EP1144725A2

EP1144725A2 - Method for coating reactors for high pressure polymerisation of 1-olefins

Info

Publication number: EP1144725A2
Application number: EP99965554A
Authority: EP
Inventors: Stephan Hüffer; Andreas Deckers; Wilhelm Weber; Roger Klimesch; Dieter Littmann; Jürgen STURM; Götz LERCH
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1998-12-30
Filing date: 1999-12-24
Publication date: 2001-10-17
Anticipated expiration: 2019-12-24
Also published as: ATE237006T1; WO2000040775A3; CN1636305A; DE59906313D1; ES2204184T3; KR20010100013A; EP1144723B1; WO2000040774A2; US6513581B1; EP1144723A3; KR20010100009A; WO2000040773A2; JP2003511551A; KR20010103724A; US6509103B1; ES2197710T3; WO2000040775A2; DE59903362D1; DE19860526A1; JP2002534605A

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

Process for coating reactors for the high-pressure polymerization of I-01efins

description

The invention relates to a method for coating reactors for the high-pressure polymerization of 1-olefins. Furthermore, this invention relates to reactors and high-pressure reactor systems for the polymerization or copolymerization of 1-olefins, in particular ethylene, containing the reactors coated according to the invention, and to a process for producing ethylene homo- and copolymers in the reactors according to the invention.

The production of homopolymers and copolymers of

High-pressure ethylene is a large-scale industrial process. In this process, pressures above 500 bar and temperatures of 150 ° C and higher are used. The process is generally carried out in high-pressure autoclaves or in tubular reactors. High-pressure autoclaves are known in so-called compact or elongated embodiments. The well-known tubular reactors (Ulimann's Encyclopedia of Technical Chemistry, Volume 19, p. 169 and p. 173 ff (1980), Verlag Chemie Weinheim, Deerfield Beach, Basel) are characterized by simple handling and low maintenance and are different from stirred autoclaves advantageous. The sales achievable in the above mentioned devices are limited.

In order to increase the capacity of the existing equipment, efforts are made to achieve the highest possible sales. However, the limitation is the polymerization temperature and the polymerization pressure, which have a specific upper limit depending on the product type. For low-density LDPE waxes and LDPE polymers, this upper limit is approx. 330 ° C; Above this, spontaneous decomposition of ethylene can occur. Below a temperature of 150 ° C there can be problems with heat dissipation. Furthermore, the pressure loss that occurs is limiting; this pressure loss increases with falling temperature.

Good heat dissipation is crucial for the operation of a tubular reactor for ethylene polymerization. This heat dissipation is preferably carried out by jacket cooling. A cooling medium, generally water, is guided through the so-called cooling circuit. The temperature of the cooling medium is very important. At cooling medium temperatures below 150 ° C, a laminar layer of polyethylene can form, which acts as an insulator and can drastically reduce heat dissipation. If the temperature of the cooling medium is too high selected, the temperature difference between the reaction medium and the cooling medium is too small, which also leads to unsatisfactory heat transfer numbers (see, for example, E. Fitzer, W. Fritz, Chemische Reaktionstechnik, 2nd edition, page 152 ff., 5 Springer Verlag Heidelberg, 1982) .

In practice, however, a slowly flowing layer of polyethylene is observed even at temperatures above 150 ° C, which leads to a reduction in heat dissipation. A method of

10 to hinder this layer consists in the so-called "stimulation". (EP-B 0 567 818, p. 3, line 6 ff.) By periodically lowering the pressure, the flow rate is drastically increased and the laminar layers are removed for a short time. Due to the periodic pressure drop, however, the mean pressure during

15 of the plant, which lowers the density of the ethylene and thus reduces the turnover and molecular weight of the product. In addition, the periodic lowering of pressure causes considerable mechanical stress in the apparatus, which leads to increased repair costs and thus brings economic disadvantages.

