Novel approach to determination of sorption in pervaporation process: a case study of isopropanol dehydration by polyamidoimideurea membranes

Development of novel membranes with optimal performance, selectivity, and stability is a key research area in membrane technology. In the present work aromatic polyamidoimideurea (PAIU) is synthesized and tested as promising membrane material for separation of water and alcohol mixtures. The PAIU membrane structure, density, and transport properties are studied. Mass transfer of water and isopropanol through the membrane is estimated by sorption and pervaporation tests to determine equilibrium sorption degree, diffusion coefficients, flux through the membrane, and separation factor. Two techniques of sorption study from liquid and from vapor phases are used as novel approach to experimental study of mass transfer. The vapor sorption calorimetry permits to analyze the behavior of the polymer material in sorption process. In pervaporation of water-isopropanol mixture, almost pure water mainly permeates through PAIU membrane. To improve the performance, a double layer membrane containing a thin PAIU layer on the surface of porous poly(phenylene oxide) support is developed. The double layer membrane is extremely effective in dehydration of isopropanol.Russian Science Foundation (RSF): grant 16-13-10164

Thermal and mechanical properties of chitosan nanocomposites with cellulose modified in ionic liquids

In this paper, ionic liquid treatment was applied to produce nanometric cellulose particles of two polymorphic forms. A complex characterization of nanofillers including wide-angle X-ray scattering, Fourier transform infrared spectroscopy, and particle size determination was performed. The evaluated ionic liquid treatment was effective in terms of nanocrystalline cellulose production, leaving chemical and supermolecular structure of the materials intact. However, nanocrystalline cellulose II was found to be more prone to ionic liquid hydrolysis leading to formation larger amount of small particles. Each nanocrystalline cellulose was subsequently mixed with a solution of chitosan, so that composite films containing 1, 3, and 5% mass/mass of nanometric filler were obtained. Reference samples of chitosan and chitosan with micrometric celluloses were also solvent casted. Thermal, mechanical, and morphological properties of films were tested and correlated with properties of filler used. The results of both, tensile tests and thermogravimetric analysis showed a significant discrepancy between composites filled with nanocrystalline cellulose I and nanocrystalline cellulose II

Phase diagram and physiochemical properties of the n-octyl a D-glucoside/water system

Four experimental methods were used to study the phase diagram, as well as the thermodynamic and structural properties of the binary system n-octyl -D-glucoside/water in the temperature range 25-130°C. Sorption calorimetry allows one to determine the activity of water and enthalpy of mixing as functions of water content at constant temperature, while DSC scans temperature at constant composition and provides information on enthalpies of phase transitions. Therefore, the combination of the two calorimetric methods is a powerful tool to study composition-temperature phase diagrams. While calorimetry can be used to determine boundaries of the phases, NMR and SAXS methods are used to study their structures. A detailed phase diagram of the system is presented. A liquid crystalline cubic phase previously not reported in the system was found. The hydration in the system is endothermic, excluding the exothermic formation of hydrates. Using the sorption calorimetric method the lengths of the very short tie lines between the isotropic micellar and liquid crystalline phases were determined. Van der Waalss differential equation was used to calculate the slopes of the phase boundaries. The parameters of the lamellar, cubic and hexagonal liquid crystalline phases were determined by means of SAXS. It was found that the area per surfactant headgroup in the liquid crystalline phases varied with composition

Glassy Crystalline State and Water Sorption of Alkyl Maltosides

A differential scanning calorimetric and sorption calorimetric study of two alkyl maltosides, C(8)G(2) and C(10)G(2), was performed. In the dry state, C(8)G(2) and C(10)G(2) do not form solid crystals but undergo a glass transition upon temperature change. The glass is partly ordered and has the same lamellar structure as the liquid crystals formed by the two maltosides. To reflect the presence of the glass transition and the structure, the terms "glassy crystals" and "glassy liquid crystals" can be used. A mechanism of the relaxation of the glassy crystals based on the results of small-angle X-ray scattering experiments is proposed. Experiments on water sorption showed that the glassy crystals turn into lyotropic liquid crystals upon sorption of water at constant temperature. This isothermal glass transition can be characterized by water content and change of partial molar enthalpy of mixing of water. A method to calculate the phase diagram liquid crystals-glassy liquid crystals is proposed

Lysozyme-Water Interactions Studied by Sorption Calorimetry

Hydration of hen egg white lysozyme was studied by using the method of sorption calorimetry at 25, 40, and 50degreesC. Desorption calorimetric measurements were performed at 25 and 40degreesC. The activity of water and partial molar enthalpy of mixing of water were determined as functions of water content. Hydration of lysozyme occurs in four steps: slow penetration of water into the protein-protein interface; gradual glass transition, which occurs in every protein molecule independently of other molecules; further water uptake with disaggregation of protein aggregates and formation of a monolayer of water; and accumulation of free water. The amount of bound water found in desorption experiments is 420 water molecules per lysozyme molecule. Two hysteresis loops were found in the sorption isotherm of lysozyme. The small loop is caused by the slow penetration of water molecules into the protein-protein interface at very low water contents, while the large loop is due to the slow kinetics of aggregation of protein molecules upon desorption. The phase diagram of the lysozyme-water system is presented