Ind. Eng. Chem. Process Des. Dev., Vol. 17, No. 3, 1978
377
Electrolytic Reduction of Alumina with and without High Voltage Pulsing Sir: In his present communication, Diller is forced to selectively omit part of our published data (experiment no. 6, Acton et al., 1976) in order to computationally demonstrate “activation”. The back emf (intercept at zero current) of 1.6 V determined from all of our data (cf. our Figure 3, Acton et al., 1976) in fact agrees with the value quoted by Diller from the data of Schlain et al. (1963); i.e. our data show no perceptible “activation” regardless of whether or not other “baseline” data are invoked. Actually, by employing Diller’s method of data analysis, virtually any set of experimental current-voltage data could be incorrectly shown to demonstrate “activation” simply by exploiting the inevitable scatter in any suitably chosen pair of data points, and ignoring other valid data. I t is noteworthy that Diller now acknowledges that our measurements were carefully made, credible, and that our experimental parameters indeed fall within the ranges specified in his patent (Diller, 19741, as we, of course, intended. However, Diller’s recent communication contains no new experimental evidence, nor any valid criticism of our earlier,
documented experiments. Thus, there is no reason to alter our previous conclusion (Acton et ai., 1977) that high voltage pulsing causes no significant after-effect on the normal electrolysis current/voltage relation for parametric ranges specified in our paper.
Literature Cited Acton, C. F., Nordine, P. C., Rosner. D. E., Ind. Eng. Chem. Process Des. Dev., 15, 285 (1976).
Acton, C. F. Nordine, P. C., Rosner, D. E., Ind. Eng. Chem. Process Des. Dev., 16, 261 (1977).
Diller, I. M., U.S. Patent 3 244 604 (Apr 5, 1966). Schlain, D., Kenahan, C. B., Swift, J. H., U . S . Bur. Mines Rep?.Invest.,No. 6265 (1963).
High Temperature Chemical Reaction Engineering Laboratory Department of Engineering and Applied Science Yale University New Hauen, Connecticut 06520
Constance F. Acton*l Paul C . Nordine Daniel E. Rosner
Olin Metals Research Laboratories, New Haven, Conn. 06504.
CORRESPONDENCE
Survey of Propane Pyrolysis Literature Sir: The recent publication by Volkan and April (1977) includes features with which I agree but several features with which I disagree. This disagreement is, in part, caused by pyrolysis results reported in 1975 or later that were not included in the survey. Volkan and April have certainly made a major effort to collect and analyze 103 technical papers. Making sense out of so many publications that contain divergent conclusions is not easy. Several recent publications that were not surveyed, however, address themselves directly to some of the areas of controversy relative to propane pyrolysis. Papers in this category were presented in symposia at the 169th National Meeting of the American Chemical Society, Philadelphia, Pa., March 1975, and at the First Chemical Congress of the North American Continent in Mexico City (1975). Most papers in these two symposia were published in 1976 in the ACS Symposium Series. Features of the review by Volkan and April that I would like to discuss include the following. (A) By-products. Several products formed in smaller amounts have been discussed, but three by-products of importance have not been adequately discussed. Coke or carbon formation was never really discussed. Coke formation is, however, of major concern in all commercial pyrolysis units including those using propane as a feedstock. Several factors affecting coke formation include the material of construction of the reactor, past history or pretreatment of the reactor, and operating conditions (Brown and Albright, 1976; Crynes and Albright, 1976; Dunkleman and Albright, 1976a,b; Herriott and Eckert, 1972). Coke is formed by a t least two mechanisms. First the metal surface of a reactor catalyzes the growth of a filamentary type coke. The resulting coke contains metal granules and is magnetic in character; these 0019-7882/78/1117-0377$01.00/0
metal granules are extracted from the surface of reactors constructed of high alloy steels. Such coke occurs for example on the surfaces of nickel-chromium-iron alloys used in commercial reactors but not on glass or aluminized metal surfaces. Second, some coke is formed by condensation, polymerization, or agglomerating mechanisms in the gas phase. This coke is nonmagnetic in nature. Additional evidence on coke formation during pyrolysis was presented at the Anaheim ACS Meeting (Albright and McConnell, 1978; Albright and Yu, 1978; Albright et al., 1978). Acetylene that is a precursor for coke is always formed in small but nevertheless significant amounts whenever propane is pyrolyzed commercially. Coke formation from acetylene has recently been investigated in considerable detail (Baker, 1977; Baker and Waite, 1975; Baker et al., 1973; Bernard0 and Lobo, 1975; Lobo and Trimm, 1973). Many details of the coking mechanism have been determined. A filament-type coke is formed in some cases. Other probable coke precursors include ethylene, propylene, butadiene, and benzene, all of which are produced to at least some extent during most propane pyrolyses. Carbon oxides were mentioned in Table IV of the review; it is indicated, or a t least implied, that they are formed as acetylene and steam react in the gas phase. Carbon oxides are always formed in significant amounts during pyrolysis in high-alloy reactors (including commercial reactors) but are not formed in Vycor reactors. Most, if not all, carbon oxides are formed by reactions between coke or carburized metal surfaces and steam (Dunkleman and Albright, 1976a;Tsai and Albright, 1976). Metal surfaces act in part at least to catalyze the formation of carbon oxides. Heavy hydrocarbons include, in addition to those listed in the review, aromatics. (B) Surface Effects. In the review, it was stated that the walls of the reactor play a role in the initiation and termination
62 1978 American Chemical Society
