WO2009135942A1 - Method for the semi-adiabatic, semi-isothermic implementation of an endothermic reaction using a catalytic reactor and design of said reactor - Google Patents

Abstract

The invention relates to an endothermic reaction that is implemented in a semi-adiabatic, semi-isothermic manner using a catalytic reactor. The reactor has a first and a second flow path (10, 20), which exchange heat between one another. In the first flow path (10), the endothermic reaction takes place on a catalyst and in the second flow path (20), the oxidation and reduction of a metal take place alternately, in order to provide the temperature required for the endothermic reaction.

Description

 description

A method for semi-adiabatic, semi-isothermal carrying out an endothermic reaction using a catalytic reactor and forming this reactor

Technical area

The invention relates to a method for semi-adiabatic, semi-isothermal carrying out an endothermic reaction using a catalytic reactor having a first and a second flow path, which are in heat exchange with each other, wherein in the first flow path to the endothermic reaction a catalyst takes place and an exothermic reaction takes place in the second flow path to provide the temperature necessary for the endothermic reaction. The invention further relates to a reactor suitable for carrying out the process.

State of the art

Reactors are commonly used for a wide variety of catalytic reactions. The use of radial reactors is known from US-A-4,880,603 and US-A-5,250,270 in ammonia synthesis plants.

A common endothermic chemical process employing radial reactors is the dehydrogenation of hydrocarbons, eg the dehydrogenation of ethylbenzene to styrene. In this process, ethylbenzene is reacted with superheated steam at elevated temperatures in the presence of a dehydrogenation catalyst, eg, iron oxide, to form styrene. Such a method is known from US-A-4,551,571 and US-A-6,096,937. The conversion of ethylbenzene to styrene in industrial plants is usually not carried out in a single reactor but in a series of radial reactors connected in series. Radial reactors for making styrene are known from US-A-3,475,508, US-A-3,515,763 and US-A-3,918,918. Such radial reactors are generally elongated, cylindrical, vertical constructions, which can be very large and have a diameter of 1.5 to 6 meters or more and a height of 1.5 up to 30 m or more. Such reactors are known from JP-A-49039971 and JP-A-49039972.

Since the dehydrogenation of ethylbenzene to styrene is endothermic, the temperature of the catalyst and starting materials decreases from the beginning to the end of the first flow path, i.e., from the beginning to the end of the first flow path. from the beginning to the end of the catalyst bed. For example, in an adiabatic plant with two reactors connected in series, the inlet temperature of the ethylbenzene / steam mixture into the first reactor is 615 ° C. and the outlet temperature of the first reactor is 534 ° C. The exiting gas mixture from the first reactor is heated and the inlet temperature in the second reactor is 620 ° C and the outlet temperature of the second reactor 563 ° C. The conversion rate of ethylbenzene over the catalyst bed in the first reactor is 38.5 wt%. The total conversion rate of ethylbenzene over both reactors is 65.8 wt%. After cooling the product stream gaseous components remain in the exhaust stream, such as hydrogen, carbon dioxide, carbon monoxide, nitrogen, methane, ethane, ethylene, propane, propylene and uncondensed residue of water, benzene, toluene, ethylbenzene and styrene. The composition of the dry exhaust gas of the main components is 95.9 mole% hydrogen, 3.2 mole% carbon dioxide, 0.1 mole% carbon monoxide, 0.5 mole% methane, 0.3 mole% ethylene. Nitrogen was not considered because it is used in small amounts as purge gas.

EP 0 871 537 B1 discloses various catalytic processes whose common feature is the use of an oxygen transfer material which is readily oxidizable in the reduced state or easily reducible in the oxidized state, and which is alternately oxidized or reduced. As the oxygen transfer material in particular metals, such as silver, copper or iron or their oxides are called. The heat generated by the oxidation of the oxygen transfer material is used to release volatile organic compounds to allow the cold start of catalysts or to provide the necessary energy in the production of hydrogen. The Exothermic and endothermic reactions occur in each of the proposed catalytic processes in the same reaction chamber.

EP 0 457 352 A1 discloses a cylindrical reactor for

Conduct exothermic reactions with two spatially separated, transverse to each other and in thermal contact flow paths. The reaction medium is passed in succession through both flow paths. However, the exothermic reaction takes place only in one of the two flow paths. The reaction medium in the other flow path is used exclusively to absorb and dissipate the heat generated during the exothermic reaction. EP 0 457 352 A1 does not disclose a method by which the heat energy required for an endothermic reaction can be provided.

