Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-07-14
2002-06-04
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S087000, C526S901000
Reexamination Certificate
active
06399720
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the avoidance of instability during the gas phase polymerization of rubber when using low volatility monomers, characterized in that the low volatility monomers are fed into the fluidized bed reactor supported on a particulate material.
BACKGROUND OF THE INVENTION
The gas phase polymerization of polyolefins is a process which has long been known and was first implemented on a large industrial scale as long ago as 1968 (
Ullmanns Enzyklopädie der technischen Chemie
, 4th edition 1980, volume 19, pp. 186 et seq.).
In this process, the actual polymerization-reaction proceeds in a fluidized bed reactor which consists of a reaction zone and an equalizing zone thereabove, in which the solid particles are largely separated from the gas phase. The monomers, additives and the catalyst are introduced into the reaction zone. A recirculating gas stream is also introduced into the reactor, likewise from beneath, in order maintain an adequate fluidized bed. This recirculating gas stream, which substantially consists of unreacted monomers, is drawn off again from the top of the reactor, residual particles are removed, the gas cooled and recirculated into the reactor. The resultant polymer is continuously or semi-continuously drawn off from the reaction zone and further processed.
One of the greatest problems in gas phase polymerization is feeding low volatility monomers in liquid form. One the one hand, a homogeneous distribution may be achieved only with difficulty, which gives rise to unwanted non-uniformities in the products, and, on the other, the fluidized bed is susceptible to disruption by the introduction of the liquid. The growing polymer particles swell on addition of the liquid monomer, which results in agglomeration and agglutination which, at worst, may require the reactor to be shut down.
Numerous publications address feeding liquid monomers into the polymerization reactor: DE-A-2357848 describes the injection of volatile liquids into a reactor with the assistance of swing check valves. EP-A-780404, EP-B-241947 and EP-B-089691 describe various methods for introducing a gas/liquid mixture into a gas phase reactor. EP-A-697421, WO-96/4322 and WO-96/4321 describe various methods for introducing a gas/liquid mixture into a gas phase reactor which is operated at below the dew point of at least one of the constituents of the mixture. WO-94/28032 describes the introduction of volatile liquids into a gas phase reactor in order to raise the space-time yield. WO-94/25497 and WO-94/25495 describe various methods for introducing volatile liquids into a gas phase reactor in order to raise the space-time yield depending upon the apparent density of the fluidized bed.
The literature also describes the addition of inert support materials or also separating agents.
EP-A-0 422 452, for example, discloses performing the polymerization reaction in the presence of 0.3-80 wt. % of an inert material, which has an average particle diameter of 0.01 to 10 &mgr;m.
EP-A-0 530 709 discloses a process for the production of tacky polymers, in which the polymerization reaction is performed in the presence of 0.3-80 wt. % of an inert material, which has an average particle diameter of 0.01 to 150 &mgr;m.
EP-A-0 266 074 proposes performing the polymerization reaction merely in the presence of 0.005 to 0.2 wt. % of an inert pulverized material. Using this method, it is possible to select polymerization temperatures which are close to the softening temperature of the polymer to be produced.
U.S. Pat. No. 5,162,463, in contrast, teaches that agglomeration of tacky particles in a fluidized bed may be avoided by introducing an inert material coated with a polysiloxane layer into the fluidized bed.
Finally, WO-97/08211 describes the addition of stabilizers in supported form.
In all the processes described, the slightest deviations from the optimum feed rate of the monomers may cause disruption of the fluidized bed, which may, at worst, result in a reactor shut-down.
SUMMARY OF THE INVENTION
The object arises of providing a process for the avoidance of instability during the gas phase polymerization of rubber when feeding low volatility monomers, which process does not exhibit the disadvantages of the prior art.
The object is achieved according to the invention by the provision of a process in which the low volatility monomers are fed into the fluidized bed reactor supported on a particulate material.
It was completely unexpected for the person skilled in the art that using the supported monomers according to the invention should minimize the effects of low volatility monomers on the stability of the fluidized bed. The person skilled in the art would furthermore not expect that polymerization output (kg of product/h) would not be affected or would even be further raised by using the supported monomers according to the invention.
DETAILED DESCRIPTION
The supported monomers according to the invention may be used in any, preferably continuous, gas phase polymerization in which, in particular, low volatility monomers are used.
Suitable monomers are, for example, 1,3-butadiene, isoprene, styrene, 2-chlorobutadiene, 5-ethylidene-2-norbornene (ENB), 1,4-hexadiene, dicyclopentadiene, vinyl norbornene, norbornadiene, acrylonitrile, malonic acid esters, vinyl acetate, acrylic acid esters, methacrylic acid esters, as well as further olefins, dienes or trienes.
The supported monomers according to the invention may be used in combination with further gaseous monomers and/or only with inert gases, such as for example nitrogen, argon, krypton.
The supported monomers according to the invention may be used in combination with any desired fluidized bed reactor. Preferably, however, a fluidized bed reactor in particular for the gas phase production of rubber is used, the lower portion of the wall of which is of a cylindrical shape which subsequently develops into a continuously opening cone, wherein the angle of the cone, relative to the central axis, is 2-10° and the fluidized bed is higher than the cylindrical portion.
The supported monomers are preferably both added and stored under an inert gas blanket.
Suitable inorganic supports are in particular silica gels, precipitated silicas, clays, aluminosilicates, talcum, zeolites, carbon black, inorganic oxides, such as silicon dioxide, aluminum oxide, magnesium oxide, titanium dioxide, silicon carbide. Silica gels, precipitated silicas, zeolites and carbon black are preferred, with precipitated silicas and carbon black being particularly preferred. Inert in this case is taken to mean that the solids are of a nature such that or are pretreated by a pretreatment, such as for example calcination, in such a manner that the reactive surface does not prevent the formation of an active catalyst, or does not react with the monomers.
The stated inorganic solids which meet the above-stated specification and are thus suitable for use are described in greater detail, for example, in
Ullmanns Enzyklopädie der technischen Chemie
, volume 21, pp. 439 et seq. (silica gels), volume 23, pp. 311 et seq. (clays), volume 14, pp. 633 et seq. (carbon blacks), volume 24, pp. 575 et seq. and volume 17, pp. 9 et seq. (zeolites).
The inorganic solids may be used individually or as a mixture with each other.
Suitable organic solids also comprise polymeric materials, preferably in the form of free flowing powders, which are of a nature such that or are pretreated by pretreatment, such as for example drying, in such a manner that the reactive surface does not prevent the formation of an active catalyst or does not react with the monomers and have a grain size in the range from 10 to 1000 &mgr;m and a pore volume in the range from 0.3 to 15 ml/g. One example of such a material is pulverulent polypropylene.
The materials usable as supports according to the invention are preferably inert with regard to the polymerization reaction. Particulate, inorganic or organic solids are used which have a specific surface area of greater than 10, preferably of 1
Dauben Michael
Nentwig Wolfgang
Schneider Jürgen M.
Bayer Aktiengesellschaft
Cheung Noland J.
Cheung William K
Gil Joseph C.
Wu David W.
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