U.S. patent application number 12/361181 was filed with the patent office on 2010-07-29 for moving bed hydrocarbon conversion process.
Invention is credited to Christopher Naunheimer.
Application Number | 20100187159 12/361181 |
Document ID | / |
Family ID | 42353308 |
Filed Date | 2010-07-29 |
United States Patent
Application |
20100187159 |
Kind Code |
A1 |
Naunheimer; Christopher |
July 29, 2010 |
Moving Bed Hydrocarbon Conversion Process
Abstract
Moving bed hydrocarbon conversion processes are provided for
contacting a catalyst moving downward through a reaction zone with
a hydrocarbon feed, withdrawing the catalyst from the reaction zone
and conveying the catalyst to a regeneration zone wherein the
catalyst moves downward. The catalyst is withdrawn from the
regeneration zone and passed downward to an upper zone of a
particle transfer apparatus wherein the transfer of catalyst from
the upper zone through a middle zone to a lower zone is regulated
by varying the pressure of the middle zone, the flow rate of gas
passing through an upper valveless conduit, and a valve in a lower
valved conduit. The catalyst from the lower zone of the particle
transfer apparatus is conveyed to the reactions zone.
Inventors: |
Naunheimer; Christopher;
(Arlington Heights, IL) |
Correspondence
Address: |
HONEYWELL/UOP;PATENT SERVICES
101 COLUMBIA DRIVE, P O BOX 2245 MAIL STOP AB/2B
MORRISTOWN
NJ
07962
US
|
Family ID: |
42353308 |
Appl. No.: |
12/361181 |
Filed: |
January 28, 2009 |
Current U.S.
Class: |
208/141 |
Current CPC
Class: |
B01J 8/125 20130101;
C10G 35/12 20130101; C10G 47/28 20130101; C10G 49/14 20130101 |
Class at
Publication: |
208/141 |
International
Class: |
C10G 35/14 20060101
C10G035/14 |
Claims
1. A moving bed hydrocarbon conversion process comprising: (a)
contacting a catalyst moving downward through a reaction zone with
a hydrocarbon feed; (b) withdrawing the catalyst from the reaction
zone; (c) conveying the catalyst to a regeneration zone wherein the
catalyst moves downward through the regeneration zone; (d)
withdrawing the catalyst from the regeneration zone and passing the
catalyst downward to an upper zone of a particle transfer
apparatus; (e) transferring the catalyst downward from the upper
zone of the particle transfer apparatus to a middle zone of the
particle transfer apparatus through an upper valveless conduit of
the particle transfer apparatus; (f) increasing the middle zone
pressure; (g) opening a valve in a lower valved conduit of the
particle transfer apparatus; (h) transferring the catalyst downward
from the middle zone to a lower zone of the particle transfer
apparatus through the lower valved conduit, and transferring gas
from the middle zone upward through the upper valveless conduit
into the upper zone of the particle transfer apparatus; (i) closing
the valve in the lower valved conduit; (j) decreasing the middle
zone pressure; and (k) conveying the catalyst from the lower zone
to the reaction zone; wherein a pressure of the lower zone is
greater than a pressure of the upper zone.
2. The process of claim 1 further comprising: introducing oxygen to
the regeneration zone, purging a reaction zone gas from the
catalyst with nitrogen prior to the introduction of oxygen, purging
oxygen from the catalyst withdrawn from the regeneration zone with
nitrogen, and introducing a reducing gas to the catalyst before it
is transferred to the middle zone of the particle transfer
apparatus.
3. The process of claim 2 further comprising reducing the catalyst
at a temperature between about 315.degree. C. and about 540.degree.
C. at super atmospheric pressure in an upper portion of the
reaction zone wherein the catalyst is conveyed to the upper portion
of the reaction zone in the reducing gas and the reducing gas
comprises hydrogen.
4. The process of claim 2 further comprising reducing the catalyst
at a temperature between about 315.degree. C. and about 540.degree.
C. at super atmospheric pressure in the upper zone of the particle
transfer apparatus wherein the reducing gas comprises hydrogen.
5. The process of claim 2 wherein the reaction zone gas is purged
from the catalyst prior to conveying the catalyst to the
regeneration zone.
6. The process of claim 1 wherein the regeneration zone comprises:
a combustion zone, a halogenation zone, a drying zone, and a
cooling zone.
7. The process of claim 1 wherein the hydrocarbon conversion
process is a reforming process, the hydrocarbon feed comprises
naphtha, a reaction zone pressure ranges from about 240 kPa(g) to
about 3450 kPa(g), and a regeneration pressure ranges from about 0
kPa(g) to about 345 kPa(g).
8. The process of claim 1 wherein the hydrocarbon conversion
process is a dehydrocyclodimerization process, the hydrocarbon feed
comprises C.sub.2-C.sub.6 aliphatic hydrocarbons, a reaction zone
pressure ranges from about 0 kPa(g) to about 2068 kPa(g), and a
regeneration pressure ranges between about 0 kPa(g) and about 103
kPa(g).
9. The process of claim 1 wherein the hydrocarbon conversion
process is a dehydrogenation process, the hydrocarbon feed
comprises a paraffin, a reaction zone pressure ranges between about
0 kPa(g) and about 3500 kPa(g), and a regeneration pressure ranges
between about 0 kPa(g) and about 103 kPa(g).
10. The process of claim 1 further comprising introducing a gas
stream into at least one of the upper zone and the lower zone of
the particle transfer apparatus.
11. The process of claim 1 further comprising sensing the level of
catalyst in the middle zone, and transmitting a signal to initiate
step 1 (i) when the catalyst level in the middle zone falls below a
low level set point.
12. The process of claim 1 wherein the valve in the lower valved
conduit is opened when the middle zone pressure is within about 35
kPa of a pressure in the lower zone.
13. The process of claim 1 wherein the valve in the lower valved
conduit is opened when the middle zone pressure is within about 7
kPa of a pressure in the lower zone.
14. The process of claim 1 further comprising determining a
differential pressure between the middle zone pressure and a
pressure in the lower zone during step 1 (f) and initiating step 1
(g) when the differential pressure reaches a predetermined set
point.
15. The process of claim 1 further comprising during step 1 (e)
forming a continuous mass of particles comprising particles in the
upper zone, particles in the upper valveless conduit, and particles
in the middle zone.
16. The process of claim 1 further comprising introducing a gas
stream to the middle zone to increase the middle zone pressure in
step 1 (f) and venting gas from the middle zone to the upper zone
through the upper valveless conduit in step 1 (j).
17. The process of claim 1 further comprising transferring at least
a portion of gas from the lower zone to the middle zone through a
first gas conduit to increase the middle zone pressure in step 1
(f), and venting gas from the middle zone through a second gas
conduit in step 1 (j).
18. The process of claim 17 wherein the middle zone is vented
through the second gas conduit to the upper zone in step 1 (j).
19. The process of claim 1 wherein during step 1 (f) the middle
zone pressure is equilibrated with the lower zone pressure, and
during step 1 (j) the middle zone pressure is equilibrated with the
upper zone pressure.
20. The process of claim 1 wherein the pressure in the middle zone
is greater than a pressure in the upper zone during at least a
portion of step 1 (f).
