EP1144725B1 - Method for coating reactors for high pressure polymerisation of 1-olefins - Google Patents

Abstract

The present invention relates to a process for coating apparatuses and apparatus parts for chemical plant construction-which are taken to mean, for example, apparatus, tank and reactor walls, discharge devices, valves, pumps, filters, compressors, centrifuges, columns, dryers, comminution machines, internals, packing elements and mixing elements-wherein a metal layer or a metal/polymer dispersion layer is deposited in an electroless manner on the apparatus(es) or apparatus part(s) to be coated by bringing the parts into contact with a metal electrolyte solution which, in addition to the metal electrolyte, comprises a reducing agent and optionally the polymer or polymer mixture to be deposited in dispersed form, where at least one polymer is halogenated.

Description

The invention relates to a method for coating reactors for the high pressure polymerization of 1-olefins. Farther This invention relates to reactors and high pressure reactor plants for the polymerization or copolymerization of 1-olefins in particular Ethylene containing those coated according to the invention Reactors, and a process for the production of ethylene homound Copolymers in the reactors according to the invention.

The production of homopolymers and copolymers of High pressure ethylene is an industrial scale carried out process. In these procedures, pressures above 500 bar and temperatures of 150 ° C and higher used. The process is generally carried out in high pressure autoclaves or carried out in tubular reactors. High pressure autoclaves are in so-called compact or elongated embodiments known. The well - known tubular reactors (Ullmanns Encyclopedia of technical chemistry, volume 19, p. 169 and p. 173 ff (1980), publisher Chemie Weinheim, Deerfield Beach, Basel) are characterized by simple Handling and low maintenance and are agitated against Autoclaves an advantage. The in the above equipment achievable sales are limited.

In order to increase the capacity of the existing equipment, one is strives to achieve the highest possible sales. limiting but are polymerization temperature and polymerization pressure, which have a specific upper limit depending on the product type. For low density LDPE waxes and LDPE polymers have this upper limit approx. 330 ° C; Above that, spontaneous ethylene decomposition can occur come. Below a temperature of 150 ° C it can be too Heat dissipation problems come up. Furthermore, the pressure loss that occurs limiting; this pressure loss increases with decreasing Temperature too.

Crucial for the operation of a tubular reactor for ethylene polymerization is good heat dissipation. This heat dissipation takes place preferably by jacket cooling. Here, a cooling medium in General water, led through the so-called cooling circuit. The The temperature of the cooling medium is very important. At coolant temperatures A laminar layer can develop below 150 ° C Form polyethylene, which act as an insulator and heat dissipation can drastically lower. The temperature of the cooling medium is too high selected, so is the temperature difference between the reaction medium and cooling medium too low, which is also unsatisfactory Heat transfer numbers (see e.g. E. Fitzer, W. Fritz, Chemical Reaction Engineering, 2nd edition, page 152 ff., Springer Verlag Heidelberg, 1982).

In practice, however, even at temperatures above 150 ° C slow flowing layer of polyethylene observed that too leads to a reduction in heat dissipation. A method of emergence To hinder this layer consists in the so-called "stimulation". (EP-B 0 567 818, p. 3, line 6 ff.) By periodic Lowering pressure drastically increases the flow rate and temporarily removes the laminar layers. By periodic However, lowering the pressure becomes the mean pressure operation, which lowers the density of ethylene and thus Sales and molecular weight of the product decreased. Moreover the periodic drop in pressure causes a significant mechanical Stress in the equipment, resulting in increased repair costs leads and thus brings economic disadvantages.

The formation of laminar boundary layers in tubular reactors or also has stirred autoclaves for ethylene polymerization adverse consequences for the quality of the ethylene polymers. the one Material with a significantly longer dwell time in the Reactors is mostly high molecular weight, which is macroscopic in the formation of so-called specks. Stipp containing However, material has less good mechanical properties because of it forms predetermined crack locations in the material where a material failure takes place, and is also disadvantageous from the visual impression.

