白俄罗斯辐射化学领域的研究与发展现状

本文扼要介绍了白俄罗斯共和国在辐射化学领域具有代表性的仪器设备及主要的研究进展 。     

The pH of CO2-saturated water at temperatures between 308 K and 423 K at pressures up to 15 MPa

We report pH measurements for CO₂-saturated water in the pressure range from (0.28 to 15.3) MPa and temperatures from (308.3 to 423.2) K. Commercially available pH and Ag/AgCl electrodes were used together with a high pressure equilibrium vessel operating under conditions of precisely controlled temperature and pressure. The results of the study indicate that pH decreases along an isotherm in proportion to −log₁₀(x), where x is the mole fraction of dissolved CO₂ in H₂O. The expanded uncertainty of the pH measurements is 0.06 pH units with a coverage factor of 2. The reported results are in good agreement with the literature in pressure ranges up to 16 MPa at temperatures below 343 K. An empirical equation has been developed to represent the present results with an expanded uncertainty of 0.05 pH units. We also compare our results with a chemical equilibrium model and find agreement to within 0.1 pH unit.     

Radial Corrugations of Multi-Walled Carbon Nanotubes Driven by Inter-Wall Nonbonding Interactions

We perform large-scale quasi-continuum simulations to determine the stable cross-sectional configurations of free-standing multi-walled carbon nanotubes (MWCNTs). We show that at an inter-wall spacing larger than the equilibrium distance set by the inter-wall van der Waals (vdW) interactions, the initial circular cross-sections of the MWCNTs are transformed into symmetric polygonal shapes or asymmetric water-drop-like shapes. Our simulations also show that removing several innermost walls causes even more drastic cross-sectional polygonization of the MWCNTs. The predicted cross-sectional configurations agree with prior experimental observations. We attribute the radial corrugations to the compressive stresses induced by the excessive inter-wall vdW energy release of the MWCNTs. The stable cross-sectional configurations provide fundamental guidance to the design of single MWCNT-based devices and shed lights on the mechanical control of electrical properties.     

Thermal analysis of the droplet solidification in the PGSS-process

In this work, a manufacturing process for powders from polybutylenterephthalate (PBT) is analysed in terms of the formation of differently shaped particles. For the micronization of the polymer the particles from gas saturated solutions (PGSS) process is used. Several applications require specific particle shapes and particle size distributions. In particular, spherical particles are required to obtain a free flowing powder. To optimise the quality, powders were produced at different spray temperatures and pressures and with varying mass flows of polymer and gas. With different spray conditions, powders with various shapes, morphologies and apparent densities were obtained. The temperatures before and after the expansion appear to have the main influence on the sphericity. To obtain further knowledge about the solidification process, the temperature distribution in the spray was analysed. For this purpose, heat images of the spray were taken. Based on the results, a simple model is introduced, which is able to estimate the temperature field in a polymer droplet during the spray process. An explanation for the formation of differently shaped particles is proposed.     

High-pressure phase behaviour of two poly-aromatic molecules in the presence of toluene and carbon dioxide

Asphaltene precipitation and deposition is a serious problem in oil recovery, oil transportation and refinery operations. Understanding of the phase behaviour of systems containing asphaltenes is very important to develop effective asphaltene deposition mitigation strategies. In order to get a better understanding of asphaltenes and in particular to get more insight in relations between molecular structural features and observed macroscopic behaviour, the phase behaviour of two poly-aromatic molecules (violanthrone-79 and hexa-tert-butylhexa-peri-hexabenzocoronene) was studied. Although both compounds do not represent all specific features of real asphaltenes, it is expected that to some extend they do. For instance, real asphaltenes are ill-defined mixtures and hard to characterize, while the selected poly-aromatic compounds form a well-defined system with toluene and CO₂. The poly-aromatic compounds were selected based on their molecular features and their tendency to self-assemble. The phase behaviour of solutions of these compounds in toluene was studied in the presence of different concentrations of carbon dioxide with a so-called Cailletet apparatus. The results in this work showed that the concentration of carbon dioxide affects the precipitation of the poly-aromatic compounds. At low concentration there is no precipitation, i.e., carbon dioxide acts as a co-solvent, while at higher concentration, carbon dioxide acts as an anti-solvent and the poly-aromatic molecule in the ternary system precipitates. As far as the phase behaviour is concerned, hexa-tert-butylhexa-peri-hexabenzocoronene resembles that of a real asphaltene.     

An efficient,basic resin mediated,one-pot synthesis of O-alkyl-S-methyl dithiocarbonates from the corresponding alcohols

A novel process for the one-step conversion of primary and secondary alcohols into their O-alkyl-S-methyl dithiocarbonates was developed using Amberlite IRA 400 (basic resin) in presence of carbon disulfide. O-Alkyl-S-methyl dithiocarbonates of various alcohols were isolated in very good to excellent yields. This protocol is mild and efficient compared to other existing methods.     

An efficient,basic resin-mediated,one-pot regioselective synthesis of 2-hydroxy alkyl dithiocarbamates from corresponding epoxides

A mild and efficient one-pot regioselective synthesis of 2-hydroxy alkyl dithiocarbamates was accomplished in high yields from the corresponding amines and epoxides using carbon disulfide mediated by Amberlite IRA 400 (basic resin).     

精脱硫工序积碳与结焦的对策

介绍了甲醇生产中焦炉煤气精脱硫系统积碳与结焦的危害以及应对方法。通过设备改造及工艺调整等措施,减少各种杂质进入精脱硫系统,使加氢催化剂保持良好效果,实现设备长周期运行。     

Numerical simulation of asymmetric flow of coupled heat and mass transfer in a square cavity

The heat and mass transfer of fluid in a square cavity with a solutal and thermal source is numerically investigated. For different Rayleigh numbers, buoyancy ratio, Soret and Dufour numbers, the bifurcation characteristics of heat and mass transfer in a symmetrical square cavity are studied systematically. The results show that there is a critical Ra_c for onset of bifurcation that changes the fluid flow pattern. When Ra < Ra_c, the streamline, temperature and concentration are symmetrically distributed; when Ra > Ra_c, the transition from a symmetrical state to a stable asymmetric state is observed. The fluid is more prone to bifurcation with increasing of buoyancy. An increment to the Soret and Dufour effects enhances heat transfer symmetry and increases the critical Rayleigh number for breaking symmetry.