EFFECTS OF SOLVENT POLARITY ON INFINITE DIFFUSION COEFFICIENTS IN SUPERCRITICAL ETHANOL

Ethanol has more accessible critical properties (Tc = 241℃, Pc =6.38 MPa) than water and stronger solubility power than carbon dioxide. Nearcritical and supercritical ethanol is a compressible fluid exhibiting great tunability with both temperature and pressure. It offers a great potential as an     

一些有机物在高压乙醇中无限稀释扩散系数的测定与计算

在40～200℃、0-16MPa范围内,运用Taylor分散技术实验测定了苯、吡啶和对硝基苯胺在乙醇中的无限稀释扩散系数。对于上述三种溶质,低温下扩散系数几乎不随压力变化;当温度超过100℃时,扩散系数随压力的增加明显下降,温度越高下降趋势越明显。使用修正的Wilke-Chang方程和Yang-Ma-Chen方程预测了高压乙醇体系的无限稀释扩散系数。与实验测量值的对比结果表明,温度低于100℃时修正的Wilke-Chang方程、Yang—Ma-Chen方程均能很好地预测高压乙醇体系的无限稀释扩散系数,平均偏差分别为7.3％和6．4％;但在高温条件下,除温度因素外．压力对缔合因子也有很大影响,从而使模型计算值远高于实验测定结果。吡啶和对硝基苯胺在乙醇中的无限稀释扩散系数未发现有文献报导。     

高压乙醇中的无限稀释扩散系数:实验测定与模型评价

The infinite diffusion coefficients of benzene, toluene, naphthalene, pyridine and p-nitroaniline in ethanol were measured by Taylor dispersion technique under 318-473 K and 0-16 MPa. The measurement accuracy of the established apparatus was first checked. The measured diffusion coefficient of the five organic solutes in ethanol did not change with pressure at low temperature, but it was significantly reduced with pressure increase when the temperature is higher than 373 K. Of the correlations available for polar solvents, the modified Wilke-Chang equation, the Yang-Zhang equation as well as the He-Yu equation were used to calculate the infinite diffusion coefficient. At low temperature,the three equations all agreed well with experimental results for both polar and non-polar solutes.However, the prediction accuracy was decreased sharply when the temperature was higher than 373 K,where the association factor of the solvent was varied with temperature as well as pressure.     

植物乳杆菌发酵对富硒发芽糙小米饮料风味特征的影响

为研究植物乳杆菌发酵对富硒、发芽以及富硒发芽等不同处理下糙小米饮料风味特征的影响,采用感官评定以及电子鼻、电子舌和固相微萃取气相色谱?质谱联用技术分别测定植物乳杆菌发酵前后,普通、富硒、发芽以及富硒发芽等不同糙小米饮料的挥发性风味物质的组成。结果表明：植物乳杆菌发酵后糙小米饮料感官品质发生明显改善,苦味、涩味降低,酸味增强;其中富硒发芽糙小米发酵饮料感官评价风味最佳,共检测到23 种挥发性物质,主要包括1 种醛类、7 种醇类、1 种烷类、7 种酸类、3 种酚类、3 种酮类、1 种酯类。香气成分主要集中在醇类和酸类,呈香物质有2?乙基?1?己醇、4?乙烯基苯酚和壬酸等。对植物乳杆菌发酵前后的糙小米饮料挥发性成分进行聚类分析,热图显示大多数的醇类和酸类含量在糙小米发酵后明显增加,而醛类含量明显降低,增加的醇类和酸类可能对糙小米饮料的风味有重要贡献。     

溶剂极性对超临界乙醇中无限稀释扩散系数的影响

INTRODUCTION Ethanol has more accessible critical properties(Tc =241 ℃, Pc =6.38 Mpa) than water and stronger solubility power than carbon dioxide. Nearcritical and supercritical ethanol is a compressible fluid exhibiting great tunability with both temperature and pressure.