Reuse after Modification

The processes mainly used to these ends are direct reuse after separation and/or modification, chemical treatment or pyrolysis for recovery of monomers and/or other products, and burning or incineration. 

It was demonstrated that these effects did not result from a permanent modification of the nature of the catalyst after recycling the catalyst used in styrene and reusing it in CH2CI2. Indeed, under these conditions the same stereoselectivities were obtained as with the use of the fresh catalyst in... 

Half an hour before the reaction was started, the catalyst had to be activated by adding some drops of distilled water to develop its full catal3d ic activity in organic solvents. After the reaction the catalyst can be filtered off, washed and reused for further reductions. At temperatures above 70°C, the catalyst changes its colour fi om reddish-brown to black. After this colour change, most of its activity is lost. Obviously the active iron oxide hydroxide modification is transformed into a thermod3mamic ly more stable modification with lower H-transfer activily. 

The catalyst is now dispersed in the ionic liquid phase, from which the pure product separates as a new liquid phase that can be easily decanted after the reaction. The ionic liquid catalyst phase is stiU active and can be reused. It is important that standard hydrosilylation catalysts can be used without further modification. Degussa has been running this process on a pilot scale achieving conversions of >99%. In most cases the detectable platinum content of the products was < 1 ppm. 

At Hanford, for example, an evaporator is used to reduce the volume of waste entering the high-level storage tanks. The standard practice for ten years of evaporator operation was to use filtered river water, which was then sent for wastewater treatment after one use. This year, we made process modifications that allow the reuse of condensate water instead of the filtered river water. The expected dollar savings per year of operation is 3.1 million, and savings in filtered river water not used is 2.1 million gallons (over 8 million liters). We now require the consideration and incorporation of waste minimization features in the design process for all new facilities. 

Wilson and Guazzaroni (1989) devised a modification of the Luche reaction by using a solid organic phase, such as reverse-phase C-18 silica gel, instead of tetrahydrofuran as the cosolvent. The solid organic phase can be reused and disposal of the solvent after the reaction is environmentally safe. Unfortunately, the synlanti-selectmty was not improved regarding the Luche conditions. No chelation control was observed with p-alkoxyaldehydes. 

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