This thesis concerns the determination of limiting activity coefficients exclusively using the inert gas stripping (IGS) technique. An extensive investigation of activity coefficients at infinite dilution for various systems has been carried out, using the inert gas stripping (IGS) method. The original equipment was designed for the use of the single-cell technique by Soni (2004).
Another n-hexane in NMP test system was used to compare the two techniques, Le. the results of the single-cell technique with the results of the two-cell technique. Systems where the inert gas removal technique was not used to determine activity coefficients at infinite dilution were also investigated. In addition, the suitability and diversity of the inert gas removal technique was described, along with the advantages and disadvantages of the technique.
CHAPTER 1: INTRODUCTION
CHAPTER 2 : EXPERIMENTAL AND PREDICTIVE TECHNIQUES 1 Experimental Methods
CHAPTER 3: THE INERT GAS STRIPPING METHOD
CHAPTER 4, EQUIPMENT AND EXPERIMENTAL PROCEDURE
CHAPTER 5: EQUILIBRIUM CELL DESIGN
CHAPTER 6: PRINCIPLES AND THEORY
CHAPTER 7: EXPERIMENTAL RESULTS Part I: Test Systems
CHAPTER 8: DISCUSSION 1 Discussion
Uncertainty in Temperature Readings 8.1.15.2 Uncertainty in Mass Readings
Experimental Difficulties 8.1.16.2 Experimental Errors
CHAPTER 9 : CONCLUSION
CHAPTER 10: RECOMMENDATIONS
Comparison of limiting activity coefficients at three different flow rates for the system n-hexene (1) + o-cresol (2). Comparison of limiting activity coefficients for the system n-hexene (1) + 0-cresol (2) at constant inert gas flow rate (D = 10 ml/min). Limiting activity coefficients at different temperatures for the system n-hexane (1) + NMP (2) obtained using SCT.
Limiting activity coefficients for the system n-hexene (1) + NMP (2) for 30 mUmin and at four different temperatures. Limiting activity coefficients for the system n-hexene (1) + o-cresol (2) estimated using the equation proposed by Hovorka and Dohnal (1997) for different experimental conditions. Average limiting activity coefficients for the system n-hexene (1) + NMP (2) Average limiting activity coefficients calculated for the system n-hexene (1) + o-cresol (2).
IGS GLC
TENS CIRC
The Inert Gas Stripping Method
Since the method was established by Leroi et al. a) The correction of Duhem and Vidal (1978) for the liquid concentration of the solute for partitioning between the vapor phase and the liquid phase in the equilibrium cell. This decay rate allows a direct calculation of the infinite dilution activity coefficient of the solute in the solvent. Using the IGS technique as a basis for the analysis, they derived equations for determining Henry's constants.
This will therefore lead to errors in the obtained values of the limiting activity coefficients for the solvenUs. Of the two techniques, the choice of which technique to use depends on the nature (single or multi-component) and the volatility of the solvent in the solution. The design of the cell depends on the value of the infinite dilution activity coefficient.
Equipment and Experimental Procedure
Water from the water bath (61) is used to maintain the temperature of the gas flowing through the heat exchanger. Gas bubbles are formed as the gas passes through the 10 capillaries (C/32 inch ID) and rises to the top of the cell and into the vapor phase. The small gas bubbles rise to the top of the cell and leave the cell at the gas outlet (8).
The limiting activity coefficient is very sensitive to the value of the nitrogen gas flow rate. The temperature of the gas is also higher than the system temperature because it passes through the heated lines before reaching the cold trap. The cold trap allows for complete condensation of the solute and solvent vapor flowing with the nitrogen into the coil.
A Vanan 3300 GC was used to analyze the gas in the sample loop of the 6-port gas sampling valve. The design of the equilibrium cells is primarily based on the rate of mass transfer that takes place within the cells. The solute is transferred from the solvent to the gas through the interface between the bubbles in two steps.
The change in liquid concentration is negligible as long as the gas bubbles are in the solution and are supposedly perfectly stirred. The determination of the liquid diffusion coefficient is not limited to the equation of Wilke and Chang (1955). Assuming that diffusion in the gas phase of the bubble is very fast (Richon et al.
P and physical constants of the gas and liquid are negligible for bubbles passing through the cell.
Principles and Theory
An increase in selectivity often leads to a decrease in the capacity of a solvent or solvent mixture; however, it is important for the economic efficiency of a separation process. It is seen that the separation of the final traces of a component requires the greatest effort, because the least favorable values of the separation factor occur at high dilution. In the case of positive deviations from Raoult's law (y I > I), the greatest separation effort is required at the top of the column (xI --+ 1).
At the bottom of the column (xj --+ 1), the effort involved in the separation is greatest for negative deviations from Raoult's law (ri < 1). Taking into account limiting activity coefficients also improves the reliability of the description in the dilute region when reliable g E model parameters need to be fitted or in the development and improvement of group contribution methods. These equations, depending on the nature of the solvent, can be used to calculate limiting activity coefficients for most systems. 1977) equations that take into account some of the simplifying assumptions that are not usually valid for most systems.