Description
FIELD OF THE INVENTION
[0001] This invention generally relates to the art of solid
particle transport. More specifically, the invention relates to
hydrocarbon conversion processes including a reaction zone, a
regeneration zone, and a particle transfer zone where catalyst
moves through the zones.
BACKGROUND OF THE INVENTION
[0002] There are many chemical processes where it is necessary to
bring into contact a fluid and a solid particulate matter, such as
adsorbents and catalysts. Frequently, chemical reactions as well as
physical phenomena occur for a predetermined period of time in the
contact zone, e.g. a reaction or adsorption zone. In many of these
processes, the particles are transported between two or more
particle containing vessels. The particles may be transported for a
variety of reasons depending on the process. For example, particles
may be transported from one contacting vessel or zone into another
contacting zone in order to take advantage of different process
conditions to improve product yields and/or purity. In another
example, particles may be transported from a reaction zone into a
regeneration zone in order to rejuvenate the particles, and after
rejuvenation, the particles may be transported back to the reaction
zone. The particles may be introduced to and withdrawn from the
vessels or zones in a continuous or semi-continuous manner
sufficient to maintain the desired contacting process
continuously.
[0003] The vessels between which the catalyst is transported are
not necessarily adjacent. The outlet of the source vessel from
which the catalyst is transported may be a significant distance
horizontally and/or vertically from the inlet of the destination
vessel to which the catalyst is transported. Pneumatic conveying
through a conduit is a well known and commonly used method of
transferring catalyst over vertical and horizontal distances. One
characteristic of pneumatic conveying is that because of the
pressure difference across the conduit between the source and
destination, the destination pressure must be less than the source
pressure to account for the pressure drop across the pneumatic
conveying system. However, process conditions may require the
destination vessel to operate at a higher pressure than this value
(source pressure minus pneumatic conveying system pressure drop).
Examples include circulating particles between two zones maintained
at different pressures; and transferring particles from one vessel
to another where both vessels are maintained at the same pressure.
Under such conditions, a pneumatic conveying system alone is
insufficient to transfer the particles.
[0004] A lock hopper is commonly used to transfer particles from a
lower pressure zone to a higher pressure zone. The use of lock
hoppers in conjunction with pneumatic conveying is also well known
in the art to transfer particles between vessels or zones that are
maintained at different pressures. First, a lock hopper transfers
particles from the upper, low pressure source zone to a middle
zone, and then to a lower, high pressure zone. A pneumatic
conveying system then transfers the particles from the high
pressure zone to the destination zone. Although the destination
zone has a pressure less than that of the high pressure zone, the
destination zone pressure may be greater than that of the low
pressure source. In the art, the term "lock hopper" has been used
to designate the combination of the upper, middle, and lower zones,
and "lock hopper" has been used to designate only the middle
zone.
[0005] In one example, the flow of particles from an upper vessel
into the middle zone and out of the middle zone into a lower zone
is controlled by valves located in the conduits or transfer pipes
that connect the zones. The valves may be double block-and-bleed
ball valves. Thus, a batch of particles may be transferred to the
middle zone through the upper valve or valves when the lower valve
or valves are closed. The middle zone may then be isolated by
closing the upper valve(s). Various conduits may be connected to
the isolated volume to introduce or remove the fluid phase, usually
gas, or change the pressure inside the middle zone. For example, a
regenerated catalyst may enter the vessel, be purged with nitrogen
to remove oxygen, and pressured with hydrogen before being
transferred to the reactor which is at a higher pressure than the
regenerated catalyst. After catalyst exits the middle zone, the
middle zone can be purged with nitrogen to remove the hydrogen
before filling again with catalyst. Apparatus using valves in
conduits that convey particles are disclosed in U.S. Pat. No.
3,692,496 and U.S. Pat. No. 5,840,176.
[0006] U.S. Pat. No. 4,576,712 discloses a method and apparatus for
maintaining a substantially continuous gas flow through particulate
solids in two zones. The solids are moved from a low pressure zone
to a high pressure zone by means of a valveless lock hopper system.
Maintenance of gas flow while simultaneously transferring particles
between zones is accomplished without the use of moving equipment
such as valves.
[0007] U.S. Pat. No. 4,872,969 discloses a method and apparatus for
controlling the transfer of particles between zones of different
pressure using particle collection and particle transfer conduits.
The solids are moved from a low pressure zone to a high pressure
zone by means of a valveless lock hopper system that vents all of
the gas from the collection zones through the particle collection
conduits. The venting of gas is accomplished by varying the size of
the transfer conduits between zones.
[0008] As is known in the art, physical characteristics of the
particles and basic process information such as the operating
pressure in the upper and lower zones and the acceptable range of
gas flow rates are initial design information. Processes are
designed from this basic information and standard particle and gas
engineering principles to routinely provide stable operating units.
Surprisingly, it has been found that a particular valveless lock
hopper unit will operate predominantly in a stable manner but
experience sporadic upsets. These upsets involving a sudden surge
of particles from one zone to another, which may reverse the
particle flow, have been unpredictable with respect to which unit
will be affected, and which particle transfer cycle will experience
an upset in an affected unit. These upsets occur despite
conformance to the same design methods. Such upsets interrupt the
consistent flow of particles and can physically damage the
particles as well as the equipment.
[0009] Consequently, there is desire to eliminate these sporadic
upsets in order to minimize damage to the equipment and particles
and ensure the consistent flow of particles. The consistent flow or
transfer of particles involves a series of steps which can be
repeated in a cyclic manner to transfer the particles in batches.
Although it remains unpredictable whether an upset will occur
during any particular cycle in an apparatus, it has been discovered
that the upsets usually occur during the middle zone
depressurization step or the middle zone empty step. The invention
provides an improved method and apparatus that eliminates these
sporadic upsets.
SUMMARY OF THE INVENTION
[0010] The invention is a method and apparatus for transferring
particles from an upper zone through a middle zone to a lower zone
where the upper and middle zones are connected by a valveless
particle transfer conduit and the middle and lower zones are
connected by a valved particle transfer conduit. The lower zone may
have a higher pressure than the upper zone. The transfer of
particles from the upper zone to the lower zone is controlled by
varying the pressure of the middle zone, the flow rate of gas
passing upwards through the valveless conduit, and a valve in the
valved transfer conduit. The combination of an upper valveless
conduit and a lower valved conduit provides a more stable particle
transfer system by eliminating the unexpected and unpredictable
upsets. The invention also demonstrates that there is little or no
damage to the particles and/or the equipment despite the presence
of moving equipment such as valves in a particle transfer
conduit.
[0011] In a broad embodiment, the invention is a method for
transferring particles from an upper zone, through a middle zone,
to a lower zone comprising: transferring particles downward from
the upper zone to the middle zone through an upper valveless
conduit; increasing the middle zone pressure; opening a valve in a
lower valved conduit; transferring particles downward from the
middle zone to the lower zone through the lower valved conduit, and
transferring gas from the middle zone upward through the upper
valveless conduit into the upper zone; decreasing the middle zone
pressure; and closing the valve in the lower valved conduit.
