Energy & Fuels, Vol.25, No.11, 5360-5365, 2011
Stability Change of Asphaltene in the Residue during Slurry-Phase Hydrocracking
Asphaltenes play a key role in the stability of the residue during processing. When asphaltenes reach their solubility limit in the residue, they would begin to aggregate, so that a new phase, called the mesophase, would separate from the oil phase, which eventually leads to coke formation. To relate coking characteristics, the changes in stability of the residue were studied during a slurry-phased hydrocracking reaction. The results indicated that the coke formation is obviously restrained by H-2 and a catalyst such that the coke induction period is prolonged and the coke content is also reduced significantly compared to the coke content only in the presence of H-2. The colloidal stability parameters (CSPs) determined by means of flocculation onset titration and the colloidal stability function (CSF) calculated on the basis of saturate, aromatic, resin, and C-7-asphaltene (SARA) composition of the residue have a similar variation trend, which could be related to coking characteristics. First, the coking onset and the maximum asphaltene content in the residue were in correspondence with the turning point in the downward trend of the stability of the residue. The stability of the residue deteriorated significantly during the coke induction period, and the decreased trend tended to smooth after the coking onset point. Second, it is confirmed that the downward trend of stability is inhibited effectively in the presence of H-2 and a catalyst, so that the ability of the residue against thermal disturbance is enhanced to reduce the coke formation. The changes in structure parameters of asphaltenes also showed that the catalyst could inhibit or delay the excessive condensations of asphaltenes to reduce the coke formation.