Note: Descriptions are shown in the official language in which they were submitted.
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~0 97/20787 PCTrUS96/13468
ISOPAFUaFFIN/O~EFIN ALKYI~.TION PROCESS USING
~U~RE-EARTH EXCHU~NGED F~,U~ASITE CATALYSTS
.
- The instant invention relates t~ an isoparaf~in-olefin
alkylation process which is carried out in the presence of
a rare-earth exchanged faujasite such as ultra-stable Y-
zeolite (R~-USY), or ultra-stable X-zeolite (RE-USX).
Catalysts useful are those typically used in FCC
~applications, having a particle size range from 50 to 150
microns and an attrition index o~ less than 10 preferably
less than 5. The alkylate product is useful, inter alia, as
an octane enhancer for gasoline.
As a result of curtailing the use of tetraethyl lead
as an octane-improving additive Eor gasoline, the octane
number specification of all grades of gasoline has
increased as well as the product:ion of unleaded gasoline.
Isoparaffin-olefin alkylation is a key route to the
production of highly branched paraffin octane enhancers
which are to be blended into gasoline.
Alkylation involves the addition of an alkyl group to
an organic molecule. Thus, an isoparaffin can be reacted
with an olefin to provide an isoparaffin of higher
molecular weight. Industrially, alkylation often involves
the reaction of C2-Cs olefins with isobutane in the presence
of an acidic catalyst. Alkylates are valuable blending
components for the manufacture of premium gasolines due to
their high octane ratings.
. In the past, alkylation proresses have included the
use of hydrofluoric acid or sulfuric acid as catalysts
under controlled temperature conditions. Low temperatures
are utilized in the sulfuric acid process to minimize the
undesirable side reaction of olefin polymerization and the
acid strength is generally maintained at 88-94 percent ~y
the continuous addition of fresh acid and the continuous
withdrawal of spent acid. The hydrofluoric acid process is
less temperature-sensitive and the acid is easily recovered
and purified.
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The typical types of alkylation currently used to
produce high octane gasoline blending component, that is,
the hydrofluoric acid and sulfuric acid alkylation
processes, have inherent drawbacks including environmental
concerns, acid consumption and disposal of corrosive
materials. With the increasing demands for octane and the
increasing environmental concerns, it has been desirable to
develop an alkylation process based on a solid catalyst
system. The catalyst of the present invention offers a
refiner a more environmentally acceptable alkylation
process than the currently used hydrofluoric and sulfuric
acid al~ylation processes.
Crystalline metallosilicates, zeolites, and molecular
sieves generally have been widely investigated for use in
the catalysis of isoparaffin-olefin alkylation. For
example, U.S. Pat. No. 3,251,902 describes the use of a
fixed bed of ion-exchanged crystalline aluminosilicate
having a reduced number of available acid sites for the
liquid phase alkylation of C4-C20 branched-chain paraffins
with C2-Cl2 olefins. The patent further discloses that the
C4-C20 branched-chain paraffin should be allowed to
substantially saturate the crystalline aluminosilicate
before the olefin is introduced to the alkylation reactor.
U.S. Pat. No. 3,450,644 discloses a method for
regenerating a zeolite catalyst used in hydrocarbon
conversion processes involving carbonium ion intermediates.
U.S. Pat. No. 3,549,557 describes the alkylation of
isobutane with C2-C3 olefins usin~ certain crystalline
aluminosilicate zeolite catalysts in a fixed, moving or
fluidized bed system, the olefin being preferably injected
at various points in the reactor.
U.S. Pat. No. 3,644,565 discloses the alkylation of a
pa~affin with an olefin in the presence of a catalyst
comprising a Group vIIr noble metal present on a
crystalline aluminosilicate zeolite, the catalyst having
been pretreated with hydrogen to promote selectivity.
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.
