GB2210286A

GB2210286A - Method of performing endothermic catalytic reactions

Info

Publication number: GB2210286A
Application number: GB8822593A
Authority: GB
Inventors: John Tudor Griffith; David Alan Gardner
Original assignee: Electricity Council
Current assignee: Electricity Council
Priority date: 1987-09-29
Filing date: 1988-09-27
Publication date: 1989-06-07
Anticipated expiration: 2008-09-27
Also published as: GB2210286B; GB8822593D0; GB8722847D0

Abstract

A method of performing endothermic catalytic reactions in which heat is supplied to the reaction by inductively heating the catalyst for the reaction, the electrically conducting catalyst or catalyst support acting as the secondary winding of a transformer.

Description

A METHOD OF PERFORMING ENDOTHERMIC CATALYTIC REACTIONS The present invention relates to a method of performing an endothermic chemical reaction.

Many endothermic catalytic reactions are known and are used industrially in the manufacture of various chemicals. Examples of certain of the more important industrial endothermic catalytic reactions are given below.

Dehvdroaenation a) styrene from ethylbenzene

H = 1.39 X 105 kJ/kgmol Current methods for industrial production involve an adiabatic process in which steam is heated to 800 to 9500C and mixed in a ratio of about 15:1 with preheated ethylbenzene. The reaction is carried out at a pressure of about 140 kPa. An alternative process is an isothermal process which is conducted in a tubular reactor to which heat is supplied by indirect heat exchange.

b) Butadiene from butene

H = 1.52 X 105 kJ/Kgmol The current method for industrial production involves a high temperature adiabatic reaction in which a steam to butene ratio of about 20:1 is used with a reactor pressure of about 20 kPa. The temperature of the reactor is maintained at about 6000C for good conversion.

Catalvtic Reformina In these reactions the number of carbon atoms remain the same. Examples of such reactions are

cyclohexane = benzene n-heptane > toluene The main process variables in these reactions are pressure, temperature, space velocity and catalyst. To replenish the heat of reaction lost by the conversion of cycloparaffins to aromatics, semi-regenerative processes may have three to four sets of alternating furnaces and reactors.

Catalytic steam Reforming In the catalytic steam reforming of hydrocarbons a hydrocarbon feedstock is passed mixed with steam over a catalyst for example of 16 to 20% Ni as Nio supported on alumina, calcium aluminate or calcium aluminium titanate. Outlet gas temperatures are 870 to 8850C and the pressure in the catalytic reformer is 2.34 - 2.51 MPA.

We have now developed a process for carrying out endothermic catalytic reactions in which heat is supplied to the reaction by inductively heating the catalyst for the reaction rather than heat being supplied to the reaction by the use of super heated steam or by heat exchange.

Accordingly, the present invention provides a method of performing an endothermic catalytic reaction which method comprises heating the catalyst for the reaction or an electrically conductive support for the catalyst for the reaction in an induction heater in which the electrically conducting catalyst or catalyst support acts as the secondary winding of a transformer with a ferromagnetic core, such that the ferromagnetic core passes centrally through the catalyst or catalyst support, means generating an alternating magnetic field in the ferromagnetic core, and a reaction vessel which surrounds the catalyst and that part of the ferromagnetic core passing through the catalyst and having the catalyst for the endothermic reaction disposed therein in a manner such that it is heated inductively.

The catalyst for the endothermic chemical reaction may be doped in order to render it electrically conductive and thereby enable an electric current to be induced therein.

Alternatively, or in addition, the catalyst may be supported on an electrically conductive support, such as a nickel, stainless steel or perforated conducting plate. In this manner the support has an electric current induced therein and thereby becomes heated and the heat is transferred to the catalyst for the reaction and to the reactants. Methods of preparing supported catalysts, in the form of plates, are known and are described, for example, in Ind. Eng. Chem.

Processes Des. Dev. 1986, 25, 143-150, EP-A-0201614, DE-A-3519731.5 and JP-62-144751.

It will be understood that whilst the catalyst for the reaction is heated by means of an induced electrical current, additional heat may also be supplied to the endothermic reaction, for example by the methods known in the art.

It will furthermore be understood that although the catalyst or catalyst support acts as the secondary winding of the transformer, the primary winding of the transformer may be wound on that part of the core external to the reaction vessel.

