Effects of Ozone on Catalytic and Physicochemical Properties of Cu–Ce–Al–O Catalysts for Soot Combustion

The elimination of carbon particles at the level of the exhaust line is one of the present challenges of the car manufacturer. In this study, the catalytic combustion of carbon particles has been investigated in the presence of Cu–Ce–Al oxides. The influence of ozonation on the catalytic and physicochemical properties of Cu–Ce–Al oxides at the reaction of diesel soot combustion was examined by thermal analysis and EPR methods.     

Carbon black oxidation mechanism in loose and tight contacts with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and CeO<Subscript>2</Subscript> catalysts

The catalytic combustion of carbon black was investigated in the presence of CeO₂ and Al₂O₃. The influence of contact type between carbon particles and these oxides was examined by thermal analysis, the BET specific area, and EPR spectroscopy. For tight contact carbon black-catalyst mixtures, a new paramagnetic species is observed and can be considered as a fingerprint of the contact between the two solids. These new paramagnetic species increase the reactivity of the catalytic reaction of carbon black (CB) combustion and take part in the oxidation mechanism of CB. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 6, pp. 899–904. This article was submitted by the authors in English.     

Particle discrimination effects in the determination of trace metals in natural fresh waters

Instrumental neutron activation analysis (i.n.a.), atomic absorption spectrometry (a.a.s.), and inductively-coupled plasma atomic emission spectrometry (i.c.p.a.e.s.) have been applied to the determination of Na, K, Mg, Ca, Al, Mn, Fe and Zn in fresh waters containing naturally occurring particles. Scattered results were obtained for the total concentrations of trace metals which were associated to some extent with particles retainable by 0.45-μm filter membranes. Particle discrimination effects are indicated and the fraction of elements included in the final result depends on the method used. For the simultaneous determination of the total concentrations of Al, Mn, Fe and Zn, i.n.a.a. is preferred, as all element fractions present are included in the result. When a.a.s. or i.c.p.a.e.s. is applied, lower results are obtained when particulate matter is present, the results referring only to the acid-soluble low-molecular-weight fraction (< 0.45 μm diameter). When particles are removed prior to the quantifying step, the results obtained on the filtrates by all methods are in good agreement. However, considering the low concentrations of several elements in the separated fractions, i.n.a.a. is most favourable for the determination of aluminium while graphite-furnace a.a.s. is most suitable for zinc. Both methods are applicable for manganese. For Ca, Fe, K, Mg and Na, i.c.p.a.e.s. is recommended.     

Effect of Combustion Improver on Combustion Behavior of Cigarette Paper by Simultaneous TG/DSC Detection

Combustion behavior of cigarette paper containing different content of combustion improver was investigated in order to provide direct experiment data to elucidate lower components in cigarette smoke caused by combustion improver in cigarette paper. The content of the combustion improver was denoted as "organic" potassium index and determined by atomic absorption spectroscopy and ionic spectroscopy. The combustion process obtained by simultaneous thermal analysis was divided into four stages: weight loss due to loss of absorbent water, decomposition of the cellulose, the oxidation of the cellulose char and decomposition of calcium carbonate. Combustion improver reduced the temperature of cellulose decomposition 3–12 K and contributed to oxidation of the cellulose char. Ignition point was gained and reduced 3–8 K by combustion improver. Above results were further verified by samples from two other cigarette paper factories. Mechanism of lower components in cigarette smoke by the combustion improver in cigarette paper was discussed.     

The adsorptivity of organic substances with various physico-chemical properties

The adsorption isotherms of benzene,n-hexane, cyclohexane, and 1,2-dibromo-1,1,2,2-tetrafluoroethane on a nonporous carbon adsorbent, carbon black, were calculated from the results of a gas-chromatographic experiment at 373 K. A general equation of adsorption isotherm for vapors of organic substances on nonporous sorbents that was proposed earlier is shown to be valid in the range of relative pressures,p/p _s, of 10^–7–1 and temperatures of 293–373 K.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1381–1383, August, 1993.     

