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Title: Thin film composite membranes and their derivatives in desalination by reverse osmosis
Author: Abdulsalam Ebrahim, Mahmood
ISNI:       0000 0004 7963 7951
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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Thin film composite (TFC) membranes formed via the interfacial polymerisation of m-phenylenediamine (MPD) and trimesoyl chloride (TMC) on a polysulfone (PSf) or polyethersulfone ultrafiltration support are the most widely used membranes in desalination. This work aims to develop high flux seawater reverse osmosis (SWRO) membranes. An analogue TFC membrane formed via the interfacial reaction of MPD and TMC was fabricated; and its performance was compared to five commercial RO membranes. The influence of sodium chloride concentration in the feed solution on the transport properties of the membranes was evaluated by varying the feed concentration between 0 to 70 g.L^(-1) NaCl, in order to simulate the commonly encountered operating conditions of SWRO desalination at a recovery of 50%. The analogue membrane showed comparable performance to the commercial RO membranes over the experimental range. Mixed matrix ultrafiltration (MMUF) supports were prepared by incorporating titanium dioxide (TiO2) nanoparticles and nanotubes in the polysulfone support membrane. MMUF supports showed an increase in the pure water permeance by up to 200% relative to the pure PSf support. A selective polyamide layer was fabricated via interfacial polymerisation of MPD and TMC on the MMUF, and on the pure PSf support membranes; and their desalination performance was tested. TFC membranes made on TiO2 nanotubes incorporated MMUF showed around 8% improvement (up to 2.7 L.m^(-2).h^(-1).bar^(-1) at 60 bar) compared to the TFCs fabricated on pure PSf support and 99% rejection of NaCl at steady state. The results of this work and the recent advances in the development of graphene-based membranes suggest that the development of porous ultrathin carbon (UtC) nanofilms is a potential route to obtain high flux RO membranes. UtC nanofilms were obtained from pyrolysis of polyamide nanofilms made via interfacial polymerisation at 500 - 1100°C under an Ar/H2 atmosphere, to provide nanofilms with thicknesses down to 3 nm, and the properties of UtC nanofilm sheets and powders are reported. Ultrathin carbon nanofilms showed limited utility as reverse osmosis membranes, with water permeance of 0.01 L.m^(-2).h^(-1).bar^(-1) and low rejection of sodium chloride. Although the small pore width and hydrophobic nature of these films resulted in low water permeance, ultrathin carbon nanofilms could potentially be useful in different applications.
Supervisor: Livingston, Andrew G. ; Li, Kang Sponsor: British Petroleum ; International Centre for Advanced Materials
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral