Note: Descriptions are shown in the official language in which they were submitted.
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ENHANCED OXYGENATE CONVERSION
AND PRODUCT CRACKING INTEGRATION
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to the conversion of oxygenates to
olefins and,
more particularly, to light olefins.
[0002] A major portion of the worldwide petrochemical industry is concerned
with the
production of light olefin materials and their subsequent use in the
production of numerous
important chemical products via polymerization, oligomerization, alkylation
and the like
well-known chemical reactions. Light olefins include ethylene, propylene and
mixtures
thereof. These light olefins are essential building blocks for the modern
petrochemical and
chemical industries. A major source for these materials in present day
refining is the steam
cracking of petroleum feeds. For various reasons including geographical,
economic, political
and diminished supply considerations, the art has long sought a source other
than petroleum
for the massive quantities of raw materials that are needed to supply the
demand for these
light olefin materials.
[0003] The search for alternative materials for light olefin production has
led to the use of
oxygenates such as alcohols and, more particularly, to the use of methanol,
ethanol, and
higher alcohols or their derivatives such as dimethyl ether, diethyl ether,
etc., for example.
Molecular sieves such as microporous crystalline zeolite and non-zeolitic
catalysts,
particularly silicoaluminophosphates (SAPO), are known to promote the
conversion of
oxygenates to hydrocarbon mixtures, particularly hydrocarbon mixtures composed
largely of
light olefins.
[0004] Such processing of oxygenates to form light olefins is commonly
referred to as a
methanol-to-olefin (MTO) process, as methanol alone or together with other
oxygenate
materials such as dimethyl ether (DME) is typically an oxygenate material most
commonly
employed therein. Such processing typically produces or results in a range of
olefin reaction
products as well as unreacted oxygenates and other trace oxygenates. Typical
or common
MTO processing schemes include an oxygenate absorber whereby circulated water
is used to
absorb oxygenates, e.g., methanol and DME, from the light olefin product. This
oxygenate-
containing circulated water is subsequently stripped in an oxygenate stripper
to recover
methanol and DME, with such recovered materials ultimately recycled to the
oxygenate
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conversion reactor. The oxygenate conversion product stream resulting from the
oxygenate
absorber is passed to a CO2 removal zone wherein the dewatered oxygenate
conversion
product stream is contacted with caustic solution to remove carbon dioxide and
produce a
caustic treated reactor product stream such as for subsequent processing
through an
appropriate light olefins recovery system.
[0005] Carbonyls, such as acetaldehyde, are common trace oxygenates in the
oxygenate
conversion reactor effluent and will typically be absorbed in the circulated
water. Aldehydes
in MTO effluent may, for example, include formaldehyde, acetaldehyde,
propionaldehyde,
butyraldehyde, and crotonaldehyde. These compounds may be in the MTO reactor
feed,
created as reaction side products, or formed in processing downstream of the
reactor.
[0006] The amounts of light olefins resulting from such oxygenate to olefin
processing
can be further increased by reacting, i.e., cracking, heavier hydrocarbon
products, particularly
heavier olefins such as C4 and C5 olefins, to light olefins. For example,
commonly assigned,
US 5,914,433 to Marker discloses a process for the production of light olefins
comprising
olefins having from 2 to 4 carbon atoms per molecule from an oxygenate
feedstock. The
process comprises passing the oxygenate feedstock to an oxygenate conversion
zone
containing a metal aluminophosphate catalyst to produce a light olefin stream.
A propylene
stream and/or mixed butylene is fractionated from said light olefin stream and
cracked to
enhance the yield of ethylene and propylene products. This combination of
light olefin
product and propylene and butylene cracking in a riser cracking zone or a
separate cracking
zone provides flexibility to the process which overcomes the equilibrium
limitations of the
aluminophosphate catalyst. In addition, the invention provides the advantage
of extended
catalyst life and greater catalyst stability in the oxygenate conversion zone.
[0007] Molecular sieves such as silicalite catalyst materials used in olefin
cracking
desirably convert oxygenates to olefins. Such processing, however, also
typically produces or
forms coke and water. The formation coke may act to at least temporarily
deactivate the
catalyst. Such catalysts can generally be regenerated by burning or otherwise
removing the
coke. Permanent catalyst deactivation, however, can occur such as through the
mechanism of
hydrothermal dealumination of silicalite catalyst materials.
[0008] Thus, while the integration of an olefin cracking processing, such as
to
advantageously monetize the C4+ olefins via conversion of a substantial
portion of such C4+
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olefins to generally more commercially desirable propylene and ethylene, is of
significant
economic interest, such processing integration can be subject to certain
processing
complications or limitations.
