Example 11-3: Adiabatic Liquid-Phase Isomerization of Normal Butane. Can you explain why the CSTR volume is  smaller than the PFR volume?

Example 11-3

Normal butane, C₄H₁₀, is to be isomerized to isobutane in a plug-flow reactor. Iso-butane is a valuable product that is used in the manufacture of gasoline additives. For example, isobutane can be further reacted to form iso-octane. The 2014 selling price of n-butane was $1.5/gal, while the trading price of isobutane was $1.75/gal. Once again, you can buy a cheaper generic brand of n–C₄H₁₀ at the Sunday markets in downtown Riça, Jofostan, where there will be a special appearance and lecture by Jofostan’s own Prof. Dr. Sven Köttlov on February 29th, at the CRE booth. This elementary reversible reaction is to be carried out adiabatically in the liquid phase under high pressure using essentially trace amounts of a liquid catalyst that gives a specific reaction rate of 31.1 h^–1 at 360 K. We want to process 100000 gal/day (163 kmol/h) and achieve 70% conversion of n-butane from a mixture 90 mol % n-butane and 10 mol % i-pentane, which is considered an inert. The feed enters at 330 K.
1. Set up the CRE algorithm to calculate the PFR volume necessary to achieve 70% conversion.
2. Use an ODE software package (e.g., Polymath) to solve the CRE algorithm to plot and analyze X, X_e, T, and –r_A down the length (volume) of a PFR to achieve 70% conversion.
3. Calculate the CSTR volume for 40% conversion. The economic incentive $ = 1.75/gal versus 1.50/gal
Additional information:

Transcribed Image Text:

AHRX=-6900 J/mol n-butane, Activation energy-65.7 kJ/mol KC-3.03 at 60C, CA0-9.3 mol/dm3=9.3 kmol/m3 Butane i-Pentane CPn-B=141 J/mol K,CPi-P=161 J/mol K, CPI-B=141 J/mol K=141 kJ/kmol K