INDUCTION HEATED AROMATIZATION OF HIGHER HYDROCARBONS

Abstract

A reactor system for aromatization of higher hydrocarbons within a given temperature range T upon bringing a reactant stream including higher hydrocarbons into contact with a catalytic mixture. The reactor system includes a reactor unit arranged to accommodate a catalytic mixture. The catalytic mixture includes a catalyst material and a ferromagnetic material. The catalyst material is arranged to catalyze the aromatization of higher hydrocarbons. The ferromagnetic material is ferromagnetic at least at temperatures up to an upper limit of the given temperature range T, where the temperature range T is the range from between about 400 C. and about 700 C. or a subrange thereof. The reactor system also includes an induction coil arranged to be powered by a power source supplying alternating current, whereby the ferromagnetic material is heated to a temperature within the temperature range T by means of an alternating magnetic field.

Claims

1. A reactor system for aromatization of higher hydrocarbons within a given temperature range T upon bringing a reactant stream comprising higher hydrocarbons into contact with a catalytic mixture, said reactor system comprising: a reactor unit arranged to accommodate a catalytic mixture, said catalytic mixture comprising a catalyst material and a ferromagnetic material, where said catalyst material is arranged to catalyze the aromatization of higher hydrocarbons and said ferromagnetic material is ferromagnetic at least at temperatures up to an upper limit of the given temperature range T, wherein the given temperature range T is the range between about 400 C. and about 700 C. or a sub-range thereof, an induction coil arranged to be powered by a power source supplying alternating current and being positioned so as to generate an alternating magnetic field within the reactor unit upon energization by the power source, whereby the ferromagnetic material is heated to a temperature within said temperature range T by means of said alternating magnetic field.

2. A reactor system according to claim 1, wherein the Curie temperature of the ferromagnetic material equals an operating temperature at substantially the upper limit of the given temperature range T of the aromatization reaction.

3. A reactor system according to claim 1, wherein the Curie temperature of the ferromagnetic material is above about 500 C.

4. A reactor system according to claim 1, wherein the induction coil is placed within the reactor unit or around the reactor unit.

5. A reactor system according to claim 1, wherein said ferromagnetic material comprises one or more ferromagnetic macroscopic supports susceptible for induction heating, where said one or more ferromagnetic macroscopic supports are ferromagnetic at temperatures up to an upper limit of the given temperature range T, where said one or more ferromagnetic macroscopic supports is/are coated with an oxide and where the oxide is impregnated with catalyst material.

6. A reactor system according to claim 1, wherein said catalytic mixture comprises bodies of catalyst material mixed with bodies of ferromagnetic material, wherein the smallest outer dimension of a plurality of the bodies are in the order of about 1-2 mm or larger.

7. A reactor system according to claim 6, wherein the catalytic mixture has a predetermined ratio between said bodies of catalyst material and said bodies of ferromagnetic material.

8. A reactor system according to claim 6, wherein the predetermined ratio between said catalyst and said ferromagnetic materials is a predetermined graded ratio varying along a flow direction of said reactor.

9. A reactor system according to claim 1, wherein the distance between windings of said induction coil varies along the flow direction of the reactor.

10. A catalytic mixture arranged for catalyzing aromatization of higher hydrocarbons in a reactor in a given temperature range T upon bringing a reactant stream comprising higher hydrocarbons into contact with said catalytic mixture, said catalytic mixture comprising a catalyst material and a ferromagnetic material, where said catalyst material is arranged to catalyze the aromatization of higher hydrocarbons and said ferromagnetic material is ferromagnetic at least at temperatures up to an upper limit of the given temperature range T, wherein the given temperature range T is the range between about 400 C. and about 700 C. or a sub-range thereof.

11. A catalytic mixture according to claim 10, wherein said catalytic mixture comprises bodies of catalyst material mixed with bodies of ferromagnetic material.

12. A catalytic mixture according to claim 10, wherein the Curie temperature of the ferromagnetic material substantially equals an operating temperature at substantially the upper limit of the given temperature range T of the aromatization reaction.

