Group NB
(IUPAC 4) metal
oxide modified with an oxyanion of a Group VIB (IUPAC 6) metal such as
zirconia modified
witll tungstate. US 6,184,430 B 1 teaches a method of cracking a feedstock by
contacting the
feedstock with a metal-promoted anion modified rnetal oxide catalyst where the
metal oxide is
one or more of Zr02, Hf02, Ti02 and Sn02, the modifier is one or more of SO4
and W03, and the
metal is one or more of Pt, Ni, Pd, Rh, Ir, Ru, Mn, and Fe.
[0006] Others have added a noble metal such as platinum to the tungstated
zirconia catalysts
above, see US 5,719,097; US 6,080,904 B 1; and US 6,118,036 B 1. A catalyst
having an oxide of
a Group NB (IUPAC 4) metal modified with an anion or oxyanion of a Group VIB
(IUPAC 6)
metal and a Group 1B (IUPAC 11) metal or metal oxide is disclosed in US
5,902,767. In US
5,648,589 and US 5,422,327, a catalyst having a Group VIII (1TJPAC 8, 9, and
10) metal and a
zirconia support impregnated with silica and tungsten oxide and a process of
isomerization using
the catalyst is disclosed. A process for forming a diesel fuel blending
component uses an acidic
solid catalyst having a Group IVB (IUPAC 4) metal oxide modified with an
oxyanion of Group
VIB (IUPAC 6) metal and iron or manganese in US 5,780,703 Bl.
[0007] US 5,310,868 and US 5,214,017 teach catalyst compositions containing
sulfated and
calcined mixtures of (1) a support containing an oxide or hydroxide of IUPAC 4
(Ti, Zr, Hf), (2)
an oxide or hydroxide of IUPAC 6 (Cr, Mo, W); IUPAC 7 (Mn, Tc, Re), or ILJPAC
8, 9, and 10
(Group VIII) metal, (3) an oxide or hydroxide of ILJPAC 11 (Cu, Ag, Au), lUPAC
12 (Zn, Cd,
Hg), IUPAC 3 (Sc, Y), IUPAC 13 (B, Al, Ga, In, Tl), IUPAC 14 (Ge, Sn, Pb),
IUPAC 5 (V, Nb,
Ta), or I[TPAC 6 (Cr, Mo, W), and (4) a metal of the lanthanide series.
[0008] Applicant has developed a more effective catalyst that has proved to be
surprisingly
superior to those already known for the isomerization of hydrocarbons and
especially C7 and C8
hydrocarbons.
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SUMMARY OF THE INVENTION
[0009] The present invention is an improved catalyst and process for
hydrocarbon conversion
reactions. The invention also provides improved technology to upgrade naphtha
to gasoline and
more specifically an improved catalyst and process for the isomerization of
full boiling point
range naphtha to obtain a high-octane gasoline component. This invention is
based on the
discovery that a catalyst containing lanthanide series and platinum-group
components provides
superior performance and stability in the isomerization of full boiling point
range naphtha to
increase its isoparaffin content.
[0010] The invention is a catalyst comprising a tungstated support of an oxide
or hydroxide
of a Group IVB (IUPAC 4) metal, preferably zirconium oxide or hydroxide, at
least a first
component which is a lanthanide series element and/or yttrium component, and
at least a second
component being a platinum-group metal component. The first component
preferably consists of
a single lanthanide-series element or yttrium and the second component
preferably consists of a
single platinum-group metal. Preferably, the first component is ytterbium,
holmium, yttrium,
cerium, europium, or mixtures thereof, and the second component is platinum.
The catalyst
optionally contains an inorganic-oxide binder, especially alumina. One method
of preparing the
catalyst of the invention is by tungstating or tungstating and the Group IVB
(IUPAC 4) metal
oxide or hydroxide, incorporating a first component which is at least one
lanthanide element,
yttrium, or any mixture thereof, and the second component which is a platinum-
group metal, and
preferably binding the catalyst with a refractory inorganic oxide.
