Density data 3

[ridge2481]

hi

I am in need of data for ethanol that relates concentration (% v/v) and density at various temperatures. I have looked into Chemical engineering hand book, they have the density data at wt%.
If anyone can suggest any reference material to get density data for ethanol concentrations in % v/v it would be very helpful.

Thanks
RW

 

[katmar]

If you Google for "AlcoDens" you will find this.

 

[ridge2481]

Dear Katmar,

Thanks for your valuable suggestion. It did help me but its a commercial software that i have to buy.
1) I am actually looking for some data reference book, like Perry in which the conversions are listed.

2) can you suggest any other method that can be developed on our own to relate the densities of ethanol both in % v/v and % w/w.

Thanks in advance
RW

 

[25362]

At the end of the following site you'll find a table showing the data you are after:

http://www.miracosta.edu/home/dlr/210exp5.htm

 

[ridge2481]

Dear 25362

Again thanks for the link, its exactly what I wanted. But still, I would like to ask your suggestion, since a website cannot be quoted as a reference, is there any standard data book that could provide this kind of data?

Regards,

RW

 

[25362]

And I thought the link was insufficient since it shows the correlations at only one temperature...

Try books on enology, they might have the wanted info. Good luck.

 

[katmar]

RW,

You can combine both your points (1) and (2) above as they really are the same thing. Use Perry (or whatever) as your reference and build a spreadsheet to convert M/M to V/V percent.

The Perry table will give you the density (and therefore the volume of a given amount) for the mixture and the pure ethanol at your chosen temperature(s). The spreadsheet can convert these to percent. It doesn't get easier than this.

 

[25362]

Katmar, please give your opinion on the following comments:

1. Ethanol and water mixtures show volume contraction.

2. The actual (molar) volumes "occupied" by ethanol and water molecules in a mixture depend -however not linearly- on their mol fraction, with an inversion point at about an ethanol mol fraction of 0.08.

3. The volume proportions of the separate components aren't equal to those after mixing -at a given temperature-.

If the above is correct, the vol% of ethanol, as calculated from the unmixed components just by using their densities and that of the mix, wouldn't reflect the actual volume percentage it has in the homogeneous mix.

The question, of course, is whether when one says 100 proof, one means 50% vol of the unmixed ethanol, or 50% vol after the solution is made.

Thanx.

 

[katmar]

To 25362 and RW,

The first thing we must do is agree on our definitions, otherwise we will go down the same confusing route as when we start using "Standard" temperatures and pressures to do gas calculations.

I will not even try to define 100 proof because it means different things in different countries and will only add to our confusion. I have also seen people work with v/m and m/v strengths (see the last column in 25362's table), but this should be avoided at all costs!

In the potable alcohol industry the commonly used strength parameter of vol/vol percent means the volume of pure ethanol (before mixing) in a given volume of mixture (converted to percent of course).

For example, to make a solution of 60 v/v % you would take 60 ml of pure ethanol and then add water until the volume of the mixture reached 100 ml. As 25362 has pointed out, ethanol and water mixtures show volume contraction. This means you would find that you had added 43.6 ml of water to take the 60 ml of ethanol to 100 ml of mixture.

So our mixture has a volume strength of 60% on an ethanol basis and 43.6 % on a water basis. I cannot do design calculations with numbers like this (that don't add up to 100!), so I always work in mass %. Unfortunately the volume strength convention is very deeply entrenched in the industry, so calculation results always have to be converted back to a volume basis.

25362 - this convention goes way back into history and has nothing to do with anything so scientific as "partial molar volumes". If anyone is doing ethanol calculations on this basis it will be in a lab somewhere and not out in industry.

RW - having gone through all this explanation I must apologise to you for saying nothing could be easier. I suppose because I work with these numbers on a regular basis it seems easy to me. But it is potentially a very confusing subject. Please forgive me if I am going overboard by now giving too much detail, but for the sake of clarity let me work through one example of a m/m to v/v conversion.

I have taken the following example from the table referred to by 25362 (which is at 20 degrees C). Perry has the same data, expanded for more temperatures.

For a mixture with a mass (weight) strength of 75% the density is 0.85564 g/ml. Working on a basis of 100 gram of mixture, we can calculate that it contains 75 gram ethanol and 25 gram water. The volume of this 100 gram of mix is 100.0/0.85564 = 116.87 ml.

At 20 deg C pure ethanol has a density of 0.78934 g/ml (from the same table). The 75 gram of ethanol therefore has a volume (before mixing) of 75.0/0.78934 = 95.02 ml

The strength on a volume basis is therefore (95.02 * 100.0)/116.87 = 81.30%, which agrees exactly with the figure given in 25362's table.

I recently did some work in a potable ethanol distillery where we overcame this confusion on the ethanol flow rates by using Coriolis Meters for the flow meters. These meters read out in mass flow units, but of course the client wanted to know the strength in volume % and to know the flowrate in volumetric terms. Fortunately the Coriolis Meters also give density and temperature signals, so we were able to put correlations into the DCS system to give everybody the numbers they wanted.

Hope this clears up the confusion
regards
Katmar

 

[25362]

Katmar, thanks for the enlightening explanation.

Therefore, for those of us that aren't acquainted with the definitions of ethanol-water concentrations, there are three possible vol% estimations given the mass proportions:

1. The industrially-accepted one, explained by Katmar, based on the volume of pre-mixed ethanol (from density values) divided by the (contracted) volume of the mix as obtained from converting its mass into volume using (tabulated) density; in this example 81.3%.

2. The "physical chemistry" approach that contends to express the right "actual" concentration, based on "corrected molar volumes", nearing 80% vol. for this example.

3. The premix estimation, that discards any volume contraction, resulting from dividing the volume of 75 gr ethanol by the sum of the volumes of 25 gr of water and 75 gr ethanol, which would bring the result for the given example to about 79.1% vol.. This estimation would concur with the results obtained when separating and recovering ethanol using, for example, distillation.

Thanks again.

 

[ridge2481]

Dear Katmar and 25362,

thanks for the help...

Regards and good luck

RW