Effect Of Gas Atmosphere Research Articles

Fast Pyrolysis of Rice Husk in a Fluidized Bed: Effects of the Gas Atmosphere and Catalyst on Bio-oil with a Relatively Low Content of Oxygen

The pyrolysis of rice husk is carried out in a fluidized-bed reactor at atmospheric pressure. The effects of pyrolysis parameters, i.e., gas atmosphere and catalyst, on the carbon conversion of rice husk and composition of bio-oils are studied. The experiments with catalysts under a hydrogen atmosphere to produce bio-oils with a much lower oxygen content compared to those under a nitrogen atmosphere are performed. The results show that the oxygen content of bio-oils is markedly reduced because the oxygenated hydrocarbons are hydrocracked, resulting in the formation of H2O, CO, and CO2, when catalysts are introduced under a nitrogen atmosphere and decreases even more under a hydrogen gas atmosphere (hydropyrolysis). The oxygen content of bio-oil under a hydrogen atmosphere decreases from over 31.1% without a catalyst to 25.91, 20.51, 26.51, and 10.1% with Ni/Al2O3, Ni/LY, dolomite, and CoMo/Al2O3, respectively. The use of CoMo/Al2O3 and Ni/LY catalysts under a hydrogen atmosphere shows high activity to dec...

Template removal processes within individual micron-sized SAPO-34 crystals: Effect of gas atmosphere and crystal size

In situ UV–Vis micro-spectroscopy has been employed to reveal physicochemical insight in the template removal process of morpholine-containing micron-sized SAPO-34 crystals at the single particle level. The differences in UV–Vis absorption bands and the related rate of their formation and disappearance demonstrate the generation of different intermediates when the detemplation process is performed in either oxygen or nitrogen. A series of detemplation experiments in oxygen with SAPO-34 crystals ranging between 7.5 and 58 μm indicate the formation of five major Gaussian functions with band maxima at 405, 450, 505, 555 and 608 nm, building up the experimental UV–Vis absorption spectra. These Gaussian functions, assigned to different carbonaceous deposits and their precursors, demonstrate that two separate temperature trends can be distinguished. The first one is related to the formation of small organic compounds, characterized by band maxima at 405 and 450 nm, which lead to a bimodal intensity distribution at the low and high end of the heating ramp for large-sized SAPO-34 crystals, while the more extended poly-aromatic compounds, characterized by band maxima at 555 and 608 nm, generate a mono-modal distribution at intermediate heating temperatures for both small- and large-sized SAPO-34 crystals. These features provide evidence for a crystal size dependent relationship between pore blocking and the formation of small and more extended molecular compounds within SAPO-34 porous networks when performing a thermal detemplation process.

Carbothermal reduction of ilmenite concentrates and synthetic rutile in different gas atmospheres

Carbothermal reduction of ilmenite concentrates and synthetic rutile was studied in isothermal experiments in hydrogen, argon and helium in a tube reactor. Concentrations of CO, CO2 and CH4 in the off gas were measured online using an infrared gas analyser. The reaction products were analysed by X-ray diffraction. Pseudorutile and ilmenite were the main phases in ilmenite concentrates. Reduction of ilmenite concentrates and synthetic rutile in hydrogen was significantly faster than that in inert atmosphere. The effect of gas atmosphere became stronger for lower grade ilmenite containing more iron oxides. The conversion rate of titania to titanium oxycarbide in hydrogen decreased with increasing grade of ilmenite concentrate. In inert gas, the reduction rates of secondary ilmenite and HYTI70 were close to that of primary ilmenite. Reduction of synthetic rutile was faster in comparison with ilmenite concentrates.

Study on the Stability of Sorbents Removing H2S from Hot Coal Gas

Mixed metal oxide containing iron with the high-sulfur capacity and reactivity is considered as one of the most favorable sorbents for desulfurization in hot gas. The stability and life of iron-based sorbents are the main challenges for the hot gas cleanup techniques. Not only the effect of gas atmosphere but also the effect of ZnO and MgO on the stability of iron-based sorbent was studied in this work. The mechanism and factors influencing sorbent stability are discussed. The results showed that the coexistence of CO and H2 result in the instability of the zinc−iron-based sorbents. The reaction of carbon deposit is the crucial step affecting the stability of sorbent for hot gas desulfurization. ZnO in the sorbent is adverse to the physical stability of the iron-based sorbents. MgO in the sorbent hardly affects the physical stability of the iron-based sorbents but improves the capacity of removing the hydrogen sulfide from hot coal gas at 773 K.

