It is demonstrated that thermal and mutual diffusivities of binary mixtures of n-octacosane (n-C28H58) with carbon monoxide (CO), hydrogen (H2), and water (H2O) are simultaneously accessible by dynamic light scattering (DLS). As the light-scattering signals originating from thermal and concentration fluctuations appear in similar time scales, different data evaluation strategies were tested to achieve minimum uncertainties in the resulting transport properties. To test the agreement of the respective theoretical model with the DLS signals in the regression, an improved multifit procedure is introduced. With the selected data evaluation strategy, uncertainties of 4 to 15% and 4 to 30% in the thermal and mutual diffusivities, respectively, could be obtained for the binary mixtures. The mutual diffusivities for the mixtures measured at temperatures ranging from 398 to 523 K and pressures of 5 to 30 bar at saturation conditions are in good agreement with molecular dynamics simulations and data from the literature.

The behavior of water in silicalite and dealuminated zeolite Y (DAY), two highly hydrophobic zeolites, was investigated at different temperatures in the range 100−600 K by molecular dynamics simulations using the Compass force field. The full flexibility of water molecules and the zeolite framework was considered. This study confirmed behavior of water in silicalite pores reported previously by several authors, and extended previous work to include the different behavior of water in DAY pores. The results show that the behavior of water is more complex in silicalite than in DAY. Three different activation energies for water diffusion were obtained in silicalite in the range 250−600 K compared to two for DAY. The values of these activation energies are discussed in detail and are related to the strength of hydrogen bonds and the zeolite structure. Moreover, from the radial distribution functions (RDFs), it is shown that water mostly exists in the gas phase at room temperature in silicalite, whereas liquidlike water is observed in DAY. The self-diffusion coefficients of water and the RDFs were obtained as functions of temperature in order to explain the different behaviors of water in the two all-silica zeolites. The influence of loading on the self-diffusion coefficients also was investigated for both crystals. The results compare favorably with previous experimental and theoretical studies.

The present work represents a continuation of a former study where the simultaneous determination of thermal and mutual diffusivity for binary mixtures of n-octacosane (n-C28H58) with dissolved carbon monoxide (CO), hydrogen (H2), or water (H2O) by using dynamic light scattering (DLS) was demonstrated. Here, the same properties are studied for binary mixtures of the n-alkanes n-dodecane (n-C12H26) or n-tetracontane (n-C40H82) with dissolved CO, H2, or H2O. In most cases, expanded relative uncertainties (k = 2) ranging from 2 to 12 % and 3 to 25 % for the thermal and mutual diffusivities could be obtained. The experimental mutual diffusivities for mixtures of n-C12H26 with CO, H2, or H2O measured at temperatures from 398 to 524 K and pressures from 0.2 to 4.2 MPa at saturation conditions agree well with molecular dynamics (MD) simulations using atomistic models and with experimental data from literature. Binary mixtures of n-C40H82 with dissolved CO, H2, or H2O were investigated in a temperature range from 447 to 498 K and pressures from 0.3 to 3.9 MPa. For mixtures with n-C40H82, the accessible temperature range was limited due to a change in the optical characteristics of the sample at elevated temperatures where DLS measurements suffered from absorption effects and particle scattering.

The affinity that adsorbents have for water can influence their effectiveness in organics removal from drinking water due to competitive adsorption. The extent of the affinity of microporous zeolites for water is determined, in part, by AlO4(-) tetrahedral sites (T-sites) in the crystal lattice and lattice defects in the form of silanol nests. In this study, water adsorption isotherms in silicalite and in dealuminated zeolite Y (DAY) were simulated using the Compass force-field. The results show that the simulations can predict the shape of water adsorption isotherms and predict adsorption levels comparable to literature results. Moreover, simulations revealed that the results are influenced significantly by the presence of AlO4(-) T-sites. The results confirm the capacity of the Compass force-field to predict water sorption properties in silicalite and in DAY.

Theoretical approaches suggest that dynamic light scattering (DLS) signals from low-molecular-weight ternary mixtures are governed by fluctuations in temperature as well as two individual contributions from fluctuations in concentration that are related to the eigenvalues of the Fick diffusion matrix. Until now, this could not be proven experimentally in a conclusive way. In the present study, a detailed analysis of DLS signals in ternary mixtures consisting of n-dodecane (n-CH) and n-octacosane (n-CH) with dissolved hydrogen (H), carbon monoxide (CO), or water (HO) as well as of n-CH or n-CH with dissolved H and CO is given for temperatures up to 523 K and pressures up to 4.1 MPa. Thermal diffusivities of pure n-CH and n-CH as well as thermal and mutual diffusivities of their binary mixtures being the basis for the ternary mixtures with dissolved gas were studied for comparison purposes. For the investigated ternary mixtures, three individual signals could be distinguished in the time-resolved analysis of scattered light intensity by using photon correlation spectroscopy (PCS). For the first time, it could be evidenced that these signals are clearly associated with hydrodynamic modes. In most cases, the fastest mode observable for ternary mixtures is associated with the thermal diffusivity. The two further modes obviously related to the molecular mass transport are observable on different time scales and comparable to the modes associated with the concentration fluctuations in the respective binary mixtures. Comparison of the experimental data with results from molecular dynamics simulations revealed very good agreement.