US 6 620 386 B1 also discloses a reactor having a first flow path which is transverse to a second flow path, the flow paths being in heat exchange relationship with each other. The reactor can be used to convert ethylbenzene to styrene. The heat required to carry out the endothermic process is supplied to the reactor by superheated steam, by combustion or by an electric heating element.

JP 06-111838 A and US 6,482,375 B1 describe reactors for simultaneously carrying out an exothermic and an endothermic reaction in adjacent reaction lines for heat exchange. The endothermic reaction here is a reforming reaction (JP '838) or the dehydrogenation of ethylbenzene to styrene (US' 375). The exothermic reaction is a combustion reaction in both cases. The reaction lines are parallel to each other.

US 5 567 398 A discloses a reactor for carrying out endothermic reactions. The heat needed to effect the exothermic reaction is generated by the combustion of fuel and air in a combustion chamber. If the reactor is used to recover hydrogen, then an additional catalytic material can be used, which on the one hand increases the hydrogen yield and on the other hand reduces carbon monoxide emissions. The reaction lines are parallel to each other.

US Pat. No. 6,180,846 B1 describes the indirect introduction of heat into a first reaction zone in which an endothermic reaction takes place by contacting the reactants with combustion gases formed in a second reaction zone. An example is the reaction of ethylbenzene by catalytic dehydrogenation to styrene. The heat required for this purpose is generated by combustion of the hydrogen formed in this reaction. The two reaction zones are arranged parallel to one another.

From US-A-2007/0054801 a dehydrogenation catalyst bed system for olefin production is known, which works with a conventional chromia / alumina dehydrogenation catalyst and contains an additional component which is catalytically inert for the dehydrogenation reaction or side reactions but which generates heat when exposed to reducing or oxidizing reaction conditions. The heat-generating inert component may, for example, have a similar density and heat capacities as α-alumina, and may in particular be copper oxide on an alumina support, the copper oxide constituting at least 8% by weight of the heat-generating, inert component. Similar to the Houdry process known from US Pat. No. 2,419,997, the dehydrogenation is carried out in several stages, wherein the catalyst bed is evacuated, reduced with hydrogen and evacuated, and then an aliphatic hydrocarbon is introduced and dehydrogenated, whereupon the catalyst bed is purged with steam and is regenerated. This cycle is repeated, starting with the reduction.

One might think of the temperature in the outlet of the

Catalyst bed by installing heat exchanger tubes to increase. However, the installation of heat exchanger tubes only in the outlet area of the catalyst bed would not significantly improve the temperature profile as long as conventional methods of heat generation exist would be used. In fact, the passage of combustion gases through small diameter tubes would result in overheating of the inlet area of the tubes and low temperatures in the outlet area of the tubes, ie a large temperature gradient along the heat exchanger tubes and in the catalyst bed, which in turn would degrade selectivity.

Presentation of the invention

The object underlying the invention is a method for carrying out an endothermic reaction using a catalytic reactor which is substantially semi-adiabatic and semi-isothermal.

According to the invention, this object is achieved in a method of the type mentioned above in that the second flow path metal / metal oxide on a support and in the second flow path alternately oxidizes the metal and the metal oxide are reduced. The carrier may in particular be particles or the inside of tubes. Although the two flow paths have thermal contact with each other, but they are spatially separated from each other.

In the method according to the invention, the volume of the second

Flow path filled with particles, which are provided with the metal or metal oxide, or the inner sides of the walls defining the second flow path are coated with the metal / metal oxide, which can be reduced or oxidized. The catalyst is operated cyclically with reduction and oxidation phases wherein the alternating oxidation and reduction of metal or metal oxide in the second flow path is controlled to achieve the desired temperature. The length of the reduction and oxidation phases also depends on the size of the reactor and the size of the particles. The larger the reactor and the larger the metal / metal oxide particles, the longer the reduction and oxidation phases. A cycle consisting of a reduction phase and an oxidation phase can be between 3 Take seconds and 15 minutes. Preferably, its duration is between 1 and 2 minutes.

Characterized in that the heat is generated distributed over the second flow path, formed within the second flow path no temperature gradient, but the temperature along the second flow path is thus constant so that it is semi-isothermal. The heat generated within the second flow path is also absorbed almost completely in the first flow path and therefore does not penetrate outward, so that the method is semi-adiabatic.

