Multidimensional gas chromatography for the characterization of permanent gases and light hydrocarbons in catalytic cracking process

An integrated gas chromatographic system has been successfully developed and implemented for the measurement of oxygen, nitrogen, carbon monoxide, carbon dioxide and light hydrocarbons in one single analysis. These analytes are frequently encountered in critical industrial petrochemical and chemical processes like catalytic cracking of naphtha or diesel fuel to lighter components used in gasoline. The system employs a practical, effective configuration consisting of two three-port planar microfluidic devices in series with each other, having built-in fluidic gates, and a mid-point pressure source. The use of planar microfluidic devices offers intangible advantages like in-oven switching with no mechanical moving parts, an inert sample flow path, and a leak-free operation even with multiple thermal cycles. In this way, necessary features such as selectivity enhancement, column isolation, column back-flushing, and improved system cleanliness were realized. Porous layer open tubular capillary columns were employed for the separation of hydrocarbons followed by flame ionization detection. After separation has occurred, carbon monoxide and carbon dioxide were converted to methane with the use of a nickel-based methanizer for detection with flame ionization. Flow modulated thermal conductivity detection was employed to measure oxygen and nitrogen. Separation of all the target analytes was achieved in one single analysis of less than 12 min. Reproducibility of retention times for all compounds were found to be less than 0.1% (n=20). Reproducibility of area counts at two levels, namely 100 ppm(v) and 1000 ppm(v) over a period of two days were found to be less than 5.5% (n=20). Oxygen and nitrogen were found to be linear over a range from 20 ppm(v) to 10,000 ppm(v) with correlation coefficients of at least 0.998 and detection limits of less than 10 ppm(v). Hydrocarbons of interest were found to be linear over a range from 200 ppb(v) to 1000 ppm(v) with correlation coefficients of greater than 0.999 and detection limits of less than 100 ppb(v).