JP2003518433A - Method and apparatus for producing a homogeneous mixture of a vaporous aromatic hydrocarbon and an oxygen-containing gas - Google Patents

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

Detailed Description of the Invention

The present invention relates to a homogeneous mixture of vaporized aromatic hydrocarbons and oxygen-containing gases for catalytic gas phase reactions, in particular vaporized o-xylene and / or naphthalene and air for the production of phthalic anhydride. A method and an apparatus for producing a mixture.

Phthalic anhydride (PSA) is an important intermediate product for producing synthetic resins, phthalate plasticizers, phthalocyanine dyes and even fine chemicals. PS
A is produced today mainly from o-xylene, which is also largely by gas phase oxidation of o-xylene using air as the oxidant.

The equipment for carrying out such a PSA production process consists essentially of a functional unit for the production of an o-xylene vapor-air mixture, a reactor for the reaction of an o-xylene vapor-air mixture and a PSA-consists of equipment for separation and post-treatment.

Reactions by catalytic gas phase oxidation are often carried out with V ₂ O ₅ containing catalysts. For this, o-xylene is evaporated, mixed with excess air and passed at 340 ° C. to 440 ° C. through the catalyst into the tubes of a tube bundle reactor. The catalyst is, for example, 6 × 6 mm
It consists of a mixture of V ₂ O ₅ and TiO ₂ with cocatalyst on a ceramic body such as porcelain or SiC-spheres or rings of dimensions. The large reactor has 10 tubes in the bundle.
It has 000 to 40,000 tubes. Normally, o-xylene is oxidized to PSA with a selectivity of 78% -80%. This oxidation itself has a strong exotherm at -1110 kJ / mol.

When carrying out the process, among other things, the following important points must be taken into account: The mixture of o-xylene and air (excess oxygen), on the other hand, is in the explosive range ( Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Volume A20, 85
), And many of the 10,000 to 40,000 tubes must flow a gas mixture of the same cross-sectional area and constant over time, so the reaction proceeds equally rapidly in all tubes, and For example, some of them do not progress particularly rapidly or particularly slowly. Moreover, a strongly negative enthalpy of reaction can lead to the catalyst being sintered, melted or deactivated in the individual tubes upon departure from the regulated conditions. This is associated with a considerable risk for the equipment.

Moreover, due to the heterogeneity of the feed, the reaction conditions are different in the tube. Thereby reducing the yield and having to be separated from the PSA in a subsequent cleaning step,
And the by-products that have to be disposed of in waste are produced in increased amounts.

From DE-A1793453 is known a process for preparing a homogeneous mixture of vaporized o-xylene and air for the catalytic oxidation to phthalic anhydride. In the case of this known method,
The o-xylene stream is atomized into droplets having a diameter of less than 1 mm, eg predominantly less than 0.3 mm and is passed into a preheated air stream above the boiling point of o-xylene. This air flow is turbulent; Reynolds numbers above 200,000 are recommended. The residence time of the o-xylene injection to the reactor should be at least 0.2 seconds in order to obtain a homogeneous gas mixture and thus a homogeneous charge of all tubes.

Despite this improvement that the method according to DE-A1793453 shows, in particular when the operating conditions change-droplet size changes and impeding evaporation can occur. This can be due to a variety of causes: The raw material can be somewhat contaminated. Air, especially _{NO x, H} 2 S, sulfur oxides, for example as it can contain the salts thereof with _SO 2, NH ₃ and example CO _2, this may lead to constriction of one or more nozzles . Corrosion particles can also change the size and shape of the sprayed o-xylene jet droplets.
A similar effect occurs due to nozzle corrosion during extended operation. In addition, o-xylene may also contain m- and p-xylene, toluene, ethylbenzene, isopropylbenzene, nonane and small amounts of styrene. Such compounds are o
-Can affect the surface tension of xylene. For example, droplets that fly farther than those listed above having a size of less than 0.3 mm may occur. They are,
The wall of the reaction tube can be wetted and a liquid film can be formed there. An additional difficulty is that in practice it is not possible to mount the nozzle used for atomizing the o-xylene stream in such a way that the droplets of the atomized o-xylene stream do not come into contact with the walls of the guide tube. It is possible.

Also, in the case of the method according to DE-A1793453, the adjusted parameters, such as pressure and temperature and the air content, can change unintentionally and negatively. In addition, the starting material air and the contaminants contained in the o-xylene can be introduced and the sprayed droplets of the o-xylene stream can come into contact with the tube wall. In that sense,
The methods listed above are still in need of improvement.

Accordingly, the present invention provides an improved process for producing a homogeneous mixture of a vaporized aromatic hydrocarbon for catalytic gas phase reactions, such as o-xylene and / or naphthalene, and an oxygen-containing gas, especially air. There has been the problem of providing such a method and device. In particular, the drawbacks mentioned above should be avoided or at least minimized.

