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31.
This study describes the optimisation of an analytical method to determine 54 volatile organic compounds (VOCs) in air samples by active collection on multisorbent tubes, followed by thermal desorption and gas chromatography-mass spectrometry. Two multisorbent beds, Carbograph 1/Carboxen 1000 and Tenax/Carbograph 1TD, were tested. The latter gave better results, mainly in terms of the peaks that appeared in blank chromatograms. Temperatures, times and flow desorption were optimised. Recoveries were higher than 98.9%, except methylene dichloride, for which the recovery was 74.9%. The method's detection limits were between 0.01 and 1.25 μg m−3 for a volume sample of 1200 ml, and the repeatability on analysis of 100 ng of VOCs, expressed as relative standard deviation for n = 3, was lower than 4% for all compounds. Urban and industrial air samples from the Tarragona region were analysed. Benzene, toluene, ethylbenzene and xylenes (BTEX) were found to be the most abundant VOCs in urban air. Total VOCs in urban samples ranged between 18 and 307 μg m−3. Methylene chloride, 1,4-dichlorobenzene, chloroform and styrene were the most abundant VOCs in industrial samples, and total VOCs ranged between 19 and 85 μg m−3. 相似文献
32.
Summary A method is described for the determination of shortchain aliphatic amines in ambient air based on impinger sampling in dilute H2SO4, selective enrichment across a PTFE gas membrane and quantification by gas chromatography. The enrichment step is carried out in a flow system directly connected to the chromatograph. The separation is performed on a packed column with nitrogen selective detection. The enrichment per sample volume was in the range 7.3 to 8.2 mL–1 for C1–C6 amines. Detection limits were ca 3–10 nM with enrichment of a 2.9 mL liquid sample. After impinger sampling of 5 m3 air in 10 mL absorption solution, this corresponds, to 0.4–0.8 ng/m3 (ca 0.2–0.5 ppt by volume) in air. 相似文献
33.
The capillary gas chromatography of the C2-C5 lower aliphatic aldehydes (e.g.,acetaldehyde, propionaldehyde, n- and i-butyraldehydes, n- and i-valeraldehydes) which, in the free form in air, have unpleasant odors and low threshold odor values, has been studied using cold-trap preconcentration with liquid oxygen. The capillary column outlet was connected to enable simultaneous detection by FID, ECD, FPD AND FTD (SID). 相似文献
34.
Sampling and sample-preparation strategies based on solid-phase microextraction for analysis of indoor air 总被引:3,自引:0,他引:3
Applications of solid-phase microextraction (SPME) to the sampling and analysis of volatile organic compounds in indoor air are reviewed, including a summary of quantification methods, coatings, compounds, concentrations, sampling locations and times, and detection limits. Strategies for on-site and off-site sampling and analysis, advantages and challenges associated with SPME for air sampling are discussed. 相似文献
35.
Adam Sokoowski Jan Chlebicki Kazimiera A. Wilk 《Colloids and surfaces. A, Physicochemical and engineering aspects》1993,80(2-3):243-249
The surface tension isotherms for pure oligooxypropylenated piperidine and morpholine at the aqueous solution—air interface were determined and interpreted. The surface excess concentration, Γ, the surface area per molecule, A, and the standard free energy of adsorption, ΔG°, were calculated according to a new empirical adsorption equation. The standard free energy contribution for the oxypropylene group (PO) in morpholine derivatives,ΔG° (PO) = −3.34 kJ mol−1, is substantially lower than that for the PO group located in the piperidine derivatives, i.e. ΔG° (PO)= −3.12 kJ mol−1. 相似文献
36.
37.
Decomposition of Toluene and Acetone in Packed Dielectric Barrier Discharge Reactors 总被引:2,自引:0,他引:2
Chung-Liang?ChangEmail author Tser-Sheng?Lin 《Plasma Chemistry and Plasma Processing》2005,25(3):227-243
The influences of TiO2 catalytic material and glass pellet packing on the decomposition efficiency of toluene and acetone in air by dielectric barrier discharge (DBD) reactors were experimentally investigated in this study. The effects of both packing materials on the formation of byproducts such as CO and CO2 were also evaluated. Experimental results indicate that the introduction of glass materials into the plasma zone of a wire-tube reactor would improve the decomposition efficiency of toluene and acetone compared to a nonpacked reactor. The apparent decomposition rate constant of a glass packed-bed reactor was 4.5–4.8 times greater than that of a nonpacked reactor. The results also indicate that the decomposition rate constant of toluene was approximately 2.6 times higher than that of acetone no matter which type reactor was utilized. The application of TiO2 coated pellets in DBD reactors will enforce the hydrocarbon byproducts to further be oxidized to CO2, notwithstanding, it will not significantly improve the performance of the reactors in the decomposition of toluene and acetone, and in the formation of CO. The results show that the best selectivity of CO2 for acetone decomposition in a TiO2 coated pellets packed-bed reactor was approximately 40% higher than that in a glass packed-bed reactor. 相似文献
38.
