U.S. patent application number 14/515660 was filed with the patent office on 2015-02-05 for method for quenching paraffin dehydrogenation reaction in counter-current reactor.
The applicant listed for this patent is UOP LLC. Invention is credited to Laura E. Leonard, David N. Myers, Wolfgang A. Spieker.
Application Number | 20150038757 14/515660 |
Document ID | / |
Family ID | 45353155 |
Filed Date | 2015-02-05 |
United States Patent
Application |
20150038757 |
Kind Code |
A1 |
Spieker; Wolfgang A. ; et
al. |
February 5, 2015 |
METHOD FOR QUENCHING PARAFFIN DEHYDROGENATION REACTION IN
COUNTER-CURRENT REACTOR
Abstract
A process is presented for quenching a process stream in a
paraffin dehydrogenation process. The process comprises cooling a
propane dehydrogenation stream during the hot residence time after
the process stream leaves the catalytic bed reactor section. The
process includes cooling and compressing the product stream, taking
a portion of the product stream and passing the portion of the
product stream to the mix with the process stream as it leaves the
catalytic bed reactor section.
Inventors: |
Spieker; Wolfgang A.;
(Glenview, IL) ; Leonard; Laura E.; (Western
Springs, IL) ; Myers; David N.; (Hoffman Estates,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UOP LLC |
Des Plaines |
IL |
US |
|
|
Family ID: |
45353155 |
Appl. No.: |
14/515660 |
Filed: |
October 16, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12824640 |
Jun 28, 2010 |
|
|
|
14515660 |
|
|
|
|
Current U.S.
Class: |
585/659 |
Current CPC
Class: |
C07C 5/333 20130101;
C07C 5/333 20130101; Y10S 585/903 20130101; Y10S 585/911 20130101;
C07C 11/06 20130101; Y10S 585/91 20130101 |
Class at
Publication: |
585/659 |
International
Class: |
C07C 5/333 20060101
C07C005/333 |
Claims
1. A process for controlling temperatures in a dehydrogenation
reactor, comprising: passing a catalyst to a dehydrogenation
reactor, such that the catalyst flows down through the reactor;
passing a paraffin rich stream to the dehydrogenation reactor such
that the paraffin rich stream flows up through the reactor section,
thereby creating a process stream in a separation section above the
reactor section comprising catalyst and dehydrogenated hydrocarbons
and some unconverted paraffins; separating the vapor phase from the
process stream thereby creating a product stream; passing the
product stream to a cooling unit, thereby creating a cooled product
stream; and passing a portion of the cooled product stream to the
separation section.
2. The process of claim 1 wherein the cooled product stream is
passed to the process stream above where the catalyst enters the
dehydrogenation reactor.
3. The process of claim 1 wherein the cooled unit comprises passing
the product stream through a contact cooler.
4. The process of claim 1 wherein the product stream is cooled,
thereby creating a cooled product stream; the cooled product stream
is compressed, thereby creating a compressed product stream; the
compressed product stream is cooled, thereby creating a compressed
cooled product stream; and a portion of the compressed cooled
product stream is mixed with the process stream.
5. The process of claim 1 wherein the superficial velocity of the
process stream is between 0.1 and 1.4 m/sec.
6. The process of claim 5 wherein the superficial velocity of the
process stream is between 0.2 and 1 m/sec.
7. The process of claim 1 wherein the cooled product stream is
passed to the process stream at a position proximate to the top of
the uppermost catalyst bed.
8. The process of claim 1 wherein the cooling unit is a combined
feed heat exchanger.
9. A process for controlling temperatures in a dehydrogenation
reactor, comprising: passing a catalyst to a dehydrogenation
reactor through at least one catalyst inlet port; passing a propane
rich stream to the dehydrogenation reactor through a distributor at
the bottom of the reactor, thereby creating a process stream
comprising catalyst and dehydrogenated hydrocarbons; separating the
catalyst from the process stream in a separation section thereby
creating a product stream, comprising light olefins; cooling the
product stream in a cooling unit, thereby creating a cooled product
stream; and passing a portion of the cooled product stream to the
process stream to the separation section at a position above the
reactor section.
