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The following diagram shows a staged absorption column in

Elementary Principles of Chemical Processes | 3rd Edition | ISBN: 9780471687573 | Authors: Richard M Felder ISBN: 9780471687573 143

Solution for problem 6.64 Chapter 6

Elementary Principles of Chemical Processes | 3rd Edition

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Elementary Principles of Chemical Processes | 3rd Edition | ISBN: 9780471687573 | Authors: Richard M Felder

Elementary Principles of Chemical Processes | 3rd Edition

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Problem 6.64

The following diagram shows a staged absorption column in which n-hexane (H) is absorbed from a gas into a heavy oil. Equipment Encyclopedia absorber Gas effluent ncN(mol/s) YN(mol H/moll 1-----"""1 Stage N nc(mol/s) nL(mol/s) Yi(mol H/mol) Xi _ 1(mol H/mol) ..-- 8 Stagei+l Stage i - - - -~ H Stage i I---,;,j Stage 2 I---+~ Stage 1 nc(molls) nL(molls) Yi + I (mol H/mol) x/(mol H/mol) Liquid effluent nL1(mOl/s) xI(mol H/mol) Liquid feed 200 mol oil/s Gas feed nc = 100 molls 0 Yo =0.050 mol H/mol A gas feed stream containing 5.0 mole% hexane vapor and the balance nitrogen enters at the bottom of an absorption column at a basis rate of 100 molls, and a nonvolatile oil enters the top of the column in a ratio 2 mol oil fed/mol gas fed. The absorber consists of a series ofideal stages (see 6.63), arranged so that gas flows upward and liquid flows downward. The liquid and gas streams leaving each stage are in equilibrium with each other (by the definition of an ideal stage), with compositions related by Raoult's law. The absorber operates at an approximately constant temperature T cae) and pressure P(mm Hg). Of the hexane entering the column, 99.5% is absorbed and leaves in the *Computer problem. 297 liquid column effluent. At the given conditions it may be assumed that N2 is insoluble in the oil and that none of the oil vaporizes. (a) Calculate the molar flow rates and mole fractions of hexane in the gas and liquid streams leaving the column. Then calculate the average values of the liquid and gas molar flow rates in the column, ndmol/s) and nc(moVs). For simplicity, in subsequent calculations use these values as the molar flow rates of the liquid and gas streams leaving each stage. (b) Estimate the mole fraction of hexane in the gas leaving the bottom stage of the column (YI) and in the liquid entering this stage (X2)' (c) Suppose that Xi and .Vi are the mole fractions of hexane in the liquid and gas streams leaving stage i. Derive the following formulas and verify that they yield the answers you calculated in part (b): (1) (2) (d) Create a spreadsheet to determine the number of stages (N) required to reduce the moie fraction of hexane to its required final value [calculated in part (a)] or less for P = 760 torr and temperatures of 30e. 50C, and 70C. The spreadsheet should have the following structure (some calculated values are shown): Hexane Absorption I I I I I I I I P=- I 760 PR =- 1 I I 0.05 I I I I Yo = Xl = Ye = . 2.63E-04 I i i I I nCN = nLl =- I nc = nL =- I I I A=- 6.8776 I B= I 1172 C= 224.366 ! i I I I I I I I I I ! T p*(T) I T p*(T) T p*(T) ! I I I I 30 187.1 II I I 50 I , 70 I I I I i I x(i) y(i) I i I x(i) y(i) i x(i) y(i) I 0 I 5.00E-02 I 0 5.00E-02 I 0 5.00E-02 ! I I I i I I 1 2.43E-02 5.98E-03 I i 1 I I I 1 ! I I I 7.56E-04 I , I 2 3.07E-03 2 I 2 ! ! I I I \ 3 5.57E-04 1.37E-04 I 3 3 Enter the values of Xi, YN, he"" nLt ' and the average flow rates hc and nL calculated in parts (a) and (b). Then in the appropriate cells for the calculation at 30C, enter the Antoine formula for the vapor pressure, the value of XI, the formula for YI (Equation 1), and the formulas for X2 and Y2 (Equations 2 and 1). Then copy the formulas into successive rows, proceeding until the value of Yi is less than or equal to the calculated effluent value (YN)' The results (which should match the ones shown) indicate that three stages are required to achieve the specified hexane recovery at 30e. Repeat the calculations for the other two temperatures. (You should be able to do so entirely by copying cells from one location to another on the spreadsheet.) Do not go beyond 25 stages for any temperature, whether or not you achieve the required separation. 298 Chapter 6 Multiphase Systems Encyclopedia Equipment evaporator (e) You should have found that at 70C and 760 mm Hg the hexane mole fraction in the vapor levels out at a value above the target value, which means that the specified separation cannot be achieved at those conditions. Explain this result. Then use your spreadsheet to determine the minimum pressure at which the target absorption can be achieved at that temperature.