P. C. Schulz M. A. Morini M. E. Gschaider de Ferreira 《Colloid and polymer science》1998,276(3):232-238
The system dodecyltrimethylammonium hydroxide (DTAOH)–water was studied by surface tension, ion-selective electrodes and
evaporation in an electrobalance. Results confirmed earlier conclusions about a stepwise aggregation mechanism in DTAOH solutions.
The aggregation process started at a total concentration C
T=(2.51±0.10)×10-4 mol dm-3) which probably corresponds to the formation of dimers. At C
T= (1.300±0.041)×10-3 mol dm-3 there was a change in the surface and evaporation behavior, corresponding to the formation of small, fully ionized aggregates
which grew with increasing concentration. At C
T= (1.108±0.010)×10-2 mol dm-3 the formation of true micelles with hydroxide counterions in the Stern layer did not change significantly the evaporation
and adsorption behavior. This means that between this concentration and C
T=(3.02±0.28)× M28.8n10-2 mol dm-3, the changes in structure were gradual. At the latter concentration there was a sudden change in the monolayer state at the
air/water interface, with a strong surfactant desorption, and a major change in evaporation behavior. The changes are compatible
with the formation of few, large aggregates reducing the total concentration of kinetically independent solute units, which
in turn increased the activity of the solvent. This phenomenon is in agreement with literature information. The reduction
in the evaporation rate of water was mainly due to the reduction of the water activity, caused by colligative effects. The
reduction of the effective area available for evaporation had only a slight effect in water evaporation.
Received: 9 January 1997 Accepted: 19 October 1997 相似文献
39.
Long-term study of an intermittent air sparged MBR for synthetic wastewater treatment 总被引:6,自引:0,他引:6
Membrane bioreactors (MBR) combine biological processes with membrane filtration. Advantages of MBR in municipal wastewater treatment include high effluent quality and reduced space requirements. Steady operation of membrane plants requires careful management of membrane fouling. Even though it might be impossible to prevent, fouling can be limited by techniques such as gas sparging. The injection of gas bubbles increases the shear stress and removes fouling material from the membrane surface. Most cited literature on air sparging refers to short-term experiments, often times in bench scale. The aim of this study was therefore long-term investigations in pilot plant scale of a 70 L reactor fed with glucose-based synthetic wastewater. The main focus was on enhancing permeate flux by air sparging. The results showed that using air sparging significantly increased the permeate flux was doubled even over several weeks. The findings were interpreted using the dimensionless fouling and shear stress number. The fouling resistance was found to decrease significantly with air injection ratios between 0.4 and 0.5. When air sparging was applied after a period without air sparging, the shear stress number doubled. This increase in shear led to a reduction of the fouling number by approximately 30%. During several weeks air sparging only a slow fouling number increase was. In contrast to that after air sparging was ceased, an exponential increase of the fouling number was observed. 相似文献
40.
催化湿式氧化中铜基催化剂的流失与控制 总被引:9,自引:0,他引:9
制备了催化湿式氧化处理有机废水用铜基催化剂,并用XRD,XRF和TG-DTG等手段对催化剂进行了表征,对催化剂及其前驱体的组成和结构进行了分析鉴定.结果表明,由类水滑石结构的前驱体焙烧得到的催化剂Cu-Al-Zn-O,其活性组分铜的流失得到了控制;在氧化降解苯酚、十二烷基苯磺酸钠和磺基水杨酸时,在初始氧分压0.5MPa和160~220℃的反应条件下,催化剂活性组分铜的流失量小于0.3mg/L.对催化剂活性组分不易流失的原因进行了理论解释和计算. 相似文献