10. The process of claim 9 wherein the dehydrogenation reactor
comprises reactor internals for spreading the catalyst and flowing
the catalyst across the trays and down through the reactor.
11. The process of claim 9 wherein the catalyst flows down through
the reactor.
12. The process of claim 9 wherein the catalyst is passed to the
dehydrogenation reactor through at least one catalyst inlet ports,
and wherein each inlet port admits catalyst to a separate reactor
internal.
13. The process of claim 9 wherein the dehydrogenation reactor
comprises a lower section for contacting the propane rich stream
with the catalyst and an upper section for separation of the
process stream from the catalyst.
14. The process of claim 13 wherein the cooled product stream is
passed proximate to the lower portion the upper section.
15. The process of claim 13 wherein the cooled product stream is
passed to the upper portion of the reactor to maintain a
superficial velocity between 0.1 m/s to 1.4 m/s.
16. The process of claim 15 wherein the cooled product stream is
passed to the upper portion of the reactor to maintain a
superficial velocity between 0.2 m/s to 1 m/s.
17. A process for controlling temperatures in a dehydrogenation
reactor, comprising: passing a catalyst to a dehydrogenation
reactor through at least one catalyst inlet port, wherein the
dehydrogenation reactor has a lower reactor section for contacting
catalyst with a feedstream and an upper section for separation of
catalyst from a process stream; passing a paraffin rich stream to
the dehydrogenation reactor through an inlet distribution system at
the bottom of the reactor; contacting the catalyst and the paraffin
rich stream in a counter-current flow system with the catalyst
flowing downward through the reactor and the paraffin rich stream
flowing upward through the reactor, thereby creating a process
stream separating the catalyst from the process stream thereby
creating a product stream, comprising olefins; passing the product
stream to a cooling unit, thereby creating a cooled product stream;
and passing a portion of the cooled product stream to the upper
section of the dehydrogenation reactor.
18. The process of claim 17 wherein the cooled product stream is
passed to the bottom of the upper section of the reactor.
19. The process of claim 17 wherein the cooled product stream is
passed to the upper section of the reactor at a rate to maintain a
superficial velocity of the process stream mixed with the cooled
product stream at a velocity between 0.2 m/s to 1 m/s.
20. The process of claim 17 further comprising: passing the portion
of the cooled product stream through a compressor, thereby creating
a compressed product stream; and cooling the compressed product
stream thereby creating a cooled compressed product stream, wherein
the cooled compressed product stream is passed to the process
stream.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a Continuation application of copending
application Ser. No. 12/824,640 filed Jun. 28, 2010, all the
teachings of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention involves processes for the
dehydrogenation of paraffins. The processes generate a hot product
stream and the invention is related to the cooling of the hot
product stream.
BACKGROUND OF THE INVENTION
[0003] The production of light olefins, and in particular ethylene
and propylene, are important for the production of numerous
plastics, and for the production of commercially important
monomers. The plastics include polyethylene and polypropylene, and
monomers include vinyl chloride, ethylbenzene, ethylene oxide, and
some alcohols. Light olefins are traditionally produced through
cracking, both steam and catalytic cracking, of hydrocarbon
feedstocks comprising larger hydrocarbons. Feedstocks include
naphthas, and other heavier hydrocarbon streams.
[0004] The traditional method of olefin production is the cracking
of petroleum feedstocks to olefins. The cracking of petroleum
feedstocks is done through catalytic cracking, steam cracking, or
some combination of the two processes. The olefins produced are
generally light olefins, such as ethylene and propylene. There is a
large market for the light olefin products of ethylene and
propylene. As petroleum feedstocks from crude oil face increasing
prices it is advantageous to provide for other sources of ethylene
and propylene. It is also known that olefins can be produced from
oxygenates. The most common conversion of oxygenates to olefins is
the production of light olefins from methanol, wherein methanol can
be produced from other sources, including biomass, and natural
gas.
