Changes in molecular aggregate of vacuum residue fractions analyzed by slow step scan XRD

A vacuum residue (VR) and its fractions of hexane-soluble (HS) and hexane-i nsoluble (HI) were analyzed by using a horizontal-type X-ray diffractmeter by slow step scan mode at variable temperatures, in order to clarify the ch anges in molecular aggregate structure during heating, solvation, adsorptio n, and hydrotreatment. The VR fractions showed a broad peak around 20 degre es with sharp peaks around 22 and 24 degrees which are ascribed to aliphati c chain entanglement and ordered packing of n-paraffins, respectively. They also showed a shoulder around 26 degrees which is ascribed to aromatic rin g stacking interactions. The asphaltene (I-II) and the polar fraction in HS showed a rather clear peak around 26 degrees, reflecting their stronger ar omatic ring stacking. The peak of 26 degrees in the HI decreased by the hea ting to 300 degrees C with or without the existence of the HS, although the extent was smaller without HS solvent. The addition of toluene was also ef fective for the reduction of the peak around 26 degrees. Ketjen Black (KB: carbon nanoparticles) rather selectively adsorbed the asphaltene fraction f rom VR at 60 degrees C. The adsorbate (THF insoluble: THFI) strongly adsorb ed on KB even after THF extraction and washing showed a broad peak around 2 6 degrees, while the peak of THF extracted fraction (HI but THF soluble: HI -THFS) decreased by the adsorption treatment. The aggregate structure of th e asphaltene through the aromatic plane stacking may be loosened by the hea ting or solvent addition. The hydrotreatment with NiMo/KB or a commercial N iMo/Al2O3 catalyst decreased the content of the asphaltene (HI) fraction by its conversion to maltene (HS) fraction at reaction temperatures below 400 degrees C, while the hydrotreatment at 420 degrees C increased the content of HI with its aromaticity. Based on the above results, the designs of pro per solvent and the nanoparticle carbon catalysts with meso-pores are sugge sted very important for the solvation, depolymerization, demetallation, hyd rocracking of the asphaltene without retrogressive reactions such as coke f ormation.