Ind. Eng. Chem. Res. 2004, 43, 7103-7112
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Selective Rejection of Inorganic Fine Solids, Heavy Metals, and Sulfur from Heavy Oils/Bitumen Using Alkane Solvents Xiang-Yang Zou,† Leisl Dukhedin-Lalla,‡ Xiaohui Zhang,§ and John M. Shaw* Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2G6, Canada
Bitumen and heavy oil + alkane solvents exhibit complex phase behaviors. For example, organic components of these materials can be solubilized and inorganic solids dispersed into a highpressure gas phase. Conversely, they can also be partitioned into as many as three bulk phases: a gas phase, a liquid phase that is largely free of inorganic solids, and a phase comprising essentially all of the inorganic solids and a small fraction of the organic material. The outcome depends on the temperature, pressure, and solvent-to-feed ratio. Mass balance results for a screening survey for Athabasca vacuum bottoms (ABVB) + alkane solvents (pentane, heptane, decane, and dodecane) are reported along with a limited number of phase composition data for ABVB + pentane and dodecane mixtures. Reversible phase behavior and irreversible thermolysis conditions were considered. The key findings are that inorganic solids are readily partitioned from ABVB irrespective of the solvent and operating conditions employed, while key heavy metals, such as vanadium, require a combination of phase behavior and mild thermolysis. Sulfurand nitrogen-containing species possess low rejection selectivities in this solvent series. Introduction Heavy oil and bitumen feedstocks are becoming more and more important sources for transport fuels and petrochemical feeds. The development of tailored separation and reaction processes that maximize the production of these products from such resources is an area of intense research interest even though the high content of asphaltene, inorganic fine solids, heavy metals, and heteroatoms present in heavy oils and bitumen poses a host of severe problems for the refining industry, such as solids dropout and catalyst deactivation.1-3 More and more stringent environmental and health regulations also force refiners to further reduce the levels of heavy metals and heteroatoms in finished products. Consequently, selective removal of fine solids, heavy metals, and heteroatoms from petroleum is a key challenge to refiners all over the world. Inorganic fine solids, heavy metals, and heteroatoms appear throughout the entire boiling range of crude oil but tend to concentrate in the heaviest fractions, such as resins and asphaltenes.4,5 Thus, a fraction of fine solids, heavy metals, and heteroatoms can be removed along with asphaltenes as precipitates.1,2,4,6a,b,7,8 Conventional deasphalting processes, such as the propane deasphalting process and the residuum oil supercritical extraction (ROSE) process, now widely employed in industry, were developed on the basis of this principle. In the ROSE process, for example, a heavy feedstock is split into two or more phases in the presence of a near-critical/supercritical solvent. Asphaltenes and other undesirable constituents are concentrated in one phase, * To whom correspondence should be addressed. Tel.: (780) 492-8236. Fax: (780) 492-4534. E-mail:
[email protected]. † Present address: Oilphase-DBR, Edmonton, Alberta, Canada. E-mail:
[email protected]. ‡ Present address: Zeton Inc., Burlington, Ontario, Canada. E-mail:
[email protected]. § E-mail:
[email protected].
while the other phase comprises readily upgradeable constituents. However, this successful industrial process is not sufficiently selective for use with heavy oils and bitumen because up to 50% of the feed material reports to the “reject stream”.8 Such product losses are unacceptable particularly given that 35-60% of asphaltenes9,10 can be upgraded to middle distillates. More selective separation of objectionable constituents is clearly desired. Other paraffinic solvent-based deasphalting processes have been developed for this application, such as the Demex Process and the Solvahl process,11 but are not yet optimized. The Canadian Oilsands Network for Research and Development, CONRAD, has targeted the development of low-pressure processes where reject fractions comprise 10 wt % of the feed material but 90 wt % of fine solids, heavy metals, and heteroatoms. Here the potential for selectively separating Athabasca vacuum bottoms (ABVB) using alkane solvents is assessed with the above targets in mind. The multiphase behavior of ABVB + alkane solvents was investigated using our X-ray view-cell technology.12,13 Detailed phase diagrams for these systems, exhibiting diverse multiphase behaviors, comprise a companion paper.14 Figure 1 illustrates the complexity of the phase behaviors observed and the phase-naming scheme employed. Four-phase L1L2L3V phase behavior was observed for pentane + 45 wt % ABVB over a narrow range of pressures. An example showing the relative volumes of each phase at 120 °C and 906 kPa is shown. Because this was the largest number of liquid phases observed simultaneously, they are labeled L1, L2, and L3, where L1 is the least dense liquid phase and L3 the most dense liquid phase. The appearance and disappearance of these phases were tracked with variations in pressure, composition, and temperature. Phase diagrams comprise a separate contribution, but the same phase-naming scheme is employed here. As the number of liquid phases changes with the pressure, tempera-
10.1021/ie0499153 CCC: $27.50 © 2004 American Chemical Society Published on Web 09/25/2004
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Ind. Eng. Chem. Res., Vol. 43, No. 22, 2004
Table 1. Summary of Sample Analyses sample
ABVB
50 wt % ABVB
40 wt % ABVB
30 wt % ABVB
20 wt % ABVB
L3
L2
L2
L2
L2
L1
saturates aromatics resins asphaltenes
6.80 41.99 19.04 32.18
4.80 28.90 11.84 54.47
SARA Analysis (wt %) 9.42 2.09 7.62 43.11 19.18 51.16 19.75 7.32 18.75 27.72 71.41 22.48
carbon hydrogen nitrogen sulfur
81.66 9.54 0.65 6.87
80.31 8.87 0.91 4.68
Elemental Analysis (wt %) 83.01 78.11 83.29 9.84 8.07 9.92 0.68 0.99 0.69 5.87 6.60 5.31
tin (Sn) lead (Pb) copper (Cu) aluminum (Al) silicon (Si) iron (Fe) chromium (Cr) silver (Ag) zinc (Zn) magnesium (Mg) nickel (Ni) barium (Ba) sodium (Na) calcium (Ca) vanadium (V) phosphorus (P) molybdenum (Mo) boron (B) manganese (Mn) titanium (Ti)
0.7 1 1 734 898 322 3