In general, the reactor is cylindrical and preferably the first flow path from the center of the cylindrical reactor extends radially from the inside to the outside, wherein the supply of the reactants takes place through an axial, central channel of the reactor. By contrast, the second flow path preferably runs parallel to the axis in heat exchanger tubes. The arrangement of the heat exchanger tubes, the temperature profile can be controlled within the first flow path. The paraxial heat exchanger tubes of the second flow path are therefore arranged in the region of the reactor in which the temperature of the first flow path is to be increased. Since on the first flow path, i. As the catalyst bed undergoes an endothermic reaction, the temperature normally decreases toward the end of the first flow path. By arranging the heat exchanger tubes within the first flow path, this temperature drop can be compensated, so that a very uniform temperature distribution along the first flow path is achieved. Thereby, over the entire course of the first flow path, the temperature can be kept at the value which is optimal for the endothermic reaction carried out and gives the highest yield or conversion.

The tube diameter may be between 10 mm and 20 cm and the number of tubes may be between 10 and 10,000, wherein the number is greater, the smaller the tube diameter. The tubes are generally round, but may be of any cross section. at an elongated rectangular cross-section, the ratio of surface to volume is greater than a round cross-section, so that then the heat output is increased.

In the feed pipes of the heat exchanger tubes are installed valves which allow rapid switching from an oxygen-containing gas such as air to a reducing gas, e.g. allow a hydrogen-containing gas, preferably between them, a purging of the system with nitrogen, water vapor or an inert gas.

The metal used for the heat generation is selected on the basis of the kinetics of the oxidation and reduction reactions, since it is important to carry out these reactions as quickly as possible. In addition, the metal must have sufficient stability in a reducing and oxidizing environment. During the reduction and oxidation cycles, the material introduced into the heat exchanger generates heat that can be stored by heat generating material and transferred directly to the heat exchange surfaces. In this case, the highly heated solid transfers the heat to the heat exchange surfaces and gas mixtures generated during the reduction and oxidation.

As the metals of the oxidation / reduction cycle in the

US-A-2007/0054801 in question, in particular copper, bismuth, chromium and nickel. For their oxides, the reduction with hydrogen or methane is exothermic. Also suitable are iron, molybdenum, zinc, cobalt, tin, cerium and manganese. For these metals, reduction with hydrogen or methane is slightly endothermic. Since the oxidation reaction is exothermic in all the metals mentioned, an exothermic effect always results for the entire oxidation / reduction cycle.

The preferred metal is copper. It is preferably e.g. to 10

Wt .-% on a support of α-alumina, wherein the carrier may have spherical shape, ring shape or tablet form or may be an extrudate of any cross-sectional shape, for example a star-shaped cross-section (ribtrusion). The tubes can also be provided on the inside with a wash coating of the metal or metal oxide.

The equations for the reduction and oxidation are the following when using a hydrogen-methane mixture as the reducing gas and oxygen as the oxidizing gas:

Reduction: MeO + CH ₄ + H ₂ → Me + CO ₂ + H ₂ O + ΔH Oxidation: Me + O ₂ → MeO + ΔH

The total amount of heat produced during a cycle is the sum of the reduction and oxidation enthalpy.

In a particularly preferred embodiment of the invention, the hydrogen formed in the dehydrogenation of ethylbenzene from the styrene / ethylbenzene / water vapor / hydrogen mixture is used for the reduction phase and may optionally also be mixed with methane.

The metal compounds used for the reduction and oxidation can either be introduced into the tubes, in which case the endothermic reaction takes place in the space of the reactor surrounding the tubes. Conversely, the metal compound used for the reduction and oxidation can be filled in the space of the reactor surrounding the tubes, and then the endothermic reaction takes place inside the tubes.

For more efficient dehydration, lower pressure loss is important. Since small catalyst pellets cause a high pressure drop, a certain size of the catalyst pellets should not be undercut. However, the pressure loss also depends on the length of the first flow path, i. in a cylindrical reactor of its radius, which is equal to the bed depth. For example, with a bed depth of 80 to 90 cm, the size of the catalyst pellets may be 2 to 6 mm.

Brief description of the drawings

Embodiments of the invention are explained below with reference to the drawing. Show it:

Figure 1 in vertical section a reactor for the dehydrogenation of ethylbenzene, in which the additional heat within the Heat exchanger tubes is generated, and

2 shows in horizontal section the reactor of Fig. 1st

Way (s) for carrying out the invention

The reactor shown in Figures 1 and 2 is substantially cylindrical. It has a first flow path 10 and a second flow path 20, which are spatially separated from each other and which are only in thermal contact with each other.

