Note: Descriptions are shown in the official language in which they were submitted.
CA 02340821 2001-03-14
"PARAFFIN-ISOMERIZATION CATALYST AND
PROCESS
Background of the Invention
s The isomerization of light naphtha is an increasingly important process for
the
upgrading of petroleum refiners' gasoline pool. There is a long history of
catalyst and
process technology for the isomerization of light alkanes. The recent
expansion of
interest, however, has led to significant improvements in this technology.
Catalyst and
process developments have led to lower operating temperatures, wherein product
io octane is favored by isomer equilibrium. Substantial reduction in the
hydrogen
requirement for a stable operation has resulted in a significant cost
reduction, principally
through elimination of the need for a hydrogen-recycle system. Both of the
aforementioned developments have led toward a predominance of liquid in the
isomerization reactor feed, in contrast to the vapor-phase operation of the
prior art.
is Catalysts exhibiting dual hydrogenation-dehydrogenation and cracking
functions are applied widely in the petroleum refining and petrochemical
industries to
the reforming and isomerization of hydrocarbons. Such catalysts generally have
the
cracking function imparted by an inorganic oxide, zeolite, or halogen, with a
platinum-
group component usually imparting the hydrogenation-dehydrogenation function.
A
2o catalyst useful in isomerization should be formulated to balance its
hydrogenation-
dehydrogenation and cracking functions to achieve the desired conversion over
a
prolonged period of time, while effectively utilizing the expensive platinum
group metal
component.
The performance of a catalyst in isomerization service typically is measured
2s by its activity, selectivity, and stability. Activity refers to the ability
of a catalyst to
isomerize the reactants into the desired product isomers at a specified set of
reaction
conditions. Selectivity refers to the proportion of converted feed reacted
into the desired
product. Stability refers to the rate of change of activity and selectivity
during the life of
the catalyst. The principal cause of low catalyst stability is the formation
of coke, a high
3o molecular-weight, hydrogen-deficient, carbonaceous material on the
catalytic surface.
Workers in the isomerization art thus must address the problem of developing
catalysts
having high activity and stability, and which also either suppress the
formation of coke
or are not severely affected by the presence of coke.
CA 02340821 2001-03-14
Catalysts for paraffin isomerization containing a platinum-group metal
component and a halide on an alumina support are known in the art. For
example, US-
A-3,963,643 teaches a method of manufacturing a catalyst useful in the
isomerization of
paraffins by compositing a platinum-group metal with gamma or eta alumina and
s reacting the composite with a Friedel-Crafts metal halide and a polyhalo
compound.
US-A-5,607,891 teaches a catalyst consisting of chlorine, Group VIII metal,
and a
support consisting essentially of 85-95% eta alumina and the remainder gamma
alumina and its use for benzene reduction and isomerization. However, the art
does not
suggest a catalyst having the particular characteristics of the present
catalyst or the
io surprising benefits of using this catalyst in the context of modern,
primarily liquid-phase,
isomerization operations.
SUMMARY OF THE INVENTION
This invention is based on the discovery that a catalyst comprising a Friedel-
is Crafts metal halide and a platinum-group metal on a primarily eta-alumina
support
having defined critical characteristics demonstrates surprising results in
increasing the
octane number of C5/Cg naphtha streams.
It is an object of the present invention to provide a novel catalyst useful
particularly for the isomerization of isomerizable hydrocarbons. A corollary
object of the
2o invention is to provide a process for isomerizing isomerizable
hydrocarbons, particularly
alkanes having from four to seven carbon atoms per molecule.
A broad embodiment of the present invention is an isomerization catalyst
comprising a Friedel-Crafts metal halide and a platinum-group metal component
on a
principally eta-alumina support which has critical diffusion-path, pore-size
and acidity
2s characteristics. Platinum is the preferred platinum-group component and
aluminum
chloride is the preferred Friedel-Crafts metal halide. The catalyst support
preferably
comprises eta and gamma alumina in an eta:gamma ratio on a mass basis of from
4:1
to 99:1, with the ratio more preferably being at least 9:1 and optionally at
least 24:1;
optimally, the support consists essentially of eta and gamma alumina. A
triclover
3o extrudate is a preferred shape of the catalyst of the invention.
A preferred catalyst has an average pore diameter of between 35 and 60
angstroms and a extruded trilobal cross-section.
