Interphase Surface Stability in Liquid-Liquid Membrane Contactors Based on Track-Etched Membranes

A promising solution for the implementation of extraction processes is liquid–liquid membrane contactors. The transfer of the target component from one immiscible liquid to another is carried out inside membrane pores. For the first time, highly asymmetric track-etched membranes made of polyethylene terephthalate (PET) of the same thickness but with different pore diameters (12.5–19 nm on one side and hundreds of nanometers on the other side) were studied in the liquid–liquid membrane contactor. For analysis of the liquid–liquid interface stability, two systems widely diverging in the interfacial tension value were used: water–pentanol and water–hexadecane. The interface stability was investigated depending on the following process parameters: the porous structure, the location of the asymmetric membrane in the contactor, the velocities of liquids, and the pressure drop between them. It was shown that the stability of the interface increases with decreasing pore size. Furthermore, it is preferable to supply the aqueous phase from the side of the asymmetric membrane with the larger pore size. The asymmetry of the porous structure of the membrane makes it possible to increase the range of pressure drop values between the phases by at least two times (from 5 to 10 kPa), which does not lead to mutual dispersion of the liquids. The liquid–liquid contactor based on the asymmetric track-etched membranes allows for the extraction of impurities from the organic phase into the aqueous phase by using a 1% solution of acetone in hexadecane as an example.

Estimating the effect of aqueous cationic latex from the class of thermal elastic plastics on the properties of bitumen emulsions

To produce cationic bitumen emulsions, bitumen is used, whose penetration is not lower than 90 mm-1. Such bitumen has a small plasticity interval, which leads to a deterioration in its heat resistance at elevated temperatures and narrows the scope of application of emulsions based on it. Based on the review of emulsion modification methods, the modification has been proposed that involves mixing the finished bitumen emulsions with aqueous cationic latex. The process of interaction between a bituminous emulsion and an aqueous cationic latex has been considered. A mechanism for the disintegration of the modified bitumen emulsion on the surface of mineral materials was proposed. The emulsifiers have been selected and the composition of the aqueous phase has been chosen based on the analysis of surface tension isotherms. The influence of the modification on the properties of bitumen emulsions was investigated. It was established that the main physicochemical characteristics of the interphase surface accept similar values for the aqueous phase and emulsions based on it. It has been proven that the introduction of aqueous cationic latex quite moderately affects the basic physical-mechanical properties of emulsions, which makes it possible not to change the main technological parameters when using them. It was established that increasing the concentration of the polymer in the emulsion has a positive effect on the physical-mechanical properties of the binder. With an increase in the concentration of the polymer to 6 % the softening temperature increases by 16 °C, elasticity is 74 %, and the holding capacity at minus 25 °C is approaching 100 %. Improving the physical-mechanical properties of residual binder as a result of emulsion modification could increase the durability of layers in a roadbed based on bitumen emulsions and expand the scope of their application in the construction and repair of motorways

Self-preservation Effect of Gas Hydrates

This work was performed to improve the storage and transportation technology of gas hydrates in nonequilibrium conditions. At atmospheric pressure and positive ambient temperature, they gradually dissociate into gas and water. Simulation of the gas hydrate dissociation will determine optimal conditions for their transportation and storage, as well as minimize gas loss. Thermodynamic parameters of adiabatic processes of forced preservation of pre-cooled gas hydrate blocks with ice layer were determined theoretically and experimentally. Physical and mathematical models of these processes were proposed. The scientific novelty is in establishing quantitative characteristics that describe the gas hydrates thermophysical parameters thermophysical characteristics influence on the heat transfer processes intensity on the interphase surface under conditions of gas hydrates dissociation. Based on the results of experimental studies, approximation dependences for determining the temperature in the depths of a dissociating gas hydrate array have been obtained. Gas hydrates dissociation mathematical model is presented.

Method for determining the starting moment of hydrate formation on the basis of optical effects

The problem is analyzed of hydrate formation in the systems of gathering and treating of oil and gas products. The methods are studied for prevention of complications associated with the gas hydrates accumulation in the pipelines and process lines. Attention is focused on the significant material costs to prevent the hydrate formation and ways to reduce them. The necessity of constant laboratory monitoring for reservoir systems at industrial facilities to determine the hydrate formation parameters has been substantiated. The need to improve the method for determining the hydrate formation parameters for complex reservoir systems based on a mixture of hydrate-forming gases has also been proved. The purpose of the work is to improve the research method of reservoir systems immediately at the facilities of products mining and treatment. The peculiarities are analyzed of the method of visual laboratory observation in the study of gas hydrates. During experimental studies, optical effects of image distortion are observed due to the formation of a gas hydrate layer in the form of a film on the interphase surface. The mechanism of their formation, as well as the processes determining them have been substantiated. Based on this effect, a method of fixing the hydrate formation initial stage (beginning of crystal growth – mass crystallization) is proposed. For increasing the informative ability of the obtained images of hydrate formation processes, it is proposed to “paint” them with the help of colored light sources, as well as to regulate the intensity and direction of illumination. A number of photos are presented, which clearly illustrate the processes described in the paper.

