Products Of Chemical Reactions Research Articles

Selective H2S sensing characteristics of hydrothermally grown ZnO-nanowires network tailored by ultrathin CuO layers

Random networks of ZnO nanowires (ZnO-NWs) have been fabricated on the Si/SiO2 substrates by hydrothermal process using ZnO-nanoparticles as seed. The ZnO-NWs networks have been modified by depositing ultrathin CuO layers (nominal thickness: 10nm) using thermal evaporation of Cu followed by oxygen annealing at 600°C. The results of photoluminescence measurements on ZnO-NWs and CuO:ZnO-NWs networks suggest formation of a p–n junction between p-CuO and n-type ZnO. The gas sensing characteristics of both ZnO-NWs and CuO:ZnO-NWs networks have been investigated. It has been demonstrated that CuO:ZnO-NWs network has selective response toward H2S with a sensitivity of ∼40 (for 10ppm) at an operating temperature of 200°C. A sensing mechanism based on the destruction of p–n junctions due to the formation of metallic CuS (product of chemical reaction between CuO and H2S) has been proposed.

Stability of reactive interfaces in saturated porous media under gravity in the presence of transverse flows

AbstractThe stability of a horizontal interface between a solution of reactant $A$ on top of another solution of reactant $B$ is analysed. A chemical product $C$ is generated at the interface as a result of a bimolecular chemical reaction $A+ B\ensuremath{\rightarrow} C$. In general, all chemical components are assumed to have different densities and viscosities, and a transverse velocity is introduced parallel to the interface between the reactants. Although the transverse flow is known for its stabilizing effect in viscously unstable non-reactive systems in the presence of an injection velocity, it is shown here that it can actually destabilize an initially stable reactive front. An expression for the critical transverse velocity beyond which an initially stable interface is destabilized is derived in the case of an initial sharp interface for reactants of the same viscosity. The analysis is extended to a diffused profile, and purely buoyancy-driven flows are analysed first in the absence of viscosity contrast and then in the presence of transverse flows and viscosity contrast. Various possible density fingering scenarios are determined based on the relative contribution of each chemical component to the density profile. It is found that the chemical reaction can destabilize a buoyancy-stable initial interface by generating a non-monotonic density profile. Unlike the viscous fingering of a reactive interface, a symmetry in the stability characteristics with respect to density increase or decrease by chemical reaction product is observed in the case of chemically buoyancy-driven flows for identical reactants.

Characterization of La0.6Sr0.4Co0.2Fe0.8O3–δ + La2NiO4+δ Composite Cathode Materials for Solid Oxide Fuel Cells

AbstractThe structure, electrical conduction, thermal expansion and electrochemical properties of the La0.6Sr0.4Co0.2Fe0.8O3–δ + La2NiO4+δ (LSCF‐LNO) composite cathodes were investigated with regard to the volume fraction of the LNO composition. No chemical reaction product between the two constituent phases was found for the composite cathodes sintered at 1,400 °C for 10 h within the sensitivity of the XRD. Compared to the performance of the LSCF cathode, the LNO composition in the composite cathode plays a role in deteriorating both electrical conductivity and electrochemical properties, however, improving the thermal expansion properties. The trade‐off between electrical conducting and thermal expansion classifies the composite cathode containing 30 volume percent (vol.%) LNO as the optimum composition. For characterizing cathode performance in a single cell, a slurry spin coating technique was employed to prepare a porous cathode layer as well as a YSZ/Ce0.8Sm0.2O3–δ (SDC) electrolyte. The optimum conditions for fabricating the YSZ/SDC electrolyte were investigated. The resulting single cell with 70 vol.% LSCF‐30 vol.%LNO (LSCF‐LNO30) cathode shows a power density of 497 mW cm–2 at 800 °C, which is lower than that of the cell with a LSCF cathode, but still within the limits acceptable for practical applications.