According to the invention, in the process according to this type, the atomization of the liquid aromatic hydrocarbons is carried out by the use of nozzles, preferably swirl nozzles (Drallduese), for the formation of atomizing hollow cones (Zerstaeubungshohlkegel). Resolve the issues listed above. The spray hollow cone first adheres to its liquid hydrocarbon
(zusammenhaengend) film, which is torn further apart from the swirl nozzle into smaller pieces, which are reduced by interfacial forces into individual droplets having a diameter of less than 1 mm.

The subject of the invention is therefore the vaporized aromatic hydrocarbons for catalytic gas phase reactions, such as o
A process for the preparation of a homogeneous mixture of xylene and / or naphthalene and an oxygen-containing gas, for example air, in which the liquid aromatic hydrocarbon is atomized into droplets having a diameter of less than 1 mm and the aromatic hydrocarbon is Is injected into a preheated oxygen-containing gas stream above the boiling point of the liquid aromatic hydrocarbons, which is sprayed with a nozzle for the formation of hollow cones, preferably with a swirl nozzle. It is characterized by

The process according to the invention consists of gaseous oxygen and hydrocarbon vapors, preferably in air or other oxygen-containing gases, and is very homogeneous and streaming-free (straehnenfr
ei) Allow the production of mixtures.

The process according to the invention preferably produces carboxylic acids or carboxylic anhydrides by catalytic gas phase oxidation of aromatic hydrocarbons such as xylene, in particular o-xylene and / or naphthalene, in a fixed bed reactor. Used in the case of. Illustrative here may be the production of phthalic anhydride (PSA).

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

In the case of the method according to the invention, the spray hollow cone is preferably between 30 ° and 70 °.
Has an opening angle of. Particularly preferably, the spray hollow cone has an opening angle of about 60 °.

The axis of the atomizing hollow cone is in the direction of flow of the oxygen-containing gas, ie air for example, but may be deflected up to 30 °. This means that the central axis of the spray hollow cone of the hydrocarbon stream is -30 ° to +30 relative to the central axis of the preheated gas stream.
Means at an angle of °. Thereby it is achieved that most drops of the hollow cone do not touch the wall. Another means for this may be to keep a constant distance from the wall, for example about 1/3 of the tube radius. Preferably a plurality of nozzles, for example 2 to 6, preferably 4 to 6, are used with approximately the same spacing.

According to the invention, preferably so-called swirl nozzles are used for atomizing liquid hydrocarbons. This swirl nozzle, which is also referred to as the hollow cone nozzle (Hohlkegelduese), preferably has, in front of the outlet opening, a guide body with an inclined flow surface which imparts a swirl or rotation around the flow axis to the liquid to be sprayed. Such swirl nozzles are known for other uses, for example for rapid shock transmission in water jet pumps, jet condensers etc. (Grassmann “Physika
lische Grundlagen der Verfahrenstechnik ”, Verlag Sauerlaender (1970), 3
(See pages 55 and 805). The use of hollow cone nozzles is especially preferred in the method according to the invention, but in another embodiment of the invention the solid cone nozzle (Vollk
egelduesen) or slit nozzles can also be used. It is also possible, for example, to use a two-fluid nozzle which can be charged with o-xylene to be atomized and with the propellant air.

If a swirl nozzle or hollow cone nozzle is used for the production of the spray hollow cone according to the invention, it is preferably operated at a feed pressure of 2 to 20 bar, with which 30 ° to It is guaranteed that a spray hollow cone with the preferred opening angle according to the invention of 70 ° will result.

In the process according to the invention, the liquid hydrocarbon stream is less than 1 mm, preferably 0.
Atomized into droplets having a diameter of less than 8 mm. Particularly preferably the liquid flow is 0.02
~ 0.2 mm droplets are sprayed.

The swirl nozzle used for the formation of the spray hollow cone with an opening angle of 30 ° to 70 ° is preferably a supply for the liquid to be sprayed, inside the tube flowed by oxygen gas. Arranged annularly on a tube having a section. However, it is also possible for an annular supply pipe for the liquid to be arranged around the oxygen conduit and for the nozzle to lead from the outside into the oxygen conduit. In this case, the nozzle outlet opening is oriented in the direction of gas flow. However, as already mentioned above, the axis of the hollow cone may be deflected up to 30 ° in the direction of gas flow. Hereby it can be achieved that most drops of the hollow cone do not touch the wall.

