Question

A mixture of propionic and n-butyric acids, which can be assumes to form ideal solutions, is to be separated by distillation a distillate containing 95 mol% propionic acid and a bottoms of 98 mol% n-butyric acid. Determine the type of condenser and estimate the distillation operating pressure. The normal boiling point for propionic acid is 141 C and n-butyric is 163.5 C.

Answer 1

Distillation of ideal solutions is carried out by fractional method or fractional distillation is used to separate ideal solutions. To carry out fractional distillation air or Vigreux condenser is used, as it slows down the rate of rising of hot vaporsand gives better distillation. The distillation temperature is decided by the cooling utility of the overhead condenser. It can be made more clear with one example, if cooling water is at 30 degree C. then taking 5 eg. C approach we will set dew point at 35 deg. C and we will calculate the pressure corresponding to that dew point and this pressure will be distillation pressure. Similarly, if we will be having a chilled water say at 10 deg. C. in that case we will find distillation pressure corresponding to 15 deg. C. dew point. So, that means operating pressure depends on the temperature of the coloumn and the temp used for cooling from which we will calculate dew point of the component and hence operating distillation pressure.