Configurational diffusion of asphaltenes in fresh and aged catalyst extrudates. Quarterly progress report, March 20, 1996--June 20, 1996

Abstract

This quarter, hindered diffusion of one coal and two petroleum asphaltenes was studied by adsorptive uptake in THF from a bath surrounding a commercial NiMo/Al{sub 2}O{sub 3} catalyst. Several asphaltene fractions were defined via SEC (size exclusion chromatography), with the molecular weight of each fraction being determined by its elution characteristics using polystyrene standards. It was found that both the coal and petroleum asphaltenes have very broad molecular weight distributions; however, the molecular weights of the coal asphaltenes (50--1000) were much smaller than those of the two petroleum asphaltenes (300--10000 and 300--20000 respectively). Simulation results showed that even though the properties of coal and petroleum asphaltenes were quite different, the values of model parameters for the fractions of the three asphaltenes had the same trend; with increasing molecular weight of the fraction, the adsorption constant monotonically increases, and the effective diffusivity decreases. The experimental diffusion data of the three asphaltenes were well represented by similar mathematical models.