Note: Descriptions are shown in the official language in which they were submitted.
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
"SIMPLIFIED PLATE CHANNEL REACTOR ARRANGEMENT"
BACKGROUND OF THE INVENTION
This invention relates generally to plate type exchanger arrangements for
containing a reaction zone and indirectly heating the reaction zone with a
heat exchange
fluid.
In many industries, like the petrochemical and chemical industries, contact of
reaction fluids with a catalyst in a reactor under suitable temperature and
pressure
conditions effects a reaction between the components of one or more reactants
in the
fluids. Most of these reactions generate or absorb heat to various extents and
are,
therefore, exothermic or endothermic. The heating or chilling effects
associated with
exothermic or endothermic reactions can positively or negatively affect the
operation of
the reaction zone. The negative effects can include among other things: poor
product
production, deactivation of the catalyst, production of unwanted by-products
and, in
extreme cases, damage to the reaction vessel and associated piping. More
typically, the
undesired effects associated with temperature changes will reduce the
selectivity or yield
of products from the reaction zone.
Exothermic reaction processes encompass a wide variety of feedstocks and
products. Moderately exothermic processes include methanol synthesis, ammonia
synthesis, and the conversion of methanol to olefins. Phthalic anhydride
manufacture by
naphthalene or orthoxylene oxidation, acrylonitrile production from propane or
propylene,
acrylic acid synthesis from acrolein, conversion of n-butane to maleic
anhydride, the
production of acetic acid by methanol carbonylation and methanol conversion to
formaldehyde represent another class of generally highly exothermic reactions.
Oxidation
reactions in particular are usually highly exothermic. The exothermic nature
of these
reactions has led to many systems for these reactions incorporating cooling
equipment into
their design. Those slcilled in the art routinely overcome the exothermic heat
production
with quench or heat exchange arrangements. Extensive teachings detail methods
of
indirectly exchanging heat between the reaction zone and a cooling medium. The
art
currently relies heavily on tube arrangements to contain the reactions and
supply indirect
contact with the cooling medium. The geometry of tubular reactors poses layout
1
CA 02432082 2008-03-13
.
constraints that require large reactors and vast tube surface to achieve high
heat transfer
efficiencies.
Other process applications accomplish indirect heat exchange with thin plates
that
define channels. The channels alternately retain catalyst and reactants in one
set of
channels and a heat transfer fluid in adjacent channels for indirectly heating
or cooling the
reactants and catalysts. Heat exchange plates in these indirect heat exchange
reactors can
be flat or curved and may have surface variations such as corrugations to
increase heat
transfer between the heat transfer fluids and the reactants and catalysts.
Many
hydrocarbon conversion processes will operate more advantageously by
maintaining a
temperature profile that differs from that created by the heat of reaction. In
many
reactions, the most beneficial temperature profile will be obtained by
maintaining
substantially isothermal conditions. In some cases, a temperature profile
directionally
opposite to the temperature changes associated with the heat of reaction will
provide the
most beneficial conditions. For such reasons it is generally known to contact
reactants
with a heat exchange medium in cross flow, cocurrent flow, or countercurrent
flow
arrangements. A specific arrangement for heat transfer and reactant channels
that offers
more complete temperature control can be found in US-A- 5,525,311. Other
useful plate
an-angements for indirect heat transfer are disclosed in US-A-5,130,106 and US-
A-5,405,586.
Isolating reactants from coolants or heating fluids at the inlets and outlets
of plate
exchanger arrangements leads to elaborate designs and intricate manufacturing
procedures.
Many such designs increase the size of reactors by requiring manifolds and/or
piping to
communicate adjacent channels. Simplification of the fluid transfer between
adjacent
channels can also lead to simplified distribution and collection of fluids at
the inlets and
outlets of plate exchangers. Improved arrangements for injecting reactants at
intermediate
locations along the flow path through channels can also improve reactor
performance.
Channel reactor arrangements often retain particulate catalyst. When the
catalyst
deactivates replacement of the catalyst becomes necessary. Complicated
manifold
arrangements for the distribution and collection of heat exchange fluids and
reactants can
make catalyst change out cumbersome and time consuming.
