Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED PROCE~SS FOR OL~FINS TO GASOLINE CONVERSION
This invention relates to an improved process for the
conversion of light olefins to gasoline boiling range hydrocarbons.
In particular, the inYentiOn relates to an improved technique for
the recovery and separation of liquefied petroleum gas( LPG) from an
olefins to gasoline conversion process effluent stream.
Conversion of olefins to gasoline and/or distillate product
is disclosed in U.S. Patents 3,960,978 and 4,021,502 (Givens,Plank
and Rosinski) wherein gaseous olefins in the range of ethylene to
pentene, either alone or in admixture with paraffins, are converted
into an olefinic gasoline blending s~ock by contacting the olefins
with a catalyst bed made up of 2SM-5 or related zeolite. In U.S.
Patents 4,150,062 and 4,227,992 Garwood et al discloses the
operating conditions for the Mobil Olefin to Gasoline/Distillate
(M0GD) process for selective conversion of C3~ olefins. A
fluidized bed process for converting ethene-containing light
olefinic streams, sometimes referred to as the Mobil Olefin to
Gasoline (MOG) process is described by Avidan et al in U.S. Patent
Application 006,407, filed 23 Jan 1987. The phenomena of
shape-selective polymerization are discussed by Garwood in ACS
Symposium Series No. 218, Intrazeolite Chemistry, "Conversion of
C2-C10 to Higher Olefins over Synthetic 2eolite ZSM-5", 1983
American Chemical Society.
In the process for catalytic conversion of olefins to
~5 heavier hydrocarbons by catalytic oligomerization using an acid
crystalline metallosilicate zeolite, such as ZSM-5 or related shape
sélective catalyst, process conditions can be varied to favor the
formation of either gasoline or distillate range products. In the
gasoline operating mode, or MOG reactor system, ethylene and the
other lower olefins are catalytically oli~omerized at elevated
temperature and moderate pressure. Uhder these conditions ethylene
conversion rate is greatly increased and lower olefin
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oligomerization is nearly complete to produce C5~ hydrocarbons in
good yield.
The olefins contained in an FCC gas plant are an
advantageous feed for ~CG. U.S. Fatent No. 4,090,949 discloses
upgrading olefinic gasoline by conversion in the presence of carbon
hydrogen-contributing fragments including olefins and a zeolite
catalyst and where the contributing olefins may be obtained from a
gas plant. U.S. Patent Nos. 4,~71,147 and 4,504,691 disclose an
MOG/D process using an olefinic feedstock derived from FCC
effluent. In these two latter patents the first step involves
prefractionating the olefinic feedstock to obtain a gaseous stream
rich in ethylene and a liquid stream containing C3+ olefin.
The conventional MOG process design is concerned with
converting ethylene in a fuel gas stream, such as an FCC off-gas, to
gasoline. In the conventional MOG design no LPG recovery facility is
provided since the LPG content of the MOG reactor effluent is
relatively small. However, when it is desired to convert propene
and/or butene to gasoline by processing olefinic-paraffinic LPG the
unreacted paraffinic LPG, unconverted olefinic LPG and LPG produced
in the conversion step constitute a significant portion of the MOG
reactor effluellt. In this case~ processing the reactor efflu~nt in
the conventional MOG design is unacceptable since a major portion of
reactor effluent LPG will be lost to fuel gas. ~owever, with an
adequate recovery and separation design for the LPG content of an
MOG process wnverting C2-C4 olefins the performance of the MOG
process could be improved where the process would represent a viable
alternative to acid catalyzed alkylation as a route to high octane
gasoline. Further, an economical recovery and separation step will
open up the MOG process to utilize a wider range of available
feedstock, particularly FCC light olefinic products, routinely
available in the refinery setting. The provision of an improved MOG
process as an alternative to the economically and environmentally
beleaguered alkylation process would constitute a very noteworthy
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contribution to the options available to the refinery arts for the
production of high octane.
