O. P. Strausz

Mechanism of the homogeneous oxidation of sulfur dioxide in the troposphere

Abstract An evaluation has been made of the existing kinetic data related to the elementary, homogeneous reactions of SO 2 within the troposphere. A set of preferred values of the rate constants for these reactions is presented. Simulations using these data provide significant new evidence that the oxidation of SO 2 can occur at substantial rates through these homogenous reaction paths. The direct photo-oxidation of SO 2 by way of the electronically excited states of SO 2 is relatively unimportant for most conditions which occur within the troposphere. The oxidation of SO 2 within the natural troposphere is expected to occur largely by way of reactions 39, 31 and 33, with reaction 39 being the dominant path: HO + SO 2 (+ M ) → HOSO 2 ( + M ) (39); HO 2 + SO 2 → HO + SO 3 (31); CH 3 O 2 + SO 2 →CH 3 O + SO 3 (33). By combining our kinetic estimates with the Crutzen and Fishman calculation of [HO], [HO 2 ] and [CH 3 O 2 ] for the troposphere, we estimate that the total rates of SO 2 oxidation as high as 1.5%h −1 are expected at midday in July in the midlatitudes. Theoretical estimates of the monthly rates averaged over the northern hemisphere vary from a low of 0.1 %h −1 in January to a maximum of about 0.2% h −1 in July. From our computer simulations of the reactions within an SO 2 , NO x , hydrocarbon, CO, aldehyde-polluted lower troposphere, it is predicted that the three reactions, 39. 31 and 33 occur with about equal rates; SO 2 oxidations for this case can proceed homogeneously at rates as high as 4% h −1 . Considerations of the reactions in stack gas plumes suggest that a small maximum in the SO 2 photo-oxidation rate may occur during the early stages of the dispersion of a parcel of the stack gases into the air. This should be followed by a short period of slower oxidation. In theory the initial burst is expected to arise from NO 2 and HONO photolysis followed by reaction 39 and the reaction. O ( 3 P) + SO 2 (+ M)→ SO 3 (+ M). After the extensive dilution of the stack gases by polluted urban air, the rate of SO 2 homogeneous oxidation is expected to approach that for a typical polluted urban atmosphere (~4%h −1 ).

The molecular structure of asphaltene: an unfolding story

Abstract From detailed chemical and thermal degradation studies, a host of structural units have been identified in Alberta asphaltenes. It has been shown that the extent of aromatic condensation is low and that highly condensed pericyclic aromatic structures are present in very low concentrations. From the available data reported to date, it is concluded that petroleum asphaltenes were mainly derived through the catalytic cyclization, aromatization and condensation of n -alkanoic, probably fatty acids, precursors.

Pyrolysis of asphaltenes: a source of geochemical information

Abstract Pyrolysis of asphaltenes from crude oils yields significant amounts of crude oil-like material. Studies of asphaltenes and their pyrolysis products from biodegraded and non-biodegraded oils show that biodegradation does not affect the composition of asphaltene. The overall composition of the oil produced from them on pyrolysis is similar to, yet significantly different from, that of the parent oil. From these compositional differences, it is concluded that asphaltene and its pyrolysis products contain geochemical information which is characteristic, and therefore may shed light on the history of the oil prior to asphaltene formation.

The origin of the oil sand bitumens of Alberta: a chemical and a microbiological simulation study

Abstract An analytical method involving computerized gas Chromatographic mass spectrometric “Multiple Ion Cross Scan” technique has been developed for the study of chemical transformations in the biodegradation of crude oils. The technique has been employed in the study of the bitumens of the Alberta oil sands. Comparison of results from the in vitro simulation experiments with those from field samples of Alberta Lower Cretaceous oils and oil sands suggests that the Alberta oil sand bitumens have arisen from the biodegradation of conventional crude oils.

Geochemistry of the thiourea adduct fraction from an Alberta petroleum

Abstract The thiourea adducted saturated hydrocarbon fraction (TUA) from a mature Alberta crude oil has been studied in detail. The predominating classes of compounds were found to be the acyclic isoprenoids, alkylcyclohexanes and alkylmethylcyclohexanes. Simulation experiments indicated that the alkylcyclohexanes and the alkylmethylcyclohexanes may have been formed by the advanced diagenesis of biologically occurring fatty acids.

Chemical composition of Athabasca bitumen

Abstract A detailed analysis has been carried out on the deasphaltened Athabasca bitumen using two different series of Chromatographic separations followed by i.r., u.v., n.m.r. and computerized GC/MS studies of the separated fractions: saturates (22–25%), monoaromatics (10.3–10.8%), diaromatics (4.6–5.3%), polyaromatics and non-specific polar compounds (28.6%), acids (16.5%), bases (7.8%), and neutral nitrogen compounds (1.6%). The acyclic paraffin content of the maltene is low: straight-chain paraffins and the isoprenoids, phytane and pristane, are present in very low concentrations. Polycyclic saturates represent about 90% of the saturate fraction. The presence of C-27 and C-29–C-35 hopanes of the 17α(h):21β(H) series and C-21–C-30 steranes was established. The mono- and diaromatic fractions were analysed by computerized mass spectrometry. The monoaromatic fraction contains alkylbenzenes, naphthenebenzenes and dinaphthenebenzenes in a ratio of 1.0:1.7:1.3. The ratio for naphthalenes, acenaphthenes + dibenzofurans and fluorenes in the diaromatic fraction is 1:0.9:0.5.

