Optimizing biogas methanation over nickel supported on ceria-alumina catalyst: Towards CO2-rich biomass utilization for a negative emissions society.

Biogas methanation emerges as a prominent technology for converting biogas into biomethane in a single step. Furthermore, this technology can be implemented at biogas plant locations, supporting local economies and reducing dependence on large energy producers. However, there is a lack of comprehensive studies on biogas methanation, particularly regarding the technical optimization of operational parameters and the profitability analysis of the overall process. To address this gap, our study represents a seminal work on the technical optimization of biogas methanation obtaining an empirical model to predict the performance of biogas methanation. We investigate the influence of operational parameters, such as reaction temperature, H2/CO2 ratio, space velocity, and CO2 share in the biogas stream through an experimental design. Based on previous research we selected a nickel supported on ceria-alumina catalyst; being nickel a benchmark system for methanation process such selection permits a reliable data extrapolation to commercial units. We showcase the remarkable impact of studied key operation parameters, being the temperature, the most critical factor affecting the reaction performance (ca. 2 to 5 times higher than the second most influencing parameter). The impact of the H2/CO2 ratio is also noticeable. The response surfaces and contour maps suggest that a temperature between 350 and 450 °C and an H2/CO2 ratio between 2.5 and 3.2 optimize the reaction performance. Further experimental tests were performed for model validation and optimization leading to a reliable predictive model. Overall, this study provides validated equations for technology scaling-up and techno-economic analysis, thus representing a step ahead towards real-world applications for bio-methane production.

Is the RWGS a viable route for CO2 conversion to added value products? A techno-economic study to understand the optimal RWGS conditions.

Understanding the viability of the RWGS from a thermodynamic and techno-economic angle opens new horizons within CO2 conversion technologies. Unfortunately, profitability studies of this technology are scarce in literature and mainly focused on overall conversion and selectivity trends with tangential remarks on energy demands and process costs. To address this research gap, herein we present a comprehensive techno-economic study of the RWGS reaction when coupling with Fischer-Tropsch synthesis is envisaged to produced fuels and chemicals using CO2 as building block. We showcase a remarkable impact of operating conditions in the final syngas product and both CAPEX and OPEX. From a capital investment perspective, optimal situations involve RWGS unit running at low temperatures and high pressures as evidenced by our results. However, from the running cost angle, operating at 4 bar is the most favorable alternative within the studied scenarios. Our findings showcase that, no matter the selected temperature the RWGS unit should be preferentially run at intermediate pressures. Ultimately, our work maps out multiple operating scenarios in terms of energy demand and process cost serving as guideline to set optimal reaction conditions to unlock the potential of the RWGS for chemical CO2 recycling.

Sustainable routes for acetic acid production: Traditional processes vs a low-carbon, biogas-based strategy.

The conversion of biogas, mainly formed of CO2 and CH4, into high-value platform chemicals is increasing attention in a context of low-carbon societies. In this new paradigm, acetic acid (AA) is deemed as an interesting product for the chemical industry. Herein we present a fresh overview of the current manufacturing approaches, compared to potential low-carbon alternatives. The use of biogas as primary feedstock to produce acetic acid is an auspicious alternative, representing a step-ahead on carbon-neutral industrial processes. Within the spirit of a circular economy, we propose and analyse a new BIO-strategy with two noteworthy pathways to potentially lower the environmental impact. The generation of syngas via dry reforming (DRM) combined with CO2 utilisation offers a way to produce acetic acid in a two-step approach (BIO-Indirect route), replacing the conventional, petroleum-derived steam reforming process. The most recent advances on catalyst design and technology are discussed. On the other hand, the BIO-Direct route offers a ground-breaking, atom-efficient way to directly generate acetic acid from biogas. Nevertheless, due to thermodynamic restrictions, the use of plasma technology is needed to directly produce acetic acid. This very promising approach is still in an early stage. Particularly, progress in catalyst design is mandatory to enable low-carbon routes for acetic acid production.

Modelling approaches for biomass gasifiers: A comprehensive overview.

