Search Results (243)

In this study, the effects of graphene-based nanomaterials—specifically graphene nanoplatelets (GNPs) and graphene oxide (GO) nanosheets—on methane (CH₄) production during anaerobic digestion (AD) of thermally hydrolyzed sewage sludge were investigated. Anaerobic digestion was carried out over a 40-day period under mesophilic conditions in batch digesters with a volume of 2.65 L. The influence of various dosages of GNPs and GO nanosheets on methane yields was assessed, including a comparison between GNPs with different specific surface areas (320 m²/g and 530 m²/g). The highest CH₄ yield (194 mL/g-VS_added) was observed with a GNP dosage of 5 mg/g-TS and a surface area of 530 m²/g, showing an increase of 3.08% compared to the control. This treatment group had the greatest positive effect also on the degradation of organic matter, with total solids (TS) and volatile solids (VS) removal reaching 34.35% and 44.18%, respectively. However, the GO dosages that significantly decreased cumulative CH₄ production were determined to be 10–15 mg/g-TS. Graphene oxide at dosages of 10 and 15 mg/g-TS reduced specific cumulative CH₄ yields by 4.03% and 5.85%, respectively, compared to the control, indicating CH₄ yield inhibition. This lab-scale study highlights the potential for integrating GNPs into full-scale, continuously operated wastewater treatment anaerobic digesters for long-term use in future applications. Full article

This study presents a detailed analysis of the combustion dynamics of stoichiometric H₂–air and CH₄–air mixtures in a 20 L closed vessel over an initial temperature range of 298–423 K. We integrate experimental pressure–time P(t) measurements with numerical analysis to extract laminar burning velocity (LBV) and deflagration index (K_G) values, and we assess three independent kinetic mechanisms (KiBo_MU, University of San Diego, Lund University) via simulations. For H₂–air, LBV increases from 0.50 m/s at 298 K to 0.94 m/s at 423 K (temperature exponent α ≈ 1.79), while for CH₄–air, LBV rises from 0.36 m/s to 0.96 m/s (α ≈ 2.82). In contrast, the deflagration index K_G decreases by ca. 20% for H₂–air and ca. 30% for CH₄–air over the same temperature span. The maximum explosion pressure (P_max) and peak pressure rise rate ((dP/dt)_max) also exhibit systematic increases with temperature. A comparison with model predictions shows agreement within experiments, providing data for safety modeling and kinetic mechanism validation in H₂- and CH₄-based energy systems. Full article

This work deals with the catalytic steam reforming of raw syngas to increase the efficiency of coupling gasification with downstream processes (such as fuel cells and catalytic chemical syntheses) by producing high-temperature, ready-to-use syngas without cooling it for cleaning and conditioning. Such a combination is considered a key point for the future exploitation of syngas produced by steam gasification of biogenic solid fuel. The design and construction of an integrated gasification and gas conditioning system were proposed approximately 20 years ago; however, they still require further in-depth study for practical applications. A 3D model of the freeboard of a pilot-scale, fluidized bed gasification plant equipped with catalytic ceramic candles was used to investigate the optimal operating conditions for in situ syngas upgrading. The global kinetic parameters for methane and tar reforming reactions were determined experimentally. A fluidized bed gasification reactor (~5 kWth) equipped with a 45 cm long segment of a fully commercial filter candle in its freeboard was used for a series of tests at different temperatures. Using a computational fluid dynamics (CFD) description, the relevant parameters for apparent kinetic equations were obtained in the frame of a first-order reaction model to describe the steam reforming of key tar species. As a further step, a CFD model of the freeboard of a 100 kWth gasification plant, equipped with six catalytic ceramic candles, was developed in ANSYS FLUENT^®. The composition of the syngas input into the gasifier freeboard was obtained from experimental results based on the pilot-scale plant. Simulations showed tar catalytic conversions of 80% for toluene and 41% for naphthalene, still insufficient compared to the threshold limits required for operating solid oxide fuel cells (SOFCs). An overly low freeboard temperature level was identified as the bottleneck for enhancing gas catalytic conversions, so further simulations were performed by injecting an auxiliary stream of O₂/steam (50/50 wt.%) through a series of nozzles at different heights. The best simulation results were obtained when the O₂/steam stream was fed entirely at the bottom of the freeboard, achieving temperatures high enough to achieve a tar content below the safe operating conditions for SOFCs, with minimal loss of hydrogen content or LHV in the fuel gas. Full article

