Effect of temperature on the volumetric properties of (cyclohexanone + an aromatic hydrocarbon)

The excess molar volume of (cyclohexanone + benzene, or toluene, or ethylbenzene, or styrene) were obtained from the densities measured by means of a vibrating-tube densimeter over the whole composition range at temperatures (293.15, 303.15, 313.15, 323.15, 333.15, 343.15, 353.15) K and atmospheric pressure. The excess molar volume provide the temperature dependence of in the temperature range of (293 to 353) K. The results were correlated using the fourth-order Redlich-Kister equation, with the maximum likelihood principle being applied for the determination of the adjustable parameters. It was found that the in the systems studied increase with rising temperature.     

Silicone glue coated stainless steel wire for solid phase microextraction

A new solid phase microextraction (SPME) fiber based on high-temperature silicone glue coated on a stainless steel wire is presented. The fiber coating can be prepared easily in a few minutes, it is mechanically stable and exhibits relatively high thermal stability (up to 260 °C). The extraction properties of the fiber to benzene, toluene, ethylbenzene, and xylenes (BTEX) were examined using both direct and headspace SPME modes coupled to gas chromatography-flame ionization detection. The effects of the extraction and desorption parameters including extraction and desorption time, sampling and desorption temperature, and ionic strength on the extraction/desorption efficiency have been studied. For both headspace and direct SPME the calibration graphs were linear in the concentration range from 0.5 μg L⁻¹ to 10 mg L⁻¹ (R² > 0.996) and detection limits ranged from 0.07 to 0.24 μg L⁻¹. Single fiber repeatability and fiber-to-fiber reproducibility were less than 6.8 and 21.5%, respectively. Finally, headspace SPME was applied to determine BTEX in petrol station waste waters with spiked recoveries in the range of 89.7-105.2%.     

Field analysis of benzene, toluene, ethylbenzene and xylene in water by portable gas chromatography-microflame ionization detector combined with headspace solid-phase microextraction

In this work, portable gas chromatography-microflame ionization detection (portable GC-μFID) coupled to headspace solid-phase microextraction (HS-SPME) was developed for the field analysis of benzene, toluene, ethylbenzene and xylene (BTEX) in water samples. The HS-SPME parameters such as fiber coating, extraction times, stirring rate, the ratio of headspace volume to sample volume, and sodium chloride concentration were studied. A 65 μm poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) SPME fiber, 900 rpm, 3.0 ml of headspace (1.0 ml water sample in 4.0 ml vial), and 35% sodium chloride concentration (w/v) were respectively chosen for the best extraction response. An extraction time of 1.0 min was enough to extract BTEX in water samples. The relative standard deviation (R.S.D.) for the procedure varied from 5.4% to 8.3%. The method detection limits (MDLs) found were lower than 1.5 μg/l, which was enough sensitive to detect the BTEX in water samples. The optimized method was applied to the field analysis of BTEX in wastewater samples. These experiment results show that portable GC-μFID combined with HS-SPME is a rapid, simple and effective tool for field analysis of BTEX in water samples.     

Modelling of toluene solid-phase microextraction for indoor air sampling

Solid-phase microextraction (SPME) is a convenient and efficient sampling technique recently applied to indoor air analysis. We propose here a theoretical model of the adsorption kinetics of toluene on SPME fibre under static extraction conditions. We discuss the effects of sampling volume and initial concentration of analyte on the adsorption kinetics. This model is used to estimate the limits of detection taking into account operating conditions and to calculate theoretical calibration curves. Results of comparison with experimental data are encouraging: only 11% difference for calibration curves and 30% for the estimation of the limit of detection. On the basis of this kinetics model, the solid concentration gradient in the Carboxen coating was modelled with Fick’s second law of diffusion in unsteady-state mass-transfer mode. Mass diffusion from the gas sample to the SPME fibre was also investigated. It was shown that diffusion is the limiting step of the mass-transfer process in the static mode. Thus, the model developed, allows a better understanding of adsorption on Carboxen fibre and in the future could be a useful tool for cheap and time-saving development of SPME methods and the estimation of sampling performance. Figure PDMS/Carboxen SPME fibre (scanning electron microscopy – magnification x 220)     

食品包装材料上油墨中残留烷基苯成分分析及其迁移性的GC-MS研究

建立了一种食品包装材料上多色油墨中残留烷基苯成分的提取和气相色谱-质谱联用(GC-MS)分析方法. 采用选择离子检测(SIM)模式, 以内标定量法对某些食品包装材料上多色油墨中烷基苯残留量进行了准确定量分析. 对油墨中残留烷基苯向食品中迁移的初步研究结果表明, 包装材料上油墨中的苯及苯系物等有害物质可能透过薄膜进入食品而造成污染.     