In another aspect, the invention is a preferred method of preparing the
present
catalyst by a procedure comprising peptizing an alumina source, forming
extrudates
2
CA 02340821 2001-03-14
from the resulting base material, calcining the extrudates at defined critical
conditions,
impregnating a platinum-group metal component on the calcined extrudates,
oxidizing
and reducing the impregnated extrudates and subliming the Friedel-Crafts metal
component onto the catalyst.
s In yet another aspect, the invention comprises a process for the use of the
present catalyst to isomerize isomerizable hydrocarbons. The preferred
feedstock
comprises C4 to C7 alkanes which are upgraded with respect to their degree of
branching and octane number.
BRIEF DESCRIPTION OF THE DRAWINGS
io Figure 1 shows comparative isomerization activity for catalysts of the
invention
and control catalysts in relation to a pore-acidity index.
Figure 2 shows the cross section of an extruded triclover catalyst.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The alumina support utilized in the isomerization catalyst of the present
invention
is consists essentially of the crystalline aluminas known as the eta- and
gamma-aluminas
in a respective ratio of between 4:1 and 99:1. The alumina can be formed into
any
desired shape or type of carrier material known to those skilled in the art
such as rods,
pills, pellets, tablets, granules, extrudates, and like forms by methods well
known to the
practitioners of the catalyst material forming art. Spherical carrier
particles may be
2o formed, for example, from this alumina by: (1 ) converting the alumina
powder into an
alumina sol by reaction with a suitable peptizing acid and water and
thereafter dropping
a mixture of the resulting sol and a gelling agent into an oil bath to form
spherical
particles of an alumina gel which are easily converted to a gamma-alumina
carrier
material by known methods; (2) forming an extrudate from the powder by
established
2s methods and thereafter rolling the extrudate particles on a spinning disk
until spherical
particles are formed which can then be dried and calcined to form the desired
particles
of spherical carrier material; and (3) wetting the powder with a suitable
peptizing agent
and thereafter rolling the particles of the powder into spherical masses of
the desired
size.
3
CA 02340821 2001-03-14
A favored form of alumina support is a cylindrical extrudate generally having
a
diameter of up to 3.3 mm, with 0.8 mm being preferred. The length-to-diameter
ratio
generally is from 1:1 to 5:1, with 2:1 usually being optimal. Alternative
extrudate forms
within the scope of the invention include those with a polylobal or ring cross-
section as
s disclosed in US-A-4,028,227, incorporated herein by reference; a trilobal or
triclover
cross-section, extruded through a die having a trilobal or triclover shape, is
preferred.
Other catalyst forms are described in Fulton, ""Selecting the catalyst
configuration,"
Chemical Engineering, May 12, 1986, pp. 97-101, also incorporated by
reference.
Further extrudate forms within the knowledge of the skilled routineer also may
be
io suitable. Optimally the diffusion path, defined as the maximum distance
from the
external surface to the interior of an extrudate particle, is no more than
0.3, and
preferably no more than 0.25, times the overall diameter of the particle; the
overall
diameter is defined as the diameter of a circle circumscribed around the cross
section of
the particle. The diffusion path of the trilobal cross section is 0.23 times
the overall
is diameter of the particle.
An eta-rich alumina support is produced from a suitable alumina base material
by
the dehydroxylation of one or more preferably of bayerite, nordstrandite and
gibbsite.
The ratio of eta:gamma alumina in the finished catalyst preferably is from 4:1
to 99:1,
and more preferably at least 9:1; optionally the ratio is between 24:1 and
99:1 LaRoche
2o Versal B is one example of a suitable alumina source. The extrudate
particle form of
the carrier material may be prepared by mixing alumina powder with water and
suitable
peptizing agents such as nitric acid, acetic acid, aluminum nitrate, and the
like material
until an extrudable dough is formed. The amount of water added to form the
dough is
typically sufficient to give a Loss on Ignition (L01) at 500°C of 30 to
65 mass %, with a
2s value of 35 to 45 mass % being especially preferred. The acid addition is
generally
sufficient to provide 2 to 7 mass % of the volatile-free alumina powder used
in the mix,
with a value of 3 to 4 mass % being especially preferred. Preferably from 0.1
to 10
mass-% of an extrusion aid such as Methocel, and more preferably from 1 to 5
mass-%,
is included in the mix. The resulting dough optimally is then mulled and
extruded
3o through a suitably sized die to form extrudate particles as described
hereinabove.
