Romain Privat

A simple and unified algorithm to solve fluid phase equilibria using either the gamma–phi or the phi–phi approach for binary and ternary mixtures

Abstract A new algorithm is proposed for calculating phase equilibria in binary systems at a fixed temperature and pressure. This algorithm is then extended to ternary systems (in which case, the mole fraction of one constituent in a given phase must be fixed in order to satisfy the Gibbs’ phase rule). The algorithm has the advantage of being very simple to implement and insensitive to the procedure used to initialize the unknowns. Most significantly, the algorithm allows the same solution procedure to be used regardless of the thermodynamic approach considered ( γ – φ or φ – φ ), the type of phase equilibrium (VLE, LLE, etc.) and the existence of singularities (azeotropy, criticality and so on).

Predicting the Phase Equilibria of Carbon Dioxide Containing Mixtures Involved in CCS Processes Using the PPR78 Model

Carbon dioxide is an extremely important product of the chemical, pharmaceutical and petrochemical industries. Its main applications are production of coal liquids, petroleum processes such as enhanced oil recovery and separation and supercritical fluid extraction. CO2 is however a greenhouse gas that affects the Earths temperature and many efforts are devoted to the reduction of CO2 emissions. The design and operation of many processes dealing with the CO2 capture and storage (CCS) greatly depend on knowledge about pressurevolume-temperature-composition (PVTxy) and mixing properties (hM, cP) of mixtures involved in these processes. A typical CO2 capture and storage (CCS) chain consists of four main steps: CO2 capture, conditioning (dehydration, non-condensable gas separation and/or liquefaction, and compression/pumping), transport and storage.

Thermodynamic Models for the Prediction of Petroleum-Fluid Phase Behaviour

Petroleum fluids, which include natural gases, gas condensates, crude oils and heavy oils are in the category of complex mixtures. A complex mixture is defined as one in which various families of compounds with diverse molecular properties are present. In petroleum fluids, various families of hydrocarbons such as paraffins, naphthenes and aromatics exist. Such mixtures also contain some heavy organic compounds such as resins and asphalthenes and some impurities such as mercaptans or other sulphur compounds. Non hydrocarbons are typically nitrogen (N2), carbon dioxide (CO2), hydrogen sulphide (H2S), hydrogen (H2) among few others. Water is another fluid that is typically found co-existing with naturally occurring hydrocarbon mixtures.

Estimation of Solvation Quantities from Experimental Thermodynamic Data: Development of the Comprehensive CompSol Databank for Pure and Mixed Solutes

The Gibbs energy of solvation measures the affinity of a solute for its solvent and is thus a key property for the selection of an appropriate solvent for a chemical synthesis or a separation process. More fundamentally, Gibbs energies of solvation are choice data for developing and benchmarking molecular models predicting solvation effects. The Comprehensive Solvation—CompSol—database was developed with the ambition to propose very large sets of new experimental solvation chemical-potential, solvation entropy, and solvation enthalpy data of pure and mixed components, covering extended temperature ranges. For mixed compounds, the solvation quantities were generated in infinite-dilution conditions by combining experimental values of pure-component and binary-mixture thermodynamic properties. Three types of binary-mixture properties were considered: partition coefficients, activity coefficients at infinite dilution, and Henry’s-law constants. A rigorous methodology was implemented with the aim to select dat...

Experimental and thermodynamic comparison of the separation of CO 2 /toluene and CO 2 /tetralin mixtures in the process of organogel supercritical drying for aerogels production

An organogel is firstly prepared by synthesizing an aminoacid-type organogelator which is able to immobilize aromatic solvents, such as tetralin or toluene. Aerogels are obtained from organogels by extracting the solvent with a stream of supercritical CO2 in an autoclave. The CO2/solvent mixture leaving the autoclave is separated in a cascade of three cyclone separators. The experimental results showed a good solvent recovery rate in the case of tetralin, exceeding 90%, but an unsatisfactory separation for toluene with a yield below 65%. A thermodynamic study was carried out to model the separation for both solvents. The Peng–Robinson equation of state with van der Waals mixing rules and temperature-dependent binary interaction coefficients was selected to predict the CO2/solvent thermodynamic behavior. Measurements of isothermal bubble points of the CO2/tetralin system were conducted using a high-pressure variable-volume visual cell confirming the relevancy of this model. Then, the first separator was simulated as a simple theoretical equilibrium stage. Simulations using PRO/II software were in good agreement with experimental solvent recovery rate for both toluene and tetralin. The best operating pressure and temperature for the separation were computed by a numerical parametric study.Graphical abstractThermodynamic study to explain theoretical recovery in organogel supercritical drying: comparison between two solvents (T=20 °C, P=50 bar).

