JOHN: I'm gonna briefly describe
how to use this interactive simulation
for multi-stage batch distillation.
The idea is we place one kilomole
of a binary mixture in the still.
We let the system get to steady state
before the simulation is even started.
And steady state is obtained by having
complete reflux, total reflux.
And then, when we hit "collect,"
we collect in this flask,
'cause it says here an amount to evaporate
one-tenth of moles, so I'm showing the simulation
after we've already evaporated one-tenth of a mole.
This is the second flask.
And we started out with initial mole fraction
of 0.25 of component B.
That's something that we can change with the slider.
As some is evaporated, notice now
the mole fraction is 0.17, and the mole fraction
when we start to collect this second flask
is gonna be 0.92 initially,
and that happens when we hit this "collect" button here.
Now, we can change the amount that evaporates.
Instead of evaporating one-tenth a mole each time,
we could make it two-tenths of a mole, for example.
0.25.
We can change the number of equilibrium stages,
and more equilibrium stages gives us better separation.
We can change the reflux ratio.
Higher reflux ratio gives us better separation.
And then we can select what we display on the right side.
Right now, selected the x-y plot,
but I could select the temperature x-y plot,
or I could select a view of the flask
that we are collecting.
So far, we've collected one.
It would show what's the composition in that flask.
And then, there's a "reset" button
when we want to restart, change mole fractions,
change stages, et cetera.
So, the simulation is set such that
when the moles in the still gets to 0.2,
the simulation stops, we can't evaporate anymore.
So, what we're gonna do now is look at
the actual simulation and observe
how, as we change things, the system changes.
So, here's the simulation, and let's
increase the number of equilibrium stages.
And then, when we evaporate a tenth of a mole,
we do that by hitting "collect,"
and we see we're collecting the first batch,
first flask, and the mole fraction is 0.92,
so we've enriched from 0.25 to 0.92,
mole fraction of B, and then, of course,
the mole fraction of B in the still
has gone down because we preferentially
depleted B, the more volatile component.
If I hit "collect" again,
we'll collect the next 0.1 moles,
and now, the mole fraction is decreased
in the second flask because you've depleted it
in the still, and we can continue doing that
until we get down to two-tenths of a kilomole in the flask.
But notice, now we're dramatically decreasing
the amount of B in the still.
We've actually done a pretty good separation.
The remaining liquid in the still
is 96% of component A.
Now, we could look, instead of the collective flask,
we could look at the x-y plot.
And let's reset this to make it a little easier to see.
And so, when we start out,
mole fraction of B in the still is 0.5.
That's the blue dot in the diagram, the x-y diagram.
And the mole fraction we're collecting is 0.99,
so you can see, with a batch distillation,
we have the potential to get very high
concentrations, very high separations, and that's
the point here, the red point.
And then, as we collect,
these compositions shift on the x-y plot.
So now, the mole fraction in the still is decreasing,
and also the mole fraction in the distillate is decreasing.
Continue to do that,
goes down some more.
Now, instead of the x-y plot,
we can look at the T-x-y plot.
And let's continue to collect.
So, of course, both mole fractions
are decreasing, and notice,
the temperature in the still in increasing.
The blue dot, I'll do one more collection,
you can see the temperature in the still
continues to go up.
If we look at the...
Hold the mouse over the stages,
we can see the compositions and the temperature
in each stage.
Here, we can see the composition being collected.
Let's reset this.
We can get better separations
by increasing the number of equilibrium stages
and increasing the reflux ratio.
And so I'm going to display the flask if we...
And let's collect more.
We collect, notice now, the mole fraction's 0.997
of the initial material coming over,
so with more stages and high reflux,
we can get very high purity component B.
So the first 0.19 moles, kilomoles,
that we collect, is 99.6% of component B,
and we've depleted a significant amount of B in the still.
So, best distillation has the potential
to give us very high separations,
if we have stages and reflux.