Vacuum flash drying technique

Vacuum Flash Drying. In this most recent technique, drying takes place m a vacuum vessel similar to an atmospheric tower but smaller. The soap is similarly heated before flashing but under less pressure, so that boiling (actually drying of the soap) occurs in the heat exchangers. Since there is boiling in the heaters, the moisture of the dried soap depends primarily upon soap flow rate, soap pressure, and steam pressure to the heater and to a minor extent on the absolute pressure in the vacuum chamber The final temperature of the soap depends entirely upon the absolute pressure m the vacuum chamber. 

Purification. The commercial LDPE was dissolved in hot toluene and precipitated in methanol. The resulting small chips were dried in a vacuum oven overnight at 80° C. HDPE was purified in the same manner, except that in this case much of the commercial material was insoluble in toluene, and so significant fractionation apparently occurs during t.he purification. The model compounds were purified by the flash chromatographic technique of Still et al. (10). 

A great variety of driers and drying techniques have been used for soap (McCutcheon, 1958). Specific methods such as frame cooling, drum cooling and atmospheric flash drying are still widely used for laundry-grade soaps in particular. By far the most important class of driers for toilet-grade soaps are the vacuum spray driers of which the Mazzoni type are widely used (Mazzoni, 1959). 

An improved method, utilizing a capillary Pasteur pipet for introducing the sample onto the chromatographic column approximately doubles the effectiveness (theoretical plates) of the column. Dry-column flash chromatography has been adapted for use in the instructional laboratory. The "column" consists of a dry bed of silica gel in a sintered glass funnel placed in a standard vacuum filtration flask the solvent is eluted by suction. Small (16 X 150-mm) test tubes inserted into the flask below the stem of the funnel are used to collect the fractions. This technique has been used successfully to separate mixtures ranging from 150 to 1000 mg. 

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