Effect Of Reaction Atmosphere Research Articles

Combustion characteristics of millimeter-sized aluminum particles in fluidized bed under various O2/CO2/H2O atmospheres

Aluminum is an attractive alternative fuel, but it burns very inefficiently due to the formation of a dense Al2O3 layer which prevents O2 from diffusion to the surface of Al particles. In previous experiments, the combustion of millimeter-sized Al (mAl) particles in the fluidized bed has achieved a substantial increase in the combustion efficiency, but further improvements are still needed. In this study, the effects of reaction atmosphere on the fluidized combustion of mAl particles were investigated. The experiments with different O2/H2O/CO2 concentrations were conducted. The experimental results indicate that the combustion efficiency of mAl particles in fluidized bed increases as the mole fraction of O2, H2O or CO2 increases, and the highest combustion efficiency can reach 38.7%. After the analysis of the oxide film on the surface of aluminum particles, it was found that it is easier to generate the unstable θ-Al2O3 under CO2 atmosphere, and it is easier to generate the unstable γ-Al2O3 and θ-Al2O3 under H2O atmosphere. The unstable Al2O3 film is more likely to be abraded in the fluidized bed, which leads to the effective improvement of the combustion efficiency.

Improved photocatalytic activity of carbon-based polymeric semiconductor for efficient decontamination of wastewater: Effect of reaction atmosphere and pyrolysis temperature

Novel graphitic-carbon nitride (g-C3N4) photocatalyst was synthesized by thermal-pyrolysis of melamine. Pyrolysis reaction temperature (500–700 °C) and gas atmosphere, were optimized to achieve an efficient visible light active photocatalyst. In-depth studies indicate that the reaction temperature of 650ᵒC is an optimum condition for the synthesis of the g-C3N4 photocatalyst. Air atmosphere dominantly favoured a formation of layered g-C3N4structure compared to those pyrolyzed under argon or nitrogen atmosphere. In contrast to other samples, the optimized g-C3N4 photocatalyst showed significant photodegradation, with a degradation rate of 4.4 × 10−2 min−1, for Rhodamine B(RhB) degradation under simulated solar radiation. A large surface area of 42 m2g-1 and suitable band energetics is attributed to better degradation performance.

Spectroscopic Analysis of Products from Low-Rank Coal Microwave Pyrolysis: Effect of Reaction Atmosphere

The pyrolysis of low-rank coal is considered as the optimal method of realizing clean and efficient production of blue coke, tar, and gas. The experiments of low-rank coal microwave pyrolysis under CO2, CH4, H2, and circulating gas (CG) are studied in a custom-designed microwave oven to clearly clarify the effects of reaction atmospheres on pyrolysis temperature, products yields, and spectroscopic characteristics of pyrolysis products by the analysis techniques of FT-IR and GC-MS. The results show that among four pyrolysis atmospheres, the temperature-rise rate and final pyrolysis temperature under H2 atmosphere are both highest, taking only 5.6 min to arrive at 750°C, and the final temperature is greater than 950°C. The liquid yields under CO2, CH4, H2, and CG atmospheres are 21.8, 24.4, 28.2, and 26.8 wt.%, respectively. The contents of –OH, aromatic ring C=C double bond, and –C=O in the solid product under CH4 atmosphere are highest, possibly because of the thermal polycondensation and the secondary degassing of the solid product. The hydrogenation of H free radicals dissociated from “rich hydrogen” gas results in an improvement in the alkane content and a decrease in the aromatic hydrocarbon content in tar, which is confirmed by the change in oxygen content in the solid product. The hydrogenation technique of circulating coal gas on low-rank coal microwave pyrolysis is economical, energy-efficient, and feasible, which is helpful in the development of coal processing technologies.

