Industrial production of ethanol requires fermentation using Saccharomyces cerev
ID: 899365 • Letter: I
Question
Industrial production of ethanol requires fermentation using Saccharomyces cerevisiae, a type of yeast. The element formula of S. cerevisiae is CH1.83O0.56N0.17. Suppose you want to produce ethanol (C2H6O) in a batch process at 25.0 C. You plan to add 0.25 lbm NH3 and 5.0 lbm glucose to the yeast for the following (unbalanced) reaction:
C6H12O6(s) + NH3(g) C3H8O3(l) + C2H6O(l) +CH1.83O0.56N0.17(s) + CO2(g) + H2O(l)
Note that 1.0 mol glucose produces 0.50 mol glycerol and that the ratio of NH3 to H2O is 1:1. During preparation, you accidentally add too much glucose. However, you decide to let the bioreactor run anyway. After the reaction goes to completion (at least one of the starting reactants is used up), you discover that 1.4 lbm ethanol had been produced. How much heat had been produced and subsequently removed from the system? How much glucose did you initially add to the reactor? Assume that the heat of combustion of S. cerevisiae is -21.2 kJ/g.
Explanation / Answer
C6H12O6(s) + NH3(g) C3H8O3(l) + C2H6O(l) + CH1.83O0.56N0.17(s) + CO2(g) + H2O(l)
mass of ethanol = 1.4 lbm = 635 gram
FIRST BALANCE THE REACTION ACCORDING TO GIVEN INFO IN QUESTION
5.22C6H12O6(s)+NH3(g) 2.61C3H8O3(l)+5.34C2H6O(l)+5.88CH1.83O0.56N0.17(s)+6.95 CO2(g) + H2O(l)
From stiochiometry,
we have 635g of ethanol so total moles of ethanol = 635/46=13.8 moles
For 5.34 moles of ethanol, 5.88 moles of S. cerevisiae is formed,
for 1 moles of ethanol, 5.88/5.34 moles of S. cerevisiae is formed.
So for 13.8 moles of ethanol, we get moles S. cerevisiae = 13.8 x 5.88/5.34 =15.19 moles
the heat of combustion of S. cerevisiae is -21.2 kJ/g.
bY combustion of S. cerevisiae we can get heat =15.19 x 21.2x (molecular mass of S. cerevisiae ) KJ