Results Of Phase Equilibria Studies Research Articles

Standard state Gibbs energies of hydration of hydrocarbons at elevated temperatures as evaluated from experimental phase equilibria studies

Experimental results of phase equilibria studies at elevated temperatures for more than twenty hydrocarbon-water systems were uniformly correlated within the framework of the Peng-Robinson-Stryjek-Vera equation of state in combination with simple mixing rules. This treatment allows evaluation of the Gibbs energy of hydration for many alkanes, 1-alkenes, cycloalkanes (derivatives of cyclohexane) and alkylbenzenes up to 623 K at saturated water vapor pressure and up to 573 K at 50 MPa. Results for homologous series show regular changes with increasing carbon number, and confirm the applicability of the group contribution approach to the Gibbs energy of hydration of hydrocarbons at elevated temperatures. The temperature dependence of group contributions to the Gibbs energy of hydration were determined for CH 3, CH 2, and CH in aliphatic hydrocarbons; C=C and H for alkenes; c-CH 2 and c-CH in cycloalkanes; and CH ar and C ar in alkylbenzenes (or aromatic hydrocarbons). Close agreement between calculated and experimental results suggests that this approach provides reasonable estimates of Gibbs energy of hydration for many alkanes, 1-alkenes, alkyl cyclohexanes and alkylbenzenes at temperatures up to 623 K and pressures up to 50 MPa.

Primitive basalts and andesites from the Mt. Shasta region, N. California: products of varying melt fraction and water content

Quaternary volcanism in the Mt. Shasta region has produced primitive magmas [Mg/(Mg+Fe*)>0.7, MgO>8 wt% and Ni>150 ppm] ranging in composition from high-alumina basalt to andesite and these record variable extents ofmelting in their mantle source. Trace and major element chemical variations, petrologic evidence and the results of phase equilibrium studies are consistent with variations in H2O content in the mantle source as the primary control on the differences in extent of melting. High-SiO2, high-MgO (SiO2=52% and MgO=11 wt%) basaltic andesites resemble hydrous melts (H2O=3 to 5 wt%) in equilibrium with a depleted harzburgite residue. These magmas represent depletion of the mantle source by 20 to 30 wt% melting. High-SiO2, high-MgO (SiO2=58% and MgO=9 wt%) andesites are produced by higher degrees of melting and contain evidence for higher H2O contents (H2O=6 wt%). High-alumina basalts (SiO2=48.5% and Al2O3=17 wt%) represent nearly anhydrous low degree partial melts (from 6 to 10% depletion) of a mantle source that has been only slightly enriched by a fluid component derived from the subducted slab. The temperatures and pressures of last equilibration with upper mantle are 1200°C and 1300°C for the basaltic andesite and basaltic magmas, respectively. A model is developed that satisfies the petrologic temperature constraints and involves magma generation whereby a heterogeneous distribution of H2O in the mantle results in the production of a spectrum of mantle melts ranging from wet (calc-alkaline) to dry (tholeiitic).

ChemInform Abstract: Ternary Pnictides MNi2‐xPn2 (M: Sr and Rare Earth Metals, Pn: Sb, Bi) with Defect CaBe2Ge2 and Defect ThCr2Si2 Structures

Abstractare prepared by annealing mixtures of the elements at 750‐800 °C for about one week.

Ternary pnictides MNi 2− xPn 2 (M ≡ Sr and rare earth metals, Pn ≡ Sb, Bi) with defect CaBe 2Ge 2 and defect ThCr 2Si 2 structures

The compounds MNi 2− x Sb 2 (M ≡ La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) and MNi 2− x Bi 2 (M ≡ La, Ce, Pr, Nd, Sm, Gd, Tb, Dy) crystallize with a defect CaBe 2Ge 2 structure, which was refined from single-crystal X-ray data for LaNi 1.51Sb 2 ( R = 0.014 for 17 variable parameters and 328 structure factors). SrNi 2− x Sb 2 and EuNi 2− x Sb 2 have a defect ThCr 2Si 2 structure, which was refined for EuNi 1.53Sb 2 to a residual of R = 0.030 (10 variables, 189 structure factors). The compounds have relatively large homogeneity ranges with differences in the cell volumes of up to 3%. The temperature dependence of the electrical conductivity of LaNi 2− x Sb 2 indicates metallic behaviour. Some results of phase equilibria studies of the corresponding ternary systems are reported. The defect formation for nickel sites is qualitatively rationalized from bonding considerations.

