| 摘要 |
For the fractionation of viscous silicones, oily or polymeric diorganosilicones with a chain length of between 2 and 10 000 are separated into a top and a bottom product, preferably continuously in an extracting column, using compressed hydrocarbons such as ethane, propane and n- or i-butane, or mixtures thereof, at temperatures of between 25 and 250° C., pressures of between 20 and 500 bar and a gas density >160 kg/m3. To avoid viscosity problems, either an organic solvent in the form of a C5-8 alkane or up to 85 wt. % of the compressed gas (mixture) can be added to the starting materials prior to fractionation. With this process, high-quality viscous silicone fractions are obtained, which have a chain length of 200 to 10 000 and/or a viscosity of 100 to 500 000 mPas, and whose total oligomer content D4 to D20 is less than 0.05 wt. %.
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