2
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
BRIEF DESCRIPTION OF THE INVENTION
This invention provides sections of perforations in plates defining channels
for the
indirect heat exchange between fluids in a plate reactor arrangement. The
sections of
perforations extend over only portions of the plates defining the channels to
allow
communication of fluid between adjacent channels while maintaining a
substantial channel
length over which reactants or heat exchange fluids may pass on their way
through the
reactor. The partial sections of perforations located at one end of the
perforated plates
allow any number of channel passes to be made by a single fluid stream through
the plate
channel reactor. Pressure drop and heat exchange requirements pose the only
practical
limitation on the number of passes any one fluid may make through the channel
reactor
arrangement of this invention.
Suitable channel arrangements will exchange heat directly across a common heat
exchange surface. The arrangements may use an isolated heat exchange stream to
provide
heat or cooling to reaction channels or may use a heat exchange fluid or
reactant from one
channel as the reactant or heat exchange fluid in an adjacent channel In
particular the feed
or reacted stream from the reaction channels may provide fuel for combustion
and in situ
heat generation in adjacent channels. Of course the heat exchange channels may
also serve
as combustion channels and receive fuel for combustion in isolation from the
fluid in the
reaction channels.
Useful arrangements may also use different portions of common channels for
different functions. Such functions include passing an intermediate fluid
through adjacent
channels to transfer heat out of a reaction channel at one location and
transfer heat back
into the heated channels at a downstream channel location. In other
arrangements the
intermediate channels and the reaction channel may lie in a parallel
arrangement between
heated channels to adjust the temperature in the reaction channels through the
heated
channels.
- Accordingly in a broad embodiment this invention is a reaction apparatus for
contacting reactants with a catalyst in a reaction zone while indirectly
heating or cooling
the reactants in the reaction zone by indirect heat exchange with a heat
exchange fluid. The
apparatus comprises a plurality of spaced apart plates defining a first
plurality of channels
having a fluid inlet at one end and a second plurality of channels having a
fluid outlet at
3
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
one end. At least one section of perforations communicates fluid between the
first and
second plurality of channels. At least a portion of the spaced apart plates
define the
perforation at one of their ends with each section of perforations extending
over only a
portion of the plate that defines the perforations.
In particular variations of the invention, the catalyst loading within the
reaction
channels and the addition of catalyst for supplementary exothermic or
endothermic
reactions may satisfy different processing objectives. For example, short
loading of
catalyst in reaction channels can provide a space above or below the reaction
zone for
additional feed preheat or effluent cooling. Again, extending heating channels
can provide
additional surface area for open channel heat exchange against the exiting
reaction zone
effluent or the incoming reactants.
In regard to catalyst, this invention has particular advantages. The
simplification or
elimination of manifolds for distribution or collection of heat exchange and
reactants
affords space to permit the unloading of catalyst. Typically the apparatus
will utilize a
distribution manifold at the top of the reaction apparatus that distributes
and collects fluid
from the fluid inlets and fluid outlets at the top of the channels. Locating
the manifold at
the top makes it possible for the channels to define particle outlets at their
bottoms and
incorporate the catalyst unloading device. Thus, the area below the channels
may be kept
free from manifolds for withdrawing catalyst. The absence of any need to
provide screens
or other permeable surfaces at the bottom of the channels allows a simple
catalyst
retaining device to control retention of catalyst in the channels. The device
will occlude
the particle outlets when in a catalyst retention position and open the
particle outlets when
in an unloading position. Therefore, the channels may remain completely open
for catalyst
withdrawal when doors or other suitable closures are removed from the bottom
of the
channels. It is also possible by the simplification of this arrangement to
continue fluid
flow through the channels while allowing on stream removal and replacement of
catalyst
particles.
With respect to fluid flow in general the perforated plate section will
dictate the
direction of fluid flow. Adjacent channels connected by the perforated plate
sections will
always have relative countercurrent flow between channels. Nevertheless by
isolating heat
exchange fluids and reactants, cocurrent flow arrangements are also possible.
4
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
The plates defining the channels for containing the reactions and heat
exchange
gases may have any configuration that produces narrow channels. A preferred
form of the
heat exchange elements is relatively flat plates having corrugations defined
therein. The
corrugations serve to maintain spacing between the plates while also
supporting the plates
to provide a well supported system of narrow channels. Additional details on
the
arrangement of such plate systems are shown in US-A- 5,525,311.
