Enzymatic corn wet milling: engineering process and cost model

Authors: Ramirez, Edna; Johnston, David; McAloon, Andrew; SINGH, VIJAY - UNIV. OF ILLINOIS,URBANA

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2008
Publication Date: 1/21/2009
Citation: Ramirez, E., Johnston, D., Mcaloon, A.J., Singh, V. 2009. Enzymatic corn wet milling: engineering process and cost model. Biotechnology for Biofuels. 2:2.

Interpretive Summary: Enzymatic corn wet milling is a new process we have developed for the recovery and purification of starch and several coproducts (germ, gluten and fiber)from corn kernels. This process eliminates the need to use a hazardous chemical pretreatment (sulfites) prior to separation, as is currently practiced in the conventional process, by replacing the chemical pretreatment with a protease (enzyme). To evaluate and compare the economic viability of this “green” process with the conventional process, detailed process and economic models were constructed. The model includes grain cleaning, enzyme treatment, germ separation and recovery, fiber separation and recovery, gluten separation and recovery and starch separation. Based on the information generated using the developed models, we demonstrated that under certain fluctuations of corn and enzyme prices the enzymatic corn wet milling can be either more or less economical relative to the conventional process. Under the current corn and enzyme costs, the enzymatic process has a slight economic advantage. Beside the environmental advantages, this process becomes more economically desirable when the price of corn is above $3/bushel. This research will benefit researchers studying the adoption of this new process in industry as well as scientists and engineers in academia and government.

Technical Abstract: Enzymatic Corn Wet Milling (E-Milling) is a proposed alternative process to conventional wet milling for the recovery and purification of starch and coproducts using proteases to eliminate the need for sulfites and to decrease the steeping time. In 2005, the total starch production in USA by conventional wet milling equaled 22.9 billion kilograms, including modified starches and starches used for sweeteners and ethanol production (CRA 2006).Process engineering and cost models for an E-Milling process have been developed for a processing plant with a capacity of 2.54 million kg of corn per day (100,000 bu/day). These models are based on the previously published models for a traditional wet milling plant with the same capacity. The process includes grain cleaning, pretreatment, enzymatic treatment, germ separation and recovery, fiber separation and recovery, gluten separation and recovery and starch separation. Information for the development of the conventional models was obtained from a variety of technical sources including commercial wet milling companies, industry experts and equipment suppliers. Additional information for the present models was obtained from our own experience with the development of the E-Milling process and trials in the laboratory and at the pilot plant scale. The models were developed using process and cost simulation software (SuperPro Designer®) and include processing information such as composition and flow rates of the various process streams, descriptions of the various unit operations and detailed breakdowns of the operating and capital cost of the facility. Based on the information from the model, we can estimate the cost of production per kilogram of starch using the input prices for corn, enzyme and other wet milling coproducts. The work presented here describes the E-Milling process and compares the process, the operation and costs with the conventional process. The E-Milling process was found to be cost competitive with the conventional process during periods of high corn feedstock costs since the enzymatic process enhances the yields of the products in a corn wet milling process.