Dewatering of super absorbent polymers: Alternatives to thermal desorption by liquid phase extraction using dimethyl ether

Abstract

The high saturation potential of highly hygroscopic desiccants makes their drying potential reuse an energetically unfavorable challenge. Perhaps there are other ways beyond dehydration the extract saturated water from these structures. That was the premise of the proposed experiments in which an existing method was redesigned in which condensed Dimethyl Ether (DME) was used aqueous fluids from commercial grade superabsorbent polymers (SAPs) similar to those found in commercial diapers. It was hypothesized that liquid extraction could be energetically less intensive than thermally dehydrating the SAP. By toggling between pressures above and below 0.6 MPa at room temperature, using gravity assistance, and nitrogen gas as driving forces, the DME condenses and interacts with the saturated SAP. The system successfully dewatered both DI water and saline saturated SAP. Roughly 90% of deionized water and ~80% of artificial urine are extractable from SAP when the chamber was pressurized 3 times. The salts in the artificial urine also conveyed in the aqueous extract and not concentrated in the dehydrated SAP. Energy assessments linked with each DME loading consumed 12.6 kJ or ~5 kJ/g of water extracted, more than required for thermal evaporation. The dehydrated superabsorbent polymer structure appears morphologically different by microscopy, but it can re-swell up to 35 times its dry mass in water and 15 times its mass in artificial urine. Overall, aqueous phase extraction using condensed DME dewaters saturated superabsorbent polymers allowing their reuse as other forms of desiccants but it is less efficient than by dehydration.