U.S. Pat. No. 3,647,916 describes an isoparaffin-
, ~olefin alkylation process featuring the use of an ion-
exchanged crystalline aluminosilicate, isoparaffin/olefin
~mole ratios below 3:1 and regeneration of the catalyst. In
this patent, particle sizes are limited to less than 40
microns and are prepared by ball milling. In the instant
invention, particle sizes range from 50 to 150 microns.
U.S. Pat. No. 3,655,813 discloses a process for
-alkylating C4-C5 isoparaffins with C3-Cg olefins using a
~crystalline aluminosilicate zeolite catalyst wherein a
j halide adjuvant is employed in the alkylation reactor. The
isoparaffin and olefin are introduced into the alkylation
~ reactor at specified concentrations and catalyst is
continuously regenerated outsid,e the alkylation reactor.
15 l U.S. Pat. No. 3,893,942 describes an isoparaffin-
ole~in alkylation process employing, as catalyst, a Group
VIII metal-containing zeolite w]hich is periodically
hydrogenated with hydrogen in t]he gas phase to reactivate
1 the catalyst when it has become partially deactivated.
U.S. Pat. No. 3,236,671 discloses the use, in
alkylation, of crystalline aluminosilicate zeolites having
silica to alumina mole ratios above 3 and also discloses
the use of various metals exchanged and/or impregnated on
such zeolites.
U.S. Pat. No. 3,706,814 discloses another zeolite
catalyzed isoparaffin-olefin al~ylation process and further
provides for the addition of C5~- paraffins such as Udex
raffinate or C5+ olefins to the alkylation reactor feed and
~ the use of specific reactant proportions, halide adjuvants,
etc. U.S. Pat. No. 3,624,173 d~scloses the use, in
isoparaffin-olefin alkylation, of zeolite catalysts
cont~; n; ng gadolinium.
U.S. Pat. No. 3,738,977 discloses alkylation of
-paraffins with ethylene employing a zeolite catalyst which
possesses a Group VIII metal component, the catalyst having
been pretreated with hydrogen.
"' ''~~ '' ' ' ' ,
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U.S. Pat. No. 3,865,894 describes the alkylation of
C4-Cg monoolefin employing a substantially anhydrous acidic
zeolite, for example acidic zeolite Y (zeolite HY), and a
halide adjuvant.
U.S. Pat. No. 3,917,738 describes a process for
alkylating an isoparaffin with an olefin using a solid,
particulate catalyst capable of absorbing the olefin. The
isoparaffin and the olefin are admixed to form a reactant
stream in contact with catalyst particles at the upstream
end of an adsorption zone after which the reactants are
passed concurrently with the catalyst so that a controlled
amount of olefin is adsorbed onto the catalyst before the
combination of reactants and catalyst is introduced into an
alkylation zone. This controlled olefin adsorption is said
to prevent polymerization of the olefin during alkylation.
U.S. Pat. No. 4,377,721 describes an isoparaffin-
olefin alkylation process utilizing, as catalyst, ZSM-Z0,
preferably HZSM-20 or rare earth cation-exchanged ZSM-20.
This catalyst may be in the form of a finely divided
powder, but specific size limitations are not given.
Furthermore, attrition indices (heretofore discussed
primarily in regard to FCC catalyst applications) are not
mentioned.
U.S. Pat. No. 4,384,161 describes a process of
alkylating isoparaffins with olefins to provide alkylate
employing as catalyst a large pore zeolite capable of
absorbing 2,2,4-trimethylpentane, e.g., ZSM-4, ZSM-20, ZSM-
3, ZSM-18, zeolite Beta, faujasite, mordenite, zeolite Y
and the rare earth metal-containing forms thereof, and a
Lewis acid such as boron trifluoride, antimony
pentafluoride or aluminum trichloride. The use of a large
pore zeolite in combination with a Lewis acid in accordance
with this patent is reported to greatly increase the
activity and selectivity of the zeolite thereby effecting
alkylation with high olefin space velocity and low
isoparaffin/olefin ratio.
