I S D U S T R I A L A S D ESGI-VEERISG CHEMISTRY
June, 1931
721 ~____
NOTES AND CORRESPONDENCE Kinetics of a Type of Heterogeneous Reactions The Mechanism of Combustion of Pulverized Fuel Editor of Industrial and Engineering Chemistry:
In a paper under this title [IND. ENG.CHEM.,23, 406 (1931)] an oversight of some importance was made in the calculation of the mass of oxygen diffusing through the stagnant film surrounding a burning particle. The ordinary equation of diffusion, based on experiment, was employed, which is
Jf
bC bX
= - 6-
where -11is the mass diffusing in unit time across a unit area perpendicular to the direction x, 6 is the coefficient of diffusion, and C is the concentration expressed as mass per unit volume. If, however, the temperature varies with x , Equation 1 is not correct. If a gas mixture of uniform composition is subjected to a temperature gradient, diffusion does not occur, although bC/dx has a value other than zero. The proper equation t o be employed under these conditions is
6 b(CT) Jf = - -
T
3s
where T is the absolute temperature. T h a t this equation meets the necessary requirements can readily be seen from the fact that (2) reduces t o (1) when T is constant. Also, if CT is constant, then .If = 0, as must be the case if the gas obeys Charles’ law. In the original paper Equation 14 should therefore read:
and (17) should read:
(17’) Further calculation is considerably simplified by making the approximation that 6 is actually proportional to the square of the absolute temperature instead of to the 1.75th power. Then, for the temperature range considered, Equation 12 must be replaced by :
6
=
0.19
:
P
(&)?
(12’)
and the final expression for the mass of oxygen diffusing to the carbon as shown in Equation 20 becomes:
The other calculations are subject t o a corresponding modification, but the general method of calculation is unchanged. The effect of these changes is slightly to lower the temperature of the particle surfaces and to lengthen the time of combustion. Thus, in Figure 2 the temperature curves will be displaced downwards and in Figure 3 the curves will be displaced upwards. I t is also worthy of mention t h a t the work of Schack and others [ Z . tech. P h y s i k , 6 , 530 (1925)] indicates that the carbon particles, as they become small in size, will not obey the usual radiation law assumed in Equation 21, but will radiate a t a somewhat
slower rate. As yet the function connecting intensity of radiation, particle size, and temperature is unknown, so that a more accurate statement of Equation 21 cannot be made. However, it is t o be expected that such a correction will result in an increase in the surface temperature and a corresponding decrease in time of combustion. T o some degree, therefore, the two corrections mentioned in this note offset each other. S. P. BURKE T . E. UT.SCHUMANN \ V E S T \‘IRGINIA MORGANTOWN,
rNIVERSITY
1%‘. V A .
April 26, 1931
Aluminum Chloride and the FriedelCrafts Reaction Editor of Industrial and Engineering Chemistry: With reference to the article under this title by P. H. Groggins ANI) ENGINEERING CHEMin the February issue of INDUSTRIAL ISTRY, the writer suggests corrections on certain minor points. The company referred to as the “Savell-Sayre Electro Chemical Company” is properly known as “Savell Sayre & Company, Inc.” Contrary t o M r , Groggins’ statement, this company was the first t o introduce anhydrous aluminum chloride to the chemical industry in this country. At the time this was done, which was the early part of 1921, U‘eiss and Downs, working in the laboratory of the Barrett Company, were developing their anthraquinone process. All the material used for this development was made by Savell & Frost, the partnership which preceded the incorporation of Savell Sayre & Company. At the completion of the laboratory work, the phthalic anhydride and anthraquinone processes were transferred from the Barrett Company t o the National ,4niline and Chemical Company, of Buffalo, IT,Y . Savell Sayre & Company, Inc., were making considerable shipments to the Buffalo plant before Jacobson had placed any of his product on the market. The process called the “Savell-Sayre process” should really be called “Savell-Frost process,” since it was developed by the writer and J. G. G. Frost, the former’s partner. This process is entirely a chemical process and, except for the fact that both chlorine and aluminum are products of electrochemical operations, it is not electrochemical in any sense. Metallic aluminum and chlorine are brought together a t approximately 900” C. and the reaction proceeds rapidly with the generation of considerable heat. iv,L. S A V E L L T H EMATHIRSON A L K A L IW O R K S , I x c 2.50 P A R K .%\’E., S E W I‘ORK, N. Y. April 13, 1931
Editor of Industrial and Engineering Chemistry: I n the preparation of the paper “Aluminum Chloride and the Friedel-Crafts Reaction,” we were guided by the available literature, which showed that A . M. McAfee took out applications for patents in this field as early as 1916 (V. S. Patent 1,217,471), and Jacobson applied for his U. S. Patent 1,445,082 in June, 1921. The latter date appears, therefore, t o coincide with the early activities of Savell and Frost. P. H . GROGGINS BUREAUOF
CHEMISTRY A N D SOILS
WASHINGTON,
April 22, 1931
D C