For both solvent and solute, the reference state is the pure liquid at zero pressure. BIf, is the virial coefficient that characterizes the bimolecular interaction between molecule j and molecule j, while BM is the second virial mixing coefficient, T is the temperature, and R is the universal gas constant. If the solute is very dilute in the solvent and if the solubility of the carrier gas in the liquid phase is negligible, the activity coefficient of the solute can be approximated to its value at infinite dilution.
It can be shown that in most cases this approximation is valid if the mole fraction of the solute xsol is less than 10-3 (Leroi et al. The mole fraction of the solvent in the liquid phase and the activity coefficient r s can be obtained equal to 1 in equation 6.5, under the same conditions If nand N are respectively the total number of moles of solute and solvent in the equilibrium cell at time l, the amounts (- dn ) and (- dN ) withdrawn from the solution during dt from the carrier gas flow are.
Dz is the total volumetric rate of gas flowing from still converted to pressure (P) and temperature (T).
NYW' P
Asol is the area of the solute peak from the GC analysis and K is the proportionality constant. As already mentioned, the change in the amount of solute in the measuring cell is measured as a function of time. Due to presaturation, the change in the amount of solvent present can be neglected.
A water vapor volume flow must be added to the carrier gas flow due to the presaturation. The fundamental thermodynamic quantity to characterize air·water partitioning is the limiting activity coefficient of the solute in water. Vapor phase non-ideality corrections and the effect of the vapor space in the cell are neglected.
The correction factor k3 is always greater than 1 and increases with the volatility of the solute and with the increasing ratio between the volume of the vapor space and the amount of solvent in the cell. Henry's constant is directly related to the residual chemical potential of the solute at infinite dilution. The liquid level in the cell should not be lower than 1 cm from the top of the cell.
The volume of gas outside the equilibrium cell is proportional to the composition of the vapor phase removed from the solution. The term PDt/(P - ~StJI) in Equation 6.29 is approximately equal to the volume of saturated vapor (V). In general, the existence of the vapor phase in the cell affects the estimation of Henry's constants for the degassing method.
The difference in the Henry constants is mainly proportional to the initial volume of the vapor phase in the cell.
Test Systems
A plot showing the slopes for the system cyclohexane (1) + NMP (2) at different nitrogen gas flow rates (0) is illustrated in Figure 7-1. The effect of temperature on the limiting activity coefficients for the system cyclohexane (1) + NMP (2) was then investigated. Figure 7·3: Comparison of experimental and literature values of limiting activity coefficients for the system cyclohexane (1) + NMP (2) from Equation 6.55.
Limiting activity coefficients for the n-heptane system in NMP, evaluated using Equation 6.55, can be found in this section. Moving profiles to determine the slope of a for the n-hexane (1) + NMP (2) system using ocr. Straight line profiles for the determination of the slope a for the n-hexane (1) + NMP (2) system using SCT.
Table 7~5: Limiting activity coefficients at different temperatures for the system n-hexane (1) + NMP (2) obtained using SCT. The limiting activity coefficients determined using SeT are similar to those of OCT. Figure 7·9: Comparison of all calculated activity coefficients at infinite dilution for the system cyclohexane (1) + NMP (2) with predetermined literature values.
The limiting activity coefficients are in good agreement, but not as good as that for the n-heptane (1) + NMP (2) system. The third test system under investigation is n-hexane (1) + NMP (2) and the limiting activity coefficients are found in Table 7-14 for OCT. Table 7·14: Limiting activity coefficients calculated from equation 6.65 for the n-hexane (1) + NMP (2) system using DCT at constant inert gas flow rates and temperatures.
Table 7·15: Limiting activity coefficients for the system n-hexane (1) + NMP (2) using SCT at a constant flow rate and at different temperatures.
Experimental Results Part 11 : New Systems
Limiting activity coefficients as a function of temperature for the system n-hexene (1) + NMP (2) for literature and experimental. This section reports the limiting activity coefficients for the system n -hexene (1) + NMP (2) obtained using the Leroi et al. Figure 7·19: Comparison of experimental limiting activity coefficients with literature values for the system n-hexene (1) + NMP (2).
Figure 7·22: Comparison of the limiting activity coefficients at three different flow rates for the system n-hexene (1) + o-cresol (2). The limiting activity coefficients show excellent agreement for the three fluxes at the corresponding temperatures. A comparison of the limiting activity coefficients evaluated from the four equations for the system n-hexene (1) + o-cresol (2) is shown in Figure 7-24.
Figure 7.26: Comparison of limiting activity coefficients for the system n-hexene (1) + 0-cresol (2) at three flows and four temperatures. All limiting activity coefficients calculated for the system n-hexene (1) + o-cresol (2) show a strong agreement with each other.