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U.S. Pat. Nos, 4,992,615; 5,012,033; and 5,073,665
describe an isoparaffin-olefin alkylation process
utilizing, as a catalyst, a zeolite designated as MCM-22.
U.S. Pat. Nos. 5,258,569 and 5,254,792 disclose isoparaffin
5 ~ olefin alkylation processes which utilize MCM-36 and MCM-49
respectively, as catalysts.
U.S. Pat. No. 5,292,981 describes a process for
isoparaffin-olefin alkylation in which a slurry of zeolite
- particles and a feed of liquid reactants comprising
lo isoparaffins and olefins is circulated in a reactor. The
isoparaffin/olefin ratio is less than lO0/1 in the slurry.
A first portion of the slurry is recycled to provide a
ratio of at least 500/1. A second portion of the slurry is
~ passed to a separating means wherein alkylate product is
separated from the zeolite.
U.S. Pat. No. 5,366,948 discloses a process of the
preparation of a catalyst intended for catalytic cracking
purposes. It may be prepared with an attrition index of
less than 10 and is prepared by spray drying. It is
20 I generally in the form of a fine powder of 10-200 microns.
The instant invention is concerned with a process for
the alkylation of isoparaffins with olefin molecules in the
presence of a composite catalyst. The catalyst comprises a
rare-earth exchanged faujasite such as an ultra stable X-
zeolite(RE-USX) or ultra-stable Y-zeolite(RE-USY). The
most suitable catalyst for use in the instant invention is
a fluidizable catalyst in the particle size range of 50-150
microns, having an attrition index of less than lO and
preferably of less than 5.
A low attrition index for a catalyst indicates low
loss of catalyst over a cycle of operation. The sodium
content of the FCC catalyst is preferably less than 1.0 wt%
and more preferably less than 0.5 wt%. The degree of rare
earth exchange in the zeolite component is preferably
higher than 30% and more preferably high than 60~. Such
.
.
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catalysts have traditionally been used in applications
involving fluid catalytic cracking (FCC) units. The high
quality alkylate produced in the instant invention may be
used as octane blending stock for gasoline manufacturing.
In FCC operations catalysts comprising RE-USY or RE-
USX provide gasoline products with improved octane number.
They also produce lower amounts of coke than catalysts
which do not comprise rare-earth faujasites. The amount of
rare-earth exchange in the catalyst is inversely
proportional to the amount of coke make. Similar benefits
may also be obtained if these catalysts are employed in the
alkylation of isoparaffins with olefins.
The alkylation of isobutane with light olefins is
important in the manufacture of high octane gasoline
blending stocks. Alkylation typically comprises 10-15 % of
the gasoline pool. It has high RON and MON, is low in
sulfur content, contains no olefins or aromatics,
demonstrates excellent stability and is clean burning.
Feed
Feedstocks useful in the present alkylation process
include at least one isoparaffin and at least one olefin.
The isoparaffin reactant used in the present alkylation
process may be one possessing up to 20 carbon atoms and
preferably has from 4 to 8 carbon atoms. Representative
examples of such isoparaffins include isobutane,
isopentane, 3-methylhexane, 2-methylhexane, 2,3-
dimethylbutane and 2,4-dimethylhexane.
The olefin component of the feedstock includes at
least one olefin having from 2 to 12 carbon atoms.
Representative examples of such olefins include butene-2,
isobutylene, butene-1, propylene, ethylene, pentene,
hexene, octene, and heptene merely to name a few. The
preferred olefins include the C4 olefins, for example,
butene-l, butene-2, isobutylene, or a mixture of one or
more of these C4 olefins, with butene-2 being the most
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preferred. Suitable feedstocks for the process of the
present invention are described in U.S. Pat. No. 3,862,258
to Huang et al. at column 3, lines 44-56, the disclosure of
which is incorporated by reference.
