Keng H. Chung

Athabasca oil sands: effect of organic coated solids on bitumen recovery and quality

Abstract The Canadian oil sands deposits in northern Alberta contain about 1.3 trillion barrels of crude oil equivalent. The largest of the four major formations is found in the Athabasca region where bitumen is heterogeneously distributed throughout an unconsolidated mineral matrix. About one-tenth of the oil sands in this deposit is economically recoverable by conventional surface mining techniques. The Hot Water Extraction Process (HWEP) is used commercially to recover bitumen from surface mined oil sands ore. The viability of this process relies on the existence of a thin water film around each solid particle in the ore matrix. However, a completely water-wet mineral condition is not generally the case for oil reservoirs, including oil sands deposits. In the latter case, it has been shown that certain solid fractions are associated with significant amounts of toluene insoluble organic matter (TIOM), physically or chemically adsorbed onto particle surfaces. These fractions are generically described as ‘organic rich solids’ (ORS). In bitumen separation processes, the organic matter associated with various ORS fractions represents an impediment to optimum bitumen separation and upgrading. In this sense, these solids are considered to be ‘active’ relative to the ‘inactive’ water wetted quartz particles comprising the bulk of the oil sands ore. Preliminary results indicate that the ORS content of an ore appears to be a better predictor for ore processability than the traditional use of bitumen or fines (−44 μm) contents. Two types of ORS have received particular attention. The first is a coarser fraction, usually less than 44 μm but also occurring as particles greater than 100 μm in diameter. This material typically occurs as aggregates of smaller particles bound together by humic matter and precipitated minerals. During the bitumen separation process, these heavy aggregates carry any associated bitumen into the aqueous tailings, thus reducing overall bitumen recovery. The second important fraction comprises very thin, ultra-fine clay particles with a major dimension of

Bitumen—sand interaction in oil sand processing

Abstract Bitumen—sand interaction was studied as a function of pH, particle size, temperature and solvent addition to bitumen. Sand particles can be easily detached from the bitumen surface at pH > 6. At pH

Characterization of sulfide compounds in petroleum: selective oxidation followed by positive-ion electrospray Fourier transform ion cyclotron resonance mass spectrometry.

A novel analytical method for identifying sulfides in petroleum and its fractions was developed. Sulfides in petroleum were selectively oxidized into sulfoxides using tetrabutylammonium periodate (TBAPI) and identified by positive-ion electrospray ionization (ESI) Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). A variety of model sulfur compounds were examined to evaluate the selective oxidization and ionization efficiencies for sulfur compounds in petroleum. Two fractions, straight-run diesel and saturates of Athabasca oilsands bitumen were investigated using this approach. The oxidization process was highly selective for sulfides from thiophenes and aromatic hydrocarbons. Oxidation generated sulfoxides were ionized by positive-ion ESI and analyzed by FT-ICR MS. Mass spectra revealed the composition characteristics of sulfides in the diesel by contrasting the double bond equivalence (DBE) and carbon number distribution of sulfur compounds before and after oxidation. The abundant sulfides in the straight run diesel and saturates fraction of oilsands bitumen had DBE values of 1-3 and 1-4, respectively.

Hot water extraction process mechanism using model oil sands

A mechanism for the hot water extraction process is proposed based on new results from extraction tests using model oil sand. It was found that bitumen can be completely liberated from the oil sand matrix and forms aerated droplets during slurrying with water without adding process aids. However, the aerated bitumen droplets were unable to float due to the attachment of sand particles on the surface of the bitumen droplets. When sodium hydroxide (NaOH) was added, the sand particles were released from the bitumen droplets, resulting in bitumen recovery. High recoveries were obtained by adding NaOH to either connate water or slurry water. Bitumen loss was attributed to incomplete bitumen/sand separation and oil-in-water (o/w) emulsification resulting from deficiency and overdose of NaOH, respectively. The use of commercial sodium naphthenate or sodium laurate as process aids had no effect. The size of the aerated bitumen droplets increased as the oil content and/or the size of the sand particles increased. The bitumen recovery and the size of the aerated bitumen droplets increased when the sand was pretreated with NaOH. Liberation of bitumen from the oil-wet model oil sand could be achieved by using excess NaOH, but the liberated bitumen was non-recoverable due to emulsification. Increasing the amount of slurry water had a detrimental effect on aeration.

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.

Analysis of saturated hydrocarbons by redox reaction with negative-ion electrospray Fourier transform ion cyclotron resonance mass spectrometry.

