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- Recent Advances in Renewable Hydrogen Purification Technologies: A General ReviewPublication . Copa Rey, José; Nobre, Catarina; Rijo, Bruna; Longo, Andrei; Brito, Paulo; Mateos-Pedrero, CeciliaRenewable hydrogen purification is a critical yet often underemphasised step in enabling its use as a clean energy carrier. Hydrogen produced from biomass-based thermochemical and biological routes typically contains CO2, CO, CH4, H2S, and other impurities that must be removed to meet stringent requirements for fuel cell, industrial, and grid-injection applications. This review provides a critical and up-to-date assessment of renewable hydrogen purification technologies, focusing on their suitability for variable and impurityrich renewable hydrogen streams. Established benchmark technologies, including pressure swing adsorption and cryogenic separation, are described, with emphasis on their operating principles, material innovations, and process integration strategies. Recent advancements in inorganic, polymeric, and mixed-matrix membranes are highlighted, with particular focus on how advanced porous materials enhance selectivity, permeability, and flexibility. Additionally, a comparative techno-economic assessment is presented, evaluating each purification method based on technology readiness level, capital and maintenance costs, energy efficiency, and operational lifespan. By incorporating recent research trends, this approach facilitates the selection and design of purification systems that are not only efficient and scalable but also cost-effective, tailored to both decentralised and centralised renewable hydrogen production.
- Char Produced from Waste and Biomass Blended Pellets: Comprehensive Thermochemical Behavior AssessmentPublication . Santos, Santa Margarida; Gonçalves, Margarida; Brito, Paulo; Nobre, CatarinaThe growing demand for carbon-based energy materials requires sustainable alternatives to fossil fuels. This study explored the production and characterization of char obtained from refuse-derived fuel (RDF) and biomass blended pellets in varying proportions (0%, 15%, 25%, 50%, and 100% RDF). The objective was to evaluate their potential as highenergy-density solid fuels while addressing operational challenges related to ash behavior. Chars were produced at 400 ◦C for one hour in a muffle furnace in closed crucibles. A set of analytical techniques (calorimetry, infrared spectroscopy, thermogravimetry, inductively coupled plasma, and X-ray fluorescence) was employed to assess physicochemical properties. RDF content strongly affected mass yield, energy yield, and thermochemical behavior. Among the tested formulations, char with 50 and 25% of RDF (C_RDF50:BW50 and C_RDF25:BW75) ignited at lower temperatures (≈150 ◦C) and showed high flammability (C) values (1.97–2.03 × 10−5 ), indicating greater flammability. They also reached higher combustion temperatures (716–746 ◦C), suggesting improved thermal stability during the final combustion stage. Both chars presented increased high heating values (18–19 MJ/kg, dry basis) and a few surface functional groups. This supports a lower devolatilization rate, meaning that although ignition is easy, combustion remains stable and controllable. All chars showed very high acid–base indices, indicating a strong tendency for ash melting. However, low slag viscosity and alkalinity values suggest viscous, poorly mobile slag, reducing adhesion and buildup on reactor surfaces. This study combines thermogravimetric combustion analysis with ash chemistry–based slagging and fouling indices to provide an integrated assessment of the operational behavior of RDF–biomass-derived char fuels. The results highlight the technical feasibility of chars produced from RDF and biomass blended pellets, whose thermal properties make them promising candidates for use as solid fuels.
