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A method is developed for calculating the values of concentration polarization during the separation of an aqueous solution containing anionic surfactants for ultrafiltration membranes with ideal and non-ideal rejection coefficients in a wide range of changes in the values of the diffusion Peclet number.

We perform X-ray diffractometry, electron-microscopic, and kinetic studies of the surface layers of UAM-50 and UAM-100 ultrafiltration membranes. The crystallinity of the membranes is studied by X-Ray diffraction in the region of large angles 2θ from 2° to 40°, using a DRON-3 diffractometer with modern methods of the computer processing of experimental data. Comparative analysis of the X-ray diffraction patterns reveal the coincidence of the diffraction angles for the working and air-dry samples of ultrafiltration membranes, while the membrane samples have three pronounced maxima located approximately in the angular range from 17.50° to 25.60°. The crystallinity for the air-dry samples is 68% for UAM-50 and 74% for UAM-100, and for the working samples, it is 32 and 41% for UAM-50 and UAM-100, respectively. Investigations of the surface of drainage layers of the UAM-50 and UAM-100 ultrafiltration membranes are carried out by scanning electron microscopy. The thickness of the active layer is 27 nm for the UAM-50 membrane and 15 nm for the UAM-100 membrane. Pores of different sizes are visible on the surface of the active layer of the membrane; the pore sizes range from 2.5 to 40 nm for UAM-50 and from 10 to 40 nm for UAM-100. Kinetic studies of the ultrafiltration membranes confirm that they have an asymmetric pore structure. Small pores in the membrane trap contaminant molecules, while large pores allow the permeate to pass quickly to a more open permeate carrier, that is, a purified solution. The water permeability of the working membrane increases with an increase in the transmembrane pressure due to an increase in the driving force of the process and rearrangement of the crystal structure (a decrease in the size of crystals in the working sample of the membrane) and a decrease in the crystallinity of the membranes.

The influence of the structure of the surface cellulose acetate layer on the transport characteristics of ultrafiltration composite membranes is considered using the methods of IR spectroscopy and of scanning electron microscopy. The amorphous phase of ultrafiltration cellulose acetate composite membranes is formed at a certain stage of the technological cycle of obtaining a composite membrane. IR spectra are presented where the forms of the absorption bands of valence vibrations of hydroxylic groups at ν = 3339.14–3366.2 cm–1 alter the asymmetry parameter from ~1 for an air-dry sample and to 0.79 for a water-saturated one, which allows the assertion of formation of volumetric supermolecular structure of a cellulose acetate layer of an air-dry sample by two types of hydrogen bonds and dipole–dipole interactions of carbonyl groups. The decrease of the asymmetry parameter to 0.79 of the absorption bands of hydroxylic groups and of the intensity of absorption bands of methyl groups by 2.56, 3.3, and 3.8 times in water saturated samples of membranes occurs because of the destruction of supermolecular structure and reorganization of hydrogen bonds between the active groups of cellulose acetate and molecules of water. The data obtained by the method of scanning electron microscopy allow one to note that the surface layer of ultrafiltration membranes has an asymmetric pore structure. The surface layer of a membrane can be divided into two components: a selectively permeable layer with pores of small size and a pore substrate, in which the pores increase in their diameter as they approach the substrate.

A classification of chemical purification technologies, membrane processes, depending on the pore size in membranes is given. It has been established that environmentally friendly membrane methods for separating liquid media are an alternative to traditional methods for separating technological solutions and industrial waste waters.

The paper considers works on methods for calculating design and technological parameters, design of membrane equipment, research of technological features of membrane devices, selection of design schemes, methods for calculating strength and stiffness. A method has been developed for calculating mechanical loads and determining the thickness of plates and toroidal shells of a membrane apparatus of the combined type, which makes it possible to assess the strength properties of apparatus of this class. An example of a calculation, which makes it possible to assess the adequacy of the application of this technique to devices of the combined type, is given.

