MXPA00000105A - Method of inductively igniting a chemical reaction - Google Patents

Abstract

An improved method of igniting a catalyzed gas phase chemical reaction involving the act of providing a reactor vessel (10), wherein the gaseous reactant, continuously passing through the reactor, makes contact with a solid phase metallic catalyst media (18), with an inductive coil (14) within the reactor (10) on the inlet side of the catalyst and a porous thermal, spark and radiation barrier (17) between the induction coil (14) and solid catalyst (18). According to the improved method of ignition, the metallic catalyst media (18) is inductively heated in order to ignite the chemical reaction and after ignition the inductive heating is suspended and the exotherm of the chemical reaction is thereafter relied upon to sustain the reaction temperature. Such a reactor and method of operation is particularly useful for continuous production of hydrogen cyanide by the Andrussow process.

Description

Method to Inductively Light a Chemical Reaction FIELD OF THE INVENTION: This invention relates to a new method for ignite a chemical reaction in the gas phase in the presence of a solid catalyst. More specifically, but not by way of limitation, the invention relates to a continuous flow gas phase reaction wherein the ammonia reacts with a hydrocarbon in the presence of oxygen and a metal catalyst of the platinum group to produce hydrogen cyanide, and to the use of an induction coil inside the reactor to inductively heat the metal catalyst and ignite the exothermic reaction.

BACKGROUND OF THE INVENTION: The concept of using inductive heating to heat a catalyst during a chemical reaction in gas phase at elevated temperature is generally known in the art. For example, Pat. U.S. No. 5,110,996 describes a process for producing vinylidene fluoride by reacting dichlorofluoromethane with methane in an inductively heated reaction tube, which contains a non-metallic packing material and REF .: 32211 optionally a metal catalyst. Similarly, patent application WO 95/21126 of the PCT describes the preparation of hydrogen cyanide by reacting ammonia and a hydrocarbon gas in an inductively heated quartz tubular reactor. In this description a metal catalyst of the platinum group inside the tubular reactor is heated by the presence of an inductive coil wound helically around the outside of the quartz tube. This coil is energized by an induction power source that could also supply pulsed 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 1,200 ° C. The induction coil, wound around the outer part of the tubular reactor, is in itself a metal tube through which cooling water circulates. The reference also suggests various forms of metal catalyst including wire cloth, ceramic substrate having metal dispersed on the surface, or ceramic particles covered with metal, provided that these catalysts have an electrical conductivity of at least 1.0 Seimens per meter , so that they are effectively heated by induction. It is also generally recognized in the art that hydrogen cyanide could be produced by either of the two gas phase reactions involving the catalytic reaction of ammonia and a hydrocarbon. Thus, hydrogen cyanide is most commonly produced industrially, either by the Andrussow exothermic process or the Degussa endothermic process. In the Degussa process, ammonia and typically methane are converted, in the absence of oxygen, to hydrogen cyanide and hydrogen. Since the reaction develops at elevated temperatures (typically in excess of 1,200 ° C) and is endothermic, heat transfer is a significant pragmatic problem. In contrast, the Andrussow process uses oxygen (i.e., air) which results in an exothermic reaction with water as a by-product. The use of excess hydrocarbon and oxygen also provides the opportunity to supply the heat energy necessary to maintain the desired elevated reaction temperature. Thus the Andrussow process could, in principle, have an advantage over the Degussa process in terms of solving problems associated with heat transfer, but is at a relative disadvantage in failing to produce a potentially valuable coproduct. In both the Andrussow and Degussa processes, the hot product leaving the reactor must be cooled to a temperature below about 300 ° C to avoid thermal degradation. In the Andrussow process, the catalytic reaction must be initiated by a high temperature ignition that has been confined to the proximity of the catalyst and does not allow propagation in the reactive current of the fuel that continuously enters the reactor feed. Thus it is known in the art to employ porous thermal barriersof sparks and radiation between the solid catalyst and the gaseous reactive stream and having a heat resistant wire embedded in the catalyst medium. However, such a method for igniting the reaction has been proven to be completely less reliable. The present invention addresses this problem.

