Application of advanced pyrolysis for the analysis of biogeochemically and environmentally significant macromolecular organic materials : microfossils, macerals and drilling fluid additives

摘要

Polymers are omnipresent in the living world. All organisms contain different types of natural polymers that are responsible for different tasks, e.g. the formation of the molecular framework (lignin, cellulose) and energy reservoirs of plants (starch) or building up the genetic substance (DNA). Dead biomass is subjected to various abiotic and biotic transformation processes. With ongoing sedimentation the influence of increased temperature and pressure leads to further, partly significant, alteration of the original chemical structure, depending on its stability. Manmade macromolecules are another important group. These synthetic polymers are used in various fields of application and can be considered as ubiquitous. Some of them can be exposed to the environment in different ways and may disturb the aquatic and terrestrial biosphere. The chemical analysis of macromolecular substances is quite challenging due to their high molecular mass and, thus, their high boiling points. Spectroscopic methods as well as destructive degradation techniques are widely applied to characterise those polymers. The present study examined bisaccate pollen, handpicked out of six kerogen concentrates, with thermal maturities ranging from immature (0.48% VRr) to overmature (1.45% VRr). The main aim was the analysis of the thermal alteration of bisaccates in comparison to the bulk kerogens. Therefore, spectroscopic and pyrolysis methods were applied. The results obtained from invasive and non-invasive methods, as well as from micro- and macro analyses were compared. FTIR, µ-FITR and Laser-Pyrolysis–GC/MS (La-Py–GC/MS) analyses showed similar trends, for instance defunctionalisation and increasing aromatisation. Results from Curie Point–Pyrolysis-GC/MS (CP-Py–GC/MS) differed significantly, especially at higher stages of maturity. In addition to the spatially resolving analyses the kerogen concentrates were sieve fractionated (10 µm, 10–20 µm and 20–40 µm) and each fraction examined separately. The results of all fractionations were similar with regard to general trends with increasing maturation. The amorphous fraction (10 µm) released the highest amount of aliphatic compounds at all thermal maturity levels. In summary, this study indicated that invasive and non-invasive methods are suitable for bulk and spatially resolving analyses of fossil macromolecular materials and their combination provided comprehensive information about the chemical composition of the sample material. The high potential of La-Py–GC/MS as a spatially resolving and time efficient pyrolysis method for the analysis of tiny particles was shown in the first part of this study. However, the energy of the laser beam is quite difficult to control and the final temperature difficult to determine. Therefore, six biomacromolecules of different chemical composition, geological age and thermal maturity were subjected to La-Py–GC/MS and CP-Py–GC/MS. The main objective was to obtain information about the comparability of both methods and to estimate the temperature of the laser beam. The qualitative composition of the pyrolysates was similar in both methods, whereas La-Py–GC/MS released shorter aliphatic chains. Some samples showed linear trends of the relative composition with increasing pyrolysis temperature. Here, the laser-temperature was estimated to be higher than the highest Curie-temperature applied in this study (920 °C). All in all, La-Py–GC/MS is a suitable method for the analysis of highly mature and/or mainly aromatic materials, whereas for extant or immature materials CP-Py–GC/MS is more recommended. In the third part, three synthetic polymers that are commonly used in drilling fluids were examined to identify specific marker substances for the identification of contamination caused by drilling activities. Reference materials of the main constituents of these drilling fluids (CMC, HEC, PAA) were analysed to detect potential indicators. Additional analyses of seven CMC-, HEC- and PAA-based drilling fluids detected all previously identified compounds. Pyrolysis analysis of drill cuttings, with no information about the applied drilling fluid(s) provided no evidence for the use of one of the previously analysed samples but spiking experiments proved their traceability. All in all, this study confirmed pyrolysis to be a suitable analytical method for the chemical characterisation of various extant and fossil biomaterials as well as synthetic polymers. Its reproducibility (CP-Py) and spatial resolution (La-Py) combined with highly sensitive detector systems (GC/MS) provide significant advantages compared to other degradation methods.