MXPA99006918A - Catalytic converter and method for highly exothermic reactions - Google Patents

Abstract

A reactor (5, 15, 301) and process for the production of oxirane compounds by reaction of an olefin such as propylene with an organic hydroperoxide using a solid contact catalyst, characterized by the following features:(1) the reactor is divided into a series of separate zones (8, 10, 16, 19, 304, 311), each zone (8, 10, 16, 19, 304, 311) containing a bed of solid epoxidation catalyst;(2) about 25-75%of the heat of reaction is removed by preheating cold reactor feed by direct contact with a heated recycle stream from the reactor;and (3) about 25-75%of the heat of reaction is accounted for by a reaction mixture temperature rise of 20-100°F and by vaporization of 15-40%of the net reactor product.

Description

CATALYTIC CONVERTER AND METHOD FOR HIGHLY EXOTHERMAL REACTIONS BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a catalytic converter or a reactor system of a process for carrying out a highly exothermic reaction such as that between an olefin and an organic hydroperoxide to form an oxidized compound.

Description of the Prior Art Substantial difficulties are encountered in carrying out highly exothermic reactions, wherein the reactants and / or the products are sensitive to temperature. For example, the catalytic liquid phase reaction of propylene and an organic hydroperoxide to produce propylene oxide is a highly exothermic reaction, and the selectivity to the desired product is very sensitive to temperature. The removal of the exothermic heat from the reaction without causing an increase in excess temperature presents a serious problem. Conventional reactors for exothermic reactions are usually of two types: (1) The type of extinction, which consists of multiple fixed beds with cold feed extinction injected between the beds, (2) Tubular type, where the catalyst is placed in the tubes of a vertical protection and tube heat exchanger. If the heat of the reaction is high, the first type does not provide sufficient heat removal. This can be overcome by recirculating a cold effluent to the reactor, but results in the disadvantages associated with backmixing reactors. The cost of the tubular reactor becomes prohibitive when very high heats of reaction have to be removed through the surfaces of the heat exchanger operating with a low thermal transfer coefficient. There is also a temperature gradient from the center of the tube, which is usually dangerous for the process that requires absolutely isothermal conditions. European patent application 0 323 663 describes a fixed bed catalytic reactor and a process for carrying out the epoxidation of an olefin through the reaction with an organic hydroperoxide at substantially isothermal conditions. As described in this European patent, all the heat generated by the exothermic reaction is removed through evaporation of the low-boiling reaction mixture component, propylene in the case of a propylene / organic hydroperoxide system. Sufficient propylene is fed to the reactor to remove all of the exotherm from the reaction, and the reactor is operated at the boiling pressure of the reaction mixture, so as to provide a concurrent downward flow of one liquid and one gas phase. The process is said to represent an improvement over the methods then currently employed involving a multiple reactor discipline with cooling between stages. The method and apparatus described in the European patent 0 323 663 have a number of severe disadvantages. When the exotherm of the reaction is removed through vaporization of the 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, which necessarily involves the recovery and recirculation of large volumes of propylene at a higher cost. Furthermore, although the European patent 0 323 663 appears to describe a reactor outlet pressure of approximately 26 bar, this could not seem consistent with the vapor pressure of the liquid reaction mixture. More likely, the actual outlet pressure could be 10.3 bar or less and this results in an additional and very important problem, which is the requirement for cooling and / or recompression of the higher propylene recirculation stream. A further problem with the system of European patent 0 323 663 is the poor reaction selectivity, which results from the low concentration of propylene in the lower phase of the reactor.

BRIEF DESCRIPTION OF THE INVENTION According to the invention, there is provided a reaction system and a process, which are especially useful for the production of oxirane compounds, through the reaction of an olefin such as propylene with an organic hydroperoxide, using a solid contact catalyst, the invention is characterized by the following aspects: (1) the reaction is carried out in a plurality of separate reaction zones; (2) about 25-75% of the total heat of the reaction (reaction exotherm) for the system is removed by preheating the cold reactor feed through direct contact of the cold feed with one or more process streams from a reaction zone; (3) about 25-75% of the total heat of the reaction (reaction exotherm) for the system that is effectively removed as sensible heat in the liquid and vapor outflow currents, due to an increase in the temperature of the mixture of reaction to rise from -7 to 38 ° C through the reaction system and as heat of vaporization vaporizing 15-40% by weight of the net reactor product from the reaction system.

