U.S. patent application number 13/774723 was filed with the patent office on 2013-07-04 for propylene production process.
This patent application is currently assigned to Equistar Chemicals, LP. The applicant listed for this patent is Robert S. Bridges, Lawrence M. Candela, Steven T. Coleman, Gary A. Sawyer, Shaotian Wang. Invention is credited to Robert S. Bridges, Lawrence M. Candela, Steven T. Coleman, Gary A. Sawyer, Shaotian Wang.
Application Number | 20130172647 13/774723 |
Document ID | / |
Family ID | 44925675 |
Filed Date | 2013-07-04 |
United States Patent
Application |
20130172647 |
Kind Code |
A1 |
Coleman; Steven T. ; et
al. |
July 4, 2013 |
PROPYLENE PRODUCTION PROCESS
Abstract
Processes and systems for forming propylene are described
herein. The processes generally include reacting a metathesis feed
stream including at least 95 wt. % 2-butene with ethylene in the
presence of a metathesis catalyst to form a metathesis product
stream including propylene, and recovering propylene from the
process.
Inventors: |
Coleman; Steven T.; (Humble,
TX) ; Sawyer; Gary A.; (Media, PA) ; Bridges;
Robert S.; (Friendswood, TX) ; Wang; Shaotian;
(Downingtown, PA) ; Candela; Lawrence M.;
(Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Coleman; Steven T.
Sawyer; Gary A.
Bridges; Robert S.
Wang; Shaotian
Candela; Lawrence M. |
Humble
Media
Friendswood
Downingtown
Houston |
TX
PA
TX
PA
TX |
US
US
US
US
US |
|
|
Assignee: |
Equistar Chemicals, LP
Houston
TX
Lyondell Chemical Technology, L.P.
Houston
TX
|
Family ID: |
44925675 |
Appl. No.: |
13/774723 |
Filed: |
February 22, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12903794 |
Oct 13, 2010 |
8395005 |
|
|
13774723 |
|
|
|
|
61762427 |
Feb 8, 2013 |
|
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Current U.S.
Class: |
585/329 ;
585/644 |
Current CPC
Class: |
C07C 2523/30 20130101;
C07C 5/2512 20130101; C07C 2531/14 20130101; Y02P 20/52 20151101;
C07C 5/2512 20130101; C07C 2/36 20130101; C07C 2521/08 20130101;
C07C 2/36 20130101; C07C 2531/24 20130101; C07C 6/04 20130101; C07C
6/04 20130101; C07C 11/08 20130101; C07C 2521/10 20130101; C07C
11/08 20130101; C07C 11/06 20130101; C07C 11/06 20130101; C07C
11/08 20130101 |
Class at
Publication: |
585/329 ;
585/644 |
International
Class: |
C07C 6/04 20060101
C07C006/04 |
Claims
1. A process for forming propylene comprising: separating a butene
feed stream in a butene fractionation system that, in operation,
separates 1-butene from 2-butene; recovering 2-butene from the
butene fractionation system and utilizing the 2-butene to form a
metathesis feed stream comprising at least 95 wt. % 2-butene;
reacting the metathesis feed stream with ethylene in the presence
of a metathesis catalyst to form a metathesis product stream
comprising the propylene; and recovering the propylene from the
process.
2. The process of claim 1, wherein the metathesis feed stream
reacts with the ethylene in the absence of an amount of
isomerization catalyst sufficient to isomerize butene.
3. The process of claim 1, wherein the metathesis feed stream
reacts with the ethylene in the absence of an isomerization
catalyst.
4. The process of claim 1, wherein the metathesis feed stream
consists essentially of 2-butene.
5. The process of claim 1, wherein the metathesis feed stream
comprises at least 98 wt. % 2-butene.
6. The process of claim 1, wherein the metathesis feed stream
comprises a molar ratio of 2-butene:1-butene of at least 49:1.
7. The process of claim 1, wherein the metathesis feed stream
comprises less than 5 wt. % 1-butene.
8. The process of claim 1 further comprising: contacting a first
feed stream comprising ethylene with a dimerization catalyst to
form a dimerization product stream comprising 2-butene, wherein the
butene feed stream comprises the dimerization product stream.
9. The process of claim 8, wherein the dimerization catalyst is
selected from metal oxides, nickel complexes, aluminum complexes
and combinations thereof.
