U.S. patent application number 11/260026 was filed with the patent office on 2006-07-13 for dispersion-intensified, coalescence-intensified chemical reactor and method.
Invention is credited to Edward G. Hauptmann.
Application Number | 20060153754 11/260026 |
Document ID | / |
Family ID | 36653436 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060153754 |
Kind Code |
A1 |
Hauptmann; Edward G. |
July 13, 2006 |
Dispersion-intensified, coalescence-intensified chemical reactor
and method
Abstract
Apparatus for intensifying heterogeneous chemical reactions is
described. For the case of liquid-liquid reactions, with drops of a
reactant distributed throughout the second continuous reactant, the
physical phenomena of drop dispersion (break up) and drop
coalescence are identified as the main physical steps affecting
reaction rates. A basic flow cell structure is described in which
the respective actions of dispersion and coalescence can be greatly
intensified through the creation of enhanced body forces and shear
flow zones. The basic cell structure can be arranged into pipe flow
reactors to suit any production or process requirements. The basic
cell structure is equally applicable to gas-liquid reactions with
drops of one reactant being conveyed by a moving gas stream.
Inventors: |
Hauptmann; Edward G.; (West
Vancouver, CA) |
Correspondence
Address: |
KOLISCH HARTWELL, P.C.
200 PACIFIC BUILDING
520 SW YAMHILL STREET
PORTLAND
OR
97204
US
|
Family ID: |
36653436 |
Appl. No.: |
11/260026 |
Filed: |
October 26, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60622264 |
Oct 26, 2004 |
|
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|
Current U.S.
Class: |
422/600 ;
422/200 |
Current CPC
Class: |
B01J 14/00 20130101;
B01J 19/006 20130101; B01J 19/2415 20130101; B01J 2219/182
20130101; B01J 2219/00768 20130101; B01J 19/2405 20130101; B01F
5/0606 20130101; B01J 2219/00777 20130101 |
Class at
Publication: |
422/195 ;
422/200 |
International
Class: |
B01J 8/04 20060101
B01J008/04 |
Claims
1. Apparatus to allow chemical reactions between reactants
comprising: a vessel through which the reactants flow; a baffle
structure within the vessel to define at least one flow cell having
an interior and at least one inlet to allow flow to pass into the
cell interior as a jet to define a dispersion zone for the
reactants, and an obstruction spaced from the at least one inlet to
redirect the flow and form a coalescence zone for the reactants
adjacent the obstruction, and at least one outlet to allow flow to
exit the flow cell.
2. Apparatus as claimed in claim 1 in which the obstruction is
positioned to redirect flow essentially transversely to the flow of
the jet such that the obstruction imparts a shearing action to the
flow and imparts centrifugal forces to the flow to cause
coalescence.
3. Apparatus as claimed in claim 1 in which the at least one flow
cell comprises a plurality of flow cells with each cell having a
first end wall formed with the at least one inlet, a second end
wall defining the obstruction formed with the at least one outlet,
and side walls extending past the first and second end walls, the
second end wall with the at least one outlet of one of the
plurality of cells forming the first end wall and inlet of a
subsequent, adjacent flow cell.
4. Apparatus as claimed in claim 3 in which the side wall in
proximity to the inlet defines an additional coalescence zone for
the reactants.
5. Apparatus as claimed in claim 3 in which the flow cells are
arranged to extend along a longitudinal axis of the vessel.
6. Apparatus as claimed in claim 5 in which the flow cells are
arranged to extend radially from the longitudinal axis of the
vessel.
7. Apparatus as claimed in claim 1 in which the at least one inlet
and outlet comprises a slot.
8. Apparatus as claimed in claim 1 in which the at least one inlet
and outlet comprises a plurality of discrete openings.
9. Apparatus as claimed in claim 1 in which the vessel comprises a
hollow body having a longitudinal axis, and the baffle structure is
formed from a plurality of elements arranged within the body to
define an array of interconnected flow cells that communicate with
each other by virtue of the outlet of one flow cell being the inlet
of one or more other flow cells.
10. Apparatus as claimed in claim 9 in which the plurality of
elements includes members of generally T-shaped cross-section, the
members being arranged through the hollow body in a repeating
pattern to define the array of interconnected flow cells.
11. Apparatus as claimed in claim 10 in which the hollow body
includes outer side walls and the elements extend between the outer
sidewalls to define linear slot inlets and outlets to each flow
cell that extend transversely to the longitudinal axis between the
side walls.
12. Apparatus as claimed in claim 11 in which each member of
generally T-shaped cross-section has a head portion and a base
portion, and each member is positioned such that the head portion
is aligned transversely to the longitudinal axis of the hollow body
and the base portion is aligned parallel to the longitudinal axis,
the members being arranged in a plurality of parallel rows
extending along the longitudinal axis of the hollow body with every
second row being offset such that the base portion of one member in
an intermediate row extends between the head portions of other
members in adjacent rows.
13. Apparatus as claimed in claim 9 in which the plurality of
elements include a central core element of cylindrical
configuration aligned along the longitudinal axis of the hollow
body having a plurality of spaced first annular elements extending
radially outwardly from the core element and a plurality of spaced
second annular elements extending radially inwardly from the hollow
body, the first and second annular elements co-operating to define
a plurality of interconnected flow cells of annular configuration
within an annular space about the central core element.