Attempts to coat the pipes with PTFE (polytetrafluoroethylene) did not lead to success. PTFE is a heat-resistant, material incompatible with polyethylene, however it acts as an insulator and deteriorates even in thin layers the heat transfer. Similar problems also arise with procedures observed the application of monolayer silane layers include the surface to be protected (Polymer Mater. Sci. and Engineering, Proceedings of the ACS Division of Polymeric Materials Science and Engineering (1990), volume 62, pages 259. bis 263).

• ein Verfahren bereitzustellen, durch das der Umsatz in Reaktoren insbesondere zur Hochdruckpolymerisation von Ethylen verbessert werden konnte, wobei dieses Verfahren auf der Beschichtung der Reaktoren beruhen sollte;
• entsprechend behandelte Reaktoren bereitzustellen,
• diese Reaktoren zum Bau von Hochdruckreaktoren zu nutzen sowie
• in den erfindungsgemäßen Reaktoren Polymerisate von 1-Olefinen herzustellen.

So the task was

• to provide a process by which the conversion in reactors, in particular for the high-pressure polymerization of ethylene, could be improved, this process being based on the coating of the reactors;
• to provide appropriately treated reactors,
• to use these reactors to build high pressure reactors as well
• to produce polymers of 1-olefins in the reactors according to the invention.

A method for coating a reactor has now been found characterized in that a metal layer or a metal-polymer dispersion layer on the inner surface of the reactor of a reactor for high pressure polymerization of ethylene without current deposit by covering the surfaces with a metal electrolyte solution contacted, in addition to the metal electrolyte, a reducing agent and optionally a halogenated to be deposited Contains polymer in dispersed form. Furthermore, were Reactors coated according to the invention for high-pressure polymerization of ethylene found. Finally, the reactors according to the invention for the high pressure polymerization of Ethylene is used and a process for high pressure polymerization of ethylene found.

The one with an anti-adhesive metal coating or metal-polymer dispersion layer coated reactors allow one significantly improved sales compared to non-coated Reactors.

This object of the invention is a method for electroless chemical deposition of metal layers or Underlying metal-polymer dispersion phases, which is known per se is (w. Riedel: Functional nickel plating, Verlag Eugen Leize, Saulgau, 1989, pages 231 to 236, ISBN 3-750480-044-x). The Deposition of the metal layer or the metal-polymer dispersion phases serves to coat the inner walls of the known High-pressure reactor. The according to the inventive method metal layer to be deposited comprises an alloy or an alloy-like one Mixed phase from a metal and at least one another element. The metal-polymer dispersion phases according to the invention additionally comprise a polymer, in the context of Invention a halogenated polymer in the metal layer is dispersed. The metal alloy is preferred a metal-boron alloy or a metal-phosphorus alloy with a boron or phosphorus content of 0.5 to 15% by weight.

In a particularly preferred embodiment of the invention Coatings are so-called "chemical Nickel systems "are phosphorus-containing nickel alloys a phosphorus content of 0.5 to 15% by weight; very particularly preferred are high phosphorus nickel alloys with 5 to 12 Wt .-%.

In contrast to galvanic deposition, chemical or autocatalytic deposition of the metal phosphorus or metal boron the electrons required for this are not through an external one Power source provided, but by chemical Reaction generated in the electrolyte itself (oxidation of a reducing agent). The coating is carried out, for example, by immersion of the workpiece in a metal electrolyte solution a stabilized polymer dispersion was previously mixed.

As metal electrolyte solutions, commercially available or freshly prepared metal electrolyte solutions are usually used, to which the following components are added in addition to the electrolyte: a reducing agent such as a hypophosphite or boranate (for example NaBH ₄ ), a buffer mixture for adjusting the pH, an alkali metal fluoride such as NaF, KF or LiF, carboxylic acids and a deposition moderator such as Pb ²⁺ . The reducing agent is selected so that the corresponding element to be installed is already present in the reducing agent.

Commercial nickel electrolyte solutions which contain Ni ²⁺ , hypophosphite, carboxylic acids and fluoride and optionally deposition moderators such as Pb ²⁺ are particularly preferably used. Such solutions are sold, for example, by Riedel, Galvano- und Filtertechnik GmbH, Halle, Westphalia and Atotech Deutschland GmbH, Berlin. Solutions which have a pH around 5 and about 27 g / l NiSO ₄ .6H ₂ O and about 21 g / l NaH ₂ PO ₂ .H ₂ O with a PTFE content of 1 to 25 g are particularly preferred / l included.

