Construction and Use of Raschig's Laboratory Fractionating Column

Construction and Use of Raschig's Laboratory Fractionating Column. H. M. Evans, R. E. Cornish, S. Lepkovsky, R. C. Archibald, G. Feskiv. Ind. Eng. Che...
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I S D V S T R I A L A S D E S G T S E E R I S G CHEMISTRY

Julv 15, 1930

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Construction and Use of Raschig's Laboratory Fractionating Column' H. M. Evans, R. E. Cornish, S. Lepkovsky, R. C. Archibald, and G. Feskov k i A T O M l C . 4 L LABORATORY, U h I V E R S I T Y OF C A L I F O R X I A , BERKELEY,

CALIF.

Fittings for t h e Raschig laboratory fractionating Dewar (4) states that silverEVERAL devices facilicolumn are described, which simplify t h e construction ing reduces the rate of boiling tate t h e u s e of the and operation of a small intermittent laboratory of liquid air to one-sixth the Raschig (17') fractionatfractionating still. I t is shown t h a t t h e natural rerate with the u n s i l v e r e d ing column-i. e., a column placement, during t h e course of the distillation, of one vacuum jacket. From Marks filled v-ith hollow cylinders liquid in t h e column by another, supplies t h e equiva(11) the radiating power of open a t their ends-on a labolent of considerable reflux heat a t cutting points, this glass (at 70" F.) is about 95 ratory scale, to deliver from heat being t h e heat of vaporization of the replaced per cent that of a "black 5 to 50 cc. of finished disliquid. The heat capacity of the column, packing, body." Taking the radiatillate per m i n u t e . T h e and jacket also contributes considerable reflux heat tion for a silvered vacuuni complete still is simple to a t t h e cutting point, b u t this heat, unlike t h e other, is jacket as 16 per cent of construct a n d operate, so proportional to t h e difference between the boiling points Uarks' black-body value, n.e that one may often allow it of t h e two successive fractions. calculate Table I. to run for hours without atA laboratory vacuum fractionating still is described, Thick insulation should be tention, although i n such as well as a simple still which recovers waste alcohol used. The relative advancases heating by steam is prefas 95 per cent by volume, t h e latter with practically no tage of commercial covrririg erable because of fire hazard. attention by the operator. I t is shown t h a t for columns over the vacuum is decreased In adopting R a s c h i g ' s operating above 100" C. t h e silvered vacuum jacket is, with smaller size pipe and column for its efficiency, as in insulating power, inferior to ordinary high-grade increased w i t h t h e larger well as simplicity, the writers commercial steam-pipe covering, assuming t h e column sizes, assuming the thickness are supported by Hill and diameter to be 2 inches (50 m m . ) or more. Results of the commercial covering Ferris (e), who found colare given of actual distillations, including attempted to be a t least as great a> the umns c o n t a i n i n g I/d-inch separation of isotopes, and t h e mixture carbon tetrapipe diameter. (6.4-mm.) Raschig rings to chloride-benzene is suggested as a standard for testing I n a t e s t (condensation be but slightly inferior to the fractionating apparatus. method, 212" F. or 100" e.) best elaborate laboratory cola 2-foot (61-em.) standard umns of similar height, arid all are inferior to TT ha