Oxygen distribution and hydrogen bonding in Athabasca asphaltene

Abstract The oxygen distribution in the Athabasca asphaltene has been investigated. On the average, 75% of the oxygen is present in the form of hydroxyl groups. I.r. studies indicate that these hydroxyl groups exist almost entirely as hydrogen-bonded complexes which do not dissociate in carbon tetrachloride. The decrease in the molecular weight of the acetylated, methylated and silylated asphaltene suggests that the hydrogen bonding is intermolecular in character. The i.r. spectra of the asphaltene fractions extracted with polar solvents showed the presence of free OH, NH and carbonyl groups. The strong hydrogen-bonding properties of the Athabasca asphaltene were confirmed in i.r. measurements of the interaction with phenol, and molecular weight determinations of asphaltene 2,7-naphthalenediol and 4,4′-dihydroxy-3,3′-dimethyldiphenyl mixtures.

Sulfides in petroleum

Abstract The homologous series of terpenoid sulfides previously reported to be present in Athabasca bitumen have been detected in a variety of petroleums from the Western Hemisphere. All 22 samples examined, ranging in age from Devonoan to Cretaceous, contained the terpenoid sulfides. A method is described for the isolation of sulfides from petroleums based on the selective oxidation of sulfides to more polar sulfoxides which are easily removed from the mixture and their subsequent reduction to sulfides. The sulfide content in the petroleum maltenes examined ranged from 0.3 to 16.1% w/w. In addition to the bicyclic and tetracyclic terpenoid sulfides a new series of tricyclic terpenoid sulfides has been identified, and the details of the isoprenoid side chain have been elucidated for all three homologous series. The distributions by carbon number of the bicyclic and tetracyclic homologous series of terpenoid sulfides show pronounced variations which are attributed to thermal maturity and degree of water washing of the petroleum, thus the ability to identify terpenoid sulfides should provide a useful tool for oil-oil and oil-source rock correlation studies. The bicyclic and tricyclic terpenoid sulfides have the same carbon framework as the carotenoids which suggest that these sulfides were accessory pigments in photosynthesis.

Absorption and emission spectra of Athabasca asphaltene in the visible and near ultraviolet regions

Abstract Absorption, excitation and emission spectra in the visible and ultra-violet region were recorded at room temperature for Athabasca (Alberta, Canada) asphaltene and five of its fractions separated according to molecular weight (MW) by gel permeation chromatography (g.p.c.) on Bio-Beads SX-1. Strong concentrations effects were observed on the profiles of all the excitation and emission spectra at concentrations higher than 5.0 mg l−1. The proper excitation and emission spectra were taken at concentrations lower than 5.0 mg l−1 where the profiles are independent of concentration. All the spectra obtained were broad, structureless bands with the exception of that of the lowest MW fraction, which shows the sharp Soret band characteristic of the vanadyl porphyrin complex. The absorbance of the whole asphaltene was found to be equal to the weighted sum of absorbances of the fractions at a given wavelength and a given weight concentration. This additive property was not observed among the intensities in the emission spectra. The profiles of all the excitation and absorption spectra are identical throughout the asphaltene fractions, suggesting that the basic absorbing chromospheres are the same throughout the fractions and independent of MW of the fractions. In addition the absorption spectra are not significantly affected by the Tyndall scattering. From the examination of absorptivity and the position of the absorption band, the average number of aromatic rings in the average absorbing chromophores throughout the fractions was found to consist of approximately two to three. The fluorescence spectra, on the other hand, show a very rapid decrease of intensity at a constant weight concentration and a gradual shift of the band maxima toward longer wavelength with increasing number average MW. The origin of the fluorescence band is considered to be exciplexes. The average rate of non-radiative processes decreases steadily with decreasing MW from fraction 1 to fraction 5. The influence of various solvents was explored on the absorption, excitation and emission spectra of the lowest MW (1200) asphaltene fraction.

The far ultraviolet and HeI photoelectron spectra of alkyl and fluorine substituted silane derivatives

The HeI photoelectron and vacuum uv absorption spectra of a number of methyl, ethyl, methylfluoro, and ethylfluoro derivatives of silane are presented. The spectra can be interpreted on the basis of their similarity to those of the related methane or ethane derivatives. The lowest lying excited states are related to transitions to 4s, 4p, and 3d orbitals having mixed Rydberg–valence shell character. The spectra can be divided into two categories: methane (’’round field’’) or ethane (’’long field’’) types. Fluorine substitution influences these spectra in a characteristic way.