Thermodynamic properties of a CO2 – rich mixture (CO2 + CH3OH) in conditions of interest for carbon dioxide capture and storage technology and other applications

https://doi.org/10.1016/j.jct.2016.03.026Get rights and content

Highlights

  • A thermodynamic study related to CCS technology and other applications is conducted for CO2 + (3%) CH3OH.

  • Accurate experimental values for the speed of sound and density are presented.

  • A calculation method for thermodynamic properties up to high pressures is applied.

  • The calculation method is adapted for the first time to compressed gases.

  • Both experimental and calculated values are compared with the PC-SAFT and GERG EoSs.

Abstract

Methanol can be an impurity in transported and stored anthropogenic CO2 in carbon dioxide capture and storage technology; likewise, methanol is one of the most useful CO2 modifiers for supercritical processes. Therefore reliable values of thermodynamic properties of CO2 – rich mixtures CO2 + CH3OH are needed. We measured the following properties of a (CO2 + CH3OH) mixture with xCO2=0.9700 in dense phase at six temperatures from 263.15 K to 313.15 K:

  • The speed of sound, c, up to 194.49 MPa, using a double-path pulse-echo method at 5 MHz, for which a repeatability study gave an overall standard uncertainty of c, u(c) = 5.9 × 10−4c.

  • The density, ρ, at pressures ⩽20.00 MPa using a vibrating-tube densimeter with a standard uncertainty, u(ρ) = 0.4 kg/m−3.

Combining our c and ρ experimental values and the isobaric specific heat capacity, cp, from the GERG equation of state (EoS), we calculated ρ, cp, the volume-dependent solubility parameter, δV, and the Joule–Thomson coefficient, μJT, at pressures ⩽195.0 MPa. We are the first to report the adaptation for compressed gases of a calculation method based on numerical integration previously used only for liquids. The experimental and calculated values were compared with those from the PC-SAFT and GERG EoSs, allowing us to validate both EoSs to represent the experimental properties of the system under most conditions studied and the calculation method up to 195.0 MPa.

Introduction

Carbon dioxide capture and storage (CCS) is considered one of the most important technologies to reduce the world’s emissions of greenhouse gases. In the International Energy Agency’s two-degree scenario (2DS), CCS is expected to help reduce global CO2 emissions by storing approximately 7 gigatons per year by 2050 [1]. This amount is much greater than that used for enhanced oil and gas recovery purposes (approximately 50 megatons per year in the USA [2]). To optimize the process efficiency, the CO2 will have to be transported from the capture plants to reservoirs predominantly in high-pressure pipelines [3].

CCS technology comprises three main steps: anthropogenic CO2 capture, transport and storage. The design of each step is influenced by the thermodynamic procedure used to model the fluid behaviour [3]. Whether using an existing procedure or developing a new one, experimental data on the physicochemical properties of CO2 mixtures with the impurities typically present in anthropogenic CO2 are needed in wider composition, temperature and pressure ranges than those associated with CCS technology [4]. However, the paucity of experimental values precludes the development of a reference model for this technology, especially an equation of state (EoS), which is one of the most critical future challenges [5].

To develop an EoS, the essential data are the volumetric properties (pressure–density–temperature, pρT) and the vapor-liquid equilibrium, VLE, although reliable values for the speed of sound, c, and the isobaric specific heat capacity, cp are necessary as well. Using acoustic results to formulate EoSs is particularly attractive given that the speed of sound can be measured with outstanding precision over wide temperature and pressure ranges. Furthermore, all the thermodynamic properties of a fluid can be obtained from speed of sound measurements by integrating the partial differential equations that relate c to other thermodynamic properties [6]. Currently, accurately measuring the speed of sound propagation in high-pressure fluids is one of the standard methods to precisely determine such fluids’ thermophysical properties [7].

In practice, reliable pρT values, among others, are necessary to evaluate parameters related to transport, injection and storage [8]. Moreover, the speed of sound enables detection of the pressure drop along the pipeline and leaks, monitoring of changes in composition and the performance of seismic studies [9], [10], [11].

