Question

MASS TRANSFER QUESTION. DO NOT COMMENT CHEMICAL ENGINEERING. IF YOU DONT KNOW IT DONT COMMENT. READ PROBLEM CAREFULLY, AND DRAW DIAGRAM WITH EVERY STEP AND UNIT CONVERSIONS! DO PART A,B, &C.

1-propanol diffuses across a liquid water film in a distillation tower. The temperature is 25 degrees Celsius. The film is 10mm thick and the mole fractions of propanol on either side are 0.020 and 0.0505. The molar density of the film is 55.0 kmol/m^3, and the diffusivity of 1-propanol in water at 25 degrees Celsius is 0.87 * 10^-9 m^2/s

a. Draw a diagram of the system, label it, and draw the flux.

b. Do we have EMD (eqimolar counter diffusion) or UMD (unimolecular diffusion) ? How do we know?

c. Find the fluxes of water and propanol, relative to the bulk flow and to stationary coordinates, at both edges of the film.

Please show every single step and all work! and correct unit conversions! Thank you!

Answer 1

c. Diffusivity of 1-propanol in water = 0.87 x 10^-9 m²/s

                                                                                                    

where

            D_AB = molecular diffusivity of A in B

            P_t= total pressure of system

            R = universal gas constant

            T = temperature of system in absolute scale

            z = distance between two planes across the direction of diffusion

            p_A1 = partial pressure of A at plane 1, and

            p_A2 = partial pressure of A at plane 2

D_AB= 0.87 x 10^-9 m²/s; P_t = 1 atm = 1.01325x10⁵ N/m²; T = 25°C = 298 K;

z = 10 mm = 0.002 m; p_A1 = 0.02x1 = 0.02 atm; p_A2 = 0.0505x1 = 0.0505 atm

When we substitute the values in the above equation we get the solution.

Substituting these in (1.6), we get,

= 4.55x10 ^–5 kmol/m ².sec