The group contribution equation of state (GC-EOS) was applied to predict the phase behavior of binary systems of ionic liquids of the homologous families 1-alkyl-3-methylimidazolium hexafluorophosphate and tetrafluoroborate with CO2. Pure group parameters for the new ionic liquid functional groups [-mim][PF6] and [-mim][BF4] and interaction parameters between these groups and the paraffin (CH3, CH2) and CO2 groups were estimated. The GC-EOS extended with the new parameters was applied to predict high-pressure phase equilibria in binary mixtures of the ionic liquids [emim][PF6], [bmim][PF6], [hmim][PF6], [bmim][BF4], [hmim][BF4], and [omim][BF4] with CO2. The agreement between experimental and predicted bubble point data for the ionic liquids was excellent for pressures up to 20 MPa, and even for pressures up to about 100 MPa, the agreement was good. The results show the capability of the GC-EOS to describe phase equilibria of systems consisting of ionic liquids.
Aggregation of a model asphaltene compound hexa-tert-butylhexa-perihexabenzocoronene (HTBHBC) in toluene/heptane mixtures was monitored in real time by using Dynamic Light Scattering. The observed aggregation behavior was compared to that of real asphaltenes. It was found that heptane induces aggregation of HTBHBC and that the growth rate of the aggregates depends on the toluene/heptane ratio, closely resembling the aggregation kinetics of real asphaltenes. For the conditions studied in this work only diffusion-limited aggregation was observed. We thus confirm that a single well-defined compound can be successfully used for modeling the process of asphaltene aggregation.
FricDiff (friction difference) is a recently introduced separation technology. The separation occurs because of differences in interspecies friction in a multicomponent mixture. We present a description of a FricDiff unit. Such a unit consists of two compartments, the feed-side and the sweep-side, with a porous screen in between. The gas mixtures at the feed-side and the sweep gas interdiffuse through the screen. The basic modeling assumption is that the binary interaction of each feed-component with a counterflowing sweep gas is dominant. The interaction between the components diffusing in the same direction is neglected. This assumption leads us to introduce the number of "binary transfer units". We show that more detailed models introduced earlier are approximated well by this approach. Also, experiments seem to exhibit the same scaling, although the constants needed to fit the experimental results deviate quite a lot from the theoretical predictions. The equations derived can be used straightforwardly for incorporating a FricDiff unit in a process design.
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