Stagewise Contacting and Transfer Units - Mass Transfer - Chemical Engineering Previous Year Questions

Water is used to absorb ammonia from a gas mixture in a single separation stage contactor. The process is schematically represented in the figure below.
The molar gas and liquid flow rates, and the inlet mole fractions are given in the figure. Both the liquid and the gas phases are well mixed, and the equilibrium relation between y and x is given by y* = x.
If the stage is ideal, then the value of y is

A crosscurrent cascade of N ideal stages is used to treat a feed stream of molar flow rate E. The feed stream contains a solute which is to be recovered by a pure solvent having a molar flow rate S. The solvent is divided equally between these N stages. The linear equilibrium curve relating the mole fractions x and y* of the solute in the raffinate and the extract respectively, is given by y* = m x. Assume dilute conditions. The ratio of the solute mole fraction in the original feed to that in the exit raffinate stream i.e. (\(x_N / x_o\)) is given by

In a countercurrent stripping operation using pure steam, the mole ratio of a solute in the liquid stream is reduced from 0.25 to 0.05. The liquid feed flowrate, on a solute-free basis, is 3 mol/s. The equilibrium line for the system is given in the figure below.
The MINIMUM flowrate of pure steam for this process, rounded to 1 decimal place, is ______ mol/s.

SO₂ from air is absorbed by pure water in a counter current packed column operating at constant pressure. The compositions and the flow rates of the streams are shown in the figure. In addition, use the following data and assumptions: • Column operates under isothermal conditions • At the operating temperature of the column, \(y^* = 40x\), where \(y^*\) is the mole fraction of SO₂ in the gas that is in equilibrium with water containing SO₂ at a mole fraction of \(x\) • Solution is dilute and the operating line is linear • Negligible amount of water evaporates The number of transfer units (NTU) for this column is

In a solvent regeneration process, a gas is used to strip a solute from a liquid in a countercurrent packed tower operating under isothermal condition. Pure gas is used in this stripping operation. All solutions are dilute and Henry’s law, \(y* = mx\), is applicable. Here, \(y*\) is the mole fraction of the solute in the gas phase in equilibrium with the liquid phase of solute mole fraction \(x\), and \(m\) is the Henry’s law constant.

Let \(x_1\) be the mole fraction of the solute in the leaving liquid, and \(x_2\) be the mole fraction of solute in the entering liquid.

When the value of the ratio of the liquid-to-gas molar flow rates is equal to \(m\), the overall liquid phase Number of Transfer Units, \(NTU_{OL}\), is given by

A liquid \( L \) containing a dissolved gas \( S \) is stripped in a countercurrent operation using a pure carrier gas \( V \). The liquid phase inlet and outlet mole fractions of \( S \) are 0.1 and 0.01, respectively. The equilibrium distribution of \( S \) between \( V \) and \( L \) is governed by \( y_s = x_s \), where \( y_s \) and \( x_s \) are the mole fractions of \( S \) in \( V \) and \( L \), respectively. The molar feed rate of the carrier gas stream is twice as that of the liquid stream. Under dilute solution conditions, the minimum number of ideal stages required is __________ (in integer).

Gas containing 0.8 mol% component A is to be scrubbed with pure water in a packed bed column to reduce the concentration of A to 0.1 mol% in the exit gas. The inlet gas and water flow rates are 0.1 kmol/s and 3.0 kmol/s, respectively.
For the dilute system, both the operating and equilibrium curves are considered linear. If the slope of the equilibrium line is 24, the number of transfer units, based on the gas side, \(N_{OG}\) is ____ (rounded off to 1 decimal place).