Page 163 - Modelling in Transport Phenomena A Conceptual Approach
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5.3. RATE OF GENERATION IN MASS TRANSPORT 143
where c, is the initial total molar concentration.
When more than one reaction takes place in a reactor, Eq. (5.3-10) takes the
(5.3-19)
where
nij = number of moles of ith species in the jth reaction
nij, = initial number of moles of ith species in the jth reaction
aij = stoichiometric coefficient of ith species in the jth reaction
~j = extent of the jth reaction
Summation of Eq. (5.3-19) over all reactions taking place in a reactor gives
(5.3-21)
Example 5.4 The following two reactions occur simultaneously in a batch reac-
tor:
C2H6 = C2H4 + H2
C2Hs + H2 = 2CH4
A mixture of 85 mol % C2Hs and 15% anerts is fed into a reactor and the reactions
proceed until 25% C2H4 and 5% CH4 are formed. Determine the percentage of each
species in a reacting mixture.
Solution
Basis: 1 mole of a reacting mixture
Let ~1 and ~2 be the extents of the first and second reactions, respectively. Then,
the number of moles of each species can be expressed as
nCzH6 = 0.85 - - €2
nCzH4 = El
nH2 = €1 - EP
ncH, = 2E2
ninert = 0.15
The total number of moles, nT, is
nT=l+El