Catalytic converter system and process

IS 2 155 677 T3

DESCRIPTION

Catalytic converter system and corresponding procedure.

Field of the invention

The present invention relates to a catalytic converter system and a process for carrying out highly exothermic reactions between liquid reactants, such as the reaction between propylene and ethylbenzene hydroperoxide to form propylene oxide, using a solid heterogeneous catalyst.

Description of the prior art

Substantial difficulties are encountered in carrying out highly exothermic reactions in which the reactants and / or products are temperature sensitive. For example, the liquid phase catalytic reaction of propylene and an organic hydroperoxide to produce propylene oxide is a highly exothermic reaction, and the selectivity of the reaction for the desired product is quite sensitive to temperature. Thus, the elimination of the exothermic heat of the reaction without causing an excessive rise in temperature presents a serious problem.

Conventional reactors for exothermic reactions are usually of two types:

(1) Rapid cooling type consisting of multiple fixed beds with cold feed injected suddenly between the beds, (2) Tubular type in which the catalyst is placed in the tubes of a vertical heat exchanger with cover and tubes.

If the heat of reaction is high, the first type does not provide sufficient heat removal. This can be overcome by recycling the cold reactor effluent, but this results in the disadvantages associated with fully mixed reactors.

The cost of the tubular reactor becomes prohibitive when high heat of reaction is to be removed by heat exchanger surfaces operating with a low heat transfer coefficient. There is also a temperature gradient from the center of the tube, which is often detrimental for a process that requires near isothermal conditions.

European Patent 0 323 663 describes a fixed bed catalytic reactor and a process for carrying out the epoxidation of an olefin by reaction with an organic hydroperoxide under substantially isothermal conditions. As described in this European Patent, all the heat generated by the exothermic reaction is removed by vaporization of the low boiling component of the reaction mixture, propylene in the case of a propylene / organic hydroperoxide system. Sufficient propylene is fed to the reactor to remove all the exotherm from the reaction. The reactor is operated at the boiling pressure of the reaction mixture in such a way that a downward flow of the same direction current of a liquid and a gas phase is provided. It is mentioned that the procedure represents an improvement over the methods currently employed at the time, which involve a multi-reactor discipline with inter-stage cooling.

The method and apparatus described in European Patent 0 323 663 has a number of serious disadvantages. When the exotherm of the reaction is removed by vaporization of propylene, as required in the European Patent, excessive amounts of propylene must be fed as a liquid to the system. In fact, the European Patent shows the feeding of 16.67 moles of propylene per mole of ethylbenzene hydroperoxide to the reactor. When epoxidation is considered to be essentially equimolar to propylene and hydroperoxide, it can be appreciated that the process of the European Patent necessarily involves the recovery and recycling of high volumes of propylene at high cost.

Additionally, although European Patent 0 323 663 appears to describe a reactor outlet pressure of 26 x 10⁵ Pa, this does not seem consistent with the vapor pressure of the liquid reaction mixture. Mine probably the actual output pressure would be around 10.3448 x 10⁵ or less, and this results in the additional and very important problem of cooling and / or recompression of the large propylene recycle stream.

An additional problem with the system of European Patent 0 323 663 is the poor selectivity of the

ES 2 155 677 T3 reaction that would result at the low concentrations of propylene in the liquid phase in the lower part of the reactor.

Brief description of the invention

According to the invention, there is provided a reactor and a process that is especially useful for the production of oxirane compounds by reacting an olefin, such as propylene, with an organic hydroperoxide, using a solid contact catalyst, the invention being characterized by the following: following characteristics:

(1) the reactor is divided into a series of separate zones, each zone containing a bed of solid epoxidation catalyst;

(2) conditions are maintained to provide the liquid phase without substantial vapor formation throughout the entire reactor;

(3) a cold reactor feed is provided that is preheated to reaction temperature by separate indirect heat exchange with reaction liquid from the various separate reactor zones;

(4) the reaction liquid from the last of the series of reaction zones is reduced in pressure to form a gas-liquid mixture at a lower temperature, and this gas-liquid mixture is heated by indirect heat exchange with the liquid. reaction of at least one of the separated reactor zones. Description of the drawings

The attached Figure illustrates the invention.

Detailed description

The practice of the invention is especially applicable to highly exothermic reactions such as those between an olefin, for example propylene, and an organic hydroperoxide, for example ethylbenzene hydroperoxide, and can be better described with reference to the accompanying drawing.

Referring to the drawing, reactor 1 is a vertical cylindrical reactor having five separate beds of solid heterogeneous epoxidation catalyst, catalyst beds 2, 3, 4, 5 and 6. Retention means (not shown) are provided to maintain the Solid catalyst in place while allowing liquid to pass through.

