High-pressure Flow Calorimeter Research Articles

Heat capacities of different amine aqueous solutions at pressures up to 25 MPa for CO2 capture

A high-pressure flow calorimeter is used to determine isobaric heat capacities for aqueous solutions of some amines such as MEA, DEA TEA, DMAE, MDEA, PZ from T = (293.15 to 353.15) K and up to 25 MPa. The experimental device can measure heat capacities with an estimated total uncertainty better than 1% for a coverage factor k = 2. The isobaric heat capacity values are analysed in conjunction with their temperature and pressure dependencies. Furthermore, empirical equations are proposed to fit isobaric heat capacities as functions of temperature and pressure for given conditions, for this kind of mixtures, obtaining standard deviations within the uncertainty of the measurements. Finally, DMAE shows the highest value of heat capacity and TEA the lowest value, when they are compared at the same conditions of temperature, pressure and composition.

Isobaric heat capacity at high pressure, density, and viscosity of (diphenyl ether + biphenyl) mixtures

In order to choose an adequate heat transfer fluid (HTF) for particular applications, it is necessary to know accurately the thermophysical properties, such as isobaric heat capacity, density, or viscosity. In this work, we have performed density and dynamic viscosity measurements of pure diphenyl ether and three different binary mixtures of diphenyl ether and biphenyl, including the eutectic composition, over a broad temperature range, i.e., from (288.15 to 373.15)K. A rotational Anton Paar Stabinger SVM 3000 device was used to obtain these experimental values. Moreover, isobaric heat capacities have been measured for these samples in the liquid phase at temperatures from (293.15 to 353.15)K and pressures up to 25MPa using a high-pressure flow calorimeter. From these measurements we have analysed how they depend on temperature and/or pressure. We have also determined the Prandtl, reference Grashof, and reference Rayleigh numbers. In addition, several equations were used to describe the temperature behaviour of viscosity and density, as well as the temperature and pressure dependences of the experimental isobaric heat capacities.

Excess molar enthalpies for mixtures of supercritical CO2 and ethyl acetate and their role in supercritical fluid applications

Mixtures of supercritical CO2 and ethyl acetate (EA) are very often involved in supercritical fluid applications and their thermodynamic properties are required to understand and design these processes. Excess molar enthalpies (HmE) for (CO2+EA) mixtures were measured using an isothermal high-pressure flow calorimeter under conditions of temperature and pressure typically used in supercritical processes: pressures from (9.00 to 18.00)MPa and temperatures from (313.15 to 333.15)K. Mixtures showed exothermic mixing; excess molar enthalpies exhibited a minimum in the CO2-rich region. The effects of pressure and temperature on the excess molar enthalpy of (CO2+EA) are large. The most exothermic HmE values were observed for a coincident CO2 mole fraction value of 0.737 at T/K=(323.15 and 333.15) and P/MPa=9.00: (−4489 and −4407)J·mol−1, respectively. Two-phase splitting was observed in the CO2-rich region at T/K=333.15 and P/MPa=9.00; in this region HmE varies linearly with CO2 mole fraction. For a given mole fraction and temperature, mixtures become more exothermic as pressure decreases. These trends were analyzed in terms of molecular interactions, phase equilibria, density and critical parameters previously reported for (CO2+EA). Excess molar enthalpies here reported were correlated using the Soave–Redlich–Kwong and Peng–Robinson equations of state, and the classical mixing rule with two binary interaction parameters. The influence of the thermal effects on the phase behavior of (CO2+EA) mixtures formed in supercritical antisolvent precipitation experiments was discussed.

An experimental setup for isobaric heat capacities for viscous fluids at high pressure: Squalane, bis(2-ethylhexyl) sebacate and bis(2-ethylhexyl) phthalate

A high-pressure flow calorimeter has been used to determine highly accurate isobaric heat capacities for different viscous fluids, squalane (SQN), bis(2-ethylhexyl) sebacate (DEHS) and bis(2-ethylhexyl) phthalate (DEHP) from T=(293.15 to 353.15)K and up to 30MPa. The experimental device was adapted for viscous liquids at high pressure and it can measure heat capacities with an estimated total uncertainty better than 1%. The isobaric heat capacity values were analysed together with their temperature and pressure dependences. In addition, a fitting equation of the experimental molar isobaric heat capacity for these viscous fluids as a function of temperature and pressure was proposed.

