U.S. patent application number 10/213643 was filed with the patent office on 2002-12-26 for retrofit reactor including gas/liquid ejector and monolith catalyst.
Invention is credited to Broekhuis, Robert Roger, Machado, Reinaldo Mario.
Application Number | 20020197194 10/213643 |
Document ID | / |
Family ID | 24293145 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020197194 |
Kind Code |
A1 |
Machado, Reinaldo Mario ; et
al. |
December 26, 2002 |
Retrofit reactor including gas/liquid ejector and monolith
catalyst
Abstract
This invention relates to apparatus suited for gas-liquid
reactions such as those employed in the hydrogenation or oxidation
of organic compounds. The apparatus comprises the following: a tank
having at least one inlet for introduction of liquid, at least one
outlet for removal of liquid, and at least one outlet for removal
of gas; a pump having an inlet and an outlet; a liquid motive gas
ejector having at least one inlet for receiving liquid, at least
one inlet for receiving a reactant gas and, at least one outlet for
discharging a resulting mixture of said liquid and said reactant
gas to a monolith catalytic reactor. Circulation of liquid is
effected from the tank to the ejector, to the monolith catalytic
reactor and then back to the tank. Gas is drawn from the tank to
the ejector and mixed with the liquid prior to entry to the
catalytic reactor.
Inventors: |
Machado, Reinaldo Mario;
(Allentown, PA) ; Broekhuis, Robert Roger;
(Allentown, PA) |
Correspondence
Address: |
AIR PRODUCTS AND CHEMICALS, INC.
PATENT DEPARTMENT
7201 HAMILTON BOULEVARD
ALLENTOWN
PA
181951501
|
Family ID: |
24293145 |
Appl. No.: |
10/213643 |
Filed: |
August 6, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10213643 |
Aug 6, 2002 |
|
|
|
09573726 |
May 18, 2000 |
|
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|
Current U.S.
Class: |
422/600 ;
422/211; 423/659 |
Current CPC
Class: |
B01J 8/025 20130101;
B01J 19/2485 20130101; B01J 19/26 20130101; B01J 2219/00166
20130101; B01J 2219/00162 20130101; B01J 2219/00024 20130101; B01J
2219/00033 20130101; B01J 19/1881 20130101; Y10S 423/13 20130101;
B01J 2219/00094 20130101 |
Class at
Publication: |
422/190 ;
423/659; 422/211 |
International
Class: |
B01J 035/04; B01J
008/00 |
Claims
1. An apparatus for gas-liquid reactions such as those employed in
the hydrogenation or oxidation of organic compounds which comprises
the following: a tank having at least one inlet for introduction of
liquid, at least one outlet for removal of liquid, and at least one
outlet for removal of gas; a pump having an inlet and an outlet; a
liquid motive gas ejector having at least one inlet for receiving
liquid, at least one inlet for receiving a reactant gas, and at
least one outlet for discharging a mixture of said liquid and said
reactant gas; a monolith catalytic reactor having an inlet and an
outlet; wherein: the inlet of said pump is in communication with
said outlet from said tank for removal of liquid and said outlet of
said pump is in communication with said inlet of said liquid motive
gas ejector for receiving liquid; the outlet from said liquid
motive gas ejector for discharging the resultant mixture of liquid
and gaseous reactant is in communication with the inlet to said
monolith catalytic reactor and the outlet of said monolith
catalytic reactor is in communication with at least one inlet to
said tank; and, the outlet from the tank for removal of gas is in
communication with said inlet of the liquid motive gas ejector for
receiving gas.
2. The apparatus of claim 1 wherein the monolith catalytic reactor
contains between 10 and 1000 channels per square inch of
cross-sectional area.
3. The apparatus of claim 2 wherein the monolithic structure is
made of metal, ceramic or carbon, or combinations thereof.
4. The apparatus of claim 3 wherein the channels of the monolith
are filled with catalyst particles and the monolith catalytic
reactor has from 10 to 50 channels per square inch.
5. The apparatus of claim 3 wherein the support is coated with
catalytic metal.
6. The apparatus of claim 5 wherein the support has from 200 to
1000 channels per square inch.
