Measurement and modelling methodology for heavy oil and bitument vapour pressure
Date
2012
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Abstract
Both the refining of heavy oil and solvent-based recovery processes for heavy oil require the prediction of phase behaviour. Petroleum fluids are typically characterized using distillation (or gas chromatography based assays correlated to boiling points); however, the heaviest fraction (residue) of the oil is left undetermined because the components in this fraction have boiling points higher than the cracking temperature. Current commercial methods are capable of distilling about 25 to 30 wt% of heavy oil and bitumen which leaves about 70% of the oil undetermined. To improve this characterization, true boiling point and vapour pressure of residue cuts are required. At present, few data are available in the open literature. Neither a standard procedure nor appropriate equipment is available commercially for direct vapour pressure measurement and deep vacuum distillation of heavy hydrocarbons. A high vacuum vapour pressure measurement system was designed, constructed, and tested. The system operates at medium to high vacuum conditions (atmospheric to 10-7 kPa) and temperatures ranging from 25 to 300 °C. The apparatus was used to measure the vapour pressure of three pure components, seven biodiesel samples, and three bitumen fractions with repeatability and reproducibility of literature data, when available, within 4%. The apparatus was also used to systematically fractionate 58 wt% of a bitumen sample with repeatability within 5%. The amount fractionated more than doubles that obtained by commercial spinning band distillation (25 wt%). In addition, a methodology was proposed to extrapolate the vapour pressure of heavy oil fractions beyond the accurate-measurable range (below 10-4 kPa) using calorimetric data. The vapour pressure was modeled with a correlation, such as the Cox equation, or an equation of state, such as the Advanced Peng Robinson EoS (APR EoS) implemented by Virtual Materials Group Inc. The heat capacity is related to the vapour pressure through the Clausius_ Clapeyron relationship and was used to constrain the correlation or equation of state parameters. Both the correlation and equation of state approaches were tested on the biodiesel samples. Both approaches fit the vapour pressures and heat capacities to within 8% and 3%, respectively. The equation of state approach was used for the heavy oil. The non-distillable maltene fractions were represented with a Gaussian distribution and the asphaltene fraction was represented with a Gamma distribution to account for asphaltene self-association. The vapour pressure and heat capacity were predicted to within 7% and 4%, respectively. A preliminary protocol was developed for deep vacuum fractionation of heavy oil and bitumen. An experimental procedure was defined and an inter-conversion method to obtain atmospheric equivalent boiling points was formulated. Specifications for additional experimental vapour pressure and heat capacity of fractions obtained with the protocol were laid out to standardize and validate the inter-conversion method. The high vacuum vapour pressure measurement system and associated modeling methodologies expand the capability to characterize heavy oils for phase behaviour modelling from approximately 30 wt¾ of the oil to 60 wt¾ of the oil.
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Bibliography: p. 245-258
Many pages are in colour.
Many pages are in colour.
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Citation
Castellanos Diaz, O. (2012). Measurement and modelling methodology for heavy oil and bitument vapour pressure (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/5050