Search Results (40)

In the present paper, impedance spectroscopy was employed to study the corrosion and anodic oxidation of stainless steel (AISI 316L at 280 °C/9 MPa) in contact with the boron-free primary coolant of a small modular reactor at two levels of KOH concentration. Analysis of impedance spectra with a distribution of relaxation times revealed contributions from the oxide layer and its interface with the coolant. Glow-Discharge Optical Emission Spectroscopy (GDOES) was used to estimate the thickness and elemental composition of the formed oxides. A quantitative interpretation of the impedance data using the Mixed-Conduction Model allowed us to estimate the kinetic and transport parameters of oxide growth and dissolution, as well as iron dissolution through oxide. The film thicknesses following exposure agreed with ex-situ analyses. The obtained corrosion and release rates were used for comparison with laboratory and industrial data in nominal pressurized water reactor primary coolants. Full article

Passive films that form on Alloy 600 and Alloy 690 during four hours in simulated Primary Water (PW) of Pressurized Water Nuclear Reactors (PWRs) at 320 °C were investigated by in situ surface-enhanced Raman spectroscopy (SERS). Similar tests conducted on unalloyed nickel, unalloyed chromium, and laboratory alloys of Ni-10Cr, Ni-20Cr, Ni-5Cr-8Fe, and Ni-10Cr-8Fe aided in assigning the peaks in the surface-enhanced Raman (SER) spectra of the passive films of Alloy 600 and Alloy 690. SERS indicates an inner layer (IL) of Cr₂O₃/CrOOH forms on both Alloy 600 and Alloy 690 and that Alloy 690’s IL was more protective against corrosion due to its greater resistance to ion transport. The outer layer (OL) of Alloy 600 consists of NiO and spinels, FeCr₂O₄—M(Cr,Fe)₂O₄. The OL of Alloy 690 contains no spinel. A comparison of SER spectra in 320 °C PWR PW to the spectra following cooling down to room temperature and after exposure to air indicates some differences between in situ films and ex situ films. Full article

The end-of-life management of plastic represents a significant environmental challenge, largely due to its limited use, low biodegradability, and high volume of disposed material, in the order of 400 million tonnes by 2019. Several types of polymers can be recycled by mechanical means, but some others, like plastics, sometimes require chemical methods for their reuse. In this context, gasification is one of the most promising chemical recycling techniques. Gasification is a thermochemical process performed at moderate temperatures of work (800–1100 °C) that converts carbonaceous materials into rich hydrogen gas, which can be used for energy obtention or the Fisher–Tropsch process. However, this procedure can also produce undesirable by-products like tar and char. The products’ composition and relative quantities are highly dependent on the overall process configuration and the input fuel. The current study evaluates the catalytic gasification of the most common plastic waste, seeking to obtain higher gas yields and syngas with high energy. The text focuses on the current state of development and recent advances in various publications over the last fifteen years, with emphasis on thermoplastics and thermosets. The search showed that temperatures, the type of fluidizing gas, and the catalyst have a major influence on the quality of the obtained gas. Optimal gasification conditions, such as temperatures between 600 and 900 °C, depending on the plastic feedstock, steam-to-feedstock ratios > 1, the appropriate selection of a gasifying agent according to gas requirements and energy optimization, and the composition and location of the catalyst in the system (in situ, in the reactor, or ex situ), are identified as critical for maximizing H₂ and CO production and minimizing tar. Finally, we provide summaries of the last advanced patent in the field, where the main focus appears to be feedstock pretreatment intended to ensure handling feasibility due to the variety of plastic wastes. Full article

This work compares two technologies for the remediation of metal-polluted mine tailings based on lab-scale bioleaching experiments performed in (a) conventional agitated slurry-phase reactors and (b) in situ electrokinetic percolation. While ex situ bioleaching in agitated reactors has been widely studied, only a few previous works have studied the in situ option that couples bioleaching and electrokinetics. Real mine tailings from an abandoned sphalerite mine in southern Spain were used. The leaching medium was externally generated in a bioreactor using an autochthonous acidophilic culture and then added to tailings in batch experiments. This medium enabled metal leaching from mine tailings without the stringent operating conditions required by a classic bioleaching process. Metal removal efficiencies and kinetic rate constants after 15 d of treatments were calculated. Additionally, advantages or disadvantages between the two methods were discussed. The results for the innovative EK-percolation method showed rates and efficiencies that were comparable to, and in some cases better than, those achieved with conventional stirred slurry systems. Full article

