Hydrogen sulfide (H₂S) is to be removed from natural gas by absorption into amine solutions in a process known as natural gas sweetening. Experiments were done to measure the rate of absorption of pure H₂S at 30°C and 1 atm absolute pressure in a laminar liquid jet apparatus using either water or an aqueous solution containing 1.0 × 10^-3 mol/cm³ of an amine. The jet is 5 cm long and has a dimeter of 0.1 cm. The liquid flow rate is 4.0 cm³/s. H2S reacts with the amine according to the reaction:

The reaction is essentially infinitely fast and the physical solubility of H₂S in water and in the amine solution is 8.0 × 10^-5 mol/cm³ atm. The rate of absorption of H₂S was determined to be 0.14 cm³/s for the water jet and 1.5 cm³/s for the amine jet. Based on these data:

(a) Determine the mass transfer coefficient and diffusivity of H₂S in water.

(b) Determine the enhancement factor for absorption in the amine solution and the diffusivity of the amine.

(c) Suppose that the results are used to predict the rate of absorption in a gas-absorption column operated at 10 atm absolute pressure and 30°C at a point where the mole fraction of H₂S in the gas phase is 0.01, the amine concentration in the liquid is 1.0 × 10^-3 mol/cm³, and the liquid-side and gas-side mass transfer coefficients are  = 6.0 × 10^-4 mol/cm³ sand  = 1.5 × 10^-3 mol/cm³ s, respectively. What is the rate of absorption in mol/cm³ s for these conditions if the gas-side resistance is neglected?
What is the rate of absorption in mol/cm³ s for these conditions if the gas-side resistance is considered?

Transcribed Image Text:

ak