Search Results (1,063)

The increasing generation of plastic waste has intensified the search for sustainable recycling technologies capable of recovering valuable resources while minimizing environmental impacts. Among emerging solutions, thermochemical recycling processes such as pyrolysis, gasification, and hydrothermal liquefaction have gained significant attention. However, the presence of chlorine-containing polymers, particularly poly(vinyl chloride) (PVC), represents a major challenge due to the release of hydrogen chloride (HCl), catalyst deactivation, equipment corrosion, and contamination of valuable products. Consequently, effective dechlorination pretreatments are essential for improving process performance and product quality. This review provides a comprehensive overview of current pretreatment technologies for chlorine management in plastic solid waste. Mechanical sorting, density-based separation, chemical extraction, alkaline treatments, hydrothermal processing, thermal dehydrochlorination, catalytic methods, and emerging photocatalytic approaches are critically analyzed and compared. The mechanisms, operating conditions, chlorine removal efficiencies, technological readiness levels, and industrial applicability of each method are discussed. Moreover, particular attention will be devoted to integrating different pretreatment technologies to achieve an overall enhanced chlorine removal efficiency before thermochemical technologies. Finally, reported techno-economic, environmental, and safety indicators are compared where quantitative data are available, while the principal data gaps and technological barriers to large-scale implementation are identified. Full article

Oil palm empty fruit bunches (EFB) are lignocellulosic residues generated in large quantities by the palm oil industry and represent a potential biomass resource for renewable hydrogen production. This study evaluated the inherent safety of an indirect gasification process of empty fruit bunches (EFB) for hydrogen production, coupled with purification via pressure swing adsorption (PSA), using the Inherent Safety Index (ISI) methodology. The assessment considered critical operating variables, including temperature and pressure, and integrated chemical sub-indices (toxicity, flammability, chemical interaction, and corrosivity) with process sub-indices (inventory, temperature, pressure, equipment, and process structure). The analysis yielded a total ISI of 36, exceeding the reference value of 24 used in the original ISI framework and indicating an unfavorable inherent-safety profile under the evaluated conceptual design conditions. The main hazard drivers were the combined flammability, explosiveness, and toxicity contribution governed by CO; the high individual explosiveness of H₂; the toxicity of SO₂; the potential formation of explosive mixtures following air ingress; and the relatively large process inventory. The indirect gasification section, reaching a maximum verified temperature of 900 °C and a maximum operating pressure of 60 bar, governed the temperature and pressure sub-indices, respectively. These findings identify significant inherent-safety challenges that should be addressed during subsequent process development. In particular, inventory minimization, prevention of air ingress, and evaluation of less severe temperature and pressure conditions where technically feasible represent relevant priorities for inherently safer design before industrial-scale implementation. Full article

This review provides a comprehensive analysis of waste-to-hydrogen (WtH) pathways for the conversion of various types of WtH, focusing on hydrogen generation, energy efficiency, environmental implications, and economic viability. The result shows that feedstock characteristics influence each pathway’s feasibility and performance. Thermochemical treatment, particularly gasification, demonstrates high hydrogen yield and the processing versatility of heterogeneous wastes. Hydrogen concentrations of 10–45 vol% can be obtained by dry gasification, while 35–55 vol% H₂ and 70–90% carbon conversion can be obtained by plasma-assisted gasification. Hydrothermal gasification converts 45–70% of the energy in the feedstock, suitable for wet feedstocks. Pyrolysis produces H₂-rich gas along with bio-oil and char, while plasma-assisted pyrolysis could enhance H₂ production by up to threefold compared with conventional catalytic systems. Biological pathways are more suitable for wet and biodegradable wastes. Dark fermentation provides lower H₂ recovery than thermochemical routes, whereas sequential dark and photo-fermentation improves substrate utilization, achieving hydrogen yields of 4.44–4.96 mol H₂/mol glucose and hydrogen production efficiencies of 45.31–82.67%. Among the evaluated feedstocks, plastic waste achieved a hydrogen production rate of 189.6 kg H₂/h, but also generated up to 4.3 kg CO₂-eq/kg H₂. Mixed plastic waste achieved 0.29 kg H₂/kg waste at a levelized cost of hydrogen (LCOH) of 3.41 USD/kg H₂. Integrated systems demonstrated performance improvements, including 71.3% energy efficiency for anaerobic digestion and gasification with heat recovery, 61.6% for gasification coupled with electrochemical CO₂ reduction, and more than 99% CO₂ capture in the latter configuration. The LCOH from investigated pathways vary from 0.3 to 13.37 USD/kg H₂ for different feedstock, conversion technology, system configuration, and carbon management requirements. Overall, gasification appears promising for heterogeneous and energy-dense wastes, as well as biological routes for wet biodegradable fractions, while integrated configurations offer a promising strategy for balancing hydrogen recovery, energy efficiency, economic performance, and environmental impacts. Full article

Off-grid agricultural cold chains suffer from high energy conversion losses due to intermediate electrical stages in traditional refrigeration. This study addresses the lack of empirical quantification by comparing Direct Mechanical Drive (DMD) and Electrical Power Generation (EPG) drive trains for an R-134a vapor compression refrigeration system. Under steady-state conditions (randomized block design), DMD achieved a statistically significant 13.89% reduction in biomass consumption over EPG (1840.0 vs. 2136.7 g/h; p < 0.001). The biomass consumption was evaluated based on the measured charcoal mass flow under the same lower heating value basis. Conversely, refrigeration COP was statistically equivalent (2.74 vs. 2.73; p = 0.815), confirming that drive-train architecture does not alter internal vapor compression thermodynamics. Only 19.6% of the compressor shaft power appeared as useful fluid-side compression work under this fractional-load operating condition, a volumetric rather than mechanical deficiency arising from operation at 7.7–15.5% of the compressor’s rated capacity. Referenced consistently to the primary biomass chemical energy input, the First-Law biomass-to-cooling system efficiency was 3.66% (equivalent to 5.34% when referenced to the syngas delivered to the engine), with a corresponding biomass-referenced exergy efficiency of 0.44%. Component exergy analysis revealed that the internal combustion engine (59.13% of total exergy destruction, ε = 13.1%) and the gasifier (32.4%, ε = 67.7%) dominated total system exergy destruction (15.49 kW). Furthermore, a 10-year life-cycle cost (LCC) analysis indicates DMD-Syngas yields net present value savings of 21,071.57 USD over gasoline-EPG, yielding a 0.14-year (~50-day) simple payback period on the 400.12 USD net incremental hardware capital cost (the gasification subsystem less the alternator–motor drive train that the direct-drive configuration does not require, and excluding one-time installation and training costs). When the fully installed cost is accounted for—including site preparation, process-water supply and effluent handling, low-voltage provision, installation labor, operator training and contingency—the incremental investment rises to 1298–2405 USD and the payback period extends to approximately 162–301 days. Under the least favorable combination examined, in which commercially purchased charcoal is imposed simultaneously with the upper installed-cost bound, capital recovery extends to approximately 1.4 years; the base case nevertheless recovers the incremental investment within the first operating year. An operational-phase (gate-to-gate) carbon assessment indicates near parity with the gasoline baseline on a strictly attributional basis (+120 to +1200 kg CO₂e yr⁻¹); a net saving of 8880–13,320 kg CO₂e yr⁻¹ arises only under the consequential scenario in which open-field burning of orchard residues is displaced and is further contingent on including black carbon in the accounting basket. This is not a full ISO 14040/44 life-cycle assessment, and the environmental outcome is therefore scenario-dependent rather than intrinsic to fuel substitution. These results demonstrate that mechanical drive-train optimization substantially enhances fuel economy without compromising refrigeration performance, providing a rigorous evidence base for scalable biomass-powered off-grid cold chains. Full article

Gasification is a route for cattle manure resource utilisation and emission mitigation, but its mass-change mechanism under an O₂/H₂O atmosphere remains unclear. This work aims to reveal the staged apparent mass-gain behaviour and its underlying coupling mechanism during cattle manure thermochemical conversion under O₂/H₂O atmospheres, so as to provide support for biomass gasification process optimisation and industrial circulating fluidised-bed gasifier parameter regulation. Thermogravimetric (TG) experiments were conducted under five O₂:H₂O mass ratios (1:4, 1:2, 1:1, 2:1 and 4:1), set with reference to the typical gas–steam ratio of circulating fluidised beds, combined with four heating rates (5, 10, 15 and 20 °C min⁻¹), and the mass-change behaviour was interpreted using multiple characterisation techniques. The strongest peak appeared at 634 °C at an O₂:H₂O mass ratio of 1:2 and a heating rate of 10 °C min⁻¹, with a maximum mass-gain rate of 11.0% min⁻¹. The main mass-loss peaks occurred between 242 and 291 °C and were associated with organic-structure cracking and volatile release. The medium-temperature (297–457 °C) mass gain was attributed to oxidative adsorption on active char surfaces and transient oxygen-containing intermediates, whereas the high-temperature (521–864 °C) response was linked to ash mineral restructuring and char–mineral interfacial reactions. Full article

