Aromaticity and degree of aromatic condensation of char

The aromatic carbon structure is a defining property of chars and is often expressed with the help of two concepts: (i) aromaticity and (ii) degree of aromatic condensation. The varying extent of these two features is assumed to largely determine the relatively high persistence of charred material in the environment and is thus of interest for e.g. biochar characterization or carbon cycle studies. Consequently, a variety of methods has been used to assess the aromatic structure of chars, which has led to interesting insights but has complicated the comparison of data acquired with different methods. We therefore used a suite of seven methods (elemental analysis, MIR spectroscopy, NEXAFS spectroscopy, 13C NMR spectroscopy, BPCA analysis, lipid analysis and helium pycnometry) and compared 13 measurements from them using a diverse sample set of 38 laboratory chars. Our results demonstrate that most of the measurements could be categorized either into those which assess aromaticity or those which assess the degree of aromatic condensation. A variety of measurements, including relatively inexpensive and simple ones, reproducibly captured the two aromatic features in question, and data from different methods could therefore be compared. Moreover, general patterns between the two aromatic features and the pyrolysis conditions were revealed, supporting reconstruction of the highest heat treatment temperature (HTT) of char

Aromaticity and degree of aromatic condensation of char

The aromatic carbon structure is a defining property of chars and is often expressed with the help of two concepts: (i) aromaticity and (ii) degree of aromatic condensation. The varying extent of these two features is assumed to largely determine the relatively high persistence of charred material in the environment and is thus of interest for, e.g., biochar characterization or carbon cycle studies. Consequently, a variety of methods has been used to assess the aromatic structure of chars, which has led to interesting insights but has complicated the comparison of data acquired with different methods. We therefore used a suite of seven methods (elemental analysis, MIR spectroscopy, NEXAFS spectroscopy, ¹³C NMR spectroscopy, BPCA analysis, lipid analysis and helium pycnometry) and compared 13 measurements from them using a diverse sample set of 38 laboratory chars. Our results demonstrate that most of the measurements could be categorized either into those which assess aromaticity or those which assess the degree of aromatic condensation. A variety of measurements, including relatively inexpensive and simple ones, reproducibly captured the two aromatic features in question, and data from different methods could therefore be compared. Moreover, general patterns between the two aromatic features and the pyrolysis conditions were revealed, supporting reconstruction of the highest heat treatment temperature (HTT) of char.Keywords: Aromaticity, Stability, Aromatic condensation, Pyrolysis, Char, Biochar, Pyrogenic organic matter, Heat treatment temperatur

Translating analytical pyrolysis fingerprints to Thermal Stability Indices (TSI) to improve biochar characterization by pyrolysis-GC-MS

Biochar thermosequences produced from the charring of poultry manure and freshwater macroalgae feedstocks between 300 and 700 °C were analyzed by pyrolysis-GC-MS to assess the nature of the thermochemical conversion of N-rich feedstocks. With increasing charring temperature (TCHAR), the products of intact lignin, protein and polysaccharides decreased whereas those of charred aromatic domains (monocyclic and polycyclic aromatic hydrocarbons, benzonitriles) increased. These results are in agreement with thermosequences obtained from lignocellulosic feedstocks under the same analytical conditions. Therefore, we aimed to create a universal proxy of the degree of thermochemical alteration of biochar thermosequences from diverse series of feedstocks (gorse wood, chestnut wood, rice straw, poultry manure, freshwater algae and tannin) using Principal Components Analysis (PCA). From the PCA the relation of pyrolysis products with charring intensity was established and translated to Thermal Stability Indices (TSIp), which then gave rise to calculations of TSI of the biochars (TSIb). The TSIp varied only slightly between the different feedstocks suggesting that they could be used in future research to interpret pyrolysis fingerprints for a wide range of different biochars. In addition, TSIb can be used as a thermostability proxy for biochars and were found to be more reliable than other pyrolytic proxies such as the benzene/toluene or naphthalene/C1-naphthalenes ratios. This study marks the first attempt to develop a single proxy of stability for biochars at TCHAR from pyrolysis fingerprints using 157 common pyrolysis products. These proxies will provide a simple measure for the usefulness of a biochar for C sequestration and/or soil amelioration

