Dissolution and demetallation behaviors of vacuum residues (Arabian Heavy:AH-VR and Brazilian Marlim: Ma-VR) were investigated using carbon adsorbent and/or an oil-soluble Mo complex (Mo-DTC: Modithiocarbamate) with an aromatic solvent (LCO: Light cycle oil) at variable temperatures of 60-200 degreesC under the atmospheric pressure. An Arabian-Light atmospheric residue (AR) was also treated under the same conditions without addition of solvent and oil-soluble Mo complexes for the comparison of adsorption behaviors of the asphaltene fraction, in which metallic and heteroatom-containing compounds are concentrated. Heating of VRs up to around 150 degreesC during the adsorption treatment enhanced the selective adsorption of the polar asphaltene fraction as the irreversibly adsorbed THF-insoluble (THFI) component. The adsorbed amount as THFI fraction was always higher with carbon black adsorbents than with active carbons. Active carbons with relatively high surface area and mesoporous structure were found to be favorable for the selective removal of the polar and heavy asphaltene. Addition of 20-40% LCO (light cycle oil) solvent was also effective for the selective adsorption of the heavy asphaltene of THFI fraction with the less amount as low as 1 wt%, being the similar level to the adsorbed amount with AR. It is noted that heating of VRs and solvent addition to VRs may keep the viscosity of the VR solution to the same level of AR, facilitating the selective adsorption of the polar and heavy component in the asphaltene. A small amount of Mo-DTC (0.1-0.5 wt% based on VR) decreased the amount of HI-THFS fraction in AH-VR from 17.7 to 14.9 and 13.1 with 0.3 and 0.5% addition, respectively. It is revealed that some portions of aggregated asphaltene may be liberated through the interactions with carbon adsorbent of meso-porous surface and/or oil-soluble Mo complex with the aid of aromatic solvent. (C) 2004 Elsevier Ltd. All rights reserved.