Coking propensity of Athabasca bitumen vacuum bottoms in the presence of H-donors — formation and dissolution of mesophase from a hydrotreated petroleum stream (H-donor)

Abstract

The effect of H-donors (hydrogenated aromatic hydrocarbons — HHAP) derived from a petroleum stream on mesophase formation during thermal hydrocracking of Athabasca bitumen vacuum bottoms (ABVB, +525°C) was investigated using real time high pressure and temperature microscopy (hot-stage) under a nitrogen atmosphere. When ABVB was treated alone, mesophase formed at a relatively fast rate after only 66–70 min (at 440°C). When HHAP was treated alone under the same conditions, it showed a highly fluid behavior. This material did not develop any mesophase even after a prolonged first cycle of heating (>140 min), but eventually formed mesophase during a second cycle of prolonged heating. Two distinct mesophase types were observed during thermal treatment of HHAP. One type of mesophase dissolved upon heating at moderate temperatures and re-appeared upon cooling, an indication of “thermotropic transformation” typical of true liquid crystalline material derived from low molecular weight components. The other type of mesophase that was most likely derived from high molecular weight components did not dissolve but formed bulk mesophase. ABVB was then mixed with 5 wt.% HHAP to observe the effect of an H-donor on mesophase formation from bitumen. In the presence of HHAP, both the rate and the amount of mesophase formed from ABVB were reduced significantly. Furthermore, the mesophase appearance time (induction period) was prolonged by as much as 20 min. This paper demonstrates the usefulness of hot-stage microscopy as a tool for screening potential additives in visbreaking and fouling operations.