7. In a process for the catalytic reaction of compounds wherein a
liquid compound is contacted with a gaseous reactant in the
presence of a catalytic component, the improvement which comprises
effecting the reaction in a catalytic retrofit for a slurry reactor
wherein: (a) circulating a feed mixture of gaseous reactant and
liquid compound to a liquid motive gas ejector under conditions for
mixing said gaseous reactant and said liquid compound; (b) removing
the mixture of liquid compound and reactant gas from said liquid
motive gas ejector and charging said mixture to the inlet of a
monolith catalytic reactor; (c) effecting reaction between said
liquid compound and said gaseous reactant and thereby forming a
reaction product containing unreacted liquid compound, unreacted
gaseous reactant and final product; (d) removing the reaction
product from the exit of the monolith catalytic reactor and
introducing to a tank; (e) removing reaction product and additional
liquid compound from said tank; (f) removing gas from said tank;
(g) circulating the reaction product which had been discharged to
the tank in step (d) to the liquid motive gas ejector and combining
it with gas from the headspace of said tank per step (f), and, then
through the monolith catalytic reactor until the desired conversion
is effected, and then, (h) removing final product from the process
when the reaction has reached desired conversion.
8. The process of claim 7 wherein the residence time through the
monolith catalytic reactor is from 0.5 to 60 seconds.
9. The process of claim 7 wherein the monolith catalytic reactor
has from 10 to 50 channels per square inch and the channels are
filled with catalyst particles.
10. The process of claim 7 wherein the pressure differential from
the inlet to the monolith catalytic reactor to the exit of said
monolith catalytic reactor is from 0.5 to 30 pounds per square
inch.
11. The process of claim 7 wherein the channel density in the
monolith catalytic reactor is from 200 to 1000 channels per square
inch and the catalyst is coated on the support walls.
12. In an apparatus suited for effecting catalytic reactions
between a reactant gas and reactant liquid, the improvement which
comprises in combination: a liquid motive gas ejector having at
least one inlet for receiving liquid, at least one inlet for
receiving a reactant gas, and at least one outlet for discharging a
mixture of said reactant liquid and said reactant gas; and, a
monolith catalytic reactor having an inlet for receiving reactant
gas and reactant liquid in communication with said outlet of said
liquid motive gas ejector and an outlet for discharging a reaction
product.
13. The apparatus of claim 12 wherein the monolith catalytic
reactor has from 200 to 1000 channels per square inch and the
catalytic material is coated on the walls of the support.
14. The apparatus of claim 13 wherein the monolith catalytic
reactor has a transition metal catalyst coated on the channel walls
of the support.
15. The apparatus of claim 12 wherein the monolith catalytic
reactor has from 10 to 50 channels per square inch and the channels
are filled with catalyst particles.
Description
BACKGROUND OF THE INVENTION
[0001] Many industrial reactions, particularly those that involve
the hydrogenation of organic compounds, are performed in stirred
tank reactors employing a slurry catalyst system. Slurry catalysts
are solid-phase, finely divided powders and are carried in the
liquid reaction medium. The catalytic reaction is carried out,
then, by contacting a reactive gas, such as hydrogen or oxygen,
with the liquid organic compound in the presence of the solid-phase
catalyst. On termination of the reaction, the catalyst is removed,
generally by filtration, and the reaction product is recovered.
[0002] Slurry catalyst systems are inherently problematic in a
number of areas, including industrial hygiene, safety,
environmental, waste production, operability, selectivity and
productivity. One problem, for example, is that these catalysts
often are handled manually during a typical hydrogenation operation
in a stirred tank reactor. Another is that many of the catalysts,
hydrogenation catalysts in particular, are pyrophoric and thereby
create additional safety concerns. These problems are compounded to
a certain extent in that reaction rate often is a function of the
catalyst concentration and, thus, catalyst concentrations generally
are kept at high levels.
[0003] Monolith catalysts have been suggested for use in industrial
gas-liquid reactions, but have achieved limited success. One of the
advantages of monolith catalysts over slurry catalysts is that they
eliminate the handling of powdered catalysts, including catalyst
charging and filtration when the reaction is complete.
[0004] The following articles and patents are representative of
catalytic processes including hydrogenation of organic
compounds.
