CO2 dissolution

The terrestrial weathering of organic matter derived from shales and soils results in the oxidation of carbon, which generates CO2. Dissolution of this CO2 in water produces carbonic acid. This weak acid serves to enhance chemical weathering reactions... 

Example 2.4. Thermodyanmics of COi Dissolution in Water Describe the variations in the entropy, enthalpy, and Gibbs energy with extent of CO2 dissolution for a two-phase system comprising a gas phase and an aqueous phase. Find the equilibrium state. Initially, a liter of gas at 1 atm total pressure contains 2 X 10 mol of CO2. It is brought into contact with a liter of pure water. The dissolution process is... 

It is assumed that the parameters n, x, and a are constant and the viscosity reduction due to the CO2 dissolution could be described only by the changes in zero-shear viscosity. The zero-shear viscosity, vjo, is given as a function of free volume fraction as described by... 

To predict the viscosity reduction, the change in the free volume fraction caused by CO2 dissolution has to be calculated. Extending the definition of free volume fraction, the free volume fraction is given as a function of temperature, pressure, and dissolution of gas ... 

Since zero-C02 concentration is taken as a reference condition, the parameter is not a function of CO2. Then, f, oc, and jS can be determined from the PVT measurement of the neat polymer. There remains only gas concentration coefficient, (p, a. a. variable affected by CO2 dissolution. The gas expansion coefficient, (p, is determined by solubility measurements, the models with these parameter values could predict the viscosity of polymer/C02 single-phase mixtures. ... 

Figure 15 RTVE of Hexane (a) effect of pressure and (b) effect of CO2 dissolution (45).

However, its value is negative because the molar volume of solution vl decreases with CO2 dissolution. So there is no expansion as such, inasmuch as the molar volume of the solution is mostly less than that of the pure solvent... 

It may be noted that the occurrence of a minimum value of the molar volume of the binary (solvent-C02) solution is due to the reduction of the partial molar volume of the solvent vi, which is the actual indicator for lowering its solvent power for the solid solute, rather than RTVE or RMVE per se (47). With increasing CO2 dissolution, the liquid molar volume of solution Vl or simply v decreases, since vl < vi- It passes through a minimum, when V = vi = V2, and then increases if vi > V2, as follows ... 

The first term on the right-hand side of Eq. (42) is negative and small, and the seeond term is initially negative and later positive. Aeeordingly, the liquid molar volume initially deereases and later inereases with CO2 dissolution owing to the increase of the second term at high pressures, close to the vapor pressure of CO2 at a subcritical temperature or near the mixture critical pressure of the solvent-C02 system at supercritical temperatures. It may be recalled that the RTVE behavior also shows an exponential increase with pressure at such pressures. 

The variation in the molar volume of the solution at a high CO2 dissolution is relatively less sensitive than the partial molar volume of the solvent. The plots in Figure 22 compare the molar volume v and the partial molar volumes of solvent and CO2 for hexane-C02 and ethyl acetate-C02 systems. It can be observed that the plots of vi, v, and vi intersect at a high value of 1, at which v tends to pass through a minimum, though not prominently, since all three values are equal at this value of Xi. In other words, the value of Xi corresponding to the minimum molar volume can be obtained graphically only from the point of intersection of these three plots. 

The solubilities of pure 3-carotene in ethyl acetate and cholesterol in acetone, predicted by using Eq. (46), compare well with the corresponding experimental data reported in the literature (52,53). The behavior of the curve for Z3 vs Xi is similar to that for V2 vs Xi in that both are drastically reduced at high values of Xi, although both remain almost invariant at lower values of X. This was further validated by experimental data (54) from comparisons of the antisolvent effects on the reduction of solubility of pure 3-carotene in hexane and in ethyl acetate. This trend was also observed for a lecithin-hexane system (55). The solute solubility is negligible at zero or negative values of V2, which occur at a very high CO2 dissolution. 

Figure 24 PMVF of different solvents in binary mixtures with CO2 dissolution in toluene at 298 K ( ), acetone at 318 K ( ), acetone at 308 K(), n-butanol at 298 K (O) (57).