10. The process of claim 1, wherein the metathesis catalyst
comprises a transition metal oxide.
11. The process of claim 1, wherein the metathesis catalyst
comprises tungsten oxide.
12. The process of claim 1, wherein the metathesis product stream
comprises less than 1 mol. % pentene.
13. The process of claim 1, wherein the metathesis product stream
further comprises C.sub.2 to C.sub.6 olefins and wherein recovering
the propylene comprises fractionating within a propylene
fractionation system the metathesis product stream to form a
propylene product stream, at least one recycle stream comprising
olefins selected from butene, ethylene and combinations thereof,
and a bottoms stream comprising olefins selected from C.sub.5
olefins, C.sub.6+ olefins and combinations thereof.
14. The process of claim 13 further comprising passing the recycle
stream from the propylene fractionation system to the metathesis
reaction without passing through an isomerization reaction.
15. The process of claim 13, wherein the propylene fractionation
system comprises: a first stage that, in operation, separates
ethylene from other components present in the metathesis product
stream to form a de-ethenized product stream; and a second stage
that, in operation, separates propylene from C4 and heavier olefins
in the de-ethenized product stream.
16. The process of claim 1, wherein the process produces at least
100 MM lbs/yr of propylene.
17. The process of claim 1, wherein the metathesis reaction
exhibits a propylene selectivity of at least 95%.
18. A process for forming propylene comprising: reacting a first
feed stream comprising ethylene with a dimerization catalyst to
form a dimerization product stream; fractionating the dimerization
product stream to form a 2-butene stream; reacting the 2-butene
stream with ethylene in the presence of a metathesis catalyst to
form a metathesis product stream comprising the propylene, wherein
the 2-butene stream reacts with the ethylene in the absence of an
amount of isomerization catalyst sufficient to isomerize butene;
and recovering the propylene from the process, wherein the process
produces at least 100 MM lbs/yr of the propylene.
19. The process of claim 18, wherein the metathesis reaction
exhibits a propylene selectivity of at least 95%.
20. The process of claim 18, wherein the metathesis catalyst
comprises a transition metal oxide.
21. The process of claim 18, wherein the metathesis product stream
comprises less than 1 mol. % pentene.
22. The process of claim 18, wherein the metathesis feed stream
consists essentially of 2-butene.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of and priority of U.S.
Provisional Application No. 61/762,427 filed on Feb. 8, 2013, and
is a continuation-in-part of and claims benefit of U.S.
Non-Provisional application Ser. No. 12/903,794 filed on Oct. 13,
2010, all of which are incorporated herein by reference in their
entirety.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention generally relates to methods and
systems of forming propylene.
[0004] 2. Related Art
[0005] This section introduces information from the art that may be
related to or provide context for some aspects of the technique
described herein and/or claimed below. This information is
background facilitating a better understanding of that which is
disclosed herein. This is a discussion of "related" art. That such
art is related in no way implies that it is also "prior" art. The
related art may or may not be prior art. The discussion is to be
read in this light, and not as admissions of prior art.
[0006] Metathesis reactions to produce propylene generally include
feeding a metathesis feed stream comprising butene, generally a
mixture of 1-butene and 2-butene, to a metathesis reactor loaded
with a mixture of metathesis catalyst and an isomerization
catalyst. Such process provide for efficiencies by utilizing a
single process for the production of propylene from available
feedstocks. However, reaction of 1-butene can cause side reactions,
forming undesirable by-products, such as pentene and hexene, for
example.
[0007] The present invention is directed to resolving, or at least
reducing, one or all of the problems mentioned above.
SUMMARY
[0008] Various embodiments of the present invention include
processes of forming propylene. The processes generally include
separating a butene feed stream in a butene fractionation system
that, in operation, separates 1-butene from 2-butene; recovering
2-butene from the butene fractionation system and utilizing the
2-butene to form a metathesis feed stream including at least 95 wt.
% 2-butene; reacting the metathesis feed stream with ethylene in
the presence of a metathesis catalyst to form a metathesis product
stream including propylene; and recovering propylene from the
process.
[0009] One or more embodiments include the process of the preceding
paragraph, wherein the metathesis feed stream reacts with the
ethylene in the absence of an amount of isomerization catalyst
sufficient to isomerize butene.
[0010] One or more embodiments include the process of the preceding
paragraph, wherein the metathesis feed stream reacts with the
ethylene in the absence of an isomerization catalyst.
