Reaction Eng

Topics: Chemical reaction, Chemical engineering, Chemistry Pages: 2 (386 words) Published: December 13, 2012
Reaction Engineering
CGC035 / CGC052

Problem Sheet 3 - Fluid-fluid reactions

1. The reaction rate for the heterogeneous reaction A(g) + B(l)→ products is second order according to the expression -rA=kCACB and it is relatively slow compared to mass transfer so it takes place in the bulk of the liquid. Combine the following rate expressions for diffusion through the gas and liquid films, -rA=kAga(pA-pAi) and -rA=kAlaCAi-CA, with Henry’s law pAi=HACAi and the reaction rate equation given above, to eliminate the pressure and concentration at the interface (pAi and CAi) and to prove that the final rate expression for the overall rate of the process is -rA=pA1kAga+HAkAla+HAkCB

-rA=kAga(pA-pAi) (1)
-rA=kAlaCAi-CA, (2)
pAi=HACAi (3)
-rA=kCACB (4)

From (1) -rA=kAgapA-pAi=kAgapA-kAgapAi
-rA=kAgapA-kAgapAi=kAgapA-kAgaHACAi (5)
From (2) if we solve for CAi
-rA=kAlaCAi-kAlaCA and
CAi=-rA+kAlaCAkAla (6)
We substitute (6) in (5)
-rA=kAgapA+rAkAgaHAkAla-kAgaHACA (7)

From (4)
-rA=kCACB→CA=-rAkCB (8)
We substitute (8) in (7)


2. Combine the following relationships for mass transfer through the gas and liquid films with Henry’s law NA=kAgpA-pAi, NA=KAgpA-pA*
to show that the overall coefficient for mass transfer is given by the expression 1KAl=1HAkAg+1kAl


NA=KAlCA*-CA (1)


3. Consider the reaction A(g) + B(l) → products, described by the reaction rate equation -rA=kpACB. Sketch the pressure and concentration profiles for the...
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