This study presents the results of an investigation of carbonate-containing sorbents for CO₂ capture with natural support materials—kaolin and calcium carbonate—at various loadings of the active phase of Na₂CO₃. The effects of the support type on the distribution of the active component, phase composition, and pore structure of the sorbents were studied. It was found that a Na₂CO₃ loading of 25 wt.% provides the best balance between sorption capacity and technological feasibility. The thermal stability and regeneration capacity of the sorbents were evaluated under high-temperature conditions, revealing high thermal stability of the Na₂CO₃/CaCO₃ system up to 1000 °C, along with its durability over multiple adsorption–desorption cycles. Kinetic studies on the Na₂CO₃/CaCO₃ sorbent using the shrinking core model demonstrated that the overall CO₂ chemisorption process is controlled by surface chemical reaction at temperatures below 50 °C. The obtained results demonstrate the high potential of CaCO₃-based sorbents for practical applications in low-temperature CO₂ capture technologies. A promising direction for the use of such sorbents within CCUS is the development of integrated systems, where CO₂ capture is combined with its conversion into valuable products (e.g., methane, methanol, formic acid) through catalytic processes. Full article

Anaerobic digestion (AD) is a sustainable strategy for converting hazardous wastes into renewable energy while supporting Sustainable Development Goals (SDGs). This study aimed to evaluate the effect of inoculum on optimizing biogas production from sewage sludge (SS) and cattle manure (CM). Bench-scale digesters were fed with 0, 20, and 40% inoculum prepared at a 1:3 SS:CM ratio. Substrate and digestate were analyzed for physicochemical properties, and biogas production data were fitted using nonlinear models. Kinetic parameters ranged from 0.0770 to 0.4691 L·kg⁻¹ for Y_max, from 1.0263 to 2.1343 L·kg⁻¹·week⁻¹ for μ_max, and from 0.8168 to 8.0114 weeks for λ, depending on the ratio. The 1:3 SS:CM with 40% inoculum significantly improved biogas production by reducing the lag phase and increasing weekly yield, with the Gompertz model showing the best fit to the digestion kinetics. This was particularly evident due to the favorable conditions for microbial adaptation and efficient substrate degradation. The results reinforce the concept of optimization as defined in this study, wherein the application of inoculum enhances the performance of AD by improving the physicochemical conditions of the substrate and accelerating microbial activity, thereby resulting in increased methane (CH₄) generation and overall biogas yield. Full article

Solid oxide fuel cells (SOFCs) represent a pivotal technology in renewable energy due to their clean and efficient power generation capabilities. Their role in potential carbon mitigation enhances their viability. SOFCs can operate via a variety of alternative fuels, including hydrocarbons, alcohols, solid carbon, and ammonia. However, several solutions have been proposed to overcome various technical issues and to allow for stable operation in dry methane, without coking in the anode layer. To avoid coke formation thermodynamically, methane is typically reformed, contributing to an increased degradation rate through the addition of oxygen-containing gases into the fuel gas to increase the O/C ratio. The performance achieved by reforming catalytic materials, comprising active sites, supports, and electrochemical testing, significantly influences catalyst performance, showing relatively high open-circuit voltages and coking-resistance of the CH₄ reforming catalysts. In the next step, the operating principles and thermodynamics of methane reforming are explored, including their traditional catalyst materials and their accompanying challenges. This work explores the components and functions of SOFCs, particularly focusing on anode materials such as perovskites, Ruddlesden–Popper oxides, and spinels, along with their structure–property relationships, including their ionic and electronic conductivity, thermal expansion coefficients, and acidity/basicity. Mechanistic and kinetic studies of common reforming processes, including steam reforming, partial oxidation, CO₂ reforming, and the mixed steam and dry reforming of methane, are analyzed. Furthermore, this review examines catalyst deactivation mechanisms, specifically carbon and metal sulfide formation, and the performance of methane reforming and partial oxidation catalysts in SOFCs. Single-cell performance, including that of various perovskite and related oxides, activity/stability enhancement by infiltration, and the simulation and modeling of electrochemical performance, is discussed. This review also addresses research challenges in regards to methane reforming and partial oxidation within SOFCs, such as gas composition changes and large thermal gradients in stack systems. Finally, this review investigates the modeling of catalytic and non-catalytic processes using different dimension and segment simulations of steam methane reforming, presenting new engineering designs, material developments, and the latest knowledge to guide the development of and the driving force behind an oxygen concentration gradient through the external circuit to the cathode. Full article