Description of the Invention From the above point of view, it has now been discovered that the ignition of the process can be improved by placing the induction coil directly into the tubular reactor, providing gas flowing through it and using this coil directly as the source of induction. The catalyst will be heated inductively to the ignition temperature of the process, without a need for direct electrical contact. These improvements could be rationalized in part, since the ability to control the spatial relationship between the induction coil and the inductively heated metal catalyst, i.e., both the most uniform radial distribution within the reactor and the closest proximity, must be improved. This in turn allows scaling to larger reactor cross sections without significantly reducing either conversion or selectivity, even in cases of gas-phase reactions sensitive to temperature such as the production of hydrogen cyanide from ammonia and a hydrocarbon in the presence of oxygen. Thus the present invention provides an improved method for igniting a catalyzed reaction in gas phase comprising the steps of: (a) providing a reactor for gas phase comprising: (i) a reactor vessel comprising at least one gaseous reagent inlet medium and at least one product outlet means, for introducing gaseous reagent and withdrawing product from the reactor vessel, respectively, (ii) a solid phase catalyst medium operatively positioned within the reactor vessel, such that it contacts the gaseous reactant that passes from the reagent entry medium to the reactor. Product output means and operatively adapted, such that inductively hot, (iii) an induction coil means is operatively positioned within the reactor vessel, such that inductively hot solid phase catalyst medium is positioned. operatively for the passage of gas through it, and (iv) a means of thermal barrier porous, sparks and radiation positioned operatively. between the solid phase catalyst and the gaseous reactant, to confine the chemical reaction to the catalyst region and prevent the reaction from spreading towards the inlet; (b) introducing gaseous reactants into the inlet of the reactor vessel; (c) igniting the reagents inductively, by heating the catalyst medium in solid phase using the induction coil means as the inductive power source; and (d) discontinuing the induction heating and maintaining the reaction temperature by use of the exothermic reaction heat. The present invention further provides an alternate embodiment of the method for igniting a catalysed gas phase reaction, wherein the solid phase catalyst medium is operatively adapted from such that in addition to inductively heating it comprises at least one conductive susceptor medium for increase the inductive efficiency during the start of the reaction.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of an embodiment of an atmospheric reactor for gas phase, useful for performing the improved inductive ignition method according to the present invention. Figure 2 is a cross-sectional view of an alternative embodiment of a chemical reactor for gas phase, useful for carrying out the improved inductive ignition method according to the present invention.

