Elsevier

Chemical Engineering Journal

Volume 314, 15 April 2017, Pages 311-319
Chemical Engineering Journal

Improving the pollutant removal efficiency of packed-bed plasma reactors incorporating ferroelectric components

https://doi.org/10.1016/j.cej.2016.11.065Get rights and content

Highlights

  • Pollutant removal is investigated using packed-bed dielectric barrier plasmas.

  • Electrode size and ferroelectric material design influence the removal efficiency.

  • Addition of a ferroelectric plate enhances the process efficiency.

  • Results are discussed in terms of the electrical performance of the reactors.

Abstract

In this work we have studied the plasma removal of air contaminants such as methane, chloroform, toluene and acetone in two parallel plate packed-bed dielectric barrier discharge (DBD) reactors of different sizes. Removal and energy efficiencies have been determined as a function of the residence time of the contaminated air within the reactor, the kind of packed-bed material (ferroelectrics or classical dielectric materials), the frequency and the incorporation of a ferroelectric plate onto the active electrode together with the inter-electrode ferroelectric pellets filling the gap. Results at low frequency with the small reactor and the ferroelectric plate showed an enhancement in energy efficiency (e.g., it was multiplied by a factor of six and three for toluene and chloroform, respectively) and in removal yield (e.g., it increased from 22% to 52% for chloroform and from 15% to 21% for methane). Such enhancements have been attributed to the higher energy of plasma electrons and a lower reactor capacitance found for this plate-modified configuration. A careful analysis of reaction efficiencies and electron energy distributions for the different investigated conditions and the simulation of the electric field at the necks between ferroelectric/dielectric pellets complete the present study. Overall, the obtained results prove the critical role of the barrier architecture and operating conditions for an enhanced performance of pollution removal processes using DBD systems.

Introduction

One of the most common applications of dielectric barrier discharge (DBD) plasmas is the decomposition removal of gaseous pollutants [1], [2], [3], [4]. A great number of works have been published about the use of these plasma discharges for the removal of volatile organic compounds (VOCs) present in the air as a result of different industrial and in-door activities [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. However, although a large variety of reactor set-ups and working conditions have been proposed to maximize the efficiency of these processes [19], [20], [21], [22], [23], most studies have addressed the kinetics of the removal process and paid little attention to the analysis of the plasma, the electrical operation parameters or the effect of the reactor configuration. Common working conditions in these works are a low concentration of pollutants in air, of the order of hundreds or, maximum, thousands ppms, and the pursuit of the full oxidation of VOCs to CO2 and H2O (and other fully oxidized sub-products if the pollutant contains heteroatoms) with no formation of intermediate hazardous molecules.

Advanced arrangements of DBD reactors for gas reaction processes such as the reforming of hydrocarbons, CO2 conversion or the synthesis of ammonia incorporate a ferroelectric moderator between the metallic electrodes [24], [25], [26], [27], [28]. This design is advantageous with respect to classical configurations incorporating dielectric materials because the operating voltages can be smaller [29], [30] and high plasma currents can be maintained for relatively large separation gaps between electrodes [31], [32]. Among other factors, these improvements could be linked with the substantial amount of electrons that, emitted by polarized ferroelectric materials [33], [34], may contribute to increase the plasma current and to decrease the breakdown voltage. In this work we have used pellets of lead zirconate titanate (PZT), a rather seldom ferroelectric material when dealing with plasma DBD reactors. The study presents a fundamental study about the design of DBD reactors and the effect of ferroelectric materials on their performance for the abatement of VOCs and other hazardous gases like methane in air. For this purpose, a series of ferroelectric packed bed reactors with a parallel electrode configuration (most geometrical configurations in the literature use a cylindrical geometry and a two coaxial electrodes system [12], [15], [16]) have been used to test the influence of the electrode area (i.e., size of the reactor) and the effect of incorporating a ferroelectric plate together with the ferroelectric pellets filling the inter-electrode space. Although ferroelectric plates incorporated onto DBD electrodes have been demonstrated to be quite effective in reducing the ignition voltage in surface discharge plasmas [35], to our knowledge their incorporation together with pellets in a packed-bed reactor has not been intended up to now. This unprecedented trial has effectively demonstrated that these kinds of mixed barriers render more efficient the packed-bed reactors. Besides analyzing the influence of the ferroelectric material distribution within the reactor, we have also studied the effect of reactant flow and other working parameters on the process efficiency. Finally, a comprehensive study of the electrical response of the reactor, both theoretically by means of the COMSOL software [36] and experimentally through the determination of the average electron energy and system capacitance, has allowed us to correlate the efficiency of the decontamination processes with the architecture of the ferroelectric barrier and other operating parameters. Such an analysis has provided important clues to understand the system behavior and the possibilities for improvement and extrapolation to other reactor configurations. We think that the obtained results can be relevant to design more efficient packed-bed plasma reactors through the adjustment of the average energy of plasma electrons to values higher than the threshold required to effectively oxidize organic pollutant compounds in air.

