Tuesday, April 8, 2014

Experimental Setup for Reversed-Flow Gas Chromatography (RF-GC) system

The experimental arrangement consists of a small modification of a commercial gas chromatograph (Figure 1), so that it includes a six-port gas-sampling valve, and a simple cell placed inside the chromatographic oven. This cell suppresses the effects of the carrier gas flow on the physicochemical phenomena-taking place in the stationary phase.

Figure 1:       Shimadzu GC-14B
The apparatus used is a conventional gas chromatograph (Shimadzu GC-14B) with a flame ionization detector contained in its oven (Figure 2) with two sections of lengths l’ and l of a stainless-steel chromatographic column containing no chromatographic material. The empty stainless steel is a ¼ inch chromatographic tube with 4 mm internal diameter and length, L= 28.5 cm and l=l’=57 cm. They are connected at the junction x=l’ by a ¼ inch Swagelok tee union. Another sample ¼ inch union is used to connect a short tube (2 cm) containing 4 ml of liquid at the end of diffusion column L.


Figure 2:       Instrumentation of the reversed flow gas chromatography technique for the simultaneous measurement of the diffusion coefficients and rate transfer coefficients of the evaporating liquids.
A stainless-steel diffusion column, consisted of the section z, was connected perpendicularly at its upper end to the middle of the column l’+l (57 cm+57 cm). The reactant (AR Grade) was injected at a middle point of the column as the stationary phase, and the direction of carrier gas flow was reversed from time to time instead of stopping it. This created extra chromatographic peaks ‘sited’ on the continuous signal. At the end of sectiozn is located a container, in which the liquid was contained. The end D1 of the sampling column l’+l was connected, via a six-port valve, to the carrier gas (nitrogen) supply, while the other end D2 was connected to the flame ionization detection (FID) system. After waiting for the monotonously rising concentration– time curve to appear in the detector signal, we started the chromatographic sampling procedure by reversing the direction of the carrier gas flow for 6 s, which is a shorter time period than the gas hold-up time in both column sections l and l’. When the gas flow was restored to its original direction, sample peaks were recorded. The pressure drop along l+l’ was negligible and the pressure inside the whole cell was 1 atm. The carrier gas flow-rate was kept constant (1.0 cm3 s -1).







Figure 3:       Internal close-up of the RF-GC system

Reference:

Mohammad, H. H., Mohd. Zain, S., Atta Rashid, K., & Khalid, K. (2013). Study the Effect of Imposing Surfactants toward the Evaporation of Low Molecular Weight Alcohol. International Journal of Environmental Science and Development, 4(4), 5. doi: 10.7763/IJESD.2013.V4.381