The mass balances for batch distillation are somewhat different from those for continuous distillation. In batch distillation we are more interested in the total amounts of bottoms and distillate collected than in the rates. For a binary batch distillation, mass balances around the entire system for the entire operation time are
The feed into the column is F kg moles of mole fraction xF of the more volatile component. The final moles in the reboiler at the end of the batch is Wfinal ...