Submitted to: Chemical Engineering Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2008
Publication Date: 9/24/2008
Citation: Dickey, L.C., Kurantz, M.J., Parris, N., Moreau, R.A. 2008. Separation of buoyant particles from an aqueous dispersion of corn germ particles using a bubble column. Chemical Engineering Science 63 (18), p.4555-4560.
Interpretive Summary: Dry grind production of ethanol from corn creates a byproduct, distillers’ dried grains, DDG. In the US, DDG contains roughly 300 million gallons of corn oil that can be converted into a similar volume of biodiesel. The embryo of the corn, also called the germ, contains > 90% of the oil in the kernel and can be separated prior to fermentation by several new processes. Corn oil can then be separated from the germ and made available for uses other than animal feed, keeping the vegetable oil price stable despite increased oil consumption for biodiesel production. Sale of germ as a byproduct, in place of some of the distillers’ dried grains, should significantly increase the overall ethanol production revenues and thereby benefit this industry. More dry-grind ethanol production will bolster the U.S. corn market, reduce petroleum imports and slow depletion of world petroleum reserves. Corn germ price and its impact on dry grind profitability will increase if the cost of separating the oil from the germ can be reduced. Using an aqueous method, instead of hexane extraction, is one approach to cheaper oil separation. The cost of removing oil from an aqueous mixture is mostly due to centrifugation and this study shows that about half of the oil was extracted from 400 g batches of germ using a step that concentrated half the oil in a quarter of the original volume. These conditions and the process used will be the starting point for larger scale trials.
Technical Abstract: As part of a larger program on developing solvent-free aqueous methods to extract oil from corn germ, experiments were conducted to study the use of a bubble column to separate oil from dispersions prepared by grinding corn germ particles in buffered aqueous solution. Particles and aggregates as large as 1 mm which incorporated oil droplets about 1-2 micron in size were suspended in the dispersions. The suspension was subsequently heated and dosed with enzyme to release oil droplets. The buoyant fine particles and aggregates were carried to the top of a dispersion column by nitrogen bubbles and were incorporated into a foam layer at the top of the liquid. The rising foam was drained through a port a few cm above the top of the dispersion. The collected foam was subsequently centrifuged to separate a free oil layer. The oil yields were comparable to those obtained by centrifuging entire dispersions churned in an incubator/shaker with no bubbling or foaming. With only endogenous surfactant present in the dispersion, about half of the oil in the dispersion was collected from the foam as free oil and another quarter as oil droplets too fine to separate by centrifugation from the collected foam which comprised a quarter of the dispersion. Oil content of the collected foam was maximized by churning the germ dispersion long enough to fully digest the germ and coalesce the oil droplets prior to foam collection.