the amount of the effective electrical energy feedback. The Acton data have been partially salvaged. Notwithstanding deviations from the patents, it is now documented that the Yale team actually obtained considerable enhancement. Deviations from the patents can predictably lead to lesser results. The experiments described in the patents were not replicated. The deviant experiments should be interpreted as a success even though they did not achieve all the Diller results. In any event, external data cannot alter any of the hundreds of observations that have already been determined in the Diller laboratories. Moreover, no thermodynamic law nor any other major law of physical science has been presented that is in irreconcilable conflict with the Diller data. This author’s suggestion would be to select an example in the patents and t o pursue that example completely, while maintaining full regard for the context of the entire patent. The cooperation of Schlain and Cammarota, respectively, of the U S . Bureau of Mines, in supplying additional or differently oriented information by telephone is acknowledged.
As indicated above, considerable parametric differences, the explanations for which are less than axiomatic, exist among the shielded and concentrated Bureau of Mines cell, the reduced scale cells used by Diller, and the industrial cells. I t is hoped that even the gain that was obtained with the limiting Acton cell will enable an industrial operator to determine whether a substantial pilot operation for testing the proprietary Diller discovery, in close accordance with the patents, is indicated. L i t e r a t u r e Cited Acton, C. F.. Nordine, P. C., Rosner, D. E. Ind. Eng. Chern., Process Des. Dev., 15, 285 (1976). Cammarota, V. A,, Jr., Schlain, D., J. Nectrochem. SOC., 117, 282 (1970). Diller, I. M. U.S. Patent 3 244 604 (Apr 5, 1966). Dilier, i. M., Nature (London), 224, 877 (Nov 29, 1969). Diller, I. M.. U S . Patent 3 806 433 (Apr 23, 1974). Hinshelwood, C. N., “Kinetics of Chemical Change”, Oxford, 1933. Schlain, D., Kenahan, C. E., Swift, J.,H., U.S. Bur. Mines Rept. Invest., No. 6265 (1963).
50 Park Auenue
Neu: York, Neu: York 10016
Isaac M. Diller
Electrolytic Reduction of Alumina with Activated Cryolite Sir: In our recent publication (Acton e t al., 1976), we documented our unsuccessful attempts to reproduce the reported effect (Diller, 1966) that the energy consumption in aluminum extraction via the Hall process can be significantly reduced by kilovolt pulse “activation” of the molten salt electrolyte. In the above-captioned correspondence Diller offers no new evidence, but rather a number of misleading statements regarding the validity of our published research. As shown below, his analysis of the results we have reported is subjective and illogical. In view of the availability of our fully documented paper it is neither necessary nor appropriate t o pursue every inconsistency in Diller’s recent comments. For the benefit of the reader, however, we address below his specific criticisms. 1. Thermodynamic Limitations on Minimum E n e r g y Requirement f o r Aluminum Production. Since our thermodynamic analysis is model-free, explicit consideration of any particular carbon consumption reactions invoked by Diller is unnecessary. The calculated (second law) minimum electrical energy requirement for aluminum extraction by the overall reactions stated is 1.43 kWh/lb of Al(1). Diller’s claims of “some net value less” would require repeal of the second law of thermodynamics, which we judge to be premature based on the evidence Diller presents. 2. C r i t e r i a f o r Assessing Existence of Pulsing Effect. We have clearly stated that an appropriate test for “activation” in our laboratory equipment is a reproducible lowering of cell voltage a t fixed current compared to the prepulse cell voltage. A comparison of voltage/current relationships from one run to another, as suggested by Diller, or, worse still, from other investigations, to establish a “base line” for proving “activation” is technically unsound. Our only observed voltage change (-0.20 V for only 7 s) in experiment no. 6 could not be reproduced and was within the scatter of our data. Accordingly, we believe it to be an exper-
