J. R. Woods

DISTRIBUTION AND TYPES OF SOLIDS ASSOCIATED WITH BITUMEN

ABSTRACT In the conventional Hot Water Extraction Process bitumen is separated as a froth that is then diluted with naphtha and subjected to two stages of centrifugation. The resulting bitumen solution still contains residual water, dissolved salts and mineral solids. Before upgrading the solvent and other volatile components are removed by topping at 524°C. The salts and mineral solids remain with topped bitumen; their presence can lead to serious operational problems in the bitumen upgrading process. In the present work the solids associated with bitumen (BS) have been identified as mainly ultra-fine (nano sized) aluminosilicate clays coated with strongly bound toluene insoluble organic material having “asphaitene characteristics”. It is proposed that these ultra-fine clays with their strong tendency to collect at oil-water interfaces, are the key component responsible for the presence of intractable water and associated salts in bitumen froth.

Molecular transformation of Athabasca bitumen end-cuts during coking and hydrocracking

Abstract The use of supercritical pentane, under increasingly severe conditions of temperature and pressure, allows residual oils to be separated into fractions with progressively higher molecular weight without significant chemical degradation. Characterisation of these individual fractions provides a more complete picture of bitumen resid chemistry than average values determined for the whole sample. In the work described here, this approach has been applied to resid samples taken from the bitumen upgrading units at the Syncrude Canada Ltd. plant in Northern Alberta (Oil Gas J, 20 (1997) 66; Rev Process Chem Engng, 1 (1998) 41). A significant amount of each sample was non-extractable under even the most severe conditions. These end-cuts from virgin bitumen pitch (P-EC), hydrocracking product resid (HC-EC) and coking product resid (CK-EC) were compared to pentane insoluble asphaltenes (ASP) from a conventional coker feed bitumen. In addition, the P-EC sample was subjected to further fractionation based on its solubility in different blends of toluene and pentane. The P-EC sample comprises about 55%(w/w) highly aromatic heavy molecules, rich in heteroatoms and metals. Smaller molecules, with much lower aromaticity and polarity, represent the remaining 45%(w/w). Owing to a their high heteroatom and metals content, the heavier molecules in this material are considered to be major coke precursors under thermal cracking conditions. However, in hydrocracking the free radicals generated by the cleavage of carbon–carbon and sulphur–carbon bonds are suppressed by hydrogen capping. As a result, the “difficult to crack” aromatic “cores” of the heavier components remain toluene soluble. Although these components do not form coke under hydrocracking conditions, they may cause fast catalyst deactivation. In existing commercial processes the residue from hydrocracking is recycled to extinction in a coker. Because of its intractable nature, this heavy resid may not be conducive to the production of lighter liquid products. It is suggested that, prior to hydrocracking, the heaviest portion of bitumen pitch be removed to avoid these problems.

Solids contents, properties and molecular structures of asphaltenes from different oilsands

Abstract As the Canadian supply of light crudes has diminished in recent years, refineries have necessarily been required to deal with difficult to process oilsands bitumens and heavy oils. Bitumen in particular exhibits unique behavior during upgrading; nearly 50% (w/w) of the feedstock is an intractable residuum. The fast catalyst deactivation and high coke forming propensity displayed by this feedstock have been attributed to the asphaltene and associated solids contents of extracted bitumen. The variability of these intractable components in bitumens from mined and in-situ Athabasca oilsands were examined and compared with bitumens from Nigerian and Utah oilsands. Except for the in-situ bitumen, all of the samples were found to contain significant amounts of fine solids. Unexpectedly, the in-situ bitumen also contained the least amount of asphaltene and the highest amount of the intractable heteroatoms nickel and vanadium. Solids-free asphaltene samples were characterized by several complementary analytical techniques to determine the relative abundance of different carbon types and to calculate their average three-dimensional molecular conformations. Even though the parent bitumens came from geographically diverse sources the corresponding asphaltene fractions had similar structures. Each sample comprised basic units, or ‘cores’, of condensed aromatic rings connected by bridges. The main differences relate to the number and complexity of the basic units.

A benchmark assessment of residues: comparison of Athabasca bitumen with conventional and heavy crudes

Abstract Compared to benchmark crude oils, bitumen does not respond well to conventional upgrading processes. In order to improve our understanding of this problem, we compare the chemical and physical properties of fractions from super critical fluid extraction of bitumen pitch with the corresponding fractions of residua from Venezuelan heavy oil, a Saudi Arabian light crude and a Chinese Daqing conventional crude. Relatively minor differences in chemical structure were observed between the corresponding residua fractions from Athabasca bitumen, Venezuelan heavy oil and Saudi Arabian light crude. Only the Chinese Daqing showed significant variance; this sample is much more aliphatic and has greater geometrical dimensions than the corresponding samples from the other residua. The end-cut from Athabasca bitumen pitch contained ultra-fine solids together with much higher levels of nickel, vanadium and nitrogen than the conventional crude end-cuts. These components are among the most intractable in upgrading and could be responsible for the problems encountered in bitumen upgrading, especially by catalytic processes.