[0011] One or more embodiments include the process of the preceding
paragraph, wherein the metathesis feed stream is formed essentially
of 2-butene.
[0012] One or more embodiments include the process of any preceding
paragraph, wherein the metathesis feed stream includes at east 98
wt. % 2-butene.
[0013] One or more embodiments include the process of any preceding
paragraph, wherein the metathesis feed stream includes a molar
ratio of 2-butene:1-butene of at least 49:1.
[0014] One or more embodiments include the process of any preceding
paragraph, wherein the metathesis feed stream includes less than 5
wt. % 1-butene.
[0015] One or more embodiments include the process of any preceding
paragraph further including contacting a first feed stream
including ethylene with a dimerization catalyst to form a
dimerization product stream including 2-butene, wherein the butene
feed stream includes the dimerization product stream.
[0016] One or more embodiments include the process of any preceding
paragraph, wherein the dimerization catalyst is selected from metal
oxides, nickel complexes, aluminum complexes and combinations
thereof.
[0017] One or more embodiments include the process of any preceding
paragraph, wherein the metathesis catalyst includes a transition
metal oxide.
[0018] One or more embodiments include the process of any preceding
paragraph, wherein the metathesis catalyst includes tungsten
oxide.
[0019] One or more embodiments include the process of any preceding
paragraph, wherein the metathesis product stream includes less than
1 mol. % pentene.
[0020] One or more embodiments include the process of any preceding
paragraph, wherein the metathesis product stream further includes
C.sub.2 to C.sub.6 olefins and wherein recovering the propylene
includes fractionating within a propylene fractionation system the
metathesis product stream to form a propylene stream, a recycle
stream including olefins selected from butene, ethylene and
combinations thereof, and optionally a bottoms stream including
olefins selected from C.sub.5 olefins, C.sub.6+ olefins and
combinations thereof.
[0021] One or more embodiments include the process of the preceding
paragraph further including passing the recycle stream from the
propylene fractionation system to the metathesis reaction without
passing the recycle stream through an isomerization reaction.
[0022] One or more embodiments include the process of the preceding
paragraph, wherein the propylene fractionation system includes a
first stage that, in operation, separates ethylene from other
components present in the metathesis product stream to form a
de-ethenized product stream; and a second stage that, in operation,
separates propylene from C.sub.4 and heavier olefins in the
de-ethenized product stream.
[0023] One or more embodiments include the process of any preceding
paragraph, wherein the process produces at least 100 MM lbs/yr of
propylene.
[0024] One or more embodiments include the process of any preceding
paragraph, wherein the metathesis reaction exhibits a propylene
selectivity of at least 95%, wherein "propylene selectivity" is
defined as the propylene production divided by the propylene plus
C.sub.5 and heavier olefins produced in the metathesis reaction,
expressed as a percentage.
[0025] One or more embodiments include a process for forming
propylene including reacting a first feed stream including ethylene
with a dimerization catalyst to form a dimerization product stream;
fractionating the dimerization product stream to form a 2-butene
stream; reacting the 2-butene stream with ethylene in the presence
of a metathesis catalyst to form a metathesis product stream
including propylene, wherein the 2-butene stream reacts with the
ethylene in the absence of an amount of isomerization catalyst
sufficient to isomerize butene; and recovering propylene from the
process, wherein the process produces at least 100 MM lbs/yr of
propylene.
[0026] The above paragraphs present a simplified summary of the
presently disclosed subject matter in order to provide a basic
understanding of some aspects thereof. The summary is not an
exhaustive overview, nor is it intended to identify key or critical
elements to delineate the scope of the subject matter claimed
below. Its sole purpose is to present some concepts in a simplified
form as a prelude to the more detailed description set forth
below.
BRIEF DESCRIPTION OF DRAWINGS
[0027] The claimed subject matter may be understood by reference to
the following description taken in conjunction with the
accompanying drawings, in which like reference numerals identify
like elements, and in which:
[0028] FIG. 1 illustrates a simplified process flow diagram for
various embodiments described herein.
[0029] FIG. 2 illustrates a specific embodiment of a propylene
production process.
[0030] FIG. 3 illustrates an alternative embodiment of a propylene
production process.