Section snippets

Materials and methods

According to Fig. 1(a), the reactors utilized for the present investigation have a parallel plate configuration with a fixed gap space of 3 mm. The inter-electrode space was filled with quasi-spherical pellets of PZT (lead zirconate titanate) with 1.25 mm of average diameter that were synthesized in our laboratory according to a complex process described in detail in [26] and that involves the sintering and sieving of pellets. The relative dielectric constant of PZT is approximately 1900 (APC

Results and discussion

Safety of decomposition products, energy consumption and removal efficiency are three major concerns by the construction and operation of DBD reactors intended for decontamination purposes [1], [2], [3], [4], [18], [19], [23]. In this regard, incorporation of catalysts in the packed bed is a general strategy in order to favor the total oxidation of organic pollutants [5], [11], [24]. Since in the present study no significant traces of other byproducts apart from CO2 and H2O could be detected in

Conclusions

The previous results and discussion have shown that packed bed parallel plate DBD reactors are quite efficient for the removal of VOCs and other contaminants (results are shown for acetone, toluene, chloroform or methane) in air. They have also proved that a parallel plate design permits to assess the effect of increasing the active discharge area, and therefore the reactor size, without affecting other working parameters such as distance between electrodes or gas flow distribution. In this

Acknowledgments

This work has been carried out thank to the financial support of the Junta de Andalucía (project P12-FQM-2265) and EU social founds MINECO-CSIC (project RECUPERA 2020). One of the authors, A. Gómez-Ramírez acknowledges financial support from MINECO (Spain) through the “Formación Postdoctoral 2013”.

References (65)

  • E.M. Bourim et al.

    Creep behavior of undoped and La–Nb codoped PZT based micro-piezoactuators for microoptical modulator applications

    Sensor. Actuators A-Phys.

    (2009)
  • K.-S. Shin et al.

    Sensitivity enhancement of bead-based electrochemical impedance spectroscopy (BEIS) biosensor by electric field-focusing in microwells

    Biosens. Bioelectron.

    (2016)
  • U. Kogelschatz

    Dielectric-barrier discharges: their history, discharge physics, and industrial applications

    Plasma Chem. Plasma Process.

    (2003)
  • H. Kim

    Nonthermal plasma processing for air-pollution control: a historical review, current issues, and future prospects

    Plasma Process. Polym.

    (2004)
  • T. Zhu

    VOCs removal using the synergy technology basing on nonthermal plasma technology

  • M. Bahri et al.

    Plasma-based indoor air cleaning technologies: the state of the art-review

    Clean – Soil Air Water

    (2014)
  • M.P. Cal et al.

    Destruction of benzene with non-thermal plasma in dielectric barrier discharge reactors

    Environ. Prog. Sustainable Energy

    (2001)
  • A. Ogata et al.

    Methane decomposition in a barium titanate packed-bed nonthermal plasma reactor

    Plasma Chem. Plasma Process.

    (1998)
  • C. Fitzsimons et al.

    The chemistry of dichloromethane destruction in atmospheric-pressure gas streams by a dielectric packed-bed plasma reactor

    J. Phys. Chem. A

    (2000)
  • Y. Li et al.

    Removal of volatile organic compounds (VOCs) at room temperature using dielectric barrier discharge and plasma-catalysis

    Plasma Chem. Plasma Process.

    (2014)
  • L. Jiang et al.

    Conversion characteristics and production evaluation of styrene/o-xylene mixtures removed by DBD pretreatment

    J. Environ. Res. Public Health

    (2015)
  • C.W. Parka et al.

    Susceptibility constants of airborne bacteria to dielectric barrier discharge for antibacterial performance evaluation

    J. Hazard. Mater.

    (2013)
  • T. Kuwahara et al.

