Process for the synthesis of nitriles

Abstract

In a process for the synthesis of a nitrile by endothermic catalyzed reaction of ammonia with a hydrocarbon using heating obtained by passing an alternating current through a metallic coil, the endothermic reaction between ammonia and the hydrocarbon takes place in a reactor with direct inductive heating in the reaction zone. The heating is extremely fast, which makes the reaction practically instantaneous.

Claims

1. A process for the synthesis of a nitrile by catalyzed reaction of ammonia with a hydrocarbon using heating obtained by passing an alternating current through a metallic coil in a synthesis reactor with a catalyst, wherein the endothermic reaction between ammonia and the hydrocarbon takes place in the synthesis reactor with direct inductive heating in a reaction zone, wherein the coil is mounted within the synthesis reactor, and all of the catalyst is placed inside the coil.

2. A process for the synthesis of a nitrile by catalyzed reaction of ammonia with a hydrocarbon using heating obtained by passing an alternating current through a metallic coil in a synthesis reactor with a catalyst, wherein the endothermic reaction between ammonia and the hydrocarbon takes place in the synthesis reactor with direct inductive heating in a reaction zone, wherein the coil is mounted within the synthesis reactor, and the catalyst is placed inside the coil, wherein the coil is made of Fe—Cr—Al alloy wire.

3. The process according to claim 1, wherein the inductive heating is carried out using an induction heater which is a ferromagnetic metal structure provided with a suitable coating, and wherein the heating is generated by magnetic hysteresis losses.

4. The process according to claim 3, wherein the metal structure is a metal selected from Fe—Cr and Al—Ni—Co alloys.

5. The process according to claim 4, wherein the metal structure is coated with a porous oxide surface impregnated with a catalytic phase.

6. The process according to claim 5, wherein the catalytic phase contains a catalyst based on Co or Sn.

7. The process according to claim 1, wherein the hydrocarbon is methane, ethane, propane, iso-butane or an olefin.

8. The process according to claim 3, wherein the induction heater comprises a ferromagnetic catalyst.

9. The process according to claim 8, wherein the catalyst is diluted with a magnetic material.

10. The process according to claim 1, wherein the coil is arranged to have a direct electrical contact to the catalyst.

11. The process according to claim 10, wherein the coil is not subject to electrical isolation.

12. The process according to claim 1, wherein the coil is a wire comprising at least one selected from copper, constantan, an iron-chromium-aluminum alloy, and a copper-manganese-nickel alloy.

13. A process for the synthesis of a nitrile by catalyzed reaction of ammonia with a hydrocarbon using heating obtained by passing an alternating current through a metallic coil in a synthesis reactor with a catalyst, wherein the endothermic reaction between ammonia and the hydrocarbon takes place in the synthesis reactor with direct inductive heating in a reaction zone, wherein the coil is a wire comprising at least one selected from copper, constantan, an iron-chromium-aluminum alloy, and a copper-manganese-nickel alloy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows how the temperature of an Fe—Cr alloy subjected to varying magnetic fields develops as a function of time.

(2) FIG. 2 shows how the temperature of an Al—Ni—Co alloy subjected to varying magnetic fields develops as a function of time.

DETAILED DESCRIPTION

(3) Thus, the present invention relates to a process for the synthesis of a nitrile by catalyzed reaction of ammonia with a hydrocarbon using heating obtained by passing an alternating current through a metallic coil, wherein the endothermic reaction between ammonia and the hydrocarbon takes place with direct inductive heating in the reaction zone.

(4) Induction heating enables heating with a heat output of more than 70 W/g, which gives heating rates of more than 150° C./s. Thus, induction heating offers a way of very fast and effective heating. This is illustrated in FIG. 1 and FIG. 2 showing how the temperature of Fe—Cr and Al—Ni—Co alloys subjected to varying magnetic fields develops as a function of time.

(5) Among the possible combinations of a ferromagnetic structure and a suitable coating, the best cases were found to be those in which the structure is composed of metals of Fe—Cr or Al—Ni—Co alloys.

(6) The Fe—Cr alloy has a Curie temperature, which is the temperature at which certain materials lose their permanent magnetic properties, of around 560° C. The coating is oxide-based, and it can be an oxide made of a combination of Al, Zr, Ce etc.

(7) The coated metal structure has a porous oxide surface which can be impregnated with practically any catalytic phase. It can therefore be matched to any conventional catalysts for nitrile synthesis, such as catalysts based on Co and Sn.

(8) It may be difficult to obtain sufficient activity in this manner. Thus, an alternative possibility is to dilute the conventional catalyst with a magnetic material.

(9) Since the heating is supplied from inside the reactor, which makes the catalyst the hottest part of the reactor, no large and expensive heating equipment is needed for the reaction. The extremely fast heating makes the reaction practically instantaneous.

(10) Representative reactions between ammonia and hydrocarbons within the scope of the present invention include the following:
CH.sub.4+NH.sub.3.Math.HCN (hydrogen cyanide)+3H.sub.2
C.sub.2H.sub.6+NH.sub.3.Math.CH.sub.3CN (acetonitrile)+3H.sub.2
C.sub.3H.sub.8+NH.sub.3.Math.C.sub.2H.sub.3CN (acrylonitrile)+4H.sub.2
C.sub.3H.sub.8+NH.sub.3.Math.C.sub.2H.sub.5CN (propionitrile)+3H.sub.2
iso-C.sub.4H.sub.10+NH.sub.3.Math.iso-C.sub.3H.sub.5CN (methacrylonitrile)+4H.sub.2

(11) Temperatures between 600 and 900° C. are required to overcome equilibrium limitations, because the reactions are highly endothermic.

(12) The high heat needed for the synthesis of these nitriles can be provided as electrical or inductive heating. It is of crucial importance that the heat is provided fast for these reactions to be able to minimize the thermal carbon deposition. Induction heating also provides a more efficient heat transfer to the catalyst particles, unlike that obtained by using a reactor wall medium that is heated externally, which causes loss of heat.

(13) Different heating zones can be effectively employed again with minimum heat transfer losses in a reactor design. As the reactions are highly endothermic, the conversion profile throughout the reactor can be improved by modulating the isothermal conditions at varying parts of the reactor.

(14) It is possible to use bimetallic catalysts, which could also be used as ferromagnetic materials to provide heating for these reactions. Even in case the bimetallic catalysts are not ferromagnetic, they can be mixed with or surrounded by ferromagnetic materials to be used with inductive heating.

(15) The invention is illustrated further in the example which follows below.

Example

(16) The nitrile synthesis is carried out at a low pressure. A mix of alkane or olefinic hydrocarbons with ammonia is used, possibly along with a carrier gas like nitrogen or methane. The gas mixture is heated to 450-550° C. by heat exchange, and then it enters the induction-heated reaction zone.

(17) The induction heater consists, if possible, of a ferromagnetic catalyst with a high electric coercivity (the ability of a ferromagnetic material to withstand an external electric field without becoming depolarized). Alternatively, the catalyst can be mixed with a ferromagnetic material having a high coercivity. This material should be inert towards the gases in the reaction mixture.

(18) The reaction takes place at a reactor temperature between 600 and 800° C., and after leaving the reactor the effluent gas is cooled to a temperature below 200° C. in the feed/effluent heat exchanger. The desired products are separated, while the unconverted hydrocarbons are mixed into the make-up gas.