An improved inverse gas chromatographic method involving the use of a mass-specific detector for the determination of the glass transition temperature of polymeric materials is described. The new method allows the use of several probe solutes simultaneously with an automated, closed-loop injector and stepped temperature programming. The result is a single continuous chromatogram for each probe solute over a range of temperatures encompassing the glass transition temperature, T(g). Several different methods for the exact determination of T(g) from the chromatogram were investigated, including the classical van't Hoff-type plots with retention volumes calculated from both the peak maximum and first moment values of the elution peaks. Two new methods are also proposed for the evaluation of T(g) from either the temperature dependence of the second moments of the elution peaks for probe solutes or simple inspection of the variation of elution peak height (width) with temperature. All four methods for the determination of T(g) are evaluated with three probe solutes and four different polymers, viz., poly(methyl methacrylate), poly(ethylene terephthalate), polycarbonate, and two batches of polystyrene with different molecular weights and T(g) values. Three phenomenological models were used to interpret the chromatographic retention mechanisms of the solute probes in glassy and rubbery polymers. These are (i) the classical adsorption/absorption model for glass and rubber polymers, (ii) the single absorption mechanism model, and (iii) a dual-mode model previously used to explain the sorption of gases, such as CO(2), in glassy polymers. It is concluded that no single approach is adequate to interpret the experimental results for all of the systems, although each model is adequate for some individual solute/polymer combinations.
The complexity of petroleum crude oils necessitates a combination of analytical techniques to gain the in-depth compositional knowledge needed to enhance oil production or develop optimal refining strategies. This study focuses on the fractionation of four Arabian crude oils through gel permeation chromatography (GPC) to obtain chemically well-defined fractions, which are then characterized in detail using atmospheric pressure photoionization Fourier transform-ion cyclotron resonance mass spectrometry, and field desorption time-of-flight mass spectrometry. GPC is found to be a valuable tool because the described methodology produces petroleum fractions with nonpolar components reproducibly separated by total alkyl chain length. While the early-eluting fractions contained large saturated compounds and small aromatic systems with extensive alkyl chains, as well as potential asphaltene material, the later-eluting GPC fractions contained molecules with a wide range of aromatic rings but very limited alkyl chains. The molecular size contribution of aromatic rings did not change the elution time of the studied petroleum components as it appears counterbalanced by non-size effects. Preliminary tandem mass spectrometry experiments revealed the presence of noncondensed aromatic rings alongside species with up to nine fused aromatic rings in the late-eluting GPC fractions, as demonstrated for S2 class species. Finally, the GPC separation was also tested on a South American crude oil sample and found to fractionate it by the same molecular criterion, i.e., total alkyl chain length, independent of the crude oil API gravity, total sulfur and nitrogen contents, or geographical origin.
Abstract One of the most important issues in oilfield chemistry is the troublesome occurrence of organic and inorganic solids which may form downhole in the reservoir, wellbore, topsides and/or in pipelines. Asphaltenes are a class of compounds in crude oils, defined in solubility terms that under certain conditions are known to precipitate and deposit. This may lead to very expensive remediation and treatment operations. Over the years much research has been carried out on asphaltenes. Yet the exact chemical nature of these species still remains unknown. The determination of asphaltene molecular weight distributions in conjunction with the identification of compound classes is a major challenge in the prediction of asphaltene problems with petroleum fluids. Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) is a technique well-suited for this purpose, due to its unmatched resolution and the possibility of providing information otherwise not available from more traditional bulk elemental analysis methods. We have designed a preliminary analytical protocol with this objective in mind. It involves the sample preparation (e.g. sulfur selective chromatography and derivatization) in combination with FT-ICR MS. Initial data show that the predominant compounds in the asphaltene samples investigated were species in the mass range of 200-1100 Daltons containing various functionalities, including nitrogen-, sulfur- and oxygen-heterocycles. It was possible to see clear differences between asphaltene field samples and solubility fractions. Further work should target the correlation of this information with the precipitation of asphaltenes from problematic fluid samples.
VIDWAN, an excellent source of background information of subject experts working at leading academic institutions and R & D organisations involved in teaching and research, provides a platform for finding potential experts with similar expertise. This paper aims to explore the application of emerging technologies in VIDWAN subject expert database and discusses particularly about the expert's selection methods, database feature and functionalities and its benefits. The article reviewed the current situation of the VIDWAN subject expert database and national researcher's network in India and recommends that it is the time to populate the database not only in India but also worldwide and in all scientific areas. Universities, R & D organisations and other academia too have an important role in populating this database.
Base oils, blended for finished lubricant formulations, are classified by the American Petroleum Institute into five groups, viz., groups I–V. Groups I–III consist of petroleum based hydrocarbons whereas groups IV and V are made of synthetic polymers. In the present study, five base oil samples belonging to groups I and III were extensively characterized using high performance liquid chromatography (HPLC), comprehensive two-dimensional gas chromatography (GC×GC), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) equipped with atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) sources. First, the capabilities and limitations of each analytical technique were evaluated, and then the availed information was combined to reveal compositional details on the base oil samples studied. HPLC showed the overwhelming presence of saturated over aromatic compounds in all five base oils. A similar trend was further corroborated using GC×GC, which yielded semiquantitative information on the compound classes present in the samples and provided further details on the carbon number distributions within these classes. In addition to chromatography methods, FT-ICR MS supplemented the compositional information on the base oil samples by resolving the aromatics compounds into alkyl- and naphtheno-subtituted families. APCI proved more effective for the ionization of the highly saturated base oil components compared to APPI. Furthermore, for the detailed information on hydrocarbon molecules FT-ICR MS revealed the presence of saturated and aromatic sulfur species in all base oil samples. The results presented herein offer a unique perspective into the detailed molecular structure of base oils typically used to formulate lubricants.
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