Krzysztof Krawczyk

The properties of cobalt oxide catalyst for ammonia oxidation

Abstract A cobalt oxide catalyst for ammonia oxidation of high and stable activity and selectivity has been obtained and tested in a fluidized bed laboratory reactor. Its active component is Co 3 O 4 . It has been found that much less nitrous oxide is produced in ammonia oxidation on this catalyst than on platinum. The macrostructure of the cobalt catalysts, and especially the presence of mesopores of diameter 3 /g. A hypothetical model has been presented to explain the effect of the catalysts macrostructure on its properties.

Decomposition of chloromethanes in gliding discharges

Gliding discharge plasma was used for decomposition of tetrachloromethane and trichloromethane. Air containing 8000 ppm or 20 ppm of water vapor was the carrier gas. The course and yield of the process were studied as a function of initial concentration of tetrachloromethane and trichloromethane, gas flow rate, and water vapor content. The conversion was high in all cases—it reached 90% for tetrachloromethane and 100% for trichloromethane. The conversion rate of the chloromethane compounds increased with increasing initial concentration of these compounds in the reaction mixture. Changing the water vapor content in the reaction mixture from 20 ppm to 8000 ppm increased the conversion rate of chloromethanes.

Conversion of Nitrous Oxide by Positive Pulsed Corona Discharge

The conversion of nitrous oxide in a positive pulsed corona discharge (PPCD) was studied using two stainless-steel corona reactors with the inner high-voltage electrode made of metal wire (0.3 mm in diameter). The length of the active zone was 0.75 m (reactor R1) or 0.45 m (reactor R2). In the experiments with 5% of oxygen (reactor R1), the overall conversion of N₂O (to oxygen, nitrogen, and NO_x) considerably decreased, which was about 50% smaller than that in argon alone under the same conditions. The presence of a small amount of oxygen in the gas, containing N₂O, allowed us to carry out the process using a considerably lower initial concentration of nitrous oxide. For the initial N₂O concentration below 1%, it was observed that the corona discharge is not stable and changes into a spark discharge. When the N₂O conversion was carried out in argon and oxygen (5% by volume), the conversion of N₂O to NO_x was 11.7% for the initial N₂O concentration of 2%. The influence of oxygen in Ar + N₂O (10%) on the overall conversion and conversion of N₂O to NO_x was also investigated. The increase of oxygen concentration from 5% to 45% resulted in a decrease of the overall N₂ O conversion and its conversion to NO_x . PPCD could have been unstable and changed into a spark discharge when the N₂O concentration was low.

Methane Conversion into C2 Hydrocarbons and Carbon Black in Dielectric-barrier and Gliding Discharges

Abstract The methane conversion into C2 hydrocarbons, carbon black, and hydrogen was studied under plasma conditions at atmospheric pressure using dielectric barrier discharges (DBD) and gliding discharges. Ethane was the main product of the methane conversion under the filamentary DBD action in the mixtures CH4+Ar, thus it may be concluded that under the conditions of DBD microdischarges, the methane transformation can be terminated after one of the first steps of the chain reaction when ethane is produced. The methane conversion rate increased in the presence of dielectric granular packing (quartz glass and silica gel). Using the gliding discharges, two processes were examined: the methane conversion into unsaturated hydrocarbons C2 (mainly acetylene) and into carbon black. For these processes, it was found that the methane concentration in the starting gas mixtures (CH4+H2 and CH4+Ar) is one of the main parameters influencing the conversion rate and the unit energy consumption. The equilibrium in the CH4+H2 mixtures at the pressures of 1 and 10 bar was examined and the temperature ranges of the solid carbon stability were determined.

Carbon Tetrachloride Decomposition by Pulsed Spark Discharges in Oxidative and Nonoxidative Conditions

The estimation of pulsed-spark-discharge efficiency for destroying unwanted stable gaseous impurities is an object of the present study. A laboratory-scale reactor was developed to study the efficiency of pulsed spark discharges (PSDs) for CCl₄ decomposition under oxidative and nonoxidative conditions at atmospheric pressure. In the discharge, chlorine gas was the main product produced from CCl₄ in addition to minor amounts of additional products. These products were the following: 1) C₂Cl₄, C₂Cl₆, and solid deposits containing chlorine and carbon for the inlet CCl₄ + Ar mixture and 2) CO₂ with small amounts of COCl₂ for CCl₄ + O₂ mixture. For both diluting gases, it was possible to reach a high CCl₄ conversion (98% for CCl₄ + O₂ and 93% for CCl₄ + Ar). CCl₄ was chosen as a model substance, because of its simple chemical composition and high stability of its structure. For this reason, the positive result of experiments with CCl₄ gave evidence that using the PSD may be an effective way for the abatement of gaseous pollutant emission.