[0005] Hatziantoniou, et al. in "The Segmented Two-Phase Flow
Monolithic Catalyst Reactor. An Alternative for Liquid-Phase
Hydrogenations,", Ind. Eng. Chem. Fundam., Vol. 23, No.1, 82-88
(1984) discloses the liquid-phase hydrogenation of nitrobenzoic
acid to aminobenzoic acid in the presence of a solid palladium
monolithic catalyst. The monolithic catalyst consisted of a number
of parallel plates separated from each other by corrugated planes
forming a system of parallel channels having a cross sectional area
of 1 mm.sup.2 per channel. The composition of the monolith
comprised a mixture of glass, silica, alumina, and minor amounts of
other oxides reinforced by asbestos fibers with palladium metal
incorporated into the monolith in an amount of 2.5% palladium by
weight. The reactor system was operated as a simulated, isothermal
batch process. Feed concentrations between 50 and 100 moles/m.sup.3
were cycled through the reactor with less than 10% conversion per
pass until the final conversion was between 50% and 98%
[0006] Hatziantoniou, et al. in "Mass Transfer and Selectivity in
Liquid-Phase Hydrogenation of Nitro Compounds in a Monolithic
Catalyst Reactor with Segmented Gas-Liquid Flow", Ind. Eng. Chem.
Process Des. Dev., Vol. 25, No.4, 964-970 (1986) disclose the
isothermal hydrogenation of nitrobenzene and m-nitrotoluene in a
monolithic catalyst impregnated with palladium. The authors report
that the activity of the catalyst was high and therefore
mass-transfer determined the rate. Hydrogenation was carried out at
590 and 980 kPa at temperatures of 73 and 103.degree. C. Less than
10% conversion per pass was achieved.
[0007] U.S. Pat. No. 4,743,577 discloses metallic catalysts which
are extended as thin surface layers upon a porous, sintered metal
substrate for use in hydrogenation and decarbonylation reactions.
In forming a monolith, a first active catalytic material, such as
palladium, is extended as a thin metallic layer upon a surface of a
second metal present in the form of porous, sintered substrate and
the resulting catalyst used for hydrogenation, deoxygenation and
other chemical reactions. The monolithic metal catalyst
incorporates such catalytic materials such as palladium, nickel and
rhodium, as well as platinum, copper, ruthenium, cobalt and
mixtures. Support metals include titanium, zirconium, tungsten,
chromium, nickel and alloys.
[0008] U.S. Pat. No. 5,063,043 discloses a process for the
hydrogenation of anthraquinones using a monolithic reactor. The
reactor is operated in a down-flow configuration, in which liquid
is distributed to the top of the reactor, and hydrogen is drawn
into the reactor by the action of gravity on the descending liquid.
In the preferred implementation, in which there is no net pressure
difference between the inlet and the outlet of the reactor, this
mode of operation can be characterized as gravity downflow.
BRIEF SUMMARY OF THE INVENTION
[0009] This invention relates to apparatus suited for gas-liquid
reactions such as those employed in the hydrogenation or the
oxidation of organic compounds and to a process for effecting
gas-liquid reactions. The apparatus comprises the following:
[0010] a tank having at least one inlet for introduction of liquid,
at least one outlet for removal of liquid, and at least one outlet
for removal of gas;
[0011] a pump having an inlet and an outlet;
[0012] a liquid motive gas ejector having at least one inlet for
receiving liquid, at least one inlet for receiving a reactant gas,
and at least one outlet for discharging a mixture of said liquid
and said reactant gas;
[0013] a monolith catalytic reactor having an inlet and an
outlet;
[0014] wherein:
[0015] the inlet of said pump is in communication with said outlet
from said tank for removal of liquid and said outlet of said pump
is in communication with said inlet of said liquid motive gas
ejector for receiving liquid,
[0016] the outlet from said liquid motive gas ejector for
discharging the resultant mixture of liquid and gaseous reactant is
in communication with the inlet to said monolith catalytic reactor
and the outlet of said monolith catalytic reactor is in
communication with at least one inlet to said tank, and,
[0017] the outlet from the tank for removal of gas is in
communication with said inlet of the liquid motive gas ejector for
receiving gas.