The Effect of Phase Equilibria on the CO2 Displacement Mechanism

Abstract Carbon dioxide flooding under miscible conditions is being developed as a major process for enhanced oil recovery. This paper presents results of research studies to increase our understanding of the multiple-contact miscible displacement mechanism for CO2 flooding. Carbon dioxide displacements of three synthetic oils of increasing complexity (increasing number of hydrocarbon components) are described. The paper concentrates on results of laboratory flow studies, but uses results of phase-equilibria and numerical studies to support the conclusions.Results from studies with synthetic oils show that at least two multiple-contact miscible mechanisms, vaporization and condensation, can be identified and that the phase-equilibria data can be used as a basis for describing the mechanism. The phase-equilibria change with varying reservoir conditions, and the flow studies show that the miscible mechanism depends on the phase-equilibria behavior. Qualitative predictions with mathematical models support our conclusions.Phase-equilibria data with naturally occurring oils suggest the two mechanisms (vaporization and condensation) are relevant to CO2 displacements at reservoir conditions and are a basis for specifying the controlling mechanisms. Introduction Miscible-displacement processes, which rely on multiple contacts of injected gas and reservoir oil to develop an in-situ solvent, generally have been recognized by the petroleum industry as an important enhanced oil-recovery method. More recently, CO2 flooding has advanced to the position (in the U.S.) of being the most economically attractive of the multiple-contact miscibility (MCM) processes. Several projects have been or are currently being conducted either to study or use CO2 as an enhanced oil-recovery method. It has been demonstrated convincingly by Holm and others that CO2 can recover oil from laboratory systems and therefore from the swept zone of petroleum reservoirs using miscible displacement. However, several contradictions seem to exist in published results.. These authors attempt to establish the mechanism(s) through which CO2 and oil form a miscible solvent in situ. (The solvent thus produced is capable of performing as though the two fluids were miscible when performing as though the two fluids were miscible when injected.) In addition, little experimental work has been published to provide support for the mechanisms of multiple-contact miscibility, as originally discussed by Hutchinson and Braun.One can reasonably assume that the miscible CO2 process will be related directly to phase equilibria process will be related directly to phase equilibria because it involves intimate contact of gases and liquids. However, no data have been published to indicate that the mechanism for miscibility development may differ for varying phase-equilibria conditions.This paper presents the results of both flow and phase-equilibria studies performed to determine the phase-equilibria studies performed to determine the mechanism(s) of CO2 multiple-contact miscibility. These flow studies used CO2 to displace three multicomponent hydrocarbon mixtures under first-contact miscible, multiple-contact miscible, and immiscible conditions. Results are presented to support the vaporization mechanism as described by Hutchinson and Braun, and also to show that more than one mechanism is possible with CO2 displacements. The reason for the latter is found in the results of phase-equilibria studies. SPEJ P. 242

Phase Equilibria in Fluid Mixtures at High Pressures: The Neon–Argon System

Results of phase equilibria studies are reported for the neon–argon system at temperatures from 87.34 to 123.83°K and pressures to 3880 atm. These results, combined with those of earlier studies, provide a complete description, partly quantitative and partly qualitative, of the lines and surfaces comprising an important segment of the three-dimensional, pressure–temperature–composition, phase diagram for neon–argon. A three-dimensional sketch of the diagram is used to show the important phase boundary lines and the qualitative features in the region of transition from fluid to solid at high pressures. The relevance of these studies to problems of deep atmosphere structures in the outer planets is briefly discussed.