An elementary reaction with stoichiometric A + 2B rightarrow 3 R what is the rat

Question

An elementary reaction with stoichiometric A + 2B rightarrow 3 R what is the rate expression for r_A, r_B and how r_A, r_B and r_R are related? Remember to account for the signs, + or In a CSTR bioreactor it is observed that the zero-order rate constant for a pollutant removal (k) was 3 mug/IL-min. What water retention time would be required to reduce the concentration from 1 mg/L in the influent to half of its initial value in the effluent of a reactor? What would be the retention time if the bioreactor was a PFR reactor? 6

Explanation / Answer

since it is elementary reaction A+2B---------->3R

-dCA/dt= -dCB/2dt = dCR/3dt

where 1, 2 and 3 are coefficients of A, B and R

-rA= K1[A] [B]2

-rA= -rB/2 = rC/3, rA, rB and rC are rate of reactions with respect to A, B and C

2. for a PFR and for zero order reaction, CA= CAO-KT

where T= retention time, CAO= initial concentration and CA= concentration at the given time

K= rate constant = 3ug/L.min =3*0.001 ug/L.min=0.003 ug/L.min

given CA= CAO/2

CA= 1/2 =0.5

hence 0.5= 1- 0.001*T

T= 0.5/0.001 = 500 min

for CSTR, T= CAOXA/-rA = CAOXA/K= (CAO*0.5/K)= 0.5/K=0.5/0.001= 500min

for zero order reaction, retention time is indepdent of type of reactor.

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