MXPA99011458A - Inductively heated catalytic reactor - Google Patents

Abstract

An improved gas phase reactor (10) for continuously conducting a catalyzed chemical reaction at elevated temperature involving a reactor vessel (11) wherein the gaseous reactant passing through the reactor makes contact with an inductively heated solid phase catalyst media (17). By placing the induction coil (14) used to inductively heat the catalyst (17) directly within the reactor in close proximity to the solid catalyst improved temperature control and uniform heating of the catalyst is achieved. Such a reactor is particularly useful for continuous production of hydrogen cyanide.

Description

INDUCTIVELY HEATED CATALYTIC REACTOR TECHNICAL FIELD This invention relates to a new apparatus for producing a gas phase reaction at elevated temperature in the presence of a solid catalyst. More specifically, the invention relates to a continuous flow gas phase reactor wherein a metal catalyst is heated inductively by the use of an induction coil within the reactor.

BACKGROUND OF THE INVENTION The concept of using induction heating to heat a catalyst during a gas phase chemical reaction at elevated temperature is generally known in the art. For example, U.S. Patent No. 5,110,996 describes a process for producing vinylidene fluoride by reacting dichlorofluoromethane with methane in an inductively heated reaction tube containing a REF .: 32172, non-catalytic packaging material and optionally a metallic catalyst. Similarly, PCT patent application 095/21126 describes the preparation of hydrogen cyanide by reacting ammonia and a hydrocarbon gas in an inductively heated quartz reactor tube. In this description, a metal catalyst of the platinum group is heated inside the reactor tube by the presence of an inductive coil, wound helically around the outside of the quartz tube. This spiral is energized by a source of induction power that can also supply pulse power. For the particular endothermic reaction employed in this reference, a frequency range of 0.5 to 30 MHz is suggested to maintain the reaction temperature between 600 and about 1200 ° C. The induction coil wound around the outside of the reactor tube is in itself a metal tube through which cooling water is being circulated. The reference also suggests various forms of the metallic catalyst including wire cloth, ceramic substrate having metal dispersed on the surface or ceramic particles coated with the metal with the proviso that these catalysts have an electrical conductivity of at least 1.0 Seimens per meter such as for be heated effectively by induction. Although the inductively heated tubular reactor is generally known in the art and has been shown to be useful in the production of hydrogen cyanide by the endothermic reaction of ammonia and a hydrocarbon such as methane, it has now been discovered that there are certain deficiencies that they can be attributed, at least in part, to the design of the prior art reactors. The problems are in principle with regard to the scaling of the reactor size and will be particularly critical for reactions that are sensitive to temperature, potentially being reflected in one or more of the following: decreased conversion to desired product, products of lateral reactions, unwanted, increased, and / or selectivity less than optimal. In addition, the construction material of the reactor could present a significant challenge during design and scaling. The present invention challenges these problems.

DESCRIPTION OF THE INVENTION In view of the above potential problems, associated with the gas-phase, inductively heated gas-phase reactors of the prior art, it has now been discovered that by placing the main inductive coil directly into the tubular reactor substantially through the cross section , complete the reactor, providing gas flow through, and using this spiral directly as the power source improves the temperature control and more even heating of the metal catalyst can be achieved. These improvements can be partly rationalized as being due to the improved ability to control the spatial relationship between the induction power source and the heated metal catalyst in a mannerinductive, that is, both a more uniform radial distribution inside the reactor and in close proximity. This in turn allows scaling to larger cross sections of the reactor without significantly reducing or converting or selectivity even in case of temperature sensitive gas phase reactions such as the production of hydrogen cyanide from ammonia and a hydrocarbon or the like. In this manner, the present invention provides an improved apparatus for continuously carrying out a gas phase reaction, catalyzed at an elevated temperature, comprising: (a) a vapor vessel comprising at least one gaseous reagent inlet medium and at least one product outlet means for introducing the gaseous reactant into and removing the product from the reactor vessel, respectively; (b) at least one solid phase catalyst medium operatively positioned within the reactor vessel such to make contact with the gaseous reagent that passes from the reagent inlet medium to the reagent exit means and operatively adapted such as to be heated inductively; and c) at least one induction coil means operatively positioned within the reactor vessel such as to inductively heat the solid phase catalyst medium and operatively positioned for passage of the gas therethrough.