Fluid Viscosity-Residual Entropy Correlation

Chemical reaction engineering, process engineering, and product engineering models are used for design and analysis. Often, transport coefficient models are needed in equipment and in-situ models to account for the importance of momentum, heat, and mass transfer. Previous work+ demonstrated a novel component-based reference equation of state approach for correlating self-diffusion coefficient and viscosity over the entire fluid region (liquid, gas, and critical fluid). In this paper, a segment-based approach is used to extend the previous work+ from a limited number of individual component correlations to a predictive fluid viscosity correlation for a class of components consisting of n-alkanes, up to 1300 molecular weight, covering a wide range of components, temperatures, and pressures. A scaled segment viscosity-segment residual entropy correlation (V-S model) was introduced and evaluated here. PC-SAFT segment parameters and residual entropy were used in a correlation model linking viscosity to the PC-SAFT equation of state. Experimental evaluation of this V-S model used 3122 data points for eighteen n-alkanes, ranging from methane up to 2390 molecular weight linear polyethylene. Temperatures ranged from 96 °K to 650 °K, and pressures ranged from 10-4 atmospheres to 4990 atmospheres. The conditions studied are relevant to oil and gas reservoir engineering and other in-situ processes. Based on this work, covering the entire fluid region, the V-S model was found to result in a group correlation squared (R2) of -0.998 and group average absolute deviation (AAD) of 3.9%. Individual viscosity segment correlation parameters (Bseg and Aseg) were fitted to molecular weight and used in the predictive mode. In the predictive mode, a group AAD of 6.7% was obtained for n-alkanes from methane up to 1300 molecular weight linear polyethylene, over the entire fluid region. The scaled segment viscosity-segment residual entropy model introduced here has potential for a much broader range of applications. In addition, this model would be easy to embed in existing in-house and commercial simulators to provide predictive properties and rate-based modeling capability. + Novak, http://www.bepress.com/ijcre/vol9/A63

Kinetics of the Reaction of Dense CaO Particles with SO2

The kinetics of the reaction of dense CaO particles (2.5 mm dia.) with sulfur dioxide was studied using a thermogravimetric technique under the conditions of 750–950 °C, 1000–5000 ppm SO2, and 6 h reaction time. The growth of CaSO4 product layer was observed using a scanning electron microscope. The effect of internal structural change due to reaction, which complicates the kinetic analysis of porous particles, was eliminated in the present case. The thickening of the product layer behaved as the shrinking-core type reaction. The product layer was composed of many CaSO4 grains, the size of which increased singnificantly with increasing temperature. The long-term reaction kinetics was well described by the shrinking-core model for changing particle size by considering the product layer diffusion and intrinsic chemical reaction. The apparent reaction order of SO2 was 0.3 and close to 1.0 only at low CaO conversions. The values of chemical reaction rate constant and the activation energy for chemical reaction rate constant or product layer diffusivity were in the range reported by previous investigators, but the values of the product layer diffusivity were much higher. The model equations for the case involving the inward or outward solid-state diffusion of ions were derived. The reaction kinetics can be explained by considering both the diffusion of Ca2+ and O2– ions and the diffusion of gaseous reactants. The product layer tended to fracture continually and form more cracks at higher temperatures, thus resulting in higher values of product layer diffusivity and a high activation energy for diffusivity, and leading to an apparent SO2 reaction order smaller than first order.

Process engineering development for the manufacturing of manganese octoate on a pilot plant scale

A technically and economically feasible process is developed for the manufacturing of manganese octoate as a powerful paint drier in a pilot plant unit. Such material is an environmentally safe through drier, catalyzes cross linking within the whole coating layer and is highly recommended for both hard and durable finishes. Scaling-up is based upon successful studying, evaluation and optimization of all operating parameters affecting process chemical reaction kinetics, product recovery and purification, and finally the vacuum crystallization stage. The performance of the pilot unit, overall conversion of reactants (>85%) were in excellent conformity with laboratory results.Full characterization of the final product is accomplished through practicing a variety of instrumental XRF, FTIR, XRD, ED-XRF, elemental and HPLC analyses. The developed product has been used in different commercially practiced formulations proved excellent drier characteristics including adhesive strength, film hardness and ductility.The design capacity of the pilot plant could match excellently with local commercial market demands that depend on price–consumption rate relationships. The process techno-economic evaluation reveals high profitability potentials including % annual return on investment and payback period.

Argovin, a novel natural product secreted by the fungus Meira argovae, is antagonistic to mites

A metabolite of the fungus Meira argovae Boekhout, Scorzetti, Gerson & Sztejnberg (Exobasidiomycetidae) was assayed as an antagonist of mites. Separation of extracted fungal metabolites by reversed phase liquid chromatography (RPLC), with subsequent testing of the obtained fractions, allowed us to isolate a single mite-antagonistic fraction (also active against a bacterium) that primarily includes one major component. This active compound (herein termed ‘argovin’) was identified by analyzing its spectral characteristics as 4,5-dihydroxyindan-1-one, which has previously only been described as a product of chemical reactions. The growth rate of the fungus was higher at a neutral pH than at an acidic one. Meira argovae adjusts the pH of its media to values optimal for its colony growth and toxic secretions. RPLC-cleaned argovin at 0.2 mg ml−1 killed 100% of a population of the citrus rust mite, Phyllocoptruta oleivora (Ashmead) (Acari: Eriophyidae). This trait may be used to control citrus rust mites in the field, as well as for toxin production for industrial and pharmaceutical uses.

