Biogenic Carbon Fraction of Biogas and Natural Gas Fuel Mixtures Determined with 14C

This study investigates the accuracy of the radiocarbon-based calculation of the biogenic carbon fraction for different biogas and biofossil gas mixtures. The focus is on the uncertainty in the C-14 reference values for 100% biogenic carbon and on the C-13-based isotope fractionation correction of the measured C-14 values. The separately (AMS) measured CO2 and CH4 fractions of 8 different biogas samples showed C-14 values between 102% and 116% (pMC). The delta C-13 values of these samples varied between -6% and +31% for the CO2 fraction and between -28% and -62% for the CH4 fraction. The uncertainty in calculated biogenic carbon fractions due to uncertainty in the C-14 reference values depends on the available information about the origin of the used biogenic materials. It varies between +/- 0.5% and +/- 3.5% (absolute) depending on the type of biogas. A method is proposed to minimize this uncertainty for different groups of biogases. The calculated biogenic carbon fraction deviates up to +/- 2.5% for biofossil gas mixtures, if the applied isotope fractionation correction is based on the delta C-13 value of the mixed biofossil sample instead of the biogenic delta C-13 value. Combination of both error sources shows that the uncertainty in the calculated biogenic carbon fraction varies between +/- 0.7% and +/- 4.5%, depending on the type of biogas in the sample

RADIOCARBON DATING CREMATED BONE:A CASE STUDY COMPARING LABORATORY METHODS

Radiocarbon (C-14) results on cremated bone are frequently published in high-ranking journals, but C-14 laboratories employ different pretreatment methods as they have divergent perceptions of what sources of contaminants might be present. We found pretreatment protocols to vary significantly between three laboratories (Brussels [RICH], Kid [KIA], and Groningen [CIO]), which all have a long history of dating cremated bone. We present a case study of 6 sets of replicate dates, to compare laboratory pretreatment protocols, and a further 16 sets of inter-laboratory replicate measurements, which compare specific steps of the conversion and measuring process. The C-14 results showed dates to be reproducible between the laboratories and consistent with the expected archaeological chronology. We found that differences in pretreatment, conversion to CO2 and accelerator mass spectrometry (AMS) measurement to have no measurable influence on the majority of obtained results, suggesting that any possible diagenesis was probably restricted to the most soluble</p

Cross-comparison of last glacial radiocarbon and OSL ages using periglacial fan deposits

Two cores from a Weichselian periglacial alluvial fan were dated using 14C and OSL, to verify the reliability of both methods and check the upper dating limit of the 14C method. Both dating methods yielded a similar chronology for core Eerbeek-I, with infinite 14C dates for the lower part where OSL dates indicated ages of over 45 ka. Finite 14C dates were obtained throughout the core for Eerbeek-II, despite stratigraphic and OSL evidence suggesting ages beyond 14C limits. Apparently, additional chemical pre-treatment to remove younger carbon fractions did not work adequately for samples from this core. We hypothesize that this may be related to a larger influence of younger-age humin fractions in the mainly sandy Eerbeek-II deposits compared to those buffered by a thick peat layer of Eerbeek-I. We suggest that (local) stratigraphy, percolation and humification processes may impact 14C ages of organic deposits more than commonly assumed, and should receive more attention. In addition, we introduce a new method to assess robustness and validity of OSL dates and demonstrate the applicability of OSL dating methods in this setting. Our results highlight that the 14C method requires additional verification methods, such as OSL, for deposits older than 30 ka

Catalytic Depolymerization of Lignin and Woody Biomass in Supercritical Ethanol:Influence of Reaction Temperature and Feedstock

The one-step ethanolysis approach to upgrade lignin to monomeric aromatics using a CuMgAl mixed oxide catalyst is studied in detail. The influence of reaction temperature (200-420 °C) on the product distribution is investigated. At low temperature (200-250 °C), recondensation is dominant, while char-forming reactions become significant at high reaction temperature (&gt;380 °C). At preferred intermediate temperatures (300-340 °C), char-forming reactions are effectively suppressed by alkylation and Guerbet and esterification reactions. This shifts the reaction toward depolymerization, explaining high monomeric aromatics yield. Carbon-14 dating analysis of the lignin residue revealed that a substantial amount of the carbon in the lignin residue originates from reactions of lignin with ethanol. Recycling tests show that the activity of the regenerated catalyst was strongly decreased due to a loss of basic sites due to hydrolysis of the MgO function and a loss of surface area due to spinel oxide formation of the Cu and Al components. The utility of this one-step approach for upgrading woody biomass was also demonstrated. An important observation is that conversion of the native lignin contained in the lignocellulosic matrix is much easier than the conversion of technical lignin.</p

The protohistoric briquetage at Puntone (Tuscany, Italy):A multidisciplinary attempt to unravel its age and role in the salt supply of Early States in Tyrrhenian Central Italy