[0031] While the invention is susceptible to various modifications
and alternative forms, the drawings illustrate specific embodiments
herein described in detail by way of example. It should be
understood, however, that the description herein of specific
embodiments is not intended to limit the invention to the
particular forms disclosed, but on the contrary, the intention is
to cover all modifications, equivalents, and alternatives falling
within the spirit and scope of the invention as defined by the
appended claims.
DETAILED DESCRIPTION
[0032] Illustrative embodiments of the subject matter claimed below
will now be disclosed. In the interest of clarity, not all features
of an actual implementation are described in this specification. It
will be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions must be made
to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort, even if complex and
time-consuming, would be a routine undertaking for those of
ordinary skill in the art having the benefit of this
disclosure.
[0033] In the description below, unless otherwise specified, all
compounds described herein may be substituted or unsubstituted and
the listing of compounds includes derivatives thereof. Further,
various ranges and/or numerical limitations may be expressly stated
below. It should be recognized that unless stated otherwise, it is
intended that endpoints are to be interchangeable. Further, any
ranges include iterative ranges of like magnitude falling within
the expressly stated ranges or limitations.
[0034] Processes for forming propylene are described herein. The
processes generally include reacting a metathesis feed stream
including 2-butene with ethylene in the presence of a metathesis
catalyst to form a metathesis product stream including
propylene.
[0035] In one or more specific embodiments, the metathesis feed
stream may be formed by contacting a first feed stream including
ethylene with a dimerization catalyst to form a dimerization
product stream including 2-butene. As used herein, the term
"dimerization" refers to a chemical reaction in which two identical
molecular entities react to form a single dimer. In the present
embodiments, the identical molecular entities are generally
ethylene, while the dimer is generally butene.
[0036] The dimerization catalyst may include catalyst known in the
art to be capable of converting ethylene to linear C.sub.4 olefins
(i.e., n-butene) upon reaction. For example, dimerization catalysts
may include homogenous catalyst compounds including nickel. Many
catalysts containing nickel are known to dimerize ethylene to
butenes (e.g., U.S. Letters Pat. No. 4,528,415, U.S. Letters Pat.
No. 3,513,218 and U.S. Letters Pat. No. 3,452,115).
[0037] Alternatively, the dimerization catalyst may include an
organoaluminum compound of the formula R.sub.nAlX.sub.3-n, wherein
R is selected from alkyls, such as butyl, ethyl and methyl, X is
selected from halogens, such as chlorine and n is 0, 1 or 2, for
example.
[0038] Although the dimerization may be carried out in any reactor
type, such as a loop reactor, for example. The dimerization may be
carried out under moderate conditions, such as temperatures of from
20.degree. C. to 400.degree. C., or from 25.degree. C. to
150.degree. C. or from 30.degree. C. to 55.degree. C. and pressures
of from 200 psig to 400 psig, or from 250 psig to 350 psig or from
265 psig to 315 psig, for example.
[0039] Depending on the embodiment, the dimerization product stream
and/or an isomerization product stream generally include n-butenes,
including 1-butene and 2-butene. The processes described herein
includes embodiments wherein the metathesis feed stream includes
primarily 2-butene. For example, in one or more embodiments, the
metathesis feed stream includes less than 5 wt. %, or less than 4
wt. %, or less than 3 wt. %, or less than 2 wt. % or less than 1
wt. % 1-butene. Accordingly, the metathesis feed stream may include
at least 95 wt. %, or least 97 wt. %, or at least 98 wt. % or at
least 99 wt. % 2-butene, for example. Alternatively, the metathesis
feed stream may include a molar ratio of 2-butene:1-butene of at
least 20:1, or at least 49:1, or at least 100:1, for example.
[0040] One or more embodiments include separating the dimerization
product stream via a separation process. The separation process may
include those known in the art, such as fractionation. As used
herein, the term "fractionation" refers to processes for the
separation of components based on the relative volatility and/or
boiling point of the components. The fractionation processes may
include those known in the art and the term "fractionation" can be
used interchangeably with the terms "distillation" and "fractional
distillation" herein.
[0041] In one or more specific embodiments, the dimerization
product stream may be separated in a butene fractionation system.
The butene fractionation system may include a first section and a
second section. The first section may include a column or columns
adapted to separate butene from other components present in the
isomerization product stream, such as unreacted ethylene and
trimers and heavier oligomers of ethylene, for example. The second
section may include a column adapted to separate 1-butene from
2-butene.
