Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in two or more physically distinct zones
Reexamination Certificate
2002-02-01
2003-02-18
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in two or more physically distinct zones
C526S335000, C526S346000, C526S329200
Reexamination Certificate
active
06521720
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a continuous process for producing elastomers based on conjugated dienes or based on conjugated dienes and vinyl aromatic compounds or based on alkenes, polymerization being carried out while maintaining certain residence times of the monomers used and the elastomers obtained in the reactors.
BACKGROUND OF THE INVENTION
It is known to carry out the polymerization of conjugated dienes or of conjugated dienes and vinyl aromatic compounds or of alkenes in the presence of, for example, Ziegler-Natta catalysts or in the presence of anionic initiators.
It is also known and customary in practice to carry out polymerization in one or more reactors, the catalysts and the monomers used, optionally distributed over the various reactors used, being metered into the polymerization mixture. If a plurality of reactors is used, it is customary in the known process for the residence time of the monomers used and the elastomers obtained to be longer in the remaining reactors than in the first reactor.
However, it has proven to be disadvantageous in the processes for producing elastomers based on the above-mentioned monomers carried out to date that there is gelling of the reactors during prolonged operation thereof, so the reactors have to be cleaned frequently and therefore have a short service life. Furthermore, the catalyst consumption in polymerization reactions carried out in this way is relatively high and this adversely affects. the economic viability of the process. The product quality obtained by the previous processes is also capable of improvement, in particular as regards the gel content, and, when using chlorine-containing catalysts, the chlorine content, the metal ion content, the ash content and, optionally, the cis-1,4 compound content in the polymer.
SUMMARY OF THE INVENTION
The object of the present invention is therefore, inter alia, to improve the economic viability of the previous processes for producing diene polymers as well as the product quality of the polymers obtained.
It has now been found that, with the process according to the invention, the disadvantages described can be avoided and this can be combined with an increase in the economic viability or productivity and the product quality.
The subject of the present invention is, therefore, a continuous process for producing elastomers based on conjugated dienes or based on conjugated dienes and vinyl aromatic compounds or based on alkenes, characterized in that polymerization is carried out in the presence of an inert solvent and in the presence of polymerization catalysts in at least two reactors connected in series, the residence time of the monomers used and the elastomers formed in the first reactor being adjusted such that the residence time of the monomers used and the elastomers formed in the first reactor to the residence time of the monomers used and the elastomers formed in the remaining reactors is in the range of 1:1 to 4:1, the temperature gradient in the first reactor being ≦25° C. and the temperature in the individual reactors during polymerization being in the range of 0 to 140° C.
DETAILED DESCRIPTION OF THE INVENTION
The residence time of the monomers used and the elastomers formed in the first reactor is preferably adjusted such that the residence time of the monomers used and the elastomers formed in the first reactor to the residence time of the monomers used and the elastomers formed in the remaining reactors is in the range of 1:1 to 3:1, preferably, in the range of 1.1:1 to 2.5:1, and more preferably in the range of 1.2:1 to 2:1. In the event of two or more reactors being connected in series, it is important for the entire residence time ratio, that the residence time of the monomers and elastomers in the remaining reactors—meaning the reactors which are connected downstream of the first reactor—is divided such that the claimed ratio always results. Therefore, distribution of the respective residence times in the remaining reactors can be arbitrarily selected, it being possible for the most favorable distribution to be easily ascertained by appropriate preliminary tests. The type of reactors used, the type of catalysts and monomers used inter alia play a role in the distribution of the residence times.
Of course, it is possible in the process according to the invention to distribute the residence time of the monomers used and the elastomers formed among a plurality of reactors connected in parallel instead of to a first reactor, which reactors are then to be considered as a first reactor. For example, instead of a first reactor, two or three reactors can be connected in parallel and therefore function as a first reactor. It is important for the process according to the invention that, in addition to the first reactor or the first reactors, additional reactors are also used which are then connected in series. The number of reactors connected in series is dependent inter alia on economic considerations relating to the process and can amount to 2 to 10, preferably 2 to 7, more preferably 2 to 3, additional reactors.
In addition to the residence time ratio of the monomers used and the elastomers formed in the individual reactors, it is important for the process according to the present invention that the temperature gradient in the first reactor or the first reactors connected in parallel is ≦25° C., preferably ≦15° C., and more preferably ≦10° C. In this case, the temperature gradient is taken to mean the temperature difference in the first reactor resulting from the measurement of the temperature at the inlet of the monomers used and at the outlet of the product stream issuing from the first reactor or the first reactors, which essentially contains solvent, elastomers formed and monomers used.
The temperature during polymerization in the individual reactors is preferably in the range of 10 to 130° C., more preferably 20 to 120° C.
In the process according to the present invention, the polymerization reactors known for this purpose can be used as reactors. Preferably, stirred-tank reactors are used.
The process according to the present invention is carried out in the inert organic solvents known for this process, examples being butanes, butenes, pentanes, hexanes, heptanes, methylcylcopentane or cyclohexane. Both the straight-chain and the branched isomers of aliphatic solvents are examples thereof. Furthermore, aromatic solvents such as benzene, toluene or ethylbenzene can also be used. The solvents can be used both individually or mixed with one another.
The quantity of solvent used is not critical. The most favorable quantity can be ascertained by appropriate preliminary tests and depends inter alia on economic considerations.
All known dienes which are conventional in the production of corresponding elastomers can be used in the process according to the present invention as conjugated dienes. Examples are: 1,3-butadiene, isoprene, piperylene, 1,3-hexadiene, 1,3-octadiene and 2-phenyl-1,3-butadiene, preferably 1,3-butadiene and isoprene.
The known vinyl aromatic compounds which can be copolymerized together with the conjugated dienes are also examples of vinyl aromatic compounds. Examples include styrene, p-methylstyrene, &agr;-methylstyrene, 3,5-dimethylstirene, vinyinaphthalene, p-tert.-butylstyrene, divinylstyrene and diphenylethylene, preferably styrene.
The quantity of vinyl aromatic compounds used is conventionally 5 to 55 wt. %, preferably 10 to 45 wt. %, and the quantity of conjugated dienes used corresponds to 45 to 95 wt. %, preferably 55 to 90 wt. % in the copolymerization of the above-mentioned conjugated dienes with the above-mentioned vinyl aromatic compounds.
Furthermore, alkenes such as ethylene and propylene, can be used in the process according to the present invention to form the elastomers. These may optionally be reacted in a known manner with non-conjugated polyenes, such as ethylenenorbornene, vinylidenenorbornene, dicyclopentadiene, 2-methyl-1,5-hexadiene, 3,3-dimethyl-1,5-hexadiene, 1,6-heptadiene, 1,
Knauf Thomas
Naunheim Josef-Werner
Wiemann Klaus
Bayer Aktiengesellschaft
Cheung Noland J.
Cheung William K
Seng Jennifer R.
Wu David W.
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