Yeast converts glucose to ethanol according to the following reaction:

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The fermentation in a stirred tank reactor (STR) is run in batch mode at 32 C. The reactor has a total volume of 50 L and is filled up to 2/3 of the height. A 60% (w/v) solution of glucose and water are available to prepare the feed medium of 40% (w/v) glucose. The pump rate for the 60% (w/v) glucose solution (density: 1.1 g cm-3 ) is 0.2 kg s -1 and the pump rate for water (density: 1 g cm-3 ) is 3 kg min-1 . 2.2 kg of glucose are not consumed.

The fermenter is inoculated with yeast to an initial biomass concentration of 2 g L-1 . After fermentation, the mass percent of yeast is 8 %. It is assumed that 1 kg glucose was taken up per 1 kg yeast. It is assumed that inoculation and growth do not change the volume of the fermentation broth.

1) Draw the flow sheet of the fermenter and the corresponding streams.

2) What is the filling volume of the tank? How much water and glucose solution (60% w/v) is needed and how long does it take to fill the reactor if (i) one or (ii) two pumps can be used?

3) Create a table for the mass balance of the fermentation. Give the general mass balance equation. Calculate the missing values [kg] for all components.

i) What is the total mass in the STR after filling?

ii) What is the generated mass of yeast?

iii) How much glucose is consumed?

iv) How much ethanol and carbon dioxide are produced?

4) Determine the theoretical and observed yield of ethanol from glucose.

5) Assuming an ideal gas and standard conditions (0C, 1 atm), what is the volume of the resulting carbon dioxide?