Immersed boundary method for multiphase transport phenomena

Multiphase flows with momentum, heat, and mass transfer exist widely in a variety of industrial applications. With the rapid development of numerical algorithms and computer capacity, advanced numerical simulation has become a promising tool in investigating multiphase transport problems. Immersed boundary (IB) method has recently emerged as such a popular interface capturing method for efficient simulations of multiphase flows, and significant achievements have been obtained. In this review, we attempt to give an overview of recent progresses on IB method for multiphase transport phenomena. Firstly, the governing equations, the basic ideas, and different boundary conditions for the IB methods are introduced. This is followed by numerical strategies, from which the IB methods are classified into two types, namely the artificial boundary method and the authentic boundary method. Discussions on the implementation of various boundary conditions at the interphase surface with momentum, heat, and mass transfer for different IB methods are then presented, together with a summary. Then, the state-of-the-art applications of IB methods to multiphase flows, including the isothermal flows, the heat transfer flows, and the mass transfer problems are outlined, with particular emphasis on the latter two topics. Finally, the conclusions and future challenges are identified.

The effect of nanocrystalline cellulose and TEMPO-oxidized nanocellulose on the compatibility of polypropylene/cyclic natural rubber blends

The effect of nanocrystalline cellulose (NCC) and nanofiber cellulose (NFC) was estimated as a means of reinforcing and compatibilizing agent of polypropylene/ cyclic natural rubber (PP/CNR) blend in terms of mechanical and thermal properties. The morphological effect of NCC and NFC on the PP/CNR blend property was determined through several characterization techniques, i.e. SEM, contact and TGA/DTG. Scanning electron microscopy (SEM) images revealed that the addition of NCC and NFC became more homogenous than without the addition of nanocellulose. The improvement of nanocomposites was also observed on the result of interphase surface tension and thermal stability. This improvement was assumed as the result of physically/ chemically interaction of nanocellulose with the backbone of PP and CNR, in which the nanocellulose can be imagined acting as a bridge to link the PP and CNR’s backbone.

SWIRL STAGES FOR HEAT AND MASS EXCHANGE EQUIPMENT

The results of experimental studies of hydrodynamics and mass exchange at vortex stages in bubbling mode are presented, as well as data of numerical simulation by finite element method using models of k-ε This made it possible to establish the presence of circulation movement of liquid at the stage, to determine profiles of phase speeds, to obtain the value of initial speed of gas phase movement, at which coordination of experimental and design values of liquid speed is observed. The design method shows the effect of the cylindrical partition installed between the swirler and the stage wall on the fluid velocity profile and its distribution in the working volume. It is proposed to use the obtained results of numerical modeling when designing multi-element stages to provide the required hydrodynamics on it. New vortex contact devices with annular channels, having lower hydraulic resistance compared to tangential devices and providing a developed interfacial surface, stable without fluctuations, operation of the stage at high gas and liquid flow rates, have been investigated. Data are presented for determination of hydraulic resistance of vortex stage, value of interfacial surface, coefficients of mass output and efficiency in investigated range of loads of liquid and gas L/G = 10-150. Designs of vortex contact stages for industrial brew column have been developed. Contact devices with ring channels allow to bring dissipation of energy in a gas phase in the bubbling and ring mode to 5 W/kg, to increase an interphase surface to 2000 m-1 and to reach the size of superficial coefficient of a massotdacha about (0.5-0.8)·10-3 of m/s.

Energy consumption of emulsification processes in small-sized mix apparatuses

There is given in this thesis a general method of calculation of power consumption for emulgation in systems liquid-liquid in small-size mixing devices (rotor-pulsation apparatuses and rotor-disc mixers). This mixing devices, have shown a high efficiency at processing of liquid-liquid systems and are wide using chemical processes. The base of calculation method is an energy ratio to describe of developed turbulent motion, pulsation intensity of which is enough for create of dispersed particles of given size and concentration, which provide a necessary surface of phases contact. It is shown, that in determination of energy consumption it is need to take in account energy dissipation processes, due to viscous friction forces, which have a significant influence at high gradients of turbulent motion. There is obtained a ratio, which connects an angular velocity of rotor rotation of mixing device and a characterized size of dispersed phase particles.There is given an experimental dependencies of consumed power of rotor-disc mixers on rotor rotations number of mixing device and characterized sizes of dispersed particles for systems water-diesel fuel. It was determined, that are decreasing of dispersed particles sizes and in increasing of volumetric flow of processing mixture a value of consumed power increases, and it is related with by increase of energy consumption for creating of interphase surface. It was determined, that a power, consumed by rotor-disc mixer, for emulsion making with averaged dispersion size of particles at range 5-25 mkm, increases by increase of rotation numbers ~n0.37. Comparison of theoretical equations and experimental data have shown adequacy of supposed calculation method of energy consumption.

Механизм роста пар--кристалл--кристалл Au-каталитических GaAs-нитевидных нанокристаллов

The mechanism of the vapor–solid–solid growth of Au-catalyzed GaAs nanowires in the temperature range of 420–450°C is investigated. For the first time, the effect of elastic stresses caused by a difference in the atomic densities of the catalyst and nanowire material on the solid-phase nucleation rate is considered. By assuming that the growth of the GaAs nucleus at the catalyst–nanowire interface is limited by the As-diffusion flux in the catalyst, it is shown that vapor–solid–solid growth can be implemented through the polycentric-nucleation mode in the temperature range under consideration. The intensity of the nucleation of coherent islands upon vapor–solid–solid growth is shown to be higher than the intensity of nucleation in the case of vapor–liquid–solid growth because a low interphase surface energy is implemented at coherent solid–solid conjugation. It is proved that the nucleation of Au-catalyzed GaAs nanowires by the vapor–solid–solid mechanism is possible only when GaAs-island growth proceeds due to As diffusion along the catalyst–nanowire interface.