Performance of non-thermal DBD plasma reactor during the removal of hydrogen sulfide

Destruction of hydrogen sulfide using dielectric barrier discharge plasma in a coaxial cylindrical reactor was carried out at atmospheric pressure and room temperature. Three types of DBD reactor were compared in terms of specific energy density (SED), equivalent capacitances of the gap (Cg) and the dielectric barrier (Cd), energy yield (EY), and H₂S decomposition. In addition, byproducts during the decomposition of H₂S and destruction mechanism were also investigated. SED for all the reactors depended almost linearly on the voltage. In general, Cg decreased with increasing voltage and with the existence of pellet material, while Cd displayed the opposite trend. The removal efficiency of H₂S increased substantially with increasing AC frequency and applied voltage. Longer gas residence times also contributed to higher H₂S removal efficiency. The choice of pellet material was an important factor influencing the H₂S removal. The reactor filled with ceramic Raschig rings had the best H₂S removal performance, with an EY of 7.30 g/kWh. The likely main products in the outlet effluent were H₂O, SO₂, and SO₃.     

Nascent tar formation during polyvinylchloride (PVC) pyrolysis

Pyrolysis experiments of polyvinylchloride (PVC) were performed to investigate the effects of peak temperature, holding time, and heating rate on the formation of nascent tar. The nascent tar samples were collected using a wire-mesh reactor where the secondary reactions of the evolved volatiles were minimized. The small compounds, such as benzenes and alkanes, were not detected in nascent tar in wire-mesh reactor, whose components are quite different from those of other tars in tube type reactor and vacuum reactor. At a heating rate of 1000 K/s, the quasi-3 rings and 3 rings group aromatics were the major components in nascent tar; while the content of 2 rings group aromatics increased from 7.02% to 31.75% with increasing peak temperature from 500 to 800 °C. At a longer holding time of 300 s, an increase of 2 rings group aromatics from 7.02% to 50.33% was also observed for the nascent tar at 500 °C, indicating that the tar composition significantly changed at different stages of PVC pyrolysis. It seems that 3–4 rings compounds form in the early stage and then 2 rings compounds release in the later stage of PVC pyrolysis. Based on the experimental results in this work, a new four-stage mechanism, including (1) dechlorination accompanied with inner cyclization, (2) aromatic chain scission, (3) release of quasi-3 rings or 3 rings group, and (4) release of 2 rings group, of the PVC tar formation was proposed.     

Removal of four kinds of volatile organic compounds mixture in air using silent discharge reactor driven by bipolar pulsed power

A silent discharge reactor initiated by bipolar pulsed power substituting the traditional ac power was used to remove the volatile organic compounds (VOC_s) mixture of acetone, benzene, tetrachloroethylene and m-xylene. The results indicated that the silent discharge driven by bipolar pulsed power could effectively input pulsed energy, produce strong instant discharge and energetic particles, and thus enhance the removal efficiency of the mixed VOC_s. The order of the removal efficiency of mixed VOC_s followed as acetone < benzene < tetrachloroethylene < m-xylene no matter what power supply was used. Comparing with single-compound, the removal efficiency of m-xylene only fell a little but those of the other three components fell a lot in the process of the mixed VOC_s treatment. In addition, controlling the status of electrical discharge plasma by changing the discharge parameters (such as capacitance of the pulse capacitor and pulse repetitive rate) was found to be an efficient way to enhance the removal efficiency of the mixed VOC_s. In this system, the Cp = 2 nF was the optimal capacitance for the bipolar power supply combined with the silent discharge reactor that had the best energy conversion efficiency for removal of mixed VOC_s. A higher pulse repetitive rate and longer residence time could also increase the removal efficiency of mixed VOC_s.     