[0005] An ethylene plant is a very complex combination of reaction
and gas recovery systems. The feedstock is charged to a cracking
zone in the presence of steam at effective thermal conditions to
produce a pyrolysis reactor effluent gas mixture. The pyrolysis
reactor effluent gas mixture is stabilized and separated into
purified components through a sequence of cryogenic and
conventional fractionation steps. A typical ethylene separation
section of an ethylene plant containing both cryogenic and
conventional fractionation steps to recover an ethylene product
with a purity exceeding 99.5% ethylene is described in an article
by V. Kaiser and M. Picciotti, entitled, "Better Ethylene
Separation Unit." The article appeared in HYDROCARBON PROCESSING
MAGAZINE, November 1988, pages 57-61 and is hereby incorporated by
reference.
[0006] Methods are known for increasing the conversion of portions
of the products of the ethylene production from a zeolitic cracking
process to produce more propylene by a disproportionation or
metathesis of olefins. Such processes are disclosed in U.S. Pat.
No. 5,026,935 and U.S. Pat. No. 5,026,936 wherein a metathesis
reaction step is employed in combination with a catalytic cracking
step to produce more propylene by the metathesis of C.sub.2 and
C.sub.4 olefins obtained from cracking. The catalytic cracking step
employs a zeolitic catalyst to convert a hydrocarbon stream having
4 or more carbon atoms per molecule to produce olefins having fewer
carbon atoms per molecule. The hydrocarbon feedstream to the
zeolitic catalyst typically contains a mixture of 40 to 100 wt-%
paraffins having 4 or more carbon atoms per molecule and 0 to 60
wt-% olefins having 4 or more carbon atoms per molecule. In U.S.
Pat. No. 5,043,522, it is disclosed that the preferred catalyst for
such a zeolitic cracking process is an acid zeolite, examples
includes several of the ZSM-type zeolites or the borosilicates. Of
the ZSM-type zeolites, ZSM-5 was preferred. It was disclosed that
other zeolites containing materials which could be used in the
cracking process to produce ethylene and propylene included zeolite
A, zeolite X, zeolite Y, zeolite ZK-5, zeolite ZK-4, synthetic
mordenite, dealuminized mordenite, as well as naturally occurring
zeolites including chabazite, faujasite, mordenite, and the like.
Zeolites which were ion-exchanged to replace alkali metal present
in the zeolite were preferred. Preferred alkali exchange cations
were hydrogen, ammonium, rare earth metals and mixtures
thereof.
[0007] European Patent No. 109,059B1 discloses a process for the
conversion of a feedstream containing olefins having 4 to 12 carbon
atoms per molecule into propylene by contacting the feedstream with
a ZSM-5 or a ZSM-11 zeolite having a silica to alumina atomic ratio
less than or equal to 300 at a temperature from 400 to 600.degree.
C. The ZSM-5 or ZSM-11 zeolite is exchanged with a hydrogen or an
ammonium cation. The reference also discloses that, although the
conversion to propylene is enhanced by the recycle of any olefins
with less than 4 carbon atoms per molecule, paraffins which do not
react tend to build up in the recycle stream. The reference
provides an additional oligomerization step wherein the olefins
having 4 carbon atoms are oligomerized to facilitate the removal of
paraffins such as butane and particularly isobutane which are
difficult to separate from C.sub.4 olefins by conventional
fractionation. In a related European Patent No. 109,060B1, a
process is disclosed for the conversion of butenes to propylene.
The process comprises contacting butenes with a zeolitic compound
selected from the group consisting of silicalites, boralites,
chromosilicates and those zeolites ZSM-5 and ZSM-11 in which the
mole ratio of silica to alumina is greater than or equal to 350.
