K. C.
D. Hickman was born in London in 1896, educated a t the Royal College
of Science, and received his B.S. and Ph.D. at London University. H e spent three years with the Chemical W a r f a r e Service, then returned to the Royal College of Science in 1979 to do research in color photography. In 7925 he joined the staff of Eastman Kodak Company. In 7938 he became vice president and director o f research a t Distillation Products, lnc., Rochester, N. Y., where he has been ever since. H e is responsible for the method o f analytical molecular distillation and for the centrifugal high-vacuum still. His published research includes the washing of photographic materials, electrolytic recovery of silver in motion-picture laboratories, vacuum technology, and studies in biochemistry and physiology of vitamin E. Hickman is recipient of the 7923 Williamson Award for Photographic Research, O p t i c a l Society of America's 1929 Award for Best Scientific Instrument, I930 Award for Best Scientific Instrument sponsored by the Review of Scientific Instruments, and the 7939 M o d e r n Pioneer Award from the National Association of Manufacturers
MOLECULAR DISTILLATION K. C. D. Hickman and G.C. Mees LTHOUGH no new kinds of short-path high-vacuum st'ills have appeared during the past few years, existing types have been improved and enlarged to a point where they render relatively inexpensive, trouble-free service. The early commercial stills employed the falling-film principle, where the distilland was allowed to cascade down a heated circular pole contained within an evacuated tube. These were augmented in 1939 by centrifugal stills in which the oil was spun from the center over the surface of a heated disk about a foot in diameter, housed under a glass bell jar. In 1941 the falling-film stills were entirely replaced by 32-inch centrifugals having shallow cones rotating horizontally on a vertical axis. Experiments with larger sizes showed the desirability of using steeper conical evaporators rotating on vertical shafts. The distilland is admitted to the narrow end of the cone and climbs up the sides under centrifugal force. The condensing arrangements are suspended in the center, and means have been devised t o withdraw distillates through the bottom of the rot'or or pump them out over the top. Stills operating on this design, with rotors 5 feet in diameter and an active distilling area of 5 square yards, were put into service recently, and at once set interesting standards for high-vacuum evaporation. They showed, for instance: (1) When using electrical heat, even without the advantage of countercurrent exchange or reflecting condensers, the power consumption was less than 0.1 kw. hr. per pound of distilland. (The consumption per pound of distillate varies too widely to be quoted exactly but is ordinarily within the range 0.2 to 0.5 kw. hr.) (2) Over-all operating costs, including poiver, labor, amortization and net factory overhead, are in the region of one cent per pound per pass of distilland. Of course, many chemical separations require multiple passes and feed-back of distillate which increase the cost of distillation. There are residues and light ends of small value; in the case of the oil-soluble vitamins, there are chemical losses that must be debited against operating cost. (3) Capital cost in relation t o volume handled compared favorably with conventional processes. Indeed, a week's throughput may represent a greater investment lhan the stills. A single &foot rotor can handle two tank cars of distilland in a week and evolve anywhere from a few hundred gallons of distillate in a stripping operation t o 6000-8000 gallons in a complete distillation. The capacity of an unobstructed evaporat,or to transfer material a t a saturation pressure as low as a micron (1/760,000 atmosphere) is quite large, a square yard evolving about 0.75 gram per second. The &foot rotor thus evaporates 30 pounds per hour a t this pressure or, say, 300 pounds when the distillation is pushed up to 10 p . Evaporating
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surfaces aggregating a quarter mile square and operating at a micron would transfer about 100,000,000,000 pounds a year, or about all the vegetable and marine oil and a goodly proportion of petroleum residue out'put of the world. The process itself has been uscd on a small scale in a few laboratories, not,ably at the IT. S. Department of Agriculture, the University of Wisconsin, and various govcrument regional laboratories. Laboratory falling-film stills are known to be in operation) in England, Russia, and India, With the exception of a plant operating at The British Drug Houses in England, the commercial' development is believed t o have been undertaken exclusively by Distillation Products, Inc. What follows is therefore necessarily a description of the work of that company. Our publication policy has been to augment patents with somewhat copious technical publication. Six reviews, two of them lengthy, have appeared from our pcn, and a valuable independent, appraisal of the process has been issued by Theodore R. Olive. Little can be said here that is not already available to the readerwith one exception. Previous articles have stressed the difficulties and expense of molecular distillation; the present one definitely announces the stills' abilities to compcte in heavy industry. Laboratory, falling-film, molecular stills are now being supplied under a reasonable agreement to academic and commercial research laboratories where they can be put to a variety of investigational uses. A new 14-inch cent,rifugal still has also been designed for laboratory purposcs; and since this has a much higher capacity, its use is growing where larger volumes of material are required. Since 1941 the 32-inch still units have been in practically coritinuous operation on marine oils at Distillat,ion Products, xvith minor modifications of design. These have now been brought t o standardized pat,terns of single- and multiple-effect installations which operate reliably over long periods. Stills of this type have not been installed elsewhere but are now available to interested parties under license. A battery of &foot stills, as mentioned, is in operation on a miscellaneous schedule of marine, veget'able, and mineral oils and heavy chemicals at a rate of 100 to 150 gallons of oil per hour, depending upon the type of product handled. A new vacuum system, devoid of mechanical pumps, has been devised which enables these large units t o operate at pressures equal to or lower than the earlier models. The &foot stills are adaptable either t o stripping a small percentage cut from the original material or t o distilling practically all of the input. A system of differential setting of the rotor and a multiple-zone condenser enables one to take off a number of fractions from a single plate.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 38. No. 1
G.C. M e e s i s the son of C. E. K. Mees, director ofresearch at the Eastman Kodak Company. G. C. M e e s was born in Croydon, England, in 1910, but was educated in the Unitedstates where he obtained his B.S. from the University of Rochester in 1930, and his M.B.A. from the Graduate School of Business Administration of Harvard University in 1933. H e was commercial manager a t Distillation Products, Inc., a t Rochester from its inception in 1939 until last January when he was appointed vice president in charge of sales and purchasing.
In spite of the difficulties attendant on new developments during wartime, plans were completed for a new factory building which is now under construction. Besides being equipped with the usual clarifying, refining, and bleaching equipment, the factory will have batteries of molecular stills ranging from 3 inches to 10 feet in effective diameter. The 10-foot centrifugals h a v e an anticipated capacity of one to two tank cars per day per rotor. All this equipment will be available for custom processing, and where indicated similar apparatus may be installed by license agreement elsewhere. The molecular still has grown up in the service of the fatsoluble vitamin industry. While the early models could be used profitably for removing vitamin A esters from high-potency marine oils, present-day machines do not need the premium of
vitamin extraction to process oils profitably. Here are some of the uses to which the still has been p u t : removal of vitamins from natural oils, purification of plasticizers, reclamation of industrial residues, preparation of high-vacuum pump fluids, processing of heavy chemicals, separation of petroleum greases. Molecular distillation seldom provides a complete manufacturing process. It takes its place as a tool of industry t o be applied a t apprdpriate stages in more complex processes. I t is not a substitute for alkali refining or solvent extraction or low-temperature crystallization; it is a unit process of unique character which may or may not perform a ncw and useful purpose, according to circumstances. COMMUNICATION No. 83 from the laboratories of Distillation Products, Inc.
Commercial Size Molecular Still
January, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
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