Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-04-20
2002-02-26
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...
C526S340400
Reexamination Certificate
active
06350833
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for the suspension polymerization of conjugated dienes in hydrocarbon mixtures, particularly butadiene and/or isoprene, in industrial C
4
hydrocarbon mixtures.
BACKGROUND OF THE INVENTION
Polybutadiene with a high content of cis-1,4 units has long been produced industrially on a large scale, and is used for the production of tires and other rubber products. For this application, polymerization is conducted in a liquid phase using very different catalyst systems in solution.
Polybutadienes with a particularly high content of cis-1,4 units are particularly advantageously produced as described in EP-A-0,111,184. The catalyst system which is disclosed consists of a rare earth carboxylate, an aluminum trialkyl and/or an alkyl-aluminum hydride and an additional Lewis acid.
IT-764 295 discloses the polymerization of butadiene in C
4
fractions which have been freed from isobutanes and which contain 5 to 20% of aromatic compounds in order to improve the solubility of the polybutadiene.
The polymerization of conjugated dienes in solution has the disadvantage that the solution is viscous and the solids concentration is therefore generally limited to 10 to 20% by weight.
It is also known that the polymerization of conjugated dienes can be conducted in the pure liquid monomers without the addition of solvents. In this procedure, however, large amounts of heat have to be dissipated at high conversions. This can only be effected with difficulty on account of the high viscosity of the reaction mixture, and therefore necessitates costly equipment and results in a certain potential hazard.
Polymerization in the gas phase has the decisive disadvantage of a very low conversion which is achieved per pass through the reactor. A corresponding method is described in U.S. Pat. No. 4,994,534.
Suspension polymerization methods could constitute an improvement here. In methods such as these, polymerization is conducted in the presence of a diluent which is insoluble in the resultant polymer. The polymer is produced in finely divided form and is suspended in the diluent. Therefore, in contrast to solution or bulk polymerization methods, suspensions such as these only exhibit a very low viscosity, due to which the dissipation of heat and the flow properties are considerably improved, and high solids concentrations and high productivity is therefore possible.
DE-A1-229,138 discloses a method for the selective polymerization of butadene from C
4
fractions using lithium catalysts. However, average molecular weights of up to 10,000 are achieved, which are extremely low, and moreover, cis-polybutadienes cannot be obtained by means of lithium catalysts.
EP-A 773,243 discloses a process for the polymerization of oc-olefins and optionally of diolefins in suspension. An inert solvent/diluent system is used here, and butadiene is added, for example. The butadiene must be present in its pure form for this purpose.
The butadiene which is required for the production of polybutadiene is produced nowadays in a manner which is costly on an industrial scale, namely by the separation of butadiene from industrial C
4
hydrocarbon mixtures. It would be desirable to dispense with this additional separation step, but industrial C
4
hydrocarbon mixtures often contain undesirable constituents, particularly 1,2-butadiene.
There was, therefore, a continuing need for a method for the polymerization of dienes in hydrocarbon mixtures comprising a volume fraction greater than 80% of C
4
hydrocarbons to form cis-containing polydienes.
SUMMARY OF THE INVENTION
This object is achieved according to the present invention by a method for the suspension polymerization of conjugated dienes in hydrocarbon mixtures comprising a volume fraction greater than 80% of C
4
hydrocarbons, characterized in that polymerization is conducted in the presence of a rare earth compound, of one or more aluminum compounds, and optionally of an additional Lewis acid.
DETAILED DESCRIPTION OF THE INVENTION
Conjugated dienes in the sense of the present invention are 1,3-butadiene and isoprene, in particular.
The hydrocarbon mixtures according to the present invention contain at least 80% by volume of C
4
hydrocarbons, particularly at least 90% by volume of C
4
hydrocarbons, and most particularly, at least 95% by volume of C
4
hydrocarbons.