Pulsed corona discharge driven by Marx generator: Diagnostics and optimization for NOx treatment

A compact, repetitive Marx generator with an external trigger is constructed and coupled with a wire-to-plate corona reactor for a positive pulsed corona discharge studies. The reactor resistance and capacitance behavior during the pulse was observed. It was found that the reactor's capacitance increases three times during the pulse due to the streamer propagation from anode to grounded electrode. Using the time development of the capacitance and resistance during the pulse and the reactor inter-electrode distance, the streamer velocity has been calculated to be 1 × 10⁶ m/s, for system arrangement presented in this work. As an indicator of chemical activity of pulsed corona, ozone production was measured. Emission spectroscopy measurements in the UV region were performed to detect species that appear in the discharge and to determine vibrational and rotational temperatures, which are found to be 3200 K and 340 K respectively. As a measure of pollution control potential of the constructed pulsed corona system, NO oxidation efficiency was investigated and compared with results presented in literature. It was shown that pulsed corona systems with significantly longer pulse durations are competitive with several times shorter pulse duration systems, which implies that chemical efficiency of secondary streamers is comparable with efficiency of primary streamers.     

Ferro-electric pellet shape effect on C/sub 2/F/sub 6/ removal by a packed-bed-type nonthermal plasma reactor

Ceramic dielectric material pellet shape effects on the performance of perfluoroethane (C/sub 2/F/sub 6/) gas removal from simulated semiconductor process gas using packed-bed reactor are experimentally investigated. The bench-scale cylindrical shaped (plasma part: 30-mm inner diameter and 20-mm length) plasma reactor consists of two metal mesh electrodes packed with spherical, cylindrical, or hollow cylindrical shaped ferro-electric pellets with various dielectric constants. The 60-Hz ac high voltage was applied to the mesh electrode. The 3000 ppm C/sub 2/F/sub 6/ gas diluted with nitrogen was used as simulated gas with flow rate of 30 mL/min. The C/sub 2/F/sub 6/ concentration was monitored using Fourier transform Infrared absorption spectroscopy measurements. The results show that the packed-bed plasma reactor with the hollow cylindrical-shaped pellets removed the C/sub 2/F/sub 6/ gas with energy efficiency of 3.7 g/kWh. This value was almost 1.5 times higher than the efficiency 2.5 g/kWh in case of the spherical pellets. The discharge characteristics in the reactor were also changed with the pellet shape. The discharge onset voltage decreases by changing the pellets shape from sphere to hollow cylinder. The quantity of charges accumulated with the microdischarge currents increases by changing the pellet shape from sphere to hollow cylinder in spite of fact that the energy consumed in the reactor decreases.     

Electrochemical properties of Mn-doped activated carbon aerogel as electrode material for supercapacitor

Carbon aerogel (CA) was prepared by a sol-gel polymerization of resorcinol and formaldehyde, and it was activated with KOH to obtain activated carbon aerogel (ACA). Specific capacitance of carbon aerogel and activated carbon aerogel was measured by cyclic voltammetry and galvanostatic charge/discharge methods in 6 M KOH electrolyte. Activated carbon aerogel showed higher specific capacitance than carbon aerogel (136 F/g vs. 90 F/g). In order to combine excellent electrochemical performance of activated carbon aerogel with pseudocapacitive property of manganese oxide, 7 wt% manganese oxide was doped on activated carbon aerogel by an incipient wetness impregnation method. For comparison, 7 wt% manganese oxide was also doped on carbon aerogel by an incipient wetness impregnation method. It was revealed that 7 wt% Mn-doped activated carbon aerogel (Mn/ACA) showed higher specific capacitance than 7 wt% Mn-doped carbon aerogel (Mn/CA) (168 F/g vs. 98 F/g). The enhanced capacitance of 7 wt% Mn-doped activated carbon aerogel was attributed to the outstanding electric properties of activated carbon aerogel as well as the faradaic redox reactions of manganese oxide.     

Ultrasound-assisted soil washing processes for the remediation of heavy metals contaminated soils: The mechanism of the ultrasonic desorption

