WO1992010291A2

WO1992010291A2 - Catalyst support for oxidation reactions

Info

Publication number: WO1992010291A2
Application number: PCT/US1991/009131
Authority: WO
Inventors: Charles M. Finley; Charles L. Kissel
Original assignee: Cnc Development, Inc.
Priority date: 1990-12-07
Filing date: 1991-12-06
Publication date: 1992-06-25
Also published as: WO1992010291A3; AU9177191A

Abstract

A catalyst support for use in promoting oxidation reactions composed of metal particles is described. The metal particles are selected from the group of aluminum, tantalum, titanium, tungsten, niobium and mixtures thereof, where aluminum is preferred. The metal particles may have a rough diameter of from 0.02 to 5.0 mm. The particles may be in the form of spheres, shavings, irregular granules and the like. When the catalyst support is to be used in a tubular reactor, the ratio of the diameter of the reactor to the diameter of the catalyst may range from 2:1 to 200:1. The metal catalyst supports are inert in the reaction and give excellent uniformity in heat distribution throughout the catalyst bed. In oxidation reactions, the catalyst support may bear a metal oxide catalyst to give good results.

Description

CATALYST SUPPORT FOR OXIDATION REACTIONS

Field of the Invention The invention relates to catalyst supports, and more particularly, the invention relates, in one aspect, to catalyst supports for oxidation reactions.

Background of the Invention Catalyst supports are well known in the art. For example, various clays with high proportions of surface area to volume are known.

Representative examples include montmorillonite clays, bentonite clays, Fuller's earth, kaolin clays, sepiolite clays, attapulgite days, zeolites and mixtures thereof. Silica (sand) is also a commonly used catalyst support. Diatomaceous earth (diatomite; kieselguhr; infusorial earth) is also a common catalyst support. Ceramic-type materials, such as activated alumina, are also known as catalyst supports.

However, a common problem among conventional catalysts, whether used in fixed, fluidized or spouted beds, is that the heat distribution throughout the bed is poor, resulting in "hot spots" in the bed, which at a minimum degrade the product through unwanted side reactions and at worst cause runaway reactions with disastrous results.

Metals are known to provide better heat distribution through bodies of material, but metals are not used as catalyst support because they are also known to have catalytic activity themselves which can catalyze the reactants or products in undesirable side reactions. It is known to use metals themselves as catalysts without separate supports.

Summary of the Invention Accordingly, it is an object of the present invention to provide a catalyst support useful in oxidation reactions which gives good temperature distribution throughout the catalyst bed.

It is another object of the present invention to provide a catalyst support which can be readily manufactured. Another object of the present invention is to provide a catalyst support for oxidation reactions which does not adversely affect the oxidation reaction or its reactants or products.

In carrying out these and other objects of the invention, there is provided, in one form, a catalyst support for use in promoting oxidation reactions, -the support being metal particles where the metal particles are from the group of aluminum, tantalum, titanium, tungsten, niobium and mixtures thereof.

The catalyst is deposited on the supports of this invention, such as metal particles, such as spheres, shavings or the like. Depositing the catalyst on the metal particles improves temperature control and can significantly improve product yield.

A portable, self-contained system for generating dilute solutions of various products in significant quantities on-demand and on-site is ideal for use with the catalyst support of this invention, although it is expected that the catalyst support will find utility in other systems. With the portable system, the products are not produced and shipped in a concentrated liquid form, but instead are produced and used in a relatively short time on site in a dilute solution in a liquid compatible with the liquid to be treated.

A reactor using the catalyst supports of this invention can give a high yield to products from a reaction zone of about equal to or less than 18 inches long. Conventional prior art reactors are 10 to 30 times longer, making them impractical for use in portable units. A preferred configuration of a reactor in which the catalyst support of this invention may be employed uses an air pump, if air is one of the reactants; a storage tank for another of the reactants, if appropriate; a pump for water or other liquid into which the product is to be dissolved or absorbed, if appropriate; a high-temperature reactor thermally insulated and suitably shaped (for example, substantially in the form of a cube) for minimum consumption and loss of energy; an absorber system to collect product, if gaseous, from the reactor and place it into a liquid at high efficiency; an exhaust gas purifier; and a control system using gauges, valves, sensors, and electrical circuits for positive, safe operation. The system can be sufficiently small to be mounted on a skid or a trailer, and only the reactants, the liquid and either electricity or fuel for an electrical generator are required to permit on-site and on-demand generation of the product dissolved in a flowing liquid stream. With this invention, there is no need to produce a concentrated liquid product, thus avoiding any inherent hazards that might be present with a product in that form.