The invention is useful in heat producing reactions or heat absorbing
reactions.
One process that can advantageously use the arrangement of this invention is
the
production of ethylene oxide. A particularly beneficial process application
for this
invention is in the production of phthalic anhydride (PA) by the oxidation of
orthoxylene.
The reaction apparatus feeds the orthoxylene feed to a distribution manifold
that injects a
controlled amount of oxygen in admixture with the orthoxylene. Injection of
the oxidation
compound into the manifold prevents the presence of the orthoxylene and oxygen
in
explosive proportions. The plate arrangement of the heat exchange reactor
quickly
dissipates the high heat of reaction associated with the synthesis of the PA.
The enhanced
temperature control improves product selectivity while also permitting
increased
throughput.
It is an further object of this invention to simplify the feed and recovery of
reactants and heat exchange fluid from a heat exchange reactor that uses a
channel
arrangement to make channel reactor arrangements more compact, and to simplify
integration of flow channels with manifolding.
Another object of this invention is to move reactants or heat exchange fluid
in
multiple passes through a channel reactor arrangement with a reduced number of
manifolds.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic illustration of a reactor arrangement of this
invention.
Figure 2 is a section of Figure 1 taken at line 2-2.
Figure 3 is a cross-section of a perforated plate of this invention.
5
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
Figure 4 is a three dimensional view of a corrugated plate section used in
this
invention.
Figure 5 is a view of single corrugated sheet containing a section of
perforations.
Figure 6 is a cross-sectional view schematically showing a reactor arranged in
accordance with this invention.
Figure 7 is a section of Figure 6 taken at line 7-7.
Figure 8 is a cross-section showing a schematic arrangement for an alternative
embodiment of the reactor of this invention.
Figure 9 is a section of Figure 8 taken at line 9-9.
Figures 10 and 11 are graphs showing the temperature profile and conversion
parameters along the path length of tubes in a tubular arrangement for PA
production by
orthoxylene oxidation.
Figures 12 through 17 are graphs showing the temperature profile and
conversion
parameters along the path length of channels in plate heat exchange reactor
arrangements
for producing PA by orthoxylene oxidation.
DETAILED DESCRIPTION OF THE INVENTION
This invention may be useful in any endothermic or exothermic process where a
reactant or a portion of a reactant provides a heat source for heating an
endothermic
reaction or a heat sink for cooling an exothermic reaction in an arrangement
of plate
exchanger elements. Additional requirements for the compatibility of any
process with a
plate exchanger arrangement are typically relatively low differential
temperature (OT) and
differential pressure (OP) between any heat exchange zone and reaction zone.
Differential
temperatures of 200 C or less are preferred for this invention. Differential
pressures will
remain low and typically reflect pressure drop requirements through the
catalyst bed.
Ordinarily the differential pressure across plate elements will not exceed .5
MPa.
At least the reaction channels will usually contain a catalyst for promoting
the
reaction. Suitable catalysts for the previously mentioned processes as well as
other
process applications are well known to those skilled in the art. Catalyst in a
particulate
form may fill the reaction channels as necessary for reaction time and any pre-
reaction
6
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
heating or post-reaction cooling in the reaction channels. As an alternate to
a particulate
catalyst, the catalyst may also be coated on the surface of the plates in the
various
reforming zones. It may be particularly advantageous to coat the reaction
catalyst onto the
plates to provide an upper catalytic section and a lower catalyst-free section
that is
maintained in heat exchange relationship across the channel defining plates
with a
secondary catalytic zone.
The heat exchange fluid used in the process or apparatus of this invention may
be
any type of fluid that can provide the necessary cooling or heating capacity.
A wide
variety of heat exchange fluids may satisfy the requirement for heating or
cooling. Such
fluids will include integral process streams as well as auxiliary fluids. The
fluid may
absorb or release heat by sensible, latent or reactive means. For highly
exothermic
processes, molten salts or metals may be particularly useful as a heat
exchange medium.