Ultrasound-assisted soil washing processes were investigated for the removal of heavy metals (Cu, Pb, and Zn) in real contaminated soils using HCl and EDTA. The ultrasound-assisted soil washing (US/Mixing) process was compared with the conventional soil washing (Mixing) process based on the mechanical mixing. High removal efficiency (44.8% for HCl and 43.2% for EDTA) for the metals was obtained for the most extreme conditions (HCl 1.0 M or EDTA 0.1 M and L:S = 10:1) in the Mixing process. With the aide of ultrasound, higher removal efficiency (57.9% for HCl and 50.0% for EDTA) was obtained in the same extreme conditions and similar or higher removal efficiency (e.g., 54.7% for HCl 0.5 M and L:S = 10:1 and 50.5% for EDTA 0.05 M and L:S = 5:1) was achieved even in less extreme conditions (lower HCl or EDTA concentration and L:S ratio). Therefore, it was revealed that the US/Mixing was advantageous over the conventional Mixing processes in terms of metal removal efficiency, consumption of chemicals, amount of generated washing leachate, and volume/size of washing reactor. In addition, the heavy metals removal was enhanced for the smaller soil particles in the US/Mixing process. It was due to more violent movement of smaller particles in slurry phase and more violent sonophysical effects. In order to understand the mechanism of ultrasonic desorption, the desorption test was conducted using the paint-coated beads with three sizes (1, 2, and 4 mm) for the free and attached conditions. It was found that no significant desorption/removal of paint from the beads was observed without the movement of beads in the water including floatation, collision, and scrubbing. Thus, it was suggested that the simultaneous application of the ultrasound and mechanical mixing could enhance the physical movement of the particles significantly and the very high removal/desorption could be attained.     

Improving efficiency for removal of ammoniacal nitrogen from wastewaters using hydrodynamic cavitation

The present study reports significant improvements in the removal of ammoniacal nitrogen from wastewater which is an important problem for many industries such as dyes and pigment, distilleries and fisheries. Pilot plant studies (capacity, 1 m³/h) on synthetic wastewater using 4-amino phenol as model nitrogen containing organic compound and two real industrial effluents of high ammoniacal nitrogen content were carried out using hydrodynamic cavitation. Two reactor geometries were evaluated for increased efficiency in removal-orifice and vortex diode. Effect of initial concentration (100–500 mg/L), effect of pressure drop (0.5–5 bar) and nature of cavitating device (linear and vortex flow for cavitation) were evaluated along with effect of salt content, effect of hydrogen peroxide addition and aeration. Initial concentration was found to have significant impact on the extent of removal: ~ 5 g/m³ removal for initial concentration of 100 mg/L and up to 12 g/m³ removal at high concentration of 500 mg/L. Interestingly, significant improvement of the order of magnitude (up to 8 times) in removal of ammoniacal nitrogen could be obtained by sparging air or oxygen in hydrodynamic cavitation and a very high removal of above 80% could be achieved. The removal of ammoniacal nitrogen by vortex diode was also found to be effective in the industrial wastewaters and results on two different effluent samples of distillery industry indicated up to 75% removal, though with longer time of treatment compared to that of synthetic wastewater. The developed methodology of hydrodynamic cavitation technology with aeration and vortex diode as a cavitating device was found to be highly effective for improving the efficiency of the conventional cavitation methods and hence can be highly useful in industrial wastewater treatment, specifically for the removal of ammoniacal nitrogen.     

Disinfection characteristics of an advanced rotational hydrodynamic cavitation reactor in pilot scale

Hydrodynamic cavitation is a promising technique for water disinfection. In the present paper, the disinfection characteristics of an advanced hydrodynamic cavitation reactor (ARHCR) in pilot scale were studied. The effects of various flow rates (1.4–2.6 m³/h) and rotational speeds (2600–4200 rpm) on the removal of Escherichia coli (E. coli) were revealed and analyzed. The variation regularities of the log reduction and reaction rate constant at various cavitation numbers were established. A disinfection rate of 100% was achieved in only 4 min for 15 L of simulated effluent under 4200 rpm and 1.4 m³/h, with energy efficiency at 0.0499 kWh/L. A comprehensive comparison with previously introduced HCRs demonstrates the superior performance of the presented ARHCR system. The morphological changes in E. coli were studied by scanning electron microscopy. The results indicate that the ARHCR can lead to serious cleavage and surface damages to E. coli, which cannot be obtained by conventional HCRs. Finally, a possible damage mechanism of the ARHCR, including both the hydrodynamical and sonochemical effects, was proposed. The findings of the present study can provide strong support to the fundamental understanding and applications of ARHCRs for water disinfection.     

