Suoqi Zhao

Adsorption of polycyclic aromatic hydrocarbons from water using petroleum coke-derived porous carbon

Porous carbons were prepared from petroleum coke by KOH chemical activation, characterized and used as adsorbents for uptaking a mixture of polycyclic aromatic hydrocarbons (PAHs): naphthalene, fluorene, phenanthrene, pyrene and fluoranthene from aqueous solutions. The specific surface area (SSA) of these carbons ranges from 562 to 1904 m2/g, while their point of zero charge (pH(PZC)) varies from 2.6 to 8.8. The equilibrium adsorption of PAHs on all four carbons follows the non-linear Freundlich equation well. For any given PAH in the group, the adsorption capacity parameter K(f), increases with the SSA and pH(PZC) of the carbons, confirming the roles of dispersive interactions. For any given carbon, the value of K(f) follows the order of naphthalene > fluorene > phenanthrene > pyrene. This dependence of K(f) on molecular size suggests a certain degree of molecular sieving behavior of these carbons toward large PAHs. Under the condition studied, the uptake process is likely controlled by diffusive transport processes. And, it is unlikely that the competitive adsorption played any important roles in determining equilibrium adsorption of the mixed PAHs. Overall, the petroleum coke-derived porous carbon is very effective in adsorbing these PAHs.

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.

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.

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.

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.

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.

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.

Characterization of heavy petroleum fraction by positive-ion electrospray ionization FT-ICR mass spectrometry and collision induced dissociation: Bond dissociation behavior and aromatic ring architecture of basic nitrogen compounds

This paper examined the bond dissociation behavior and aromatic ring architecture of basic nitrogen compounds in Sudan heavy petroleum fraction. Both broadband and quadrupole isolation modes positive-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with collision induced dissociation (CID) techniques were used to characterize a low sulfur crude oil derived vacuum residuum (VR). The appropriate CID operating condition was selected by comparing the molecular weight distributions of the basic nitrogen compounds under various CID operating conditions. Both odd- and even-electron fragment ions were observed from the mass spectrum, indicating that the heterolytic and homolytic bond cleavages occurred simultaneously during the CID process. The odd-electron fragment ions were predominant in each class species, indicating preferential heterolytic bond cleavages. At the optimal CID condition, the alkyl groups decomposed deeply and just left the aromatic cores of the nitrogen compounds. No significant variation in double bond equivalent (DBE) value was observed between the fragment and parent ions, revealing that the domination of single core structure.

Upgrading Heavy Oil Using Syngas as the Hydrogen Source with Dispersed Catalysts

Abstract Upgrading heavy oil using syngas (CO + H2) as an alternative hydrogen source with a dispersed catalyst was investigated. Finely dispersed catalysts for upgrading were prepared by means of microemulsion, and their performance was investigated in a batch-type autoclave. This process was compared to the traditional pure hydrogen hydro-upgrading process. Feedstock conversion, light-oil yield, coke yield, product distribution, sulfur, nitrogen and viscosity were investigated comprehensively to optimize the process. The addition of finely dispersed catalysts could improve the distribution and performance of cracking products, and inhibit the cracking gas and coke formation. This work shows that residue-syngas coprocessing is promising for heavy oil upgrading.