A novel approach to heat removal and temperature control in fed-batch extractive ethanol fermentation using CO2

Abstract

This study proposes a novel approach to remove heat and maintain the broth temperature constant during fed-batch ethanol extractive fermentations by using a carbon dioxide (CO₂) flow rate. The method offers an alternative to traditional cooling methods, such as water-based plate heat exchangers, which can be inefficient in distilleries located in hot regions. A mathematical model was developed and used to find the optimal CO₂ flow rate to maintain constant the broth temperature in simulated fermentations at 30, 32, and 34 °C. The results showed that using multiple CO₂ flow rates over an 8-hour stripping period could effectively reduce temperature deviations from the set-point while minimizing the total amount of CO₂ used. However, finding the optimal combination of flow rates becomes computationally expensive as the stripping period is split in a greater number of time subintervals. A comprehensive study was carried out to assess the adequate number of time subintervals to keep the broth temperature constant. Experimental fermentation carried out at 34 °C using eight-time subintervals confirmed the accuracy of the model's predictions. A temperature deviation of less than 0.5 °C from the set-point highlights the potential of extractive fermentation for controlling temperature and offers insights to enhance process efficiency.