In a specific embodiment of the invention, the induction spiral is a pancake-type spiral consisting essentially of a flat spiral of metallic pipe having a spiral spacing between the successive turns to adjust the gas flow therebetween. In this embodiment, the plane of the pancake spiral is placed substantially through the complete gas flow within the reaction vessel in the vicinity of the solid phase catalyst medium. In another specific embodiment, the induction coil is a spiral of conical shape and consists essentially of a conical spiral of metallic tubing having spiral and helical spacing between successive turns to adjust the gas flow.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of a quartz reactor according to the present invention particularly suitable for producing hydrogen cyanide.

Figure 2 is a cross-sectional view of a stainless steel reactor according to the present invention particularly suited for producing hydrogen cyanide.

Figure 3 is a cross-sectional view of an alternative embodiment of a stainless steel reactor of Figure 2.

MODES FOR CARRYING OUT THE INVENTION The improved inductively heated reactor according to the present invention, how it is used to carry out a gas phase chemical reaction at elevated temperature, how it operates and differs from previously known inductively heated reactors, and the associated advantages and benefits With their use they can perhaps be better explained and understood by reference to the drawings. For example, Figure 1 illustrates a quartz reactor, designated generally by the number 10, which is particularly useful for producing hydrogen cyanide so commonly referred to as the Degussa process. The Degussa process comprises the catalytic reaction of ammonia and a hydrocarbon such as methane at elevated temperature, typically more than 1200 ° C to produce hydrogen cyanide according to the following endothermic reaction; CH4 + NH3? HCN + 3 H2 Figures 2 and 3 illustrate alternative embodiments of the stainless steel reactors, designated in general by the numbers 20 and 30, respectively. In contrast to the reactor of Figure 1, reactors 20 and 30 are particularly useful for producing hydrogen cyanide either by the Degussa process or by what is commonly recognized as the Andrussow exothermic process. It should be further appreciated that although the improved reactor inductively heated according to the present induction which is being described and illustrated in a specific manner with respect to the high temperature gas phase production of hydrogen cyanide, it is perceived that the invention is not It should be seen as being limited to no new reaction. Many of the advantages and benefits associated with the improved reactor are likewise realized in other reactions and gas phase, high temperature processes. As for any interpretation of the following description and claims, this should not be unduly limited. As illustrated in Figure 1, the inductively heated reactor 10 in this embodiment comprises a quartz-lined or quartz-lined reactor vessel 11, generally cylindrical, having at one end a conically shaped inlet 12 through which it is introduced. the methane and ammonia reagents. At the other end is a similar outlet 13 in a conical shape for the removal of the product hydrogen cyanide and hydrogen. Inside the reactor vessel 11 there is a spiral spiral type 14, spirally, with the conductors 15 and 15 'entering and leaving the reactor. The spiral 14 type pancake is made from metal pipe (for example, copper pipe or similar) and as such could have cooling water or other means of heat exchange passing through it.