Olive mill wastewater (OMWW) has high energetic potential due to its organic load, but its complex composition and toxicity limit efficient energy recovery. This study proposes an innovative integrated process combining continuous resin adsorption with anaerobic digestion to detoxify OMWW and recover renewable energy simultaneously. It studies the recovery of polyphenols, methane production, and substrate degradation efficiency using resin column bed heights (C1: 5.7 cm, C2: 12.1 cm, C3: 18.5 cm), as well as kinetic modeling of organic matter degradation. Adsorption reduced chemical oxygen demand (COD) by up to 80% and polyphenols by up to 64%, which significantly improved substrate biodegradability from 34% to 82%, corresponding to a methane yield of 287 mL CH₄/g COD. Organic matter was fractioned into rapid (S₁), moderate (S₂), and slow (S₃) biodegradable fractions. The highest degradation kinetics was C3, with methane production rates of K₁ = 23.86, K₂ = 2.47, and K₃ = 2.92 mL CH₄/d. However, this condition produced the lowest volumetric methane production due to excessive COD removal, including readily biodegradable matter. These results highlight the importance of optimizing the adsorption step in order to find to a balance between detoxification and energy recovery from OMWW, thus supporting the principles of circular economy and promoting renewable energy production. Full article

In chemical vapor deposition (CVD)-mediated graphene growth, copper foil serves as both a catalyst for methane decomposition and as a substrate for graphene nucleation and growth. Due to the low solubility of carbon in copper and the ease of transferring graphene from its surface, copper—particularly the Cu(111) facet—is widely favored for high-quality, monolayer graphene synthesis. In this article, the thermodynamic processes involved in methane dissociation and graphene nucleation on the Cu(111) surface were investigated using density functional theory (DFT). Molecular dynamics simulations were performed for structural optimization and to evaluate the reaction energies. Additionally, the average adsorption energies (ΔEad) of carbon clusters with varying atomic numbers on the Cu(111) surface were calculated. The graphene growth process was further modeled using the kinetic Monte Carlo (KMC) method to simulate carbon atom migration and nucleation dynamics. Thermodynamic analysis based on equilibrium component data was conducted to examine the influence of key operational parameters—temperature, pressure, and the CH₄/H₂ partial pressure ratio—on the graphene deposition rate. Full article

This study achieves the particle-resolved modeling of biomass pyrolysis via a novel approach of integrating the Discrete Element Method (DEM) with a semi-detailed chemical kinetic mechanism. By coupling CFD-DEM with a 36-step reaction network, the multiscale interactions between particle-scale hydrodynamics and the formation kinetics of 19 tar components under varying temperatures (630–770 °C) are elucidated. Levoglucosan (44.79%) and methanol (18.64%) are identified as primary tar components. Combined with these, furfural (C₅H₄O₂, 7.22%), methanal (CH₂O, 6.75%), and glutaric acid (C₅H₈O₄, 4.20%) account for over 80% of all the tar components. The secondary decomposition pathways are successfully captured, and changes in the reaction rates, as seen in triglycerides (R23: 307.30% rate increase at 770 °C) and tannins (R24: 265.41% acceleration), are quantified. This work provides the ability to predict intermediate products, offering critical insights into reactor optimization. Full article