Biomass resources have the potential to become a viable renewable technology and play a key role within the future renewable energy paradigm. Since CO2 generated in bio-energy production is equal to the CO2 absorbed during the growth of the biomass, this renewable energy is a net zero emissions resource. Biomass gasification is a versatile method for transforming waste into energy in which biomass material is thermochemically converted within a reactor. Gasification's superior flexibility, including both in terms of biomass type and heat generation or energy production alternatives, is what stimulates biomass gasification scientific and industrial potential. Downdraft gasifiers seem to be well-suited for small-scale generation of heat along with energy, whereas fluidised bed and entrained flow gasifiers currently attain significant economies of scale for fuel production. The operation of gasifiers is influenced by several factors, including operational parameters, feedstock types, and reactor design. Modelling is a valuable tool for building a unit based on the results of model predictions with different operational parameters and feedstock in such scenarios. Once verified, a suitable model may be used to assess the sensitivity of a gasifier's performance to changes in various operational and design factors. Effective models may help designers to theorise and predict the impacts of a variety of characteristics without the need for further empirical observations, which can help in the design and implementation of this technology. This work provides an overview of gasification technologies and a succinct guidance to the modelling decisions and modelling strategies for biomass gasification to enable a successful biomass to fuel conversion. A technical description and critical analysis of thermodynamic, kinetic, computational fluid dynamic and data-driven approaches is provided, including crucial modelling considerations that have not been explored in earlier studies. The review aims to aid researchers in the field to select the appropriate approach and guide future work.

Biogas upgrading to biomethane as a local source of renewable energy to power light marine transport: Profitability analysis for the county of Cornwall.

In this work, the use of biomethane produced from local biogas plants is proposed as renewable fuel for light marine transport. A profitability analysis is performed for three real biogas production plants located in Cornwall (United Kingdom), considering a total of 66 different scenarios where critical parameters such as distance from production point to gas grid, subsidies, etcetera, were evaluated. Even though the idea is promising to decarbonize the marine transport sector, under the current conditions, the approach is not profitable. The results show that profitability depends on the size of the biogas plant. The largest biogas plant studied can be profitable if feed-in tariffs subsidies between 36.6 and 45.7 €/MWh are reached, while for the smallest plant, subsidies should range between 65 and 82.7 €/MWh. The tax to be paid per ton of CO2 emitted by the shipping owner, was also examined given its impact in this green route profitability. Values seven times greater than current taxes are needed to reach profitability, revealing the lack of competitiveness of renewable fuels vs traditional fuels in this application. Subsidies to make up a percentage of the investment are also proposed, revealing that even at 100% of investment subsidized, this green approach is still not profitable. The results highlight the need for further ambitious political actions in the pursuit of sustainable societies.

K-Promoted Ni-Based Catalysts for Gas-Phase CO2 Conversion: Catalysts Design and Process Modelling Validation.

The exponential growth of greenhouse gas emissions and their associated climate change problems have motivated the development of strategies to reduce CO2 levels via CO2 capture and conversion. Reverse water gas shift (RWGS) reaction has been targeted as a promising pathway to convert CO2 into syngas which is the primary reactive in several reactions to obtain high-value chemicals. Among the different catalysts reported for RWGS, the nickel-based catalyst has been proposed as an alternative to the expensive noble metal catalyst. However, Ni-based catalysts tend to be less active in RWGS reaction conditions due to preference to CO2 methanation reaction and to the sintering and coke formation. Due to this, the aim of this work is to study the effect of the potassium (K) in Ni/CeO2 catalyst seeking the optimal catalyst for low-temperature RWGS reaction. We synthesised Ni-based catalyst with different amounts of K:Ni ratio (0.5:10, 1:10, and 2:10) and fully characterised using different physicochemical techniques where was observed the modification on the surface characteristics as a function of the amount of K. Furthermore, it was observed an improvement in the CO selectivity at a lower temperature as a result of the K-Ni-support interactions but also a decrease on the CO2 conversion. The 1K catalyst presented the best compromise between CO2 conversion, suppression of CO2 methanation and enhancing CO selectivity. Finally, the experimental results were contrasted with the trends obtained from the thermodynamics process modelling observing that the result follows in good agreement with the modelling trends giving evidence of the promising behaviour of the designed catalysts in CO2 high-scale units.

Characterization of emissions of condensable particulate matter under real operation conditions in cement clinker kilns using complementary experimental techniques.