Where suitable for balancing heat requirements of a particular reaction, those
skilled in the art are aware of particular catalysts for promoting
complimentary exothermic
and endothermic reactions. Such catalysts may advantageously reside in the
heat exchange
channels to provide reactive cooling as well as cooling from the sensible or
latent heat of
the reactants. An example of such an endothermic and exotllermic catalyst
combination is
autothermal reforming of a light hydrocarbon, typically methane, to the
provide what is
generally referred to as "synthesis gas" or "syn-gas". Synthesis gas
substantially consists
of hydrogen and carbon monoxide, lesser amounts of carbon dioxide, unconverted
hydrocarbons, and other components which may include nitrogen and other inert
components. The strongly endothermic refonning reaction is efficiently
balanced against a
strongly exothermic oxidation reaction that may be effected by partial
catalytic or thermal
oxidation of the hydrocarbons. Varying the mols of hydrocarbon in either the
reforming or
oxidation reaction serves to balance the heat released and the heat absorbed.
Such an arrangement is particularly suited for incorporation into a multiple
pass
channel arrangement that interconnects only two pairs of adjacent channels and
places an
exothermic reaction channel between alternate heating channel and endothermic
reaction
channels. In a configuration providing a three pass arrangement the relatively
cold
reactants flow into the heating channels where indirect heat exchange with the
reaction
channels provides the respective heating and cooling. Flowing the reacted
stream from the
7
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
exothermic reaction channels into the endothermic reaction channels provides
additional
cooling to the reaction channels across the shared plates that define the
endothermic
reaction channels as well as the adjacent exothermic reaction channels.
Figures 1 and 2 illustrates a basic reactor arrangement for this invention. In
this
arrangement, a reactor 11 contains a single group of channel pairs 12.
Imperforate plates
19 separate the pairs of heat exchange channels into downflow channels 15 and
upflow
channels 18. A manifold 13 delivers the entering fluid into inlets 14 of
downflow
channels 15. Perforated sections 16 defined in the bottom of the perforated
plates 17
deliver the fluid to upflow channels 18.
Manifold 13 contains inlet chambers 20 and outlet chambers 21 as shown in
Figure
2. Partition plates 22 segregate the volume of inlet chamber 20 and outlet
chamber 21. As
indicated by the symbol, incoming fluids flow from line 23, along inlet
chamber 20
down inlets 14 into channels 15. Blankoff sections 24 of upflow channels 18
prevent fluid
carried by inlet chamber 20 from flowing into the upflow channels 18.
Similarly, outlet
chambers 21 collect the fluid from the upflow channels 18 as indicated by the
O symbols
for withdrawal by outlet streams 25 while blankoff sections 26 prevent outflow
of fluid
from the channels 15 into outlet chamber 21.
Channels 15 and 18 may serve a number of different functions. Channels 15 may
provide cooling by preheating reactants for an endothermic reaction that takes
place in
channels 18. Conversely, channels 15 may receive a heated reactant stream that
provides
additional heat input for an endothermic reaction that takes place in channels
18.
Alternately, channels 15 may contain an oxidation catalyst for combustive
heating of
reactants that enter channels 18.
The channels of this invention are particularly suited for use with
particulate
catalyst. Figure 1 shows one catalyst loading arrangement for an exothermic
reaction.
The cold incoming reactants enter via line 23 and pass downwardly into
channels 15. As
the entering reactants pass through the upper part of channels 15, the upper
part of
channels 18 serve as a heat exchange zone to preheat the entering feed against
the exiting
reactants. The exiting reactants have been heated by the exotherniic reaction
that takes
place in the lower portion of channels 18. As the reactants pass into the
lower portion of
channels 15, they receive further heating directly opposite the exothermic
reaction taking
8
CA 02432082 2008-03-13
place in the lower portions of channel 18. As the heated reactants pass
through the
perforated section 16 at the bottom of perforated plate 17, they pass into
catalyst particles
27 that partially fill the bottoms of channels 18. The perforations on the
perforated plate 17
are sized to block the passage of catalyst particles from channels 18 into
channels 15 while
permitting flow of reactant fluids from channels 15 into channels 18.
