Thermal Decomposition Kinetics of Woods with an Emphasis on Torrefaction

The pyrolysis kinetics of Norwegian spruce and birch wood was studied to obtain information on the kinetics of torrefaction. Thermogravimetry (TGA) was employed with nine different heating programs, including linear, stepwise, modulated and constant reaction rate (CRR) experiments. The 18 experiments on the 2 feedstocks were evaluated simultaneously via the method of least-squares. Part of the kinetic parameters could be assumed common for both woods without a considerable worsening of the fit quality. This process results in better defined parameters and emphasizes the similarities between the woods. Three pseudo-components were assumed. Two of them were described by distributed activation energy models (DAEMs), while the decomposition of the cellulose pseudo-component was described by a self-accelerating kinetics. In another approach, the three pseudo-components were described by n-order reactions. Both approaches resulted in nearly the same fit quality, but the physical meaning of the model, based on three n-order reactions, was found to be problematic. The reliability of the models was tested by checking how well the experiments with higher heating rates can be described by the kinetic parameters obtained from the evaluation of a narrower subset of 10 experiments with slower heating. A table of data was calculated that may provide guidance about the extent of devolatilization at various temperature residence time values during wood torrefaction

CO2 gasification of chars prepared from wood and forest residue

The CO2 gasification of chars prepared from Norway spruce and its forest residue was investigated in a thermogravimetric analyzer (TGA) at slow heating rates. The volatile content of the samples was negligible; hence the gasification reaction step could be studied alone, without the disturbance of the devolatilization reactions. Six TGA experiments were carried out for each sample with three different temperature programs in 60 and 100% CO2. Linear, modulated, and constant-reaction rate (CRR) temperature programs were employed to increase the information content available for the modeling. The temperatures at half of the mass loss were lower in the CRR experiments than in the other experiments by around 120 degrees C. A relatively simple, well-known reaction kinetic equation described the experiments. The dependence on the reacted fraction as well as the dependence on the CO2, concentration were described by power functions (n-order reactions). The evaluations were also carried out by assuming a function of the reacted fraction that can mimic the various random pore/random capillary models. These attempts, however, did not result in an improved fit quality. Nearly identical activation energy values were obtained for the chars made from wood and forest residues (221 and 218 kJ/mol, respectively). Nevertheless, the forest residue char was more reactive; the temperatures at half of the mass loss showed 20-34 degrees C differences between the two chars at 10 degrees C/min heating rates. The assumption of a common activation energy, E, and a common reaction order, v, on the CO2, concentration for the two chars had only a negligible effect on the fit quality

Pyrolysis of medium-density fiberboard: optimized search for kinetics scheme and parameters via a genetic algorithm driven by Kissinger's method

The pyrolysis kinetics of charring materials plays an important role in understanding material combustions especially for construction materials with complex degradation chemistry. Thermogravimetric analysis (TGA) is frequently used to study the heterogeneous kinetics of solid fuels; however, there is no agreed method to determine the pyrolysis scheme and kinetic parameters for charring polymers with multiple components and competing reaction pathways. This study develops a new technique to estimate the possible numbers of species and sub-reactions in pyrolysis by analyzing the second derivatives of thermogravimetry (DDTG) curves. The pyrolysis of a medium-density fiberboard (MDF) in nitrogen is studied in detail, and the DDTG curves are used to locate the temperature of the peak mass-loss rate for each sub-reaction. Then, on the basis of the TG data under multiple heating rates, Kissinger’s method is used to quickly find the possible range of values of the kinetic parameters (<i>A</i> and <i>E</i>). These ranges are used to accelerate the optimization of the inverse problem using a genetic algorithm (GA) for the kinetic and stoichiometric parameters. The proposed method and kinetic scheme found are shown to match the experimental data and are able to predict accurately results at different heating rates better than Kissinger’s method. Moreover, the search method (K–K method) is highly efficient, faster than the regular GA search alone. Modeling results show that, as the TG data available increase, the interdependence among kinetic parameters becomes weak and the accuracy of the first-order model declines. Furthermore, conducting TG experiment under multiple heating rates is found to be crucial in obtaining good kinetic parameters

When is anterolateral complex augmentation indicated? Perspectives from the 2024 Freddie Fu Panther Sports Medicine Symposium

