4. Importance of product purity in chemical engineering

Synthesis of various chemicals usually is carried out in a reactor which may or may not be followed by separator. Either the case may be choice of design variable is very important. The market value of overhead product or the bottom product relies on its purity. Also the need of any further treatment for enhancing the purity relies on the initial product composition. In view of this, the degree of freedom for the column should be zero; that means the number of variables should be the same or equal to the number of equations involved in modeling. For example for a distillation column, if a designer specifies reflux ratio or boil up ratio and a distillate rate, then there will be corresponding unique set of distillate and bottom composition with respect to a fixed feed flow rate.