A developed design of a combined-type electro-baromembrane apparatus for separating solutions into two successive circuits is presented. As well as allowing differential ion separation in the flows of cathode and anode permeate in the form of bases and acids at the first stage of separation, the baromembrane design leads to reduced hydraulic resistance per unit volume and improved solution separation efficiency. The methodology used for calculating the technological characteristics of the apparatus is described.

The paper presents the structural organization of the surface (selective) layer. The amorphous phase of the cellulose acetate composite membrane is formed at a certain stage of the technological cycle of producing the cellulose acetate membrane. It presents a mass of broken, entangled, and twisted macromolecular chains connected by a network of hydrogen bonds of various strengths. Analysis of the IR spectra, where the shapes of the absorption bands of the valence vibrations of hydroxyl groups at ν = 3339.14–3366.2 cm–1 with the asymmetry coefficient varying from ~1 for a dry sample to 0.79 for a wet sample, suggests that the bulk supramolecular structure of the cellulose acetate layer of the air-dry sample is formed by two types of hydrogen bonds and the dipole–dipole interactions of the carbonyl groups. The interactions of macromolecules in the equatorial plane are formed by a network of hydrogen bonds of the OH…O type with the participation of a single hydroxyl group of the pyranose ring in cellulose acetate. In the axial direction, the supramolecular structure is organized through the hydrogen bonds of the CH…O=C type between the methane and carbonyl groups, as well as possibly the dipole–dipole interactions between the coplanar ordered dipoles of the C=O groups. The coefficient of asymmetry of the absorption bands of hydroxyl groups is reduced to 0.81–0.79 and the intensity of the absorption band of methyl groups is reduced by factors of 2.56, 3.3, and 3.8 in water-saturated samples due to the destruction of the supramolecular structure and the reorganization of the hydrogen bonds between the active groups of cellulose acetate and water molecules. The absence of an absorption band of ν = 873.53–851.9 cm–1 in the water-saturated samples indicates a conformational rearrangement of the macromolecules into a linear form with the formation of narrow mesopores of cellulose acetate between the macromolecules.

Results are presented from investigating active and drainage layers of composite films (membranes) UPM-50 and UPM-100 before and after exposure to transmembrane pressure by means of IR spectra of reflection, X-ray scattering, and raster electron microscopy. It is found that changes in the IR spectrum of the working sample are caused by the destruction of weak bonds of C=O···H–N amide fragments of the polysulfonamide film. A drop in (C=O) vibration frequency ν by Δν = 20 cm−1 indicates redistribution of the electron density between C=O-groups and benzene rings as a result of the inductive effect of coupling, which results in the formation of charged functional groups CO−. The presence of CO– groups fragments a new supramolecular structure whose stability due to the dipole–dipole interaction of carbonyl anions. X-ray scattering of the initial and working samples in the 10°–35° range of angles 2θ is determined by three intense reflections at angles 2θ ~ 17.23°, 22.24°, 25.41° from crystallographic planes ((010), (100), and (110)) corresponding to the crystalline structure of lavsan (polyethylene terephthalate). A comparative analysis of the reduced intensities of reflections from crystallographic planes (010), (100) and the sizes of lamellas indicates that transmembrane pressure initiates conformational rearrangement of crystallites with crystallographic axis b oriented parallel to the film plane.

