Using Reverse Osmosis Membrane at High Temperature for Water Recovery and Regeneration from Thermo-Responsive Ionic Liquid-Based Draw Solution for Efficient Forward Osmosis

Abstract

Forward osmosis (FO) membrane process is expected to realize energy-saving seawater desalination. To this end, energy-saving water recovery from a draw solution (DS) and effective DS regeneration are essential. Recently, thermo-responsive DSs have been developed to realize energy-saving water recovery and DS regeneration. We previously reported that high-temperature reverse osmosis (RO) treatment was effective in recovering water from a thermo-responsive ionic liquid (IL)-based DS. In this study, to confirm the advantages of the high-temperature RO operation, thermo-sensitive IL-based DS was treated by an RO membrane at temperatures higher than the lower critical solution temperature (LCST) of the DS. Tetrabutylammonium 2,4,6-trimethylbenznenesulfonate ([N4444][TMBS]) with an LCST of 58 °C was used as the DS. The high-temperature RO treatment was conducted at 60 °C above the LCST using the [N4444][TMBS]-based DS-lean phase after phase separation. Because the [N4444][TMBS]-based DS has a significantly temperature-dependent osmotic pressure, the DS-lean phase can be concentrated to an osmotic pressure higher than that of seawater at room temperature (20 °C). In addition, water can be effectively recovered from the DS-lean phase until the DS concentration increased to 40 wt%, and the final DS concentration reached 70 wt%. From the results, the advantages of RO treatment of the thermo-responsive DS at temperatures higher than the LCST were confirmed.

New Insights into the Mechanical Behavior of Thin-Film Composite Polymeric Membranes

“…Thus, it is critical to evaluate the mechanical characteristics of those membranes to explore the failure processes, such as surface damage, chemical and mechanical degradation, delamination, and lack of membrane stability under different conditions. The majority of published research was concerned with the desalination of saltwater or membranes for wastewater treatment, with emphasis on surface modification [ 4 , 5 , 6 ], membrane processing [ 7 , 8 , 9 ], and antifouling characteristics [ 10 , 11 , 12 ]. According to the Scopus database, the number of papers published each year on the mechanical properties of thin-film composite (TFC) membranes still only accounts for 5% of the yearly publications on water membranes [ 13 ].…”