13. A catalytic mixture according to claim 10, wherein the ferromagnetic material is a material comprising iron, an alloy comprising iron and chromium, an alloy comprising iron, chromium and aluminum, an alloy comprising iron and cobalt, or an alloy comprising iron, aluminum, nickel and cobalt.

14. A catalytic mixture according to claim 10, wherein the catalyst material comprises a catalytically active material supported on a zeolite.

15. A catalytic mixture according to claim 14, wherein said catalytically active material is an active phase of one or more of the following elements: zinc, gallium, molybdenum, platinum.

16. A catalytic mixture according to claim 14, wherein said zeolite is a HZSM, a ZSM or a SAPO zeolite.

17. A catalytic mixture according to claim 10, wherein said ferromagnetic material comprises one or more ferromagnetic macroscopic supports susceptible for induction heating, where said one or more ferromagnetic macroscopic supports are ferromagnetic at temperatures up to an upper limit of the given temperature range T, where said one or more ferromagnetic macroscopic supports is/are coated with an oxide and where the oxide is impregnated with catalyst material.

18. A catalytic mixture according to claim 10, wherein the catalytic mixture has a predetermined ratio between said catalyst material and said ferromagnetic material.

19. A method for aromatization of higher hydrocarbons in a given temperature range T in a reactor system, said reactor system comprising a reactor unit arranged to accommodate a catalytic mixture, said catalytic mixture comprising a catalyst material and a ferromagnetic material, where said catalyst material is arranged to catalyze the aromatization of higher hydrocarbons and said ferromagnetic material is ferromagnetic at least at temperatures up to an upper limit of the given temperature range T, and an induction coil arranged to be powered by a power source supplying alternating current and positioned so as to generate an alternating magnetic field within the reactor unit upon energization by the power source, whereby the catalytic mixture is heated to a temperature within the given temperature range T by means of said alternating magnetic field, wherein the temperature range T is the range from between about 400 C. and about 700 C. or a subrange thereof, said method comprising the steps of: (i) generating an alternating magnetic field within the reactor unit upon energization by a power source supplying alternating current, said alternating magnetic field passing through the reactor unit, thereby heating catalytic mixture by induction of a magnetic flux in the material; (ii) bringing a reactant stream comprising higher hydrocarbons into contact with said catalyst material; (iii) heating said reactant stream to a temperature within the given temperature range T within said reactor by the generated alternating magnetic field; and (iv) letting the reactant stream react in order to provide a product to be outlet from the reactor.

20. A method according to claim 19, wherein the reactant stream is preheated in a heat exchanger prior to step (ii).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0053] FIG. 1 is a graph showing a temperature profile of catalyst in a reactor unit heated by induction heating as compared to a preheated reactant stream;

[0054] FIGS. 2A and 2B show schematic drawings of two embodiments of a reactor system.

DETAILED DESCRIPTION OF THE FIGURES

[0055] FIG. 1 is a graph showing a temperature profile of catalyst in a reactor unit heated by induction heating as compared to a preheated reactant stream.

[0056] In both situations, the reactor unit is a longitudinal flow reactor unit comprising catalyst material arranged for carrying out aromatization of higher hydrocarbons, viz. an endothermic reaction. As shown in FIG. 1 this reaction takes place at temperatures between about 550 C. and 700 C.

[0057] The dotted line indicates the temperature profile along the length of a reactor for a preheated reactant stream, corresponding to the situation where the reactor is an adiabatic reactor. As shown in FIG. 1, the reactant gas in the situation where the reactor unit is an adiabatic reactor is preheated to a temperature of about 700 C. When the gas passes along the longitudinal direction of the reactor unit, the temperature thereof decreases since the value of the Gibbs free energy of the aromatization reaction is negative. In order to ensure that the temperature of the reactant stream stays above about 550 C. throughout the reactor length, the reactant gas stream has been preheated to about 700 C. even though such a relatively high temperature results in a high risk of carbon formation in the catalyst bed of the reactor.

[0058] In comparison, the solid curve shows the temperature throughout the longitudinal direction of the reactor unit in a case where the reactor system and catalyst within the reactor system is arranged for inductive heating. In the situation shown in FIG. 1, the reactant gas stream enters the reactor unit at a temperature of about 150 C. Within the first approximately 10% of the length of the reactor unit, the temperature of the reactant gas stream increases to about 550 C. due to the inductive heating of the catalyst within the reactor unit. The temperature of the gas within the reactor remains at about 550 C. throughout the remaining 90% of the length of the reactor unit.

[0059] In addition to the advantageous delivery of heat directly to the catalyst material and the resulting possibility of reducing the maximum temperature of the feed or reactant gas, induction heating offers a fast heating mechanism, which potentially could make upstart of a aromatization reactor relative fast.

[0060] FIGS. 2A and 2B show schematic drawings of two embodiments 100a and 100b, of a reactor system. In FIGS. 2A and 2B, similar features are denoted using similar reference numbers.

[0061] FIG. 2A shows an embodiment of the reactor system 100a for carrying out dehydrogenation of alkanes to alkenes and subsequent aromatization of the alkenes upon bringing a reactant stream comprising alkanes into contact with a catalytic mixture 120. The reactor system 100a comprises a reactor unit 110 arranged to accommodate a catalytic mixture 120 comprising a catalyst material and a ferromagnetic material, where the catalyst material is arranged to catalyze the dehydrogenation of alkanes to alkenes and the subsequent aromatization of alkenes. The ferromagnetic material is ferromagnetic at least at temperatures up to about 600 C.

[0062] Reactant is introduced into the reactor unit 110 via an inlet 111, and reaction products formed on the surface of the catalyst mixture 120 is outlet via an outlet 112.

[0063] The reactor system 100a further comprises an induction coil 150a arranged to be powered by a power source 140 supplying alternating current. The induction coil 150a is connected to the power source 140 by conductors 152. The induction coil 150a is positioned so as to generate an alternating magnetic field within the reactor unit 110 upon energization by the power source 140. Hereby the catalyst mixture 120 is heated to a temperature within a given temperature range T relevant for dehydrogenation of alkanes, such as between 350 C. and about 500 or 700 C., by means of the alternating magnetic field.

[0064] The induction coil 150a of FIG. 2A is placed substantially adjacent to the inner surface of the reactor unit 110 and in physical contact with the catalytic mixture 120. In this case, in addition to the induction heating provided by the magnetic field, the catalyst material 120 adjacent the induction coil 150a is additionally heated directly by ohmic/resistive heating due to the passage of electric current through the windings of the induction coil 150a. The induction coil 150a may be placed either inside or outside the catalyst basket (not shown) supporting the catalytic mixture 120 within the reactor unit 110. The induction coil is preferably made of kanthal.

[0065] The catalytic mixture 120 may be divided into sections (not shown in the figures), where the ratio between the catalytic material and the ferromagnetic material is varies from one section to another. At the inlet of the reactor unit 110, the reaction rate is high and the heat demand is large; this may be compensated for by having a relatively large proportion of ferromagnetic material compared to the catalytic material. The ferromagnetic material may also be designed to limit the temperature by choosing a ferromagnetic material with a Curie temperature close to the desired reaction temperature.

[0066] Placing the induction coil 150a within the reactor unit 110 ensures that the heat produced due to ohmic resistance heating of the induction coil 150a remains useful for the dehydrogenation reaction. However, having an oscillating magnetic field within the reactor may cause problems, if the materials of the reactor unit 110 are magnetic with a high coercivity, in that undesirably high temperatures may be the result. This problem can be circumvented by cladding the inside of the reactor unit 110 with materials capable of reflecting the oscillating magnetic field. Such materials could e.g. be good electrical conductors, such as copper. Alternatively, the material of the reactor unit 110 could be chosen as a material with a very low coercivity. Alternatively, the induction coil 150 could be wound as a torus.

