Chemistry of hydrocarbon compounds – Adding hydrogen to unsaturated bond of hydrocarbon – i.e.,... – Hydrocarbon is aromatic
Reexamination Certificate
2001-01-16
2003-01-21
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Adding hydrogen to unsaturated bond of hydrocarbon, i.e.,...
Hydrocarbon is aromatic
C585S269000, C585S270000
Reexamination Certificate
active
06509510
ABSTRACT:
The invention provides a process for hydrogenating aromatic polymers, which is characterised in that Group VIII metals are present together with a support of silicon dioxide or aluminium oxide or mixtures thereof. The catalysts have a specific pore size distribution. This enables the aromatic units of aromatic polymers to be hydrogenated completely, without a significant decrease in molecular weight.
Hydrogenation of aromatic polymers is already known. DE-AS 1 131 885 describes the hydrogenation of polystyrene in the presence of catalysts and solvent. Aliphatic and cycloaliphatic hydrocarbons, ethers, alcohols and aromatic hydrocarbons are mentioned as the solvents. A mixture of cyclohexane and tetrahydrofuran is named as preferable. Silicon dioxide and aluminium oxide catalyst supports are mentioned in a general manner, their physico-chemical structure not, however, being described.
EP-A-322 731 describes the preparation of predominantly syndiotactic polymers based on vinyl cyclohexane, wherein a styrene-based polymer is hydrogenated in the presence of hydrogenation catalysts and solvents. Cycloaliphatic and aromatic hydrocarbons, but not ethers, are mentioned as the solvents.
DE 196 24835 (=EP-A 814 098) for the hydrogenation of polymers with ruthenium or palladium catalysts, in which the active metal is applied to a porous support, describes the hydrogenation of olefinic double bonds of polymers.
The hydrogenation level of aromatic regions is less than 25% and is generally within the range 0 to approximately 7%. The choice of solvents is not critical here.
It is furthermore known (WO 96/34896=U.S. Pat. No. 5,612,422) that in the hydrogenation of aromatic polymers small pore diameters (200-500 Å) and large surface areas (100-500 m
2
/g) of silicon dioxide-supported catalysts result in incomplete hydrogenation and in degradation of the polymer chain. The use of specific silicon dioxide-supported hydrogenation catalysts (WO 96/34896) permits virtually complete hydrogenation with an approximately 20% decrease in molecular weight. The silicon dioxide of the named catalysts has a specific pore size distribution which is characterised in that 98% of the pore volume is defined by pores of a diameter greater than 600 Å. The named catalysts have surface areas of between 14 and 17 m
2
/g and average pore diameters of from 3800 to 3900 Å. The hydrogenation levels achieved on dilute polystyrene solutions in cyclohexane at a concentration of between 1% and 8% maximum are greater than 98% and less than 100%.
The examples described in the named specifications show a decrease in the absolute molecular weight of the hydrogenated polystyrene when polymer concentrations are less than 2%. Decreased molecular weight generally leads to a deterioration in the mechanical properties of a hydrogenated polystyrene.
The Comparative Example according to WO 96/34896 of a commercially available catalyst 5% Rh/Al
2
O
3
(Engelhard Corp., Beachwood, Ohio, USA) yields a 7% hydrogenation level and shows that the activity of the aluminium oxide support is lower than that of the silicon dioxide-supported catalyst.
It has surprisingly now been found that aromatic polymers are hydrogenated completely and with no significant decrease in molecular weight when specific catalysts are used which comprise Group VIII metals together with a support of silicon dioxide, aluminium oxide or a mixture thereof, which are defined in that at least 10%, preferably 15%, of the pore volume is defined by pores of a diameter less than 600 Å, and they have an average pore diameter of 900 Å maximum, a BET surface area of at least 40 m
2
/g and a defined pore size distribution.
The invention provides a process for hydrogenating aromatic polymers in the presence of catalysts, wherein the catalyst is a metal or a mixture of metals from Group VIII of the Periodic Table together with a support of silicon dioxide, aluminium oxide or a mixture thereof, and the catalyst pore volume defined by pores of diameters between 100 and 1000 Å, measured by mercury porosimetry, is generally from 100 to 15%, preferably from 90 to 20% and most particularly preferably 80 to 25%, in particular 70 to 25%, in relation to the total pore volume, measured by mercury porosimetry.