DESCRIPTION OF THE DRAWINGS The appended Figure 1 illustrates a practice of the invention. Figures 2 and 2a illustrate cold feed preheating methods. Figure 3 illustrates an alternative practice of 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. Several important considerations associated with the present invention include: (1) the use of a reactor system having a plurality of separate reaction zones; (2) the provision of cold feed to the reaction system and the use of 25-75% of the system reaction exotherm to preheat the cold feed through direct contact with a stream from the reactor system; and (3) remove the remaining 25-75% of the total heat of the reaction as sensible heat in the exit streams resulting in a moderate increase in the temperature of -7 to 38 ° C of the reaction mixture during the passage to through the reaction system and removing 15-40% by weight of the net reaction mixture as steam from the reaction system. The invention can be illustrated by reference to the specific embodiment presented in the attached Fig. 1. With reference to the production of propylene oxide through the reaction of propylene and ethylbenzene hydroperoxide, a relatively cold liquid feed (eg, 38 ° C) composed of ethylbenzene oxidate, ie ethylbenzene, 1-phenylethanol and hydroperoxide of ethylbenzene, is fed through line 2 as well as propylene, which is fed through line 3 to contact zone 1. By cold feed, it is meant a feed that is 10-66 ° C below the reaction temperature. Also the feed to zone 1 1, through lines 4 and 1 2 in this mode, is propylene vapor recirculated from reactor 5, which was vaporized by and contains exothermic heat from the reaction from the reaction of epoxidation in reactor 5, zones 8 and 10. In the described mode, two reactors, reactors are used and 15, each having two reaction zones packed with solid epoxidation catalyst. The contact zone 1 is a conventional liquid-to-liquid contact zone conveniently having several sieve trays, whereby the vapor and liquid streams are intimately mixed. Through this contacting and mixing, the exothermic heat of reaction resulting from the vaporization of the propylene in the reactor 5 is used to heat the relatively cold feed components to the reaction temperature. In the process, the most part of the propylene va of reactor 5 is condensed. As a result of this thermal exchange, 25-75% of the total system exotherm is effectively removed and used to preheat the cold feed streams. Alternative configurations for zone 1 are shown in Figures 2a and 2b. In Figure 2a, contact is achieved through the spraying of the cold liquid feed into the vessel receiving the propylene vapor. A portion of liquid is introduced as a jet to increase the pressure of condensed liquid. In Figure 2b, the contact is mainly achieved through a "static mixer". An additional contact is achieved by introducing the liquid vapor mixture below the liquid level. The economy will dictate the optimal part for a particular practice. From the contact zone 1, the hot liquid mixture is pumped through the line 6 to the upper zone 7 of the reactor 5. If the available heat of the propylene vapor streams is not sufficient to heat the liquid mixture completely at the reaction temperature, supplemental heat can be provided through the heater 24, which in any case is useful during startup. From the upper zone 7, the liquid reaction mixture passes, under reaction conditions, through zone 8, which contains a packed bed of the titania catalyst on silica prepared as described in Example VII of the patent from the USA 3,923,843. During the passage through the catalyst bed in zone 8, the exothermic reaction of propylene with ethylbenzene hydroperoxide occurs with the formation of propylene oxide. As a result of the reaction exotherm in zone 8, there is a modest increase in the temperature of the reaction mixture, for example, -12 to 4 ° C. In addition, the remaining reaction exotherm is consumed through vaporization of the propylene component of the reaction mixture. The reaction mixture passes through the solid catalyst in zone 8 to the separation zone 9, where the liquid and vapor components are separated. The propylene vapor is removed through line 4 and passes to contact 1, where, as described above, the steam used to preheat the cold feed. The liquid reaction mixture passes from the separation zone 9 to zone 10, which is also packed with the silica titania catalyst used in zone 8. In zone 10, the additional exothermic reaction of propylene with ethylbenzene hydroperoxide it occurs to form propylene oxide. Again, the exothermic heat of the reaction is represented by a modest increase in the temperature of the reaction mixture in the zone 10 together with the vaporization of the propylene. The reaction mixture passes from zone 10 to separation zone 11, where the liquid and vapor components are separated. The propylene vapor passes through line 12 to contact 1, where, as described above, steam is steam used to preheat the cold reaction feed.

