The influence of mole fraction and nature of the cations in positions A and B of the pyrochlores containing Na+, Ca2+, Cd2+, U4+, Nb5+, Ta5+, Ti4+, Sb5+, Zr4+, V3+, V4+, W5+, W6+ synthesized under hydrothermal conditions at 800 °C, 200 MPa and controlled oxygen fugacity in NaF solution of 1.0 mol·kg−1 H2O on lattice parameters has been considered. The unit cell parameters of the fluorpyrochlores where for Nb5+ or Ta5+ were substituted by other cations showing distinct linear variations from the effective cations radii in positions A and B. Based on the literary data analysis, the two-parameter nonlinear equation describing dependence of pyrochlore lattice parameters on the cation radii for the oxide-pyrochlores has been proposed
A scheme for the combined processing of coal to produce synthetic jet fuel is proposed and experimentally verified. It has been established that using an approach including coal coking followed by gasification, Fischer–Tropsch synthesis, and hydroisomerization, the resulting kerosene fractions are characterized by low density values (0.741–0.751 kg/dm3 at 20°С) relative to the level specified by the technical requirements for Jet A-1 and T-8B jet fuel brands used today. With the use of the hydroisomerization process (Т = 330–345°С, pH2 = 72 bar) in the presence of a 2% Pt/Al-HMS (10) catalyst, it has been possible to obtain an isoparaffin fraction with the crystallization temperature below −56°С. The coal tar produced by coking of coal was subjected to deep hydrogenation to obtain a naphthenic jet fuel component characterized by the boiling range of 150–250°С, a density of about 0.873 kg/dm3 (20°С), and low sulfur and aromatics contents (3 ppm and 23 wt %, respectively). By compounding the isoparaffin and naphthenic fractions produced, experimental samples of synthetic jet fuels have been obtained that meet the technical requirements for Jet A1 and T-8B fuels.
MgPd2 is an intermetallic compound with a reversible hydrogen uptake near ambient conditions. Hydrogenation occurs near room temperature at pressures below 0.1 MPa to form a hydrogen-rich MgPd2H0.88 phase. In this work, hydrogen sorption isotherms were measured at 283 K ≤ T ≤ 328 K as well as at a cryogenic temperature of 77 K and pressure values up to 0.1 MPa by manometric and gravimetric methods. In addition, the gravimetric hydrogen sorption uptake under isobaric conditions was determined and compared with the structural information based on the previous work by Götze et al. At lower pressures we suggest the formation of the MgPd2H0.14 phase at isobaric conditions of p = 2.5 MPa and T > 437 K. We propose a model combining the hydrogen sorption properties and the volume expansion during the hydrogenation process for describing the phase diagram of the MgPd2-H system. The model was used to describe the experimental data in the temperature range of 283 K ≤ T ≤ 328 K and extrapolate them to higher temperatures. The critical point of MgPd2H0.88 was calculated to be at Tc = 358 K and pc = 0.23 MPa. Below this critical point, two phases – the hydrogen-poor and the hydrogen-rich ones – coexist. However, the critical temperature is much lower than in PdH-systems (563 K), which makes it more attractive for potential applications at moderate temperatures and pressures than PdHx. The calculated enthalpy of the H2 absorption into MgPd2H0.88 is ΔHabs = -38.7 (mol-1 H2), whereas the calculated enthalpy of desorption is ΔHdes = 42.4 kJ (mol-1 H2). The resulting Gibbs free energy of nearly ΔG ≈ -3.7 kJ mol-1 indicates a reversible absorption and desorption process at temperature and pressure values close to ambient conditions.
Fully atomistic molecular dynamics simulations are employed to study impregnation of the poly(methyl methacrylate) (PMMA) matrix with carbamazepine (CBZ) in supercritical carbon dioxide. The simulation box consists of 108 macromolecules of the polymer sample with the polymerization degree of 100, 57 molecules of CBZ, and 242,522 CO2 molecules. The simulation is performed at 333 K and 20 MPa. It is found that by the end of the simulation, the CBZ uptake reaches 1.09 wt % and 50 molecules are sorbed by PMMA. The main type of interaction between PMMA and CBZ is hydrogen bonding between the carbonyl oxygen of PMMA and the hydrogen atoms of the CBZ NH2-group. At the polymer surface, CBZ exists not only in the molecular form, as inside the polymer and in the bulk solution, but also in the form of dimers and trimers. The energy of formation of the hydrogen-bonded complexes is estimated within ab initio calculations.