Optimization of gas–liquid hybrid pulsed discharge plasma for p-nitrophenol contaminated dredged sediment remediation

p-Nitrophenol (PNP) removal in dredged sediment during pulsed discharge plasma process was studied in terms of adjustable trim capacitance, electrode distance and gas-flow rate. PNP degradation efficiency reached up to 88.5% under the conditions of adjustable trim capacitance of 2.0 nF, electrode distance of 16 mm, and air flow rate of 0.8 L min⁻¹. To a certain extent, increasing the adjustable trim capacitance and decreasing the electrode distance leaded to high PNP degradation efficiency. An appropriate air flow rate was determined for gaining relatively high PNP removal efficacy. PNP mineralization was analyzed by UV–Vis spectrum, COD, and TOC evolution.     

Ultrasound-assisted fabrication of Ti3C2Tx MXene toward enhanced energy storage performance

Ti₃C₂Tx MXenes are normally fabricated by removal of main group element from the corresponding transition metal carbides, and they have been actively studied due to their superior energy storage performance. However, the low efficiency in removal of main group element (named as chemical etching) has significantly limited the application of MXene or MXene-related materials. Herein, we demonstrated an ultrasound-assisted approach to synthesize Ti₃C₂Tx MXene material by using Ti₃AlC₂ as the precursor. The experimental results indicate that the efficiency of chemical etching of Ti₃AlC₂ was dramatically promoted by ultrasound. The etching time was greatly shortened to 8 h while typically 24 h is sufficient in dilute hydrofluoric acid. Particularly, the high etching efficiency was achieved by using 2% hydrofluoric acid under the aid of ultrasound, which is lower in concentration than those reported in the previous literature. The specific capacitance of the 8 h sonicated sample is 155F/g, which is much higher than that of the un-sonicated sample prepared under the same experimental conditions. Additionally, the specific capacitance retention of the prepared 8 h sonicated sample was 97.5% after 20,000 cycles of charging/discharging, exhibiting an outstanding energy storage stability compared with the materials reported in previous literatures. It was proposed that removal of AlF₃ from the surface of the etched particles was significantly promoted and the hydrogen bonds between the terminations of two different adjacent layers were broken by the acoustic cavitation effect of ultrasound.     

Electrochemical aspects of sol-gel synthesized MgCoO2 for aqueous supercapacitor and alkaline HER electrocatalyst applications

We report here the cost-effective synthesis of Magnesium Cobalt Oxide (MgCoO₂) sample by the sol-gel synthesis route labeled as MCO - 3. In presence of aqueous 1 M Lithium Sulphate (Li₂SO₄) electrolyte, we obtained a capacitance of 56 F/g, an energy density of 38 Wh/kg and a capacitance retention of 92.53 % (at 5 A/g) after undergoing 1000 charge-discharge cycles. For the aqueous 1 M Sodium Perchlorate (NaClO₄) electrolyte system, we found the capacitance, energy density and capacitance retention of 47 F/g, 31 Wh/kg and 91.41% (at 3.5 A/g for 1000 charge-discharge cycles), respectively. These results establish MgCoO₂ as suitable electrode material in aqueous lithium-ion and sodium-ion supercapacitor devices. Further, MCO - 3 in the presence of aqueous 1 M Potassium Hydroxide (KOH) electrolyte showed an overpotential of 400 mV and a Tafel slope of 174 mV/dec, making it a suitable candidate for alkaline Hydrogen Evolution Reaction (HER) electrocatalyst.     

The influence of combined low-strength ultrasonics and micro-aerobic pretreatment process on methane generation and sludge digestion: Lipase enzyme,microbial activation,and energy yield

