EP1239944A1

EP1239944A1 - Method and device for production of a homogeneous mixture of a vapour-forming aromatic hydrocarbon and an oxygen-containing gas

Info

Publication number: EP1239944A1
Application number: EP00985245A
Authority: EP
Inventors: Ulrich Block; Rolf Seubert; Bernhard Ulrich; Helmut Wunschmann
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1999-12-23
Filing date: 2000-12-22
Publication date: 2002-09-18
Anticipated expiration: 2020-12-22
Also published as: TW581710B; JP2003518433A; ES2218265T3; KR20020062374A; AU2172001A; WO2001047622A1; ATE262372T1; DE19962616A1; EP1239944B1; JP4669184B2; CN1411392A; KR100655339B1; US20030013931A1; MXPA02005852A; MY125936A; CN1174793C; DE50005821D1

Abstract

A process and an apparatus for producing a homogeneous mixture of a gaseous aromatic hydrocarbon and an oxygen-containing gas for catalytic gas-phase reactions, in particular a homogeneous mixture of gaseous o-xylene and/or naphthalene and air for preparing phthalic anhydride, are provided. The liquid aromatic hydrocarbon is atomized to form droplets having a diameter of less than 1 mm and injected into an oxygen-containing gas stream (12) preheated to above the boiling point of the aromatic hydrocarbon. According to the invention, the liquid aromatic hydrocarbon is atomized by means of nozzles (15) which form a hollow cone (16), preferably by means of swirl nozzles. The o-xylene/air mixture is advantageously produced in a chamber which is bounded by side walls (18) heated to above the boiling point of the hydrocarbon.

Description

Method and device for producing a homogeneous mixture of a vaporous aromatic hydrocarbon and an oxygen-containing gas

5

The invention relates to a method and a device for producing a homogeneous mixture of a vaporous aromatic hydrocarbon and an oxygen-containing gas for catalytic gas phase reactions, in particular a homogeneous

10 NEN mixture of vaporous o-xylene and / or naphthalene and air for the production of phthalic anhydride.

Phthalic anhydride (PA) is an important intermediate for the production of synthetic resins _15, phthalate,

Phthalocyanine dyes and other fine chemicals. Nowadays PSA is mainly produced from o-xylene and mainly by gas phase oxidation of o-xylene with air as an oxidant.

20 plants for carrying out such a PSA manufacturing process consist essentially of the functional units for the production of the o-xylene vapor-air mixture, the reactor for the implementation of the o-xylene vapor-air mixture and a device for PSA separation and processing.

25

The reaction by catalytic gas phase oxidation mostly takes place on V ₂ Os-containing catalysts. For this purpose, o-xylene is evaporated, mixed with an excess of air and passed at 340 ° C to 440 ° C over the catalyst in the tubes of a tube bundle reactor.

30 The catalyst consists, for example, of a mixture of V ₂ 0 ₅ and Ti0 ₂ with promoters on ceramic bodies, such as porcelain or SiC balls or rings, for example 6 x 6 mm in size. Large reactors have 10,000 to 40,000 tubes in the tube bundle. Usually, the o-xylene with a selectivity of

35 78% to 80% oxidized to PSA. This oxidation itself is strongly exothermic at -1,110 kJ / mol.

When carrying out the procedure, i.a. the following critical points must be observed: on the one hand there is the

40 o-xylene with air (excess oxygen) in the explosion area (Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, volume A 20, page 85), furthermore the large number of 10,000 - 40,000 tubes with one in the entire cross section must be the same and flow of gas mixture constant over time, so that the

45 Reaction takes place at the same rate in all tubes and not particularly quickly or particularly slowly in some. In addition, the strongly negative enthalpy of reaction can lead to the catalytic converter In the event of deviations from the set conditions, the analyzer sinters, melts or becomes inactive in individual tubes. This is associated with considerable risks for the plant.