Woody biomass is often promoted as a low-carbon energy source in global decarbonization efforts. However, LCA (life cycle assessment) evaluations of woody biomass-to-energy systems show very different environmental performance. Variations in technology and methodology across investigations can cause these inconsistencies. This review paper analyzes methodologies of LCAs of woody biomass conversion routes such as combustion, combined heat and power, gasification, pyrolysis, torrefaction-assisted systems, and new bioenergy with carbon capture configurations. A systematic literature review was conducted using Scopus, SpringerLink, and ScienceDirect, identifying 4272 records, of which 98 studies were retained for detailed analysis following the application of defined inclusion and exclusion criteria. Functional unit selection, from biomass mass per unit to power or heat per unit, is highly variable, affecting comparability. Forest carbon stock fluctuations, infrastructure, and end-of-life treatment are inconsistently included in cradle-to-grave system boundaries. Static GWP100 methods are often used in biogenic carbon removal without considering temporal carbon dynamics. The importance of pretreatment steps like drying, pelletizing, and torrefaction cannot be overstated, even though they have a direct impact on the quality of the fuel, the efficiency of transportation, and the effectiveness of the conversion process downstream. The large range of stated emission levels for comparable technologies is further influenced by logistics assumptions, plant scale, and allocation mechanisms in cogeneration systems. The review synthesizes these methodological differences and proposes a harmonization methodology to increase woody biomass LCA transparency and comparability. By identifying important sources of outcome variability, this study helps policymakers, project developers, and industry stakeholders evaluate biomass energy investments and bring clarity to environmental decisions. Full article

This study presents an integrated and sustainable approach for the valorization of polystyrene (PS) plastic waste into methanol, contributing to circular carbon utilization and waste-to-fuel strategies. Two simulation models were developed in Aspen plus. In Case 1, PS is converted to syngas through steam gasification, followed by its conversion into methanol. In Case 2, a steam methane reforming (SMR) unit is integrated with the gasification unit, using the heat from the gasifier-derived syngas to boost hydrogen production and overall methanol yield. This integration boosts the hydrogen-to-carbon ratio, doubling methanol production in Case 2 compared to Case 1. In terms of energy performance, Case 2 exhibits a process efficiency of 81% and exergy efficiency of 73%, both significantly higher than 48% and 60%, compared to Case 1. From an economic standpoint, Case 2 requires greater capital investment and annual operational expenditure, yet it proves to be more cost-effective in the long run compared to Case 1 due to the higher methanol production. The methanol production cost is reduced by 50%, from $1.001/kg in Case 1 to $0.505/kg in Case 2. These improvements are driven by increased throughput and process integration that supports sustainable and circular carbon management. Full article

Co-processing organic waste in coal–water slurry (CWS) gasifiers offers high gasification efficiency and robust stabilization of hazardous substances, representing a crucial pathway for waste valorization and low-carbon chemical processing. This review systematically examines the key influencing factors, control strategies, environmental risks, and operational challenges of this technology. We compare the adaptability of various gasifier designs for handling organic waste and propose operational strategies to balance slurryability and gasification performance under complex feedstock conditions. Furthermore, this paper elucidates the mechanisms underlying adverse effects on equipment (e.g., slagging and corrosion) and emission risks induced by problematic waste components, such as high ash, alkali metals, chlorine, and heavy metals. Finally, we highlight future research directions, emphasizing the synergistic management of multi-source wastes, developing multi-scale reaction modeling, and conducting life cycle assessments (LCA) and economic evaluations to advance CWS co-processing toward highly efficient, stable, and low-carbon operations. Full article