Microwave-assisted acid hydrolysis of toluene diamine conjugates in urine samples for biomarkers in toluene diisocyanate analysis

Toluene diamines (TDAs) in urine have been used widely to determine the amount of toluene diisocyanate (TDI) absorbed by humans. Conventional hydrolysis to prepare a sample of urine takes approximately 16 h. An attempt is made to apply microwave-assisted heating (MAH) to reduce the duration of analysis. Urine collected from rats exposed to a mixture of 2,4- and 2,6-TDI was diluted with non-exposed human urine 1/1250-, 1/500- and 1/250-fold. The urine samples were hydrolyzed by both conventional heating and MAH. The hydrolysis efficiency obtained using MAH significantly exceeded that obtained using conventional heating. Hydrolysis by MAH required only 20 min, 48 times faster than with conventional heating. The use of the MAH method in hydrolysis was demonstrated to be reproducible, timesaving and efficient technique in measuring the concentration of urinary TDAs.     

钨酸铋担载钯纳米粒子光催化甲苯及其衍生物到醛的氧化反应

甲苯及其衍生物的选择性氧化是化学工业中重要的一环.氧化产物醛、酮和酸类化合物是各种农药、染料、防腐剂、阻燃剂、香料、塑料的合成中间体.在传统的化工过程中,通常在苛刻的条件下,如高温、高压以及酸性溶剂中进行甲苯的选择性氧化.光催化有机合成作为一种"绿色"的合成方法受到越来越多的关注.我们发现钨酸铋作为可见光响应的光催化剂,可以利用氧气作为氧化剂,对甲苯及其衍生物进行催化氧化反应.通过调节水热法合成钨酸铋的酸碱条件,控制其成核生长过程,改变其形貌,发现在pH值为0.49时,得到花状钨酸铋粉末活性最高.X射线衍射、扫描电镜、紫外可见吸收光谱和比表面测定结果发现,花状钨酸铋粉末表现出最佳的甲苯氧化活性很可能是与它最大的比表面积有关系.为了进一步提高催化的活性,我们将助催化剂担载在钨酸铋粉末上,发现Pd的担载量为0.1 wt%时甲苯氧化反应活性最高.将邻、间、对位甲基取代以及对位甲氧基和氯取代的甲苯衍生物进行反应,发现均可高选择性地得到目标产物.在加入电子牺牲剂硝酸银和空穴牺牲剂草酸铵到反应体系后,发现反应被完全禁阻,说明在甲苯氧化反应过程中电子和空穴都起到了相应的作用.通过电化学测试发现,钯作为助催化剂担载在钨酸铋表面后,产生更强的氧化和还原信号,说明其在电子和空穴发生反应的过程中都起到了相应的促进作用.由此推测,在甲苯的氧化反应中,钨酸铋材料表面吸收可见光,产生光生电子和空穴,而钯的担载则促进了电子和空穴进行氧气还原和甲苯氧化的过程.     

