Evaporators for Coarse Vacuum

For evaporation under coarse vacuum a variety of evaporator types is available. They represent a historical development, and each type has its specific field of application. Some typical evaporator types are described here. 

Working pressures between 80 and 800 mbar abs characterise the coarse vacuum. Water temperatures between 42 and 93 C correspond to these pressures. Most of the watery solutions are evaporated in this range. The evaporator types which are used here are hardly different from those used in the pressure range. 

Exhaust steam processes with liquids, however, are mainly operated in the fine vacuum range down to pressures of 1 mbar. The construction of the evaporators which are used here is very different from that of evaporators working under coarse vacuum. 

For the selection of an evaporator different substance-specific and economical criteria have to be considered. 

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The tar is dissolved in acetone (300 mL, 02-free) and added to a solution of excess [Et4N]Br (12.0 g) in ethanol (200 mL, 02-free). After evaporation of about 400 mL of solvent in vacuo, 600 mL of water (02-free) is added to precipitate the product. [Note A dry-ice/acetone trap (—78°C) is needed to prevent moisture from diffusing back into the inert-gas manifold of the vacuum line during this and subsequent operations involving water ] The yeUow-brown solid is collected on a large (70-mm-diameter) coarse-porosity frit, thoroughly washed with 2 X 20 mL of water, and dried in vacuo for 12 h. Note If appreciable... 

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