The extrudate particles are dried at a temperature of 150° to
200°C, and then
calcined at a temperature of 500° to 650°C for a period of 0.2
to 10 hours to effect the
preferred form of the refractory inorganic oxide as a catalyst base. In order
to obtain the
distinctive properties of the present catalyst, the calcination preferably is
effected within
3s a critical temperature range of from of 545° to 610°C, and
more preferably from 560° to
4
CA 02340821 2001-03-14
580°C. Calcination conditions are established to provide a finished-
catalyst surface
area of 160 to 250 m2/g (preferably no more than 230 m2/g) with an average
pore
diameter of from 35 to 60 angstroms.
An essential ingredient of the catalyst is the platinum-group metal component.
Of
s the platinum group, i.e., platinum, palladium, rhodium, ruthenium, osmium
and iridium,
palladium is a preferred component and platinum is especially preferred.
Mixtures of
platinum-group metals also are within the scope of this invention. This
component may
exist within the final catalytic composite as a compound such as an oxide,
sulfide,
halide, or oxyhalide, in chemical combination with one or more of the other
ingredients
io of the composite, or as an elemental metal. Best results are obtained when
substantially all of this component is present in the elemental state. This
component
may be present in the final catalyst composite in any amount which is
catalytically
effective, but relatively small amounts are preferred. In fact, the surface-
layer platinum-
group metal component generally will comprise 0.01 to 2 mass % of the final
catalyst,
is calculated on an elemental basis. Excellent results are obtained when the
catalyst
contains 0.05 to 1 mass % of platinum.
Typical platinum-group compounds which may be employed in preparing the
catalyst of the invention are chloroplatinic acid, ammonium chloroplatinate,
bromoplatinic acid, platinum dichloride, platinum tetrachloride hydrate,
platinum
2o dichlorocarbonyl dichloride, dinitrodiaminoplatinum, palladium chloride,
palladium
chloride dehydrate, palladium nitrate, etc. Chloroplatinic acid is preferred
as a source of
the especially preferred platinum component. A surface-layer platinum
component may
be impregnated onto the catalyst from a solution of chloroplatinic acid in the
absence of
strong mineral acids such as hydrochloric and nitric acid.
2s An optional embodiment of the catalyst of the present invention is that the
platinum-group metal component is concentrated in the surface layer of each
catalyst
particle. In defining the present invention, a "surface-layer" component has a
concentration in the micron surface layer of the catalyst particle that is at
least 1.5 times
the concentration in the central core of the catalyst particle. Preferably,
the surface-layer
. 3o concentration of platinum-group metal is at least about twice the
concentration in the
central core. As exemplified hereinbelow, the surface layer may be 100 or 150
microns
deep and the central core may be 50% of the volume or 50% of the diameter of
the
particle; however, other quantitative criteria are not excluded thereby.
Further details of
the characteristics and preparation of a surface-layer platinum-group metal
component
3s are contained in US-A-5,004,859, incorporated herein by reference.
s
CA 02340821 2001-03-14
It is within the scope of the present invention that the catalyst may contain
other
metal components known to modify the effect of the platinum-group metal
component.
Such metal modifiers may include rhenium, tin, germanium, lead, cobalt,
nickel, indium,
gallium, zinc, uranium, dysprosium, thallium, and mixtures thereof.
Catalytically
s effective amounts of such metal modifiers may be incorporated into the
catalyst by any
means known in the art. Preferably, however, the catalyst consists essentially
of the
alumina support, platinum-group metal component, and Friedel-Crafts metal
halide.
The composite, before addition to the Friedel-Crafts metal halide, is dried
and
calcined. The drying is carried out at a temperature of 100° to
300°, followed by
io calcination or oxidation at a temperature of from 375° to
600°C in an air or oxygen
atmosphere for a period of 0.5 to 10 hours in order to convert the metallic
components
substantially to the oxide form.
Another essential component of the catalyst of the present invention is a
Friedel
Crafts metal halide. Suitable metal halides of the Friedel-Crafts type include
aluminum
is chloride, aluminum bromide, ferric chloride, ferric bromide, zinc chloride
and the like
compounds, with the aluminum halides and particularly aluminum chloride
ordinarily
yielding best results. Generally, this component can be incorporated into the
catalyst of
the present invention by way of the conventional methods for adding metallic
halides of
this type; however, best results are ordinarily obtained when the metallic
halide is
2o sublimed onto the surface of the support according to the preferred method
disclosed in
U.S. Pat. No. 2,999,074, which is incorporated by reference.
