Vol 58, No 12 (2018)

The review describes theoretical approaches based on computer simulations at various levels of details (from quantum chemical calculations to atomistic and coarse-grained models) to study asphaltenes and systems containing asphaltenes. The used methods are described, their advantages and disadvantages are discussed in terms of computational costs and time- and spatial-scales available for simulations. The results of studies of the asphaltenes interactions with each other and their aggregation behavior in low-molecular solvents are presented. The most promising approaches of computer simulations of asphaltenes-based systems are determined.

The catalytic properties of composite catalyst systems based on zeolite HZSM-5 modified with magnesium, rhodium, and chitosan have been studied. The introduction of a rhodium–chitosan composite has a significant effect on the catalytic properties of the zeolite catalyst providing a significant increase in the activity and stability of the catalyst. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has revealed that the use of chitosan leads to a decrease in the total acidity of the zeolite catalyst mostly owing to a decrease in the number of strong Brønsted acid sites. It has been shown that the pretreatment of Mg–Rh*chitosan–HZSM-5 with synthesis gas leads to an increase in the time-on-stream stability of the catalyst.

Synthesis of isobutylene from ethanol in the presence of ZnO/ZrO₂ catalysts has been studied. The samples have been synthesized by incipient wetness impregnation of zirconium hydroxide derived from zirconyl chloride with zinc nitrate and subsequent calcination at 550°C. The synthesized samples have been studied by low-temperature nitrogen adsorption, SEM, XRD, IR spectroscopy of adsorbed CO, and TGA–DTA. Studies of the effect of the catalyst composition and the test conditions have revealed that, during the synthesis of isobutylene from ethanol, an optimum Zr : Zn molar ratio providing the production of isobutylene with a selectivity of 45–50% is 8–20 and optimum conditions for ethanol conversion to isobutylene are 500°C, a feed space velocity of 3 g/(g h), and a feedstock in the form of a 50% ethanol solution in water. According to thermogravimetric analysis, an increase in the zinc content in the samples leads to a decrease in the amount of coke deposits.

The influence of MEL zeolite synthesis conditions on the set of physicochemical properties and catalytic activity of the zeolites in the oligomerization reaction of butylenes has been studied. The number of synthesis stages and the concentration of tetrabutylammonium hydroxide template in the reaction mixture have been used as the variable parameters for the synthesis of MEL zeolites. It has been found that the use of two-stage crystallization comprising the low-temperature stage at 90°C and the high-temperature stage at 170°C promotes a decrease in the size of MEL zeolite crystals and provides a more complete involvement of the source materials in the crystallization process. The interval of template concentration in the reaction mixture in which the pure phase of zeolite MEL free of zeolite MFI can be obtained has been determined. It has been shown that during the two-stage crystallization of the reaction mixture with a template/SiO₂ molar ratio of 0.2, MEL zeolite is formed with crystals of 200–300 nm in size, whose surface is depleted in aluminum. It has been found that the nanocrystalline zeolite MEL exhibits high resistance to deactivation in the oligomerization reaction of butylenes due to a decrease in the number of acid sites on the outer surface of nanocrystals. No significant differences in the product distribution have been revealed for the oligomerization of butylenes on zeolites of the MEL and MFI structural types possessing identical physicochemical properties.

The component composition of the distillate of straight-run fuel oil after thermocatalytic cracking in the presence of zinc, iron(II), and nickel(II) 2-ethylhexanoates has been studied using GLC. It has been noted that metal nanocatalysts behave in different manners in the chemical transformations of hydrocarbons of straight-run fuel oil.

Lubricating greases based on pentaerythritol and trimethylolpropane esters and dioctyl sebacate have been synthesized using diureas as a thickener prepared by reactions of toluene diisocyanate, aniline, and primary aliphatic amines of various structures. The physicochemical properties of the greases, such as ultimate strength, yield stress, modulus of elasticity, dropping point, and colloid stability, have been characterized, and data on their antiwear activity have been obtained. The relationship between the structure of grease components, its rheology, and antiwear properties has been revealed.

In this study, the effect of NaCl, KCl, CaCl₂, MgCl₂, MgSO₄, and CaCl₂ salts in brine in the range of low (1000−5000 ppm) and intermediate (5000−40 000 ppm) salinity water on the amount and offset pressure of asphaltene precipitation was investigated. The measurements were performed at reservoir temperature (350.15 K) and high pressures (0−100 bar). The IFT (Interfacial Tension) values increased with pressure and a sudden increase was observed at a specific pressure namely, an offset pressure of asphaltene precipitation in APE (Asphaltene Precipitation Envelope). For all brines, the amount of IFT with increasing concentration was in descending order and after a minimum value it changed to uptrend. Likewise, similar results were obtained for the precipitated asphaltene amount. All the brines intensified the asphaltene precipitation. Monovalent cations like Na⁺ and K⁺ showed higher values of IFT and hence more asphaltene precipitation, however, MgCl₂ showed the least IFT, offset pressure and the amount of asphaltene precipitation.

This research has focused on modeling and optimization of a radial flow tubular reactor to produce methanol from synthesis gas (syngas) at steady state condition. A heterogeneous one-dimensional model is developed based on the material and energy balance laws to predict the performance of proposed radial flow configuration. To verify the accuracy of developed model, the simulation results of a conventional Lurgi type reactor are compared with the available plant data. In the optimization stage, methanol production capacity is maximized considering the feed temperature, cooling side temperature and feed pressure as decision variables using the genetic algorithm method. Then, the performance of optimized radial flow reactor is compared with the conventional radial flow configuration. The comparison between efficiency of optimized radial flow, conventional radial and axial flow reactors shows an acceptable enhancement in the syngas conversion to methanol and lower pressure drop in the optimized radial flow reactor.