W. B. H E C K . J R .
R. L. JOHNSON
ALUMINUM ALKYLS S AI
HANDLING
Fires result j i o m just exposing thse compounds to air. But handling them is no mwe &$cult than handling strong acid or caustic-if it is done the rzght way nowledge is safety-techniques
and
equipment
K can be designed to nullifyRecautions the very dangerous must be
properties of aluminum alkyls. SC~UPUIOUSIYobserved. Education and training play
a most important part in any program of handling aluminum alkyls. All personnel must know thoroughly the nature of the materials, the operating procedures, a n d the equipment. The need for proper use of personal protective equipment must be deeply ingrained. Personnel must respect these materials-not fear them. Ethyl Corp. has worked with aluminum alkyls for several years in laboratory, pilot plant, and commercial operations. There have been no serious accidents because of the continuing attention given to the proper safety precautions. Cardinal rules to be followed fall into three groups: CONTAIN-Prevent uncontrolled escape of alkyls and contact with reactive materials. GUARD --In case aluminum alkyls should escape from their enclosed system, shield operators and equipment from potential leaks, sprays, or splashes. PROTECT-& a third line of defense, require that personnel wear full personal protective equipment when there is a possibility of exposure. Aluminum Alkyls Are
Used by the Ton
The term, aluminum alkyls, now often used in the chemical industry, broadly covers the compound family containing alumi&m, alkyl groups, and sometimes halogens. Triethylaluminum, triisobutylaluminum, and diethylaluminum chloride are used commercially. Tri-n-propylaluminum, trimethylaluminum, ethylaluminum dichloride, and diethylaluminum hydride may soon have commercial use.
Large amounts of aluminum alkyls are used in Zicgler catalyst systems for polyethylene, polypropylene, and stereo rubbers. Triethylaluminum is used in one U. S. plant for making straight chain alcohols; it can also be used for making long-chain alpha olefins. Ethyl Corp. uses the alkyls in their manufacturing operation. Continuing research is leading to new uses: ignitor systems in ramjets, afterburner sustainem for jet engines, aluminum gas plating compounds, high energy fuels, reducing agents, and intermediates for organometallics. New C h e m i s k y 4 n v Hozord C o m b M o n
Aluminum alkyls are highly reactive. Butyls and the lower alkyls are pyrophoric; that is, they ignite spontaneously in air, a t ambient temperatures. They react violently with water, and burn the skin severely on contact. Increasing the molecular weight or substituting halogens for alkyls generally reduces pyrophoric reactivity. Pentyls and the higher alkyls give off dense smoke in air, but usually do not ignite by themselves a t normal temperatures. However, they will bum when ignited, react violently with water, and burn the skin severely. Even alkyls up to CI, undergo autoxidation when exposed to air. Heat release from burning alkyls approximates that of burning gasoline, pound for pound. Diluting aluminum alkyls with hydrocarbon solvents can make them nonpyrophoric and less hazardous. Benzene, hexane, and heptane can be used, but chlorinated solvents may react violently. The nonpyrophanic concentration varies with alkyl temperamre and solvent: For C I and below, 10 to 20 weight % alkyl is generally nonpyrophanic; for Cs and up, the concentration can be increased to 20 to 30%. Even the diluted alkyls smoke in air, bum the ski, and have flammable vapors. VOL 5 4
NO. 1 2
DECEMBER 1 9 6 2
35
Note that spilled dilute alkyls create a greater potential for a vapor “flash-back” type of accident than would an equivalent spill of solvent or undiluted alkyl. This results from accelerated vaporization of solvent by the heat of the air-alkyl reaction.
Once Started, Fires Are Hard to Control
Certainly fire prevention is the easiest and most economical approach to control of fire losses. Should fire occur, proper and decisive action will minimize loss and prevent injury. The fire control problem has two aspects: control and extinguishment of a burning pyrophoric material and control of the evolution of flammable vapors from the diluted, nonpyrophoric materials. The only effective control is by blanketing and absorbing the liquid. Water and water-based foams react violently with aluminum alkyls. They must not be used except on fires from very dilute solutions. Water in contact with dilute solutions will cause a rapid increase in temperature, and an excessive rate of flammable vapor evolution. Carbon tetrachloride must not be used I t can react to create toxic fumes, and it will not kill the fire. Chlorobromomethane should not be used; it also reacts to create toxic fumes. I t will put out a pyrophoric fire, but reflashing ill occur. Carbon dioxide ill not put out an aluminum alkyl fire, but can be used on fires involving dilute nonpyrophoric solutions. Sodium bicarbonate in large amounts can control small shallow spill fires. Sodium bicarbonate will not control fires in deep spills; it sinks into the burning liquid, decomposes, and spews out burning droplets.
Sand, diatomaceous earth, Celite, and other inert particulate materials are good extinguishers, if dry. These materials are denser than alkyls. Therefore enough material must be used to absorb the liquid and build up over the surface bv 4 to 6 inches. Air contact
will be removed, the liquid will cool, vapor evolution will slow, the fire will subside, and fuming will stop. Met-L-Kyl, as shown by Ansul Chemical Co.’s test data, is a very satisfactory extinguishing agent. This also must be applied in sufficient quantity to absorb and blanket a spill. The application ratio recommended is 8 to 10 pounds of agent per pound of alkyl. Expanded vermiculite, a mica-like mineral, is an effective extinguishing agent. The medium sizes, grade 2 or 3 or “plaster aggregate,” should be used. With a bulk density of 7 pounds per cubic foot, vermiculite floats on the aluminum alkyls and kills the fir? quickly by blanketing off air. I t will eventually sink, so sufficient material should be available to form an overlying blanket at least 4 inches thick. Vermiculite controls aluminum alkyl fires and fuming, from both concentrated and dilute solutions. I t is dry when purchased and stays dry in the shipping bags; it is nonflammable and inert; it is inexpensive, 25 to 50 cents per cubic foot; it is readily available from lumber yards, building supply houses, and from wholesalers. After fire and smoking have subsided, active alkyl may remain under the blanketing materials. Small gas or vapor fires above the blanket can be extinguished by the gentle application of a small cloud of sodium bicarbonate or COz. Do not apply water-it will sink through the blanket and cause a violent reaction. Two disposal methods may be employed: rabble the absorbent slowly to bring alkyl to the surface for controlled burning at a low heat release rate, or shovel the alkyl-absorbent mixture into metal containers for disposal elsewhere-this method will require the addition of absorbent to kill sporadic fires. Toxicity I s Not the Major Hazard
iVhen aluminum alkyls or their dilute solutions burn or react with air or water, they release a finely divided fume of aluminum oxide. Breathing this oxide may cause the flu-like symptoms of metal-fume fever. The
O F PROPERTIES
SAFETY FOLLOWS K N O W L E D G E
I I
j Abbreaiation Abbreniation Tri-n-propylalurninum Triisobutylalurninum
1
Diethylaluminum chloride
1
Ethylaluminum dichloride
-
Diethylaluminum hydride
I
i TIBA
-1
-
Formula
~
TNPA
1
I
156.3
1
