cumvented. I n the 1968 tests in some cases, coverage was maintained up t o 30 km/hr (18.6 mph). Trials were made with slurried alcohol with 10% monoethoxylated alcohol added. After the 1967 tests, the orifices had been enlarged. This required, in turn, an increase in the dilution and resultant amounts of water t o be pumped. The pumps were changed, and the pumping system was redesigned. Tahal has been studying the data and is preparing a comprehensive report. The data collected are being processed, based on energy balance and not on direct measurements of quantities. The major contributioiis thus far are as follows: .critical I wind-speed limit was established above which even double quantities of alcohol did not preserve the monolayer. During two full seasons, large-scale tests were carried out, and comprehensive data were collected as to the percentage of coverage obtained, especially a t various wind speeds which tend t o break up the film. On a lake of 3 km2 (700 acreh), a critical wind speed n a s about 25 km,’hr (15.5 mph), above which it is unfeasible to maintain the lake cover, even when using much increased quantities of alcohol. The dispersing system (suspension process) was further improved, proving i t capable of long-range application, and a foolproof system for easy maintenance and operation is being worked out. Quantitative data, collected from five fully controlled test series of 10 days each, confirmed that i t is feasible t o maintain a high percentage of coverage for long periods.
literature Cited Chem. Eng. Sews, 36, 44 (June 30,1958). Crow, F. R., Agr. Eng., 42,240-43 (May1961). Dressler, R. G., I$. Eng. Chem., 56, 36 (July 1964). Dressler, R. G., Retardation of Evaporation by Monolayers,” V. K. LahIer, Ed., pp 203-11, Academic Press, New York,
N.Y., 1962. Dressler, R. G., U.S. Patent 2,903,330 (1959). Dressler, R. G., Johnson, A. G., Chem. Eng. Progr., 54 (I), 66-9 (1958).
Drew, H. F., Report of S. W. Evaporation Research Council, Texas Water Board, Austin, Tex., 1958. Foulds, E. L., Dressler, R. G., Ind. Eng. Chem. Prod. Res. Develop., 7 , 7 5 (1968). Frenkiel, J., “Evaluation of Evaporation Reduction in Field Trials,” lecture given at symposium on Water Evaporation Control, Poona, India, December 1962. Frenkiel,, J.., “EvaDoration Reduction,” Unesco, Paris, France, 1965.
Langbein, W. B., Hains, C. H., Culler, R. C., U.S. Geol. Survey Circ. No. 110, 1951. Mansfield, W. W., Nature, 175,247 (1955). hleinke, W. W.,. Wddrip, W. J., “Research on Evaporation in Small Reservoirs, Texas Water Comm. Bull. 6401, March 1964. Xoe. E. R.. Dressler. R. G., Ind. Ena. Chem. Prod. Res. Develov.. ., 6,‘132, (1967).
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Reiser, C. O., I n d . Eng. Chem. Proc. Design Develop., 8 , 63 (1969). Roberts, W. J., J. Geophys. Res., 64 (lo), 1605-10 (1959). Simko, A. J., Dressler, R. G., Ind. Ena. Chem. Prod. Res. Develop., _ . 8,446-50 (1969).
Vines, R. G., “Retardation of Evaporation by Monolayers,” p 137, Academic Press, New York, N.Y., 1962. RECEIVED for review December 11, 1972 ACCEPTEDDecember 15, 1972 Presented at the Division of Colloid Chemistry, 164th Meeting, ACS, New York, N.Y., August 29,1972.
Size and Shape of Asphaltene Particles in Relationship to High-Temperature Viscosity Hendrik Reerink KoninklijkelShell-Laoratorium (SheU Research B.V.), Amsterdam, The Netherlands
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EDITOR‘S NOTE The manuscript for this paper was duly studied, and in the judgment of a respected reviewer, certain conclusions require qualification. The author countered with (in his professional judgment) appropriate explanations and interpretations. These, however, have not satisfied the reviewer’s concepts, though he recommends that the work be published. W e have here a classical instance of two competent scientists advancing a segment of technology by objective debate. Fortunately, the Signals section provides an opportunity to publish, while at the same time offering a medium for each party to submit “Correspondence” in future issues.
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Vol. 12, No. 1, 1973
Bitumens can be split by means of n-alkanes into a n extremely viscous oil (maltenes) and a solid precipitate (asphaltenes) , The rheological properties of bitumens depend strongly on the asphaltene content. This is clearly demonstrated in Figure 1, which has been constructed from data obtained by Mack (1932) in measuring the viscosity of solutions of asphaltenes in the parent maltenes. I n the books of Pfeiffer (1950) and Hoiberg (1964), the role of the asphaltenes is also stressed. T h a t asphaltenes are of relatively high molecular weight is apparently of importance. I n a survey, Dickie and Yen (1967) quote values for the molecular weight ranging from about lo3 to above 105. The high molecular weight itself cannot explain the influence on rheology, For instance, if the asphaltene molecules were spherical and nonsolvated, a 10 vol solution would
have a viscosity of about 1.3 times t h a t of the solvent, irrespective of the particle (molecular) size and provided specific particle interaction is absent. From Figure 1, however, we see t h a t in reality the relative viscosity ranges from 5 to 50. The asplialteiies either are nonspherical, immobilize part of the solvent, or are strongly interacting, or we have t o deal with a combination o f these factors. From dilute solution viscosity, voluminosities of 2-5 have been obtained (Pfeiffer, 1950; Lorenz e t al., 1961; Girdler, 1965), which means t h a t the asphaltenes give the same contribution to viscosity as iionsolvated spheres when the volume concentration of the latter would be 2-5 times as high as that of the former. Voluminosities of asphaltenes as high as 40 in crude oils (Lorenz et al., 1961) are erroneous, because in the measurements i t was not only the concentration of asphaltenes but also t h e composition of the solvent that varied. The voluminosity of asphaltenes has often been ascribed to swelling or solvation of approximately spherical particles (Pfeiffer, 1950; Lorenz et al., 1961; Girdler, 1965; Winniford, 1963). T h a t viscosity in poor solvents is higher than in good solvents (Pfeiffer, 1950; Altgelt, 1968) casts doubt on this euplanation. I n addition, from what is known about the structure of asphaltenes (Dickie and Yen, 1967), swelling by penetration of a relatively large amount of solvent into t h e molecules is not likely, and neither is the bonding of four volumes of solvent in