In the preferred method, wherein the calcined refractory inorganic-oxide
support
is impregnated with a Friedel-Crafts metal halide component, the presence of
chemically combined hydroxyl groups in the refractory inorganic oxide allows a
reaction
2s to occur between the Friedel-Crafts metal halide and the hydroxyl group of
the support.
For example, aluminum chloride reacts with the hydroxyl groups in the
preferred
alumina support to yield AI--O--AIC12 active centers which enhance the
catalytic
behavior of the catalyst. Since chloride ions and hydroxyl ions occupy similar
sites on
the support, more hydroxyl sites will be available for possible interaction
with the
3o Friedel-Crafts metal halide when the chloride population of the sites is
low. Therefore,
potentially more active Friedel-Crafts type versions of the catalyst will be
obtained when
the chloride content of the support is in the low range of the 0.1 to 10 mass%
range.
The Friedel-Crafts metal halide may be impregnated onto the catalyst by
sublimation of the Friedel-Crafts metal halide onto the calcined support under
conditions
3s to combine the sublimed Friedel-Crafts metal halide with the hydroxyl
groups of the
6
CA 02340821 2001-03-14
calcined support. This reaction is typically accompanied by the elimination of
0.5 to 2.0
moles of hydrogen chloride per mole of Friedel-Crafts metal halide reacted
with the
inorganic-oxide support. In subliming aluminum chloride, which sublimes at
184°C,
suitable impregnation temperatures range from 190°C to 700°C,
with a preferable range
s being from 200°C to 600°C. The sublimation can be conducted at
atmospheric
pressure or under increased pressure and in the presence of absence of diluent
gases
such a hydrogen or light paraffinic hydrocarbons or both. The impregnation of
the
Friedel-Crafts metal halide may be conducted batch-wise, but a preferred
method for
impregnating the calcined support is to pass sublimed AICIg vapors, in
admixture with a
io carrier gas such as hydrogen, through a calcined catalyst bed. This method
both
continuously deposits and reacts the aluminum chloride and also removes the
evolved
HCI.
The amount of Friedel-Crafts metal halide combined with the calcined composite
may range from 1 up to 15 mass % to the Friedel-Crafts metal-halide-free,
calcined
is composite. The final composite containing the sublimed Friedel-Crafts metal
halide is
treated to remove the unreacted Friedel-Crafts metal halide by subjecting the
composite
to a temperature above the sublimation temperature of the Friedel-Crafts metal
halide
for a time sufficient to remove from the composite any unreacted Friedel-
Crafts metal
halide. In the case of AIC13, temperatures of 400°C to 600°C and
times of from 1 to 48
2o hours are sufficient.
In a preferred embodiment of the present invention, the resultant oxidized
catalytic composite is subjected to a substantially water-free and hydrocarbon-
free
reduction step prior to its use in the conversion of hydrocarbons. This step
is designed
to selectively reduce the platinum-group metal component to the corresponding
Zs elemental metal and to insure a finely divided dispersion of the metal
component
throughout the carrier material. Preferably substantially pure and dry
hydrogen (i.e.,
less than 20 vol. ppm H20) is used as the reducing agent in this step. The
reducing
agent is contacted with the oxidized composite at conditions including a
temperature of
425°C to 650°C and a period of time of 0.5 to 2 hours to reduce
substantially all of the
3o platinum-group component to its elemental metallic state. This reduction
treatment may
be performed in situ as part of a start-up sequence if precautions are taken
to predry the
plant to a substantially water-free state and if substantially water-free and
hydrocarbon-
free hydrogen is used.
The catalyst of the present invention may contain an additional halogen
3s component. The halogen component may be either fluorine, chlorine, bromine
or iodine
CA 02340821 2001-03-14
or mixtures thereof or an organic polyhalo component. Chlorine is the
preferred
halogen component. The halogen component is generally present in a combined
state
with the inorganic-oxide support. Although not essential to the invention, the
halogen
component is preferably well dispersed throughout the catalyst. The halogen
s component may comprise from more than 0.2 to 15 mass-%, calculated on an
elemental
basis, of the final catalyst. Further details of halogen components and their
incorporation into the catalyst are disclosed in US-A-5,004,859 referenced
above.
