Fast Thermoanalytical Profiling of Petrochemical Samples by Evolved Gas Analysis using Photoionsation-MS and Ultra-Fast Gas Chromatography

摘要

Mass Spectrometry (MS) with soft photoionisation (PIMS, enabling fragmentation-free ionisation of organic compounds including saturates such as alkanes) enables the direct detection of traces of intact molecules from complex organic vapours [1]. PIMS is well for Evolved Gas Analysis (EGA) in Thermal Analysis (TA). In particular it allows the determination of the molecular organic signatures (i.e. intact organic molecules) of desorption-, pyrolysis- and combustion-processes [2]. State of the art TA-PIMS systems were applied for detection of the evolved signatures of intact organic molecules from thermal analyses of petrochemical samples. In addition to the soft MS separation also a newly developed ultra-fast cycling gas chromatography technique was implemented. The fast cycling GC technique is based on a rapidly IR-radiation heatable (and quickly coolable) gas chromatograph inserted between the TA and PIMS device. The system allows separating isobaric compounds evolving from the thermal process. The TG-PIMS approach is used for the detailed analysis of the thermochemical behaviour of petrochemical samples. In the case of crude oil the yield and chemical composition of the different distillation fractions was determined (50-400 C). At higher temperatures cracking products of the non-volatile residue (resins, asphaltenes etc.) are fingerprinted. From very heavy matrices and source rock samples the amount and composition of the thermally extractable volatile organic compounds were determined. For examples the composition of shale-oil and -gas as well as the temperature-dependence of the hydrocarbon formation dynamics was measured. Another application is the profiling of asphaltene fractions. Asphaltenes properties are important for oil production and refining (e.g. for flow assurance). The photoionisation system was applied to differentiate between the aromatic cores and aliphatic cracking products of the pyrolyzed higher molecular weight fractions of heavy crudes. In summary the potential of TA hyphenated to soft photoionisation mass spectrometry for industrial- as well as for fundamental-research applications in the petrochemical field is demonstrated and discussed. The TG-PIMS and TG-fast GC-PIMS results suggest a broad applicability of the laboratory instruments for simulation and optimization of industrial petrochemical processes.