[0018] The apparatus described herein enables one to effect a
catalytic retrofit of a slurry reactor and thereby offer many of
the following advantages:
[0019] an ability to eliminate slurry catalysts and thereby
minimize handling, environmental and safety problems associated
with slurry catalytic processes;
[0020] an ability to interchange catalytic reactors when changing
to a different chemistry in the same equipment;
[0021] an ability to effect multiple (sequential or parallel)
reactions by using multiple catalytic reactors arranged either in
series or in parallel;
[0022] an ability to maintain a separation of the reactants and
reaction products from the catalyst during heat-up and cool-down
and thereby minimize by-product formation and catalyst
deactivation; and,
[0023] an ability to precisely start and stop a reaction by
initiating or terminating circulation of the reactor contents
through the liquid motive gas ejector and monolith catalytic
reactor.
BRIEF DESCRIPTION OF THE DRAWING
[0024] The drawing is a view of a stirred tank reactor retrofitted
for use with a monolith catalytic reactor.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Slurry processes often suffer from the problem of excessive
by-product formation and catalyst fouling or deactivation. These
problems are in addition to those of handling and separation in
slurry catalyst operation. One explanation for byproduct formation
and catalyst deactivation is that during start-up and shutdown of a
process, the catalyst is in contact with the liquid phase and the
reactants and/or reaction products therein for an extended period
of time. Conditions during start-up and shutdown involve heat-up,
cool-down, pressurization, and venting of the stirred tank which
may have an adverse effect on the product quality and catalyst
activity. For example, the changing conditions, particularly during
shutdown when the catalyst is in contact with the reaction product,
often promote byproduct formation and catalyst deactivation. Thus,
the extended contact of the catalyst with the reactants and
reaction product limits the ability of the operator to control
reaction conditions.
[0026] To facilitate an understanding of the retrofitted stirred
tank reactor equipped with a monolith catalyst and to understand
how it addresses the above problems and achieve the many advantages
that can result therefrom, reference is made to FIG. 1. FIG. 1 is a
schematic of a retrofit apparatus for a stirred tank reactor
employing a monolith catalytic reactor. The retrofit system 2
comprises a tank 4, a circulation pump 6, a liquid motive gas
ejector 8 and a monolith catalytic reactor 10.
[0027] Tank 4, which commonly existed before the retrofit as a
stirred tank slurry reactor, has a jacket 12 for effecting heating
and cooling of the contents therein and an agitator 14. Other
means, e.g., external exchangers for heating and cooling and
agitation of tank contents, such as are commonly encountered in
industrial practice may be used in the retrofit apparatus 2. Tank 4
is equipped with at least one liquid feed inlet, typically two or
more. As shown, inlet 16 provides for introduction of liquid feed
or reactant, which may consist of a liquid compound or a solution
of such a compound in a suitable solvent. Inlet line 18 provides
for the introduction of reaction effluent from the outlet from
monolith catalytic reactor 10. A liquid effluent which consists of
reaction product, and may, depending upon conditions, contain
unreacted feed, flows via outlet 20 from tank 4 to the inlet of the
circulation pump 6.
[0028] The circulation pump 6 transfers the liquid reactant to the
liquid motive gas ejector 8 via circulation line 22 and liquid flow
rate is controlled either through control valve 23 or circulation
pump 6. Circulation pump 6 provides the motive energy for drawing
reactant gas from the headspace of tank 4 via line 24 or from
makeup gas line 26 to the gas inlet of the liquid motive gas
ejector. The maximum gas flow is determined by the flow rate of
liquid. It may be controlled to a smaller flow by means of valve
27.
[0029] The monolith catalytic reactor 10 itself comprises a
structure having parallel channels extending along the length of
the structure. The structure, commonly referred to as a monolith,
may be constructed from ceramic, carbon or metal substrates, or
combinations thereof. The structure may be coated with a catalytic
material directly or through the use of a washcoating or
carbon-coating procedure, using methods known in the art of
catalyst preparation. Alternatively, catalyst particles may be
placed in the channels rather than coating catalyst materials onto
the surface of the channels. The monolith catalytic reactor
channels may be of various shapes, e.g., circular, square,
rectangular, or hexagonal. The structure may contain from 10 to
1000 cells per square inch of cross-sectional area. A monolith
support filled with catalyst may have from 10 to 50 cells per
square inch while monolith supports having catalyst coated on the
surface may have from 200 to 1000 cells per square inch.