14. Apparatus as claimed in claim 9 in which the plurality of
elements includes: a ring cell element comprising an annular
cylindrical member having an opening therethrough of a first
diameter and an annular disc member having a central opening of a
second diameter less than the first diameter positioned against an
end of the annular cylindrical member; a plurality of the ring cell
elements of different first diameters being arranged through the
hollow body centred about the longitudinal axis in a repeating
pattern to define an array of interconnected annular flow
cells.
15. Apparatus as claimed in claim 1 in which the vessel comprises a
hollow body having a longitudinal axis and formed with a plurality
of internal baffles extending transversely to the longitudinal axis
to restrict axial flow and direct flow radially within the body
with an array of flow cells extending between adjacent baffles, the
flow cells having inlets and outlets oriented to permit radial flow
through the cells.
16. Apparatus as claimed in claim 15 in which the internal baffles
comprise alternating disc and annular plates spaced along the
longitudinal axis of the hollow body to define a series of
interrupted central channels for flow extending between pairs of
disc plates and a series of interrupted annular perimeter channels
for flow extending between pairs of annular plates, the interrupted
channels communicating through arrays of flow cells extending
between adjacent overlapping plate surfaces in an annular
configuration, whereby flow through the hollow body is directed
longitudinally along a central channel, radially outwardly through
one of the arrays of flow cells, longitudinally along an annular
perimeter channel, and radially inwardly through another of the
arrays of flow cells.
17. Apparatus as claimed in claim 1 including a vessel inlet for
introducing at least one of the reactants into the vessel.
18. Apparatus as claimed in claim 17 in which the vessel inlet
comprises at least one pipe extending radially into the vessel.
19. Apparatus as claimed in claim 18 in which the at least one pipe
includes openings to introduce the at least one of the reactants
into the other reactants which are already flowing through the
vessel.
20. Apparatus as claimed in claim 19 in which the at least one pipe
includes openings along the pipe positioned to introduce the at
least one reactant into multiple flow cells.
21. Apparatus to allow chemical reactions between reactants
comprising: a vessel through which the reactants flow including a
first reactant distributed as drops throughout a second reactant; a
baffle structure within the vessel to define at least one flow cell
having an interior and at least one inlet to allow flow to pass
into the cell interior as a jet to define a dispersion zone for the
drops, and an obstruction spaced from the at least one inlet to
redirect the flow and form a coalescence zone for the drops, and at
least one outlet to allow flow to exit the flow cell.
22. A method for promoting chemical reactions between reactants
comprising: delivering the reactants through a vessel in a mixed
flow including a first reactant distributed as drops throughout a
second reactant; and controlling the flow through the vessel to
create a flow path that alternates between dispersing the drops and
coalescing the drops to increase the reaction rate.
23. The method of claim 22 in which the step of controlling the
flow includes forming the flow into a jet to disperse the
drops.
24. The method of claim 23 in which the step of controlling the
flow includes redirecting the flow past an obstruction to coalesce
the drops due to shear zone forces and intensified body forces.
25. The method of claim 22 in which the step of controlling the
flow includes directing the flow through at least one flow cell in
the vessel, the flow cell having at least one inlet to allow flow
to pass through the inlet as a jet to define a dispersion zone for
the drops, and an obstruction spaced from the at least one inlet to
redirect the flow and form a coalescence zone for the drops within
an interior of the flow cell adjacent the obstruction, and at least
one outlet adjacent the obstruction to allow flow to exit the flow
cell.
26. The method of claim 25 in which the at least one flow cell is
arranged in an array of a plurality of flow cells within the vessel
positioned to intercept and control flow through the vessel.
27. The method of claim 25 including a side wall in proximity to
the jet to provide an additional zone of coalescence of the drops
due to fluid shear forces at the side wall.
28. The method of claim 22 in which the first and second reactants
are liquids, with the drops of the first liquid reactant being
distributed throughout the second reactant
29. The method of claim 22 in which the first reactant is a liquid,
and the second reactant is a moving gas stream.
30. Apparatus to allow chemical reactions between reactants
comprising: a vessel through which the reactants flow including a
first reactant distributed as drops throughout a second reactant;
and means for controlling the flow of reactants through the vessel
to intensify the dispersion and coalescence of the drops
comprising: means for creating a zone of dispersion for the drops;
and means for creating a zone of coalescence for the drops.
31. Apparatus as claimed in claim 30 in which the means for
controlling the flow of reactants through the vessel comprises a
baffle structure within the vessel to define at least one flow cell
having an interior, the flow cell being formed with the means for
creating a zone of dispersion for the drops and means for creating
a zone of coalescence for the drops.
32. Apparatus as claimed in claim 31 in which the means for
creating a zone of dispersion comprises at least one inlet to the
flow cell shaped to create a jet flow into the cell interior.
33. Apparatus as claimed in claim 32 in which the means for
creating a zone of coalescence comprises an obstruction spaced from
the at least one inlet and extending transverse to the flow.
34. Apparatus as claimed in claim 31 including at least one outlet
to allow flow to exit the flow cell.
35. Apparatus as claimed in claim 32 in which the means for
creating a zone of coalescence comprises a surface in proximity to
the jet.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C. .sctn. 119
and applicable foreign and international law of U.S. Provisional
Patent Application Ser. No. 60/622,264 filed Oct. 26, 2004 which is
hereby incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to an apparatus and method to allow
for heterogeneous chemical reactions. The invention finds
application in reactions where the reactants are immiscible. The
invention is of particular application in the nitration of aromatic
hydrocarbons using mixed acids in aqueous solution.
