聚合条件对丙烯酸丁酯反应动力学的影响

采用溶液聚合方法,通过改变聚合条件研究丙烯酸丁酯转化率随聚合时间变化的关系,考察其聚合反应动力学.改变引发剂过氧化苯甲酰(BPO)含量发现,BPO质量百分数提高聚合反应速率加快,单体转化率差别不大;提高温度有利于聚合速率的提高,但同时会导致单体最终转化率的降低;单体浓度越高,聚合速率越快,凝胶化现象明显;采用乙苯为溶剂...     

气相色谱法测定氟西汀残留有机溶剂含量

目的:建立氟西汀中乙醇、乙醚、正己烷、乙酸乙酯和甲苯残留量的测定方法。方法:采用DB-624毛细管色谱柱(30m×0.53mm,3.0μm),用二甲基亚砜作为溶剂,载气为氮气(0.03MPa),氢火焰离子化检测器(FID),检测器温度240℃;柱温为程序升温;进样口温度150℃;分流比:1:20;进样量1μL。结果:乙醇、乙醚、正己烷、乙酸乙酯和甲苯的线性范围分别为37.89～947.16μg.mL-1(r=0.9999)、39.96～998.90μg.mL-1(r=0.9999)、1.32～32.97μg.mL-1(r=0.9999)、36.02～900.50μg.mL-(1r=0.9996)、6.93～173.20μg.mL-(1r=0.9999),平均回收率(n=9)分别为99.7%、98.5%、100.2%、97.9%和98.6%。结论:该方法操作简单,灵敏度高,结果准确,是测定氟西汀原料中有机残留溶剂的可靠方法。     

Nickel removal from nickel-5,10,15,20-tetraphenylporphine using supercritical water in absence of catalyst: a basic study

Reactions of nickel-5,10,15,20-tetraphenylporphine (Ni-TPP) were studied in supercritical water in the presence of toluene without the addition of any catalyst, H(2) or H(2)S that is called a green process. The objective of this study was to remove nickel from Ni-TPP, the most common metal compound present in heavy crude, in high extent at low reaction time. All experiments were carried out in an 8.8 mL batch reactor fabricated from hastelloy C-276. The ability of supercritical water (SCW) to remove nickel from Ni-TPP was studied at temperatures of 450-490 °C and water partial pressures of 25-35 MPa. Water partial pressure had no effect on overall conversion at temperatures of 450 °C and a reaction time of 60 min. The overall Ni-TPP conversion was 89.80%, a figure above that of previous catalytic studies. The percentage of nickel removal was estimated as a function of reaction time and temperature. It were temperature 490 °C and pressure 25 MPa at reaction time 90 min where 65.68% nickel were removed by the action of SCW and toluene, as a co-solvent. It was determined that Ni-TPP undergoes a series of reactions, ending in demetallation and ring fragmentation. The obtained results suggest that supercritical water has a capability to remove nickel from Ni-TPP.     

Simultaneous removal of ethyl acetate and toluene in air streams using compost-based biofilters

Biofitration was successfully applied to treat air streams containing a mixture of ethyl acetate and toluene. The experiment was performed by two identical bench-scale biofilters, which were acclimated by ethyl acetate and toluene, respectively. During a 3 month steady-state performance, the two biofilters showed equivalent elimination capacity (EC) for toluene (50 g/m(3) bed/h of pure toluene). However, the biofilter acclimated with ethyl acetate showed a much higher EC for ethyl acetate (400 g/m(3) bed/h of pure ethyl acetate) than that acclimated with toluene (250 g/m(3) bed/h). The concurrent biofiltration of toluene was inhibited by the presence of ethyl acetate. The results also showed that more nitrogen and phosphorus were consumed in the process of the biofiltration of toluene compared with the treatment of ethyl acetate. After the 3 month experiment, the pH of the media treating ethyl acetate dropped from 6.71 to 5.50, whereas the pH of the media treating toluene increased from 6.71 to 7.08.     