The arrangement of Figure 1 is particularly suited for changing out catalyst
in
channels 15, 18, or both. In the particular arrangement show in Figure 1,
catalyst 27 only
resides in the channels 18 that are used for the exothermic reaction. Once
catalyst 27 has
deactivated or needs replacement, a catalyst unloading device, shown generally
at 28, will
permit unloading of the catalyst fiom channels 18. At minimum, the unloading
device can
consist of a single set of doors 29 that at least block the bottoms 30 of
channels 18 to
prevent catalyst from dropping out of the channels when the doors 29 are in a
closed
position - as shown by the solid lines. Moving doors 29 to the open position -
as shown by
the dashed lines - opens bottoms 30 of channels 18 for discharge of catalyst
particles.
Unloading device 28 may further incorporate a secondary set of doors for
selectively retaining and unloading catalyst from channels 15. The second set
of doors 31
is shown in an open catalyst unloading position. Secondary doors 31 have slots
32
separating sealing fingers 33. When door 31 is swung upward across the bottoms
34 of
channels 15, sealing fingers 33 block bottoms 34 of channels 15 to prevent any
catalyst
discharge. Slots 32 allow catalyst in channels 18 to flow around second doors
31 for
complete unloading prior to unloading catalyst from channels 15 by nloving
doors 31 to
the open position as shown in Figure 1. Once catalyst has been emptied from
channels 18
opening doors 31 permits catalyst to flow out channels 18 without any
intermixing of the
different catalyst particles.
Catalyst is readily loaded into channels 18 and, optionally, channels 15 from
the
top of reactor 11. For catalyst loading, manifold 13 can be removed from the
top of the
channels to expose the open areas of the channels and inlet and outlet
chambers 20 and 21,
respectively. When only utilizing catalyst in channels 18, fixed screens may
cover inlets
14 of the channels 15 to prevent particles from flowing therein. When catalyst
loading
occurs over both channels, an appropriate slotted plate may be incorporated
and placed
9
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
over the tops of channels 15 and 18 to selectively block the channels not
receiving catalyst
during a particular cycle in the loading operation.
It is also possible to move catalyst while circulating reactants or heat
exchange
fluid through the reactor 11. The inlet and outlet chambers 20 and 21 may
provide a
distribution space for dispersion of catalyst over the tops of the channels
that remain open
in each particular chamber. In such an arrangement, a chamber or series of
chambers may
replace the doors 29 and 31 to provide an unloading device in the form of
collection
chambers for receiving particulate material. Suitable collection chambers may
have an
arrangement similar to that shown in Figure 2 for gathering catalyst from
selected
channels. Regulated withdrawal and addition of catalyst from the top and
bottom of
reactor 11 can provide any desired catalyst level within the reactor.
The invention relies on relatively narrow channels to provide efficient heat
exchange across the thin plates. In general, the channel width should be less
than one inch
on average with an average width of less than lh inch preferred. Suitable
plates for this
invention will comprise any plates that allow a high heat transfer rate. Thin
plates are
preferred and usually have a thickness of from 1 to 2mm. The plates are
typically
composed of ferrous or non-ferrous alloys such as stainless steel. Preferred
alloys for the
plates will withstand extreme temperatures and contain high proportions of
nickel and
chrome. The plates may be formed into curves or other configurations, but flat
plates are
generally preferred for stacldng purposes. The flat plates may have channels
formed by
machining, chemical etching or other methods. Again each plate may be smooth
and
additional elements such as spacers or punched tabs may provide fluid
turbulence in the
channels.
Preferably each plate has corrugations that are inclined to the flow of
reactants and
heat exchange fluid. The corrugations maintain a varied channel width defined
by the
height of the corrugations. In the case of corrugations, the average channel
width is most
practically defined as the volume of the channels per the cross-sectional area
parallel to the
primary plane of the plates. By this definition corrugated plates with
essentially straight
sloping side walls will have an average width that equals half of the maximum
width
across the channels.
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
Figure 3 shows the preferred corrugation arrangement for the plates 17 that
divide
channels 15 and channels 18. The corrugation pattern can serve at least two
functions.
One function is to structurally support adjacent plates. The other function is
to promote
turbulence for enhancing heat exchange efficiency in the narrow reaction
channel. Figure
3 shows corrugations defined by ridges 37 and valleys 38. The frequency or
pitch of the
corrugations may be varied as desired to promote any varying degree of
turbulence.