The average pore diameter, determined by mercury porosimetry, is 900 Å maximum.
The mercury method is, however, sufficiently accurate only for pores larger than 60 Å. Pore diameters of less than 600 Å are therefore determined by nitrogen sorption according to Barret, Joyner, Halenda (DIN 66 134).
The catalysts therefore additionally have a 100 to 10%, preferably 80 to 10%, in particular 70 to 15% pore volume, measured by nitrogen sorption, which is defined by pores of diameters of less than 600 Å. The pore volume, measured by nitrogen sorption, relates to the total pore volume, measured by mercury porosimetry.
The average pore diameter and the pore size distribution are determined by mercury porosimetry in accordance with DIN 66 133.
The average pore diameter is generally from 10 to 1000 Å, preferably 50 to 950 Å, most particularly preferably 60 to 900 Å.
Methods for characterising hydrogenation catalysts are described, for example, in WO 96/34896 (=U.S. Pat. No. 5,612,422) and Applied Heterogeneous Catalysis, Institut Francais du Pétrole Publication, pp. 189-237 (1987).
The catalysts consist of Group VIII metals which are present together with a support of silicon dioxide or aluminium oxide or mixtures thereof.
The surface area of the catalyst is determined in accordance with BET (Brunauer, Emmett and Teller) processes by nitrogen adsorption, in accordance with DIN 66 131 and DIN 66 132.
The specific nitrogen surface areas (BET) are generally from 40 to 800 m
2
/g, preferably 50 to 600 m
2
/g.
Group VIII metals, preferably nickel, platinum, ruthenium, rhodium, palladium, in particular platinum, palladium and nickel, are generally used.
The metal content, in relation to the total weight of the catalyst, is generally from 0.01 to 80%, preferably 0.05 to 70%.
The 50% value of the cumulative distribution of particle size is generally from 0.1 &mgr;m to 200 &mgr;m, preferably 1 &mgr;m to 100 &mgr;m, most particularly preferably 3 &mgr;m to 80 &mgr;m, in the batch process.
Conventional solvents for hydrogenation reactions are aliphatic or cycloaliphatic hydrocarbons, aliphatic or cycloaliphatic saturated ethers or mixtures thereof, for example, cyclohexane, methylcyclopentane, methylcyclohexane, ethylcyclohexane, cyclooctanes, cycloheptane, dodecane, dioxane, diethylene glycol dimethyl ether, tetrahydrofuran, isopentane, decahydronaphthalene.
If aliphatic or cycloaliphatic hydrocarbons are used as solvents, they preferably contain water in a quantity of generally from 0.1 ppm to 500 ppm, preferably 0.5 ppm to 200 ppm, most particularly preferably 1 ppm to 150 ppm, in relation to the total solvent.
The process according to the invention generally leads to practically complete hydrogenation of the aromatic units. The hydrogenation level is generally ≧80%, preferably ≧90%, most particularly preferably ≧99% to 100%. The hydrogenation level can be determined by NMR or UV spectroscopy, for example. The process according to the invention results most particularly preferably in hydrogenated aromatic polymers, in particular polyvinyl cyclohexane, wherein the quantity of diads having syndiotactic configuration is greater than 50.1% and less than 74%, in particular from 52 to 70%.
Aromatic polymers which are selected, for example, from among polystyrene optionally substituted in the phenyl ring or on the vinyl group, or copolymers thereof with monomers selected from the group comprising olefins, (meth)acrylates or mixtures thereof, are used as starting materials. Further suitable polymers are aromatic polyethers, in particular polyphenylene oxide, aromatic polycarbonates, aromatic polyesters, aromatic polyamides, polyphenylenes, polyxylylenes, polyphenylene vinylenes, polyphenylene ethylenes, poly
Rechner Johann
Wege Volker
Zirngiebl Eberhard
Bayer Aktiengesellschaft
Gil Joseph C.
Preis Aron
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