Wet chemical synthesis of ZnO nanocrystals: dependence of growth and morphology on the solvent composition

Zinc oxide (ZnO) nanocrystals were prepared using a wet chemical route starting from zinc acetate dihydrate dissolved in pure ethanol, pure water, and mixtures of ethanol and water. X-ray diffraction (XRD) studies along with thermogravimetric analyses results show that ZnO begins to crystallize at a temperature lower than 100 °C in a starting solution having 1:4 ethanol–water volume ratio. For other starting solutions, ZnO forms above 150 °C. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies confirm the formation of nanoparticles of size ~15–20 nm and XRD analysis shows that the particles crystallize in the wurtzite structure. SEM and TEM studies show that ZnO particles grown in pure ethanol, pure water and in ethanol–water mixtures (other than the 1:4 mixture) have similar morphology, with the nanocrystals forming randomly grouped clusters. In the case of 1:4 solvent, however, the morphology is different, ZnO in this case growing in the form of chain like structures which appear like rods. Room temperature photoluminescence spectra exhibit a strong emission band in the red region probably caused by transitions between deep levels involving zinc interstitials.     

Catalytic performance of nanosized Pt-Au alloy catalyst in oxidation of methanol and toluene

The alloy formed between a group-VII metal such as platinum and a group-IB metal such as gold changes the catalytic behavior compared to the monometallic phase, increasing the selectivity toward certain products and also decreasing the deactivation rate. Pt-Au alloy nanoparticles coated on alumina support were found to be catalytically very active for complete oxidation of methanol and toluene. Furthermore, the nanosized Pt-Au particles were added to ZnO/Al2O3 on monolith catalyst. Also, effect of various parameters such as concentration of methanol and toluene and feed flow rate was investigated. Au particles were sized in 20 approximately 30 nm and Pt particles were well dispersed. In case of alumina supported powder catalyst, complete oxidation of methanol occurred at a temperature lower than that of toluene. From oxidation activity of monolithic honeycomb with Pt and Au particles, the conversion of methanol was increased with increasing the concentration of methanol, but conversion of toluene showed a decreasing tendency as the concentration of toluene increased. Also, conversion of methanol over honeycomb catalyst was not largely affected by feed flow rate, while conversion in toluene oxidation was decreased rapidly as feed flow rate was increased. As a result, the Pt-Au/ZnO/Al2O3/M catalyst used is likely to efficiently treat a large volume of exhaust gas containing VOCs.     

Reutilization of Cr-Y zeolite obtained by biosorption in the catalytic oxidation of volatile organic compounds

This work aims at the reutilization of a Cr-loaded NaY zeolite obtained by biorecovery of chromium from water as catalyst in the oxidation of volatile organic compounds (VOC). Cr-NaY catalysts were obtained after biosorption of Cr(VI) using a bacterium, Arthrobacter viscosus, supported on the zeolite. The biosorption experiments were conducted at different pH values in the range 1-4. The catalysts were characterized by several techniques, namely ICP-AES, SEM-EDS, XRD, XPS, Raman, H₂-TPR and N₂ adsorption. The zeolite obtained at pH 4 has the highest content of chromium, 0.9%, and was selected as the best catalyst for the oxidation of different VOC, namely ethyl acetate, ethanol and toluene. For all VOC tested, the catalyst with chromium showed higher activity and selectivity to CO₂, in comparison with the starting zeolite NaY. The presence of chromium shifted also the reaction pathways. In terms of selectivity to CO₂, the following sequence was observed: ethyl acetate > toluene > ethanol.     

Extent of oxidation of Cr(III) to Cr(VI) under various conditions pertaining to natural environment

