Question

Nitrogen (N2) and hydrogen (H2) gases are fed to a reactor in stoichiometric quantities to react to form ammonia (NH3). The reactor is operated to achieve a fractional nitrogen conversion of 0.25. The exit stream from the reactor is fed to a separator, which separates unreacted nitrogen and hydrogen from the ammonia. (a) Draw and label a PFD for the process described above. [10%] (b) Write down a balanced stoichiometric equation for the reaction. [5%] (c) If the feed is stoichiometric, show that the mole fraction of nitrogen in the feed stream is 0.25. [5%] (d) Show that the mole ratio of nitrogen gas to hydrogen gas, in all streams containing both of these gases, is the same as in the feed stream. [5%] (e) Assuming a basis of 100 tonne/day of ammonia production, determine the molar flow rates (moles/day) and the compositions (expressed in mole fractions) of all process streams. [40%] (f) Express the composition of the exit gas stream from the reactor in terms of mass fractions. [10%] (g) The single-pass mode of operation described above is very wasteful of the feed gases. To achieve the same ammonia production rate, an alternative process is suggested, in which the exit gas from the separator is mixed with a feed stream (again, consisting of a stoichiometric mixture of N2 and H2), such that the feed to the reactor is the same as for the original process. (i) Draw and label a PFD of the new process. (ii) Determine the new mass feed rate to the process. Comment briefly on the result. [25%]

Answer 1