- Mobile Pyrolysis Systems for Decentralized Biomass Valorization: Technologies, Products, and ApplicationsPublication . Nobre, Catarina; Santos, Santa Margarida; Copa Rey, José; Longo, Anbdrei; Rijo, Bruna; Panizio, Roberta; Brito, Paulo; Mateos-Pedrero, CeciliaMobile pyrolysis systems offer a practical pathway for the decentralized valorization of biomass waste, addressing the high logistical and economic burdens of transporting low-density, moisture-rich feedstocks to centralized facilities. By operating directly at the source, these systems convert diverse agricultural and forestry residues into biochar, bio-oil, pyrogas, and wood vinegar, while reducing transport volumes and associated emissions. Reported mobile reactors process between 4 kg per batch and 10 t/day, achieving biochar yields of 33–44 wt.% at 400 ◦C and bio-oil yields of 55–68 wt.% in fast pyrolysis at 500–550 ◦C, demonstrating performance comparable to stationary installations. This review synthesizes current mobile pyrolysis technologies, including reactor configurations, feedstock suitability, operational constraints, and recent advances in automation, real-time monitoring, and machine learning-based optimization. The agricultural and industrial applications of pyrolysis products are examined, with emphasis on soil health enhancement, biopesticide activity, renewable gas generation, and carbon sequestration. Emerging international projects and commercial efforts are highlighted, illustrating growing interest in flexible, low-carbon pyrolysis solutions for rural waste management and distributed bioresource utilization, while outlining the technological gaps that remain to be addresse
- Social Awareness as a Catalyst for Biochar Adoption in the Agricultural and Forestry SectorsPublication . Janiszewska-Latterini, Dominika; Ortigueira, Joana; Lopes, Tiago F.; Goscianska-Lowinska, Julia; Augustyniak-Wysocka, Dobrochna; Leszczyszyn, Ewa; Nobre, CatarinaBiochar, a carbon-rich material produced from the pyrolysis of organic matter, has garnered attention for its potential agricultural and environmental benefits, including soil improvement, enhanced crop yields and climate change mitigation. Despite its promise, biochar adoption has been hindered by limited social awareness, particularly in industrialised countries. This review explores the factors influencing biochar's acceptance in agriculture and forestry, focusing on the social aspects that affect its integration. A systematic literature review was conducted to identify studies on social awareness and acceptance, revealing significant barriers such as a lack of knowledge among farmers, high production costs and insufficient infrastructure. In industrialised countries, while technical research on biochar has progressed, farmers often remain unfamiliar with its benefits, and resistance to adoption is common. Studies show that social factors such as age, education level and access to funding play a crucial role in biochar adoption. Furthermore, a lack of government incentives and unclear regulatory frameworks exacerbate the challenge. Conversely, studies from lower-income countries suggest that small-scale, cost-effective biochar production systems may hold promise. The review also identifies strategies to enhance biochar's social acceptance, including targeted education programs, financial incentives and clearer regulatory standards. Despite varying levels of social awareness, the literature suggests that with increased outreach, biochar could significantly contribute to sustainable agricultural practices globally. This review underscores the need for further research into the social dimensions of biochar adoption and the implementation of policies to foster its widespread use.
- Potential of “Montado” Waste as Feedstock for Thermal GasificationPublication . Krop, Nadezhda; Carmo-Calado, Luis; Copa Rey, José; Mateos-Pedrero, Cecilia; Rijo, Bruna; Longo, Andrei; Brito, Paulo; Nobre, CatarinaThis study examines the feasibility of utilizing acorn wastes from Montado systems in the Alentejo region of southern Portugal as a sustainable feedstock for bioenergy production through thermal gasification. Approximately 45% of the annual acorn harvest remains unused, representing a locally available biomass resource with significant valorization potential. Acorn waste was characterized by proximate, ultimate, and calorimetric analyses, revealing moisture and volatile matter contents within ranges suitable for gasification. The relatively high ash content indicates potential challenges for fuel quality and process performance. Gasification experiments were carried out in a fixed-bed downdraft reactor at temperatures between 600 and 700 °C using air as the gasifying agent. The produced syngas consisted mainly of N₂, H₂, CO, CO₂, and CH₄, with