A process for microbial synthesis of 1,3-propanediol is being developed for the manufacture of ‘green’ polyester fabric from renewable resources. Polyesters are also common polymers used in biomedical applications (i.e. scaffolds for tissue engineering and drug delivery systems). Under anaerobic conditions, a selected strain of Klebsiella pneumoniae converts glycerol (C3H8O3) to 1,3- propanediol (C3H8O2) and acetic acid (C2H4O2), with minimal formation of other fermentation products such as butyric acid, ethanol, and H2 gas. The fermentation and cell growth equation can be written as: 

68C3H8O3 + 3NH3--> 3C4H7O2N + 49 C3H8O2 + 15C2H4O2 + 15CO2 + 40H2O 

where C4H7O2N represents the biomass. 

A continuous fermenter is set up for 1,3-propanediol production at 37°C and atmospheric pressure. Anaerobic conditions are maintained by sparging the broth with nitrogen gas at a flow rate of 1000 litres min−1. The feed rate of medium into the fermenter is 1000 kg h−1; the medium contains ammonia and 14% w/w glycerol. The yield of 1,3-propanediol is strongly affected by glycerol concentration, which must be kept above a certain level to suppress the formation of undesired by- products. Accordingly, the fermentation process is designed so that the product stream contains an unreacted glycerol concentration of 3% w/w.

a. Draw the process flow diagram. Label the inputs and outputs, show the boundary condition.

b. determine the composition of each stream (inputs and product), total mass of each stream, and total mass of each component in each stream.

c. What is the volumetric flow rate (L/h) and composition (in vol %) of the off-gas?

d.  What minimum concentration of NH3 is needed in the feed stream (in wt %)?

e.  If the NH3 concentration from (g) is used, what is the concentration of 1,3-propanediol in the product stream?