Distillation Adapter for On-The-Fly Sampling

By: Paula Freemantle, Chemfiles Volume 10 Article 4

Paula Freemantle
Product Manager
labware@sial.com

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Distillation is the most widely used bulk separation method used in the laboratory as well as industry. Beyond purifi cation, it is widely used to characterize complex fl uids (such as fuels) through measurement of the distillation curve, a plot of the boiling temperature against volume distilled. A common theme in both of these applications is the desire to understand the composition. In purifi cation, the goal is to monitor the distillation progress, and in fl uid characterization, one seeks to relate the composition to the temperature data.

The distillate sampling adapter (Figure 1) installed following a condenser or distillation column, can provide this important capability without the need for cumbersome, expensive and often unreliable fraction collectors.1-3 The fl ow of the distillate is focused to drop into a 0.05 mL “hammock” that is positioned directly below the fl ow path. The sampling port, equipped with a vacuum tight valve, allows access to the hammock with a standard chromatographic syringe, through a septum. To sample the distillate, one simply positions the chromatographic syringe, preferably equipped with a blunt tipped needle, in the well of the hammock. It is a simple matter to withdraw samples as the distillation progresses. The sample can then be directly injected into the gas chromatograph or spectrometer, or injected into an autosampler vial for analysis later. Indeed, any analytical technique that is applicable for liquid samples ranging in volume from 1 to 50 microliters can be used to characterize the distillate.

This adapter has been used for many complex fl uid analyses, including gasolines, diesel fuels, rocket kerosenes, jet fuels, crude oils, transformer fl uids, waste oils and arson accelerants. Some of the analytical techniques applied to distillate fraction analysis include gas chromatography (with mass selective, fl ame ionization and chemiluminescence detection), FTIR spectroscopy, Karl Fischer coulombic titrimetry and refractometry. The ability to couple quantitative analysis with the distillation opens the door to thermochemical determinations such as the enthalpy of combustion of fuels, as a function of distillate cut. The adapter has also been used to measure corrosivity of crude oil fractions, with a copper coupon test performed at various distillate cuts.

Figure 1: Distillate sampling adapter.

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References

  1. Bruno, T. J., Ott, L.S., Lovestead, T.M., Huber, M.L., The composition explicit distillation curve technique: relating chemical analysis and physical properties of complex fl uids. J. Chromatogr. 2010, A1217, 2703–2715.
  2. Bruno,T. J., Ott, L.S., Lovestead, T.M., Huber, M.L., Relating complex fl uid composition and thermophysical properties with the advanced distillation curve approach. Chemical Eng. Tech. 2010, 33,(3), 363–376.
  3. Bruno, T. J., Ott, L.S., Smith, B.L., Lovestead, T.M., Complex fl uid analysis with the advanced distillation curve approach. Anal. Chem. 2010, 82, 777–783.

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