Starch Particles, Energy Harvesting, and the "Goldilocks Effect".

This study reports on the unique water vapor adsorption properties of biomass-derived starch particles (SPs). SPs offer an alternative desiccant for air-to-air energy exchangers in heating, ventilation, and air conditioning systems because of their remarkable adsorption-desorption performance. SP has a particle diameter ( ) of 15 μm with a surface area (SA) of 2.89 m/g and a pore width ( ) of 80 Å. Microporous starch particles (SP) were compared with high amylose starch (HAS; SA = 0.56 m/g, = 15 μm, = 46 Å) and silica gel (SG; SA = 478 m/g, = 13 μm, = 62 Å). Transient water vapor tests were performed using a customized small-scale energy exchanger coated with SP, HAS, and SG. The water swelling (%) for SP was ca. 2 orders of magnitude greater with markedly higher (ca. three- and six-fold) water vapor uptake compared to HAS and SG, respectively. At similar desiccant coating levels on the energy exchanger, the latent effectiveness of the SP system was much improved (4-31%) over the HAS and SG systems at controlled operating conditions. SP is a unique desiccant material with high affinity for water vapor and superior adsorption properties where ca. 98% regeneration was achieved under mild conditions. Therefore, SPs display unique adsorption-desorption properties, herein referred to as the "Goldilocks effect". This contribution reports on the utility of SPs as promising desiccant coatings in air-to-air energy exchangers for ventilation systems or as advanced materials for potential water/energy harvesting applications.