Historically, the emission of particles from clinker kiln stacks has been one of the main environmental concerns in cement manufacturing processes. Up to now, environmental regulations have only focused on determining and controlling filterable particulate matter (FPM) in industrial emission sources. However, in recent years a growing interest in determining and analysing condensable particulate matter (CPM) has been evidenced due to the significant and established contribution of CPM to total emissions of particulate matter (PM). In this work, total PM (FPM + CPM) emissions from a clinker kiln in a cement manufacturing process have been characterized. A series of tests were performed to simultaneously collect FPM and CPM using a sampling train patented by University of Seville. The results showed very low level of emissions compared to regulatory limits. The average FPM and CPM concentrations obtained in the kiln were in the same order of magnitude, at 3.4 mg/Nm3 and 2.8 mg/Nm3, respectively. The CPM analysed was predominantly inorganic and represented 46% of total PM emissions. In addition, a microscopic morphological analysis was carried out on the samples and confirmed the presence of CPM with a size of less than 2 µm, as well as establishing the principal constituent elements of the same. The main element components were Al, Ca, Fe, Si, C and O. Compounds such as CaCO3, alite, ferrite and dolomite were detected with analytical characterization techniques, such as infrared spectroscopy (FTIR) analysis and X-ray diffraction (XRD), providing a better understanding of the sources of contamination within CPM.

Synergizing carbon capture and utilization in a biogas upgrading plant based on calcium chloride: Scaling-up and profitability analysis.

Herein we analyze the profitability of a novel regenerative process to synergize biogas upgrading and carbon dioxide utilization. Our proposal is a promising alternative which allows to obtain calcium carbonate as added value product while going beyond traditional biogas upgrading methods with high thermal energy consumption. Recently we have demonstrated the experimental viability of this route. In this work, both the scale-up and the profitability of the process are presented. Furthermore, we analyze three representative scenarios to undertake a techno-economic study of the proposed circular economy process. The scale-up results demonstrate the technical viability of our proposal. The precipitation efficiency and the product quality are still remarkable with the increase of the reactor size. The techno-economic analysis reveals that the implementation of this circular economy strategy is unprofitable without subsidies. Nonetheless, the results are somehow encouraging as the subsides needed to reach profitability are lower than in other biogas upgrading and carbon dioxide utilization proposals. Indeed, for the best-case scenario, a feed-in tariff incentive of 4.3 €/MWh makes the approach profitable. A sensitivity study through tornado analysis is also presented, revealing the importance of reducing bipolar membrane electrodialysis energy consumption. Overall our study envisages the big challenge that the EU faces during the forthcoming years. The evolution towards bio-based and circular economies requires the availability of economic resources and progress on engineering technologies.

Preparation of sorbents derived from bamboo and bromine flame retardant for elemental mercury removal.

This work showcases cost-effective elemental mercury capture strategy enabled by bamboo saw dust and bromine flame retardant (BFR) derived sorbent prepared by a novel hydrothermal-pyrolysis method. The hydrothermal treatment of bamboo and BFR blend was conducted in subcritical water resulting in a hydrothermal char. Subsequently, the hydrothermal char was pyrolyzed in nitrogen atmosphere leading to an improved pore architecture. The resulting biomaterials were proven highly effective for Hg removal. A thorough analysis of the physicochemical properties of the samples was conducted by means of BET, SEM, XRD, XPS and FT-IR. Key parameters such as bamboo/BFR ratio, hydrothermal temperatures and pyrolysis temperatures influence Hg0 removal capacity of our bio-sorbents. Overall, the optimal bamboo/BFR ratio, hydrothermal temperature and pyrolysis temperature are 2:1, 320 °C and 800 °C, respectively. Under these optimized conditions, a very promising elemental mercury removal efficiency of 99% is attained. The kinetics and mechanism of Hg0 removal are also proposed. The experimental data fit well with a pseudo-second-order model, indicating that Hg0 adsorption over sorbents was dominated by chemisorption. Our results indicate that the C-Br groups in sorbents provide active sites for oxidizing Hg0 into HgBr2.

Understanding the effect of Ca and Mg ions from wastes in the solvent regeneration stage of a biogas upgrading unit.

This paper reveals the effect of calcium and magnesium ions in carbonation experiments carried out to regenerate sodium hydroxide from a biogas upgrading unit. This novel study arises as an alternative to standard physical process whose elevated energy consumption imposes economic restrictions. Previous works employed alkaline waste to turn them into value added product. Nevertheless, no attractive economical results were obtained due to the low regeneration efficiencies. Our hypothesis is that both calcium and magnesium waste composition percentages have an impact in the result, hence this work propose an isolated study aiming to determine the of each one in the global performance. To this end, the operational parameters (reaction time, reaction temperature and molar ratio) were tuned as well as physicochemical properties of the final solid samples were analyzed by several techniques. The results indicate that calcium is much more prone than magnesium to reach high efficiencies in aqueous carbonation experiments. Additionally, higher quality products were achieved with calcium. The results of this study suppose an important step for understanding the aqueous carbonation through waste in the path to achieve a more sustainable city and society.