Effects of reaction atmosphere on physico-chemical properties of V-doped FeNb11O29

FeNb11O29, pure or doped with metal transition ions, is a very promising material with advanced multifunctionalities and interesting applicative perspectives. It is isostructural with Nb12O29, one of the rare compounds in which Nb displays a local magnetic moment and shows both antiferromagnetic ordering and metallic conductivity at low temperatures. In this work we have synthesized and studied Fe0.8V0.2Nb11O29 monoclinic powders. In particular we monitored the effects on structural, electronic and magnetic properties in samples produced in different atmospheres to stabilize cations with different oxidation states.We have demonstrated that the reaction atmosphere influences the phase homogeneity, the crystallite size and the amount of paramagnetic centres, with a transformation of Fe3+ in Fe2+ when an inert atmosphere is used, as proved by the absence, in this case, of any electron paramagnetic resonance signal. Also the Raman spectra result to be affected due to the change of coordination polyhedra. Subsequent re-oxidation of reduced powders brings to the monophasic iron niobate again containing Fe3+ demonstrating the reversibility of redox process. This reversibility is accompanied by a complete restoring of monoclinic structure evidenced by X-ray diffraction data and by Raman measurements, which allowed also to follow in situ the spectral changes induced by laser heating.

Effect of reaction atmosphere on photodeposition of Pt nanoparticles and photocatalytic hydrogen evolution from SrTiO3 suspension system

We systematically investigated the impact of reaction atmosphere on the Pt cocatalyst photodeposition and hydrogen evolution. A long induction period which is hardly found in close-system appears in the presence of oxygen, and is affected by the concentration of chloroplatinic acid. The Pt cocatalyst is metal state and contributes to the electronic states near Fermi level judging from the valence band X-ray photoelectron spectrum. The cocatalyst metal Pt will reduce the surface photovoltage signals due to the metal feature. The hydrogen evolution rate increased and reached a platform with increasing the Pt coverage on the surface of photocatalyst which is characterized by the Pt:Ti atomic ratio.

Effect of reaction atmosphere on the products of slow pyrolysis of coals

Slow pyrolysis of semianthracite (SA) and high volatile bituminous C (HVBC) coals was performed under two reaction atmospheres (CO2 and N2) and three different particle size distributions. It was found that the physicochemical properties of a char and its respective combustibility depend significantly on the reaction atmosphere under which it was produced. For SA char particles larger than 0.7mm, the BET surface area increases when the atmosphere is enriched in CO2 due to intraparticle side reactions, differences in the thermal-diffusive properties of N2 and CO2, and the reactive effects of the latter. When particle size ​​decreases below 45μm, no mesoporous surface area developed with either atmosphere. The combustibility of char formed in CO2 was higher than in N2; furthermore, the pore size distribution (PSD) is different in both environments. ATR-FTIR spectrometry indicates that char formed under N2 is more aromatic. Additionally, FE-SEM visualization showed the occurrence of softening more evident in N2 than in CO2; however the char obtained in CO2 looked as if it had lost more material, which agrees with other experiments showing lower elemental and fixed carbon contents for this condition.

TG analysis and kinetic study of organic constituents in wastewater from coal‐gasification process

AbstractIn the paper, the thermal reactivity of organic constituents from coal‐gasification wastewater is performed through physicochemical and thermogravimetric (TG) analysis. The effects of reaction atmosphere, oxygen concentration, heating rate, and final temperature on both solids conversion and degradation rate are experimentally studied. The results indicate that organic constituents mainly consist of aliphatic hydrocarbon, phenols, and ammonium, and so on. The thermal degradation of organic constituents in various atmospheres can be divided into four regions: 100–200, 200–300, 300–410, and 410–900 °C. The TG/DTG curves present considerable differences in the last region compared with that in the first three regions. In addition, the degradation rate shows a considerable increase and moves toward higher temperature region with heating rate. Furthermore, the kinetic parameters of organic constituents are analyzed by one multi‐heating rate method. The calculated results show that apparent activation energy of organic constituents varies between 82.8 and 91.3 kJ mol−1 under various reaction atmospheres. This information is potentially useful for the design and retrofitting of the large‐scale equipment to recover industrial wastewater. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.

