Pierce Modifies Schiemann Process Process makes fluoroaromatics continuously from diazonium salt, improves control, cuts costs

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pound is machinable. Fabricators can remove the tough outer shell with diamond or carbide tools, then use conventional cutting tools to make a variety of shapes.

The density of oxide-bonded hexa-boron suicide after sintering varies from 1.7 to 2.1 grams per cc. Its abra­sion resistance is about the same as that of silicon carbide. Electrical re­sistivity of the hexaboron compound seems to vary with the method of treatment, A-C says. Thus, while the oxide-bonded material is an electrical insulator, the self-bonded type has an electrical resistivity of 0.01 ohm-cm., and functions as a semiconductor.

Solid Solution. One unusual prop­erty of the suicides is the difference in their behavior at high temperatures. While hexaboron suicide melts above 3500° F., the tetraboron compound becomes thermodynamically unstable at about 2200° F. Above this tem­perature, the latter suicide dispropor-tionates into the hexaboron compound and silicon which tends to form a solid solution with the hexaboron sui­cide. Formation of silicon gives added oxidation resistance to the material. So tetraboron suicide, Dr. Colton points out, may be better than the hexaboron derivative for some uses.

A-C's nuclear power department has already recognized the potential of these suicides, is now checking their radiation properties. x'Uthough it cur­rently uses boron carbide as a neutron control material, the department feels that the suicides may have better water corrosion resistance than the carbides, in addition to higher tem­perature uses in oxidizing atmospheres.

Other potential uses in the nuclear area include shielding structures and burnable poisons. With their good oxidation and thermal shock resist­ance, the compounds will also find uses in general refractory areas, A-C says. Another possibility is missiles.

The company is offering both sui­cides in three purity grades (free silicon is the major impurity). It plans to market them at these prices:

• AA (about 1% free Si)—12 cents per gram, -$50 per lb.

• A (about 5% free S i ) -10 cents per gram, $44 per lb.

• B (about 15% free Si)—8 cents per gram, $35 per lb.

Availability of the suicides from A-C may have yet another, more significant meaning. They are the first chemicals the company has offered commercially.

A continuous process for converting diazonium fluoborates to fluorinated aromatics in the second step of the Schiemann reaction has been de­veloped by Pierce Chemical, Rock-ford, 111. According to the company, the modified process is faster, gives better control and less product carry­over loss, compared with a batch op­eration. This means lower costs, faster production runs, and could help the company meet growing foreign com­petition.

Pierce, a manufacturer of specialized research and analytical chemicals, is now using the process to make 12 basic chemicals in its line of fluoro­aromatics. In addition to being end products in their own right, these chemicals are intermediates in pro­ducing some 32 other products offered by the company.

Pierce sticks with the conventional Schiemann technique in the first step, which is a batch operation. Here, an aromatic amine, nitrite, and a fluo-borate salt react under acid conditions to form a solid diazonium fluoborate. Batch size is limited only by the size of the reactor. The solid diazonium salt is filtered, washed, and dried to complete the first step.

Then, in a second step, the diazo­nium salt is fed continuously into a ves­

sel heated by steam. Here it breaks down into the fluoroaromatic, nitro­gen, and boron trifluoride. Fluoro­aromatic product is removed from the reactor. The gases and any carry­over fluoroaromatic pass through water-cooled condensers, where the fluoroaromatic condenses out. Water absorbs the boron trifluoride in packed scrubbing towers downstream, and the nitrogen exhausts through a fan. The difference between this and conven­tional conversion is a screw feeder, which can be set to control rate of salt addition, and a fan, which keeps a net draft on the screw feeder to keep decomposition gases out.

This modification overcomes several problems that have plagued the Schie­mann reaction, according to Dr. Alan Pierce, company president. For ex­ample, some diazotized aromatics, such as the diazonium fluoborate salt used to make o-fluorotoluene, are ex­tremely sensitive, he notes. These decompose so quickly that only small amounts can be added to a hot re­action vessel at any one time. Other­wise, gas pressure build-up would be excessive. The time and attention necessary to add the diazonium salt a little at a time make the batch method expensive for such chemicals. With the modified process, on the other

A P R I L 2 4, 1961 C & E N 65

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hand, Pierce says it can produce 0-fluorotoluene, for example, in one half to one third the time required by batch methods.

