2 replies to this topic

[Dumpmeadrenaline]

Given an initial mixture of 25 % Ethanol and 75 % Water at room temperature. I want to produce a product with an Ethanol concentration of 75%. 

In practice, how is separation carried out?

I Imagine the apparatus for batch distillation requires the following

1) A heat source which causes the initial mixture to vaporize

2) An outlet tube for the vapor to pass.

3) A condenser above the pot which cools the vapor back to a liquid stream.

4) A water pump.

 

As heat is added to the mixture, vapor molecules escape the liquid surface and they come into contact with the interior of tube which is cooler. If they lose enough energy to the interior they will condense and drip down back to the pot. The interior warms and progressively the following vapor molecules will travel further the tube. The process of heating, vaporizing, contacting and cooling continues until they reach the condenser and condense into a liquid stream which is more concentrated in the more volatile component, namely Ethanol. To ensure the  desired purity is achieved the process is stopped and the distillate is analyzed.

 

1) If the mixture is heated to high temperatures, the vapor will contain more of the less volatile component worsening the desired distillate purity. So, how to find the "right" temperature at which the vapor molecules will have enough energy to escape the liquid surface, move through the tube as vapor into the condenser and still have the desired purity.

 

[Pilesar]

You do not pick the boiling temperature. The boiling temperature depends on the composition and pressure. As vapor is removed from the distillation stage, the liquid composition changes. Therefore the boiling temperature also changes continually. You can treat this system as a simple single-stage vapor/liquid flash. You just begin the boil and collect the distillate. Stop the boil when the desired concentration of collected distillate is reached. At the start of the distillation run, the vapor overhead will be higher than 75% ethanol. At the end of the batch run, the vapor overhead will be lower than 75% ethanol. Your task would seem to be to first determine the composition of the first drop of condensed vapor. What would be the composition of the vapor after 1% of the liquid were boiled away? What would be the composition at 2% and 10% and 50% and all the points in between? Add up the component flow rates of those drops over time to calculate the bulk distillate composition and total quantity. When that is determined, the batch distillation procedure would be something like: 1) charge vessel with feed, 2) boil off x% of the charge while condensing the vapor and collecting the distillate.

  About 90 years ago or so, my grandfather operated his own ethanol distillery and my father helped him avoid governmental interference and deliver product to customers. I don't know if he used single-stage batch distillation, but he would have had better product yield if he had used multiple stages in his distillation.

[breizh]

Hi,

I've attached a few documents to support your work .

Good luck

Breizh