Spectroscopic and Kinetic Investigations of the Permeability of the Surface Layers of Membranes in the Process of Microfiltration Separation of Water-Organic Solutions

IR spectroscopy was used to study the structure of the surface layer of air-dry, water-saturated and working samples of microfiltration composite membranes MMK-0.45 and MFFC-2G based on polyamide and fluoroplast, respectively. IR spectra were analyzed in the frequency ranges 500–1700 and 2800–3400 cm^–1. In the case of the polyamide membrane, the main peaks of the functional groups of polymers in the IR spectra of dry, water-saturated, and working samples coincide. The absorption bands of polyamides range from 650 to 5000 cm^–1, corresponding to the peptide bond. In the absorption band of 1650 cm^–1, bending vibrations of the carbonyl group occur, and in the band of 1550 cm^–1, bending vibrations of the N–H bond are observed. The 3500–3000 cm^–1 region is the stretching vibrations of the NH, OH and water groups. In the case of the working sample of the MFFC-2G fluoroplastic membrane, the stretching vibrations of the fluorine-substituted groups lie in the range 1100–1400 cm^–1; they correspond to the C–F stretching vibrations (1198 and 1171 cm^–1). The IR spectrum also shows two peaks in the region 2800–3000 cm^–1; they are characteristic of biodiesels from vegetable oils. Studies of the specific output flow and the change in the pH of the permeate depending on time and transmembrane pressure were carried out. There are several periods of a decrease in the specific output flux depending on time, which is most likely due to the unblocking of the membrane pores by organic compounds in the solution being separated, and the possible formation of a boundary gel layer. The decrease in the pH of the permeate with an increase in the transmembrane pressure on the MMK-0.45 and MFFC-2G microfiltration membranes is probably due to an increase in the rate of migration of organic acids through the helium layer and the working layer of the membrane.