โ Scribed by R.H.O.
No coin nor oath required. For personal study only.
Seldom has any new use of refrigeration become so important so quickly as the one now being applied to the making of penicillin.
This drug must be moisture-free or it won't keep. Sumcient heat to drive off the water cannot be used as this would kill the life of the penicillin. (The finished product is sealed and must be stored at 5 ยฐ deg. F.)
The problem of renqoving the tremendous amount of water vapor at low temperature was solved-in a novel manner by the National Research Corp., a Boston concern specializing in high vacuum operations. They designed, built and installed equipment that combines low temperatures (down to 75 deg. F. below zero) with the highest vacuum ever applied to commercial dehydration work (I/xoo of one millimeter of mercury or less).
The full sized plant making penicillin by vacuum diffusion process was built by the Commercial Solvents Corp., at Terre Haute, Indiana, in just I6O working days. Several plants using similar equipment are in use elsewhere in this country, and four of them are being supplied to our a!ly, Russia, for drying bloodplasma.
Concentration of extract from the vegetable mold is a story in itself, but after the penicillin is placed in bottles, each holding Ioo,ooo units, it is first deep frozen. The bottles are then put on shelves in drying chambers, called "ovens." Pipes above the battery of ovens lead to vacuum pumps which are in two stages. Evaporation of the ice occurs without any melting: In fact the moisture "sublimes" with a refrigerating effect, and to hasten the process a low heat has to be added through hot water headers leading to the shelves.
A sloping shell in the vacuum line serves as a moisture freezer or condenser. It is jacketed with very cold ammonia from a booster system, and equipped with revolving blades for scraping off the condensed vapor that forms inside, as the low temperature and high vacuum are applied. The ice falls into an air tight vessel below; this is heavily insulated and is refrigerated, through a jacket, to keep the moisture from re-sublimating. A small area in t.he slanted shell suffices to handle a large cooling load. Under the intense vacuum, molecules of moisture race toward the cold surface with terrific speed. Frost deposits on the surface as fast as the blades of the scraper can sweep it into the chamber below.
This drying process was originally developed as a means of dehydrating foods without "cooking" them or destroying their flavor or vitamins. Thus color, even the form, of the food is retained. Moisture content is reduced to less than Iยฐ/o, whereas the usual air drying methods leave about 5 to lO%. By adding cold water the food may be restored to its initial freshness in a few seconds, the moisture entering through the minute holes in the cells through which it had passed when sublimated.
R. H. O.
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