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How to Distill Butane From 2-Methylpropane

Although butane and 2-methylpropane are chemically identical, they have different properties which allow them to be separated by distillation. The key difference is in the shape of these molecules. Where n-butane is a chain of four hydrocarbon molecules in a row (represented as CH3CH2CH2CH3), the 2-methylpropane is shaped like the letter Y with one hydrocarbon in the attached to three others, represented as (CH3)2CHCH3. This structural difference results in different boiling points. N-butane's is 31.1 degrees F (-0.5 C), while 2-methylpropane's is 10.94 F (-11.7 C). You can thus distill the chemical with the lower boiling point off first to separate them. Because of the closeness of their boiling points, a fractionating distillation column is added to a regular distillation set up, but with the right equipment, you can easily do this yourself.

Things You'll Need

2 distilling flasks
2 clamp-stands
Fractionating column
Heat source
Glass still-head (also called a distilling adapter)
Glass thermometer
Thermometer adapter
Grease
Condenser column
2 keck clips
Bent glass vacuum adapter

Instructions

- 1
  Pour your liquid butane and 2-methylpropane mixture into one of the round-bottomed distilling flasks. Secure the flask in a clamp above your heat source (which should be off).
- 2
  Dabble two drops of grease 180 degrees apart on the end of the fractionating column that fits into the distilling flask. Put this end in the flask and turn it to spread the grease around the whole junction. Make sure to apply the grease where the top of the junction is to prevent the grease from mixing with your solution; This grease makes a seal to keep your solution from escaping once it is vaporized.
- 3
  Grease the ends of your glass Y-shaped still-head where it fits into the top of the fractionating column and into the condenser column (that is, the two prongs at the angle of your Y-shaped still-head which is then turned up side down). Secure the end that is on the straight line of the Y into the fractionating column in the same way you did with the column and the flask, by turning it a few times.
- 4
  Fit the other greased end of your still-head into the condenser column and give it a few turns to create the grease seal. Secure the condenser column in place with another clamp-stand. Make sure the small glass hose connection nearest the still-head is facing up.
- 5
  Secure the bent glass vacuum adapter to the condenser with a keck clip with the claws of the clip holding the ridge of the adapter securely to the column. Use your other keck clip to connect the other distilling flask to the bottom of the adapter. No grease is needed for this step as your chemical will be a liquid at this stage.
- 6
  Insert your thermometer into its adapter such that the red bulb is sticking through the rubber end past the end of the glass side. Grease the glass end of your thermometer adapter and put the thermometer head into the top of your still-head. Adjust the thermometer head so that the top of the red bulb is exactly even with the Y-joint of your still-head. Don't forget to give the adapter a twist to spread the grease around to create a vapor seal!
- 7
  Turn your heat source on a very low power to make your solution boil very gently. You want the temperature to raise to the 2-methylpropane's boiling point very slowly.
- 8
  Watch the temperature as it rises to just about 11 degrees F. When it reaches this temperature you will see it stop rising for a while, as all the 2-methylpropane boils off through the column. You will also start seeing drops of liquid dripping into the collecting flask as the boiled vapor is then condensed by the cold air in the condensing column. When the temperature begins to rise again from the 11 degrees, shut off and remove your heat source. You have now successfully separated your 2-methylpropane from the butane still in the first flask by distillation!

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