[0011] The catalyst of the invention may be used for converting hydrocarbons
such as in the
isomerization of isomerizable hydrocarbons. The hydrocarbons preferably
comprise a full boiling
point range naphtha which is isomerized to increase its isoparaffin content
and octane number as
a gasoline blending stock.
[0012] These as well as other embodiments will become apparent from the
detailed
description of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a plot of the conversion of n-heptane achieved by selected
catalysts made in
Example 1.
[0014] FIG. 2 is a plot of the selectivities of the catalysts of FIG. 1 for n-
heptane
isomerization.
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[0015] FIG. 3 is a plot of the selectivities of the catalysts of FIG. 1 for
the isomerization of n-
heptane to 2,2-dimethylpentane and 2,4-dimethylpentane.
[0016] FIG. 4 is a plot of the yields of the catalysts of FIG. 1 for the
isomerization of n-
heptane to 2,2-dimethylpentane and 2,4-dimethylpentane.
[0017] FIG. 5 is a plot of the conversion of n-heptane achieved by selected
catalysts made in
Example 1 where ytterbium is a modifier.
[0018] FIG. 6 is a plot of the selectivities of the catalysts of FIG. 5 for n-
heptane
isomerization.
[0019] FIG. 7 is a plot of the selectivities of the catalysts of FIG. 5 for
the isomerization of n-
heptane to 2,2-dimethylpentane and 2,4-dimethylpentane.
[0020] FIG. 8 is a plot of the yields of the catalysts of FIG. 5 for the
isomerization of n-
heptane to 2,2-dimethylpentane and 2,4-dimethylpentane.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The support material of the catalyst of the present invention comprises
an oxide or
hydroxide of a Group IVB (IUPAC 4) metal, see Cotton and Wilkinson, Advanced
Inorganic
Chemistry, John Wiley & Sons (Fifth Edition, 1988) and including zirconium,
titanium and
hafnium. Preferably, the metal is selected from zirconium and titanium, with
zirconium being
especially preferred. The preferred zirconium xide or hydroxide is converted
via calcination to
crystalline form. Tungstate is composited on the support material to form, it
is believed without
so limiting the invention, a mixture of Bronsted and Lewis acid sites. A
component of at least one
lanthanide-series element, yttrium, or mixtures thereof, is incorporated into
the composite by any
suitable means. A platinum-group metal component is added to the catalytic
composite by any
means known in the art to effect the catalyst of the invention, e.g., by
impregnation. Optionally,
the catalyst is bound with a refractory inorganic oxide. The support,
tungstate, metal components,
and optional binder may be composited in any order effective to prepare a
catalyst useful for the
conversion of hydrocarbons, and particularly the isomerization of
hydrocarbons.
[0022] Production of the support of the present catalyst may be based on a
hydroxide of a
Group IVB (IUPAC 4) metal as raw material _ For example, suitable zirconium
hydroxide is
available from MEI of Flemington, New Jersey. Alternatively, the hydroxide may
be prepared
by hydrolyzing metal oxy-anion compounds, for example ZrOC12, ZrO(NO3)2,
ZrO(OH)NO3,
ZrOSO4, TiOC12 and the like. Note that comrnercial ZrO(OH)2 contains a
significant amount of
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Hf, 1 weight percent. Zirconium alkoxides such as zirconyl acetate and