Purification of the gas after pyrolysis in coupled plasma-catalytic system

Abstract Gliding discharge and coupled plasma-catalytic system were used for toluene conversion in a gas composition such as the one obtained during pyrolysis of biomass. The chosen catalyst was G-0117, which is an industrial catalyst for methane conversion manufactured by INS Pulawy (Poland). The effects of discharge power, initial concentration of toluene, gas flow rate and the presence of the bed of the G-0117 catalyst on the conversion of C7H8, a model tars compounds were investigated. Conversion of coluene increases with discharge power and the highest one was noted in the coupled plasma-catalytic system. It was higher than that in the homogeneous system of gliding discharge. When applying a reactor with reduced G-0117 and CO (0.15 mol%), CO2 (0.15 mol%), H2 (0.30 mol%), N2 (0.40 mol%), 4000 ppm of toluene and gas flow rate of 1.5 Nm3/h, the conversion of toluene was higher than 99%. In the coupled plasma-catalytic system with G-0117 methanation of carbon oxides was observed.

Decomposition of Cyclohexane on Ni3Al Thin Foil Intermetallic Catalyst

Micro-grained thin foils made of Ni3Al intermetallic alloy were fabricated, according to a previously described procedure, and tested as catalyst for decomposition of cyclohexane. The conversion efficiency of the catalyst was evaluated in a synthetic air atmosphere, and found to be as high as 98.7% ± 1.0% at 600 °C and 86.7% ± 3.6% at 500 °C. During the reaction, the growth of carbon nanofibers on the catalysts surface was observed. The chemical and phase composition of the nanofibers was investigated with scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD), finding them to be made of graphitic carbon. Additionally, nanoparticles of nickel appear to be incorporated in the fibers. The obtained material is promising for large scale fabrication in industrial applications because of its high efficiency in the hydrocarbon decomposition, the simple fabrication procedure, and the form of self-supporting foils with the presence of additional carbon nanofibers that increase its efficiency.

A comparison of carbon tetrachloride decomposition using spark and barrier discharges

Abstract The decomposition of CCl4 in air was investigated at atmospheric pressure in two discharges. Reactors used to generate electrical discharges were powered by the same electric power supply. In both reactors, nearly 90% conversion of CCl4 was obtained. All chlorine was in the form of Cl2 in the process carried out in the barrier discharge, while in the spark discharge, COCl2 was formed. The conversion of CCl4 to COCl2 ranged from 2 to 12%. NO was formed in both discharges but the NO content in the gas leaving the reactors was 1.7–2.7% for the spark discharge and 0.045–0.06% for the barrier discharge. O3 was produced only in the barrier discharge and its content ranged from 0.1 to 0.2%. Graphical Abstract

Microwave Reactor for Nitrous Oxide Processing

Abstract The processing of nitrous oxide in microwave discharge plasma coupled with gliding discharge was investigated. The studies were carried out in a quartz reactor with diameter of microwave discharge space 13 mm or 6mm. The use of the smaller reaction space enabled to achieve a higher overall conversion rate of N2O (to oxygen, nitrogen, and nitric oxide), as well as higher conversion rate of N2O to NO. The conversion rate of nitrous oxide depended also considerably on the flow rate of the gas mixture. The increase of the gas flow rate from 200Nl/h to 400Nl/h resulted in a twice as high conversion rate of nitrous oxide. This refers to both the overall conversion rate of N2O and conversion rate of N2O to NO.

Plasma-Catalytic Processes in Gliding Discharges

Abstract Two kinds of plasma-catalytic processes initiated by gliding discharges (GD) were examined: 1) nitrous oxide decomposition and 2) methane non-oxidative coupling to C2 hydrocarbons. In the first case, the GD reactor with stationary catalyst bed was used. It was found that the selected catalysts CuO/Al2O3 and Fe2O3/ Al2O3 may increase the conversion rate of N2O into N2 and O2 in the plasma-catalytic system, not affecting, however, its oxidation to NO. For the methane coupling, a new model of GD reactor has been developed with a mobile (spouted) bed of catalyst particles. In that process, C2 hydrocarbons were the dominant reaction products, however, some amounts of non-volatile substances (e.g. soot) were also produced. When using alumina-ceramic particles, acetylene was the main product with none or traces of other C2 hydrocarbons. In the presence of Pt/Al2O3, however, much more ethylene and ethane were produced.