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USEFUL HINTS FOR SODIUM HANDLING IN THE LABORATORY ARTHUR S. HAWKES, EUGENE F. HILL and MARSHALL SITTIG Ethyl Corporation, Detroit, Michigan
SODIUM, long an important commercial chemical, has recently been in the news because of its possible application t o heat-transfer systems in nuclear power plants. However, chemical synthesis is more important volumewise as a consumer of sodium. Currently being consumed at a rate of 300 million pounds a year, sodium finds large-scale use in the manufacture of tetraethyllead, in the reduction of natural esters t o long-chain alcohols in detergent manufacture, and in the manufacture of sodium peroxide and sodium cyanide. Other large-scale uses are on the horizon. This large industrial use of sodium may come as a surprise to many. However, sodium is economically attractive (only iron, zinc, and lead are less expensive) and is available in increasing amounts. Indeed, the surface has only been srrat.ched in the field of sodinm applications. It might be well, therefore, t o look more closely at ways of handling this reactive metal, which is a promising material for academic and industrial research. Let 0 5 10 15 us consider for a moment the possibilities of using TIME IN MINUTES sodium dispersed in inert hydrocarbons. Here, the rim- 1 already reactive metal is made even more reactive, as shown by Figure 1 which presents data on the reaction laboratory to a separate room or building in a large rates of octanol with sodium in various degrees of snb- laboratory. On the laboratory bench, however, sodium division. As you may know, the preparation of alkox- may be stored dry in rust-free, friction-top metal cans ides of higher alcohols is an extremely time-consuming or in cans under a layer of dry hydrocarbon, such as operation, when pieces of sodium are used. Yet here kerosene or toluene. Glass containers, where used, we have decreased the reaction time greatly and done it should be placed inside metal pails to confine sodium with sodinm in easy-to-handle liquid form. Moreover, spillage in case of breakage. Before going on to specifir sodium handling operasodium dispersions are unique, permitting reactions which were previously unknown to be carried out. The tions, let's consider some generalities regarding the use of sodium in the laboratory. preparation of sodium alkyl amides by the reaction (1) Know the physical and chemical properties of sodium and consider the potentialities of your reaction. is one example.' Thus, dispersions are not just another ( 2 ) Plan the disposal of sodium residues in advance. means of introducing sodium to a reaction. Dispose of scrap promptly and do not allow it to Now that some insight bas been gained on the inter- accumulate. esting possibilities of using sodium, let ns review the (3) Make initial trials of the reaction on a small latest techniques for its convenient handling, scale. Control the reaction rate by adding sodium in Sodium is most conveniently received for laboratory small increments and by dilution of the reactants with use in one-pound, key-opening cans. Manufacturers inert solvents. of sodium also have larger cans or pails, containing lots (4) Wear goggles or a face shield, and long-sleeved of from 10 to 25 pounds, if desired. lab coat or shirt. Wear gloves when handling sodium A designated storage area should be provided for metal. sodium. This may vary from a steel box in a small (5) Have soda ash or other approved extinguishing materials at hand in case of fires; never use water. "Preparation of Dispersions from 'Ethyl' Sodium," Ethyl (6) Use shallow metal pans on bench tops which can Corporation, 100 Park Avenue, New York 17, New York (availcontain spillage in case of acrident. able on request). 4617
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Figure 2
Figure 2 shows a sodium reaction bring conduct,ed in accordance with these recommendations. Let us go on now to a consideration of specific handling t e c h n i q ~ e s . ~ Cutting Sodium. Sodium may be cut fairly easily at room temperature. I t offers about the same resistance to cutting as does a hard rheese. A refined mineral oil may be used to coat both the knife and the sodium, in order to prevent oxide format,ion on freshly cut surfaces. A sharp knife may be used, or a hinged knife mounted on a base like a paper cutter may be preferred. Weighing Sodium. Sodium can be weighed under a tared layer of an inert hydrocarbon in a beaker. It can also be weighed dry in a weighing bott,le or can in a lowhumidity atmosphere. Volume displacement may be used where exact weight is not necessary, or uniform
pellets may be used. Figure 3 illustrates a simple device, made from a bottle capper, which has been used to prepare such pellets. Melting Sodium. Molten sodium is a very useful form for laboratory use because the rate of addition can be readily controlled, because only a small amount of sodium remains unconsumed in the reactor at any one time, and because the mo1t)en metal is dispersed so readily in the reaction mass. Two alternate designs for sodium melters and dispensers are shown in Figures 4 and 5 . The dexign shown in Figure 4 offers the advantage of using a I-pound brick direct from the can, with a
1111110s INSULATION
"Handling 'Ethyl' Sodium-In the Laboratory-In the Plant," Ethyl Corporation, 100 Park Avenue, New York 17, Xew York (available on request).