Low-frequency ultrasonics is a potential technology to reduce the hydrolysis phase period in anaerobic digestion process. In this study, the influence of combined low frequency ultrasonics and micro-aerobic (MA) pretreatment on sewage sludge solubilization, enzyme activity and anaerobic digestion were assessed. Initially, the effect of ultrasonic density (0.012, 0.014, 0.016, 0.018, 0.1, 0.12 and 0.14 W/mL) and irradiation time (1, 3, 5, 8, 9, 10 and 12 min) of 20 kHz frequency waves were investigated. Accordingly, the effect of micro-aerobic pretreatment (Air flow rate (AFR) = 0.1, 0.2, 0.3 and 0.5 VVM) within 20, 30, 40.48 and 60 h were examined. In addition, the effect of combined pretreatment on COD solubilization, lipase enzyme activation, ATP, percentage of live bacteria and methane gas production during the anaerobic process were examined. The results showed that the highest lipase activity (14.9 Umol/mL) was obtained under the effect of ultrasonic density of 0.1 W/ml within 9 min. The highest solubilization (65%) was observed under optimal micro-aerobic conditions: AFR = 0.2 (VVM) and micro-aerobic time: 40 h. Combined ultrasonic and micro-aerobic (US + MA) pretreatment increases the solubilization (70%), microbial activity (2080%) and lipase enzymatic activity (129%) compared to individual pretreatment. The Biogas production during anaerobic digestion pretreated with combined methods increased by 193% compared to the control, while the elevated values of biogas production in reactors pretreated by ultrasonic and micro-aerobic pretreatment alone were observed to be 101% and 165%, respectively. The net energy in reactor with the combined pre-treatment methods was calculated to be 1.26 kWh, while this value for control, pretreated ultrasonic and micro-aerobic reactors were obtained to be 0.56, 0.67 and 1.2 kWh, respectively.     

Investigation of electrochemical performance of MgNiO2 prepared by sol-gel synthesis route for aqueous-based supercapacitor application

In this work, we have successfully synthesized MgNiO₂ using a sol-gel wet chemical synthesis technique named MNO - 3. Electrochemical measurements in the presence of aqueous 1 M Li₂SO₄ electrolyte indicate that MNO - 3 samples exhibit a capacitance value of about 30 F/g and an energy density of about 20 Wh/kg. Subsequently, in the experiment involving aqueous 0.5 M Na₂SO₄ electrolyte system, it has been found that the capacitance for MNO - 3 sample is about 34 F/g and the energy density is about 23 Wh/kg for MNO - 3 sample. Finally, in the presence of aqueous-based 1 M Mg(ClO₄)₂ electrolyte, MNO - 3 sample is found to exhibit a capacitance of about 26 F/g and an energy density of about 17 Wh/kg, respectively. In all three electrolyte systems, the MNO -3 sample exhibit a long cycle capacitance retention of greater than 85% for 1000 charge-discharge cycles.     

Extraction of tungsten from scheelite using hydrodynamic and acoustic cavitation

The primary purpose of this study is to investigate the effects of hydrodynamic and acoustic cavitation (HAC) on the leaching efficiency of tungsten. The aim is to reduce energy use and to improve the recovery rate. The goal is also to carry out a leaching process at a much lower temperature than in an autoclave process that is currently used in the industry. Energy-efficient initiation and collapse of cavitation bubbles require optimization of (i) vibro-acoustic response of the reactor structure, (ii) multiple excitation frequencies adapted to the optimized reactor geometry, and (iii) hydrodynamic cavitation with respect to orifice geometry and flow conditions. The objective is to modify and apply a previously in house developed high power cavitation reactor in order to recover tungsten by leaching of the dissolution of scheelite in sodium hydroxide. In this process, various experimental conditions like dual-frequency excitation, different orifice geometry have been investigated. The numerically optimized reactor concept was excited by two frequencies 23 kHz and 39–43 kHz in various flow conditions. The effects of leaching time, leaching temperature, ultrasonic power and geometry of orifice plates have been studied. The leaching temperature was varied from 40 °C to 80 °C. The concentration of leaching reagent sodium hydroxide (NaOH) was 10 mol/L.The results were compared to conventional chemical leaching. Energy supplement with acoustic cavitation of 130 kWh/kg concentrate resulted in a leaching recovery of tungsten (WO₃) of 71.5%, compared to 36.7% obtained in absence of ultrasound. The results confirm that the method developed is energy efficient and gives a recovery rate potentially better than current autoclave technology.     

Preparation and characterization of metal-doped carbon aerogel for supercapacitor

Carbon aerogel was prepared by polycondensation of resorcinol and formaldehyde using sodium carbonate as a catalyst with a resorcinol to catalyst ratio of 500. Co-doped carbon aerogels were then prepared by an impregnation method with a variation of cobalt content (1, 3, 5, 7, 10, and 15 wt.%), and their performance for supercapacitor electrode was investigated by measurement of specific capacitance in 1 M H₂SO₄ electrolyte at a scan rate of 10 mV/s. Among the samples prepared, 7 wt.% Co-doped carbon aerogel showed the highest capacitance (100 F/g) and stable cyclability. The enhanced capacitance of Co-doped carbon aerogel was attributed to the faradaic redox reactions of cobalt oxide. On the basis of this result, 7 wt.% Cu-, Fe-, Mn-, and Zn-doped carbon aerogels were also prepared by an impregnation method for use as a supercapacitor electrode. Among the metal-doped carbon aerogels, Mn-doped carbon aerogel showed the highest capacitance (107 F/g) while Cu- and Fe-doped carbon aerogels exhibited the most stable cyclability.     

