1,721,227 research outputs found
Linking pyrolysis and anaerobic digestion (Py-AD) for the conversion of lignocellulosic biomass
No full textBiogas is a mixture of CO2 and CH4 produced by a consortia of Bacteria and Archeae operating in anaerobic digestion (AD) plants. Biogas can be burnt as such in engines to produce electricity and heat or upgraded into biomethane. Biomethane is a drop-in fuel that can be injected in the natural gas grid or utilised as a transport fuel. While a wide array of biomass feedstock can be degraded into biogas, unconverted lignin, hemicellulose and cellulose end up in the co-product digestate leaving a large portion of chemical energy unutilised. Pyrolysis (Py) transforms in a single step and without chemical reagents the lignocellulose matrix into gaseous (syngas), liquid (bio-oil, pyrolysis oil) and solid (biochar) fractions for the development of renewable fuels and materials. The Py route applied downstream to AD is actively investigated in order to valorise the solid digestate presently destined only for soil applications. Coupling Py upstream to AD is an emerging field of research aimed at expanding the feedstock towards biologically recalcitrant substrates (wood, paper, sludge). The biomethanation potential was demonstrated for gaseous (H2/CO) and water soluble pyrolysis products, while the influence of insoluble pyrolytic lignin remains fairly unexplored. Biochar can promote the production of biomethane by acting as a support for microorganism colonisation, conductor for direct interspecies electron transfer, sorbent for hydrophobic inhibitors, and reactant for in situ biogas upgrading. Enhancing the advantages (carbon source) over the side effects (toxicity) of Py fractions represents the main challenge of Py-AD. This can be addressed by increasing the selectivity of the thermochemical process or improving the ecological flexibility of mixed bacterial consortia towards chemically complex environments
Biochar enables anaerobic digestion of aqueous phase from intermediate pyrolysis of biomass
No full textIntermediate pyrolysis produces a two-phase liquid whose aqueous phase is characterized by low heating
value and high water content (aqueous pyrolysis liquid, APL). Anaerobic digestion can be the straightest
way to produce a fuel (methane) from this material. Batch tests showed poor performance in anaerobic
digestion of APL, which underlined the inhibition of biological process. Nutrient supplementation was
ineffective, whereas biochar addition increased yield of methane (60 ± 15% of theoretical) with respect
to pure APL (34 ± 6% of theoretical) and improved the reaction rate. On the basis of batch results, a
semi-continuous biomethanation test was set up, by adding an increasingly amount of APL in a 30 ml
reactor preloaded with biochar (0.8 g ml1). With a daily input of 5 g d1 l1 of APL (corresponding to
overall amount of 0.1 kg l1 added before the end of the study) the yield of methane was 65 ± 5% of
the theoretical
Opt Out or Top Up? Voluntary Health Care Insurance and the Public vs. Private Substitution
Full text linkWe investigate whether in a mixed insurance system, people enrolled into voluntary health care insurance (VHI) substitute public consumption with private (opt out) or just enlarge their private consumption without reducing reliance upon public provisions (top up). We specify a joint model for public and private specialist visits counts, allowing for different degrees of endogenous supplementary insurance coverage. We find evidence of opting out: richer and wealthier individuals consume more private services and concomitantly reduce those services publicly provided through selection into for-profit VHI. Accounting for VHI endogeneity in the joint model of the two counts is crucial to this conclusion
Testing Exogeneity of Multinomial Regressors in Count Data Models: Does Two-stage Residual Inclusion Work?
Full text linkWe study a simple exogeneity test in count data models with possibly endogenous multinomial
treatment. The test is based on Two Stage Residual Inclusion (2SRI), an estimation method which has been proved to be consistent for a general class of nonlinear parametric models. Results from a broad set of simulation experiments provide novel evidence on important features of this approach. We find differences in the finite sample performance of various likelihood-based tests, analyze their robustness to misspecification arising from neglected over-dispersion or from incorrect specification of the first stage model, and uncover that standardizing the variance of the first stage residuals leads to better results. An original application to testing the endogeneity status of insurance in a model of healthcare demand corroborates our Monte Carlo findings
Machine learning surrogate models for Hertzian contact stress prediction in gear design: A comparative study of multiple approaches
Full text linkAccurately predicting contact stress in gears is essential for ensuring durability and optimizing performance during the design stage. This study investigates machine learning surrogate models for predicting Hertzian contact stress in involute gear pairs, aiming to accelerate the gear design process. Unlike approaches based on finite element simulations or experimental data, the proposed method relies solely on stress values from ISO 6336 formulations. A comprehensive dataset covering various macro geometries and loading conditions is used to train and evaluate several regression models, including Elastic Net, Support Vector Regressor, ensemble methods, and Neural Networks. To improve computational efficiency and address the high dimensionality of the input space, Principal Component Analysis is explored as a dimensionality reduction technique. The study provides a detailed comparison of surrogate modeling approaches based on predictive accuracy and generalization. Results show that surrogate models can accurately reproduce ISO based predictions, offering a faster alternative to traditional methods. Focusing on Hertzian stress, rather than root stress, offers deeper insight into surface fatigue and pitting resistance for gear life improvement. This work establishes the foundation for future surrogate models that optimize gear pairs by balancing multiple design objectives and constraints, aiding engineers in selecting
optimal configurations
Pyrolysis-GC-MS to trace terrigenous organic matter in marine sediments: a comparison between pyrolytic and lipid markers in the Adriatic Sea.
