Separation units often use membranes, absorbers, and other...

Separation units often use membranes, absorbers, and other devices to reduce the mole fraction of selected constituents in gaseous mixtures. Consider a mixture of hydrocarbons that consists of 60 percent (by volume) methane, 30 percent ethane, and 10 percent propane. After passing through a separator, the mole fraction of the propane is reduced to 1 percent. The mixture pressure before and after the separation is $100 \mathrm{kPa}$. Determine the change in the partial pressures of all the constituents in the mixture.

Key Concepts

Gas Separation Processes

Gas separation processes, including methods like membrane separation and absorption, are techniques that alter the composition of gas mixtures by selectively reducing the concentration of certain components. The understanding of how changes in mole fractions influence partial pressures is fundamental in designing and analyzing these separation units.

Dalton's Law of Partial Pressures

Dalton's law states that the total pressure of a mixture of non-reacting gases is equal to the sum of their individual partial pressures. This principle allows one to determine how changes in the mole fraction of any constituent of the mixture, such as through a separation process, directly affect its partial pressure.

Mole Fraction

Mole fraction is the ratio of the number of moles of a given component to the total number of moles in a mixture. It is a dimensionless quantity that helps in quantifying the composition of a mixture and is crucial for determining the properties of each component when the system parameters, like total pressure, are known.

Partial Pressure

Partial pressure is the pressure that each gas in a mixture would exert if it occupied the entire volume by itself at the same temperature. It is calculated by multiplying the mole fraction of a component by the total pressure of the mixture, following Dalton’s law of partial pressures.

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