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

# 9 29 is applied in the following form for each of the

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Unformatted text preview: ter method: Rigorous Chemcad: Component Feed, Vapor Stripped Vapor Stripped lbmol/h product, liquid, product, liquid, lbmol/h lbmol/h lbmol/h lbmol/h C1 59.5 59.5 0.0 59.5 0.0 C2 73.6 73.6 0.0 73.6 0.0 C3 153.2 153.1 0.1 153.1 0.1 nC 4 173.5 147.6 25.9 150.8 22.7 nC 5 58.2 12.3 45.9 12.7 45.5 nC 5 33.6 6.2 27.4 2.6 31.0 Total: 551.6 452.3 99.3 452.3 99.3 The Edmister method is uncertain because average temperature and vapor rate are difficult to estimate. Exercise 9.28 Subject: Comparison of FUG method with Edmister group method for distillation. Given: Bubble-point liquid feed in kmol/h of 100 ethylbenzene, 100 paraxylene, 200 metaxylene, and 100 orthoxylene. Column pressures of 25 psia at the top and 35 psia at the bottom. Distillate to contain 1 kmol/h of orthoxylene and bottoms to contain 2 kmol/h metaxylene. Column to be equipped with a total condenser and partial reboiler. Assumption: Applicability of Raoult's law for estimating K-values. Find: (a) Number of stages and reflux ratio by the FUG method for R/Rmin = 1.1 Feed-stage location by the Kirkbride equation. (b) Distribution of components between distillate and bottoms by Edmister method. Analysis: Need K-values at distillate, feed, and bottoms conditions. Because metaxylene and paraxylene have very close boiling points, assume the d/b ratio of paraxylene is the same as that for metaxylene. Therefore, have 1 kmol/h of paraxylene in the bottoms. Use Chemcad to obtain K-values by running bubble points on the feed, and estimated distillate and bottoms compositions. The results are: K-values: b, 25 psia, 30 psia, 35 psia, Component d, kmol/h kmol/h 159.3oC 168.4oC 180.5oC Ethylbenzene, EB 100 0 1.051 1.080 1.206 Paraxylene, PX 99 1 0.986 1.012 1.131 Metaxylene, MX 198 2 0.982 1.012 1.136 Orthoxylene, OX 1 99 0.855 0.884 0.996 Total: 398 101 distillat feed bottoms e (a) Using the Fenske equation (9-12), with MX as the LK and OX as the HK, with a geometric mean relative volatility = [(0.982/0.855)(1.136/0.996)]1/2 = 1.144 log N min = d MX bOX d OX bMX log ( α MX,OX )avg log = (198 ) ( 99 ) (1) ( 2 ) log1.144 = 68. 3 To compute the distribution of nonkey components at total reflux, use for the lighter than light key components, LLK, Eq. (9-15), with OX as the reference component, r, and the above value of Nmin. Exercise 9.28 (continued) Analysis: (a) (continued) Thus, for the LLK, i, bi = fi d N min 1 + OX α i,OX bOX = fi 1 68.3 1+ α i,OX 99 (1) Using geometric mean values of αi, OX, with Eq. (1) and the material balance, fi = di + bi , the following results are obtained: kmol/h: Component Feed Distillate Bottoms EB 100 99.99 0.01 PX 100 99.00 1.00 MX 200 198.00 2.00 OX 100 1.00 99.00 Total: 500 397.99 102.01 Because it is highly likely that PX, and possibly EB, will distribute, use the Class 2 Underwood equation, Eq. (9-28),which for a bubble-point feed, using relative volatilities at the feed conditions is: α i ,OX zi , F 12217(0.20) 11448(0.20) 11448(0.40) 100(0.20) . . . . (2) = 1− q = 0 = + + + 12217 − θ 11448 − θ 1144...
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