Also, other diazonium fluoborates, while not so sensitive, may decompose at temperatures very near the product boiling point. For instance, fluoroben-zene is formed at 80° C. and boils at 81° C. In such a system, much prod­uct passes over to the condensers, and losses during batch addition can be significant, Dr. Pierce notes. The con­tinuous method eliminates this prob­lem.

Market Problems. Producers of analytical and research chemicals face problems somewhat different * from those of quantity producers. Most specialty chemical business comes from research organizations. Since research can turn in any direction, it is almost impossible to forecast demand. But at the same time, demand must be met with minimum delay. Large stockpiles, however, aren't practical.

For this kind of situation, synthesis of the 12 intermediates by the con­tinuous process is ideal, Dr. Pierce points out. The faster process lets the company compromise between large inventories and undue delays in filling orders. Instead of keeping large stockpiles of all 44 products, Pierce now need keep only the 12 in­termediates in sizable quantities.

Foreign competition in specialized organics may pose a threat, Dr. Pierce notes. While not yet extensive, it could come from areas of Europe where labor costs are low, he says. But improvements such as this one should enable American producers to stay competitive, he believes.

BRIEFS

A method for fixing radioactive wastes in glass is being developed by the chemical engineering division, Atomic Energy Research Establishment of the U.K. Atomic Energy Authority at Har­well, England. By converting radio­active wastes into insoluble glass-like solids, AERE scientists hope to sim­plify disposal problems. The method involves making a slurry of silica and borax in a nitric acid solution of the concentrated wastes. When evapo­rated to red heat, the slurry sinters and melts, and on cooling solidifies to a glass of chosen composition. A typi­cal product might contain from 20 to 30% by weight of waste oxides, AERE says. A pilot plant designed to handle

1000 curies of active waste per batch is now being designed. According to AERE, experimental work has shown that the properties of the glass remain basically unchanged when it is sub­jected to a radiation dose of 1011 rads —a dose comparable to what the glass would receive in 500 years if it con­tained high activity waste.

Removal of soluble contaminants from sewage treatment plant effluents will be studied by Dow Chemical's industrial service division under a con­tract with the Public Health Service. Under the $25,200 contract, Dow will study the use of specially activated carbons to remove the soluble impuri­ties. Although used by water utilities to treat raw water, the method has not been applied to sewage treatment processes, Public Health Service says. The contract is the first of a series to university and industrial laboratories to study new and unconventional sew­age treatment methods. Techniques to be investigated include separation of impurities by foam fractionation, freezing, gas hydration, and adsorp­tion.

Los Alamos Molten Plutonium Reac­tor Experiment No. 1 (LAMPRE-1) has gone critical. The experiment is part of AEC's plutonium fuel development program under way at Los Alamos Scientific Laboratory in New Mexico. Molten plutonium fuels are being con­sidered for use in fast breeder reactors. Initial fuel for LAMPRE-1 is a molten alloy of plutonium and iron. In later experiments, other plutonium alloy fuels will be tried. If the molten fuel concept proves successful, the low melting point of metallic plutonium may turn out to be an asset, rather than a drawback, according to AEC. Design power level of LAMPRE-1 is 1000 thermal kw. Circulating molten sodium cools the fissioning fuel.

A magnesium oxide recovery system has been exported by Babcock & Wil­cox to Sweden for use in a new pulp mill being erected by Nymolla Aktie-bolag, a subsidiary of Hylte Bruks Aktiebolag. Scheduled to go on stream in 1962, the system is designed to reclaim the chemicals from spent sulfite liquor for re-use in the pulping process. The recovery equipment will process 560,000 lb. of magnesia-base liquor a day, B&W says.

A P R I L 24, 1961 C & E N 67

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