[0012] In another broad embodiment, the invention is an apparatus
for transferring particles comprising: an upper zone; a middle
zone; a lower zone; an upper valveless conduit extending from the
upper zone to the middle zone; a lower valved conduit comprising a
first valve, the lower valved conduit extending from the middle
zone to the lower zone; and a first gas conduit in fluid
communication with the middle zone.
[0013] In another broad embodiment, the invention is a moving bed
hydrocarbon conversion process comprising: contacting a catalyst
moving downward through a reaction zone with a hydrocarbon feed;
withdrawing the catalyst from the reaction zone; conveying the
catalyst to a regeneration zone wherein the catalyst moves downward
through the regeneration zone; withdrawing the catalyst from the
regeneration zone and passing the catalyst downward to an upper
zone of a particle transfer apparatus; transferring the catalyst
downward from the upper zone of the particle transfer apparatus to
a middle zone of the particle transfer apparatus through an upper
valveless conduit of the particle transfer apparatus; increasing
the middle zone pressure; opening a valve in a lower valved conduit
of the particle transfer apparatus; transferring the catalyst
downward from the middle zone to the lower zone through the lower
valved conduit, and transferring gas from the middle zone upward
through the upper valveless conduit into the upper zone; closing
the valve in the lower valved conduit; decreasing the middle zone
pressure; and conveying the catalyst from the lower zone to the
reaction zone; wherein a pressure of the lower zone is greater than
a pressure of the upper zone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a representative view depicting the zones of the
apparatus in different vessels and an embodiment of the lower
valved conduit.
[0015] FIG. 2 is a representative view depicting another embodiment
of the lower valved conduit and an arrangement of gas conduits used
in an embodiment of the invention.
[0016] FIG. 3 illustrates another embodiment of the gas conduits of
the invention and shows the zones of the apparatus may be within a
single vessel.
[0017] The Figures are intended to be illustrative of the invention
and are not intended to limit the scope of the invention as set
forth in the claims. The drawings are simplified diagrams showing
exemplary embodiments helpful for an understanding of the
invention. Details well known in the art, such as cone deflectors,
control valves, instrumentation, and similar hardware which are
non-essential to an understanding of the invention may not be
shown.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The invention may be used to transfer solid particulate
matter from an upper zone, through a middle zone, to a lower zone
where the lower zone pressure is greater than the upper zone
pressure. Generally, particles received in an upper zone are
transferred through an upper valveless standpipe or transfer
conduit to a middle zone. That is, the upper transfer conduit does
not include moving equipment such as valves which would block the
particle flow path to the middle zone. A lower valved standpipe or
transfer conduit is used to transfer the particles from the middle
zone to a lower zone. That is, the lower transfer conduit comprises
at least one valve. Thus, the zones and transfer conduits may be in
particle communication and the transfer conduits may provide
particle communication.
[0019] The invention can be used within and/or between a variety of
process units to transfer particles, such as catalyst and
adsorbents. The upper zone of the invention may receive particles
from a separate process zone and the lower zone may deliver the
particles to another separate process zone. For example, an
associated process unit may include a separate vessel that operates
as a reaction zone which provides catalyst particles to the upper
zone, and the lower zone may deliver catalyst to a separate process
vessel such as a feed hopper of a pneumatic conveying apparatus
which in turn delivers the catalyst to the top of another reactor.
In another embodiment, the invention may be arranged so that the
upper zone and/or the lower zone are integrated with a process unit
such that one or more process steps, or portions thereof, occurs
within the upper and/or lower zones or the vessel(s) which contain
the upper and/or lower zones. For example, the upper zone may be
the lower portion of a reduction zone vessel or the entire
reduction zone vessel of a process unit and/or the lower zone may
be the upper portion of a surge vessel or the entire surge vessel
of a process unit. The surge vessel in turn may introduce the
particles into other zones of the same or a different process
unit.
[0020] The invention may communicate with or the invention may
comprise a portion of a process unit which provides for changing
the fluid that contacts the particles. For example, the process
unit may involve contacting catalyst with a gas containing
hydrocarbons and/or hydrogen in a reaction zone and removing carbon
deposits from the catalyst using a gas containing oxygen in a
regeneration zone. As the catalyst is transferred between the
reaction and regeneration zones, care must be taken to prevent
mixing of the hydrocarbon/hydrogen atmosphere and the oxygen
atmosphere. Examples of hydrocarbon conversion processes that may
employ the invention include: alkylation, hydrorefining,
hydrocracking, dehydrogenation, hydrogenation, hydrotreating,
isomerization, dehydroisomerization, dehydrocyclization, and steam
reforming. One widely practiced hydrocarbon conversion process that
may employ the invention is catalytic reforming using particles of
catalyst. Exemplary reaction and regeneration zones are disclosed
in, e.g., U.S. Pat. No. 5,858,210.
[0021] The upper, middle, and lower zones of the invention may be
separate vessels or portions of separate vessels that are connected
by the transfer conduits. In another embodiment, a single vessel
comprises the upper zone, the middle zone, and optionally the lower
zone. The upper, middle, and lower zones of the invention may also
provide one or more functions or process steps of an associated
process unit. In an embodiment, the upper, middle, and lower zones
may be aligned sufficiently vertically to allow catalyst to flow,
at least in part, by gravity from at least one vessel at a higher
elevation to at least one vessel at a lower elevation. Thus, one or
both of the upper and lower particle transfer conduits may be
oriented vertically. In an embodiment one or both of the upper and
lower particle transfer conduits is angled relative to true
vertical.
[0022] In general, flow of the particles into and out of the middle
zone may be controlled by regulating the pressure of the middle
zone, the flow rate of gas through the upper valveless particle
transfer conduit, and a valve in the lower valved particle transfer
conduit. The flow path of the gas may also be varied. The same
basic method steps may be accomplished by various configurations of
gas and particle conduits to introduce, vent, and change the flow
path of the gas used to control particle transfers. Existing
configurations and control schemes can be readily adapted to employ
the invention.
[0023] The method of transferring particles from upper zone 10 to
lower zone 30 may be accomplished by repeating the following four
step cycle: 1) a fill or load step wherein particles are
transferred from the upper zone to the middle zone; 2) a
pressurization step wherein the middle zone pressure is increased;
3) an empty step wherein particles are transferred from the middle
zone to the lower zone; and 4) a depressurization step wherein the
middle zone pressure is decreased. The steps may overlap. For
example, transfer of particles to the middle zone may begin while
the middle zone pressure continues to decrease and the middle zone
pressure may begin to increase or decrease while particles continue
to transfer.
[0024] A single cycle results in the transfer of one batch of
particles from the upper zone to the lower zone. The time required
to complete one cycle, i.e. the cycle time, will depend on a
variety of factors including: the properties of the particles; the
batch size, or amount of particles transferred per cycle; and the
times needed to change the pressure of the middle zone. The
invention is not limited by the cycle time. In an embodiment, the
cycle time may be about 50 seconds. In another embodiment, the
cycle time may be less than about 10 minutes, and the cycle time
may be between about 2 minutes and about 4 minutes. A controller
such as process control computers and programmable controllers may
be used to regulate the cycle. The controller may receive various
inputs, e.g. signals from particle level sensors, pressure gauges
or indicators, differential pressure sensors, and timers such as
for an individual step and/or the overall cycle. The controller may
also send signals for example to open, close, and adjust valves to
control the flow pattern and rate of various gas steams and the
valve or valves in the lower valved conduit. Such a controller and
related signals are not shown in the Figures as they are not
essential to the invention and are well known to the skilled
artisan.