Effect of particle size on the flocculation behaviour of ultra-fine clays in salt solutions

Currently, two commercial plants are operating to produce ~20% of Canadas petroleum requirements from the Athabasca oil sands deposit in Alberta. The hot water extraction process is used to extract the bitumen from this resource. During processing, mechanical dispersion forces cause mobilization of ultra-fine clays into the process water (Kotlyar et al., 1992a, 1993). The resulting slurry is transported to sedimentation ponds where the U/F interact with naturally occurring salts present in the water to form thixotropic gels that ultimately produce mature fine tailings (MFT) with a high water holding capacity. In previous corcmmnlcatzon5 t ,~ , ,~ -, 9 ~,:,o, 1996) we reported on aggregation of U/F particle mixtures having a broad range of sizes. The work presented here comprises a fundamental study of the colloidal characteristics of narrow particle size

MOLECULAR NATURE OF ATHABASCA BITUMEN

ABSTRACT Athabasca bitumen is a heavy hydrocarbon recovered from oil sands. During upgrading, bitumen is first distilled to remove lighter components which are processed in hydrotreaters. This distillable portion, heavy gas oil, accumulates nearly 80 w/w% of the saturates present in the original material. The aromatic character and heteroatoms content of the molecules in this fraction increase with the boiling point of the components. The residue from distillation, bitumen pitch, is subjected to thermal cracking followed by hydrotreating. The extractable front fractions from pitch show a trend for increasing aromatic content with a concomitant decrease in H/C atomic ratios. This is a reflection of greater numbers of aromatic rings with a higher degree of condensation and decreasing degree of substitution. The insoluble end- cut from pitch is characterised by the presence of “core” structures comprising condensed polyaromatic rings associated with heteroatoms (N) and trace metals (Ni, V). The heaviest sub-fractions from the end-cut contain more than 10 condensed aromatic rings and are enriched in heteroatoms (N) and metals (Ni, V). By comparison, the lighter end-cut material comprises relatively non-polar molecules with an average of only 7 aromatic ring structures. Because these “cores” are both coke precursors and strong chromophors, their light absorbing propensity, measured by K/C values, may be indicators of coke forming propensity.

Biwetted ultrafine solids and structure formation in oil sands fine tailings

A high water holding capacity of oil sands fine tailing has been attributed to the presence of ultrafine (< 0.2 μm) clay fractions. On the basis of hydrophobic character two major types of ultrafines are recognized: biwetted, associated with a significant coverage or organic matter and preferentially hydrophilic solids. The effect of biwetted solids on the colloidal stability of ultrafine clays in aqueous suspensions has been studied by dynamic light scattering and 2 H n.m.r. methods. The organic matter associates with the surfaces of the biwetted solids is believed to be responsible for their accelerating effect on aggregation. The results indicate that prevention, or reduction, of the amount of biwetted solids entering the tailings pond could be beneficial.

Colloidal Clay Gelation: Relevance to Current Oil Sands Operations

Abstract Ultrafines are predominantly delaminated colloidal clays with dimensions <0.3 μm that exist naturally in oil sands and are released during conditioning of surface-mined ores. Critical concentrations of these ultrafines and the cations present in process water are capable of forming flocculated structures with a very high water holding capacity. During primary separation of bitumen these ultrafines are detrimental to recovery as a result of increased slurry viscosity as well as through slime coating of released bitumen. Disposition into tailings ponds eventually produces mature fine tailings (MFT) as a result of thixotropic gel formation that entraps coarser solids. The ultrafines concentration of ~3 wt% observed in MFT coincides with the critical gelation concentration determined for suspensions of ultrafines in salt solutions with cationic concentrations representative of that in pond water. This observation accounts for 100% of the water holding capacity of MFT and also explains why virtually no water is released once an MFT gel state has been formed. Here, we review earlier research in this area and identify the harmful effects of ultrafines in some current problematic ores.

Comparative study of organic matter derived from Utah and Athabasca oil sands

Abstract Asphaltenes derived from Athabasca and Utah oil sands have been characterized using different techniques. Several factors were found to differentiate these asphaltenes. Number average molecular weight of Utah asphaltene was significantly higher, which correlated with its higher light absorbing capacity, compared with that for Athabasca asphaltene. In Athabasca asphaltene, V and Ni were higher and Al, Mn, Mg, Ca, Ti, Fe were lower than those in Utah asphaltene. Structural models for these asphaltenes, as determined using a combination of 1 H and 13 C n.m.r. spectroscopy, were different with higher aromaticity and degree of condensation of aromatic rings for Athabasca asphaltene. 13 C structural parameters for humic acids extracted from demineralized fines separated from Utah oil sands were compared with Athabasca oil sand humic acid. As in the Athabasca sample, aromatic carbon in Utah humic acid was shown to be the predominant type of carbon.

The effect of asphaltene content on solvent selection for bitumen extraction by the SESA process

Abstract Bitumen is a complex mixture, containing a high proportion of poorly soluble asphaltenes. Unpredictable precipitation of this component can cause process problems during bitumen extraction. Consequently, the selection of an appropriate solvent is an important factor in the optimization of bitumen separation by solvent extraction. This aspect is discussed in the context of bitumen extraction from oil sands using the solvent extraction spherical agglomeration (SESA) process. The SESA process is a solvent extraction method which utilizes concurrent particle aggregation in order to overcome difficulties normally encountered in solid-liquid separation in the presence of fines.