zirconium propoxide
may be used as well. The hydrolysis can be effected using a hydrolyzing agent
such as
ammonium hydroxide, sodium hydroxide, potassium hydroxide, sodium sulfate,
(NH4)2HPO4
and other such compounds known in the art. The metal oxy-anion component may
in turn be
prepared from available materials, for example, by treating ZrOCO3 with nitric
acid. The
hydroxide as purchased or generated by hydrolysis preferably is dried at a
temperature of from
100 C to 300 C to vaporize volatile compounds.
[00231 A tungstated support is prepared by treatment with a suitable
tungstating agent to
form a solid strong acid. Liquid acids whose strength is greater than sulfuric
acid have been
termed "superacids". A number of liquid superacids are known in the literature
including
substituted protic acids, e.g., trifluoromethyl substituted H2SO4, triflic
acid and protic acids
activated by Lewis acids (HF plus BF3). While determination of the acid
strength of liquid
superacids is relatively straightforward, the exact acid strength of a solid
strong acid is difficult
to directly measure with any precision because of the less defined nature of
the surface state of
solids relative to the fully solvated molecules found in liquids. Accordingly,
there is no
generally applicable correlation between liquid superacids and solid strong
acids such that if a
liquid super acid is found to catalyze a reaction, there is no corresponding
solid strong acid
which one can automatically choose to carry out the same reaction. Therefore,
as will be used
in this specification, "solid strong acids" are those that have an acid
strength greater than
sulfonic acid resins such as Amberlyst -15. Additionally, since there is
disagreement in the
literature whether some of these solid acids are "superacids" only the term
solid strong acid as
defined above will be used herein. Another way to define a solid strong acid
is a solid
comprising of interacting protic and ]Lewis acid sites. Thus, solid strong
acids can be a
combination of a Bronsted (protonic) acid and a Lewis acid component. In other
cases, the
Bronsted and Lewis acid components are not readily identified or present as
distinct species,
yet they meet the above criteria.
[0024] Tungstate ions are incorporated into a catalytic composite, for
example, by treatment
with ammonium metatungstate in a concentration usually of 0.1 to 20 mass
percent tungsten and
preferably from 1 to 15 mass percent tungsten. Compounds such as metatungstic
acid, sodium
tungstate, armnonium tungstate, amrnonium paratungstate, which are capable of
forming
tungstate ions upon calcining, may be employed as alternative sources.
Preferably, ammonium
metatungstate is employed to provide tungstate ions and form a solid strong
acid catalyst. The
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tungstate content of the finished catalyst generally is in the range of 0.5 to
25 mass-%, and
preferably is from 1 to 25 mass-% on an elemental basis. The tungstate
composite is dried,
preferably followed by calcination at a temperature of 450 C to 1000 C
particularly if the
tungstanation is to be followed by incorporation of the platinum-group metal.
[0025] A first component, comprising one or more of the lanthanide-series
elements, yttrium,
and mixtures thereof, is another essential component of the present catalyst.
Included in the
lanthanide series are lanthanum, cerium, praseodymium, neodymium, promethium,
samarium,
europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium
and lutetium.
Preferred lanthanide series elements include ytterbium, cerium, holmium,
europium, and mixtures
thereof. Ytterbium and holmium are the most preferred first components of the
present catalyst,
and it is especially preferred that the first component consists essentially
of a ytterbium or
holmium component. The first component may in general be present in the
catalytic compo site in
any catalytically available form such as the elemental metal, a compound such
as the oxide,
hydroxide, halide, oxyhalide, carbonate or nitrate or in chemical combination
with one or rrnore of
the other ingredients of the catalyst. The first component is preferably an
oxide, an intermetallic
with platinum, a sulfate, or in the zirconia lattice. The materials are
generally calcined betv-een
600 C and 900 C and thus in the oxide form. Although it is not intended to so
restrict the present
invention, it is believed that best results are obtained when the first
component is present in the
composite in a form wherein substantially all of the first component is in an
oxidation state above
that of the elemental state such as in the form of the oxide, oxyhalide or
halide or in a mixture
thereof and the subsequently described oxidation and reduction steps that are
preferably used in
the preparation of the instant catalytic composite are specifically designed
to achieve this end.
The first component can be incorporated into the catalyst in any amount which
is catalytically
effective, suitably from 0.01 to 10 mass-% first component in the finished
catalyst on an
elemental basis. Best results usually are achieved with 1 to 5 mass-% of the
first componernt,
calculated on an elemental basis.
[0026] The first component is incorporated in the catalytic composite in any
suitable rnanner
known to the art, such as by coprecipitation, coextrusion with the porous
carrier material, oz
impregnation of the porous carrier material either before, after, or
simultaneously with tungstate
though not necessarily with equivalent results. For ease of operation, it is
preferred to
simultaneously incorporate the first cornponent with the tungstate. It is most
preferred to
incorporate the platinum-group metal component last. As to the lanthanide
element(s), yttrium, or
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mixture thereof and the platinum-group rnetal, the order of addition between
the two does riot
have a significant impact.
