Abstract
A coupled plasma-catalytic system (CPCS) for the conversion of toluene was investigated and compared to the homogeneous system of gliding discharge plasma. Toluene was used as a model compound, which is present in tars. The study was carried out at atmospheric pressure, in a gas composition similar to the one obtained during pyrolysis of biomass. The effect of the initial toluene concentration, energy supplied to gliding discharge (GD) and the presence of a catalyst on the conversion of toluene was studied. Both the composition of outlet gas and its calorific value were monitored. Based on the obtained results it can be concluded that the conversion of toluene increases with the increase of gliding discharge power. The highest toluene conversion (89%) was received in the coupled plasma-catalytic system (catalyst: RANG-19PR) under the following conditions: CO (0.13 mol. fr.), CO2 (0.12 mol. fr.), H2 (0.25 mol. fr.), N2 (0.50 mol. fr.) and 4400 ppm of toluene with a gas flow rate of 1000 Nl/h. The composition of the outlet gas in the homogeneous system and in the CPCS changed in the range of a few percents. Toluene levels were reduced tenfold. Benzene, C3 and C4 hydrocarbons, as well as acetylene, ethylene and ethane, were detected in the outlet stream in trace amounts. Carbon deposits were present in the reactor. The products of methanation of carbon oxides were detected in the both studied systems. A mechanism of toluene decomposition in the CPCS was proposed. The application of the catalyst brought about an increase in the calorific value of the outlet gas. It was above the minimal level demanded by engines and turbines.
Highlights
Biomass is currently considered the most promising source of renewable energy
On the basis of the obtained results, it has been found that the gliding discharge is an effective technique for the decomposition of toluene in the pyrolysis gases with low toluene concentrations
The presence of Ni + NiO/Al2O3 (RANG19PR) in the plasma zone increased the conversion of toluene and methanation of carbon oxides
Summary
The conversion of toluene has been investigated in a homogeneous plasma system and a CPCS21 All of these studies show that high temperature is required and none of them led to the development of an effective method of purification of the gas after pyrolysis, which is beneficial on an industrial scale. The investigation of the CPCS of gliding discharge with a spherical, commercial nickel catalyst (RANG 19PR), allowing to operate at lower temperatures with a high toluene conversion, is beneficial and can be considered for an industrial scale. P – discharge power [kW] W – calorific value [MJ/m3] Qp – the heat of combustion [kJ/m3] a – molar fraction The morphology of the catalyst’s surface was tested using Quanta 3D FEG (Thermo Fisher Scientific) scanning electron microscope equipped with detectors of secondary (SE) and backscattered (Zcont) electrons and an Apollo X energy dispersive x-ray spectrometer (EDAX). The X-ray diffraction (XRD) analysis was carried out with a Seifert 3003 diffractometer using CuKα radiation
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