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Figure 2.
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Build-up of nitrogen-15 during run 3
Approximately 1.2 grams of high purity nitrogen-1 5 were produced per day
The only explanation for this increase is that there was a slow increase in the efficiency of the packing, which led to a shorter stage height in the large column as time went on. This could have been caused by a cleaning action of the solution, or by a slight etching of the packing. As the system was not allowed to come to equilibrium a t total reflux but only with product removal, the maximum value possible for nitrogen-1 5 enrichment was not attained. The stage height was less than 3.1 inches for the large column and less than 1.4 inches for the small column. Conclusions T h e Nitrox system is a n attractive method for the concentration of nitrogen isotopes. Dependable, automatic oper-
ation of all the cascade components was demonstrated over a long period of time. The only critical element involved in the scale-up of the cascadt. \vas the design of the product reflusers: these cannot be successfull>-scaled up as a simple function of any single parameter, but must be completel>- redesigned for each ne\v size. The major problem to be solved is effective removal of the large quantities of heat evolved in the very small volume occupied by the reaction interface. If product 1cflusei.s more than 5 or 6 inches in diameter must be used, the material of construction becomes a n important problem. For smaller refluxers, glass serves very \veil. Holvever, for large refluxers glass is impractical and few metals ivithstand the drastic corrosive conditions in the S 0 2 - H S 0 3
I ..
reaction zone Porcelain or ceramiclined metals appear to be kdsible materials of construction for larger refluxers. if adequate heat transfer properties can be obtained. With properlv designed refluxers, the loss of product nitrogen in the sulfuric acid waste stream is negligiblx small. It appears unlikely thdt these losses \$ill become important. even in plants c o n t i n i n g very large refluxers. The only other apparent major scale-up problem is a n economic one In the large-scale production of nitrogen15, the favorable economic position of the h-itrox process is dependent upon credit received from the sale of byproduct nitric and sulfuric acids More than 50 tons of low grade sulfuric acid is formed in the production of each pound of 95y0nitrogen-15 It does not appear economically feasible to upqrade this sulfuric acid to commercial standards. For a plant producing 100 pounds per day of 95% nitrogen-15, economically favorable disposition of more than 5000 tons per day of low-grade sulfuric acid lvould be required. If no credit Ivere obtained for this sulfuric acid. ics disposition Lvould become a n expense and the economic advantage ol the Nitrox process would be lost. The technical feasibility of producing large amounts of nitrogen-13 by the Nitrox process seems \vel1 established. However, the economic feasibility depends on the size of the plant and the market for sulfuric acid in the community in irhich the plant is located. literature Cited (1) Brown, L. L., Begun, G. XI,,“Xitrogen Isotopic Fractionation between Nitric Acid and the Oxides of Nitrogen,” J . Chem. Phys. 30, 1206-9 (1959). (2) Hayford, D. A,, Johnson, W. S . , Levin, S. A., Shacter, J., Von Halle, E., “Feasibility of Large-Scale Nitrogen-15 Production for Nuclear Reactors,” Oak Ridge Gaseous Diffusion Plant Rept. K-1232 (Aug. 17, 1955). (3) Klima, B. B., Ward, \V. T.. Chem. Eng. Progr. 52,381-7 (1956). (4) Klima, B. B., LVard, 1.V. T., It‘iethaup. R. R., Drury, J. S., Oak Ridge National Laboratory Rept. ORNL-CF-55-1-22 (Jan. 14, 1955). (5) Spindel, LV., Taylor, T. I., J . Chem. P h y ~ 23, . 981-2 (1955). 16) Ibid., 24,626-7 (1956).
RECEIVED for review December 13, 1958 ACCEPTED May 14, 1959 Based on work performed for the L. S. Atomic Energy Commission by Union Carbide Corp.
Correction Under New Books [IND.ESG. CHEM. 51, No. 4, 9 5 A (1959)] the correct title of the book by Maurice G. Larian should be “Fundamentals of Chemical Engineering Operations.” 1038
INDUSTRIAL AND ENGINEERING CHEMISTRY