Thermogravimetric analysis of peat decomposition under different oxygen concentrations

Smoldering combustion of peat is of global concern as a natural hazard to consume sequestered carbon and form wide-area haze. It is affected by thermal decomposition kinetics of peat and the diffusion and availability of oxygen. In this work, thermal decomposition behavior of peat was investigated using thermogravimetric analysis under the atmosphere with different oxygen concentrations. The results showed that thermal decomposition process of peat could be divided into three stages: dehydration, oxidative pyrolysis of organic matters into volatiles and char, and oxidation of the generated char. The apparent activation energies of peat decomposition under different oxygen concentrations were calculated by model-free methods of Kissinger, FWO, Starink, Gyulai, and Friedman. A two-step reaction model was proposed to describe thermal decomposition kinetics of peat (excluding dehydration stage) and the effect of oxygen concentration on the kinetic parameters was discussed. These results provide basic data for smoldering modeling of peat.     

Source apportionment of atmospheric carbonaceous particulate matter based on the radiocarbon

A method was established to quantitatively estimate sources of atmospheric carbonaceous matter, using a combination of radiocarbon technology, linear regression of organic carbon (OC) -K⁺ and elemental carbon (EC) tracer method. Fractional contributions of fossil fuels, biomass burning, biogenic secondary organic carbon (BSOC) and soil dust to the atmospheric size-resolved carbonaceous matters in Shanghai suburb were estimated using this new method. The fossil carbon contributed most of the OC in particles smaller than 0.49 μm, and its fraction decreased with the increase of particle size. Biomass burning contributed 17–28 % to the OC. The BSOC contributed comparable proportions to the OC in particles smaller than 3.0 μm with the biomass burning, but larger in the particles lager than 3.0 μm. The soil dust contributed least fraction to the OC of each size with a proportion of 2–13 %. The biomass burning and fossil sources shared comparable fraction of the EC in all size range.     

Caracterisation De Catalyseurs ZrxCe1–xO2 et Etude De Leur Reactivite Dans L'Oxydation Des Suies Par ATD/ATG

Thermal analysis has been used to investigate the crystallization of Zr_xCe_1-xO₂ mixed oxides, prepared by co-precipitation of corresponding hydroxides. For x≤0.5, small crystals of CeO₂, were formed at low temperatures (373 K). For x>0.5an exothermic peak at 420°C (693 K) was observed after calcination under a flow of air ofhydroxide samples. This peak was associated with the formation of a Zr_xCe_1-xO₂ solid solution (XRD) in a tetragonal phase (Raman). The solids calcined at 700°C (973 K) present a reactivity towards the carbon black oxidation. The thermal analysis coupled with a gas chromatograph (GC) were used to follow this reactivity. Simultaneous study of the activity (thermal analysis) and the selectivity (GC) in CO or CO₂ of the different catalysts revealed an important parameter: acatalyst-soot particle contact. We also obtained a more precise comparison of Zr_xCe_1-xO₂ oxides in the catalytic soot combustion. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of black carbon particles on the efficiency of water droplet freezing

Black carbon particles emitted by natural and anthropogenic sources of combustion are potential nuclei of ice formation of cirri in troposphere. The freezing of the ensembles of water microdroplets containing black carbon particles of different origins, including those modified with organic substances, is studied. Ice-forming ability is shown to be predetermined by the density and sizes of black carbon agglomerates, as well as the chemistry and wettability of their surface. Ice formation is most efficient in dispersions of black carbon particles that are stable with respect to sedimentation and have a uniform distribution of particles over the droplet volume. In the presence of oxygen-containing groups on the particle surface, freezing temperature increases. The efficiency of the ice formation decreases in the presence of noticeable amounts of water-soluble substances on the particle surface. The maximum freezing ability is inherent in ensembles of water droplets containing hydrophilic particles. Characteristics ensuring a high ice forming ability of nuclei are determined.     

