Biochemical Reactions

This problem is an example of ASPEN property methods being used to model biochemical systems, specifically a fermentation process, in order to analyze the effectiveness of ASPEN in modeling such a system. The system to be modeled is a fermentation process used to make kombucha, specifically the aerobic growth of yeast on glucose. The specific biochemical system is given below:

C₆H₁₂O₆ + 3O₂ + 0.48NH₃ -> 0.48C₆H₁₀NO₃ + 4.32H₂O + 3.12CO₂

where C₆H₁₂O₆ represents glucose and C₆H₁₂NO₃ represents yeast cells (BP: 365.8 °C, 144.15 g/mol). The reaction rate depends on the concentrations of glucose and yeast, with k=0.7 and E=0. The fermentation vessel is kept at 70 °F and 0.1 L per day is added to the vessel to achieve 1 L by the end of 10 days. The following initial mole fractions are assumed: 0.01 mole fraction yeast, 0.2 mole fraction NH₃, 0.56 mole fraction O₂, and 0.23 mole fraction glucose.

The goal of this problem is to use the NRTL property method in order to produce a molar composition plot of the reactants inside the fermentation vessel over time, and suggest a time based on this plot to let the vessel sit before removing the products for kombucha production. The composition plot is given below:

Based on the plot, the reaction reaches equilibrium at approximately 24 hours as the composition is constant over time after this point. However, the actual recommended time for this fermentation reaction is 10-14 days. This indicates that the current method of using NRTL to model this reaction is not a sufficient method to model this reaction realistically. It is not realistic due to the fact that NRTL is an oversimplified model of this biochemical system, which in reality, is far more complex than the chemical reaction given above. This illustrates the limitations of the NRTL property method as well as the limitations of ASPEN to model biochemical systems under the current assumptions. More notes related to this problem is given below: