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I fired up my ps II high cap last evening with just water in the kettle to check for leaks as instructed to do before first run. I had approx 8 gal in the kettle. I have 2 ea. 4500 watt 240 volt elements both running off 110. RSC has not arrived yet so I was just experimenting. To speed the process along a little, after 45 min. of element heating, I fired up the turkey fryer under the diffuser plate and voile, after another 20 min or so I had a good rolling boil, steam out of the condenser, and 190 deg at the therm at the top of the column. It was slowly climbing (about 1 degree every minute) and the therm read about 75 deg. Then in a matter of seconds I had a full boil. My question is approx. what temp are you looking for before you ease the heat (turn off the propane and work off the element(s) and roll on the water supply? I don't want to overcook it and waste it, but I don't want to sit around for 4 hours either waiting for it to get hot?
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You will not be able to adjust boil based on temperature. Once you are at a boil the liquid temperature will not increase beyond its boiling point, regardless of how much heat you add.
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Rank: Junior Member Groups: Registered
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The basis of the question is an observation of the climbing temp in the column at the top where the thermometer is located. It went up slowly and then all of a sudden became a foil rolling boil (with water ). I was wondering at what temperature (roughly) do you expect to see on the thermometer when the wash is close to say 165 degrees so I would know when to start easing off the heat and rolling on the cooling water. I understand that the boiling point of a liquid is a finite number. Once it boils it continues to boil at its boiling temp not rise.
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Until vapor reaches the top of your column the temperature will remain at roughly ambient temperature. As a result, when vapor finally reaches the top of the column you will see the temperature suddenly jump from ambient temperature to that of the vapor (eg. 212F for water). It sounds like this is what you experienced, and it is completely normal.
When running in reflux I suggest keeping an eye on how high up the column the vapor is and turning on the cooling water when vapor reaches about half way up the column, as it will begin to rise more quickly at that point. You can touch the side of the column to find how high the vapor has gone, but BE CAREFUL, as the column will be extremely hot where the vapor has reached. The entire time that the vapor is rising it is heating the column and column packing, and simultaneously being cooled, so it is gradually separating and setting up an equilibrium in the column. This can seem to take forever, but when vapor finally breaks past the cooling lines the temperature at the column head will suddenly jump, and a few seconds later you will start to collect distillate. :-)
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Rank: Junior Member Groups: Registered
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THATS the info I needed!! Thank you very much. I was looking for a way to tell when that "time" was getting close and now I know what to look for. I was feeling the heat in the column as it was rising but had no idea it would be that dramatic when it hit the top. I will be more aware of the rising heat in the column and make my adjustments before it hits the top and gets out of control. Thanks again.
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Rank: Administration Groups: Administrators
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Not a problem. It can be a shock to see the temperature suddenly jump like that, but when you consider that the lowest boiling point compound in a wash is around 149F then it stands to reason that you will not see any significant change in temperature at the top of the column until that first compound gets there- and then you will go from 0-60 (or in this case 70-150  ) almost instantly.
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