[0009] For example, trace oxygenates and water are commonly present in the C4+
olefinic product stream produced via MTO processing. Consequently, processing
such trace
oxygenate and water-containing C4+ olefinic product streams in an olefin
cracking reactor
can detrimentally result in a more rapid permanent deactivation of the olefin
cracking catalyst
and can at least temporarily suppress activity through additional coke
formation. Moreover,
oxygenates in the feed can decompose to form water. Thus, the cumulative
effects of water
present in the olefin cracking feed and water generated from oxygenate
decomposition can
contribute to permanent deactivation.
[0010] In view thereof, there is an ongoing need and a demand for improved
processing
and systems for the conversion of oxygenates to olefins and, more
particularly, for such
processing and systems such as to result in an increase in the relative amount
of light olefins
such as via either or both more effective and more efficient integration of
oxygenate
conversion and product olefin cracking.
SUMMARY OF THE INVENTION
[0011] A general object of the invention is to provide or result in improved
processing of
an oxygenate-containing feedstock to light olefins.
[0012] A more specific objective of the invention is to overcome one or more
of the
problems described above.
[0013] A general object of the invention can be attained, at least in part,
through a
process for producing light olefins from an oxygenate-containing feedstock. In
accordance
with one preferred embodiment, such a process involves contacting the
oxygenate-containing
feedstock in an oxygenate conversion reactor with an oxygenate conversion
catalyst and at
reaction conditions effective to convert the oxygenate-containing feedstock to
form an
oxygenate conversion effluent stream comprising light olefins, C4+
hydrocarbons and
oxygenates. At least a portion of the oxygenate conversion product stream is
treated in a
hydrocarbon recovery system to recover light olefins and to form a C4+
hydrocarbon fraction
stream including C4+ hydrocarbons and oxygenates. The C4+ hydrocarbon fraction
stream is
treated to form a treated C4+ hydrocarbon fraction stream containing
oxygenates in a relative
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amount of less than 800 ppmw equivalent water. The process further involves
contacting at
least a portion of the treated C4+ hydrocarbon stream in an olefin cracking
reactor with an
olefin cracking catalyst and at reaction conditions effective to convert C4
and C5 olefins
therein contained to a cracked olefins effluent stream comprising light
olefins.
[0014] The prior art generally fails to provide processing schemes and
arrangements for
the conversion of an oxygenate-containing feedstock to olefins, particularly
light olefins and
which processing is as effective and efficient as may be desired for the
integration of
oxygenate conversion and product olefin cracking. More particularly, the
presence of
oxygenates and/or water in oxygenate conversion products streams and thus in
the feed to
downstream product olefin cracking has not been addressed by the prior art in
a manner that
is as effective or efficient as may be desired.
[0015] A process for producing light olefins from an oxygenate-containing
feedstock, in
accordance with yet another embodiment involves similarly contacting the
oxygenate-containing feedstock in an oxygenate conversion reactor with an
oxygenate
conversion catalyst and at reaction conditions effective to convert the
oxygenate-containing
feedstock to an oxygenate conversion product stream comprising light olefins,
C4+
hydrocarbons and oxygenates. At least a portion of the oxygenate conversion
product stream
is treated in a hydrocarbon recovery system to recover light olefins and to
form a C4+
hydrocarbon fraction stream including C4+ hydrocarbons and oxygenates. The C4+
hydrocarbon fraction stream is washed in a contactor with a wash fluid
comprising a sulfite-
containing material to form a washed C4+ hydrocarbon fraction stream
containing oxygenates
in a relative amount of less than 600 ppmw equivalent water. At least a
portion of the treated
C4+ hydrocarbon stream is contacted with an olefin cracking catalyst in an
olefin cracking
reactor at reaction conditions effective to convert C4 and CS olefins therein
contained to a
cracked olefins effluent stream that includes light olefins.
[0016] A system for converting oxygenates to light olefins in accordance with
yet another
embodiment also includes a reactor for contacting an oxygenate-containing
feedstream with
catalyst and converting the oxygenate-containing feedstream to form an
oxygenate
conversion effluent stream. The oxygenate conversion effluent stream includes
light olefins,
C4+ hydrocarbons and oxygenates. The system includes a hydrocarbon recovery
system to
recover light olefins and to form a C4+ hydrocarbon fraction stream including
C4+
hydrocarbons and oxygenates. The system further includes a treatment system
for treating at
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least a portion of the C4+ hydrocarbon fraction stream with a wash stream to
form a treated
C4+ hydrocarbon fraction stream containing oxygenates in a relative amount of
less than 800
ppmw equivalent water. The system also further includes a reactor for
contacting at least a
portion of the treated C4+ hydrocarbon fraction stream with catalyst and
converting C4 and C5
olefins therein contained to a cracked olefin effluent stream comprising light
olefins.