The conversion is carried out at a temperature from 500.degree. C.
to 600.degree. C. and at a space velocity of from 5 to 200 kg/hr of
butenes per kg of pure zeolitic compound. The European Patent No.
109,060B1 discloses the use of silicalite-1 in an ion-exchanged,
impregnated, or co-precipitated form with a modifying element
selected from the group consisting of chromium, magnesium, calcium,
strontium and barium.
[0008] Paraffin dehydrogenation represents an alternative route to
light olefins and is described in U.S. Pat. No. 3,978,150 and
elsewhere. This is an important process as it provides control
through the selection of the feedstream. One can selectively
dehydrogenate a feedstream comprised primarily of the paraffin of
choice, such as the conversion of propane to propylene. However,
problems exist in the conversion of paraffins, and in undesired
side reactions that affect the yields, and therefore affect the
economics of producing light olefins through paraffin
dehydrogenation.
SUMMARY OF THE INVENTION
[0009] The invention provides a new process for controlling the
temperatures of an exiting process stream from a dehydrogenation
reactor. The process includes passing a hot catalyst to the
dehydrogenation reactor wherein the catalyst flows down through the
reactor. A paraffin rich stream is passed to the dehydrogenation
reactor wherein the paraffin stream flows up through the reactor,
contacting the catalyst and generating a process stream. The
process stream comprises olefins and carries some catalyst fines
from the reaction section of the reactor. The catalyst and catalyst
fines are separated from the process stream to generate a product
stream. The product stream is cooled and compressed to create a
cooled product stream. A portion of the cooled product stream is
passed to the dehydrogenation reactor to quench the process stream.
The cooled product stream portion is passed to a position proximate
to the top of the catalytic reaction section of the reactor.
[0010] The invention provides for cooling of the process stream to
prevent undesired side reactions, while not incurring additional
separation costs, or complexity to a dehydrogenation process. This
is of particular use in the production of light olefins, and in
particular the conversion of propane to propylene.
[0011] Additional objects, embodiments and details of this
invention can be obtained from the following drawing and detailed
description of the invention.
BRIEF DESCRIPTION OF THE DRAWING
[0012] The FIGURE is a process flow diagram of the dehydrogenation
process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The production of propylene is important for the production
of polypropylene. An important aspect is the selectivity in the
economics of the production process. The process involves high
temperature reactions, and can lead to undesired side reactions
that decreases the propylene production. One aspect is the hot
residence time of the process stream before the product stream
leaves the reactor. The hot residence time during separation of the
catalyst from the process stream leads to non-selective cracking.
Minimizing hot residence time improves product quality, which can
be performed by quenching of the hot process stream. Normal
quenching processes involve the injection of steam or an inert gas,
or even hydrogen. However, each of these quenching materials
present problems, and can increase costs through additional
separation sections. The present invention provides for cooling, or
quenching, of the process stream and decreases, or prevents,
unwanted cracking, thereby improving propylene yields.
[0014] The present invention is illustrated in the FIGURE showing
the process flow for controlling the temperature of the product
coming from the dehydrogenation reactor. The process comprises
passing catalyst to a dehydrogenation reactor 10 through a catalyst
inlet port 12. The catalyst is cycled through the reactor and a
regenerator. The reactor can be a bubbling bed reactor, or other
type of reactor where the catalyst flows through the reactor and
has an average residence time before being recycled to a
regenerator. In one embodiment, the catalyst is distributed over a
series of trays with openings to allow the catalyst to flow down
through the reactor section 14. A paraffin rich stream is passed to
the dehydrogenation reactor 10 through a feedstream inlet port 16.
