In distillation column design, the McCabe-Thiele procedure is inadequate and a Ponchan-Savarit procedure is needed, when

ANS:D - a total condenser is used.

When the latent heat of vaporization of the more and less volatile components in a distillation system are significantly different and a total condenser is used, it can present challenges in the design and operation of the distillation column. Here's an explanation:

1. Latent Heat of Vaporization Difference: The latent heat of vaporization is the amount of heat required to convert a unit mass of a liquid into vapor at a constant temperature. When the latent heat of vaporization of the more volatile and less volatile components in a mixture are greatly different, it means that one component requires significantly more energy to vaporize compared to the other component.
2. Total Condenser: In a distillation column with a total condenser, all the vapor leaving the top of the column is condensed back into liquid form. This results in a reflux ratio of 100%, meaning that all the condensed liquid is returned to the column as reflux.

When the latent heat of vaporization of the components is significantly different and a total condenser is used:

• The more volatile component, which typically has a lower latent heat of vaporization, tends to condense and reflux back into the column more readily.
• The less volatile component, with a higher latent heat of vaporization, may not condense as readily and may remain in the vapor phase longer before condensing.

As a result, the distillation column may experience issues such as:

• Reduced separation efficiency: The differences in the rates of condensation and vaporization can lead to less effective separation of the components, especially if the less volatile component tends to remain in the vapor phase for longer periods.
• Fluctuations in tray temperatures: The differences in latent heat of vaporization can cause fluctuations in tray temperatures along the column, affecting the equilibrium conditions and potentially leading to deviations from ideal separation behavior.
• Operating challenges: Designing and operating a distillation column under these conditions may require adjustments to operating parameters such as reflux ratio, column temperature profile, and tray design to achieve the desired separation efficiency.

In summary, when the latent heat of vaporization of the components in a distillation system is significantly different and a total condenser is used, it can complicate the design and operation of the distillation column, potentially leading to reduced separation efficiency and operational challenges.