A systematic approach for modelling the affinity coefficient in the Dubinin-Radushkevich equation

An unbiased evaluation of predictive models for the affinity coefficient of the Dubinin-Radushkevich equation was performed. The first step involved the selection of a minimum number of representative and chemically diverse organic compounds, the training set. This set, isopropylamine, heptane, dichloromethane, 2-chloro-2-methylpropane, 2-butanone, 1-chloropentane, acetonitrile, and benzene, covering five compounds classes, was selected with the help of PCA and statistical design. Secondly, experimental affinity coefficients of the training set compounds were determined from adsorption isotherms on Norit R1 activated carbon. In a third step, 45 physico-chemical properties were assembled for the training set compounds. A model was developed, based on PLS analysis, which correlates the measured affinity coefficients and the physico-chemical properties. Finally the model was validated by comparing model predictions of the affinity coefficients with literature data for an external validation set of 40 compounds. It was found that the predictive power of this model (RMS error=0.090) is better than using traditional methods based on parachor, molar polarizability or molar volume. The proposed new model for the affinity coefficient is based on three parameters only, the molecular weight and VdW volume of the compound and the calculated energy of interaction between the compound and a graphite model surface.     

脂肪族含氧有机物沸点的定量构效关系

引言沸点是化合物最基本的物理性质之一,也可以用来预测和估算化合物的其他物理化学性质,如临界性质、闪点等。沸点与分子结构和分子间作用力密切相关,实验测定是获得沸点最直接的方法,但     

Partition coefficients for a mixture of two lubricant oligomers

Universal base oils that remain pourable over wide temperature ranges would have important advantages for lubrication applications. The model system used in this project was a poly(α‐olefin) synthetic base oil modified with polydimethylsiloxane (PDMS) to lower the pour‐point temperature. Although the blend was miscible at room temperature, phase separation occurred at temperatures lower than 258 K. Partition coefficients of such nonideal oligomer mixtures can (1) help define operating temperature ranges and (2) provide a basis for designing molecular weight distributions of each lubricant that control or prevent phase separation. The poly(α‐olefin) base oil family is branched oligomers with two to five n‐mers at levels greater than 1 wt %, whereas PDMS additives are linear oligomers having between 10 and 50 sequential n‐mers at levels greater than 0.5 wt %. In this study, Fourier transform infrared measurements of the poly(α‐olefin) and PDMS compositions in each phase provided an overall material balance. Poly(α‐olefin) oligomers were detected with size exclusion chromatography with a differential refractive‐index detector, and PDMS oligomers were detected with matrix‐assisted laser desorption/ionization–time‐of‐flight mass spectrometry. The best sets of measurements for the individual oligomers in each phase were selected by minimization of the overall material balance errors. For both oligomers, components with high molecular weights were preferentially excluded from the phase rich in the other polymer and were relatively independent of temperature. The partition coefficients of poly(α‐olefin) components increased with increasing oligomer length, whereas the partition coefficients of the PDMS components decreased with increasing oligomer length. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Comparison of two methods for extraction of volatiles from marine PL emulsions

The dynamic headspace (DHS) thermal desorption principle using Tenax GR tube, as well as the solid phase micro‐extraction (SPME) tool with carboxen/polydimethylsiloxane 50/30 µm CAR/PDMS SPME fiber, both coupled to GC/MS were implemented for the isolation and identification of both lipid and Strecker derived volatiles in marine phospholipids (PL) emulsions. Comparison of volatile extraction efficiency was made between the methods. For marine PL emulsions with a highly complex composition of volatiles headspace, a fiber saturation problem was encountered when using CAR/PDMS‐SPME for volatiles analysis. However, the CAR/PDMS‐SPME technique was efficient for lipid oxidation analysis in emulsions of less complex headspace. The SPME method extracted volatiles of lower molecular weights more efficient than the DHS method. On the other hand, DHS Tenax GR appeared to be more efficient in extracting volatiles of higher molecular weights and it provided a broader volatile spectrum for marine PL emulsion than the CAR/PDMS‐SPME method.     

