Abstract
The paper reports the occurrence of multiple steady-state zones in most of the constructions of fixed-bed photocatalytic reactors. Such a phenomenon has not been ever observed in a field of photocatalytic reactors. The simulation has been provided for a common case in a photocatalysis—the degradation of colored compounds. The mathematical model of the photocatalytic reactor with immobilized bed has been stated by a simple ideal mixing model (analogous to the CSTR model). The solution has been continued by the two parameters—the Damköhler number and the absorption coefficient related to the inlet stream concentration. Some branches of steady states include the limit point. The performed two-parametric continuation of the limit point showed the cusp bifurcation point. Besides the numerical simulation, the physical explanation of the observed phenomenon has been provided; the multiple steady-states occurrence is controlled by light absorption–reaction rate junction. When the reaction rate is limited by the light absorption, we can say that a light barrier occurs. The dynamical simulations show that when the process is operated in a field of multiple steady states, the overall reactor efficiency is related to the reactor set-up mode.
Highlights
Colored Compounds Degradation.Photocatalytic wastewater treatment is developed as a low-cost, environmentally friendly process which provides non-selective oxidation of water impurities
It is expected that multiple steady states may occur in photocatalytic reactors
Only significantly high light absorption results in occurrence in the multiple steady states appear in the fixed-bed photocatalytic reactors
Summary
The multiple steady states are one of the phenomena which is present in many cases of chemical reactors and it can affect the process efficiency. Case may be illustrated by the adiabatic reactor, where the multiple steady states may be related to both hydrodynamics of the reactor and the heat exchanger, which provides the proper heat transfer conditions [18]. Photocatalysis is a heterogeneous process that is related to the light incident on the catalyst surface For such many reasons, it is expected that multiple steady states may occur in photocatalytic reactors. In the second part I presented the simple multiple steady-states analysis where the liquid stream inside the reactor is only partially mixed in the axial direction This simulation is simple, in order to clearly illustrate that such a phenomenon may be applied in the real case
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