Unformatted text preview: he crucial quantity!
selectivity Why? ChE
ChE 400 - Reactive Process Engineering Selectivity: Complications… L11-5
L11- Selectivity: SB = N B − N B ,0 νB ⋅ νA
N A − N A,0 Definition ambiguous if product formed from more than one reactant!
Example: Andrussov process (HCN synthesis)
Conversions of methane and ammonia can be very different. Extent to which
reaction proceeds via (2) or (3) rather than (1) will be different. Hence:
SHCN,CH4 ≠ SHCN,NH3 Selectivity needs a reference point!
Selectivity needs a reference point! ChE
ChE 400 - Reactive Process Engineering Si: even more problems… L11-6
L11- Selectivity: SB = What if I don’t know the reaction equations (hence no νi!) ?
(Often the case for very complex reactant mixtures, networks of many parallel and
(Simplified) Example: Methane Coupling
2 CH4 + 1/2 O2 <=> C2H6 + H2O
CH4 + 2 O2 => CO2 + 2 H2O (1)
(2) Assume equal amounts of methane rea...
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