In the sense of the present invention, the expression “C
4
hydrocarbons” denotes all the saturated, singly- or multiply-unsaturated hydrocarbons comprising 4 C atoms, which are known to one skilled in the art, with the exception of alkynes. Examples of C
4
hydrocarbons according to the present invention include butanes such as n-butane, i-butane and cyclobutane, butenes such as 1-butene, 2-butene and i-butene, and butadienes such as 1,3-butadiene and 1,2-butadiene. One particular advantage of the method described herein is that 1,2-butadiene does not have to be removed as it does in prior art methods. This is not only advantageous economically, but is also advantageous environmentally. For this reason, the C
4
hydrocarbons according to the present invention preferably contain admixed 1,2-butadiene which has not been removed. Alkynes impair the method and should be substantially removed.
C
4
hydrocarbon mixtures of the following composition by volume are preferably used:
1,3-butadiene
30-50%
butene
33-53%
butane
5-15%
1,2-butadiene
0.001-1%
alkynes
0.05%,
balance
0.1-1%
In addition, C
4
hydrocarbon mixtures of the following composition by volume are preferably used as diluents:
1,3-butadiene
0-2%
butene
66-80%
butane
18-33%
1,2-butadiene
0.001-0.4%
alkynes
0
balance
0-0.6%
C
4
hydrocarbon mixtures which are also preferred (C
4
Hydrocarbons and Derivatives: Resources, Production, Marketing, J. Schulze, M. Homann, Springer-Verlag Berlin, 1989, Chapter 1.2-1.4) are those which are known to one skilled in the art as a C
4
cut, raffinate 1 and raffinate 2. These can also, of course, contain 1,2-butadiene in addition.
These industrial C
4
hydrocarbon mixtures preferably originate directly from a steam cracker and after removing the alkynes are used without a further purification or concentration stage.
In addition, pure butane or mixtures of butane and 1,2-butadiene with a content of up to 5% by volume of 1,2-butadiene are also preferably used.
It is obvious to one skilled in the art that the said fractions by volume of the individual components of the C
4
hydrocarbon mixture must add up 100%.
If the C
4
hydrocarbon mixtures, which can be used according to the present invention already contain polymerizable conjugated dienes, these can be used directly in the method according to the present invention without further intermediate steps. The C
4
hydrocarbon mixture then acts both as a diluent and as a source of monomers. However, it is also possible, of course, to admix further conjugated dienes or to increase the concentration of conjugated dienes which are already present. It should be ensured here, however, that the method still constitutes suspension polymerization and does not constitute solution polymerization. Suitable concentrations of monomer or monomers can readily be determined by just a few preliminary tests. The monomer concentrations usually range between 0.1 and 60% by volume, particularly between 5-50 and most particularly 10-40% by volume.
The hydrocarbon mixtures which can be used may contain a volume fraction of up to 20% of higher hydrocarbons. However, it should be ensured that the latter do not have a disadvantageous effect on polymerization. Suitable higher hydrocarbons include linear, branched cyclic hydrocarbons, which may be saturated, unsaturated or aromatic, e.g. C
5
-C
50
alkanes such as n-pentane, i-pentane, cyclopentane, n-hexane, i-hexane, cyclohexane, n-heptane, i-heptane, n-octane, i-octane, nonane, decane or undecane; C
5
-C
50
alkenes such as pentene, cyclopentene, hexene, cyclohexene, heptene, octene, nonene, decene or undecene; non-conjugated, multiply-unsaturated hydrocarbons such as 1,4-pentadiene, hexadiene, cyclohexadie
Knauf Thomas
Osman Akhtar
Schmid Claudia
Sylvester Gerd
Bayer Aktiengesellschaft
Cheung Noland J.
Gil Joseph C.
Wu David W.
LandOfFree
Method for the suspension polymerization of conjugated dienes does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for the suspension polymerization of conjugated dienes, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for the suspension polymerization of conjugated dienes will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2942647