Effect of Reaction Atmosphere and Heating Rate During Reactive Sintering of Ni–Ti Intermetallics

The effect of reaction atmosphere and heating rate during reactive sintering of nickel and titanium powder blend (Ni: 52 at.%, particle size <150μm, >99.99% purity, Ti: 48 at.%, particle size <44μm, >99.5% purity) were studied. The powder mixtures were uniaxially compressed under pressure of 637MPa and sintered at temperatures 500, 650, 900 and 1100°C in air, vacuum, argon and nitrogen atmospheres. Two heating rates were applied: 200 and >300K.min-1. The results show that a significant effect of reaction atmosphere in terms of the quantity of the Ti2Ni phase applies especially at very high heating rate. In terms of phase morphology, oxygen causes refinement of the structure, regardless of heating rate. Mechanism and kinetics of the reactions leading to Ni–Ti phases were determined by DTA and thermogravimetry. It was found that the Ti2Ni phase forms already at 500°C. At 650°C this phase undergoes a reaction with nickel to NiTi and Ni3Ti.

Enhanced photochemical decomposition of environmentally persistent perfluorooctanoate by coexisting ferric ion and oxalate.

Perfluorooctanoic acid (PFOA), an environmentally persistent pollutant, was found to be quickly decomposed under 254nm UV irradiation in the presence of ferric ion and oxalic acid. To understand the PFOA decomposition mechanism by this process, the effects of reaction atmosphere and concentrations of ferric ions and oxalic acids on PFOA decomposition were investigated, as well as decomposition intermediates. PFOA mainly decomposes via two pathways: (i) photochemical oxidation via Fe(III)-PFOA complexes and (ii) one-electron reduction caused by carboxylate anion radical (CO2 (•-)), which was generated by photolysis of ferrioxalate complexes. Under excess oxalic acid, PFOA decomposition was accelerated, and its corresponding half-life was shortened from 114 to 34min as ferric concentration increased from 7 to 80μM. Besides fluoride ions, six shorter chain perfluorinated carboxylic acids (PFCAs) bearing C2-C7 were identified as main intermediates. The presence of O2 promoted the redox recycling of Fe(3+)/Fe(2+) and thus avoided the exhaustion of the Fe(III).

The effect of reaction atmosphere and growth duration on the size and morphology of boron nitride nanotubes

Observations of BNNTs grown in the reaction atmosphere of argon, ammonia and nitrogen.

Enhanced direct sunlight photocatalytic oxidation of methanol using nanocrystalline TiO2 calcined at different temperature

The present study focused on photocatalytic oxidation of methanol to formaldehyde using nanocrystalline TiO2 (Degussa P-25) photocatalyst calcined at different temperature having different ratio of anatase (A)–rutile (R) phase composition under direct sunlight irradiation. The calcined nanocrystalline TiO2 was characterized using powder X-ray diffraction, N2 adsorption, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, and UV–Visible diffuse reflectance spectroscopy techniques. The determination of hydroxyl radical formation during the course of the reaction was carried out using fluorescence technique with terephthalic acid as a probe molecule. The photocatalytic activity of catalysts was evaluated by methanol oxidation under direct sunlight irradiation and activity was compared with pure anatase TiO2. The result revealed that nanocrystalline TiO2 (P-25) calcined at 500 °C displays higher photocatalytic activity and the order of rate of HCHO formation is P25-500 (A74 %:R26 %) > P25 (A80 %:R20 %) > AT (A100 %) > P25-600 (A12 %:R88 %) > P25-700 (R100 %). The result also infers that TiO2 with mixed phase exhibit higher photocatalytic activity than TiO2 with pure anatase or rutile phase. The rapid transfer of photogenerated electron from rutile to anatase leads to increase in the charge separation and enhances the photocatalytic activity under direct sunlight irradiation. Effect of operational parameters like amount of catalyst and effect of reaction atmosphere have been investigated on the photocatalytic oxidation of methanol under direct sunlight irradiation.

The Effects of Reaction Atmosphere on Composition, Oxygen Distribution, and Heating Value of Products from the Hydrothermal Liquefaction of Corn Stalk

The hydrothermal liquefaction of corn stalk under different atmospheres (N2, H2, and CO) was performed in a high pressure autoclave (500 mL) at 380°C for 30 min, and the compositions of the liquefaction products were characterized by elemental analysis. It was found that the order of conversion of biomass, yield, and H/C ratio of liquid product follows: CO > H2 > N2; 10–13% oxygen is preserved in the liquid product and most of the oxygen in biomass is removed as CO2 and H2O; 64–79% and 24–31% of the original biomass' heating value is preserved in the liquid product and solid organic matter.

