Question

Topic: Mass Transfer (Chemical or Mechanical Engineer)

Problem:

Ninety‐eight (96%) of carbon disulfide (CS2) is to be removed by absorption from a nitrogen stream entering at 297 [K], 747 [torr] and at a rate of 25 [mol/s]. The partial pressure of carbon disulfide in the incoming gaseous stream is 70 [torr]. Countercurrent absorption with a paraffinic oil, assume to be pure octadecane (C8H18) in a packed column will be used for this purpose. Octadecane and carbon disulfide conform an ideal solution and thus equilibrium is governed by Raoult’s law. The paraffinic oil enters the column at a rate equal to 1.4 times the minimum value.

Design data:

For Plastic Hiflow rings, 25 [mm]: (Fp=20 ft²/ft³, a = 117.1 [m²/m³], ε = 0.924, C_h=1.038 C_p= 0.327)

Use a flooding approach of 65% ( f =.65)

Physical properties:

The column will operate essentially at the gas inlet temperature and pressure. At these conditions, the oil viscosity is 4 [cP], its density is 810 [kg/m3], and its surface tension is 30 [dyne/cm]. The average molar mass of the oil is 0.254 [kg/mol]. The carbon disulfide vapor pressure is 346 [torr], its molar mass is 76.1 [g/mol], its diffusivity in nitrogen is 0.114 [cm2/s], and in the oil is 0.765×10–5 [cm2/s]. The gas viscosity is 1.7×10–5 [Pa∙s] (0.017[cP]). Nitrogen has a molar mass of 0.028 [kg/mol].

(a) The minimum liquid flow rate, in [mol/s].
(b) The mole fraction of the carbon disulfide in the exit streams.
(c) The liquid and gas flow rate at the bottom of the tower, in [kg/s].
(d) The column diameter, in [m].
(e) The total pressure drop, in [kPa].
(f) Mass‐transfer coefficients, in [mol/m2∙s] (gas) and [m/s] (liquid).
(g) Volumetric, mass‐transfer coefficients, in [mol/m3∙s] (gas) and [1/s] (liquid).