methane concentrations remaining relatively stable across the tested temperatures (3.1–4.0 vol%). Increasing the gasification temperature reduced tar and char formation and improved cold gas efficiency, reaching a maximum of 68.5% at 700 °C, with a syngas lower heating value of up to 5.7 MJ/Nm³. Based on the experimental results, a techno-economic assessment was conducted for a decentralized gasification system with a nominal thermal capacity of 1.0 MWth operating 8,000 h per year. The system requires approximately 244 kg/h of acorn waste and achieves an overall electrical efficiency of 24.0%, converting 80.5% of the input energy into useful outputs. The economic analysis indicates project feasibility, with a positive net present value (0.47 M€), an internal rate of return of 12.1%, a levelized cost of electricity of 0.10 €/ kWh, and a payback period of 14.2 years. These results demonstrate that acorn waste from Montado management can support decentralized bioenergy production, contributing to circular economy strategies and renewable energy targets
- Modelling Syngas Combustion from Biomass Gasification and Engine Applications: A Comprehensive ReviewPublication . Copa Rey, José Ramón; Longo, Andrei; Rijo, Bruna; Mateos-Pedrero, Cecilia; Brito, Paulo; Nobre, CatarinaSyngas, a renewable fuel primarily composed of hydrogen and carbon monoxide, is emerging as a viable alternative to conventional fossil fuels in internal combustion engines (ICEs). Obtained mainly through the gasification of biomass and organic waste, syngas offers significant environmental benefits but also presents challenges due to its lower heating value and variable composition. This review establishes recent advances in understanding syngas combustion, chemical kinetics, and practical applications in spark-ignition (SI) and compression-ignition (CI) engines. Variability in syngas composition, dependent on feedstock and gasification conditions, strongly influences ignition behavior, flame stability, and emissions, demanding detailed kinetic models and adaptive engine control strategies. In SI engines, syngas can replace up to 100% of conventional fuel, typically at 20–30% reduced power output. CI engines generally require a pilot fuel representing 10–20% of total energy to start combustion, favoring dual-fuel (DF) operation for efficiency and emissions control. This work underlines the need to integrate advanced modelling approaches with experimental insights to optimize performance and meet emission targets. By addressing challenges of fuel variability and engine adaptation, syngas reveals promising potential as a clean fuel for future sustainable power generation and transport applications.
- Synergistic Valorization of Refuse-Derived Fuel and Animal Fat Waste Through Dry and Hydrothermal Co-CarbonizationPublication . Longo, Andrei; Brito, Paulo; Gonçalves, Margarida; Nobre, CatarinaThe demand for clean energy to improve waste valorization and enhance resource utilization efficiency has been increasingly recognized in the last few years. In this context, the co-carbonization of different waste streams, aiming at solid fuel production, appears as a potential strategy to address the challenges of the energy transition and divert waste from landfills. In this work, refuse-derived fuel (RDF) samples were subjected to the cocarbonization process with low-quality animal fat waste in different proportions to assess the synergistic effect of the mixture on producing chars with enhanced fuel properties. Dry (DC) and hydrothermal carbonization (HTC) tests were conducted at 425 ◦C and 300 ◦C, respectively, with a residence time of 30 min. The RDF sample and produced chars with different animal fat incorporation were analyzed for their physical, chemical, and fuel properties. The results demonstrated that increasing the fat proportion in the samples leads to an increase in mass yield and apparent density of the produced chars. Furthermore, char samples with higher fat addition presented a proportional increase in high heating value (HHV). The highest values for the HHV corresponded to the char samples produced with 30% fat incorporation for both carbonization techniques (27.9 MJ/kg and 32.9 MJ/kg for dry and hydrothermal carbonization, respectively). Fat addition also reduced ash content, improved hydrophobicity in hydrochars, and lowered ignition temperature, although additional washing was necessary to reduce chlorine to acceptable levels. Furthermore, fat incorporation reduced concentrations of elements linked to slagging and fouling. Overall, the results demonstrate that incorporating 30% fat into RDF during DC or HTC is the most effective condition for producing chars with improved physical, chemical, and fuel properties, enhancing their potential as alternative solid fuels.