This study evaluates the potential of spent coffee grounds (SCGs) as a co-substrate to improve anaerobic co-digestion (AcD) performance, with a focus on biogas yield, methane (CH₄) content, and the removal of volatile solids (VS) and total chemical oxygen demand (TCOD). Biochemical methane potential (BMP) tests were conducted in two stages. In Stage I, SCGs were blended with active sludge (AS) and the organic fraction of municipal solid waste (OFMSW) at varying ratios. The addition of 25% SCGs increased biogas production by 24.47% (AS) and 20.95% (OFMSW), while the AS50 mixture yielded the highest methane yield (0.302 Nm³/kg VS, 66.42%). However, SCG concentrations of 75% or higher reduced process stability. In Stage II, we evaluated the impact of mixing. The AS25 configuration maintained stable biogas under varying mixing conditions, showing system resilience, whereas OFMSW25 showed slight improvement. Biogas production kinetics were modeled using modified Gompertz, logistic, and first-order equations, all of which demonstrated high predictive accuracy (R² > 0.97), with the modified Gompertz model offering the best fit. Overall, SCGs show promise as a sustainable co-substrate for the improvement of methane recovery and organic matter degradation in AcD systems when applied at optimized concentrations. Full article

Supercritical oxy-fuel combustion, which allows for the high efficiency of power generation with near-zero CO₂ emissions, is considered a promising method to reduce the carbon footprint in the power energy sector. One of the problems in the widespread use of oxy-fuel combustion is a lack of comparative studies on the existing oxy-fuel combustion kinetic mechanisms depending on mixture composition, which complicates the choice of a kinetic mechanism for modeling oxy-fuel combustion. In this paper, a comparative verification of the kinetic mechanisms of GRI-Mech 3.0, UoS sCO₂ 2.0, OXY-NG, and Skeletal was performed using published experimental data on the ignition delay time of methane under conditions of oxy-fuel combustion. A comparative numerical study of the kinetic mechanisms in the wide range of pressures, CO₂ mass fractions in oxidizer (γ), and excess oxidizer ratios (α) by the ignition delay time is also carried out. It was found that the limits of applicability of all of the mechanisms studied are absent when modeling the ignition delay time, the most accurate mechanism to model the IDT of methane in oxy-fuel conditions being UoS sCO₂ 2.0, while the other three mechanisms are overall much inferior to it in terms of accuracy. However, Skeletal and GRI-Mech 3.0 mechanisms can be used to model the IDT during the oxy-fuel combustion of methane under both atmospheric and supercritical conditions, although only in a narrow range of γ. Full article

Poly(lactic acid) (PLA) is derived from sugar-based materials. While it is a leading sustainable biopolymer, PLA has been integrated with other agricultural coproducts (e.g., lignin, protein, and starch) to reduce its cost and enhance its modulus and biodegradability. Cottonseed oil and meal are the byproducts of the cotton fiber industry. In this work, four biocomposites were formulated with PLA, cottonseed oil, washed cottonseed meal, and plasticizing reagent glycerol with different formulation ratios. The thermal degradation behaviors were examined via thermogravimetric (TG) analysis under air and nitrogen conditions with the neat PLA sample as a control. The thermal decomposition characteristic values were impacted by both the biocomposite formulation and the heating rates of 1, 2, 5, and 10 °C min⁻¹. Results from two kinetic modeling methods that were examined indicated that the activation energy was relatively steady for the neat PLA in the whole degradation process. Generally, the low activation energy values of biocomposites other than PLA under nitrogen conditions implied that these cottonseed byproduct constituents promote the thermal decomposition of these biocomposites. However, the presence of oxygen would confound the thermal decomposition of the biocomposites, as shown by variable activation energy curves with higher values under air conditions. TG-FTIR analysis revealed that the major gaseous compounds were carbonyl, carbon dioxide, carbon monoxide, methane, and water, which were derived from the thermal decomposition of the biocomposites. Full article