20th

The formation of laminar boundary layers in tubular reactors or stirred autoclaves for ethylene polymerization also has disadvantageous consequences for the quality of the ethylene polymers. The material with a significantly longer dwell time in the

25 reactors are usually of high molecular weight, which can be seen macroscopically in the formation of so-called specks. Material containing specks has less good mechanical properties, however, since it forms predetermined cracks in the material at which material failure occurs, and is also disadvantageous in terms of the visual impression.

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Attempts to coat the pipes with PTFE (polytetrafluoroethylene) were unsuccessful. Although PTFE is a heat-resistant material that is incompatible with polyethylene, it also acts as an insulator and deteriorates even in thin layers

35 the heat transfer. Similar problems are also observed in processes which involve the application of monolayer silane layers to the surface to be protected (Polymer Mater. Sei. And Engineering, Proceedings of the ACS Division of Polymeric Materials Science and Engineering (1990), volume 62, pages 259 . to

40 263).

45 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 for the construction of 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 is electrolessly deposited on the inside of the reactor of a reactor for the high-pressure polymerization of ethylene by the surfaces being coated with a metal -electro- lyt solution contacted, which in addition to the metal electrolyte contains a reducing agent and optionally a halogenated polymer to be separated in dispersed form. Furthermore, reactors coated according to the invention for the high-pressure polymerization of ethylene were found. Finally, the reactors according to the invention were used for the high-pressure polymerization of ethylene and a process for the high-pressure polymerization of ethylene was found.

The reactors coated with an anti-adhesive metal coating or metal-polymer dispersion layer enable a significantly improved conversion compared to non-coated reactors.

This inventive solution to the problem is based on a method for electroless chemical deposition of metal layers or metal-polymer dispersion phases, which is known per se (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 high-pressure reactor known per se. The metal layer to be deposited by the method according to the invention comprises an alloy or alloy-like mixed phase composed of a metal and at least one further element. The metal-polymer dispersion phases according to the invention additionally comprise a polymer, in the context of the invention a halogenated polymer, which is present in the metal layer is dispersed. The metal alloy is preferably a metal-boron alloy or a metal-phosphorus alloy with a boron or phosphorus content of 0.5 to 15% by weight.

A particularly preferred embodiment of the coatings according to the invention is a so-called “chemical nickel system”, that is to say phosphorus-containing nickel alloys with a phosphorus content of 0.5 to 15% by weight; particularly preferred are high phosphorus-containing nickel alloys with 5 to 12% by weight.

In contrast to galvanic deposition, chemical or autocatalytic deposition of metal phosphorus or metal boron does not provide the electrons required for this through an external power source, but rather through chemical conversion in the electrolyte itself (oxidation of a reducing agent). The coating is carried out, for example, by immersing the workpiece in a metal electrolyte solution which has been mixed beforehand with a stabilized polymer dispersion.

Commercial or freshly prepared metal electrolyte solutions are usually used as metal electrolyte solutions, 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 Wert, 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, if appropriate, 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. Particularly preferred are solutions which have a pH around 5 and about 27 g / 1 NiS0-6 H ₂ 0 and about 21 g / 1 NaH ₂ Pθ ₂ -H ₂ 0 with a PTFE content of 1 to 25 g / 1 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 - to C ₈ -alkoxy units),

Copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ether, for example perfluorovinyl propyl ether. Poly- tetrafluoroethylene (PTFE) and perfluoroalkoxy polymers (PFA, according to DIN 7728, part 1, Jan. 1988).

Commercially available polytetrafluorethylene dispersions (PTFE dispersions) can preferably be used as the insert form. PTFE dispersions with a solids content of 35 to 60% by weight and an average particle diameter of 0.05 to 1.2 μm, in particular 0.1 to 0.3 μm, are preferably used. Spherical particles are preferably used because the use of spherical particles leads to very homogeneous composite layers. The advantage of using spherical particles is faster layer growth and better, in particular longer, thermal stability of the baths, both of which offer economic advantages. This can be seen particularly clearly in comparison to systems using irregular polymer particles which are obtained by grinding the corresponding polymer. In addition, the dispersions used can be a nonionic detergent (for example polyglycols, alkylphenol ethoxylate or, if appropriate, mixtures of the substances mentioned, 80 to 120 g of neutral detergent per liter) or an ionic detergent (for example alkyl and haloalkylsulfonates, alkylbenzenesulfonates, Alkylphenol ether sulfates, tetraalkylammonium salts or optionally mixtures of the substances mentioned, 15 to 60 g of ionic detergent per liter) to stabilize the dispersion.

