EP1412104A1

EP1412104A1 - Method for removing deposits from chemical reactors

Info

Publication number: EP1412104A1
Application number: EP02754846A
Authority: EP
Inventors: Claus-Peter Reisinger; Sven Michael Hansen; Peter Fischer; Konrad Triebeneck; Joachim Helbig
Original assignee: Bayer MaterialScience AG
Current assignee: Covestro Deutschland AG
Priority date: 2001-07-19
Filing date: 2002-07-08
Publication date: 2004-04-28
Also published as: US20040194805A1; TW583019B; CN1289216C; DE10135318A1; US6986816B2; JP2004538135A; WO2003008116A1; CN1533310A

Abstract

The invention relates to a method for removing deposits of solids arising from a liquid reaction mixture in a reaction device, characterized in that particles from an inert material in reaction conditions are introduced into the reaction apparatus, said particles are displaced throughout the reactor by suitable types of mechanical circulation of said reaction mixture, whereby they are knocked against the walls or other fittings and deposits thereon are removed by abrasion during said reaction.

Description

Process for removing deposits on chemical reactors

The invention relates to a method for removing deposits which result from the precipitation of solids from a gaseous, liquid or liquid / gaseous reaction mixture or a suspension in a reaction apparatus.

Such deposits on reactors or other surfaces in contact with the reaction medium can e.g. consist of crystallizing organic or inorganic solids, metal mirrors, polymers, tarred reaction residues or other solids adsorbed on the reactor surfaces.

According to the prior art, such deposits are generally removed batchwise by mechanical and / or chemical cleaning operations which take place as long as the reaction apparatus is not in operation (cf. EP 121 263 AI, WO99 / 05251). This cleaning thus induces an economically unfavorable lower time utilization of the reaction apparatus.

This procedure also results in a relatively long service life for this precipitation.

Deposits on reactor walls, pipes and internals that are not removed early can lead to unfavorable secondary reactions in chemical reactions. Precipitation can age, compact or crystallize. The longer residence time in the reactor compared to the reaction mixture can lead, for example due to condensation, polymerization or crosslinking, to deposits which are more difficult to remove chemically or mechanically. Organic compounds can crack or carbonize. If such deposits peel off in an uncontrolled manner, they can adversely affect the product properties. The deposits can also be valuable components of a reaction mixture, such as homogeneous catalysts or their degradation products. If these expensive components cannot be removed from the reaction apparatus with the reaction mixture, they escape a subsequent work-up or separation step and can therefore not be used in the reaction in a reprocessed form.

An example of the appearance of deposits in a chemical reaction is the process of direct carbonylation of hydroxyaromatics to diaryl carbonates. It is known that organic carbonates can be prepared by oxidative reaction of an aromatic hydroxy compound with carbon monoxide in the presence of a noble metal catalyst (DE-A-2 738 437). Palladium is preferably used as the noble metal. In addition, a cocatalyst (e.g. manganese, lead or cobalt salts), a base, a quaternary salt, various quinones or hydroquinones and drying agents can be used. Here, in a solvent such as e.g. Acetonitrile, monochlorobenzene or dimethylacetamide can be worked.

In this process, catalyst components can precipitate out and deposit on the surfaces of the reactor. It is assumed that the deposits are essentially unusual

Palladium metal is involved, but the exact chemical composition of these deposits is irrelevant for the process according to the invention. Due to the high palladium costs, this has to be recovered from the reaction mixture. However, the quantities of palladium in the reactor cannot be fed to a separation and treatment step.

It is therefore desirable to develop a process which removes such deposits and enables the deposits with the reaction mixture to be discharged from the reactor. The present application relates to such a method for removing deposits which result from the precipitation of solids from a gaseous, liquid or liquid / gaseous reaction mixture, a suspension or a sol in a reaction apparatus, characterized in that in the reaction apparatus or others from the reaction medium Touched surfaces particles are emitted from a material that is inert under the reaction conditions, which are moved over the surfaces by suitable mechanical circulation of the reaction mixture in such a way that they abrasively remove deposits adhering to the walls or other internals.

All highly viscous liquids or solids that can be deposited on the surfaces of the reaction apparatus can be used as deposits. These can be starting materials, their impurities, reaction products, intermediates, by-products, catalysts, phase mediators, stabilizers or other auxiliaries. These can be organic or inorganic crystals or glasses. The deposits can be in low molecular weight or polymeric form.