To estimate the temperature variations at various stages of the process, precise data from additional thermodynamic properties such as cp and the Joule–Thomson coefficient, μJT, are required [9], [12]. The solubility parameter, δ, provides information about the interactions between the injected fluid and other substances present in the storage reservoir.

All these properties are affected to a great extent by the nature and quantity of the impurities present in the anthropogenic CO2, which, in turn, depend on the CO2 source and the capture and conditioning processes [5]. Although the main impurities are N2,H2,O2,Ar,SO2,NOx,CO and water [4], [13], methanol can be present in transported and injected anthropogenic CO2 because of its use as a hydrate inhibitor and as a residue from pipeline drying. Thus, quantification of the effect of this impurity on the thermodynamic properties that influence CCS processes is necessary.

Furthermore, supercritical CO2, ScCO2, is the most widely used supercritical solvent in a broad range of applications, and methanol is one of the most common modifiers added to enhance the solvating power of ScCO2 to target polar species [14]. The solvent strength of a supercritical fluid solvent is related to its density, and it may be quantitatively represented by the solubility parameter [15]. In addition, cp and μJT of the (CO2 + CH3OH) system acting as the mobile phase affect to resolution properties in supercritical fluid chromatography [16].

Density and VLE have been widely studied in the literature [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37] for the (CO2 + CH3OH) system, however we note that little information is available on its volumetric behaviour at T313K and at mole fractions of CO2, xCO2, greater than 0.75 [19], [20], [21], [32], [34]. Values of δ have been obtained at T313K [14], [38], [39], [40]; however, no numerical values for c, cp or μJT are available in the literature.

The aim of this work was to conduct an extensive thermodynamic study of a CO2 – rich mixture with CH3OHxCO2=0.9700 under T and p conditions compatible with CCS and other applications. We therefore:

  • (i)

    Adapted and used an experimental apparatus to measure accurately the speed of sound in mixtures containing sufficiently dense compressed gases. We also determined the uncertainty of the experimental speed of sound measurements for the (CO2 + CH3OH) system.

  • (ii)

    Experimentally measured the following properties for the (CO2 + CH3OH) mixture with xCO2=0.9700:

    • The speed of sound, pcT, between 263.16 K and 313.15 K and at pressures up to 194.49 MPa.

    • The density, pρT, from 263.15 K to 313.15 K and up to 20.00 MPa.

  • (iii)

    Adapted and validated a calculation method to obtain ρ and cp values and derived properties such as the volume-dependent solubility parameter, δV, and μJT for systems containing compressed gases at pressures up to 195.0 MPa. All properties were obtained for (CO2 + CH3OH) with xCO2=0.9700 within the working temperature range. Several authors [41], [42], [43], [44], [45] have used the same fundamental approach for liquid compounds; however, this work represents its first application to compressed gases.

  • (iv)

    Compared either the experimental results or the calculated values of the aforementioned thermodynamic properties with two different formulation EoS: PC-SAFT [46], [47] and GERG [48], [49].

In summary, in this article we implement an experimental setup to measure c in mixtures containing compressed gases. We present the experimental results for the speed of sound (at pressures up to 194.49 MPa), and density (up to 20.00 MPa) for the (CO2 + CH3OH) mixture xCO2=0.9700; together, these results allow us to evaluate the predictive power of the PC-SAFT and GERG EoSs for these properties. From our c values and both our ρ and the GERG EoS cp at a reference pressure, we calculate ρ, cp, δV, and μJT for pressures up to 195.0 MPa. This method of calculating thermodynamic properties up to high pressures, which is applied here to compressed gases for the first time, is validated by comparing the results with the values obtained from the PC-SAFT and GERG EoSs.

Section snippets

Chemicals

Methanol from Sigma–Aldrich (biotech. grade, mole fraction 0.9993) and carbon dioxide from Air Liquide (mole fraction >0.99998) were used without further purification. The details, including purities and sources of the materials used in this work are listed in Table 1.