[0017] As used herein, references to "light olefins" are to be understood to
generally refer
to C2 and C3 olefins, i.e., ethylene and propylene, alone or in combination.
[0018] "Oxygenates" are hydrocarbons that contain one or more oxygen atoms.
Typical
oxygenates include alcohols and ethers, for example.
[0019] References to "Cs hydrocarbon" are to be understood to refer to
hydrocarbon
molecules having the number of carbon atoms represented by the subscript "x".
Similarly, the
term "C, -containing stream" refers to a stream that contains CX hydrocarbon.
The term "CX+
hydrocarbons" refers to hydrocarbon molecules having the number of carbon
atoms
represented by the subscript "x" or greater. For example, "C4+ hydrocarbons"
include C4, C5
and higher carbon number hydrocarbons.
[0020] "Equivalent water" is defined as the sum total oxygen in a stream
present as
oxygenates and water, expressed as water.
[0021] Other objects and advantages will be apparent to those skilled in the
art from the
following detailed description taken in conjunction with the appended claims
and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. I is a simplified schematic diagram of an integrated oxygenate
conversion
and olefin cracking process in accordance with one preferred embodiment.
[0023] FIG. 2 is a simplified schematic diagram of an integrated oxygenate
conversion
and olefin cracking process in accordance with another preferred embodiment.
[0024] FIG. 3 is a simplified schematic diagram of an integrated oxygenate
conversion
and olefin cracking process in accordance with yet another preferred
embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0025] As described above, oxygenate conversion processing to produce olefins
can
advantageously be integrated with olefin cracking processing to result in
increased relative
amounts of light olefin products through either or both reducing the water
content and/or
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reducing the oxygenate content of the feed to the olefin cracking zone. Such
processing may
be embodied in a variety of processing arrangements. As representative, FIG. I
illustrates a
simplified schematic process flow diagram for a process scheme, generally
designated by the
reference numeral 310, for the conversion of oxygenates to olefins and
integrated with
product olefin cracking for increased light olefin production in accordance
with one preferred
embodiment.
[0026] More particularly, in the process scheme 310, an oxygenate-containing
feedstock
or feedstream 312 such as generally composed of light oxygenates such as one
or more of
methanol, ethanol, dimethyl ether, diethyl ether, or mixtures thereof, is
introduced into an
oxygenate conversion zone or reactor section 314 wherein the oxygenate-
containing
feedstock contacts with an oxygenate conversion catalyst at reaction
conditions effective to
convert the oxygenate-containing feedstock and to form an oxygenate conversion
effluent
stream comprising fuel gas hydrocarbons, light olefins, and C4+ hydrocarbons,
in a manner as
is known in the art, such as, for example, utilizing a fluidized bed reactor.
[0027] As will be appreciated by those skilled in the art and guided by the
teachings
herein provided, such a feedstock may be commercial grade methanol, crude
methanol or any
combination thereof. Crude methanol may be an unrefined product from a
methanol synthesis
unit. Those skilled in that art and guided by the teachings herein provided
will understand and
appreciate that in the interest of factors such as improved catalyst
stability, embodiments
utilizing higher purity methanol feeds may be preferred. Thus, suitable feeds
in such
embodiments may comprise methanol or a methanol and water blend, with possible
such
feeds having a methanol content of between 65% and 100% by weight, preferably
a methanol
content of between 80% and 100% by weight and, in accordance one preferred
embodiment,
a methanol content of between 95% and 100% by weight.
[0028] A methanol-to-olefin unit feedstream may comprise between 0 and 35 wt-%
and
more preferably between 5 and 30 wt-% water. The methanol in the feedstream
may
comprise between 70 and 100 wt-% and more preferably between 75 and 95 wt-% of
the
feedstream. The ethanol in the feedstream may comprise between 0.01 and 0.5 wt-
% and
more typically between 0.1 and 0.2 wt-% of the feedstream although higher
concentrations
may be beneficial. When methanol is the primary component in the feedstream,
the higher
alcohols in the feedstream may comprise between 200 and 2000 wppm and more
typically
between 500 and 1500 wppm. Additionally, when methanol is the primary
component in the
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feedstream, dimethyl ether in the feedstream may comprise between 100 and
20,000 wppm
and more typically between 200 and 10,000 wppm.
