Experiment 6: Fractional Distillation.
Separation of Petroleum Hydrocarbons
A mixture of cyclohexane and toluene were separate from one another by fractional distillation in order to measure the composition of each fraction and prepare the sample for gas chromatography.
Distillation has been used since antiquity to separate the components of mixtures. This method has been used to manufacture different organic chemicals but the most recent application is the refining of petroleum in order to produce fuels, lubricants and petrochemicals. In this experiments, the separation of 2 distilates were carried out using the differences in boiling points ...view middle of the document...
When the temperature reached 75° c the first fraction collector was replaced with the second fraction collector. When the temperature reached 80°c, the second fraction collector was replaced with the third fraction collector. When the temperature reached 83°c the third fraction collector was replaced by the fourth fraction collector. When the temperature reached 90°c the heat source was removed and the liquid that remained in the column was drained into the boiling flask, and the flask was cooled the remaining liquid was disposed in the organic waste and the area was cleaned. The fractions were then used for analysis in a gas chromatography machine. The temperature was recorded prior to each distillation fraction and after each 2ml of distillate which was recorded in table 1. The system was turned off and cooled down letting the remaining condensed vapor drain into the round bottomed flask. Using a micro syringe, 2 to 3 micro milliliters was obtained from each vial. Each sample was placed into a gas chromatography machine which recorded areas of peaks and the data was printed out for later use.
Vial | Temp. Range (C ) |
1 | 75-80 |
2 | 80-83 |
3 | 83-88 |
4 | 88-90 |
5 | 93 |
Flow Chart of Process
Mixture of 1 & 2
Mixture in flask in a fractional distillation setup
Collect fractions in labeled vials
Run each sample through gas chromatography machine
Vial 1: 85.55% x .663g/84g/mol = 6.75 x 10-3 cyclohexane
14.44% x .663g/92g/mol =1.04 x 10-4 toluene
Vial 2: 73.92% x 5.93g/84g/mol = 5.21 x 10-2 cyclohexane
26.07% x 5.93g/92g/mo/l = 1.68 x 10-2 toluene
Vial 3: 50.83% x 3.99g/84g/mol = 2.41 x 10-2 cyclohexane
49.16% x 3.99g/92g/mol = 2.13 x 10-2 toluene
Vial 4: 21.30% x 5.631g/84g/mol = 1.42 x 10-3 cyclohexane
78.69% x 5.631g/92g/mol = 4.81 x 10-2 toluene
Vial 5: 0.31% x 4.24g/84g/mol = 0.015 x 10-2 cyclohexane
99.68% x 4.24g/92g/mol = 4.59 x 10-3 toluene
*as the separation continues, the amount of cyclohexane is less at the end in vial 5 and the toluene amount is near 100%
There are different things that affect the distillation process and the results of the mixture composition analysis. The degree of separation not only depends on the column packing used but also on such factors as stability of the heat source, the rate of distillation and the way the column is packed. Good separation requires a low rate of distillation to maintain a high reflux ratio. In this experiment the insulation step was omitted, even though the insulation is to help prevent heat loss that might reduce efficiency or prevent distillation entirely. The assumption here is that the composition of each component is not as accurate as it would be if the insulation step was carried out. Another problem often encountered is flooding of the distillation column, in which the column becomes partially or entirely filled with liquid. Flooding was not observed in this experiment which...