The Fischer–Tropsch Synthesis process is projected to have a significant impact in the near future due to its potential for synthesizing sustainable fuels from biomass, carbon dioxide and organic wastes. In this catalytic process, catalyst activation plays a major role in the overall performance of Fischer–Tropsch Synthesis. Catalyst activation temperatures are considerably higher than the typical operating conditions of industrial reactors. Consequently, ex situ activation is often required for industrial Fischer–Tropsch Synthesis processes. This study evaluated the influence of different activation approaches (in situ, ex situ, passivation and low-temperature activation). Catalytic experiments were conducted in a fixed-bed reactor at 230 °C and 20 bar·g using a reference supported Co/γ-Al₂O₃ catalyst. Experimental results demonstrate that catalysts can be effectively reduced ex situ. This work reveals that re-activation of the catalyst after ex situ reduction is unnecessary, as the reaction conditions themselves re-reduce any superficial oxides formed, owing to the reducing nature of the reactant mixture. This approach could simplify reactor design by enabling temperature requirements to match operating conditions (e.g., 230 °C), thereby reducing both investment and operational costs and eliminating additional catalyst preparation steps. Full article

This study investigates a continuous deoxygenation of bio-oil vapor in a catalytic fixed-bed reactor coupled to a continuous drop tube reactor (DTR) for biomass pyrolysis. Beech wood pyrolysis was initially examined without catalysts at various temperatures (500–600 °C). The products were characterised using GC-MS, Karl Fischer titration, GC-FID/TCD, and thermogravimetric analysis. The highest bio-oil yield (58.8 wt.%) was achieved at 500 °C with a 500 mL/min N₂ flow rate. Subsequently, ex situ catalytic pyrolysis was performed using an HZSM-5 catalyst in a fixed-bed reactor at a DTR outlet, operating at 425 °C, 450 °C, and 500 °C. The HZSM-5 catalyst exhibited declining deoxygenation efficiency over time, which was evidenced by decreasing conversion rates of chemical families. Principal component analysis was employed to interpret the complex dataset, facilitating a visualisation of the relationships between the experimental conditions and product compositions. This study highlights the challenges of continuous operation as experimental durations were limited to 120 min due to clogging issues. This research contributes to understanding continuous biomass pyrolysis coupled with catalytic deoxygenation, providing insights into the reactor configuration, process parameters, and catalyst performance crucial for developing efficient and sustainable biofuel production processes. Full article

Biomethane production via biogas upgrading is regarded as a future renewable gas, further boosting the biogas economy. Moreover, when upgrading is realized by the biogas CO₂ conversion to CH₄ using surplus renewable energy, the process of upgrading becomes a renewable energy storage method. This conversion can be carried out via microorganisms, and has attracted scientific attention, especially under thermophilic conditions. In this study, mesophilic conditions were imposed using a previously developed enriched culture. The enriched culture consisted of the hydrogenotrophic Methanobrevibacter (97% of the Archaea species and 60% of the overall population). Biogas upgrading took place in three lab-scale bioreactors: (a) a 1.2 L bubble reactor (BR), (b) a 2 L trickling bed reactor (TBR) filled with plastic supporting material (TBR-P), and (c) a 1.2 L TBR filled with sintered glass balls (TBR-S). The gas fed into the reactors was a mixture of synthetic biogas and hydrogen, with the H₂ to biogas CO₂ ratio being 3.7:1, lower than the stoichiometric ratio (4:1). Therefore, the feeding gas mixture did not make it possible for the CH₄ content in the biomethane to be more than 97%. The results showed that the BR produced biomethane with a CH₄ content of 91.15 ± 1.01% under a gas retention time (GRT) of 12.7 h, while the TBR-P operation resulted in a CH₄ content of 90.92 ± 2.15% under a GRT of 6 h. The TBR-S operated at a lower GRT (4 h), yielding an effluent gas richer in CH₄ (93.08 ± 0.39%). Lowering the GRT further deteriorated the efficiency but did not influence the metabolic pathway, since no trace of volatile fatty acids was detected. These findings are essential indicators of the process stability under mesophilic conditions. Full article