Due to inhomogeneities in the loading, the reaction conditions in the tubes also differ. This results in an increased amount of by-products which reduce the yields and which have to be separated from the PSA and disposed of in later cleaning stages. 0

DE-A 1 793 453 discloses a process for producing a homogeneous mixture of vaporous o-xylene and air for the catalytic oxidation to phthalic anhydride. In the known method, an o-xylene stream is sprayed into drops with a diameter of less than 1 mm, for example in a size of predominantly less than 0.3 mm, and introduced into an air stream preheated above the boiling point of o-xylene. This airflow is turbulent; a Reynolds number above 200,000 is recommended. The dwell time from the o-xylene injection to the reactor must be at least 0.2 seconds in order to obtain a homogeneous gas mixture and thus an even exposure to all tubes.

_g Despite this improvement, which is the method according to DE-A 1 793 453, changes in the droplet size and disturbances in the evaporation can take place, particularly in the case of fluctuations in the operating conditions. Different causes can be considered: 0

The raw materials can be more or less contaminated. The air can contain, inter alia, N0 _X , H ₂ S, sulfur oxides such as S0 ₂ , NH ₃ and their salts, for example with C0 ₂ , which can lead to narrowing of one or more nozzles. Corrosion particles can also change the drop size and shape of the atomized o-xylene jet. Similar effects arise from erosion of the nozzles in long-term operation. Furthermore, the o-xylene can also contain m- and p-xylene, toluene, ethylbenzene, isopropylbenzene, nonane and small amounts of styrene. Such compounds can affect the surface tension of the _Q o-xylene. Drops can occur that fly farther than the aforementioned drops with a size of, for example, predominantly below 0.3 mm. These can wet the wall of the reaction tube and form a liquid film there. Another difficulty is that it is not possible in practice to install the nozzles used to atomize the o-xylene stream in such a way that no drops of the atomized o-xylene stream come into contact with the wall of the guide tube. The method according to DE-A 1 793 453 can also lead to unintentional, negatively acting changes in the set parameters, such as pressure and temperature and the amount of air. Furthermore, admixtures containing air and o-xylene can be added and the drops of the atomized o-xylene stream can touch the pipe wall. In this respect, the above-mentioned method is still in need of improvement.

It is therefore the object of the present invention to provide an improved method and a device for producing a homogeneous mixture of a vaporous aromatic hydrocarbon, such as o-xylene and / or naphthalene, and an oxygen-containing gas, in particular air, for catalytic gas phase reactions To make available. In particular, the disadvantages described above should be avoided or at least minimized.

The invention solves the above-mentioned problems in that, in a generic method, the atomization of the liquid aromatic hydrocarbon takes place by using a nozzle to form a hollow atomizing cone, preferably a swirl nozzle. The atomizing hollow cone can initially be a coherent film made of the liquid hydrocarbon, which at greater distance from the swirl nozzle tears into small pieces that contract to form individual drops with a diameter of less than 1 mm due to interfacial forces.

The present invention therefore relates to a method for

Generation of a homogeneous mixture of a vaporous aromatic hydrocarbon, such as o-xylene and / or naphthalene and an oxygen-containing gas, such as air, for catalytic gas phase reactions, whereby the liquid aromatic hydrocarbon is atomized into drops with a diameter of less than 1 mm and in an oxygen-containing gas stream preheated above the boiling point of the aromatic hydrocarbon is injected, the process being characterized in that the liquid aromatic hydrocarbon is atomized by means of nozzles to form a hollow cone, preferably by means of swirl nozzles.

The method according to the invention enables the generation of a very homogeneous, streak-free mixture of gaseous oxygen, preferably in air or another gas containing oxygen, and a hydrocarbon vapor. The process according to the invention is preferably used in the production of carboxylic acids or carboxylic anhydrides by catalytic gas-phase oxidation of aromatic hydrocarbons, such as xylenes, in particular o-xylene and / or naphthalene, in fixed bed reactors. The production of phthalic anhydride (PSA) may be mentioned here as an example.

