Search Results (27)

The growing demand for air connectivity, coupled with the forecasted increase in passengers by 2040, implies an exigency in the aviation sector to adopt sustainable approaches for net zero emission by 2050. Sustainable Aviation Fuel (SAF) is currently the most promising short-term solution; however, ensuring its overall sustainability depends on reducing the life cycle carbon footprints. A key challenge prevails in hydrogen usage as a reactant for the approved ASTM routes of SAF. The processing, conversion and refinement of feed entailing hydrodeoxygenation (HDO), decarboxylation, hydrogenation, isomerisation and hydrocracking requires substantial hydrogen input. This hydrogen is sourced either in situ or ex situ, with the supply chain encompassing renewables or non-renewables origins. Addressing this hydrogen usage and recognising the emission implications thereof has therefore become a novel research priority. Aside from the preferred adoption of renewable water electrolysis to generate hydrogen, other promising pathways encompass hydrothermal gasification, biomass gasification (with or without carbon capture) and biomethane with steam methane reforming (with or without carbon capture) owing to the lower greenhouse emissions, the convincing status of the technology readiness level and the lower acidification potential. Equally imperative are measures for reducing hydrogen demand in SAF pathways. Strategies involve identifying the appropriate catalyst (monometallic and bimetallic sulphide catalyst), increasing the catalyst life in the deoxygenation process, deploying low-cost iso-propanol (hydrogen donor), developing the aerobic fermentation of sugar to 1,4 dimethyl cyclooctane with the intermediate formation of isoprene and advancing aqueous phase reforming or single-stage hydro processing. Other supportive alternatives include implementing the catalytic and co-pyrolysis of waste oil with solid feedstocks and selecting highly saturated feedstock. Thus, future progress demands coordinated innovation and research endeavours to bolster the seamless integration of the cutting-edge hydrogen production processes with the SAF infrastructure. Rigorous techno-economic and life cycle assessments, alongside technological breakthroughs and biomass characterisation, are indispensable for ensuring scalability and sustainability. Full article

In order to investigate the formation pathway of hydrochar during hydrothermal carbonization (HTC) and to identify the optimal process conditions for producing high-quality pyrolysis feedstock, the effect of hydrothermal temperature (220, 250, and 280 °C) on tar and hydrochar properties were analyzed by GC-MS, XRD, XPS, FT-IR, and SEM using protein-rich brewer’s spent grain (BSG) as raw material. The results showed that aromatic compounds play a major role in tar production. Increasing hydrothermal temperature significantly enhanced volatile matter removal and consequently increased the fixed carbon content from 23.14 wt.% in HC-220 to 27.07 wt.% in HC-280, while the catalytic effect of H₃O⁺ produced by high-temperature water facilitated the dehydration and decarboxylation reactions, resulting in a reduction in the H/C atomic ratio from 1.44 in HC-220 to 1.25 in HC-280 and the O/C atom ratio from 0.32 in HC-220 to 0.25 in HC-280. HC-280 exhibited superior fuel properties, with a high heating value (HHV) of 35.4 MJ/kg. XPS analysis indicated that elevated temperatures promote the conversion of sp³ C to sp² C (the value of sp² C/sp³ C increased from 1.13 in HC-220 to 1.49 in HC-280), significantly increasing the aromatic condensation degree of hydrochar. The more pronounced reduction in the -OH content compared to -COOH indicated that dehydration reactions predominated over decarboxylation. Finally, the formation pathways of hydrochar during HTC were revealed based on the properties of different products. The results demonstrate that HTC is an effective method for converting BSG into pyrolysis feedstock with potential applications in energy production. Future work should focus on the technical–economic assessment of the process at a pilot scale and evaluating the hydrochar’s performance in real pyrolysis systems. Full article

Pruned branches from persimmon trees are a largely untapped agricultural waste resource. This study explores the conversion of these branches into an enhanced fuel source through hydrothermal carbonization. The branches were subjected to hydrothermal treatment under various conditions to identify the optimal parameters. Higher temperatures and longer treatment durations increased the carbon content to 69.2% and reduced the oxygen content to 20.4%. A Van Krevelen diagram showed that dehydration was the primary reaction, with decarboxylation occurring at 250 °C. The energy value increased from 18.2 MJ/kg for raw branches to 28.5 MJ/kg under the optimal conditions, indicating a 57% improvement. These findings demonstrate that hydrothermal carbonization effectively utilizes persimmon pruning waste, offering a sustainable method for converting biomass into energy and aiding agricultural waste management. Full article

