Receiving high-grade alcohol (195 proof / 97.5%)

[Alex_Sor]

Receiving high-grade alcohol (195 proof / 97.5%)

To me on this forum, there were several appeals with similar questions.
People were wondering if they could get 195 proof/97.5% alcohol on the equipment they have, including using "Raschig rings" and tower heights up to 2 meters.

I see that this question needs to be explained in more detail.
Miracles do not happen in this life 🙂 unfortunately...

I decided to count some variants of "columns filled with Raschig rings" and this is what I got. I think it will be useful for everyone to see.

Regarding your case (if you have a question for me): I need to know the length of the nozzle, i.e. that part of the column, in height, where you want to fill the Rashig rings. I can calculate "theoretical plates" for your case. But I want to say right away: if the length is less than 1.6 meters, then you are unlikely to get more than 7 theoretical plates ...

The "theoretical plate" has an efficiency of 100%, and usually in practice it should be understood that the efficiency will be approximately 45=55%, i.e. To get one theoretical plate, you need to put two real ones.
Calculations (my calculations) show exactly "theoretical plates", which means that in order for you to achieve these indicators, you need to multiply the number of theoretical ones by 2. (Efficiency is usually = 45-55%).
Those. you need to double the height of the column (with backfilling with Raschig rings). But this increase doesn't always work...

Let's make an analytical calculation of the column (option 1):
Calculation of the column, column diameter = 6 inches, height of the part where the rings = 2 meters,
if you use ceramic Raschig rings 6 mm in size,
The alcohol content is 10% of the total. volume in a cube (tank) of the mixture.
Initial temperature 20 Celsius
Heating power 20000 W
Backfill height (part of column with Raschig rings) = 2 m
Distillation power 10000W
Column diameter 0.153 m (=6 inches).
Reflux (reflux number) = 1.8

Column Performance Evaluation:
Approximate estimate of the column:
Equivalent height = 1 theoretical dish (HETP): = 0.242 m
(depending on backflow ratio, nozzle type and size)
Number of theoretical plates: = 8.3 (height/HETP)
Boiling time: : 46 minutes (93.5 oC)

Alcohol yield per hour = 4.846 liters, 93.8% strength.

Larger Raschig rings (13mm size) result in fewer plates (5.4 with 13mm rings). So there's no way you can get 20 plates that would take the alcohol above 96%...

I played around with the numbers, and so, if you use "stainless steel spirals", you get 15.3 theoretical plates with a reflux ratio of 1.8, with 2 meters of backfill.
But the yield of alcohol will be only 95.2%...

In general, the task of obtaining alcohol above 96% is a very difficult task.
It is necessary to at least double the length of the pipe (height) or divide the column into two parts and put two columns of 2 meters in series. But this will add problems with alcohol condensate ... and in general, no one breaks the nozzle into two parts this is a bad decision.
In my country, 45-60 plate epuration columns are used to obtain 96+% alcohol.
This is a real industrial distillery.

You can try the solution named Paul Hall (Affordable Distillery), he has options with two columns with more plates and pumping intermediate alcohol back into the tank.
But I do not see (according to calculations) a solution how to push a solution with an alcohol yield of 96+% into a 2-meter column

You can try to use metal dishwashing nets as padding inside the column but I don’t have data for such a calculation. But it will add theoretical plates.