[0029] The invention, however, also contemplates and encompasses embodiments
wherein the oxygenate-containing feedstock is primarily dimethyl ether and, in
certain
embodiments, the oxygenate-containing feedstock is essentially dimethyl ether,
either alone
or with no more than insubstantial amounts of other oxygenate materials.
[0030] Reaction conditions for the conversion of oxygenates to light olefins
are known to
those skilled in the art. Preferably, in accordance with particular
embodiments, reaction
conditions comprise a temperature between 200 and 700 C, more preferably
between 300
and 600 C, and most preferably between 400 and 550 C. As will be appreciated
by those
skilled in the art and guided by the teachings herein provided, the reactions
conditions are
generally variable such as dependent on the desired products. The light
olefins produced can
have a ratio of ethylene to propylene of between 0.5 and 2.0 and preferably
between 0.75 and
1.25. If a higher ratio of ethylene to propylene is desired, then the reaction
temperature is
generally desirably higher than if a lower ratio of ethylene to propylene is
desired. In
accordance with one preferred embodiment, a feed temperature range between 120
and
210 C is preferred. In accordance with another preferred embodiment a feed
temperature
range of between 180 and 210 C is preferred. In accordance with one preferred
embodiment,
the temperature is desirably maintained below 210 C to avoid or minimize
thermal
decomposition.
[0031] As described above, the oxygenate conversion reactor section 314
produces or
results in an oxygenate conversion product or effluent stream 316 such as
generally
comprising hydrocarbon product materials such as fuel gas hydrocarbons, light
olefins, and
C4+ hydrocarbons; by-product water; and remaining oxygenates such as methanol,
dimethyl
ether (DME) and other trace oxygenates including carbonyls such as
acetaldehyde. The
oxygenate conversion effluent stream 316 is passed to a hydrocarbon recovery
system such as
includes an effluent treatment zone 320 such as results in at least a
compressed oxygenate
conversion effluent vapor stream 322, an oxygenate conversion effluent liquid
stream 323, a
heavily laden water stream 394 containing heavy oxygenates and other heavy
hydrocarbons,
a relatively clean water stream 396 and a stream of circulated water 324. In
practice, such a
compressed oxygenate conversion effluent stream 322 may be the result of one
or more
compressor stages. Further, the stream of circulated water 324 may include
water from one or
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more interstage condensations as well as water from various product recovery
units or zones
including, for example, wash water columns and the like.
[0032] In practice, C4+ hydrocarbons, water and residual oxygenates will
typically be
present in both the oxygenate conversion effluent vapor stream 322 and the
oxygenate
conversion effluent liquid stream 323.
[0033] The compressed oxygenate conversion effluent stream 322 or at least a
portion
thereof, is introduced into an oxygenate absorber zone 326, such as in the
form of at least one
absorber column. In the oxygenate absorber zone 326, at least a portion of
oxygenates such as
methanol, dimethyl ether (DME) and other trace oxygenates including carbonyls
such as
acetaldehyde such as may be present therein can be absorbed in circulated
water, such as here
represented by the flow stream 328, and thus are separated from the
hydrocarbon product
materials.
[0034] The oxygenate absorber zone 326 forms or results in an oxygenate-rich
water
stream 336 such as comprises such oxygenate materials in water and a stream
340 such as
comprises such hydrocarbon product materials. As discussed in greater detail
below, the
hydrocarbon product material stream 340 may additionally contain some residual
amounts of
oxygenates.
[0035] The hydrocarbon product material stream 340, if desired, can be further
processed
such as by being introduced into a caustic scrubber zone 344 and appropriately
treated, such
as by being conventionally washed with a caustic solution, such as introduced
through the
line 346 to neutralize acid gases, and dried forming a purge stream 347 and a
treated stream
348.
[0036] The treated stream 348 can then be appropriately introduced into a
desired gas
concentration and product recovery system 350. Gas concentration and product
recovery
systems such as used for the processing of the effluent resulting from such
oxygenate
conversion processing are well known to those skilled in the art and do not
generally form
limitations on the broader practice of the invention as those skilled in the
art and guided by
the teachings herein provided will appreciate.
[0037] In the gas concentration and product recovery system 350, the remaining
hydrocarbon product material can be processed such as to form desired
hydrocarbon fraction
streams. For example, the gas concentration and product recovery system 350
may desirably
form a fuel gas stream 352, an ethylene stream 354, a propylene stream 356 and
a mixed C4+
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hydrocarbon stream 358, such as generally composed of butylene and heavier
hydrocarbons,
and may additionally contain some trace or small amounts of oxygenates.
