(584d) Effect of Dehydration on Reverse Osmosis Desalination Performance in Fully Aromatic Polyamide Membranes Containing TEMPO-Oxidized Cellulose Nanocrystals (TOCNs)

Lack of access to safe drinking water is an increasing problem across the world. One of the most effective methods for producing drinking water is the desalination of seawater or brackish water. Fully aromatic polyamide thin film composite (TFC) membranes are the most commonly used material for desalination by reverse osmosis. Thin film nanocomposite membranes (TFNs) incorporate nanoparticles in the selective layer of TFCs to improve their performance. Both TFCs and TFNs are limited by a tradeoff between flux and salt rejection and by limitations in use conditions. Of particular interest for this study is the fact that drying of TFC membranes is known to decrease their performance, likely due to a collapse of the pore structure of the polyamide resulting in decreased water transport. This potentially limits the ease with which RO membranes can be stored and transported, as they must remain hydrated to maintain performance, or must undergo a potentially time-consuming rehydration process. We have created novel TFNs by incorporating functionalized rod-like cellulose nanocrystals (CNCs) in the polyamide layer resulting in improved desalination performance, particularly when membranes are dried and rehydrated.

The CNCs used for this study were modified to produce 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanocrystals (TOCNs). CNCs are selected for their high aspect ratio, low cost, availability, and sustainability. The flux and salt rejection were investigated for TFNs containing varying amounts of TOCNs. TFNs were either stored in ultrapure water or dried under vacuum prior to testing to investigate effects of dehydration. Water flux increased with the addition of TOCNs without any decrease in sodium ion rejection, and the maximum water flux was observed at an intermediate loading level. There was a 22% maximum increase in water flux relative to the unloaded hydrated membrane and 146% maximum increase relative to the unloaded dried membrane.