Study of NaCl permeability through a non-porous polypropylene film

Wettability Studies of Capillary PTFE Membranes Applied for Membrane Distillation

In the present study, the membrane distillation (MD) process was studied with the use of commercial polytetrafluoroethylene (PTFE) capillary membranes. For this purpose, both solutions with NaCl concentrations up to 300 g/L and brines contaminated with oil (70-120 mg/L) were used as feeds. The membrane's wetting resistance was tested by conducting long-term experiments for over 3500 h. Using detailed studies, it has been shown that increasing the salt concentration from 35 to 300 g/L resulted in a 50% reduction in the permeate flux. Nevertheless, the membranes retained 100% of the salt rejection after 2000 h of the module's operation. Moreover, it has been found that performing the MD process with brines contaminated with oil (120 mg/L) led to the wetting of some membranes pores, which it turn resulted in an increase in the distillate's conductivity to 450 µS/cm after 700 h running the process. The mechanism of pore wetting by oil droplets adsorbed on the membrane's surface was presented. Finally, the proposed method of membrane cleaning with the use of a solvent allowed restoring the initial MD module's performance. Consequently, both the permeate flux and distillate conductivity were stable during the MD of the feed containing 35 g/L of NaCl over the next 280 h.

Analysis of the Thermal Behavior of Polypropylene-Camphor Mixtures for Understanding the Pathways to Polymeric Membranes via Thermally Induced Phase Separation

An experimental phase diagram of the isotactic polypropylene-camphor system is constructed using an original optical method. It considerably deviates from the dynamic diagram, which can be obtained using conventional differential scanning calorimetry (DSC), and contains an additional boundary line that describes camphor solubility in the polymer. An accurate phase diagram makes it possible to perform a detailed and consistent thermodynamic analysis of the DSC, optical, and scanning electron microscopy data on the cooling of prehomogenized mixtures of different compositions, which leads to the formation of capillary-porous bodies via thermally induced phase separation. The removal of camphor results in the formation of polypropylene membranes, the morphology and functional properties of which, such as the total pore volume, mean pore size, permeability coefficient, and breaking stress, appear to be highly dependent on the composition of the initial binary system. It is shown that thermally induced phase separation induces the formation of microscopic cracks in the studied membranes. The crack density decreases with the polymer content in the initial system, but at 53 wt % of polypropylene, the membrane becomes completely impermeable to isopropanol despite the presence of large ∼4 μm pores, thus questioning the perspectives of its practical use. In general, the study makes it possible to achieve a deeper understanding of the membrane formation process via thermally induced phase separation in the mixtures of semicrystalline polymers with low molar mass substances.

Permeation of a Range of Species through Polymer Layers under Varying Conditions of Temperature and Pressure: In Situ Measurement Methods

Minimising the transport of corrosive reactants such as carbon dioxide, hydrogen sulfide and chloride ions to the surfaces of carbon steel pipes by the use of polymer barrier layers is of major interest in the oil and gas sector. In these applications, there is a requirement to assess the performance of these barrier layers although it is difficult to perform long-term predictions of barrier properties from the results of short-term measurements. New methodologies have been successfully developed to study the permeability of carbon dioxide (CO₂) and hydrogen sulfide (H₂S) through polymer layers under variable conditions of elevated temperatures of 100 °C and pressures of the order of 400 barg. In situ variation of the temperature and the inlet pressure of the gas (or gas mixture) allowed the activation energy and pressure dependence of the permeability to be determined without outgassing of the specimen. These methodologies have been applied to the measurement of the permeability of moulded polyphenylene sulfide (PPS) to supercritical CO₂ in the presence of H₂S. The diffusion coefficients of sodium chloride and potassium chloride through both PPS and polyether ether ketone (PEEK) at ambient temperature and pressure have also been measured.