Speed of sound data acquisition: experimental setup and procedure

To determine the speed of sound, we used a 5 MHz ultrasonic pulse device previously described for its application to pure fluids [50]. It was originally designed to work with liquids, and we demonstrated that it is also adequate

Calculation method of thermodynamic properties up to high pressures

Various methods have been proposed in the literature to obtain other thermodynamic properties from the speed of sound [51], thus exploiting the high precision of its experimental determination. These methods use experimental values of c obtained at high pressures and several temperatures and ρ and cp both at a reference pressure p and as a function of temperature. From these data, calculated values of ρ, the isobaric thermal expansivity, αp, the isothermal compressibility, κT, and cp are

Equations of state

In this work, we compared both our experimental values (c,ρ), and the calculated values explained previously (ρ,cp,δV,μJT) with data obtained from the PC-SAFT and the GERG EoS using VLXE [58] and REFPROP 9.0 [54] software, respectively.

Experimental results obtained using the newly implemented apparatus to measure the speed of sound in mixtures

The system (CO2 + CH3OH) was studied to develop the experimental procedure for mixtures containing sufficiently dense compressed gases and to determine the uncertainty of the speed of sound measurements in those gases. The chosen compositions were xCO2=(0.7534,0.8502,0.9250and0.9803) at nominal temperatures of 263.15 K, 298.15 K and 323.15 K and pressures from 6.00 MPa to 190.04 MPa. The pcT values used in this section are listed in Table S2.

The overall standard uncertainty of the experimental c

Discussion

The repeatability and overall standard uncertainty results obtained in this work, together with the agreement with the data from the literature, allow us to use our experimental c and ρ values to evaluate whether the PC-SAFT and GERG EoSs properly predict the studied thermodynamic behaviour for (CO2 + CH3OH). If the two EoSs are successful, we will use both to validate the method for calculating ρ,δv,cP and μJT up to 195.0 MPa.

Conclusions

An ultrasonic pulse apparatus and the experimental procedure were adapted to measure the speed of sound in mixtures containing compressed gases, and c was measured for four (CO2 + CH3OH) mixtures (xCO2=0.7534,0.8502,0.9250and0.9803) at nominal temperatures T=(263.15,298.15,and323.15)K and at pressures up to 190.04 MPa. The overall standard uncertainty of the experimental speed of sound was evaluated for the (CO2 + CH3OH) system, where the contributions of temperature, pressure, composition and

Acknowledgements

This research received funding from the Ministry of Economy and Competitiveness of Spain ENE2013-44336-R and from the Government of Aragon and the European Social Fund.

References (66)

  • Z. Huang et al.

    Sep. Purif. Technol.

    (2013)
  • F. Gritti et al.

    Effect of methanol concentration on the speed-resolution properties in adiabatic supercritical fluid chromatography

    J. Chromatogr. A

    (2013)
  • L. Gil et al.

    Experimental determination of the critical loci for {n-C6H14 or CO2 +alkan-1-ol} mixtures. Evaluation of their critical and subcritical behaviour using PC-SAFT EoS

    J. Supercrit. Fluids

    (2012)
  • E. Brunner et al.

    Fluid mixtures at high pressures IV. Isothermal phase equilibria in binary mixtures consisting of (methanol + hydrogen or nitrogen or methane or carbon monoxide or carbon dioxide)

    J. Chem. Thermodyn.

    (1987)
  • C.J. Chang et al.

    Densities and P-x-y diagrams for carbon dioxide dissolution in methanol, ethanol, and acetone mixtures

    Fluid Phase Equilib.

    (1997)
  • C.J. Chang et al.

    A new apparatus for the determination of P-x-y diagrams and Henry’s constants in high pressure alcohols with critical carbon dioxide

    J. Supercrit. Fluids

    (1998)
  • D.L. Goldfarb et al.

