Ethanol Concentration Measurement

An easier way would be to do careful volume measurement, and blending.

We have ratio control control loop designed for the same.

The concentration measurement will be done at the outlet of the tank, to cross verify & correct any changes.

30% +/-what%?

As ethanol and water have similar densities, more or less, the problem is that the concentration curve is flat-ish. A small change in density yields a large change in concentration. Further, nothing has been stated about temperature variations.

The smart money is still on volume measurement and blending.

Is there an agitator in the tank?

What is the mean residence time in the tank (volume divided by output flowrate)?

If ratio control is in place, why is the tank there?

can you measure with a Alcohol Refractometer? There relatively inexpensive, about $100.00-$150.00 for a good one.

Yes you can, but it may not be practical.

I have Micromotion Coriolis sensors that continously measure both density & temperature (both are required for this!) very accurately; I would imagine that competing brands offer similar features.

You would have to know the level of water purity initially as this will affect its density. Then you will have to blend the 2 materials (you can meter them in through the sensor to obtain an accurate feed), circulate them through the sensor & read the density & temperature, ensuring that it is consistent. Then you will have to derive the concentration of the ethanol/water solution from the density & temperature measurements, keeping in mind that this will exhibit a mid-range depression of the density & cannot be taken from a linear scale.

Did I mention that these things are jolly expensive?

Or- you could use a load cell mounted vessel, check your water purity and the batch cerificate of analysis for the supply ethanol (which should also tell you what denaturant & the level used, which will also throw your density calculation off kilter) and calculate the required quantities of each. In the end this (or the process of metering it through the sensor) will probably actually be more accurate than the value you derive from your calculations.

You haven't told us if the analysis is required for a batch certificate or what the purpose is, or how accurate your check needs to be. So you can also easily directly check the Brix level with a refractometer as mentioned earlier, or take a sample and check it in a specific gravity cup on a lab balance and perform your calculations. Either of these cost far less than a mass sensor; you have to be the one to determine what fits your need.

Just watch "Moonshiners", they put it in a jar and shake it, they can tell exact amount of ethanol by the bubbles or you could use a hydrometer.

Use an ohm meter. I do not know if you are making the Ethanol but a friend of mine owns a brewry and a distilary. ( Spelling sorry) He just checks the conductivity. That is assuming you have calibrated the meter and that all things are consistant as any change in mineral content in the H2O will change the reading of the ohm meter. If we assume all is relativly = at all times as far as quality and that the mix is mixed then you should be fine. If it were me I would do that and get a pair of variable valves and control them using Natiional instraments to program a small computer to Monitor the conductivity and if it is off in one direction or the other the valves can be changed to get the mix back to what ever proof you want. 30% Ethanol would be 60 proof. Not sure what you are making here. But regardless you can have any programer do this for you or use National instraments to set it up without knowing anything aboout programing and control the valves. That again Assuming the water and Ethanol are consistant. it has to be very constant else you can be off a few %. for example 1 tsp of Backing soda or Sodium Cloride in a gallon of water will through thing totaly out of kilter unles that amount is always the same. So you make one batch and make sure it is exact and take the measurmant. that is you base. then install the electrodes and make sure they are secure as the distance beteen them can not change. One reason I like this way is you can have the readout monitored from anywhere and or controled from anywhere. All of the ways including densaty mesurments all depend on the consitancy of the materials and the mixing. The fellow that said to do what the moonshiners do is acctualy the best. Or just take a taste or two. I am not trying to be funny. Jim

We used to do that in college, 60 proof from pure grain alcohol.

30% by Volume, or Weight?

Alcohol molecules "Nest" in the molecular spaces of water,making concentrations calculations vary between the two methods.

Big difference if measurement is critical to a downstream process.

More info required.

A refractometer is the quickest, cheapest and best way.

You can make a mix with a known cheap fluorescent dye in the ethanol. Mix homogeneous and use a UV light and Photocell (working in the emitting spectrum) and measure the output through a looking glass. That is how we use ethanol coatings on high speed paper coatings. (300 m/min) Works very well. You will need to make a calibration first.

Since it is a batch process and not a continuous flow it should be easy to use a hydrometer. Try an internet search on "measuring alcohol content with a hydrometer".