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Solvent Extraction Problems
Don't Phase Me! |
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Chapter 17 - Single Stage Solvent Extraction
In this problem set you are given ternary systems (translation: three chemicals) that form two immiscible liquids phases. One phase (the solvent) will be used to extract a third chemical (the solute) from the other phase (the diluent).
17.1 100 mol/min of methanol with 15 mol% benzene is extracted with 100 mol/min of pure heptane at 20oC.
a. Construct an LLE graph with benzene mole fraction on the ordinate (y-axis) and methanol on the abscissa (x-axis). For your convenience, the data and a formatted graph are found in Excel "MBH Data" below. Now, find the extract and raffinate compositions and amounts using graphical methods.
b. Fit the extract and raffinate curves with polynomial functions: y = f(x). Also, construct a graph of tie line slope vs. corresponding extract benzene composition and fit it with a polynomial. These will represent your equilibrium data - the compositions of any phases in equilibrium will satisfy all three polynomial equations. For your convenience, a DIY PFD for this problem is already set up in Excel "MBH Data". Find the extract and raffinate compositions and amounts using mathematical methods. Compare parts a and b. In fact, plot F-M (mix point)-S and R-M-E compositions on the graph and it should look just like your graphical solution.
Why this system? Methanol can be added to gasoline to increase octane number. Unfortunately, under some conditions of temperature and composition, it can phase separate. Benzene and heptane are model compounds to represent the very complex composition of gasoline.
17.2 100 mol/h of a mixture with 70 mol% benzene and 30 mol% ethanol is extracted with 100 mol/h of pure glycerol at 25oC.
a. Construct an LLE graph with ethanol mole fraction on the ordinate (y-axis) and benzene on the abscissa (x-axis). For your convenience, the data and a formatted graph are found in Excel "BEG Data" below. Now, find the extract and raffinate compositions and amounts using graphical methods.
b. Fit the extract and raffinate curves with polynomial functions: y = f(x). Also, construct a graph of tie line slope vs. corresponding extract methanol composition and fit it with a polynomial. These will represent your equilibrium data - the compositions of any phases in equilibrium will satisfy all three polynomial equations. For your convenience, a DIY PFD for this problem is already set up in Excel "BEG Data". Find the extract and raffinate compositions and amounts using mathematical methods. Compare parts a and b. In fact, plot F-M (mix point)-S and R-M-E compositions on the graph and it should look just like your graphical solution.