A promising approach for carbon dioxide (CO₂) valorization and storing excess electricity is the biological methanation of hydrogen and carbon dioxide to methane. The primary challenge here is to supply sufficient quantities of dissolved hydrogen. The newly developed Inverse Membrane Reactor (IMR) allows for the spatial separation of the required reactant gases, hydrogen (H₂) and carbon dioxide (CO₂), and the degassing area for methane (CH₄) output through commercially available ultrafiltration membranes, enabling a reactor design as a closed circuit for continuous methane production. In addition, the Inverse Membrane Reactor (IMR) facilitates the utilization of hydraulic pressure to enhance hydrogen (H₂) input. One of the process’s advantages is the potential to utilize both carbon dioxide (CO₂) from conventional biogas and CO₂-rich industrial waste gas streams. An outstanding result from investigating the IMR revealed that, employing the membrane gassing concept, methane concentrations of over 90 vol.% could be consistently achieved through flexible gas input over a one-year test series. Following startup, only three supplemental nutrient additions were required in addition to hydrogen (H₂) and carbon dioxide (CO₂), which served as energy and carbon sources, respectively. The maximum achieved methane formation rate specific to membrane area was 87.7 L_N of methane per m² of membrane area per day at a product gas composition of 94 vol.% methane, 2 vol.% H₂, and 4 vol.% CO₂. Full article

Throughout recent years, the implementation of nanoparticles into the microstructure of additively manufactured (AM) parts has gained great attention in the material science community. The dispersion strengthening (DS) effect achieved leads to a substantial improvement in the mechanical properties of the alloy used. In this work, an ex situ approach of powder conditioning prior to the AM process as per a newly developed fluidized bed reactor (FBR) was applied to a titanium-enriched variant of the NiCu-based Alloy 400. Powders were investigated before and after FBR exposure, and it was found that the conditioning led to a significant increase in the TiN formation along grain boundaries. Manufactured to parts via laser-based powder bed fusion of metals (PBF-LB/M), the ex situ FBR approach not only revealed a superior microstructure compared to unconditioned parts but also with respect to a recently introduced in situ approach based on a gas atomization reaction synthesis (GARS). A substantially higher number of nanoparticles formed along cell walls and enabled an effective suppression of dislocation movement, resulting in excellent tensile, creep, and fatigue properties, even at elevated temperatures up to 750 °C. Such outstanding properties have never been documented for AM-processed Alloy 400, which is why the demonstrated FBR ex situ conditioning marks a promising modification route for future alloy systems. Full article

Time-dependent deformation in nuclear graphite is influenced by the creation and migration of radiation-induced defects in the reactor environment. This study investigates the role of pre-existing defects such as point defect clusters and Mrozowski cracks in nuclear graphite IG-110. Separate specimens were irradiated with a 2.8 MeV Au²⁺ beam with a fluence of 4.38 × 10¹⁴ cm⁻² and an 8 MeV C²⁺ beam with a fluence of 1.24 × 10¹⁶ cm⁻². Microscopic specimens were either mechanically loaded inside a transmission electron microscope (TEM) or subjected to ex situ indentation-based creep loading. In situ TEM tests showed significant plasticity in regions highly localized around the Mrozowski cracks, resembling slip or ripplocation bands. Slip bands were also seen near regions without pre-existing defects but at very high stresses. Ex situ self-ion irradiation embrittled the specimens and decreased the creep displacement and rate, while heavy ion irradiation resulted in the opposite behavior. We hypothesize that the large-sized gold ions (compared to the carbon atoms) induced interplanar swelling as well as cross-plane channels for increased defect mobility. These findings illustrate the role of pre-existing defects in the dynamic relaxation of stresses during irradiation and the need for more studies into the radiation environment’s impact on the mechanical response of nuclear graphite. Full article

The construction sector is among the most polluting industries globally, accounting for approximately 37.5% of the European Union’s total waste generation in 2020. Therefore, it is imperative to develop strategies to enhance the sustainability of this sector. This paper proposes a multiscale COMSOL Multiphysics numerical model for an ex situ mineral carbonation process of hydrated lime. The carbonation process is characterized at both the micro- and macroscale levels, encompassing interactions within and between the particles. This model incorporates both reaction and diffusion phenomena, considering the effects of porosity and liquid-water saturation parameters. Generally, liquid-water saturation enhances the reaction kinetics but not CO₂ diffusion, while porosity improves CO₂ diffusion throughout the granular bed. The model has been experimentally validated, showing promising results by accurately characterizing carbonation tendencies and the influence of the CO₂ flow rate and the initial water-to-solid ratio on the carbonation process. The proposed mathematical model facilitates the study of various parameters, including particle radius, reactor geometry, and material porosity. This analysis is valuable for both current and future projects, as it aims to identify the most profitable configurations for the hydrated lime carbonation process. Full article