Brief Description of the Drawings These and other aspects of the invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 schematically shows a reactor that may contain the catalyst support of this invention connected to receive a mixture of two gases, and to discharge the reaction products into an absorber;

FIG. 2 is a view taken on line 2-2 of FIG. 1 showing details of the reactor in σoss-section;

FIG. 3 is a perspective view of one of the parallel plates in the reactor;

FIG. 4 is an enlarged view taken in the area 4-4 of FIG. 2; and FIG. 5 is a schematic diagram showing a circuit for controlling the temperature of the catalyst in the reactor.

Detailed Description of the Invention It has been discovered that in oxidation reactions that catalyst supports may be devised from materials heretofore believed unsuitable. It has been surprisingly found that metals and mixtures and alloys of metals of the group aluminum, tantalum, titanium, tungsten and niobium have been found to be useful. While these materials are known to have catalytic activity themselves in some contexts, in these oxidation reactions they are inert supports with the advantage of excellent temperature distribution throughout the catalyst bed.

The catalyst support has been actually used in conjunction with a relatively small, modular reactor can be devised, which may be easily moved from place to place to catalytically produce various chemical products. However, it will be appreciated that the catalyst support of this invention will find utility in other reactors and is not limited to the particular reactor system described in detail here. The reactor is an apparatus for making an organic product from at least two reactants, the apparatus having a catalyst chamber with an inlet and an outlet. A permeable bed of catalyst support of this invention may be in the chamber between the inlet and the outlet, and a catalyst which promotes the reaction of the reactants to form the product is present on at least some of the support partides. A mechanism is provided for introducing the reactants through the inlet to the reaction chamber, and another mechanism is provided for removing the organic product from the reaction chamber through the outlet. Although it is conceivable that the catalyst support of the present invention may find utility in the production of inorganic materials, it is expected that it will find more applications in the manufacture of organic compounds, particularly those compounds produced in oxidation reactions. As noted, the catalyst support of the present invention may be metal partides, where the metal partides are from the group of aluminum, tantalum, titanium, tungsten, niobium and mixtures thereof. The term "mixtures" as used herein indudes alloys of the above-listed metals with each other as well as other ways in which the various suitable metals may be mixed, such as simply being blended or dad together or used physically adjacent to one another. Typically, the partides may be from about 0.02 to 5.0 mm in diameter, and preferably from about 1-2 mm in diameter. The ratio of the reaction chamber diameter to the catalyst support diameter may range from about 2:1 to 200:1, and preferably from about 5:1 to about 20:1. The catalyst is provided on the partides in a uniform, adherent coating. In one embodiment for oxidation reactions, the catalyst is a metal oxide or a mixture of metal oxides.The resultant material does not dump together, nor does the catalyst become powdery and fall away from the aluminum partides during mixing or loading into the reaction chambers of the reactor. Aluminum is a preferred support in some embodiments. Other metal partides can also be used as a catalyst support, as long as the metal has good thermal conductivity, and does not adversely affect the production of acrolein. The catalyst support partides need not be perfect spheres, but can be granular and in other irregular shapes, such as pieces of metal shavings, saddles, rings and the like. Fabrication of the metal supports can be accomplished by any readily available and suitable metal production or machining process.

An apparatus capable of serving as the reaction chamber for the catalyst support can have various shapes, such as cylindrical or rectangular blocks, each containing hollow passageways capable of containing the catalyst and the reaction. These passageways may be tubular in nature, or they may be configured as to form a fixed-bed chamber, or numerous single tubes can be assembled in various arrays. Spouted beds or fluidized reactor zones could also be used. Though these later reaction chamber types have ineffident temperature/heating characteristics, the catalyst support of this invention will help improve those characteristics.

