Elimination Of Extraneous Separation Materials

The most obvious example of an extraneous material used for separation is a solvent, either aqueous or organic. An acid or alkali can be used to precipitate other materials from a solution. When these extraneous materials used for separation can be recycled with high efficiency, no major problem exists. Sometimes, however, they cannot, and the discharge of that material creates waste. Reducing this waste involves using an alternative method of separation, such as evaporation instead of precipitation.

A flowsheet for a liquid-phase, vinyl chloride process is shown in Figure 3.8.6. The reactants, ethylene and chlorine dissolved in recirculating dichloroethane, are reacted to form more dichloroethane. The temperature is maintained between 45 and 65°C, and a small amount of ferric chloride is present to catalyze the reaction. The reaction generates considerable heat.


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