Hollow fibre polymeric membranes for desalination by membrane distillation technology: A review of different morphological structures and key strategic improvements

Membrane distillation (MD) is a separation technology that is gaining increasing importance for desalination because of its optimal separation performance and its ability to treat highly concentrated saline solutions. Among all membrane morphological structures, hollow fibre (HF) exhibits some peculiar advantages, does not require any support to withstand the operation conditions and can be arranged in modules reaching high packing density and optimal fluid dynamics reducing both temperature and concentration polarization effects on MD desalination performance. In general, hollow fibre membranes are prepared by spinning a dope solution following different techniques. The HF membrane morphology can be tuned by modifying a large number of spinning conditions as well as by improving the membrane structure by preparing single layer, mixed matrix or dual layered hollow fibres. This review analyses the research studies developed so far on the design and preparation of different types of hollow fibres together with a critical evaluation of the effects of the involved preparation conditions on MD desalination performance, and some useful remarks to improve hollow fibre characteristics, desalination performance and thermal efficiency. Among the proposed HF for MD desalination, dual layered HF membranes exhibit high permeate fluxes up to 98.6 kg/m2 h with good salt rejection factors.