[0025] Broad embodiments of the invention will now be described
with reference to FIG. 1. In step 1 of the method, particles are
transferred from upper zone 10 to middle zone 20 through upper
valveless conduit 40. The upper and middle zones are at
approximately the same pressure during step 1. Gas ascending
through upper valveless conduit 40, if any, is insufficient to
retain the particles in conduit 40. During step 1, gas may enter
lower zone 30 through optional gas inlet conduit 11. Gas may also
enter lower zone 30 from an associated process zone, not shown.
Valve 12 may regulate the quantity of gas flowing into lower zone
30; this flow rate may be varied independently of the invention by
means, not shown, for controlling the pressure of lower zone 30.
Gas used in the invention is selected to be compatible with the
particles being transferred and may be the same gas as used in the
associated process unit. Nitrogen, hydrogen, and air are
non-limiting examples of gas that may be used.
[0026] During step 1, valve 52 in lower valved conduit 50 is closed
to retain the particles in middle zone 20. Valve 52 may be referred
to as a particle retention valve. Valve 52 may also provide a gas
tight seal. Valves used in particle transfer apparatus are
commercially available and well known in the art. In an embodiment,
valve 52 may be a rotary shaft valve, rotating disc valve, or a
slide valve. Rotary shaft valves include, but are not limited to:
ball type, segmented ball type, and v-notch ball type. Additional
valves such as valve 54 may be used in lower valved conduit 50. In
an embodiment, valve 54 is a gas tight valve to essentially prevent
the flow of gas between the middle and lower zones through valved
conduit 50. As is well known in the art, closed valves may leak
even when operating properly. Valves may be classified by how much
they leak when closed compared to the full open valve capacity. See
for example,
http://www.engineeringtoolbox.com/control-valves-leakage-d.sub.--
-484.html, last viewed on Dec. 19, 2008. The term "gas tight" as
used herein means that the gas leakage through the valve when
closed is equal to or less than a Class IV valve per ANSI standard
FCI 70-2 1976(R1982). Such valves may also be referred to as "metal
to metal" and are classified as having a leakage of 0.01% of full
open valve capacity under the test conditions. Valves that are not
gas tight will have higher leakage values than this gas tight
standard and may be described as providing fluid communication when
closed.
[0027] Various configurations of the gas flow path may be used. For
example, gas may be introduced to upper zone 10 from an associated
process zone and/or via gas conduit 15, which functions as a gas
inlet conduit in this embodiment. The pressure of upper zone 10 may
be controlled independently of the invention by means, not shown,
while the pressure in the upper and middle zones is equilibrated by
gas flowing through upper valveless conduit 40. In an embodiment,
valve 52 is not gas tight and gas may flow upwards from lower zone
30 through valved conduit 50 and closed valve 52 into middle zone
20. That is valve 52, even when closed, may provide fluid
communication between the middle and lower zones. Although not
required, gas may be introduced to middle zone 20 during step 1
such as through gas conduit 13 in FIGS. 1 and 3 or gas conduits 17
and 13 in FIG. 2. Gas may also be introduced into middle zone 20
from lower zone 30 through gas conduit 13 and valve 14 as shown in
FIG. 2. A portion of the gas entering middle zone 20 during step 1,
if any, may flow through gas conduit 15 and valve 16 to upper zone
10 as shown in FIG. 2. In other embodiments not illustrated, a
portion of the gas introduced to middle zone 20 may flow through
gas conduit 15 to another destination or simply be vented. In the
embodiment illustrated in FIG. 3, which depicts the three zones of
the apparatus in one vessel, upper valveless conduit 40 has a
sufficiently large diameter such that any gas entering middle zone
20 during step 1 may flow upward through upper valveless conduit 40
at a flux which is insufficient to retain the catalyst therein.
[0028] Upper valveless particle transfer conduit 40 and/or lower
valved particle transfer conduit 50 may have a restriction, that
is, a smaller cross-sectional area for particle flow than the
balance of the respective conduit. The cross-sectional areas of the
restrictions if present and the balance of the conduit may be any
regular or irregular shape including a circle, oval, square,
rectangle, and triangle. The cross-sectional area shape of a
conduit may be the same or it may differ over its length and may be
the same or different in the upper and lower conduits. The
cross-sectional area of a restriction and the balance of the
conduit may have different shapes or the same shape. The
restriction may be located in a lower portion of the conduit, that
is, in the lower 1/3 of the respective conduit's height. The
restrictions may be created in a wide variety of ways including
crimping the conduit, using an insert, and forming the conduit with
the restriction. Restrictions may be located proximate an outlet in
the lowermost end of the conduit. In an embodiment, the conduit, or
a portion thereof is tapered toward the outlet to form the
restriction at the outlet. The type, cross-sectional area shape,
and/or location of restrictions in upper and lower conduits may be
the same, or they may differ.
[0029] Step 1 ends when middle zone 20 is filled to its operating
capacity with particles. As shown in FIG. 1, upper valveless
conduit 40 may extend into middle zone 20 to define its operating
capacity. That is, particles stop flowing into the middle zone when
particles in the middle zone accumulate to reach upper valveless
conduit outlet 45. Thus, there may be a continuous mass of
particles from a lower portion of upper zone 10 through upper
valveless conduit 40, and middle zone 20. In another embodiment,
the operating capacity of middle zone 20 is predetermined and an
optional upper level particle sensor, not shown, is used to detect
when particles rise to this preset level. In such an embodiment,
particles need not reach upper valveless conduit outlet 45 and
upper valveless conduit 40 need not extend past the shell of middle
zone 20. In other embodiments, the operating capacity of middle
zone 20 may be determined by a preset time interval. Use of an
adjustable timing interval or high level set point enables the size
of each particle batch to be varied from cycle to cycle. The
particle levels and/or time increments may be measured and a signal
sent to a controller to initiate step 2 when the middle zone has
been filled. Thus, particles may continue to flow into middle zone
20 for a time after step 2 begins if the particles are below upper
valveless conduit outlet 45 at the end of step 1. In other
embodiments, the particle flow may be stopped at this point in the
cycle and the apparatus may be held with middle zone 20 filled to
its operating capacity until it is desired to continue the particle
transfer cycle. This portion of the cycle may also be known as a
separate hold or ready step. For example, valve 52 is closed to
retain the particles in middle zone 20 and particles in the middle
zone contact outlet 45 preventing the further transfer of particles
out of upper zone 10. Gas may also be introduced to middle zone 20
and directed upwards through upper valveless conduit 40 at a
sufficient rate to stop particles from flowing out of the upper
zone. In the embodiment of FIG. 2, gas may be introduced to middle
zone 20 as discussed above and valve 16 may be closed to force all
the gas upwards through upper valveless conduit 40. Similarly, in
the embodiment of FIG. 3, valve 14 can be opened to accomplish the
same effect.
[0030] In step 2 of the cycle, the pressure within middle zone 20
is increased. The middle zone pressure may be increased to stop the
transfer of particles from the upper zone. In an embodiment, the
middle zone pressure is increased to equilibrate with the higher
pressure in lower zone 30. This may be accomplished by introducing
gas into middle zone 20 through gas conduit 13. Gas to gas conduit
13 may be supplied from a variety of sources including, but not
limited to: gas inlet conduit 11, gas inlet conduit 17, lower zone
30, and separate supply sources such as facility headers and other
zones in the associated or other process units. In the embodiment
illustrated in FIG. 2, valve 14 is opened and valve 16 is closed to
pressurize middle zone 20. In the embodiment shown in FIG. 3,
middle zone 20 is pressurized by opening valve 14. There is no need
to change the gas flow path as the cycle moves from step 2 to step
3. However, as explained above there are numerous ways of routing
the gas flow path to control the desired particle movement. Thus,
the invention encompasses changing the gas flow path between and/or
within steps 2 and 3 to equilibrate the middle and lower zone
pressures and retain particles within upper valveless conduit
40.
[0031] Step 3 may be referred to as the empty or unload step of the
cycle, and Step 3 may begin when particles begin to flow out of the
middle zone. In another embodiment, Step 3 begins when valve 52
opens. After the pressure in the middle zone is increased, valve 52
is opened and particles flow from middle zone 20 through lower
valved conduit 50 to lower zone 30. The middle zone pressure may
increase further after valve 52 is opened. Lower valved conduit 50
preferably extends into lower zone 30 as shown in FIG. 1, though
this extension into lower zone 30 is not required. A number of
different events may be used to trigger the opening of valve 52.
For example, valve 52 may be opened based on a preset time interval
for the particle transfer cycle, or based on a preset time interval
from the beginning of step 2. In an embodiment, valve 52 opens in
response to one or more pressure indicators. For example, FIG. 1
shows middle zone pressure indicator 28 and lower zone pressure
indicator 38 either or both of which may transmit signals to a
controller, not shown. The controller may send a signal to open
valve 52 when the middle zone pressure reaches a predetermined set
point. In another embodiment, the controller compares the middle
and lower zone pressures and sends a signal to open valve 52 when
the middle and lower zone pressures are sufficiently similar. It is
preferable to avoid a pressure differential between the middle and
lower zones that is high enough to cause a sudden particle surge
when valve 52 opens as this may cause damage to the particles
and/or the equipment. Valve 52 may be opened when the middle zone
pressure is above, at, or below the lower zone pressure as the
particles may flow at least in part by gravity.
[0032] In another embodiment as illustrated in FIG. 2, a delta P
cell or differential pressure indicator 48 receives signals from
the middle and lower zones; determines the difference in pressure
between the middle and lower zones; and sends a signal to a
controller, not shown. The controller sends a signal to open valve
52 when the differential pressure reaches a predetermined set
point. As with other elements illustrated in the Figures, there are
myriad, well known ways to measure pressures and send signals
giving information about the measurements. The Figures do not limit
use of a particular pressure indicator, sensor, or signaling
element to the illustrated embodiment. For example, the pressure
indicators of FIG. 1 may be used in other embodiments including
those illustrated in FIGS. 2 and 3 and different pressures
indicators may be used in the embodiment of FIG. 1. In an
embodiment, valve 52 is opened to begin step 3 when the middle zone
pressure is within about 35 kPa of the lower zone pressure. In
another embodiment, valve 52 is opened to begin step 3 when the
middle zone pressure is within about 7 kPa of the lower zone
pressure; and valve 52 may be opened when the middle zone pressure
is within about 3.5 kPa of the lower zone pressure. During step 3,
gas continues to flow upward through upper valveless conduit 40 at
a sufficient rate to prevent the transfer of particles from upper
zone 10 into middle zone 20. The level of particles in middle zone
20 falls as particles flow out of lower valved conduit 50 into
lower zone 30.
[0033] Particles may remain in middle zone 20 at the end of Step 3
when valve 52 is closed. However, this may result in some particle
and/or equipment damage as valve 52 closes on the still flowing
particle stream. In another embodiment, Step 3 may end when
substantially all of the particles are transferred from middle zone
20 to lower zone 30. Although some particles may still remain in
the lower valved conduit 50 and/or middle zone 20, the continuous
flow of particles through lower valved conduit 50 may end before
valve 52 is closed. That is, particles are no longer being
discharged as a continuous mass from outlet 55 of lower valved
conduit 50 into the lower zone when valve 52 closes. Preferably,
middle zone 20 is empty, i.e. substantially all of the particles
have passed through valve 52 before it is closed at the end of step
3.
[0034] Again, a wide variety of events can be used to close valve
52. For example, valve 52 may be closed based on a preset time
interval for the particle transfer cycle, or based on a preset time
interval from the beginning of step 3. Valve 52 may be closed in
response to one or more level indicators. For example, a particle
level sensor, not shown, may detect a high level of particles in
lower zone 30 and send a signal to a controller which in turn sends
a signal to close valve 52. In another embodiment, low level
particle sensor 25 may detect the absence of particles at the low
level set point and send a signal to a controller to close valve
52. Multiple inputs may be used to manage the particle transfer
cycle steps. In an embodiment, the length of step 3 may be
controlled by a timer with low level particle sensor 25 being used
to end step 3 earlier than the preset time interval if the
particles fall below the middle zone low level set point faster
than expected. In another embodiment, valve 52 is closed in
response to the signal from low level particle sensor 25 and a
predetermined time interval or delay to allow the remaining mass of
particles to flow past or clear valve 52 before it closes. The same
inputs may also be used to control multiple actions. For example,
the signal from low level particle sensor 25 may be used, either
with or without an additional delay time, to close valve 52 and
initiate step 4, depressurizing or venting the middle zone. In an
embodiment, different time delays may be added by the controller to
the same signal, such as, from low level particle sensor 25 so that
step 3 ends and step 4 begins at different times. Although the
middle zone pressure may begin to decrease before valve 52 closes,
it is preferred that valve 52 closes before or at the same time as
the middle zone pressure begins to decrease.
[0035] With more than one valve in lower valved conduit 50, Step 3
may begin when the last closed valve opens. In an embodiment, the
uppermost valve is the last valve that is opened. With more than
one valve in lower valved conduit 50, Step 3 may end when the first
valve closes. In an embodiment, the uppermost valve is the first
valve that is closed. Multiple valves may opened and/or closed
simultaneously. Such sequencing of opening and closing multiple
valves, if present, is not required but favored to minimize valves
moving on the particles and may be readily accomplished for example
by a controller with appropriate set points and/or programming.
[0036] In step 4, the depressurization step, the pressure in middle
zone 20 may be decreased to equilibrate the middle and upper zone
pressures. This may be accomplished for example by re-establishing
the optional gas flows that were discussed in step 1. In the
embodiment of FIG. 2 valve 14 may be closed and valve 16 opened so
that gas flows through gas conduit 15 to equalize the pressure
between the upper and middle zones. A portion of the gas in middle
zone 20 may flow through gas conduit 15 to another destination, not
illustrated, or simply be vented such as through gas conduit 13 in
FIG. 1. In the embodiment illustrated in FIG. 3, valve 14 may be
closed and the pressure between the upper and middle zoned
equilibrated through the upper valveless conduit 40. As in step 1,
gas may be introduced to middle 20 during step 4 even though the
pressure in the middle zone is being decreased.
