What are the methods to lower the boiling point of materials?
Thread Content
What are the methods to lower the boiling point of a substance? Besides reducing pressure, what other methods exist?
According to the phase rule, for a pure substance at the coexistence of vapor and liquid phases, it has 1 degree of freedom, meaning that only one of temperature and pressure can vary; the saturated vapor pressure at a given boiling point is also fixed. Therefore, there is no other way to change the boiling point except by altering the pressure. For multi-component mixtures, the boiling point can be changed by altering the composition of the mixture.
To correct that, for multi-component mixtures it is more accurately the bubble point, rather than the boiling point, unless an azeotrope is formed.
Reply to 3# yezi20081202: In other words, when the concentration of the mixture changes, the partial pressure changes as well, and thus its boiling point also changes, right?
Reply to 3# yezi20081202: The temperature at which the first bubble appears when the temperature is increased under certain pressure is known as the bubble point temperature of the mixture. When the molar fractions of the relatively light components and the relatively heavy components in the original solution are different, the bubble point temperature also differs. If the molar fraction of the light component is high, the bubble point temperature is low; otherwise, it is high.
If it is not possible to reduce the pressure while still wishing to lower the boiling point (more precisely, the operating temperature during vaporization), the method of introducing non-condensable gas can be employed.
Reply to 6# cl6119: That’s good. Introducing non-condensable gas actually means changing the composition of the substance, that is, increasing the concentration of the light components.
Use the method of adding an azeotrope; its boiling point is lower than that of the substance.
Reply to 7# yezi20081202: Introducing non-condensable gas into the system results in a corresponding decrease in the partial pressures of each component, under the condition that the total pressure remains constant; the effect is identical to that of reducing the operating pressure. Since non-condensable gases do not condense into a liquid phase, this is different from increasing the content of light components; in such cases, the distillation process essentially turns into a stripping process. This allows the operating temperature to be reduced, but it requires an additional gas circulation system. This is also a method used for the distillation separation of heat-sensitive materials.
Introducing non-condensable gas means using a carrier gas to increase the evaporation rate.
On the 9th floor, then introducing non-condensable gas might make operation more difficult, as it can easily lead to excessively high tower pressure