Nonthermal Plasma Flow Research Articles

Nanoparticle dynamics in the spatial afterglows of nonthermal plasma synthesis reactors

Nonthermal plasma flow tube reactors are industrially scalable systems for the production of nanocrystal (NC) based materials and coatings. One key advantage of nonthermal plasma synthesis is the ability to both synthesize NCs and deposit films in a single reactor, as at the reactor outlet, NCs can be inertially deposited onto a target substrate. The size and morphology of deposited particles can substantially influence the film structure and function. Though NCs are typically near-spherical and monodispersed as-produced in plasma synthesis reactors, NC charge and growth dynamics can be altered substantially when NCs are sampled out of the plasma and through the spatial afterglow region, affecting deposition. Experiments have demonstrated changes of NC size and charge in the spatial afterglow; however, these dynamics remain unexplored and unexplained via theory and simulation. To address this, we developed a constant number Monte Carlo (CNMC) simulation model to examine the mechanisms of NC decharging and growth in the spatial afterglow of plasma flow tube reactors. Collisions between NC and plasma species, diffusive deposition, and electron desorption from NCs are incorporated in the CNMC simulation. The simulation results are specifically compared with previous experiments on Si NCs synthesized from a low pressure Ar-SiH4 nonthermal plasma reactor. The experiment-model comparison shows that CNMC models can be implemented which accurately model NC size distribution evolution in a spatial afterglow. Simultaneously, results show that improved collision models, energetic species diffusion models, and electron desorption models will be necessary to accurately depict NC dynamics in spatial afterglows.

Adsorbed CO2 Dissociation Using Argon and Helium Nonthermal Plasma Flows

In recent years, global warming has become a worldwide problem. Carbon dioxide (CO2) is one of the primary substances causing global warming, and its emission should be reduced. A promising technology is the conversion of CO2 to carbon monoxide (CO) using plasma treatment, so that the CO itself or its conversion to methane can be used as fuel for combustion engines. In this article, a CO2 dissociation or reduction treatment system using an adsorbent and nonthermal plasma (NTP) flow is investigated. To improve the conversion efficiency, the conversion efficiency for Ar or He plasma is evaluated. In the physical adsorption process, ∼10% CO2 gas with a flow rate of 10 L/min is prepared, and then, it is introduced into the flow channel; CO2 is adsorbed by the adsorbent. After the adsorption process, the circulation flow channel is set, and then, the Ar or He NTP flow is generated with a blower. As a result, the adsorbed CO2 is desorbed with CO2 concentrations of 20% and 23% by the Ar NTP flow and the He NTP flow, respectively. The CO2 conversion efficiency reaches 21%, and the energy efficiencies reach 13% and 10% with plasma in the cases using the Ar and He NTP flows, respectively. The energy efficiency with regard to CO is better with the Ar plasma, but more atomic carbon can be generated using the He plasma.

Oxidative Decomposition of Adsorbed Toluene Using Ozone Concentrated by Nonthermal Plasma Flow

Toluene decomposition is performed using an adsorbent and a nonthermal plasma (NTP) induced radical flow system that consists of a surface discharge and circulation flow. The liquid toluene is vaporized in the circulation channel connected to a blower and the surface discharge plasma reactor in series, and the toluene gas is adsorbed by the adsorbent. In order to accelerate the oxidative decomposition of the adsorbed toluene, two techniques are tested. In the first technique, concentrated ozone injection is utilized and the adsorbed toluene is decomposed using the NTP flow. This occurs after introducing the concentrated ozone in advance, through the bypass channel connected in parallel with the adsorbent. In the other technique, toluene decomposition occurs under the reduced pressure of the adsorbent chamber during the decomposition process, because accelerated toluene decomposition on the surface of the adsorbent is expected. This reduced pressure is in the range of −3 to −7 kPa and is achieved by regulating the ball valve located upstream of the adsorbent chamber. When the concentrated ozone is introduced into the circulation channel, the adsorbent temperature increases drastically and the conversion ratio of toluene to $\text{CO}_{x}$ (CO and CO2) increases by a factor of 2.0 in comparison with that without the concentrated ozone injection. In addition, the energy efficiency of the conversion increases by a factor of 1.9, even when the energy required for the concentrated ozone is included. However, there was no noticeable effect of the reduced pressure on the toluene decomposition under experimental conditions.