[0027] One method of depositing the first component involves impregnating the
support
with a solution (preferably aqueous) of a decomposable compound of the first
component. By
decomposable is meant that upon heating, the compound is converted to element
or oxide with
the release of byproducts. Illustrative of the decomposable compounds without
limitation are
complexes or compounds such as, nitrates, halides, sulfates, acetates, organic
alkyls, hydroxides,
and the like compounds. Conditions for decomposition include temperatures
ranging from 200 C
to 400 C. The first component can be impregnated onto the carrier either prior
to, simultarneously
with, or after the platinum-group metal component, although not necessarily
with equivalent
results. If a sequential technique is used, the composite can be dried or
dried and calcined in
between impregnations.
[0028] A second component, a platinum-group metal, is an essential ingredient
of the
catalyst. The second component comprises at least one of platinum, palladium,
ruthenium,
rhodium, iridium, or osmium; platinum is preferred, and it is especially
preferred that the
platinum-group metal consists essentially of platinum. The platinum-group
metal component may
exist within the final catalytic composite as a compound such as an oxide,
sulfide, halide,
oxyhalide, etc., in chemical combination with one or more of the other
ingredients of the
composite or as the metal. Amounts in the range of from 0.01 to 2 mass-%
platinum-group metal
component, on an elemental basis, are effective, and from 0.1 to 1 mass-%
platinum-group metal
component, on an elemental basis, are preferred. Best results are obtained
when substantially all
of the platinum-group metal is present in the elemental state.
[0029] The second component, a platinum-group metal component, is deposited on
the
composite using the same means as for the first component described above.
Illustrative of the
decomposable compounds of the platinum group metals are chloroplatinic acid,
ammonium
chloroplatinate, bromoplatinic acid, dinitrodiamino platinum, sodium
tetranitroplatinate,
rhodium trichoride, hexa-anuminerhodium chloride, rhodium carbonylchloride,
sodium
hexanitrorhodate, chloropalladic acid, palladium chloride, palladium nitrate,
diamminepalladium hydroxide, tetraamminepalladium chloride, hexachloroiridate
(IV) acid,
hexachloroiridate (III) acid, ammoniurn hexachloroiridate (IIl), ammonium
aquohexachloroiridate (IV), ruthenium tetrachloride, hexachlororuthenate, hexa-
ammineruthenium chloride, osmium trichloride and ammonium osmium chloride. The
second
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component, a platinum-group component, is deposited on the support either
before, after, or
simultaneously with tungstate and/or the first component though not
necessarily with equivalent
results. It is preferred that the platinum-group component is deposited on the
support either after
or simultaneously with tungstate and/or the first component.
[0030] In addition to the first and second components above, the catalyst may
optionally
further include a third component of iron, cobalt, nickel, rhenium or mixtures
thereof. Iron is
preferred, and the iron may be present in amounts ranging from 0.1 to 5 mass-%
on arn elemental
basis. The third component, such as iron, may function to lower the amount of
the first
component, such as ytterbium, needed in the optimal formulation. The third
componernt may be
deposited on the composite using the same means as for the first and second
components as
described above. When the third component is iron, suitable compounds would
include iron
nitrate, iron halides, iron sulfate and any other soluble iron compound.
[0031] The catalytic composite described above can be used as a powder or can
be formed
into any desired shapes such as pills, cakes, extrudates, powders, granules,
spheres, etc., and they
may be utilized in any particular size. The composite is formed into the
particular shape by means
well known in the art. In making the various shapes, it may be desirable to
mix the cornposite
with a binder. However, it must be emphasized that the catalyst may be made
and successfully
used without a binder. The binder, when employed, usually comprises from 0.1
to 50 inass-%,
preferably from 5 to 20 mass-%, of the finished catalyst. Refractory inorganic
oxide are suitable
binders. Examples of binders without limitation are silica, aluminas, silica-
alumina, rnagnesia,
zirconium and mixtures thereof. A preferred binder material is alumina, with
eta- andlor
especially gamma-alumina being favored. Usually the composite and optional
binder are mixed
along with a peptizing agent such as HCI, HNO3, KOH, etc. to form a
homogeneous rnixture
which is formed into a desired shape by forming means well known in the art.