The optionally used halogenated polymer of the process according to the invention is preferably fluorinated. Examples of suitable fluorinated polymers are polytetrafluoroethylene, perfluoroalkoxy polymers (PFA, for example with C ₁ - to C ₈ -alkoxy units), copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ether, for example perfluorovinyl propyl ether. Polytetrafluoroethylene (PTFE) and perfluoroalkoxy polymers (PFA, according to DIN 7728, Part 1, Jan. 1988) are particularly preferred.

Commercial polytetrafluoroethylene dispersions are preferred as the use form (PTFE dispersions) can be used. Prefers PTFE dispersions with a solids content of 35 up to 60% by weight and an average particle diameter of 0.05 up to 1.2 µm, in particular 0.1 to 0.3 µm, used. Prefers spherical particles are used because the use of spherical Particle leads to very homogeneous composite layers. Advantageous using spherical particles is faster Layer growth and better, especially longer, thermal stability of the bathrooms, both of which offer economic advantages. This is particularly evident when compared to systems below Use of irregular polymer particles, which by grinding of the corresponding polymer can be obtained. In addition, the dispersions used a nonionic detergent (for example Polyglycols, alkylphenol ethoxylate or mixtures of the substances mentioned, 80 to 120 g neutral detergent per liter) or an ionic detergent (for example alkyl and haloalkyl sulfonates, Alkylbenzenesulfonates, alkylphenol ether sulfates, Tetraalkylammonium salts or optionally mixtures of the above Substances, 15 to 60 g ionic detergent per liter) for stabilization of the dispersion included.

Coating is carried out at a slightly elevated temperature, but which must not be so high that it destabilizes the dispersion comes. As temperatures have 40 to 95 ° C as proven suitable. Temperatures of 80 to 91 ° C. and 88 ° C. is particularly preferred.

• Durch höhere Temperaturen wird die Abscheidegeschwindigkeit erhöht, wobei es eine Maximaltemperatur gibt, die beispielsweise durch die Stabilität der optional zugegebenen Polymer-Dispersion begrenzt ist. Durch niedrigere Temperaturen wird die Abscheidegeschwindigkeit gesenkt.
• Durch höhere Elektrolytkonzentrationen wird die Abscheidegeschwindigkeit erhöht, durch niedrigere gesenkt; wobei Konzentrationen von 1 g/l bis 20 g/l Ni²⁺ sinnvoll sind, bevorzugt sind Konzentrationen von 4 g/l bis 10 g/l; für Cu²⁺ sind 1 g/l bis 50 g/l sinnvoll.
• Durch hohere Konzentrationen an Reduktionsmittel lässt sich die Abscheidegeschwindigkeit ebenfalls erhöhen;
• Durch Erhöhung des pH-Wertes lässt sich die Abscheidegeschwindigkeit erhöhen. Bevorzugt stellt man einen pH-Wert zwischen 3 und 6, besonders bevorzugt zwischen 4 und 5,5 ein.
• Zugabe von Aktivatoren wie beispielsweise Alkalifluoriden, beispielsweise NaF oder KF, erhöht die Abscheidegeschwindigkeit.

Deposition rates of 1 to 15 µm / h have been found to be useful. The deposition speed can be influenced as follows by the composition of the immersion baths:

• The deposition rate is increased by higher temperatures, there being a maximum temperature which is limited, for example, by the stability of the optionally added polymer dispersion. The separation speed is reduced by lower temperatures.
• The deposition rate is increased by higher electrolyte concentrations and reduced by lower ones; where concentrations of 1 g / l to 20 g / l Ni ^{2+ are} useful, concentrations of 4 g / l to 10 g / l are preferred; for Cu ²⁺ 1 g / l to 50 g / l are advisable.
• The deposition rate can also be increased by higher concentrations of reducing agent;
• The deposition rate can be increased by increasing the pH. It is preferred to set a pH between 3 and 6, particularly preferably between 4 and 5.5.
• Addition of activators such as alkali fluorides, for example NaF or KF, increases the deposition rate.

