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A multidimensional gas chromatographic (GC) method for on-line analysis of all gas-phase reaction products obtained from the selective oxidation of  n -butane to maleic anhydride in an automated catalyst testing reactor is described. A dimethylpolysiloxane megabore column and a multidimensional sequence of packed columns that contain molecular sieve 5A and Hayesep R are shown to provide resolution of  n -butane, maleic anhydride, various oxygen-containing byproducts, oxygen, nitrogen, and all total combustion products by using a single temperature programmed GC with simultaneous injection of two gas samples from a multiport valve. For applications where various C 1 -C 4  hydrocarbon byproducts are either known or suspected to be present in the product gas and precise resolution is required, an Al 2 O 3 /KCl PLOT column can be connected to the dimethylpolysiloxane column by using a series-bypass arrangement with a multiport valve. All hydrocarbons and oxygen-containing hydrocarbons are detected with a flame-ionization detector, and a thermal conductivity detector is used for the permanent gases, total combustion products, and  n -butane. To quantify the raw GC peak areas, both absolute and relative response factors are also derived for all species by using gas-phase and liquid-phase calibration standards. Comparisons between experimental and theoretical values for the relative effective carbon numbers of maleic anhydride with those of  n -butane are also used to confirm that solute adsorption is linear and reversible on the selected megabore column. Effective carbon numbers for the other analytes detected by the flame-ionization detector are also derived and compared with the theoretical values. Statistical characterization of the response factors and effective carbon numbers is also performed so that an assessment of the errors associated with any derived quantities in future applications of the method, such as gas compositions, reactant conversions, and product yields, will be possible. Incorporation of the proposed method into an automated fixed-bed catalyst test facility and typical results obtained for  n -butane oxidation to maleic anhydride over a known metal oxide catalyst are also described. Advantages of the proposed technique over previously reported GC methods for analysis of the reaction products from butane oxidation are also suggested.

A Multidimensional Gas Chromatographic Method for Analysis of n -Butane Oxidation Reaction Products