29.16 Ozone gas (O3, solute A) dissolved in high-purity water is commonly used in wet cleaning processes associated with

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29 16 Ozone Gas O3 Solute A Dissolved In High Purity Water Is Commonly Used In Wet Cleaning Processes Associated With 1 (134.57 KiB) Viewed 21 times

29.16 Ozone gas (O3, solute A) dissolved in high-purity water is commonly used in wet cleaning processes associated with semiconductor device fabrication. It is desired to produce a liquid water stream containing 3.0 gmole 03/m³ (238 mg/L) by a process that does not create any gas bubbles. One engineer's idea is show in the figure below. Liquid water containing 1.0 gmole O3/m³ enters a well-mixed tank at a volumetric flow rate 0.050 m³/h. A pressurized gas mixture of O3 diluted in inert N₂ is continuously added to the headspace of the tank at a total pressure of 1.5 atm. Both the liquid and gas inside the tank are assumed to be well mixed. The gas-liquid surface area inside the tank is 4.0 m². The process is maintained at 20°C. At 20°C, the solution density is 992.3 kg/m³. For a well-mixed, non-bubbled ozonation tank, the appropriate film mass-transfer coefficients for the liquid and gas films are k = 3.0 x 106 m/s and kc = 5.0 x 103 m/s, respectively. Equilibrium distribution data for O3 gas dissolved in water at 20°C follows Henry's law, with H=68.2 m³.atm/kgmole based on the definition pai= H · Cali - N₂+O3 GAS gas IN well-mixed Water + dissolved O3 IN V = 0.05 m³/h CALD 1.0 gmole/m³ Closed Tank P= 1.5 atm PA=? Absorption AL 1000 N₂+O₂0000 gas OUT 60000 Water + dissolved Og OUT LIQUID = 0.05 m³/h CAL= 3.0 gmole/m³ a. What are m, and the Henry's law constant H in units of atm? Is O3 very soluble in water? m = 2510; H = 3760 atm b. What is the overall mass-transfer coefficient KG, based on the overall gas-phase driving force? KG = 4.40 x 10.8 kgmole/(m². s. atm) C. What is the overall mass-transfer coefficient KL, based on the overall liquid-phase driving force? KL 3.00 x 10-6 m/s
C. What is the overall mass-transfer coefficient KL, based on the overall liquid-phase driving force? KL 3.00 x 10-6 m/s d. For the process to operate as intended, what are the required partial pressure (pA) and mole fraction (y) of ozone (O3) in the gas phase inside the tank? As part of your solution, develop a material balance model in algebraic form for solute A that contains the following terms: Vo, volumetric flow rate of liquid (m³/hr); CALO, inlet concentration of solute A in liquid (gmole A/m³); CAL, outlet concentration of solute A in liquid (gmole 03/m³); KG, overall mass-transfer coefficient based on gas-phase driving force (gmole/m² s atm); p^, partial pressure of O3 in bulk gas phase (atm); H, Henry's law constant for O3 between gas and liquid (m³ atm/gmole); S, surface area for interphase mass transfer (m²). What is the total transfer rate of O3, WA? e. WA 2.78 x 10-5 gmole/s f. Is the mass-transfer process gas film controlling, liquid film controlling, or neither? Comment on the relative contributions of the film mass-transfer coefficients and the equilibrium distribution relationship on the controlling mass-transfer resistance.