Also, the pancake-type spiral 14 is further adapted to act as the primary induction coil when being joined (not shown) to an induction power source. This pancake spiral is suspended substantially through the interior of the reactor vessel 11 directly adjacent to a perforated diffuser plate 16. The diffuser plate 16 consists of a pattern of small diameter holes drilled in established rows such as to fill about one third of the surface area of the diffuser plate. Typically, this diffuser plate is made of quartz or non-conductive ceramic product. Alternatively, the diffuser plate can be made from a ceramic foam. The diffuser plate also serves to electrically isolate the induction coil 14 from the inductively heated catalyst 17 placed on the other side of the diffuser plate 16. This catalyst 17 in this specific embodiment is a form of layers of fabric, wire or platinum wire (for example Pt-Rh wound on alumina or the like). A pair of cylindrical quartz spacers 18 and 18 and the support ring 19 compressively support the diffuser plate 16 and the catalyst 17 suspended within the reactor vessel 11 in the vicinity of the pancake spiral 14 during use. It should be appreciated that various other types of structure and support members can be used to hold the catalyst and the induction spiral suspended within the reactor vessel. Figure 2 illustrates a stainless steel reaction vessel 21 with the reagent inlet 22 and the product outlet 23. - Similar to Figure 1, a pancake spiral 24 is suspended within the reactor 20 which substantially covers the entire cross section of the interior of the reaction vessel 21 and perpendicular to the gas flow path. In this specific embodiment, the pancake spiral 24 is directly adjacent to a Fiberfrax blanket 25 which minimizes heat loss and provides a final filtration of the feed gas passing through it. Directly below the Fiberfrax mantle 25 is a layer of alumina foam that serves as a radiation shield 26 (ie, which protects the gaseous mixture of reagents entering the reactor from premature ignition). Below this radiation shield 26 is the metal catalyst means 27. The catalyst 27 rests in a perforated ceramic sub-supported layer 28 having smaller diameter water-carriers than the catalyst particles that are supported. Below this ceramic sub-support is a second ceramic sub-support 29 of even larger perforations. This specific embodiment illustrated in Figure 2 further demonstrates how the inductively heated improved reactor of the present invention is seen as being generally applicable and useful for a variety of different types of high temperature gas phase catalytic reactions. More specifically and as illustrated, the catalyst is not limited to being a metallic wire, woven or wire mesh, but in the fact of being in the form of particles, coated particles or mixtures of different types of particles. Also, the use of a thermally insulating layer and / or radiation shield layer between the induction coil and the heated catalyst medium gives the opportunity to use these reactors in a number of different reactions and minimizes the temperature increase (that is, in the flow of the cooling medium) through the induction spiral. Figure 3 illustrates an alternative embodiment of the reactor shown in Figure 2. In this specific embodiment, the reactor, designated generally by the number 30, contains essentially the same insulating, thermal layer, the radiation shield layer, the catalyst and the sub-support members like those shown in figure 2. However, the induction coil 32 in this embodiment is a helical, helical, metallic tubular spiral wound inside the reactor 30 directly above the catalyst. The actual construction of the improved reactor according to the present invention comprises any of the conventional materials generally known in the art as being useful in the manufacture of heated reactors. Preferably and as illustrated in the figures, the reactor is made of materials such as quartz, quartz lining, ceramic product, coated with ceramic product, stainless steel or the like. It is also contemplated that various coatings or protective veneers may be advantageously used depending on the particular reaction conditions. The particular manufacturing techniques employed to assemble the reactor can be similarly any of the methods generally known in the art including, but not limited to, welding of metal components, and / or bonding with ceramic-type adhesives. Epoxy or comprehensive joints and similar. In general, the choice of particular materials as well as the catalyst medium depends on the particular chemical reaction and the particular conditions that will be used. The catalyst means comprises a metallic metal compound which is capable of being heated inductively. In general, this catalyst means can be in the form of one or more layers of metallic fabric, (for example, laser-perforated metal sheet, woven or non-woven wire mesh, or the like), metallic, flat, discrete objects ( for example metallic foam) or multiple layers of agglomerated catalyst particles. These catalyst forms are described more fully and are described in WO / 95/21126 and the co-pending United States patent application commonly assigned serial number 08 / 887,549, filed July 3, 1997, incorporated by reference for these purposes. It is further contemplated that the use of alternating layers of catalyst and induction coil within an individual reactor will be operative for the purpose of the present invention. The inductively heated tubular reactor of the present invention is seen as being useful over a wide frequency range from typically 50 Hz to about 30 MHz. In principle, any gas-phase, catalyzed, high temperature chemical reaction can be carried out in the improved reactor according to the present invention. Preferably, a metal catalyst medium of the platinum group is used to make hydrogen cyanide by reacting ammonia and a hydrocarbon. Further details of this reaction and methods for achieving same can be found in the incorporated references WO 95/221126 and U.S. Patent Application Serial No. 08 / 887,549. The following examples are presented to more fully demonstrate and further illustrate various individual aspects and features of the present invention and the samples are proposed to further illustrate the differences and advantages of the present invention. As such, the examples are seen to be non-limiting and are intended to illustrate the invention, but are not intended to be unduly limited.