In the following, purely by way of example, reference is made to the particularly preferred use of the process according to the invention in the production of PSA by catalytic gas phase oxidation. The aromatic hydrocarbon is o-xylene and the oxygen-containing gas is air.

In the method according to the invention, the hollow atomizing cone preferably has an opening angle of 30 ° to 70 °. The atomizing hollow cone particularly preferably has an opening angle of approximately 60 °.

The axis of the hollow atomizing cone lies in the direction of flow of the oxygen-containing gas, that is to say approximately the air, but can deviate from this by up to 30 °. This means that the central axis of the hollow atomizing cone of the hydrocarbon stream is at an angle of -30 ° to + 30 ° to the central axis of the preheated gas stream. This means that fewer drops of the hollow cone touch the wall. A further measure for this can in particular be to maintain a certain distance, approximately one third of the pipe radius, from the wall. It is preferable to use several nozzles, approximately 2 to 6, preferably 4 to 6, at approximately equal intervals.

According to the invention, so-called swirl nozzles are preferably used to atomize the liquid hydrocarbon. These swirl nozzles, which are also referred to as hollow cone nozzles, preferably have a guide body with oblique inflow surfaces in front of the outlet opening, which impart swirl or rotation about the flow axis to the liquid to be atomized. Swirl nozzles of this type are known for other uses, such as rapid impulse transmission in water jet pumps, injection condensers, etc. (cf. Grassmann "Physical principles of process engineering", Verlag Sauerländer (1970), pages 355 and 805). Although the use of hollow cone nozzles is particularly preferred in the method according to the invention, full cone nozzles or slot nozzles can also be used in other embodiments of the invention. The use of two-component nozzles, which can be charged with the o-xylene to be sprayed and the blowing agent air, is also possible. If a swirl or hollow cone nozzle is used to produce the hollow atomizing cone according to the invention, this is preferably operated with a pre-pressure of 2 to 20 bar, in order to ensure that a hollow atomizing cone with the opening angle of 30 ° to 70 ° preferred according to the invention is produced ,

In the method according to the invention, the liquid hydrocarbon stream is atomized into drops with a diameter of less than 1 mm, preferably less than 0.8 mm. Most preferably, the liquid stream is atomized into drops of 0.02 to 0.2 mm.

The swirl nozzles used to form the hollow atomizing cone with an opening angle of 30 ° to 70 ° are advantageously in¬

15 within a tube through which the oxygen gas flows arranged in a ring on a tube with a feed line for the liquid to be atomized. However, one can also arrange the ring-shaped feed pipe for the liquid around the oxygen feed pipe and the nozzles from the outside into the oxygen feed pipe

Introduce 20. In this case, the nozzle outlet openings are directed in the direction of the gas flow. As already mentioned above, however, the axis of the hollow cone can deviate from the direction of flow of the gas by up to 30 °. It can thereby be achieved that fewer drops of the hollow cone touch the wall.

25

Axial hollow cone nozzles of the type KS 1 (Lechler, Metzingen, Germany) are particularly suitable for the purposes of the method according to the invention. Such nozzles enable generation

30 of a hollow cone with the preferred cone angle of 60 °. The hollow cone diameter is then about 200 mm at a distance of 250 mm from the outlet opening. According to the invention, small drops with a diameter of less than 1 mm, preferably less than 0.8 mm, particularly preferably 0.02 to 0.2 mm, form. The latter evaporate very quickly and are already in an ent

35 distance from 200 to 500 mm from the nozzle outlet completely evaporated. However, drops of 0.8 to 1 mm can fly 50 to 100 cm until they evaporate completely, touching and wetting the wall.