The present invention provides a process ~erein a
fractionation step is incorporated into the recovery and separation
of the effluent from the olefins to gasoline (MOG) process such that
the LNG components of the effluent stream are separated and
recovered as well as a stream comprising C5+ gasoline range
boiling liquids. In a preferred embodiment of the present invention
the effluent stream is separated in high temperature and low
temperature separators and the low boiling fraction is deethanized
in a conventional absorber-sponge absorber system while hi8her
boiling component, following stripping, is passed to the
depropanizing-debutanizing section of the process.
It has further been discovered that the process of the
present invention can be integrated with an unsaturated gas plant
debutanizer upstream of the olefins to gasoline conversion reactor.
In this embodiment the feedstream to the FCC debutanizer, comprising
wild gasoline and FCC wet gas is passed to the FCC debutanizer and
the vapor overhead fraction therefrom is passed to the MKG reactor
~O system. Optionally , the FCC debutanizer can be replaced with a
depropanizer and a common debutanizer utilized to separate both the
MOG effluent after deethanization and depropanization and the
bottoms effluent from the FCC depropanizer.
More specifically, an improved process for the conversion
2s for lower olefinic hydrocarbon feedstock to C5~ gasoline range
hydrocarbons has been discovered comprising: contacting a
h~drocarbon stream containing C3- and/or C4-olefinic
hydrocarbons with a medium pore shape selective solid catalyst in
oligomerization zone under oligomerization conditions to produce an
effluent stream rich in C5l gasoline range hydrocarbons;
separating said effluent stream to provide a C3- hydrocarbon
stream and a C3~ hydrocarbon stream; fractionating said C
hydrocarbon stream to produce a C5l gasoline range
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hydrocarbon stream, a stream rich in C4 hydrocarbons and a stream
rich in C3 hydrocarbons.
In the drawings, Figure 1 is a schematic flow dia8ram
illustrating the basic process design of the instant invention.
Figure 2 is a flow diagram showing the novel MCG process
integration with FCC unsaturated gas plant for the purpose of
converting C4- olefins in MOG.
Figure 3 is a process flow diagram further illustrating the
novel MOG process integration with unsaturated gas plant or the
purpose of converting C3-olefins in MOG.
The present invention provides a system for upgrading light
olefins such as FCC product components obtained from a FCC main
column overhead product debutanizer or depropanizer, to liquid
hydrocarbons. The invention utilizes a continuous process for
producing fuel products by oligomerizing olefinic components to
produce higher hydrocarbon products for use as fuel or the like. It
provides a separation technique for use with processes for
oligomeri~ing lower alkene-containing light gas feedstock,
optionally containing ethene, propene, butenes or lower alkanes, to
produce predominantly C5 hydrocarbons, including olefins.
The preferred feedstock contains C2-C4 alkenes
(mono-olefin) in the range of 10 to 90 wt~. Non-deleterious
components, such as methane and other paraffins and lnert gases, may
be present. A particularly useful feedstock is a li~ht gas
by-product of FCC gas oil cracking u~its containing typically 10-40
mol ~ C2-C4= olefins and 5-35 mol % H2 with varying amounts
of Cl-C3 paraffins and inert gas, such as N2. The process may
be tolerant of a wide range of lower alkanes, from 0 to 95%.
Preferred feedstocks contain more than 50 wt % Cl-C4 lower
aliphatic hydrocarbons, and contain sufficient olefins to provide
total olefinic partial pressure of at least 50 kPa. Under the
reaction severity conditions e~ployed in the present invention lower
alkanes, especially propane, may be partially converted to C
products.
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Conversion of lower olefins, especially ethene, propene and
butenes, over HZS~-5 is effective at moderately elevated
temperatures and pressures. The conversion products are sought as
liquid fuels, especially the C5 hydrocarbons. Product
distribution for iiquid hydrocarbons can be varied by controlling
process conditions, such as temperature, pressure and space
velocity. Gasoline (eg, C5-Cg) is readily formed at elevated
temperature (e.g., up to 400C) and moderate pressure from ambient
to 5500 kPa, preferably 250 to 2900 kPa. Under appropriate
conditions of catalyst activity, reaction temperature and space
velocity, predominantly olefinic gasoline can be produced in good
yield and may be recovered as a product. Operating details for
typical olefin oligomerization units are disclosed in U.S. Patents
4,456,779; 4,497,968 (Owen et al.) and 4,433, 185 (Tabak).
