Comparison of microscale sealed vessel pyrolysis (MSSVpy) and hydropyrolysis (Hypy) for the characterisation of extant and sedimentary organic matter

Microscale sealed vessel pyrolysis (MSSVpy) and catalytic hydropyrolysis (Hypy) combined with gas chromatography–mass spectrometry have emerged in recent years as useful and versatile organic analytical and characterisation methods. Both now commercially available, these pyrolysis methods complement traditional flash pyrolysis analysis which can be limited by excessive degradation or inadequate chromatographic resolution of pyrolysates of high structural polarity. To assess the versatility and merits of these two pyrolysis methods they were separately applied to several organic samples reflecting different thermal maturities. This comparison revealed many product similarities, but also several important features unique to each. Both produced C27–C33 hopane products from a bacterial isolate and a membrane biofoulant from a water filtration system. Increased concentrations of higher MW and ββ-stereoisomeric hopanes detected by Hypy reflect more selective bond cleavage, attributed to a relatively short residence time and catalyst assisted reduction of volatilisation temperatures, of the mostly C35 (ββ-) bacteriohopanepolyol precursors established by corresponding LC–MS analysis. When applied to the asphaltene fraction of a biodegraded oil both pyrolysis methods were able to regenerate similar distributions of liquid n-alkanes and source diagnostic hopane and sterane biomarkers removed from the free phase of oil by the biodegradation. The detection of low MW (<C8) products was only supported with the online GC–MS analysis of the MSSVpy procedure. This advantage was again evident in the MSSVpy detection of low MW alkyl (<C2) thiophenes from the S-rich Kimmeridge clay. Similar distributions of higher MW alkyl benzothiophenes and alkyl dibenzothiophenes were detected directly by MSSVpy, and after derivatisation of the polar fraction of the Hypy extract, consistent with the sensitive detection of other heteroatom bound structural units previously demonstrated by both methods.