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green-owl
green-owl, Electrical Engineer
Category: Engineering
Satisfied Customers: 4834
Experience:  Lot of experiences with design, build of prototypes and production systems,
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TO DISTILL OIL IN A VACUUM COLUMN. i HAVE A GAGE THAT READS

Customer Question

i'M TRYING TO DISTILL OIL IN A VACUUM COLUMN. i HAVE A GAGE THAT READS IN KPA
0 TO A MINUS 100 AND THE SAME GAGE READS INCHS OF hg 0 TO 30. when WE OPERATE THE VACUUM PUMP, THE iNCHES .hG READS 26 WHAT DOES THIS MEAN? WE KNOW THAT OUR OIL WILL VAPORIZE AT AT ABOUT 730 f UNDER OUR VACUUM CONDITIONS WHAT IS THE TEMPERATURE THAT THE OIL WILL VAPORIZE AT 26 hg? WE ARE IN UTAH BUT I DON'T KNOW HOW HIGH WE ARE ABOVE SEA LEVEL. CAN YOU ANSWER MY QUESTIONS?
mIKE ********
Submitted: 7 months ago.
Category: Engineering
Expert:  green-owl replied 7 months ago.

Hi. 30 hg is milimeter of mercury, about 101 KPA. 26 hg is close to 88 KPA. That mean your vacuum pump is working. When vaporizing oil you want a very low pressure because it help to prevent needing too high temperature. You can't heat oil too much, it need to stay below the particular "smoke point" for the type of oil you have.

Expert:  green-owl replied 7 months ago.

Oil is a complex compound. it is easier to know the evaporation by individual compound. Here is a list of various compound that may be present in it at 101 KPA of pressure:

http://www.engineeringtoolbox.com/boiling-points-fluids-gases-d_155.html

You then have to find an evaporation table of temperature vs pressure for each separate compound in the oil.

Expert:  green-owl replied 7 months ago.

Here is what that kind of curve look like for water:

http://www.engineeringtoolbox.com/boiling-point-water-d_926.html

If you want to know the temperature for "your oil" as a whole , you need to find the temperature of the hardest to evaporate compound. But at that point the operation would be pointless as a distilation process.

Expert:  green-owl replied 7 months ago.

As for the elevation concern, this is only a matter if you are in an open environment to the air. If you are in a closed environment like in a vaccum, the absolute pressure given by the instruments will need to be used.

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