The method is preferably used to remove metallic deposits. The method is particularly preferably used to remove

Deposits from metals used in homogeneous catalysis, in particular the VTTI and IB group of PSE, such as. B. Nickel, rhodium, palladium and platinum, copper and silver arise.

The process is particularly well suited for removing deposits which arise during the direct carbonylation of hydroxyaromatics to diaryl carbonates with carbon monoxide in the presence of palladium and other cocatalysts.

The particles used to remove the deposits should be inert under the reaction conditions, ie they should not react with any component of the reaction mixture, not catalyze side reactions or components of the Reaction mixture dissolved, swollen or otherwise impaired in its properties.

Under the pressure and temperature conditions of the reaction, they must have sufficient mechanical strength so that on the one hand they can remove the deposits, but on the other hand they do not break themselves into ever smaller particles, the abrasive effect of which would decrease if the temperature falls below a certain limit, the subsequent separation of the particles was difficult to remove.

Because of their excellent mechanical properties, polymers such as. B. elastomers, thermoplastics or thermosets are used. Thermoplastics are particularly preferred because they can be used to easily produce particles of the desired shape which have sufficient hardness and abrasion resistance. The thermoplastics are preferably in the partially crystalline or glassy state under the reaction conditions. They can be linear or branched.

The property of chemical inertness towards most reaction media is particularly fulfilled by fluoropolymers. These fluoropolymers can be blends with at least one polymer component containing form, homo- or copolymers of different fluorinated or fluorinated with non-fluorinated building blocks. The architectures of copolymers known to the person skilled in the art, e.g. Alternating, statistical, random graft or block copolymers can be used.

Because of their commercial availability, partially fluorinated polymers such as polychlorotrifluoroethylene, polyvinylidene fluoride or copolymers of ethylene and / or propylene together with tetrafluoroethylene and / or hexafluoropropylene or perfluorinated polymers such as copolymers of tetrafluoroethylene and hexafluoropropylene, polytetrafluoroethylene or perfluoroalkoxypolymer are particularly suitable. In addition, depending on the chemical nature and aggressiveness of the reaction medium, other, possibly less expensive, known to those skilled in the art and chemically inert under the reaction conditions such as. B. polyethylene, polypropylene, polystyrene and its copolymers, polyvinyl chloride, polyoxymethylene, polymethyl methacrylate, polyimide, polyether ether ketone, polyphenylene sulfide, polyphenylene oxide,

Polyethylene terephthalate, polybutylene terephthalate or polyamide can be used.

In addition to the polymers mentioned, other substances than inert auxiliary bodies, for example glass or carbon fibers, glass splinters, clay balls, metal balls, filing and sawdust, pumice, quartz sand, layered silicates such as talc, if appropriate in any mixture of these substances, can be used if their mechanical and chemical stability and hardness allow use under the specified conditions.

The particles used must have a certain minimum size in order to be able to remove the deposits, in order to be easy to handle and easy to separate. It is therefore sensible to use particles that have a dimension of about 50 micrometers to about 5 cm in their longest Cartesian axis. Particles with a longest dimension of 500 micrometers to 3 cm are preferred. Particles with a longest dimension of approximately 1 mm to 2 cm are particularly preferred.

The particles are preferably not too anisotropic, i.e. the ratio of all Cartesian dimensions of the particle relative to one another is approximately 0.1 to 10. They are preferably approximately spherical, rhombic, cylindrical or deformed cylindrical in the form of a parallelepiped with an elliptical cross section. The granulate forms customary in commercial thermoplastics are quite suitable for the task.

The use of particle mixtures of different sizes is particularly suitable for uniform distribution on all surfaces in the reactor space.

Particles that float on the reaction mixture are particularly suitable for

Remove deposits that are on the walls of the reactor near the Liquid surface, e.g. B. by evaporation and drying or reactions with the gas phase above the liquid. However, it is often desirable to remove deposits from as many of the surfaces of the reaction apparatus as possible. For this it makes sense that the particles have a higher density than the reaction mixture. Particles with densities greater than approximately are therefore preferred

1.1 g cm ^"3 , particularly preferably particles with densities greater than about 1.2 g cm ^{" 3} .

Therefore, the fluoropolymers mentioned are particularly suitable, since their density is significantly higher than that of most reaction media.

The hardness of the particles used should preferably be lower than that of the material of the reaction apparatus or other surfaces in contact with them, in order not to damage the surface thereof. The mass and thus the dimension of the particles should preferably be chosen to be at least small enough that mechanical impacts on parts of the reaction apparatus cannot occur in the case of the impacts against the surfaces.

The deposits can preferably be removed in reactions whose reaction medium is so low-viscosity that the particles have a significant proportion of the momentum obtained during the circulation of the reaction mixture to the surfaces of the

Can deliver reactor. Reactions in the gas and / or liquid phase are therefore particularly suitable. Suitable liquid reaction media are e.g. homogeneous solutions, melts, micro and macro emulsions, as well as suspensions or brine.

The process is particularly suitable for removing deposits in homogeneously catalyzed reactions, especially in oxidative carbonylation.

In particular, the deposits in the oxidative carbonylation of hydroxy aromatic compounds to diaryl carbonates, eg. B. the carbonylation of phenol

Diphenyl carbonate can be removed very easily with this process. The method can be used to remove or prevent deposits on all surfaces that come into contact with media that tend to form deposits. For example, these are reactors, pipelines (supply and discharge lines), storage, storage and buffer vessels. Pipelines are preferably kept free of deposits by turbulent flushing with the mixture containing the particles.

The method is preferably used to remove or prevent deposits on containers which contain the reaction mixture, particularly preferably of reaction apparatus. The reaction apparatuses for the process according to the invention are e.g. Stirred kettles, autoclaves, loop reactors and bubble columns and other apparatuses known to the person skilled in the art are suitable, these being able to be used as individual reactors or as a cascade. 2 to 15, preferably 2 to 10, particularly preferably 2 to 5 reactors can be connected in series in a cascade.

In order to circulate the reaction mixture, the stirred containers to be used according to the invention are equipped with suitable stirrers. Such stirrers are known to the person skilled in the art. Examples include: disc, impeller, propeller, blade, MIG and Intermig stirrers, tube stirrers and various types of hollow stirrers, e.g. B. those that allow effective mixing of gases and liquids, for example, hollow tube gassing stirrer, propeller stirrer etc. The combination of different stirrer types on a shaft, or several stirrers of one type on a shaft is sometimes suitable, the solid particles evenly on all surfaces in the reactor space to distribute.

The following types can be used as bubble columns in the process according to the invention: simple bubble columns, bubble columns with internals, such as: bubble columns with parallel chambers, cascade bubble columns with sieve trays or single-hole trays, bubble columns with packings, with static mixers, pulsating

Sieve-bottom bubble columns, loop reactors such as: mammoth loop reactors, current loop reactors, jet loop reactors, free jet reactors, jet nozzle reactors, bubble columns with liquid immersion lamps, downstream-upstream bubble columns and other bubble column reactors known to the person skilled in the art (Chem. Ing. Tech. 51 (1979) No. 3, pp. 208-216; W.-D. Deckwer , Reaction technology in bubble columns, Otto Salle Verlag 1985).

The reaction mixture can also be circulated in a loop by pumping around. Another possibility of circulating the reaction mixture is to introduce an inert or reaction gas with excess pressure or to spray a liquid. The preferred method of circulation is to stir the reaction mixture.

The power input by the stirring or circulating element should at least be so great that the particles can reach all surfaces that are in contact with the reaction medium. Possibly. the circulation of the reaction mixture should be designed by suitable internals in the reaction apparatus so that the

Particles can impact against all surfaces of the reaction apparatus so that deposits can be removed as quantitatively as possible.

The abrasive removal of particles works particularly well if the particles can transmit a sufficient impulse to the surfaces of the reaction apparatus. The flow rate of the auxiliary bodies to the surfaces is preferably at least about 2 km / h.

The reaction mixture can be withdrawn from the reaction apparatus continuously or batchwise after the reaction. By means of separation processes known to those skilled in the art, such as sieving, filtering, sedimenting or centrifuging, the particles can be separated from the reaction mixture and returned to the reaction apparatus or retained there. A method is preferred in which the particles are retained in the reaction apparatus by sieves or filters with mesh sizes or pore sizes which are smaller than the smallest Cartesian dimension of the particles.

The method according to the invention is preferably carried out so that the

Particles detached deposits are either discharged from the reactor together with the reaction mixture and then separated, or particularly preferably directly at the outlet by a suitable separation operation such as B. sieving, sedimentation or filtration are separated from the reaction mixture and thus retained in the reactor.