The structural organization of the surface (active) layer and the state of water in composite ultrafiltration membranes have been investigated by means of the methods of vibrational IR spectroscopy and differential scanning calorimetry (DSC). Analysis of the shape of the absorption band of stretching vibrations of hydroxyl groups at ν = 3366.2 cm–1 with an asymmetry coefficient of ~1 and the activity of vibrations of methyl groups with ν = 2884.02 and 2942.35 cm—1 has demonstrated that the bulk supramolecular structure of a cellulose acetate layer of a dry sample is formed by two types of hydrogen bonds and dipole–dipole interactions of carbonyl groups. The interaction of macromolecules in the equatorial plane is formed by a lattice of hydrogen bonds of the (OH…O) type with participation of the only hydroxyl group of a pyranose ring in cellulose acetates. In the axial direction, the supramolecular structure is organized by hydrogen bonds between methine and carbonyl groups of the (CH…O=C) type and dipole interactions of coplanar ordered dipoles of (C=O) groups. The decrease in the intensity and the coefficient of asymmetry down to 0.81 of the absorption band of hydroxyl groups and the absorption band of methyl groups with frequencies ν = 2884.02–2942.35 cm–1 by 2.56 and 3.3 times in water-saturated samples occurs due to the destruction of the supramolecular structure and the reorganization of hydrogen bonds of active groups of cellulose acetate and water molecules blocking intermolecular interactions of the macromolecules. The manifestation of hydroxyl groups with frequencies of 3302.7 and 33 105 sh cm–1 and ν = 3600.6 and ν = 3598.8 sh cm–1 on the absorption band indicates the interaction of associated water molecules of the bound and capillary forms. The absence of the absorption band with ν = 873.53 cm–1 in the water-saturated sample is explained as an empirical indicator of the conformational transition of macromolecules into a linear form. Deconvolution of the endothermic peak on the DSC curve in the temperature range from 50 to 110°C into five Gaussians has demonstrated the multilevel structural organization of water molecules sorbed in pores and between macromolecules of the amorphous phase.

A membrane separation of solutions, along with other purification methods, plays an important role in the effective and ecological safety of food production enterprises and is used for softening and demineralization of water, separation, concentration and purification of technological solutions, as well as for other processes. An important problem of membrane and electromembrane separation methods is to increase the used membrane selectivity. Therefore, the aim of this work was to study the structure transformation effect of ion-exchange membranes on a separation processes efficiency of technological solutions and an ecological safety of food production enterprises using the methods of X-ray diffraction analysis and differential scanning calorimetry (DSC). The analysis of the calculated values of crystallinity degree (CD) by X-ray diffractograms allowed us to identify the different effect of water saturation on the studied membranes. The structure of their material changes, which in turn affects the transport characteristics of the membranes, the efficiency of separation and, ultimately, the environmental ecological safety food enterprises. The cation-exchange membrane MK-40L was characterized by an increase in CD by 5.83%, and the anion exchange membrane MA-41P on the contrary was characterized by a decrease in CD by 5.87%. The crystallite sizes were distributed in the range of 0.096-0.345 nm for the MA-41P membrane and 0.096-0.193 nm for the MK-40L membrane. During thermal studies by DSC one endothermic and exothermic sections were revealed on the obtained curves in the temperature range of 30-202 and 202-498 °C for the MK-40L membrane and 30-223 °C and 223-498 °C for the MA-41P membrane, respectively. The endothermic sections of the curves were characterized by one endothermic peak. Four or five pronounced exothermic peaks were registered on the exothermic sections. At the same time, the MK-40L membrane was characterized by more intense peaks in a water-saturated sample and the MA-41P membrane in the dry one.

Conformational transformations in the structure of the surface layer and the substrate of initial and working nanofiltration films have been investigated in this work using large-angle X-ray scattering. It has been determined that the mechanical load caused by excess pressure corresponding to 1.5 MPa in the case of OFAM-K porous-composition film has resulted in conformational changes of Phenylon C-4 macromolecules in crystal and amorphous intercrystallite phases; in this case, the calculated degrees of crystallinity have decreased from 49 to 36%. It has been noted that there is the polymorphous rearrangement of the crystal phase with the change of the sizes of crystal cell toward the crystal axis (c) and an increase in the crystallinity from 44 to 55% in the working specimen of the OPMN-P-composition nanofiltration film; in this case, the amorphous phase opens. A full calculation of the radial-distribution function of the atoms of initial and working films has been carried out, which confirms that there is rearrangement of lattice cells due to the increase in atomic distance.

The design of a newly developed membrane device and technique of calculating the effective operation life of semipermeable ultrafiltration membranes by means of which the length of the period of effective realization of the process of purification, concentration and demineralization of industrial solutions may be determined is presented. In the newly developed technique, the estimated length of the effective life of ultrafiltration membranes under different conditions of the industrial purification process, which varies from 96 to 125 hours, is determined. Computed average calculated values of the diffusion coefficients in ultrafiltration membranes and the maximum contact stresses are presented.