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th th Chapter 7 from “Introductory Chemistry” by Zumdahl and Decoste, 7 /8 edition *Majority of the chemical reactions that take place in our bodies occur in aqueous solutions Ex: oxygen dissolving into blood stream Pg 137. PREDICTING IF A REACTION WILL HAPPEN Driving Force: “changes that make reactions go in the direction of the arrow,” the cause of the product Most common driving forces: 1. Forms a solid 2. Forms of water 3. Transfers electrons 4. Forms a gas -if two or more chemicals are joined together and any of these happened, there most likely is a chemical reaction REACTION: SOLID FORMS Precipitation: process by which a solid is formed Precipitate: the solid formed

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Chapter 6, Problem 6.64 is Solved
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Textbook: Elementary Principles of Chemical Processes
Edition: 3
Author: Richard M Felder
ISBN: 9780471687573

Since the solution to 6.64 from 6 chapter was answered, more than 535 students have viewed the full step-by-step answer. The answer to “The following diagram shows a staged absorption column in which n-hexane (H) is absorbed from a gas into a heavy oil. Equipment Encyclopedia absorber Gas effluent ncN(mol/s) YN(mol H/moll 1-----"""1 Stage N nc(mol/s) nL(mol/s) Yi(mol H/mol) Xi _ 1(mol H/mol) ..-- 8 Stagei+l Stage i - - - -~ H Stage i I---,;,j Stage 2 I---+~ Stage 1 nc(molls) nL(molls) Yi + I (mol H/mol) x/(mol H/mol) Liquid effluent nL1(mOl/s) xI(mol H/mol) Liquid feed 200 mol oil/s Gas feed nc = 100 molls 0 Yo =0.050 mol H/mol A gas feed stream containing 5.0 mole% hexane vapor and the balance nitrogen enters at the bottom of an absorption column at a basis rate of 100 molls, and a nonvolatile oil enters the top of the column in a ratio 2 mol oil fed/mol gas fed. The absorber consists of a series ofideal stages (see 6.63), arranged so that gas flows upward and liquid flows downward. The liquid and gas streams leaving each stage are in equilibrium with each other (by the definition of an ideal stage), with compositions related by Raoult's law. The absorber operates at an approximately constant temperature T cae) and pressure P(mm Hg). Of the hexane entering the column, 99.5% is absorbed and leaves in the *Computer problem. 297 liquid column effluent. At the given conditions it may be assumed that N2 is insoluble in the oil and that none of the oil vaporizes. (a) Calculate the molar flow rates and mole fractions of hexane in the gas and liquid streams leaving the column. Then calculate the average values of the liquid and gas molar flow rates in the column, ndmol/s) and nc(moVs). For simplicity, in subsequent calculations use these values as the molar flow rates of the liquid and gas streams leaving each stage. (b) Estimate the mole fraction of hexane in the gas leaving the bottom stage of the column (YI) and in the liquid entering this stage (X2)' (c) Suppose that Xi and .Vi are the mole fractions of hexane in the liquid and gas streams leaving stage i. Derive the following formulas and verify that they yield the answers you calculated in part (b): (1) (2) (d) Create a spreadsheet to determine the number of stages (N) required to reduce the moie fraction of hexane to its required final value [calculated in part (a)] or less for P = 760 torr and temperatures of 30e. 50C, and 70C. The spreadsheet should have the following structure (some calculated values are shown): Hexane Absorption I I I I I I I I P=- I 760 PR =- 1 I I 0.05 I I I I Yo = Xl = Ye = . 2.63E-04 I i i I I nCN = nLl =- I nc = nL =- I I I A=- 6.8776 I B= I 1172 C= 224.366 ! i I I I I I I I I I ! T p*(T) I T p*(T) T p*(T) ! I I I I 30 187.1 II I I 50 I , 70 I I I I i I x(i) y(i) I i I x(i) y(i) i x(i) y(i) I 0 I 5.00E-02 I 0 5.00E-02 I 0 5.00E-02 ! I I I i I I 1 2.43E-02 5.98E-03 I i 1 I I I 1 ! I I I 7.56E-04 I , I 2 3.07E-03 2 I 2 ! ! I I I \ 3 5.57E-04 1.37E-04 I 3 3 Enter the values of Xi, YN, he"" nLt ' and the average flow rates hc and nL calculated in parts (a) and (b). Then in the appropriate cells for the calculation at 30C, enter the Antoine formula for the vapor pressure, the value of XI, the formula for YI (Equation 1), and the formulas for X2 and Y2 (Equations 2 and 1). Then copy the formulas into successive rows, proceeding until the value of Yi is less than or equal to the calculated effluent value (YN)' The results (which should match the ones shown) indicate that three stages are required to achieve the specified hexane recovery at 30e. Repeat the calculations for the other two temperatures. (You should be able to do so entirely by copying cells from one location to another on the spreadsheet.) Do not go beyond 25 stages for any temperature, whether or not you achieve the required separation. 298 Chapter 6 Multiphase Systems Encyclopedia Equipment evaporator (e) You should have found that at 70C and 760 mm Hg the hexane mole fraction in the vapor levels out at a value above the target value, which means that the specified separation cannot be achieved at those conditions. Explain this result. Then use your spreadsheet to determine the minimum pressure at which the target absorption can be achieved at that temperature.” is broken down into a number of easy to follow steps, and 797 words. This full solution covers the following key subjects: mol, gas, stage, hexane, liquid. This expansive textbook survival guide covers 13 chapters, and 710 solutions. The full step-by-step solution to problem: 6.64 from chapter: 6 was answered by , our top Chemistry solution expert on 11/15/17, 02:42PM. This textbook survival guide was created for the textbook: Elementary Principles of Chemical Processes, edition: 3. Elementary Principles of Chemical Processes was written by and is associated to the ISBN: 9780471687573.

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The following diagram shows a staged absorption column in