DIFFUSION-CONTROLLED ADSORPTIVE UPTAKE OF COAL AND PETROLEUM ASPHALTENES IN A NIMO AL2O3 HYDROTREATING CATALYST/

In this work, hindered diffusion of one coal and two petroleum asphalt enes was studied by adsorptive uptake in THF from a bath surrounding a NiMo/Al2O3 catalyst. A mathematical model for the adsorption-diffusio n of asphaltenes was developed. The model parameters were obtained by simulating the experimental data with the model solution. Several asph altene fractions were defined via SEC (Size Exclusion Chromatography), with the molecular weight of each fraction being determined by its el ution characteristics. It was found that both the coal and petroleum a sphaltenes have very broad molecular weight distributions; however, th e molecular weights of the coal asphaltenes (50-2000) were much smalle r than those of the petroleum asphaltenes (200-30000). The uptake rate s for asphaltene fractions with different molecular weights varied, de pending on their diffusion rates and adsorption constants. Simulation results showed that even though the properties of coal and petroleum a sphaltenes were quite different, the values of model parameters for th e fractions of the three asphaltenes had the same trend and could be e stimated by same numerical expressions; with increasing molecular weig ht of the fraction, the adsorption constant monotonically increased, a nd the effective diffusivity decreased. The experimental uptake data f or the three asphaltenes as a function of molecular weight were well r epresented by same mathematical model.