DE102016002679A1 - Apparatus and method for carrying out heterogeneously catalyzed exothermic gas phase reactions - Google Patents

Abstract

The invention relates to a reactor and method for carrying out heterogeneously catalyzed gas phase reactions with high heat of reaction, wherein the reaction in a contact tube bundle reactor 1, the tubes 2 are filled with catalyst and in the jacket space via attached at the two ends ring lines 12, 13 by means of at least one external Pump 17 and cooler 16 are maintained in the known heat exchange medium circuit, the supply of the heat exchange medium via the lower ring 13 and the educt gas on the upper reactor hood 5 and the reactor shell with at least one or more additional ring lines 19 and corresponding shell openings 18 equipped is, as viewed from the gas inlet side in the upper half of the jacket space are arranged and by a controlled removal and / or addition of subsets of heat exchange means, a temperature increase of not more than 10 K in Strömungsrichtu ng the heat exchange medium over the removal or addition cross section lying jacket space is effected, wherein the addition of the subset via an additional pump and the subset may be additionally heated externally.

Description

The invention relates to a process for carrying out exothermic, heterogeneously catalyzed gas phase reactions, such as, for example, the partial oxidation of o-xylene and / or naphthalene air mixtures to phthalic anhydride (PSA). To carry out such reactions, especially in the gas-phase oxidation of hydrocarbons to aldehydes, acids or acid anhydrides, tube reactors have been almost exclusively used in the art in which the feed gas mixture is passed through a plurality of vertically arranged, catalyst-filled tubes (contact tubes) and the tubes be lapped with a cooling medium (heat exchange medium). The contact tubes are usually sealingly secured with their ends in tube sheets and each open into a connected at the top or at the bottom of the reactor vessel hood. About these hoods, the addition of the feed mixture or the removal of the product mixture. The catalysts usually have the form of spheres or rings, in many cases they consist of inert ceramic support material which are provided with a thin coating of catalytically active material. This mass is porous so that the starting materials penetrate into the catalytically active layer and there the chemical conversion can take place. The reaction gas mixture produced is passed back into the gas stream by diffusion. The heat generated in the reaction is transported via the gas flow to a large extent to the tube wall and discharged from there to the heat exchange medium.

The heat transfer medium is usually via a ring line in the lower reactor area, ie at the gas outlet side, with the aid of a pumping system via a plurality of shell openings in the jacket space formed by the two tube plates and reactor jacket and flows while receiving the heat of reaction in one at the top of the Reactor (gas inlet side) attached further ring line via shell openings from the reactor, is then cooled by means of a heat exchanger to the desired heat exchange medium inlet temperature and recycled to the reactor. Through installations in the coolant space the highest possible and homogeneous heat transfer is achieved, so that a uniform reaction can take place in all pipes. In this way, the temperatures in the reaction tubes should be kept as constant as possible in order to achieve a high product yield and product quality. Depending on the nature of the hydrocarbon, its concentration and catalyst used, the temperatures of the coolant can be above 400 ° C, in the case of PSA production these z. B. between 350 and 420 ° C. As the cooling medium can evaporable liquids such as water or as in the case of PSA production serve a liquid eutectic salt mixture which circulates around the outside of the tubes and emits the heat of reaction to an external cooler. This method is described in many patents, inter alia WO 2003022418 . DE 2000124342 described in detail.

The achievable with this method molar yields are the example of PSA production from o-xylene with the currently available catalysts at about 80 mol% and thus still significantly below the theoretically possible. About 20% of the o-xylene used is lost through conversion to other organics and total oxidation to carbon dioxide and monoxide, with over-oxidation to CO and CO2 accounting for much more of the loss. Significant in highly exothermic processes carried out in tubular reactors, the forming temperature peaks in the catalyst bed, called hot spots, are caused by the limited heat transfer via the gas phase to the tube wall, specifically in the catalyst zone with the highest conversion rate. As a rule, this zone is always in the first half of the reactor from the gas inlet side. In commercial plants for the production of PSA, the temperature peaks in this range can be up to 100 ° C above the temperature of the salt bath and thus reach up to 500 ° C. High temperatures mean overoxidation and thus loss of yield. This is a fundamental problem of this process or the reactors used: for reasons of required product quality, the formation of suboxidation products (such as phthalide) should be avoided as much as possible, which can only be ensured by a higher temperature of the salt bath, a temperature that is suitable for a high product yield would actually not be required.

