Separation And Molecular Characterization Of Ketones In A Low Temperature Coal Tar

Oxygen-containing compounds are abundant in low temperature coal tars(LTCT),which are mainly presented in phenolic structures.Ketones have been known as another major oxygen-containing species in coal tars,however the molecular composition of these compounds were rarely characterized by mass spectrometry due to its relative weak molecular polarity which restraint it for the selective ionization from complex hydrocarbon matrix.Given their reactivity,ketones may have much effect on the performance and storage stability of coal tars.It is of great significance to study the chemical and physical properties of ketone compounds.In this study,we used a LTCT sample that from Lurgi coal gasification plant as the research objective.In addition to extrographic extraction and acid-base extraction,a reasonable separation scheme of enriched ketones from LTCT was set up through the chemical derivatization and the hydrolysis-reduction of derivatives.Thereby we achieved the separation of the long alkyl ketone compounds from the aromatic ketones which do not contain the side chain or have only short side chain.Isolated ketones were characterized by gas chromatography(GC)coupled with a quadrupole mass spectrometry(MS),high resolution Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS)and Orbital ion trap mass spectrometer(Orbitrap MS).A separation method of enriched ketones from LTCT was developed by two extrographic extraction.After the separation and purification steps,more detailed molecular composition information of ketones could be seen in GC-MS.There was no obvious loss in purification process.However,there was also a slight bulb in each subfraction,which contained other compounds that were similar in polarity to the carbonyl group and can not be completely identified.This separation method is difficult to realize the subject of concentrating ketones with high purity.A reasonable separation scheme of enriched ketones from LTCT was set up through chemical derivatization and hydrolysis-reduction of derivatives.Chemical derivatization and hydrolysis reduction were reverse reactions under different conditions.The Girard T reagent reacts with ketones under weakly acidic conditions and introduced a charged quaternary ammonium moiety into the poorly ionizable carbonyl compounds to form water-soluble hydrazones.The resulting derivatives show an enhanced sensitivity in ESI in the positive mode and are reversibly reduced to the original ketones under strongly acidic conditions to selectively separate long alkyl ketone compounds from the aromatic ketones which do not contain the side chain or have only short side chain.The method was validated by ketone model compounds and performed on a LTCT successfully.The ketones were assigned to 11 molecular classes: O1-5、O1S1、N1O1-4、N2O1 with O1 showing highly relative abundance.The long chain alkyl ketones such as aliphatic 2-,3-,4-ketones,alkylcyclopentanones,alkyl phenyl ketones and aromatic ketones such as indanone,cyclopentenone,Tetrahydronaphthalenone,acetonaphthone,dihydro-phenanthrenone,benzophenone,dihydro-acenaphthenone,Dihydrogen benzoinrenone,fluorenone,fluorenyl formaldehyde,anthrone,anthracene formaldehyde,acetylanthracene,acetylphenanthrene,acetylfluorene,benzofluorenone were identified by GC-MS.In addition,C18-isoprenoid methyl ketone and one or two oxygen-containing terpenoids and steranes were identified in the low temperature coal tar for the first time.In this paper,the molecular composition of ketones in low temperature coal tar was deeply studied on molecular level.Many new understandings have been obtained,which provide a reference for the composition analysis of ketone compounds.