    Odor removal characteristics of a laminated film-electrode packed-bed nonthermal plasma reactor

    Sensors

    (2011)
  • T. Matsumoto et al.

    Non-thermal plasma technic for air pollution control

  • A.M. Harling et al.

    Industrial scale destruction of environmental pollutants using a novel plasma reactor

    Ind. Eng. Chem. Res.

    (2008)
  • A.A. Assadi et al.

    Treatment of gaseous effluents by using surface discharge plasma in continuous reactors: process modelling and simulation

    Can. J. Chem. Eng.

    (2015)
  • K. Takaki et al.

    Effect of electrode shape in dielectric barrier discharge plasma reactor for NOx removals

    IEEE International Conference on Plasma Science

    (2003)
  • G. Xiao et al.

    Non-thermal plasmas for VOCs abatement

    Plasma Chem. Plasma Process.

    (2014)
  • F. Holzer et al.

    Influence of ferroelectric materials and catalysts on the performance of non-thermal plasma (NTP) for the removal of air pollutants

    Plasma Chem. Plasma Process.

    (2005)
  • A.M. Montoro de Damas et al.

    Plasma reforming of methane in a tunable ferroelectric packed-bed dielectric barrier discharge reactor

    J. Power Sources

    (2015)
  • A. Gómez-Ramírez et al.

    Efficient synthesis of ammonia from N2 and H2 alone in a ferroelectric packed-bed DBD reactor

    Plasma Sources Sci. Technol.

    (2015)
  • D. Mei et al.

    Plasma-assisted conversion of CO2 in a dielectric barrier discharge reactor: understanding the effect of packing materials

    Plasma Sources Sci. Technol.

    (2015)
  • Cited by (30)

    • Morphology-modulated rambutan-like hollow NiO catalyst for plasma-coupled benzene removal: Enriched O species and synergistic effects

      2023, Separation and Purification Technology
      Citation Excerpt :

      On the other hand, the introduction of catalysts into DBD affects the plasma discharge. There have been many studies on the catalyst properties such as volume, dielectric, and electrical conductivity [29,46–49]. Still, it is unclear how different morphologies of the same catalyst affect the plasma.

    • Plasma-coupled catalysis in VOCs removal and CO<inf>2</inf> conversion: Efficiency enhancement and synergistic mechanism

      2022, Catalysis Communications
      Citation Excerpt :

      As catalytic material, ferroelectric material can demonstrate a more unique role in plasma catalysis because of its spontaneous polarization in the electric field to increase the local microscopic discharge and electric field strength. The introduction of ferroelectric LiNbO3 can effectively enhance the efficiency of plasma VOCs removal, such as methane and chloroform [84], and it was found that the ferroelectrics significantly influenced the shape of the current-voltage Lissajous figure, effectively reducing the capacitance of the reactor. It may be related to the large number of electrons emitted by the polarized ferroelectric material, which helps to increase the plasma current and reduce the breakdown voltage [85].

    • Non-thermal plasma coupled with catalysis for VOCs abatement: A review

      2021, Process Safety and Environmental Protection
      Citation Excerpt :

      Reactive radicals form during plasma discharge, can easily break carbon-chlorine bonds (4.11 eV), and then initiate the oxidation process; therefore, decomposition in NTP offers a safe and environmentally solution. As summarized in Table 5, researchers have proposed the use of NTP combined with catalytic treatment for chlorine-containing VOCs (Gomez-Ramirez et al., 2017; Shahna et al., 2017; Chang and Lee, 2004). Not only that NTP-catalysis technology can solve the bottleneck in the application of current single technology but also the synergy between NTP-catalysis and biotechnology will greatly improve the removal load and operational stability of current biological treatment system to VOCs with low water solubility and biodegradability.

    • Non-thermal plasma in honeycomb catalyst for the high-throughput removal of dilute styrene from air

      2021, Journal of Environmental Chemical Engineering
      Citation Excerpt :

      The decomposition efficiency of VOCs using NTP with catalysts mainly depends on the reactor configuration and the type of catalysts. Several types of NTP reactor configurations, such as corona discharge [1,26], dielectric barrier discharge (DBD) [5,22,27–29], surface discharge [23,30,31], and gliding arc discharge [32,33], are available for processing VOCs. Each one of these configurations has its advantages and disadvantages.

    View all citing articles on Scopus
    1

    These authors contributed equally.

    View full text