Granular activated carbon impregnated with sulfur is used to remove mercury vapor from natural gas and from air. Because chemical reaction converts the mercury to mercuric sulfide, the adsorption is irreversible, and the capacity is as high as 20 weight percent. 

(a) Assuming that the adsorption rate for removal of mercury from air is controlled by external mass transfer, calculate the overall coefficient for a

bed of 4 x 6-mesh carbon at 20°C and a superficial velocity of 75 cm/s. 

(b) If the inlet concentration is 10 μg/Nm³ (micrograms per normal cubic meter, with the gas volume evaluated at standard conditions) and the treated gas must contain less than 10^-3 μg/Nm. what is the minimum bed length? 

(c) For a bed 50 cm deep, what is the predicted time to breakthrough?