Coating is carried out at a slightly elevated temperature which, however, must not be so high that the dispersion is destabilized. Temperatures of 40 to 95 ° C have proven to be suitable. Temperatures of 80 to 91 ° C. are preferred and 88 ° C. is particularly preferred.

Deposition rates of 1 to 15 μm / h have proven 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 / 1 to 20 g / 1 Ni ^{2+ are} useful, concentrations of 4 g / 1 to 10 g / 1 are preferred; for Cu ²⁺ 1 g / 1 to 50 g / 1 are advisable. The deposition rate can also be increased by higher concentrations of reducing agent;

The rate of separation 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.

The addition of activators such as alkali fluorides, for example NaF or KF, increases the rate of separation.

The polymer content of the dispersion coating is mainly influenced by the amount of polymer dispersion added and the choice of detergents. The concentration of the polymer plays the greater role here; high polymer concentrations of

Immersion baths lead to a disproportionately high proportion of polymer in the metal-phosphorus-polymer dispersion layer or metal-boron-polymer dispersion layer.

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

An annealing at 200 to 400 ° C., especially at 315 to 380 ° C., is preferably carried out after the dipping process. 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 achieves the object of the invention in a special way.

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

The electroless chemical application of a 1 to 15 μm thick metal-phosphor layer to improve the adhesion is again carried out using metal electrolyte baths, to which, however, no stabilized polymer dispersion is added in this case. For tempering is preferably dispensed with at this time, since this generally has a negative effect on the adhesiveness of the subsequent metal-polymer dispersion layer. After the metal-phosphor layer has been deposited, the workpiece is placed in a second immersion bath which, in addition to the metal electrolyte, also comprises a stabilized polymer dispersion. This forms the metal-polymer dispersion layer.

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

As stated above, high-pressure autoclaves or tubular reactors are used as reactors for the high-pressure polymerization of ethylene, tubular reactors being preferred. Tubular reactors can be coated particularly well by a preferred variant of the process according to the invention, by pumping the metal-electrolyte solution or the metal-electrolyte-polymer dispersion mixture through the reactor to be coated.

In the case of an embodiment which uses tubular reactors, the coated tubes according to the invention can be easily installed in polymerization plants for high-pressure polymerization and non-coated tubes can be replaced in the process.

The ethylene polymerization in the plants according to the invention, which contain the tubes according to the invention, usually takes 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, preferably 160 to 250 ° C.

Ethylene is particularly suitable as a monomer in the polymerization process according to the invention. It is also possible to prepare copolymers with ethylene, 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, methyl methacrylate, methacrylic acid n-butyl ester or methacrylic acid ester. -butyl ester;

Vinyl carboxylates, 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.

Hydrogen, aliphatic aldehydes, ketones, CH-acidic compounds such as mercaptans or alcohols, olefins and alkanes are suitable as molecular weight regulators.

The polymerization can be started with oxygen-containing gases such as air, but also with organic peroxo compounds or with organic azo compounds such as AIBN (azobisisobutyronitrile). Organic peroxo compounds are preferred, with benzoyl peroxide and di-tert-butyl peroxide being 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.

The low number of specks, which is usually specified in the form of a speck grade, is particularly advantageous in the ethylene polymers prepared according to the invention, a low speck grade usually corresponding to a low number of specks. The polymers produced according to the invention are particularly suitable for the production of moldings and flat structures, such as films 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 Nikkeisalzlösung, the solution the following Composition had: 27 g / 1 NiS0 ₄ -6 H ₂ 0, 21 g / 1 NaH ₂ P0-2 H ₂ 0, lactic acid CH ₃ CHOHC0 ₂ H 20 g / 1, propionic acid C ₂ H ₅ C0 ₂ H 3 g / 1, Na citrate 5 g / 1, NaF 1 g / 1 (Note: 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 speed 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.