An important advantage of this mode of operation resides in the fact that the preponderance of the propylene vapor from the reactor 5 is condensed in the contact 1 and recirculated to the reactor 5. The use of very high propylene to hydroperoxide ratios in the Reaction feed, in this way is avoided. The liquid reaction mixture passes from reactor 5 through line 13. Level control means 52 are provided to ensure that an appropriate level of liquid is maintained. The supplemental liquid propylene can be introduced through line 50 to maintain the ratio of the desired reagent and the mixture of the reaction liquid from reactor 5 and the newly added propylene passes through line 51 to line 14 of the reactor 15 and from zone 14 to reaction zone 16, which contains a packed bed of the titania catalyst on silica used in reactor 5. In zone 16 another isothermal reaction of propylene and ethylbenzene hydroperoxide to form propylene oxide is presented. . The exothermic heat of the reaction from the reaction in zone 16 is represented by an increase in the reaction mixture temperature of about -12 to 10 ° C and through vaporization of propylene. From zone 16, the mixture passes to separation zone 17, where the vapor and liquid are separated. The propylene vapor is removed through line 18 and the reaction liquid is passed to the packed catalyst reaction zone 19 for the final reaction of propylene and ethylbenzene hydroperoxide. Zone 19 contains the titania catalyst on silica used in the previous reaction zones and the reaction of butylene and ethylbenzene hydroperoxide is presented there. The exotherm in the zone of 19 is represented by, as previously, a small increase in temperature and vaporization of propylene. The reaction mixture at a temperature of -7 to 38 ° C higher than the temperature of the reaction mixture entering reactor 5 passes into the separation zone 20, where the vapor and liquid are separated. The propylene vapor is removed through line 21 and the liquid reaction product mixture is removed through line 22. The steam streams removed through lines 23, 18 and 19, as well as the liquid stream removed through line 22, they are sent to a distillation or depropanizer operation, where the lighter components are separated through distillation of the heavier materials according to known procedures. When appropriate, light components such as propylene are recovered and recirculated. According to the invention, the steam streams removed through the lines 23, 18 and 21 comprise, by weight, from 15 to 40% of the net reaction mixture removed, that is, the sums of the streams 23, 18 , 21 and 22. The heavier materials are also separated through conventional procedures to products, as well as currents for recirculation. The embodiment of the invention has been described in the context of a system of two reactors, each reactor having two reaction zones. The two reactors can be combined in an individual apparatus, or alternatively, a number of reactors greater than two can be conveniently used, if the total economy so indicates. The use of two reactors allows the first reactor to be operated at a high enough pressure to return the propylene vapor to the feed contact zone 1. The second reactor can be operated at a lower pressure consistent with the optimum temperature and the concentration of propylene required for the final reaction phase. As indicated above, Figures 2a and 2b describe alternative contact means for preheating the cold feed through contact with the recirculating propylene vapor. In Figure 2a, the cold feed is introduced to the contact zone 101 through the lines 102 and 103. The liquid