Thin stillage fractionation using ultrafiltration: resistance in series model

Area of Science:

• Biochemical Engineering
• Separation Processes
• Renewable Energy

Background:

• The corn-based dry grind process is dominant in US fuel ethanol production.
• Thin stillage, a byproduct, requires water evaporation for solids concentration, leading to high costs and operational issues.
• Evaporation necessitates excess capacity, increasing capital expenses and causing revenue loss due to plant slowdowns.

Purpose of the Study:

• To evaluate membrane filtration, specifically ultrafiltration, as a viable alternative to evaporators for thin stillage processing.
• To assess the efficiency of regenerated cellulose membranes in recovering solids from thin stillage.
• To model and understand permeate flux decline and fouling mechanisms during membrane separation.

Main Methods:

• Fractionation of thin stillage using two regenerated cellulose ultrafiltration membranes (10 kDa and 100 kDa MWCO).
• Experimental determination of permeate flux, transmembrane pressure, temperature, and resistance components.
• Development and application of a resistance-in-series model to predict flux decline and fouling.

Main Results:

• Membrane separation recovered total solids comparable to commercial evaporators.
• Permeate flux decline was modeled using a resistance-in-series approach, with high agreement between model and experimental data (R² > 0.98).
• Optimal operating conditions for maximum flux rates were identified by analyzing transmembrane pressure and temperature effects.

Conclusions:

• Membrane filtration presents a cost-effective and efficient alternative to evaporation for concentrating thin stillage in the ethanol industry.
• The developed model accurately predicts flux decline, aiding in process optimization and maintenance strategies.
• This technology can enhance the value of thin stillage and improve the overall economics of fuel ethanol production.