Role of excess molar enthalpies in supercritical antisolvent micronizations using dimethylsulfoxide as the polar solvent

The role of excess molar enthalpies ( H m E ) in the supercritical antisolvent (SAS) micronizations using dimethylsulfoxide (DMSO) as the polar solvent was investigated. Excess molar enthalpies for CO 2 + DMSO mixtures were measured using an isothermal high-pressure flow calorimeter under conditions of temperature and pressure typically used in SAS micronizations. In most cases, mixtures showed very exothermic mixing. A local temperature increase can be expected in the precipitation chamber as a consequence of the heat evolved when CO 2 dissolves in DMSO. Based on the H m E measurements, local temperature increases were calculated and shown to explain immiscibility of CO 2 and DMSO and agglomerated or irregular particles for average temperature and pressure conditions where complete miscibility and uniform particles could have been expected. H m E data were also discussed in terms of molecular interactions, phase equilibria, density and critical parameters previously reported for CO 2 + DMSO.

Measurements and modeling of high-pressure excess molar enthalpies and isothermal vapor–liquid equilibria of the carbon dioxide + N, N-dimethylformamide system

Mixtures of supercritical CO 2 and N, N-dimethylformamide (DMF) are very often involved in supercritical fluid applications and their thermodynamic properties are required to understand and design these processes. Excess molar enthalpies ( H m E ) for CO 2 + DMF mixtures were measured using an isothermal high-pressure flow calorimeter under conditions of temperature and pressure typically used in supercritical processes: 313.15 and 323.15 K at 9.00, 12.00, 15.00 and 18.00 MPa and 333.15 K at 9.00 and 15.00 MPa. The Peng–Robinson and the Soave–Redlich–Kwong equations of state were used in conjunction with the classical mixing rules to model the literature vapor–liquid equilibrium and critical data and the excess enthalpy data. In most cases, CO 2 + DMF mixtures showed very exothermic mixing and excess molar enthalpies exhibited a minimum in the CO 2-rich region. The lowest H m E value (−4526 J mol −1) was observed for a CO 2 mole fraction value of 0.713 at 9.00 MPa and 333.15 K. On the other hand, H m E at 9.00 MPa and 323.15 and 333.15 K varies linearly with CO 2 mole fraction in the two-phase region where a gaseous and a liquid mixture of fixed composition are in equilibrium. The effects of pressure and temperature on the excess molar enthalpy are large. For a given mole fraction, mixtures become less exothermic as pressure increases or temperature decreases. These excess enthalpy data were analyzed in terms of molecular interactions, phase equilibria, density and critical parameters previously reported for CO 2 + DMF. All throughout this paper, the key concepts and modeling tools originate from the work of van der Waals: the paper is intended as a small piece of recognition of van der Waals overwhelming contributions to thermodynamics.

Enthalpies of Absorption of Carbon Dioxide in Aqueous Sodium Glycinate Solutions at Temperatures of (313.15 and 323.15) K

The enthalpies of absorption (ΔrH) of carbon dioxide in aqueous sodium glycinate (SG) solutions of 0.10 in mass fraction were determined at temperatures of (313.15 and 323.15) K and a pressure of 12.00 MPa using an isothermal high-pressure flow calorimeter. Very exothermic absorption enthalpies are obtained at the two temperatures studied. ΔrH values expressed in kJ·mol−1 of SG decrease very quickly as CO2 loading increases until saturation is reached; from this point, a slowly decreasing value is obtained for the absorption enthalpy. CO2 loading is expressed as mol CO2/mol amine (α). The calorimetric data provide a means to determine the saturated loading point of CO2 in the solution; values of (0.90 and 0.86) mol CO2/mol SG were estimated for this magnitude at temperatures of (313.15 and 323.15) K, respectively. Enthalpies of solution of CO2 were also calculated. These enthalpies become more exothermic as α decreases until a limit value characteristic of each amine is observed for low CO2 loading. This ...

Excess molar enthalpies for mixtures of supercritical CO 2 and linalool

Excess molar enthalpies ( H m E ) for mixtures of supercritical CO 2 and linalool were measured at conditions of temperature and pressure typical of supercritical extraction processes: 313.15 and 323.15 K and 7.64, 10.00 and 12.00 MPa. The measurements were carried out using an isothermal high-pressure flow calorimeter. The effects of pressure and temperature on the excess molar enthalpy are large. Mixtures formed by low-density carbon dioxide and linalool show very exothermic mixing and excess molar enthalpies exhibit a minimum in the CO 2-rich region. The lowest H m E values (≈−4000 J mol −1) are observed for mixtures at 313.15 K and 7.64 MPa. Mixtures formed by high-density carbon dioxide and linalool show considerably endothermic mixing (≈400–600 J mol −1) in the linalool-rich region and moderately exothermic mixing for the other compositions. On the other hand, H m E at 7.64 MPa and 313.15 and 323.15 K varies linearly with CO 2 mole fraction in the two-phase region where a gaseous mixture and a liquid mixture of fixed composition, for a given condition of temperature and pressure, are in equilibrium. Results are analyzed in terms of phase equilibria, pure carbon dioxide density and CO 2–terpene molecular interactions. Excess molar enthalpies are simultaneously correlated using the Soave–Redlich–Kwong and Peng–Robinson equations of state and the classical mixing rule. The significance of these large variations of H m E with temperature and pressure in the design of supercritical fluid deterpenation processes is discussed.

