Coking pseudo-steady-state

As illustrated in Fig. 1, the activated carbon displays the highest conversion and selectivity among all the catalysts during the initial reaction period, however, its catalytic activity continues to decrease during the reaction, which is probably caused by coke deposition in the micropores. By contrast, the reaction over the CNF composites treated in air and HN03 can reach a pseudo-steady state after about 200 min. Similiar transient state is also observed on the CNFs and the untreated composite. Table 3 collects the kinetic results after 300 min on stream over catalysts tested for the ODE, in which the activity is referred to the BET surface area. The air-treated composite gives the highest conversion and styrene selectivity at steady state. 

A pseudo steady-state for the reversible coke is reached at the end of the first point in the experiments (after about 5 hours). The last assumption leads to the following equation ... 

Masamune and Smith [25] applied the approach used by Froment and BischofT [12] to the situation discussed here. If the rate of coke formation is small compared to the rate of the main reaction, a pseudo steady state may be assumed and the following continuity equations for A and the coke may be written, provided the reaction is irreversible and of the first order and the particle is isothermal ... 

In Eq. 5.3.d-l it has again been assumed, in accordance with the pseudo-steady-state hypothesis, that the amount of A involved in the coking reaction is small. Also, the effective diffusivity is presumed to be unaffected by the coke formation. deactivation function, assumed to be described by... 

---