imental artifact (produced, perhaps, by a bubble or piece of carbon breaking away from the anode) rather than a sign of a patentable phenomenon. 3. Design of Experiment; Regime of Operation. Our laboratory cell (our Figure 1)and electronic circuitry (Figure 2) were designed to give readily interpretable and reproducible results. The exact specifications and conditions for the experimental parameters are delineated in our Table I11 and are seen to be bracketed by those specified in Diller’s patents. 4.Salts and Crucibles Used in Experiment. Having first claimed that our experiment 5 was designed such that activation “could not have been achieved”, Diller then goes on to claim that “activation” was seen in experiment 6 due to the residue of “activated” salts left over from experiment 5! Actually, none of our experiments shows evidence for activation, and, as explicitly stated in our paper, fresh salts and crucible were used in experiment 6. 5. Measurement/Control of Electrical Parameters. Diller apparently does not realize that our experiments were conducted a t constant current such that “activation”, if present, would be seen as a drop in cell uoltage. His criticism that the observed current would be too high for our power supply (50 A ) incorrectly assumes that we were conducting a constant voltage test. Incidentally, Diller also compares total applied voltage with net cell voltage in his comments on our use of a 2 V (net cell voltage) base vs. his 5 V (total applied voltage). He also mentions 5 V to mean 5 kV in his discussion of our experiment no. 6. 6. Use of G r a p h i t e Anode. Nuclear grade graphite is the usual material employed in laboratory aluminum electrolysis cells because of its physical, chemical, and mechanical stability. While the chemical nature of the electrode material can have an effect on the magnitude of anode polarization, if the molten salt conductivity and/or structure exhibited a long Ind. Eng. Chem., Process Des. Dev., Vol. 16, No. 2, 1977
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term change as a result of high voltage pulsing (as Diller claims), it should have been observable in a cell using a graphite anode. Summary Based on our scientific and technological interest in energy-efficient means of metal extraction, the effects of kilovolt pulsing on Hall cell A1 production claimed by Diller (1966) attracted our attention. The independent feasibility experiments conducted a t Yale, as documented in Acton et al. (1976), failed to show evidence for any long-term effect of kilovolt pulsing on post-pulse molten salt electrical conductivity. While, of course, every possible configuration/condition was not employed, our experiments were evidently well within the ranges claimed to be necessary in Diller’s patent work (see our Table 111). Diller’s present comments on our paper are imaginative, but they offer no new experimental evidence, nor any criticism of our experiments which stands up to scrutiny. Accordingly, we reiterate our earlier conclusion that kilovolt pulsing has no significant aftereffect on the normal current/
voltage relationship in the parameter ranges specified. We hope that the publication of our fully documented experiments and ancillary thermodynamic analysis is useful in guiding future approaches to improving the energy efficiency of electrochemical aluminum extraction processes. Indeed, we hope the publication ofsur work will stimulate the release of similar research, of whichbe have only recently become aware, from within the aluminum industry. Literature Cited Acton, C. F., Nordine, P. C.,Rosner, D. E., Ind. Eng. Chem., Process Des. Dev.. 15, 285 (1976). Diller, I. M.,U.S. Patent 3 244 604 (Apr 5 , 1966).
High Temperature Chemical Reaction Engineering Laboratory Department of Engineering and Applied Science Yale University N e u Hauen, Connecticut 06520
Present address: Olin Metals Research Laboratories, New Haven, Ct. 06504.
CORRECTION The article, “Backmixing and Liquid Holdup in a GasLiquid Cocurrent Upflow Packed Column,” by G. J. Stiegel and Y. T. Shah [Ind.Eng. Chem., Process Des. Deu., 16,3743 (1977)] has the following errors. In eq 15,the value of the exponent c on ReG should be equal to -0.19, the same as is shown in Figure 3. Also, the variable a in a few correlations should read as a,.
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Ind. Eng. Chem.. Process Des. Dev., Vol. 16, No. 2, 1977
Constance F. Acton’ 1 Paul C. Nordine Daniel E. Rosner