Thermal Analysis Characteristics of the Eucalyptus Leaves under Various N&lt;sub&gt;2&lt;/sub&gt;/O&lt;sub&gt;2&lt;/sub&gt; Conditions

Thermal chemical conversation of biomass is studied as a means to reduce the greenhouse gases and pollutant emission caused by the traditional fossil fuel. Eucalyptus is one of the fast growing tress in the south of China, which has great potential as a kind of renewable energy sources. An experimental study on eucalyptus leaves was carried out in thermogravimetric analyzer to investigate the effects of reaction atmosphere on thermal chemical characteristics. The volume fraction of oxygen was 0, 0.21, 0.27 and 0.33 respectively. Experimental results show that with the increasing of the oxygen concentration, the reaction time decreased significantly. The kinetic Parameters were also calculated, including the activation energy (E) and pre-exponential factor (A).

Evaluation of the Effect of Sulfur on Iron-Ore Oxygen Carrier in Chemical-Looping Combustion

Chemical-looping combustion (CLC) is an emerging combustion technology that can be used to meet the demand of energy production with inherent separation of CO2. Because of the presence of sulfur contaminants in fossil fuels, the gaseous products of sulfur species and the interactions between these sulfur contaminants and the oxygen carrier are significant concerns in chemical-looping combustion. Experiments on chemical-looping combustion of a sulfur-containing gaseous fuel with iron ore as the oxygen carrier were performed by thermogravimetric analysis and Fourier transform infrared (TGA–FTIR) spectroscopy. The effects of reaction atmosphere (N2 and CO2), H2S concentration, and pressure on the reactivity of iron ore in the presence of H2S were investigated. The evolution of gaseous sulfur species was also investigated in both N2 and CO2 atmospheres. With a higher concentration of H2S in the gaseous fuel, the weight loss was slower, and a weight gain was even observed due to the sulfidation of iron ore. Sulfidation of iron ore was observed in both N2 and CO2 atmospheres, and elevated pressure contributed to a higher sulfidation rate. Compared with N2 atmosphere, CO2 atmosphere gave higher concentrations of COS and an initial SO2 peak but a lower concentration of CS2. Furthermore, the effect of sulfidation on the structure of the iron ore was investigated in a fluidized bed, and scanning electron microscopy with energy-dispersive analysis by X-rays (SEM-EDAX) and X-ray diffraction (XRD) were utilized to characterize the iron ore. The sulfidation of iron ore caused a decrease in both surface area and pore volume, and the porous surface of the oxygen carrier became smoother and almost imperforate. FeS was the only iron sulfide observed during the sulfidation process. The vulcanized iron ore could be regenerated with air calcination treatment, and the addition of H2O in the gaseous fuel could prevent the sulfidation of iron ore. The addition of CaO in the oxygen carrier was effective in mitigating the sulfidation and reducing the emission of gaseous sulfur species.

Effect of reaction atmosphere on combustion synthesis of Ti2AlN

Combustion synthesis of Ti2AlN was carried out in air and pressurised N2 respectively. The reaction atmosphere had an evident effect on the phase composition and microstructure of the products. By combustion synthesis in 2 MPa N2, Ti2AlN was synthesised as the major product, but in the samples prepared in air, Ti2AlN was obtained only as a minor phase, and the predominant phases were Ti–Al intermetallics. The reaction mechanism has been studied, suggesting that TiN is a key intermediate in the formation of Ti2AlN. It is proposed that, in the combustion synthesis of Ti2AlN, the flux of N2 plays an important role in determining both reaction kinetics and phase composition of the products.

Preparation Research of CaB&lt;sub&gt;6&lt;/sub&gt; Powder by Self-Propagating High-Temperature Synthesis

Self-propagating High-temperature Synthesis (SHS) method was adopted to synthesize powder containing CaB6, and the power was leaching by sulfuric acid. Effects of reaction atmosphere, magnesium addition, H2SO4 acidity and leaching temperature on the performances of CaB6 powderwas investigated, the microstructure of products were researched by SEM and XRD, the results show that the phases of products by SHS are CaB6、Mg3B2O6 and Ca3B2O6, and high purity CaB6 powders are obtained after the products by SHS was leaching by Sulfuric acid. The SHS conditions are the vacuum atmosphere and 30% excessive magnesium addition and the leaching conditions are 55% acidity of Sulfuric acid and 40°C leaching temperature, the perfect and uniform grain of CaB6 powers are obtained at the above conditions.

