Experimental and Modeling Study of the Phase Behavior of (Heptane + Carbon Dioxide + Water) Mixtures

A method has been developed for predicting the critical temperatures and critical pressures of binary mixtures of carbon dioxide, hydrogen sulfide, nitrogen, hydrogen, carbon monoxide and oxygen with the normal paraffin hydrocarbons. For carbon-dioxide and hydrogen-sulfide systems, relations are presented that take into account the peculiar behavior of mixtures with closely boiling components, such as carbon dioxide-ethane and hydrogen sulfide-propane mixtures which exhibit minimum critical temperature points. For hydrogen, nitrogen and carbon-monoxide systems, the extreme critical behavior caused by wide differences in pure component properties is established. In addition, those fixed gas-paraffin systems which resemble paraffin-paraffin systems are also accounted for. For a mixture of known composition, the pure component critical temperatures, critical pressures and normal boiling points are all that are required to determine its critical point. Graphical relations are presented relating Tc and Pc of the mixture to the pure component properties. From the treatment of 12 carbon-dioxide and hydrogen-sulfide systems reported in the literature (74 mixtures), the expected error for the critical temperature is approximately 1.5 per cent, and for the critical pressure, approximately 2 per cent. From the treatment of six hydrogen, nitrogen and carbon-monoxide systems reported in the literature (30 mixtures), the expected error for both the critical temperature and critical pressure is approximately 2.5 per cent. The relationships, which have been developed with only normal paraffins as the hydrocarbon components, may be extended to those isoparaffins and olefins which fall within the allowable volatility ranges. Introduction Many of the fixed gases - carbon dioxide, hydrogen sulfide, nitrogen, hydrogen, carbon monoxide and oxygen - occur in natural mixtures with hydrocarbons. Carbon dioxide and hydrogen sulfide are frequent components of the fluids produced from underground petroleum reservoirs. Nitrogen, carbon dioxide and hydrogen sulfide are present in varying quantities in most natural gases and gas-condensate well effluents. Hydrogen mixtures are of considerable interest in many phases of refining processes of petroleum. The determination of the critical temperatures and critical pressures of such mixtures is of value in vapor-liquid equilibrium studies, for the prediction of the characteristics of underground reservoirs, and for reduced-state correlations of PVT, transport and thermodynamic properties. The accurate estimation of the critical point for binary mixtures is an important initial step toward a complete analysis for the establishment of the critical temperatures and pressures of multicomponent mixtures. Methods for predicting the critical temperatures and critical pressures of binary hydrocarbon systems have already been presented in the literature. It is possible to apply these existing methods to fixed gas-paraffin mixtures but due to their unusual critical behavior, values calculated deviate considerably from experimental values. For systems containing trace quantities of the fixed gases, these methods are acceptable; however, for systems containing more than 5 mol per cent of the fixed gases, these utterly fail to produce reasonable critical values. Consequently, in this study a method has been developed for handling such binary mixtures over the entire composition range. CARBON-DIOXIDE AND HYDROGEN-SULFIDE SYSTEMS The critical behavior and the vapor pressure behavior of mixtures of carbon dioxide and hydrogen sulfide with paraffinic hydrocarbons may be quite similar or quite dissimilar to that of paraffin-paraffin mixtures, depending on the volatilities of the components involved. The critical temperature and normal boiling point of carbon dioxide are very close to the corresponding values for ethane, while its critical pressure is considerably higher than that of ethane. SPEJ P. 197^

Experimental and molecular modelling study of the three-phase behaviour of (propane + carbon dioxide + water) at reservoir conditions

Phase behavior of carbon dioxide mixtures with n-alkanes and n-perfluoroalkanes

Phase behavior of carbon dioxide—low-molecular weight triglycerides binary systems: measurements and thermodynamic modeling

Modeling phase behavior of multicomponent mixtures of wood preservatives in supercritical carbon dioxide with cosolvents

