Basic Research On The Phase Separation Behavior Of Residue Blended With Cracked Heavy Oil

In several domestic refineries, Blending cracked heavy oil into residue often causes fouling in the storage tanks and heat exchanger, coking in the furnace tubes and nozzles, or the variation of the product distribution during delayed coking processing, which seriously affected the normal operation of petroleum refinery.In order to go sight into these problems and effectively evaluate or predict the stability of mixed feedstock and find the methods of enhancing the stability of the system, the phase separation of the mixed feedstocks was firstly studied. The effect of compositon of the mixed feedstocks, thermal treatment temperature and additives on the phase separation behavior was comprehensively carried out. The colloidal chemistry stability, the mechanism of macromolecular association, the chemical structure and the distribution of compositon were all studyed. Thus we can understand the internal reasons of phase separation and deposition which can help us bulid up theoretical and experimental foundation for the use and deep processing of these poor-quality raw materials.The result indicated that if raw materials were mixed in a certain proportion at a suitable temperature range, the system became much steadier. The stability of the system of residue or a variety of mixed oils depended predominantly upon the mutual compatibility between dispersed phase and dispersion medium. The residue colloidal system belonged to peptizing system in which asphaltenes were generally taken as the dispersed phase and maltenes as the dispersion medium. Furthermore resins played a role of peptizator on the stability of asphaltenes while aromatics and saturates were diluted dispersant. The results showed that the lower H/C atomic ratio asphaltenes had, the more polarity they had, the higher aromaticity and condensation degree were, the worser peptizing ability of asphaltenes was. Asphaltenes had more powerful effect on the stability of system. Meanwhile the closer the structure of maltenes was to asphaltenes, the stronger its dispersed ability was and the bigger the coefficient of stability was. Among hydrocarbon medium aromatic components helped to keep asphaltenes stable. If the aromaticity decreased, the stability of petroleum colloid will drop. Only when the nature of dispersed phase and dispersion medium was similar with each other, including relatively uniform molecular weight distribution and the peptizing state between dispersed phase and dispersion medium, was the colloidal stability strong.In the foundation of above study, the methods of preventing phase separation were researched. Four types of phase separation inhibitors were chosen to evaluate the precautionary effect. The results indicated that the key factor of choosing inhabitor was the compatibility between the inhabitor and the oil.