Calculations show that oxidation of chromium oxide (Cr2O3) by oxygen and oxidation of chromium hydroxide (Cr(OH)3) by manganese dioxide (MnO2) are thermodynamically feasible in both aerobic and mildly anoxic environments. Experiments were carried out to determine the rate and extent of chromium oxidation under various conditions, i.e., when Cr2O3 was heated in the presence of oxygen, when Cr(OH)3 and MnO2 mixtures were suspended in aerobic or anoxic aqueous media at various pH values, when Cr(OH)3 and MnO2 mixtures interacted in moist aerobic conditions and when chromium assumed to be Cr(OH)3 and manganese assumed to be MnO2 interacted in the presence of competing electron donors/acceptors, as is the case in chromium-contaminated sludge. Results indicate that trivalent chromium in Cr2O3 could be readily converted to hexavalent chromium at a temperature range of 200-300 degrees C, with conversion rates of up to 50% in 12 h. In aqueous media, Cr(OH)3 was slowly converted to dissolved Cr(VI) in the presence of MnO2, both in aerobic and anoxic conditions, with conversion rates of up to 1% in 60 days. In moist aerobic conditions and in the presence of MnO2, Cr(OH)(3) slowly converted to hexavalent chromium, with up to 0.05% conversion observed in 90 days. Chromium oxidation also occurred in sludge samples, especially under aerobic conditions. However, such transformation was found to be transitory, with the Cr(VI) formed being ultimately reduced back to Cr(III) due to the presence of various reducing agents in the sludge. Nevertheless since up to 17% conversion of Cr(III) to Cr(VI) occurred in sludge under aerobic conditions by 30 days, there is real danger under field conditions of spreading Cr(VI) pollution due to possible intervening rainfall, runoff and percolation.     

Effect of temperature on cosolvent flooding for the enhanced solubilization and mobilization of NAPLs in porous media

This paper examines the potential for enhanced NAPL recovery from the subsurface through the combined application of hot water and cosolvent flushing. Batch experiments were conducted to determine the effect of temperature on fluid properties and the multiphase behavior of the ethanol-water-toluene system and to assess the impact of temperature on the capillary, Bond and total trapping numbers and on flooding stability. Column flooding experiments were also conducted to evaluate toluene NAPL recovery efficiency for different ethanol contents and flushing solution temperatures. The ethanol content considered ranged from 20 to 100% by mass, while the flushing solution temperatures were varied from 10 to 40°C. It is shown that small variations in the system temperature can strongly influence the solubilization, mobilization and stability of the multiphase system, but that the impact of temperature on the enhanced NAPL recovery is also dependent on the ethanol content of the flushing solution. The impact of hot water on NAPL recovery was most pronounced at intermediate ethanol contents (40-60% by mass) where the increase in system temperature led to enhanced NAPL solubilization as well as NAPL mobilization. This study demonstrates that coupling of hot water with in situ cosolvent flooding is a potentially effective remedial alternative that can optimize NAPL recovery while reducing the amount of chemicals injected into the subsurface.     

NUCLEATION OF INTERGRANULAR CRACKS DURING HIGH TEMPERATURE LOW CYCLE FATIGUE OF SUS316 STAINLESS STEEL

Fundamental behaviour of intergranular cracking of SUS316 stainless steel which characterises the high temperature low cycle fatigue process has been studied with a special emphasis on the interaction between oxidation and a grain boundary sliding. Two types of specimens were prepared for fatigue experiment to extract a sole effect of surface oxidation on crack nucleation. One was heat-treated in air and the other was in vacuum so that the specimens had the same history of heat treatment except oxidation to the surface. Results of fatigue tests of these specimens well explain the relationship between oxidation and surface cracking as follows. The morphology of the oxidised surface of the specimen subjected to low-cycle fatigue at 700°C is quite different from that of the oxidised surface caused by simply holding at the same temperature in air for several hours with no applied stress. Localised oxidation along the grain boundary is a characteristic feature for the specimen fatigued at 700°C, while no localised oxidation was observed when the specimens were simply held at the same 700°C, i.e. with no fatigue loading. Accordingly, intergranular cracking in high temperature low cycle fatigue in air occurs when grain boundary sliding due to cyclic loading is accelerated by localised oxidation along the grain boundary.     