Surface modification of mineral dust particles by sulphuric acid processing: implications for ice nucleation abilities

Abstract. The ability of coated mineral dust particles to act as ice nuclei (IN) was investigated at LACIS (Leipzig Aerosol Cloud Interaction Simulator) during the FROST1- and FROST2-campaigns (Freezing of dust). Sulphuric acid was condensed on the particles which afterwards were optionally humidified, treated with ammonia vapour and/or heat. By means of aerosol mass spectrometry we found evidence that processing of mineral dust particles with sulphuric acid leads to surface modifications of the particles. These surface modifications are most likely responsible for the observed reduction of the IN activation of the particles. The observed particle mass spectra suggest that different treatments lead to different chemical reactions on the particle surface. Possible chemical reaction pathways and products are suggested and the implications on the IN efficiency of the treated dust particles are discussed.

Investigation of formation of a spatial position of longitudinal discharge in a supersonic flow by fitting the configuration of an anode under conditions of injection of propane and kerosene into the discharge zone

Results of gas-dynamic and spectroscopic studies of the possibility of a longitudinal discharge formation in a supersonic flow using an artificial zone of low pressure behind an anode under conditions of hydrocarbon fuel injection in the discharge region are presented. An absence of the connection of the combustion zone to the walls of combustion chamber is a feature of the investigated configuration of module. An advantage of this module is the creation of the stabilization effect of the combustion zone with simultaneous intensification of fuel mixing and plasma-chemical reactions due to the use of an incipient gas-dynamic peculiarity of the flow and a nonequilibrium electric discharge. Experiments are carried out at the Mach number M = 2 and static pressure in the flow ∼3.47 × 104 Pa (260 Torr) in a wind tunnel with a closed test section with a cross section of 120 × 120 mm2. The discharge current is kept at a level of 1 A; the consumption of propane, used as a hydrocarbon fuel, is 1.2 g/s; and the consumption of kerosene is 1.3 g/s. A comparison between the intensity distributions of the radiation of incipient products of chemical reactions given different variants of fuel injection in the discharge zone is carried out.

Characterization and kinetics of reduction of CaSO 4 with carbon monoxide for chemical-looping combustion

Chemical-looping combustion (CLC) of fuels via the cyclic reduction and oxidation of an oxygen carrier is a novel process for CO 2 capture. CaSO 4 has emerged as an alternative material with much lower cost and higher oxygen storage capacity compared to metal oxide based oxygen carrier. In principle, CaSO 4 is reduced by CO and H 2 (coal gasification products) generating CaS, CO 2 and H 2O, and then the solid product CaS is regenerated back to CaSO 4 in air. Research on the reactions of CaSO 4 and CaS is not only important for understanding the reaction mechanism and parameters for the new CLC technology but also of high interest in understanding the sulfur chemistry in fluidized bed combustion and gasification. This paper focuses on the reduction reaction of CaSO 4 with CO to CaS and CO 2 (CaSO 4 + 4CO → CaS + 4CO 2) by thermodynamics, characterization and kinetics analysis. Phase diagram of CaSO 4–CaO–CaS indicates the operation regime of reduction–oxidation cycle by delicate control of temperature and partial pressure of reaction gases. The kinetics of the reduction reaction of a low cost natural anhydrite as oxygen carrier was investigated in an isothermal differential bed reactor where a thin layer of CaSO 4 particles were exposed to a plug flow of CO balanced by N 2. Prior to the kinetics modeling, extensive physical and chemical characterization analyses, such as X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDX), and N 2 adsorption–desorption were carried out to understand the reaction mechanism. External mass transfer and heat effects were minimized and the operation regime for intrinsic kinetics was determined. The experimental data was described with a gas–solid shrinking unreacted core model (SCM) with both chemical reaction control and product layer diffusion resistance considered.

Development of macro- and micromixing in confined flows of reactive fluids

Simultaneous development of macro- and micromixing in confined axis-symmetric reacting flows has been determined experimentally. Mixing of aqueous solutions of acid (internal jet) and base (coflow) with the coflow-to-jet flow rate ratio Q = V ˙ c / V ˙ j = 5.0 , at which the velocity at the jet exit was higher than the co-flow one, was examined in a co-axial jet mixer. The two-color PLIF method was used: the dyes – sodium fluorescein and rhodamin B – were premixed to the jet. The reaction product concentration or molecular mixing was determined by measuring the radiated light intensity of sodium fluorescein. The fluorescence of rhodamin B highlighted turbulent transfer by vortices or mixture fraction development. Variations of reactant concentrations were calculated using the mass conservation equation and the simultaneously measured distributions of mixture fraction and chemical reaction product concentration. The analysis of mixing parameters showed a significant difference in the dynamics of turbulent and molecular mixing.