Excess molar enthalpies for binary mixtures related to supercritical antisolvent precipitation: Carbon dioxide + N-methyl-2-pyrrolidone

An isothermal high-pressure flow calorimeter has been used to measure excess molar enthalpies ( H m E ) for mixtures of supercritical CO 2 and N-methyl-2-pyrrolidone (NMP) under conditions of temperature and pressure typically used in supercritical CO 2 antisolvent precipitation (SAS): 313.15 and 338.15 K and 9.48, 15.00 and 20.00 MPa. Mixtures showed exothermic mixing; excess molar enthalpies exhibited a minimum in the CO 2-rich region. The effects of pressure and temperature on the excess molar enthalpy of CO 2 + NMP are large. The lowest H m E values (≈−4500 J mol −1) were observed for mixtures at 338.15 K and 9.48 MPa. On the other hand, H m E at this condition of temperature and pressure varies linearly with CO 2 mole fraction in the two-phase region where a gaseous and a liquid mixture of fixed composition are in equilibrium. These data were analyzed in terms of phase equilibria data and critical locus for CO 2 + NMP and the related SAS experiments. Very exothermic excess molar enthalpies were obtained for conditions of temperature and pressure with marked coalescence phenomena for micro and submicro particles of tetracycline, amoxicillin and ampicillin produced by SAS. Excess molar enthalpies here reported and those previously measured at 298.15 K and 7.50, 10.60 and 12.60 MPa were correlated using the Soave–Redlich–Kwong and Peng–Robinson equations of state and the classical mixing rule with two binary interaction parameters.

Excess molar enthalpies for mixtures of supercritical carbon dioxide and 1,8-cineole

Excess molar enthalpies ( H m E ) for mixtures of supercritical CO 2 and 1,8-cineole were measured at 308.15, 313.15 and 323.15 K and 7.64 MPa and at 308.15 and 323.15 K and 10.00 MPa using an isothermal high-pressure flow calorimeter. The effects of pressure and temperature on the excess molar enthalpy of [CO 2 ( x) + 1,8-cineole (1 − x)] are large. Mixtures at 308.15 K and 10.00 MPa show slightly endothermic mixing in the 1,8-cineole-rich region and moderately exothermic mixing for x > 0.2. Excess molar enthalpies become very exothermic at the other conditions of temperature and pressure studied. The lowest H m E values (≈−4900 J mol −1) are observed for CO 2-rich mixtures at 313.15 K and 7.64 MPa. These data are examined together with phase equilibria and critical parameters previously reported for [CO 2 + 1,8-cineole]. The large negative values of H m E are related to the carbon dioxide change of state from that of a low-density fluid to that of a liquid-mixture component in CO 2-rich mixtures.

Excess molar enthalpies for mixtures of supercritical carbon dioxide and limonene

Excess molar enthalpies (HmE) for mixtures of supercritical CO2 and limonene were measured at 308.15, 313.15 and 323.15K and 7.64 and 10.00MPa using an isothermal high-pressure flow calorimeter. The effects of pressure and temperature on the excess molar enthalpy of [CO2(x)+limonene(1−x)] are large. Mixtures at 308.15K and 10.00MPa show slightly endothermic mixing in the limonene-rich region and moderately exothermic mixing for x>0.5. Mixtures at the other conditions of temperature and pressure studied show exothermic mixing, excess molar enthalpies exhibit a minimum in the CO2-rich region. The lowest HmE values (≈−4500Jmol−1) are observed for mixtures at 313.15K and 7.64MPa. On the other hand, HmE at 7.64MPa and 308.15, 313.15 and 323.15K varies linearly with CO2 mole fraction in the two-phase region where a gaseous and a liquid mixture of fixed composition, for a given condition of temperature and pressure, are in equilibrium. These data are examined together with phase equilibria and critical parameters previously reported for CO2+limonene. Excess molar enthalpies are simultaneously correlated using the Peng–Robinson equation of state and the classical mixing rule with one binary interaction parameter.

