Work Instruction: Calculating Weight and Volume Percents for Ethanol Formulas
Rev 1.0, 3/5/03, PD
One of the most important things to remember when calculating weight percents for
ethanol formulas is that theory does not equal practice in regards to 190 proof ethanol.
This issue comes into play when customers require that the %water is reported by weight
or volume.
For instance, 190 proof Ethanol is considered to be 95% Ethanol and 5% water.
However when you make 190 proof Ethanol, due to the contraction of the ethanol-water
azeotrope it actually takes 6 gallons of water and 95 gallons of 200 proof ethanol to make
100 gallons of 190 proof ethanol.
Therefore:
When calculating weight and volume percent of 190 proof ethanol take the total volume.
Multiply the volume by 95% to come up with the Ethanol component. Then multiply the
total volume by 6% to come up with the water component.
For instance. If you have a tanker of 190 proof Ethanol and its filled to 7,000 gallons the
volume by ethanol is 7,000 x 0.95 and the volume by water is 7,0000 by 0.06.
In order to get the true original volumes you divide the individual amounts by the total
amount. Keep in mind however that as soon as you mix the water with ethanol the 101
gallons of material (95 ethanol and 6 water) will contract to 100 gallons. Technically
speaking you end up with 100 gallons of 190 proof ethanol that contains 101 gallons of
ethanol and water if separated.
Because of this phenomena, 190 proof ethanol is often reported as 190 proof ethanol and
the water component is not split out. If that becomes necessary then many companies
have chosen to report weight percent, because the while the volume of 101 gallons of
material changes to 100 gallons, the weight of 101 gallons of material (95 gallons of
ethanol and 5 gallons of water) does not change. (95 gallons of pure 200 proof and 5
gallon of pure water does not equal the weight of 100 gallons of 190 proof ethanol)
Calculating Weight Percent of 190 formulas where the water must be reported:
In order to get the weight percent, multiply the total volume by 95% for Ethanol and 6%
for water. Multiply the gallons of ethanol by 6.61 lbs. per gallon and the water by 8.33
lbs per gallon. Total the weights and divide each individual number by the total to get the
weight percents. If you have a more complex formula add each component into the mix
likewise.
If you need to be very precise then take the proof of the product. Calculate the % water
by dividing the proof by 2 and subtracting from 100. Now multiply this number by 1.2%
to get the true percentage of water.
Example: You have a 7,000 gallon load of SDA 39C, 190 proof. You must report the
weight percent of each component. The proof of the tanker is 190.2 You made this
tanker by taking 6,930 gallons of 190 proof ethanol and adding 70 gallons of DEP to it.
190.4 / 2 = 95.2 – 100 = 4.8% water x 1.2 = 5.76% true water by volume.
0.0576 x 6,930 = 399 gallon x 8.33 = 3325 lbs.
.952 x 6,930 = 6,597 gallons x 6.61 = 43,609 lbs.
70 gallons of DEP x 9.1lb per gallon = 637 lbs.
Total weight = 47,571 lbs
Wt % water = 3325/ 47571 = 6.99%
Wt% DEP = 637/ 47571 = 1.33%
Wt% Etoh = 43609/ 47571 = 91.67%
Round everything to equal 100%
II.) The second way of doing this is by using the SG formula worksheet (WI changing
SG).
You can use this formula to calculate the true volume percent of water in a 190 proof
formula and then follow the same procedures above.