Tuning poly(vinyl chloride) membrane morphology to suit vacuum membrane distillation: Focusing on membrane preparation process based on phase separation

Abstract

Nowadays, water scarcity is a paramount concern all over the world. Water desalination has been proposed as an applicable solution to face this problem. In this work, water desalination based on distillation technique using Poly(vinyl chloride) (PVC) membrane was considered. PVC membranes were fabricated via nonsolvent-induced phase separation (NIPS). Parameters involved in membrane production process were changed to tune the PVC membrane morphology for vacuum membrane distillation (VMD). These parameters include (1) polymer concentration in casting dope, (2) exposure of cast solution to the water vapor before immersing in nonsolvent bath, (3) addition of a hydrophilic polymer such as polyvinyl pyrrolidone (PVP) with different concentrations to the casting dope and (4) casting thickness. It was shown that the investigated parameters significantly affect the morphology and VMD performance of the PVC membranes. Additionally, enough evidence was provided to demonstrate that PVC concentration in the casting dope is the parameter using which PVC membrane morphology can be easily and effectively tuned to suit the VMD. Utilizing appropriate PVC concentrations, membranes with a suitable combination of both macrovoids and cellular pores can be produced. Note that although macrovoids are beneficial to enhance membrane flux, they adversely influence the membrane liquid entry pressure of water (LEP w ). An optimum LEP w is essential to resist against membrane wetting and achieve a high flux and long-term performance during the VMD. Therefore, the length and density of macrovoids within the membrane structure must be optimized to obtain a membrane, which is suitable for the VMD. It can be best achieved by changing the PVC concentration in the casting dope. The influence of VMD operational parameters on the performance of PVC membranes produced using a casting solution with appropriate PVC concentration was further investigated. It was shown that in spite of the feed salt concentration, the temperature and flow rate of feed solution positively affect membrane flux while the salt rejection remains unchanged. • Tuning the PVC membrane morphology to suit VMD is comprehensively explored. • The appropriate PVC membrane morphology for VMD is disclosed. • For VMD, membrane morphology can be best tuned by changing solution concentration.