Spectroscopic Study of Water-Hydrocarbon Mixtures at High Temperatures and Pressures.

我们阐明了混合流体在高温高压下的以下性质：(1)在恒压下，富烃相的水浓度最初随着温度的升高而急剧增加，在接近一相临界曲线的温度时达到最大值，然后在更高的温度下急剧下降。(2)在低于523K的温度下，苯和烷基苯中的水分子以单体或二聚体的形式存在。水和苯环之间的π-氢键作用即使在高温加压下也存在。(4)在一定的温度-压力范围内，水和烃的混合物发生了反常的大体积膨胀。这一发现可以通过对流体混合物的原位红外测量首次观察到。对于水-苯混合物，在(A)水的气液平衡曲线，(B)三相平衡曲线的延长线和(C)混合物的单相临界曲线所包围的区域内，体积膨胀特别大。(5)苯在水中的溶解度比水在苯中的溶解度小一个数量级，在恒温下，苯在水中的溶解度随着压力的增加而增加，而水在苯中的溶解度则减小。(6)对于高温高压水，发现(1)在压缩气体或类气体条件下，存在单体-二聚体平衡，二聚热为(-15±3)kJ/mol；(2)即使在673K，400bar，也有相当一部分水分子自由旋转；(3)氢键的形成与摩尔密度有关，与温度无关。

We have elucidated the following properties of mixed fluids at high temperatures and pressures.(1) Water concentration in a hydrocarbon-rich phase initially increases dramatically as temperature rises at constant pressure, and reach maximum at a temperature close to one-phase critical curve, and then steeply decreases at higher temperatures.(2) Water molecules in benzene and alkylbenzene at temperatures below 523K exist as monomers or dimers, and the relative ratio of the dimers increases with increasing temperature.(3) π-hydrogen bonding interaction between water and a benzene ring exists even at high temperatures under pressure.(4) An anomalously large volume expansion occurs on mixing of water and hydrocarbons in a certain temperature-pressure range. This finding could be observed for the first time by the in situ infrared measurements of the fluid mixtures. For water-benzene mixtures, the volume expansion is particularly large in the region enclosed by (a) the gas-liquid equilibrium curve of water, (b) an extended line of the three-phase equilibrium curve, and (c) the one-phase critical curve of the mixtures.(5) Solubility of benzene in water is an order of magnitude smaller than that of water in benzene, and the solubility of benzene in water increases with increasing pressure at constant temperature, while that of water in benzene decreases. This asymmetry of the mutual solubilities can be understood by differences in molecular size and in isothermal compressibility between water and benzene.(6) For high-temperature-pressure water, it is found that (i) in the compressed gas or gas-like condition a monomer-dimer equilibrium exists and the dimerization enthalpy is estimated to be (-15±3)kJ/mol, (ii) an appreciable proportion of water molecules rotate quite freely even at 673K at 400 bar, and (iii) ratio of hydrogen bond formation is dependent on molar density irrespective of temperature.