Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
1999-12-22
2001-09-18
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S025000, C528S029000, C528S015000, C556S445000, C526S064000, C526S065000
Reexamination Certificate
active
06291622
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a continuous process for preparing organomodified polysiloxanes by a transition metal-catalyzed addition of polysiloxanes containing SiH groups onto substances containing C—C multiple bonds. In addition, a suitable industrial apparatus for carrying out the process of the present invention is also described.
BACKGROUND OF THE INVENTION
Among processes for forming and modifying organosiloxanes, hydrosilylation catalyzed by transition metals is of particular importance since hydrosilylations make a wide variety of SiC linkages possible. However, regardless of the wide application opportunities for this reaction, industrial implementation of prior art hydrosilylations is frequently accompanied by considerable difficulties. Central to these problems is the catalyst activity which can change over time and is subject to many interfering influences. Since hydrosilylation reactions liberate energy (i.e., the reactions are exothermic), a fluctuating catalyst activity in batch processes not infrequently leads to critical operational states because reactants can accumulate in between and can thus build up a hazard potential. The batch process represents the customary state of the art for industrial hydrosilylations, not least because experience has shown that a preactivation phase to form the catalytically active species from the inactive precursor material is absolutely necessary. The fluctuating reaction behaviors of industrial hydrosilylation reactions require the presence of many qualified employees.
One particular hazard potential results from the material systems in hydrosilylation processes, which systems have a high hydride hydrogen density. Apart from monomeric silanes, specific mention is made of the derivatives of poly(methylhydrogen)siloxane.
Along with the hazard potential, the critical systems also give undesired by-products, i.e., the selectivity of the intended reaction suffers.
The known chemical processes for preparing organofunctionalized poly(methylhydrogen)siloxanes therefore make conspicuous efforts to minimize the steady-state concentration of active SiH groups in the SiC linkage step.
For example, WO 98/05700 describes a (semi)continuous process for preparing multifunctional polyorganosiloxanes containing Si-alkyl and Si-alkoxy groups in a multistage reaction apparatus comprising a combination of a dehydrocondensation reactor with a hydrosilylation reactor. The dehydrocondensation reactor is supplied with an SiH-containing polyorganosiloxane and a deficiency, based on the polyorganosiloxane, of an alkyl or thioalkyl in the presence of a platinum catalyst, forming, with liberation of H
2
, a mixed alkoxyhydrogensiloxane or thioalkoxyhydrogensiloxane which is then immediately subjected to alkylation by an olefin to form an SiC bond in a downstream hydrosilylation reactor. Attention is paid in WO 98/05700 (see, Page 2, line 29-Page 3, line 3) to the hazard potential involved in handling SiH-containing compounds, even compounds having partly alkoxy- or thioalkoxy-functionalized chains. For this reason, the actual hydrosilylation is therefore deliberately carried out only after the partially deactivating reaction (dehydrocondensation); operation of this process brings with it the technical problem of ensuring complete removal of alcohol/thiol and hydrogen gas prior to the hydrosilylation. In terms of the apparatus, a complicated and costly solution is therefore necessary.
Continuous hydrosilylation processes which are already known per se also seek to lower the in-situ concentration of active SiH groups. DE 196 32 157 A discloses a process for the continuous preparation of organosilicon compounds of the 3-halopropyl-organosilane type having the general structure R
b
H
3-a-b
X
a
SiCH
2
CH
2
CH
2
Y by reaction of an allyl halide with an excess of a silane having at least one H atom. Propyl-organosilanes which cannot be utilized are formed as undesired by-products. The essential feature of this prior art process is that by-product formation is suppressed by setting a partial conversion of the starting materials of 10-80%, based on the component present in a deficiency.
A further process for continuously carrying out hydrosilylation reactions is disclosed in DE 196 19 138 A. This document describes a process for preparing vinylated organosilicon compounds in which an organosilicon compound containing at least one SiH group is reacted with an excess of acetylene in a largely inert liquid phase in the presence of a catalyst. To ensure intensive mixing of the reaction matrix, a jet loop reactor is employed.
Continuous gas-phase processes in a flow reactor which have been previously described include: the molecular addition of acetylene onto methyldichlorosilane over a Wilkinson catalyst immobilized on chrysotile asbestos (Appl. Organomet. Chem. (1987), 1 (5), 459-63); and the hydrosilylation of acetylene using trichlorosilane over Rh- and Ru-phosphine complexes fixed to SiO
2
, which proceeds with limited selectivity (Appl. Organomet. Chem. (1987), 1 (3), 267-73).
The prior art thus documents three methods of diluting active SiH groups:
(i) the partial conversion procedure;
(ii) the use of an inert liquid phase; and
(iii) the reaction in a gas space.
SUMMARY OF THE INVENTION
In view of the drawbacks with prior art hydrosilylation processes, it is an object of the present invention to provide a process and an apparatus which make it possible to carry out the hydrosilylation reaction economically and reproducibly while avoiding known hazardous potentials even in difficult material systems, while at the same time refraining from using a complicated and expensive apparatus. In addition, the process should ensure consistently high product quality while making sparing use of high-priced noble metal catalysts. Furthermore, the process should be usable for virtually complete conversion, without use of an inert auxiliary phase and also for relatively high molecular weight reactants which cannot be vaporized without decomposition.
REFERENCES:
patent: 5986022 (1999-11-01), Austin et al.
patent: 196 19 138 A1 (1997-11-01), None
patent: 196 32 157 A1 (1998-02-01), None
patent: WO 98/05700 (1998-02-01), None
Marciniec, B., et al., (1987) “Catalysis of hydrosilylation XIII. Gas-phase hydrosilylation of acetylene by trichlorosilane on functionalised silica supported rhodium and ruthenium phosphine complexes”,Applied Organometallic Chemistry, pp 267-273. (No month).
Marciniec, B., et al., (1987) “Catalysis of hydrosilylation. XV. A poly(phosphino-organosiloxanyl)silicate-supported rhodium(I) catalyst for gas-phase hydrosilylation of acetylene”,Applied Organometallic Chemistry, pp 459-463. (No month).
Drose Jurgen
Geisler Hubertus
Hiersche Wolfgang
Klein Klaus-Dieter
Knott Wilfried
Goldschmidt AG
Moore Margaret G.
Scully Scott Murphy & Presser
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