Catalytic combustion of ethyl acetate on supported copper oxide catalysts

Total oxidation of ethyl acetate on supported copper oxide catalysts was investigated. The catalysts have been prepared by wet impregnation method and characterized by XRD, TEM and XPS. Among the catalysts with the supports of TiO2, CeO2/TiO2 and CeO2-ZrO2/TiO2, CeO2-ZrO2 solid solutions doped TiO2 supported catalyst gives the highest catalytic activity. Catalyst with the composition of 5 wt.% CuO/10 wt.% CeO2-ZrO2-TiO2 shows the total oxidation of ethyl acetate at about 270 degrees C with the 100% CO2 selectivity. The characterization studies of supported copper oxide catalysts showed that the highly dispersed CuO is one of the active phase which contacts intimately with the support, the action of the interface between the components was not be ignored.     

MnOx-CeO2-Al2O3 mixed oxides for soot oxidation: activity and thermal stability

MnO(x)-CeO(2)-Al(2)O(3) mixed oxides were prepared by impregnating manganese acetate and cerium nitrate on alumina powders using the sol-gel method. The thermal stabilities of MnO(x)-CeO(2) and Al(2)O(3)-modified mixed oxides were evaluated by treating at 800 °C in dry air flow for 20h. The introduction of Al(2)O(3) markedly increases the textural stability of the catalyst with a relatively high dispersion of MnO(x) and CeO(2), remaining a strong synergistic effect between these two oxides. The NO oxidation activity of the ternary oxides experiences a smaller loss after high-temperature calcination, and a low soot oxidation temperature is attained in the presence of NO.     

Cleaning of air of ethyl acetate impurity with the aid of a pulsed corona discharge

The study presents experimental data for cleaning of gas—air mixtures containing ethyl acetate (EA) impurities with the aid of a pulsed corona discharge. A test laboratory bench for investigating cleaning of flue gases is described. Dependences of EA conversion on the discharge parameters and on the temperature of the initial gas—air mixture and the content of water vapor in it are given.     

Secondary ion mass spectrometry and multireflection infrared analyses of conversion coatings on Fe–Cr–Al stainless steels for catalysis: study of thermal stability

Abstract

The thermal stability of three stainless steel conversion coatings for high temperature applications (e.g. photothermal conversion catalysis) are investigated. The thermal oxidation in air up to 1000°C of Fe–17Cr, Fe–18Cr–1·3Al, and Fe–22Cr–5Al coatings (all wt-%) are compared. This study has revealed a critical temperature below which the coating thickness is preserved; the critical temperature increases and the thermal oxidation of the conversion coating decreases with higher chromium and aluminium content. This is attributed to the difference in the substitution ratio of γ lacunar phase (additionally oxidised substituted magnetite), which is the main component of the conversion coatings. The thermal stability of this phase is higher when it is richer in chromium or aluminium. Higher contents of these elements raise the temperature of formation of chromite (FeCr₂O₄) and alumina, the occurrence of which causes thickening of the coating during thermal treatment.

MST/1891     

Promoted wet air oxidation of polynuclear aromatic hydrocarbons

The treatment of an aqueous solution of four polycyclic aromatic hydrocarbons, namely acenaphthene, phenanthrene, anthracene and fluoranthene, under moderate conditions of temperature and pressure has been conducted in the presence and absence of free radical promoters (hydrogen peroxide or potassium monopersulfate). With no addition of promoters, the process achieves PAH conversion values in the range 80-100% at 190 degrees C and 50 bars of air pressure (80 min of reaction). Similar results are obtained in the presence of hydrogen peroxide, however, in this case, the time required is just 60 min with a sharp decrease in PAH concentration in the first 10-20 min. Additionally, temperature can be lowered to values in the range 100-150 degrees C. If potassium monopersulfate is used instead of hydrogen peroxide, an analogous behaviour is experienced, in the latter case, temperatures above 120 degrees C lead to an inhibition of anthracene oxidation, likely due to ineffective decomposition of the monopersulfate molecule.     

Low-temperature direct conversion of Cu-In films to CuInSe₂ via selenization reaction in supercritical fluid

In this study, we achieve the direct conversion of metallic Cu-In films to compound semiconductor CuInSe(2) films, at quite low temperature around 300 °C using less hazardous metalorganic selenium source in supercritical fluid (SCF). We investigated the effects of temperature and fluid (ethanol) density, and found that supercritical ethanol plays a crucial role in this low-temperature selenization reaction. Such SCF-assisted direct conversion reactions can facilitate large-scale, low-temperature, and rapid synthesis of CuInSe(2) films, which can potentially lead to the low-cost production of solar cells.     