[0037] When the pressure of middle zone 20 is decreased in step 4
to equilibrate with upper zone 10 and increased in step 2 to
equilibrate with lower zone 30 it is understood that the pressures
in the two zones, superior and inferior, being equilibrated may or
may not be the same. For example, pressure differences may exist,
if there is some gas flow between the two equilibrated zones, or if
they are being controlled independently. Also, there is no
requirement that the inferior zone be at the same or lower pressure
than the superior zone of the two zones being equilibrated. That
is, particles may transfer from either superior zone to the
respective inferior zone even though the pressure of the inferior
zone is higher than the pressure of the superior zone. The gas flow
paths described for the embodiments of FIGS. 2 and 3 show that the
invention may provide for the continuous flow of gas to each of the
upper, middle, and lower zones throughout a cycle. Further, the
embodiment of FIG. 2 may provide an uninterrupted flow of gas from
the lower zone through the middle zone and into the upper zone
throughout the cycle. In other embodiments not illustrated, various
gas conduits may be used to control the middle zone pressure and
the gas flow rates through the upper valveless particle transfer
conduit to regulate the particle movement as herein described.
[0038] It is understood that the step numbers used herein are
arbitrary and a transfer cycle may be considered to begin with any
step and each step is employed at least once during a cycle. The
invention encompasses various orders of the steps and some steps
may be repeated in the course of transferring a single batch of
particles from the upper zone to the lower zone. For example, the
transfer of particles in step 1 may be interrupted by employing
steps 2 and 4 multiple times during a transfer cycle. Likewise,
step 3 may be interrupted by opening and closing valve 52 multiple
times during a transfer cycle, though this is not preferred. Thus,
in an embodiment, the order of steps may be 1--transfer particles
from the upper zone to the middle zone; 2--increase the middle zone
pressure to stop the transfer of particles; 4--decrease the middle
zone pressure to equilibrate the middle and upper zone pressures;
1--transfer particles from the upper zone to the middle zone;
2--increase the middle zone pressure to equilibrate the middle and
lower zone pressures; 3--transfer particles from the middle zone to
the lower zone; and 4--decrease the middle zone pressure to
equilibrate the middle and upper zone pressures. In another
embodiment the order of steps may be 1, 2, 4, 1, 2, 3, 4, 2, 3, and
4. Other steps such as purging the middle zone may be included in a
transfer cycle.
[0039] During the particle transfer cycle, the inventory in upper
zone 10 may be continuously and/or intermittently replenished with
particles such as from an associated or integrated process zone
and/or as added from a fresh particle feed hopper. Likewise,
particles delivered to lower zone 30 may be withdrawn from or pass
out of the lower zone continuously and/or intermittently. It is
preferred that an inventory or surge volume of particles be
maintained in both the upper and lower zones throughout the
particle transfer cycle. As previously described, upper zone 10 may
also provide one or more functions of an associated or integrated
process unit including regeneration zones. Non-limiting examples
include: a particle feed hopper, a reaction zone, an atmosphere
purge zone, another catalyst transfer zone, a reduction zone, and
an elutriation zone. The internal pressure of upper zone 10 may be
independently controlled by means well known in the art. For
example, upper zone 10 may be in fluid communication with a process
zone so that the upper zone pressure depends upon and varies with
the pressure in that process zone. The upper zone pressure is not
critical and may be atmospheric, sub-atmospheric, or super
atmospheric.
[0040] Lower zone 30 may be a holding vessel, or surge zone from
which the particles are transferred by other means such as
pneumatic conveying. In other embodiments, lower zone 30 may
provide one or more functions of an associated or integrated
process unit including regeneration zones. Non-limiting examples
include: a particle feed hopper, a reaction zone, an atmosphere
purge zone, another catalyst transfer zone, a reduction zone, and
an elutriation zone. The internal pressure of lower zone 30 may be
independently controlled by means well known in the art. For
example, lower zone 30 may be in fluid communication with a process
zone so that the lower zone pressure depends upon and varies with
the pressure in that process zone. In an embodiment, the upper zone
pressure may be higher than the lower zone pressure for a portion
of the transfer cycle. In another embodiment, lower zone 30 may be
maintained at a higher pressure than upper zone 10. For example,
upper zone 10 may be maintained at a nominal pressure of 34 kPa (g)
and permitted to vary within a range from about 14 to about 55 kPa
(g) while the nominal pressure of lower zone 30 may be 241 kPa (g)
within a range from about 207 to about 276 kPa (g). In another
embodiment, upper zone 10 may be maintained at a nominal pressure
of 241 kPa (g) and permitted to vary within a range from about 172
to about 310 kPa (g) while the pressure of lower zone 30 may be
within a range from about 345 to about 2068 kPa (g). Thus, the
differential pressure between the lower zone 30 and upper zone 10
might range from about 35 to about 1896 kPa. However, this
invention may be used when the pressure differential between zones
is as little as about 0.7 kPa and in excess of 2000 kPa. Middle
zone 20 serves as an intermediate zone, and its nominal pressure is
adjusted to regulate the flow of the particles.
[0041] The apparatus of the invention may be used as a solids flow
control device for an entire process, since the flow rate of
particles from the upper zone to the lower zone can be varied, as
discussed above. The upper, middle, and lower zones may contain
other non illustrated apparatus known in the art such as baffles,
screens, and deflector cones which may be used to facilitate
particle flow and/or direct the particles or the gas through a zone
in a desired manner. The components of the present invention may be
fabricated from suitable materials of construction, such as metals,
plastics, polymers, and composites known to the skilled artisan for
compatibility with the particles, and operating conditions, e.g.
gas, temperature, and pressure. The size, shape, and density of the
particles is only limited by the size of the equipment and the type
and flow rates of the gas or gases used. In an embodiment, the
particles are spheroidal and have a diameter from about 0.7 mm to
about 6.5 mm. In another embodiment, the particles have a diameter
from about 1.5 mm to about 3 mm. The particles may be catalysts an
example of which is disclosed in U.S. Pat. No. 6,034,018.
[0042] As previously noted, particle transfer apparatus of the
prior art may be adapted to incorporate the invention. Likewise,
standard engineering principles especially those related to the
flow of solids and gases and known design methods may be used in
this invention. For example, it is well known to those skilled in
the art of designing solids flow systems to conduct experiments to
determine flow characteristics of the particular solid involved. In
addition to the teachings herein, the design considerations and
methodology described in U.S. Pat. No. 4,576,712 and U.S. Pat. No.
4,872,969 may be used to practice this invention. For example, the
pressure in the upper and lower zones, the minimum and maximum gas
flow rates upwards through the zones and the valveless conduit, and
the required particle transfer rate are design factors that are
often fixed by the associated process unit. The length of the
particle column inside the valveless conduit, the height of
particles in the zone above the valveless conduit, and the diameter
of the valveless conduit may be balanced so that changing the
pressures and gas flow paths as described herein controls whether
particles will flow down through or be retained within the
valveless conduit. The design method includes limiting the gas flow
rates and pressure differentials to avoid fluidizing particles
within the zones and to prevent particles from being suddenly
forced up or down the valveless conduits.
