Catalyst compositions and their use for hydrogenation of nitrile rubber

Abstract

This invention relates to novel catalyst compositions based on ruthenium or osmium carbene-complex catalysts, pref. of the Grubbs-I, -II or -III type or fluorenylidene analogues thereof, and terminal olefins, pref. enol ethers such as ethyl vinyl ether (EVE or VEE) as co-catalysts and to a process for selectively hydrogenating nitrile rubbers in the presence of such catalyst compositions, pref. with a preceding metathesis step using the same complex catalyst as in the hydrogenation step.

Description

FIELD OF THE INVENTION[0001]This invention relates to novel catalyst compositions obtainable from reacting Ruthenium- or Osmium-based complex catalysts with specific co-catalysts and to a process for selectively hydrogenating nitrile rubbers in the presence of such novel catalyst compositions.BACKGROUND OF THE INVENTION[0002]The term “acrylonitrile-butadiene rubber” or “nitrile rubber”, also named as “NBR” for short, shall be interpreted broadly and refers to rubbers which are copolymers or terpolymers of at least one α, β-unsaturated nitrile, at least one conjugated diene and, if desired, one or more further copolymerizable monomers.[0003]Hydrogenated NBR, also referred to as “HNBR” for short, is produced commercially by hydrogenation of NBR. Accordingly, the selective hydrogenation of the carbon-carbon double bonds in the diene-based polymer must be conducted without affecting the nitrile groups and other functional groups (such as carboxyl groups when other copolymerizable monome...

AI Technical Summary

Benefits of technology

[0360]One major advantage of the present invention resides in the fact that the catalyst composition used is very active, so that the catalyst residue in the final HNBR products can be low enough to make the catalyst metal removal or recycle step alleviated or even unnecessary. However, to the extent desired, the catalysts used during the process of the present invention may be removed. Such removal can be performed e.g. by using ion-exchange resins as described in EP-A-2 072 532 A1 and EP-A-2 072 533 A1. The reaction mixture obtained after the completion of the hydrogenation reaction can be taken and treated with an ion-exchange resin at e.g. 100° C. for 48 hours under nitrogen and then be precipitated in cold methanol

[0361]The nitrile rubber used in the process of the present invention is a copolymer or terpolymer of at least one α,β-unsaturated nitrile, at least one conjugated diene and, if desired, one or more further copolymerizable monomers.

[0362]The conjugated diene can be of any nature. Preference is given to using (C4-C6) conjugated dienes. Particular preference is given to 1,3-butadiene, isoprene, 2,3-dimethylbutadiene, piperylene or mixtures thereof. Very particular preference is given to 1,3-butadiene and isoprene or mixtures thereof. Especial preference is given to 1,3-butadiene.

[0363]As α,β-unsaturated nitrile, it is possible to use any known α,β-unsaturated nitrile, preferably a (C3-C5) α,β-unsaturated nitrile such as acrylonitrile, methacrylonitrile, ethacrylonitrile or mixtures thereof. Particular preference is given to acrylonitrile.

[0364]A particularly preferred nitrile rubber used in the process of this invention is thus a copolymer having repeating units derived from acrylonitrile and 1,3-butadiene.

[0365]Apart from the conjugated diene and the α,β-unsaturated nitrile, the hydrogenated nitrile rubber may comprise repeating units of one or more further copolymerizable monomers known in the art, e.g. α,β-unsaturated (preferably mono-unsaturated) monocarboxylic acids, their esters and amides, α,β-unsaturated (preferably mono-unsaturated) dicarboxylic acids, their mono-oder diesters, as well as the respective anhydrides or amides of said α,β-unsaturated dicarboxylic acids.

Problems solved by technology

Such processes suffer from drawbacks such as high prices for the catalyst metals and the cost involved in catalyst metal removal / recycle.

However, they are prone to gel formation and may cause a certain degree of cross-linking during hydrogenation.

Therefore, these types of Os or Ru catalysts cannot be used for NBR metathesis / degradation to produce NBR with reduced molecular weight.

Another problem of the HNBR production is that HNBR with a low Mooney viscosity is difficult to manufacture by the direct hydrogenation of commercially available NBR.

The relatively high Mooney viscosity places restrictions on the processability of HNBR.

Thus, the Mooney viscosity range of marketed HNBR is limited by the lower limit of the Mooney viscosity of the NBR starting material.

Secondly, the molar mass of the NBR feedstock to be used for the hydrogenation cannot be reduced at will since otherwise work-up in the NBR industrial plants available is no longer possible because the rubber becomes too sticky.

However, WO-A-2005 / 080456 does not provide any disclosure or teaching how to influence the two simultaneously occurring reactions, i.e. metathesis and hydrogenation or how to control the activity of the respective catalysts regarding metathesis and hydrogenation.

However, WO-A-2011 / 079799 does not provide any disclosure or teaching how to influence the different catalytic activities of the catalysts for depolymerisation (metathesis) and hydrogenation.

It is accepted that while hydrogenation takes place simultaneously metathesis leads to a degradation of the molecular weight in uncontrolled manner.

However, there is no disclosure at all about polymer degradation via metathesis or hydrogenation of unsaturated polymers.

However, this reference does not deal with hydrogenation processes subsequently to olefin metathesis at all.

It can be seen from the above that:(1) up to now, hydrogenation catalysts which are very active for the selective hydrogenation of nitrile rubbers are known and Rh- and Pd-based catalysts are already used in industrial hydrogenation processes; however, cheaper Ru-based hydrogenation catalysts are still facing the gel formation problem when used for NBR hydrogenation.

However, hitherto there is not a single literature reporting the preparation of hydrogenated nitrile rubber with controlled molecular weight and therefore controllable Mooney viscosity only using one kind of ruthenium- or osmium-based catalyst which is otherwise known for its metathetic activity.

Also, up to now, there is no hydrogenation catalyst which can be used at a very low concentration for NBR hydrogenation to high conversion.

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