There has therefore been no lack of attempts in the past to improve the above-mentioned procedure. Patents claim the use of 2- and multi-zone reactors in which different reaction zones can be selectively controlled via separate cooling circuits in order to find the optimum operating conditions for a high yield and required product quality ( WO 2007/082827 A1 . EP 0453 951 B1 ). Since multi-zone reactors cost considerably more than single-zone reactors, such reactors are used in only a few individual cases. In the commercial production of phthalic anhydride, only single-zone reactors, ie reactors with a single external heat exchange medium circuit, are used.

In the patents DE 2201 528 B1 and DE 100 24 342 A1 Although reactor variants based on single-zone reactors are proposed which allow the introduction or discharge of an adjustable amount of heat exchange agent by the installation of at least one additional loop at an intermediate point, in this way to change the temperature characteristics in a certain way. The measures disclosed in both documents have in common that in the upper reactor area, in particular in the area of the hot spot zone, the salt bath temperature can not or only be lowered (in the direction of the inlet temperature). A temperature increase (in the direction of the outlet temperature) is only possible for the areas below the hot spot zone.

The measures claimed in the cited patents therefore aim u. a. on the limitation of hot-spot temperatures via "additional cooling", a goal that can be achieved in an economic way on the optimization of the catalysts or catalyst systems used. Exactly this way was also trodden.

Thus, the use of differently active and selective catalysts has prevailed, which are arranged in layers in the reaction tubes, wherein usually the most active catalyst is arranged towards the gas outlet, the inactive catalyst layer is located at the gas inlet ( WO 2007/135104 A1 . WO 2011/095416 A1 , This reduces the high reaction rate due to the high input material concentration in the front (upper) reaction zone in order to limit the resulting hot spot temperatures. On the other hand, much more active catalyst layers are used in the lower part of the reactor. There, in the main, only the oxidation of the remaining feed and under oxidation products to PSA takes place, which is associated with a comparatively lower heat generation. In the last fifteen years, the principle of multilayer catalysts has been further refined, usually so-called four-layer catalyst systems are used ( WO 2011/095416 A1 ).

However, a still optimized multi-layer catalyst system can not solve a problem: the partial deactivation of the catalysts, which is associated with increasing duration of use. The high temperatures which occur in particular in the hot spot range lead to a partial damage to the catalyst associated with increasing transit time, which shifts the reaction process deeper into the catalyst bed, recognizable by a displacement of the hot spot zone. Investigations of Anastasov et. al. (Braz J. Chem. Eng. Vol. 25 no. 2 , have shown that the original activity of an upper-layer catalyst in the hot-spot zone may already have fallen by about 30% after only 12 months, while the more active catalyst layer in the lower reactor region has only decreased by about 10%. The consequence of this shift of the reaction into deeper active and less selective catalyst layers is associated with a significant yield reduction and product quality degradation. Especially at high concentrations of feedstock in conjunction with aged catalysts, the problem of attainable product yield and product quality becomes more important. This can lead so far that the entire catalyst system must be replaced relatively soon, which is associated with loss of production and high costs.

One way of counteracting the hot-spot migration in the so-called single-zone reactors, is an increase salt bath temperature, but in the current state of the art always relates to the entire reaction range, or a reduction in the amount of input mixture consisting of air and feedstock (eg B. o-xylene). The former means increase in total oxidation, equal to noticeable decrease in yield, since the temperature increase over the entire reactor takes place. The latter means that although the selectivity of the reaction remains constant with a constant hot-spot position, the productivity of the system decreases. A great advantage would therefore be a method in which the temperature in the upper half of the reactor can be selectively raised without changing the conditions in the lower half of the reactor, provided that the necessary reaction unit is still economically feasible.