introduced through the line 102 is sprayed through the spray nozzles 104 to the zone 101., while the liquid introduced through the line 103 is passed through a jet 105 to the zone 101. The propylene vapor is introduced through the line 106 and in the zone 101 the propylene vapor intimately makes contact and preheat the liquid feed. The non-condensed vapor leaves the zone 101 through line 107 and the hot feed comes out through line 108. In Figure 2b, the cold feed is introduced through line 201 and the propylene vapor through the from line 202 to static mixing zone 203. Zone 203 has deflectors, which ensure total vapor / liquid mixing. From zone 203, the mixture passes through line 204 to vessel 205, where it is preferably introduced below the liquid surface. The preheated liquid passes through line 206 to the reactor, while the non-condensed propylene is removed through line 207. As will be evident, other means of contact may be employed depending on the economy of the particular practice of the invention. The degree to which the exothermic reaction occurs in the various reaction zones can be easily controlled. Through appropriate regulation of the reagent composition, flow rates, temperature, pressure, and contact time of the catalyst in a reaction zone, the reaction can occur in that zone and, therefore, the reaction exotherm that it is generated, it can be adequately regulated. According to the embodiment of the present invention, as described above, about 25-75% of the total reaction exotherm is used to vaporize propylene in reaction zones 8 and 10, and this reaction exotherm is essentially used to preheat the cold feed in contact zone 1, a small amount of the steam is not condensed and is removed through line 23. Of the remaining 25-75% of the total reaction exotherm, it is represented as sensible heat in the output streams of the net system as a result of a modest increase in the temperature of the reaction mixture after passing through zones 8, 10, 16 and 19 of about -7 to 38 ° C, and as heat of vaporization to through vaporization of propylene in zones 16 and 19, resulting in the removal of propylene vapor in lines 23, 18 and 21, comprising approximately 15-40% by weight of total paddle streams lives of the reactor 15 through lines 23, 18, 21 and 22. An alternative practice of the invention, which employs a slightly simpler equipment, is illustrated in Figure 3. Referring to Figure 3, a reactor 301, which has two sections packed with the solid epoxidation catalyst. The cold feed composed of ethylbenzene hydroperoxide, as previously described, and propylene, is introduced through line 302 into zone 303, where it is intimately mixed with a portion of the liquid reaction mixture from reactor zone 304. As a result of this contact and the mixing of a portion of the exothermic heat of the reaction generated in zone 304, this is used to preheat the cold feed to the reaction temperature. The hot feed and the recirculation reaction liquid are passed from zone 303 to zone 304, where they are contacted with the solid epoxidation catalyst and wherein the ethylbenzene and propylene hydroperoxide reacts to form propylene oxide. The reaction mixture passes to the separation zone 305, from which the propylene, which is vaporized by the reaction exotherm, is removed through line 306. The liquid reaction product mixture is removed from the zone. 305 through line 307 and pump 308 and is divided into two parts, one being recirculated through line 309 to zone 303, where it is mixed with and preheated cold feed as previously described, and the other passing through line 310 to reaction zone 311.