Design of reinforced high strength concrete beam-column joint

130 σ.Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Δομοστατικός Σχεδιασμός και Ανάλυση των Κατασκευών”Στην παρούσα μεταπτυχιακή εργασία αναλύσαμε το σχεδιασμό στοιχείων εξωτερικών κόμβων δοκών –υποστυλωμάτων από οπλισμένο σκυρόδεμα υψηλής αντοχής. Αρχικά σχεδιάσαμε τους ακραίους κόμβους σύμφωνα με τις διατάξεις των ισχυόντων ευρωπαϊκών κανονισμών EC2 και EC8 .Στη συνέχεια υπολογίστηκε η αντοχή των ακραίων κόμβων και ο οπλισμός τους με μία νέα μέθοδο σχεδιασμού ,η οποία υιοθετεί ένα μηχανισμό αντίστασης αυτού του διαγώνιου θλιπτήρα για την παραλαβή και μεταφορά των δυνάμεων που ασκούνται στους κόμβους από τα στοιχεία που συντρέχουν σε αυτούς. Χρησιμοποιήθηκαν δοκίμια με τρεις διαφορετικές διατάξεις του φορέα ,για μήκος δοκού l=1,20 m και l=3,00m αντίστοιχα για σκυρόδεμα αντοχής C50 και C90 και χάλυβα B500C. Για τους υπολογισμούς χρησιμοποιήθηκαν οι μέσες τιμές των αντοχών των υλικών . Στο τέλος της εργασίας επισυνάπτονται δυο παραδείγματα σχεδιασμού ακραίων κόμβων δοκού –υποστυλώματος και με τις δυο μεθόδους.In this thesis we analyzed the design of reinforced high strength concrete beam – column joint. We design beam – column joints in accordance with the earthquake-resistance design provisions of European codes EC2 and EC8. Then we calculate the strength and the reinforcement of the beam – column joints with a new design method , which adopts the diagonal strut mechanism of resistance for transferring the forces which are applied to the joints by the elements that exist in them. We test three different arrangements of the structure for beam length l = 1,20 m and l = 3,00 m respectively for concrete C50 and C90 and steel B500C. We use the average values of the strength of materials to the calculations. Finally, we attach two examples for the design of beam - column joints with both methods.Θεοδώρα Μ. Τεντόμ

The carbon isotope composition of semi-labile and stable pyrogenic carbon in a thermosequence of C₃ and C₄ derived char\ud

To better elucidate the reactions forming pyrogenic carbon (PyC) during pyrolysis, we investigated the carbon isotope fractionation trends in thermosequences for biomass types utilizing C₃ and C₄ photosynthetic pathways. PyC remaining after pyrolysis was treated using hydrogen pyrolysis to isolate the stable polycyclic aromatic carbon (SPAC) component and the semi-labile carbon component (PyC(SL)) was estimated from mass balance (the component that survived pyrolysis, but was not SPAC). C isotope fractionation trends as a function of pyrolysis temperature were determined for each of these three components (PyC, SPAC and PyC(SL)) relative to the C isotope composition of the bulk raw biomass. Although the isotope fractionation patterns for all materials were similar for total PyC, differences were noted between C₄ and C₃ biomass for isotope fractionation patterns of SPAC. The δ¹³C values of SPAC were higher than the original biomass for C₃ material, yet similar for C₄ material at formation temperature 300–700 °C. The δ¹³C values of PyC(SL) for all materials displayed distinct and progressively lower isotope composition relative to original biomass at higher temperature. The results, in combination with Fourier transform infrared patterns, indicated that the dominant source of SPAC is cellulose, and that lignin decomposes at higher temperature with very low δ¹³C MeO-rich lignin moieties preferentially surviving in PyC(SL). The δ¹³C values of SPAC were 0.2 ± 1.2‰ of the starting material, suggesting that this component might be used to determine the dominant source of PyC, although environmental mixtures of PyC in natural settings are more complex than those studied

