Fractional Distillation - Separation of Petroleum Hydrocarbons

INTRODUCTION:

This experiment was designed to determine the value of the HETP (height equivalent to a theoretical plate) of the column needed based on the efficiency of the packing material. This experiment uses fractional distillation and gas chromatography to separate, purify and analysis the composition of the fractions of a mixture of two petroleum hydrocarbons, toluene & cyclohexane. The distillation separates by using the difference in boiling points of the two components of the mixture. By collecting the distillation in different vials as the processes goes on, there is change in the purity of the fraction. The gas chromatography will analysis the percent composition of the mixture collected at varying temperature ranges.

MATERIAL & METHODS

As described in the directions of Experiment 6 page 57 and operation 27 in the appendix of the book, 40 mL equimolar mix of Cyclohexane and Toluene were distilled through a column of Copper packing material measuring 17.5 cm high. Column and flask were wrapped around sides with fiberglass and foil for insulation. Mixture was allowed to distill and was collected at described in direction on page 58. All vials were weighed, sealed and left for 2 weeks.

When returning the HETP vial had evaporated. All other fractions were subjected to gas chromatography analysis as described in operation 32 in the appendix of the book. Separation during chromatography is based on volatility of compounds, column properties (phenylmethylsilox) & length as well as the flow rate of mobile phase.

RESULTS

Total number of theoretical plates = 3 – the boiling flask = 2

Total number of theoretical plates = log (nA/nB)

Log ?

Let nA = moles of cyclohexane @ 83°C

Let nB = moles of toluene @ 83°C

Let ? = 2.33

Cyclohexane 3.91 g / 84.2 g/mol = 0.0464 x 0.8972 = 0.0517

Toluene 3.91 g / 92.2 g/mol = 0.0424 x 0.1028 = 0.0044

For Gas Chromatography results, see attached. 4 total pages.

See Table 1 for information listed below:

Started with 40 mL of mixture and distilled a total of 31.14g by weight. When distilling the first 5 drops of HETP weighed in at 0.10 g, but evaporated before the gas chromatography. At the 83°C range the fraction weighed 3.91g. At the 91°C range there needed to be 2 vials used and together their fractions weighed 12.91 g. At the 102°C range the fraction weighed 7.37g. And at the 107°C range the fraction weighed 6.85g.

See Table 2 & Graph for information listed below:

During gas chromatography at the 83°C range the percent composition was 89.72% Cyclohexane 10.28% Toluene with a retention time of 0.805 & 0.905 respectively. At the 91°C range the percent composition was 79.17% Cyclohexane 20.83% Toluene with a retention time of 0.806 & 0.906 respectively. At the 102°C range the percent composition was 28.20% Cyclohexane 71.80% Toluene with a retention time of 0.808 & 0.909 respectively. At the 107°C range the percent composition was 20.85% Cyclohexane 79.15% Toluene with a retention time of 0.806 & 0.909 respectively.

Reflux Ratio: 0.2820

Column height: 17.5 cm

ANALYSIS/CONCLUSIONS

Based on the equation from the lab manual on page 56 and the information collected during