Detection of Polycyclic Aromatic Compounds at Jungfraujoch High-Alpine Research Station using Two-Step Laser Mass Spectrometry

Jungfraujoch (JFJ) is considered to be a location for background free troposphere measurements. Aerosol particles collected at JFJ are analyzed to characterize adsorbed polycyclic aromatic compounds (PACs). Aerosol samples were collected from March 21 to 25, 2000 and from August 1 to 9, 2000. Samples were then analyzed by two-step laser mass spectrometry (L2MS). The mass spectra show higher relative concentrations of PACs present on samples collected during the August sampling period versus the March sampling period. L2MS data from March indicates good correlation with black carbon aerosol data measured in parallel. This suggests that long range transport of aerosol from combustion is responsible for the majority of PACs observed. Data from August unexpectedly showed markers indicative of environmental tobacco smoke (ETS). The contribution to total aerosol may be small, but the relative signal of ETS markers correlates well with the number of visitors coming daily to JFJ, pointing to a local source of ETS.     

Oxygenated interface on biomass burn tar balls determined by single particle scanning transmission X-ray microscopy

Carbonaceous particles originating from biomass burning can account for a large fraction of organic aerosols in a local environment. Presently, their composition, physical and chemical properties, as well as their environmental effects are largely unknown. Tar balls, a distinct type of highly spherical carbonaceous biomass burn particles, have been observed in a number of field campaigns. The Yosemite Aerosol Characterization Study that took place in summer 2002 occurred during an active fire season in the western United States; tar balls collected during this field campaign are described in this article. Scanning transmission X-ray microscopy and near-edge X-ray absorption fine structure spectroscopy are used to determine the shape, structure, and size-dependent chemical composition of approximately 150 individual spherical particles ranging in size from 0.15 to 1.2 mum. The elemental composition of tar balls is approximately 55% atomic carbon and approximately 45% atomic oxygen. Oxygen is present primarily as carboxylic carbonyls and oxygen-substituted alkyl (O-alkyl-C) functional groups, followed by moderate amounts of ketonic carbonyls. The observed chemical composition, density, and carbon functional groups are distinctly different from soot or black carbon and more closely resemble high molecular weight polymeric humic-like substances, which could account for their reported optical properties. A detailed examination of the carboxylic carbonyl and O-alkyl-C functional groups as a function of particle size reveals a thin oxygenated interface layer. The high oxygen content, as well as the presence of water-soluble carboxylic carbonyl groups, could account for the reported hygroscopic properties of tar balls. The presence of the oxygenated layer is attributed to atmospheric processing of biomass burn particles.     

Application of dsc to study crystallization kinetics of polypropylene containing fillers

The present work is concerned with the comparison of nucleating efficiency of various organic and inorganic fillers of isotactic polypropylene: talc, chalk, wood flour, nano clay particles, carbon black, chitosan in the form of powder of the same content equal to 5 mass%. The kinetics of isothermal crystallization of isotactic polypropylene in the composite systems was evaluated by using DSC. Avrami equation was applied to the results. Calculated K and n parameters depend on filler applied. The σσ_e surface free energies were also found. The best nucleating agent found here was talc and carbon black. The organic filler as a chitosan powder forms amorphous inclusions in the composites on which IPP molecules cannot be adsorbed. Their presence disturbs a macromolecular diffusion and delays crystallization process of IPP. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fractionated combustion analysis of carbon in forest soils — new possibilities for the analysis and characterization of different soils

The fractionated combustion analysis of carbon allows the sequential analysis of the total organic carbon (TOC), total inorganic carbon (TIC) and total carbon (TC) fractions in forest soils. Magnesium carbonate and calcium carbonate of the inorganic carbon fraction can also be detected separately. Soils from various forest stands cause different combustion characteristics of the organic carbon fraction, also depending on the soil profile depth. This automatic combustion technique is suitable to characterize the organic carbon fraction of different soil types.     