[0038] The oxygenate conversion effluent liquid stream 323 or at least a
portion thereof
can be further processed such as being passed to a wash zone 362 such as
comprising at least
one wash column wherein the oxygenate conversion effluent liquid stream 323
can be
appropriately treated such as via countercurrent contact with a wash fluid of
recycle water
364, to form an appropriately washed stream 366 and a resulting recycle water
stream 368.
[0039] In the embodiment shown in FIG. 1, the mixed C4+ hydrocarbon stream 358
and
the washed stream 366 are combined to form a stream 374 that is introduced
into a treatment
zone, designated by the reference numeral 376. In accordance with a preferred
embodiment
and as described in greater detail below, in the treatment zone 376, the
combined C4+
hydrocarbon fraction stream 374 is treated to form a treated C4+ hydrocarbon
fraction stream
380 containing oxygenates in an appropriately reduced or minimized relative
amount.
[0040] In the treatment zone 376, the process scheme 310 treats the combined
feed
stream 374 with wash fluid of preferably a sulfite-containing material such as
introduced into
the treatment zone 376 as shown by the line 382 from a sulfite-containing
reservoir 384
added to in order to form the treated C4+ hydrocarbon fraction stream 380
containing
oxygenates in an appropriately reduced or minimized relative amount.
[0041] As used herein, references to a "sulfite-containing material" are to be
understood
to include sulfite compounds, bisulfite compounds and mixtures thereof. Sodium
bisulfite is
an example of one preferred "sulfite-containing material" for use in practice
of such aspect of
the invention.
[0042] The effective treatment of such C4+ containing feed streams with such a
sulfite-containing material in accordance with one preferred embodiment can be
realized by
washing or otherwise effectively treating the combined stream 374 with a
solution of a sulfite
compound comprising an alkali metal or an alkaline earth metal cation in an
element such as
a sulfite wash column. Examples of suitable such cation materials include
sodium, potassium,
magnesium and calcium.
[0043] If desired or required, the treated C4+ hydrocarbon fraction stream
380, in whole
or in part, can then be introduced into a drier section 370 wherein such
stream materials can
be appropriately dried, such as in a manner known in the art, to remove or
otherwise
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effectively reduce the water or moisture content thereof and such as to form a
dried treated
C4+ hydrocarbon fraction stream 372.
[0044] At least a portion of the dried treated C4+ hydrocarbon fraction stream
372 is
subsequently appropriately introduced into an olefin cracking reactor section
386 wherein the
at least a portion of the process stream 372 contacts with an olefin cracking
catalyst and at
reaction conditions, in a manner as is known in the art, effective to convert
C4 and C5 olefins
therein contained to a cracked olefins effluent stream 388 comprising light
olefins.
[0045] In accordance with a preferred embodiment, it is desirable that the
feed to such an
olefin cracking reactor preferably contain oxygenates in a relative amount of
less than 800
ppmw equivalent water. In certain, more preferred embodiments, it is desirable
that the feed
to such an olefin cracking reactor preferably contain oxygenates in a relative
amount of less
than 600 ppmw equivalent water. In certain, even more preferred embodiments,
it is desirable
that the feed to such an olefin cracking reactor preferably contain oxygenates
in a relative
amount of less than 200 ppmw equivalent water.
[0046] If desired, the cracked olefins effluent stream 388 or selected
portions thereof can
subsequently be appropriately processed in manner known in the art or as will
be recognized
by those skilled in the art and guided by the teaching herein provided. For
example, the
cracked olefins effluent stream 388 or selected portions thereof can
subsequently be
appropriately processed through one or more cooler sections to appropriately
cool the stream
contents, one or more product separation sections to appropriately separate
product materials
therein contained and/or one or more product recovery sections to permit
appropriate
recovery of selected products therefrom. In one preferred embodiment, such
subsequent
processing involves processing of the cracked olefins effluent stream 388 or
selected portions
thereof through the hydrocarbon recovery section 318 or at least selected
portions thereof,
e.g., the gas concentration and product recovery system 350.
[0047] Those skilled in the art and guided by the teachings herein provided,
as an
alternative to such sulfite treatment for oxygenate content reduction or
minimization, may
consider modification of the design or operation of the water wash column of
the wash zone
362. More specifically, by appropriately increasing the water flow rate and
the number of
stages in such a water wash column, the remaining oxygenate content in the
resulting treated
stream can be appropriately reduced.
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[0048] The washed stream can then be introduced into a drier section 370
wherein the
washed stream can be appropriately dried, such as in a manner known in the
art, to remove or
otherwise effectively reduce the water or moisture content thereof and such as
to form the
dried stream 372. For example, the washed materials can be routed to a
depropanizer column
or other suitable drying column to effect the desired removal of water.
Alternatively, a feed
drier and an oxygenate recovery unit (ORU), such as known in the art, may be
employed.
[0049] Those skilled in the art and guided by the teachings herein provided
will generally
understand and appreciate that in the absence of such water wash column
modification, such
oxygenate conversion and subsequent product processing will typically result
in the bulk of
the oxygenates being present in the process stream resulting from the wash
zone, e.g., in the
water wash column overhead stream. Thus, FIG. 2 illustrates a simplified
schematic process
flow diagram for a process scheme, generally designated by the reference
numeral 410, for
the conversion of oxygenates to olefins and integrated with product olefin
cracking for
increased light olefin production in accordance with another preferred
embodiment and
wherein the process stream resulting from a wash zone, as described above, is
alone treated
with sulfite-containing material to effect the desired reduction or
minimization of oxygenate
content.
[0050] The process scheme 410 is in general respects similar to the process
scheme 310
described above. For example, in the process scheme 410, an oxygenate-
containing feedstock
or feedstream 412, such as described above, is introduced into an oxygenate
conversion zone
or reactor section 414 wherein the oxygenate-containing feedstock contacts
with an
oxygenate conversion catalyst at reaction conditions effective to convert the
oxygenate-
containing feedstock and to form an oxygenate conversion effluent stream
comprising fuel
gas hydrocarbons, light olefins, and C4+ hydrocarbons, in a manner as is known
in the art,
such as, for example, utilizing a fluidized bed reactor.
[0051] As described above, the oxygenate conversion reactor section 414
produces or
results in an oxygenate conversion product or effluent stream 416 such as
generally
comprising hydrocarbon product materials such as fuel gas hydrocarbons, light
olefins, and
C4+ hydrocarbons; by-product water; and remaining oxygenates such as methanol,
dimethyl
ether (DME) and other trace oxygenates including carbonyls such as
acetaldehyde. The
oxygenate conversion effluent stream 416 is passed to a hydrocarbon recovery
system such as
includes an effluent treatment zone 420 such as results in at least a
compressed oxygenate
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conversion effluent vapor stream 422, an oxygenate conversion effluent liquid
stream 423, a
heavily laden water stream 494 containing heavy oxygenates and other heavy
hydrocarbons,
a relatively clean water stream 496 and a stream of circulated water 424.
[0052] As identified above, C4+ hydrocarbons, water and residual oxygenates
will
typically be present in both the oxygenate conversion effluent vapor stream
422 and the
oxygenate conversion effluent liquid stream 423.
[0053] As in the above-described embodiment, the compressed oxygenate
conversion
effluent stream 422 or at least a portion thereof, is introduced into an
oxygenate absorber
zone 426, such as in the form of at least one absorber column. As in the above-
described
embodiment, in the oxygenate absorber zone 426, at least a portion of
oxygenates such as
methanol, dimethyl ether (DME) and other trace oxygenates including carbonyls
such as
acetaldehyde such as may be present therein can be absorbed in circulated
water, here
designated and represented by the flow stream 428, and thus are separated from
the
hydrocarbon product materials
[0054] As described above, the oxygenate absorber zone 426 forms or results in
an
oxygenate-rich water stream 436 such as comprises such oxygenate materials in
water and a
stream 440 such as comprises such hydrocarbon product materials.
[0055] The hydrocarbon product material stream 440, if desired and as
described above,
can be further processed such as by being introduced into a caustic scrubber
zone 444 and
appropriately treated, such as by being conventionally washed with a caustic
solution, such as
provided via a line 446, to neutralize acid gases and appropriately dried,
forming a purge
stream 447 and a treated stream 448.
[0056] The treated stream 448 can then be appropriately introduced into a
desired gas
concentration and product recovery system 450 such as described above such as
to form
desired hydrocarbon fraction streams. For example, the gas concentration and
product
recovery system 450 may desirably form a fuel gas stream 452, an ethylene
stream 454, a
propylene stream 456 and a mixed C4+ hydrocarbon stream 458, such as generally
composed
of butylene and heavier hydrocarbons.