Purpose: This study aimed to determine the trends and indications for anterolateral complex augmentation during anterior cruciate ligament reconstruction (ACL-R) among international orthopedic sports surgeons. Methods: An electronically distributed survey was sent out to international surgeons with high-volume experience in complex ligament reconstructions and revision surgery attending the 2024 Freddie Fu Panther Sports Medicine Symposium. The survey was sent prior to the meeting with questions related to the use of lateral extra-articular tenodesis (LET) or anterolateral ligament reconstruction (ALL-R) during ACL-R. Sessions pertaining to anterolateral complex augmentation were held during the symposium to inform about current clinical practices among attendees. Results: A total of 49 surgeons were identified from 5 different geographic regions prior to the meeting date and were sent an electronic survey, of which 48 responded (98% response rate). Among the surgeons who reported performing anterolateral complex augmentation procedures (n = 45), a total of 39 (87%) respondents reported using only the LET technique, 2 (4%) reported using only the ALL-R technique, and 4 (9%) reported using both techniques during ACL-R. The most common indication for anterolateral complex augmentation was a high-grade pivot shift, which 39 of 43 (91%) respondents ranked in their top 3 indications. In the setting of primary ACL-R, respondents added LET when using hamstring tendon autograft in 38% of cases on average compared with 34% of cases when using either bone-patellar tendon-bone autograft or quadriceps tendon autograft. In the setting of revision ACL-R, LET was added in an average of 68% of cases for a first-time revision ACL-R and in 84% of cases for a multiple-revision ACL-R. Conclusion: The most common indication for ACL-R with anterolateral complex augmentation was a high-grade pivot shift and most respondents preferred LET over ALL-R. Respondents performed LET in a comparable percentage of cases of primary ACL-R using hamstring tendon, bone-patellar tendon-bone, and quadriceps tendon autografts, and this number increased with the number of revision ACL-Rs. Based on the results of this survey, surgeons may consider adding LET in cases of revision ACL-R or in patients with a high-grade pivot shift. Level of evidence: Level V

Kinetic Behavior of Torrefied Biomass in an Oxidative Environment

The combustion of four torrefied wood samples and their feedstocks (birch and spruce) was studied at slow heating programs, under well-defined conditions by thermogravimetry (TGA). Particularly low sample masses were employed to avoid the self-heating of the samples due to the huge reaction heat of the combustion. Linear, modulated and constant-reaction rate (CRR) temperature programs were employed in the TGA experiments in gas flows of 5 and 20% O2. In this way the kinetics was based on a wide range of experimental conditions. The ratio of the highest and lowest peak maxima was around 50 in the experiments used for the kinetic evaluation. A recent kinetic model of Várhegyi et al. [Energy & Fuels 2012, 26, 1323-1335] was employed with modifications. This model consists of two devolatilization reactions and a successive char burn-off reaction. The cellulose decomposition in the presence of oxygen has a self-accelerating (autocatalytic) kinetics. The decomposition of the non-cellulosic parts of the biomass was described by a distributed activation model. The char burn-off was approximated by power-law (n-order) kinetics. Each of these reactions has its own dependence on the oxygen concentration that was expressed by power-law kinetics, too. The complexity of the applied model reflects the complexity of the studied materials. The model contained 15 unknown parameters for a given biomass. Part of these parameters could be assumed common for the six samples without a substantial worsening of the fit quality. This approach increased the average experimental information for an unknown parameter by a factor of 2 and revealed the similarities in the behavior of the different samples

Influence of Antioxidant Sericin in Tris Extender on Oxidative Markers during Cryopreservation (–196ºC) of Bovine Semen

This investigation was carried out during winter season on the semen of three mature, healthy breeding bulls each of Gir cattle and Murrah buffalo breeds. The aim was to assess the effect of different concentration of antioxidant Sericin (0.0, 0.1, 0.25, 0.50 and 1.0%, w/v) in standard Tris fructose egg yolk glycerol (TFYG) extender on cryopreservability of bovine semen based on sperm motility and oxidative markers in seminal plasma of freshly diluted and cryopreserved semen. The mean sperm motility observed in freshly diluted and frozen-thawed Gir bull semen, irrespective of Sericin levels, were 76.93±0.39 and 43.47 ± 0.58 % and in Murrah bulls 78.20±0.38 and 44.10 ± 0.48 %, respectively. The values of malondialdehyde (MDA, μmol/ml) in seminal plasma of freshly diluted and frozen-thawed semen of Gir bulls, irrespective of Sericin levels, were 21.68±0.38 and 24.99 ± 0.56, and in Murrah bulls 21.49±0.57 and 25.60±0.94, respectively. The corresponding values of superoxide dismutase (SOD, U/ml) were 1.77 ± 0.06 and 1.37 ± 0.05 in Gir and 1.18 ± 0.06 and 0.85 ± 0.04 in Murrah bulls, and those of glutathione peroxidase (GPx, nmol/min/ml) 417.10 ± 12.00 and 349.76 ±11.92 in Gir and 385.71±9.21 and 320.02±9.49 in Murrah bull semen. Sperm motility and activities of all three enzymes differed highly significantly (plessthan00.01) between stages. SOD was significantly (plessthan00.05) lower in buffalo than cattle semen. Inclusion of 0.5% and/or 0.25% Sericin in TFYG extender gave better protection to spermatozoa over other levels against ROS mediated injuries as the MDA production was significantly reduced with increased sperm motility and higher levels of SOD and GPx enzymes in the seminal plasma.</jats:p