BACKGROUND OF THE INVENTION
[0003] Heterogeneous chemical reactions are an important class of
industrial processes in which the reactants are separate and to a
large extent mutually insoluble. Many combinations of phases and
dispersions are possible. Two of the more common arrangements are:
liquid-liquid reactants with one liquid as a continuous phase
having the second liquid dispersed throughout, generally in the
form of drops; and, liquid-gas reactions with gas the continuous
phase having drops of the liquid reactant dispersed throughout. In
some cases the reactions are aided by the presence of a catalyst,
either in homogeneous or heterogeneous form.
[0004] Two important examples of heterogeneous reactions are:
nitration reactions, where typically an aromatic compound is
dispersed throughout a solution of mixed acids; and
desulfurizations, where a sulfur-laden hydrocarbon is sprayed into
a hydrogen environment and passed over a catalyst bed. In the
former example of nitration reactions, the mixed acids are usually
nitric and sulfuric acid, with the sulfuric acid playing the role
of a de facto catalyst, dissociating the nitric acid and forming a
nitronium ion which comprises the reactive species.
[0005] An important example of an industrial nitration process is
the nitration of benzene in a nitric-sulfuric acid mix to form
mononitrobenzene (MNB), a precursor in the production of
polyurethanes, among other important products. Another example,
amongst many, is the nitration of toluene to dinitrotoluene, also a
precursor in polyurethane production.
[0006] Reactions in heterogeneous systems generally take place near
the interface between the reactants. For example in the case of
liquid-liquid reactants, with one dispersed as drops throughout the
second continuous reactant, it is well established that the actual
reactions take place in the continuous phase just beyond the
surface of the drop. This is also evident in the case of liquid-gas
reactions such as normal combustion processes, where the fuel drop
vaporizes into the surrounding oxygen rich mixture of gases, and
the subsequent reaction occurs in the gas phase.
[0007] In the aforementioned simple liquid-gas combustion process,
the drop of fuel continues to volatilize, the combustion products
are swept away in the continuous phase, and the burning continues.
Liquid-liquid reactions are somewhat more complex, as the reaction
products formed near the interface must find their way into either
of the reactants by diffusion or with the aid of other mass
transfer phenomena. As the products of the reaction may remain in
the reaction zone for a considerable time, the rate at which fresh
reactants can be brought to the reaction zone is limited and the
reaction slows.
[0008] The overall rate of reaction in liquid-liquid systems in
particular can be increased by intensifying the two distinct steps
of the process: dispersion, or break-up of drops, and coalescence,
FIG. 1 shows these dispersion and coalescence steps schematically
in an idealized way. In the dispersion step indicated by arrow 3,
new, smaller drops 4 are continuously formed from larger drops 2
with the smaller drops having new fresh surface area between the
reactants. In the coalescence step indicated by arrow 7, smaller
drops 5 are brought together and join into larger drops 6 so that
the reaction products can be mixed and withdrawn from the reaction
zone.
[0009] The main forces that produce break-up or dispersion of drops
in a flowing liquid are: local pressure fluctuations on account of
turbulence; and shear forces adjacent to solid surfaces (that may
either be moving or stationary). The main forces producing
coalescence are: once again, pressure fluctuations due to natural
turbulence that can propel the drops together; body forces such as
gravity, which promote stratification and bringing together of the
lighter component fluids, and fluid shear forces which can promote
agglomeration or coalescence adjacent to a wall.
[0010] The role of dispersion in determining the overall reaction
rate is well understood as being the creation of large amounts of
fresh, new interfacial area between reactants (i.e. small drops).
An appreciation of the importance of coalescence in determining the
overall reaction rate can be gained by imagining the behavior of a
drop with incremental steps in time as shown schematically in FIGS.
2a-2c. The situation illustrated is that of reaction products being
much more soluble in the drop than in the continuous phase, as in
the example generally of nitration of aromatic compounds in mixed
acid.
[0011] FIG. 2(a) shows an idealized drop 2 freshly introduced into
a second surrounding reactant 8 before any reaction has occurred.
As the reaction is understood to take place in a region of the
continuous phase just beyond the surface of the drop, after a short
period, reaction products are formed (indicated by the darker band
10 around the drop 2) as shown in FIG. 2(b). If the drop were
completely immobile, the reaction products would slowly diffuse
into the drop, while the unreacted material would diffuse to the
drop surface and thereby react further.
[0012] The role of coalescence is to accelerate the admixing of
reacted with unreacted material by physically merging adjacent
drops together. FIG. 2(c) shows the idealized situation after drops
have coalesced, with reaction products 10 distributed throughout
the unreacted material of a newly coalesced drop 6. Fresh unreacted
material is now available at the drop surface to continue with the
reaction.
[0013] It is appreciated that the description above is highly
idealized, as the processes of dispersion and coalescence occur
simultaneously in flowing liquid-liquid mixtures. New drops are
continuously formed while old drops are merged by the combined
actions of dispersion and coalescence, thereby sustaining the
reaction. It becomes apparent however, that intensifying dispersion
and coalescence phenomena can increase overall reaction rates.
[0014] Two conventional means for carrying out liquid-liquid
reactions are in a so-called continuously stirred tank reactor 20
(CSTR), shown schematically in FIG. 3, or in a tubular, or pipe
flow reactor 28 (PFR) shown in FIG. 4.
