Submitted to: Bioprocess and Biosystems Engineering
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/9/2008
Publication Date: 1/1/2009
Citation: Arora, A., Dien, B.S., Belyea, R.L., Wang, P., Singh, V., Tumbleson, M.E., Rausch, K.D. 2009. Thin Stillage Fractionation Using Ultrafiltration: Resistance in Series Model. Bioprocess and Biosystems Engineering. 32(2):225-233. Interpretive Summary: Corn ethanol production has grown considerably over the past decade and there is considerable interest in further refining the process so as to lower waste water and to save energy costs. Ultrafiltration is a processing unit operation that uses a membrane for recovering water from process streams that contain dilute solids. It is viewed as an alternate technology to multi-effect evaporators. Ultrafiltration is more energy efficient than evaporation because it avoids the need for a phase change (e.g., liquid water to steam). However, ultrafiltration has not found widespread application in the corn ethanol industry because of concern with regard to membrane life - the membrane at the heart of the system becomes fouled with corn residues and needs to be repeatedly cleaned. The operation costs are highly dependent upon how often the membrane needs to be cleaned and the number of cleaning cycles it can withstand before needing to be replaced. This paper examines the former issue by modeling the rate of fouling as related to flux across the membrane and pressure increases.
Technical Abstract: Fractionation of thin stillage using ultrafiltration was conducted to evaluate membranes as an alternative to evaporators in the ethanol industry. Two regenerated cellulose membranes with molecular weight cut offs of 10,000 and 100,000 kDa, respectively, were evaluated. Total solids (suspended and soluble) recovered through the membrane separation process were similar to those from commercial evaporators. Flux decline of thin stillage using a resistance in series model was determined. Each of the four components of total resistance were evaluated experimentally. Effects of operating variables such as transmembrane pressure and temperature on permeate flux and resistance were determined and optimum conditions for maximum flux were evaluated. Model equations were developed to evaluate the resistance components that are responsible for fouling and to predict total flux decline with respect to time. Modeling results were in agreement with experimental results (R**2>0.98).