Therefore, more shallow corrugations, with respect to the fluid flow
direction, as shown by
ridges 37 and valleys 38 will produce less turbulence, whereas a greater
corrugation pitch
with respect to the direction of fluid flow, as shown by ridges 39 and valleys
40, provide
increased turbulence where desired. The pitch of the corrugations and the
frequency may
also be varied over a single heat exchange channel to vary the heat transfer
factor in
different portions of the channel. Preferably, the channels may contain a flat
portion 41
about their periphery to facilitate closure of the channels about the sides
and tops where
desired. Except for perforations, plates 19 are essentially the same as plates
17 and
preferably contain corrugations and may vary the pitch of the corrugations to
vary
turbulence and flow factors for heat exchange and other purposes as desired.
Perforation section 16 extends across plate 17. Perforations 42 normally have
a
relatively small diameter that permits the fluid flow across the perforated
section but
prevents catalyst migration through the perforated section. The perforations
will usually
vary in size from about 1.5 mm to about 10 mm. Perforation section 16 could be
located
in an intermediate portion of a plate to provide fluid bypassing in particular
process
applications, but will normally have a position at one end of the plates.
Positioning the
corrugation at one end of the plates maximizes the fluid flow path through the
channels.
The flow area provided by the perforated section will usually at least equal
the net flow
area along the channel flow path. When one of the channels contains
particulate catalyst
material, the net flow area would consist of the average open area between the
catalyst
particles across the transverse section of the channels 18. In most cases the
extent of
perforations will be less than half the channel length and, typically, less
than 25% of the
channel length. Preferably, the perforated section of the channel will extend
no more than
10% of its length in order to maximize the fluid flow path along the channel.
11
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
Figure 4 shows a typical cross-section of a corrugated plate arrangement
wherein
the corrugations of plates 44 extend in an opposite direction to the
corrugations of plates
46 thereby defining alternate channels 47 and 48. Holes 49 provide the
perforations of this
invention through plates 44. Figure 4 illustrates the preferred arrangement of
corrugated
plates where the herringbone pattern on the faces of opposing corrugated
plates extends in
opposite directions and the opposing plate faces contact each other to form
the flow
channels and provide structural support to the plate sections. Figure 5
further illustrates
another possible plate configuration.
It is not necessary to the practice of this invention that each reaction
channel be
alternated with a heat exchange channel. Possible configurations of the
reaction section
may place two or more heat exchange channels between each reaction channel to
reduce
the pressure drop on the heat exchange medium side. Double channel
arrangements may
be defined by a perforated plate that separates adjacent heat exchange
channels and that
contains perforations over its entire surface. The use of packing or
perforated plates can
enhance heat transfer with the reaction channels while providing good
circulation over the
entire cross-section of the heated channel.
Figures 6 and 7 show an arrangement where two independent groups of channel
pairs circulate different fluids in isolation from opposite ends of a reactor
arrangement 50.
An inlet stream 51 supplies fluid to a manifold arrangement 52 having upper
inlet
chambers 53 and upper outlet chambers 54. Inlet chamber 53 distributes upper
inlet
stream 51 to channel pairs 55 as shown by the symbol. Upper outlet stream 56
collects
fluid from the first group of channel pairs 55 through upper outlet chambers
54 in the
channel openings indicated by the O symbol. A perforated section 57 connects
the two
channels in the first group of channel pairs 55. Similarly, a lower input
stream 58 is
distributed to a second group of channel pairs 59 via a manifold arrangement
60. An
upper perforated section 61 in the second group of channel pairs 59
communicates the
channels for withdrawal of a lower outlet stream 62 via manifold 60.
By this arrangement, two different fluids may be circulated in the heat
exchange
reaction in a complete cross-flow relationship using simple manifold
arrangements at the
opposite ends of the reactor arrangement. In this way, the first group of
channel pairs can
define heat exchange channels for circulating a heat exchange fluid and the
second group
12
CA 02432082 2008-03-13
of channel pairs can define reaction channels for receiving a reactant stream
and delivering
a reacted stream.