40

Because of this wetting possibility, it is provided according to a particularly preferred embodiment of the method according to the invention to generate the mixture, for example the o-xylene-air mixture, in a space which is limited by side walls heated above the boiling point of the carbon _4g hydrogen. The side walls of the room are advantageously formed by a heated pipe, for example a double-jacket pipe, in particular a thermoplate (thermoplates of this type are used in Germany, for example, produced by the companies BUCO, Geesthacht or DEG, Gelsenkirchen). Droplets of hydrocarbon that hit the heated pipe cannot deposit as a liquid film, but are evaporated immediately. This finally creates the desired mixture of hydrocarbon vapor and air, for example.

The pipe gap of the double jacket pipe can be heated with high pressure steam, preferably with water steam of approx. 20 bar with a temperature of 214 ° C. The above-mentioned thermoplates can have a particularly narrow pipe gap. Thermo sheet metal tubes are relatively simple and therefore more cost-effective. Intensive heating can prevent cold spots in the thermo sheet. 5

For complete homogenization, the steam-air mixture is then passed through a mixing device in accordance with a further advantageous process variant. 0

Static mixers are preferably used as the mixing device. These are baffles attached in the flow-through tube, which divide the flow to be mixed several times and bring it back together, as a result of which the homogenization ₅ takes place completely. Static mixers of this type are manufactured, for example, by Sulzer, Winterthur, Switzerland. Static mixers are also described in German patent applications DE 25 250 20 AI, DE 196 223 051 AI and DE 196 23 105 AI.

The present invention also relates to a device for producing a homogeneous mixture of a vaporous aromatic hydrocarbon and an oxygen-containing gas with gas channels for a preheated, oxygen-containing gas stream, an atomization device opening into the gas channels for a stream of a liquid aromatic hydrocarbon , which is characterized in that the atomizing device has swirl nozzles, and that the gas channels have walls, at least downstream of the swirl nozzles, which can be heated at least to the boiling point of the hydrocarbon.

The gas channels preferably comprise a heatable tube, in particular a double-jacket tube or a tube made of thermoplate. A static mixer is particularly preferably arranged downstream of the swirl nozzles in the gas channels. The temperature on the hot tube wall is set so that 5 to 50% by weight of the liquid hydrocarbon, in particular 5 to 40% by weight, particularly preferably 5 to 30% by weight, meet the tube wall and can be evaporated there, the exact Proportion depends on the contamination of the raw materials, the shape of the hollow cone and the change in the nozzle (erosion) during operation.

At the above-mentioned functional unit, further functional units may be about connect for the production of PSA, for example, 0 _{t he} reactor for reacting the o-xylene to PSA, and the device for PSA separation and PSA obtain pure, as known from the prior art are.

The invention is explained below with reference to an embodiment shown schematically in the accompanying drawing and by an application example.

In the figure of the drawing is a device 10 for generating a homogeneous mixture of vaporous o-xylene and / or

Naphthalene and air are shown. The device has gas channels 11 which bring a preheated air flow (symbolized by arrow 12 in the figure). The gas channels 11 are designed as a tube in the example shown. A ₅ atomizing device 13 is provided in the tube 11, which consists of supply lines 14 for liquid o-xylene and swirl nozzles 15 arranged at the end of the lines. The feed lines 14 are fed by a supply pipe (not shown) concentrically surrounding the pipe 11. The swirl nozzles 15 produce a hollow cone 16 made of liquid o-xylene, which disintegrates into the finest drops with an average diameter between 0.02 and 0.2 mm. The fine drops evaporate very quickly in the preheated air flow, so that a homogeneous mixture of air and o-xylene vapor is formed. To further improve the homogeneity, a static mixer 17 is arranged in the tube 11, through which the steam / air mixture is passed. Downstream of the swirl nozzles 15, the tube 11 is designed as a heatable double-jacket tube 18. The tube is heated with steam to a temperature above the boiling point of o-xylene. Atomized o-xylene droplets falling on the

Hit the pipe wall, are immediately evaporated there and do not deposit 0 as a liquid film. At 19, the tube 11 opens into a tube bundle reactor in which phthalic anhydride is produced by catalytic gas phase oxidation of the o-xylene.