The reactor 10 comprises a reactor section 14 and a separation
section 18, wherein the separation section is disposed above the
reactor section. The reactor section 14, comprising a catalyst bed,
generates a process stream comprising dehydrogenated hydrocarbons,
some unconverted paraffins and some catalyst that is entrained in
the process stream. The catalyst is separated from the process
stream in a separation section 18 above the reactor section 14,
thereby creating a product stream 22, comprising dehydrogenated
hydrocarbons. The product stream 22 is cooled and a portion of the
cooled product stream 24 is passed back to the reactor 10 to mix
with the process stream.
[0015] Preferably, the cooled product stream 24 is passed to a
position in the reactor 10 just above the catalyst, or proximate to
the top of the reactor section 14 of the reactor 10. Catalyst
entering the reactor 10 is preferably passed through a distributor
for depositing catalyst in a substantially uniform manner over the
top of the reactor section 14. The cooled product stream 24 is
preferably passed to a position above the catalyst distributor.
[0016] In one embodiment, the product stream 22 is passed through a
combined feed heat exchanger 26, wherein the product stream 22 is
cooled, and a combined feed of hydrogen and paraffins are preheated
before passing the paraffin rich feedstream to the dehydrogenation
reactor 10. The cooled product stream 30 can be further cooled
through a contact heat exchanger 32 to further cool the product
stream and to recover any catalyst fines. In one embodiment, the
contact heat exchanger 32 is a direct liquid contact cooler. The
cooled product stream 34 is compressed to generate a compressed
product stream 36. The compressed product stream 36 is further
cooled to remove the heat of compression, and a compressed cooled
product stream is generated. 38. A portion 24 of the compressed
cooled product stream 38 is then passed to the dehydrogenation
reactor 10.
[0017] One method of controlling the amount of cooling can be
assisted through the setting of the compression level of the
product stream. The product stream can be compressed to a level
above the reactor pressure, and the expansion of the compressed and
cooled product stream when entering the reactor can provide some
additional cooling. The amount of product stream passed to quench
the process stream is determined by the cooling load necessary to
reduce the process stream temperature to below typical cracking
temperatures.
[0018] The reactor is sized to process a feedstream having a
superficial velocity between 0.1 and 1.4 m/sec. The reactor
separation section 18 is also sized to maintain a superficial
velocity of the process stream and the returned cooled product
stream to a value between 0.1 and 1.4 m/sec. To that extent, the
separation section has an enlarged diameter, relative to the
reaction section diameter, to maintain the superficial velocity
within the design range. In a preferred process, the superficial
velocity is more tightly controlled to be in the range of 0.2 and 1
m/sec, and a more preferred range of 0.3 and 0.8 m/sec, and most
preferably the superficial velocity is approximately 0.6 m/sec.
[0019] By the term "superficial velocity", it is meant the velocity
of the gas as it flows through the vessel. The superficial velocity
is typically determined by dividing the volumetric flow rate of the
gas by the cross-sectional area of the vessel. The vessel design is
such that the separation zone has a diameter that is greater than
the diameter of the reaction vessel in the region of the catalyst
beds. The initial expansion allows for significant settling out of
the catalyst from the process stream. The vessel diameter is
increased to accommodate the increased gas flow from the recycled
cooled product stream to maintain a superficial velocity in the
desired range.
[0020] Catalyst flows through the reactor section 14 of the reactor
10, and is passed to a regeneration unit 40. The catalyst is
regenerated through combustion of the carbon that accumulates on
the catalyst during the dehydrogenation process. The carbon is
combusted to heat up the catalyst with compressed air 42 in the
regenerator 40. Additional fuel 44 can be added to the regenerator
40 to control the combustion. Regenerated catalyst is then passed
out of the regenerator 40 to the dehydrogenation reactor 10.