The polymer portion of the dispersion coating is mainly by the amount of polymer dispersion added and the choice of detergents. The concentration of the Polymers the bigger role; high polymer concentrations of Immersion baths lead to a disproportionately high proportion of polymer in the metal-phosphor polymer dispersion layer or metal-boron polymer dispersion layer.

It was found that the surfaces treated according to the invention allow good heat transfer, although the coatings have a not inconsiderable thickness of 1 to 100 µm can. 3 to 20 μm, in particular 5 to 16 μm, are preferred. The The polymer content of the dispersion coating is 5 to 30 % By volume, preferably 15 to 25% by volume, 19 being particularly preferred up to 21 vol.%. The surfaces treated according to the invention have excellent durability.

Subsequent to the dipping process, an annealing is preferably carried out at 200 to 400 °, especially at 315 to 380 ° C. The tempering period is generally 5 minutes to 3 hours, preferably 35 to 60 minutes.
Another object of the present invention is a method for producing a coated reactor, which has a particularly adhesive, durable and heat-resistant coating and therefore solves the problem according to the invention in a special way.

This method is characterized in that before application the metal-polymer dispersion layer additionally a 1 to 15 microns, preferably 1 to 5 microns thick metal-phosphor layer is applied by electroless chemical deposition.

Electroless chemical application of a 1 to 15 µm thick metal-phosphor layer to improve adhesion is done by Metal electrolyte baths, but in this case none stabilized Polymer dispersion is added. For tempering is preferably dispensed with at this time, since this is the Adhesion of the subsequent metal-polymer dispersion layer generally adversely affected. After the deposition of the metal-phosphor layer the workpiece is placed in a second immersion bath, which in addition to the metal electrolyte also a stabilized one Includes polymer dispersion. This forms the metal-polymer dispersion layer.

An annealing at 100 to 450 ° C. is then preferably carried out, performed in particular at 315 to 400 ° C. The annealing time is generally 5 minutes to 3 hours, preferably 35 to 45 minutes.

As reactors for the high pressure polymerization of ethylene, as stated at the beginning, high-pressure autoclaves or tubular reactors used, with tubular reactors being preferred. tubular Reactors can be particularly well by a preferred Coating variant of the method according to the invention by the metal electrolyte solution or the metal electrolyte polymer dispersion mixture pumps through the reactor to be coated.

In one embodiment, the tubular reactors served, the coated tubes of the invention without problems in polymerization plants for high pressure polymerization install, replacing uncoated pipes.

The ethylene polymerization in the plants according to the invention, the the pipes according to the invention usually take place at Temperatures from 400 to 6000 bar, preferably from 500 to 5000 bar and particularly preferably 1000 to 3500 bar.

The reaction temperature is 150 to 450 ° C, 160 are preferred up to 250 ° C.

• 1-Olefine wie Propylen, 1-Buten, 1-Penten, 1-Hexen, 1-Octen und 1-Decen,
• Acrylate wie Acrylsäure, Acrylsäuremethylester, Acrylsäureethylester, Acrylsäure-n-butylester oder Acrylsäure-tert.-butylester;
• Metnacrylsäure, Methacrylsäuremethylester, Metnacrylsaureethylester, Methacrylsäure-n-butylester oder Methacrylsäuretert.-butylester;
• Vinylcarboxylate, wobei Vinylacetat besonders bevorzugt ist,
• Ungesättigte Dicarbonsäuren, besonders bevorzugt ist Maleinsäure,
• ungesättigte Dicarbonsäurederivate, besonders bevorzugt sind Maleinsäureanhydrid und Maleinsäurealkylimide wie beispielsweise Maleinsäuremethylimid.

Ethylene is particularly suitable as a monomer in the polymerization process according to the invention. Copolymers with ethylene can also be prepared, in principle all olefins which can be copolymerized with ethylene by free radicals are suitable as comonomers. Are preferred

• 1-olefins such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene and 1-decene,
• Acrylates such as acrylic acid, acrylic acid methyl ester, acrylic acid ethyl ester, acrylic acid n-butyl ester or acrylic acid tert-butyl ester;
• Methacrylic acid, methacrylic acid methyl ester, methacrylic acid ethyl ester, methacrylic acid n-butyl ester or methacrylic acid tert-butyl ester;
• Vinyl carboxylates, with vinyl acetate being particularly preferred,
• Unsaturated dicarboxylic acids, maleic acid is particularly preferred,
• unsaturated dicarboxylic acid derivatives, maleic anhydride and maleic alkylimides such as maleic acid methylimide are particularly preferred.

