Specification of the nitrogen functional group in a hydrotreated petroleum molecule using hydrogen/deuterium exchange electrospray ionization high-resolution mass spectrometry.

Hydrotreatment is extensively used for the production of clean fuel. Attaining an understanding of the structural conversion of the nitrogen species during hydrotreatment is very challenging due to the compositional complexity and the absence of a proper characterization method. In the presented work, we coupled hydrogen/deuterium exchange (HDX) with positive-ion electrospray ionization high-resolution mass spectrometry ((+) ESI HR MS) to investigate the difference between the composition of the nitrogen-containing species and the functional groups before and after hydrotreatment. The solvent and additive were optimized for HDX (+) ESI HRMS through systematic evaluations on model nitrogen-containing compounds. We found that adding deuterated water (D2O) and deuterated formic acid (DCOOD) significantly increased the degree of HDX and thus facilitated the identification of nitrogen functional groups. After application to the hydrotreated petroleum samples, the compositional variation of intermediate amine compounds during the heavy petroleum hydrotreatment process was clearly revealed.

Molecular Characterization of Thiols in Fossil Fuels by Michael Addition Reaction Derivatization and Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

Thiols widely occur in sediments and fossil fuels. However, the molecular composition of these compounds is unclear due to the lack of appropriate analytical methods. In this work, a characterization method for thiols in fossil fuels was developed on the basis of Michael addition reaction derivatization followed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). Model thiol compound studies showed that thiols were selectively reacted with phenylvinylsulfone and transformed to sulfones with greater than 98% conversions. This method was applied to a coker naphtha, light and heavy gas oils, and crude oils from various geological sources. The results showed that long alkyl chain thiols are readily present in petroleum, which have up to 30 carbon atoms. Large DBE dispersity of thiols indicates that naphthenic and aromatic thiols are also present in the petroleum. This method is capable of detecting thiol compounds in the part per million range by weight. This method allows characterization of thiols in a complex hydrocarbon matrix, which is complementary to the comprehensive analysis of sulfur compounds in fossil fuels.

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.

Preparation of Mesophase Pitch through Supercritical Fluid Extraction of Coal Tar Pitch.

This paper explores the preparation of mesophase pitch by employing supercritical fluid extraction on coal tar pitch sourced from a coal chemical company. The raw material undergoes pretreatment using various extraction solvents, and the resulting refined components are thermally polycondensed in a laboratory microreactor to create mesophase pitch. Qualitative and quantitative analyses of the mesophase pitch's structure are conducted through polarized light microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and other analytical methods to identify an optimal supercritical fluid extraction pretreatment solvent for coal tar pitch. The results reveal that using n-hexane solvent in the supercritical fluid extraction process yields a mesophase pitch with a remarkable mesophase content of 90.07%, displaying excellent optical texture distribution, superior directional arrangement and order, the closest lamellar accumulation, and the highest degree of anisotropy and graphitization.

Observation of CO2 and solvent adduct ions during negative mode electrospray ionization Fourier transform ion cyclotron resonance mass spectrometric analysis of monohydric alcohols.

RATIONALE: Monohydric alcohols are common in natural products, bio-oils, and medicine. We have found that monohydric alcohols can form O3 (ions containing three oxygen atoms) and O4 adduct ions in negative electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), which would significantly affect the composition analysis of alcohols, especially in a complex mixture. It is necessary to study the reaction pathways and the method to eliminate or reduce the 'artifact' adducts. METHODS: Octadecanol, cholesterol, squalanol and two complex monohydric alcohol mixtures were selected as model compounds. These samples were subjected to negative ion ESI FT-ICR MS analysis. The composition and formation mechanism of adducts were studied by the ultrahigh-resolution accurate mass measurement for elemental composition, along with the MS(2) isolation and collision-induced dissociation (CID) experiments for structural determination. RESULTS: The reaction pathway of O3 adduct formation is the coupling of a monohydric alcohol ion with a CO2 to form a stable O3 ionic species by likely a covalent bond (source of CO2 is not clear). The O4 species are formed by O3 ionic species adducted with an alcohol molecule of the solvent, such as methanol or ethanol, by likely a hydrogen bond. These adduct ions could be eliminated or reduced by increasing collision energy. However, excessive collision energy would fragment monohydric alcohol ions. CONCLUSIONS: The formation mechanisms of O3 and O4 adducts from monohydric alcohols in negative ion ESI FT-ICR MS were proposed. The solvent adduction effects can be eliminated or reduced by optimizing the collision energy of CID in FT-ICR MS.

Analysis of the Contribution of Petroleum Acid Components to the Viscosity of Heavy Oils with High TAN.