    Dielectric and volumetric properties of supercritical carbon dioxide (1) + methanol (2) mixtures at 323.15 K

    Fluid Phase Equilib.

    (1999)
  • R. Sih et al.

    Viscosity measurements on gas expanded liquid systems – methanol and carbon dioxide

    J. Supercrit. Fluids

    (2007)
  • M. Maiwald et al.

    On-line 1H NMR spectroscopic investigation of hydrogen bonding in supercritical and near critical CO2–methanol up to 35 and 403 K

    J. Supercrit. Fluids

    (2007)
  • M. Kariznovi et al.

    Experimental measurements and predictions of density, viscosity, and carbon dioxide solubility in methanol, ethanol, and 1-propanol

    J. Chem. Thermodyn.

    (2013)
  • A.H. Jalili et al.

    Measuring the solubility of CO2 and H2S in sulfolane and the density and viscosity of saturated liquid binary mixtures of (sulfolane + CO2) and (sulfolane + H2S)

    J. Chem. Thermodyn.

    (2015)
  • M.G. Sajilata et al.

    Development of efficient supercritical carbon dioxide extraction methodology for zeaxanthin from dried biomass of Paracoccus zeaxanthinifaciens

    Sep. Purif. Technol.

    (2010)
  • Z. Huang et al.

    Effect of the polar modifiers on supercritical extraction efficiency for template removal from hexagonal mesoporous silica materials: solubility parameter and polarity considerations

    Sep. Purif. Technol.

    (2013)
  • M.M. Piñeiro et al.

    High-pressure speed of sound measurements in methyl nonafluorobutyl ether and ethyl nonafluorobutyl ether

    Fluid Phase Equilib.

    (2004)
  • D. González-Salgado et al.

    Study of the volumetric properties of weakly associated alcohols by means of high-pressure speed of sound measurements

    J. Chem. Thermodyn.

    (2006)
  • M.J. Dávila et al.

    Thermodynamic properties of mixtures of N-methyl-2-pyrrolidinone and methanol at temperatures between 298.15 K and 343.15 K and pressures up to 60 MPa

    J. Chem. Thermodyn.

    (2009)
  • M. Dzida et al.

    Speed of sound, density, and heat capacity for (2-methyl-2-butanol + heptane) at pressures up to 100 MPa and temperatures from (293 to 318) K. Experimental results and theoretical investigations

    J. Chem. Thermodyn.

    (2010)
  • F. Peleties et al.

    Thermodynamic properties and equation of state of liquid di-isodecyl phthalate at temperature between (273 and 423) K and at pressures up to 140

    J. Chem. Thermodyn.

    (2010)
  • IEA

    Energy Technology Perspectives 2012. Pathways to a Clean Energy System

    (2012)
  • US DOE

    Interagency Task Force on Carbon Capture and Storage

    (2010)
  • A.F. Estrada-Alexanders et al.

    Determination of thermodynamic properties from the speed of sound

    Int. J. Thermophys.

    (1995)
  • S.T. Blanco et al.

    Discussion of the influence of CO and CH4 in CO2 transport, injection, and storage for CCS technology

    Environ. Sci. Technol.

    (2014)
  • A.W. Francis

    Ternary systems of liquid carbon dioxide

    Chem. Ber.

    (1954)
  • Cited by (4)

    • High-pressure speed of sound in pure CO<inf>2</inf> and in CO<inf>2</inf> with SO<inf>2</inf> as an impurity using methanol as a doping agent

      2016, International Journal of Greenhouse Gas Control
      Citation Excerpt :

      For the studied compositions, c in the fluid increased with increasing pressure and decreasing temperature. We did not identify speed of sound data in the literature for this system, except data published by ourselves (Rivas et al., 2016), which are in agreement with this work. A detailed explanation of the application of the PC-SAFT EoS to CO2 + methanol is given in previous works (Gil et al., 2012; Rivas et al., 2016) in which we studied vapor-liquid equilibrium, critical locus, density and c over a wide range of temperature and pressure.

    View full text