The mass transfer rate and the power density are presented here using a pressure retarded osmosis membrane process. This process was researched for more than two decades as an energy production process, mixing seawater and river water through a selective membrane layer. According to this process, the osmotic pressure difference, due the difference in ion-concentrations across the membrane, can provide a portion of liquid with relatively high pressure, which can then produce energy by means of a turbine. However, according to the present state of art of this process, applying seawater and river water pair, it is not enough economic yet due to the limited performance of the membrane as well as the relatively low osmotic pressure of the seawater. That is why alternate process might be the realization of the energy production in a closed-loop with regeneration of the solutes, which then makes possible to use much higher draw solute concentration and due to it, with much higher energy density. The usage of ionic liquids is thought to be a possible solution because they can be regenerated and can be using for more cycles. The study discusses, partly here, and partly in the presentation, the possible application of a home-prepared ionic liquid for energy generation.