Another problem, especially with the new multilayer catalysts, is that starting a fresh catalyst system has become increasingly complex and time consuming. In the WO 2011/095416 A1 is addressed in more detail on these problems and the solutions. All new multilayer catalyst systems have in common that in the start-up phase by varying the amount of air and initially higher salt bath temperatures, the height and position of the hot spot is set and sometimes a deliberate shift of the hot spot zone is required. With a device that would allow a targeted temperature moderated limited to the first half of the reactor (gas inlet) in a simple manner, would be of great value. The start-up time until a reactor with freshly changed catalyst system drove to the optimum performance (yield, capacity, quality), could be considerably shorter. Also errors during retraction with negative consequences for yield / capacity and life of the catalyst system could be significantly reduced.

What is desired is an economically viable apparatus based on a one-zone multi-tube reactor for carrying out processes for heterogeneously catalyzed exothermic gas phase oxidation reactions, with which a hot spot migration into deeper catalyst layers can be counteracted without adversely affecting the reaction conditions prevailing in the underlying catalyst layers. A moderate and controllable increase in temperature via the heat exchange medium would be advantageous only in the first half of the reactor (gas inlet side). The start-up procedures or the start-up of fresh PSA catalyst systems sometimes complex start-up procedures could be considerably simplified and shortened with a correspondingly modified reactor or process. Errors during retraction with negative consequences for yield / capacity and lifetime of the catalyst system could thus be avoided or significantly minimized.

• a) die Zuführung des Reaktionsgases in den Reaktor immer entgegengesetzt der Zuführung des Wärmeaustauschmittels erfolgt und
• b) mindestens eine zusätzliche Ringleitung (1, 18a) in der 1. Hälfte des Reaktors, also auf Seite des Gaseintrittes, angebracht ist, um eine regelbare Teilmenge an Wärmeaustauschmittel abzunehmen und diese an den externen Wärmeaustauscher weitergeleitet wird. Durch die abgeführte Menge an Wärmeaustauschmittel kommt es zu einer geringen Minderung des Wärmeübergangs in dem darüber liegendem Reaktorteilbereich, in Strömungsrichtung des Wärmeaustauschmittels, was zu einer moderaten Temperaturerhöhung in diesem Bereich führt. Die Teilmengenentnahme ist dabei so zu regeln, dass die maximale Temperaturzunahme (Delta T) maximal 10 K, bevorzugt maximal 5 K, besonders bevorzugt 3 ist. Als Bezugspunkt wird jeweils die vor der Entnahme gemessene Temperatur herangezogen.

A solution to the problem consists of an additional installation of at least one device, which allow the additional supply or discharge of an adjustable amount of heat exchange medium in the manner in which

• a) the supply of the reaction gas in the reactor is always opposite to the supply of the heat exchange medium and
• b) at least one additional loop ( 1 . 18a ) in the first half of the reactor, so on the side of the gas inlet, is mounted to remove a controllable subset of heat exchange means and this is forwarded to the external heat exchanger. The amount of heat exchanging agent removed leads to a slight reduction in the heat transfer in the overlying reactor section, in the flow direction of the heat exchange medium, which leads to a moderate increase in temperature in this area. The partial quantity removal is to be regulated so that the maximum temperature increase (delta T) is at most 10 K, preferably at most 5 K, particularly preferably 3. The reference point used is the temperature measured before removal.

This small increase in temperature leads to a corresponding slightly increased conversion in the overlying catalyst layer, associated with an increase in the local catalyst temperature, which may be higher than that of the heat exchange medium. The decrease of the subset of heat exchange medium is controlled so that the hot spot in position and height remains as constant as possible over the term or, if desired, is optimized. As a result, the yield as well as the product quality remains optimal over a much longer period of time. The conditions (temperature, fluid dynamics) below the additional ring channel remain unaffected by this measure. Preferably, the intended for removal ring channel is mounted so that it is directly above a mounted on the container wall deflection plate ( 1 . 7 )

Another possible solution is the addition of a subset of heat exchange agent via an additional annular channel by means of a pump, this subset has a higher temperature than the temperature of the heating means in the reactor immediately below the feed point ( 2 . 18b ). The temperature and the proportion of the added heat exchange medium is also to be chosen so that there is only moderate or low temperature increase in the lying in the flow direction of the heat exchange means over the reactor section. The partial amount addition should be regulated so that the maximum temperature increase (delta T) is at most 10 K, preferably at most 5 K, particularly preferably 3 K. Preferably, in this embodiment, the subset of heat exchange medium from the upper annular channel ( 2 . 12 ) or from its derivation ( 2 . 14 ) come to the external cooler. If required, an additional heating section ( 2 23 ) are switched on. Preferably, the ring channel intended for the addition is mounted in such a way that it can be moved under a deflection disk () attached to the container wall (FIG. 2 . 7 ) is arranged.