It has been found that C2-C4 rich olefinic light gas
can be upgraded to liquid hydrocarbons rich in olefinic gasoline by
catalytic conversion in a turbulent fluidized bed of solid acid
zeolite catalyst under low severity reaction conditions in a single
pass or with recycle of gaseous effluent components. This technique
is particularly useful for upgrading LPG and FCC light gas, which
usually contains significant amounts of ethene, propene, butenes,
C2-C4 paraffins and hydrogen produced in cracking heavy
petroleum oils or the lil~ce.
Recent developments in zeolite technology have provided a
group of medium pore siliceous materials having similar pore
geometry. Most prominent among these intermediate pore size
zeolites is ZSM-5, which is usually synthesized with Bronsted acid
active sites by incorporating a tetrahedrally coordinated metal,
such as Al, Ga, or Fe, within the zeolytic framework. Ihese medium ~;
pore zeolites are favored for acid catalysis; however, the
advantages of ZSM-5 structures ~ay be utilized by employing highly
siliceous materials or crystalline metallosilicate having one or
more tetrahedral species having varying degrees of acidity. ZSM-5
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crystalline structure is readily recognized by its X-ray diffraction
pattern, which is described in U.S. Patent No. 3,702,866 ~Argauer,
et al.).
The oligomeri~ation catalyst preferred for use in olefins
conversion includes the medium pore (i.e., 5-7 x 10 7 mm
(Angstroms)) shape selective crystalline aluminosilicate zeolites
having a silica to alumina ratio of 20:1 or greater, a constraint
index of 1-12, and acid cracking activity (alpha value) of 10-200.
Representative of the shape selective zeolites are ZSM-5, ZSM-ll,
ZSM-12, ZS~I-22, ZSM-23, ZSM-35, ZSM~38, and ZSM-48. ZSM-5 is
disclosed in U.S. Patent No. 3,702,886 and U.S. Patent ~o. Reissue
29,948. Other suitable zeolites are disclosed in U.S. Patent Nos.
3,709,979 (ZSM-ll); 3,832,449 (ZSM-12); 4,076979; 4,076842 (ZSM-23);
~,016,245 (ZSM-35); and 4,375,573 (ZSM-48).
While suitable zeolites having a coordinated metal oxide to
silica molar ratio of 20:1 to 200:1 or higher may be used, it is
advantageous to employ a standard ZSM-5 having a silica alumina
molar ratio of 25:1 to 70:1, suitably modified. A typical zeolite
catalyst component having Bronsted acid sites may consist
2n essentially of aluminosilicate ZSM-5 zeolite with 5 to 95 wt %
silica, clay and/or alumina binder.
These siliceous zeolites may be employed in their acid
forms ion exchanged or impregnated with one or more suitable metals,
such as Ga, Pd, Zn, Ni, Co and~or other metals of Periodic Groups
III to VIII. Ni-exchanged or impregnated catalyst is particularly
useful in converting ethene under low severity conditions. ~he
zeolite may include other components~ generally one or more metals
of group IV, IIB, IIIB, VA VIA or VIIIA of the Periodic Table
(IUPAC). Useful hydrogenation components include the noble metals
of Group VIIIA, especially platinum, but other noble metals3 such as
palladium, gold, silver, rhenium or rhodium, may also be used~ Base
metal hydrogenation components may also be used, especially nickel,
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cobalt, molybdenum, tungsten, copper or zinc. The catalyst
materials may include two or more catalytic components, such as a
metallic oligomerization component (eg, ionic Ni 2, and a
shape-selective medium pore acidic oligomerization catalyst, such as
ZSM-5 zeolite) which components may be present in admixture or
combined in a unitary bifunc~ional solid particle. It is possible
to utilize an ethene dim~ri~ation metal or oligomerization agent to
effectively convert feedstock ethene in a continuous reaction zonel
Certain of the ZSM-5 type medium pore shape selective catalysts are
sometimes known as pentasils. In addition to the preferred
aluminosilicates, the borosilicate, ferrosilicate and "silicalite"
materials may be employed.
