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The approach for quantitative estimation of asphaltene sizes in crude oils in situ via precise simulation of electron spin resonance (ESR) spectra of the slowly rotating VO2+-containing fragments was developed. The method is based on the correlation between the size of the paramagnetic particles and their characteristic rotational time that can be determined by ESR in situ while incomplete averaging of anisotropic hyperfine interactions is observed. The precise simulation of the ESR spectra of heavy molecules, labeled naturally with vanadyl ions, allows one to find their size distribution in crude oils. In particular, the method is demonstrated to be an effective tool for the quantitative determination of the asphaltene sizes in different oil fractions in situ.

The potential of physical methods for in situ studies of the phase stability and physicochemical evolution of heavy oils is analyzed. The basic principles of in situ application of the methods are outlined; the scope and limitations of each approach are discussed. Particular attention is paid to the visualization of the asphaltene aggregation process using attenuated total reflection Fourier transform IR spectroscopy and magnetic resonance imaging, as well as small-angle X-ray and neutron scattering, electron spin resonance and electron and optical microscopy. These methods provide complementary information on the properties and behaviour of oil disperse systems on various spatial and temporal scales ranging from the rotational mobility of asphaltene molecules and the dynamics of their local environment with a characteristic time of [?] 10[?]10 s and evolution of the size characteristics and shape of asphaltene aggregates to visualization of asphaltene aggregation and formation of precipitates in crude oils and their blends with spatial resolution from a few to thousands of micrometres with a characteristic time from seconds to hundreds of hours. The approaches described can be efficiently applied in a wide range of temperatures and pressures, as well as in the presence of chemicals that affect the stability of heavy oils.The bibliography includes 241 references.

The work demonstrates the results of the first experimental PFG NMR study in situ of the complex phase behavior of asphaltenes in the presence of high-pressure CO2. To perform the experiments, a series of sealed, thick-walled quartz capillaries were prepared with a mixture of CO2and asphaltenes dissolved either in chloroform or benzene at different initial concentrations. Then, the temperature dependence of the diffusion coefficients of the asphaltene aggregates was measured for each sample after the mixture reached its equilibrium state, at which, in accordance with the solubility limit, only part of the initial asphaltenes remained dissolved. Despite quite low residual asphaltene concentrations in solution, experimental data clearly demonstrated the presence of aggregated structures (up to 70–80 wt %) attributed solely to nanoaggregates, with no signs of the presence of macroaggregates in the samples. Temperature dependencies of aggregate diffusivity clearly showed that the scenario, according to which the evolution of the asphaltene aggregates will develop, strongly depends on the initial asphaltene concentration, mass fraction of CO2loaded into the system, and chemical nature of the solvent used. In particular, the most diluted asphaltene solution, expected to be the most resistive to the aggregation processes in a high-pressure CO2environment, revealed the most pronounced aggregation-dependent translational dynamics as compared to those with a moderate initial asphaltene concentration. Contrarily, the concentrated asphaltene solution may not show drastic aggregation processes if the mass fraction of the CO2loaded will not appear to be so high. Finally, the experimental results provide evidence that the temperature-triggered structural transformation of asphaltene aggregates due to the noncovalent bond breakup is not hindered under high-pressure CO2, but instead becomes more emphasized. The results obtained shed new light on asphaltene aggregate dynamics and brought new knowledge about the fundamental behavior of asphaltene in high-pressure CO2conditions.

The effect of transition alumina (γ‐, η‐, χ‐Al2O3) on the activity and stability of model chromia/alumina catalysts with 4 wt% Cr in isobutane dehydrogenation is studied. It is shown that a fresh catalyst with η‐Al2O3as a support has the highest activity, while with χ‐Al2O3has the lowest one. The characterization of the catalysts by N2adsorption, X‐ray diffraction (XRD), electron spin resonance (ESR) spectroscopy, and X‐ray photoelectron spectroscopy (XPS) is used to describe changes in the catalysts induced by high‐temperature treatment at 800, 1000, and 1200 °C in air. It is shown that sintering of the alumina support and formation of chromia‐alumina solid solutions are the reasons of irreversible decline in the catalytic activity. Cr/γ‐Al2O3is found to be the most stable to sintering and phase transformation, whereas Cr/χ‐Al2O3is found to be the least stable. Due to its highest initial activity, the η‐Al2O3‐supported catalyst loses its dehydrogenation activity most rapidly as the calcination temperature is raised. The segregation of sodium impurities is observed in the course of heat treatment, which may be an additional cause of deactivation. Alumina supports of chromia‐alumina dehydrogenation catalysts not only provide different catalytic activity of the as‐prepared catalysts but also exert an effect on their thermal stability. The intensity of Cr/Al2O3irreversible deactivation upon high‐temperature heat treatment in air lowers from Cr/χ‐Al2O3through Cr/η‐Al2O3to Cr/γ‐Al2O3, revealing a pronounced structural stability of the γ‐Al2O3‐based catalyst.

The potential of physical methods for in situstudies of the phase stability and physicochemical evolution of heavy oils is analyzed. The basic principles of in situapplication of the methods are outlined; the scope and limitations of each approach are discussed. Particular attention is paid to the visualization of the asphaltene aggregation process using attenuated total reflection Fourier transform IR spectroscopy and magnetic resonance imaging, as well as small-angle X-ray and neutron scattering, electron spin resonance and electron and optical microscopy. These methods provide complementary information on the properties and behaviour of oil disperse systems on various spatial and temporal scales ranging from the rotational mobility of asphaltene molecules and the dynamics of their local environment with a characteristic time of ∼ 10−10s and evolution of the size characteristics and shape of asphaltene aggregates to visualization of asphaltene aggregation and formation of precipitates in crude oils and their blends with spatial resolution from a few to thousands of micrometres with a characteristic time from seconds to hundreds of hours. The approaches described can be efficiently applied in a wide range of temperatures and pressures, as well as in the presence of chemicals that affect the stability of heavy oils.