Investigation of the main properties of reverse osmosis membranes and their influence on changes in the physico-chemical composition of aqueous solutions

Abstract

The article discusses the relevance and features of the use of reverse osmosis when adjusting the physico-chemical composition of aqueous solutions and especially the composition of drinking water. The main element of any reverse osmosis plant is a semi-permeable membrane, which is a polymer composite material of uneven density. It has been shown that reverse osmosis membranes must meet certain requirements, the main of which are selectivity to the components that are removed at this functional stage, compliance with a high level of permeability, i.e. stable physical and chemical properties during their operation. The main physicochemical properties of membranes (selectivity, specific productivity, concentration reduction factor, separation factor) and methods for their calculation are described. The effect of temperature on the change in the selectivity and specific productivity of a semipermeable membrane for MgCl₂ and CaCl₂ salts has been experimentally studied. It has been proven that an increase in the temperature of the solution leads to an increase in the selectivity of the membrane and a linear decrease in the specific productivity. Experimental studies were carried out on model solutions to study the effect of pressure on the change in membrane selectivity. It is shown that the shrinkage of the membrane structure is especially noticeable in the first hours of its operation, which leads to a decrease in the selectivity of the membrane. A practically steady state in terms of selectivity usually occurs in 4–5 hours. It was studied that with an increase in the concentration of salts in the initial solution, a decrease in the specific productivity of the membrane and an increase in selectivity occur. It is shown that the selectivity of the studied membrane in the presented range of concentrations is higher for electrolytes of the 2:2 type than for electrolytes of the 2-1 type. The parametric dependences of the change in selectivity and the concentration reduction factor of the Filmtec TW30-1812-50 membrane over time for the components of a “model multicomponent solution” at a pressure of P = 18 atm are given.