[0067] To make the catalyst bed susceptible for induction, different approaches may be applied. One approach is to support the catalyst material on the ferromagnetic material. For example, the ferromagnetic material comprises one or more ferromagnetic macroscopic supports susceptible for induction heating, and the one or more ferromagnetic macroscopic supports are ferromagnetic at temperatures up to an upper limit of the given temperature range T. The one or more ferromagnetic macroscopic supports is/are coated with an oxide and the oxide is impregnated with catalyst material. Another approach is to mix catalyst material powder and ferromagnetic material powder and treat the mixture to provide bodies of catalytic mixture. Additionally or alternatively, the catalytic mixture comprises bodies of catalyst material mixed with bodies of ferromagnetic material, wherein the smallest outside dimension of the bodies are in the order of about 1-2 mm or larger.

[0068] The catalytic mixture preferably has a predetermined ratio between the catalyst material and the ferromagnetic material. This predetermined ratio may be a graded ratio varying along a flow direction of the reactor.

[0069] In another approach, ferromagnetic macroscopic supports are coated with an oxide impregnated with the catalytically active material. This approach offers a large versatility compared to the ferromagnetic nanoparticles in the catalyst, as the choice of catalytic active phase is not required to be ferromagnetic.

[0070] FIG. 2B shows another embodiment 100b of the reactor system for carrying out dehydrogenation of alkanes to alkenes and subsequent aromatization of the alkenes upon bringing a reactant stream comprising alkanes into contact with a catalytic mixture 120. The reactor unit 110 and its inlet and outlet 111, 112, the catalytic mixture 120, the power source 140 and its connecting conductors 152 are similar to those of the embodiment shown in FIG. 2A.

[0071] In the embodiment of FIG. 2B, an induction coil 150b is wound or positioned around the outside of the reactor unit 110.

[0072] In both embodiments shown in FIGS. 2A and 2B, the catalytic mixture can be any catalytic mixture according to the invention. Thus, the catalytic mixture may be in the form of catalyst material supported on the ferromagnetic material, e.g. where in the form of ferromagnetic macroscopic support(s) coated with an oxide, where the oxide is impregnated with catalyst material, miniliths, a monolith, or bodies produced from a mixture of catalyst material powder and ferromagnetic material powder. Thus, the catalyst material is not limited to catalyst material having relative size as compared to the reactor system as shown in the figures. Moreover, when the catalyst material comprises a plurality of macroscopic supports, the catalyst material would typically be packed so as to leave less space between the macroscopic supports than shown in the FIGS. 2A and 2B. Furthermore, in the two embodiments shown in FIGS. 2A and 2B, the reactor unit 110 is made of non-ferromagnetic material. In the two embodiments shown in FIGS. 2A and 2B, the power source 140 is an electronic oscillator arranged to pass a high-frequency alternating current (AC) through the coil surrounding at least part of the catalyst material within the reactor system.

Example

[0073] The catalyst material comprises for example Zn as the catalytically active material supported on a zeolite, e.g. a HZSM, a ZSM or a SAPO zeolite. The ferromagnetic material is e.g. beads of iron, an alloy comprising iron and chromium, an alloy comprising iron, chromium and aluminum, an alloy comprising iron and cobalt, or an alloy comprising iron, aluminum, nickel and cobalt.

[0074] The frequency of the alternating current through the induction coil is e.g. 50 kHz and the alternating current has e.g. a root mean square value of 10 A. Such an alternating current field generates a magnetic field of about 0.05 T. The magnetic field heats the ferromagnetic material, e.g. the FeCrAlloy beads, to a temperature of about 550 C. and the energy is transferred to the catalyst material. When a reactant stream entering the reactor at a temperature of about 100 C., it is rapidly heated to 550 C. which will facilitate aromate synthesis over the catalyst material. The product from the reaction is a mixture of benzene, toluene, xylene, hydrocarbons and hydrogen. In a further step, the product from the reaction may be purified.

[0075] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms comprising or comprises do not exclude other possible elements or steps. Also, the mentioning of references such as a or an etc. should not be construed as excluding a plurality. Furthermore, individual features mentioned in different claims may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.