Question

what is the purpose of the trap that is used during a vacuum distillation performed with an aspirator?

Answer 1

Vacuum distillation is simply distillation at pressures below one atmosphere. Reduced pressure permits vaporization at reduced temperatures. For example, at atmospheric pressure water boils at 100°C, but under vacuum this boiling point can drop to 57°C or lower. This has two distinct advantages:

1. Thermal decomposition and degradation of the fluid and its additives are avoided.

2. The energy requirement for both heating and cooling is reduced.

The role of trap comes here, as under vaccume the boiling points of components decrease, and low boiling components are present in gaseous form. Under such condition there is a chance that these gases can directly enter to the aspirator which is maintaining the low pressure of the system. So, a trap, kept at low temperature (using ice or liquid nitrogen) condences (traps) these low boiling components either in liquid or solid form in it and does not allow these to go into aspirator.