Effects of Gas Atmosphere and Temperature on the Respiration Rates of Whole and Sliced Mushrooms (Agaricus bisporus)— Implications for Film Permeability in Modified Atmosphere Packages

An open flowthrough respirometer was used to determine the respiration rates of whole and sliced mushrooms as a function of O2, CO2, and storage temperature. Respiration rates were measured under the following O2 concentrations: 20, 15, 10, 5, and 2% at 5 temperatures (4, 8, 10, 13, and 16 degrees C). The effects of 5 CO2 concentrations (0, 2, 5, 10, 15%) at two O2 levels (2 and 20%) were also examined at these temperatures. Mushroom respiration increased with temperature following an Arrhenius-type relationship; activation energies and corresponding Q10 values were calculated. Lowering the oxygen concentration significantly decreased the respiration rate. The effects of reducing O2 levels were greater at higher storage temperatures. Both activation energies and Q10 values were lower under reduced O2 atmospheres compared with those in air. A Michaelis-Menten enzyme kinetics model was evaluated for describing the influence of gas concentrations on respiration rate. The effects of O2 fitted the O2 enzyme kinetics model well. CO2 exhibited small inhibitory effects on respiration of whole and sliced mushrooms, especially at low O2 concentrations and low temperatures. The enzyme model was used to predict respiration under an optimal modified atmosphere for mushrooms, and the required film O2 and CO2 permeabilities were defined for key pack design parameters.

Gold cementation from thiocyanate solutions by iron powder

Gold cementation with iron powder from thiocyanate solutions was conducted without de-aeration. The effects of various parameters such as pH, thiocyanate concentration, gold concentration, iron/gold mass ratio, temperature, stirring speed and presence of iron(III) in the solution were examined. These parameters were varied according to the ranges typically found in the literature. The effect of gas atmosphere on cementation of gold was also examined by flowing nitrogen gas through the solution during the runs and the recovery of gold was enhanced. The presence of iron(III) results in the low efficiency of gold precipitation as well as the low grade of the cements. It was established that the rate of the reaction was first-order with respect to the gold concentration. The activation energy was found to be 9.3 kJ/mol and the cementation process was considered to be diffusion-controlled. A general mechanism for gold cementation is proposed.

Reduction of Zinc Oxide in Manganese Furnace Dust with Tar

Manganese furnace dust is formed when volatiles and fines are cleaned by wet scrubbers from the off-gases from manganese alloy smelting furnaces. Impediments to the recycling of the manganese furnace dust back to the ferroalloy furnaces are handling due to the presence of tar, and the potential accumulation of zinc in the furnaces, which can cause irregularities in their operation. This paper examines reduction of zinc oxide from manganese furnace dust formed during ferromanganese and silicomanganese production at Tasmanian Electro Metallurgical Company. Zinc oxide was reduced by tar in the furnace dust above 800°C. The reduction rate increased with increasing temperature with almost complete zinc removal at 1100°C. The effects of gas atmosphere, pellet size, pressure applied in pellet preparation, as well as mixing of furnace dust with manganese ore, on zinc oxide reduction and removal were studied.

RF 스퍼터링으로 Si 기판위에 제작된 ZnO 박막에서 ZnO 버퍼층의 가스분위기 영향

The effects of gas atmosphere and in-situ thermal annealing in buffet layers on the characteristic of the ZnO grown by RF magnetron sputtering have been investigated. It was shown that the introduction of buffer layers grown at the gas atmospheres of the mixed and the in-situ thermal treatment of the ZnO buffer layer improved the structural and optical properties. In addition, the ZnO films on the buffer layer thermal-annealed at gas ambience showed the strong emission of the near band gap exciton with narrow linewidth by combining the high-temperature growth of the ZnO film.