ZSM-5 type pentasil zeolites are particularly useful in the
process because of their regenerability, long life and stability
under the extreme conditions of operation. Usually the zeolite
crystals have a crystal size from ~.01 to over 2 x 10 3mm or re,
with 0.02-1 micron being preferred.
A further useful catalyst is a medium pore shape selective
crystalline aluminosilicate zeolite as described above containing at
~0 least one Group VIII metal, for example Ni-ZSM-5. This catalyst has
been shown to convert ethylene at moderate temperatures and is
disclosed in commonly assigned U.S. Patent 4,717,782.
Referring now to Fi~Jre 1, the novel process of the instant
invention is shown which allows the utilization of LPG streams
containing propene and butene as feedstock to the MCG process in
addition to fuel gas containing ethene. Feedstock is introduced to
the MOG reactor by conduits 101 and/or 102. In the present
embodiment the feedstock may be drawn from any refinery source. The
effluent from the conversion reactor is passed 103 after cooling 104
to a high temperature separator 105 for separation of a high boiling
fraction 106 containing C5l hydrocarbons. That fraction is passed
to stripper means 107. The vapor fraction 108 from the high
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temperature separator is cooled 109 and passed to a low temperature
separator 110 and a hi8her boiling component of that fraction is
separated and passed 111 to stripper 107. The light fraction 112
from separator 110 comprising light hydrocarbons is passed to
absorber and sponge absorber system 113 and 114 for deethanization
and recovery of C2- off-gas 115. The overhead fraction 116 ~rom
stripper 107 is recycled to the high temperature separator and the
bottom fraction 108 comprising C4~ hydrocarbons is passed through
the novel depropanizer debutanizer of the present invention 117
where bottom C5~ MOG gasoline fraction is separated 118. Stream
119 is withdrawn from a mid-portion of fractionator 117. This more
efficiently separates C3 and C4 components as a bo-ttom C4
stream and an overhead C3 stream 121 which is recycled to a top
portion of fractionator 117 for separation as an overhead stream
comprising C3 hydrocarbons 122.
An important advantage of the present invention is to be
found in those embodiments wherein the downstream separation of the
effluent from an MOG reactor is integrated with an existing
unsaturated gas plant such as the unsaturated gas plant (USGP)
~0 commonly incorporated as part of a fluid catalytic cracking ~FCC)
operation. The advantages inherent in these embodiments of the
present invention lie in two general directions: the ability to
double up on the utilization of USGP separation towers which affords
a significant economic advantage in the costs associated with
separation of the MGG reactor effluent; the opportunity to down-load
USGP towers by shifting deethanization, depropanization and
debutanization operations in large part to the towers integrated
into the design of the MOG reactor effluent separation, inherent
within the present invention.
Figures 2 and 3 present process flow diagrams
representative of embodiments of the present invention ~herein the
invention involves an integration of the MOG product separation
operations with unsaturated gas plant operations in a generic way,
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they are illustrative of the integration of MOG product effluent
separation and USGP operation. The configuration of actual
integrations may vary depending upon site specific and market
specific opportunities in ways which can obviously be derived from
s the generic embodiments presented herein by those skilled in the art.
Referring now to Figure 2, PCC wild gasoline 210 and the
product outlet from the after-cooler from an FCC wet gas compressor
211 are passed to an FCC debutanizer 212 af~er separation of the
after-cooler outlet stream into vapor and liquid components 213 and
lo 214. A bottom stream 215 is separated from the debutanizer
comprising C5+ FCC gasoline and the overhead stream 216 comprising
C4-hydrocarbons is passed to the MOG reactor 217. Optionally, feed
from other process units comprising C2-C4 olefins is also passed
218 to the reactor. lhe MOG reactor effluent 219 is cooled and
separated into liquid and vapor fractions in a low temperature
separator 220. The liquid portion is passed to stripper 221 and the
bottom portion therefrom is passed 222 to debutanizer 223 for
separation into C4-overhead 224 and C5~ M05 gasoline 225. Yapor
from low temperature separator 220 is passed 226 to an absorber/
~o sponge absorber system 227,228 for deethanization. A portion of
stream 215 is passed 235 to absorber 227 as lean oil. The less
volatile FCC gasoline stream 215 is the preerred lean oil because
less volatile lean oil usage results in less gasoline carry over to
the sponge absorber. The overhead from stripper 221 and the bottom
fraction from absorber 227 is recycled 229 and 230 to low
temperature separator 220.