A liquid reaction mixture, composed of propylene and ethylbenzene hydroperoxide, which has been heated to the reaction temperature, is introduced, through pipe 7 to a lower zone 8 of the reactor. As shown in the drawing, upward flow of the reaction mixture takes place but downward flow of liquid is also equally feasible.

The reaction mixture passes from zone 8 through catalyst bed 2 where propylene oxide is formed by reaction of propylene and ethylbenzene hydroperoxide according to known procedures. Conditions are regulated to provide a modest temperature rise, for example -12 to 10 ° C, as a result of the reaction exotherm in bed 2.

The reaction mixture of catalyst bed 2 passes to zone 9 from which zone it is extracted from reactor 1 via pipe 10 and is passed to indirect heat exchanger 11.

Feed to the system propylene and relatively cold feed ethylbenzene oxidation material, for example 27 to 49^°C, containing ethylbenzene hydroperoxide, goes through pipes 12 and 13, respectively, and then as a combined stream goes through pipe 14. A portion of this cold feed passes to exchanger 11 via pipe 15 where it is heated by exchange of indirect heat up to reaction temperature. The cooled reaction mixture, whose exothermic reaction heat has been removed, passes via pipe 16 to zone 17 of reactor 1, while the preheated feed passes to zone 8 of reactor 1 via pipes 18 and 7.

From zone 17, the reaction liquid passes through catalyst bed 3 where a further reaction of propylene and ethylbenzene hydroperoxide takes place to form propylene oxide.

IS 2 155 677 T3

Again, the conditions are controlled to provide a modest rise in temperature, eg, -12 to 10 ° C, as a result of the exotherm of the reaction in bed 3.

The reaction mixture from catalyst bed 3 passes to zone 19, from which zone it is withdrawn from reactor 1 via line 20 and passed to indirect heat exchanger 21.

A second portion of the relatively cold feed passes through pipe 22 to exchanger 21 where it is heated by indirect heat exchange to reaction temperature. The cooled reaction mixture, from which the exothermic heat of reaction has been removed, passes via pipe 23 to zone 24 of reactor 1 while the preheated feed passes to zone 8 of reactor 1 via pipes 25 and 7.

From zone 24, the reaction liquid passes through catalyst bed 4 where a further reaction of propylene and ethylbenzene hydroperoxide takes place to form propylene oxide. Conditions are controlled to provide a modest temperature rise, e.g. -12 to 10^°C, as a result of the exotherm of the reaction in bed 4.

The reaction mixture from catalyst bed 4 passes to zone 26, from which zone it is extracted from reactor 1 via pipe 27 and passed to indirect heat exchanger 28.

The remainder of the relatively cold feed passes through pipe 44 to exchanger 28 where it is heated by indirect heat exchange to reaction temperature. The cooled reaction mixture, from which the exotothermic heat of reaction has been removed, passes through pipe 29 to zone 30 of reactor 1, while the preheated feed passes to zone 8 of reactor 1 via pipes 31 and 7.

From zone 30, the liquid reaction mixture passes through catalyst bed 5 where a further reaction of propylene and ethylbenzene hydroperoxide takes place to form propylene oxide. There is a modest use of temperature, for example -12 to 10^°C, as a result of the exotherm of the reaction in bed 5.

The reaction mixture from catalyst bed 5 passes to zone 32, from which zone it is withdrawn from reactor 1 via pipe 33 and passed to indirect heat exchanger 34.

In exchanger 34, the reaction mixture from bed 5 is cooled and the exothermic heat of reaction is removed by indirect heat exchange, and the cooled reaction mixture passes via pipe 35 to zone 36 of reactor 1.

From zone 36, the reaction mixture passes through catalyst bed 6 where the final reaction of propylene and ethylbenzene hydroperoxide takes place to form propylene oxide. The pressure is maintained at a high level throughout reactor 1 to avoid substantial vaporization of the components of the reaction mixture. Illustrative pressures maintained throughout reactor 1 are generally in the range of 34 x 10⁵ Pa at 55 x 10⁵ Pa. In catalyst bed 6 there is a modest temperature rise, for example -12 to 10^°C, as a result of the exotherm of the reaction in bed 6.

The reaction mixture passes through catalyst bed 6 to zone 37 and is removed from reactor 1 via line 38. The removed mixture, which is essentially liquid, passes through pressure reducing media whereby pressure is reduced. pressure to a value where there is vaporization of the lighter component, for example propylene, and a reduction in temperature due to vaporization to a level where it is substantially lower, for example -1 to 16^°C, below the temperature of the reaction mixture removed from zone 32 via pipe 33. As illustrated in the drawing, a control valve 39 can be used to achieve pressure reduction resulting in a mixed phase. in pipe 40. Generally, the pressure is reduced from that maintained in reactor 1 to about 17 x 10⁵ Paa24x10⁵ Pa in order to achieve vaporization and temperature reduction.

