Germanium tetrachloride (GeC14) and silicon tetrachloride (SiC14) are used in the production of optical fibers. Both chlorides
Question:
Germanium tetrachloride (GeC14) and silicon tetrachloride (SiC14) are used in the production of optical fibers. Both chlorides are oxidized at high temperature and converted to glasslike particles. However, the GeC14 oxidation is quite incomplete and it is necessary to scrub the unreacted GeC14 from its air carrier in a packed column operating at 25°C and 1 atm with a dilute caustic solution. At these conditions, the dissolved GeC14 has no vapor pressure and mass transfer is controlled by the gas phase. Thus, the equilibrium curve is a straight line of zero slope. Why? The entering gas is 23,850 kg/day of air containing 288 kg/day of GeC14. The air also contains 540 kg/day of C12, which, when dissolved, also will have no vapor pressure. The two liquid-phase reactions are
It is desired to absorb 99% of both GeC14 and C12 in an existing 2-ft-diameter column that is packed to a height of 10 ft with 1/2-in. ceramic Raschig rings. The liquid rate should be set so that the column operates at 75% of flooding. For the packing: є = 0.63, Fp = 580 ft-1, and Dp = 0.01774 m. Gas-phase mass-transfer coefficients for GeC14 and C12 can be estimated from the following empirical equations developed from experimental studies, where μ, ρ, and Di are gas-phase properties:
where
S = column cross sectional area, m2
ky = kmol/m2-s
V = molar gas rate, kmol/s
Dp = equivalent packing diameter, m
μ = gas viscosity, kg/m-s
ρ = gas density, kg/m3
Nsc = Schmidt number = μ/ρ Di
Di = molecular diffusivity of component i in the gas, m2/s
a = interfacial area for mass transfer, m2/m3 of packing
L = liquid mass velocity, kg/m2-s
V' = gas mass velocity, kg/m2-s
For the two diffusing species, take
Determine:
(a) The dilute caustic flow rate in kilograms per second.
(b) The required packed height in feet based on the controlling species (GeC14 or Cl2). Is the 10 ft of packing adequate?
(c) The percent absorption of GeC14 and C12 based on the available 10 ft of packing. If the 10 ft of packing is not sufficient, select an alternative packing that is adequate.
Step by Step Answer:
a Determine entering dilute caustic flow rate from the 75 of flooding specification using the flooding curve of Fig with the correction factors of Fig...View the full answer
