Question

Question 5. Carbon dioxide (CO2) gas is absorbed into water in a packed tower. The CO2 mass transfer coefficient on the gas side, given in terms of pressure, is 9.3 x 10-6 mol/(mas Pa) The CO2 mass transfer coefficient on the liquid side, given in terms of mole fraction, is 1.2 mol/(ms). The Henry's law constant is 7.6 x 106 Pa for CO2. (a) Write down expressions describing the flux of CO2 to the gas/liquid interface from (i) the gas side, and (ii) the liquid side. [4 marks) Write down the two boundary conditions that occur at the gas/liquid interface. [2 marks] (b) (c) Use your answers to (a) and (b) to demonstrate that the overall mass transfer coefficient (K) is given by the expression: 11. H кk, k, where: kp is the gas phase mass transfer coefficient kx is the liquid phase mass transfer coefficient His Henry's law constant [8 marks) (d) The overall gas-side mass transfer coefficient (KG) is given by: 1.1.H Ko ke k and the overall liquid-side mass transfer coefficient (Kx) is given by: 1.1.1 к конк, (i) To what limit does the overall gas-side mass transfer coefficient approach when then gas is very soluble in the liquid phase? [3 marks] QUESTION CONTINUES OVERLEAF

Answer 1

Chemical Engineering Given that Gas side, mass Transfer Coefficient = 9.3x10-6 od m.s. Pa liquid side, mass Transfer coefficient = 1.2 mol mes Henry's law Content = 7.6 X 166 Pa Ca) 03 Gas side flux (NA) = KG CPA, - PA₂) KG = gas side, m.tc. based on pressure so, here INA = 9.3x10 6 (PA, - PA2) liquid side flux (NA) = K (NA - HA₂) mole Ka = liquid side, mit.c. based on fraction NA= 1-2 (20,- HA) » Interface YAL Boundary Conditions 6 at the interface Hai > HAI (2) In the beelk fluid liquid ges seni MAD YA > Yai HAb and ni? Gas film You = gas phate concentrechin at Tveterphase SALT mi liquid prose concentretin at Interphase in bulk liquid film in bulk VA:

lets asseme that igas phave more tradton Cano) - Mole fraution in liquid pharse which is in equllikssum with bulle more faction in gas phase which is in equilitsium with bull liquiel Phase more freation (AA) So, flux by ges phase NA = Kp (YA-YAI) flux by liquid phase NA = Kage (Nai - Hom) Yar = HAL Plus by overall mass transfer coefficknt NA = K (YAL-YA We know that " YA - Alt - The SAL-YA VA SA & H.NA Kg L It H K kp koge > kp Cd) Overall mass Transfer coefficient of gas Phouse I. tt H KG if gas is highly soluble in the liquid than -Hao ku It Hro kp Kn KG Ky=ke kp