Increased power density with low salt flux using organic draw solutions for pressure-retarded osmosis at elevated temperatures

Abstract

Pressure retarded osmosis (PRO) is an emerging technology that uses salinity gradients to produce energy. In this study, the impact of temperature on PRO performances is investigated when operating with an organic draw solution. These results are compared to PRO performances while using the commonly used solute sodium chloride (NaCl) as a draw solution. It has been observed that NaCl draw solution (1 M) can produce almost ~34% (6.7 Wm−2 to 9.0 Wm−2) more energy when the temperature is increased from 20 °C to 40 °C. However, high reverse salt flux was encountered. In addition, potassium acetate and sodium propionate show a ~31% (8.5 Wm−2 to 11.1 Wm−2) and ~27% (8.1 Wm−2 to 10.3 Wm−2) increase in power density when increasing the temperature from 20 °C to 40 °C. It was found that reverse salt flux while using these organic salts is ~5 to 8 times lower when compared to NaCl. A comparison shows that at 40 °C, potassium acetate and sodium propionate produce 23% and 14.5% higher power density, respectively, over NaCl solutions. Based on these results, increased energy at higher temperatures, coupled with lower reverse salt flux, have demonstrated the potential of using organic salts as a draw solution in future research towards a feasible PRO process.