- A review of cleaning technologies for biomass-derived syngasPublication . J.R.C. Rey; A. Longo; B. Rijo; C.M. Pedrero; L.A.C. Tarelho; P.S.D. Brito; C. NobreBiomass gasification is a promising thermochemical conversion technology with substantial potential for sustainable global energy development. It can replace various fuels and chemicals derived from fossil fuels, producing a gas composed of CO, H2, and CH4 as targeted compounds and CO2, H2O, and N2 as adulterating compounds. However, the gas also contains impurities like tars, particulate matter, nitrogen and sulfur compounds, hydrogen halides, and trace metals, posing challenges for its use. Efficient gas purification is essential before application in internal combustion engines, gas turbines, or chemical processes. This paper provides a comprehensive survey of gas purification technologies arising from biomass gasification. Two main categories are explored: wet purification systems, notably using wet scrubbers, and dry purification systems, which are more appealing due to avoiding gas cooling and associated energy losses. Traditional particulate removal devices and modern catalysts for tar, acid gases, and trace metal elimination are examined in the dry purification category. Furthermore, this work describes alternative gasification concepts such as integrated gasification, supercritical-water gasification, and, chemical loop gasification, also addressing carbon capture technologies for syngas conversion. Finally, advances in syngas cleaning methods are revised and commercially available purification systems are presented and discussed, offering insights into current outcomes in this field
- A review of solid oxide cell technologies for power, fuel, and reversible energy storagePublication . Rijo, Bruna; Mateos-Pedrero, Cecilia; Copa Rey, José R.; Longo, Andrei; Brito, Paulo; Nobre, CatarinaSolid oxide cell (SOC) technologies, encompassing solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs), and reversible solid oxide cells (rSOCs), are emerging as key components in the transition to sustainable energy systems due to their high operating efficiency, fuel flexibility, carbon–neutral fuel production potential, and compatibility with renewable energy sources. This work reviews current SOC technologies for renewable electricity generation and sustainable fuel production, examining their working principles and system configurations. Recent advances in materials, stack design, and control strategies are reviewed alongside significant challenges in material stability, dynamic response, electrode degradation, thermal management, and scalability. The paper highlights demonstration projects and provides an economic feasibility analysis of each SOC technology. Among electrolysis technologies, SOEC has higher capital expenditure (CAPEX) and operational expenditures (OPEX), but lower hydrogen production costs. A Strengths, Weaknesses, Opportunities, and Threats (SWOT) analysis reveals that SOEC possesses high hydrogen production efficiency, while SOFC offers great flexibility in fuel usage. However, it also points out that thermal stress and component degradation are significant challenges that need to be addressed. For rSOC, the analysis highlights the advantages of flexibility for twoway operation, along with concerns about stack cell degradation. The review also identifies innovation pathways needed to transition these systems from advanced prototypes to reliable components of decarbonised energy infrastructure, focusing on cost-effective materials development, electrode optimisation, and enhanced mathematical modelling
- Consumer-driven selection of low-emission vehicles for sustainable urban centers: An AHP-based approachPublication . Brito, Filipe Cardoso; Saba, Hugo; Panizio, Roberta Mota; Nobre, Catarina Pereira; Guarieiro, Lilian Lefol Nani; Ferreira, Cristiano Vasconcellos; Ferreira, Paulo; Santos, Alex Álisson Bandeira; Nascimento Filho, Aloísio S.In densely populated urban areas, air quality is one of the main concerns, affecting human health and the environment. In developing and emerging countries, an alternative method for reducing the effects of air pollution is to select vehicles with lower pollutant emissions, as a way of making these large centers more sustainable. Since the complete elimination of vehicle emissions is not possible in the short term. The aim of this work is conducting a selectivity study of low-emission vehicles to increase the proportion of less polluting vehicles by using a dynamic combination of technical information while simultaneously meeting consumer preferences. An adapted Analytic Hierarchy Process (AHP), a multi-criteria technique, was applied on secondary data on vehicle characteristics. The Brazilian Labeling Program was the main resource used in this research. The research innovatively promotes vehicle selection considering environmental aspects. In addition to being adaptable, dynamic, and interactive, it facilitates its use in different vehicle markets and contributes to policies for reducing pollutant emissions. Thus, the study presents a strategy to minimize vehicle emissions in urban centers until the energy transition is consolidated, especially in emerging countries like Brazi