The mixture of the reaction product of steam and liquid passes through pipe 40 to exchanger 34 in which, by indirect heat exchange, the mixture is heated with the exothermic heat of the reaction of bed 5. The reaction mixture of the zone 32, from which the exotherm has been removed, passes via pipe 35 to zone 36 of reactor 1 as described above.

As a result of indirect heat exchange in exchanger 34, it is transferred from the

ES 2 155 677 T3 reaction mixture from zone 32 to the vapor / liquid mixture in line 40 the heat necessary to separate components C₃, such as propylene, of the heavier components of the mixture in a subsequent conventional distillation operation. Without the pressure reduction described in the medium 39 and the accompanying temperature reduction, proper heat transfer could not take place.

The vapor and liquid product mixture passes from exchanger 34 via pipe 41 for the separation of the various components according to known procedures.

The epoxidation reaction of the present invention is carried out under known conditions. See, for example, US Patent 3,351,635, the description of which is incorporated herein by reference.

Generally, temperatures are in the range of 66 to 121^°C, usually 82 to 107^°C, and the pressures are sufficient to maintain the liquid phase in reactor 1, for example 34 x 10⁵ Paa55x10⁵Pa.

In general, the temperature increase in the various reaction zones is kept at a modest level, for example -12 to 10^°C, in order to achieve a high selectivity of the reaction. It is generally advantageous to cool the reaction mixture in each zone to around reactor feed temperature in order to approach isothermal reaction conditions.

Known solid heterogeneous catalysts are used. In this regard, reference is made to European Patent Publication 0 323 663, UK Patent Publication 1,249,079, US Patent 4,367,342, 3,829,392, 3,923,843 and 4,021,454, the descriptions of which are incorporated here.

The invention is especially applicable to the epoxidation of alpha-olefins, having 3-5 carbon atoms, with aralkyl hydroperoxide.

The following example illustrates an especially preferred practice of the invention as described in the accompanying drawing.

Referring to the drawing, a propylene feed is introduced at about 38^°Cy48x10⁵ Blow pipe 13 at a flow rate of about 100 kg / s. The ethylbenzene oxidation material is also introduced at 38^°Cy48x10⁵ Blow pipe 12 at a flow rate of about 71 kg / s. The feed streams are combined in pipe 14.

The feed stream is divided, passing the portion to heat exchangers 11, 21 and 28. About 60 kg / s passes through pipe 15 to heat exchanger 11 where it is heated to about 91^°C by indirect heat exchange with the reaction mixture from zone 9 of reactor 1.

About 60 kg / s of the feed goes through pipe 22 to heat exchanger 21 where it is heated to about 91^°C by indirect heat exchange with the reaction mixture from zone 19 of reactor 1.

The remaining portion of the feed, 51 kg / s, passes through pipe 44 to heat exchanger 28 where it is heated to about 91^°C by indirect heat exchange with the reaction mixture from zone 26 of reactor 1.

The preheated feed streams are recombined and fed via pipe 7 to zone 8 of reactor 1 to 91^°C and 39 x 10⁵ Pa.

Reactor 1 is a vertical cylindrical reactor having five separate zones containing separate beds 2, 3, 4, 5 and 6 of solid heterogeneous epoxidation catalyst which was prepared as described in Example VII of Dutch Patent 145,233.

The feed liquid is introduced into zone 8 and passes through catalyst bed 2 whereby the exothermic reaction of ethylbenzene hydroperoxide and propylene takes place to form propylene oxide. The reaction liquid passes through bed 2 to zone 9, and then to 107^°Cy48x10⁵Pa, the liquid passes via pipe 10 to heat exchanger 11 where a portion of the feed to the reactor is heated by indirect heat exchange, as described above.

The reaction mixture, from which the reaction exotherm of bed 2 has been removed, becomes about 92^°C and 48 x 10⁵ Via pipe 16 to zone 17 of reactor 1. From zone 17, the reaction mixture

ES 2 155 677 T3 passes through catalyst bed 3 in which the exothermic reaction of ethylbenzene hydroperoxide and propylene takes place to form propylene oxide. From bed 3 of the catalyst, the reaction mixture passes to zone 19, and then, at 107 ° C and 47 x 10⁵ Pa, the mixture passes via pipe 20 to heat exchanger 21. In heat exchanger 21, a portion of the reactor feed is heated to reaction conditions, as described above, by indirect heat exchange with the reaction mixture.