[0043] Thus, it is known that the internal pressures of the upper
and lower zones, the minimum and maximum gas flow rates, the
identities of the gas and the particles, and the required range of
particle transfer rates, may be used to determine various
parameters of the invention. These parameters include: the normal
minimum and maximum volumes occupied by the particles in the zones,
the particle heights required in the upper zone above the valveless
transfer conduit, the diameter of the transfer conduits, the bore
or opening size of the valve or valves in the valved transfer
conduit, and the lengths of the transfer conduits. These and other
parameters such as the gas conduit size and arrangement may
characterize a particular embodiment encompassed by the
invention.
[0044] In an embodiment, a hydrocarbon feed is contacted with
catalyst particles moving downward through a hydrocarbon conversion
process reaction zone. The catalyst is withdrawn from the reactor
and conveyed upwards to a top portion of a regeneration zone. The
catalyst passes downward through the regeneration zone undergoing
one or more treatment steps. The catalyst is withdrawn from the
regeneration zone and passed downward to an upper zone of a
particle transfer apparatus. The upper zone pressure may be less
than the reaction zone pressure. The particle transfer apparatus
transfers the catalyst from the upper zone to the lower zone as
described above. The catalyst, now at a higher pressure, may be
conveyed upwards to a top or upper portion of the reaction zone by
a known pneumatic transport system such as described in U.S. Pat.
No. 5,716,516 and U.S. Pat. No. 5,338,440.
[0045] Moving bed systems and processes which employ them are well
known in the art. See for example U.S. Pat. No. 3,725,249 and U.S.
Pat. No. 3,692,496. The reaction zone is oriented substantially
vertically (i.e. sufficiently vertical for catalyst to flow
downward at least in part by gravity) and may be divided into
multiple reactors or sub zones, for example, to manage the heat of
reaction. The reaction zone may consist of a single vertical stack
of one or more sub zones, or the reaction zone may be split into
two or more vertical stacks to manage structural height
limitations. A stack may comprise more than one vessel. It is also
important to note that the reactants may be contacted with the
catalyst bed in either an upward, downward, or radial flow fashion
with the latter being preferred. In addition, the hydrocarbon feed
may be in the vapor phase when contacting with the catalyst bed.
That is, the catalyst moves gradually downward in the reaction and
regeneration zones as a non-fluidized, dense phase or compact bed
that is withdrawn from the bottom or lower portion of the reaction
and regeneration zones and is replenished by adding catalyst to the
top portion of these zones. The catalyst withdrawn from the
reaction zone is lifted to the top of the regeneration zone by
equipment known in the art including mechanical devices such as
screw or bucket conveyors or star valves. Preferably, the catalyst
is lifted by a pneumatic transport system.
[0046] In the reaction zone, the catalyst may deactivate over time
by one or more mechanisms including deposition of carbonaceous
material or coke upon the catalyst, sintering or agglomeration of
catalyst metals, loss of catalytic promoters such as halogens, and
exposure to the reaction atmosphere at reaction temperatures up to
760.degree. C. and pressures ranging from about 0 to about 6,900
kPa(g). As used herein, "reaction temperature" means the weighted
average inlet temperature (WAIT), which is the average of the inlet
temperature to the first bed of catalyst contacted with the feed
and each subsequent bed of catalyst following a heating or cooling
stage to manage the heat of reaction weighted by the quantity of
catalyst in the corresponding reactor. Frequently, the reaction
conditions include the presence of hydrogen that may be introduced
separately or combined with the hydrocarbon feed. Hydrocarbon
products from the reactor are often cooled and separated into vapor
and liquid streams such as in a flash drum or vapor/liquid
separator. All or a portion of the vapor stream, containing
hydrogen may be recycled to the reaction zone while the liquid
stream may be sent to storage, blended with other streams or
processed further.
[0047] The regeneration zone is designed and operated to restore or
rejuvenate the catalyst performance and may include multiple zones
and/or treatment steps. Non-limiting examples include a burn or
combustion zone, a halogenation zone, a drying zone, and a cooling
zone. The regeneration zone may include other known zones such as
an elutriation zone and a disengaging zone. The regeneration zone
may comprise one or more vessels which are substantially vertically
aligned in one or more stacks. Additional regeneration zone details
are available in the art such as U.S. Pat. No. 6,034,018. The
regeneration zone may operate at a pressure ranging generally from
about 0 to about 6900 kPa(g) and a temperature from about
370.degree. C. to about 538.degree. C. Often, the regeneration zone
includes an atmosphere containing oxygen in contrast to the
reaction zone hydrocarbon/hydrogen atmosphere. Thus, separation of
the reactor and regenerator atmospheres may be important to prevent
undesirable side reactions. Various known elements such as nitrogen
seals or bubbles, isolation valves, and pressure differentials to
maintain desired purges and gas flows may be used to prevent the
hydrogen and oxygen atmospheres from mixing.
[0048] The catalyst being withdrawn from the reaction zone may be
purged with hydrogen to keep excess hydrocarbons in the reaction
product stream. In an embodiment, the reaction zone atmosphere such
as hydrogen and/or remaining hydrocarbon gas surrounding the
catalyst is purged with nitrogen before the catalyst enters the
oxygen containing atmosphere. Oxygen may be introduced to the
regenerator vessel, or oxygen may be added upstream of the
regenerator, for example, in a disengaging vessel or isolation
valves of the regeneration zone. This change from the reaction zone
atmosphere to an inert or nitrogen atmosphere may be conducted
before or after the catalyst is lifted or conveyed from the bottom
of the reaction zone to the top of the regeneration zone. Likewise,
the change from the regeneration zone oxygen atmosphere may be
accomplished by a nitrogen purge followed by introduction of a
reaction zone gas or reducing gas, such as hydrogen. This
atmosphere change is usually completed below the regeneration zone
before the catalyst enters the upper zone of the particle transfer
zone or apparatus. However, this atmosphere change may be
accomplished within the particle transfer apparatus or after the
catalyst exits the particle transfer apparatus, before or after the
catalyst is lifted to the top of the reactor zone. Low pressure
differentials ranging for example from about 2 to about 14 kPa may
be sufficient to maintain proper nitrogen purges or flows to keep
the regeneration and reaction zone atmospheres separated. Catalyst
may be purged with nitrogen in a conduit or the catalyst may enter
a nitrogen containing vessel as it moves through the process.
[0049] The catalyst may also undergo a reduction step. If needed,
the reduction step is normally performed after the catalyst leaves
the regenerator vessel when the catalyst is under a reducing gas or
reaction zone gas atmosphere. In an embodiment, the reduction step
occurs in the upper zone of the particle transfer apparatus. In
another embodiment, the reduction step occurs in a reduction zone
located atop the reactor in the reaction zone. Typical reduction
conditions include an atmosphere comprising hydrogen, a temperature
ranging from about 315.degree. C. to about 540.degree. C., and a
super atmospheric pressure.