One apparatus for making acrolein indudes a reactor as described above with at least one pair of substantially parallel plates disposed side- by-side. Each plate indudes catalyst or reaction chambers which each have a respective inlet and outlet. A catalyst on the catalyst support of this invention in each chamber promotes the reaction, for example, the oxidation of propylene to acrolein, and a mechanism is provided for introdudng the reactants, such as a mixture of propylene and oxygen, into the catalyst chambers through the inlets. A heating element or panel between the plates heats the reactants and the catalyst to a temperature which causes the reactants to react with each other in the presence of the catalyst on the support to form the reaction products. A mechanism is also provided for removing the reaction products from the outlets of the catalyst chambers. In one configuration of this reactor, each plate is in the shape of a rectangular slab having major sides many times greater than the thickness of the slab. The slab has a first minor end and a second minor end opposite the first minor end. For example, each plate may be a rectangular slab about 1" thick, with opposing major faces each being approximately square and having a dimension of about 18" on each side. A plurality of elongated and laterally spaced bores extend through each plate in a direction substantially parallel to the major faces of the plate beginning at the first minor end and terminating at the second minor end, to provide as many as 20 to 30 parallel catalyst chambers in each plate. The reaction chambers may be said to extend from one minor end to an opposing minor end on opposite sides of the plate, beginning at one end with their inlet and terminating at the other with their outlet.

A thin, panel-shaped flat heating element may be sandwiched between adjacent major faces of a pair of plates to form a heated pair, or cell, the temperature of which is controlled by a thermostat mounted in a face of one of the plates adjacent the heating element. Preferably, heat insulation around the assembled plates which form the reactor limits the amount of external energy which must be applied to the apparatus. A separate respective capillary tube is connected at one end to a respective catalyst or reaction chamber inlet, and at the other end to a reactant supply pipe, whidi supplies a mixture of reactants to each catalyst chamber inlet through a respective capillary tube. These capillary tubes are fed by a common header containing pressurized mixed starting materials. This arrangement uses frictional drag in the tubes to control the flow rates through each of the separate reaction chambers. Although capillaries are preferred for flow control, other devices, such as orifices or adjustable valves, may also be used.

A separate elongated collection header over the outlets of the catalyst chambers in each plate collects reaction products leaving the reaction chambers. Each of the catalyst chambers is packed with a bed of catalyst on the catalyst support of the invention, which catalyst prefer¬ entially promotes the reaction, such as the oxidation of propylene to acrolein.

An embodiment of the reactor system indudes a plurality of pairs of parallel plates, each pair being constructed and arranged with a panel- shaped heating element as described above. A suffident number of the pairs of plates are staked together to form an array, or a reactor, essentially in the shape of a cube to minimize heat loss. In another embodiment, the plates could be curved or flat and arranged concentrically. The space between adjacent pairs of plates is thermally insulated to provide good temperature control in each pair of plates served by a respective panel- shaped heating element.

Preferably, the plates are made of a metal selected from the group of aluminum, tantalum, titanium, tungsten, niobium or mixtures thereof, or at least the inner surfaces of the reaction chambers are made from these metals. It is additionally preferred that all internal surfaces contacted by the gases and /or liquids passing through the catalyst chambers and collection headers, absorber, if present, and conduits connecting the headers and absorbers or other pieces of equipment are made of metals selected from that group. It is possible that some tubing and conduits not subjert to high temperatures may be made from inert polymeric plastics, elastomers and the like.

The cross-sectional area of each chamber is between 0.70 and 3.0 cm², and preferably is in the range of about 1.2 to 1.7 cm². Suitable mechanisms are provided for sensing the temperature of the catalyst and controlling the heat supplied by the heaters to keep the catalyst temperature within its operating range. Of course, if the expected reaction temperature range exceeds the softening point of the metal used to line the reaction chambers, for example of aluminum, one should plan to use a different material selected from the above-enumerated list.

The system also indudes a pump for taking a stream of liquid from a source of liquid which is to be treated with the reaction product. Spray nozzles connected to the pump outlet, or other source of liquid under pressure, spray liquid into an absorber, through which the reaction products from the catalyst chambers pass. The reaction product is absorbed in the liquid stream from the liquid supply, and added to the system which is to be treated, either as a stream diluted by the system to be treated, or undiluted if the system to be treated is composed wholly of the product stream from the reactor. If gases are a product, those which are not absorbed in the liquid sprayed into the absorber pass through a catalytic purifier.

