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The aggregation of asphaltenes by pressure depletion both in a live crude oil and model systems of asphaltenes in toluene/pentane solvents is studied. Near-infrared spectroscopy utilizing a high-pressure NIR cell with a maximum operating pressure of 325 bar is used to study the onset of asphaltene aggregation. The NIR spectra are subject to a principal component analysis (PCA) in order to detect the asphaltene aggregation onset pressure. The effect of fluid compressibility on the NIR spectra is also demonstrated. The aggregation behavior of asphaltenes in model systems is shown to resemble the aggregation behavior for the crude oil. However, while the asphaltene aggregation in the crude oil is more or less completely reversible with repressurization, indications of only a partial redissolution are seen in the model systems. The kinetics of the redissolution is quite slow. A time of 72 h to equilibrate at the original pressure of 300 bar was required to redissolve the asphaltene aggregates formed within the crude oil by depressurization of the sample. Near-infrared spectroscopy in combination with principal component analysis is shown to be an efficient tool in detecting both bubble points and asphaltene aggregation onset pressures in high-pressure systems.

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Emf contributions f Liquidjunctions / Activity coefficients f Mobility variationsThe contribution to the emf of an electrochemical cell from the liquid junction is the topic of this paper. Different kinds of liquid junctions between KG solution of 4 kmol m"3 and dilute solutions of HC1 were investigated experimentally and theoretically. Our method of theoretical calculations involves only operationally defined quantities. This permits a detailed analysis of the different contributions and a separation of the approximations introduced. vcrmindertcr Diffusion sowiedie Brückccincrhandelsüblichcn Referenzelektrode wurdcn mit eincr Briicke mil linearem Konzentrationsprofil verglichcn. Erhebliche Diffcrcnzcn in den gemessenen EMK-Werten zeigten. daB die Niiherung nach Henderson zur Ermittlung genauer Wcrte nichl anwendbar ist. Als eine Folgerung ergibt sich. daB man bei einer Zelle fiir analytische Zwecke ein rein Nernstsches Verhalten nicht erwarten kann. nicht einmal bei verdünnten Lösungen.

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