For the purposes of the method according to the invention, in particular a shaft-hollow cone nozzle (L
echler, Metzingen, Germany) are suitable. Such nozzles
Allows the generation of hollow cones with a 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, less than 1 mm, preferably less than 0.8 mm, particularly preferably 0.0
Small droplets with a diameter of 2-0.2 mm are formed. The latter evaporates very quickly and is already completely evaporated at a distance of 200-500 mm from the nozzle outlet opening. However, 0.8-1 mm droplets can fly as far as 50-100 cm far to complete evaporation and then come into contact with and wet the walls.

Due to this wetting possibility, according to a particularly preferred embodiment of the process according to the invention, the mixture, for example an o-xylene-air-mixture, is separated by a heated sidewall above the boiling point of the hydrocarbon. It is designed to be generated in the open space. Advantageously, the side wall of the space is formed by a heated tube, for example a double jacket tube, in particular a Thermoblech tube (such a Thermoblech tube is used in the Federal Republic of Germany, for example BUCO, Geesthacht or DEG). Company, manufactured by Gelsenkirchen). Hydrocarbon droplets that strike a heated tube cannot be deposited as a liquid film, but are immediately vaporized. This ultimately results in the desired mixture of hydrocarbon vapor and, for example, air.

The tube gap of the double jacketed tube can be heated with high pressure steam, preferably with steam of about 20 bar having a temperature of 214 ° C. The Thermoblech tubes listed above may have a particularly narrow tube gap. Thermoblech tubes are relatively easy to assemble and are thereby less expensive. Due to the intense heating, cold places can be eliminated in the case of thermoblech tubes.

For complete homogenization, the steam-air mixture is subsequently passed to a mixing device according to another advantageous process variant.

A static mixer is preferably used as the mixing device. This is a baffle mounted in a flow-through tube which divides and recombines the streams to be thoroughly mixed, whereby complete homogenization takes place. Such static mixers are manufactured, for example, by Sulzer, Winterthur, Switzerland. Patent application for the static mixer in the Federal Republic of Germany
It is also described in DE2525020A1, DE196223051A1 and DE19623105A1.

Moreover, the subject of the present invention is a gas channel for a preheated oxygen-containing gas stream,
An apparatus for producing a homogeneous mixture of a vaporized aromatic hydrocarbon and an oxygen-containing gas with a spraying device flowing into a gas channel for the flow of liquid aromatic hydrocarbons, which spraying device comprises It is characterized by having a swirl nozzle and having a wall at least downstream of the swirl nozzle capable of heating to at least the boiling point of the hydrocarbon.

[0028] Preferably, the gas channel comprises a heatable tube, in particular a double jacket tube or a tube made of thermoblech. Particularly preferably, a static mixer is arranged in the gas channel downstream of the swirl nozzle.

The temperature of the hot pipe wall is such that 5 to 50% by weight of the liquid hydrocarbons, in particular 5 to 40% by weight, particularly preferably 5 to 30% by weight, impinge on the pipe wall and can be evaporated there. The exact proportion depends on the impurities in the raw material, the shape of the hollow cone and the nozzle change (corrosion) during operation.

The functional units listed above may, for example, be known from the state of the art,
Further functional units for the production of PSA, for example a reactor for the conversion of o-xylene into PSA, and a device for PSA-separation and PSA-pure isolation may be connected.

The invention is explained in more detail below on the basis of the embodiments schematically shown in the accompanying drawings and by way of example of use.

In the figures of the drawings, an apparatus 10 for producing a homogeneous mixture of vaporized o-xylene and / or naphthalene and air is shown. The device is equipped with a preheated air stream (
(Symbolized by arrow 12 in the figure). The gas channel 11 is formed as a tube in the example shown. In the tube 11, liquid o-
A spraying device 13 consisting of a supply pipe 14 for xylene and a swirl nozzle 15 arranged at the end of the conduit is provided. The supply tube 14 is supplied by a supply tube (not shown) that concentrically surrounds the tube 11. Swirl nozzle 15 is 0.02
This results in a hollow cone 16 of liquid o-xylene that breaks into the finest droplets with an average diameter of .about.0.2 mm. The fine droplets evaporate very quickly in the preheated air stream, resulting in a homogeneous mixture of air and o-xylene vapor.
To further improve the homogeneity, a static mixer 17 is arranged in the tube 11 to which the steam / air-mixture is passed. Downstream of the swirl nozzle 15, the tube 11 is formed as a heatable double jacket tube 18. The tube is heated with steam to a temperature above the boiling point of o-xylene. Thus, the droplets of atomized o-xylene that hit the tube wall are immediately vaporized there,
And it is not deposited as a liquid film. At 19, tube 11 flows into a tube bundle reactor where phthalic anhydride is produced by catalytic gas phase oxidation of o-xylene.