Ways of Carrying Out the Invention The improved method of inductively igniting a gas phase reaction according to the present invention, how it is incorporated into a reactor used to conduct a chemical reaction in gas phase at elevated temperature, how it operates and differs from heated reactors. Inductively prior and prior ignition methods, and the advantages and benefits associated with their use may perhaps be better explained and understood by reference to the drawings. For example, Figure 1 illustrates a continuous reactor for gas phase, designated in general by the number 10, which when operating according to the method of the present invention is particularly useful for producing hydrogen cyanide, which is commonly referred to as the Andrussow process . The Andrussow process typically involves the catalytic reaction of ammonia and a hydrocarbon, such as methane, in the presence of oxygen at an elevated temperature, typically greater than 1100 ° C, to produce hydrogen cyanide according to the following exothermic reaction: CH4 + NH3 + 3/2 02 r HCN + 3 H20 It should be evident that, although the improved method of inductively igniting a gas phase reaction catalyzed according to the present invention is described and illustrated specifically with respect to the production of hydrogen cyanide in the gas phase at high temperature, it is perceived that the invention should not be seen as being limited to any given reaction. Many of the advantages and benefits associated with the improved inductive ignition method are also realized in other reactions and processes in gas phase at elevated temperature, where the reaction, which is otherwise exothermic and self-sustaining, initially requires firing. In such a way that any interpretation of the following description and claims should not be unduly limited. As illustrated in Figure 1, the inductively ignited reactor 10 in this specific embodiment generally involves a cylindrical reactor vessel 11 having at one end a conically shaped inlet 12, through which methane, ammonia reagents are introduced. and oxygen (or air). The other end is an outlet 13 to remove the product, hydrogen cyanide and water. Inside the reactor vessel 11 there is a circular turn coil 14 with paths 15 and 15 'entering and leaving the reactor. This coil 14 is made of metal tube or metal roller (e.g., copper tube or the like) and as such could have cooling water or other heat exchange medium passing therethrough. Also, coil 14 is further adapted to act as the primary induction coil by joining it (not shown) to an induction power source. The circular turn of the coil is suspended through a portion of the interior of the reactor vessel 11, directly adjacent to a Fiberfrax 16 blanket that minimizes heat loss and provides a final filtration of the feed gas passing therethrough. Directly below the Fiberfrax blanket 16 is a layer of alumina foam that serves as a radiation shield 17 (i.e., shields the reactive gas mixture entering the premature ignition reactor). Downstream of this radiation shield 17 is the metal catalyst medium 18. The catalyst 18 remains in a support layer under perforated ceramic 19, which has holes of smaller diameter than the catalyst particles that are supported. Below this ceramic support is a second ceramic support 20 with even larger perforations. This specific modality illustrated in Figure 1 is intended to demonstrate how the inductively improved ignition reactor of the present invention is applicable and useful for a variety of different types of high temperature gas phase catalytic reactions. More specifically and as illustrated, the catalyst medium can be any solid phase particulate material capable of inductively igniting (heating) and simultaneously capable of catalyzing the desired reaction in the gas phase. However, it should be further appreciated that the solid phase catalyst medium is not limited to any given physical form, including that it is a particulate material. In general, this catalyst means (as well as the susceptor used in the alternating embodiment of Figure 2) may also be in the form of one or more layers of fabric structure or metal gauze (eg, laser-perforated metal sheet, woven or nonwoven wire, or the like), discrete flat metallic objects (eg, metallic foam) or multiple layers of pellet type catalyst particles. Such catalyst forms are set forth and described more fully in PCT patent application WO 95/21126 and are commonly assigned, co-pending in PCT patent application number 08 / 887,549 filed on July 3, 1997. Thus, for example , in the specifically preferred embodiment employing the Andrussow process, the catalyst 18 is a plurality of structure layersmetal wire, cloth, or platinum gauze (e.g., Pt-Rh rolled in alumina or the like). In any induction heating system, only a part of the electrical power entering the coil is actually dissipated in the intended workpiece, in this case the catalyst medium. The rest of the power dissipates in the same coil, which is usually made of copper. The power dissipated in the coil is normally removed through a cooling medium such as water, which flows into the coil. The power ratio dissipated in the workpiece intended for total power is called coil efficiency. In the process of this invention, the efficiency of the coil is important because the ignition speed, and if the ignition temperature is reached, depends on the input power to the catalyst medium. In addition, in some cases the coil cooling via "water or other liquid may not be feasible due to safety considerations." The efficiency of the coil is dependent on a number of variables, mainly coil and site conductivity. work, and geometric factors such as distance from the coil of the work piece In a given induction heating system the efficiency of the coil is maximized for a certain conductivity interval of the work piece, in this case the medium of catalyst Very low or very high conductivity leads to low efficiency.

In certain cases, the electrical conductivity of the catalyst medium is such that the efficiency of the coil is too low. An example of this is when the catalyst is electrically non-conductive. Another example is when the catalyst has too much electrical conductivity; and yet another example is when the distance from the coil to the catalyst needs to be large in relation to the conductivity of the catalyst. The present invention provides an ignition method for these cases, wherein a conductive susceptor of appropriate geometry and conductivity are placed in the vicinity of the induction coil and the catalyst medium. Figure 2 illustrates such alternate modality employing a conductive susceptor. As shown in Figure 2, a platinum wire 21 is used as a susceptor and is kept away from the main body of the catalyst medium 18 by a layer of porous ceramic 22 (the other elements and function are identified by numbers as it was previously described with respect to Figure 1). The coil 14 in this mode is more efficient in heating the susceptor layer 21 for two reasons. First, the higher resistance of the thin layer of the susceptor increases the efficiency of induction, and second, due to the thermal insulation between the layer of the susceptor and the main catalyst medium, the heat generated in the susceptor is not conducted far away; therefore it is easier to achieve a high ignition temperature in the susceptor. After the reaction begins in the susceptor layer, it propagates to the main body of the catalyst medium. In many cases the use of a liquid cooler, such as water introduced through coiled coil 14, is not feasible due to a leakage potential of the cooling medium and the possibility of risking the safety or contamination of the process. In such cases, instead of a hollow metal material, a solid metal material could be used for the construction of the induction coil. The solid metallic material, due to the higher mass, would not heat up so fast, and gives the catalyst medium or susceptor sufficient time to heat and ignite before the coil temperature increases. Increasing the coil temperature beyond a certain limit could have many negative effects, such as ignition of the process at the wrong location, and deterioration or melting of the coil material. In addition, a heating of the coil would increase the electrical resistance, and increase the energy release to the coil instead of the catalyst medium.

