University researchers have found an alternative and energy-efficient way to dry corn ethanol, and their proof is in the pudding.
Michael Ladisch, a distinguished professor of agricultural and biological engineering at Purdue University, West LaFayette, Ind.; Youngmi Kim, a Purdue research scientist; and Ahmad Hilaly, director of process research at Archer Daniels Midland, found that the shape and structure of tapioca pearls are well-suited for removing water from ethanol.
After fermentation, ethanol contains between 6 percent and 12 percent water, which must be removed to make it fuel-grade. Many ethanol plants use corn grits, which absorb water, or molecular sieves, which are silica-based particles with tiny pores that retain only water molecules. Ladisch and Kim found that tapioca pearls work better than the conventional corn grit adsorbents.
"Any starch will absorb water. That's how you cook rice or pasta," Kim says. "The tapioca pearl is made of aggregated cassava starch granules that can adsorb more water."
Ladisch says tests found tapioca collected about 34 percent more water than corn. Molecular sieves, while effective, eventually wear out and create waste that must be disposed of. The tapioca can be dried and reused, and when they wear out, they can be used to make more ethanol.
"Tapioca is very efficient, and it's all-natural," Ladisch says. "There are no disposal issues. It's much more environmentally friendly."
Tapioca pearls, essentially spherical, are structured differently than corn grits, Ladisch says. While corn grits are solid, irregularly shaped particles, tapioca pearls contain a gelatin starch core upon which dry starch granules are aggregated, significantly increasing surface area. Also, while tapioca pearls are 100 percent starch, corn grits also contain fiber, protein and other substances that are not efficient for absorbing water.
Starch-based adsorbents like tapioca pearls also take up the heat created during drying, allowing that heat to be reused to evaporate water during regeneration of the drying bed.
"This combines fundamental biochemistry, biology and engineering with thermodynamics to obtain an efficient separation system," Ladisch says.
The findings were reported in the July issue of theIndustrial & Engineering Chemistry Research.