A comparison of direct thermal desorption with solvent extraction for gas chromatography-mass spectrometry analysis of semivolatile organic compounds in diesel particulate matter

Direct thermal desorption-gas chromatography-mass spectrometry (DTD-GC-MS) is a technique that is finding application in the characterisation of the semivolatile organic carbon fraction of ambient and combustion source particulate matter (PM) collected on filters. In this study, three DTD-GC-MS methods were assessed and compared to a conventional solvent extraction method for analysis of a mixture of target analytes in solution and of diesel PM collected on quartz filters. The target analytes included n-alkanes, hopanes, steranes and polycyclic aromatic hydrocarbons. This study showed that while the three DTD-GC-MS methods were generally comparable to the solvent extraction method, (1) the choice of calibration strategy and calibration materials has a significant impact on the measured accuracy of a method; (2) very large variations were seen in all methods for the more volatile compounds such as C₁₀ to C₁₃ n-alkanes and naphthalene; (3) accuracy, defined as difference from the known concentration of a liquid sample, ranged from 5% to 32%; (4) precision, defined as the relative standard deviation, ranged from 4% to 16%. The average difference of DTD-GC-MS results from the solvent extraction results for the diesel PM filters ranged from 20% to 40%. This difference was driven by the large number of target analytes present at relatively low concentrations (<25 pg/mm²) and their corresponding higher variability. Differences in performance among the compound classes were noted. Minimum detection limits for the DTD-GC-MS methods were on the order of 0.1 to 1 pg/mm² and were as good as or better than those obtained for the solvent extraction method.     

Integration of biomass drying with combustion/gasification technologies and minimization of emissions of organic compounds

Moisture content (MC) of green biomass or raw biomass materials (wood, bark, plants, etc.) commonly exceeds 50 mass % (wet basis). The maximum possible MC of biomass fuel for big scale combustion (e.g. fluidized bed combustion with low external heat losses) is approximately 60–65 mass %. Higher biomass MC generally causes operational problems of biomass combustors, lower stability of burning and higher CO and VOC emissions. Gasification of biomass with higher MC produces fuel gas of lower effective heating values and higher tar concentrations. In this review, various technological schemes for wood drying in combination with combustion/gasification with the assessment of factors for possible minimization of emissions of organics from the drying processes are compared. The simple direct flue gas biomass drying technologies lead to exhaust drying gases containing high VOC emissions (terpenes, alcohols, organic acids, etc.). VOC emissions depend on the drying temperature, residence time and final MC of the dried biomass. Indirect biomass drying has an advantage in the possibility of reaching very low emissions of organic compounds from the drying process. Exhaust drying gases can be simply destroyed as a part of the total combustion air (gas) in a combustion chamber or a gasifier. Liquid, condensed effluents have to be treated properly because they have relatively high content of organic compounds, some of them accompanied by odor. Drying of biomass with superheated steam offers more uniform drying of both small and bigger particles and shorter periods of higher temperatures of the dried biomass, particularly if drying to the final MC below 15 mass % is required. In practical modern drying technologies, biomass (mainly wood) is dried in recirculated gas of relatively high humidity (approaching saturation) and the period of constant rate drying is longer. Drying of moist wood material (saw dust, chips, etc.) is required in wood pellet production. Emissions of organics in drying depend on biomass properties, content of resins, storing time and on operational aspects of the drying process: drying temperature, drying medium, final MC, residence time, and particle size distribution of the dried biomass (wood). Integration of biomass drying with combustion/gasification processes includes the choice of the drying medium (flue gas, air, superheated steam). Properties of the drying media and operational parameters are strongly dependent on local conditions, fuel input of the combustion/gasification unit, cleaning of the exhaust drying media (gas, steam, wastewater), and on environmental factors and requirements.     