The finished catalyst has a surface area of 160 to 250 m2/g (preferably no
more
than 230 m2/g) with an average pore diameter of from 35 to 60 angstroms. A
catalyst
io of the invention also is characterized by a pore-acidity index, calculated
as 100 x (P° X
A°~a~ty~SA SA ) wherein PD =average pore diameter in angstroms; Acidity
= mmols TMP/g
C~ 120°C and SA= surface area in m2/g. Catalysts of the invention have
a pore-acidity
index of at least 7Ø It is believed, without so limiting the invention, that
mass-transfer
and reaction-kinetics rates are thereby balanced to effect superior
isomerization
is selectivity with high activity.
Surface area is measured using nitrogen by the well known BET (Brunauer-
Emmett-Teller) method, which also indicates average pore diameter. Acidity is
measured by loading the samples as powder in a glass tube and pretreating
under high
vacuum (ca. 10-6 torr) at 600°C for 2 hours. The samples are cooled to
120°C, exposed
2o to trimethylphosphine (TMP) for 15 minutes followed by a 45-minute
equilibration time,
and then degassed with high vacuum. The amount of adsorbed TMP is calculated
from
the vapor-pressure change after condensation on the samples from the known
volume
of vacuum line.
2s In the process of the present invention, an isomerizable hydrocarbon
feedstock,
preferably in admixture with hydrogen, contacts a catalyst of the type
hereinbefore
described in a hydrocarbon-isomerization zone to obtain an isoparaffin-rich
product.
Contacting may be effected using the catalyst in a fixed-bed system, a moving-
bed
system, a fluidized-bed system, or in a batch-type operation. In view of the
danger of
3o attrition loss of the valuable catalyst and of operational advantages, it
is preferred to use
a fixed-bed system. In this system, a hydrogen-rich gas and the charge stock
are
preheated by suitable heating means to the desired reaction temperature and
then
passed into an isomerization zone containing a fixed bed of the catalyst as
previously
characterized. The isomerization zone may be in a single reactor or in two or
more
3s separate reactors with suitable means therebetween to insure that the
desired
s
CA 02340821 2001-03-14
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. The reactants may be contacted with the catalyst in either upward,
s 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, with
excellent
results being obtained by application of the present invention to a primarily
liquid-phase
operation.
In the group of isomerizable hydrocarbons suitable as feedstock to the process
of
io the present invention, alkanes having from 4 to 7 carbon atoms per molecule
(C4-C7)
are preferred. These may be contained in such streams from petroleum refining
or
synthetic-fuel production as light straight-run naphtha, light natural
gasoline, light
reformate, light raffinate from aromatics extraction, light cracked naphtha,
normal-
butane concentrate, field butanes and the like. An especially preferred
feedstock is light
is straight-run naphtha, containing more than 50% of C5 and Cg paraffins with
a high
concentration of low-octane normal paraffins; this feedstock is particularly
susceptible to
octane-number upgrading by isomerization. The light straight-run naphtha and
other
feedstocks also may contain naphthenes, aromatics, olefins, and hydrocarbons
heavier
than Cg. The olefin content should be limited to a maximum of 10% and the
content of
2o hydrocarbons heavier than Cg to 20% for effective control of hydrogen
consumption,
cracking reactions, heat of reaction and catalyst activity.
It is generally known that high-chloride platinum-alumina catalysts of this
type are
highly sensitive to sulfur- and oxygen-containing compounds. The feedstock
therefore
must be relatively free of such compounds, with a sulfur concentration
generally no
2s greater than 0.5 ppm. The presence of sulfur in the feedstock serves to
temporarily
deactivate the catalyst by platinum poisoning. Activity of the catalyst may be
restored
by hot hydrogen stripping of sulfur from the catalyst composite or by lowering
the sulfur
concentration in the incoming feed to below 0.5 ppm so that the hydrocarbon
will desorb
the sulfur that has been adsorbed on the catalyst. Water can act to
permanently
3o deactivate the catalyst by removing high-activity chloride from the
catalyst and replacing
it with inactive aluminum hydroxide. Therefore, water and oxygenates that can
decompose to form water can only be tolerated in very low concentrations. In
general,
this requires a limitation of oxygenates in the feed to 0.1 ppm or less. The
feedstock
may be treated by any method that will remove water and sulfur compounds.
Sulfur
3s may be removed from the feed stream by hydrotreating. Adsorption systems
for the
9
CA 02340821 2001-03-14
removal of sulfur and water from hydrocarbon streams are well known to those
skilled in
the art.
