Antoine equation constants

Your task in this problem will be to use a spreadsheet to generate a Txy diagram for a two-component system, using Raoult s law to express the vapor-liquid equilibrium distribution of each species. The spreadsheet will be constructed for the chloroform-benzene system at 1 atm (for which Raouit s law is not a very good approximation), but it can then be used for any other system by substituting different Antoine equation constants. 

In this table, A, B, and C are Antoine equation constants, al, av, and bv are the coefficients of the given heat capacity formulas Tbp(°C) and DHv(kJ/mol) (A v) are the normal boiling point and heat of vaporization, xF(mol pentane/mol) is the mole fraction of pentane in the feed. TfCC) is the feed temperature, P(mm Hg) is the system pressure. HAF (Haf) and HBF (Hbf) are the specific enthalpies of pentane and hexane in the feed stream, pA is the vapor pressure of n-pentane (to be determined using the Antoine equation), x and nL x and l) are the mole fraction of pentane in the liquid product stream and the molar flow rate of that stream, respectively, y and nV are the corresponding properties of the vapor product stream. HAL is the specific enthalpy of pentane in the liquid product stream, and DH (A//) is the expression given in Equation 5 for the change in total enthalpy from inlet to outlet. 

Vapor pressure (mm Hg) of the condensable substance at temperature T. Antoine equation constants for the condensable substance,... 

Cox Chart Vapor Pressure Plots Vapor Pressure of Water Antoine Equation Constants... 

Assumptions Ideal gas behavior, validity of Raoult s law and the Antoine equation, constant temperature and pressure in the pipe connecting the column and the condenser, column operates at steady state. 

Figure 8.6 contains, implicitly, aU the data in Table 8.1. If we were told, for example, that at 1 atm pressure a liquid with acetone = 0.05 had yacetone = 7.04 and ywater = 1.01 (and that the gas phase was practically an ideal gas), then that information plus the Antoine equation constants from Table A.2 would be enough information to compute both the equilibrium temperature and the value... 

This is a repeat of Example 3.5. We must find, by trial and error, the temperature at which the sum of the computed ideal solution vapor-phase mol fractions is 1.00. For our first try, we guess r=80°C. Using the Antoine equation constants in Table A.2, we compute that at 80°C the two pure species vapor pressures for acetone and for water are 2.11 and 0.47 atm. Then multiplying each of these by the corresponding liquid mol fractions and dividing by 1 atm, we find that the computed vapor mol fractions are 0.106 and 0.444, and that their sum is 0.55. This is less than 1.00, so our assumed temperature is too low. These values are shown as the first data row in Table 8.A. The calculation was done on a spreadsheet, with which one can quickly repeat the calculation for various assumed temperatures and display the results in subsequent rows of Table 8. A. The assumed temperature that makes the sum of the vapor-phase mol fractions equal 1.00 is T = 96.406 °C. (We should not believe that we know any boiling temperature 0.001°C, we should report the calculated boiling temperature as 96.4°C). ... 

The equations to be solved are shown in Table 8.E. The Antoine equation constants are from Table A.2. We divided the two Antoine equations by 760 torr/atm, to have the vapor pressure in atm. 

The constants in the Antoine equation may be estimated by selecting three widely spaced data points and substituting in the following equations in sequence ... 

Two empirical parameters are evident in equation 7, the heat of vaporization and the integration constant, I. Experimental data indicate that the linear relationship suggested by Clausius-Clapeyron may not be followed over a large temperature range (4) therefore additional adjustable parameters have been added to equation 7 to improve its correlating abiUty. The most prominent of these is the Antoine equation ... 

The equation developed by the Design Institute for Physical Property Data (DIPPR) is another successful correlating tool for vapor pressure (4). It is an empirical extension of the Antoine equation and has two additional constants, D and E ... 

The Antoine equation does not fit data accurately much above the normal boiling point. Thus, as regression by computer is now standard, more accurate expressions applicable to the critical point have become usable. The entire DIPPR Compilation" is regressed with the modified RiedeP equation (2-28) with constants available for over 1500 compounds. 

Example 4.5 2-Propanol (isopropanol) and water form an azeotropic mixture at a particular liquid composition that results in the vapor and liquid compositions being equal. Vapor-liquid equilibrium for 2-propanol-water mixtures can be predicted by the Wilson equation. Vapor pressure coefficients in bar with temperature in Kelvin for the Antoine equation are given in Table 4.113. Data for the Wilson equation are given in Table 4.126. Assume the gas constant R = 8.3145 kJ-kmol 1-K 1. Determine the azeotropic composition at 1 atm. 

The system methanol-cyclohexane can be modeled using the NRTL equation. Vapor pressure coefficients for the Antoine equation for pressure in bar and temperature in Kelvin are given in Table 4.176. Data for the NRTL equation at 1 atm are given in Table 4.186. Assume the gas constant R = 8.3145 kIkmol 1-K 1. Set up a spreadsheet to calculate the bubble point of liquid mixtures and plot the x-y diagram. 

This can be empirically modified by introducing additional parameters to give the three-parameter Antoine equation by replacing T with (T + C), where C is a constant, which is the most common vapor pressure correlation used to represent experimental data (Zwolinski and Wilhoit 1971, Boublik et al. 1984, Stephenson and Malanowski 1987, and other handbooks). 

The saturation vapour pressures are calculated as a function of temperature using the Antoine equation, equation 11.6, and the constants given in Example 11.3, and then, from Raoult s Law, Equation 11.1, the actual vapour pressures are given by ... 

Rearrangement of the Antoine equation (7.4.1) leads to the following equation, which permits the estimation of boiling points from known Antoine constants within the applicable range for a given pressure ... 

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