Ind. Eng. Chem. Res. 1992,31, 1424
1424
Response to Comments on "Solubility of Carbon Dioxide in Tar Sand Bitumens: Experimental Determination and Modeling" Sir: We thank Mehrotra et al. (1992) for their interest in our work (Deo et al., 1991) and their comments. We acknowledge the great deal of data and understanding on Canadian bitumens compiled by Mehrotra et al. (1992). The purpose of our work on Utah bitumens was not to review all the work on heavy oils and bitumen, but to bring the Utah oil sand reservoirs into perspective. Athabasca bitumen is not a pure substance. There are bound to be compositional variations in the bitumen depending on the location and depth from which the samples were obtained. Significant compositional variations were observed in the Whiterocks bitumen taken from two locations only a few hundred meters apart. (Figures 1and 2). The data in Figures 1 and 2 were obtained by identifying about 100 compounds in the saturate fraction of the bitumen by gas chromatography and mass spectrometry. These figures illustrate the differences in distributions with respect to carbon number and molecular type between two locations from the same deposit. It was reasoned that these differences were due to different degrees of biodegradation of the bitumen at the two locations. Speight (1991) states that the data on the composition of oil sand bitumen suffer from the disadvantage that the identification of the source is too general (i.e., Athabasca bitumen) and is often not site specific. This compositional variation may be one of the reasons for the discrepancy between data reported by Deo et al. (1991) and Mehrotra et al. (1992). The conclusion by Mehrotra et al. (1992) that at least one set of solubilities reported by Deo et al. (1991) was in error would be valid only in the case of comparative analyses on identical samples under controlled conditions. The procedure for separating the bitumen from the sand has a strong influence on the bitumen properties. Minor variations in this procedure may be another reason for the observed differences. Viscosity was used as an indirect correlating parameter. For this purpose, the viscosity-temperature relationship that we adopted was adequate. Deo et al. (1991) did not survey the literature for all the available viscosity-temperature correlations. Registry No. CO,, 124-38-9.
.r".
i
II
7
'5
18
2
26
27
3C
Carbon Number
33
36
39
42
Figure 1. Carbon number distributions of the saturate fraction of the Whiterocks bitumen from two different locations as determined by gas Chromatography and mass spectrometry. 3
LC
- 0 i ~ j c l r naphthenei r I - Tetracyclic nsphthcnes -- Naohlhena-aiarnatici Pentacyclic naphlhcnes ARC - Ardrnaties I 0CN
TCI TRN
1 Northwest
- Tricyclic naphthcnes
ESSE3 Southwest
PCN NAC
,11
""
BCV
-CZ
T?Y
"CN
YAC
ARC
Figure 2. Compound type distributions of the saturate fraction of the Whiterocks bitumen from two different locations as determined by gas chromatography and mass spectrometry. Mehrotra, A. K.; Svrcek, W. Y.; Hepler, L. G.; Xu, Y.; Fu, C. Commenta on "Solubility of Carbon Dioxide in Tar Sand Bitumens: Experimental Determination and Modeling". Znd. Eng. Chem. Res. 1992, preceding paper in this issue. Speight, J. G. The Chemistry and Technology of Petroleum, 2nd ed.; Marcel Dekker: New York, NY; 1991.
Milind D. Deo,* Peter E. Rose, Francis V. Hanson
Literature Cited Deo, M. D.; Wang, J.; Hanson, F. V. The Solubility of Carbon Dioxide in Tar Sand Bitumens: Experimental Determination and Modeling. Znd. Eng. Chem. Res. 1991, 30, 532.
Fuels Engineering Department University of Utah Salt Lake City, Utah 84112
0888-5885/92/2631-1424$03.00/00 1992 American Chemical Society