The catalyst support of this invention has been successfully used to catalytically produce (1) acrolein from air and propylene; (2) methacrolein from isobutylene and air; and (3) acrylonitrile from propylene and ammonia. The example of making acrolein from propylene and air will be used from time to time throughout this description as representative of an actual use of the catalyst support, but the invention should not be limited to only this example.

Referring to FIG. 1, a reactor 10 in the general shape of a cube receives a gas mixture of air, as one reactant, and propylene, as the other reactant, from a plurality of horizontal and parallel supply lines 12 (see FIG.2), each connected at respective inlet ends through a respective T- joint 14 to the discharge of a respective air pressure regulator 16, -the inlet of which is connected by an air manifold line 18 to the discharge of air pump 20 having an inlet 22 connected to a filter 24, through which air is drawn. -

A tank of one of the reactants, propylene for example, has a disdiarge line 28 connected through a primary pressure regulator 30 and a filter 32 to a gas supply line 34 connected through a secondary pressure regulator 36 to the T-joint 14. Obviously, if liquid reactants are used, these gaseous sub-systems would be replaced by the liquid tanks, supply lines, etc

Reaction products from the upper side of the reactor are carried by a delivery pipe 38 (see FIG. 1) to an absorber 40, which indudes a housing 42 divided into first, second, third and fourth absorption zones 44, 46, 48 and 50, respectively. A first vertical baffle 52 extends from the top of the housing 42 downwardly to terminate just above a pool 54 of liquid, which may be water, fuel, or other liquid which absorbs acrolein. A second vertical baffle 56 mounted in the housing parallel to, and spaced horizontally from, the first baffle extends from below the level of liquid pool 54 and a short distance below the top of the housing. A third vertical baffle 58 parallel to, and spaced from, the second baffle extends from the top of the housing down to terminate just above the surface of the liquid pool 54. Each of the baffles extends entirely across the housing in a direction perpendicular to the plane of FIG. 1 so that the three baffles divide the housing 42 into the four absorption zones 44, 46, 48 and 50. A separate respective group of spray nozzles 60 mounted in the upper end of each absorption zone are supplied liquid from a liquid supply pipe 62 connected through a pressure regulator 63 to the disdiarge of a pump 64, which has as its inlet connected through a suction pipe 66 to a main body or stream of liquid flowing through a main pipe 68. line 66 and pump 64 may be replaced by other suitable sources, such as pressurized water lines typical of fire hydrants and hose bib stand pipes. In any event, the pressure of the incoming fluid is determined by a pressure regulator 63, or other suitable flow-monitoring device. A drain pipe 70 extends from the liquid pool 54 in the housing through a control valve 72 and a return pump 73 to return product- containing liquid in the absorber to the main pipe 68. Alternatively, the product-containing liquid may be sent to storage for future use. An exhaust conduit 74 carries unabsorbed gases from the upper end of the fourth absorption zone 50 to a catalytic purifier 76, which oxidizes the remaining hydrocarbons and any carbon monoxide to water and carbon dioxide, which are discharged to the atmosphere.

As shown in FIG. 2, the reactor 10 may be a sandwich assembly or array 80 of a plurality of flat, rectangular plates or slabs 82 disposed side-by- side so the reactor is substantially in the shape of a cube to minimize heat loss from a given volume for the reactor. A layer 83 of thermal insulating material surrounds the reactor to reduce heat loss and energy consump¬ tion. Each plate 82 has a first minor end 78 containing the inlets to the reactor plate, and a second minor end 79 opposite the first minor end containing the outlets. First minor end 78 and second minor end 79 are generally perpendicular to the major face of slab 82.