These forming
means include extrusion, spray drying, oil dropping, marumarizing, conical
screw mixing, etc.
Extrusion means include screw extruders and extrusion presses. The forming
means will
determine how much water, if any, is added to the mixture. Thus, if extrusion
is used, then the
mixture should be in the form of a dough, whereas if spray drying or oil
dropping is u_sed, then
enough water needs to be present in order to form a slurry. These particles
are calcined at a
temperature of 260 C to 650 C for a period of 0.5 to 2 hours.
[0032] The catalytic composites of the present invention either as synthesized
or after
calcination can be used as catalysts in hydrocarbon conversion processes.
Calcination is
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required, for example, to form zirconium oxide from zirconium hydroxide.
Hydrocarbon
conversion processes are well lmown in the art and include cracking,
hydrocracking, alkylation
of both aromatics and isoparaffins, isomerization, polymerization, refonniag,
dewaxing,
hydrogenation, dehydrogenation, transalkylation, dealkylation, hydration,
dehydration,
hydrotreating, hydrodenitrogenation, hydrodesulfurization, methanation, ring
opening, and
syngas shift processes. Specific reaction conditions and the types of feeds,
which can be used in
these processes, are set forth in US 4,310,440 and US 4,440,871. A preferred
hydrocarbon
conversion process is the isomerization of paraffins.
[0033] In a paraffin isomerization process, common naphtha feedstocks boiling
within the
gasoline range contain paraffins, naphthenes, and aromatics, and may comprise
sma11 amounts of
olefins. Feedstocks which may be utilized include straight-run naphthas,
natural gasoline,
synthetic naphthas, thermal gasoline, catalytically cracked gasoline,
partially reformed naphthas
or raffinates from extraction of aromatics. The feedstock essentially is
encompassed by the range
of a full-range naphtha, or within the boiling point range of 0 C to 230 C.
[0034] The principal components of the preferred feedstock are alkanes and
cycloaikanes
having from 4 to 10 carbon atoms per molecule, especially those having from 7
to 8 carbon atoms
per molecule. Smaller amounts of aromatic and olefinic hydrocarbons also may
be present.
Usually, the concentration of C7 and heavier components is more than 10 mass-%
of the
feedstock. Although there are no specific limits to the total content in the
feedstock of cyclic
hydrocarbons, the feedstock generally contains between 2 and 40 mass-% of
cyolics comprising
naphthenes and aromatics. The aromatics contained in the naphtha feedstock,
although generally
amounting to less than the alkanes and cycloalkanes, may comprise from 0 to 20
mass-% and
more usually from 0 to 10 mass-% of the total. Benzene usually comprises the
principal aromatics
constituent of the preferred feedstock, optionally along with smaller amounts
of toluene and
higher-boiling aromatics within the boiling ranges described above.
[0035] Contacting within the isomerization zones maybe effected using the
catalyst in a
fixed-bed system, a moving-bed system, a fluidized-bed system, or in a batch-
type operation. A
fixed-bed system is preferred. The reactants may be contacted with the bed of
catalyst particles in
either upward, downward, or radial-flow fashion. The reactants may be in the
liquid phase, a
mixed liquid-vapor phase, or a vapor phase when contacted with the catalyst
particles, with
excellent results being obtained by application of the present invention to a
primarily liquid-phase
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operation. The isomerization zone may be in a single reactor or in two or more
sepaxate reactors
with suitable means therebetween to ensure that the desired isomerization
temperature is
maintained at the entrance to each zone. Two or more reactors in sequence are
preferred to enable
improved isomerization through control of individual reactor temperatures and
for partial catalyst
replacement without a process shutdown.