Determination of nanoparticle collision cross section distribution functions in low pressure plasma synthesis reactors via ion mobility spectrometry

Low pressure (<20 Torr) non-thermal plasma flow tube reactors are commonly used for the synthesis of high purity nanoparticles (NPs) via nucleation and subsequent growth from vapor phase precursors. In spite of their utility, process monitoring (i.e. output NP size characterization) in such reactors is difficult, as there is a dearth of techniques available for online NP size distribution function measurement. In this study, we developed and applied an ion mobility spectrometry (IMS) system consisting of a low pressure differential mobility analyzer (LPDMA) and electrical detector to determine the collision cross section distribution functions of Si NPs synthesized in a radio frequency non-thermal SiH4–Ar plasma operated at ∼2 Torr (266 Pa). The collision cross section, roughly proportional to projected area, is a parameter quantifying the size and structure of nanometer scale species in the vapor phase. We introduce the collision cross section distribution function as a metric for potential use in online process monitoring in NP synthesis. Proper inversion of the collision cross section distribution function requires a priori knowledge of the LPDMA transfer function. We utilized a tandem differential mobility analyzer approach, coupled with a Twomey–Markwoski based scheme to determine LPDMA transfer functions. Subsequent application of these transfer functions in collision cross section distribution function determination showed that at the outlet of the non-thermal plasma flow tube reactor, both negatively and positively charged Si NPs persisted with nearly identical collision cross section distribution functions. NPs were found to have mode ‘mobility equivalent’ diameters near 10 nm, and via TEM analysis were found to persist at the reactor outlet as small aggregates composed of ∼5 nm diameter primary particles. Size distribution functions inferred from collision cross section measurements were compared to size distribution functions inferred from TEM images; excellent agreements were found between IMS and TEM for both mean mobility equivalent diameter and distribution function width. In total, this study shows that (1) IMS is a viable approach for process monitoring in non-thermal plasma NP flow tube synthesis systems, (2) although NPs are modestly aggregated at low-pressure plasma reactor outlets, the extent of aggregation is considerably less than observed in most atmospheric pressure and equilibrium NP synthesis systems (e.g. flames), and (3) after exiting the plasma reactor, the decharging of NPs from highly negative charge levels to a bipolar charge distribution likely drives aggregation on the plasma boundary.

High-Efficiency Carbon Dioxide Reduction Using Nonthermal Plasma Desorption

We present a highly efficient carbon dioxide (CO2) reduction treatment technique using an adsorbent and nonthermal plasma flow at the laboratory scale. The plasma reactor consists of twelve surface discharge elements, which are energized by a 10-kHz bipolar pulsed high-voltage power supply. As an adsorbent, the molecular sieve zeolite 13X is used, and it is placed downstream of the plasma reactor. In the physical adsorption process, approximately 10% CO2 gas with flow rate 10 L/min is prepared by 99.5% CO2/N2 cylinder and a nitrogen cylinder. It is then introduced into the flow channel, and CO2 is adsorbed by the adsorbent. After the adsorption process, the circulation flow channel is set and the N2 plasma flow is generated with a blower. Consequently, CO2 adsorbed by the adsorbent is desorbed with higher concentration (currently ∼20%) and reduced to CO with high efficiency. The generated CO can be reused as a fuel. We evaluate the experimental results by calculating the conversion efficiency of CO2 to CO and the energy efficiency of the plasma. When the number of repetitions of experiments is 5, a maximum CO concentration of 5% and a maximum CO2 concentration of 20% are reached. The energy efficiency associated with the conversion of desorbed CO2 to CO reaches 14% with the plasma power of 300 W. Discussions are carried out by comparing the value with those obtained in other studies on the plasma reduction of CO2.

CO2 reduction using adsorption followed by nonthermal plasma treatment

Carbon dioxide (CO2) is one of the main substances linked to global warming, and its emission should be reduced. In this study, a CO2 reduction treatment using an adsorbent and a nonthermal plasma flow is investigated. This treatment comprises a physical adsorption process and nitrogen (N2) plasma reduction process. In the physical adsorption process, CO2 is adsorbed by the adsorbent. In the N2 plasma reduction process, the adsorbed CO2 is reduced to CO by a nonthermal plasma flow that is generated by a plasma reactor with a circulating N2 plasma flow. The generated CO can be reused as a fuel. We estimate this experimental results by calculating conversion efficiency of CO2 to CO. In the N2 plasma reduction process, the CO concentration reaches approximately 1%, regardless of the number of experiments, and conversion efficiency reaches at most 5.3%.

