Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-01-16
2002-07-16
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S330300, C525S330900, C525S333300, C525S339000, C525S390000, C525S396000, C525S397000, C525S419000, C525S437000, C525S442000, C525S534000, C525S535000, C525S537000
Reexamination Certificate
active
06420491
ABSTRACT:
The invention relates to a process for the hydrogenation of aromatic polymers, which is characterized in that metals of sub-group VIII are present together with a support of silicon dioxide or aluminium oxide or mixtures thereof. The catalysts have a pore size distribution which is characterized in that the pore volume between 100 and 1,000 Å is less than 15%. The process is carried out in the presence of an oxygen-containing hydrocarbon which accelerates the reaction, and hydrogenates aromatic polymers completely with respect to their aromatic units and without significant degradation of the molecular weights.
The hydrogenation of aromatic polymers is already known. DE-AS 1 131 885 describes the hydrogenation of polystyrene in the presence of catalysts and solvents. Aliphatic and cycloaliphatic hydrocarbons, ethers, alcohols and aromatic hydrocarbons are mentioned as solvents. A mixture of cyclohexane and tetrahydrofuran is mentioned as preferred. Silicon dioxide and aluminium oxide supports of the catalysts are mentioned generally, but their physico-chemical structure is not described.
EP-A-322 731 describes the preparation of chiefly syndiotactic polymers based on vinylcyclohexane, a styrene-based polymer being hydrogenated in the presence of hydrogenation catalysts and solvents. Cycloaliphatic and aromatic hydrocarbons, but not ethers, are mentioned as solvents.
The ruthenium or palladium catalysts described in DE-OS 196 24835 (=EP-A 814 098) for the hydrogenation of polymers, in which the active metal is applied to a porous support, catalyse the hydrogenation of olefinic double bonds of polymers.
It is furthermore known (WO 96/34896=U.S. Pat. No. 5,612,422) that small pore diameters (200-500 Å) and large surface areas (100-500 m
2
/g) of catalysts assisted by silicon dioxide lead to incomplete hydrogenation and to degradation of the polymer chain in the hydrogenation of aromatic polymers. The use of specific hydrogenation catalysts assisted by silicon dioxide (WO 96/34896) allows an almost complete hydrogenation with approx. 20% degradation of the molecular weights. The catalysts mentioned have a specific pore size distribution of the silicon dioxide, which is characterized in that 98% of the pore volume has a pore diameter greater than 600 Å. The catalysts mentioned have surface areas of between 14 and 17 m
2
/g and an average pore diameter of 3,800-3,900 Å. Dilute polystyrene solutions in cyclohexane (polymer concentration between 1% and a maximum of 8%) are hydrogenated to degrees of hydrogenation of greater than 98% and less than 100%.
The examples described in the publications mentioned show a degradation of the absolute molecular weights of the hydrogenated polystyrene at polymer concentrations of less than 2%. Generally, molecular weight degradation leads to a deterioration of the mechanical properties of a hydrogenated polystyrene.
The comparison example according to WO 96/34896 of a commercially available catalyst of 5% Rh/Al
2
O
3
(Engelhard Corp., Beachwood, Ohio, USA) leads to a degree of hydrogenation of 7% and shows a lower activity of the aluminium oxide support compared with the catalyst assisted by silicon dioxide.
Surprisingly, it has now been found that if commercially available standard hydrogenation catalysts for low molecular weight compounds which comprise metals of sub-group VIII, together with a support of silicon dioxide, aluminium oxide or a mixture thereof, and which are defined in that the pore volume between 100 and 1,000 Å is less than 15% are used in the presence of an oxygen-containing hydrocarbon, aromatic polymers hydrogenate completely and without a significant degradation of the molecular weights.