The development of advanced electrochemical devices for energy conversion and storage requires fine tuning of electrode reactions, which can be accomplished by altering the electrode/solution interface structure. Particularly, in case of an alkali-salt electrolyte the electric double layer (EDL) composition can be managed by introducing organic cations (e.g. room temperature ionic liquid cations) that may possess polar fragments. To explore this approach, we develop a theoretical model predicting the efficient replacement of simple (alkali) cations with dipolar (organic) ones within the EDL. For the typical values of the molecular dipole moment ($2-4~D$) the effect manifests itself at the surface charge densities higher than 30 $\mu C/cm^2$. We show that the predicted behavior of the system is in qualitative agreement with the molecular dynamics simulation results.
Due to their high durability and immobilization properties, cementitious materials have found a considerable application in the design and construction of radioactive waste repositories in the last decades. During cement paste production, organic additives are introduced to modify various properties of cement. The presence of such organic complexants may negatively affect the immobilizing properties of cement with respect to radionuclides. For better understanding and prediction of the effects of interactions between organic molecules and cementitious materials with radionuclides, we have developed several representative models consisting of three principal components: (i) calcium silicate hydrate (C-S-H) phase - the main binding phase of cement; (ii) gluconate, a simple well-described molecule, as a representative of organic additives; (iii) U(VI), as one of the most studied radionuclides of the actinide series. The C-S-H phase with low Ca/Si ratio (~0.83) typical for â€œlow-pHâ€ and degraded cement pastes has been selected for this modelling study. Structural, and energetic aspects of the sorption processes of uranyl, gluconate, and their mutual correlations on the surface of cement were quantitatively modeled by classical molecular dynamics (MD) and potential of mean force (PMF) calculations. The ternary surface complex formation between uranyl hydroxides and Ca2+ cations at the C-S-H aqueous interfaces is shown to have an important role in the overall sorption process. In the presence of gluconate, U(VI) sorption on C-S-H is facilitated by weakening the Ca2+ binding with the surface. Additionally, Na+ is proven to be an important competitor for certain surface sorption sites and can potentially affect the equilibrium properties of the interface.
We performed constant reservoir composition molecular dynamics (CRC-MD) simulations at 323 K and 124 bar to quantitatively study the partitioning of fluid species between the nano- and mesopores of clay and a bulk reservoir containing an equimolar mixture of CO2 and CH4. The results show that the basal (001) and protonated edge (010) surfaces of illite both demonstrate a strong preference for CO2 over CH4 adsorption; that the (001) surfaces show a stronger preference for CO2 than the (010) surfaces, especially with K+ as the exchangeable cation; and that the structuring of the near-surface CO2 by K+ is stronger than that by Na+. The protonated (010) surfaces have a somewhat greater preference for CH4, with the concentration near them close to that in the bulk fluid. The effects of the surfaces on the fluid composition extend to approximately 2.0 nm from them, with the fluid composition at the center of the pore becoming essentially the same as the bulk composition at a pore thickness of ~5.7 nm. The preference of nano- and mesopores bounded by clay minerals for CO2 over CH4 suggests that injection of CO2 into tight reservoirs is likely to displace CH4 into larger pores, thus enhancing its production.
Statistical information on the edge surface area and edge crystallographic orientation of clay nanoparticle surfaces is essential for proper accounting of the protonation-deprotonation reactions as a part of mechanistic surface complexation models. A combination of atomic-force microscopy (AFM) measurements and molecular dynamics computer simulations made it possible to quantify the relative contributions of the most frequently occurring montmorillonite edge surfaces to the total edge surface area. Edge surfaces normal to the  and  crystallographic directions are found to be the most abundant (~60% and ~20%, respectively), in agreement with previous estimations.
The optimum loading on the iron-containing catalytic dispersion of the three-phase Fischer—Tropsch synthesis was 25 nL/hr when using an autoclave reactor. The linear velocity of the synthesis gas corresponded to 0.003 cm/sec. Under these conditions, the following synthesis parameters were achieved, including CO conversion of 80%, liquid hydrocarbon productivity 400 g kg Fe/hr. Based on the data obtained, when modeling a column reactor for three-phase Fischer-Tropsch synthesis, 1.6 m height and 0.045 m internal diameter were calculated.