[0015] In the CSTR 20, a rotating impeller 22 imparts an overall
circulation to the bulk fluid confined in a tank 24. While this can
provide adequate mixing of miscible fluids, the situation with
drops dispersed throughout a continuous fluid poses different
issues. The greatest degree of dispersion occurs in the immediate
vicinity of the rotating impeller as a result of the relatively
high shear forces imparted by the moving surfaces. Although the
bulk circulation is usually turbulent, drop dispersion rates are
much lower in the bulk circulation than near the impeller.
Turbulence in the bulk circulation however is responsible for most
of the coalescence in the CSTR, and being relatively low,
contributes to generally larger residence times being required to
complete the reactions in a CSTR.
[0016] Pipe flow reactors (PFRs) 28, or in-line mixers as they are
commonly called, have, as their name implies, the goal of mixing
miscible fluids together. Many examples of PFRs are in general
industrial use. They generally comprise an enclosure 30 through
reactants flow past insertable elements 32 which act to mix the
flow. They often rely on a range of insertable elements 32 for use
in different process and fluid conditions. Although certain
specific types of elements can provide a modest degree of
dispersion for immiscible drops, no particular amount of
coalescence beyond that provided by the turbulent flow is achieved.
Nevertheless this type mixer has been used as a reactor for
nitrating benzene as described in European Patent Specification EP
077927081 assigned to Mitsui Chemicals, Inc. The Mitsui patent
describes nitration experiments with this type of reactor, and
cites results that show high byproduct formation for instances
having acceptable conversion rates of the incoming nitric acid.
Conversely, the results showed low byproduct formation occurred at
unacceptably low rates of nitric conversion.
[0017] Perhaps the first commercially successful reactor to
deliberately use highly intensified dispersion zones is described
in U.S. Pat. No. 4,994,242. The so-called jet-impingement reactor
(assigned to Noram Engineering and Constructors Ltd.) uses a set of
baffles, either flat, cylindrical or spherical having a series of
holes allowing the passage of fluid. The intensified dispersion is
achieved by high rates of shear generated in the flow as it passes
adjacent to the sharp edge of a hole through the baffle. The holes
in the adjacent baffles are slightly staggered in a lateral
direction to avoid channeling through aligned holes, The high shear
rates near the edge of the hole generate a high degree of
dispersion as already mentioned, followed downstream by turbulent
shear layers which merge into a turbulent jet. A certain degree of
coalescence occurs in the jet downstream of a hole owing to the
highly turbulent nature of the flow, but no other means are
provided to intensify coalescence. In practice, a certain length of
coalescing zone (usually a length of pipe) follows a set of
baffles, typically 3-6 times the diameter of the baffles.
Coalescence in this zone is generally low and is simply due to
natural turbulence.
[0018] A reactor similar in design to the jet-impingement reactor
is described in U.S. Pat. No. 6,506,949 issued Jan. 14, 2003 and
assigned to Dow Global Technologies Inc. This reactor also uses a
set of baffles with holes for drop dispersion, followed by sections
of straight pipe to allow drop coalescence. A key feature
distinguishing the Dow reactor from the Noram reactor is that the
Dow design requires the reactor to be horizontal, whereas the Noram
reactor can be arranged either horizontally or vertically. The
baffle holes in the Dow reactor are located in the bottom part of
the baffles. The claimed benefit of this arrangement when used for
nitrating benzene in mixed acids is that, passing into a
coalescence zone of straight pipe following a baffle, the
benzene-MNB drops, being lighter than the surrounding mixed acid,
will rise upward and coalesce in the upper portion of the pipe. As
gravity is a relatively weak body force, a considerable length of
pipe is needed to produce any significant coalescence (a most
preferable coalescence zone length of 120 times the pipe diameter
is cited in the Dow patent). This requirement leads to impractical
reactor lengths and very long residence times, generally
undesirable features.
SUMMARY OF THE INVENTION
[0019] To address the shortcomings of the prior art, the present
invention makes use of the principle that reaction rates for
heterogeneous reactions can generally be increased by promoting
both dispersion and coalescence. In other words, by intensifying
the principal processes that control the availability of fresh
reactants to the reacting interface, reaction rates can be
increased.
[0020] Accordingly, the present invention provides apparatus to
allow chemical reactions between reactants comprising:
[0021] a vessel through which the reactants flow;
[0022] a baffle structure within the vessel to define at least one
flow cell having an interior and at least one inlet to allow flow
to pass into the cell interior as a jet to define a dispersion zone
for the reactants, and an obstruction spaced from the at least one
inlet to redirect the flow and form a coalescence zone for the
reactants adjacent the obstruction, and at least one outlet to
allow flow to exit the flow cell.
[0023] The present invention also provides apparatus to allow
chemical reactions between reactants comprising:
[0024] a vessel through which the reactants flow including a first
reactant distributed as drops throughout a second reactant;
[0025] a baffle structure within the vessel to define at least one
flow cell having an interior and at least one inlet to allow flow
to pass into the cell interior as a jet to define a dispersion zone
for the drops, and an obstruction spaced from the at least one
inlet to redirect the flow and form a coalescence zone for the
drops, and at least one outlet to allow flow to exit the flow
cell.