The process is distinguished by the fact that no noticeable degradation of the end product occurs, in particular also at high polymer concentrations (e.g. >20%). Furthermore, on addition of oxygen-containing hydrocarbons, an increase in the activity of the catalyst is to be observed, which manifests itself by lower reaction temperatures at shorter reaction times for complete hydrogenation (example 2, 3). The addition of this oxygen-containing hydrocarbon allows higher polymer-catalyst ratios for complete hydrogenation than the use of purely aliphatic systems. The reactions can be carried out under identical conditions at lower pressures for complete hydrogenation.
The invention provides a process for the hydrogenation of aromatic polymers in the presence of catalysts and in the presence of an oxygen-containing hydrocarbon, wherein the catalyst is a metal or mixture of metals of sub-group VIII of the periodic table together with a support of silicon dioxide, aluminium oxide or a mixture thereof and the pore volume of the pore diameter of the catalyst between 100 and 1,000 Å, measured by mercury porosimetry, is less than 15% (preferably 2 to 12%), based on the total pore volume, measured by mercury porosimetry. The average pore diameter, determined by mercury porosimetry, is not more than 900 Å.
However, the mercury method is only sufficiently accurate for pores which are greater than 60 Å. Pore diameters of less than 600 Å are therefore determined by nitrogen absorption, the process according to Barrett, Joyner and Halenda, according to DIN 66 134.
The catalysts additionally have a pore volume, measured by nitrogen absorption, of 100 to 10%, preferably 80 to 10%, in particular 70 to 15% for pore diameters of <600 Å. The pore volume, measured by nitrogen absorption, is based on 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 66133.
The catalysts comprise metals of sub-group VIII, which are present together with a support of silicon dioxide or aluminium oxide or mixtures thereof.
The catalysts characterized in this way have a pore size distribution which is characterized in that 100 to 10% preferably 80 to 10%, especially preferably 70 to 15% of the pore volume has a pore diameter of less than 600 Å determined by nitrogen absorption, from the total pore volume measured by mercury porosimetry (pore diameter of 36.8 Å to 13 &mgr;m).
The average pore diameter is in general 10 to 1,000 Å, preferably 50 to 950 Å, especially preferably 60 to 900 Å.
The specific nitrogen surface areas (BET) are in general 80 to 800 m
2
/g, preferably 100 to 600 m
2
/g.
Metals of sub-group VIII, preferably nickel, platinum, ruthenium, rhodium and palladium, are in general used.
The metal content is in general 0.01 to 80%, preferably 0.05 to 70%, based on the total weight of the catalyst.
The 50% value of the cumulative distribution of the particle size in the process carried out discontinuously is in general 0.1 &mgr;m to 200 &mgr;m, preferably 1 &mgr;m to 100 &mgr;m, especially preferably 3 &mgr;m to 80 &mgr;m.
The conventional solvents for hydrogenation reactions are used as solvents. These are in general aliphatic and cycloaliphatic hydrocarbons, ethers, alcohols and aromatic hydrocarbons. Cyclohexane, tetrahydrofuran or a mixture thereof are preferred.
Some or all the solvent is replaced by an oxygen-containing hydrocarbon or a mixture of such compounds.
Oxygen-containing hydrocarbons are preferably ethers having up to 20 carbon atoms and up to 10, preferably up to 6 oxygen atoms, polyether with C
1
-C
4
-alkyl units between the oxygen atoms and molecular weights of between 100 and 100,000 g mole
−1
, C
1
-C
20
-alkanols or C
1
-C
8
-alkoxy-C
1
-C
8
-alkyl compounds, or cyclic ethers having 3-12 carbon atoms and 1 to 6 oxygen atoms.
The alkyl radicals are in each case straight-chain or branched.
Diethyl ether, ethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, tetrahydrofuran, dioxane, trioxane and crown ethers, e.g. [18]-crown-6 and [12]-crown-4, are particularly preferred.
The reaction is in general carried out at concentration
Rechner Johann
Wege Volker
Zirngiebl Eberhard
Franks James R.
Gil Joseph C.
Lipman Bernard
Preis Aron
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