Figure 25 Comparison of predicted liquid mole fraction X3 of different solid solutes for ternary S-L equilibrium with CO2 dissolution from PMVF of solvent in binary mixtures by Eq. (50) with experimental mole fractions of (a) naphthalene in toluene solution at 298 K (56), (b) phenanthrene in toluene solution at 298 K (56), (c) p-carotene in ethyl acetate solution at 298 K (52), (d) p-carotene in toluene solution at 298 K (50), (e) cholesterol in acetone at 308 K (53), (f) cholesterol in acetone solution at 318K (53), (g) acetaminophen in n-butanol solution at 298 K (50), (h) salicylic acid in 1-propanol solution at 303 K ( sA = 0.132), experimental (58), (i) salicylic acid in 1-propanol solution at 288 K (XsA = 0.132) (58), (j) salicylic acid in 1 -propanol solution with at 288 K (XsA = 0.144) (58).

The concept of a CO2 lake is based on a desire to minimize leakage to the atmosphere and exposure to biota. This would require more advanced technology and perhaps higher costs, as the depth of the lake should be at least 3000 m, which exceeds the depths at which the offshore oil industry currently works. The CO2 in the lake would be partly in the form of solid hydrates. This would limit the CO2 dissolution into the water column, further slowing leakage to the atmosphere from that shown in Figure 2, which... 

CO2 dissolution is seen to be largely dependent on the degree offluorination in the anion, following the general trend [BMIM][PFg] > [BMIM][BF4] > [BMIMJfNOj] [5]. 

In pure water CO2 sorption from gaseous phase is slow because the formation of carbonic acid is slow too. The presence of OH iorts in liquid phase exerts double effect they increase the carbonate ions concentration and accelerate the hydrolysis of CO2 molecttles and then CO2 dissolution. According to Payne and Dodge [357], at terrrperature of 30 °C CO2 sorption in KOH solution of concentration 0.2 mol/1 is ten times faster than in prrre water. One shotrld underline that the effect of KOH is... 

Figure 6. Density ratio of DMAE-based solntions to water with the influence of PZ addition and CO2 dissolution (O 30 wt% DMAE, 30 wt% DMAE + 0.8 mol/L CO2, A 30 wt% DMAE + 1.4 mol/L CO2, X 25 wt% DMAE + 5 wt% PZ, 20 wt% DMAE + 10 wt% PZ, dashed lines linear fits).

To assist in choosing gas-specific solvents for NGCC-CCS, VLE data for CO2 and aqneons amine solntions were obtained in this work. The cyclical CO2 capacity in the DMAE- and AMP-based solvents is approximately twice that of the benchmark MEA solution. The partial replacement of the principal amine by PZ can increase CO2 dissolution into the aqueous solutions. The density and viscosity of these amine solutions were also measured, with the addition of PZ, CO2 loading, and temperatiu e being the parameters of interest. Both the DMAE- and AMP-based solvents exhibited a higher viscosity compared to MEA solution at the same concentration and temperature. The effect of dissolved CO2 on the viscosity of AMP-based solutions is much more significant than for DMEA-based solutions. 

In this section the main results obtained up to date in the production of nanoporous structures following the previously described approach (ie, combining nanostructured polymers with CO2 dissolution foaming process) are described. In addition, the... 

The porous structures obtained by CO2 dissolution foaming from the different precursors previously described are reported in this subsection according to these main parameters. 

In nature a slight increase in acidity of an aqueous system, can be noticed when CO2 is dissolved. This raises a question on CO2 dissolution into water, in the case of an aqueous system which has an increased H+ concentration, i.e. a low pH value. Scheme 5 shows pH changes as a function of sulphuric acid addition in open and closed systems using artificial seawater with 3.5 wt.% salinity. The salt composition is also displayed. 

The viscosity of water is only slightly influenced by the dissolved carbon dioxide as shown in Fig. 15.17 for 293 K [22]. A comparison with literature data for pure water [21] at 293 K show that with increasing pressure the viscosity of CO2-saturated water rises. Dittmar explains that the ions formed by the CO2 dissolution in water (HCO3, H+, OH—) have a reinforcing effect on the molecular structure... 

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