Hydrogen is admixed with the isomerizable hydrocarbon feed to provide a mole
ratio of hydrogen to hydrocarbon feed of 0.01 to 5. The hydrogen may be
supplied
s totally from outside the process or supplemented by hydrogen recycled to the
feed after
separation from 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.
io Although there is no net consumption of hydrogen in the isomerization
reaction,
hydrogen generally will be consumed in a number of side reactions such as
cracking,
disproportionation, and aromatics and olefin saturation. Such hydrogen
consumption
typically will be in a mol ratio to the hydrocarbon feed of 0.03 to 0.1.
Hydrogen in
excess of consumption requirements is maintained in the reaction zone to
enhance
is catalyst stability and maintain conversion by compensation for variations
in feed
composition, as well as to suppress the formation of carbonaceous compounds,
usually
referred to as coke, which foul the catalyst.
In a preferred embodiment, the hydrogen to hydrocarbon mol ratio in the
reactor
effluent is equal to or less than 0.05. Generally, a mol ratio of 0.05 or less
obviates the
2o need to recycle hydrogen from the reactor effluent to the feed. It has been
found that
the amount of hydrogen needed for suppressing coke formation need not exceed
dissolved hydrogen levels. The amount of hydrogen in solution at the normal
conditions
of the reactor effluent will usually be in a ratio of from 0.02 to less 0.01.
The amount of
excess hydrogen over consumption requirements that is required for good
stability and
2s conversion is in a ratio of hydrogen to hydrocarbons of from 0.01 to less
than 0.05 as
measured at the effluent of the isomerization zone. Adding the dissolved and
excess
hydrogen proportions show that the 0.05 hydrogen to hydrocarbon ratio at the
effluent
will satisfy these requirements for most feeds. The catalyst of the present
invention
show excellent results in a primarily liquid-phase process operation with
reactor-effluent
3o hydrogen-to-hydrocarbon mol ratios of 0.05 or less.
Isomerization conditions usually comprise temperatures ranging from
40° to
250°C. Lower reaction temperatures are generally preferred since the
equilibrium
directionally favors higher concentrations of isoalkanes relative to normal
alkanes.
Lower temperatures are particularly useful in processing feeds composed of C5
and Cg
3s alkanes, as lower temperatures favor equilibrium mixtures having the
highest
io
CA 02340821 2001-03-14
concentration of high-octane highly branched isopentane and isohexanes. When
the
feed mixture is primarily C5 and Cg alkanes, temperatures in the range of from
40° to
160°C are preferred. When it is desired to isomerize significant
amounts of butanes,
higher reaction temperatures in the range from 145° to 225°C are
required to maintain
s catalyst activity.
Operating pressures generally range from 100 kPa to 10 MPa absolute, with
preferred pressures in the range of from 2 to 3.5 MPa. Liquid hourly space
velocities
range from 0.25 to 12 liquid volumes of isomerizable hydrocarbon feed per hour
per
volume of catalyst, with a range of 0.5 to 5 hr-1 being preferred.
io The isomerization process generally also requires the presence of a small
amount of an organic chloride promoter. The organic chloride promoter serves
to
maintain a high level of active chloride on the catalyst, as low levels are
continuously
stripped off the catalyst by the hydrocarbon feed. The concentration of
promoter in the
combined feed preferably is maintained at from 30 to 300 mass ppm. The
preferred
is promoter compound is carbon tetrachloride. Other suitable promoter
compounds
include oxygen-free decomposable organic chlorides such as propyldichloride,
butylchloride, and chloroform, to name only a few of such compounds. The need
to
keep the reactants dry is reinforced by the presence of the organic chloride
compound
which may convert, in part, to hydrogen chloride. As long as the hydrocarbon
feed and
2o hydrogen are dried as described hereinabove, there will be no adverse
effect from the
presence of small amounts of hydrogen chloride.
The isomerization product from the especially preferred light-naphtha
feedstock
will contain some low-octane normal paraffins and intermediate-octane
methylhexanes
as well as the desired highest-octane isopentane and dimethylbutane. It is
within the
Zs scope of the present invention that the liquid product from the process is
subjected to
separate and recycle the lower-octane portion of this product to the
isomerization
reaction and to recover an isoparaffin concentrate as a net product.
Generally, low-
octane normal paraffins may be separated and recycled to upgrade the octane
number
of the net product. Less-branched Cg and C7 paraffins also may be separated
and
3o recycled, along with lesser amounts of hydrocarbons which are difficult to
separate from
the recycle. Techniques to achieve this separation are well known in the art,
and
include fractionation and molecular-sieve adsorption.