[0036] Isomerization conditions in the isomerization zone include reactor
temperatures
usually ranging from 25 C to 300 C. Lower reaction temperatures are generally
preferred in order
to favor equilibrium mixtures having the highest concentration of high-octane
highly branched
isoalkanes and to minimize cracking of the feed to lighter hydrocarbons.
Temperatures in the
range of 100 C to 250 C are preferred in the process of the present invention.
Reactor operating
pressures generally range from 100 kPa to 10 MPa absolute, preferably between
0.3 and 4 MPa.
Liquid hourly space velocities range from 0.2 to 25 hr-i, with a range of 0.5
to 10 hr-1 being
preferred.
[0037] Hydrogen is admixed with or remains with the paraffinic feedstock to
the
isomerization zone to provide a mole ratio of hydrogen to hydrocarbon feed of
from 0.01 to 20,
preferably from 0.05 to 5. The hydrogen may be supplied totally from outside
the process or
supplemented by hydrogen recycled to the feed after separation from the
reactor effluent. Light
hydrocarbons and small amounts of inerts such as nitrogen and argon may be
present in the
hydrogen. Water should be removed from hydrogen supplied from outside the
process, preferably
by an adsorption system as is known in the art. In a preferred embodiment, the
hydrogen to
hydrocarbon mol ratio in the reactor effluent is equal to or less than 0.05,
generally obviating the
need to recycle hydrogen from the reactor effluent to the feed.
[0038] Upon contact with the catalyst, at least a portion of the paraffinic
feedstock is
converted to desired, higher octane, isoparaffin products. The catalyst of the
present invention
provides the advantages of high activity and improved stability.
[0039] The isomerization zone generally also contains a separation section,
optimally
comprising one or more fractional distillation columns having associated
appurtenances and
separating lighter components from an isoparaffin-rich product. Optionally, a
fractionator may
separate an isoparaffin concentrate from a cyclics concentrate with the latter
being recycled to a
ring-cleavage zone.
[0040] Preferably part or all of the isoparaffin-rich product and/or the
isoparaffin concentrate
are blended into finished gasoline along with other gasoline components from
refinery processing
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including, but not limited to, one or more of butanes, butenes, pentanes,
naphtha, catalytic
reformate, isomerate, alkylate, polymer, aromatic extract, heavy aromatics,
gasoline from
catalytic cracking, hydrocracking, thermal cracking, thermal reforming, steam
pyrolysis and
coking, oxygenates such as methanol, ethanol, propanol, isopropanol, tert-
butyl alcohol, sec-butyl
alcohol, methyl tertiary butyl ether, ethyl tertiary butyl ether, methyl
tertiary amyl ether and higher
alcohols and ethers, and small amounts of additives to promote gasoline
stability and uniformity,
avoid corrosion and weather problems, maintain a clean engine and improve
driveability.
[0041] The following examples serve to illustrate certain specific embodiments
of the present
invention. These examples should not, however, be construed as limiting the
scope of the
invention as set forth in the claims. There are many possible other
variations, as those of ordinary
skill in the art will recognize, which are within the scope of the invention.
EXAMPLE 1
[0042] Catalyst samples of Table 1 were prepared starting with zirconium
hydroxide that had
been prepared by precipitating zirconyl nitrate with ammonium hydroxide at 65
C. The
zirconium hydroxide was dried at 120 C, ground to 40-60 mesh. Multiple
discrete portions of
the zirconium hydroxide were prepared. Solutions of either ammonium
metatungstate or a
metal salt (component 1) were prepared and added to the, portions of
zirconiurn hydroxide. The
materials were agitated briefly and then dried with 80 C to 100 C air while
rotating. The
impregnated samples were then dried in a muffle oven at 150 C for 2 hours
urider air.
Solutions of a metal salt (component 2, where component 2 is not the same as
component 1)
were prepared and added to the dried materials. The samples were briefly
agitated and dried
while rotating. The sarnples were then calcined at 600 C to 850 C for 5 hours.
