17.3.3 Technical questions

1. In what way operating the CSTR In liquid phase is beneficial ?

Ans: Liquids have higher mass transfer coefficients than solids. Therefore, if the reaction needs be facilitated with two components, if they are in liquid phases, then reactions could be faster. Therefore, pressure can play an important role in both altering the selectivity as well as conversion of the series reactions scheme.

2. Why ammonia + water needs to be separated from the second tower i.e., water separation tower ?

Ans: Ammonia dissolves instantaneously in water to form ammonia solution. This chemical affinity of ammonia is very difficult to get it through. On the other hand, despite using flash unit, some ammonia will remain the water consisting of ethanolamines and heavy ends. Therefore, the second water separation tower is required to remove once again ammonia + water from the solution.

3. Why vacuum is used in the second and third distillation towers ?

Ans: The diethanol and triethanolamines dissociate at high operating temperatures. Therefore, vacuum is used to reduce the operating temperature of the distillation columns (second and third).

4. What process modifications you can suggest for better operation ?

Ans: When higher quantitites of di or triethanolamine is desired, then the monoethanolamine can be sent to another reactor in which ethylene oxide is added. Its not advisable to recycle it the CSTR shown in the process flow sheet as it can form amino-ethers but not diethanolamine.

5. Can solvents (extraction) be used instead of vacuum distillation for the separation of di and triethanolamines ?

Ans: No, this is due to the reason that solvents tend to have similar solubility factors for both di and triethanolamines.

 

References:

1. Dryden C. E., Outlines of Chemical Technology, East-West Press, 2008

2. Kirk R. E., Othmer D. F., Encyclopedia of Chemical Technology, John Wiley and Sons, 1999-2012