The molecular weight regulators are hydrogen, aliphatic aldehydes, Ketones, CH-acidic compounds such as mercaptans or alcohols, Suitable for olefins and alkanes.

The polymerization can be carried out with oxygen-containing gases such as for example air can be started, but also with organic Peroxo compounds or with organic azo compounds such as for example AIBN (Azobisisobutyronitrile). Are preferred organic peroxo compounds, with benzoyl peroxide and di-tert.butyl peroxide are particularly preferred.

The polymers of ethylene produced by the process according to the invention can have very different molar masses depending on the reaction conditions. Preferred molar masses M _w are between 500 and 600,000 g.

Particularly advantageous in those produced according to the invention Ethylene polymers are their small number of specks is usually specified in the form of a speck note, a low speck grade is usually a low one Number of specks corresponds. The polymers produced according to the invention are particularly suitable for the production of moldings and sheets, such as foils or bags.

The invention will be explained using a working example.

Working Example: 1. Chemical nickel system

The removed reactor tube (length 150 m, diameter 15 mm) was contacted at a temperature of 88 ° C. with an aqueous nickel salt solution, the solution having the following composition: 27 g / l NiSO ₄ .6 H ₂ O, 21 g / l NaH ₂ PO ₂ .2 H ₂ O, lactic acid CH ₃ CHOHCO ₂ H 20 g / l, propionic acid C ₂ H ₅ CO ₂ H 3 g / l, Na citrate 5 g / l, NaF 1 g / l (note: Chemically electroless nickel electrolyte solutions of this and other concentrations are commercially available, for example from Riedel Galvano- und Filtertechnik GmbH, Halle, Westphalia; or from Atotech Deutschland GmbH, Berlin)). The pH was 4.8. To achieve uniform layer thicknesses, the solution was pumped through the pipe at a flow rate of 0.1 m / s. At a deposition rate of 12 µm / h, the process is finished after 75 min. The layer thickness achieved was 16 µm. The coated tube was then rinsed with water, dried and annealed at 400 ° C. for one hour.

2. Nickel-PTFE system

The production took place in two stages. First, the removed reactor tube (length 150 m, diameter 15 mm) was contacted at a temperature of 88 ° C. with an aqueous nickel salt solution, the solution having the following composition: 27 g / l
NiSO ₄ .6H ₂ O, 21 g / l NaH ₂ PO ₂ .2H ₂ O, 20 g / l lactic acid CH ₃ CHOHCO ₂ H, 3 g / l propionic acid C ₂ H ₅ CO ₂ H, 5 g / l Na -Citrate, 1 g / l NaF. The pH was 4.8. To achieve uniform layer thicknesses, the solution was pumped through the pipe at a flow rate of 0.1 m / s. At a deposition rate of 12 µm / h, 25 min. worked to get the achieved layer thickness of 5 microns.

No rinsing was carried out after this step.

Then the nickel salt solution was also added 1% by volume of a PTFE dispersion with a density of 1.5 g / ml added. This PTFE dispersion contained 50% by weight solids. The process was at a deposition speed of 8 µm / h finished in two hours (layer thickness 16 µm). That coated The tube was rinsed with water, dried and at 350 ° C annealed for an hour.

3. Polymerization Examples 1 to 3

The polymerization was carried out in a total reactor 400 m. A detailed description of the reactor and the Polymerization conditions can be found in DE-A 40 10 271. The reactor was divided into 3 zones; at the beginning of each zone was initiated with peroxide solution. The dimensions of the zones are shown in Table 1.

It was polymerized at a pressure of 3000 bar. As Molecular weight regulator propionaldehyde was used. The Temperature of the cooling medium water was 200 ° C. The maximum Reaction temperatures were - as with high-pressure tube reactors usual - by dosing the appropriate amount of peroxide solution set.