Figures 8 and 9 show an arrangement of reaction channels that uses an odd
number
of passes to provide a simplified inlet and outlet manifold arrangement. In
Figure 8 an
inlet stream 65 enters an inlet manifold 66 having a single chamber. Fluid
entering inlet
manifold 66 flows downwardly into inlet channels 68 of a series of three pass
channel
arrangements 67. Perforated sections 78 at the bottom of plate 69 pass the
fluid from inlet
channel 68 to middle channel 70 and an upper perforated section 74 continues
the
communication of fluid from middle channel 70 into outlet channel 71. A
manifold 72,
1o again comprising a single open chamber, collects the effluent from outlet
channel 71 for
withdrawal by an outlet stream 73. In this manner, the arrangement of Figure 8
positions
the perforated sections at alternate ends of the plates defining the channels
to define a flow
path that delivers the fluid at one end of the channels and collects the fluid
from an
opposite end of the channels.
Figure 9 shows a further modification of the arrangement of Figure 8 wherein
side
manifolds 75 extend between multiple banks 76 of heat exchange channels.
Single fluids
or multiple fluids may be delivered to the heat exchange channels by the
manifold
arrangements depicted in Figures 6 through S. Side channel 75 can distribute
or collect
liquid from the sides 77 of one or more of the channels as defined by the
spaced apart
plates. For purposes of illustration, Figures 8 and 9 show openings 79 in the
sides of
channels 70 for deliveiy of an intermediate stream 80. Openings 79 may extend
across the
entire length of the channel that communicates with the side manifolds or only
a portion,
as shown in Figure 8, by holes 79'. From a practical construction standpoint,
the openings
in the sides of the channels may be more conveniently provided by intermittent
welding on
the sides of the channels rather than defining open holes.
Examples
The following examples present the operation of a tubular reactor base case
and
channel reactor arrangement of a type that uses the two independent flow paths
as depicted
in Figures 6 and 7. All of the examples show the oxidation of orthoxylene to
phthalic
anhydride. The numerical data uses well established kinetic data and
experimentally
developed heat transfer data. All of the catalytic data was based on
perfornmance
13
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
parameters for a silicon carbide base material surface coated
vanadiumpentoxide having a
surface area of 2000 cm2/g. All examples operated to keep the phthalide
content in the
effluent at less than 1000 ppm in the PA product. The examples also modeled
the use of
molten salt as the cooling medium.
Example 1
The example established the performance of the tubular reactor base case and
produced similar results to current industrial tubular reactor performance. In
this base case
a feedstock of air containing an orthoxylene concentration of 75 g/Nm3 feed
passes
through a three meter long tube having a diameter of 25mm at a mass flux rate
of 10,000
kg/m2/hr which produces a .3 bar pressure drop along the tube. The tubular
reactor model
uses a ring shaped particle having an outer diameter of 9mm with typically a
5mm
diameter perforation. Circulation of a salt bath at a temperature of 698 K
around the shell
side of the tubes provides cooling. The feed enters the tubular reactor at a
temperature of
about 700 K. The final phthalide content in the PA product was below 1000
ppm. Figure
10 graphically depicts the temperature profile over the length of a
representative tube. The
tube achieves a peak temperature of about 835 K within the first 50 cm of its
path length.
Figure 11 illustrates an essentially complete conversion of orthoxylene with
about the first
100 cm of tube length. As also presented by Figure 11, continued conversion in
the tubes
reduces the concentration of orthotolualdehyde and phthalide to levels of less
than 1000
ppm while raising the PA selectivity to about 83%.
Example 2
The plate heat exchanger type reactor operates at the same orthoxylene inlet
concentration and mass flux through the heat exchange channels as the tubular
reactor.