In this work we report phase equilibrium measurements on the system (methane + carbon dioxide + water) carried out with a high-pressure quasi-static-analytical apparatus. The measurements have been made under conditions of two-phase vapor-liquid equilibrium, three-phase vapor-liquid-liquid equilibrium (VLLE), and four-phase vapor-liquid-liquid-hydrate equilibrium. The compositions of three coexisting fluid phases have been obtained along eight isotherms at temperatures from (285.15 to 303.5) K and at pressures up to either the upper critical end point (UCEP) or up to the hydrate formation locus. Compositions of coexisting vapor and liquid phases have been obtained along three isotherms at temperatures from (323.15 to 423.15) K and pressures up to 20 MPa. The quadruple curve, along which hydrates coexist with the three fluid phases, was also measured along its entire length. The VLLE data obtained for this mixture have been compared with the predictions of the statistical associating fluid theory for potentials of variable range (SAFT-VR), implemented with the square-well potential and using parameters fitted to pure-component and binary-mixture data. Specifically, we used the SAFT-VR parameters reported by Mı́guez and co-workers [Mı́guez, J. M.; dos Ramos, M. C.; Piñeiro, M. M.; Blas, F. J. J. Phys. Chem. B 2011, 115, 9604]. The pressure along the quadruple curve was compared with the predictions of two different thermodynamic models. Furthermore, a detailed study of the ternary mixtures was carried out based on comparison with available ternary data of the type (CO2 + n-alkane + water) and available data for the constituent binary subsystems. In this way, we analyzed the observed effects on the solubility when the n-alkane component was changed or a third component was added.

High-pressure phase equilibria for the carbon dioxide–2-methyl-1-butanol, carbon dioxide–2-methyl-2-butanol, carbon dioxide–2-methyl-1-butanol–water, and carbon dioxide–2-methyl-2-butanol–water systems

The phase behavior of petroleum fluids under reservoir conditions provides fundamental information for an adequate crude oil production scheme. Recently, complex phase transitions have been studied for presalt crude oils, involving atypical liquid–liquid–vapor and liquid–liquid–asphalt phase transitions. In this paper, the phase behavior of synthetic mixtures containing carbon dioxide, methane, and a Brazilian presalt crude oil was investigated using PVT, coupled with near-infrared (NIR) transmittance and high-pressure microscopy (HPM) measurements. Crude oil (API 28.0, 0.68 wt % of asphaltenes) was mixed with 25.0 wt % gas (for a CH4/CO2 ratio from 0 to 62.5 wt %), and the phase behavior of the mixture was evaluated at a reservoir temperature of 343.15 K and pressures up to 100 MPa. Black oil phase behavior was detected for systems with a lower CH4/CO2 ratio and lower gas volume fraction, with no asphaltenes precipitation observed. As the CH4/CO2 ratio increased, pressure–volume curves showed a slight phase transition, with a not evident sharp break in the slope because of the minor difference of fluid compressibility. Moreover, a phase insolubility was confirmed by NIR and HPM tests for a high CH4/CO2 ratio that can be associated with the formation of an asphaltic phase. When total molar gas content increases by increasing the CH4/CO2 ratio, the asphaltic phase is formed at higher pressures. However, asphaltenes were detected as an uncommon fine dispersion with no larger fractal aggregates formation, even at pressures far below the asphaltenes onset pressure (AOP). Additionally, a nontypical behavior was observed in HPM tests with a total asphaltene dissolution when pressure reached the bubble pressure point. This atypical redissolution is in accordance with an instantaneous phase dissolving at pressures higher than the AOP, observed for the same oil at high methane ratios.

Vapor–liquid equilibria and critical points for the carbon dioxide +1-pentanol and carbon dioxide +2-pentanol systems at temperatures from 332 to 432 K

