Density, viscosity, and stability of products from combinations of visbreaking and deasphalting

Abstract

Transporting bitumen through pipelines in Western Canada is cost intensive because the oil has to be diluted with light solvents to meet pipeline specifications. The diluent requirement can be reduced by visbreaking (VIS) and solvent deasphalting (SDA), each of which decrease the viscosity and density of the oil. Combinations of the two processes can provide a greater viscosity and density reduction while minimizing the risk of asphaltene precipitation and coke formation. However, data on the product properties are required to assess these combined processes. In this study, a Western Canadian bitumen was visbroken at conversions from 24% to 42% and each product was then deasphalted with extents ranging from 50% to 96 wt.% asphaltene removal (VIS-SDA sequence). The same bitumen was deasphalted with extents from 30% to 96% and each deasphalted oil was then visbroken at conversions from 6% to 44% (SDA-VIS sequence). The following measurements were performed on the products: simulated distillation, gas yield, pentane-insoluble asphaltene content, toluene insoluble (TI) content, density, viscosity, and stability. Stability was assessed in terms of the onset of asphaltene precipitation from mixtures of oil and n-heptane. Neither the VIS-SDA nor the SDA-VIS sequence met the pipeline density specification, but both were able to reduce the diluent requirement to approximately 10 wt.% compared with 28 wt.% for the feed bitumen. The VIS-SDA sequence offered better product stability; however, the suitability of the separated asphaltenes for downstream processes has not been established. The SDA-VIS sequence produced usable asphaltenes but less stable oil products.