Hindered diffusion of asphaltenes at elevated temperature and pressure. [Semi-annual report], September 20, 1995--March 20, 1996

Abstract

In this study equilibrium adsorption isotherms were determined for two petroleum asphaltenes, AAD-1 and AAK-1, and one coal asphaltene, called No. 97500. Isotherms were determined for three different temperatures, namely 20, 35 and 50{degrees}C. The experimental data for the petroleum asphaltenes were fitted with a Freundlich isotherm. For the coal asphaltene a Freundlich isotherm was used to fit the experimental data for lower concentrations; however, for higher concentrations a linear isotherm fitted the experimental data better. The coal asphaltene showed a tendency to form multilayers on the catalyst surface. Upon comparison of the adsorption isotherms for the three different temperatures, an interesting effect was observed. Although a decrease of the asphaltenes adsorption for higher temperatures was expected, the adsorption as a function of the temperature in fact showed a maximum for the petroleum asphaltenes and a minimum for the coal asphaltenes. This interesting and unexpected behavior was speculated to be due to the formation of micelles in the coal asphaltene solution and the different dependence of micelle formation and adsorption on temperature. Comparing the adsorption isotherms for the three different asphaltenes revealed that the adsorption of the coal asphaltenes was initially lower than the adsorption of the petroleum asphaltenes, but increased more rapidly, finally becoming near and even greater than the adsorption of the petroleum asphaltenes. This was suggested to be due to the tendency of coal asphaltenes for multilayer adsorption on the solid surface.