[0030] A wide variety of catalytically active materials may be
incorporated into or onto the monolith catalytic reactor, depending
upon the reaction to be carried out. Examples include precious and
transition metals, Raney metals, metal oxides and sulfides, metal
complexes and enzymes, and combinations or mixtures thereof, such
as a palladium-nickel combination. The concentration of
catalytically active compound is determined by the rates of
reaction and mass transfer on and to the catalytic surface, and
typically ranges from 0.5 to 10% by weight, specified either
relative to the weight of the monolith or to the weight of the
washcoat, if one is employed.
[0031] The reactor diameter and length are sized to provide the
desired velocities and residence times in the reactor. The reactor
diameter is chosen to achieve a liquid superficial velocity through
the reactor of 0.05 to 1.0 meters per second, preferably 0.1 to 0.5
meters per second. These flow rates are consistent with the
necessity of obtaining high rates of mass transfer. The reactor
length is chosen to achieve a residence time in the reactor of 0.5
to 60 seconds, depending on the rate at which the chemical reaction
proceeds. Practical considerations limit the length of the reactor
to be no less than half of the diameter of the reactor, and
generally no more than about 3 meters.
[0032] It has been found that that the performance of the monolith
catalytic reactor component of the retrofit apparatus is enhanced
by including a liquid motive gas ejector at its inlet. The liquid
motive gas ejector combines the liquid with reactant gas under
conditions to enhance both mixing and enhanced mass transfer in the
monolith catalytic reactor. These improvements can be attained
because the liquid motive gas ejector allows one to control the
pressure at which the gas-liquid mixture is presented to the
monolith catalytic reactor. It is desired that the inlet pressure
established by the liquid motive gas ejector exceeds the liquid
head in the monolith catalytic reactor. The pressure differential
is expressed as pounds per square inch differential (psid).
Typically a pressure differential can range from 0 to about 30 psid
but preferably ranges from 0.5 to about 20 psid.
[0033] One of the advantages achieved through the retrofit
apparatus is the fact that the reactants and reaction product,
except for the period in which these components are in contact with
the catalyst itself during the reaction phase, are kept separate
from the catalyst. This is accomplished through the unique
configuration of the retrofit apparatus utilizing tank 4, and
allows for enhanced catalyst activity, reduced catalyst
deactivation rate and fewer byproducts. The mode of operation to
attain this enhanced performance is described in the following
paragraphs.
[0034] Liquid is charged to tank 4 via feed line 16. In some
situations it may be advantageous to feed the liquid into the
circulation line 22 upstream or downstream of the liquid motive gas
ejector or the monolith catalytic reactor. The feed generated in
the tank is circulated via the circulation pump to the liquid
motive gas ejector and mixed with gas. The process may be operated
as a batch whereby the contents in tank 4 are conveyed from the
tank, through the ejector, through the monolith catalytic reactor
and then back to the tank reactor until the desired conversion is
reached. Optionally, the process may be operated continuously by
withdrawing a portion of the liquid through product line 28. When
the process is not operated continuously, it is usually
advantageous to start liquid circulation only after all conditions
required for reaction have been attained, e.g., liquid has been
heated to temperature and reactant gas is raised to pressure.
[0035] Liquid is circulated via the circulation pump 6 from tank 4
and conveyed via line 22 to the inlet of the liquid motive gas
ejector 8. The gaseous component for the reaction is withdrawn from
the headspace of tank 4 through suction line 24, and is
simultaneously compressed by and mixed with the high pressure
liquid introduced to the liquid motive gas ejector. Generally, the
volumetric flow of reactant gas is from about 5 to 200%, typically
from 50 to 150% of the volume of reactant liquid. As reactant gas
is consumed in the catalytic reactor, it may be supplemented with
makeup gas entering through line 26. Makeup gas may be introduced
at any point in the process, such as into the headspace or liquid
contents of tank 4, into suction line 24, or into piping downstream
of the ejector.
