Using gas chromatography to characterize a direct coal liquefaction naphtha
Speciation of oxygenated compounds in direct coal liquefaction naphthas is essential considering their important roles in coal conversion reactions. This study attempts to characterize them as fully as possible using gas chromatographic systems. Firstly, GC–MS was deployed allowing the identification of a few ketones, alcohols, and phenols. This conventional analysis was complemented by the application of GC–GC-FID aiming to overcome the coelutions highlighted when using one-dimensional gas chromatography. Heart-cutting and comprehensive two-dimensional gas chromatography were used and the comprehensive system led to better performances as expected considering the complexity of the matrix. In fact, it allowed the identification of more than a hundred of oxygenated compounds belonging to five chemical families: alcohols, ketones, furans, acids and phenols. Average response factors of each of these families were determined by GC×GC-FID using calibration curves and vary from 1 (hydrocarbons) to 2.50 (carboxylic acids). Thanks to a breakthrough columns set involving a trifluoropropyl stationary phase, alcohols and phenols which represent around 14% of the sample were fully identified. A detailed quantification of these species was carried out for the first time in such matrices using the determined response factors. It was concluded that 90% (w/w) of the alcohols are aromatic (phenols), 5% (w/w) are cyclic and 5% (w/w) are linear. A quantification of hydrocarbon families was also achieved and shows that the matrix is mostly naphthenic (56%, w/w), but also contains aromatics (22%, w/w) and paraffins (8%, w/w). This detailed characterization leads to a better understanding of coal conversion processes and is essential to convert them into synthetic fuels.