Example The equipment for o-xylene vaporization in the case of an installation for PSA production has a diameter of 1
It consisted of a 200 mm vertical thermoblech tube. This allows the preheating device to
Oxidizing air, which had been preheated to 00 ° C., was passed through the reactor. The pressure is about 1.5 bar (
It was absolutely). Air was charged with o-xylene having a load of 100 g per 1 Nm ³ . Air was simply inhaled from the surroundings through an air filter without any special cleaning. The thermoblech tube was heated to 214 ° C. with 20 bar-steam. o-Xylene was injected through 6 swirl nozzles mounted on a 600 mm diameter ring and whose axis points vertically upwards. These were axial-hollow cone nozzles (steel, type 216.324 KS 1 from Lechler). The charge pressure was 8 bar. A static mixer was installed in the horizontally running tube section at a distance of 4.5 m from the back of the nozzle.

With this swirl nozzle-hot wall-mixer system, a homogeneous, streaming-free o-xylene vapor-air-mixture was produced, the homogeneity of which was not disturbed by the varying operating parameters. This was fixed at a constant PSA-production for a long time. Furthermore, no ignitions caused by mixture heterogeneity, which hinder equipment safety, were observed in the production facility. No high temperature damage or emergency shutdown was observed within the individual reactor areas or in the reactor tubes. Facility availability exceeded 99% during regular outages limited to annual maintenance.

[Brief description of drawings]

1 is a schematic diagram showing an apparatus for producing a homogeneous mixture of vaporized o-xylene and / or naphthalene and air.

[Explanation of symbols]

10 apparatus, 11 gas channel, 12 gas flow, 13 atomizer,
14 supply pipes, 15 swirl nozzles, 16 hollow cones, 17 static mixers, 18 double jacket pipes

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE, TR), OA (BF , BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, G M, KE, LS, MW, MZ, SD, SL, SZ, TZ , UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, B Z, CA, CH, CN, CR, CU, CZ, DE, DK , DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, J P, KE, KG, KP, KR, KZ, LC, LK, LR , LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, PT, R O, RU, SD, SE, SG, SI, SK, SL, TJ , TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW (72) Inventor Bernhard Ulrich             Federal Republic of Germany Bockenheim Au             Hudem Higher 28 (72) Inventor Helmut Wunsmann             Federal Republic of Germany Bruhl Römer             Strasse 13 F-term (reference) 4G035 AB01 AC01 AC39 AE13 AE15                 4G037 CA11 EA01

Claims (11)

[Claims] 1. Catalytic vapor reciprocation by atomizing liquid aromatic hydrocarbons into droplets having a diameter of less than 1 mm and injecting them into a preheated oxygen-containing gas stream above the boiling point of the aromatic hydrocarbons. In a method of producing a homogeneous mixture of vaporized aromatic hydrocarbons and an oxygen-containing gas for application, spraying liquid aromatic hydrocarbons with a nozzle for forming a hollow cone, preferably with a swirl nozzle. A method for producing a homogeneous mixture of a vaporized aromatic hydrocarbon and an oxygen-containing gas for a catalytic gas phase reaction, which comprises: 2. The method according to claim 1, wherein the spray hollow cone has an opening angle of 30 ° to 70 °. 3. The method according to claim 1, wherein the central axis of the spray hollow cone is at an angle of −30 ° to + 30 ° C. with respect to the central axis of the preheated gas stream. 4. The process according to claim 1, wherein the mixture is formed in the space bounded by the heated sidewalls above the boiling point of the hydrocarbons. 5. The method according to claim 4, wherein the side wall of the space is formed by a heated tube, in particular a thermoblech tube. 6. 5 to 50% by weight, preferably 5 to 40% by weight and particularly preferably 5 to 30% by weight of the atomized hydrocarbons are vaporized on the heated side walls.
Or the method described in 5. 7. The process according to claim 1, wherein the mixture is passed through a static mixer after evaporation of the aromatic hydrocarbons. 8. A method according to claim 1, wherein the aromatic hydrocarbon is o-xylene and / or naphthalene and the oxygen-containing gas is air, for use in the synthesis of phthalic anhydride. Method described in section. 9. A gas channel () for a preheated oxygen-containing gas stream (12).
11) for producing a homogeneous mixture of vaporized aromatic hydrocarbons and an oxygen-containing gas with a spraying device (13) flowing into a gas channel (11) for the flow of liquid aromatic hydrocarbons In the device, the atomizing device (13) has a swirl nozzle (15) and a gas channel (
11) produces at least downstream of the swirl nozzle (15) a homogeneous mixture of vaporized aromatic hydrocarbons and an oxygen-containing gas having a wall (18) capable of heating to at least the boiling point of the hydrocarbon. Equipment for. 10. The device according to claim 9, wherein the gas channel (11) comprises a heatable tube, in particular a double jacket tube or a tube made of thermoblech. 11. The device according to claim 9, wherein the static mixer is arranged in the gas channel downstream of the swirl nozzle.