Abstract
Efficient harvesting of the mixing energy from the salinity gradient between sea and river water remains a challenge. Recently, utilization of the swelling/shrinking properties of hydrogels has been explored as a new means for extracting this energy. However, former investigations are mainly limited to examining the performance of the hydrogels when lifting applied weights, and calculating the energy that could potentially be extracted. In this study, we demonstrate a novel osmotic engine with a mechanical energy transmission prototype, which can convert and store the green mixing energy in a form that can be utilized to perform mechanical work. The osmotic engine includes a cylinder containing the hydrogel, an oil-hydraulic cylinder and a hydraulic accumulator. The lifting energy from the hydrogel is transferred to the oil-hydraulic cylinder through a lever, which acts as a pump and accumulate the hydraulic oil under high pressure in the hydraulic accumulator. The system was tested with a hydrogel of poly(acrylic acid) semi-interpenetrated with poly(4-styrenessulfonic acid-co-maleic acid) sodium. This hydrogel produced up to 36 J per shrinking/swelling cycle, and exhibited an efficiency of 0.53% at optimum conditions.
Highlights
With a need of reducing CO2 emissions and replacing fossil fuel with more sustainable energy sources, great efforts are aimed at capturing and utilizing renewable energy such as solar, wind, geothermal, or ocean
In the mechanical energy transmission system, the oil flowing from the hydraulic cylinder during each cycle was stored in the accumulator and compressed the air bladder
By utilizing poly(acrylic acid)-based hydrogels that swell in freshwater and shrink in seawater, the osmotic engine could convert the mixing energy of seawater and freshwater into green, accessible power
Summary
With a need of reducing CO2 emissions and replacing fossil fuel with more sustainable energy sources, great efforts are aimed at capturing and utilizing renewable energy such as solar, wind, geothermal, or ocean. Chemical energy from the salinity gradient between seawater and freshwater is a substantial potential power source [1]. The mixing energy when river water flows into the ocean is estimated to be 2.2 kJ per liter of fresh water [2]. Concepts such as exploiting the differences in vapor pressure between salt and freshwater has been suggested [3,4], the currently most reliable techniques to harvest energy from mixing seawater with river water utilize membranes [2]. Pressure-retarded osmosis (PRO) [5e8], reverse electro-dialysis (RED) [9e11], and capacitive mixing (CapMix) [12e15] have been explored to extract salinity gradient energy
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