The Pyrolysis of Oil Sand Bitumen in the Presence of Water and Toluene

Abstract

Phase observation of bitumen in toluene, or water-toluene mixture was conducted during heating up to 380 °C or 400 °C by a view cell. In all the cases, gas (water-rich) and liquid (oil-rich) phases were observed at the final temperature. Bitumen pyrolysis in toluene or water-toluene mixture was also performed at 430 °C. For comparison, bitumen pyrolysis in the absence of solvent (so-called neat pyrolysis) was also conducted. The coke yield at a reaction time of 30 min in toluene was lower than that of neat pyrolysis, while that in water-toluene mixture was the highest among all the reaction atmospheres (neat pyrolysis, in toluene, and in water-toluene mixture). At 60 min, the coke formation was suppressed in the presence of solvents (toluene and water-toluene mixtures). From these kinetic data, the addition of water even in the presence of toluene enhanced the rate of coke formation. On the other hand, due to the extraction of light maltene (that formed oil-rich liquid phase in the neat pyrolysis) by solvents, the amount of hydrocarbons in the oil-rich liquid phase decreased and the final coke formation was lower in the presence of solvents than in the absence of them. A phase separation kinetic model was applied to the experimental results in order to evaluate rate constants of maltene degradation (kM) and coke formation (kC). The addition of toluene decreased kM. This means that maltene in the oil-rich liquid phase was extracted by toluene and its concentration was lower compared with neat pyrolysis. In toluene, kC was higher than that in neat pyrolysis and it is the same reason as the decrease of kM, that is, the extraction concentrated asphaltene in oil-rich liquid phase and the rate of coke formation was enhanced. The kM in water-toluene mixture was higher than that in toluene alone. In water-toluene mixture, some part of lighter maltene probably remains in oil-rich liquid phase because of high pressure of water. This can be explained the reason of higher value of kM. The addition of water-toluene mixture increased kC more than that in toluene. The reason is difficult to explain at this moment and further research is required.