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

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Abstract

The solubilities of carbon dioxide in different alcohols, methanol, ethanol, and 1-propanol, were measured at two different temperatures (303.2 and 323.2) K and pressures up to 6 MPa. The experimental data of saturated alcohol density and viscosity were also reported at each temperature and pressure. The solubility data shows that the solubility of carbon dioxide in alcohol increases with pressure and decreases with temperatures in the studied pressure and temperature ranges. The higher dissolution of carbon dioxide in alcohols resulted in increase in the saturated liquid densities and decrease in saturated liquid viscosities. The experimental solubility as well as saturated liquid density data were predicted with two cubic equations of state (EOS), Peng–Robinson (PR) and Soave–Redlich–Kwong (SRK). The modeling results demonstrated that both equations of state correlated the solubility data well over the studied pressure and temperature ranges. However, the saturated liquid densities calculated with the SRK EOS were much better than those of PR EOS.

Highlights

► Solubility of carbon dioxide in methanol, ethanol, and 1-propanol and saturated liquid properties. ► Experimental measurements at (303.2 and 323.2) K over pressure range (1 to 6) MPa. ► The results show that the solubility of carbon dioxide decreased from methanol to 1-propanol. ► The experimental data were modeled using the Peng–Robinson and Soave–Redlich–Kwong equations of state.

Introduction

The thermodynamic properties of binary and multi-component systems at high-pressure conditions play an essential role in the design and development of various separation processes. The experimental data for these systems provides valuable information in the fundamental understanding of the behaviour of fluid mixtures. The phase behaviour of the mixtures containing supercritical fluid (SCF) has received particular attention in the last few decades. Carbon dioxide is an available, inexpensive, nontoxic, nonflammable gas, making it one of the more popular solvents. The advantage of carbon dioxide compared to other gases, such as methane and nitrogen, is its higher solubility and corresponding miscibility condition at lower pressures.

The phase equilibrium information of mixtures such as (carbon dioxide + alkanes) and (carbon dioxide + alcohols) are of great significance in the chemical, oil and biotechnology areas, and for the development and validation of thermodynamic models [1]. The gas solubility data and saturated liquid properties of carbon dioxide containing mixtures would be applicable for optimum process design.

In our previous studies [2], [3], [4], the phase equilibria for (hydrocarbon + alcohol) mixtures have been determined. The experimental data on the phase composition, saturated liquid density and viscosity have been reported. The present study was attempted to provide a better understanding of the phase behaviour of binary systems containing carbon dioxide and alcohols. Therefore, the experimental phase equilibrium information for binary systems of (carbon dioxide + methanol + ethanol + 1-propanol) was considered.

Many researchers have measured the solubility and (vapour + liquid) equilibrium data of the above-mentioned mixtures. A comprehensive literature review on these systems has been done by Staby and Mollerup [5] until year 1993. In the current text, an extensive literature survey on the phase behaviour of (carbon dioxide + alcohol) systems since 1993 has been done [1], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49]. The experimental conditions and the available information for the binary systems of (carbon dioxide + methanol), (carbon dioxide + ethanol), and (carbon dioxide + 1-propanol) were gathered and summarized in table 1. Even if many solubilities and (vapour + liquid) equilibrium data have been reported for these systems, there is still a lack of experimental data for the saturated liquid density and viscosity.

Thus, in the present study, the solubility of carbon dioxide in methanol, ethanol, and 1-propanol at temperatures (303.2 and 323.2) K over the pressure range (1 to 6) MPa have been measured. These measurements were also undertaken to determine the properties (density and viscosity) of the saturated liquid phases. The density of pure methanol, ethanol and 1-propanol was also measured at (303.2 and 323.2) K over a wide range of pressure (1 to 10) MPa. Density measurements for pure alcohol could be used to investigate the impact of dissolution of carbon dioxide on the density of saturated alcohol. Finally, the generated experimental data for solubilities and densities were correlated with the Soave–Redlich–Kwong equation of state (SRK EOS) [50] and Peng–Robinson equation of state (PR EOS) [51].

Section snippets

Materials

The CO2 was 4.8 research grade, was purchased from Praxair. The methanol (GR ACS) was provided by EMD chemicals and the ethanol was class (E) 3 UN 1170 PG/GE II (Anhydrous) purchased from Commercial Alcohols. The 1-propanol was Baker analysed reagent and provided by Mallinckrodt Baker Inc. All materials were found to be within acceptable purity specifications and were used without further purifications. Table 2 summarizes the chemical sample specifications.

Apparatus and procedure

The schematic diagram of the apparatus

Density of pure components

The density of pure substances, methanol, ethanol, and 1-propanol, were measured at (303.2 and 323.2) K using vibrating tube density measuring cell (Section 2.2) and are given in table 3. The uncertainty of density measurements for pure components was ±0.1 kg · m−3. Density measurements for pure alcohols could be used to investigate the impact of dissolution of carbon dioxide on the density of liquid phase. The density data from this study was in good agreement with those of Nikam et al. [52].

Solubility and saturated phase properties

The

Correlation of experimental data

The measured solubilities and saturated liquid densities were correlated with two cubic EOSs, SRK and PR. The SRK EOS is presented as,P=RTvM-b-a(T)vM2+vMband PR EOS,P=RTvM-b-a(T)vM2+2vMb-b2witha(T)=ΩaR2Tc2Pcα(T),b=ΩbRTcPcα(T)=1+κ1-TTc1/22,where the parameter a is a function of temperature, b is a constant, Ωa is a constant (0.42747 for SRK EoS and 0.45724 for PR EoS) and Ωb is a constant (0.08664 for SRK EoS and 0.07780 for PR EoS), P is the pressure, Pc is the critical pressure, T is the

Conclusions

The solubility of carbon dioxide in alcohols (methanol, ethanol, and 1-propanol) and the saturated liquid density and viscosity were measured at two different temperatures and pressures up to 6 MPa. The results indicated that the solubility of carbon dioxide in alcohols increases with pressure and reduces with temperature in the investigated pressure and temperature ranges. The solubility of carbon dioxide (when reported in weight fraction) in alcohols also decreases from methanol to 1-propanol

Acknowledgment

The authors would like to express their appreciation to Natural Sciences and Engineering Research Council of Canada (NSERC) and all member companies of the SHARP Research Consortium for providing the equilibrium cells used in this research.

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