While processes involved in the protohistoric briquetage at Puntone (Tuscany, Italy) have been reconstructed in detail, the age of this industry remained uncertain since materials suited for traditional dating (14C dating on charcoal and typological dating of ceramics) were very scarce. We attempted to assess its age by radiocarbon dating organic matter and carbonates in strata that were directly linked to the industry. Microbial DNA and C isotope analyses showed that the organic matter is dominantly composed of labile organic matter, of which the age is coeval with the briquetage industry. Carbonates had a complex origin and were overall unsuited for radiocarbon dating: Shells in process residues exhibited a large, uncertain ‘marine reservoir effect’, hampering their use for dating the industry; the secondary carbonates in these residues had a quite varied composition, including much more recent carbonate that precipitated from infiltrated lateral run-off, as could be concluded from C and Sr isotope analyses. Dates found that were deemed reliable (c. 1000–100 cal BCE) show that this ancient industry, which started in the Late Bronze Age - Early Iron Age (1107–841 cal BCE), extended into the Roman Republican period and was contemporary with the saltern-based larger scale salt industry in Central Lazio

Radiocarbon-based determination of biogenic and fossil carbon partitioning in the production of synthetic natural gas

The applicability of the radiocarbon (C-14) method for the quantification of the biogenic carbon fractions at different stages of the Synthetic Natural Gas (SNG) production process is demonstrated in this study. The C-14-based biogenic carbon fractions were determined in process flue gas and raw SNG and were 38% and 89% respectively, for a mixture of wood and fossil lignite with 75 +/- 3% biogenic carbon as input material. The differences in biogenic carbon fractions between the input material, flue gas and raw SNG are caused by bio-fossil carbon partitioning during the SNG production process. This study demonstrates that the main bio-fossil carbon partitioning took place during the gasification of the input material. This is due to the large differences in volatility and char content of the wood and lignite materials. For the determination, verification or certification of the biogenic carbon fraction in process flue gas and (raw) SNG in the SNG production process, separate investigations of the gases are inevitable. The C-14 method is a useful and reliable independent method for these purposes. (c) 2015 Elsevier Ltd. All rights reserved

Carbon and nitrogen stable isotopes of well-preserved Middle Pleistocene bone collagen from Schöningen (Germany) and their palaeoecological implications

Carbon and nitrogen stable isotopes in bone collagen can provide valuable information about the diet and habitat of mammal species. However, bone collagen degrades in normal circumstances very rapidly, and isotope analyses are therefore usually restricted to fossil material with a Late Pleistocene or Holocene age. The Middle Pleistocene site of Schöningen, dated to around 300,000 years ago, yielded bones and teeth with an exceptionally good state of collagen preservation. This allowed us to measure reliable biogenic carbon and nitrogen stable isotope ratios for different herbivorous taxa from the families Elephantidae, Rhinocerotidae, Equidae, Cervidae, and Bovidae. The results provide insights regarding the palaeoenvironmental setting in which Middle Pleistocene hominins operated. The vegetation consumed by the herbivores from the famous spear horizon originates from open environments. During the climatic Reinsdorf Interglacial optimum, the landscape seems to have been relatively open as well, but certainly included parts that were forested. The results also indicate some niche partitioning; different herbivore species used different plant resources. For instance, the horses seem to have been predominantly browsers, while the straight-tusked elephants were feeding chiefly on grass

Reassessment of the C-13/C-12 and C-14/C-12 isotopic fractionation ratio and its impact on high-precision radiocarbon dating

The vast majority of radiocarbon measurement results (C-14/C-12 isotopic ratios or sample activities) are corrected for isotopic fractionation processes (measured as C-13/C-12 isotopic ratios) that occur in nature, in sample preparation and measurement. In 1954 Harmon Craig suggested a value of 2.0 for the fractionation ratio b that is used to correct C-14/C-12 ratios for shifts in the C-13/C-12 ratios and this value has been applied by the radiocarbon community ever since. While theoretical considerations suggest moderate deviations of b from 2.0, some measurements have suggested larger differences (e.g. b = 2.3, measured by Saliege and Fontes in 1984). With the high precision attained in radiocarbon measurements today (+/- 2%), even a relatively small deviation of b from 2.0 can impact the accuracy of radiocarbon data, and it is, therefore, of interest to re-evaluate the fractionation corrections. In the present study, the fractionation ratio b was determined by independent experiments on the chemical reduction of carbon dioxide (CO2) to elemental carbon (graphitization reaction) and on the photosynthetic uptake of CO2 by C-3 and C-4 plants. The results yielded b = 1.882 +/- 0.019 for the reduction of CO2 to solid graphite and b = 1.953 +/- 0.025 for the weighted mean of measurements involving C-3 and C-4 photosynthesis pathways. In addition, the analysis of over 9600 full-sized OX-I and OX-II normalizing standards measured between 2002 and 2012 confirms b values lower than 2.0. The obtained values are in good agreement with quantum mechanical estimates of the equilibrium fractionation and classic kinetic fractionation as well as with results from other light three-isotope systems (oxygen, magnesium, silicon and sulfur). While the value of the fractionation ratio varies with the relative importance of kinetic and equilibrium fractionation, the values obtained in the present study cluster around b = 1.9. Our findings suggest that a significant fraction of all samples ("unknowns") would be shifted by 2% (16 radiocarbon years) or more due to this effect: for example, for b = 1.882, between 16.8% and 25.9% of almost 60,000 radiocarbon values measured at the Keck Carbon Cycle AMS facility between 2002 and 2012 would be affected. The implications for radiocarbon dating and its accuracy are discussed. (C) 2017 Elsevier Ltd. All rights reserved