Excess molar enthalpies for mixtures of carbon dioxide + a modifier (5 mol% methanol or 1-octanol) and hexane at 308.15 K and 12.40 MPa

The effect of adding a 5 mol% alcohol modifier to carbon dioxide being mixed with hexane at 308.15 K and 12.40 MPa is investigated using an isothermal high-pressure flow calorimeter. Excess molar enthalpies ( H m E ) are determined for the ternary mixtures [CO 2( x 1) + methanol( x 2) + hexane( x 3)] and [CO 2( x 1) + octanol( x 2) + hexane( x 3)] where x 1/ x 2 = 95/5 at 308.15 K and 12.40 MPa. The ternary excess enthalpy data are then compared to excess enthalpy data for CO 2 + hexane mixtures. Mixing becomes more endothermic for both alcohols; the H m E maximum value increases ca. 200 J mol −1. Excess enthalpy data for the methanol + hexane and octanol + hexane mixtures at 308.15 K and 12.40 MPa are also reported. For both alcohols, mixtures show endothermic mixing: H m E maximum values are ca. 500 J mol −1. H m E values are discussed in terms of the critical locus and phase equilibria of the systems involved. Binary excess enthalpy data for the five binary systems involved in this study were correlated using both a Padé function and the Peng–Robinson equation of state. These correlations are used to predict ternary data. Predictions obtained using the Peng–Robinson EOS in combination with the classical mixing rule are much more accurate than those obtained using the Padé function.

Excess molar enthalpies for mixtures of supercritical carbon dioxide and water + ethanol solutions

Excess molar enthalpies ( H m E ) for mixtures of supercritical CO 2 and ethanol aqueous solutions were measured at 323.15 K and 7.64 and 15.00 MPa using an isothermal high-pressure flow calorimeter. H m E values obtained at the lower pressure are very exothermic while those obtained at the higher pressure are moderately endothermic. H m E for CO 2 + H 2O mixtures at 308.15 K and 7.64 MPa and 323.15 K and 15.00 MPa were also measured. These data are examined together with H m E data previously reported for mixtures of supercritical CO 2 and ethanol aqueous solutions, vapor–liquid equilibrium data for the ternary system CO 2 + H 2O + ethanol and the excess enthalpy data for the three related binary systems. CO 2–ethanol interactions are shown to be the main contribution to excess enthalpies when supercritical CO 2 and ethanol aqueous solutions are mixed. Ternary excess enthalpies for CO 2 + H 2O + ethanol are also obtained. Kohler's method is used for estimating these ternary data from the excess enthalpy data of the three related binary systems.

Thermodynamics of liquid (nitrogen + ethane)

The equilibrium vapour pressure of liquid {xN2+ (1 − x)C2H6}(l) has been measured atT= 90.69 K. The excess molar Gibbs energiesGmE have been calculated as a function of composition from the vapour pressure data. For the equimolar mixture GmE(x= 0.5) = (985 ± 14)J · mol−1. Excess molar enthalpies HmEhave also been measured at T= (92.1 ± 0.1) K andp= (0.79 ± 0.12) MPa using a low-temperature computer-interfaced high-pressure flow calorimeter. For the equimolar mixtureHmE (x= 0.5) = 426.9 J · mol−1. The results show that the system is only partially miscible at both temperatures. The limits of (liquid + liquid) immiscibility have been determined as 0.123 ± 0.010 <x< 0.958 ± 0.004. The results have been interpreted using the Deiters equation of state.

Thermodynamic Study of the N2O + CO2 and N2O + CO2 + Cyclohexane Systems in the Near-Critical and Supercritical Regions

Carbon dioxide, CO2, and nitrous oxide, N2O, are fluids used in supercritical extraction. Mixtures of N2O and CO2 are excellent candidates to be used as supercritical fluids. In this work, excess enthalpies, , are reported for the N2O + CO2 and N2O + CO2 + cyclohexane systems at 308.15 K and 7.64 MPa. This temperature lies between the N2O and CO2 critical temperatures, and the pressure is higher than the N2O and CO2 critical pressures. Measurements have been carried out using an isothermal high-pressure flow calorimeter. Results for the N2O + CO2 system are analyzed simultaneously with excess enthalpy data and excess volume data, , taken from the literature, using different equations of state and mixing rules. The magnitude of the heat involved is large because of the proximity of experimental conditions to the mixture's critical locus. Experimental data for the ternary system are analyzed using different equations of state and mixing rules, and several empirical and semiempirical prediction methods are t...

