Thin-Film Composite Membranes on Polyester Woven Mesh with Variable Opening Size for Pressure-Retarded Osmosis

This work discusses findings on the role of woven polyester mesh size on burst strength and mass transfer resistance of thin-film composite membranes used for pressure-retarded osmosis (PRO). Hand-cast and commercial membranes were mounted on standard woven mesh backings with different opening sizes. Characterization of the membranes was done using scanning-electron microscopy, tensile tests, and burst pressure measurements. Membrane performance was assessed by water permeance, reverse salt flux, and osmotic water flux measurements; and correlated with estimates of membrane structural characteristics. Results show that woven mesh polyester backings provide sufficient strength to the overall structure for PRO; however, the porous support layer undergoes deformations that depend on the opening size of the backing. An opening size of 125 µm or smaller provided sufficient strength to a commercial porous support layer when operating at transmembrane pressures at or below 2750 kPa. Next, it was found that the nonwoven backing contributes extensively to the value of the overall structural parameter in the case of the commercial SW30HRLE membrane. Using a woven mesh #325 as polyester backing reduced the SW30HRLE structural parameter by 74%, yielding a 48% improvement in power density. These findings support the idea that mass-transfer resistances in osmotic-driven processes like PRO, are an additive effect of the multiple layers that compose a membrane (or module), and can be reduced by using more open (yet functional) backing layers such as polyester woven mesh.