[0057] The oxygenate conversion effluent liquid stream 423 or at least a
portion thereof
can be further processed such as being passed to a wash zone 462 such as
comprising at least
one wash column wherein the oxygenate conversion effluent liquid stream 423
can be
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appropriately treated such as via countercurrent contact with a wash fluid of
recycle water
464, to form an appropriately washed stream 466 and a resulting recycle water
stream 468.
[0058] As identified above, between such a mixed C4+ hydrocarbon stream 458
and such
a washed stream 466, the vast bulk of the oxygenates will typically be present
in the washed
stream 466, this embodiment introduces such hydrocarbon-containing stream into
a treatment
zone 476, for treatment with a sulfite-containing material, such as described
above,
introduced into the treatment zone 476 as shown by the line 482 from a sulfite-
containing
reservoir 484 added to in order to form the treated C4+ hydrocarbon fraction
stream 477
containing oxygenates in an appropriately reduced or minimized relative
amount.
[0059] At least a portion of the treated C4+ hydrocarbon fraction stream 477
can
subsequently be appropriately combined with the mixed C4+ hydrocarbon stream
458 such as
to form a combined stream 478 having an appropriately reduced oxygenate
content. Such a
combined stream 478 or portion thereof can then be introduced into a drier
section 470
wherein such stream materials can be appropriately dried, such as in a manner
known in the
art, to remove or otherwise effectively reduce the water or moisture content
thereof and such
as to form a dried stream 472.
[0060] At least a portion of the dried process stream 472 is then introduced
into an olefin
cracking reactor section 486 wherein the at least a portion of the process
stream 472 contacts
with an olefin cracking catalyst and at reaction conditions, in a manner as is
known in the art,
effective to convert C4 and C5 olefins therein contained to a cracked olefins
effluent stream
488 comprising light olefins and such as may be appropriately processed as
desired.
[0061] As described above, in accordance with a preferred embodiment, it is
desirable
that the feed to such an olefin cracking reactor preferably contain oxygenates
in a relative
amount of less than 800 ppmw equivalent water, more preferably, in a relative
amount of less
than 600 ppmw equivalent water and, in accordance with certain embodiments, in
a relative
amount of less than 200 ppmw equivalent water.
[0062] While the embodiment of FIG. 2 has been described making specific
reference to
an embodiment wherein the drier section 470 acts on the combined stream 478 or
portion
thereof, those skilled in the art and guided by the teachings herein provided
will appreciate
that if desired or preferred, such a drier section may alternatively be
appropriately disposed
such as to act on, e.g., dry, the treated C4+ hydrocarbon fraction stream 477
prior to
combination, in whole or in part, with the mixed C4+ hydrocarbon stream 458.
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[0063] Now making reference to FIG. 3, there is illustrated a simplified
schematic
process flow diagram for a process scheme, generally designated by the
reference numeral
510, for the conversion of oxygenates to olefins and integrated with product
olefin cracking
for increased light olefin production in accordance with yet another preferred
embodiment.
[0064] The process scheme 510 is similar to the scheme 310 described above in
that an
oxygenate-containing feedstock or feedstream 512, such as described above, is
introduced
into an oxygenate conversion zone or reactor section 514 wherein the oxygenate-
containing
feedstock contacts with an oxygenate conversion catalyst at reaction
conditions effective to
convert the oxygenate-containing feedstock and to form an oxygenate conversion
effluent
stream comprising fuel gas hydrocarbons, light olefins, and C4+ hydrocarbons,
in a manner as
is known in the art.
[0065] As described above, the oxygenate conversion reactor section 514
produces or
results in an oxygenate conversion product or effluent stream 516 such as
generally
comprising hydrocarbon product materials such as fuel gas hydrocarbons, light
olefins, and
C4+ hydrocarbons; by-product water; and remaining oxygenates such as methanol,
dimethyl
ether (DME) and other trace oxygenates including carbonyls such as
acetaldehyde. The
oxygenate conversion effluent stream 516 is passed to a hydrocarbon recovery
system such as
includes an effluent treatment zone 520 such as results in at least a
compressed oxygenate
conversion effluent vapor stream 522, an oxygenate conversion effluent liquid
stream 523, a
heavily laden water stream 594 containing heavy oxygenates and other heavy
hydrocarbons,
a relatively clean water stream 596 and a stream of circulated water 524.
[0066] As in the above-described embodiment, the compressed oxygenate
conversion
effluent stream 522 or at least a portion thereof, is introduced into an
oxygenate absorber
zone 526, such as in the form of at least one absorber column. In the
oxygenate absorber zone
526, at least a portion of oxygenates such as methanol, dimethyl ether (DME)
and other trace
oxygenates including carbonyls such as acetaldehyde such as may be present
therein can be
absorbed in circulated water, such as here represented by the flow stream 528,
and thus are
separated from the hydrocarbon product materials.
