Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-10-21
2002-06-11
Wu, David W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S226000, C526S348200, C526S348500, C526S348600, C526S348700
Reexamination Certificate
active
06403747
ABSTRACT:
FIELD OF THE INVENTION
In one of its aspects, the present invention relates to an improved, catalytic, solution process for preparing butyl rubber polymers. More particularly, the present invention relates to such a process for preparing butyl rubber polymers with good isobutylene conversions, such polymers having weight average molecular weights of greater than 400,000 at polymerization temperatures of −100° C. to +50° C. in a readily controlled process enabling the use of low cost, inert, aliphatic hydrocarbon solvents.
BACKGROUND OF THE INVENTION
Almost all world production of butyl rubber utilizes methyl chloride as a diluent. Methyl chloride is not an ozone depleter and only a very small fraction of it occurring in the environment is the result of industrial processes. However, exposure to methyl chloride can cause injury to liver, kidneys and the central nervous system. The growing health concerns regarding methyl chloride stimulated the search for an alternative reaction medium in the process of manufacturing butyl rubber.
A process for manufacturing butyl rubber in a hydrocarbon solvent (e.g., hexane) is also useful in the preparation of halobutyl rubber since it eliminates the dissolving step and thus simplifies the whole halobutyl process.
Conventional prior art processes for preparing butyl rubber polymers in solution (solution butyl processes) chiefly employ aluminum trihalide catalyst systems, viz, those using aluminum trichioride, or aluminum tribrommide alone. For example see U.S. Pat. Nos. 2,844,569 and 2,772,255. These prior art procedures are not wholly satisfactory because they are performed at very low temperatures, e.g. −90° C. to −110° C. leading to high refrigeration costs during polymerization. At such low temperatures, polymer solutions have a very high viscosity and are difficult to handle. In addition, a high viscosity of a polymer solution causes a very low rate of heat transfer, and also poor and difficult catalyst dispersion.
Aluminum trichloride has the disadvantage of little or no solubility in many desirable hydrocarbon systems and is often introduced to the reaction feed as a solution in methyl chloride. Although aluminum tribromide is soluble in hydrocarbons, the use thereof can cause the undersirable formation of substantial amounts of very high molecular weight fractions—see U.S. Pat. No. 2,772,255 [Ernst et. al.].
Alkylaluminum dihalides are generally less reactive than the aluminum halides but offer the advantage of excellent hydrocarbon solubility. To enhance their reactivity, they are frequently used together with cocatalysts.
Canadian patent 1,019,095 [Scherbakova et al. (Scherbakova)] teaches an industrial process for manufacturing butyl rubber in solution. The catalyst system used in the process comprises an alkylaluminum halide (e.g., ethylaluminum sesquichloride ((C
2
H
5
)
2
AlCl.Cl
2
AlC
2
H,)), with water or hydrogen sulfide as a co-catalyst, and isopentane as a solvent. Not many details are known about the process, which most probably takes place at −85° C. to −80° C., with a content of solids in solution at about 10 weight percent. Some of the drawbacks of this method are listed below.
A direct reaction between water and the Lewis acid is not possible due to a violent nature of this reaction and a substantial amount of water used per alkylaluminum halide. Hence, preparation of the catalyst species is a cumbersome step in the whole process and it can take several hours. Two ways of performing this are taught in Scherbakova.
One approach to prepare the catalyst is to introduce water into the solution of the alkylaluminum halide in a hydrocarbon solvent together with an inert gas which is circulated in the system “alkylaluminum halide solution—water” and is continuously saturated with water.
The alternative method is to introduce water into the solution of the alkylaluminum halide in a hydrocarbon solvent as part of crystal hydrates of mineral salts, e.g., CuSO
4
.5H
2
O. The reactions are then not as violent than when water is introduced directly.
In the hydrolysis reactions higher alkylaluminoxanes are formed, which are filtered out and the clear solution is used to initiate the polymerizations. This represents an additional complicating step in the whole procedure to prepare the active initiating species.
A disadvantage of the both above catalyst preparation methods, beside long duration, is that the activity of the catalyst changes with time as the hydrolysis progresses. This requires the use of analytical methods to monitor the progress of the hydrolysis. This is not a simple task since alkylaluminum compounds require a special careful analytical treatment.
U.S. Pat. No. 3,361,725 [Parker et al. (Parker)] teaches that mixtures of dialkylaluminum halides, e.g., dialkylaluminum chlorides, and monoalkylaluminum dihalides, e.g., monoalkylaluminum dichlorides (in which a latter component is present in small amounts) are effective solution butyl rubber catalysts, operate at the far more economical (higher) temperatures and form excellent high molecular weight rubbers. Usually, the butyl rubber polymerizations using the above catalyst mixtures are conducted at temperatures ranging from about −87° C. to −57° C., and preferably at temperatures of −79° C. to −68° C., with excellent results being achieved with temperatures at or near −73° C. at approximately atmospheric pressure.
The polymers are soluble in the unreacted monomers as well, so that relatively minor amounts of diluent can be used. Reasonably small quantities of diluent can be employed—e.g., from 0 to 50 vol. percent diluent based on total volume of monomer and saturated catalyst solvent. Usually, however, the concentration of diluent during polymerization ranges from 0 to 20 vol. percent. The ability to use small concentrations of diluent during polymerization constitutes an economic advantage. The diluents usually employed to conduct the solution butyl polymerization reactions are C
5
to C
6
normal, iso, and cyclo paraffinic hydrocarbons which are liquids at the reaction temperatures and pressures employed. Preferably the C
5
and C
6
normal paraffins are used—e.g., n-pentane and n-hexane.
The catalyst mixture consists of from about 2 to about 10 mole percent of the monoalkylaluminum dihalide and from about 90 to 98 mole percent of the dialkylaluminum monohalide. This facilitates achievement of the most advantageous combination of ease of polymerization coupled with catalyst efficiency and good temperature control over the polymerization reaction. This latter characteristic is a significant advantage of the method. On the other hand, the reaction times require from about 50 to 100 minutes within the preferred temperature range.
It would be useful to have a method allowing good temperature control to be maintained during polymerizations but with higher reaction rates and higher molecular weight rubber formed than with the use of the catalyst taught by Parker. This should make it possible to carry out polymerizations even at more economical (higher) temperatures than with the method taught by Parker, with the rubber still displaying desirable properties.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide an improved method to manufacture solution butyl rubber.
Accordingly, the present process provides a process for preparing a butyl polymer having a weight average molecular weight of at least about 400,000, the process comprising the step of:
contacting a C
4
to C
8
monoolefin monomers with a C
4
to C
14
multiolefin monomer at a temperature in the range of from about −100° C. to about +50° C. in the presence of an aliphatic hydrocarbon diluent and a catalyst mixture comprising a major amount of a dialkylalumium halide, a minor amount of a monoalkylaluminum dihalide, and a minute amount of at least one of a member selected from the group comprising water, aluminoxane and mixtures thereof.
More specifically, the present invention is dir
Bayer Inc.
Cheung Noland J.
Cheung William K
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