When the use of liquid cooler such as water is not feasible, and cooling of the coil is also necessary, a cold gas stream such as air can be passed through the conductive, hollow coil. A suitable method for the generation of cold gas can be the use of a vortex tube. A vortex tube, which works on the basis of the expansion of compressed air, is a cheap cooling device and only uses compressed air, which is available in most industrial sites. The use of a thermal insulation layer 16 and / or a radiation shielding layer 17, between the induction coil and the heated catalyst medium (referred to herein as the "porous, sparking and radiation thermal barrier means") , provides the opportunity to use such reactors in a number of different reactions and minimizes the increase in temperature (ie, in the flow of the cooling medium) through the induction coil. This barrier means works primarily to prevent the reaction from propagating to the reagent inlet and as such serves to confine the gaseous reaction to the catalyst region. In general, any porous material as generally known in the art may be employed; including but not limited to example, porous ceramic foams or ceramic covered materials, thermally stable materials and fibers, combination of the same and similar. Typically, when a diffuser plate is used for internal support it is made of non-conductive quartz or ceramic. Alternatively, the diffuser plate can be made of ceramic foam. The diffuser plate can also serve to electrically insulate the induction coil from the inductively heated catalyst. The current construction of the improved reactor according to the present invention involves any of the materials generally known in the art, since they are useful for making inductively heated reactors. Preferably, the reactor is made of materials such as quartz, quartz line materials, ceramics, ceramic coated materials, stainless steel or the like. It is also visualized that various coatings or protective coating can be advantageously employed depending on the particular reaction conditions and the reactions involved. The particular manufacturing techniques employed to assemble the reactor can be similarly any of the methods generally known in the art, including by way of example but not limitation, the welding of metal components, and / or bonding using ceramic-epoxy type adhesives. or compressor joints and the like. In general, the choice of "particular" materials as well as catalyst medium depends on which particular chemical reaction and conditions are to be used In principle, any chemical reaction in the gas phase at elevated temperature and catalyzed can be carried out in the improved reactor according to the present invention. invention Preferably, a metal catalyst medium of the platinum group is used to manufacture hydrogen cyanide, by reacting ammonia and a hydrocarbon in the presence of oxygen or air.Additional details of such reaction and methods for carrying out the same may be found in the incorporated references WO 95/221126 and US patent application 08 / 887,549 The following examples are presented to more fully demonstrate and further illustrate various aspects and individual features of the present invention, and what is shown is intended to further illustrate the differences and advantages of the present invention, as such the examples are They recognize that they are non-limiting and are indicated to illustrate the invention but does not mean that it is unduly limited.

EXAMPLES A 5.08 cm (2 inch) laboratory-scale quartz reactor was manufactured and tested to evaluate the feasibility of using an internal copper inductor to ignite the reaction. The reactor consisted of one turn of the copper coil, a 0.476 cm (3/16 inch) thick ceramic foam catalyst support, 40 layers of platinum wire mesh and a final support of ceramic foam catalyst 0.476 cm (3/16 inch) thick. The induction frequency was 26 MHz. The tests were performed to evaluate the ignition numbers, the power input as well as to verify that it is seen if the presence of a copper coil inside the reaction chamber would cause any adverse effect. The results are as follows: TIME FLOWS NH, CH4 AIR POWER ON 1. 26 L / min 1.16 L / min 6.67 L / min 200 Watts -85 sec. 1. 26 L / min 1.16 L / min 6.67 L / min 250 Watts -40 sec. 1. 26 L / min 1.16 L / min 6.67 L / min 300 Watts -20 sec, 1. 26 L / min 1.16 L / min 6.67 L / min 350 Watts -10 sec.

