Published: July 15, 2011 r2011 American Chemical Society 3663 dx.doi.org/10.1021/ef200780d | Energy Fuels 2011, 25, 3663–3670 ARTICLE pubs.acs.org/EF Suitable Density Determination for Heavy Hydrocarbons by Solution Pycnometry: Virgin and Thermal Cracked Athabasca Vacuum Residue Fractions Lante Carbognani,* Lante Carbognani-Arambarri, Francisco Lopez-Linares, and Pedro Pereira-Almao Alberta Ingenuity Centre for In Situ Energy (AICISE), Department of Chemical and Petroleum Engineering, Schulich School of Engineering, University of Calgary, Calgary, Alberta T2N 1N4, Canada ABSTRACT: Density is an important parameter for understanding molecular packing, stability, and reactivity of petroleum fractions. The determination of density for extremely viscous residual fractions measured at high temperature (reduced viscosity) is difficult and prone to error if results are extrapolated to lower temperature ranges. This problem is addressed in the present study with fractions derived from virgin and visbroken Athabasca vacuum residua. Solution pycnometry (toluene solvent) was studied and demonstrated a feasible, fast, simple, and reliable technique, applicable to a wide variety of petroleum materials, including asphaltenes and vacuum residua. Reported densities were affected to the third decimal position [American Petroleum Institute (API) gravities found reliable to (0.15° API]. The density for mixtures of residual oil fractions was determined to be an additive property. Athabasca vacuum residue solvent deasphalting and thermal cracked fractions are studied. Thermal cracking was observed to increase asphaltene densities to values as high as those displayed by coals, suggesting that highly aromatic-condensed structures represent these species better. Further application of the methodology is illustrated by monitoring Athabasca bitumen upgrading at bench scale. 1. INTRODUCTION Bulk density for hydrocarbon fractions is an important parameter for understanding stability issues of dense asphaltenes, 1 correlations between carbon content, density, porosity, and gasification reactivity of coals, 2 and assessing oxidation/cracking balances during asphalt oxidation. 3 Density has been found as a convenient tuning para- meter for building representative average molecular structures via molecular dynamics simulation. 4 Density changes has been de- scribed for detection of onset precipitation of solids. 5 Methods for density determination of petroleum and derived products based on different properties have been standardized, as described by Speight. 6 Different measurement principles are described within these standard procedures, among them: hy- drometry (ASTM D287, ASTM D1298, ASTM D1657, and IP 160), pycnometry (ASTM D70, ASTM D941, ASTM D1217, ASTM D1480, and ASTM D1481), fluid displacement (ASTM D712), digital density meter (ASTM D4052 and IP 365), and digital density analyzer (ASTM D5002). When solid samples or extremely viscous materials, such as vacuum residua, are the analytes of interest, serious drawbacks arise because low viscosity (fluidity) is required for determina- tions using these systems. High temperatures can be set up for bringing samples to fluidity. Vacuum residua normally become mobile in the 120150 °C range. Asphaltenes normally liquefy above ∼205 °C. 7 However, nonlinear extrapolation of densities from these temperature ranges to routine ambient set points, i.e., 1525 °C, is a serious drawback from using high temperatures during the measurements. 8 Instead, wide-mouth glass pycn- ometers and water + surfactant as a displacing fluid are standard techniques described for solid asphalts. 9 However, nonmiscible displacing fluids, such as water or n-heptane, have been deter- mined to pose several problems as well as trapped gas bubbles release. Gas (helium) pycnometers have also been described for both types of solid or viscous materials. 10,11 Helium pycnometry is accepted to provide true densities of solid materials, such as coals, because this probe of small-molecular dimensions guaran- tees its access to the whole porous space of samples and is a non- interacting fluid with the solid matrix. 12,13 Aiming to run several samples simultaneously at near ambient conditions (1525 °C temperature range), glass pycnometry was evaluated during this work for the determination of density of cumbersome materials, such as sticky vacuum residua and solid asphaltenes. The present work contemplates the use of a fluid able to dissolve the analytes of interest, aiming to provide the following solutions: (1) Overcoming the solid/sticky nature of the samples, (2) use of small samples, (3) simultaneous determination of several samples, (4) simplicity and inexpensive assemblies implied, and (5) reasonable accuracy and precision. Toluene was determined to be a convenient solvent for the intended goal. Determined densities were found accurate to the third decimal position, variability that was found enough for monitoring purposes. Several applications are described in this paper with Athabasca bitumen-derived frac- tions; in particular, the effect from mild thermal cracking on Athabasca residua asphaltenes was studied in greater detail. 2. EXPERIMENTAL SECTION 2.1. Studied Samples. Selected samples from bench-scale experi- ments were studied in this work. These will be directly described within the Results and Discussion. Received: May 25, 2011 Revised: July 11, 2011