Thomas Gentzis

The effect of carbon additives on the mesophase induction period of Athabasca bitumen

Abstract The ability of solid carbonaceous material to retard the formation of coke during thermal cracking and hydrocracking of heavy hydrocarbons is well known. In this study, we used in-situ microscopy (hot-stage) to obtain additional mechanistic information on whether fine coke and fullerene soot particles retard the growth of mesophase during thermal cracking of Athabasca bitumen, thus reducing the possibility of fouling in preheaters and furnaces. The findings from this study could also have application in other non-catalytic thermal processes such as visbreaking and coking. In the absence of additives in the Athabasca bitumen feed, the formation of mesophase occurred after 61 and 67 min (measured from room temperature) at reaction temperatures of 450°C and 440°C, respectively. The addition of solid coke (ca. 5 wt.%) from a commercial delayed coking operation shortened the mesophase formation time to almost 45–50 min under similar conditions. The coke, having surface area of only 1.65 m 2 /g, resulted in enhanced bitumen fluidity and large-textured mesophase. These observations were rationalized based on the ability of delayed coker coke to release hydrocarbons into the bulk fluid during thermal cracking. Light hydrocarbons released from coke may have changed the solvating power of the liquid phase in bitumen and promoted phase separation, resulting in a shorter induction period. In contrast, adding small amounts of fine fullerene soot (ca. 1 and 5 wt.%) delayed the appearance of mesophase significantly under similar conditions. The ability of fullerene soot to physically absorb the mesophase precursors into its pore structure led to an increase in the apparent viscosity of the bulk phase, which is known to reduce mesophase size and prolong the induction period. Consistent with this, the induction period was prolonged an additional 10 min when the soot surface area was increased from 152 to 208 m 2 /g. The increase in induction period is significant with respect to reaction times and suggests that these fullerene soot materials could be effective in allowing for increased severity and liquid products yield from visbreaking, with less likelihood of fouling in the preheater tubes and furnace walls.

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.