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
3s refinery processing including but not limited to one or more of butanes,
butenes,
n
CA 02340821 2001-03-14
pentanes, naphtha, catalytic reformats, 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, TBA, SBA, MTBE, ETBE, MTAE and higher alcohols and
ethers;
s and small amounts of additives to promote gasoline stability and uniformity,
avoid
corrosion and weather problems, maintain a clean engine and improve
driveability.
EXAMPLES
to
Example I
Two control catalysts of the known art were prepared in order to demonstrate
the
advantages of the present catalyst.
An extruded gamma alumina base of the known art, having a particle diameter of
is 800 microns, was divided into two portions. Both were vacuum-impregnated in
a
solution of 3.5 mass % chloroplatinic acid, 2 mass % hydrochloric acid, and
3.5% mass
nitric acid in a volume ratio of 9 parts solution to 10 parts base to obtain
peptized
base material having a platinum to base ratio of approximately 0.9. The
resulting
mixture was cold-rolled for approximately 1 hour and evaporated until dry. The
2o composites then were oxidized and the chloride content adjusted by contact
with an IM
hydrochloric acid solution at 525°C at a rate of 45 cc/hour for 2
hours. The composites
then were reduced in electrolytic hydrogen at 565°C for approximately 2
hours and
found to contain approximately 0.25 mass-% Pt and approximately 1 mass-%
chloride.
Impregnation of active chloride to a level of approximately 7 mass-% was
accomplished
2s by sublimating aluminum chloride with hydrogen and contacting the catalysts
with the
sublimated aluminum chloride for approximately 45 minutes at 550°C.
These catalysts were designated "Catalyst X" and "Catalyst Y" and had the
following characteristics (% = mass-%; SA = surface area; PD = pore diameter
in
angstroms; Acidity = mmols TMP/g C~ 120oC):
12
CA 02340821 2001-03-14
Ca_ talystPt. % CI. S_ A. m2/aPD. Acidity
% ~
X 0.249 6.29 191.6 83 0.367
Y 0.255 7.45 193.6 96 0.345
s Example II
To illustrate the invention, catalysts were prepared from a bayerite alumina
source; the following description applies to Catalyst "A." LaRoche Versal B
alumina in
an amount of 2000 grams was placed in a muller. The muller was started and
103.2
grams of 70.7% nitric acid and 268 grams of deionized water were added over a
5-
io minute period, followed by mixing for 20 minutes. Methocel in an amount of
33.15
grams was added, and mulling was continued for 10 minutes. The mulled mixture
then
was extruded with a Bonnot extruder using a die plate with '/32" circular
holes to produce
cylindrical extrudates. The extrudates were dried for 2 hours at 100°C,
heated to 260°C
in 10% moisture, and finally calcined at 575°C in 5 mole% moisture for
30 minutes.
is The extrudates were washed with a 1 mass-% ammonium nitrate to achieve a
sodium level of less than 100 parts per million (ppm Na), dried for 2 hours at
100°C,
heated to 205°C, and calcined at 325°C. The washed extrudates
then were
impregnated in a solution of 3.5 mass % chloroplatinic acid, 2 mass %
hydrochloric acid,
and 3.5% mass % nitric acid in a volume ratio of 9 parts solution to 10 parts
base to
20 obtain peptized base material having a platinum to base ratio of
approximately 0.9. The
resulting mixture was cold-rolled for approximately 1 hour and evaporated
until dry.
The composites then were oxidized at 475°C for 2 hours and reduced in
electrolytic
hydrogen at 500°C for approximately 2 hours, and found to contain
approximately 0.25
mass-% Pt and approximately 1 mass-% chloride. The chloride content was
adjusted
2s by contact with anhydrous HCI. Impregnation of active chloride to a level
of
approximately 6-8 mass-% was accomplished by sublimating aluminum chloride
with
hydrogen and contacting the catalysts with the sublimated aluminum chloride
for
approximately 25 minutes at 470°C followed by treatment with anhydrous
HCI at 260°C.
