CHEMICAL ENGINEERING

264 CHEMICAL ENGINEERING VOLUME 1 SOLUTIONS

Henry’s law constant,KD 1. 08 ð 106 ,where:KDP/X.

Also:PD760 mm Hg

XDMol fraction in liquid

XD 760 / 1. 08 ð 106

 D 7. 037 ð 10 ^4 kmol CO 2 kmol solution (³per kmol water)

Water molar densityD 1000 / 18

 kmol/m^3

and: CAsD 7. 037 ð 10 ^4

(

1000

18

)

D 0 .0391 kmol/m^3

WhenyD0, then: NA 0 D 1. 204 ð 10 ^7 kmol/m^2 s.

WhenyD1 mm, then: NAD 4. 38 ð 10 ^9 kmol/m^2 s.

PROBLEM 10.36

Experiments are carried out at atmospheric pressure on the absorption into water of

ammonia from a mixture of hydrogen and nitrogen, both of which may be taken as

insoluble in the water. For a constant mole fraction of 0.05 of ammonia, it is found that

the absorption rate is 25 per cent higher when the molar ratio of hydrogen to nitrogen is

changed from 1 : 1 to 4 : 1. Is this result consistent with the assumption of a steady-state

gas-film controlled process and, if not, what suggestions have you to make to account for

the discrepancy?

Neglect the partial pressure attributable to ammonia in the bulk solution.

Diffusivity of ammonia in hydrogenD 52 ð 10 ^6 m^2 /s

Diffusivity of ammonia in nitrogenD 23 ð 10 ^6 m^2 /s

Solution

Using Maxwell’s Law for mass transfer ofAinBthen:

dPA

dy

DFCACBuAuB (equation 10.77)

or: RTÐ

dCA

dy

DFCACBN^0 A/CAN^0 B/CB

For an absorption processN^0 BD0 and:



dCA

dy

DN^0 A

FCB

RT

i