The research aimed to study the effects of straw-derived biochar and two types of chemically modified biochar on biomethane production from glucose as a model substrate and sugar beet pulp as a real substrate. The biochar chemical modification with H₃PO₄ acid and KOH base resulted in a change in biochar surface area properties and its functional group’s abundance and a decrease in biochar mass yield production. The anaerobic digestion process was performed in batch reactors kept at 37 °C for 20 days. The substrate-to-inoculum ratio by volatile solids was 0.5, while the mass of added biochar corresponded to 16 g·L⁻¹. The results showed that neither the addition of biochar nor the chemically modified biochar had any positive effects on biomethane production or its kinetics in the case of both substrates. The highest methane production was found in reactors without biochar added, respectively, 385 and 324 mL·g_VS⁻¹ for glucose and sugar beet pulp. It is hypothesized that the anaerobic digestion process was performed under optimal conditions, and therefore, biochar could not enhance methane production. Additionally, biochar may have adsorbed some volatile fatty acids, making them less available to anaerobic microorganisms. Full article

Hydrogen has been presented as a promising energy vector in decarbonized economies. Its singular properties can affect important aspects of industrial flames, such as the temperature, emissions, and radiative/convective energy transfer balance, thus requiring in-depth studies to optimize combustion processes using this fuel isolate or in combination with other renewable alternatives. This work aims to conduct a detailed numerical analysis of temperatures and gas emissions in the combustion of biomethane enriched with different proportions of hydrogen, with the intent to contribute to the understanding of the impacts of this natural gas surrogate on practical combustion applications. RANS k-$\omega$ and k-$ϵ$ turbulence models were combined with the GRI Mech 3.0, San Diego, and USC mechanisms using the ANSYS-Fluent 2024-R2 softwareto evaluate its performance regarding flame prediction. The Moss–Brookes model was adopted to predict soot formation for the methane flames by solving transport equations for normalized radical nuclei concentration and the soot mass fraction. The Discrete Ordinates (DOs) method with gray band model was applied to solve the Radiation Transfer Equation (RTE). The results of the experiments and numerical simulations highlight the importance of carefully selecting turbulence and chemical kinetics models for an accurate representation of real-scale industrial burners. Relative mean errors of 1.5% and 6.0% were registered for temperature and pollutants predictions, respectively, with the USD kinetics scheme and k-$omega$ turbulence model presenting the most accurate results. The operational impacts of hydrogen enrichment of biomethane flames were accessed for a practical combustion system. With 15% of hydrogen blending, the obtained results indicate a 73% penalty in CO emissions, an increase of 6% in NO emissions, and a 34 K flame temperature increase. Also, a reduction in flame radiation due to hydrogen enrichment was observed for hydrogen concentrations above 20%, a behavior that can affect practical combustion systems such as those in glass and other ceramics industries. Full article

The actual environmental and energy crises are two of the main problems existing in the world. Among the different technologies that can be implemented is anaerobic digestion, which employs waste and renewable biomass materials. To reach the optimum ratio of different raw materials or substrates in the feed of digesters, laboratory tests are necessary. This work aims to study the increase in the Organic Load Rate (OLR) (1 g VS L⁻¹d⁻¹, 2 g VS L⁻¹d⁻¹, 3 g VS L⁻¹d⁻¹ and 4 g VS L⁻¹d⁻¹, VS: Volatile Solid) and the raw materials number (sorghum (S), pig manure (P), triticale (T), corn stover (C) and microalgae biomass (M)) in the feedstock of the anaerobic digestion process. Mean values of methane yields for the evaluated set were lower in SMP and SMPTC assays (149.80 L_CH4 kg VS⁻¹ and 157.15 L_CH4 kg VS⁻¹, respectively) than SP, SM and SMPT assays (195.09 L_CH4 kg VS⁻¹, 197.69 L_CH4 kg VS⁻¹ and 195.76 L_CH4 kg VS⁻¹, respectively). Along the experiments, several parameters were evaluated, along with their interactions with OLR and number of raw materials. Two kinetic models were employed to fit the COD (Chemical Oxygen Demand) removal results. Full article