[0026] The present invention also provides apparatus to allow
chemical reactions between reactants comprising:
[0027] a vessel through which the reactants flow including a first
reactant distributed as drops throughout a second reactant; and
[0028] means for controlling the flow of reactants through the
vessel to intensify the dispersion and coalescence of the drops
comprising:
[0029] means for creating a zone of dispersion for the drops;
and
[0030] means for creating a zone of coalescence for the drops.
[0031] In a further aspect, the present invention provides a method
for promoting chemical reactions between reactants comprising:
[0032] delivering the reactants through a vessel in a mixed flow
including a first reactant distributed as drops throughout a second
reactant; and
[0033] controlling the flow through the vessel to create a flow
path that alternates between dispersing the drops and coalescing
the drops to increase the reaction rate.
[0034] The apparatus and method of the present invention provide
benefits that include the likelihood of reduced reactor size and
therefore capital costs, and perhaps more significantly, the
possibility of reducing side reactions and byproduct formation. The
apparatus to intensify dispersion and coalescence for reactant
drops is achieved in simple reactors with no moving parts, having
designs that avail themselves of simple methods of fabrication and
requiring little or no maintenance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] Aspects of the present invention are illustrated, merely by
way of example, in the accompanying drawings in which:
[0036] FIG. 1 shows schematically the dispersion and coalescence of
reactant drops which is the principle on which the apparatus of the
present invention is based;
[0037] FIGS. 2a-2c show schematically the idealized sequential
steps by which a drop is dispersed and coalesced to create
increased surface area for further reaction;
[0038] FIG. 3 is a schematic view showing a conventional
continuously stirred tank reactor (CSTR);
[0039] FIG. 4 is a schematic view showing a conventional pipe flow
reactor (PFR);
[0040] FIGS. 5a and 5b are schematic views showing how fluid body
forces and fluid shear forces are used to promote coalescence of
drops;
[0041] FIG. 6 is a schematic sectional view through a flow cell
used in the apparatus of the present invention;
[0042] FIG. 7 is a schematic cross-sectional view showing a
preferred arrangement of generally T-shaped members to create an
array of flow cells;
[0043] FIGS. 8a and 8b are schematic views showing a reactor vessel
incorporating generally linear flow cells with linear slotted
inlets;
[0044] FIGS. 9a and 9b are schematic views showing another
embodiment of a reactor vessel having annular flow cells with
annular slotted inlets;
[0045] FIG. 10 is a schematic, cross-sectional view showing a
further embodiment of a reactor vessel having flow cells arranged
to intercept radially directed flow within a reactor;
[0046] FIGS. 11a to 11c show a still further embodiment of a
reactor vessel according to the present invention having annular
flow cells and an inlet arrangement for introducing one or more
reactants;
[0047] FIG. 12 is a chart showing the effect of changing cell
spacing, gap and element height in a reactor according to the
present invention; and
[0048] FIGS. 13 to 17 show various alternative reactor designs.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] The apparatus and method of the present invention rely on
the principle of intensifying the dispersion and coalescence of the
reactants to control the availability of fresh reactants to the
reacting interface, and thereby increase the reaction rates for
heterogeneous reactions.
[0050] The simplest and most practical means for producing intense
dispersion is by creating a very highly sheared flow, as in the
case of flow through a sharp edged orifice, slot, or hole in a
baffle. This situation is well understood, and has previously been
used in industrial applications. While many other means are also
possible, this is the main principle used in the following reactor
layouts.
[0051] Means to deliberately intensify coalescence have not been
previously reported, despite the equal importance of coalescence in
setting overall reaction rates. To see how simple fluid flow
situations can be used to intensify coalescence, two main means,
fluid body forces and fluid shear forces, are considered for the
case of reacting drops dispersed throughout a second liquid
reactant.
[0052] FIG. 5a illustrates schematically the case of fluid body
forces where the drops 40 of a first reactant are lighter than the
surrounding reactant fluid 42, for example, MNB/benzene drops in a
mixed acid. The situation in FIG. 5(a) shows successive time
intervals as the coalescence of drops 40 proceeds due to the
buoyancy of the drops within reactant fluid 42. As the drops float
upwardly within the reactant fluid against the force of gravity,
the drops tend to group and combine together. The fluid body force
of buoyancy due to gravity is a relatively weak force compared to
centrifugal forces, for example. Simple turning or redirection of a
flow can produce many `g`s of centrifugal force to increase
coalescence of drops.
[0053] FIG. 5(b) shows a less appreciated means of coalescing drops
using shear forces. A shear flow, in which drops 44 flowing further
away from a solid surface 45 move faster than those closer to the
surface, will coalesce drops as the slower drops 46 are overtaken
and merge.
[0054] The design elements of importance in intensified process
reactors are the creation of artificial body or centrifugal forces
by turning the flow channels sharply, and providing solid surfaces
to provide the maximum number of shear flows possible.
[0055] Bearing in mind the above dispersion and coalescence
techniques, the apparatus of the present invention incorporates a
unique flow cell structure that acts on reactants passing through
the cell to disperse and coalesce drops of one reactant dispersed
through a second reactant. FIGS. 6 is a schematic view in
cross-section of an exemplary flow cell according to the present
invention.
[0056] FIG. 6 shows a sectional view through two cells 42, 42' that
may be incorporated into a larger, repeated-cell structure. As will
be explained in more detail below, cells 42 and 42' are positioned
within a vessel through which reactants flow including a first
reactant distributed as drops throughout a second reactant. Each
cell acts as a means for controlling the flow of reactants to
intensify the dispersion and coalescence of the drops, and each
cell includes means for creating a zone of dispersion for the drops
and means for creating a zone of coalescence for the drops.