The first flow path 10 extends from an inlet 12, which begins in the middle of the top of the reactor and extends axially through the reactor through an inlet tube 14, through the interior 16 of the reactor to an annulus 17, from which an outlet 18 lead away on the circumference of the reactor. In the wall of the inlet tube 14 and in the inner cylindrical wall of the annular space 17 are openings that allow gas passage.

The second flow path 20 extends from a

Inlet collecting space 22 at the head of the reactor through heat exchanger tubes 24 to an outlet collecting space 26 at the bottom of the reactor. In the supply lines to the inlet collecting space, valves 28 are installed which allow rapid switching from an oxygen-containing gas such as air to a methane / hydrogen mixture and to a purge gas such as nitrogen or water vapor therebetween. The heat exchanger tubes 24 are arranged axially parallel in the space 16 surrounding the inlet tube 14 in two concentric circles. The heat exchanger tubes 24 intersect the first flow path 10 and allow heat transfer or heat exchange between the first and second flow paths 10, 20. The heat exchanger tubes 24 are arranged predominantly in the central region of the first flow path 10 in order to compensate there for the otherwise occurring temperature decrease. The radius of the concentric circles on which the heat exchanger tubes 24 are arranged is therefore 50 to 95% of the radius of the reactor.

Since the temperature drop at the beginning of the first flow path 10 is the strongest, it is sometimes appropriate to arrange the heat exchanger tubes 24 already at 20% of the radius of the reactor. Ethylbenzene and superheated steam (EB + H ₂ O) at a temperature between 580 and 650 ° C is supplied via the inlet 12. Through the apertures in the wall of the inlet tube 14, the ethylbenzene-vapor mixture enters the space 16 of the reactor, which is filled with pellets of a dehydrogenation catalyst. The dehydrogenation catalyst is an iron-potassium based system. In the heat exchanger tubes 24 are pellets of a support of α-alumina provided with copper, wherein the copper accounts for a share of 8 wt.% Of the pellets. The mixture of the formed styrene, residual ethylbenzene, hydrogen and water vapor (STYR. + EB + H ₂ + H ₂ O) is withdrawn through the outlet 18.

The conversion of ethylbenzene to styrene and hydrogen is endothermic, so that the temperature of the ethylbenzene-vapor mixture would decrease as it passes through the bed of the dehydrogenation catalyst. This decrease in temperature is compensated by the supply of heat generated in the heat exchanger tubes 24 by a rapid succession of oxidation and reduction reactions of a metal and a metal oxide, respectively. In the heat exchanger tubes 24 are pellets with a supported metal. Air is supplied via the collection inlet during the oxidation phase, whereby the metal in the heat exchanger tubes 24 is oxidized. This reaction is exothermic, so that the heat exchanger tubes 24 are heated and increase over their surface the temperature of the gas mixture in the first flow path 10. As a result, the conversion of the dehydrogenation at the end of the first flow path 10 is improved, since without heat exchanger tubes 24, the temperature would drop here. The amount of air supplied is sized so that almost all of the metal surfaces of the pellets present in the heat exchanger tubes 24 are oxidized. When this is achieved, the heat exchanger tubes 24 are purged with nitrogen and then the metal surfaces of the pellets in the heat exchanger tubes are reduced again by the supply of a mixture of methane and hydrogen. By the hydrogen content or the Using only hydrogen, the heat balance of the reduction reaction can be controlled.

In the following table process parameters of two comparative examples and six embodiments of the invention are given. The embodiments describe only the first reactor and the indicated values all refer to the first reactor. The heating according to the invention by means of heat exchanger tubes is not limited to systems with a single reactor and can also be used in multi-reactor plants and there in all reactors, in individual reactors or in any combination. However, the invention makes it possible to reduce the number of reactors connected in series.

In the embodiments of the table according to the invention, the heat exchanger tubes are located approximately in the middle of the catalyst bed at a radius of between 2.0 and 2.1 m. The cross section of the heat exchanger tubes in this 0.1 m wide ring area is about 50% of the area of the catalyst bed.

In the embodiment 1a causes a heating in the

Catalyst bed center at 615 ° C an ethylbenzene conversion of 52.6 wt.% Over the entire catalyst bed while maintaining the reactor dimension as in Comparative Example 1. In order to compensate for the reduction of the active catalyst volume of dehydrogenation catalyst through the heat exchanger tubes, 1b in the embodiment of the outer diameter of the catalyst bed slightly increased to achieve the same catalyst volume as in Comparative Example 1. As a result, an ethylbenzene conversion rate of 53.3 wt% is achieved.

