please help Hydrogen Cyanide gas is to be absorbed into an aqueous sulphuric aci

Question

please help

Hydrogen Cyanide gas is to be absorbed into an aqueous sulphuric acid solution at 2 bar. The overall gas-side mass transfer coefficient is 0.7 mol.m^-2.s^-1 and the liquid film mass transfer coefficient is 0.1 mol.m^-2.s^-1. The Henry's law constant for this system is 40 Pa.m^3.kmol^-1. If the molar volume of the liquid is 1.8 times 10^-2 m^3.kmol^-1, find the gas film mass transfer coefficient and comment on the controlling mass transfer resistance, and determine the overall liquid-side mass transfer coefficient

Explanation / Answer

Dear Student,

the overall mass transfer coefficients Ky and Kx are measured on the basis of the gas phase or the liquid phase. The entire two-phase mass transfer effect can then be measured in terms of gas phase molar fraction driving force asoverall liquid phase mass transfer coefficient (Kx)

NA= Ky(yAG-y*A)...........1

where, Ky is based on the overall driving force for the gas phase, in mole/m2.s and *A y is the value of concentration in the gas phase that would be in the equilibrium with xAL. Similarly, the entire two-phase mass transfer effect can then be measured in terms of liquid phase molar fraction driving force as:

NA= KX(X*A-XAL)

where Kx is based on the overall driving force for the liquid phase, in mole/m2.s and *A x is the value of concentration in the liquid phase that would be in the equilibrium with yAG. A relation between the overall coefficients and the individual mass transfer film coefficients can be obtained when the equilibrium relation is
linear as yAL=mxAL. The linear equilibrium condition can be obtained at the low concentrations, where Henry’s law is applicable. Here the proportionality constant m is defined as m= H/P. Utilizing the relationship,yAL=mxAL , gas and liquid phase concentrations can be related by

y*A= mxAL and yAG= mx*A

Rearranging Equation (1), one can get

1/Ky=(yAG-y*A)/NA.....................2

From geometry, (yAG-y*A) can be written as

yAG-y*A=(yAG-yAL)+(yAL-y*A)..........3

Substituting Equation 3 in Equation 2

1/Ky=(yAG-y*A)/NA=(yAG-yAL)/NA+(yAL-y*A)/NA=(yAG-yAL)/NA+m(xA-xAL)/NA

therefore, 1/Ky=1/ky+m/kx

Similarly the relation of overall liquid phase mass transfer coefficient (Kx) to the
individual film coefficients can be derived as follows:

1/Kx=1/mkx+1/kx

The following relationships between the mass transfer resistances can be made is
Resistance in gas phase/Total resistance in both phases=1/Ky / 1/ky

Resistance in liquid phase/Total resistance in both phases=1/Kx / 1/kx

n be measured in terms of gas phase molar fraction driving force asoverall liquid phase mass transfer coefficient (Kx)

NA= KY(yAG-y*A)

where, Ky is based on the overall driving force for the gas phase, in mole/m2.s and *A y is the value of concentration in the gas phase that would be in the equilibrium with xAL. Similarly, the entire two-phase mass transfer effect can then be measured in terms of liquid phase molar fraction driving force as:

NA= KX(X*A-XAL)

Ky= KG P=>0.7x

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