Asphaltenes are the heaviest and most highly polarizable and polydisperse petroleum fractions in crude oils. The solubility of the asphaltenes in crude oils is usually affected by the reduction of pressure, temperature, and/or oil composition change as a result of commingling with other crude oils or gas injection. This may lead to asphaltene precipitation and deposition, decline in permeability, blockage of well and surface facilities, and finally, production decrease or termination, which has a substantial economical impact. Therefore, the ability to understand and predict asphaltene phase behavior is essential for both up-and downstream processing, so that appropriate strategies can be implemented for prevention and remediation. In our study, we present the capability and advances of the equations of state approach by applying the cubic-plus-association (CPA) and the perturbed-chain statistical associating fluid theory (PC-SAFT) equation to model asphaltene stability in live oils and compare the predictions to the various types of measured asphaltene precipitation data over wide ranges of temperature and pressure.

We present and discuss the influence of the molecular architecture on the phase equilibria behavior of ethylene glycol oligomers and their mixtures based on predictions from a molecularbased equation of state (EoS). The soft statistical associating fluid theory (SAFT) EoS is used to fit the molecular parameters from the available vapor liquid experimental data, providing a correlation of the molecular parameters with the molecular weight of the compounds, which can be used to predict the behavior of heavy members of the series. The same equation is used to describe the ethylene glycol oligomer mixtures with several compounds, including carbon dioxide, benzene, methane, and n-hexane. The performance of the soft-SAFT equation is compared with some Gibbs excess free energy models and the Peng-Robinson EoS, where soft-SAFT is superior in most of the cases. Once the performance of the equation and the molecular model are established, soft-SAFT is used as a predictive tool to systematically study the influence of the chain length, polarity, and hydrogen bonding formation on the behavior of two selected mixtures. The influence of the oligomers' chain length is noticeable in the dew points of liquidlike solutes (benzene), with almost no effect in the boiling point of these mixtures, except for the ethylene glycol mixture. On the contrary, the solubility of carbon dioxide on these oligomers strongly depends on chain length, increasing as the alkyl part of the chain increases. This is attributed to the breaking of hydrogen bonds in the shorter oligomers.

We present here phase equilibria calculations of polyethylene solutions in different solvents as obtained with two versions of the SAFT equation of state, soft-SAFT and PC-SAFT. The objective of this work is twofold: to check the accuracy of the soft-SAFT equation in providing reliable polymer solutions behavior and to propose a methodology from which systematic studies on polymer solutions can be made by the use of transferable molecular parameters. Some issues regarding the fitting of molecular parameters from polymer data as well as the numerical problems associated with polymer phase equilibria calculations are also mentioned. The methodology is applied to model the phase equilibria of polyethylene solutions with several solvents, differing in size and polarity, including n-pentane, n-hexane, butyl acetate, and pentanol, and results are compared to available experimental data. The phase behavior explored in this work is wide, from vapor-liquid equilibria to liquid-liquid equilibria, displaying upper critical solution temperatures and lower critical solution temperatures. We have also calculated the solubility of ethylene in polyethylene with the same models. Results obtained from the soft-SAFT equation are slightly more accurate in some of the cases than the PC-SAFT equation. Both equations, soft-SAFT and PC-SAFT, follow most of the experimental trends, providing accurate predictions from pure component parameters in some of the cases, while a binary interaction parameter was needed for the butyl acetate, 1-pentanol, and ethylene binary mixtures.

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The present work addresses the modeling of the phase equilibria of several poly(ethylene glycol) mixtures, with different types of solvents, by the soft-SAFT (statistical associating fluid theory) equation of state (EoS). The molecular parameters for poly(ethylene glycol) were obtained as a function of the molecular weight by extrapolation from the first four members of the ethylene glycols series, up to tetraethylene glycol, obtained in a previous work [Pedrosa et al. Ind. Eng. Chem. Res. 2005, 44, 7027]. The parameters for the different solvents were either taken from previous works or fitted for the first time to available vapor-liquid equilibrium data within the soft-SAFT during this work. Their quadrupolar nature was explicitly taken into account. The phase equilibria studied concerns the solubility of gases, such as nitrogen and propane, and vapor-liquid equilibria with both nonassociating solvents, such as benzene, and associating solvents, such as methanol, ethanol, and water. The liquid-liquid equilibria of poly(ethylene glycol) with different solvents, namely, toluene, ethylbenzene, n-propylbenzene, and tert-butyl acetate, were also described using the soft-SAFT EoS. soft-SAFT was able to provide an overall good description of all mixtures investigated here. The advantages and shortcomings of the model as well as its capability to describe the dependence of the phase equilibria with the molecular weight of the polymer are discussed.

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