[0042] The 2-butene is generally recovered from the separation
process and passed to the metathesis feed stream. In one or more
embodiments, 1-butene is recovered from the separation process
utilized as a high value feed stream for other chemical
processes.
[0043] Embodiments described herein include reacting the metathesis
feed stream with ethylene in the presence of a metathesis catalyst
to form a metathesis product stream (i.e., a metathesis reaction).
As used herein, the term "metathesis" refers to an equilibrium
reaction between two olefins where the double bond of each olefin
is broken to form intermediate reactants. These intermediates
recombine to form new olefin products. In the specific embodiments
discussed herein, the two olefins include ethylene and butene and
the new olefin product is propylene.
[0044] As discussed previously herein, the butene, preferably
2-butene, is fed to the metathesis reaction via the metathesis feed
stream. The ethylene may be fed to the reactor by methods known to
one skilled in the art. For example, the ethylene may be fed to the
metathesis reaction via an inlet separate from an inlet utilized to
feed the metathesis feed stream. Alternatively, the ethylene may be
combined with the metathesis feed stream prior to the metathesis
feed stream passing through such inlet. However, regardless of what
method is utilized to pass the ethylene to the metathesis reaction,
all references referring to the amount/concentration of 2-butene or
1-butene in the metathesis feed stream refer to such prior to
contact/mixing with ethylene.
[0045] The molar ratio of ethylene to butene contacting the
metathesis catalyst may range from 0.1:1 to 2.5:1, or from 0.8:1 to
2:1 or from 1.5:1 to 2:1, for example.
[0046] The metathesis reaction includes contacting the butene with
ethylene in the presence of a metathesis catalyst. Metathesis
catalysts are well known in the art (see, e.g., U.S. Letters Pat.
No. 4,513,099 and U.S. Letters Pat. No. 5,120,894). Generally, the
metathesis catalyst includes a transition metal oxide, such as
transition metal oxides of cobalt, molybdenum, rhenium, tungsten,
ruthenium, and combinations thereof, for example. In one or more
specific embodiments, the metathesis catalyst includes tungsten
oxide. The metathesis catalyst may be supported on a carrier, such
as silica, alumina, titania, zirconia, zeolites, clays and mixtures
thereof, for example. In one or more embodiments, the carrier is
selected from silica, alumina and combinations thereof. The
catalyst may be supported on a carrier by methods known in the art,
such as adsorption, ion-exchange, impregnation or sublimation, for
example. The metathesis catalyst may include from 1 wt. % to 30 wt.
% or from 5 wt. % to 20 wt. % transition metal oxide, for
example.
[0047] Historically, the metathesis reaction also included
contacting the butene with ethylene in the presence of an
isomerization catalyst. The isomerization catalyst was adapted to
convert 1-butene present in the metathesis feed stream to 2-butene
for subsequent reaction to propylene, thereby improving the
reaction yield of propylene (e.g., conversion rates of from 65% to
70% and selectivity rates of from 90% to 98%). However, such
contact with the isomerization catalyst often resulted in the
formation of more undesirable by-products such as pentene and
hexene, for example.
[0048] Some embodiments of this invention utilize isomerization
catalysts to catalyze the conversion of 1-butene to 2-butene.
Isomerization catalysts may include zeolites, metal oxides, mixed
metal oxides and combinations thereof, for example. In one or more
embodiments, the isomerization catalyst includes a basic
double-bond isomerization catalyst, such as a metal oxide (e.g.,
magnesium oxide, tungsten oxide, calcium oxide, barium oxide,
lithium oxide and combinations thereof). Metal oxides supported on
a carrier may be used. Suitable carriers include silica, alumina,
titania, silica-alumina and combinations thereof for example.
[0049] Isomerization catalysts capable of converting 1-butene to
2-butene may generally include metal oxides (e.g., alumina,
zirconia, sulfated zirconia), mixed oxides (e.g., silica-alumina,
zirconia-silica), acidic zeolites, acidic clays (see, e.g., U.S.
Letters Pat. No. 5,153,165; U.S. Letters Pat. No. 4,992,613; U.S.
Patent Publication 2004/0249229 and U.S. Patent Publication
2006/0084831). In one or more specific embodiments, the catalyst is
magnesium oxide. The magnesium oxide may have a surface area of at
least 1 m.sup.2/g or at least 5 m.sup.2/g, for example.