Sorption and diffusion of volatile organic compounds in fluoroalkyl methacrylate‐grafted PDMS membrane

Pervaporation is known as an excellent method for the purification of contaminated water, the extraction of aroma compounds, etc., and has been widely studied. The prediction of permeation is important for treatment, extraction, and quantitative analysis. To predict permeation, a solution–diffusion mechanism is proposed. The octanol–water partition coefficient (Pow) has been generally used in expressing hydrophobicity. The hydrophobicity, Pow, is closely related to the solubility of organic compounds. Also, the molecular volume is closely related to the diffusion of organic compounds. In this study, we improved polydimethylsiloxane (PDMS) membranes by plasma grafting of fluoroalkyl methacrylates (FALMA) to enhance the affinity of PDMS to volatile organic compounds (VOCs). Furthermore, we investigated the pervaporation through the plasma‐grafted PDMS membrane and the PDMS membrane and the solution–diffusion mechanism of various VOCs. The permselectivity of tetrachloroethylene (PCE) and toluene determined by the sorption and the diffusion characteristics permeating in the membrane was high. Because the molecular volume of the VOCs is greated than that of water and the permeates quickly penetrate in rubbery membranes like PDMS, permselectivity was not affected by the diffussivity. Solubility significantly affected the permselectibity during pervaporation through a hydrophobic rubbery membrane. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 773–783, 2000     

有机物临界体积的定量构性

采用分子模拟和多元线性回归方法,研究了有机物临界体积的定量结构-性质关系(QSPR).基于121个临界体积数据中的108个样本点,得到一个临界体积模型(残余标准差11.80 cm3/mol,拟合度0.994 2).该模型含4个分子描述码,对训练组和测试组的平均估算误差分别为8.36cm3/mol(相对误差2.52%)和9.09 cm3/mol(相对误差3.05%).研究表明,分子体积、分子支链化程度以及分子表面的静电分布等定量结构参数可以有效地估算有机物的临界体积.     

Application of polymer‐coated quartz crystal microbalance (QCM) as a sensor for BTEX compounds vapors

A sensor based on the technique of a quartz crystal microbalance (QCM) was developed for the detection of organic vapors such as benzene, toluene, ethylbenzene, and xylenes (BTEX compounds). Detection was based on the adsorption of organic vapors on a thin layer of polydimethylsiloxane (PDMS) coated at the surface of AT‐cut gold‐coated quartz crystal electrodes. The frequency shifts due to the sorption of BTEX compounds were measured. Calibration graphs were constructed by plotting the frequency changes (ΔF/Hz) against the concentration of organic compounds. Using this method, the detection of these organic vapors was carried out at the ppm level. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1062–1066, 2001     

Measurement of infinite dilution activity coefficients of selected environmentally important volatile organic compounds in polydimethylsiloxane using gas - liquid chromatography

Silicon oil, chemically known as polydimethylsiloxane (PDMS), is a high boiling point solvent highly suitable for volatile organic compounds (VOCs) absorption. To use PDMS as an absorption solvent for a specific waste gas problem, it is important to determine the infinite dilution activity coefficients of the VOCs to be separated with PDMS. This work reports activity coefficients at infinite dilution of 13 VOCs in polydimethysiloxane determined by the dynamic gas liquid chromatographic technique. The measurements were carried out at various temperatures (303.15, 313.15, 323.15., 333.15, 353.15, 373.15, 393.15 and 423.15 K). Four PDMS polymers with average molecular weight ranging from 760 to 13,000 were used as solvents. A control column packed by Perkin Elmer to our specifications was used to validate the coating and packing methods. Flow rate dependence of the elution peaks was also investigated by varying it from 10–50 ml/min. Precision was improved by reproducing the results using columns with different liquid loading, thus also studying the retention mechanism. The results compare well with the data from previous work using simple headspace and UNIFAC predictions and literature values. The successful comparison gives an indication of the GLC as a rapid, simple and accurate method for studying the thermodynamics of the interaction of a volatile solute with a nonvolatile solvent.