The viscosity of heavy oil hinders its cold production, posing a major challenge to its exploitation. The high viscosity of heavy oil can be attributed to the content of asphaltene. However, during the collection of heavy oil samples from various regions in China, we observed that heavy oils with high total acid number (TAN) but low asphaltene content also exhibit relatively high viscosity. Hence, the viscosity mechanism of high-acid crude oil, the influence of petroleum acid on heavy oil viscosity, should be investigated. In this study, Xinjiang Chunfeng heavy oil was selected for analysis, possessing a viscosity of 16,886 mPa·s at 50 °C and a high total acid number (TAN) of 17.72 mg KOH/g. Separation was performed on the deacidified oil and the acid component using an alkali-modified silica gel column. The viscosity changes of the deacidified oil and its blends with varying proportions of the acid component were determined, along with the viscosity changes of the deacidified oil and acid components in a toluene solution. The molecular composition was analyzed using a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). The findings indicated successful separation of petroleum acid from the heavy oil, the acid component yield being 16.65 wt %. Furthermore, the viscosity of the petroleum acid was significantly higher than that of the deacidified oil. The rate of viscosity change of the acid component in the toluene solvent exceeded that of the deacidified oil, and the viscosity of the deacidified oil notably increased upon the addition of acid. In conjunction with the viscosity data, it was observed that the deacidified oil exhibited the removal of O2 and O4 compounds, resulting in a 43.11% viscosity reduction at 30 °C compared with crude oil. Thus, the monoacid and diacid components considerably affected the viscosity of heavy oil.

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.

Ionization selectivity of electrospray and atmospheric pressure photoionization FT-ICR MS for petroleum refinery wastewater dissolved organic matter.

Dissolved organic matter (DOM) in petroleum refinery wastewater is an extremely complex mixture. A better understanding of chemical compositions of DOM at the molecular level is necessary for the design and optimization of wastewater treatment processes. In this study, two largely different DOM samples, one from a petroleum refinery wastewater and the other from the Suwannee river water, were characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled with positive-/negative-ion electrospray ionization (ESI), and positive-ion atmospheric pressure photoionization (APPI). For wastewater DOM, a total of 6226 molecular formulae were assigned in the three ionization modes. However, only 1182 molecular formulae were common in all three mass spectra, indicating that the techniques were highly complementary in the types of molecules they ionize. Acid Ox (x = 1-9) and basic N1Ox (x = 0-2) classes were dominant in the wastewater DOM detected in negative-ion and positive-ion ESI mode, respectively. And the wastewater DOM contains considerable amounts of polycyclic aromatic hydrocarbons that did not respond to ESI but can be ionized selectively by APPI. Compared with riverine DOM, the refinery wastewater DOM has a higher molecular complexity and is more enriched in hydrocarbon, and nitrogen- and sulfur-containing compounds. The results show that the major components of refinery wastewater DOM were distinctive from those of the natural organic matter. Though not quantitative, the results obtained by various ionization techniques were found to be complementary, and are helpful to our understanding of the selectivity of different ionization techniques as well as the molecular compositions of DOM.

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.

Carbon quantum dots derived by direct carbonization of carbonaceous microcrystals in mesophase pitch.

Aggregation of the central aromatic ring system of asphaltene molecules due to π-π interaction can lead to the formation of carbon quantum dots (CQDs). However, to date, such a roadmap has not been demonstrated. Here, we present a simple approach to the synthesis of CQDs by direct carbonization of dispersed carbonaceous microcrystals in mesophase pitch. The size of the as-prepared CQDs is modulated by adjusting the nucleation temperature for mesophase formation. Due to the oxygen-free character, the CQDs exhibit excitation-independent fluorescent behavior with a quantum yield up to 87%. The CQDs were successfully applied to fluorescent detection of Fe3+ ions with good specificity and sensitivity. Our results not only provide a scalable production of CQDs at low cost, but also give valuable clues to understand the solidification of asphaltene at nanoscale.

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.

[Analysis of composition and structure of sulfur compounds in residual oils by pyrolysis-gas chromatography].

Flash pyrolysis-gas chromatography has been used to investigate macromolecular sulphur in heavy oil. The influences of pyrolysis time and pyrolysis temperature have been studied and the analytical methods of pyrolysis were set up. Sulfur-containing products were identified by comparing with reference data and semi-quantified by a pulsed flame photometric detector (PFPD). The investigation conducted on Dagang, Gudao, Qianguo, Russia and mixed Russia-Daqing residual oils using pyrolysis-gas chromatography showed that the contents and composition of sulphur compounds demonstrated various characters in different pyrolysates of residual oils.