Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-09-12
2003-10-28
Choi, Ling-Siu (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S105000, C526S107000, C526S907000, C526S095000
Reexamination Certificate
active
06639031
ABSTRACT:
The present invention relates to a process for preparing coreactive support materials and to the heterogeneous catalysts and cocatalysts prepared therewith. The novel coreactive support materials having an increased number of coreactive groups make it possible to heterogenize catalysts, cocatalysts and ligands which are required for the polymerization of ethylene, propylene, hexene or styrene. However, they also make it possible to prepare catalysts for metathesis, hydrogenation, coupling, oxidation or hydroformylation reactions.
Catalytically accelerated reactions present a problem to the chemist if the catalyst cannot be readily separated from the product produced after conclusion of the reaction. In particular, this is frequently the case for homogeneous catalysis. It is therefore advantageous to heterogenize homogeneous catalysts. The latter leads not only to a product improvement but also brings a series of process-engineering advantages. Heterogenization can be carried out in various ways, either by physisorption or by chemisorption on a suitable support. Since no bonds to the actual catalyst are formed by physisorption, this generally leads to more rapid loss of the catalyst. On the other hand, chemisorption involves ionic or coordinate bonding of the catalyst to the surface of the support material. Catalytically active groups can also be fixed via ligand bonds to both organic and inorganic supports. Such organic support materials can be, for example, polystyrene derivatives. However, disadvantages of organic support materials are their low mechanical strength, their swellability and poor heat transfer-disadvantages from which inorganic support materials generally do not suffer.
The most important principle in the preparation of catalysts bound chemisorptively to inorganic support materials is reaction of a support oxide having hydroxyl groups on the surface. The latter can be, for example, SiO
2
, Al
2
O
3
or MgO. The surface hydroxyl groups are, for example, reacted with metal alkyls, halides or alkoxides or functionalized alkoxysilanes which are provided with a ligand group. Such reactions are known from the literature (e.g. from: J. Hagen in “Technische Katalyse”, VCH Weinheim, 1996, pp. 225-240; or: M. Z. Cai et al., Synthetic Comm., 27, 361 (1997)). However, chemisorption, which is associated with the formation of an additional bond, sometimes alters the originally advantageous properties of the homogeneous catalyst in an unfavourable way due to the change in the stereo-selective situation associated with the bond formation.
Depending on chemical structure, inorganic support materials have a variable number of reactive OH groups on the surface and these can form a bond to catalytically active organic or organometallic groups. This number is from about 4.4 to 8.5 per nm
2
for a fully hydroxylated silica gel (H. P. Boehm, Angew. Chem. 78, 617 (1966)). These values were confirmed by J. Kratochvila et al., Journal of Non Crystalline Solids 143, 14-20 (1992). At a bond length of about 1.60 Å for the Si—O bond and an angle of 150° for the Si—O—Si angle, there are about 13 Si atoms per nm
2
or per 100 Å
2
on the silica gel surface. This means that a maximum of 13 Si—OH groups occur in the surface monolayer with additional three-fold bonding of the Si via the oxidic oxygen bridges. However, only four Si—OH groups are generally to be expected in silica gel dried at room temperature (cf. Boehm and Kratochvila).
To achieve as high as possible a number of active Si—OH bonds per unit weight on a silicate support material, the surfaces of the support material can be increased in the form of pores, clefts and/or by means of very small particle diameters. Increasing the number of Si—OH groups by saturation with water or water vapour does not lead to a satisfactory solution because the additional water adsorbed on the surface leads to hydrolysis of most coreactive ligands or catalysts which are to be chemisorbed on the surface. On the other hand, severe drying leads to a decrease in the number of Si—OH groups to less than 2 per nm
2
.
However, it is not only the amount of adsorbed water on the surface of such silicate materials which influences the quality of the supported catalyst materials prepared therewith. Si—OH groups on the surface of a particle can have a significantly different stearic environment than those which are located in clefts and pores of the particle. This can lead to catalytic centres of differing activity and to selectivity losses. In the case of a normal particle surface, as is mostly present in the case of particles of spherical microgels, such differences may be expected to occur to a significantly lesser extent.
The same problems naturally also play a role if Al
2
O
3
, TiO
2
or ZrO
2
are used as support materials for the coreactive heterogenization of homogeneous catalysts.
It is therefore an object of the present invention to provide an inorganic support material which has a very high number of coreactive groups on the surface and has good thermal conductivity and very low swellability. A further object of the invention is to develop an inexpensive and easily implemented process for producing a very large number of coreactive OH groups on the surface and in the pores of the support material without causing occupation of the surface by water molecules, in order to avoid undesired hydrolysis of the coreactive ligand, catalyst or other support. Another object of the invention is to prepare heterogeneous catalysts and cocatalysts having a high loading per unit area and unit weight from the support materials obtained. These catalysts should have a high product selectivity in use.
The present object is achieved by a process for preparing support materials having an increased number of reactive OH groups, which is characterized in that an oxygen-containing, inorganic material of oxidic nature is reacted in an inert aprotic solvent with a strongly basic reagent, in particular an alkali metal hydroxide or alkaline earth metal hydroxide. This reacts via a complex with the OH group of the hydroxide formed as an intermediate with breaking of the oxidic bond of the support to give an OH group and an OM group on the surface, where M is an alkali metal or alkaline earth metal atom equivalent. From the OM groups newly formed by the reaction, the OH groups are set free by acidification with an organic or inorganic acid.
The object is also achieved by the application of chemisorptively bound ligands, catalysts or cocatalysts for the purpose of generating a functional surface, by
a) direct reaction of the OH or corresponding OM groups generated with suitable coreactive groups of the respective ligand, catalyst or cocatalyst or
b) modification of OH or corresponding OM groups generated on the surface by chemisorptively bound coreactive groups, forming a surface comprising chemisorptively bound functional organic ligands.
Here, the variant b) can be carried out via a completely different type of reaction than the variant a).
An important process variant generates the metal hydroxide required for cleavage of the oxide in situ from the physisorbed water located on the oxide. This dries the surface at the same time. Adjustment of the water content on the surface also enables the number of newly formed OH groups to be regulated. The newly formed OH groups can be converted, for example by means of hydride, into their alkali metal or alkaline earth metal salts, from which the active OH groups can be set free again in a converse manner using organic or inorganic acids.
In the process of the present invention, the natural or chemically produced, oxygen-containing, inorganic material used can be a gel, oxide or salt of silicon, boron, aluminium, titanium or zirconium.
The silicon-containing materials can be silica gel, oxygen-containing alkylsiloxanes or naturally occurring silicates derived from silicic acids having chain, band or sheet structures.
According to the invention, the silicates may be wollastonite, enstatite, diopside, trennolite, serpentine or talc.
Buchholz Herwig
Poetsch Eike
Choi Ling-Siu
Merck GmbH
Millen White Zelano & Branigan P.C.
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