Petal-like MoS2 nanostructures with metallic 1 T phase for high performance supercapacitors

Herein, we report the metallic 1 T phase MoS₂ petal-like nanostructures (MP-LNs), synthesized by the solvothermal method, for applications in supercapacitor electrodes. X-ray photoelectron spectroscopy (XPS) verified the composition and distribution of Mo and S, illustrating that the 1 T metallic phase is predominant in the MP-LNs. Electrochemical analyses were performed to explore the supercapacitor applications of the MP-LN material, demonstrating a superior cyclic voltammetry (CV), high specific capacitance, good stability. MP-LN-based supercapacitors (MP-LNS) show high specific capacitances of 811 F/g and 400 F/g at current densities of 0.1 A/g and 10 A/g, respectively. The long-term cycling stability was also studied to investigate the reproducible nature of MP-LNS and was found to display excellent specific capacitance retention of 49.3% (at 0.1 A/g) and 82.7% (at 10 A/g) after 1000 charge-discharge cycles, which indicates good reversibility of the galvanostatic charge-discharge (GCD) of the electrode material. These findings highlight the potential use of MP-LNs in supercapacitors.     

Monolithic electrochemically promoted reactors: A step for the practical utilization of electrochemical promotion

A novel dismantlable monolithic-type electrochemically promoted catalytic reactor and “smart” sensor-catalytic reactor unit has been constructed and tested for hydrocarbon oxidation and NO reduction by C₂H₄ in the presence of O₂. In this novel reactor, thin (∼ 40 nm) porous catalyst films made of two different materials are sputter-deposited on opposing surfaces of thin (0.25 mm) parallel solid electrolyte plates supported in the grooves of a ceramic monolithic holder and serve as sensor or electropromoted catalyst elements. The catalyst dispersion was higher than 10%. A 22 flat plate reactor operated with apparent Faradaic efficiency up to 100, at near complete reactants conversion, at gas flow rates up to 30 l/min. The novel design has only two external electrical connections and thus significantly facilitates the practical utilization of electrochemical promotion of catalysis.     

Concentration-dependent electrochemical supercapacitive performance of Fe2O3

This work reports the concentration-dependent electrochemical supercapacitor performance change of electrodeposited Fe₂O₃ thin films. Structural elucidation and morphological evolution studies are operated in the first stage and in second, electrochemical supercapacitive performances are investigated. The maximum specific capacitance of 540 F/g at 2.5 A/g in 1 M KOH is obtained. The electric parameters including specific energy, specific power and coulomb efficiency are measured using charge/discharge technique and finally, electrochemical impedance measurement is examined for knowing the internal charge transfer resistance. An equivalent circuit associated with the cell, with required parameters, is also designed.     

Degradation behaviors and failure analysis of Ni–BaTiO3 base-metal electrode multilayer ceramic capacitors under highly accelerated life test

The degradation in insulation resistance under highly accelerated test conditions was investigated in terms of micro-structural and micro-chemical changes in dielectric layer of multilayer ceramic capacitor. The ceramic capacitors were prepared by using BaTiO₃ powder with different size of 0.52 μm, 0.55 μm, and 0.58 μm. As the particle size of BaTiO₃ powder was increased, the capacitance and the dissipation factor were decreased. According to the result of highly accelerated test conducted at 150 °C, 75 V, and 20 h, failure in insulation resistance was increased with the particle size and the calculated FITs (failure in term) were 1.10 at 0.52 μm, 2.11 at 0.55 μm, and 6.69 at 0.58 μm, respectively. The failure was examined by X-ray photoelectron spectroscopy and transmission electron microscopy, which was attributed to the oxidation of Ni inner electrode that could create oxygen vacancies and increase electric conduction of the ceramic capacitors.