低温等离子体场内复合不同晶型氧化锰催化降解甲苯性能和机理

作为典型的挥发性有机化合物,甲苯通常来源于建筑涂料、交通运输和各种工业生产过程,是PM2.5、臭氧和光化学烟雾的重要前驱体,对环境和人类健康造成巨大影响.近年来,低温等离子体技术因具有在常温常压下就能通过高能电子、活性氧物种和羟基等活性粒子有效降解挥发性有机物的优点而受到广泛关注.然而,高能耗和大量副产物的产生是等离子体技术工业化应用的巨大障碍.当前最有效的策略之一是将等离体技术与催化技术结合,从而加快反应速率,提高产品的选择性和能源利用率.在所应用的催化剂中,MnO2因具有较好的O3分解效率而成为最有潜力的催化剂之一.但是MnO2具有不同的晶型结构、隧道结构和形貌,这些均会显著影响MnO2的催化活性.本文通过一步水热法制备了α-,β-,γ-和δ-MnO2四种MnO2催化剂,并将其用于等离子体催化降解甲苯研究,在此基础上系统考察了等离子体催化降解性能和MnO2不同晶型之间的关系.结果表明,当能量密度为160 J/L时,等离子体单独降解甲苯去除效率为32.5%.引入催化剂能够显著提高甲苯的降解效率,其中α-MnO2效果最显著,甲苯降解效率能够提升至78.1%,β-,γ-和δ-MnO2能够相应提升至47.4%,66.1%和50.0%.采用X射线衍射、拉曼光谱、扫面电子显微镜、透射电子显微镜、比表面积-孔结构分析、氢气程序升温还原和X射线光电子能谱等手段研究了催化剂的理化特性.结果表明,隧道结构、催化剂在等离子体中的稳定性、Mn–O键能和催化剂表面吸附氧均在等离子体催化降解甲苯中发挥了重要作用.在此基础上,通过GC-MS分析降解产生的气相副产物推断甲苯在等离子体和等离子体催化体系中的降解机理.在等离子体催化体系中,通过Mn4+,Mn3+和Mn2+价态的变化,等离子体产生的O3,O2*和其他活性自由基会被吸附到催化剂表面,随后与催化剂吸附的甲苯或中间副产物发生氧化还原反应,将甲苯氧化为CO2等小分子物质.此外,MnO2作为分解O3最有效的催化剂,可以吸附O3并将其分解为O?或者与H2O生成?OH参与到反应中,从而提高甲苯的降解效率.     

聚合物微球固载的N-羟基邻苯二甲酰亚胺在分子氧氧化甲苯过程中的催化性能

以交联聚苯乙烯(CPS)微球为基质,经过几步大分子反应在微球表面合成与固载了N-羟基邻苯二甲酰亚胺(NHPI),形成固载有NHPI的聚合物微球CPS-NHPI。本文主要将CPS-NHPI与过渡金属盐组成共催化体系,用于分子氧氧化甲苯的反应,考察了该非均相催化剂的催化特性与催化氧化机理。结果表明,几种过渡金属盐中,Co(OAc)2的助催化效果最好;微球CPS-NHPI与Co(OAc)2所构成的共催化体系,在温和条件(80℃和常压氧气)下可有效地将甲苯深度氧化为苯甲酸,显现出高的催化活性(甲苯转化率达到57%)与优良的选择性(苯甲酸的选择性达到84%)。催化氧化反应遵循自由基链式反应机理。主催化剂CPS-NHPI固载的NHPI与助催化剂Co(OAc)2适宜的摩尔比为14∶1,主催化剂所含NHPI为底物的12(mol)%时,催化剂用量较为合适。固体催化剂CPS-NHPI具有良好的再循环使用性能。     

A theoretical study on the destruction of typical biomass tar components (toluene,phenol and naphthalene) by OH radical

The detailed reaction mechanism of OH radical destroying toluene, phenol and naphthalene was studied through quantum chemical calculations in the research. Theoretical results indicate that for phenol and toluene, OH radical preferentially attack the ortho C atom due to the functional group on the benzene ring. But for naphthalene, OH radical preferentially attack the para-position C atoms because of its inherent benzo structure. To further study of the kinetics, the rate constant was calculated by the transition state theory. The comparison shows that the theoretical reaction rate constants for the degradation of tar by the OH radical were consistent with those obtained from literature experiments. And the rate constant of destructing naphthalene by OH radical was larger than that of destructing toluene, but lower than that of destructing phenol. The degradation sequence of OH radical to tar is: phenol ​> ​naphthalene ​> ​toluene. Because of the activation of hydroxyl group in benzene ring, phenol is the most easily attacked and destroyed by OH radical. The theoretical results can provide theoretical basis and data reference for further research on the removal of biomass tar and aromatics by OH radical.