Bitumen is a crude oil with high viscosity, and therefore reducing its viscosity to enable its transportation in pipelines is necessary. Visbreaking is one of the strategies commonly used to reduce bitumen viscosity. It is a mild thermal cracking process where vacuum residue conversion is limited by the onset of coke formation. In visbreaking, temperature and time combination can be varied to achieve the same residue conversion. In the BituMaxTM field upgrading process, asphaltenes are rejected from bitumen before visbreaking, since asphaltenes decreases the stability of the bitumen during visbreaking to limit conversion by onset of coking. However, it was observed that new asphaltenes was formed in the product. In this project, it was evaluated if different temperature-time process conditions that in principle would lead to the same conversion would also result in the same asphaltenes content. Four visbreaking conditions were investigated (417 °C/30 min, 424.6 °C/20 min, 438 °C/10 min, and 480 °C/1.24 min) that were predicted to lead to the same conversion. The impact of heat up time was also investigated in order to evaluate the changes taking place during the preheating process. The feed was the vacuum residue fraction (+560 °C) of deasphalted oil derived from bitumen from the Athabasca region. The same residue conversion (56 wt%) was expected from the reaction conditions studied, however in practice it varied between 63 and 83 wt%. The difference is because residue conversion starts to take place during the heating process, which varied, but contributed meaningfully to the overall conversion. Residue conversion was favored as reaction temperature increased and residence time decreased, while residue conversion was favored during the heating process as reaction temperature increased. The n-pentane insoluble (C5-asphaltenes) content in the products ranged from 15 to 23 wt% and C5-asphaltenes formation was favored by increasing reaction temperature and decreasing reaction time. C5-asphaltenes were also formed during heating process and it ranged from 10 to 24 wt% where its formation during heat-up was favored by increasing reaction temperature.

Evaluating the impact of process conditions on asphaltenes formation during visbreaking of vacuum residue deasphalted oil

2019 Spring National Meeting

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