Removal of n-Butyl Mercaptan Using Stripping with an Inert Gas: A Nonequilibrium Approach via Mass Balances

The stripping of n-butyl mercaptan (RSH) from neutral and alkaline aqueous solution with gaseous nitrogen is investigated at ambient temperature and pressure in a semibatch system. A model considering the dynamic state, the thiol mass balance, the effect of RSH dissociation, and the deviation from chemical equilibrium is developed and solved numerically. The assumption of chemical equilibrium between undissociated thiol and its ion (RS-) is valid at neutral pH, but at alkaline conditions, RS- (right arrow) RSH is the rate controlling step, with k = 5 × 10^-6 s^-1 at 301 K and pH 11.7. The effectiveness of inert gas stripping is mainly governed by thiolʹs hydrophobic nature and its neutral/ionic form speciation. At pH values below 8.5, thiol concentration falls in an exponential form, whereas at pH values above 10.5, it tends toward a linear form. The mass balance model is extremely sensitive to uncertainty in (gamma)( infinity), whereas k governs thiol emission rate out of the liquid system.