The channel arrangement contains a 2mm spherical catalyst in a 6 mm gap
between
channels in one of the channel .pairs. To maintain the same .3 bar pressure
drop across the
channels as across the tubes, the process flux in the plate reactor
arrangement drops to
7500 kg/m2/hr. Nevertheless, the sizing of the plate exchange reactor
maintains the same
ratio of heat transfer surface area to catalyst surface area on a per reactor
volume basis as
in the tubular reactor arrangement. At the same 75 g/Nm3 concentration of
orthoxylene in
the air feed, the process inlet temperature in the plate exchanger reactor
increases 15 C
above the tubular reactor case or to a temperature of about 713 K to maintain
the same
14
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
phthalide level in the PA product. Even with an increased inlet temperature
Figure 12
shows the peak temperature in the channels decreasing to about 815 C,
representing about
a 20 C temperature drop relative to the tubular reactor case. Again, Figure
13 shows a
rapid conversion of orthoxylene along the path length of the plate exchange
reactor with
about the same selectivity to PA and orthotolualdehyde and phthalide to levels
below 1000
ppm. Thus, the temperature reduction of this example demonstrates that the
plate heat
exchange reactor has about a 30% overall greater heat transfer ability than
the tubular
reactor.
Example 3
Example 3 evaluates increases in the concentration of the orthoxylene in the
air to
the plate exchange reactor over the range of from 75 g/Nm3 to 110 g/Nm3 to
determine the
concentration that produces the same peak temperature in the plate heat
exchange reactor
as in the tubular reactor. Heat from the additional orthoxylene oxidation
requires
increasing the circulating salt temperature from the 713 K in Example 2 to
about 717 K
to keep the phthalide concentration below 1000 ppm in the PA product. At a
concentration level of about 105 g/Nm3, the peak temperature of the plate
reactor (see
Figure 14) approaches the maximum temperatures of the tubular reactor
arrangement. As
established by Figure 15, the maximum orthoxylene concentration can increase
significantly over the tubular case reactor by use of the plate exchanger
while still
maintaining the PA selectivity of about 83 mol%.
Example 4
Example 4 demonstrates the effect on temperature and conversion of staging the
injection of orthoxylene at an intermediate point in the channels to
reestablish a maximum
concentration of 75 g/Nm3. Staged injection of feed in this case would use the
side
distribution channels of Figures 8 and 9 in combination with one of the groups
of channel
pairs as shown in Figures 6 and 7. This example decreases initial injection of
feed to
reduce the process flux at the inlet of the plate reactor to 5525 kg/m2/hr for
the first stage
of orthoxylene injection. The arrangement injects additional orthoxylene at 30
cm along
the path length of the heat exchange reactor in a middle section of one of the
channels in
each pair of the upflow and downflow channel groups. With the lower process
flux, the
CA 02432082 2003-06-18
WO 02/051538 PCT/US00/35012
temperature of the circulating salt bath drops to 700 K, the equivalent of
the tubular
reactor inlet temperature. The path length of the channels in this example
increases to a
total of 130 cm that provides an additional 30 cm for the first stage, while
maintaining the
same 100 em of second stage that was used in Examples 2 and 3. The additional
length
decreases the phthalide content below 1000 ppm in the PA product.
Nevertheless, even
with the increased length, total pressure drop remains below the .3 bar value
of the tubular
reactor example. Figure 15 displays a maximum peak temperature of below 810 K
in the
first stage. Figure 16 shows an essentially complete orthoxylene conversion
within the
first 30 cm of the injection point. Figure 17 demonstrates continued PA
selectivity at over
83 %. As a result, a process unit using the tubular type reactor to produce 50
kMta of PA
would require 33 cubic meters of catalyst. By comparison, a plate heat
exchange reactor
using multiple feed injection to produce the same amount of PA product
requires only
about 12.8 m2 of catalyst and thereby significantly reduces capital costs of
the plate reactor
arrangement relative to the tubular reactor arrangement. Looked at another
way, this
example shows an effective doubling of orthoxylene feed concentration with
staged feed
injection over that of the tubular reactor.
Overall the examples establish numerous process advantages of the plate
reactor
arrangement over the tubular reactor arrangement. A comparison of the examples
shows
the overall added heat efficiency of using a plate heat exchange reactor
arrangement that
introduces a mixture of air and othoxylene at a single inlet point for the
production of
phthalic anhydride. Using the plate reactor arrangement with an increasing
orthoxylene
concentration in the air at the single feed inlet produces additional
advantages. Moreover,
staged feed injection of the orthoxylene in the plate reactor arrangement
substantially
reduces the plate reactor arrangement costs. Such savings can include a 50%
reduction in
air compression costs and substantial reduction in capital costs due to a
smaller relative
size for plate reactor versus the tubular reactor.
16
