Abstract
A method for determining thiophenic-compounds by means of reaction gas chromatography in conjunction with a sulfide ion-selective electrode detector has been developed.
Components in the sample are separated on a gaschromatographic column using hydrogen as carrier gas.The effluent is passed through postcolumn reactor at 900°C where the separated components undergo hydrogenolysis in the presence of a platinum catalyst. Hydrogen sulfide is formed from sulfur compounds. The decomposition gases are introduced into an absorption tube in which a suitable absorption solution flows at a constant flow rate and hydrogen sulfide is absorbed by the absorption solution. The solution emerging from the absorption tube is passed into a micro-cell equipped with a sulfide ion-selective electrode as the sensing element. Changes in the sulfide ion concentration in the solution are detected by the corresponding changes in the ion electrode potential. The difference in the potential between the ion electrode and the reference electrode is fed to an antilog converter circuit and a signal directly proportional to the ion concentration is recorded. A chromatogram showing only peaks due to sulfur compounds is obtained.
In this method, the effect of temperature on the hydrogenolysis reaction was investigated. Nonthiophenic compounds decomposed nearly completely at all temperatures down to at least 700°C. Although aromatic sulfides were relatively resistant to hydrogenolysis, more than 30% of diphenyl sulfide and diphenyl disulfide were still decomposed at 700°C. On the other hand, thiophenic compounds are unreactive up to 700°C and decompose only slightly at 750°C. Consequently, when the temperature of postcolumn reactor where each component undergoes hydrogenolysis is maintained at 900°C, a chromatogram which peaks of all sulfur compounds are recorded is obtained. However, as the temperature is decreased, only the peaks due to thiophenic compounds decrease rapidly and a chromatogram which only the peaks due to thiophenic compounds are completely removed is obtained at 700°C. In this method, sulfur compounds can be easily distinguished from other compounds and thiophenic compounds can be readily identified from other sulfur compounds by comparing both chromatograms.