Effects of dissolved gas species on ultrasonic degradation of (4-chloro-2-methylphenoxy) acetic acid (MCPA) in aqueous solution

Sonochemical degradation of MCPA ((4-chloro-2-methylphenoxy) acetic acid) in dilute aqueous solutions was studied using ultrasound with a frequency of 500 kHz. The effect of gas atmosphere on MCPA degradation was investigated in nitrogen (N 2), air (O 2/N 2), oxygen (O 2), argon (Ar) and Ar/O 2 (60/40% v/v) atmospheres. For sonochemical degradation of MCPA in N 2, air (O 2/N 2), O 2 and Ar atmospheres, the rate enhancement of MCPA decomposition by sonolysis was found to be more effective in an O 2-enriched atmosphere compared to Ar atmosphere. It was considered that a higher amount of oxidants was formed in a higher O 2 partial pressure, which accelerated MCPA decomposition in a radical reaction system. On the other hand, both dechlorination and total organic carbon (TOC) removal rates were higher in Ar atmosphere, compared to those in O 2/N 2 atmosphere. It was found that, MCPA was most effectively decomposed by sonication in Ar/O 2 (60/40% v/v) atmosphere, with higher rates of decomposition, dechlorination and TOC removal.

Formation of NO x precursors during the pyrolysis of coal and biomass. Part VI. Effects of gas atmosphere on the formation of NH 3 and HCN ☆

Our results indicate that the gas atmosphere surrounding coal/char particles can greatly affect the formation of NH 3 and HCN through its influence on the availability of H radicals. Based on our results, it is believed that the chemisorption of CO 2 on the nascent char surface can consume H radicals or block the access of N-sites by H radicals for the formation of NH 3 and HCN. For the chars whose thermal cracking generates little H radicals, the gasification of char by CO 2 can also generate additional H radicals, enhancing the formation of NH 3. However, even gasification of char in CO 2 at 950 °C does not lead to the formation of HCN. The oxidation of coal with 4% O 2 at low temperatures (400–600 °C) leads to the formation of HCN as well as NH 3 due to the enhanced formation of (H) radicals. The gasification of coal with 15% H 2O drastically enhances the formation of NH 3 due to the greatly enhanced availability of H as an intermediate between the reactions of H 2O and char. These results support our reaction mechanisms proposed previously, emphasising the importance of H on the formation of NH 3 and HCN during pyrolysis, which can also be extended to the conversion of coal-N during gasification.

The Effect of Gas Atmospheres on Charging

The Effect of Gas Atmospheres on Charging

The effect of gas atmosphere used in the calcination of MgO on its basicity and catalytic performance in oxidative coupling of methane

Influence of gas atmosphere used in the calcination of MgO (flowing oxygen, air, helium, nitrogen) on its basicity has been investigated. Pure MgO of relatively low basicity and MgO of higher basicity, containing Ca and Na compounds as impurities, were examined. The surface basicity/base strength distribution was measured using a test reaction of transformation of 2-butanol and a temperature-programmed desorption of CO 2. Both methods revealed that the calcination of MgO samples in the stream of oxygen or air gave MgO of lower basicity than obtained by calcination in the stream of helium or nitrogen. This effect may indicate a different character of interactions between various gas-phase molecules and the surface. It was also shown that MgO calcined in oxygen or air when used in the catalytic oxidative coupling of methane, gave lower conversions of methane and oxygen than that calcined in the inert gas atmosphere. The choice of a gas used in the calcination of MgO, may therefore, influence the basicity and catalytic properties of calcined MgO.

Influence of gas atmosphere on removal of sulphate groups from titanium oxide

The studies were devoted to determination of the effect of gas atmosphere and its pressure on the second step of decomposition of hydrated titanium dioxide (HTD) promoted by sulfate groups. It has been found that thermal decomposition of HTD at temperatures above 300°C consists of a number of processes such as dehydroxylation, desulfuration, recrystallization and sintering of solid grains, photochemical processes (if the decomposition proceeds in the presence of light) and adsorption of gas phase components (in the presence of air or SO 2 ). Kinetic parameters characterizing this step of decomposition have been determined for processes carried out in vacuum and in argon or air atmospheres (at a pressure of 13.33 hPa). The kinetic curves of decomposition carried out in the presence of gases capable of being adsorbed on the surface of partly dehydrated HTD are featured by local extrema due to simultaneous processes of decomposition and adsorption of gas components.

