Exercise 8 Solution

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Prof. Gianpiero Groppi – Exercises – Fundamentals of Chemical Processes – A.A. 2023-2024 1 EXERCISE 8 Estimation of the composition of the streams exiting a flash unit with a supercritical component A mixture of hydrogen, n-heptane, n-hexane and n-butane with known composition is sent to a flash unit kept at 350°C and 10 bar. By assuming that the gas phase is behaving as an ideal gas and the liquid mixture is ideal with negligible Poynting correction, and assuming that H 2 is incondensable (i.e., it is not present in the liquid outlet, but only in the vapor), estimate: • Tdew of the mixture at 10 bar • Vaporization extent and composition of the liquid and vapor outlets Re-estimate the T dew and the flash unit (vaporization extent and outlet compositions ) by considering that the H2 solubility in the liquid phase is described according to Henry’s law with the provided dependencies from the liquid mixture temperature and composition. DATA zi Ai Bi Ci Antoine: ln𝑝𝑖 0=𝐴𝑖− 𝐵𝑖 𝑇+𝐶𝑖 P in Torr, T in K H2 0.40 - - - n-heptane 0.30 15.8737 2911.32 -56.51 n-hexane 0.20 15.8366 2697.55 -48.78 n-butane 0.10 15.6782 2154.90 -34.42 Prof. Gianpiero Groppi – Exercises – Fundamentals of Chemical Processes – A.A. 2023-2024 2 Henry’s law: H0H2,i(298K) [bar] ΔHDES/R H2 in n-heptane 1268.8 -734.4 H2 in n-hexane 1054.7 -397.7 H2 in n-butane 1677.2 -1418.0 Variation of the Henry constant with T for H2 in the i-th species [H in bar, T in K] 𝐻𝐻2,𝑖=𝐻𝐻2,𝑖 0 (298𝐾)⋅𝑒𝑥𝑝(𝛥𝐻𝐷𝐸𝑆,𝑖 𝑅 ⋅(−1 𝑇+ 1 298)) Variation of the Henry constant with the composition of the liquid mixture: 𝑙𝑛(𝐻𝐻2,𝑚𝑖𝑥)= ∑𝑥𝑖⋅𝑙𝑛(𝐻𝐻2,𝑖) 𝑁𝐶 𝑖≠𝐻2 EXERCISE 8 We have to calc ulate the dew temperature and the vaporiza tion extent in the presence of a n incondensable species (H2). The request is to solve the problem in two different cases • H2…