THE APPLICATION OF GAS ADSORPTION CHROMATOGRAPHY TO THE ANALYSIS OF CHEMICAL REACTIONS IN FLOW SYSTEMS S. A. GREENE Aerojet-General Corporation, Azusa, California
G A S adsorption chromatography has proved an elegant method for the separation and quantitative analysis of mixtures of gases and low-boiling liquids.' Usu/o-l
ally, gas or liquid samples from chemical reactions are obtained and introduced into appropriate columns for separation and analysis. The problems associated with the sampling and transference of gases and liquids can be further complicat,ed when one is manipulating samples which contain condensed phases. I t is the purpose of this paper to describe an apparatus in which a chemical reaction takes place in a portion of a gas chromatography loop. Reaction products are swept into the chromatography column by the carrier gas, and sampling is obviat,ed. The method also offers an excellent method for studying the kinetics of gas-phase reactions in flow systems. APPARATUS AND PROCEDURE
The apparatus was the one usually used for gas chromatography and is illustrated in Figure 1. Helium . manocarrier-gas flow rates of 50 ~ m . ~ / m i nwere
metrically measured by the pressure drop (ca. 6 in. H,O) across a calibrated orifice. Adsorption columns, containing 10 ft. of 40/60 mesh alumina or charcoal, were fabricated from '/,-in. copper tubing and immersed in an oil bath which could be heated to 240°C. The detector, a Gow-Mac thermal conductivity cell, was used in conjunction with a 0-1, 0-20-mv. adjustahle-range recording potentiometer. I t should he noted that sample and reference channels of the thermal conductivity cell are not connected in series, but that the gas flows are individually controlled. This arrangement permits the column temperature to be raised during elution while maintaining constant pressure-flow conditions in both sides of the detector. Raising the column temperature is necessary when one is eluting samples which have wide boiling ranges. During heating and elution, the sample channel-pressure regulator is continually adjusted in order to maintain constant flow through that side of the detector. The reactor for the experiments reported here was 1-ft. long, '/r-in.-thick stainless-steel tubing. For all experiments, the middle 2-in. portion was heated to redness with a burner. Gaseous reactant material was introduced through the sample volume, whereas liquid material was injected uith a hypodermic syringe through a short length of rubber tubing, immediately upstream of the reactor. RESULTS AND DISCUSSION
Figure 2 shows the results obtained with 1.0 c ~ n . ~ (STP) of air carried through the reactor which had its 2-in. center packed with charcoal and heated to redness The charcoal column, initially a t ambient temperature, was heated to 160°C. in 40 minutes in order to elute carbon dioxide. Figure 3 illustrates the products obtained from the thermal decomposition of 20 mg. of acetone carried
Figure 3. Ssperation of Decomposition Products of Acatona
JOURNAL OF CHEMICAL EDUCATION
through the unpacked reactor tube. Reaction products mere sevarated in an alumina column which was heated to 80061. in 20 minutes. Any water present would be adsorbed by the alumina. Figure 4 shows the thermal decomposition of 30 mg. of n-oentane. The alumina column, heated to 170°C. in 60 minutes, effected separation. Although reaction products were not analyzed quantitatively, this could easily he accomplished after preliminary calibration. This technique would seem to be well suited to kinetic studies. Reactor variables such as temperature, geometry, and catalyst could easily be altered, whereas residence time could he varied by changing carrier-gas-flow rates or reactor volume. This technique need not be limited to single reactants, since gas or liquid mixtures can be easily introduced into the chromatography loop.
VOLUME 34, NO. 4, APRIL, 1957
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