Coal-derived liquid asphaltenes diffusion and adsorption in supported hydrotreating catalysts
Résumé
Hindered diffusion and adsorption phenomena of coal asphaltenes inside the porous network of hydrotreating catalysts are discussed in this paper. After solvent extraction from a coal-derived liquid and solubilization in THF, asphaltenes were contacted with a series of mesoporous hydrotreating catalysts and adsorption-diffusion phenomena recorded by UV-Vis spectroscopy measurements. The effect of the porosity of various NiMo(P) catalysts supported on monomodal mesoporous or bimodal (meso-macro) alumina carrier was investigated. The parameters estimations have been performed, discussed and those obtained with the bimodal (meso-macro) alumina catalyst have been compared to petroleum asphaltenes data [31]. The range of studied concentrations corresponds to cluster formation domain. The results evidence that coal asphaltenes aggregates are smaller, have lower molecular weight and exhibit a much higher diffusion coefficient than petroleum asphaltene aggregates. These results bring important insights for the interpretation of the performance of the catalysts during coal-derived liquid upgrading. Concerning adsorption phenomena, the adsorption constants of coal asphaltenes and petroleum asphaltenes have been found equivalent. The adsorption saturation concentration of coal asphaltenes is higher than that of petroleum asphaltenes. The effective diffusion coefficients obtained at ambient temperature were correlated to the catalytic performances observed during coal-derived liquid hydrotreatment. It points out that the conversion of coal-derived liquid into the porous network of our catalyst is a hindered phenomenon, and that pore size distribution of the support has a great influence on the hydroliquefaction efficiency. (C) 2013 Elsevier Ltd. All rights reserved.