Chairman Mason $2 million worth of understanding for example, in no small way stems from the company's TV advertising. These benefits, while hard to define, have led some of the other chemical giants to TV. One of the longest running of this type of show is "Alumni Fun," sponsored by American Cyanamid. Monsanto has also used TV. About six years ago Monsanto sponsored "Conquest/' which was oriented toward developments in science and technology. Dow, too, has played a role in sponsoring regular TV shows such as "Medic," and "The Dow Hour of Great Mysteries." And Esso Research and Engineering has sponsored the "Festival of the Performing Arts" and the "Play of the Week."
Process cleans up nitric tail gas Engineers at the University of Florida have applied for a patent on a zeolite adsorption-desorption process aimed at recovering nitrogen oxides from the tail gas of nitric acid plants efficiently enough to pay for itself. The process might add 4 to 5 tons per day of 60% acid to the output of a conventional 300 ton-per-day plant, Dr. C. I. Harding of the Gainesville school's air pollution research laboratory estimated at the annual meeting of the Air Pollution Control Association in San Francisco. He and his associates are now developing the data they need to design a plant-scale unit. Tail gas from modern nitric acid plants in the U.S. generally contains 0.1 to 0.4% nitrogen oxides (NO x ) by volume (as well as 3 to 4 % oxygen, roughly 1% water, and about 9 5 % nitrogen). In this range it becomes uneconomical to recover any more of the nitrogen dioxide—formed by catalytic oxidation of ammonia—in the absorption step in an acid plant. Sometimes the nitrogen oxides must be removed anyway to avoid a pollution problem.
Where this is the case, the only method used to any extent is catalytic reduction of the tail gas after mixing with hydrogen, methane, or carbon monoxide. Adsorption has rarely been tried at NO x concentrations of 0.4% or less. Dr. Harding and his coworkers tried both silica gel and commercial zeolites (molecular sieves) as potential adsorbents for an economic recovery process. At first, they fed simulated tail gas to two stainless steel columns packed with adsorbent. Each column was 28 inches high and 3 inches in inside diameter. The zeolites performed well in the laboratory and markedly better than silica gel, which was soon dropped as a contender. Thus encouraged, the Florida group moved their equipment to a nitric acid plant to work with real tail gas. The bulk of the experimental work was done by Dr. B. B. Sundaresan, now at the University of Madras in India. Also involved were Dr. F. P. May and Dr. E. R. Hendrickson, now at Resources Research, Inc., Falls Church, Va. In the work at the plant, each of the two columns contained 4.9 pounds of the same zeolite. The upper limit for NO x in the exit gas was set arbitrarily at 0.02%. All adsorption tests were run past that point, however. In a typical run, the column was fed 2.4 s.c.f.m. of acid plant tail gas for seven hours. The gas entered at 94° F. and, adsorption being exothermic, column temperature reached a maximum of 125° F. at a point 14 inches from the base of the column after three hours. NO x content of the entering gas was 0.18%. NO x in the exit gas remained below 0.001% for three hours, then rose gradually to 0.02% after 5.3 hours and 0.8% after seven hours. Moisture content was 0.7 to 0.8% in the entering gas and remained below 0.2% in the exit gas throughout the run. The column was regenerated with hot air at 300° to 350° F. Steam at 350° F . was injected for five minutes, but hot air alone was used in some runs. Of the material adsorbed in seven hours, 80.6% was recovered in less than 30 minutes, 74.4% as nitric acid (19.4% strength) and the balance as enriched NO x . Recovery conditions can be varied to give a range of combinations of enriched NO x and nitric acid. Either enriched NO x or 20 to 2 5 % acid could be recycled to several points in the acid process. The zeolites' ability to adsorb water and NO x simultaneously suits them particularly well to treating nitric acid plant tail gas. Zeolite life is not yet certain. However, experience in dehydration indicates that it should be in the range of 2000 cycles.
Dispersed oxide strengthens lead Dispersion-strengthened lead is beginning to emerge as a contender for the storage battery and chemical construction markets now held by antimonial and chemical lead. A powder-metallurgy route developed in the U.K. by Associated Lead Manufacturers, Ltd., produces lead mill products containing a dispersed phase of lead oxide. The payoff: sharp improvement in mechanical properties over those of lead alloys generally used in chemical plants, with little change in corrosion resistance. Field trials of process equipment items, such as condenser tubes, acidservice steam coils, and unsupported tanks, made of dispersion-strengthened lead are under way now in the U.K. Some have been in progress for three years. Associated Lead, which has applied for British and U.S. patents on production of the metal, is nearing the point of making limited quantities commercially available. The product was the focus of the firm's exhibit at the International Chemical and Petroleum Engineering Exhibition, just concluded in London. In dispersion strengthening of metals, the added material is generally dispersed through the powdered parent metal by mechanical mixing, after which the blend is compacted and sintered. In Associated Lead's process, however, the metallic lead powder as formed contains the desired percentage of lead oxide. The powder is compacted and extruded cold. Sheet products can be rolled from extruded sections of the dispersion-strengthened lead. Stampings and other mill shapes as well as foil can also be formed from extrusions. Chemical leads for use in process equipment often contain small amounts of silver, copper, or tellurium to boost creep resistance and tensile strength. In storage batteries—the largest single market for lead—high fatigue strength is required to resist vibration. Antimonial lead is currently the choice for battery plates. Dispersion-strengthened lead containing 4 % lead oxide shows roughly one third higher fatigue resistance at room temperature than does 6% antimonial lead. Tensile strengths are comparable. Both antimonial and chemical lead, moreover, weaken more quickly with rising temperature. At 80° C , the fatigue and tensile strength are half again higher for dispersionstrengthened lead than for the antimonial alloy. In comparison to chemical lead at the same temperature, dispersion-strengthened lead has tensile values more than double chemical lead's and fatigue resistance four or five times as high. JULY 4, 1966 C&EN
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