Headspace Solid‐Phase Microextraction (HS‐SPME) for the Determination of Benzene,Toluene, Ethylbenzene,and Xylenes (BTEX) in Foundry Molding Sand

Abstract

The use of headspace solid‐phase microextraction (HS‐SPME) to determine benzene, toluene, ethylbenzene, and xylenes (BTEX) in foundry molding sand, specifically a “green sand” (clay‐bonded sand) was investigated. The BTEX extraction was conducted using a 75 µM Carboxen‐polydimethylsiloxane (CAR‐PDMS) fiber, which was suspended above 10 g of sample. The SPME fiber was desorbed in a gas chromatograph injector port (280°C for 1 min) and the analytes were characterized by mass spectrometry. The effects of extraction time and temperature, water content, and clay and bituminous coal percentage on HS‐SPME of BTEX were investigated. Because green sands contain bentonite clay and carbonaceous material such as crushed bituminous coal, a matrix effect was observed. The detection limits for BTEX were determined to be ≤0.18 ng g^?1 of green sand.     

Endothermic character of toluene adsorption from supercritical carbon dioxide on activated carbon at low coverage

Recasens, P., Velo, E., Larrayoz, M.A. and Puiggené, J., 1993. Endothermic character of toluene adsorption from supercritical carbon dioxide on activated carbon at low coverage. Fluid Phase Equilibria, 90: 265-287.

Heat effects and volumetric properties are analyzed for the adsorption of toluene from supercritical carbon dioxide onto activated carbon at the limit of zero coverage, based on existing data for the system. Using values of the adsorption equilibrium constant at different temperatures as a function of fluid density, large, negative partial molar volumes for toluene in the fluid were obtained, which were previously unavailable.

Numerical integration of the differential equation that expresses the isobaric temperature dependence of the equilibrium constant, coupled with parameter optimization, enabled us to estimate the differential enthalpy of toluene adsorption onto the surface from the ideal gas at the same pressure and temperature, in addition to the enthalpy of transfer from the fluid to the surface. This is found to be large and positive near the critical conditions. Using the thermodynamic analysis of Kelley and Chimowitz, our results show that in terms of the enthalpy of transfer, the isothermal adsorption from a supercritical fluid is an endothermic process, thus explaining the retrograde behavior experimentally observed for the regeneration of carbon with supercritical CO₂ at conditions not far from the solvent's critical point.     

Studies of the Effects of Alkali Metal Oxides Promoter on the Oxidative Methylation of Toluene with Methane over KY Zeolite Catalysts

Methane is the most abundant component of natural gas. The direct conversion of methane into chemical feedstock or transportable liquid fuel is an attractive process. In addition to oxidative coupling of methane, oxidative methylation of toluene with methane to styrene and ethylbenzene which has been investigated by Khcheyan et al.1, provides another possibility of methane utilization. Recently, several research groups have employed some metal oxides for the oxidative methylation of toluene w…     

Toluene Alkylation with Methanol to p-Xylene over Heteropoly Acids Supported by Clay

The alkylation of toluene with methanol for the selective formation of p-xylene was systematically studied. Very few studies have been reported on the use of superacids such as heteropolyacids on cheap supports, such as clay. This article deals with the use of different heteropoly acids (HPAs), viz, Dodeca-Tungstophosphoric acid [H3PO4·12WO3·xH2O] (TPA), Dodeca-Molybdo phosphoric acid ammonium salt hydrate [H12Mo12N3O40P aq] (DMAA), Dodeca-Molybdo Phosphoric acid (PMA) on clay (Montmorillonite, K-10) and as such plain clay. This comparative study reveals that 20%PMA/Clay shows 62% toluene conversion and 100% selectivity toward p-xylene.     

甲苯完全氧化反应中含铬催化剂的TPR研究

甲苯完全氧化反应中含铬催化剂的ＴＰＲ研究单绍纯，封雷，孙鸣鸣，伏义路（中国科学技术大学近代化学系，合肥２３００２６）关键词甲苯氧化，三氧化二铬，程序升温还原我们发现，不少非贵金属氧化物催化剂虽然有较好的反应活性，但却不能维持长久，因而影响了其开发应用...     