Another preferred embodiment consists in separating the particles together with the deposits, chemically working up the deposits, then separating the particles or recycling them back into the reaction together with the processed deposits without separation. For example, the palladium deposits formed in an oxidative carbonylation can be oxidatively z. B. to palladium bromide or palladium acetate and be transferred back into the reactor in the mixture with the particles.

Examples

example 1

50 mg / kg of palladium (as palladium bromide), 311 mg / kg of Mn (as manganese trisacetylacetonate), 3% by weight of tetrabutylamine ^' umbromide, 2% by weight of tefrabutylammonium phenolate and 14% of phenol in are introduced into an autoclave with a gassing stirrer Chlorobenzene submitted. About 8% by weight of rhombic polytetrafluoroethylene particles measuring 2 mm × 2 mm × 1 mm are added to the reaction mixture, and a gas mixture of carbon monoxide and oxygen is continuously added at 110 ° C.

(97: 3% by volume) at 3 bar total pressure. After 1 h of intensive stirring, the reaction mixture is removed. After repeating the reaction several times, the amount of solid separated in the reactor is removed mechanically and the palladium content is determined by a combination of weighing and elemental analysis (see Table 1).

Example 2 (comparative example)

The experiment is carried out analogously to Example 1, but without the addition of polytetrafluoroethylene particles.

Table 1

* as a percentage of the amount used

The data in Table 1 show that it is possible to almost completely avoid deposits in a reactor by adding particles made of an inert material.

Claims

claims

1. A method for preventing and / or removing deposits from reactions, in particular while carrying out chemical reactions in reaction apparatuses, characterized in that auxiliary bodies which are inert at least in the space of the reaction apparatus are ground by moving or stirring the reaction mixture over the surfaces touched by the reaction mixture.

2. The method of claim 1, wherein the particles in their longest Cartesian axis have a dimension of about 50 microns to about 5 cm, preferably from about 500 microns to about 3 cm, particularly preferably from about 1 micrometer to about 2 cm.

3. The method of claim 1 or 2, wherein the particles are shaped approximately spherical, cylindrical, rhombic or in the form of a parallelepiped with an elliptical cross section.

4. The method according to any one of claims 1 to 3, wherein the ratio of all Cartesian dimensions of the particle relative to each other about 0.1 to

Is 10.

5. The method according to any one of claims 1 to 4, wherein the density of the particles used is greater than that of the reaction mixture.

6. The method according to claim 5, wherein the density of the particles used is greater than 1.1 g / cm ³ , preferably greater than 1.2 g / cm ³ .

7. The method according to claim 2 to 6, characterized in that the deposits are a metal, a metal salt or an organometallic compound. contain bond, a low molecular weight organic compound or a polymer.

8. The method according to claim 7, wherein the deposits contain transition metals of group VIII or IB, preferably palladium.

9. The method according to any one of claims 1 to 8, characterized in that the inert auxiliary bodies consist of one or more polymers.

10. The method according to claim 9, characterized in that the auxiliary bodies contain a partially fluorinated or perfluorinated fluor homo- or copolymer or a blend of other polymers with a fluoropolymer.

11. The method according to claim 10, characterized in that the auxiliary body from a polychlorotrifluoroethylene, polyvinylidene fluoride or a copolymer

Ethene or propene and tetrafluoroethylene or hexafluoropropylene, or a

Contain copolymer of tetrafluoroethylene and hexafluoropropylene or a perfluoroalkoxyfluoropolymer or a polytetrafluoroethylene.

12. The method according to any one of claims 1 to 11, characterized in that the reaction mixture is a homogeneously catalyzed reaction.

13. The method according to any one of claims 1 to 12, characterized in that it is the oxidative carbonylation of a hydroxyaromatic compound, in particular phenol to a diaryl carbonate.

14. The method according to any one of claims 1 to 13, characterized in that the reaction apparatus is a stirred tank, an autoclave, a bubble acid, a tubular reactor or a loop reactor.

15. The method according to any one of claims 1 to 14, characterized in that the mass fraction of the particles based on the reaction mixture is 0.2 to 10 wt .-%, preferably 0.4 to 5 wt .-%.

16. The method according to any one of claims 1 to 15, characterized in that the particles are retained in the reactor when the reaction mixture is removed from the reactor.