Chicken manure (CM) is a nutrient-rich but environmentally problematic biomass that requires sustainable management. This study applied a three-step process consisting of hydrothermal activation (ZnCl₂ or H₃PO₄), catalytic hydrothermal carbonization (HCl or FeCl₃), and low-temperature pyrolysis (250 °C) to develop an energy-efficient method for producing biochar. The resulting biochars were systematically analyzed for their physicochemical properties, heavy metal content, and carbon sequestration potential, and compared with conventional pyrolysis-based biochars. Among the tested samples, the biochar produced via H₃PO₄ activation and HCl-catalyzed HTC [P-HTC(HCl)] exhibited the most favorable characteristics, including the highest carbon content (59.5 wt.%) and the lowest H/C ratio (0.65). As a result, it achieved the highest total potential carbon (TPC, 158.8 g_carbon/kg_biochar) and CO₂ reduction potential (CRP, 465.9 g_CO2-eq/kg_biochar), attributed to the strong dehydration and decarboxylation reactions and effective inorganic removal induced by Brønsted acid action. In contrast, conventional pyrolysis biochars showed significantly higher concentrations of heavy metals—up to 633 mg/kg of Cu and 2331 mg/kg of Zn—due to thermal concentration effects, whereas P-HTC(HCl) biochar presented a more balanced and environmentally acceptable heavy metal profile. In conclusion, the proposed low-temperature hydrothermal-assisted process demonstrates great potential for producing high-performance biochar from chicken manure with enhanced environmental safety and carbon storage efficiency. Full article

Waste polyethylene terephthalate (PET) bottles represent 12% of global plastic waste; however, only 9% are recycled. Hydrothermal processing presents the opportunity to upcycle waste PET into its monomers, particularly, terephthalic acid (TPA). In this study, post-consumer PET sparkling water bottles were neutrally hydrolysed via a hydrothermal process operating within a temperature range of 220–270 °C, a residence time of 30–90 min, and autogenous pressure of 25–90 bar. Under these conditions, the TPA yield varied between 7.34 and 81.05%, and the maximum TPA yield was obtained at 250 °C, 90 min, and 40 bar. The process temperature had a more profound impact on the PET conversion and TPA yield than the residence time. The values of the environmental factor (EF) were found to be 0.017–0.106, which were comparable to those of bulk chemicals (EF < 1). With the chosen operating conditions, the environmental energy impact (EEI) of TPA production was estimated to be 5.29 × 10⁴ °C min. The findings demonstrate that neutral hydrolysis is a feasible approach for converting PET polymers into monomers under mild environmental conditions. In addition, a GCMS analysis of the aqueous-phase product revealed a notable increase in the secondary degradation products of TPA, such as benzoic acid, rising from 66.4% to 75.7% as the process temperature increased from 220 °C to 270 °C. The degradation mechanisms of PET were found to be decarboxylation, dehydration, and oxidation. The dominant mechanism was found to be a decarboxylation reaction. Full article

Hydrothermal carbonization (HTC) is a novel thermochemical process that turns biomass into hydrochar, a substance rich in carbon that has potential uses in advanced material synthesis, energy production, and environmental remediation. With an emphasis on important chemical pathways, such as dehydration, decarboxylation, and polymerization, that control the conversion of lignocellulosic biomass into useful hydrochar, this review critically investigates the fundamental chemistry of HTC. A detailed analysis is conducted on the effects of process variables on the physicochemical characteristics of hydrochar, including temperature, pressure, biomass composition, water ratio, and residence time. Particular focus is placed on new developments in HTC technology that improve sustainability and efficiency, like recirculating process water and microwave-assisted co-hydrothermal carbonization. Furthermore, the improvement of adsorption capacity for organic contaminants and heavy metals is explored in relation to the functionalization and chemical activation of hydrochar, namely through surface modification and KOH treatment. The performance of hydrochar and biochar in adsorption, catalysis, and energy storage is compared, emphasizing the unique benefits and difficulties of each substance. Although hydrochar has a comparatively high higher heating value (HHV) and can be a good substitute for coal, issues with reactor design, process scalability, and secondary waste management continue to limit its widespread use. In order to maximize HTC as a sustainable and profitable avenue for biomass valorization, this study addresses critical research gaps and future initiatives. Full article

This study investigated the production of high-performance biochar from swine manure using a sequential carbonization process combining hydrothermal carbonization (HTC) and pyrolysis. Biochar produced through HCl-assisted sequential carbonization exhibited superior properties, including the highest fixed carbon (70.0%), higher heating value (28.48 MJ/kg, ~18.8% increase over HTC-Py), and BET surface area (279.66 m²/g, ~17 times higher than other biochars). These improvements were attributed to the catalytic role of HCl in promoting dehydration, hydrolysis, and decarboxylation, leading to a more condensed and stabilized carbon structure. Furthermore, HCl significantly enhanced heavy metal removal, reducing Zn to 343.17 mg/kg (compared to HTC-Py 1324.15 mg/kg) and lowering Cd, As, Cu, Pb, Ni, and Cr by 70–80%, demonstrating effective demineralization. This approach presents a practical strategy for producing high-quality biochar with improved carbonization, energy properties, and pollutant removal, offering potential applications in environmental and agricultural fields. Full article