The final
impregnation solutions of chloroplatinic acid were prepared and added to the
solids. The
samples were agitated and dried while rotating as before. The samples were
fi.nally calcined at
525 C in air for 2 hours. In Table 1 below, it can be seen that the catalysts
were made at
modifier levels of 2.5 rnass-% and 5 mass-%; tungstate levels of 5 mass-%, 10
mass-%, and 15
mass-%; and calcination temperatures of 650 C, 700 C, 750 C, 800 C, and 850 C
(with the
exception of Gd, which was only prepared at 650 C, 700 C, and 750 C
calcination
temperatures).
[0043] For example, the first row of Table 1 indicates that a total of 30
different catalysts
were made, a catalyst having 2.5 mass-% Ce and 5 mass-% W04 and calcined at
650 C, a
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catalyst having 5 mass-% Ce and 5 mass-% W04 and calcined at 650 C, a catalyst
having 2.5
mass-% Ce and 10 mass-% W04 and calcined at 650 C, a catalyst having 5 mass-%
Ce and 10
mass-% W04 and calcined at 650 C, a catalyst having 2.5 mass-% Ce and 15 mass-
% W04 and
calcined at 650 C, a catalyst having 5 mass-% Ce and 15 mass-% W04 and
calcined at 650 C;
a catalyst having 2.5 rnass-% Ce and 5 mass-% W04 and calcined at 700 C, a
catalyst having 5
mass-% Ce and 5 mass-% W04 and calcined at 700 C, a catalyst having 2_ 5 mass-
% Ce and 10
mass-% W04 and calcined at 700 C, a catalyst having 5 mass-% Ce and 10 mass-%
W04 and
calcined at 700 C, a catalyst having 2.5 mass-% Ce and 15 mass-% W04 and
calcined at
700 C, a catalyst having 5 mass-% Ce and 15 mass-% W04 and calcined at 700 C;
a catalyst
having 2.5 mass-% Ce and 5 mass-% W04 and calcined at 750 C, a catalyst having
5 mass-%
Ce and 5 mass-% W04 and calcined at 750 C, a catalyst having 2.5 mass- Bo Ce
and 10 mass-%
W04 and calcined at 750 C, a catalyst having 5 mass-% Ce and 10 mass-% W04 and
calcined
at 750 C, a catalyst having 2.5 mass-% Ce and 15 mass-% W04 and calcined at
750 C, a
catalyst having 5 mass-% Ce and 15 mass-% W04 and calcined at 750 C, a
catalyst having 2.5
mass-% Ce and 5 mass-% W04 and calcined at 800 C, a catalyst having 5 mass-%
Ce and 5
mass-% W04 and calcined at 800 C, a catalyst having 2.5 mass-% Ce and 10 mass-
% W04 and
calcined at 800 C, a catalyst having 5 mass- 1o Ce and 10 mass-% W04 and
calcined at 800 C, a
catalyst having 2.5 mass-% Ce and 15 mass-% W04 and calcined at 800 C, a
catalyst having 5
mass-% Ce and 15 mass-% W04 and calcined at 800 C, a catalyst having 2.5 mass-
% Ce and 5
mass-% W04 and calcined at 850 C, a catalyst having 5 mass-% Ce and 5 mass-%
W04 and
calcined at 850 C, a catalyst having 2.5 mass-% Ce and 10 mass-% W04 and
calcined at
850 C, a catalyst having 5 mass-% Ce and 10 mass-% W04 and calcined at 850 C,
a catalyst
having 2.5 mass-% Ce and 15 mass-% W04 and calcined at 850 C, a catalyst
having 5 mass-%
Ce and 15 mass-% W04 and calcined at 850 C; with all catalysts listed above
also having 0.5
mass-% platinum. Therefore, Table 1 represents a total of 228 different
catalysts that were
made.