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 / 1

NiS0 ₄ -6 H ₂ 0, 21 g / 1 NaH ₂ P0 ₂ -2H ₂ 0, 20 g / 1 lactic acid CH ₃ CH0HC0 ₂ H, 3 g / 1 propionic acid C ₂ H ₅ C0 ₂ H, 5 g / 1 Na -Citrate, 1 g / 1 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.

After this step it was not rinsed

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

Polymerization Examples 1 to 3

The polymerization was carried out in a reactor of 400 m in total. 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. Propionaldehyde was used as the molecular weight regulator. The temperature of the cooling medium water was 200 ° C. The maximum reaction temperatures were set, as is customary in high-pressure tube reactors, by metering in the appropriate amount of peroxide solution.

The speck mark was determined using an automatic in-line measuring device (Brabender, Duisburg, "Autographers"). 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.

Table 1: Dimensions of the reaction zones of the experimental reactor

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 to be expected that coating the other zones will lead to a further increase in sales.

Table 2: Polymerizations in differently coated reactors.

Claims

claims

1. A method for coating a reactor for the high-pressure polymerization of I-01efinen, characterized in that a metal layer or a metal-polymer dispersion layer is electrolessly deposited on the inner surface of the reactor by contacting the surfaces with a metal electrolyte solution, which in addition the metal electrolyte contains a reducing agent and optionally a halogenated polymer to be deposited in dispersed form.

2. The method according to claim 1, characterized in that a nickel or copper electrolyte solution is used as the metal electrolyte and a hypophosphite or a boronate is used as the reducing agent.

3. The method according to claim 1, characterized in that a dispersion of a halogenated polymer is added to the metal electrolyte solution.

4. The method according to claim 1, characterized in that a nickel salt solution is used as the metal electrolyte, which is reduced in situ with an alkali metal hypophosphite, and which is added as a halogenated polymer, a polytetrafluoroethylene dispersion.

5. The method according to claim 1 to 4, characterized in that one uses a halogenated polymer made of spherical particles with an average diameter of 0.1 to 1.0 microns.

6. The method according to claim 1 to 5, characterized in that one uses a halogenated polymer made of spherical particles with an average diameter of 0.1 to 0.3 microns.

7. The method according to claims 1 to 6, characterized in that a nickel-phosphorus-polytetrafluoroethylene layer is deposited with a thickness of 1 to 100 microns.

8. The method according to claims 1 to 7, characterized in that a nickel-phosphorus-polytetrafluoroethylene layer is deposited with a thickness of 3 to 20 microns.

9. The method according to claims 1 to 8, characterized in that a nickel-phosphorus-polytetrafluoroethylene layer is deposited with a thickness of 5 to 16 µm.

10. The method according to claims 1 to 9, characterized in that first an electroless 1 to 15 μm thick metal-phosphor layer on the inside of the reactor and then a metal-phosphor polymer dispersion.

5 layer deposits.

11. The method according to claim 1 to 9, characterized in that as an additional metal-phosphor layer, a nickel-phosphor layer, a copper-phosphor layer, a nickel-boron

10 layer or a copper-boron layer with a thickness of 1 to 5 microns.

12. Reactor coated on the inside, obtainable by a process of claims 1 to 11.

15

13. On the inside coated reactor according to claim 12, in particular tubular reactor, coated with a metal-phosphor polymer dispersion layer with a thickness of 3 to 20 microns.

20th

14. Reactor according to claims 12 and 13, under the nickel-phosphorus-polytetrafluoroethylene dispersion layer with a thickness of 3 to 20 μm carries a nickel-phosphorus layer with a thickness of 1 to 15 μm.

25

15. Use of reactors, in particular tubular reactors, according to 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 500 to 6000 bar and temperatures of up to 150 to 450 ° C, characterized in that the polymerization is carried out in a high-pressure reactor as claimed in claims 12 to 15.

35

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