Even with this possible solution, the small increase in temperature in the flow direction of the heat exchange medium leads to a corresponding increase in the conversion in the catalyst layer concerned, associated with the equivalent increase in the local catalyst temperature. The conditions for the heat exchange medium in the lying below the Zugaberingkanals container part remain unaffected by this measure. The addition should be controlled in such a way that the hot spot in position and height remains as constant as possible over the duration or, if desired, is optimized. As a result, the yield as well as the product quality over a much longer period can be kept in the optimum. The advantage of this variant is that the fluid dynamics of the coolant flow is in no way adversely affected.

Another embodiment of the method according to the invention is a combination of these variants. For this purpose, at least one second additional ring line is attached to the upper half of the reactor ( 3 . 18c ). Depending on requirements, an alternating or simultaneous addition or decrease of heat transfer agent takes place. Preferably, the additional channels are to be positioned so that the decrease over the upper loop ( 3 . 18c ), the addition to the underlying additional loop ( 3 . 18b ) he follows.

In a further embodiment of the method according to the invention, the removal and / or addition of subsets of heat exchange medium via the central tube of the reactor, which via corresponding radially mounted tube openings ( 4 . 24 . 25 ) and corresponding throttle valves ( 4 . 26 ). The control can be done for example by a hub-controlled throttle valve. The outflow of the withdrawn subset of heat exchange agent takes place via the jacket space, which is directly under the upper base plate 3 is located and positioned at the upper end of the reactor ring channel ( 12 ).

Also in this case, corresponding combinations with the aforementioned variants are possible. In the case of the addition of subsets of heat transfer medium, a pump in the central tube is required as well as appropriately controllable valves and possibly additional radially arranged cylinder openings.

In the following examples, the invention will be explained in more detail. The examples are not limitative in the sense of the present invention. The invention may comprise any embodiment known to the person skilled in the art.

1 shows in longitudinal section a reaction vessel 1 in which a variety of reaction tubes 2 are housed vertically, the tubes with their ends in an upper and lower reactor bottom 3 respectively. 4 are sealingly attached and in the upper and lower reactor hood 5 respectively. 6 lead. About these hoods, the supply of Edukt- or the removal of the product gas. The reaction tubes are filled with catalysts, which may also be different active and selective catalyst layers depending on the process. The PSA process generally uses 3-4-layer catalyst systems.

Through the tank space (shell space) separated from the gas space via the reactor bottoms, a heat exchange medium circulating around the reaction tubes is passed in order to equalize the heat balance and absorb heat in the event of exothermic reactions. The supply or discharge of the heat exchange medium into the jacket space takes place with the aid of an upper or lower ring line 12 respectively. 13 via a plurality of radially positioned shell openings 10 . 11 , The heat exchange medium is after leaving the jacket space via a supply line 14 in an external cooling device 16 brought back to its original temperature, before it over the supply line 15 and the lower annular channel or the associated shell openings 11 is recycled back to the heat transfer medium circuit to Mantelraumbehälter. The heat exchange fluid circuit is via a pump 17 guaranteed. For large diameter reactors and a large number of catalyst tubes, the heat exchange fluid circuit can be maintained via two pumps as needed, as well as cooled by additional external cooling units.

In order to ensure as uniform as possible all the reaction tubes in the reaction process, which is especially true for any horizontal plane in the reactor, a uniform flushing of the tube walls with the heat exchange medium and the highest possible heat transfer is to ensure. In the art for this purpose have installations such as deflecting 7 . 8th alternately on the container wall or on an inner tube centered in the reactor 9 are mounted and leave a passage cross-section alternately in the reactor center and on the reactor wall. Further design features of the internals to optimize the flow conditions are, for example, in the patents DE 2201528 B1 . EP 1569745 A1 described in detail. The temperature measurement in the catalyst bed as well as in the salt bath is carried out according to the prior art via so-called multipoint thermocouples (TE) which are centered in selected contact tubes. For the salt bath measurement, use is made of TE-equipped contact tubes, which are closed at the bottom and are filled with very good heat-conductive material instead of catalyst (eg SiC granules).