[0057] The means for forming zone of dispersion for the drops
comprises at least one inlet 44 in a first end wall 45 of the cell
that communicates with the interior 46 of cell 42.
[0058] Inlet 44 is shaped to create a jet flow into the cell. As
shown in FIG. 6, reactant flow enters cell 42 at the bottom left
through inlet 44 which is preferably a slot with a sharp edge 48 to
promote the formation of a downstream turbulent jet 50. Inlet 44
can also be formed as a plurality of discrete openings. Turbulent
jet 50 creates a dispersion zone 51 of dispersed drops.
[0059] The means for creating a zone of coalescence for the drops
comprises an obstruction in the form of second end wall 58. End
wall 58 causes reactant flow to turn sharply to the flow direction
of jet 50. Preferably, second end wall 58 is positioned to redirect
flow essentially transversely to the flow of the jet as indicated
by arrow 56. This results in the reactant flow encountering shear
flow along second end wall 58 to create a coalescence zone 60 along
the end wall. Turning the flow through a sharp corner also produces
a strong centrifugal force, which in turn coalesces the drops
further away from end wall 58 and forms a richly coalesced zone 62
in the central region of the cell interior 46 due to body fluid
forces.
[0060] An additional zone of intense coalescence 54 due to shear
forces is also created as the jet 50 of reactant flow passes along
side wall 52 of the cell. Coalescence zone 54 is, in fact, more
intense than the coalescence shear zone 60 along second end wall
58, and is not found in prior art jet impingement reactors.
[0061] As reactant flow continues along second end wall 58, it
encounters an outlet 64 for cell 42 which also serves as the inlet
44' into the next flow cell 42'. Outlet 64/inlet 44' is also
preferably a slot. The reactant flow turns sharply through inlet
44' into the second cell, and the flow pattern with associated
dispersion and coalescence zones is repeated. The sharp turn into
outlet 64/inlet 44' further coalesces the lighter drops in the
upper-central region of cell 42.
[0062] It will be noted that the basic cell discussed above serves
to intensify dispersion and coalescence in cases where the
dispersed drops of the first reactant are lighter or heavier than
the conveying fluid of the second reactant. The case for lighter
drops is described above. In the case of the drops being heavier
than the conveying fluid, for example, in a gas carrying drops of a
heavy hydrocarbon, it can easily be seen that the sharp turns
within the cell will cause the heavier drops to flow outward and
impact the walls of the cell, where the shear forces will form the
drops into thin films flowing along the wall, producing intense
coalescence within the film before their re-dispersion at the next
sharp inlet edge.
[0063] Practical constructions that emulate the basic flow cell
structure 42 described above can be arranged in many ways by a
person skilled in the art. A preferred arrangement that allows for
the basic cell structure to be repeated in an array of
interconnected cells is shown in FIG. 7. An array of flow cells 42
is formed from a series of members 65, each member having a
generally "T" shaped cross-section, arranged in a repeating
pattern. Each member 65 of generally T-shaped cross-section has a
head portion 68 and a base portion 70, and each member is
positioned such that head portion 68 is aligned transversely to a
flow of reactants indicated by arrow 72, and the base portion 70 is
aligned parallel to the flow. The members 65 are arranged in a
plurality of parallel rows 74, 76, 78 that extend in the direction
of reactant flow with every other row being offset such that the
base portion 70 of one member in an intermediate row 76 extends
between the head portions 68 of other members in adjacent rows 74
and 78. In this arrangement, the head portions 68 and base portions
70 of pairs of offset members 65 in adjacent rows co-operate to
form the end walls and side walls, respectively, of a flow cell.
Gaps between the head portions and the base portions of members 65
in adjacent rows create the inlets 44 and outlets 64 of the cells
such that the second end wall and outlet of one cell forms the
first end wall and inlet of a subsequent, adjacent flow cell. The
cells in FIG. 7 have an additional gap 76 in their upper left-hand
corner due to a spacing between the members 65 in each row,
however, this is a region of little, or no flow, so the flow
pattern described above and indicated generally by arrows 78 is
maintained with resulting zones of intensified dispersion and
coalescence in each flow cell 42.
[0064] As shown in FIGS. 8a and 8b, a reactor according to the
present invention is readily created by arranging the flow cells
described above within a vessel 80. In a preferred embodiment, the
vessel is a hollow body such as a pipe having a cylindrical side
wall 82 and a longitudinal axis 83. The reactants flow through the
pipe and encounter flow cells 42 formed internally within the pipe
interior 84. In the embodiment of FIGS. 8a and 8b, flow cells 42
are formed by a baffle structure 86 that includes T-shaped members
65 arranged in a repeating pattern, as described above in
conjunction with FIG. 7. The repeating pattern extends along the
longitudinal axis 83 of the vessel such that the T-shaped members
65 define an array of interconnected flow cells 42 that communicate
with each other by virtue of the outlet of one flow cell being the
inlet of one or more other flow cells as shown in FIG. 8b which is
a cross-section taken along line 8b-8b of FIG. 8a. As best shown in
FIG. 8a, which is an end view of the pipe reactor, the T-shaped
members extend transversely between the side wall 82 of the pipe to
define linear slotted inlets 44 to each flow cell that also extend
across the pipe. This configuration provides a maximum length of
sharp edge for dispersion of the drops when compared with holes or
other rounded shapes having the same amount of open area for flow
(an important concern that governs pressure drop across the
baffle). As necessary, baffle pieces, shaped in appropriate partial
circular segments are used to complete the array of T-shaped
members 65. In particular, segment pieces 90 and 92 are used at the
ends of a grouping of to complete the flow cells. Segment pieces 90
are also employed within an array of T-shaped members 65 to
complete the array adjacent pipe side wall 82.
