Desulfurization of Morupule Coal with Subcritical Aqueous Ethanol Extraction.

Coal combustion greatly contributes to global emissions of toxic gases into the atmosphere, with sulfur emissions as one of the prominent pollutants in addition to carbon dioxide. Nevertheless, Botswana utilizes Morupule's sub-bituminous coal with average sulfur and ash contents, as determined in this study being 1.9 and 24.4 % by weight with an average calorific value of 22 MJ Kg-1 to generate electricity. We report an optimized extraction method for reducing total sulfur in Morupule coal from 1.9±0.2 to 0.43±0.02 wt.% at optimum conditions of ethanol/water (90/10, v/v %) at 129 °C (105 bars) in 10 minutes. A Box-Behnken experimental design was employed to select the optimal conditions of temperature (100-180 °C), water proportion in ethanol (10-90, v/v %) and extraction time (10-30 minutes), thus reducing the total sulfur under these mild conditions compared to conventional extraction. The optimized conditions were however not efficient in removing ash.

Combating selective ionization in the high resolution mass spectral characterization of complex mixtures.

Direct "dilute and shoot" mass spectral analysis of complex naturally-occurring mixtures has become the "standard" analysis in environmental and petrochemical science, as well as in many other areas of research. Despite recent advances in ionization methods, that approach still suffers several limitations for the comprehensive characterization of compositionally complex matrices. Foremost, the selective ionization of highly acidic (negative electrospray ionization ((-) ESI)) and/or basic (positive electrospray ionization ((+) ESI)) species limits the detection of weakly acidic/basic species, and similar issues (matrix effects) complicate atmospheric pressure photo-ionization (APPI)/atmospheric pressure chemical ionization (APCI) analyses. Furthermore, given the wide range of chemical functionalities and structural motifs in these compositionally complex mixtures, aggregation can similarly limit the observed species to a small (10-20%) mass fraction of the whole sample. Finally, irrespective of the ionization method, the mass analyzer must be capable of resolving tens-of-thousands of mass spectral peaks and provide the mass accuracy (typically 50-300 ppb mass measurement error) required for elemental composition assignment, and thus is generally limited to high-field Fourier transform ion cyclotron mass spectrometry (FT-ICR MS). Here, we describe three approaches to combat the above issues for (+) ESI, (-) ESI, and (+) APPI FT-ICR MS analysis of petroleum samples. Each approach relies on chromatographic fractionation to help reduce selective ionization discrimination and target either specific chemical functionalities (pyridinic and pyrrolic species (nitrogen) or carboxylic acids (oxygen)) or specific structural motifs (single aromatic core (island) or multi-core aromatics (archipelago)) known to be related to ionization efficiency. Each fractionation method yields a 2-10-fold increase in the compositional coverage, exposes species that are undetectable using direct "dilute and shoot" analysis, and provides coarse selectivity in chemical functionalities that can both increase the assignment confidence and optimize ionization conditions to maximize compositional coverage.

Transmission geometry laser desorption atmospheric pressure photochemical ionization mass spectrometry for analysis of complex organic mixtures.

We present laser desorption atmospheric pressure photochemical ionization mass spectrometry (LD/APPCI MS) for rapid throughput analysis of complex organic mixtures, without the need for matrix, electric discharge, secondary electrospray, or solvents/vaporizers. Analytes dried on a microscope slide are vaporized in transmission geometry by a laser beam aligned with the atmospheric pressure inlet of the mass spectrometer. The laser beam initiates a cascade of reactions in the region between the glass slide and MS inlet, leading to generation of reagent ions for chemical ionization of vaporized analyte. Positive analyte ions are generated predominantly by proton transfer, charge exchange, and hydride abstraction, whereas negative ions are generated by electron capture or proton transfer reactions, enabling simultaneous analysis of saturated, unsaturated, and heteroatom-containing hydrocarbons. The absence of matrix interference renders LD/APPCI MS particularly useful for analysis of small molecules (<2000 Da) such as those present in petroleum crude oil and petroleum deposits. [M + H](+) and M(+•) dominate the positive-ion mass spectra for olefins and polyaromatic hydrocarbons, whereas saturated hydrocarbons are observed mainly as [M - H](+) and/or M(+•). Heteroatom-containing hydrocarbons are observed predominantly as [M + H](+). [M - H](-) and M(-•) are the dominant negative ions observed for analytes of lower gas-phase basicity or higher electron affinity than O2. The source was coupled with a 9.4 T Fourier transform ion cyclotron resonance mass spectrometer (FTICR MS) to resolve and identify thousands of peaks from Athabasca bitumen heavy vacuum gas oil distillates (400-425 and 500-538 °C), enabling simultaneous characterization of their polar and nonpolar composition. We also applied LD/APPCI FTICR MS for rapid analysis of sodium and calcium naphthenate deposits with little to no sample pretreatment to provide mass spectral fingerprints that enable reliable compositional characterization.

Characterization of oil sands naphthenic acids treated with ultraviolet and microwave radiation by negative ion electrospray Fourier transform ion cyclotron resonance mass spectrometry.