In the upper half of the reactor is at least one further annular channel 18a arranged, on the one hand with the shell space on all around distributed shell openings 19a and on the other hand via a connecting line 20a connected to the external cooling unit. Preferably, this additional annular channel is directly above a deflecting plate attached to the jacket wall 7 appropriate. The decrease in heat transfer agent is by a corresponding opening of a valve 21a that in the connection line 20a can be installed to the cooling unit, regulated. The decrease in heat exchange medium leads to the moderate increase in temperature described under [0011] and a slightly increased reaction process associated therewith, which can propagate to the overlying reactor areas in a reinforcing manner. The conditions (temperature, fluid dynamics) for the heat exchange medium below the sampling point (gas outlet direction) are not affected by this measure.

In 2 is another solution variant shown, which allows to raise the temperature in the upper half of the reactor in a moderate manner. It differs from the variant described in [0020] in such a way that at least one additionally arranged in the upper half of the reactor annular channel 18b with the associated shell openings 19b a subset of heat exchange agent by means of a pump 22 and a supply line 20b whose temperature is higher than the temperature of the below the feed point located heat exchange medium. This results in a moderate increase in temperature from the feed point cross-section, which again leads to an increased reaction process over the feed point and which can propagate in the overlying reactor areas in a reinforcing manner. The conditions (temperature, fluid dynamics) for the heat exchange medium below the feed cross section are not affected. Preferably, the additional annular channel with the corresponding shell openings directly below a mounted on the shell wall deflection plate 7 appropriate. The supplied subset is from the reactor leaving the heat exchange medium flow, for example in the region of the line 14 taken, whose temperature id is usually higher than that of the flowing below the point of addition heat transfer agent in the mantle space. If necessary, the subset of heat exchanging agent for addition may be provided via an additional heating element 23 In this case too, the conditions (temperature, fluid dynamics) for the heat exchange medium below the addition position (gas outlet direction) are not affected by this measure.

An extension of this process variant is the in 3 described combination of [0020] and [0024] above mentioned possible solutions in such a way that in the upper half of the reactor two ring channels 18b . 18c with corresponding shell openings 19b . 19c are located. The two additional ring channels are through the connecting lines 20c and 20b connected with each other. Acceptance and addition quantities are via appropriately arranged valves 21b and 21c controllable. So that the removal of "warmer" heat exchange medium on the annular channel 18c remains limited, the connecting lines 20b and 14 over the valve 21d separated or regulated accordingly.

With this described extension, can also be achieved by a corresponding valve positions in 1 be realized examples described:
Variant 1 Temperature increase in the front reactor area only by removal of heat transfer medium: pump 22 off, valve 21b closed, valve 21c and valve 21d on
Variant 2 Temperature increase in the upper reactor area by adding "warmer" heat exchange medium from line 14 : Pump 22 on, valve 21b and valve 21d on and valve 21c closed, if required heating element in operation.

Another embodiment of the method according to the invention is disclosed in 4 shown. Here, the removal and / or addition of subsets of heat exchange medium via the central tube of the reactor, which via corresponding radially mounted tube openings ( 24 . 25 ) and a corresponding throttle valve has ( 26 ). The control can be done for example by a controllable via the hub throttle valve. The outflow of the withdrawn subset of heat exchange agent takes place via the jacket space, which is directly under the upper base plate 3 is located and positioned at the upper end of the reactor ring channel ( 10 ).

Also in this case, corresponding combinations with the aforementioned variants are possible. In the case of the addition of subsets of heat transfer medium, a pump in the central tube is required and correspondingly necessary valves and additional radial openings in the central tube.