Influence of feedstock properties and pyrolysis conditions on biochar carbon stability as determined by hydrogen pyrolysis

We produced 18 thermosequences of biochar from common feedstocks at ten temperatures from 300 to 900 °C to investigate their influence on carbon stabilization in biochar. Using hydrogen pyrolysis we were able to isolate the stable polycyclic aromatic carbon (SPAC) fraction that is likely to be resistant to mineralization on centennial timescales. SPAC formation was generally <20% of total organic carbon (TOC) at temperatures <450 °C and rises to >80% of TOC at temperatures above 600–700 °C depending on feedstock type. SPAC formation was retarded in feedstocks with high ash contents, and further retarded in those feedstocks when the final hold time at maximum pyrolysis temperature was reduced from one hour to 10 min. Given that aromatization of organic material in many feedstocks is usually completed by ca. 450 °C, the data suggests that a significant pool of aromatic biochar carbon exists in a 'semi-labile' form that may not be persistent on centennial timescales. For most feedstocks biochar yield and SPAC content are optimized at pyrolysis temperatures of 500–700 °C

Engineering banana cropping systems to suppress soil borne diseases

Banana production in Australia is currently worth $600 million annually, but is constantly threatened by root pathogens, such as plant-parasitic nematodes and Fusarium wilt (Fusarium oxysporum f. sp. cubense). To reduce the impacts of soil borne diseases on banana production, farm management interventions are being designed to enhance organisms which suppress pathogens, while maintaining productivity. A holistic view of soil functions with an understanding of the ecological interactions is therefore required to develop productive, disease suppressive farming systems. Soil nitrogen and organic matter are two factors that have a large impact on soil organisms, and can be manipulated by farm management. Their impacts on biological processes were monitored in field trials in north Queensland using soil nematodes community structures and Community Level Physiological Profiling using MicroResp™. Nitrogen is applied to bananas to enhance vegetative plant growth and maintain production. However, high soil nitrogen inputs tended to increase bacterial domination in the soil environment and lead to an increase in root pathogens. Organic matter inputs provide carbon substrates for soil organisms. By increasing the diversity of organic matter inputs, through vegetative groundcovers, it was possible to increase soil biological diversity. Furthermore, vegetative groundcovers tended to increase the proportion of nematodes involved in organic matter recycling and reduce the proportion of plant-parasitic nematodes. The use of vegetative groundcovers also led to suppression of Fusarium wilt symptoms determined through soil bioassays. The results indicated that through the careful manipulation of nitrogen and organic matters inputs it was possible to engineer banana cropping system that suppress soil borne diseases and maintaining productivity

The influence of feedstock and production temperature on biochar carbon chemistry: a solid-state 13C NMR study

Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy was used to evaluate the carbon chemistry of twenty-six biochars produced from eleven different feedstocks at production temperatures ranging from 350°C to 600°C. Carbon-13 NMR spectra were acquired using both cross-polarisation (CP) and direct polarisation (DP) techniques. Overall, the corresponding CP and DP spectra were similar, although aromaticity was slightly higher and observability much higher when DP was used. The relative size and purity of the aromatic ring structures (i.e. aromatic condensation) were also gauged using the ring current technique. Both aromaticity and aromatic condensation increased with increasing production temperature, regardless of the feedstock source. However, there were clear differences in these two measures for biochars produced at the same temperature but from different feedstocks. Based on a relationship previously established in a long-term incubation study between aromatic condensation and the mean residence time (MRT) of biochar, the MRT of the biochars was estimated to range from <260 years to >1400 years. This study demonstrates how the combination of feedstock composition and production temperature influences the composition of aromatic domains in biochars, which in turn is likely to be related to their recalcitrance and ultimately their carbon sequestration value