[0050] Various embodiments of the present invention are capable of
forming propylene at high selectivity/productivity without the use
of the isomerization catalyst. In fact, some embodiments include
reaction of the metathesis feed stream and the ethylene in the
absence of an isomerization catalyst. The embodiments described
herein are capable of forming a metathesis product stream including
less that 2 mol. %, or less than 1.5 mol. %, or less than 1 mol. %
or less than 0.5 mol. % pentene, for example.
[0051] The metathesis reactions generally occur at more severe
reaction conditions than the dimerization and/or isomerization
reaction. For example, the metathesis reaction may occur at a
pressure of from 150 psig to 600 psig, or from 200 psig to 500
psig, for example. The metathesis reaction may occur at a
temperature of from 100.degree. C. to 500.degree. C., or from
200.degree. C. to 400.degree. C. or from 300.degree. C. to
350.degree. C., for example. The metathesis reaction may occur at a
WHSV of from 3 hr.sup.-1 to 200 hr.sup.-1 or from 25 hr.sup.-1 to
40 hr.sup.-1, for example. In one or more embodiments, the
propylene production process produces at least 100 MM lbs/year, or
at least 300 MM lbs/year, or at least 500 MM lbs/year or at least
800 MM lbs/year of propylene, for example.
[0052] The contact time needed to obtain a desirable yield of
metathesis reaction products depends upon several factors, such as
the activity of the catalyst, temperature and pressure, for
example. However, in one or more embodiments, the length of time
during which the metathesis feed stream and the ethylene are
contacted with the catalyst can vary from 0.1 s to 4 hours or from
0.5 s to 0.5 hours, for example. The metathesis reaction may be
conducted batch-wise or continuously with fixed catalyst beds,
slurried catalyst, fluidized beds, or by using any other
conventional contacting techniques, for example.
[0053] One or more embodiments include utilizing the isomerization
catalyst that historically had been utilized in the metathesis
reaction as an isomerization catalyst for use in the propylene or
butene fractionation systems, for example. Such processes provide
for the utilization of more ideal conditions (i.e., temperature and
pressure) for the isomerization catalyst than possible when
utilized in the metathesis reaction.
[0054] The metathesis product stream generally includes ethylene,
propylene, C.sub.4 olefins, C.sub.5 olefins and C.sub.6+ olefins.
Therefore, the process may further include separating the
metathesis product stream into an ethylene stream, a propylene
product stream, a C.sub.4 stream and a C.sub.5+ olefins stream.
Such separation is known in the art (see, U.S. Letters Pat. No.
7,214,841). In one or more specific embodiments, the metathesis
product stream is separated within a propylene fractionation
system. The propylene fractionation system generally separates the
metathesis product stream into a propylene stream, one or more
recycle streams and a bottoms stream. The bottoms stream may
include the C.sub.5 and C.sub.6+ olefins, for example.
[0055] The recycle stream(s) may include olefins selected from
butene, ethylene and combinations thereof, for example. In one or
more embodiments, the recycle stream(s) may pass from the propylene
fractionation system to the metathesis reaction downstream of any
dimerization reaction, to the extent a dimerization reaction takes
place, and without contacting isomerization catalyst.
[0056] In one or more specific embodiments, the propylene
fractionation system may include a first stage and a second stage.
The first stage is generally adapted to separate ethylene from
other components present in the metathesis stream. The second stage
is generally adapted to separate propylene from C.sub.4 and heavier
olefins, for example.
[0057] The recycle stream(s) may include olefins selected from
butene, ethylene and combinations thereof, for example. In one or
more embodiments, the recycle stream (or streams) may pass from the
propylene fractionation system to the metathesis reaction without
passing through a dimerization reactor or isomerization reactor.
While described as "a recycle stream" exiting the propylene
fractionation system, it is contemplated that the recycle stream
may include multiple recycle streams. For example, when utilizing
the first stage and the second stage, there may be a first recycle
stream exiting the first stage that includes ethylene, while there
may be a second recycle stream exiting the second stage that
includes unreacted butene. It is further contemplated that in one
or more embodiments, the "recycle stream" may not be recycled back
to the propylene production process at all, but utilized in other
chemical processes, for example.
