Page 128 - Plant design and economics for chemical engineers

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104 PLANT DESIGN AND ECONOMICS FOR CHEMICAL ENGINEERS

shows that the logarithm of the amount adsorbed is linear with the function T/V
[log&,/f)] where T is the temperature in K, V is the molar volume of liquid at the
normal boiling point in cm3/g mole, f, is the saturated fugacity (approximate as the
vapor pressure), and f is the fugacity of the vapor (approximate as the partial
pressure). Data for the adsorption of dichloropropane on a selected charcoal are as
follows:

Amount adsorbed T/Vtlog,o(f,/f)l
(cm&/l00 gcharcoaJ (units as given)
1 21
10 11

ff a respirator contains 100 g of this charcoal and breakthrough occurs when 82
percent of the adsorbent is saturated, how long can the respirator be used in a
dichloropropane concentration of 750 ppm when the temperature is 80“~? Assume
that the flow rate of contaminated air through the adsorbent is 45 l/min. The molar
volume of the dichloropropane may be assumed to be 100 cm3/g mole.
8. Determine which of the following liquids used in the laboratory could form flammable
air-vapor mixtures if spilled in a storage cabinet and allowed to reach equilibrium.

acetone ethyl ether
benzene methyl alcohol
carbon disulfide n-pentane

What type of fire extinguishers would be appropriate if a small spill is ignited? Note
that if equilibrium is not attained, the vapor concentrations will be lower than
calculated and a flammable air-vapor mixture could be present.
9. Estimate the flash-point of acetone and compare it with the experimental value given
in the literature. Hint: Start with the basic principle that the fugacity in the vapor
phase must equal that in the liquid phase. The lower flammable limit for acetone is
2.55 percent by volume.
10. The flash-point of a liquid mixture can be estimated by determining the temperature
at which the equilibrium concentration of the flammable vapors in the air reach a
concentration such that C(y,/LFL,) = 1.0 where yi is the vapor phase mole percent
of component i and LFLi is the lower flammability limit concentration of component
i expressed in mole percent. Estimate the flash-point of a liquid mixture containing
50 mol% n-octane and 50 mol% n-nonane. The LFL values for n-octane and
n-nonane are 1.0 and 0.8 percent by volume.
11. A number of accidents have occurred as a result of the discharge of static electricity.
The latter can be generated even by the flow of fluids. To provide additional
protection against explosion or fire due to the discharge of static electricity, deter-
mine what temperature an acetone drum filling operation would have to maintain SO
that flammable mixtures would not be produced by vapor-air mixtures in equilibrium
with the liquids. The lower flammable limit (LFL) for acetone vapor in air is 2.55
percent by volume.