Ethanol wt% to vol%

[TBeam]

I am at an ethanol refinery. We are measuring the wt% of ethanol in our beer prior to distillation. I measure the volume rate of this beer into the distillation system. I would like to convert the wt% ethanol in the stream to vol% to allow me to calculate the max 200 proof ethanol production from this stream. I've been told to multiply the wt% by 1.2, 1.23, and 1.26 by different people. I know this is temp dependent, but I don't need to be so exact. I believe these numbers may come from mixing with water and not the stream I have. The sg of the beer is 0.9385 and the sg of the stream after ethanol is removed is 0.9795 (still contains 0.05 wt% ethanol).

 

Can anyone help and maybe explain it also?

 

Thanks

[Bignose]

A water and ethanol mixture forms a non-ideal mixture. The varied wt% values you have been given may all be correct, it is not going to just be temperature dependent, but also dependent on the concentrations of water and ethanol.

 

What you want is a phase diagram. You should be able to find one in one of many different references at a good university library. One of the CRC handbooks of chemistry and physics should have it, for example.

 

It is almost (almost) unbelievable that an ethanol refinery wouldn't have such information available somewhere to a very high accuracy.

[J.C.MacSwell]

I am at an ethanol refinery. We are measuring the wt% of ethanol in our beer prior to distillation. I measure the volume rate of this beer into the distillation system. I would like to convert the wt% ethanol in the stream to vol% to allow me to calculate the max 200 proof ethanol production from this stream. I've been told to multiply the wt% by 1.2, 1.23, and 1.26 by different people. I know this is temp dependent, but I don't need to be so exact. I believe these numbers may come from mixing with water and not the stream I have. The sg of the beer is 0.9385 and the sg of the stream after ethanol is removed is 0.9795 (still contains 0.05 wt% ethanol).

 

Can anyone help and maybe explain it also?

 

Thanks

 

You can't just multiply to change wt% to volume %.

 

For example, by weight, if it was 99% water and 1% ethanol, you would need a very different multiplier than if it was 99% ethanol and 1% water.

 

The density of ethanol is 0.789 and 1 divided by 0.789 = 1.26742712 so at 1% ethanol the 1.26 suggestion from above would be pretty close.

 

At 99% ethanol this multiplier obviously wouldn't work.

[UC]

You're biggest problem is that a volume of ethanol added to a volume of water does not make a volume equal to the other two volumes you just added, and the amount of volume contraction has a lot to do with the proportions.

 

If you use the volume of the input stream and the specific gravity (density), you can calculate the mass of the input stream.

 

Volume x mass/Volume = mass.

 

Then, apply the wt% you measure to figure out what the total mass of ethanol present. Using the specific gravity and volume of the waste stream, figure out how much ethanol is not being recovered. Then, you need the density of anhydrous ethanol and you have your number.

[CaptainPanic]

Check out this old thread... it contains the definition of the volume% in post #6. I posted practically the same question, and with the answers in that thread, I was able to do the calculation.