Alternatively, the whole of the core may be contained within the reaction vessel and the primary winding may then be wound around any convenient part of the core. The said primary winding produces the magnetic field in the core which induces a current into the catalyst and/or the catalyst support. This current flow heats the catalyst, or heats the catalyst support and thereby indirectly heats the catalyst.

Since the current flows throughout the catalyst or catalyst support, uniform heating occurs. The preferred operating frequencies are 50 Hz and 60 Hz, but any frequency within the range of from 25 Hz to 2500 Hz may be used. The ferromagnetic core is preferably an iron core, whilst the reaction vessel is preferably either made from an electrically insulating material or from a laminated material which limits the current induced therein.

In this type of induction heater, the reactor is preferably cylindrical, although all manner of shapes could be employed, for example a rectangular box could be employed. The reaction vessel is provided with at least one inlet for the reactants and at least one outlet for the products of the reaction.

The residence time in the reactor may be adjusted by appropriate reactor design and by the velocity of the flow of reactants into the reactor. The catalyst may, for example, be supported on a conductive packing disposed throughout the reaction vessel, or may be in the form of or supported on a plurality of annular discs, each disc having a hole through which the core passes. It may furthermore be advantageous for the annular discs to be provided with a plurality of holes to assist the flow of reactants through the reactor. The catalyst may alternatively be in the form of a plurality of cylinders or supported on a plurality of cylinders coaxial with the core which passes through them. The cylinders may be provided with a plurality of holes to assist the flow of reactants through the reaction vessel.

The annular discs of catalytic material or supported catalytic material may be equally spaced apart, but it may be advantageous, in addition to these catalytic discs, to insert at selected intervals, particularly towards the exit end of the reactor, plates of conducting material which are not catalytic or catalytically coated to provide additional heat transfer and mixing of the reactants without further chemical reaction.

It is preferred that the method of the present invention is operated isothermally and this may be achieved by various means. For example, for a disctype reactor of the type as described above isothermal operation may be achieved by varying the thickness of the discs with the distance from the ferromagnetic core. For equal reaction rates at all points inside the reactor an isothermal profile would be achieved by imposing a uniform power density. The thickness of the discs would therefore change as the square of the distance from the ferromagnetic core.

The same change in the cross-section of the discs may also be achieved by punching holes in the discs.

Either the same sized holes may be used with the number changing with distance from the core, or the same number of holes may be used but of varying sizes. Varying power may be supplied at different positions on the discs. A similar method may be used to change the power input to different sections of the reactor. For example, it may be expected that the rate of reaction is greatest at one end of the reactor. If this is the case the discs at this end of the reactor may be modified by using thicker discs to increase the power input. An alternative to this is to use the same discs as in the rest of the reactor but, place them closer together. Such a requirement is unlikely to occur in a radial flow reactor, but in an axial flow reactor it is reasonable to expect varying rate of reaction with height of the reactor.

For a reactor in which the catalyst or supported catalyst is arranged as a plurality of cylinders coaxial with the ferromagnetic core which passes through them, isothermal operation may be achieved by each cylinder having a uniform thickness itself but being thicker than the cylinder inside it.

The present invention will be further described with reference to the accompanying drawings, in which: Figure 1 is a cross-section schematic illustration of a reaction vessel incorporating a catalyst heated according to the method of the invention; Figure 2 is a part section through a catalytic disc which may be conductively heated according to the method of the invention; Figure 3 is a part section of another catalytic disc which may be heated according to the method of the invention; and Figures 4 and 5 are cross-section schematic representations of other reaction vessels which are adapted for the catalysts contained therein to be conductively heated.

Referring to Figure 1 of the Drawings, a silicon iron core 1 passes through a reaction vessel generally shown at 2. The portion of the silicon iron core shown in Figure 1 forms part of a closed loop. An alternating magnetic field is produced in this silicon iron core by means of a coil which is wrapped around the portion of the core which is not shown in the diagram. The reactor 2 is equipped with an inlet 3 which surrounds the core 1. The reactor has an outlet 4 in the form of a substantially cylindrical passage adjacent to the outer wall of the reactor. The reactants flow into the reactor through inlet 3 and pass radially in the direction of arrows 5 into the bed of the reactor which is packed with a conductive packing material 6 which supports the catalyst for the reaction. The product and unreacted reactants leave the reactor via a exit 4.The alternating magnetic field produced in the core 1 induces current to flow in the conductive packing 6 and thereby heat the conductive packing and causes the catalyst for the reaction also to be heated. The reaction vessel 2 is preferably constructed from electrically insulating materials and preferably does not therefore have an electric current induced therein.