5 ~ Hydrocarbon streams containing a mixture of paraffins
~and olefins such as FCC butane/butene stock may also ~e
employed. The isoparaffin/olefin weight ratio in the feed
may range from l:l to over loO:l. Although the ratio in
the reactor of above 100 is desirable, a ratio of over
500:1 in the reactor is more desirable and a ratio of over
1000:1 is most desirable. A high isoparaffin/olefin ratio
may be achieved by recycle of part of the reactor effluent
or by back-mixing of the reactor content.
Al~yla~ion C~talyst
Catalysts suitable for use in the instant invention
comprise rare-earth exchanged USY(RE-USY) zeolites
described in U.S. Pat. No. 3,293,192 and rare-earth
exchanged USX (RE-USX) zeolites. The catalyst particles
range in size from 50-150 microns. The degree of rare-
earth exchange in the zeolite component is preferably
higher than 30 wt% and more preferably higher than 60 wt%.
Rare-earth ion exchange is performed by conventional
techniques in the instant invention. The zeolites are
exchanged with at least one rare-earth cation, such as
~cations of lanthAnllm or cerium. Mixtures of rare-earth
cations may also be used. The catalyst of this invention
must be at least partially dehydrated, preferably by spray-
drying. The rare-earth metals may be added by ion-exchange
either before or after spray-drying. A calcined catalyst
possesses a greater attrition resistance than does fresh
catalyst. This further dehydration can be accomplished by
heating the catalyst to a temperature in the range of from
~200~C to 595~C, in an atmosphere such as air, nitrogen,
~-etc. and at atmospheric, subatmospheric, or
superatmospheric pressure for a period of from between
1 . ,
.
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about 30 minutes to about 48 hours. The catalyst, of this
invention, being of small particle size (50-150 microns) is
in the form of a spray-dried powder.
It is desired to incorporate the catalytically active
catalyst zeolite with another material, i.e., a binder/
which is resistant to the temperatures and other conditions
employed in the isoparaffin alkylation process of this
invention. Binder materials are usually added to the
zeolite in a slurry. The entire catalyst is then spray
dried. Suitable binder materials include active and
inactive materials such as clays, silica and/or metal
oxides such as alumina. These can be either naturally
occurring or provided in the form of gelatinous
precipitates or gels including mixtures of silica and metal
oxides. Use of a binder material in conjunction with the
catalytically active crystalline material, i.e., combined
therewith, which itself is catalytically active may change
the conversion and/or selectivity of the catalyst.
Inactive materials suitably serve as diluents to control
the amount of conversion so that products can be obtained
economically and in a controlled fashion without having to
employ other means for controlling the rate of reaction.
These materials can be incorporated into naturally
occurring clays, e.g., bentonite and kaolin, to improve the
crush strength of the catalyst under ~_ -rcial operating
conditions. Good crush strength is an advantageous
attribute for commercial use since it prevents or delays
breaking down of the catalyst into fines.
Naturally occurring clays which can be composited with
the present catalyst crystals include the montmorillonite
and kaolin family, which families include the
subbentonites, and the kaolins commonly known as Dixie,
McNamee, Georgia and Florida clays or others in which the
main mineral constituent is halloysite, kaolinite, dickite,
nacrite, or anauxite. Such clays can be used in the raw
state as originally mined or initially subjected to
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9:
i calcination, acid treatment or chemical modification.
- Binders useful for compositing with catalyst crystals also
include inorganic oxides, notab'ly alumina.
The alumina binder may undergo a phase transformation
during calcination, whereby the water solubility of the
alumina is decreased. The hydroxyl content of the alumina
may be decreased by calcination. In particular,
calcination may transform the pseudoboehmite form of
alumina into gamma-alumina.
Apart from or in addition to the foregoing binder
materials, the present catalyst crystals can be composited
-with an inorganic oxide matrix such as silica-alumina,
silica-magnesia, silica-zirconia, silica-thoria, silica-
beryllia, silica-titania as well as ternary compositions
15 ~ such as silica-alumina-thoria, silica-alumina-zirconia,
silica-alumina-magnesia, silica-magnesia-zirconia, etc.