Propagation of a subdiffusion reaction front and the “aging” of particles

The minimum velocity of a subdiffusion reaction front has been determined for two cases distinguishing in details of reaction kinetics. In the first and second cases, a particle that is a product of the chemical reaction acquires the mobility of the first and second reagents, respectively. Although the diffusion properties of both reagents are the same, the front velocity in the first and second cases is nonzero and zero, respectively. The difference is explained by the fact that the propagation of the front leads to the selection of the particles of one of the reagent in mobilities. The average mobility of the particles of this reagent located in the front region is higher than that of the particles beyond the front.

High-temperature hot corrosion behavior of gadolinium zirconate by vanadium pentoxide and sodium sulfate in air

Gadolinium zirconate (Gd 2Zr 2O 7) prepared by solid state reaction exhibited a defect fluorite-type structure. Reactions between Gd 2Zr 2O 7 ceramic and vanadium pentoxide (V 2O 5), sodium sulfate (Na 2SO 4), and V 2O 5 + Na 2SO 4 mixture were investigated from 700 to 1000 °C in air using an X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). V 2O 5 reacts with Gd 2Zr 2O 7 to form gadolinium vanadate (GdVO 4) and monoclinic zirconia ( m-ZrO 2) at 900 and 1000 °C in air. However, no chemical reaction product between Na 2SO 4 and Gd 2Zr 2O 7 is found at 900 and 1000 °C in air. V 2O 5 reacts with equal molar Na 2SO 4 to form sodium vanadate (NaVO 3) at 610 °C. In the temperature range of 700–1000 °C, Na 2SO 4 + V 2O 5 mixture reacts with Gd 2Zr 2O 7 in air to form the final reaction products of GdVO 4 and m-ZrO 2.

Secondary organic aerosol formation from a large number of reactive man-made organic compounds

A photochemical trajectory model has been used to examine the relative propensities of a wide variety of volatile organic compounds (VOCs) emitted by human activities to form secondary organic aerosol (SOA) under one set of highly idealised conditions representing northwest Europe. This study applied a detailed speciated VOC emission inventory and the Master Chemical Mechanism version 3.1 (MCM v3.1) gas phase chemistry, coupled with an optimised representation of gas–aerosol absorptive partitioning of 365 oxygenated chemical reaction product species. In all, SOA formation was estimated from the atmospheric oxidation of 113 emitted VOCs. A number of aromatic compounds, together with some alkanes and terpenes, showed significant propensities to form SOA. When these propensities were folded into a detailed speciated emission inventory, 15 organic compounds together accounted for 97% of the SOA formation potential of UK man made VOC emissions and 30 emission source categories accounted for 87% of this potential. After road transport and the chemical industry, SOA formation was dominated by the solvents sector which accounted for 28% of the SOA formation potential.

Fiber laser intracavity absorption spectroscopy for in situ multicomponent gas analysis in the atmosphere and combustion environments

Intracavity absorption spectroscopy with a broadband Er3+-doped fiber laser is applied for the measurements of several molecular species revealing quantitative information about the gas concentration, temperature and chemical reactions in flames. The spectral range of measurements extends from 6200 cm−1 to 6550 cm−1 with the proper choice of the fiber length and by moving an intracavity lens. With a pulsed laser applied in this experiment, the sensitivity to absorption corresponds to an effective absorption path length of 3 km assuming the cavity is completely filled with the sample. For a cw laser, the effective absorption path length is estimated to be 50 km. Absorption spectra of various molecules such as CO2, CO, H2O, H2S, C2H2 and OH were recorded separately in the cell and/or in low-pressure methane and propane flames. The presented measurements demonstrate simultaneous in situ detection of three molecular products of chemical reactions at different flame locations. Variation of the relative strengths of OH absorption lines with the temperature enables the estimation of the local flame temperature. The sensitivity of this laser does not depend on the broadband cavity losses and it can be used for in situ measurements of absorption spectra in hostile environments such as contaminated samples, flames or combustion engines. The presented technique can be applied for various diagnostic purposes, such as in environmental, combustion and plasma research, in medicine and in the determination of stable isotope ratios.

