Improving particle separation from an ethanol extract to water: settling dependence on fine particle content

Removing solid particles from ethanolic corn extracts by gravitational settling into a water layer has been studied as part of a project to develop a low cost method to extract ethanol-soluble protein from corn meal. Settling has several advantages over industrially proven methods of liquid/particle separation: (1) less expensive equipment; (2) particles that settle at different rates can be collected from different outlets, and (3) extract liquid entrained by settling particles dissolves in the water from which the ethanol can be recovered by distillation. When fine particles were pumped as part of the extract into the 5-l settling layer at a high enough rate, they formed a particle layer at the extract/water interface. The particle layer prevents further settling and is a non-sustainable operating condition. The layer does not form when the mass fraction of particles in the extract was 0.11 or less. This value is greater than the value obtained by extrapolating published settling data for denser (mineral) particles. Overall, entrainment of extract liquid for the settling was about the same as entrainment during centrifugation. In-line measurements and recordings of ethanol concentration, density, and particle content of the water stream carrying settled coarse particles from the settling tank showed that specific entrainment was greater for the finer particles.