The relative proportions of finely divided catalyst
crystals and inorganic oxide matrix can vary widely with
the catalyst crystals content ranging from 1 to 95 percent
by weight and more usually, in the range of 2 to 80 weight
:percent of the composite.
Since the catalyst of the instant invention is
employed as small fluidized particles as is that typically
used in FCC applications, it is subject to attrition.
Catalyst attrition can cause serious losses in any
fluidized application, whether it is an FCCU or an
alkylation unit. The amount of attrition that occurs over
time with a catalyst depends on whether or not the catalyst
is fresh or has been treated. It is also dependent upon
the severity of the operating conditions employed.
Catalysts that have been calcined have approximately the
same attrition resistance as equilibrium catalysts or those
c -that have been steamed. All three have greater attrition
resista~ce than fresh catalyst.
The ability to quickly determine the attrition
resistance of the catalyst in the unit permits a timely
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change to a more attrition-resistant catalyst in order to
decrease losses, along with eliminating particle emissions, r
fines in the slurry oil, and wear in power-recovery trains.
The preferred method of deter~in;ng attrition resistance is
5 the jet-cup method, as discussed in the article "Method
speeds FCC catalyst attrition resistance determinations,"
0;1 ~nd Gas Journal, April 16, 1990, vol. 88, p. 38. This
method eliminates the need for particle size measurement or
accurate sampling procedures. Attrition resistance
10 determinations are thus made more quickly. The jet-cup
method provides data for an attrition index, WD, which is
the gradient (or slope) of a plot of cumulative weight
percent catalyst fines v. time in hours. The jet-cup test
apparatus confines most of the catalyst sample to a small
15 cup, into which a high velocity air flow is introduced.
The air agitates the catalyst sample, causing attrition of
the particles as they collide with the wall of the jet cup.
The attrition index for the jet-cup test is the
Davision Index, DI. The index expresses the jet-cup data
20 as:
DI=~[(c/m x 100) + H - G]/100 -G} x 100
where: c = weight percent catalyst fines collected
m = weight of the initial sample
G= weight of particles less than 20 microns in the sample
25 before the test
H = wt% of particles less than 20 microns left in the
sample after the test
A low ~I value indicates a good attrition-resistant
catalyst.
30 Oper~ti ng Condi~ion~ -
The operating temperature of the alkylation process
herein can extend over a fairly broad range, e.g., from
0~C. to 400~C, and is preferably within the range of from
50~C, to 200~C. The practical upper operating temperature
35 will often be dictated by the need to avoid an undue
occurrence of undesirable side reactions.
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11
The pressures employed in the present process can
extend over a considerably wide range, from atmospheric
pressure to 13790 kPa (2000 psig). The mole ratio of
~ hydrogen to olefin in the feed is controlled to be less
than or e~ual to 0.2:1.0, preferably 0.15:1Ø
The amount of catalyst used in the present alkylation
process can be varied over relatively wide limits. In
general, the amount of catalyst as measured by the weight
hourly space velocity (WHSV) based on olefin can range from
0.01 to 5 hr~1. It will, of course, be realized by those
skilled in the art that the amount of catalyst selected for
a particular reaction will be det:ermined by several
variables including the reactants involved as well as the
nature of the catalyst and the operating conditions
employed.
As discussed in the feed sec:tion, the mole ratio of
total isoparaffin to total olefin alkylating agent in the
combined hydrocarbon feed can be from 1:1 to 1000:1 and is
preferably in the range of over 500:1 and most preferably
over 1000:1.
The alkylation process of the present invention can be
carried out as a batch-type, semi-continuous or continuous
operation utilizing a fixed bed reactor, moving bed reactor
ebullating bed, slurry reactor or fluidized bed reactor.