Deposition of cBN films by ion sputtering of SiB6 and AlB12 boron-base materials

Films of cubic boron nitride were deposited on to Mo, Si, WC–Co substrates heated up to 600–800 °C in a three-electrode d.c. device with a discharge localization by magnetic field. During SiB6 and AlB12 sputtering in Ar–N2 and Ar–N2–H2 atmospheres, the low-frequency (LF) substrate bias ranged from 50 to 500 V (20 kHz), and the total pressure was 1.5 mTorr. The effects of gas atmosphere, LF substrate bias and ionization energy on structure formation and composition of the films being deposited have been studied. The film structure and composition were examined using IR spectroscopy and X-ray diffraction analysis. The deposited films have polycrystal structures with a hexagonal, wurtzitic or cubic symmetry. The predominated quantity of cubic phase is observed in films deposited using SiB6 in Ar–N2 atmosphere at a LF substrate bias of 500 V. By introducing hydrogen into the gas atmosphere at a ratio of three parts of N2 to seven parts of H2, a wurtzitic phase forms in the film. The cubic BN phase is observed in films obtained using AlB12 if the LF substrate bias is between 200 and 300 V. The Vickers microhardness of the films produced reaches 30.0–35.0 GPa.

Influence of Gas Environment on Picosecond Laser Ablation Sampling Efficiency and ICP Conditions

The effects of gas atmosphere on inductively coupled plasma excitation characteristics and picosecond laser ablation sampling are studied for enhancing atomic emission spectroscopy sensitivity. Five noble gases (He, Ne, Ar, Kr, Xe) were used in the laser ablation sampling chamber. The noble gases significantly influence the ICP excitation characteristics and the laser ablation sampling efficiency. There is an enhancement in ICP emission intensity for laser sampling in He and Ne and a decrease for Kr and Xe relative to Ar. Plasma shielding is a possible mechanism to explain the gas effects, as the behavior of laser sampling correlates with the ionization potential of the gas. The significant improvement in AES using He as the sample chamber gas is beneficial to chemical analysis, especially for trace analysis, which requires high sensitivity.

Modelling of sonochemical oxidation of the water-KI-CCl 4 system

The sonolysis of KI solution containing CCl 4 as a separate phase results in the formation of I 2, but shows characteristics which are different from those observed when KI solution alone is sonicated. By the addition of CCl 4, the rate goes up by two orders of magnitude, the rate becomes independent of KI concentration, the effect of gas atmosphere becomes less pronounced, and the rate becomes time-dependent. Further the average rate passes through a maximum as the dispersed phase hold-up is increased. These results are explained on the basis of a model which treats cavitation bubbles as microreactors which generate fragmented products from their contents and release them into the liquid phase at the end of collapse phase. The composition of the products of the microreactors is calculated assuming attainment of reaction equilibria. The significant increase in the oxidation rate has been found to be due to release of Cl 2, Cl, and HOCL which act as separate source of reactants to yield I 2. As all these quantitatively react in the reactor with KI, the rate becomes independent of KI concentration. The gas atmosphere here is found to continuously change because of formation of CO 2 and O 2. This results in the change in the composition of gas bubble with time, resulting in reduced effect of initial gas atmosphere used. The presence of a dispersed phase reduces the number of bubbles because of attenuation and scattering but increases them due to interfacial cavitation, thus yielding a maximum at a specific hold-up. The model takes these factors into account and is able to not only explain the different observed trends but also predict them quantitatively.

Misorientation and Surrounding-Atmosphere Dependence of Ductility at High Temperatures of Cu Bicrystals with Dispersed SiO2 Particles.

