The concept of pressure-retarded osmosis (PRO) was first introduced by Norman in 1974 [1], but later named as PRO [2] and extended by Loeb [2, 3] and other researchers [4-8]. The main obstacle that hinders the development of PRO and limits power production is the lack of appropriate membrane design—specifically, a highly permeable and selective barrier layer and a support layer that produces minimal internal concentration polarization (ICP). Internal concentration polarization results from hindered diffusion of feed and/or draw solutes through the porous support layer of a composite membrane. The extent of ICP is theoretically a function of the porous support layer thickness and (macro void) porosity and tortuosity. So far, the highest output reported is 3.5 W/m~2 of membrane area from a thin film composite membrane tested in the laboratory using simple salt solutions and converting the measured flux into power using a simple thermodynamic model [9]. In order for PRO to be economically viable, a membrane that generates at least 5 W/m~2 is required [10].
展开▼