A novel technique was developed for characterization of saturated hydrocarbons. Linear alkanes were selectively oxidized to ketones by ruthenium ion catalyzed oxidation (RICO). Branched and cyclic alkanes were oxidized to alcohols and ketones. The ketones were then reduced to alcohols by lithium aluminum hydride (LiAlH(4)). The monohydric alcohols (O(1)) in the products obtained from the RICO and RICO-LiAlH(4) reduction reactions were characterized using negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) for identification of iso-paraffins, acyclic paraffins and cyclic paraffins. Various model saturated compounds were used to determine the RICO reaction and ionization selectivity. The results from the FTICR MS analysis on the petroleum distillates derived saturated fraction were in agreement with those from field ionization gas chromatography time-of-flight mass spectrometry (FI GC-TOF MS) analysis. The technique was also used to characterize a petroleum vacuum residue (VR) derived saturates. The results showed that the saturated molecules in the VR contained up to 11 cyclic rings, and the maximum carbon number was up to 92.

Feedstock characteristic index and critical properties of heavy crudes and petroleum residua

Abstract Supercritical fluid extraction and fractionation was used to prepare narrow-cuts from a variety of petroleum vacuum residua. The narrow-cuts were subjected to comprehensive characterization and solubility class separation into saturates, aromatics, resins and asphaltenes fractions. Unlike the bulk property measurements, the narrow-cut characterization data show uneven distribution of key contaminants (with the concentration increasing) as the fraction becomes heavier. Narrow-cut data were used to develop a generalized feedstock characteristic index, K R , that correlates well with the feedstock hydrocarbon constituents and can be used to assess feedstock reactivity and process capability. Downstream refiners can use the narrow-cut data and K R index for process optimization by either cutting deep into the bottom of residua to increase yield or selecting appropriate process units for various residue fractions. Narrow-cut data were also used to develop critical properties of residue fractions, which can be used as input parameters for simulation studies in designing process units for heavy crude and residua.

Narrow-cut characterization reveals resid process chemistry

Abstract Supercritical fluid extraction, narrow-cut characterization of bitumen pitch, hydrocracker and once-through coker vacuum resids revealed the unexpected process chemistry of bitumen hydrocracking. Hydrocracking appears to prolong the coke formation process of the end-cut material of bitumen, by converting it to coke precursors. The conversion (or removal) mechanism for most key species (microcarbon residue (MCR), metals, N) in hydrocracking is by partitioning, which is similar to coking. Sulfur species that convert in hydrocracking are from the front-end of bitumen pitch; there is only a small sulfur reduction in the end-cut. Bitumen pitch and resid products have similar MCR distribution which is dependent on the “depth” of resid, not the conversion processes. Coke yield did not correlate with the MCR content of narrow-cut feed; coke yield was insignificant at the front-fractions and high at the end-cut. The sub-fractions of bitumen derived resid products have lower H/C ratios than those of bitumen pitch, but have the same MCR content. This can be explained by the pendant-core model, in which bitumen pitch and resid products have the same amount of aromatic cores (coke precursors). The inverse correlation of key species with H/C ratio is process dependent. The reaction products of end-cut (mainly asphaltenes) remained in resid product slate (524°C+ materials) in once-through coking and hydrocracking operations. The implications for the current commercial bitumen upgrading flowsheet are also discussed.

Approach for selective separation of thiophenic and sulfidic sulfur compounds from petroleum by methylation/demethylation.

Detailed characterization of petroleum derived sulfur compounds has been challenging, due to the complex composition of the hydrocarbon matrix. A novel method was developed for selective separation of thiophenic and sulfidic compounds from petroleum. Sulfur compounds were methylated to sulfonium salts by AgBF4 and CH3I, then the polar salts were separated by precipitation from petroleum matrix. The thiophenic and sulfidic sulfonium salts were sequentially demethylated with 7-azaindole and 4-dimethylaminopyridine, obtaining original thiophenic and sulfidic compounds, respectively. The method was validated by model compounds, and applied to a diesel and a vacuum distillation petroleum fraction. Sulfur fractions were characterized by gas chromatography (GC) coupled with a sulfur chemiluminescence detector (SCD) and quadrupole mass spectrometry (MS), and high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The technique was effective to selectively obtain high-purity thiophenic and sulfidic compounds and showed rare discrimination among sulfur compounds with ranging molecular weights and degrees of unsaturation. The method would facilitate multifaceted detailed characterization of sulfur compounds in an organic complex matrix.