Effects of reaction atmosphere on dimethyl ether conversion to propylene process over Ca/ZSM-5

Effects of reaction atmospheres (nitrogen, carbon monoxide, carbon dioxide, syngas and water vapor) on stability of the catalyst, selectivities to propylene and byproducts for dimethyl ether conversion to propylene (DTP) over Ca/ZSM-5 were investigated in a continuous flow fixed-bed reactor. Besides, the regenerated catalyst was also studied for DTP process. The results show that the catalyst exhibits best stability, highest propylene selectivity and lowest selectivities to byproducts in carbon dioxide atmosphere, followed by nitrogen, carbon monoxide and syngas atmosphere, and water vapor atmosphere exerts worst effect on DTP. The catalytic performance of the regenerated catalyst also demonstrates that carbon dioxide as reaction atmosphere is most beneficial to DTP process.

Catalytic Deoxygenation of Tall Oil Fatty Acids Over a Palladium-Mesoporous Carbon Catalyst: A New Source of Biofuels

Catalytic deoxygenation of tall oil fatty acids (TOFA) was demonstrated over palladium catalysts supported on mesoporous carbon at 300 °C using dodecane as a solvent. Maximally 95% selectivity to linear C17 hydrocarbons was achieved. The effects of reaction atmosphere and initial TOFA concentration were investigated.

Effect of Reaction Atmosphere on the Electrocatalytic Activities of Pt/C and PtRu/C Obtained in a Polyol Process

Pt and PtRu nanoparticles supported on Vulcan XC-72R carbon obtained under different atmospheres (air and N2) were prepared via a polyol process in ethylene glycol solution and denoted as Pt/C−N2, Pt/C−air, PtRu/C−N2, and PtRu/C−air, respectively. The catalysts were characterized by XRD (X-ray diffraction), TEM (transmission electron microscopy), and XPS (X-ray photoelectron spectroscopy). TEM images show that metal nanoparticles are uniform in size and are well dispersed on the carbon support for all the catalysts. The mean particle sizes of Pt/C−N2, Pt/C−air, PtRu/N2, and PtRu/C−air are 2.6, 2.7, 2.3, and 1.8 nm, respectively. Among these samples, PtRu/C−air catalyst has the smallest nanoparticle size with a narrow size distribution. The three strongest diffraction peaks of both Pt/C−N2 and Pt/C−air catalysts are located at 2θ = 39°, 46°, and 67°, corresponding to the Miller indices of (111), (200), and (220) of a Pt fcc (face-centered cubic) crystal structure. The XRD pattern of PtRu/C−N2 displays an f...

Effect of reaction atmosphere on particle morphology of TiO2 produced by thermal decomposition of titanium tetraisopropoxide

Thermal decomposition of titanium tetraisopropoxide (TTIP) was carried out in varying reaction atmospheres: nitrogen, oxygen, and nitrogen plus water vapor. The effect of reaction atmosphere on the morphology, size, and crystalline structure of produced TiO2 particles was studied. The reactor used was similar to the microreactor proposed earlier by Park et al. (2001, J. Nanopart. Res., 3, 309–319), but for a modification in the precursor evaporator. The reactor temperature was varied from 300 to 700°C and the TTIP concentration in the evaporator from 1.0 to 7.0 mol%, holding the reactor residence time at 0.7 s. The primary-particle size was in the range 25–250 nm, varying with operating condition. The crystalline structure was amorphous in nitrogen, a mixture of rutile and anatase in nitrogen plus water vapor, and anatase in oxygen atmospheres. In nitrogen, agglomerates composed of very small particles whose individual boundaries are not clearly distinguished were produced. In oxygen, the particles composing an agglomerate became larger and were clearly spherical. As the atmosphere was varied to the nitrogen plus water vapor, the particle size increased further. The variation of primary particle size with reaction atmosphere was discussed in comparison with previous experimental data.