The speck mark was determined by means of an automatic in-line measuring device (Brabender, Duisburg, "Autograder"). For this purpose, a small part of the polymer melt was shaped into a film using an approx. 10 cm wide slot die at 200 ° C., the thickness of which was approx. 0.5 mm. The number of specks was determined using a video camera and an automatic counting device. The number was then classified in the speck grade. Dimensions of the reaction zones of the experimental reactor Zone no. 1 2 3 Length [m] 150 150 100 diameter
[Mm] 15 25 25

In each case only zone number 1 was coated according to the invention and the corresponding experiments were carried out. The results are shown in Table 2. It is expected that coating the other zones will further increase sales. Polymerizations in differently coated reactors Example No. 1 2 3 (comparative example) Coating zone 1 nickel Nickel-PTFE no T _max 1 [° C] 280 280 280 T _min 1 [° C] 223 219 235 T _max 2 [° C] 280 280 280 T _max 3 [° C] 280 278 279 Product density (g / ml) .9229 0.9230 .9225 MFI [g / min] 0.8 0.79 0.8 Sales [%] 27.9 28.3 26.3 fisheye score 2.5 2 3

Claims (16)

1. A process for coating a reactor for the high-pressure polymerization of 1-olefins, which comprises depositing a metal layer or a metal/polymer dispersion layer on the internal surface of the reactor in an electroless manner by bringing the surfaces into contact with a metal electrolyte solution which, besides the metal electrolyte, comprises a reducing agent and optionally a halogenated polymer to be deposited in dispersed form.
2. A process as claimed in claim 1, wherein the metal electrolyte used is a nickel or copper electrolyte solution, and the reducing agent used is a hypophosphite or a borohydride.
3. A process as claimed in claim 1, wherein a dispersion of a halogenated polymer is added to the metal electrolyte solution.
4. A process as claimed in claim 1, wherein the metal electrolyte employed is a nickel salt solution, which is reduced in situ using an alkali metal hypophosphite and to which a polytetrafluoroethylene dispersion is added as halogenated polymer.
5. A process as claimed in claims 1 to 4, wherein a halogenated polymer comprising spherical particles having a mean diameter of from 0.1 to 1.0 µm is used.
6. A process as claimed in claims 1 to 5, wherein a halogenated polymer comprising spherical particles having a mean diameter of from 0.1 to 0.3 µm is used.
7. A process as claimed in claims 1 to 6, wherein a nickel/phosphorus/polytetrafluoroethylene layer having a thickness of from 1 to 100 µm is deposited.
8. A process as claimed in claims 1 to 7, wherein a nickel/phosphorus/polytetrafluoroethylene layer having a thickness of from 3 to 20 µm is deposited.
9. A process as claimed in claims 1 to 8, wherein a nickel/phosphorus/polytetrafluoroethylene layer having a thickness of from 5 to 16 µm is deposited.
10. A process as claimed in claims 1 to 9, wherein firstly an additional metal/phosphorus layer having a thickness of from 1 to 15 µm and then a metal/phosphorus/polymer dispersion layer are deposited on the inside of the reactor in an electroless manner.
11. A process as claimed in claims 1 to 9, wherein the additional metal/phosphorus layer deposited is a nickel/phosphorus layer, a copper/phosphorus layer, a nickel/boron layer or a copper/boron layer having a thickness of from 1 to 5 µm.
12. A reactor coated on the inside, obtainable by a process as claimed in claims 1 to 11.
13. A reactor coated on the inside as claimed in claim 12, in particular a tubular reactor, coated with a metal/phosphorus/polymer dispersion layer having a thickness of from 3 to 20 µm.
14. A reactor as claimed in claims 12 and 13, which carries a nickel/phosphorus layer having a thickness of from 1 to 15 µm below the nickel/phosphorus/polytetrafluoroethylene dispersion layer having a thickness of from 3 to 20 µm.
15. The use of a reactor, in particular a tubular reactor, as claimed in claims 12 to 14 in high-pressure processes for the polymerization or copolymerization of ethylene.
16. A process for the continuous polymerization or copolymerization of ethylene at pressures of from 500 to 6000 bar and temperatures of from 150 to 450°C, which comprises carrying out the polymerization in a high-pressure reactor as claimed in claims 12 to 15.