VISCOSITY BEHAVIOR OF PS／TOLUENE SOLUTION IN DILUTE AND EXTREMELY DILUTE CONCENTRATION REGION

The influences of both the volume of PS/toluene solution in the Ubbelohde viscometer and the precision of the time measuring on the viscosity behavior in dilute and extremely dilute concentration region are investigated. It was found that the influence of the former can neglect, but that of the latter is so prominent that the data fluctuate bitterly and linearity of the curve of the reduced viscosity vs. concentration (ηsp/c-c) becomes too bad to obey the Huggins equation down to the extremely dilute region, despite the error of the flow times Δt≤0.2s, which is permitted by the conventional method of viscosity measurement. Through strict mathematical analyses, it was found that the error (E) of the reduced viscosity is in proportion and inverse propor tion to Δt and concentration c, respectively. So the less the concentration, the more the error is. Consequently, a lowest concentration limit cL corresponding to given experimental error may exist and it will be meaningless for further operation below CL because of the great fluctuation of the data. Therefore, it needs to seriously reconsider the application of the conventional method of Ubbelohde viscosity measurement in the extremely dilute polymer solution under traditional conditions because of the great influence of the experimental error.     

Interactions of metal extractant reagents. IX. Aggregation and mixed species equilibria of tri-n-dodecylammonium chloride and nitrate in toluene at 40°C

The aggregation and mixed species formation equilibria of tri-n-dodecylammonium chloride (TLAHCl) and tri-n-dodecylammonium nitrate (TLAHNO₃) dissolved in toluene have been studied by vapor pressure osmometry at 40°C. The experimental data can be best fit by the formation of the aggregates (TLAHCl)₂ (log _2,0 = 1.35±0.06), (TLAHNO₃)₂ (log _2,0 = 1.75±0.20), (TLAHNO₃)₃ (log _0,3 = 3.6±0.1), and the mixed species (TLAHCl)(TLAHNO₃)₂ (log _1,2 = 3.3±0.2).     

Interaction of polynitro compounds with difluoroamine

Difluoroamine does not react with tetranitromethane and fluoro-, chloro-, and bromotrinitromethanes in DMF and in acidic media (CF₃COOH, ClSO₃H, FSO₃H, and oleum), but reacts with α-fluoro- and α-(difluoroamino)-α,α-dinitrotoluenes to give substitution products of the difluoroamino group for both the nitro groups,viz., PhC(NF₂)₂F and PhC(NF₂)₃, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1647–1649, August, 1998.     

Determination of gas-phase produced ethyl parathion and toluene 2,4-diisocyanate by ion mobility spectrometry, gas chromatography and liquid chromatography

Ethyl parathion and toluene 2,4-diisocyanate (2,4-TDI) vapors were generated using a vapor generation system that was designed for the evaporation of liquid samples at known flow rates. The vapor generation of parathion and 2,4-TDI posed a challenge because of their low volatility and tendency to absorb into surfaces of the vapor generation system. Experimental concentration of parathion was determined using gas chromatography-mass spectrometry (GC-MS). 2,4-TDI was derivatized with 1-(2-pyridyl)piperazine to urea derivative which concentration was analyzed using high performance liquid chromatography (HPLC). In addition, in combination with vapor generator, aspiration IMS was used for monitoring ion mobility cell (IMCell) and semiconductor cell (SCCell) responses to parathion and 2,4-TDI vapors. The chromatographic results correlated well with the IMCell response data, showing high specificity of IMS to parathion and 2,4-TDI. The concentrations of parathion and 2,4-TDI at the detection limit of IMS were significantly lower than IDLH threshold values of parathion or 2,4-TDI, demonstrating high sensitivity of IMS to both compounds. The IMS patterns of both chemicals and the influence of humidity on IMCell and SCCell sensitivity were analyzed.