4. A hydrogenation reactor converts benzaldehyde (B) to benzyl alcohol (A) by bubbling
hydrogen gas through the liquid reagents in the presence of a catalyst. The reaction is:
C7H6O (�) + H2 (�) → C7H8O (�)
However, it is possible for the reaction to proceed too far. Additional hydrogenation of
benzaldehyde produces toluene (T) and water instead, as shown in the reaction below:
C7H6O (�) + 2H2 (�) → C7H8 (�) + H2O (�)
The reactor has two feeds: a liquid stream and a gas stream. The liquid feed is 110 mol/s of pure B
at 180 °C. The gas stream is pure H2 at 25 °C, and is fed at 0.15 mol H2/mol B fed. All H2 is consumed
in the reactor, and the reactor outlet contains 2.00 mol% H2O. The reactor outlet is entirely liquid,
and it is maintained at 100 °C.
The reactor is cooled by H2O in a jacket around the reactor (the cooling H2O never contacts the
reactor contents directly, and may be considered an inert species). The water enters as a liquid at
90 °C, 1 bar absolute and it exits as a vapor at 160 °C, 1 bar absolute.
a) The standard heat of formation for liquid benzyl alcohol is not given in Table B.1. To
determine this quantity:
i) write the balanced reaction for the complete combustion of liquid benzyl alcohol, noting
the phases of all products and reactants
ii) Use Hess’s Law to calculate ΔĤf,°A(l) from tabulated values of ΔĤc° and ΔĤf° in table B.1
b) Calculate the molar flow rate of each component in the reactor outlet in mol/s
c) Calculate the required flow rate of cooling H2O in kg/s. Assume that the heat capacity of
liquid B and C is the same value as the heat capacity of liquid T.
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