Ultrafiltration (UF) is a membrane separation technology between microfiltration and nanofiltration, with an average pore size of 3–100 nm. It functions to purify, separate, and concentrate solutions. Its retention mechanism mainly includes the sieving effect and electrostatic effect of the membrane. The filter medium is the ultrafiltration membrane; driven by the pressure difference across the membrane, only low molecular weight solutes and water can pass through, thus achieving purification, separation, and concentration. UF has a wide range of applications. The earliest UF membranes used were natural animal organ membranes. Initially, UF remained an experimental field and did not see significant development until the 1970s, when it entered a phase of rapid industrial application.
Currently (2018), UF membrane materials have expanded from cellulose acetate (CA) to include polystyrene (PS), polyvinylidene fluoride (PVDF), polycarbonate (PC), polyacrylonitrile (PAN), polyethersulfone (PES), and nylon (PA), with the molecular weight cutoff increasing from 10³ to 10⁶. Because ultrafiltration has the characteristics of simple equipment, small footprint, unchanged phase, low operating pressure, low material requirements, and simple equipment, its application scope has rapidly expanded from the research field to practical application fields, such as electronics, pharmaceuticals, electrophoretic paint, beverages, food chemicals, medical treatment, and wastewater treatment and recycling.