The reaction mixture, from which the reaction exotherm of bed 3 has been removed, becomes about 92^°Cy47x10⁵ Via pipe 23 to zone 24 of reactor 1. From zone 24, the reaction mixture passes through catalyst bed 4 whereby further reaction of ethylbenzene hydroperoxide and propylene takes place to form propylene oxide. From bed 4 of the catalyst, the reaction mixture passes to zone 26, and then, to about 106^°Cy45x10⁵ Pa, I saw pipe 27 to heat exchanger 28. In heat exchanger 28, a portion of the reactor feed is heated to reaction conditions, as described above, by indirect heat exchange with the reaction mixture.

The reaction mixture, from which the exotherm of the reaction in bed 4 has been removed, becomes about 93^°Cy45x10⁵ Via line 29 to zone 30 of reactor 1. From zone 30, the reaction mixture passes through catalyst bed 5 whereby further reaction of ethylbenzene hydroperoxide and propylene takes place to form propylene oxide. From bed 5 of the catalyst, the reaction mixture passes to zone 32, and then, to about 105^°Cy45x10⁵ Pa, I saw pipe 33 to heat exchanger 34.

In heat exchanger 34, the reaction mixture from zone 32 is cooled by indirect heat exchange with the final reaction mixture from zone 37 which, as will be described, has reduced its pressure and partially vaporized.

The reaction mixture, from which the exotherm of the reaction in bed 5 has been removed, passes to about 93^°C and 45 x 10⁵ Via pipe 35 to zone 36 of reactor 1. From zone 36, the liquid mixture passes through catalyst bed 6 whereby the additional production of propylene oxide takes place by reaction of propylene with ethylbenzene hydroperoxide. . From catalyst bed 6, the liquid reaction mixture passes into zone 37, and is removed from reactor 1 via line 38 at about 107^°Cy45x10⁵ Pa.

The liquid reaction mixture passes via line 38 to a pressure reduction valve 39 where the pressure is reduced by 45 x 10⁵ Paa22x10⁵ Pa. There is a partial vaporization of the reaction mixture and, as a result of pressure reduction and partial vaporization, the temperature of the liquid and vapor decreases to about 77^°C.

From reduction valve 39, the vapor-liquid mixture passes via line 40 to about 77^°C y22x10⁵ Pa to exchanger 34. This mixture comprises about 45 kg / s of steam and about 126 kg / s of liquid.

In exchanger 34, the vapor and liquid in line 40 are heated by indirect heat exchange with the reaction mixture in zone 32; This heat exchange achieves the dual function of eliminating the reaction exotherm in bed 5 of the catalyst from feeding to zone 36 while, at the same time, providing the reaction mixture, which exits via pipe 41, heat necessary to separate, in one or more distillation stages, light components such as C3 hydrocarbons from the components of the heavy reaction mixture.

The heated product mix becomes around 83^°Cy22x10⁵ He led pipe 41 to conventional component spacing.

The following table gives the compositions in weight percent for the various process streams. The denomination of Stream No. refers to the process stream in the pipeline or corresponding zone in the attached figure.

IS 2 155 677 T3

TABLE 1

Stream composition% by weight

<td>Stream No.</td><td> 13</td><td> 12</td><td> 14</td><td> 10</td><td> 27</td><td> 33</td><td> 41</td>

<td>Propylene</td><td> 90,1</td><td> -</td><td> 52,9</td><td> 51,9</td><td> 50,1</td><td> 49,4</td><td> 48,5</td>

<td>Propane</td><td> 9,8</td><td> -</td><td> 5,8</td><td> 5,8</td><td> 5,8</td><td> 5,8</td><td> 5,8</td>

<td>Ethylbenzene</td><td> -</td><td> 58,7</td><td> 24,3</td><td> 24,3</td><td> 24,3</td><td> 24,3</td><td> 24,3</td>

<td>Ethylbenzene hydroperoxide</td><td> -</td><td> 35,0</td><td> 14,5</td><td> 11,3</td><td> 5,5</td><td> 3,1</td><td> 0,3</td>

<td>Methyl benzyl alcohol</td><td> -</td><td> 6,3</td><td> 2,6</td><td> 5,4</td><td> 10,6</td><td> 12,7</td><td> 15,2</td>

<td>(Propylene's OXID</td><td> -</td><td> -</td><td> -</td><td> 1,3</td><td> 3,8</td><td> 4,8</td><td> 5,95</td>

<td>By-product</td><td> -</td><td> -</td><td> -</td><td> -</td><td> -</td><td> -</td><td> 0,05</td>

In this example, the hydroperoxide-based conversion is 98%, and the molar selectivity of propylene to propylene oxide is 99%, thus demonstrating the efficacy and effectiveness of the invention. The costs associated with building and operating the system are substantially minimized.