Although the plates may be of any suitable dimensions, a successful reactor has been designed in which the plates are about 18" x 18" x 1". The plates are assembled with their major surfaces vertically oriented to form the assembly 80 shown in FIG.2. A plurality of vertical bores 84 extend through each plate. If the plate is about 1" thick, it has been found that bores about 1/2" in diameter, and located on about 5/8" centers form properly spaced and dimensioned reaction chambers 86 (FIG. 2). The plates may be arranged in pairs 88 (FIG.2), with a separate, respective, flat electrical heating panel 90 disposed between adjacent faces 92 of each plate in each pair. A thin, separate, respective sheet 93 of ceramic insulation is between each face of each electric panel and the adjacent face of a plate. The thin sheet of ceramic insulation, which can be of any suitable thickness, say 0.03 to 0.0?', provides a more -uniform transfer of heat from the electric heating panels 90 to the entire adjacent surfaces of the plates. Electrical power leads 94 (FIGS. 2 and 5) supply power to the heater panels.

A thermocouple 95 on the inner end of a horizontal support 96 (FIGS. 4 and 5) in a horizontal groove 98 extending from about the center of one vertical edge of a plate in each pair to about the center of that plate, and opening toward the other plate in the pair, senses the temperature of the plates surrounding the respective reaction chambers 86, each of which is filled with a bed 100 of a catalyst which promotes the reaction upon the catalyst support of this invention. In this particular non-limiting example, the catalyst was a metal oxide catalyst. A separate pair of electrical signal leads 101 (see FIGS. 4 an 5) extend from each respective thermocouple to a respective adjustable thermostat 102, which controls the amount of electrical power supplied from a generator 103 to a respective electrical heater panel 90 to keep the catalyst in the adjacent reaction chamber 86 at the required operating temperature.

A separate, respective loose plug 104 (FIG. 2) of quartz wool in the bottom of eadi reaction chamber 86 rests on the upper end of a separate, respective short nipple 105 threaded into the lower end of a respective reaction chamber to form a reaction chamber inlet. The upper end of a separate, respective capillary tube 108 is sealed at its lower end to a respective gas supply pipe 12. The capillary tubes act as flow control devices and may be of any suitable internal diameter for that purpose. Capillary tubes with an inside diameter of about 0.007' provide good flow control and distribution of reactant gas from the supply pipes 12.

A separate, elongated, rectangular header 110 rests on a separate, respective graphite gasket 112 on the upper edge of each plate and over the upper (outlet) ends of the reaction chamber in each plate to collect reaction products which flow up through the reaction chambers, through respective holes 114 in the gaskets 112, and to the delivery pipe 38 (see FIGS, l and 2).

The reactor plates and all other components with surfaces contacted by the reaction products should be made of a material which has good thermal conductivity, and which does not adversely affect the production of the desired product. For example, to produce acrolein by oxidizing propylene, aluminum is preferred because of its relatively low cost. Other metals, such as tantalum, titanium, tungsten, niobium or mixtures of these, may also be used. Aluminum alloys of the 6000-type are preferred because they are inert, machinable, and can be welded. These are unusual materials for reactors, but have been found to be particularly advantageous for catalytic oxidation reactions. These metals are the same as those found useful for the catalyst support of this invention. The use of ferrous metals within the reactor decreases the selectivity of the process to aσolein, if that is the reaction run. Brass, bronze and copper are also not used because they deteriorate chemically when contacted with such reactants as air and propylene. Similarly, these metals are not desired for the catalyst support. We are not aware of any prior art use of aluminum equipment, except for the single report of the use of aluminum tubes that were coated with copper as a catalyst described by Xing and Inoue, K gaku Kogaku Ronbunshu, Vol. 10, No. 4, p. 439-45 (1984).

A separate respective panel 121 of thermal insulation between the adjacent outer faces 122 of each adjacent pair of plates provides good temperature control for each pair of plates served by a respective heating panel 90. The panels may be of any suitable material, such as sandstone, refractory material, spun glass, and the like. Each panel has suffi ent thickness to reduce thermal flow between reactor pairs 88. Although asbestos, asbestos-filled materials such as magnesia, and transite can provide adequate protection against thermal convention, their use is discouraged due to possible environmental health hazards. Each reaction chamber was filled with a mixture of aluminum support partides coated with catalyst to provide the catalyst bed. The catalyst/aluminum mixtures seem to give better yields and fewer side products, probably because the high thermal conductivity of the aluminum partides ensures substantially uniform temperature throughout the catalyst bed.