This work presents a techno-economic assessment of hydrogen production via sorption-enhanced gasification (SEG) of hazelnut shells across three plant scales (100 kWth, 1 MWth, and 10 MWth). The overall model is developed through the integration of Aspen Plus^® process simulation, coupled with MATLAB^®-based kinetic reactor modelling, enabling the assessment of the entire process chain. The kinetic SEG model, validated against experimental literature data, was implemented to describe the fluidized bed gasifier behaviour at the three scales. The resulting process streams were subsequently integrated into Aspen Plus^® for downstream upgrading and overall system analysis. The simulations show that the SEG process produces a hydrogen-rich syngas with H₂ contents around 80 vol.%_dry-basis, which is further upgraded to a hydrogen purity of 99.95% with a recovery of 90% via pressure swing adsorption. The process exhibits stable performance across scales, with Cold Gas Efficiency values around 60% and hydrogen yields close to 1 Nm³/kg_Biomass. The economic analysis highlights a decrease in the Levelized Cost of Hydrogen (LCOH) from 41.3 €/kg at 100 kWth to 6.8 €/kg at 10 MWth. These results indicate that SEG represents a promising pathway for low-carbon hydrogen production, while enabling the valorisation of biogenic residues within a sustainable energy framework. Full article

Taking pickling sludge generated from the steel rolling process at a Chinese steel mill as the subject of study, this research investigates a combined mineral processing and metallurgical process involving gasification-reduction roasting, magnetic separation, and waste acid recovery. The main elements in this pickling sludge are Fe and Cl, with contents of 46.50% and 12.70%, respectively. The primary component is chlorine-containing iron oxide, and a significant amount of amorphous material is also present. The study investigated the effects of various calcination temperatures, calcination times, reducing agent dosages, and material thicknesses on gasification-reduction performance indicators. The results indicate that using a reduction calcination–grinding–magnetic separation process, with coal as the reducing agent, a calcination temperature of 1100 °C, a reducing agent dosage of 15%, and a calcination time of 2 h, the chlorine volatilization rate exceeds 97%. Furthermore, when the roasted ore is ground to a particle size where 85% passes through a −0.076 mm screen and is recovered via magnetic separation, an iron concentrate with a grade of over 69.50% can be obtained. This iron concentrate meets the quality requirements for high-grade iron concentrates used in direct reduced iron (DRI) production. The small amount of tailings from the iron concentration process can be utilized in the production of bricks, cement, and other products, thereby achieving the efficient comprehensive utilization of acid washing sludge. Full article

Under the carbon neutrality context, underground coal gasification combined cycle (UGCC) power generation with carbon capture and storage (CCS) technology can effectively mitigate climate change and reduce pollutant emissions. However, due to the complexity of the UCG process and significant fluctuations in syngas composition, the overall power generation efficiency of the plant may be affected to some extent. Existing studies have predominantly focused on single-link energy efficiency analysis, with a lack of full life-cycle resource–environment synergistic evaluation based on the extended exergy analysis framework, and comparative sustainability research between UGCC and integrated gasification combined cycle (IGCC) systems remains inadequate. Accordingly, this study establishes an exergy Life-Cycle Assessment model for UGCC power plants based on Aspen Plus, systematically evaluates the resource utilization rate and environmental sustainability index, identifies key influencing factors, and conducts a comparative analysis with IGCC power plants. The results indicate that the comprehensive sustainability performance of UGCC power plants is significantly enhanced after CCS retrofitting, with exergy efficiency reaching 37.56% at an oxygen-to-coal ratio of 0.6 and a water-to-coal ratio of 0.1; compared with IGCC, UGCC demonstrates a superior resource utilization rate but relatively weaker environmental sustainability; and the underground gasification unit is the critical link affecting exergy efficiency. This study offers a new perspective for sustainability assessment of energy systems and provides theoretical support and technical reference for the construction of a low-carbon reliable supply system in the power industry, thereby facilitating the implementation and refinement of a novel sustainable energy system. Full article

The increasing global demand for sustainable energy solutions has intensified the need for efficient and environmentally friendly biomass-conversion technologies. Among these, thermochemical processes, such as pyrolysis, gasification, and hydrothermal liquefaction, have emerged as promising pathways for transforming lignocellulosic and other organic waste materials into valuable biofuels and biochemicals. This paper presents a comprehensive evaluation of advanced thermochemical conversion and catalytic conversion methods, focusing on their operational mechanisms, catalytic enhancements, and product yields. The efficiency, environmental impact, and economic feasibility of various thermochemical platforms, including recent developments in catalyst design and process-integration strategies, are compared, and innovative approaches to optimize hydrogen generation, improve carbon efficiency, and minimize undesirable byproducts through tailored reaction conditions and bifunctional catalytic systems are explored. Recent advances as well as the current challenges related to feedstock variability, process scalability, and system sustainability are highlighted. By identifying critical research gaps, this study provides strategic insights aimed at guiding future improvements in thermochemical biomass utilization for clean energy production within a circular economy framework. Full article

