A novel filtration system for polyethylene glycol solutions used in the osmotic method of controlling suction

One of the problems encountered when using the osmotic technique of controlling suction is related to the possible crossing of polyethylene glycol (PEG) molecules through the semipermeable membrane. Of the various hypotheses proposed, the paper considers the hypothesis that the PEG solutions are not pure enough and have molecules that are small enough to cross the semipermeable membrane. The paper presents a novel PEG purification system in which two solutions at different concentrations are put in contact through a semipermeable membrane along a large exchange surface. A peculiarity of the system is that it creates two opposite fluxes through the membrane, where small PEG molecules go from the higher concentration solution towards the lower concentration solution, and water migrates in the opposite direction. It has been observed that a small quantity of small molecules of PEG 6000 crossed the molecular weight cutoff (MWCO) 3500 semipermeable membrane.