Chemical Processes - Isoconversional Kinetics of Thermally Stimulated Processes - page 210

Fig. 4.36 The effective
activation energy of the
reversible thermal decom-
position of CaCO 3 increases
with increase in the pressure
of CO 2 . (Data from Zawadzki
and Bretsznajder [ 105 ])

3 &2 3D

The rate of the reverse reaction is also proportional to n (P), which is the amount of
C g adsorbed on B s at given pressure P:

(4.79)

vkSn P
2

= ( .

2

Then the overall rate of decomposition is:

(4.80)

vkSvvkSkSn P = = −= −

ef 121

( ,

2

where k ef is the effective rate constant of the overall process. At the equilibrium
pressure, P 0 , the rates of the forward and reverse reactions are equal so that:

(4.81)

kknP
1

= ( .

2 0

By substituting Eq. 4.81 into 4.80, they obtain:

(4.82)

k

ef =

k nP nP [( ) − ( )].

2 0

The dependence of the adsorbed amount on pressure can be expressed in the form
similar to the Freundlich isotherm [ 1 ]:

nP KP m

(4.83)

() = ,

where m is a fit parameter (0 < m ≤ 1) and K has a meaning of the adsorption equi-
librium constant, whose temperature dependence is defined by the van't Hoff equa-
tion:

− ∆ H

RT

ad

(4.84)

KL = exp ,