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TABLE 1
Modifier Level Pt W04 Levels Calcination
Modifier
mass-% mass-% Mass-% Temp, C
Ce 2.5 5 0.5 5 10 15 650 700 750 800 850
Eu 2.5 5 0.5 5 10 15 650 700 750 800 850
Gd 2.5 5 0.5 5 10 15 650 700 750 ------ ------
Ho 2.5 5 0.5 5 10 15 650 700 750 800 850
Nd 2.5 5 0.5 5 10 15 650 700 750 800 850
Re 2.5 5 0.5 5 10 15 650 700 750 800 850
Y 2.5 5 0.5 5 10 15 650 700 750 800 850
Yb 2.5 5 0.5 5 10 15 650 700 750 800 850
EXAMPLE 2
[0044] The catalysts of Example 1 were prepared as described above in Example
1. Also,
reference catalysts were prepared as described in Example 1 but with the
addition of the
modifier step being omitted from the preparation. Approximately 95 mg of each
sample was
loaded into a multi-unit reactor assay. The catalysts were pretreated in air
at 450 C for 6 hours
and reduced at 200 C in H2 for 1 hour. n-Heptane, 8 mol-%, in hydrogen was
then passed over
the samples at 120 C, 150 C, and 180 C, approximately 1 atm, and 0.3, 0.6, and
1.2 hr-1
WHSV (based on heptane only). The products were analyzed using online gas
chromatographs.
[0045] To exemplify the data, selected results are shown in FIGs. 1- 4 for
experiments at
180 C, 1.2 hr-1 WIiSV, and using catalysts comprising 15 mass-% W, 0.5 mass-%
Pt. The
identity of the modifier (or first component), the amount of modifier, and the
calcination
temperature are identified along the x-axis of the plots of FIGs. 1- 4. Data
where the identity of
the modifier is listed as "none", corresponds to a reference catalyst
containing no modifier.
FIG. 1 is a plot of t][ae conversion of heptane achieved by each of the
catalysts. All of the
catalysts indicate activity, with ytterbium, yttrium, and holmium showing the
greatest
conversion. It is surprising, however, that many of the catalysts demonstrate
the greatest
conversion when calcined at 800 C. The more expected trend would be a
decreasing
conversion trend with increasing calcination temperatures. A number of the
catalysts of the
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present invention however, exhibit greater conversion with a calcination at
800 C than at either
750 C or 850 C. Therefore, a preferred calcination temperature is at 800 C.
[0046] FIG. 2 shows the selectivity of the catalysts for C7 isomerization.
This plot
demonstrates that even though some cracking is occurring, selectivities to C7
isomerization
remain high. FIG. 3 shows the selectivity of the catalysts for C7
isomerization to produce two of
the desired dimethyl-branched isomers, 2,2-dimethylpentane arnd 2,4-
dimethylpentane. Again, the
data demonstrates that ytterbium and yttrium show superior results and are
therefore, preferred
modifiers. Fig. 4 shows the yield of the catalysts for C7 isomerization to
produce two desired
dimethyl-branched isomers, 2,2-dimethylpentane and 2,4-dimethylpentane.
[0047] The data discussed above indicates a particular preference for
ytterbium as a modifier.
Therefore, FIGs. 5-8 present fu.rther selected results of the experiment where
ytterbium was the
modifier. On each of FIGs. 5-8, the amount of tungsten on the catalyst, the
amount of modifier on
the catalyst, the calcination temperature of the catalyst, and the weight
hourly space velocity of
the run is found on the x-axis. In FIG. 5, the y-axis is the conversion of the
n-heptane feed. The
plot demonstrates that conversion increases as the amount of tungsten
increases, but conversion
decreases as the weight hourly space velocity increases. However, with other
variables remaining
constant, increasing the amount of modifier from 2.5 mass-% to 5 mass-% does
not have a
dramatic effect on the conversion. FIG. 6 demonstrates that the selectivity
for C7 isomerization
increases with increasing space velocity. However, FIG. 7 shows that the
opposite is true when
considering the selectivity to two of the desired dimethyl-branched isomers,
2,2-dimethylpentane
and 2,4-dimethylpentane. FIG. 8 shows the yield of two of the desired dimethyl-
branched
isomers, 2,2-dimethylpentane and 2,4-dimethylpentane. In gerneral, the results
in FIG. 8 indicate
that the yield to the specific dimethylpentane isomers (1) decreases as the
space velocity is
increased; (2) is highest with a calcination temperature of 800 C; and (3) is
greater at the lower
levels of modifiers.
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