Flammability limits and explosion characteristics of toluene-nitrous oxide mixtures

Flammability limits and explosion characteristics of toluene–nitrous oxide mixtures are experimentally determined in an 8 l spherical vessel, and are compared with corresponding values of toluene–air mixtures. The experiments, performed at atmospheric pressure and at an initial temperature of 70 °C, show that the flammable range of toluene in nitrous oxide (0.25–22.5 mol%) is about three times as wide as the corresponding range of toluene in air (1.3–7.1 mol%). Maximum values of the explosion pressure ratio and the deflagration index, K_G, are clearly higher when nitrous oxide is applied as an oxidizer. This can be attributed to the increased flame temperature and burning velocity of toluene–nitrous oxide flames. Moreover, extremely high values of K_G for near-stoichiometric mixtures in combination with strong acoustic oscillations in the pressure signals of these mixtures indicate the existence of a flame accelerating mechanism. These phenomena are enhanced when an initial pressure of 6 bara is applied. Finally, when evaluating the lower flammability limit, it was found that pure nitrous oxide decomposes at pressures above 4.5 bara when applying an ignition energy of about 10 J.     

Thermal shock behavior of ZrB2--SiC ceramics with different quenching media

The thermal shock behavior of ZrB₂--SiC ceramics was studied with water, air and methyl silicone oil as quenching media, respectively. The temperature of all coolants was room temperature (25°C) and the residual strength of the ceramics after quenching was tested. The strength of the ceramics after water quenching had an obvious drop when the temperature difference, ΔT, was about 275°C, while the residual strength of the specimens quenched by air and silicone oil only varied a little and even increased slightly when the temperature difference was higher than 800°C. The different thermal conductive coefficient of the coolants and surface heat transfer coefficient resulted in the differences in the thermal shock behavior. The formation of oxidation layer was beneficial for improving the residual strength of the ceramics after quenching.     

Metal precipitation in an ethanol-fed, fixed-bed sulphate-reducing bioreactor

A batch upflow fixed-bed sulphate-reducing bioreactor has been set up and monitored for the treatment of synthetic solutions containing divalent iron (100mg/L and 200mg/L), zinc (100mg/L and 200mg/L), copper (100mg/L and 200mg/L), nickel (100mg/L and 200mg/L) and sulphate (1700 mg/L and 2130 mg/L) at initial pH 3-3.5, using ethanol as the sole electron donor. The reactor has been operated at the theoretical stoichiometric ethanol/sulphate ratio. Complete oxidation of ethanol has been achieved through complete oxidation of the intermediately, microbially produced acetate. This is mainly attributed to the presence of Desulfobacter postgatei species which dominated the sulphate-reducing community in the reactor. The reduction of sulphate was limited to about 85%. Quantitative precipitation of the soluble metal ions has been achieved. XRD and SEM-EDS analyses performed on samples of the produced sludge showed poorly crystalline phases of marcasite, covellite and wurtzite as well as several mixed metal sulphides.     

Synthesis of β-Mo(2)C thin films

Thin films of stoichiometric β-Mo(2)C were fabricated using a two-step synthesis process. Dense molybdenum oxide films were first deposited by plasma-enhanced chemical vapor deposition using mixtures of MoF(6), H(2), and O(2). The dependence of operating parameters with respect to deposition rate and quality is reviewed. Oxide films 100-500 nm in thickness were then converted into molybdenum carbide using temperature-programmed reaction using mixtures of H(2) and CH(4). X-ray diffraction confirmed that molybdenum oxide is completely transformed into the β-Mo(2)C phase when heated to 700 °C in mixtures of 20% CH(4) in H(2). The films remained well-adhered to the underlying silicon substrate after carburization. X-ray photoelectron spectroscopy detected no impurities in the films, and Mo was found to exist in a single oxidation state. Microscopy revealed that the as-deposited oxide films were featureless, whereas the carbide films display a complex nanostructure.