- #1

- 2

- 0

## Main Question or Discussion Point

Haven't taken a course in distillation in a long time and now myself and some others are working on getting a fuel ethanol still going and wanted to do the calculations before we moved forward.

We have a beer that is 12% alcohol and reaching a purity of 90% EtOH in the distillate.

The mass balances I believe would be:

total balance:

F= D + B

and

Ethanol balance:

F*xf=D*xd + B*xb

where F is the feed rate, D is distillate rate, and B is bottoms rate. xf is mole fraction ethanol in feed, xd is ethanol fraction in distillate, and xb is ethanol fraction in bottoms.

I figure the xd=0.9 and xf=0.12, what would the xb be equal to? Is it dictated by the VLE?

We have a McCabe program that does the step offs for the ideal plates, and it allows you to set the mole fractions, can these be set arbitrarily?

Additionally, are mole fractions equivalent to volume fractions (assuming ideality)? I know mass fractions are not equivalent to mole fractions. If mole fractions are not equivalent to volume fractions, how do i convert from volume fraction to mole fraction?

Thanks!

We have a beer that is 12% alcohol and reaching a purity of 90% EtOH in the distillate.

The mass balances I believe would be:

total balance:

F= D + B

and

Ethanol balance:

F*xf=D*xd + B*xb

where F is the feed rate, D is distillate rate, and B is bottoms rate. xf is mole fraction ethanol in feed, xd is ethanol fraction in distillate, and xb is ethanol fraction in bottoms.

I figure the xd=0.9 and xf=0.12, what would the xb be equal to? Is it dictated by the VLE?

We have a McCabe program that does the step offs for the ideal plates, and it allows you to set the mole fractions, can these be set arbitrarily?

Additionally, are mole fractions equivalent to volume fractions (assuming ideality)? I know mass fractions are not equivalent to mole fractions. If mole fractions are not equivalent to volume fractions, how do i convert from volume fraction to mole fraction?

Thanks!

Last edited: