Thin stillage fractionation using ultrafiltration: resistance in series model

Abstract

The corn based dry grind process is the most widely used method in the US for fuel ethanol production. Fermentation of corn to ethanol produces whole stillage after ethanol is removed by distillation. It is centrifuged to separate thin stillage from wet grains. Thin stillage contains 5-10% solids. To concentrate solids of thin stillage, it requires evaporation of large amounts of water and maintenance of evaporators. Evaporator maintenance requires excess evaporator capacity at the facility, increasing capital expenses, requiring plant slowdowns or shut downs and results in revenue losses. Membrane filtration is one method that could lead to improved value of thin stillage and may offer an alternative to evaporation. 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 and 100 kDa were evaluated. Total solids (suspended and soluble) contents recovered through membrane separation process were similar to those from commercial evaporators. Permeate flux decline of thin stillage using a resistance in series model was determined. Each of the four components of total resistance was evaluated experimentally. Effects of operating variables such as transmembrane pressure and temperature on permeate flux rate and resistances were determined and optimum conditions for maximum flux rates 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).

Membrane separations for solid–liquid clarification within lignocellulosic biorefining processes

“…Flux decline and fouling was evaluated by utilizing a resistance in series model; a common approach in many areas of membrane separation applications since the model allows for analysis of both reversible and irreversible fouling. The series resistance equation (Eq.…”

“…However, rapid fouling of the membrane, and the associated performance decline, is a major challenge to overcome before widespread application can be realized . The membrane fouling process is complex and can be caused by a variety of mechanisms (e.g., complete pore blockage, intermediate pore blockage, pore constriction, and/or cake or gel formation), which result from many different interactions between solution components (both solid particulates as well as soluble components) and the membrane material . Membrane surface charge, hydrophobicity, surface roughness, and pore size affect membrane fouling characteristics and other membrane performance properties .…”

“…1 The membrane fouling process is complex and can be caused by a variety of mechanisms (e.g., complete pore blockage, intermediate pore blockage, pore constriction, and/or cake or gel formation), which result from many different interactions between solution components (both solid particulates as well as soluble components) and the membrane material. [3][4][5] Membrane surface charge, hydrophobicity, surface roughness, and pore size affect membrane fouling characteristics and other membrane performance properties. 6 At the same time, the properties and composition of the process solution (pH, solids content and composition, and ionic strength) also play a prominent role in dictating membrane performance characteristics such as flux, selectivity, and reusability of the membrane for multiple cycles.…”

Grain Thin Stillage Protein Utilization: A Review

“…Particle removal is often an essential initial process to limit equipment fouling while enabling mass and heat transfer during compound recovery and extraction processes. Several strategies can be used to clarify G‐TS, including centrifugation (Kelsall & Piggot, ; LoCascio & Dunbar, ), clarifying agents (Castellari, Versari, Fabiani, Parpinello, & Galassi, ; Menkhaus, Anderson, Lane, & Waddell, ; Scheimann, ), dissolved air flotation (DAF) (Chadwick & Schroeder, ; Van Leeuwen, Khanal, & Pometto, ), anoxic gas flotation (AGF) (Burke, , ), filtration (Arora et al, , ), and size exclusion (Kalbfuss, Wolff, Morenweiser, & Reichl, ; Zheng & Yu, ). Ideally, preparation of a particle‐free solution could aid in recovery and extraction of valuable compounds from the complex mixture.…”

Effects of Propionic Acid and pH on Ethanol Fermentation by Saccharomyces cerevisiae in Cassava Mash

“…In fact, only 15-30% of thin stillage can be recycled at the industrial scale in long-term operation (e.g., at Henan Tianguan Fuel Ethanol Co., Ltd., China), with the remaining thin stillage needing to be treated by anaerobic-aerobic treatment. The major drawback of such biological treatment is its high investment and operational costs [4,5].…”