Figure 3 illustrates an embodiment of the present
invention integrating MOG product separation with an FCC unsaturated
gas plant utilizing a common debutanizer for separation of FCC and
MOG product. Referrin8 to Figure 3, FCC wild gasoline is passed 310
to a depropanizer 311 in conjunction with the vapor and liquid
fractions 312 and 313 from the FCC wet gas compressor after-cooler.
C3- overhead is passed 314 as a feed stream to the MCG reactor
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315. Ihe effluent therefrom 316 is separated via low temperature
separator 317 and stripper 318 to provide a C3~ fraction 319 and
an overhead fraction 320 ~ich is deethanized in absorber system 321
and 322. In ~his case the bottom stripper fraction is passed to a
depropanizer 323 and a C4+ bottom fraction 324 is separated~ lhis
fraction is passed to a debutanizer in conjunction with the bottom
fraction 325 from depropanizer 311. In the common debutanizer a
bottom fraction is separated 326 comprising MOG and FCC C5+
gasoline and an overhead fraction is collected 327 comprising MOG
and FCC C~ fractions.
In the following, (Table I) a comparison is presented
showing the advantages of the present invention over conventional
MCG operations. Column A shows the product distribution of an
unsaturated gas plant, not incorporating an MOG process unit.
Column B shows the product distribution of a conventional MCG
operation which uses as a feedstock treated FCC sponge absorber
stream. Column C shows a product distribution from MOG and IJSGP
integration o the present invention represented by Figure 2 process
flow diagram. The results clearly show a distinctly superior yield
~0 of total gasoline product in the process of the instant invention.
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TABLE I
MOG/USGP DESIGN EFFECT ON PRODUCT DISTRIBUTION
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Colu~n Colunn Column
A B C
MCG Gasoline(BPSD*) - 780 5212
FCC Gasoline " 30995 30995 30995
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Total Gasoline(BPSD) 30995 31775 36207
Butene(BPSD) 4227 4163 273
i-Butane " 1791 1840 223;
n-Butane " 1134 1149 1150
Total Liquid C4's 7152 7152 3658
Propene(BPSD) 3775 3689 116
Propane " 1155 1174 1191
Total Liqùid C~'s 4930 4863 1307
Fuel Gas(MMSCFD) 12.6 10.7 11~2
*Barrels per stream day
In Table II a comparison is presented of the equipment and
energy fractionation requirements for an unsaturated gas plant
alone and an inte8rated hlOG/USGP unit. The comparison shows the
~ advantages of MOG/U9GP of the instant invention which can be
operated with the same energy usage and equipment requirements as a
`-` USGP alone.
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TABLE II
Tower Diameter, m(Ft.) Reboiler Duty Condenser Duty
(MMBTU/~) (MMETU/H R)
USGP MOG/USGP U9GP MKG/USGP USGP MOG/USGP
Sponge 1.37 1.22
Absorber(4.5) (4.0) 0 0
Absorber/2.59 1.83
Stripper (8.5)(6.0) 70 27 0 0
FCC Gasoline 3.20 3.66
~ebutanizer (10.5) (12.0) 59 83 41 14
MOG Gasoline 1.83
; Debutanizer 0 (6.0) 0 27 0 18
Depropanizer 1.83 1.22 15 6 14 6
(6.0) (4.0)
`;~ While the invention has been shown by describing
preferred embodiments of the process, there is no intent to limit
~` the inventive concept except as set forth in the following claims.
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