Consider the absorption of carbon dioxide (CO_2) into a 20-in deep stagnant laye

Question

Consider the absorption of carbon dioxide (CO_2) into a 20-in deep stagnant layer of a liquid solution of monoethanolamine (MEA). CO_2 reacts with MEA following a first order reaction, r = k_1 CO_2, where k_1 = 1.30 middot 10^-5 1/s. a) Draw the CO_2 concentration profile in the liquid b) Calculate the Hatta number c) Calculate the absorption rate per unit area. Data: Molecular weight of CO_2, M_CO2 44 g/mol Solubility of CO_2 in MEA at 1 atm and 25 degree C is 2.50 mol/liter Diffusivity of CO_2 in the liquid at 25 degree C is 7.0 middot 10^-9 m^2/s

Explanation / Answer

Answer for a.

For drawing concentration profile of a gas we need concentration of gas in the liquid at different prsssure points at a given temperature. With the given data it's not possible to draw a profile graph against parameters in two different phases such as gas pressure and liquid concentration.

Answer for b.

Hatta number compares the rate of reaction in a liquid film to the rate of diffusion through the film.

= rate of reaction / rate of diffusion

Accordingly

rate of reaction, r = k [CO2]

where k = equilibrium constant; = 1.30 x 10-5 1/s

[CO2] = concentration of CO2 . = 2.5 mol/liter

     r = 1.30 x 10-5 [2.5] mol/liter/s

      = 3.25 x 10-5 mol/liter/s

Diffusivity of CO2 in the liquid at 25 oC = 7.0 x 10-9 m2/s

Hatta number = 3.25 x 10-5 / 7.0 x 10-9

                       = 0.4642 x 104      

Hatta number = 4642

                            

                        

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