Hydrothermal liquefaction of solid waste has been gaining more and more attention over the last few years. However, the properties of the HTL product, i.e., biocrude, are limiting its direct utilization. As a result, HTL biocrude upgrading is essential to improve its quality. The main objective of the current research is to study the hydrotreatment stabilization of HTL biocrude, produced from spent coffee grounds, utilizing commercial hydrotreated catalysts, and also to investigate the integration of the stabilized biocrude into a light cycle oil (LCO) hydrotreatment plant for coprocessing to target hybrid fuel production. The results have shown that hydrotreatment is a very promising technology that can successfully remove the oxygen content from raw biocrude by hydrodeoxygenation, decarbonylation and decarboxylation reactions, leading to a stabilized product. The stabilized product can be easily blended with the LCO stream of a typical refinery, leading to the production of jet and diesel boiling range hydrocarbons, favoring at the same time the hydrogen consumption of the process. The findings of this manuscript set the basis for future research targeting the production of renewable advanced biofuels from HTL biocrude from municipal waste. Full article

Hydrothermal carbonization (HTC) is a widely used process for converting biomass with a wide range of moisture. Biomass selection poses challenges in producing hydrochar with desired properties because of their different constituents. In this study, we investigated the fuel properties of hydrochar of sorghum bagasse (SB) and microalgae (MA) at different severity factors (SFs = 4.08, 4.43, 5.56, 5.90, and 6.63) and their potential as alternatives to coal. The results show that during HTC, both biomasses underwent dehydration, in addition to the noticeable decarboxylation of MA. Fixed carbon increasingly developed in the SB hydrochar, in contrast to the MA hydrochar, which formed volatile hydrocarbon; thus, the MA hydrochar released heat values of 26.7–36.2 MJ·kg⁻¹, which was higher than that of SB at 19.7–28.0 MJ·kg⁻¹. However, owing to the stable hydrocarbons, SB hydrochar is assumed to combust more stably and ignite more decently, as indicated by its fuel ratio (0.83), approaching 0.9–1.5. Moreover, the greater number of solids recovered in SB after carbonization makes its conversion more techno-commercially viable, retaining 1.8 times more of the original energy. Conflating these fuel properties reveals that SB hydrochar (SF = 6.63) is a promising alternative to steam coal, and MA hydrochar is an attractive alternative to both steam (SF = 4.08–5.90) and coking coals (SF = 6.63). Concisely, both biomasses are practically promising as value-added hydrochars, but only SB can be developed beyond the current HTC severity owing to the thermal stability of its hydrocarbons. Full article

Phytomining is a sustainable approach that uses hyperaccumulators for critical element extraction from various substrates, such as contaminated soils, mine tailings, and aqueous solutions. In this study, grass seeds were fed with a solution containing Y, La, Ce, and Dy, resulting in around 510 mg/kg (dry basis) of total rare earth elements (TREEs) accumulated in grass leaves. Electron probe microanalyzer (EPMA) analysis showed that rare earth elements (REEs) in the grass leaves (GL) predominantly complexed with phosphorous (P). Around 95% of Y, 93% of La, 92% of Ce, and 93% of Dy were extracted from the GL using 0.5 mol/L H₂SO₄ at a solid concentration of 5 wt.%. Subsequently, microwave-assisted hydrothermal carbonization (MHTC) was used to convert the leaching residue into hydrochar to achieve a comprehensive utilization of GL biomass. The effect of temperature on the structural properties and chemical composition of the resulting hydrochar was evaluated. Scanning electron microscopy (SEM) analysis revealed that the original structure of GL was destroyed at 180 °C during MHTC, producing numerous microspheres and pores. As the reaction temperature increased, there was a concurrent increase in carbon content, a higher heating value (HHV), and energy densification, coupled with a decrease in the hydrogen and oxygen contents of hydrochar. The evolution of H/C and O/C ratios indicated that dehydration and decarboxylation occurred during MHTC. The results showed that the waste biomass of the GL after REE extraction can be effectively converted into energy-rich solid fuel and low-cost adsorbents via MHTC. Full article

