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A tubular reactor for the isomerization of n-butane to isobutane is to be installed in a dedicated section of the naphtha upgrading unit in a chemical plant: n-C4H10 i-C4H10 r = k [n-C4H10]

A tubular reactor for the isomerization of n-butane to isobutane is to be installed in a dedicated section of the naphtha upgrading unit in a chemical plant: n-C4H10 i-C4H10 r = k [n-C4H10]

Introduction to Chemical Engineering Thermodynamics
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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1. A tubular reactor for the isomerization of n-butane to isobutane is to be installed in a dedicated section of the naphtha upgrading unit in a chemical plant: n-C4H10 r = k [n-C4H10] The reactor will operate using a pure feed of n-butane (300 m³/min), the reaction follows 1st order kinetics with a kinetic constant value of 5 sec¹¹. The reactor is a long tube, and it was designed and modeled as a PFR for a butane conversion of 70 ± 2.5%. Before installation, the design engineers noticed that the reactor was not built to the right specification, and it was too long to be fitted on the space allocated for it. The chemical engineers suggested that the reactor be split in two, have the reactors operating in parallel and the feed divided in two evenly (150m³/min of n-C4H10 on each half reactor), and that this solution would ensure the n-butane will remain within tolerance values (67.5%-72.5%). The operations manager did not like the idea because it will require additional instrumentation, pumps, piping, valves, etc. to handle a parallel flow stream. FE nBut i-C4H10 FyBut FnBut 2 FnBut 2 -L/2 -1/2 X= 70% Original design ► X=? Proposed solution by Chem. Engineers The mechanical engineers proposed an alternative solution: to carefully bend the end of the reactor, so it will fit in the space allocated. Even though the chemical engineers keep warning about backmixing (Hint: think CSTR), the mechanical engineers insisted conversion will remain within tolerance values if the flowrates, temperature and all other operation parameters remain the same. The operations manager liked the savings linked to the "bend the reactor" idea, implemented it and installed the modified reactor. Even though all operating conditions remain the same, the conversion obtained is now below specs, reaching a conversion of only 65%...
Transcribed Image Text:1. A tubular reactor for the isomerization of n-butane to isobutane is to be installed in a dedicated section of the naphtha upgrading unit in a chemical plant: n-C4H10 r = k [n-C4H10] The reactor will operate using a pure feed of n-butane (300 m³/min), the reaction follows 1st order kinetics with a kinetic constant value of 5 sec¹¹. The reactor is a long tube, and it was designed and modeled as a PFR for a butane conversion of 70 ± 2.5%. Before installation, the design engineers noticed that the reactor was not built to the right specification, and it was too long to be fitted on the space allocated for it. The chemical engineers suggested that the reactor be split in two, have the reactors operating in parallel and the feed divided in two evenly (150m³/min of n-C4H10 on each half reactor), and that this solution would ensure the n-butane will remain within tolerance values (67.5%-72.5%). The operations manager did not like the idea because it will require additional instrumentation, pumps, piping, valves, etc. to handle a parallel flow stream. FE nBut i-C4H10 FyBut FnBut 2 FnBut 2 -L/2 -1/2 X= 70% Original design ► X=? Proposed solution by Chem. Engineers The mechanical engineers proposed an alternative solution: to carefully bend the end of the reactor, so it will fit in the space allocated. Even though the chemical engineers keep warning about backmixing (Hint: think CSTR), the mechanical engineers insisted conversion will remain within tolerance values if the flowrates, temperature and all other operation parameters remain the same. The operations manager liked the savings linked to the "bend the reactor" idea, implemented it and installed the modified reactor. Even though all operating conditions remain the same, the conversion obtained is now below specs, reaching a conversion of only 65%...
FnBut FnBut X= 70% X= 65% Original design Proposed solution by Mech. Engineers a) Was the proposal by the chemical engineers correct in their prediction "cut the reactor in half, run in parallel with half the flowrate on each, we will get the same conversions"? Justify your answer using mole balances and ideal reactor equations b) Using mole balances and ideal reactor equations, quantitatively explain the reason for which the bended reactor has resulted in a conversion of 65% instead of 70%.
Transcribed Image Text:FnBut FnBut X= 70% X= 65% Original design Proposed solution by Mech. Engineers a) Was the proposal by the chemical engineers correct in their prediction "cut the reactor in half, run in parallel with half the flowrate on each, we will get the same conversions"? Justify your answer using mole balances and ideal reactor equations b) Using mole balances and ideal reactor equations, quantitatively explain the reason for which the bended reactor has resulted in a conversion of 65% instead of 70%.
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