Naphthenic acids (NAs) are concentrated in oil sand process water (OSPW) as a result of caustic oil sands extraction processes. There is considerable interest in methods for treatment of NAs in OSPW. Earlier work has shown that the combination of ultraviolet (UV) and microwave treatments in the laboratory was effective in reducing the concentration of classical NAs. Here we apply Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to further characterize NAs treated with (a) UV (254 nm) in the presence of TiO(2) catalyst; and/or (b) microwave irradiation (2.45 GHz). FT-ICR MS was used to characterize the NA fraction before and after treatment. Acidic oxygen-containing classes were most abundant in all samples whereas other heteroatomic classes were least abundant or not present in some samples. For example, the SO(2)-containing species were absent in UV- or combined UV- and microwave-treated samples. The O(2) class was dominant in all samples, indicative of NAs. However, samples treated with UV and microwave radiation have a lower relative abundance of other heteroatomic classes. We observed O(2), S(1)O(2), O(3), S(1)O(3), O(4), O(5), and O(6) classes, whereas the species with relatively high O(n) content, namely, the O(3), O(5), and O(6) classes, were present only in UV- and microwave-treated samples. The relatively high O(n) content is consistent with oxidation of the parent acids in treated samples. There may thus be potential implications for environmental forensics. For example, the monitoring of the ratio of SO(2):O(2) or tracking the relative abundances of O(2), O(3), O(4), O(5), and O(6) classes may provide insights for distinguishing naturally derived oil sands components from those that are process-related in aquatic environments.

Ultrahigh-resolution mass spectrometry of simulated runoff from treated oil sands mature fine tailings.

There is interest in using mature fine tailings (MFT) in reclamation strategies of oil sands mining operations. However, simulated runoff from different dried MFT treatments is known to have elevated levels of salts, toxic ions, and naphthenic acids, and alkaline pH and it is phytotoxic to the emergent macrophyte, common reed (Phragmites australis). Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) of the acidic species in the runoff confirmed that the distribution of oil sands naphthenic acids and associated oil sand acids was dependent on the MFT treatment. Furthermore, FT-ICR MS studies of the acidic species in hydroponic systems revealed that there was no plant-mediated change in the electrospray ionization mass spectra of the runoff. O(o)-containing species were prevalent (>90%), O(o)S(s) were predominant (<10% relative abundance), and O(o)N(n) were least abundant in all runoff water samples. O(o)S(s) species were predominant in all the samples investigated. The heteroatomic classes present in runoff water at greater than 1% relative abundance include: O(2)N(1), O(3)N(1), O(2), O(2)S(1) O(3), O(3)S(1), O(4), O(4)S(1), O(5), O(5)S(1), O(6), O(6)S(1), O(7), O(7)S(1), O(8) and O(8)S(1). Assuming the same response factor for all O(o) species, the O(4) class, presumably dicarboxylic acids, was generally more prevalent than the O(2) class in all samples. The O(2) class is indicative of classical naphthenic acids. However, dicarboxylic acids will form negative ions more readily than the monocarboxylic acids as there are two acidic hydrogens available for formation of these species.

Aquatic plant-derived changes in oil sands naphthenic acid signatures determined by low-, high- and ultrahigh-resolution mass spectrometry.

Mass spectrometry is a common tool for studying the fate of complex organic compound mixtures in oil sands processed water (OSPW), but a comparison of low-, high- ( approximately 10 000), and ultrahigh-resolution ( approximately 400 000) instrumentation for this purpose has not previously been made. High-resolution quadrupole time-of-flight mass spectrometry (QTOF MS) and ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), with negative-ion electrospray ionization, provided evidence for the selective dissipation of components in OSPW. Dissipation of oil sands naphthenic acids (NAs with general formula C(n)H(2n+z)O(2) where n is the number of carbon atoms, and Z is zero or a negative even number describing the number of rings) was masked (by components such as fatty acids, O(3), O(5), O(6), O(7), SO(2), SO(3), SO(4), SO(5), SO(6), and NO(4) species) at low resolution (1000) when using a triple quadrupole mass spectrometer. Changes observed in the relative composition of components in OSPW appear to be due primarily to the presence of plants, specifically cattails (Typha latifolia) and their associated microorganisms. The observed dissipation included a range of heteratomic species containing O(2), O(3), O(4), and O(5), present in Athabasca oil sands acid extracts. For the heteratomic O(2) species, namely naphthenic acids, an interesting structural relationship suggests that low and high carbon number NAs are dissipated by the plants preferentially, with a minimum around C(14)/C(15). Other heteratomic species containing O(6), O(7), SO(2), SO(3), SO(4), SO(5), SO(6), and NO(4) appear to be relatively recalcitrant to the cattails and were not dissipated to the same extent in planted systems.

Naphthenic acids as indicators of crude oil biodegradation in soil, based on semi-quantitative electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry.

Crude oil contaminated soil cores were collected from a basin that contained oily solids left from three decades of oil production. Hydrocarbon biomarker analyses revealed that the soil extracts were moderately biodegraded compared with the non-degraded source oil. The degree of biodegradation also decreased with core depth (7 cm to 1 m). These data were correlated to compositional changes observed in acidic NSO-compounds that were selectively ionized and mass resolved by negative ion electrospray Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). Among the NSO-compounds ionized, the increase in naphthenic acid concentration (e.g., acyclic and alicyclic carboxylic acids) best correlated with the increase in biodegradation (e.g., from non-degraded to moderately degraded) as determined by the hydrocarbon biomarker analyses. The most biodegraded surface extracts (7 cm) exhibited an 80% increase in the abundance of acids relative to the source oil. Use of an internal standard allowed the semi-quantitative determination of the total naphthenic acid concentration, which decreased significantly (P < 0.05) with soil depth. Furthermore, the shift to higher double bond equivalents (DBEs), from acyclic to alicyclic acids, indicated that the increase in acids in the soil extracts was predominantly due to biotic processes. This work demonstrates the potential of ESI FT-ICR MS as a semi-quantitative tool to monitor the production of naphthenic acids during crude oil biotransformation in the environment.