Mechanisms of Toluene Removal in Relation to the Main Components of Biosyngas in a Catalytic Nonthermal Plasma Process

Abstract

In this study, a packed-bed dielectric barrier discharge (DBD) reactor was built for the removal of biomass gasification tar. Two kinds of packing materials, glass pellets and a Ni/γ-Al2O3 catalyst, were employed for the plasma alone process and the plasma catalytic process, respectively. Toluene was used as the tar surrogate, and five typical gas combinations, N2, N2+CO2, N2+CO2+CO, N2+CO+H2 and simulated gasification gas (SGG), were selected as carrier gases. The effects of the main components of the gasification gas on toluene removal under plasma and/or catalysis treatment were studied. The results indicated that the highest removal efficiency in the plasma alone process was achieved in the N2 atmosphere, and the addition of H2, CO or CO2 to the N2 led to a decrease in the removal performance. When Ni/γ-Al2O3 was introduced into the plasma process, the best removal efficiency was obtained in the N2+CO2 atmosphere. However, the positive effect of CO2 on toluene removal switched to a negative effect when CO2 coexists with CO and H2 in the gas mixture. In addition, both the terminating effect at low temperature and the occurrence of methanation induced by CO at high temperature could significantly inhibit the removal of toluene in the plasma catalytic process. Typically, in the SGG atmosphere, the highest toluene removal efficiencies under plasma alone, catalysis alone and plasma catalysis treatment were 33.5%, 38.6% and 92.5%, respectively. Furthermore, no CN-containing or O-containing compounds were identified as major byproducts in the plasma catalytic process, which is significantly different from what was observed in the plasma alone process. Moreover, a detailed mechanism of the toluene removal under plasma and plasma catalysis treatment was proposed after analysis of gas and liquid products.

Tar Removal by Nanosecond Pulsed Dielectric Barrier Discharge

“…Discharge pulse characteristics makes SEI values achieved in this work much higher than in non-thermal plasma systems used by other researchers. Here SEI is in the range 35-7542 J/L whereas Nair et al [7] obtained 500 J/L in the pulsed corona discharge reactor, Xu et al [42] reached 768 J/L in the packed-bed DBD reactor, and Mei et al [43] used 972 J/L in the gliding arc discharge reactor. Such a big difference can give the impression that a lot of energy is lost in the nanosecond pulsed DBD reactor.…”

“…However, neither O nor H radicals are leading in the tar decomposition reactions. Due to the large amount of nitrogen molecules in the simulated producer gas the main reactions are those with N 2 (A 3 ) excited molecules [40,42]. Unfortunately, in such a complex mixture as the biomass producer gas, there are many processes that are competitive to useful reactions with excited nitrogen molecules, O and H radicals.…”

Coupled Plasma-Catalytic System with Rang 19pr Catalyst for Conversion of Tar

“…Moreover, other gases present in a gas mixture may be also excited or dissociated by electron impact (reactions 4–6) 26 :…”

“…However, 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 new articles concerning a plasma-catalytic decomposition of tar in synthetic gas after pyrolysis or steam reforming of tar were published 22–26 . In these studies, gliding discharge (GD) or dielectric barrier discharge (DBD) reactors were used.…”

Evaluating the Performance of a Ni Catalyst Supported on La2O3-MgAl2O4 for Dry Reforming of Methane in a Packed Bed Dielectric Barrier Discharge Plasma Reactor

“…In the last two decades, carbon capture, sequestration, and utilization (CCSU) are being practiced to minimize GHG emissions. , Among all, recycling of GHGs, namely, CO 2 and CH 4 , into valuable chemicals is an attractive approach to mitigate GHG emissions. However, both CO 2 and CH 4 are stable molecules, requiring large energy input for conversion into other valuable fuels. , Dry reforming of methane (DRM) (eq ) is a process to convert CH 4 and CO 2 to syngas (H 2 , CO) and other valuable chemicals. − Among the known DRM technologies, the nonthermal plasma via catalytic dielectric barrier discharge (DBD) plasma process is feasible because of its simple design and suitability for upscaling. − Additional advantages of DBD plasma are easy handling, being operable at atmospheric pressure, moderate installation cost, and feed versatility. , Furthermore, the syngas (H 2 /CO) ratio in DRM using DBD plasma may achieve unity subject to the feed ratio. H 2 /CO above unity is a suitable feedstock for downstream chemicals via Fischer–Tropsch (FT) synthesis. , Despite the above-mentioned environmental and operational benefits DBD plasma DRM faces lower reactants conversion, H 2 /CO ratio below unity due to RWGS, and lower energy efficiency (EE) .…”