(505b) Modeling and Kinetics of Phytate Adsorption from Corn Stillages on a Weak-Base Ion Exchange Resin
Dry-milling process accounts for over 80% of the total corn ethanol production in the United States and it generates at least 3 times the volume of ethanol produced as by-products, the stillages. These co-products have been processed and primarily utilized as animal feed. Phosphorus is predominantly found as phytate in corn, existing up to 80% in this form. Phytate is not fully degraded by the corn ethanol bioprocessing steps including saccharification and fermentation; and the downstream processes does not provide additional degradation of this material, which produces end-products, such as animal feed Dried Distillers Grains with Solubles (DDGS), rich in phytate phosphorus. It is not desirable to have the animal diet rich in phytate for monogastric animals, such as poultry and swine, since the digestive track of monogastrics cannot degrade this form of phosphorus, producing, alongside with other effects, a phosphorus-rich manure. This often may cause environmental concerns, especially when it is applied as fertilizer, leading to saturation of phosphorus in the soil, and runoff to waterbodies. Ion exchange has been studied to extract phosphorus compounds, and weak-base exchange resins have been utilized to extract and purify phytate from acid digestates from cereal materials, such as wheat and rice. Experimental results shows that, the weak-base resin used in this particular study has a high specificity for phytate, and does not have evident adsorption on nutritional ingredients of stillage, such as fat, fiber, proteins and residual starch. The purpose of this work is to evaluate the mass-transfer kinetics on the resin beads, understanding the breakthrough curves and Freundlich, Langmuir and Dubinin-Radushkevich adsorption models on the weak-base resin. The results for these adsorption phenomena will serve as basis for thermodynamic calculations on the resin, in order to establish enthalpies and entropies of the studied system under different conditions, such as dilution rate, pH, and temperature. Experimental set up using the weak-base resin has been able to achieve total phytate adsorption from stillage samples, and desorption values as high as 92% from the resin beads. Our studies indicate a mild-acid pH (on the range from 4 to 6) and temperature stable resin (from 4 °C to 75 °C). Understanding the kinetics and modeling is a key step in optimizing this system on a larger scale.