The catalysts prepared in this manner were designated as Catalysts A through
H,
3o differing in methylcellulose addition (A: 2.5 mass-%; B,E-G: 5 mass-%;
C,D,H: 0) and
base calcination temperature as indicated below. The catalysts had the
following
characteristics (CaIc.T = base calcination temperature, °C; % = mass-%;
SA = surface
area; PD = pore diameter in angstroms; Acidity = mmols TMP/g C~ 120°C):
13
CA 02340821 2001-03-14
Catalyst CaIc.T Pt. CI, SA. mz/a PD. Ac_
% % ~ iditv
A 575 0.275 6.7 200.8 47 0.49
B 600 0.265 6.54 183 53 0.384
C 600 0.27 6.92 198 45 0.333
s D 650 0.273 5.67 165 56 0.384
E 550 0.269 7.43 219.2 44 0.351
F 650 0.263 5.93 160.2 63 0.304
G 500 0.274 8.41 254.2 36 0.404
H 500 0.274 8.31 255 32 0.412
to Example III
A pore-acidity index was calculated for each of the catalysts A - H. As
defined
hereinabove, this index is characterized as 100 x (P° X Acidity~SA) or:
100 x (pore diameter, angstroms)x(acidity, mmols TMP/g C~3
120°C)/(surface area, mz/g)
The results are as follows:
is Catalyst Index
A 11.5
B 11.1
C 7.6
D 13.0
2o E 7.05
F 12.0
G 5.7
H 5.2
Catalysts A-D met the criteria of the invention, as did Catalyst E on a
marginal basis.
2s Catalyst F failed on the basis of surface area. The relative isomerization
activity of the
above catalysts is disclosed in Figure 1 as discussed hereinafter.
Example IV
Additional catalysts with a composition as disclosed in Example II, but with a
3o different extrudate cross section, were prepared to illustrate the
invention. The
preparation steps followed those described in Example II except that the
mulled mixture
was extruded with a triclover-form die as illustrated in Figure 2 and the
washing step
14
CA 02340821 2001-03-14
was not needed to obtain a content of less than 100 ppm Na.
The catalysts prepared in this manner were designated as Catalysts J through
M,
differing in base calcination temperature as indicated below. The catalysts
had the
following characteristics (CaIc.T = base calcination temperature, °C; %
= mass-%; SA =
s surface area; PD = pore diameter in angstroms; Acidity = mmols TMP/g C«3
120°C):
Catalyst CaIc.T Pt. CI. SA. m2/p PD. Acidi
% % ~
J 580 .26 7.9 198 54 0.395
K 560 .23 7.4 218 46 0.427
L 540 .26 7.0 248 40 0.428
io M 560 .25 7.4 213 46 0.318
Example V
A pore-acidity index was calculated for each of the catalysts J - M. As
defined
hereinabove, this index is calculated as 100 x (P° X Acidity/SA). The
results are as follows:
Cata~st I ndex
is J 10.7
K 9.0
L 6.9
M 6.9
2o Example VI
Catalysts A through H and J through M were tested for relative performance in
isomerization service. The same feedstock was used for each of the catalyst
tests, and
was a blend of C5 and C6 hydrocarbons having the following composition in mass
%:
n-Pentane 43
2s n-Hexane 47
Methylcyclopentane + cyclohexane 8
n-Heptane 2
Total 100
3o Once-through isomerization tests were performed at 450 psig, a temperature
of
116°C, 3.4 mass hourly space velocity, and 0.3 hydrogen to hydrocarbon
mol ratio.
is
CA 02340821 2001-03-14
The results are expressed below as ratios of isopentane to total pentanes
("iCs/CS") and 2,2-dimethylbutane to total hexanes ("2,2-DMB"). These ratios
are more
sensitive tests of catalyst performance than octane-number measurements,
showing the
concentration of the highest-octane isopentane and dimethylbutane isomers in
the
product with a high degree of precision in contrast to the low reproducibility
of the
measurement of product octane.
In addition, an isomerization-activity index ("Activity") is shown to equalize
the
weighting of catalyst-performance results on pentanes and hexanes,
corresponding to
[(iCs/CS) + 4x(2,2-DMB)]. Isomerization-activity indices of 100 or more
indicate an
to effective catalyst. The results are shown in Figure 1 in comparison to the
control
catalysts as a plot of the isomerization-activity index vs. pore-acidity
index:
Catalyst iC~/C~ 2.2-DMB Activi
A 56.83 13.53 111.0
B 53.86 12.36 103.3
C 53.53 12.46 103.4
D 55.46 12.93 107.2
E 50.95 11.84 98.3
F 50.62 11.03 94.7
2o G 47.41 10.69 90.2
J 54.3 13.1 106.7
K 52.9 12.7 103.7
L 50.9 12.5 100.9
M 45.4 10.4 87.0
16
