Abstract
The effect of forced periodic modulation of several input parameters on the rate of photocatalytic decomposition of formic acid over a TiO2 thin film catalyst has been investigated in a continuously stirred tank reactor. The kinetic model was adopted based on the literature and it includes acid adsorption, desorption steps, the formation of photocatalytic active sites and decomposition of the adsorbed species over the active titania sites. A reactor model was developed that describes mass balances of reactive species. The analysis of the reactor was performed with a computer-aided nonlinear frequency response method. Initially, the effect of amplitude and frequency of four input parameters (flowrate, acid concentration, temperature and light intensity) were studied. All single inputs provided only a minor improvement, which did not exceed 4%. However, a modulation of two input parameters, inlet flowrate and the acid molar fraction, considerably improved the acid conversion from 80 to 96%. This is equivalent to a factor of two increase in residence time at steady-state operation at the same temperature and acid concentration.
Highlights
The direct conversion of the small molecules (CO2, CH4, formic acid, N2, etc.) using renewable energy may be realized using three possible approaches: electrocatalysis, photocatalysis and non-thermal plasma (NTP), a limited amount of data still exist for the comparison of all three alternative pathways in terms of conversion and energy efficiency
We present a system of equations describing the continuously stirred tank reactor (CSTR) reactor coupled with the kinetics for formic acid decomposition outlined in Section 2, which gives a nonlinear system in relation to its inputs
The nonlinear frequency response (NFR) method is used to analyse the potential for improving the performance of a continuous photocatalytic reactor by forced periodic modulations
Summary
The direct conversion of the small molecules (CO2 , CH4 , formic acid, N2 , etc.) using renewable energy may be realized using three possible approaches: electrocatalysis, photocatalysis and non-thermal plasma (NTP), a limited amount of data still exist for the comparison of all three alternative pathways in terms of conversion and energy efficiency. By embedding ferromagnetic nanodomains in the catalyst support and inducing radiofrequency heating, the composite catalysts allow very fast heating and cooling rates in structured chemical reactors [12] This allows for the periodic modulation of temperature in chemical reactors that could lead to significant improvement in reactant conversion and selectivity, introducing a further element to improve the catalytic performance over stationary conditions [13]. This paper utilizes a nonlinear frequency response (NFR) method for analysis of the reactor performance in a reaction of photocatalytic decomposition of formic acid over a titania thin film catalyst.
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