As shown in the table above, the ignition can be achieved in as little as 10 seconds. No adverse effect in the short time could be found, due to the presence of copper, while the reaction is ignited. The flow rates used were lower than those of the typical ignition of the plant, due to the limiting amount of HCN that can be produced in the laboratory. An established test was mounted to verify the heating of the catalyst at the flow rate used in the ignition. Two forms of catalyst were used, unpacked (fresh) and compressed (used). The packing (compression) of the catalyst occurs during normal operation and the need to ignite the reactor could occur in several stages of compression. The nitrogen was used to simulate ignition flow conditions. The unpackaged catalyst was treated first. The results show the ability to heat to the desired firing temperatures at ignition flow rates. Initial testing of the compressed catalyst bed produced poor heating. The test with the new unit showed a greater capacity to heat but only with the coil that is in close proximity to the catalyst bed. The phenomenon of poor warming can be attributed to two factors. The first is that the electrical conductivity of a compressed bed is too high to effectively heat with induction heating and the second is that the heat transfer from the compressed bed is greater than that of the unpacked bed. The results are as follows: Results of the Catalyst Bed Test No Packed Frequency: 8.79 MHz Run # Speed Distance Power Temp. from the Max Flow. Coil Input 1 1.27 c 566 SLPM 1.2 kW 367 ° C 2 1.27 cm 566 SLPM 1.5 kW 657 ° C 3 1.9 cm 566 SLPM 3.0 kW 406 ° C 4 0.83 cm 1217 SLPM 1.5 kW 70 ° C 5 1.25 cm 1217 SLPM 1.8 kW 120 ° C 6 1.25 cm 1217 SLPM 2.1 kW 204 ° C 7 1.25 cm 1217 SLPM 2.4 kW 380 ° C Results of the Test of the Bed of Compressed Caulk Run # Distance Speed Freq, Power Temp. from Fluj or kHz e Max. Coil Input 2.54 cm 1217 SLPM 430 5 kW 45 ° C 2 1.9 cm 1217 SLPM 432 5 kW 62 ° C 3 1.27 cm 1217 SLPM 440 5 kW 107 ° C 4 0.63 cm 1217 SLPM 453 5 kW 195 ° C 0.31 cm 1217 SLPM 459 5 kW 276 ° C Results of the test with the susceptor layer To obtain the appropriate heating at a greater distance the two upper layers of the catalyst mesh were isolated, inserting a 0.5 cm thick ceramic foam between the bed balance and the two layers superiors This insulation increases the electrical resistance of the mesh that is heated, as well as the decrease in thermal conductivity. The results are shown below.

Run # Distance Speed Freq Power Temp. from Max's kHz Flow. Coil Input 2.54 cm 1217 SLPM 445 5 kW 324 ° C Industrial Applicability The benefits and advantages associated with the improved method of inductively igniting a reaction in gaseous phase catalyzed according to the present invention are perceived to be numerous and significant. The first and most notable, the use of the coil of the inductor source. inside the reactor vessel, in the vicinity of the metal catalyst medium, leads to more uniform temperature control and ignition. Also the presence of the induction cycle within the reactor provides the opportunity to scale particularly with respect to the use of larger cross-sectional dimensions. The improved contactless ignition method solves certain practical problems associated with the prior use of electrical paths and resistive heating, and in particular problems associated with the need for such paths to pass through the thermal, sparking and radiation barrier. And the improved ignition method allows to perform an Andrussow type process in larger reactors, with more design flexibility as well as the operation method. In this way the invention has been described and exemplified with a certain degree of particularity, it should be appreciated that the following claims are not for limitation, but are provided as a scope commensurate with the description of each element of the claim and the equivalents thereof. .

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (2)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A method for igniting a catalysed gas phase reaction, characterized in that it comprises the steps of; (a) providing a gas phase reactor comprising: (i) a reactor vessel comprising at least one gaseous reagent inlet medium and at least one product outlet means for introducing gaseous reagent and removing product from the gas container; reactor, respectively, (ii) a solid phase metal catalyst medium operatively positioned within the reactor vessel, such that it makes contact with the gaseous reactant that passes from the reagent inlet medium to the product outlet medium and adapts operatively in such a way that it is heated directly and inductively, (iii) an induction coil means operatively positioned within the reactor vessel, such that it inductively heats the metal catalyst medium in solid phase and is operatively positioned for the passage of gas through it, and (iv) a porous, sparking and radiation thermal barrier means operatively positioned between the cat metallic solid phase aligner and the gaseous reactant, to confine the chemical reaction to the catalyst region and prevent the reaction from spreading towards the inlet; (b) introducing gaseous reagents through the inlet and into the reactor vessel; (c) igniting the reagents by inductively heating the catalyst medium in solid phase, using the induction coil means as the source of inductive power; Y (d) discontinuing the induction heating and maintaining the reaction temperature by means of using the heat of the exothermic reaction.

2. A method for igniting a reaction in catalysed gas phase according to claim 1, characterized in that the metal catalyst medium in solid phase operatively adapted such that inductively heated further comprises at least one conductive susceptor means for increasing the inductive efficiency during the start of the reaction.