The operation of the reactor will now be described using the production of acrolein as illustrative only of an actual use of the catalyst support of the invention. With the reactor packed with beds of supported catalyst, as described above and shown in FIG. 2, a mixture of air and propylene in a ratio of 84:16, respectively, by volume, was fed into the inlets of the reaction chambers, which were heated to about 410°C. The pressure in the reaction chambers was between about 2 and about 5 lbs. /in.², and the flow rate per unit of cross-sectional area was about 100 ml/min./cm². The effluent from the reaction chambers 86 flowed through the aluminum headers and the aluminum delivery pipe 38, which were surrounded by a layer of insulation (not shown) to keep the gas in them at a temperature above about 60°C. to prevent premature condensation of acrolein, and into the upper end of the first absorption zone of the absorber. The effluent was contacted in the first absorber zone by a spray of water supplied by pump 64 to the spray nozzles. The intake of the pump was connected to main pipe 68 carrying a main stream of water to be treated with acrolein. Water droplets with absorbed acrolein fell into the pool 54 in the bottom of the absorber. Unabsorbed gases passed under the first baffle 52 and into the bottom of the second absorption zone following the arrows shown in FIG. 1, rising to meet more water droplets sprayed into the top of that zone. Additional acrolein was absorbed and carried to the pool in the bottom of the absorber. The unabsorbed gases continued over the top of the second baffle into the top of the third absorption zone for additional absorption of acrolein, and passed under the third baffle to flow up through the spray of water in the fourth absorption zone, and out the exhaust conduit 74 through the catalytic purifier 76.

The water sprayed into the absorber scrubbed more than 99.9% of the acrolein from the reactor effluent, and carried it into the liquid pool in the bottom of the absorber, where the acrolein-rich water was removed through the drainpipe 70 and returned to the main stream of water downstream of the pump inlet.

In the example just described, the concentration of the acrolein in the water pool in the bottom of the absorber was about 0.2%, by weight, and it was returned to the main water stream at a rate to give a treated solution with between about 1 and about 15 ppm aσolein for weed control in ditches through which the treated water flowed. Approximately the same concentration' ould be used for treating injection wells for secondary recovery of oil, or maintenance of gas pressure in an underground formation. In either case, the reactive nature of the acrolein in the dilute solution causes the acrolein to substantially disappear within & few days. It is possible to operate the absorber to produce a solution which contains up to about 25% aσolein by weight.

The aσolein added to water for secondary recovery can scavenge hydrogen sulfide H2S) and destroy microbes (e.g., anaerobic bacteria which consume sulfur, say from calrium sulfate which may be available in the injection water or in the formation, and convert it to H₂S, a corrosive compound), which may be in either the treated water, or downhole, or both.

Many modifications may be made in the catalyst support of the present invention without departing from its spirit and scope, which are defined only in the appended daims. For example, one skilled in the art may find that certain geometric configurations of the partides, or certain alloys of the preferred metals give particularly advantageous results. From the foregoing description, it will be seen that this invention provides a catalyst support for oxidation reactions that helps achieve uniform temperature distribution throughout the catalyst bed.

Claims

ClaimsWe Qaim:

1. A catalyst support for use in promoting oxidation reactions comprising metal partides where the metal partides are selected from the group consisting of aluminum, tantalum, titanium, tungsten, niobium and mixtures thereof.

2. The catalyst support of daim 1 where the metal partides have a rough diameter of from 1 to 2 mm.

3. The catalyst support of daim 1 where the metal is aluminum.

4. The catalyst support of daim 1 where the catalyst support is to be used in a tubular reactor of a first diameter and the catalyst support has a second diameter, and where the ratio of the first diameter to the second diameter ranges from 2:1 to 200:1.

5. The catalyst support of daim 1 where a metal oxide catalyst is present on the catalyst support

6. A catalyst support for use in promoting oxidation reactions comprising aluminum metal partides having a rough diameter of from 1 to 2 mm. and a metal oxide catalyst present thereon.

7. The catalyst support of daim 6 where the catalyst support is to be used in a tubular reactor of a first diameter and the catalyst support has a second diameter, and where the ratio of the first diameter to the second diameter ranges from 2:1 to 200:1.