Formation of carbon oxides during tobacco combustion: Pyrolysis studies in the presence of isotopic gases to elucidate reaction sequence

During the combustion of tobacco, carbon monoxide is formed by the thermal decomposition of tobacco with primary products such as carbon dioxide and water. These three processes occur in parallel and are interdependent. The temperature ranges over which each process occurs, and their relative importance have been assessed by pyrolysing tobacco in the presence of various isotopically labelled gases. Non-isothermal pyrolyses were conducted at a heating rate of 1.6 K s^?1 up to 1000°C, with the products analysed by mass spectrometer.Pyrolysis in the presence of oxygen-18 indicates that combustion of tobacco starts at 180°C. Carbon dioxide and water are formed by combustion at 180°C, while carbon monoxide is not formed as a combustion product until 460°C. The quantities of carbon monoxide and dioxide formed by thermal decomposition of tobacco above 400°C are significantly reduced by the occurrence of combustion.Pyrolysis in the presence of carbon-13 dioxide or carbon dioxide-18 shows that its major reaction, endothermic reduction to form carbon monoxide begins at 450°C. Pyrolysis in an oxygen-18/carbon-13 dioxide atmosphere has shown that this endothermic reduction of carbon dioxide occurs in parallel with the strongly exothermic oxidising reactions. 30% of the total carbon monoxide formed was produced by thermal decomposition of the tobacco. 36% was produced by combustion of the tobacco, and at least 23% was produced via carbon dioxide. The remainder was produced by an interaction of the carbon dioxide reduction and the oxidation. Similar proportion would be expected inside the reaction zone of a burning cigarette.Pyrolysis in the presence of heavy water has shown that the major reaction of the water is to quantitatively produce carbon monoxide and hydrogen above 600°C. Considerable isotopic exchange reactions also occur. Pyrolysis in the presence of carbon monoxide-18 has shown that carbon monoxide reacts with tobacco to a small extent at temperatures above 220°C mainly to abstract oxygen combined in the tobacco and produce carbon dioxide.A sequence of general chemical steps for the production of the carbon oxides and water during tobacco combustion has been deduced. This is based on the present work together with considerations of previously published studies on graphite and coal reactions.     

Thermal expansion,free volume,and molecular mobility in a carbon black-filled elastomer

The thermal expansion of a butadiene–styrene copolymer filled with carbon blacks differing tenfold in mean particle size (HAF and MT) was investigated. The glass transition was unaffected by MT and was raised only 0.2°C for every 10 parts per hundred by weight of polymer of HAF black added. The coefficient of expansion of the polymer component of the composite in the rubbery region was substantially unaffected by either carbon black, but decreased markedly with increasing black loading in the glassy state. These results suggest that free volume is not altered appreciably by the presence of the filler in the rubbery state, but expands with decreasing temperature below T_g. The latter effect is explained by dilatation due to stresses set up around filler particles, arising from differences in the expansion coefficients of filler and polymer, which are not relieved in the glassy state. The near invariability of T_g and of the rubbery fected by adsorption of polymer segments on the carbon black surface. A conservative rough estimate indicates that restriction of segmental motion is confined to a 30 Å layer around the particles in which T_g is elevated by only 10°C.     

活性碳载体对TiO2光催化降解Cl2CHCOOH性能的影响

研究了活性碳(AC)载体对TiO₂光催化降解Cl₂CHCOOH性能的影响.结果表明,加入AC载体能提高TiO₂的光催化反应速度,而且AC加入方法及含量有明显影响.本文探讨了TiO₂光催化性能提高的原因.     

高硫石油焦燃烧过程中不同赋存形态钒的变迁行为研究

采用逐级化学提取结合ICP-OES方法,研究了高硫石油焦燃烧过程中重金属元素钒的赋存形态和迁移转化行为,并结合热力学分析方法,探讨了其化学反应机理。石油焦中钒的赋存形态主要为有机质结合态和稳定态。随着燃烧温度的升高,有机质结合态的钒发生快速分解直至消失,且与Ca、Na、Fe和K等矿物质反应,转化为水溶态和部分离子可交换态、碳酸盐结合态、氧化物结合态钒。稳定态钒主要是与其他矿物质形成非晶态结构物质存在于石油焦中,在高温燃烧过程中,会部分熔融转化并释放出少量的钒。石油焦中钒的挥发性随着燃烧温度和燃尽率的升高逐渐增大,且呈现阶段性挥发的特点。温度高于1100℃,有机质结合态的钒快速分解,且部分转化为具有挥发性的VO2等化合物,致使钒的挥发率急剧增大。