Exercise 02 Solution ENG

Pagina 1

Page 1 of 6 Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta” POLITECNICO di MILANO Practical class (informatic laboratory) of Chemical Processes and Technologies (Prof. Stefania Moioli) Results 1. Vapour pressure estimation a) The Clausius-Clapeyron type equation is of the form: 𝑙𝑛( 𝑃𝑒𝑣) = 𝐵 + 𝐴 𝑇 . Using the two given pairs of values for the temperature and the vapour pressure (Pev,1 = 118.3 mmHg at 29.5 °C, and Pev,2 = 760 mmHg at 77.0 °C), it is possible to determine the two coefficients A and B by solving the following system of equations: { 𝑙𝑛( 𝑃𝑒𝑣,1) = 𝐵 + 𝐴 𝑇1 𝑙𝑛( 𝑃𝑒𝑣,2) = 𝐵 + 𝐴 𝑇2 As a result: A = -4149.8868 [K]. The value of B depends on the unit of measurement used for the vapour pressure. In particular: Unit of Pev mmHg atm bar psi B 18.4851 11.8517 11.8649 14.5393 b) The vapour pressure of ethyl acetate at 45 °C (318.15 K), using the three methods, is: Method Pev [mmHg] Clausius-Clapeyron type equation 230.7311 Antoine equation 235.1043 Linear interpolation 327.6968 In the third case (namely, “Linear interpolation”), the dependence of Pev on T has been assumed to be of the form Pev = a∙T + b, where the two parameters a and b can be determined using the two given pairs of values for the temperature and the vapour pressure. They result to be: a = 13.5095 [mmHg/K], and b = -3970.3422 [mmHg] to get Pev in mmHg. Page 2 of 6 In order to discuss the results obtained with the three methods, it is convenient to compare the calculated values with the experimental value of 233 mmHg for the vapour pressure of ethyl acetate at 45 °C (source: http://www.ddbst.com/en/EED/PCP/VAP_C21.php). It is also useful to plot Pev as a function of the temperature, as shown in Figure 1 ( it is possible to make the same plot using , for example, a Scatter plot in…