In carrying out the investigations which I commenced some years since upon the phenomena presented by the flow of different liquids through capillary tubes, the question as to what constitutes a liquid— that is in what way it differs from a gas, and how the great variance of the microrheometrical laws for the two fluids can be explained—again and again presented itself to me. Seeing that solids are soluble in gases as well as in liquids, one of the chief differences supposed to exist between the two states has disappeared ; and I have been compelled to adopt as the only definition of a liquid, that it is a fluid which has cohesion. Professor James Thomson, F. R. S., has suggested to me the use of the term contractility, instead of cohesion, and this term admirably defines the liquid state, but as it suggests (in a distant way perhaps) a voluntary power, and is used in connexion with organised structures, I shall retain the term cohesion at present. We have then the two states of fluids, first, the gaseous, in which the vis viva or heat energy of the molecules has entirely overcome cohesion, or their mutual attraction, and they are prevented from grouping ; and second, the liquid where the attractive power is greater than the vis viva, and the molecules are enabled to group themselves, but still are in sufficient motion to prevent the grouping from being permanent, hence we have cohesion, but no rigidity. We do not yet know that all solids are not also fluids, as many of them are known to flow, but this may be from other causes, but we know that the solid state is characterised by so much cohesion as to produce more or less rigidity. The most interesting point in the consideration of a liquid is that at which it approaches to the gaseous state, where its cohesion disappears, and we have what Dr. Andrews has termed the critical point, which is the termination of that property which distinguishes a liquid fluid from a gaseous fluid, or in other words the liquid becomes a gas. But a question arises. To observe this disappearance of the cohesion of a liquid, it is requisite that it should have a free surface, and this free surface has till now only been obtained by arranging the pressure that a portion of the fluid is in the gaseous state, and this only occurs at one pressure. Now, when the temperature of a liquid is raised while it is retained under very great pressure, so that it never has a free surface, but is always retained filling the vessel, does the liquid still lose its cohesion, and become a gas at the same temperature ; or, as the pressure is increased, does the temperature at which the cohesion of the liquid is overcome, also rise In the former case, the limit of the liquid state would be an isotherm, in the latter, a continuation of the boiling line. To determine which is the object of the work here described. With proper precautions, the loss of cohesion or capillarity can be noticed very accurately, and the level of the liquid in a fine capillary tube, seen to coincide with the plane surface of the liquid just before the final disappearance of the line of demarcation. One of the precautions to be taken is to obtain equable temperature, and while in my earlier experiments, X used a double air-bath, and considered this sufficient to obtain good results, I subsequently found that by the use of a triple bath of copper, every trace of irregularity of temperature disappeared, and I obtained results in which the line of division was admirably clear and sharp, and never became broad and hazy as in ordinary experiments. Another precaution to be taken is to have pure liquids, and this at first sight might appear to be an easy matter, but I find that in transferring a portion of a pure liquid to a tube, the momentary exposure to air, especially in the vicinity of the hands, hydrates the liquid sufficiently to render the line of demarcation rounded, and show a slightly greater refractive power in the lower part of the tube after the critical point has been passed. In the case of liquefied gases, such as carbon dioxide, ammonia, sulphur dioxide, and nitrous oxide, which are easily dried, the line is beautifully sharp, and the disappearing point easily noted. Alcohol cohobated over caustic lime for a week and transferred to a tube without contact with air, shows the disappearance of the line with great sharpness, and immediately after no difference in refractive power can be detected between the upper and lower portions. The least trace of moisture is sufficient to show such a difference. Whenever I notice any difference between the upper and lower portions after passing the critical point, I attribute it to moisture or other impurity, as careful treatment always removes the difference in density. In many organic liquids there is always a difference at the critical point, and sometimes before reaching this temperature, they form several layers, each having a different critical point as they seem to give rise on heating to new compounds, or form polymeric compounds having different critical points. Besides many organic compounds cannot be entirely freed from impurity they retain it even on repeated distillation. In the following experiments, therefore, such organic compounds were never used, and only perfectly anhydrous alcohol, or carbon disulphide,* or gases which can be obtained anhydrous, CO 2 , SO 2 , and NH 3 , being chosen. The apparatus used for obtaining pressure was that described in a former paper (“ Proc. Roy. Soc.,” No. 201, 1880, “ On the Solubility of Solids m Gases”). In order to determine, then, whether increased pressure applied above the critical point, would have the effect of reducing the gas to a liquid, as might easily be supposed, since the rates of expansion of gas and liquid become alike at the critical point, a new form of experiment was resorted to. It had been noticed that it was easy to determine whether the tube were filled with liquid or gas, by simply reducing the pressure somewhat quickly, when, if there were liquid present, it boiled, while if the contents were entirely gaseous, simple expansion was the result. The .boiling only takes place when the pressure is reduced so far as to be a little under the vapour pressure at that temperature, in other words, boiling cannot be observed, unless there exists a free surface, and this free surface cannot be obtained with the liquid alone above the “ critical pressure.” By the introduction of a quantity of hydrogen gas over the liquid, a free surface is obtained at any pressure, and the mixture of hydrogen and alcohol vapour being of so much less density than the alcohol, it remains divided from it by a line of demarcation for some time after the latter is undoubtedly gaseous. Now, let us see what takes place on lowering the pressure. When the temperature is even only 1°C. below the critical point, when the pressure is sufficiently reduced, the alcohol boils, showing that it still has cohesion, but if the temperature be 1° above the critical point, the fluid only expands, and no boiling is seen at any pressure, from 50 up to 200 atmospheres. Here the fluid above the critical point has just as free a surface as below it, and we see that the last trace of the liquid condition has disappeared. The line dividing the mixture of hydrogen and alcohol vapour from the pure alcohol is quite sharp, for a short time, and on altering the pressure, it moves up and down quite freely, and possesses exactly the same appearance and properties as hydrogen over carbon dioxide in a bell-jar.