302 非熱プラズマ脱着による高効率CO_2分解処理技術(大気環境保全・改善技術(1))

Carbon dioxide (CO_2) is one of the main substances linked to greenhouse effect, and its emission should be reduced. In this study, a CO_2 reduction treatment using an adsorbent and a nonthermal plasma flow is investigated. This treatment comprises a physical adsorption process and nitrogen (N_2) plasma reduction process. In the physical adsorption process, CO_2 is adsorbed by the adsorbent. In the N_2 plasma reduction process, the adsorbed CO_2 is reduced to CO by a nonthermal plasma flow that is generated by a plasma reactor with a circulating N_2 plasma flow. The generated CO can be reused as a fuel. We estimate this experiment results by calculating conversion efficiency of CO_2 to CO. In the N_2 plasma reduction process, the CO concentration reaches approximately 4.8% in maximum, and highest conversion energy efficiency of 11% is obtained.

Oxidation System of Adsorbed VOCs on Adsorbent Using Nonthermal Plasma Flow

A toluene oxidation system is developed using an adsorbent and a nonthermal plasma (NTP) flow that consists of a surface discharge and a circulation flow. The liquid toluene is vaporized in the circulation line connected with a blower, the adsorbent, and the surface discharge plasma reactor in series, and the toluene gas is adsorbed by the adsorbent. Hydrophobic zeolite pellets are used as the adsorbent. After the toluene adsorption, ozone generated by the surface discharge is supplied to the adsorbent, and adsorbed toluene is oxidized on the surface of the adsorbent. Because the gas is circulated during toluene oxidation, ozone is used to oxidize toluene effectively and without waste. As a result, adsorbed toluene is efficiently converted to CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (CO + CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) using the NTP flow; 88% and 43% conversion ratios of toluene to CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> are achieved when 1 and 6 mL of toluene are oxidized for 90 and 150 min, respectively. In addition, CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> selectivity of more than 89% is obtained when 1 and 6 mL of toluene are oxidized. The conversion rate of toluene to CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> and the energy efficiency of the toluene-to-CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> conversion increase with the amount of adsorbed toluene.

504 大気圧非平衡プラズマ流による細管内部の滅菌特性(バイオエンジニアリング)

504 大気圧非平衡プラズマ流による細管内部の滅菌特性(バイオエンジニアリング)

Analysis of a Methanol Decomposition Process by a Nonthermal Plasma Flow

In the present study, experimental and numerical analyses were adopted to clarify key reactive species for methanol decomposition processes using a nonthermal plasma flow. The nonthermal plasma flow was generated by a dielectric barrier discharge (DBD) as a radical production source. The experimental methods were as follows. Working gas was air of 1 -10 Sl/min. The peak-to-peak applied voltage was 16 - 20 kV with sine wave of 1 Hz - 7 kHz. The characteristics of gas velocity, gas temperature, ozone concentration and methanol decomposition efficiency were measured. Those characteristics were also numerically analyzed using conservation equations of mass, chemical component, momentum and energy, and state of equation. The simulation model takes into account reactive species, which have chemical reaction with the methanol. The detailed reaction mechanism used in this model consists of 108 elementary reactions and 41 chemical species. Inlet conditions are partially given by experimental results. Finally, effects of reactive species such as O, OH, H, NO, etc. on methanol decomposition characteristics are numerically analyzed. The results obtained in this study are summarized as follows. (1) Existence of excited atoms of O, N and excited molecular of OH, N 2 (B 3 Πg), N 2 (A 3 Σ + u ), NO are implied in the discharge region. (2) The methanol below 50 ppm is decomposed completely by using DBD at discharge conditions as V = 16 k Vpp and f = 100 Hz. (3) The reactive species are most important factor to decompose methanol, as the full decomposition is obtained under all injection positions. (4) In numerical analysis, it is clarified that OH is the important radical to decompose the methanol.

大気圧非平衡プラズマ流によるVOC分解プロセスの実験および数値解析(流体工学I-2)

大気圧非平衡プラズマ流によるVOC分解プロセスの実験および数値解析(流体工学I-2)

非平衡プラズマ流によるメタノールの分解特性(OS.4 機能性流体と先端融合化)

In the present study, decomposition characteristics of methanol by using nonthermal plasma flow were clarified experimentally. The plasma was generated by DBD with parallel electrodes. The operating gas was air injected at a rate of 4 Sl/min. Applied voltage was 16-20 kVpp with 1 Hz - 1 kHz under sine or square wave forms. The concentration of methanol gas was 50 ppm at maximum. The decomposition rate of methanol gas is up to 100% and the decomposition efficiency is increased with increase of the applied voltage and the frequency under square waveform.