minimum of handling. A removable filter basket retains the oxide skin from the brick. After the brick is inserted, the melter may be filled with a hydrocarbon (which is compatible with the reaction mass) to increase heat transfer and speed of melting. The design in Figure 5 features a somewhat simpler valve design, but requires that a sodium brick be cut into pieces and charged to the melter. I t is preferred for addition of small weighed amounts of sodium. Making Sodium Sand. Sodium "sand" or "shot" are terms applied to sodium particles which are commonly to 5 mm. in diameter. This form offers
SEPTEMBER, 1953
mixture to 105OC. to melt the metal, and then starting theagitation. Alternatively, a melt pot of the typeillusNITROGEN INLET trated in Figures 4 and 5 can be used, in which case THERMOMETER HOLE molten sodium is run into the solvent which has already 2.5 I N . 1.D. been heated to 105°C. In either case, the mixture STAINLESS STEEL PIPE gradually assumes the appearance of gray house paint, and agitation is stopped after 15 minutes a t maximum speed. The contents of the flask are allowed t o cool to room temperature. The final dispersion may be poured into a dry, nitroRESISTANCE W gen-flushed container. The shallow steel trays, recommended earlier for the sodium laboratory, will be useful here to contain any spills. A 10 to 20 per cent solution of isopropanol in toluene, xylene, or kerosene may he 'used to clean any residual sodium from the flask or the stirrer head. Dispersions of sodium, because of their highly reactive nature, do present special safety problems. I n contact with moist air, sodium hydroxide will form, followed by the appearance of deliquescent water. The resultant heat of reaction between sodium and the water may be NEEDLE VALVE FACE sufficient to ignite the hydrocarbon medium. Fire G R O U N D T O SEA1 < may also result from spilling a dispersion on absorbent material, such as clot,h or vaver. . . , since such materials absorb the protective hydrocarbon and expose the finely divided metal to the moisture in the air. A sodium dispersion fire is first a hydrocarbon fire, however, and advantages over chunks of sodium in increased reac- may be extinguished with conventional dry-chemical tivity and ease of handling. extinguishers. As with all sodium fires, however, water, Sodium sand may he prepared by melting sodium aqueous foams, or rhlorinated hydrocarbons shonld not under a hydrocarbon, such as kerosene or xylene, and be used. agitating while the mixture cools. If aeitation is stopped just before the freezing point of sodium is reached, the droplets solidify into tiny metallic spheres. Alternatively,molten sodium may be dropped or sprayed into a cold hydrocarhon. Making Sodium Dispersions. Perhaps the most fruitful field for sodium research in the university or in industry lies in taking advantage of the unique properties of sodium in dispersed form. Sodium may be readily dispersed in inert hydrocarbons, along with dispersing agents used to prolong storage life, to decrease ' particle size, and to improve ease of handling. These dispersions may vary from thin liquids through greaselike materials to solids, depending on the viscosity of the hydrocarbon medium and the sodium concentration used. Concentrations can range from trace quantities up to 60 per cent. A typical laboratory setup for preparation of dispersions is illustrated in Figure 6. A pound of sodium may be effectively dispersed in a 2-liter, creased, 3neck flssk. A special motor-driven agitator head is desirable, as is a Teflon seal of unique design.= Five hundred grams of hydrocarbon are added, together with 3 g. of oleic acid. This mixture is stirred until it is uniform, and the sodium is then added. This may be accomplished by adding pieces of sodium, heating the I
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DEPREE,D., J. GREBLICK, A. S. HAWKES, C. A. POEELMAN, M. Srrno, "Improved stirrers for the laboratory" (in preparation). Also, see footnote 1. AND
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Cleaning Equipment. Apparatus which has contained sodium may be cleaned by washing with a solution of 10 to 20 per cent isopropanol in toluene, xylene, or kerosene. Small amounts of scrap sodium (up to 50 g.) can he disposed of hy burning in a heavy metal dish nuder a hood, using a gas flame. The hurned residue may he disrarded by dumping it outdoors in an open area and flushing it away with water. Smaller amounts of sodium (5 to 10 g.) may he disposed of by dumping
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into a beaker of isopropyl alcohol. As experience is gained in sodium handling, it will be found that small amounts of water (up to 2 per cent,) may be added to the isopropanol to increase the rate of reaction. A combination of interesting physical and chemical properties makes this fourth-cheapest metal, sodium, an attractive material for industrial and academic research. A variety of useful techniques are now available so that sodium can be handled conveniently and safely in the laboratory.