Crossover Leung–Griffiths model and the phase behavior of binary mixtures with and without chemical reaction

Knowledge of the phase behavior of mixtures of oil with carbon dioxide and water is essential for reservoir engineering, especially in the processes of enhanced oil recovery and geological storage of carbon dioxide. However, for a comprehensive understanding, the study of simpler systems needs to be completed. In this work the system (n-decane + carbon dioxide + water) was studied as a model (oil + carbon dioxide + water) mixture. To accomplish our aim, a new analytical apparatus to measure phase equilibria at high pressure was designed with maximum operating temperature and pressure of 423 K and 45 MPa, respectively. The equipment relies on recirculation of two coexisting phases using a two-channel magnetically operated micropump designed during this work, with sampling and online compositional analysis by gas chromatography. The apparatus has been validated by comparison with published isothermal vapor-liquid equilibrium data for the binary system (n-decane + carbon dioxide). New experimental data have been measured for the system (n-decane + carbon dioxide + water) under conditions of three-phase equilibria. Data for the three coexisting phases have been obtained on five isotherms at temperatures from 323 to 413 K and at pressures up to the point at which two of the phases become critical. The experimental work is complemented here with a theoretical effort in which we developed models for these molecules within the framework of the statistical associating fluid theory for potentials of variable range (SAFT-VR). The phase behavior of the three binary subsystems was calculated using this theory, and where applicable, a modification of the Hudson and McCoubrey combining rules was used to treat the systems predictively. The experimental data obtained for the ternary mixture are compared to the predictions of the theory. Furthermore, a detailed analysis of the ternary mixture is carried out based on comparison with available data for the constituent binary subsystems. In this way, we analyzed the observed effects on the solubility when the third component was added.

Pressure–composition isotherms are obtained for the carbon dioxide + 2,2,3,3,4,4,5,5-octafluoropentyl acrylate (OFPA) and carbon dioxide + 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate (OFPMA) systems using a static apparatus at a temperature range from (313.2 to 393.2) K and pressures up to 17.86 MPa. The solubility of OFPA and OFPMA for the (carbon dioxide + OFPA) and (carbon dioxide + OFPMA) systems increases as the temperature increases at constant pressure. Liquid–liquid–vapor equilibria for the (carbon dioxide + OFPA) and (carbon dioxide + OFPMA) systems were not observed at these conditions. We determined new parameters for the critical constants by using the Joback, modified Joback, and Constantinou–Gani group contribution methods. The acentric factor was determined by using Ambrose and Walton's method. Using these parameters, the experimental results for (carbon dioxide + OFPA) and (carbon dioxide + OFPMA) systems are correlated with the Peng–Robinson equation of state (EOS) using a van der Waals...

High-pressure phase behavior of binary and ternary mixtures containing ionic liquid [C 6-mim][Tf 2N], dimethyl carbonate and carbon dioxide

The major gaseous impurities in the subquality natural gas sources are acidic components, such as hydrogen sulfide and carbon dioxide. Considering that H2S easily dissociates into hydrogen and elemental sulfur, thermodynamic properties and specially phase equilibria of liquid and gaseous systems containing hydrogen, hydrogen sulfide, carbon dioxide, other acidic components, and light hydrocarbons are of much interest to the natural gas and gas condensate production industries. In this paper we report the development of a simple and accurate cubic equation of state for prediction of thermodynamic properties and phase behavior of sour natural gas and liquid mixtures. This cubic equation of state, which is based on statistical mechanical theoretical grounds, is applied to pure fluids as well as mixtures with quite accurate results. All the thermodynamic property relations of sour gaseous and liquid mixtures are derived and reported in this report. Parameters of this equation of state are derived for different components of sour natural gas systems. The resulting equation of state is tested for phase behavior and other thermodynamic properties of simulated and natural sour gas mixtures. It is shown that the present equation of state, even though it is simple, predicts the properties of interest with ease and accuracy.