[0065] The basic "T" members 65 can be repeated along a sufficient
length of pipe in the longitudinal direction so that complete
conversion of the reactants may be accomplished. Reactants flowing
through the reactor alternate between zones of dispersion and zones
of coalescence as they move through the interconnected flow cells
42 in the general flow pattern indicated by arrows 78 in FIG. 8b.
The relative dimensions shown in FIGS. 8a and 8b are only meant to
convey the concepts and would not necessarily be those used in
industrial practice. For example, in a MNB production reactor, the
cells might typically be 3-6 cm across, and there may be from 10-20
cells arranged across the circular cross-section of the reactor.
The opening slots could be 2-6 mm wide, and the overall reactor
length might be from 3-6 m.
[0066] FIGS. 9a and 9b show an alternative arrangement of flow
cells according to another embodiment of the reactor of the present
invention. Once again, the reactor vessel is a hollow body, such as
a pipe section, having a cylindrical side wall 102 and a
longitudinal axis 103. In this arrangement, the flow cells are of
an annular configuration formed from a plurality of spaced, annular
elements aligned along the axis 103 of the pipe. There is a
cylindrical core element 104 positioned along axis 103 having
sealed ends 122 as best shown in FIG. 9b which is a section view
taken along line 9b-9b of FIG. 9a. Annular ring elements 105 extend
radially outwardly from core element 104 toward side wall 102 at
spaced intervals. Similarly, annular ring elements 120 extend
radially inwardly from side wall 102 toward core element 104 at
spaced intervals. Annular ring elements 105 and 120 overlap within
an annular perimeter space 124 within the interior of the hollow
body to define a plurality of interconnected annular flow cells 142
having annular inlets 144 and annular outlets 164.
[0067] The arrangement shown in FIGS. 9a and 9b is easily
assembled. The relative dimensions shown are only intended to
convey the concept with clarity, and would not necessarily
represent dimensions used in industrial practice. The comments
above regarding typical dimensions for the reactor embodiment of
FIGS. 8a and 8b equally apply to the reactor arrangement of FIGS.
9a and 9b.
[0068] FIG. 10 shows a still further arrangement of a reactor
according to the present invention in which the flow cell structure
to create alternating dispersion and coalescence of drops within
the reactant flow is positioned circumferentially about the
interior of the reactor 130 to handle radially directed flow. FIG.
10 is a cross-sectional view through the reactor 130 and
illustrates one portion of reactor, it being understood that
identical portions are repeated along the full length of the
reactor. In the arrangement of FIG. 10, a baffle plate 132 blocks
the axial flow 134 of reactants along longitudinal axis 135 forcing
the flow radially outwardly through annular flow cell structure 136
which has inlets and outlets oriented to permit radial flow through
the cells. Passing through an annular perimeter channel 138, the
reactant flow then returns radially inwardly to the center of
reactor 130 to flow along reactor axis 135 again.
[0069] Reactor 130 comprises a hollow body formed with a plurality
of internal baffles extending transversely to the longitudinal axis
135 to restrict axial flow 134. In addition to baffle 132 which is
preferably a disc shaped plate positioned in the centre of the
reactor to blocking axial flow, the interior of the reactor also
includes a pair of annular baffle plates 140 spaced along the
longitudinal axis of the reactor on either side of baffle 132.
Baffles 132 and 140 define a series of interrupted central channels
150 for reactant flow extending between pairs of disc baffles 132,
and a series of interrupted annular perimeter channels 138 for
reactant flow extending between pairs of annular baffle plates 140.
Interrupted channels 150 and 138 communicate through the arrays 136
of flow cells extending between adjacent overlapping plate
surfaces.
[0070] All of the above-described reactor embodiments are intended
to operate in an environment where the reactants are mixed prior to
introduction into the reactor. FIGS. 11a to 11c show another
arrangement of a reactor according to the present invention which
also includes one or more vessel inlets 151 into the vessel 152 for
introducing at least one of the reactants.
[0071] FIGS. 11a and 11b show a hollow body reactor vessel 152,
such as a pipe section, having a cylindrical side wall 153 and a
longitudinal axis 103. In this reactor, the flow cells are of an
annular configuration formed from a plurality of ring cell elements
aligned along the axis 103 of the pipe section. FIG. 11c shows in
detail an exemplary ring cell element 104 positioned about axis
103, and formed from a cylindrical member 106 having an opening 107
therethrough of a first diameter, and an annular disc member 108
having a central opening of a second diameter 109, less than the
first diameter, positioned against an end of the cylindrical
member. As best shown in FIG. 11b, which is a cross-sectional view
through the reactor taken along line 11b-11b of FIG. 11a, each ring
cell element 104 defines a pair of "T" shaped elements spaced
equidistantly apart about axis 103. Groups of ring cell elements
104 of different diameters are inserted into hollow body 153 in a
repeating, nested pattern along longitudinal axis 103 to define an
array of interconnected flow cells 142 of annular configuration.