Synergizing carbon capture storage and utilization in a biogas upgrading lab-scale plant based on calcium chloride: Influence of precipitation parameters.

Herein a strategy for biogas upgrading in a continuous flow absorption unit using CaCl2 as capturing agent is reported. This process is presented as an alternative to the standard physical regeneration processes to capture carbon dioxide (CO2) from biogas effluents with inherent high energy penalties. This work showcases a systematic study of the main parameters (reaction time, reaction temperature, and molar ratio reactant/precipitator) affecting calcium carbonate (CaCO3) precipitation efficiency in a reaction between sodium carbonate (Na2CO3) and CaCl2. In addition, the purity and main characteristics of the obtained product were carefully analysed via in a combined characterization study using Raman, XRD, and SEM. Our results indicate that acceptable precipitation efficiencies between 62 and 93% can be reached by fine tuning the studied parameters. The characterization techniques evidence pure CaCO3 in a calcite structure. These results confirmed the technical feasibility of this alternative biogas upgrading process through CaCO3 production.

Aggressive transformation of a quiescent primary bone lymphoma simulating Paget's disease.

Primary multifocal osseous lymphoma is a rare and poorly recognized entity. Here, we present an instructive case of a young man who, six years after a local contusion of the left ankle, developed a painful polylobulated large soft tissue mass. This mass turned out to have arisen from the transformation of a centro follicular non-Hodgkin's lymphoma into a diffuse large B-cell lymphoma involving the calcaneus, talus, cuboid and navicular bones. The diagnostic difficulties as well as the implications of this aggressive transformation are highlighted here.

Catacamas virus, a hantaviral species naturally associated with Oryzomys couesi (Coues' oryzomys) in Honduras.

The primary objective of this study was to extend our knowledge of the geographical distribution, genetic diversity, and natural host associations of the hantaviruses indigenous to North America. Antibody to a hantavirus was found in 5 (20.8%) of 24 Coues' oryzomys (Oryzomys couesi) and none of 41 other rodents captured near the town of Catacamas in eastern Honduras, and a hantavirus was isolated from one of the antibody-positive Coues' oryzomys. Analyses of nucleotide and amino acid sequence data indicated that the viral isolate is a strain of a novel hantaviral species (proposed species name "Catacamas virus") that is phylogenetically most closely related to Bayou virus, a hantaviral species that is principally associated with Oryzomys palustris (marsh oryzomys) in the southeastern United States. Catacamas virus is the first evidence for the occurrence of a hantaviral species in Honduras and the first evidence that a hantaviral species is naturally associated with an Oryzomys species other than O. palustris.

Gastric MALT lymphoma: clinical characteristics and prevalence of H. pylori infection in a series of 37 cases.

OBJECTIVE: to perform a retrospective review of the clinical characteristics and prevalence of H. pylori infection in patients with gastric MALT lymphoma diagnosed in our hospital during the last 15 years. METHODS: patients with gastric MALT lymphoma diagnosed in our hospital during the last 15 years were retrospectively included. Demographic, clinic, analytic, endoscopic, and histological variables were reviewed. The extension study, the staging classification, and the presence of H. pylori infection were assessed. RESULTS: thirty-seven patients with gastric MALT lymphoma were identified. Mean age was 61 years, with 62% of males. The most common presentation symptom was dyspepsia (76%), followed by digestive bleeding (11%) and constitutional syndrome (8%). At endoscopy, erosive lesions were identified in 41%, and proliferative or exophytic lesions in 43%. Most lymphomas were classified as low-grade (68%). The stage distribution was EI for 56%, EII for 13%, EIII for 3%, and EIV for 28%. The prevalence of H. pylori infection (histology in all cases, rapid urease test in 19%, and 13C-urea breath test in 24%) was 46%. When only low-grade lymphomas in stage EI were considered, H. pylori prevalence increased to 55%. When H. pylori infection was evaluated by 13C-urea breath testing (in addition to histology), the prevalence of H. pylori infection increased to 78%. CONCLUSIONS: it is probable that the reduced H. pylori prevalence found in some studies, as in ours, could be explained by false-negative results obtained when only one diagnostic method was used. Therefore, at least two (invasive) diagnostic methods should be performed. Furthermore, the performance of a non-invasive diagnostic method (such as a 13C-urea breath test) before the exclusion of H. pylori infection should be considered.