Electron Spectra Line Shape Analysis of Highly Oriented Pyrolytic Graphite and Nanocrystalline Diamond

The X-ray excited Auger electron spectroscopy (XAES), X-ray photoelectron spectroscopy (XPS) and elastic peak electron spectroscopy (EPES) methods were applied in investigating samples of nanocrystalline diamond and highly oriented pyrolytic graphite of various C sp(2)/sp(3) ratios, crystallinity conditions and grain sizes. The composition at the surface was estimated from the XPS. The C sp(2)/sp(3) ratio was evaluated from the width of the XAES first derivative C KLL spectra and from fitting of XPS C 1s spectra into components. The pattern recognition (PR) method applied for analyzing the spectra line shapes exhibited high accuracy in distinguishing different carbon materials. The PR method was found to be a potentially useful approach for identification, especially important for technological applications in fields of materials engineering and for controlling the chemical reaction products during synthesis.

Experiment study of model compound oxidation on spontaneous combustion of coal

Spontaneous combustion is one of the severest accidents in the process of coal production and transportation. Therefore it is significant to study the mechanism of coal spontaneous combustion. Based on theoretical analysis, 7 kinds of model compounds have been chosen in this paper, which are hyacinthin, anisole, diphenylmethane, phenetole, benzyl alcohol, benzhydrol, and aphenylpropanol. And they contain respectively active groups such as aldehyde group, methoxyl group, hypomethyl bond, hypomethylether bond, hypomethyl bond of a-carbon atom with hydroxyl, hypoalkyl bond of a-carbon atom with hydroxyl, and so on. According to the theory of free radical reactions, taking the model compound of coal above as research object, chemical reaction kinetic parameters, thermodynamic parameters, and products from normal temperature to 150°C have been quantitatively studied by oxidation device and analytical instrument, then the oxidation course can be deduced. The results show that all the model compounds consumed oxygen and produced CO and CO2 at different degrees after temperature programmed to 150°C. The oxidation characteristic of the active groups in coal and the effect of them on spontaneous combustion can be recognized, and spontaneous combustion mechanism can be exposited systematically in chemistry by means of studying the oxidation of model compound.

Methane steam reforming in an annular microchannel with Rh/Al2O3 catalyst

Regularities of methane conversion in the presence of water steam were obtained experimentally while activating chemical conversions on the inner convex wall of an annular microchannel. The steam methane reforming was done on the Rh/Al2O3 nanocatalyst with the heat applied through the microchannel gap from the outer wall. Concentrations of the products of chemical reactions in the outlet gas mixture are measured at different temperatures of the outer microchannel wall. The range of channel wall temperatures at which the ratio of hydrogen and carbon oxide in the outlet mixture grows substantially is determined. Data on the composition of methane conversion products for the ratio H2O/CH4 = 1.77 and the activation energy of methane steam reforming at reactor outer wall temperatures of up to 880°C are obtained. The effect of the radiation heat exchange and the external diffuse limitation on the rate of chemical conversions in methane steam reforming in an annular microchannel with external heat supply is determined.

Isotope effect in Boudouard disproportionation reaction in optically pumped CO

Isotope composition of CO 2 produced in CO–Ar mixtures optically pumped by a CO laser has been analyzed by Fourier transform infrared (FTIR) absorption spectroscopy. Carbon monoxide reactant is a higher-than-natural abundance mixture of 13CO and 12CO. Carbon monoxide in the reactor is vibrationally excited by resonance absorption of the laser radiation and is vibration–vibration (V–V) pumped up to high vibrational levels. 12CO vibrational level populations and temperature in the excited region are measured by FTIR emission spectroscopy. Highly vibrationally excited CO molecules chemically react to form CO 2, which at these conditions is expected to be enriched in 13C isotope. Chemical reaction products are analyzed by FTIR absorption spectroscopy. The results show that CO 2 in the products is enriched in 13C isotope, with enrichment coefficient varying from β = 1.25 to 1.9, and CO 2 yield varying from 70 to 170 ppm. These results are in good agreement with the master equation kinetic model.

Self-lubricating carbon nanotube reinforced nickel matrix composites

Nickel (Ni)—multiwalled carbon nanotube (CNT) composites have been processed in a monolithic form using the laser-engineered net shape (LENS™) processing technique. Auger electron spectroscopy maps determined that the nanotubes were well dispersed and bonded in the nickel matrix and no interfacial chemical reaction products were determined in the as-synthesized composites. Mechanisms of solid lubrication have been investigated by micro-Raman spectroscopy spatial mapping of the worn surfaces to determine the formation of tribochemical products. The Ni-CNT composites exhibit a self-lubricating behavior, forming an in situ, low interfacial shear strength graphitic film during sliding, resulting in a decrease in friction coefficient compared to pure Ni.