[0067] The oxygenate absorber zone 526 forms or results in an oxygenate-rich
water
stream 536 such as comprises such oxygenate materials in water and a stream
540 such as
comprises such hydrocarbon product materials. The hydrocarbon product material
stream 540
may additionally contain some residual amounts of oxygenates.
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[0068] The hydrocarbon product material stream 540, if desired and as
described above,
can be further processed such as by being introduced into a caustic scrubber
zone 544 and
appropriately treated, such as by being conventionally washed with a caustic
solution, such as
introduced through the line 546 to neutralize acid gases, and dried forming a
purge stream
547 and a treated stream 548.
[0069] The treated stream 548 can then be appropriately introduced into a
desired gas
concentration and product recovery system 550 such as to form desired
hydrocarbon fraction
streams, e.g., a fuel gas stream 552, an ethylene stream 554, a propylene
stream 556 and a
mixed C4+ hydrocarbon stream 558, such as generally composed of butylene and
heavier
hydrocarbons, and may additionally contain some trace or small amounts of
oxygenates.
[0070] The oxygenate conversion effluent liquid stream 523 or at least a
portion thereof
can be further processed such as being passed to a wash zone 562 such as
comprising at least
one wash column wherein the oxygenate conversion effluent liquid stream 523
can be
appropriately treated such as via countercurrent contact with a wash fluid of
recycle water
564, to form an appropriately washed stream 566 and a resulting recycle water
stream 568.
[0071] In the embodiment shown in FIG. 3, the mixed C4+ hydrocarbon stream 558
and
the washed stream 566 are combined to form a stream 574 that is introduced
into an
appropriate fractionation zone 577 such as in the form of a debutanizer
column. The
fractionation zone 577 forms or produces a first stream 579, such as in the
form of a bottoms
stream from such a fractionation zone debutanizer column, and having a high
concentration
of heavier oxygenates and a second stream 581, such as in the form of an
overhead stream
from such a fractionation zone debutanizer column, having a high concentration
of lighter
oxygenates (methanol and DME, for example).
[0072] The heavier oxygenates concentrated in the stream 579 can
advantageously be
processed through a sulfite treatment zone 576 wherein the materials are
treated with a
sulfite-containing material, such as described above, such as introduced into
the treatment
zone 576 as shown by the line 582 from a sulfite-containing reservoir 584 such
as to form a
treated stream 583.
[0073] If desired or required, the treated stream 583, in whole or in part,
can then be
introduced into a drier section 570 wherein the treated stream can be
appropriately dried,
such as in a manner known in the art, to remove or otherwise effectively
reduce the water or
moisture content thereof and such as to form a dried treated stream 572.
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[0074] The lighter oxygenates concentrated in the stream 581 can be processed
through
an oxygenate recovery unit (ORU), such as is known in the art and here
designated by the
reference numeral 585 and appropriately dried to form a treated stream 587.
[0075] The treated stream 583 and the dried treated stream 572, either
separately or
together as shown as a stream 589 having an appropriately low oxygenate
content can be
introduced into an olefin cracking reactor section 586 wherein the at least a
portion of the
process stream 589 contacts with an olefin cracking catalyst and at reaction
conditions, in a
manner as is known in the art, effective to convert C4 and C5 olefins therein
contained to a
cracked olefins effluent stream 588 comprising light olefins.
[0076] In such embodiment, the concentrating of the heavier oxygenates in to
C5+
material can desirably serve to reduce or minimize the size of the required
sulfite wash unit
and the material flow rates therethrough.
[0077] Those skilled in the art and guided by the teaching herein provided
will appreciate
that through the appropriate pretreatment of olefin cracking feeds produced or
resulting from
oxygenate conversion processing, such as described above, excessive loss of
olefin cracking
catalyst activity and frequency of replacement can be desirably appropriately
avoided or
minimized.
[0078] The invention illustratively disclosed herein suitably may be practiced
in the
absence of any element, part, step, component, or ingredient which is not
specifically
disclosed herein.
[0079] In the foregoing detailed description, this invention has been
described in
relation to certain preferred embodiments thereof, and many details have been
set forth
for purposes of illustration. The scope of the claims should not be limited by
the
preferred embodiments set forth in the examples, but should be given the
broadest
interpretation consistent with the description as a whole.
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