LIST OF REFERENCE NUMBERS

1

reactor vessel

2

vertical tubes filled with catalyst

3, 4

upper and lower tubesheet

5, 6

upper and lower reactor hood

7

Deflection pulleys attached to tank wall

8th

Deflection pulleys attached to vertical central tube

9

vertical central tube

10, 11,

surrounding jacket openings

12, 13

upper or lower ring channel

14, 15

Connecting cables d. Ring channels on external heat exchanger

16

external heat exchanger

17

axial pump

18a

Additional ring channel for partial removal of heat exchange medium

18b

Additional ring channel for the addition of heat exchange medium

18c

Additional ring channel for partial removal of "warmer" heat exchange medium

19a, b, c

surrounding jacket openings in the corresponding annular channels

20a

Piping from the additional ring channel to the external heat exchanger

20b

Connecting line from the connecting line of ob. Ring channel to the additional ring channel 18b with pump

21a, b, c

adjustable throttle valves for setting the a) drain or b) inflow

22

pump

23

heater

24, 25

radially mounted openings on the central tube

26

globe valve

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2003022418 [0002]
• DE 2000124342 [0002]
• WO 2007/082827 A1 [0004]
• EP 0453951 B1 [0004]
• DE 2201528 B1 [0005, 0022]
• DE 10024342 A1 [0005]
• WO 2007/135104 A1 [0007]
• WO 2011/095416 A1 [0007, 0007, 0010]
• EP 1569745 A1 [0022]

Cited non-patent literature

• Anastasov et. al. (Braz J. Chem. Eng. Vol. 25 no. 2 [0008]

Claims (9)

reactor 1 and methods for carrying out heterogeneously catalyzed high phase reaction gas phase reactions with a contact tube bundle 2 whose tubes are filled with a catalyst system, the space surrounding the catalyst tubes, bounded by bottom plates 3 . 4 and reactor jacket, via attached at both ends ring lines 12 . 13 and shell openings 10 . 11 by means of one or more pumping systems 17 a cycle of a low-viscosity heat exchange medium involving an external cooling unit 16 is maintained, wherein the flow guidance of the heat exchange medium in the reactor vessel via transverse deflecting disks 7 . 8th , which alternately leave in the reactor center and at the outer edge of the reactor a passage cross-section, is optimized in a known manner, the supply of the heat exchange medium via the lower loop 13 and the educt gas over the upper reactor hood 5 takes place and the shell space of the reactor is equipped at least one or more additional acceptance and / or adding devices for subsets of heat exchange means, characterized in that these additional devices a) only in the viewed from the gas inlet side of the first half of the tube sheets 3 . 4 and reactor shell limited jacket space are and b) the removal and / or addition of subsets of heat exchange medium exclusively leads to an increase in temperature in the flow direction of the heat exchange medium over the removal or addition cross section lying jacket space. Reactor and method according to claim 1, characterized in that the removal and / or addition of subsets of heat exchange medium is controllable and exclusively to an increase in temperature of lying over the removal or addition cross section of the container space space of a maximum of 10 K, preferably of at most 5 K, especially preferably a maximum of 3 K leads. Reactor and method according to claim 1-2, characterized in that it is in the additional devices for removal and / or addition to ring channels 18 , a, b, c with the corresponding radially arranged shell openings 19a , b, c and / or radially on the central tube 9 existing openings is. Reactor and method according to claim 1-3, characterized in that the control of the removal or addition of heat exchange means via valves and / or pumps. Reactor and process according to claims 1-4, characterized in that the subset of heat exchange medium fed into the upper jacket space is always warmer than the heat exchange medium located directly below the addition cross section in the direction of the gas outlet. Reactor and method according to claim 5, characterized in that the intended for feeding subset of heat exchange means in addition by an external heating unit 23 is preheated. Reactor and method according to claim 1-6, characterized in that the removed portion of heat exchange medium directly to the external cooling unit via the suction side of the pump 17 carried out by means of an additional pump ( 22 ) partially or completely via corresponding connecting lines ( 20b , c) and a further lower ring line ( 18b ) and corresponding shell openings ( 19b ) is returned to the viewed from the gas inlet side of the first half of the jacket space. Use of the reactor and process according to any one of claims 1-7 for carrying out heterogeneously catalyzed exothermic gas phase reactions, in particular of oxidation reactions such as the production of phthalic anhydride, maleic anhydride, acrylic acid, acrolein, methacrolein, methacrylic acid or the oxidation of ethanol to acetic acid Reactor and process according to claims 8 for the preparation of phthalic anhydride by gas-phase oxidation of o-xylene and / or naphthalene air mixtures, preferably when using multilayer catalysts.

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