[0036] The introduction of the liquid motive gas ejector presents a
considerable advantage over operation in gravity downflow mode. In
gravity downflow mode, the liquid superficial velocity is
determined to a great extent by the size of the flow passages
(monolith channels, or spacing between particles inside these
channels). Gravity downflow operation is limited in most practical
cases to monoliths having no more than 400 unobstructed channels
per square inch of cross-section. Also, gravity mode is subject to
flow instabilities and reversal of flow direction. The ability to
generate high pressure drops through the monolith catalytic reactor
and high liquid velocities allows one to attain high rates of mass
transfer. It also allows operation of the monolith at any angle to
the vertical, including an upflow mode or in a horizontal position;
it also avoids instabilities in the process.
[0037] Because the reactor component of the retrofit apparatus is
separate from the feed and reaction product maintained within tank
4, the reaction can be conducted until a desired conversion is
reached, at which time circulation through the reactor is
terminated. Final reaction product is removed via line 28. This
allows one to optimize conversion with selectivity, since often
higher conversions lead to greater by-product formation.
Furthermore, at a given conversion, by-product formation is
normally lower than in conventional stirred tank operations because
the liquid is not in constant contact with the catalyst component
of the reaction system, and because high rates of mass transfer can
routinely be attained by the combination of the ejector and the
monolith catalytic reactor.
[0038] The following examples illustrate various embodiments of the
invention and in comparison with the prior art.
EXAMPLE 1
Gravity Downflow Through Monolith Structure
[0039] In this example an apparatus incorporating the elements of
the invention (tank, pump, liquid motive gas ejector, and a
monolithic structure having a diameter of 2 inches and a length of
24 inches, and incorporating 400 channels per square inch of
cross-sectional area) was used to measure the rate of mass transfer
of oxygen from the gas phase (air) to the liquid phase (an aqueous
solution of sodium sulfite), using the steady-state sulfite
oxidation method. The liquid motive gas ejector was used as the
gas-liquid distribution device, but operated in such a way as to
simulate gravity downflow conditions.
[0040] The liquid flowrate through the ejector and the monolith
structure were chosen so that there was no net pressure drop
through the monolith structure, i.e., the frictional pressure loss
equaled the static pressure increase. This condition was attained
by limiting the liquid flow, and was established at the following
operating parameters: liquid flowrate, 9.1 liters per minute; gas
flowrate, 10.0 liters per minute; liquid pressure at inlet to the
ejector: 11 psig; net pressure drop: 0 psid.
[0041] The rate of mass transfer is described by means of the
volumetric gas-liquid mass transfer coefficient, k.sub.La. The
greater the value of k.sub.La, the greater the potential
productivity of the reactor in a reactive gas-liquid environment.
The coefficient k.sub.La was measured at this condition, and found
to be 1.45 seconds.sup.-1.
EXAMPLE 2
Ejector-Driven Flow Through Monolith Structure
[0042] Using the apparatus described in Example 1, flow conditions
were established using the ejector as both a liquid-gas
distribution device and as a gas compressor, i.e., without
restricting the liquid flow. At this condition, the corresponding
operating parameters were: liquid flowrate, 23.9 liters per minute;
gas flowrate, 36.1 liters per minute; liquid pressure at inlet to
the ejector: 65 psig; net pressure drop: .about.3.3 psid The
coefficient k.sub.La was measured at this condition and found to be
5.48 seconds.sup.-1.
1TABLE 1 Below compares the results of Examples 1 and 2.
Coefficient Superficial Superficial gas Net pressure seconds.sup.-1
liquid velocity velocity drop kLa Example 1 0.092 m/s 0.101 m/s 0
psid 1.45 Example 2 0.242 m/s 0.367 m/s 3.3 psid 5.48
[0043] Clearly, from Table 1 the gravity downflow mode of operation
limits the liquid and gas superficial velocities that can be
attained, and thereby limits the gas-liquid mass transfer
coefficient. In ejector-driven flow mode, a net positive pressure
drop can be used to increase liquid and gas superficial velocities,
which yields a great benefit in the gas-liquid mass transfer
coefficient. That large improvement in mass transfer is due to the
net pressure driving force exerted by the liquid-motive gas
ejector. The ability to achieve a positive pressure driving force
allows the use of more restricted monolith catalytic reactors and
monolith catalytic reactors having greater numbers of channels per
square inch simultaneously with high levels of mass transfer, which
then can enhance productivity.
* * * * *