The catalyst after use, is conducted to a regeneration zone
where coke is removed, e.g., by burning in an oxygen-
cont~; n ing atmosphere tsuch as air) at elevated temperature
~or by extracting with a solvent, after which the
regenerated catalyst is recycled to the conversion zone for
further contact with the organic reactants. Particular
process configurations and variat:ions may be accrued at by
substituting the present catalyst: for the catalyst as
described in U.S. Pat. Nos. 4,992,615; 5,012,033; and
5,073,665.
;
=
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~xamples
Alkylat;on Testing Procedllre
All the commercial catalysts used in these examples
were evaluated in isobutane/butene-2 alkylation conducted
in a slurry reactor using the following procedure: Prior
to the testing, catalysts were crushed to <149~ (<loo mesh)
and pretreated at 400~C for 3 hours in dry air. Each of
the catalysts tested is typically used in FCC cracking
operations. Then 10-40 grams of catalyst was placed in a
300 cc stainless steel stirred autoclave and the reactor
was filled with 200 ml of isobutane. The slurry was
stirred at 1900 rpm and heated to 120~C. The pressure was
kept at 2965 kPa (430 psig). After the desired temperature
was reached, butene-2 was continuously fed into the reactor
at a butene weight hourly space velocity of 0.1 (based on
zeolite component) until an external isobutane/butene-2
mole ratio of 21:1 was reached. At the end of the run, the
total reactor content (hydrocarbons) was discharged through
a 2 micron filter under a N2 flow into a metal bomb which
was kept at -73~C. It was then weathered to ambient
temperature and pressure. Liquid and gas products were
analyzed gas chromatographically. Each material balance
was based on the recovered liquid and gas samples.
~x~le 1
A commercial catalyst (CTX-40, manufactured by W.R.
Grace) containing approximately 25% REY and a matrix
(binder) is called Catalyst A. 40 grams of Catalyst A was
tested in isobutane/butene-2 alkylation using the above
procedure. The olefin conversion, C5t alkylate yield (g C5+
produced per g of olefin converted), and C5+ alkylate
distribution are given in the Table.
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e 2
A commercial catalyst, containing 30% REY, 4% rare
; earth oxide, 0.36% Na and a binder, is called Catalyst B.
33 grams of Catalyst B was test:ed in isobutane/butene-2
alkylation using the above procedure. The results are
; listed in the Table.
le 3
10 grams of Catalyst B was used in the same testing as
in Example 2 except that the butene WHSV was increased to
0.33 (based on zeolite). The results are shown in the
Table.
le 4
A commercial catalyst, containing 35% RE-USY, 2.5~
rare earth oxide, ~0.2% Na and a binder, is called Catalyst
15 ' C. 33 grams of Catalyst C was tested in isobutane/butene-2
alkylation using the above procedure. The results are
= _ .
-summarized in the Table.
Csncl ll~i on fro~ ~ les 1-4
- Clearly, all the commercial catalysts tested above
showed good olefin conversion and high C5+ alkylate yield.
The high C5+ alkylate yield indicated that all the
catalysts are effective for isobutane/butene alkylation.
The high trimethylpentanes (TMP) content in C8 reflected a
~-high octane quality, due to its branched nature. In
addition, RE USY (Catalyst C) was more active than REY
~(Catalysts A and B) as evidenced by the higher butene
conversion.
,
I . -
~ ' .
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14
Table
Isobutane/Butene-2 Alkvlation over Small Particle Catalvsts of Low Attrition Index
(120~C, 2965 kPa (430 psig) and l/O = 21/1)
FCC Catalvst Catalyst A Catalyst B Ca(alYst B Catalvst C
Butene WHSV 0.1 0.1 0.33 0.1
(zeolite)
Butenc WHSV 0.025 0.03 0.1 0.03
(total catalyst)
Butene Conversion, % 94 97 88 99
C5+ Alkylate Yield 1.50 1.74 1.65 1.69
C5+ Alkylate Di.,ilil,ulic,.l, v~/0
C5-c7 - 30.0 22.9 35.9
C~ - 64.7 70.9 59.2
Cg+ - 5.3 6.2 4.9
TMP in C, - 86.9 87.8 87.1
