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1.
We have optimized the analytical parameters of a homemade instrument for the simultaneous measurement of the chlorofluorocarbons CCl2F2 (CFC-12), CCl3F (CFC-11) and C2Cl3F3 (CFC-113) in seawater. Seawater samples are flame sealed into 60 ml glass ampoules avoiding any contact with the atmosphere and stored in cold, dark condition until analysis. In the laboratory, after cracking the ampoule in an enclosed chamber filled with ultra-pure nitrogen, the seawater sample is transferred to a stripping chamber, where ultra-pure nitrogen is used to purge the dissolved CFCs from the seawater. The extracted gases are then cryogenically trapped, subsequently the trap is isolated and heated and the CFCs are transferred by a carrier gas stream into a precolumn and then are separated on a gaschromatographic packed column. To separate adequately CFC-12 from N2O, during the early part of the chromatographic run, the gas stream passes through a molecular sieve, which is then isolated and backflushed. The CFCs are detected on an electron capture detector (63Ni ECD). After a careful choice of the experimental conditions, the performances of the system were evaluated. The detection limits for seawater samples are: 0.0081 pmol kg−1 for CFC-12, 0.0073 pmol kg−1 for CFC-11 and 0.0043 pmol kg−1 for CFC-113. The reproducibility of replicate samples lies within 5% for the three CFCs. The system has been successfully employed for CFC measurements in seawater samples collected in the Ross Sea (Antarctica) in the framework of the Italian Antarctic research project.  相似文献
2.
氟氯烃(CFCs)和六氟化硫(SF6)都是人工合成的卤代化合物,在海洋科学考察中是非常重要的基础观测参数,在示踪海/气交换、水团交换等一系列重要海洋学过程研究中均有特殊的应用价值;同时,也可以用于估算表观耗氧速率(Apparent oxygen utilization rate,AOUR)以及人为碳(Anthropogenic C02,Cant)等一些重要的物理及生物地球化学过程参量.CFCs,SF6在海水中的浓度非常低,测量难度大,而CFCs和SF6的联合使用对海洋学过程研究具有重大意义.本研究建立了一套吹扫捕集系统以分析海水中CFC-12和SF6,对吹扫捕集系统测定条件进行了优化,最佳的实验条件为:捕集温度-70℃,吹扫时间8min,吹扫压力310 kPa,脱附时间30 s,脱附温度90℃.本方法测定简单、灵敏度高,CFC-12和SF6的检出限分别为0.02 pmol/kg和0.03 fmol/kg,CFC-12和SF6的测定精密度分别为±1.2%和±0.5%.标准工作曲线的线性相关系数均大于0.9995.本方法成功应用于2014年中国第六次北极科学考察航次中采集的海水样品的测定.  相似文献
3.
Adsorption of ozone depleting chlorofluorocarbons (CFC) over zeolite is of major global environmental concern. The current communication describes first-principle calculation performed on faujasite models to investigate the nature of CFCs including fluoro, chlorofluoro and hydrofluoro/chloro carbons (CF4, CF3Cl, CF2Cl2, CFCl3, CHF3, CHCl3) adsorption. Experimentally it is observed that separation of halocarbons are possible using Na–Y, though the cause is unknown. Reactivity index within the helm of Hard Soft Acid Base (HSAB) principle was used to monitor the activity of the interacting CFCs using Density Functional Theory (DFT) to propose a qualitative order. The importance of both H-bonding and cation–F/Cl interactions in determining the low-energy sorption sites were monitored and rationalized. The host guest interactions show a distinctive difference between the adsorption phenomenon between H–Y and Na–Y and as well for Cl and F. It is observed that Cl has more favorable interaction with hydrogen of H–Y compared to Na–Y and for F the situation is just reversed. To validate this trend periodic optimization calculations were performed. The interaction energy as obtained matches well with the reactivity index order resulted from cluster calculations. This study is a combination of DFT and periodic calculation to rationalize the electronic phenomenon of the interaction process.  相似文献
4.
Dealumination of zeolites is regarded as a useful postsynthesis method for the modification of Si/Al ratio. Among other compounds phosgene proved to be an excellent reactant for aluminium removal from zeolite frameworks. The interaction of zeolites with chlorofluorocarbons also leads to dealumination, resulting in the formation of a phosgene intermediate that has been proven by IR and NMR spectroscopy.  相似文献
5.