The world’s food industry faces significant obstacles today as it strives to meet the nutritional needs of its rapidly expanding global population while also managing an immense amount of food processing waste (FPW) generated throughout the entire food supply chain. The widespread use of traditional disposal techniques for food waste (landfilling and incineration) regularly faces challenges related to environmental sustainability and economic efficiency. This manuscript reviews the necessary transition from a linear “take-make-dispose” approach to food production to a more circular model that recycles food waste into high-value intermediate chemicals and renewable energy through the development of biorefineries. The manuscript explores the biochemical composition of food waste, with carbohydrates, lipids, proteins, and bioactive materials, making it a suitable feedstock for different multi-stage biorefinery operations. In addition, this review will evaluate a variety of existing conversion technologies for food processing waste, such as biological methods (e.g., anaerobic digestion and fermentation) and thermochemical methods (e.g., pyrolysis, gasification, and hydrothermal liquefaction), to create various platform chemicals, including organic acids, bio-alcohols and volatile fatty acids (VFAs), as well as the production of sustainable biofuels and biopolymers. The review also elucidates the three most determinative constraints on large-scale industrial implementation of food waste valorisation: feedstock variability, techno-economic feasibility, and the need for comprehensive life cycle assessments (LCAs). The alignment of food waste management strategies with the UN SDGs (in particular, SDG 12 ‘Responsible Consumption and Production’ and SDG 13 ‘Climate Action’) reflects the opportunity for food waste to serve as a foundation for a carbon-neutral, sustainable future. This review provides a strategic roadmap for academics, practitioners, and policymakers to tap into the full potential of food waste through a sustainable circular economy model. Full article

The development of efficient and stable catalysts for ethanol steam reforming (ESR) is critical for sustainable hydrogen production. In this study, a series of Ni–Cu bimetallic catalysts supported on Gadolinium-doped ceria (GDC) were synthesized via the wet impregnation method to evaluate their performance in ESR. The catalysts were characterized by BET, XRD, SEM-EDS, H₂-TPR, and H₂ chemisorption to correlate their physicochemical properties with catalytic activity. Experimental results demonstrate that the incorporation of a small amount of Cu into the Ni/GDC system significantly enhances the resistance to carbon deposition without compromising hydrogen production rates. Among the formulations tested, 7.5%Ni-2.5%Cu/GDC exhibited superior catalytic stability at 700 °C. H₂-TPR analysis revealed that the presence of Cu facilitates the reduction of nickel species through a synergistic effect, while the GDC support provides high oxygen mobility, which promotes the gasification of surface carbonaceous species. This study provides valuable insights into the design of Ni–Cu bimetallic catalysts for mitigating coking and sintering in ESR processes, offering a robust catalyst formulation for industrial-scale hydrogen generation. Full article

This study provides the main performance estimates for new concepts, using flexible gasification operation modes, adaptable to prevailing market conditions, for the production of bio-synthetic natural gas (bio-SNG) and biochar from biogenic residues and waste, such as bark, straw, and Solid Recovered Fuel (SRF). Dedicated integrated process models were developed in Aspen Plus based on and validated against data from experimental campaigns in a gasification and gas cleaning pilot plant. Simulation runs show that the proposed concepts convert biomass to bio-SNG 10% more efficiently than the reference case, mainly due to the considerably reduced oxygen demand at the Autothermal Reformer (ATR) enabled by the improved catalyst. The co-production mode schemes showed promising results in terms of overall plant efficiency, at 76.5–78.2%, and total carbon utilisation, at 41–55.3%. The hybrid cases require an electrolyser with a power capacity almost 70% of the biomass thermal input to the gasifier, resulting in a total electricity consumption of up to 0.769 kWhe/kWh of biofuel. In return, they achieve over 50% utilisation of the carbon contained in the feedstock for biofuel production and a 70.1–76.5% total plant energy efficiency. Efficient biofuel and biochar production unlock negative emission potential, further strengthening the value of these flexible concepts. Full article