[0021] Catalyst can be passed to any reactor design that allows for
the catalyst to flow through the reactor, with the catalyst
recovered and passed to the regenerator. One such design is a
fluidized bed with catalyst added to the top of the reactor
section, and catalyst withdrawn from the bottom of the reactor
section. Another design is the use of reactor internals for
spreading the catalyst across the reactor and allowing the catalyst
to then flow downward from one reactor internal section to another
reactor internal section. An example of appropriate reactor
internals is the use of trays, or grids, having small openings,
either slits or holes, for the vapor to flow upward, and large
openings to allow for catalyst to flow downward. The larger
openings are spaced to have the catalyst flow all, or partway,
across the tray, or grid, with lower trays having the larger
openings positioned in a transverse position relative to a position
of the large openings in the tray above. The trays can also include
sections that have no holes to insure the distribution of vapor
flowing through the trays. The use of trays for flowing the
catalyst through the reactor is preferred over a series of bubbling
bed reactors as bubbling bed reactors require a space over each bed
to separate most of the catalyst. The space above the bubbling beds
provides an undesired dilute phase residence time, that is a low
catalyst to hydrocarbon ratio phase. This space has the drawback of
contributing to hot dilute phase residence time and contributes to
reducing the selectivity. The present design reduces the hot dilute
phase residence time by quenching the process stream during the
separation of catalyst from the process stream.
[0022] In one embodiment, the dehydrogenation reactor can include a
plurality of catalyst feeds to the reactor section 18. In this
embodiment, a catalyst inlet port directs catalyst above each tray
of catalyst and distributes catalyst over each tray. The catalyst
then flows down through the reactor section 18.
[0023] The dehydrogenation reactor 10 comprises a reactor section
18 that allows for the flow of catalyst down through the reactor
section 18. This includes different reactor designs, such as a
fluidized bed. The preferred reactor section design 18, comprises
perforated trays having large openings, wherein the perforations
allow for the process vapor stream to flow upward through the
reactor. The large openings allow for the flow of catalyst to pour
from one tray to a lower tray. In one design, the trays appear as
sections having large openings across the length of the trays, with
the trays positioned to have the perforated sections of the trays
overlapping the large openings such that the catalyst will flow in
a transverse direction across each tray before flowing to the next
tray below.
[0024] In one embodiment, the process comprises passing catalyst to
a dehydrogenation reactor through at least one catalyst inlet port.
The catalyst inlet port is in fluid communication with a catalyst
distribution manifold for distributing catalyst over the top of a
catalyst tray. A feedstream comprising propane is passed to the
dehydrogenation reactor through a distributor at the bottom of the
reactor. The feedstream passed through the reactor section and
creates a process stream comprising light olefins, and catalyst.
The light olefins in the process stream are predominantly
propylene. Catalyst is separated from the process stream to create
a product stream, and the catalyst is returned to the reactor
section. The product stream is passed to a cooling unit, thereby
creating a cooled product stream. The cooled product stream is
passed to mix with the process stream at a position above the
catalyst distribution manifold, thereby quenching the process
stream and limiting further thermal reactions in the process
stream, such as thermal cracking.
[0025] The preferred embodiment is a dehydrogenation reactor
comprising trays for spreading the catalyst and flowing the
catalyst across the trays and down through the reactor. In an
alternate configuration, the catalyst is passed to the
dehydrogenation reactor through a plurality of catalyst inlet
ports. Each inlet port is connected to a catalyst distribution
manifold, and each catalyst distribution manifold deposits the
catalyst over a different tray. In the embodiment with multiple
catalyst inlet ports, the cooled product stream is passed to a
position above the uppermost catalyst distribution manifold. In a
preferred embodiment, the cooled product stream is passed proximate
to the uppermost catalyst distribution manifold in a position above
the manifold. This cooled product inlet position is near the lower
portion of the upper separation section of the dehydrogenation
reactor.
[0026] While the invention has been described with what are
presently considered the preferred embodiments, it is to be
understood that the invention is not limited to the disclosed
embodiments, but it is intended to cover various modifications and
equivalent arrangements included within the scope of the appended
claims.
* * * * *