[0050] In an embodiment, the hydrocarbon conversion process is a
reforming process which is well known in the petroleum refining and
petrochemical industries. In brief, the reforming feed comprises a
petroleum fraction known as naphtha which may have an initial
boiling point from about 40.degree. C. to about 120.degree. C. and
an end boiling point from about 145.degree. C. to about 218.degree.
C. In an embodiment, the naphtha has an initial boiling point from
about 65.degree. C. to about 104.degree. C. and an end boiling
point from about 150.degree. C. to about 195.degree. C. The naphtha
feed may be a straight run petroleum fraction and/or obtained as a
product from one or more petroleum and petrochemical processes such
as hydrocracking, hydrotreating, FCC, coking, stream cracking, and
any other process which produces a hydrocarbon product in the
naphtha boiling range. A number of different reactions may occur in
a reforming process including the dehydrogenation of cyclohexanes
and dehydroisomerization of alkylcyclopentanes to yield aromatics,
dehydrogenation of paraffins to yield olefins, dehydrocyclization
of paraffins and olefins to yield aromatics, isomerization of
paraffins, isomerization of alkylcycloparaffins to yield
cyclohexanes, isomerization of substituted aromatics, and
hydrocracking of paraffins. As a result, reforming is an overall
endothermic process and it is common to use more than one reaction
zone to allow reheating of the reactants in order to obtain the
desired performance.
[0051] Reforming conditions may include reaction temperatures from
about 425.degree. C. to about 580.degree. C., preferably from about
450.degree. C. to about 560.degree. C.; a pressure from about 240
kPa(g) to about 4830 kPa(g), preferably from about 310 kPa(g) to
about 1380 kPa(g); and a liquid hourly space velocity (LHSV),
defined as liquid volume of fresh feed per volume of catalyst per
hour, from about 0.2 to about 10 hr.sup.-. The reforming reaction
is carried out in the presence of sufficient hydrogen to provide a
hydrogen/hydrocarbon mole ratio from about 0.5:1 to about 10:1. A
reforming catalyst typically comprises one or more noble metals
(e.g., platinum, iridium, rhodium, and palladium), a halogen
component, and a porous carrier or support, such as an alumina.
Exemplary catalysts are disclosed in U.S. Pat. No. 6,034,018. The
regeneration zone pressure may range from about 0 kPa(g) to about
345 kPa(g). In an embodiment, the regeneration zone pressure ranges
from about 0 kPa(g) to about 103 kPa(g), and in another embodiment
from about from about 172 kPa(g) to about 310 kPa(g).
[0052] The hydrocarbon conversion process may be a
dehydrocyclodimerization process wherein the feed comprises C.sub.2
to C.sub.6 aliphatic hydrocarbons which are converted to aromatics.
Preferred feed components include C.sub.3 and C.sub.4 hydrocarbons
such as isobutane, normal butane, isobutene, normal butene, propane
and propylene. Diluents, e.g. nitrogen, helium, argon, and neon may
also be included in the feed stream. Dehydrocyclodimerization
operating conditions may include a reaction temperature from about
350.degree. C. to about 650.degree. C.; a pressure from about 0
kPa(g) to about 2068 kPa(g); and a liquid hourly space velocity
from about 0.2 to about 5 hr.sup.-1. Preferred process conditions
include a reaction temperature from about 400.degree. C. to about
600.degree. C.; a pressure from about 0 kPa(g) to about 1034
kPa(g); and a liquid hourly space velocity of from 0.5 to 3.0
hr.sup.-1. It is understood that, as the average carbon number of
the feed increases, a reaction temperature in the lower end of the
reaction temperature range is required for optimum performance and
conversely, as the average carbon number of the feed decreases, the
higher the required reaction temperature. Details of the
dehydrocyclodimerization process are found for example in U.S. Pat.
No. 4,654,455 and U.S. Pat. No. 4,746,763.
[0053] The dehydrocyclodimerization catalyst may be a dual
functional catalyst containing acidic and dehydrogenation
components. The acidic function is usually provided by a zeolite
which promotes the oligomerization and aromatization reactions,
while a non-noble metal component promotes the dehydrogenation
function. Exemplary zeolites include ZSM-5, ZSM-8, ZSM-11, ZSM-12,
and ZSM-35. One specific example of a catalyst disclosed in U.S.
Pat. No. 4,746,763 consists of a ZSM-5 type zeolite, gallium and a
phosphorus containing alumina as a binder. Multiple reactors or
reaction zones may be used to manage the heat of reaction as
described above for the reforming process. The
dehydrocyclodimerization process regeneration zone pressure may
range from about 0 kPa(g) to about 103 kPa(g). In a particular
embodiment, the regeneration conditions may include a step
comprising exposing the catalyst to liquid water or water vapor as
detailed in U.S. Pat. No. 6,657,096.
[0054] In an embodiment, the hydrocarbon conversion process is a
dehydrogenation process for the production of olefins from a feed
comprising a paraffin. The feed may comprise C.sub.2 to C.sub.30
paraffinic hydrocarbons and in a preferred embodiment comprises
C.sub.2 to C.sub.5 paraffins. General dehydrogenation process
conditions include a pressure from about 0 kPa(g) to about 3500
kPa(g); a reaction temperature from about 480.degree. C. to about
760.degree. C.; a liquid hourly space velocity from about 1 to
about 10 hr.sup.-1; and a hydrogen/hydrocarbon mole ratio from
about 0.1:1 to about 10:1. Dehydrogenation conditions for C.sub.4
to C.sub.5 paraffin feeds may include a pressure from about 0
kPa(g) to about 500 kPa(g); a reaction temperature from about
540.degree. C. to about 705.degree. C.; a hydrogen/hydrocarbon mole
ratio from about 0.1:1 to about 2:1; and an LHSV of less than 4.
Additional details of dehydrogenation processes and catalyst may be
found for example in U.S. Pat. No. 4,430,517 and U.S. Pat. No.
6,969,496.
[0055] Generally, the dehydrogenation catalyst comprises a platinum
group component, an optional alkali metal component, and a porous
inorganic carrier material. The catalyst may also contain promoter
metals and a halogen component which improve the performance of the
catalyst. In an embodiment, the porous carrier material is a
refractory inorganic oxide. The porous carrier material may be an
alumina with theta alumina being a preferred material. The platinum
group includes palladium, rhodium, ruthenium, osmium and iridium
and generally comprises from about 0.01 wt % to about 2 wt % of the
fmal catalyst with the use of platinum being preferred. Potassium
and lithium are preferred alkali metal components comprising from
about 0.1 wt % to about 5 wt % of the fmal catalyst. The preferred
promoter metal is tin in an amount such that the atomic ratio of
tin to platinum is between about 1:1 and about 6:1. A more detailed
description of the preparation of the carrier material and the
addition of the platinum component and the tin component to the
carrier material may be obtained by reference to U.S. Pat. No.
3,745,112. Again, multiple reactors or reaction zones may be used
to manage the heat of reaction as described above for the reforming
process. The dehydrogenation process regeneration zone pressure may
range from about 0 kPa(g) to about 103 kPa(g).
* * * * *
References