A mathematical description of heat transfer is presented and a procedure is developed for calculating the temperature characteristics of electro-ultrafiltration process for separating industrial solutions in flatchamber type of apparatuses. The permeate and retentate temperatures, solution heating temperature, heating power, and amount of heat liberated in the process of separation of industrial solutions and effluents containing anionic surfactants, proteins, and phosphatic and biochemical substances are calculated by the developed procedure.

The pore space structure of MGA-95 and ESPA membranes has been investigated by the smallangle X-ray scattering (SAXS). The pore radii as the parameters forming the skeleton of the pore space of the reverse-osmosis composite membranes have been established. Three types of scattering pores (sphere, disc, and cylinder) are found in the region of the X-ray scattering vector of 0.171 < s < 0.538 nm−1, and their average radii of gyration have been determined. The pore structure of the MGA-95 and ESPA membranes, which can be described in terms of the self-affine fractal concept, has been revealed. In the region of the scattering vector of 0.245 < s < 0.342 nm−1 (the average pores with 9.2 < r

In this paper, we describe the results of the study of an MGA-95 semipermeable composite membrane with amorphous and crystalline regions, considering the effect of the three processes migration, diffusion and fluid convection of solute and solvent. It was found that during swelling the supramolecular structure of the membrane material undergoes changes caused by deformation of the crystalline and amorphous regions of the membrane sample. The data on the amorphous regions for air-dry, water-saturated and working semipermeable membrane samples were analyzed. The comparative analysis of the diffraction patterns of an MGA-95 membrane showed that the external impact does not change the intramolecular structure of the membrane. Using the experimental data and the method of small-angle X-ray scattering we calculated the size of pores for MGA-95 and ESPA composite membranes. The findings led to the conclusion about the relative uniformity of the pore distribution in the thickness of the active layer of the membrane, and made it possible to determine their configuration. The data on the pore structure morphology of semipermeable membranes indicated that sorption region of MGA-95 and ESPA membranes was formed by pores of different types with varied surface morphology; smaller radius pores had a smoother surface, while larger pores had a rough surface. The number of larger radius pores -12.9 and 16.8 nm were equal to 20 and 35.6 % for MGA-95 and ESPA, respectively. Specific surface values for MGA-95 was S sp = 9.15 × 107 m-1 and for ESPA it was S sp = 5.95 × 107 m-1.

The paper presents experimental study of physical water condition and mass transfer in cellulose acetate and dynamic semipermeable membranes by infrared spectrometric and hydrodynamic methods. The authors found that OH-groups of cellulose acetate form a nonequilibrium grid of hydrogen bonds between molecules and their fragments in the amorphous phase of the semipermeable membrane in the air-dried sample. The water molecules adsorbed on active —OH and —C = O groups, particularly in the amorphous phase, create additional negative charge on the molecules of cellulose acetate resulting from the orientation of the water dipoles, which leads to electrostatic repulsion of broken, stranded molecule fragments and straightening of polymer molecule while breaking intermolecular hydrogen bonds. Thermogravimetric studies to find out the structural organization of hydrogen bonds and water condition in the samples of the semipermeable polymeric MGA-95 membrane showed that at temperatures in the air-dry and water-saturated samples the membrane degradation process starts and ends with mass loss and endothermic effect. The research proves the fact of dynamic membranes formation on the ultrafilters from water starch solutions. Due to the changes in condition and volume of water in the dynamic layer of the membrane, it is possible to change kinetic coefficients, i.e. to regulate the process of baromembrane separation of industrial water solutions. Electro-kinetic characteristics of reverse osmosis semipermeable membranes were studied. The experimental curves of the potential depending on sorption of sodium bicarbonate by MGA-95 and LSA-100 membranes were obtained. The discrepancy between the calculated and experimental data did not exceed 10 %. The method devised for determining the membrane potential in the process of sorption of sodium bicarbonate can be used as a testing methodology of polymeric semipermeable membranes.