A new type of capillary porous-layer open tubular (PLOT) column consisting of a hydrophobic silica layer on a fused-silica capillary has been tested for the separation of a mixture of environmentally sensitive halocarbons present in tropospheric air. The column shows high retention for a wide range of halocarbons, with elution orders following both boiling point order and hydrogen bonding capability. The resolution of the halocarbons is good and only one pair of halocarbons [CHFClCF3 (HCFC 124) and CH3CF2Cl (HCFC 142b)] cannot be resolved on this column type at all column temperature profiles. Unlike alumina PLOT columns, the silica PLOT column does not dehydrohalogenate labile halocarbons. Excellent reproducibility of retention times and peak areas for halocarbons on the column are reported.  相似文献
6.
Catalytic decomposition of CCI2F2 was studied over a number of single and complex metal oxides using a fixed-bed reactor. The ZrO2–Cr2O2 catalyst exhibited the highest activity and CO2 and CCIF3 were formed at 350–450°C. Selective decomposition of CCI2F2 required the presence of both oxygen and water vapor over the catalyst. Catalytic activity gradually declined with time on stream because of the fluorination of ZrO2. Treatment of the catalyst with both oxygen and water vapor promoted the removal of fluoride ions in sub-surface layers of the catalyst, which is effective for the recovery of the activity. CCI2F2 was decomposed at 300–450°C over AIPO4. No fluorination of the AIPO4 catalyst took place after the reaction for 1000 h. CH2FCF3, an alternative CFC, was completely decomposed over the mixed catalyst of Ce promoted AIPO4 and Cr2O3 at 400–500°C. Catalytic decomposition is a rational method for destruction of used CFCs.  相似文献
7.
马臻  华伟明  高滋 《化学通报》2001,64(6):339-344
氟里昂分解已成为当今环保技术的热点之一,本文论述了氟里昂催化分解的必要性,优越性,介绍了氟里昂催化分解的概况和最新进展,并指出了今后的研究方向。  相似文献
8.
Due to increasing enthusiasm for environmental preservation, the synthesis ofchlorofluorocarbons (CFCs) alternatives and the decomposition of existing CFCs havebeen two hot topics since the production and utilization of CFCs are banned by manycountries. The former has been well carried out while the latter was rarely reported inChina. Among a dozen of decomposition approaches. catalytic hydrolysis is verypromising because of simple processes, requiring mild conditions, dioxins free and the…  相似文献
9.
Contradictory information concerning the kinetics of tetrachloromethane fluorination by anhydrous hydrogen fluoride in the presence of antimony pentachloride has been explained. The present studies were performed using a stainless steel autoclave. The exchange of the first chlorine atom was carried out in the temperature range of 35-95 °C, with the molar ratio of HF/CCl4 varied within the range of 1.2-1.7 and at a constant molar ratio of SbCl5/Cl2 equal to 1.9. The degree of conversion of CCl4 to CCl3F and the reaction rate constant as a function of temperature fit to an Arrhenius straight line. The Arrhenius constants (pre-exponential factor) and the activation energy were determined. Studies concerning the exchange of the second chlorine atom, i.e. the conversion of CCl3F to CCl2F2 have been performed. The results of kinetic investigations were created in the same way. Based on these results it was found that the Arrhenius equation is fulfilled also in the second stage of the fluorination. The same slope of the straight lines confirms that the fluorination stages proceed according to the same mechanism with the same activation energy but with different pre-exponential factors.Several kinetic problems associated with the performance of the reactor can be solved on the basis of the equations derived. However, knowledge of CCl4 conversion as a function of time, temperature, catalyst concentration and the type of the reaction is required for this purpose. Such calculations enable the selection of the optimal process parameters.  相似文献
10.
Fluorocarbon impact on ozone depletion is reviewed together with the efficacy of the Montreal Protocol in acting to correct the imbalance between stratospheric ozone production and destruction. The Protocol is also helping to reduce global warming: CFCs are shown to be currently the largest fluorocarbon contributors to climate change. Relative contributions to climate change from CFCs and their HFC substitutes are discussed, together with the consequences of control of minor greenhouse gases on an environmental impact which is dominated by carbon dioxide emissions. Both the potencies of the materials for environmental change and their concentrations in the atmosphere are important and are considered here.Trifluoroacetic acid, a minor product of atmospheric decomposition of some HCFCs and HFCs and of the pyrolysis of fluoropolymers, has been shown to be uniformly distributed in seawater to a depth of over 4000 m and so is natural, although the actual source has yet to be identified.The Montreal Protocol is only one example of action to reduce undesirable impact from fluorocarbons. Other, less universal, actions include abatement of fluoroform greenhouse gas emissions from HCFC manufacturing, process changes to eliminate trifluoromethylsulfur pentafluoride emissions from electrochemical fluorination and ceasing manufacture of perfluorooctanyl sulfonate compounds due to their persistence in human tissue.  相似文献
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