The efficiency of dehydrating desiccants by centrifugation: An assessment of superabsorbent polymers

Abstract

The centrifugal drying response from a sodium acrylate superabsorbent copolymer saturated with water, saline, and a synthetic urine mimic was evaluated. It was hypothesized that drying using mechanical methods might be more economical than through evaporation. Commercial, mid-grade, multi-welled centrifuges capable of speeds as high as 8000 rpm and spin times up to 12 min were used to perform parametric studies of the separations. For centrifugal extraction, meshes that varied average pore size from 28 to 89 micrometers were constructed to contain the saturated superabsorbent polymer while the fluid was driven from it under controlled spinning. Gravimetric determinations post-centrifugation found that 30 − 60% of fluid mass could be extracted. The ionic strength of the saline saturated superabsorbent polymers resulted in a much lower initial saturation volume compared to those saturated with deionized water, and raised the amount of polymer in each tube during centrifugation allowing for higher throughput. Higher fluid extraction is achievable with larger pores in the mesh, although the bigger pores allowed dried particles to propagate through the mesh. Longer centrifugation intervals and higher rotational speeds have only a modest effect on the efficiency and centrifugation used to isolate fluids from saturated desiccants remains incomplete. If the absorbent particles could be tethered together, mechanical drying could be more efficient. Under the best conditions, centrifugation consumes roughly 70 kJ/g (70 MJ/kg) of fluid extracted, which is more than the energy for evaporating water.