[0058] Referring now to FIG. 1, a simplified process flow diagram
of a process 100 for producing propylene according to embodiments
disclosed herein is illustrated. FIG. 1 illustrates a process 100
including introducing a metathesis feed stream 102A to a metathesis
reactor 104 having metathesis catalyst 105 disposed therein to form
metathesis product stream 106. FIG. 1 illustrates a specific
embodiment wherein ethylene 121 is mixed with the metathesis feed
stream 102 via line 108 to form metathesis feed stream 102A.
[0059] In the embodiment illustrated in FIG. 1, a first feed stream
110 is introduced into a dimerization reactor 112 having
dimerization catalyst 115 disposed therein to form dimerization
product stream 114. The dimerization product stream 114 (or a
portion thereof) is generally utilized as the metathesis feed
stream 102. However, this is not necessary for the practice of the
invention and may vary in alternative embodiments as the feed
stream 102 may be obtained in other ways in other embodiments.
[0060] A specific embodiment is illustrated in FIG. 2 wherein the
embodiment includes the dimerization reactor 112 and the metathesis
reactor 104. However, FIG. 2 illustrates a process 200 wherein the
dimerization product stream 114 is passed to a butene fractionation
system 116. The butene fractionation system 116 includes a first
column 118 adapted to separate butene present in the dimerization
product stream 114 from other components to form a stream 120
including butene and a first column bottoms stream 122. Those in
the art having the benefit of this disclosure will recognize that
there are a number of suitable separation techniques well known to
the art that may be used to achieve this separation. Any such
suitable technique may be used. The stream 120 is passed to a
second column 124 adapted to separate 1-butene from 2-butene,
forming a stream 128 including 2-butene and a stream 126 including
1-butene.
[0061] The stream 128 feeds into the metathesis feed stream 102A
which includes stream 128, ethylene 121 (via line 108), optionally
stream 134 discussed in detail below, and optionally stream 142,
also discussed in detail below. The metathesis feed stream 102A
undergoes reaction within the metathesis reactor 104, which
contains metathesis catalyst 105, to form the metathesis product
stream 106. It is significant to note that process 200 includes
reaction within the metathesis reactor 104 in the absence of
isomerization catalyst. In the specific embodiment illustrated in
FIG. 2, the metathesis product stream 106 is passed to a propylene
fractionation system 130.
[0062] The propylene fractionation system 130 includes a first
stage 132 adapted to separate ethylene from other components
present in the metathesis product stream 106, thereby forming a
stream 134 including ethylene and a first stage bottoms stream 136.
The first stage bottoms stream 136 is generally passed to a second
stage 138 adapted to separate propylene from C.sub.4 and heavier
olefins. The propylene is recovered via stream 140, the C.sub.4
olefins are recovered via stream 142. The ethylene stream 134 may
be recycled back to the metathesis feed stream 102A or directly to
the metathesis reactor 104, while the C.sub.4 olefins in stream 142
may be recycled back to the second column 124 via line 143,
directly to the metathesis reactor 104 or to the metathesis feed
stream 102A as shown. While the second stage 138 is adapted to
separate propylene, C4 olefins and C5+ olefins (heavier olefins),
FIG. 2 does not illustrate the removal of the C5+ olefins from the
second stage 138 or stream 142. Separation and removal of heavier
olefins is known in the art and may occur within the second stage
138 via a separate stream or may include further separation of
stream 142 to remove the heavier olefins therefrom. Such separation
could be achieved by recycling all or a portion of stream 142 to
the butene fractionation system 118, for example.
[0063] Another specific embodiment is illustrated in FIG. 3,
wherein the embodiment includes the dimerization reactor 112 and
the metathesis reactor 104. However, FIG. 3 illustrates a process
300 wherein the dimerization product stream 114 is passed to a
catalyst quench system 302. The catalyst quench system 302 cools
the effluent in the dimerization product stream 114 and provides
the ability to recover dimerization catalyst 115 present in the
dimerization product stream 114. The product from the catalyst
quench system passes via line 304 to a butene recovery tower 306,
which is adapted to separate butene present in the dimerization
product stream 114 from other components to form a stream 308
including butene and a bottoms stream 310. The bottoms stream 310
generally includes heavy components capable for use in gasoline,
for example. Those in the art having the benefit of this disclosure
will recognize that there are a number of suitable separation
techniques well known to the art that may be used to achieve the
butene recovery. Any such suitable technique may be used. The
stream 308 is passed to a butene dryer 312 to form stream 314,
which is subsequently passed to a butene splitter 316 adapted to
separate 1-butene from 2-butene, forming a stream 318 including
2-butene and a stream 320 including 1-butene.