Reaction zone 311 is packed with solid epoxidation catalyst and in this zone an additional reaction of ethylbenzene and propylene hydroperoxide with the formation of propylene oxide is presented. The reaction mixture passes to the separation zone 312, from which the propylene vaporized through the reaction exotherm in zone 311 is removed through line 313. The liquid reaction product mixture is discovered at through line 314. The operation of reactor 301 is controlled so that 25-75% of the total reaction heat generated in zones 304 and 311 is contained as sensible heat in the stream recirculated through line 309 and is Used to preheat the cold feed.

The remaining 25-75% of the exotherm is removed as the heat of vaporization in the steam streams on lines 306 and 313, and as sensible heat in the liquid mixture removed through line 314, which results in a increase in temperature from -7 to 38 ° C in zones 304 and 311. The steam removed by lines 306 and 313 comprises 15-40% by weight of the total of the currents in lines 306, 313 and 314.

The process of the product is achieved according to known procedures. The epoxidation reaction of the present invention is carried out according to well-known conditions. See, for example, patent of US Pat. No. 3,351,635. Generally, the reaction 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 34.5 to 55.2 bars a. Known solid heterogeneous catalysts are employed. In this regard, reference is made to the patent publication European 0 323 663, to the United Kingdom patent 1,249,079 and to the US patents. Nos. 4,367,342, 3,829,392, 3,923,843 and 4,021,454. The invention is especially applicable to the epoxidation of alpha olefins having from 3 to 5 carbon atoms with aralkyl hydroperoxide. The following examples illustrate a particularly preferred practice of the invention as described in the attached Fig. 1. Referring to Figure 1, a propylene feed is introduced at about 38 ° C and 48.3 bar to, into zone 1 through line 3 at a rate of about 0.8 kg / second. Ethylbenzene oxidate is also introduced at 38 ° C and 48.3 bar to a by line 2 at the speed of approximately 0.07 kg / second. Also a feed to zone 1 through line 4 at the rate of 0.06 kg / sec and through line 12 at the speed of 0.03 kg / sec is recirculated from propylene vapor from reactor 5, which it vaporizes through and contains exothermic heat of the reaction from the epoxidation zone in reactor 5, zones 8 and 10. The contact zone 1 is a conventional vapor-liquid contact zone conveniently having several sieve trays , so that the vapor and fluid currents are intimately mixed. Through this contacting and mixing, the exothermic heat heat of the propylene vapor from the reactor 5 is used to heat the components of the relatively cold feed to the reaction temperature. In the process, most of the propylene vapor in reactor 5 is condensed; a vapor stream composed of non-condensed steam is removed through the line 23 at a speed of 0.02 kg / second and is sent to recovery.

From the contact zone 1, the liquid mixture heated at 94 ° C through line 6 at the speed of 0.24 kg / second to the upper zone 13 outside the reactor 5. From the upper zone 7, the mixture of The liquid reaction passes to reaction conditions through zone 8, which contains a packed bed of titania catalyst on silica prepared as described in Example VII of US Patent 3,923,843. During the passage through the catalyst bed in zone 8, the exothermic reaction of propylene with ethylbenzene hydroperoxide occurs with the formation of propylene oxide. The pressure when entering zone 8 is 50.3 barias a. As a result of the reaction exotherm in zone 8, there is an increase in the temperature of the reaction mixture of 2 ° C.

In addition, the remaining exotherm is consumed through the vaporization of the propylene component of the reaction mixture.

The reaction mixture passes through the solid catalyst in zone 8 to the separation zone 9, where the liquid and vapor components are separated. The propylene vapor at 113 ° C is removed through line 4 and passes to contact 1, where, as described above, the steam is used to preheat the cold reaction feed. The liquid reaction mixture passes from the separation zone 9 to the zone 10, which is also packed with the titanium catalyst on silica used in zone 8. In zone 10 an additional exothermic reaction of propylene with hydroperoxide is presented. ethylbenzene to form propylene oxide. The exothermic heat of the reaction is represented by an increase in temperature of the reaction mixture at 121 ° C in zone 10 together with the vaporization of propylene. The reaction mixture passes from zone 10 to 48.3 barias a, to the separation zone 11, where the liquid and vapor components are separated. The propylene vapor at 121 ° C passes through line 12 to contact 1, where, as described above, the steam is used to preheat the cold reaction feed. An important advantage of this method of operation resides in the fact that the preponderance of the propylene vapor from the reactor 5 is condensed in the contact 1 and recirculated to the reactor 5. The use of very high propylene to hydroperoxide ratios in the Reaction feed in this way is avoided. The liquid reaction mixture of reactor 5 at 121 ° C, 50.3 barias a, passes through line 13 at the speed of 0.14 kg / second through the liquid level controller 52 and is mixed with 0.02 kg / second of feed of additional cold propylene. The resulting mixture passes at the rate of 0.15 kg / second through line 51 to zone 14 of reactor 15 and from zone 14 to reaction zone 16, which contains a packed bed of the titania catalyst on silica used in reactor 5. In zone 14, the pressure is reduced to 41.4 barias a, which results in the vaporization of substantial propylene and a reduction in temperature to 107 ° C.