Biogas upgrading via biomethanation has been extensively studied recently, but the influence of organic loading rate on process performance remains to be fully understood. This is particularly significant because both organic loading rate and hydrogen injection can lead to volatile fatty acid accumulation during anaerobic digestion. This study investigated the impact of a wide range of organic loading rates (from 1.25 to 3.25 g VS/L/d) on hydrogen consumption rates, organic acid accumulation, and microbial communities during in situ biomethanation. It also provided kinetics data and metabolite production data for different control reactors, including anaerobic digestion, ex situ biomethanation, and endogenous control reactors. Hydrogen was injected into parallel batch reactors using digestate from a semi-continuous lab-scale reactor subjected to increasing organic loading rates (1.25–3.25 g VS/L/d) as an inoculum. The inoculum was well adapted to each tested organic loading rate. The batch experiments were replicated following a 12 h hydrogen starvation period to assess the stability of hydrogen consumption rates. High organic loading rate values resulted in increased hydrogen consumption rates, peaking at 68 mg COD/L/h at an organic loading rate of 3.25 g VS/L/d (maximum value tested), with no significant organic acid accumulation despite the high hydrogen partial pressures. The hydrogen consumption rates were maintained after the starvation period. Furthermore, the addition of an organic substrate did not impact the hydrogen consumption rate (i.e., the in situ and ex situ rates were similar). A higher organic loading rate resulted in higher relative abundances of hydrogenotrophic methanogens (i.e., Methanospirillum sp.). This study highlights that increasing the organic loading rate can accelerate the rate of hydrogen consumption during in situ biomethanation, consequently reducing both capital and operational costs. Full article

With the increasing use of renewable energy resources for the power grid, the need for long-term storage technologies, such as power-to-gas systems, is growing. Biomethanation provides the opportunity to store energy in the form of the natural gas-equivalent biomethane. This study investigates a novel plug flow reactor that employs a helical static mixer for the biological methanation of hydrogen and carbon dioxide. In tests, the reactor achieved an average methane production rate of 2.5 $\frac{L_{{CH}_4}}{L_R\ast \mathrm{d}}$ (methane production [L_CH4] per liter of reactor volume [L_R] per day [d]) with a maximum methane content of 94%. It demonstrated good flexibilization properties, as repeated 12 h downtimes did not negatively impact the process. The genera Methanothermobacter and Methanobacterium were predominant during the initial phase, along with volatile organic acid-producing, hydrogenotrophic, and proteolytic bacteria. The average ratio of volatile organic acid to total inorganic carbon increased to 0.52 ± 0.04, while the pH remained stable at an average of pH 8.1 ± 0.25 from day 32 to 98, spanning stable and flexible operation modes. This study contributes to the development of efficient flexible biological methanation systems for sustainable energy storage and management. Full article

The biological upgrading of biogas to simulate natural gas properties contributes to the sustainable establishment of biogas technology. It is an alternative technology to the conventional physicochemical methods applied in biomethane plants and has been studied mainly in thermophilic conditions. Developing an enriched culture for converting the CO₂ of biogas to CH₄ in mesophilic conditions was the subject of the present study, which could facilitate the biological process and establish it in the mesophilic range of temperature. The enrichment took place via successive dilutions in a bubble bioreactor operated in fed-batch mode. The methane percentage was recorded at 95.5 ± 1.2% until the end of the experiment. The methane production rate was 0.28–0.30 L L⁻¹ d⁻¹ following the low hydrogen loading rate (1.2 ± 0.1 L L⁻¹ d⁻¹) applied to avoid acetate accumulation. Hydrogenotrophic methanogens, Methanobrevibacter sp., were identified at a proportion of 97.9% among the Archaea and 60% of the total population of the enriched culture. Moreover, homoacetogens (Sporomusa sp.) and acetate oxidizers (Proteiniphilum sp.) were also detected, indicating that a possible metabolic pathway for CH₄ production from CO₂ is via homoacetogenesis and syntrophic acetate oxidation, which kept the acetate concentration at a level of 143 ± 13 mg L⁻¹. It was found that adding NaHCO₃ was adequate to sustain the pH at 8.25. Full article

This publication discusses the experiments and findings of project ROCCS (Establishing a Research Observatory to Unlock European Coal Seams for Carbon Dioxide Storage), which aimed to investigate the potential for carbon dioxide storage in coal seams. The project involved large-scale ex situ laboratory tests, where CO₂ was injected into an experimental coal seam using a high-pressure reactor at the Central Mining Institute in Poland. The reactor simulated underground conditions, and the experimental coal seam measured 3.05 m in length with a cross-section of 0.4 × 0.4 m. Parameters such as gas flow, temperatures, and pressures were monitored during the experiments. In the study conducted, the sorption capacity of coal from the Polish mine “Piast-Ziemowit” for CO₂, at a sorption pressure of 30 bar, was determined to be 4.8% by weight relative to the raw coal mass. The data collected from these ex situ tests can support the design of a potential commercial-scale CO₂ storage installation. Full article