Ethanol and Distillate Blends: A Thermodynamic Approach to Miscibility Issues: Part 3 — Generalization to Other Alcohols (Methanol, Isopropanol and 1-Butanol)

In the framework of a multistep program devoted to the ternary gasoil/alcohol/water system, the authors investigated the miscibility of anhydrous and hydrated ethanol qualities with four classes of industrial gasoil having different compositions and densities. To that end, they considered a pseudo binary system made by the various hydrocarbon species on one hand and the alcohol/water sub-system on another hand. Using the UNIQUAC thermodynamic theory and the Group Contribution approach, the team computed the Minimum Miscibility Temperature (“MMT”) for a series of the gasoil/ethanol/water system having water concentrations in ethanol comprised between 0 and 10%. The TMM is the temperature above which the various components of the system form a sole phase. This work is summarized in two papers already published (Part 1: GT 2010-22126; Part 2: GT2011-45896).In the continuity of this prior work and considering the potential interest of alternative alcohols as “gasoil extenders”, the team has generalized this approach to selected C1-C4 alcohols: methanol, isopropanol (or 2-propanol) and n-butanol (or 1-butanol). While methanol is an interesting “energy vector” of coal and biomass via the CTL and BTL processes, isopropanol is a widespread commodity produced by the classical petrochemistry and 1-butanol is a promising biofuel candidate of the second, “lingo-cellulosic” generation.This third part of the project shows that the introduction of these alternative alcohols and their respective interactions with water lead to considerable changes in the liquid-liquid equilibria and important shifts of the MMTs, trends that were difficult to anticipate beforehand.Copyright

Ethanol and Distillate Blends—A Thermodynamic Approach to Miscibility Issues: Part 2—The Influence of Water

In recent years, the quest for sustainable primary energies has increased the potential interest of biogenic/fossil fuels mixes. As an example, ethanol is used as a gasoline extender to both partly substitute hydrocarbons and increase octane number while improving vehicle emissions. In a previous paper (GT2010-22126), it has been shown that ethanol and gasoil are able to blend and form homogeneous solutions only in limited proportion ranges, due to their markedly different physical and chemical properties. However the incorporation of small amounts of water in ethanol dramatically decreases this already narrow miscibility domain. Indeed, in function of the temperature, such ternary mixtures often give rise to liquid-liquid equilibria i.e. to two separated phases that are respectively lipophilic and hydrophilic. A key parameter is thus the Minimum Miscibility Temperature, i.e. the temperature above which ethanol, water and gasoil become completely miscible. On another hand, commercial gasoils do not constitute a single product but display worldwide a large range of compositions that influence the stability of these ternary blends. In this context, an investigation program intended to characterize and predict the stability of ternary ethanol + water + gasoil blends has been carried out by the LRGP laboratory (Laboratoire Reactions et Genie des Procedes). The approach is based on a thermodynamical, theoretical calculation of the liquid-liquid phase diagrams formed by ethanol, water and a mixture of various hydrocarbons representative of the diesel oil pool using the group-contribution concept. The basic idea is that whereas there are thousands of chemical compounds, the number of functional groups that constitute these compounds is much smaller. The work relies on the experimentally verified theory that a physical property of a fluid can be expressed as the sum of contributions made by molecule’s functional groups, which allows correlating the properties of a very large number of substances in terms of a much smaller number of parameters that represent the contributions of individual groups. This work shows the huge influence exerted by the water content of ethanol on the shape of the liquid-liquid phase diagram and on the value of the Minimum Miscibility Temperature (MMT). As seen in our previous paper, the paraffinic, aromatic or naphthenic character of the fossil fraction, also considerably influences the value of the MMT. Calculations were performed with a water content varying between 1 and 10%. This study concludes that the MMT expressed in kelvins is generally multiplied by two when the water content rises from 1 to 10%.© 2011 ASME

Ethanol and Distillate Blends: A Thermodynamic Approach to Miscibility Issues

In the recent years, the quest for an ever wider cluster of sustainable primary energies has prompted an increasing number of attempts to combine the emission sobriety of bio fuels with the energy density advantage of fossil fuels. A number of compositions incorporating hydrocarbons, ethanol and in some cases limited amounts of water have been proposed, especially in the forms of micro emulsions, with a variable success. Indeed due to markedly different physical and chemical properties, ethanol and gasoil are able to blend and form homogeneous solutions only in limited proportion ranges. Indeed, such mixtures often give rise to liquid-liquid equilibrium. A key parameter is thus the Minimum Miscibility Temperature (MMT), i.e. the temperature above which ethanol and gasoil become completely miscible. In fact, commercial gasoils do not constitute a monolithic product but display in the contrary a large span of compositions that influence the stability of these blends. In this context, the LRGP laboratory (Laboratoire Reactions et Genie des Procedes) has undertaken an investigation program intended to understand the factors underlying the stability of ethanol/gasoil blends. The approach is based on the calculation of the liquid-liquid phase diagrams formed by anhydrous ethanol and a mixture of various hydrocarbons representative of the diesel oil pool using the group contribution concept. Indeed, for correlating thermodynamic properties, it is often convenient to regard a molecule as an aggregate of functional groups; as a result, some thermodynamic properties (heat of mixing, activity coefficients) can be calculated by summing group contributions. In this study, the universal quasichemical functional group activity coefficient (UNIFAC) method has been employed as it appears to be particularly useful for making reasonable estimates for the studied non ideal mixtures for which data are sparse or totally absent. In any group-contribution method, the basic idea is that whereas there are thousands of chemical compounds of interest in chemical technology, the number of functional groups that constitute these compounds is much smaller. Therefore, if we assume that a physical property of a fluid is the sum of contributions made by the molecule’s functional groups, we obtain a possible technique for correlating the properties of a very large number of fluids in terms of a much smaller number of parameters that characterize the contributions of individual groups. This paper shows the large influence exerted by the paraffinic, aromatic and naphthenic character of the gasoil but also the sulfur content of the fossil fraction on the shape of the liquid-liquid phase diagram and on the value of the minimum miscibility temperature.Copyright