No full text
Analytical pyrolysis of the bioplastic PBAT poly(butylene adipate-co-terephthalate)
Full text linkPBAT (poly(butylene adipate-co-terephthalate) is an important player in the field of bioplastics for its biodegradability performance and good mechanical properties. Awareness of the forecasted increased use of PBAT has prompted researchers to develop methods for its analysis in a variety of samples. Py-GC-MS, conventional or with derivatising agents, is a technique of excellence for the analysis of polymers that relies on a detailed structural knowledge of the evolved products. This study presents a comprehensive investigation on the chemical composition of the pyrolysate of PBAT evolved at 600 ◦C alone and in the presence of various reagents (hexamethyldisilazane, HMDS; acetic anhydride, Ac2O, tetramethylammonium hydroxide, TMAH). Identification of relevant pyrolysis products was confirmed through the analysis of pure standards and associated reagents/ byproducts. A GC-MS data set of about 50 compounds was compiled, including open chain fragments of the polymer and their derivatives as well as single and mixed subunit cyclic dimers. A compound distinctive of PBAT (but-3-en-1-yl (4-((6-(but-3-en-1-yloxy)-6-oxohexanoyl)oxy)butyl) terephthalate) containing the adipic, terephthalic and butylene units was tentatively identified by its mass spectrum. Pyrolysis products with active hydrogens (alcoholic and carboxylic) were efficiently silylated by HMDS. Two pyrolysis products containing the hydroxybutyl moiety could be acetylated by pyrolysis with Ac2O. Thermally assisted hydrolysis and methylation with TMAH caused important transmethylation of the ester groups of the polymer chain with the formation of dimethyl adipate and dimethyl terephthalate. The importance of the results for the analysis of PBAT in commercial bioplastics and environmental samples was discussed
Determination of linear and cyclic volatile methyl siloxanes in biogas and biomethane by solid-phase microextraction and gas chromatography-mass spectrometry
No full textA new method based on solid-phase microextraction (SPME) followed by gas chromatography-mass spectrometry (GC-MS) was developed for the analysis of seven linear (L2 – L5) and cyclic (D3 – D5) volatile methyl siloxanes (VMS) in biogas and biomethane, directly collected into Tedlar® bags (Tedlar SPME) from anaerobic digesters and wastewater treatment plants. The method was employed to monitor VMS content in biomethane produced by biogas upgrading with a pilot-plant membrane unit and provided adequate limits of quantification (< 0.05 mg m−3) to detect trace siloxane impurities. Tedlar SPME was validated against a standard procedure based on indirect sampling of gas streams with sorbent tubes followed by solvent extraction and GC-MS. Method precision (RSD) on total and individual VMS concentrations was lower than 10%, while RSD values of the standard procedure were higher than 20%. Tedlar SPME suitably revealed high VMS levels, expressed as total volatile silicon (> 1 mgSim−3), in wastewater biogas and provided a more efficient sampling of heavier VMS in comparison to the sorbent tubes method. At low values (< 0.1 mgSim−3) typical of wood waste biogas and biomethane, no statistically significant differences were observed between the two methods. Overall, Tedlar SPME simplified the analytical procedure by reducing the procedural steps, avoiding the use of solvents and demonstrated its applicability for testing the quality of biomethane as advanced biofuel
Comparison of chemical and physical indices of thermal stability of biochars from different biomass by analytical pyrolysis and thermogravimetry
No full textA set of 22 biochars from different feedstock and pyrolysis conditions were produced using the same fixed bed pyrolysis reactor. Original substrates included softwood, hardwood and herbaceous biomass (pine, bark, cornstalk, miscanthus, poplar, switchgrass), microalgae (Desmodesmus communis, spirulina), wastes and residues (chicken manure, mushroom litter, olive pomace). Biochars were characterized by ultimate and proximate analysis and by analytical pyrolysis (Py-GC–MS). Parameters characteristics of the thermally labile fraction were obtained from thermogravimetric analysis (volatile matter, Tmax) and Py-GC–MS (molecular ratios). Volatile matter of biochars from a cornstalk thermosequence was strongly correlated with H/C ratios, while Tmax could be measured only for poorly carbonized biomass. Pyrolysis yields from Py-GC–MS were correlated with volatile matter. The molecular ratio toluene/naphthalene was governed by the extent of carbonisation and the presence of proteins in the original substrate. The 1-methylnaphthalene/naphthalene ratio was a general index of the thermal stability of biochar less influenced by the composition of the original feedstock. The indole/1-methylnaphthalene ratio was correlated with N/C ratio, while methylthiophene and benzothiophene were detected in the pyrolysate of sulphur-rich biochars from manure and litter. A coherent set of indices were obtained from TGA and Py-GC–MS for biochars with H/C > 0.3. In addition, Py-GC–MS provided information on the origin of biochar
- …
