Distillation Reflux Ratio Calculator

Work out distillation reflux ratio instantly with clear inputs, formula shown and shareable results.

About Distillation Reflux Ratio Calculator

Reflux ratio is the liquid returned to the column divided by the distillate withdrawn. Since everything condensed at the top either returns or leaves, the vapour reaching the condenser is L + D, and the internal ratio L/V is what sets the slope of the operating line. Returning 80 against 20 drawn off is R = 4, meaning 80% of the overhead vapour goes back down the column.

Formulas

Reflux ratio

R = L / D

Vapour and internal ratio

V = L + D, and L/V = R / (R + 1)

Worked example

With the default values below, Distillation Reflux Ratio Calculator returns Reflux Ratio R of 4.000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Liquid returned to the columnminimum 0 kmol/h: 80 kmol/h
Distillate drawn offminimum 0 kmol/h: 20 kmol/h

Results

Reflux Ratio R: 4.000
Vapour Rising To The Top Tray: 100.00 kmol/h
Internal Reflux Ratio L/V: 0.8000
Overhead Vapour Returned: 80.00%

Step by step

1Values used
2Reflux ratio
3Vapour and internal ratio
4Reflux Ratio R= 4.000
5Vapour Rising To The Top Tray= 100.00 kmol/h
6Internal Reflux Ratio L/V= 0.8000
7Overhead Vapour Returned= 80.00

Assumptions and limits

The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is a higher reflux ratio better for purity?

More liquid returning means more vapour-liquid contact per tray, so separation improves - at the cost of reboiler duty and condenser load.

What is total reflux?

Taking no distillate at all, so R is infinite. It gives the maximum separation and the minimum number of trays, and is used for start-up and testing.