Spectroscopic and Kinetic Studies of the Permeability of Membrane Surface Layers during the Microfiltration Separation of Aqueous-Organic Solutions

In this paper, we study the structure of the surface layer of air-dry, water-saturated, and operating samples of microfiltration composite membranes based on MMK-0.45 polyamide and MFFC-2G fluoroplast using infrared (IR) spectroscopy. The IR spectra are analyzed in the frequency ranges of 500–1700 and 2800–3400 cm–1. In the case of polyamide membrane MMK-0.45, the main peaks of the functional groups of polymers in the IR spectra of dry, water-saturated, and operating samples coincide. The absorption bands of polyamides range from 650 to 5000 cm–1, corresponding to the peptide bond. Bending vibrations of the carbonyl group occur in the absorption band at 1650 cm–1 while bending vibrations of the N–H bond are observed in the band at 1550 cm–1. The 3500–3000 cm–1 region is the stretching vibrations of the NH, OH, and water groups. In the case of the operating sample of the MFFC-2G fluoroplastic membrane, the stretching vibrations of the fluorine-substituted groups lie in the range of 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 of 2800–3000 cm–1; they are characteristic of biodiesel from vegetable oils. The specific output flow and changes in the pH of the permeate depending on time and transmembrane pressure are studied. There are several periods of decrease in the specific output flow depending on time, which is most likely due to the unblocking of pores of the microfiltration membrane by substances 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 due probably to an increase in the rate of migration of organic acids through the helium layer and the operating layer of the membrane.