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Separation Process Principles- 2n - Seader & Henley - Solutions Manual

8306 0003916 28201 for c3 the freundlich equation

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Unformatted text preview: Sg = 832 m2/g. At higher temperatures, the experimental values for adsorption are even less, with just a slight increase in α. Therefore, the measured values of adsorption are equivalent to far less than a monolayer. (c) The heat of adsorption is related to adsorption isotherm data by a rearrangement of Eq. (1517), which is a form of the Clausius-Clapeyron equation. For a constant amount adsorbed, d ln p − ∆Hads = RT 2 (1) where, R = 1.987 cal/mol-K dT Take an arbitrary value of 0.00025 mols of benzene adsorbed per gram of silica gel. For each temperature, calculate the partial pressure of benzene from the above fits of the Freundlich equation (the Langmuir equation could also be used). Evaluate d ln p/dT numerically and apply Eq. (1). The results are as follows. Temperature, Temperature, Benzene pressure, ln p d ln p/dT Tavg, K - ∆Hads, o C T, K p, atm cal/mol 70 343 0.00108 -6.831 0.05615 353 13,900 90 363 0.00332 -5.708 0.05180 373 14,300 110 383 0.00935 -4.672 0.0347 393 10,650 130 403 0.01873 -3.978 The average heat of adsorption = - 13,000 cal/mol. From the ChemCad simulation program, the heat of condensation for benzene varies from -7,500 cal/mol at 70oC to -6,620 cal/mol at 130oC. Thus, the heat of adsorption is almost twice as great as the heat of condensation. Exercise 15.7 Subject: Use of adsorption equilibria data to select the best adsorbent. Given: Langmuir adsorption equilibrium constants, K and qm in Eq. (15-24), for 3 zeolite molecular sieves and activated carbon for propylene (C3) and propane (C3=) at 25oC: Adsorbent Sorbate qm K ZMS 4A C3 0.226 9.770 C3= 2.092 95.096 ZMS 5A C3 1.919 100.223 C3= 2.436 147.260 ZMS 13X C3 2.130 55.412 C3= 2.680 100.000 Activated carbon C3 4.239 58.458 C3= 4.889 34.915 Find: (a) (b) (c) (d) Most strongly adsorbed component for each adsorbent. Adsorbent with greatest adsorption capacity. Adsorbent with greatest selectivity. Best adsorbent for the separation of propylene from propane. Analysis: (a) The Langmuir equation is: q = Kqmp/(1 + Kp) At high pressure, q approaches qm. Thus, qm is a measure of capacity. Because of the high values of K, the value of qm is reached at about 1 bar. Thus, we can make the comparisons on the basis of qm. Therefore, propylene is the most strongly adsorbed for all 4 adsorbents. (b) The activated carbon has the highest values of qm and, therefore, has the highest capacity. (c) The selectivity is measured by the ratio of qm for propylene to that of propane. With a value of 2.092/0.226 = 9.26, zeolite ZMS 4A is by far the best. (d) Because of its very high selectivity of ZMS 4A, where the second best is only 1.27, and the high capacity of ZMS 4A, although only about 40% of that of activated carbon, ZMS 4A is the best adsorbent for the separation of propylene and propane. Exercise 15.8 Subject: Fitting zeolite adsorption data to linear, Freundlich, and Langmuir isotherms. Given: NaX zeolite adsorbent. Adsorption equilibrium data at 547 K for 1,2,3,5tetramethylbenzene (TMB) as follows: 9.1 10.3 10.8 11.1...
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