Orientation-controlled Cu bicrystals with disperesed SiO2 particles were tensile tested at various temperatures in vacuum and Ar-gas atmospheres. Two kinds of bicrystals having [001] twist 12°and 30°grain boundaries were employed. 30°bicrystal specimens fractured intergranularly at around the intermediate-temperature range, although 12°ones fractured transgranularly at all the temperatures. The elongation to fracture was smaller when deformed in Ar atmosphere than in vacuum almost at all the temperatures irrespective of the bicrystal specimens. The above results could be reasonably understood by considering the difference of the mean grain-boundary strength, the inherent grain-boundary strength, and the effect of gas atmosphere which would be responsible for the acceleration of void formation and growth.

Cementation behavior of gold and silver onto Zn, Al, and Fe powders from acid thiourea solutions

Research on the cementation behavior of gold and silver from acid thiourea solutions was carried out with zinc, aluminum, and iron powders and discussed in view of industrial application. An acid thiourea pregnant solution, containing 96 mg/dm 3 gold and 534 mg/dm 3 silver was used during this investigation. The effect of gas atmosphere on cementation of precious metals was also examined by flowing nitrogen gas through the solution during the runs. According to the results, zinc cementation showed the highest rate of deposition of precious metals from acid thiourea solutions. The deposition of silver was slower than that of gold in every cementation tested. The low deposition of precious metals in aluminium cementation at low temperature was due to the oxide film on the surface of aluminum, which caused the irregularly slow rate of deposition. In addition, it was observed that the recovery of precious metals was enhanced, and that both the decomposition of thiourea and the metal dissolution were reduced considerably by employing a nitrogen atmosphere during cementation.

Effects of gas atmosphere, antimicrobial dip and temperature on the fate of Listeria innocua and Listeria monocytogenes on minimally processed lettuce

The growth and survival of inoculated strains of Listeria innocua and L. monocytogenes on minimally processed lettuce were studied. The effects of package atmospheres (lettuce sealed within packages after flushing with 100% N2 or without flushing with N2, lettuce sealed within perforated packages), antimicrobial dips (100 p.p.m. chlorine solution for 5 min, 1% citric acid solution for 5 min) and storage temperatures (3°C and 8°C) were investigated. Populations of L. innocua and L. monocytogenes on undipped lettuce stored at 3°C gradually decreased (by 1–1.5 log cycles) during a 14 day storage period. By contrast counts on lettuce stored at 8°C did not change significantly (P > 0.05). Flushing packages of lettuce with 100% N2 followed by storage at 8°C resulted in a significant increase (P < 0.05, by 2–3 log cycles) in L. innocua and L. monocytogenes counts during storage. L. innocua, strain NCTC 11288, behaviour was similar to that of L. monocytogenes (strains ATCC, 19114 and NCTC 11994) under these storage temperatures and atmospheres. Using L. innocua as a model for L. monocytogenes, it was found that dipping lettuce in a chlorine or citric acid solution followed by storage at 8°C resulted in a significant increase (P < 0.05, by 2 log cycles) in L. innocua populations compared with undipped samples. It is concluded that N2 flushing or use of antimicrobial dips combined with storage at 8°C, both enhanced the survival and growth of Listeria populations on shredded lettuce.

Effects of gas atmosphere, platelet-derived growth factor and leukemia inhibitory factor on cell numbers of rabbit embryos cultured in a protein-free medium.

While culture conditions for embryos have improved, development in vitro is not equivalent to in vivo growth. Platelet-derived growth factor (PDGF), mouse (mLIF) or human (hLIF) leukemia inhibitory factor and 10% fetal bovine serum (FBS) added to protein-free culture medium, as well as two gas atmospheres were evaluated for their effect on rabbit embryo development. Adding PDGF, mLIF or hLIF to the culture medium did not result in detectable differences in total cell number for blastocysts. The culture of rabbit embryos under a gas atmosphere of 10% CO2:5% O2:85% N2 resulted in improved total cell numbers (P < 0.01) for blastocysts compared to those developing under 5% CO2:95% air (230 vs 159, respectively). Supplementing RD (RPMI-1640 and Dulbecco's MEM, 1:1) medium with 10% FBS improved the number of total cells (264 vs 155) and inner cell mass cells (71 vs 47). These results indicate that when defined culture conditions promote a high proportion of two-cell embryos developing into blastocysts, the addition of certain growth factors did not have a detectable beneficial effect, while 10% FBS improved culture conditions.