[0064] The stream 318 feeds into the metathesis feed stream 102A
which includes ethylene 121 (via line 108). The metathesis feed
stream 102A undergoes reaction within the metathesis reactor 104,
which contains metathesis catalyst 105, to form the metathesis
product stream 106. It is significant to note that process 300
includes reaction within the metathesis reactor 104 in the absence
of an amount of isomerization catalyst sufficient to isomerize
butene. In the specific embodiment illustrated in FIG. 3, the
metathesis product stream 106 is passed to a de-ethenizer 322
adapted to separate ethylene from other components present in the
metathesis product stream 106, thereby forming a stream 328
including ethylene and a bottoms stream 324. The bottoms stream 324
is generally passed to a de-propenizer 326 adapted to separate
propylene from C.sub.4 and heavier olefins. The propylene is
recovered via stream 330 and the C.sub.4 olefins are recovered via
stream 332.
[0065] The ethylene stream 328 may be recycled back to the
metathesis feed stream 102A or optionally passed through a feed
conditioning system 325 to form conditioned ethylene in line 336,
which passes to feed stream 102A. The C.sub.4 olefins in stream 332
may be recycled back to the metathesis reactor 104. While the
de-propenizer 326 is adapted to separate propylene, C.sub.4 olefins
and C.sub.5+ olefins (heavier olefins), FIG. 3 does not illustrate
the removal of the C.sub.5+ olefins from the de-propenizer 326.
Separation and removal of heavier olefins is known in the art and
may occur within the de-propenizer 326 via a separate stream or may
include further separation of stream 332 to remove the heavier
olefins therefrom.
EXAMPLES
[0066] Metathesis reactions were compared by feeding various
feedstocks, along with ethylene into a metathesis reactor with
either a mixed catalyst system (i.e., MgO+WO.sub.3) or a metathesis
catalyst (WO.sub.3) in the absence of an isomerization catalyst.
The reaction conditions are summarized in Table 1 below.
TABLE-US-00001 TABLE 1 C.sub.3 (mol. C.sub.5 + C.sub.6 Run #
Catalyst Feed WHSV T (.degree. C.) %) (mol. %) Comp 1a MgO +
WO.sub.3 B1 + C.sub.2 10 500 46.5 5.7 Comp 1b MgO + WO.sub.3 B2 +
C.sub.2 10 500 48.7 6.5 Example 1 WO.sub.3 B2 + C.sub.2 10 500 54.4
0.99 Comp 2a MgO + WO.sub.3 B1 + C.sub.2 10 400 45.6 6.2 Comp 2b
MgO + WO.sub.3 B2 + C.sub.2 10 400 49.8 5.2 Example 2 WO.sub.3 B2 +
C.sub.2 10 400 54.6 0.44 *B1 refers to 1-butene, B2 refers to
2-butene, C.sub.2 refers to ethylene, C.sub.3 refers to formed
propylene, WHSV was calculated from reactant B1 or B2 over tungsten
catalyst. For mixed catalyst configuration, 7.5 g tungsten catalyst
and 30 g magnesium catalyst were used. Example 1 and Example 2
utilized 7.5 g tungsten catalyst alone.
[0067] It was observed that the level of C.sub.5+ olefins formed
significantly decreased when the isomerization catalyst (MgO) was
eliminated from the metathesis reaction. In fact, the amount of
C.sub.5+ olefins produced was negligible (e.g., less than 1 mol.
%).
[0068] Furthermore, when a feed composed primarily of 2-butenes was
contacted with a mixed catalyst system (i.e., the metathesis
catalyst and the isomerization catalyst), the yield of propylene
increased, however, the level of C.sub.5+ olefins produced also
increased.
[0069] The processes described herein may result in a similar or
increased propylene productivity compared to processes utilizing
mixed catalyst systems.
[0070] The particular embodiments disclosed above are illustrative
only, as the invention may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. Furthermore, no limitations
are intended to the details of construction or design herein shown,
other than as described in the claims below. It is therefore
evident that the particular embodiments disclosed above may be
altered or modified and all such variations are considered within
the scope and spirit of the invention. Accordingly, the protection
sought herein is as set forth in the claims below.
* * * * *