For example, in the illustrated reactor of FIG. 11b, three groups
of ring cell elements 104 are used with each group having a
different first diameter for opening 107, 107' or 107'' all centred
about axis 103. Each annular flow cell 142 defined by the ring cell
elements 104 includes an annular inlet 144 and annular outlet 164
formed generally by the gap between the disc member 108 of one ring
cell element and the cylinder member 106 of an adjacent ring cell
element.
[0072] The arrangement shown in FIGS. 11a-11d is easily assembled.
The relative dimensions shown are only intended to convey the
concept with clarity, and would not necessarily represent
dimensions used in industrial practice.
[0073] While the reactor embodiment of FIGS. 11a to 11c is also
shown to include vessel inlets 151, it will be understood that
inlets 151 can be incorporated into any of the previously described
reactor designs. Each vessel inlet 151 comprises at least one pipe
154 extending radially into vessel 152. Pipe 154 includes openings
156 to introduce one or more reactants into the other reactants
which are already flowing through the vessel. Openings 156 can be
positioned to introduce one or more reactants into multiple flow
cells simultaneously. For example, in the nitration of benzene, a
nitric-sulfuric acid mix would flow through the reactor as
indicated by arrow 160 and benzene would be introduced into the
reactor via inlet pipe 154 as indicated by arrow 162 to form
mononitrobenzene (MNB), a precursor in the production of
polyurethanes, among other important products.
[0074] The flow cell arrangements described above are not an
exhaustive collection, but are merely intended to illustrate means
for achieving intensified dispersion and coalescence in practical
arrangements according to the spirit of the present invention.
Other flow cell arrangements that alternate between dispersion and
coalescence of reactant drops will be apparent to a person skilled
in the art. Actual dimensions, number of cells, and overall
configuration would be suited to production rates and other process
considerations.
[0075] The intensified dispersion and coalescence processes
previously described can be effected in a variety of geometrical
arrangements, each leading to greater or lesser degrees of
intensification or coalescence. Each geometrical arrangement in
turn presents unique fabrication challenges, so that trade-offs are
required with different mechanical designs.
[0076] Specific arrangements of the flow cell spacing, gaps and
element heights/widths can have a profound influence on the
relative amount of dispersion and coalescence generated within.
FIG. 12 is a chart showing a paradigm of (two dimensional) cell
designs; the left column shows the result of increases in cell
spacing (s) (the distance between the first and second end walls),
the middle column shows the effect of cell gap (g) which affects
the dimensions of the cell inlet or outlet, and the right column
shows the effect of changing the height (h) of the side walls of
the cell.
[0077] The upper left hand panel (marked s, g, h) can be expected
to have the highest degree of both coalescence and dispersion owing
to the sharp changes in flow direction, the highest ratio of cell
wall to volume, and the narrowest fluid gaps. Correspondingly,
panel (3s, g, 0.2h) in the lower right hand corner represents an
arrangement with less intense dispersion and coalescence.
[0078] While cell (s, g, h) could be assembled from a series of
"T"-bar shapes or ring elements as previously described, cells of
the (3s, 3g, h) and (3s, g, 0.2h) type could be made much more
simply. For illustration, two further different designs are
described below.
High Dispersion
[0079] A flow cell of the (3s, g, 0.2h) type in the limiting case
can be incorporated into a simple reactor as shown in FIG. 13.
[0080] This design emulates the well-known "jet-impingement"
reactor with good dispersion characteristics. It also has the
benefit of potentially increased dispersion (owing to slots, rather
than holes) for the same pressure drop (open area). To a certain
extent coalescence can be improved by varying spacing between
plates. Great practical benefit arises from a single diameter pipe
enclosure, with a minimum number of gaskets, joints and other
potential leak points.
[0081] High Coalescence Arranging the cells as (3s, 3g, h), with
some compaction in dimensions, results in a reactor geometry as
shown in FIG. 14. The long parallel flow channels will result in
relatively greater tendency for shear-flow induced coalescence,
while maintaining some degree of dispersion as a result of the
periodic cross-struts along the flow. This design has the potential
of lower overall pressure drop being required.
High Dispersion, Modest Coalescence
[0082] The (3s, 3g, h) cell in FIG. 14 can be further extended to a
very simple design incorporating a series of slotted plates as
shown in FIG. 15.
[0083] The expected fluid flow behavior in such a simple reactor
can be appreciated from FIG. 16. Each turbulent jet issues from a
slot and spreads at an included angle of approximately 17 degrees.
The edge of the spreading jet is a region of high shear, and
therefore high dispersion. In the region of shear layers
overlapping, the turbulence level will be further increased, with
the potential increase in coalescence.
[0084] It might be noted that the geometry shown in FIGS. 15 and 16
also has the potential for moderate pressure drop, since the area
open to the flow can easily be as high as 50%.
[0085] Further, owing to the geometry of the spreading jets, the
optimum spacing between slotted plates is a function of slot width,
and so can be estimated beforehand. Fairly compact reactors are
envisioned. FIG. 17 shows as an illustration a typical plate
spacing/reactor diameter geometry.
[0086] Although the present invention has been described in some
detail by way of example for purposes of clarity and understanding,
it will be apparent that certain changes and modifications may be
practised within the scope of the appended claims.
* * * * *