Znd. Eng. Chem. Res. 1993,32, 1800
1800
CORRESPONDENCE Comments on “Moisture Desorption in Cellulosic Materials” Vincent G. Gomes Department of Chemical Engineering, McGill University, 3480 University Street, Montreal, Quebec, Canada H3A 2A7
Sir: This is with reference to the article by Sheng H. Lin (Ind. Eng. Chem. Res. 1991,30, 1833-1836). I wish to point out a few errors in the article. The values of diffusivities plotted in Figure 1 do not match with the ones calculated from eq 2. Figure 1or parameters for eq 2 are in error. The water diffusion equation is highly sensitive to temperature: a 107% variation in absolute temperature (say, around T = 320 K in Figure 2) changes moisture diffusivity (D) by about 10 times, which is much higher than expected. In contrast a 10% change in moisture concentration (C)causes a 5 %5 change in D. The range of applicability of D is given as C = 0-15% dry weight; for
what temperature range is the model valid? The author based his findings on the results given in reports by P. F. Ast (GE Report HV-ER-66-41)and D. E. Ewart (GE Report 60PT44) prepared in 1966. These reports are not in the public domain to the best of my knowledge. It would be interesting to know Ewart’s experimental technique: how the moisture concentration was determined in the paper thickness direction,if multiple plies were used, and if problems were experienced while peeling one ply from another. What kind of precision was obtained in determining C? Was the paper bone dry prior to water absorption or were experiments performed with partially wet paper? It is crucial to know these details.
ADDITIONS AND CORRECTIONS Volume 31, Number 11
Structure-Oriented Lumping: Describing the Chemistry of Complex Hydrocarbon Mixtures R. J. Quann* and S. B. Jaffe Page 2491. The paragraph beginning Rule: N4 Ring Opening on Aromatics should read: If a molecule contains an N4 increment, the naphthenic ring with four carbon atoms, the ring may open and add to the total alkyl group structure of the molecule:
The reactant must have an A6 ring to be an aromatic molecule and must, obviously, have an N4 ring to open. It is assumed also that N3, N2, and N1 rings open before the N4 ring. The product rule transforms the reactant by subtracting one N4 ring and adding the carbon to the alkyl group R. Page 2491. In the paragraph beginning Rule: Aromatic Dealkylation,the second rule (found on page 2493) should read: 2. reactant selection rule:
(A6# 0) A (R Q 3 + rings)
n
A
(R> 3)
product generation rule: product 1
The reactant and product generation rules for this reaction are
R+R-4 me-0 product 2 (isobutane)
reactant selection rule:
R+4
(A6Z0)A ( N 4 Z 0 )
A
(O=N3+N2+Nl)
product generation rule:
R-R+4 N4+N4-1
IH-1 br-1 Page 2493. In the paragraph beginning Rule: Paraffin Hydrocracking the last sentence should read: Cracking reactions that yield a methane are very slow due to unfavorable carbenium ion intermediates and therefore neglected in the present treatment.
0888-5885/93/2632-1800$04.00/00 1993 American Chemical Society