In zone 16, another exothermic reaction of propylene and ethylbenzene hydroperoxide to form propylene oxide occurs. The exotherm of the reaction in zone 16 is represented by an increase in the temperature of the reaction mixture at about 116 ° C and by the vaporization of the propylene. From zone 16, the mixture passes to the separation zone 17, where the vapor and liquid are separated. The propylene vapor has 116 ° C removed through line 18 at the rate of 0.03 kg / second and the reaction liquid is passed to the packed catalyst reaction zone 19 for final reaction of propylene and ethylbenzene hydroperoxide. Zone 19 contains the titania catalyst on silica used in the previous reaction zones and the reaction of propylene and ethylbenzene hydroperoxide is presented therein. The exotherm in zone 19 is represented by, as was previously done, a small increase in temperature and vaporization of propylene. The reaction mixture at a temperature of 117 ° C and at a pressure of 39.6 bars a, passes into the separation zone 20, where the vapor and liquid are separated. The propylene vapor is removed through line 21 at 117 ° C and 39.6 bar at, at the rate of 0.01 kg / second and the liquid reaction product mixture is removed through line 22 at 117 ° C and the speed of 0.12 kg / second. The steam streams removed through the lines 23, 18 are sent to a distillation or depropanizer operation, wherein the lighter components are separated through distillation of the heavier materials according to known procedures. As required according to the invention, the steam streams removed through lines 23, 18 and 21, comprise about 31% by weight of the net product. When appropriate, light components such as propylene are recovered and recirculated. The heavier materials are also separated through conventional procedures to products, as well as currents for recirculation. The following table presents the percentage by weight of the compositions for the various streams of the process. The designation Current in Number refers to the process current in the corresponding line or zone in Fig. 1 appended.

TABLE 1 Percentage in Weight of Composition of Current In this example, the hydroperoxide-based conversion is 98%, and the molar selectivity of propylene to propylene oxide is 99%, thus demonstrating the efficiency and effectiveness of the invention. The costs associated with the construction and operation of the system are substantially reduced to a minimum. In the previous example, 50% of the reaction exotherm was used to preheat the cold feed in contact zone 1. Approximately 18% of the reaction exotherm is represented by the temperature in reactor 5 and reactor 1 5. The remaining 32% of the exotherm is represented by the vaporization of propylene and the removal of propylene vapor through lines 23 , 1 8 and 21.

Claims (7)

1. - A process for the exothermic reaction of the catalytic liquid phase of an olefin of 3 to 5 carbon atoms with an aralkyl hydroperoxide, which comprises passing a mixture containing the olefin and the hydroperoxide at high temperature reaction and pressure conditions. Through a series of separate reaction zones, each packed with a bed of solid epoxidation catalyst, the improvement is where: (1) a reaction system is employed having a plurality of separate reaction zones, (2) the olefin feed and cold hydroperoxide is provided to the reaction system and 25-75% of the reaction exotherm generated in the reaction system is used to preheat the cold feed through direct contact with a recirculation stream from the feed system. reaction, and (3) 25-75% of the reaction exotherm in the reaction system is removed as sensible heat due to an increase in temperature of -7 to 38 ° C of the reaction mixture during passage through the reaction system and as heat of vaporization through the removal of 15-40% of the net reaction mixture as vapor from the reaction system.

2. The process according to claim 1, wherein the propylene and the ethylbenzene hydroperoxide are reacted to form propylene oxide.

3. - The process according to claim 1, wherein the solid catalyst is a titania catalyst on silica.

4. The process according to claim 1, wherein the recirculation stream in (2) is a vapor stream of propylene.

5. The process according to claim 1, wherein the recirculation stream in step (2) is a liquid reaction mixture stream.

6. A reaction system for the exothermic catalytic liquid phase reaction of an olefin of 3 to 5 carbon atoms with an aralkyl hydroperoxide, wherein a mixture containing the olefin and the hydroperoxide is passed to temperature reaction conditions elevated and pressure through a series of separate reaction zones, each packed with a bed of solid epoxidation catalyst, the improvement wherein: (1) a reaction system having a plurality of separate reaction zones is employed, ( 2) means are provided for preheating the cold feed of olefin and hydroperoxide with 25-75% of the exothermic heat of reaction of the reaction system through direct contact with a recirculation stream from the reaction system, and (3) means are provided to consume 25-75% of the exothermic heat of reaction of the reaction mixture during passage through the reaction system by an increase of temperature from -7 to 38 ° C and by vaporization of 15-40% of the net reaction mixture of the reaction system.

7. The system according to claim 4, wherein the solid epoxidation catalyst is a titania catalyst on silica.