Primary malignant schwannoma of the cervical plexus with melanocytic differentiation.

Primary malignant schwannomas are rare neoplasms of nerve sheath origin, especially in the location of the head and neck where few cases are described in the literature. These tumours may pose a diagnostic dilemma in the work-up of a neck mass. The case presented here is of a malignant schwannoma that originated in the cervical plexus with the rare histological feature of melanocytic differentiation. Histopathological examination with immunostaining techniques is essential for the diagnosis of these tumours. The management of these neoplasms is still controversial, although the treatment of choice is radical surgical excision of the lesion. The role of postoperative radiotherapy or chemotherapy is not clear, although some authors recommend its use to prevent local recurrence, for unresectable recurrent tumours or in cases of distant metastases.

Rapidly-progressive liver failure secondary to melanoma infiltration.

We describe the case of a 51-year-old man with a history of intraocular melanoma treated with radiotherapy 2 years previously. The patient was diagnosed with mild hypertransaminasemia that progressed to acute liver failure and death in a period of one month. Radiological investigations such as spiral computed tomography and abdominal ultrasonography failed to give an etiologic diagnosis. Autopsy revealed melanoma with diffuse infiltration of the hepatic parenchyma. Because diagnosis is usually delayed, the prognosis of intraocular melanoma is poor. In 40% of cases metastases are present at diagnosis, and the most frequently affected organ is the liver (93-95%). Presentation as acute liver failure can appear after a long disease-free period. For this reason, periodic laboratory tests and hepatic ultrasound examination are recommended in patients diagnosed with this malignancy.

Operative repair of popliteal aneurysms: effect of factors related to the bypass procedure on outcome.

The objective of this study was to compare patency rates following the repair of popliteal aneurysms according to the site of inflow, material of bypass graft and quality of distal runoff. Seventy bypasses were performed over an 11-year period. Autogenous saphenous vein was used in 53 procedures (75.7%) and prosthetic material was used in 17 (24.3%). Early mortality was 2.8%. Early primary and secondary patency rates were 95.7% and 97.1%, respectively. Autogenous vein showed better 10-year patency than prosthetic material (86% vs. 57%; p = 0.02). No significant differences in patency were observed according to the inflow site (87.8% groin vs. 74.7% supragenicular). Bypasses that originated in the groin showed improved patency when a saphenous vein was used (84.8% vs. 43.7%; p = 0.01). However, no influence of the graft material was noted in supragenicular bypasses (90.4% vs. 84.8%; p = 0.6). Bypasses in extremities with good runoff showed better patency than those in limbs showing poor runoff (86% vs. 55%; p = 0.003). The use of saphenous vein for the repair of popliteal aneurysms showed better results than those with prosthetic material, although in bypasses originating from the distal superficial femoral or above-knee popliteal artery, no significant differences in patency were observed. Good distal runoff was associated with improved overall outcome.

Direct admission to an extended-care facility from the emergency department.

BACKGROUND: Many patients are admitted to acute-care hospitals when their medical needs might be more appropriately met in an extended-care facility (ECF). OBJECTIVE: To describe a cohort of patients who were admitted from an emergency department to an ECF. DESIGN: Observational cohort study. PARTICIPANTS: 121 enrollees of Harvard Vanguard Medical Associates who were admitted directly from an emergency department to an ECF between October 1, 1994, and December 31, 1997. OUTCOME MEASURES: Mean length of stay, charges per patient, and discharge disposition (discharged to home, discharged to a long-term-care facility, died, or transferred to an acute-care hospital within 30 days of ECF admission). RESULTS: Patients admitted directly to an ECF were generally frail and elderly (median age, 75 years). Mean length of stay in the ECF was 11 days; the mean per-patient charge was $3290. Three quarters of patients were discharged from the ECF to their homes. Six percent (seven patients) were transferred from the ECF to an acute-care hospital within 30 days of ECF admission. None of these transfers clearly suggested that the initial decision to directly admit a patient to the ECF was inappropriate. Most patients were satisfied with direct ECF admission: Of the surviving, cognitively intact patients admitted to an ECF in 1997, 71% stated that they would choose direct admission to an ECF over admission to an acute-care hospital if they were "in a similar situation in the future." CONCLUSIONS: For selected patients, direct admission to an ECF seems to be feasible, safe, and acceptable. A randomized, clinical trial is needed to fully assess the safety and cost implications of direct ECF admission.