title: Partial Upgrading of Bitumen Through Combinations of Deasphalting and Visbreaking
Creators: name: Beleno Alcazar, Jose Angel
Publisher: name: Graduate Studies
Year: 2024
Subjects: subject: Bitumen
subject: Visbreaking
subject: Solvent Deasphalting
subject: ERT
subject: Engineering--Chemical
subject: Engineering--Petroleum

description: Reducing diluent requirements for pipeline transport of Western Canadian bitumen can increase the pipeline capacity for bitumen and pontentially reduce operating costs. One approach to do so is to combine visbreaking (VIS) and solvent deasphalting (SDA) to obtain a lower density and viscosity bitumen. Visbreaking is a mild thermal cracking process that reduces viscosity and density but risks asphaltene precipitation and coke formation at high conversions. Solvent deasphalting separates out the densest, most viscous components from the oil but would also remove too much of the valuable oil components to achieve pipeline specifications. Combinations of the two processes could reduce diluent requirements further. The goal of this thesis is to provide data and models to predict the product properties, product stability versus asphaltene precipitation, and diluent requirements for the combined processes. To collect the necessary data, an induction-heated reactor was commissioned and its performance was validated against previous data from a conventionally heated reactor. Then, 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 yet been established. The SDA-VIS sequence produced usable asphaltenes but less stable oil products. A step-wise modeling approach was completed to predict product density, viscosity, and oil stability based on conversion (defined by the change in the vacuum residue fraction) and feed properties. Step 1 was to correlate conversion to the Equivalent Residence Time (ERT), a function of the reactor temperature profile and space time. The use of ERT allows the conversion to be determined without measuring the composition of the visbroken oil. Step 2 was to correlate the distillate and SARA residue (saturates, aromatics, resins and asphaltenes) contents of visbroken products to conversion. Step 3 was to update correlations of the density and viscosity parameters of the visbroken distillates and SARA fractions to the measured and ERT-based conversions. Step 4 was to determine the product density from the component parameters using an excess volume mixing rule tuned to the feed density. Step 5 was to determine the product viscosity from the component parameters using the Expanded Fluid (EF) viscosity model tuned to the feed viscosity. Finally, Step 6 was to correlate the oil stability (onset of asphaltene precipitation) to conversion. For the SDA-VIS sequence, the updated models matched the product compositions with averge deviations of 1-3 wt%, depending on the fraction. The product density and viscosity were matched with average deviations of 3.0 kg/m³ and 44%, respectively. The onset of asphaltene precipitation (stability) was matched with an average deviation of 4.5 wt% n-heptane. For the VIS-SDA sequence, the average deviations for the density and viscosity were 4.0 kg/m³ and 43%, respectively. The stability prediction had an average deviation of 3.3 wt% n-heptane. The inputs to the models are the feed properties and reactor conditions. The models are suitable for use in preliminary design calculations for potential field upgrading processes.