Excess enthalpies and excess volumes for (ethane + propan-1-ol) at the temperatures (298.15, 323.15, and 348.15) K and at the pressures (5, 10, 12.5, and 15) MPa

Excess molar enthalpies H E mand excess molar volumes V E mhave been determined for { xC 2H 6+ (1 − x)CH 3(CH 2) 2OH} at T= (298.15, 323.15, and 348.15) K and p= (5, 10, 12.5, and 15) MPa. The H E ms were measured with a high-temperature high-pressure flow calorimeter. The V E ms were measured simultaneously with a vibrating-tube densitometer inserted in the flow line of the calorimeter past the mixing chamber. (Vapor + liquid) equilibrium is present at p= 5 MPa and T= (323.15 K and 348.15 K). The value of the pressure coefficient (∂ H E m/∂ p) T , which is large at all three temperatures, is calculated from V E mand (∂ V E m/∂ T) p . The results are in good agreement with the values obtained directly from the change in H E mwith pressure.

Bulk and surface properties of the highly non-ideal associated mixtures formed by methanol and propanal

Bulk (vapour–liquid equilibrium and excess enthalpy data) and surface (surface tension) properties of the highly non-ideal associated mixtures formed by methanol and propanal have been measured. The vapour–liquid equilibrium data have been obtained at 288.15, 298.15, 308.15 and 318.15 K using a Gibbs–Van Ness type apparatus. These mixtures show negative deviations from ideality, including a negative azeotrope in the methanol-rich region. The calculated values for the excess Gibbs energy are very large and negative, and their absolute value decreases sharply with increasing temperature. The calculated values for the concentration–concentration correlation function are lower than those corresponding to an ideal mixture and exhibit a minimum in the middle of the concentration range. The excess enthalpy data have been obtained at 4.00 MPa and 298.15 and 318.15 K by means of a high-pressure flow calorimeter. Values for the excess enthalpies are very exothermic and in agreement with those calculated from the excess Gibbs energies. The surface tension has been measured at 298.15 K. Values for the relative surface adsorption calculated from the surface tension and the chemical potentials indicate that the surface is significantly enriched in propanal for mixtures rich in methanol. A complex composition dependence of the concentration profiles can be inferred. The lattice-fluid and the lattice-fluid associated solution models have been used to describe the bulk properties of the methanol–propanal mixtures.

Excess enthalpies for (ethane + chloromethane) at the temperatures (298.15, 323.15, 348.15, and 363.15) K and pressures from 5 MPa to 16 MPa

Excess molar enthalpies HEm for (ethane + chloromethane) have been measured at the temperatures (298.15, 323.15, 348.15, and 363.15) K and pressures from (5 to 16) MPa with a high-temperature high-pressure flow calorimeter. At low pressures (vapor + liquid) equilibrium occurs, resulting in linear regions in the HEm (x) curves. (Vapor + liquid) equilibria at p = 5 MPa were determined from the calorimetric measurements, and enabled us to construct a (vapor + liquid) equilibrium isobar. A weak dependence of HEm on temperature and pressure was observed at the higher pressures, with HEm results similar to those reported earlier for (propane + chloromethane) and (butane + chloromethane) over a wider range of pressures and temperatures.

Excess volumes for (ethanol+water) at the temperatures (298.15 and 348.15) K and pressures (0.4, 5, and 15) MPa and at the temperature 323.15 K and pressures (5 and 15) MPa

An Anton-Paar vibrating-tube densitometer has been attached to the exit line of our high-temperature high-pressure isothermal flow calorimeter and used to measure the excess volume for (ethanol + water). Results are reported over the entire mole-fraction range at the temperatures (298.15 and 348.15) K and pressures (0.4, 5, and 15) MPa and at the temperature 323.15 K and pressures (5 and 15) MPa. The results at T = 198.15 K and p = 0.4 MPa are in good agreement with results reported in the literature for this mixture under ambient conditions.

Excess enthalpies of (ethanol+water) at 323.15, 333.15, 348.15, and 373.15 K and from 0.4 to 15 MPa

We report accurate measurements of H m E for (ethanol + water) at 323.15, 333.15, 348.15, and 373.15 K and from 0.4 to 15 MPa with our new high-temperature and high-pressure flow calorimeter. Results at 333.15 K and 0.4 MPa indicate that the mixture has an interesting double minimum with H m E changing sign twice. We recommend that (ethanol + water) be developed as a reference mixture for testing flow calorimeters at high temperatures and pressures.