Figure 2 illustrates a part of an annular disc 7 of catalytic material. The bed of conductive packing 6 shown in Figure 1 may be replaced by a plurality of rings 7 which are spaced one from another by means of appropriate spacers. A mesh or net is shown at 8 and this provides support to the catalyst. If the catalyst is not conductive the net 8 will be conductive. For such a radial-flow reactor the catalyst bed consists of a series of parallel plates which are perpendicular to the flow of reactants.

These plates are bolted together with suitable spacers placed between them to allow the gas to flow over them. This arrangement also facilitates easy assembly and removal of plates from the reactor.

In the arrangement shown in Figure 3 a plurality of holes 9 are provided in the annular disc of catalytic material. These holes 9 assist in the flow of the reactants through the reaction vessel.

One reaction which can be carried out in such a reactor is the dehydrogenation of ethylbenzene to form styrene. The catalyst for this reaction is preferably iron (III) oxide with additives of chrome oxide and potassium oxide. The catalyst is an extrudate available with different diameters which is coated onto a suitably conductive support either by incorporating the catalyst into an enamel frit and coating it onto a mild steel support, or forming the catalyst into a powder and spraying onto a steel surface. The exact method of coating the plates depends on the final characteristics required.

Figure 4 illustrates an alternative type of reactor which is adapted for the axial flow of the reactants therethrough. The reactor is provided with an inlet 10 and the reactants flow through inlet 10 via a distributor plate 11 which is provided with a plurality of holes therein. The reactants then flow through the bed of the reactor 13 which is filled with a conductive packing material which supports a catalyst for the endothermic reaction. The products of the reaction, together with unreacted starting materials leave the reactor via exit 12.

In one embodiment of the alternative type of reactor in Figure 4, the catalyst 13 may be carried on a series of sleeves 14, 15, 16, of conducting material as illustrated in Figure 5. These sleeves may be provided with holes 17 so that the reactants may be directed to flow radially in a similar manner to the reactor shown in Figure 1.

Claims

CLAIMS:

1. A method of performing an endothermic catalytic reaction which method comprises heating the catalyst for the reaction or an electrically conductive support for the catalyst for the reaction in an induction heater in which the electrically conducting catalyst or catalyst support acts as the secondary winding of a transformer with a ferromagnetic core, such that the ferromagnetic core passes centrally through the catalyst or catalyst support, means generating an alternating magnetic field in the ferromagnetic core, and a reaction vessel which surrounds the catalyst and that part of the ferromagnetic core passing through the catalyst and having the catalyst for the endothermic reaction disposed therein in a manner such that it is heated inductively.

2. A method as claimed in claim 1 wherein the catalyst is doped in order to render it electrically conductive.

3. A method as claimed in claim 1 or claim 2 wherein the catalyst is supported on an electrically conductive support.

4. A method as claimed in claim 3 wherein the support is a nickel or stainless steel.

5. A method as claimed in any one of the preceding claims wherein the reaction vessel is cylindrical.

6. A method as claimed in any one of the preceding claims wherein the reaction vessel is made from an electrically insulating material.

7. A method as claimed in any one of the preceding claims wherein the transformer has an iron core.

8. A method as claimed in any one of the preceding claims wherein the catalyst is supported on a conductive packing disposed throughout the reaction vessel.

9. A method as claimed in any one of the preceding claims wherein the catalyst is in the form of a plurality of annular discs or is supported on a plurality of annular discs.

10. A method as claimed in claim 9 wherein conducting discs which are not catalytic or catalytically coated are located towards the exit end of the reactor in order to provide additional heat transfer and reactant mixing.

11. A method as claimed in claim 9 wherein the discs are spaced equally from one another in the reactor.

12. A method as claimed in any one of claims 9 to 11 wherein the discs are provided with a plurality of holes to assist the flow of the reactants through the reaction vessel.

13. A method as claimed in any one of claims 1 to 8 wherein the catalyst is in the form of a plurality of cylinders or is supported on a plurality of cylinders coaxial with the core which passes through them.

14. A method as claimed in claim 13 wherein the cylinders are provided with a plurality of holes to assist the flow of the reactants through the reaction vessel.

15. A method as claimed in any one of the preceding claims which is operated isothermally.

16. A method as claimed in claim 1 substantially as hereinbefore described with reference to and as illustrated in any one of Figures 1, 4 or 5 of the accompanying drawings.