Antisolvent solubility curve

In the direct design approach, a desired supersaturation profile that falls between the solubility curve and the metastable limit of the system is followed based on feedback control of the concentration measurement. This is in contrast to the traditional first-principles approach, where a desired temperature profile or antisolvent addition rate profile is followed over time such as shown in Fig. 14. For a cooling crystallization, the direct design approach follows a setpoint profile that is solution concentration vs. temperature (or solvent-antisolvent ratio) as opposed to temperature (or addition rate) vs. time. Because the desired crystallizer temperature is determined from an in-situ solution concentration measurement, the batch time is not fixed. 

There are different approaches to implementing the feedback concentration control for the direct design. Various schemes to implement the concentration control for direct design are described in the literature for cooling and antisolvent crystallizations. " The basic steps are as follows (i) the solution concentration is estimated from IR absorbances and temperature or solvent-antisolvent ratio using the calibration model that relates IR spectra to concentration and (ii) the temperature or antisolvent flow rate setpoint is calculated from the concentration, solubility curve, and the user-specified supersaturation setpoint. 

Fig. 15 Direct design approach using concentration measurement for seeded antisolvent crystallization of paracetamol (acetaminophen) from acetone-water mixture. The concentration-% solvent profile of the batch, the setpoint profile, and the solubility curve are shown. The setpoint followed is that of a constant relative supersaturation Ac/c = 0.04 g/mLsolvent+antisolvent"...

Figure 9.3 Typical solubility curve for an antisolvent c stallization. The solubility of the target compound is given as a function ofthe fraction of antisolvent (here to the right). The solubility curve has a concave curvature, so that the straight mixing line leads to a supersaturation.

For PVP, the saturation solubility curves for the different compositions also show a decreasing and concave shape toward an increased carbon dioxide mole fraction XCO2 This proves that CO2 also acts as an antisolvent for PVP. The increase in the acetone content from 0 to 30 to 50 and up to 70 wt% leads to a continuous decrease in solubility of PVP. This can be seen in the figures in the shift toward the smaller corresponding carbon dioxide molar fractions. The same behavior for the decrease in solubility with increasing acetone content in the solvent composition can be seen for all pressures studied, represented in Fig. 24.13 (right). Fig. 24.14 (left), and Fig. 24.14 (right). 

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. 

In this chapter, the possibihty of using late transition metal catalysts to synthesize polyolefins in supercritical carbon dioxide was demonstrated [43]. The multicomponent phase behavior of polyolefin systems at supercritical conditions was studied experimentally by measuring cloud-point curves as well as by modeling polymer systems at supercritical conditions. The cloud-point measurements show that CO2 acts as a strong antisolvent for the ethylene-PEP system, which implies that the polymerization concerned will involve a precipitation reaction. The model calculations prove that SAFT is able to describe the ethylene-PEP-CO2 system accurately. Solubility measurements of the Brookhart catalyst reveal that the maximum catalyst solubility is rather low (in the order of 1x10 mol L ). However, a number of strategies are given to enhance this value. 

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