Examples 1 to 4 HCN was prepared by reacting an excess of light molar of ammonia with methane in a fixed-bed, continuous-flow reactor that was inductively heated with a pancake-type spiral as shown in Figure 1. The ratios for ammonia and methane are shown in FIG. Table 1 above. The reactor was essentially a cylindrical 5.0 cms. of diameter and 20 cms. in length with appropriate accessories to connect the power distributor and the product distribution unit. The catalyst was comprised of 20 sheets of 90% by weight platinum fabric and 10% by weight of 80 mesh rhodium having a thickness of 0.4 mm. The heating of the catalyst bed was achieved by coupling the energy from the power source to the spiral enclosed in the reactor. The reactor was designed to allow two gaseous feeds in the reaction zone at a constant flow rate. The gases were dosed and monitored using the Brooks® mass flow controllers. The identification and quantification of the product were made by gas chromatography. Induction heating was provided at a constant frequency of 26 MHz and the transmitted and reflected powers were adjusted to obtain the desired total output. The conditions of reaction, conversion, production, etc., are presented in Table 1.

TABLE 1 Example Speed Power Time Conversion Productions No, total residence flow NH3 CH4 HCN (%) NH3 CH (seconds) (watts (sccm) 1 58 50 1.6 750 79.4 80.3 66.9 2 58 50 1.6 750 80.9 81.0 68.3 3 58 50 1.6 750 81.2 81.0 69.2 4 58 50 1.6 900 95.3 94.1 79.3 INDUSTRIAL APPLICABILITY.

The benefits and advantages associated with the improved inductively heated reactor according to the present invention are perceived to be numerous and significant. First of all, the use of the induction coil within the reactor vessel in the vicinity of the metal catalyst means leads to a more uniform control of the temperature. Accordingly, the problems associated with the inductively heated reactors of the prior art such as side reactions induced by the temperature gradient and decreased conversion / selectivity are mitigated. Also, the improved reactor design offers the opportunity to scale up particularly in relation to the use of larger dimensions of the cross section. In this way, the improved reactor leads to more flexibility of design and choice of construction materials, as well as the method of operation and can be upgraded in existing reactors. The use of the induction spiral inside the reactor vessel as the energy source can also result in higher heat input per unit volume for larger diameter reactors than for external spiral cases where the height of the fact limits the number of spiral turns. Consequently, the improved reactor is useful for performing very fast gas phase reactions since it offers the use of a configuration of the fact (for example, the fact of the disk) having an imminently low pressure drop due to a lower height of the fact . Having thus described and exemplified the dimension with a certain degree of particularity, it should be appreciated that the following claims are not to be limited but a scope may be offered in proportion to the text of each element of the equivalent claims therein.

Claims (3)

1. An apparatus for continuously carrying out a gas phase reaction, catalyzed, at an elevated temperature, comprising: (a) a reactor vessel comprising at least one gaseous reagent inlet medium and at least one product outlet means for introduce the gaseous reagent into and remove the product from the reactor vessel, respectively; (b) at least one solid phase metallic catalyst medium operatively positioned within the reactor vessel such as to make contact with the gaseous reagent passing from the reagent inlet medium to the product outlet means and operatively adapted, such as to be heated inductively; and (c) at least one induction coil means operatively positioned within the reactor vessel substantially through the entire reactor vessel in the vicinity of the solid-base metal catalyst medium such as to directly and inductively heat the medium metallic catalyst of solid phase and placed in an operative way and for the passage of gas through it.

2. The apparatus according to claim 1, characterized in that the induction spiral means is a spiral consisting essentially of a flat spiral of metal pipe having a spiral spacing between the successive turns to adjust the gas flow between these and wherein the plane of the spiral is placed substantially through the complete gas flow within the reaction vessel of the proximity of the solid phase metal catalyst medium.

3. The apparatus according to claim 1, characterized in that the induction spiral means is a conical shaped spiral consisting essentially of a conical spiral of metallic pipe having a helical helical spacing between the successive turns to adjust the gas flow between these and wherein the conical shaped spiral base plane is placed substantially through the complete gas flow within the reaction vessel in the vicinity of the solid phase catalyst medium.