A chemical plant produces an ammonia-rich waste gas that cannot be released as-i

Question

A chemical plant produces an ammonia-rich waste gas that cannot be released as-is into the environment. One method to reduce the ammonia concentration in the waste gas is to bubble the waste gas through a liquid solvent. Components of the gas that are highly soluble, like ammonia, will dissolve into the liquid phase. Water is an appropriate liquid solvent for this process. The chemical plant produces 110.0 m3/hr of waste gas (? = 0.0407 mol/L) initially having a mole fraction of 0.170 NH3, and wishes to remove 90.0% of the initial amount of NH3. The maximum concentration of ammonia in water at this temperature is 0.4500 mol NH3/ mol water. Neglect the absorption of other waste gas components into the water, and the evaporation of water into the waste gas stream.

What rate is NH3 is being removed from the feed gas?

What is the minimum flow rate of water (? = 0.990 g/mL) required to scrub out 90.0% of the incoming NH3?

What is the mole fraction of NH3 in the scrubbed waste gas stream?

Explanation / Answer

initial amount of NH3/hr=

110*1000 litres/hr=waste gas

110000*.407*.170=moles nh3 in gas=761.09 mol/hr

removed =.9*761.09=684.981 moles/hr of nh3 removed

flow rate of water required=

moles of water= 684.98/.45=1522.18 moles/hr=1522.18*18/.990/1000=27.676Litres/hr

mole fraction in scrubbed gas=

total moles in gas=110000*.407=44770

moles removed=648.981

left=44121.019

mole fraction=112.11/44121.019=.0025

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