Even with insufficient heating in the catalyst bed center to only 600 ° C is an ethylbenzene conversion rate of 48.6 wt.% For the same reactor dimension (Embodiment 2a) and 49.2 wt.% For constant catalyst volume (Embodiment 2b) reached.

Table 1

By heating the invention can achieved

Conversion rates for ethylbenzene and thus the recoverable styrene levels are too high to be reasonably handled, for example, in the subsequent, already existing distillation. An alternative would be to increase the educt currents while maintaining the Conversion rate, which would also lead to increased styrene production. If this is not possible, the inlet temperature can simply be lowered. In embodiment 3a, an inlet temperature of 585 ° C with heating in the center of the catalyst bed to 585 ° C gives an ethylbenzene conversion of 38.8% by weight, or in embodiment 3b gives an inlet temperature of 583 ° C with center heating of the catalyst bed at 583 ° C an ethylbenzene conversion of 38.5 wt.%. This is the same ethylbenzene conversion rate as for an entry temperature of 615 ° C without heating in the catalyst bed, but the selectivity to styrene in Use Examples 3a and 3b is significantly improved because by-product formation is lower at lower inlet temperatures. In Comparative Example 2 without heating in the catalyst bed, even by increasing the reactor inlet temperature to 650 ° C, only an ethylbenzene conversion rate of 49.4 wt% can be achieved, but the by-product formation increases sharply due to the high reactor inlet temperature.

LIST OF REFERENCE NUMBERS

10 first flow path 20 second flow path

12 inlet 22 inlet collecting space

14 inlet tube 24 heat exchanger tubes

16 Interior 26 Outlet collection room

17 annulus 28 valve

18 outlet

Claims

claims A process for the semi-adiabatic, semi-isothermal, endothermic reaction using a catalytic reactor, the reactor having a first flow path (10) and a second flow path (20) heat exchange with each other, in the first flow path (10) the endothermic reaction takes place on a catalyst, and in the second flow path (20) an exothermic reaction takes place to provide the temperature necessary for the endothermic reaction, characterized in that the second flow path (20) contains metal / metal oxide and the second flow path (20) alternately oxidizes the metal and the metal oxide can be reduced. 2. The method of claim 1, wherein the second flow path (20) is purged between the reduction and oxidation of the metal with an oxygen- and hydrogen-free gas. 3. The method of claim 1 or 2, wherein a cylindrical reactor having a plurality of axially parallel tubes (24) is used, wherein the first flow path (10) has an axial feed and then extends in the radial direction between the tubes and the second flow path ( 20) through the tubes (24). 4. The method according to any one of claims 1 to 3, wherein the tubes (24) are filled with carrier material whose surface is provided with a metal which can be oxidized and reduced. 5. The method of claim 4, wherein the carrier material is in the form of pellets. 6. The method of claim 4 or 5, wherein for reducing the metal oxide in the tubes (24) of the second flow path (20) a mixture of partially hydrogen-containing gas is supplied thereto and for oxidation of the metal in the tubes (24) of the second flow path this an oxygen-containing gas is supplied. 7. The method of claim 6, wherein the hydrogen formed in the dehydrogenation of ethylbenzene from the Styrene / ethylbenzene / water vapor / hydrogen mixture is used for the reduction phase. 8. A process according to any one of claims 1 to 7, wherein the space between the tubes of the first flowpath is filled with dehydrogenation catalyst and ethylbenzene and superheated steam are converted to styrene and hydrogen in the first flowpath of the reactor. 9. The method according to any one of claims 1 to 8, wherein on the first flow path (10) ethylbenzene is dehydrogenated by means of superheated steam to styrene and H ₂ and on the second flow path (20) metal is alternately oxidized and reduced. 10. The method of claim 8, wherein the metal is copper. 11. Reactor for carrying out the method according to one of claims 1 to 10, having a first flow path (10) and a second flow path (20), which extend transversely to each other and are in heat exchange relationship with each other, characterized in that the second flow path (20) Metal / metal oxide and in the second flow path (20) alternately oxidizes the metal and the metal oxide are reduced. 12. The reactor of claim 11, wherein the first flow path (10) and the second flow path (20) are spatially separated. The reactor of claim 12, wherein the reactor is cylindrical and the first flow path (10) is radial and the second flow path (20) is parallel to the longitudinal axis of the reactor. 14. Reactor according to claim 13, wherein the second flow path (20) by axially parallel tubes (24) is formed. 15. Reactor according to claim 14, wherein the axially parallel tubes (24) are arranged predominantly in the end region of the first flow path (10).