_g Example The device for o-xylene evaporation in a plant for the production of PSA consisted of a vertical thermoplate with a diameter of 1200 mm. The oxidizing air, which had been preheated to 200 ° C. using a preheater, was passed through this to the reactor. The pressure was approximately 1.5 bar absolute. The air was charged with o-xylene with a load of 100 g per Nm ³ . The air was sucked in from the environment without any special purification, only through an air filter. The thermoplate was heated to 214 ° C with 20 bar steam. The o-xylene was injected via 6 swirl nozzles, which were attached to a rim 600 mm in diameter and whose axis was pointing vertically upwards. These were axial hollow cone nozzles (KS 1 type 216.324 made of steel, Lechler company). The admission pressure was 8 bar. Static mixers were installed in the horizontal pipe section at a distance of 4.5 m behind the nozzles.

With this swirl nozzle hot wall mixer system, a homogeneous, streak-free o-xylene vapor-air mixture was generated, the homogeneity of which was not disturbed by fluctuating operating parameters. This was found in the long-term constant PSA output. In addition, no ignitions within the production plant that had an adverse effect on the system and were caused by mixture inhomogeneities were observed. No damage or emergency shutdowns due to high temperatures in individual reactor areas or in reactor tubes were observed. Between the annual maintenance-related routine shutdowns, plant availability was over 99%.

Claims

claims

1. A process for producing a homogeneous mixture of a vaporous aromatic hydrocarbon and an oxygen-containing gas for catalytic gas phase reactions, wherein the liquid aromatic hydrocarbon is atomized into drops with a diameter of less than 1 mm and preheated to above the boiling point of the aromatic hydrocarbon, Oxygen-containing gas stream is injected in that the liquid aromatic hydrocarbon is atomized by means of nozzles to form a hollow cone, preferably swirl nozzles.

2. The method according to claim 1, characterized in that the atomizing hollow cone has an opening angle of 30 ° to 70 °.

3. The method according to any one of claims 1 or 2, characterized in that the central axis of the hollow atomizing cone is at an angle of -30 ° to + 30 ° to the central axis of the preheated gas stream.

4. The method according to any one of claims 1 to 3, characterized in that the mixture is produced in a space which is limited by side walls heated above the boiling point of the hydrocarbon.

5. The method according to claim 4, characterized in that the side walls of the room are formed by a heated tube, in particular a thermoplate.

6. The method according to any one of claims 4 or 5, characterized in that 5 to 50% by weight, preferably 5 to 40% by weight, particularly preferably 5 to 30% by weight of the atomized hydrocarbon are evaporated on the heated side walls.

7. The method according to any one of the preceding claims, characterized in that the mixture is passed through a static mixer after the evaporation of the aromatic hydrocarbon.

8. The method according to any one of the preceding claims for use in phthalic anhydride synthesis, wherein the aromatic hydrocarbon is o-xylene and / or naphthalene and the oxygen-containing gas is air.

5

9. Device for producing a homogeneous mixture of a vaporous aromatic hydrocarbon and an oxygen-containing gas

Gas channels (11) for a preheated, oxygen-containing

10 the gas stream (12), an atomizing device (13) opening into the gas channels (11) for a stream of a liquid aromatic hydrocarbon, characterized in that

15 that the atomizing device (13) has swirl nozzles (15) and that the gas channels (11) have walls (18) at least downstream of the swirl nozzles (15) which can be heated at least to the boiling point of the hydrocarbon.

20

10. The device according to claim 9, characterized in that the gas channels (11) comprise a heatable tube, in particular a double jacket tube or a tube made of thermal sheet.

25 11. Device according to one of claims 9 or 10, characterized in that a static mixer is arranged in the gas channels downstream of the swirl nozzles.

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