ERT 316 CHEMICAL REACTION

ENGINEERING

MULTIPLE REACTIONSBy Noor Amirah Abdul Halim

TYPE OF REACTIONS Parallel reactions

Series reactions

Complex reactions (parallel and series reactions)

Independent reactions

DESIRED & UNDESIRED REACTION

Selectivity : the ratio of (reaction rate/mol/flowrate) of desired product to the (reaction rate/mol/flowrate) of undesired product

Instantaneous selectivity Overall selectivity

Instantaneous yield Overall yield

SELECTIVITY & YIELDS

Yield : the ratio of (reaction rate/mol/flowrate) of desired product formed to the (reaction rate/mol/flowrate) the reactant either fed or consumed

Batch

flow

DESIGN EQUATION FOR REACTORS INVOLVING MULTIPLE REACTIONS

reaction rate (r j) is a NET rate of reactions

USE only molar flow rate (Fj) and concentration (Cj)DO NOT USE conversion (xj)

DO NOT USE stoichiometry table to relate change in CB and change in CA

MODIFICATION OF THE ALGORITHM FOR MULTIPLE REACTION

PARALLEL REACTIONS

Selectivity for single reactant system

Thus,

Consider some of reactor operating scenarios to maximize

the selectivity ( SD/U (max) )

Need high CA to favor D production ( to increase selectivity)

CA ~ SD/U

CA will always start at high value

CA in a perfectly mixed CSTR is always at its lowest value

Need low CA to favor D production ( to increase selectivity)

CA ~ SD/U

CA in a perfectly mixed CSTR is always at its lowest value

So, CA cannot be used as operating parameters to maximize the selectivity

Thus the solution is:

recallThus, to achieve high selectivity:

E = Activation Energy

* higher energy requires higher temperature

Selectivity for two reactant system

For high SD/U, maintain

both CA and CB as high as possible

For high SD/U, maintain

high CA and low CB

For high SD/U, maintain

both CA and CB as low as possible

For high SD/U, maintain low

CA and high CB