The 8# coal seam in the Benxi Formation of the southeastern margin of the Ordos Basin is a deep coal seam with abundant coalbed methane resources. Calcite veins are commonly developed within the 8# coal seam, and their formation processes and mechanisms have significant implications for the enrichment of deep coalbed methane. Genesis of the calcite veins was analyzed to reveal the impact of the calcite veins formation on coalbed methane accumulation, with an integrated application of petrographic study by thin section, cathodoluminescence analysis, carbon-oxygen isotope analysis, and homogeneous temperature measurements of fluid inclusions. The research findings indicate that the calcite veins in the 8# coal seam can be classified into three stages: C1, C2, and C3. The diagenetic fluids of C1 primarily originated from contemporaneous seawater. The fluids responsible for the formation of C2 primarily consist of organic fluids enriched in biogenic gas, whereas the fluids contributing to the formation of C3 are primarily associated with liquid hydrocarbons originated form decarboxylation of organic matter. Furthermore, the development of both C2 and C3 is influenced by deep hydrothermal fluids resulting from tectonic heating events during the Early Cretaceous. By combining analysis of the hydrocarbon accumulation history and burial history in the study area, it has been established that C2 formation occurred during the Late Triassic to Early Jurassic, while C3 formation took place during the Late Jurassic to Early Cretaceous. The exploration and production practices in the study area have firmly established the crucial significance of the formation and evolution of calcite veins within the 8# coal seam for the migration and accumulation of coalbed methane. The research outcomes provide valuable insights for the exploration of deep coalbed methane enrichment areas. Full article

Hydrothermal carbonization (HTC) is an attractive, green technology for the management of sewage sludge. In this study, low-value secondary sewage sludge was subjected to an HTC treatment in a 1 L batch hydrothermal reactor and transformed into a high-energy-density hydrochar under varying HTC conditions (temperature of 150–300 °C, carbonization time of 30–150 min and a solid loading of 10–30%). The resulting hydrochar fuel characteristics were analyzed for ultimate and proximate analyses, functional group composition and energetic parameters. It was found that the hydrochar yield decreased with the increasing HTC temperature and reaction time, primarily due to the loss of organic volatile matter and functional groups. Under the optimum conditions of 150 °C, 30 min of carbonization time and 30% solid loading, 80.56% of the hydrochar was recovered, providing a maximum energy yield of 90.32% and a high heating value of 18.49 MJ/kg. Compared to the raw sewage sludge (H/C ratio of 2.67 and O/C ratio of 0.51), the hydrochar also had lower H/C and O/C atomic ratios of 1.42 and 0.18, respectively. The results suggest that significant dehydration and decarboxylation during the HTC treatment of sewage sludge have resulted in the formation of carbonaceous hydrochar with energetic properties close to the sub-bituminous coals. Full article

Hydrogen peroxide catalytic activation holds great promise in the treatment of persistent pollutants. In this study, the novel Mn-Acac_air/Al, Mn-Acac_arg/Al and Mn-BTC_arg/Al catalysts, supported on Al₂O₃, were applied for rapid hydrogen peroxide activation and azithromycin antibiotic removal. The catalysts were prepared by the calcination-hydrothermal method under air or argon atmosphere. The characterization confirmed that the modification of manganese with acetylacetonate and benzene-1,3,5-tricarboxylic acid (H₃BTC) O-donor ligands highly improves the catalyst porosity, amorphousity, and abundance of coordinately unsaturated sites, which facilitate the generation of reactive oxygen species. The hydrogen peroxide activation and azithromycin removal reached 98.4% and 99.3% after 40 min using the Mn-BTC_arg/Al catalyst with incredible stability and reusability. Only a 5.2% decrease in activity and less than 2% manganese releasing in solutions were detected after five regeneration cycles under the optimum operating conditions. The removal intermediates were identified by LC-MS/MS analysis, and the pathways were proposed. The hydroxylation and decarboxylation reactions play a key role in the degradation reaction. Full article

This study explores the effects of hydrothermal carbonization (HTC) on the fuel properties of empty fruit bunches (EFB) by varying the reaction temperatures between the range of 180–300 °C. The improved properties of hydrochars following HTC were achieved by analyzing the changes in the physical and chemical properties of EFB. Moreover, it can save energy during treatment processes, in addition to evaluating the improvement of the biofuel stability based on the equilibrium moisture content and agglomeration. The results showed that the chemical structure of EFB decomposed owing to dehydration and decarboxylation reactions, leading to increased carbon and fixed carbon concentrations in the obtained hydrochar; and thus, an increased calorific value. Hydrochar generated during HTC exhibited chemical properties similar to those of conventional coal fuel. The optimal HTC reaction temperature range was ~230–250 °C. Based on the X-ray fluorescence results, hydrochar produced during HTC had smaller K and Cl contents and a smaller degree of agglomeration than the original sample, indicating that clinker production can be reduced by the HTC of EFB. The results of this study have significance in the utilization of unused waste biomass as an energy source that can replace fossil fuels. Full article

The development of an efficient catalyst especially with a high productivity for decarboxylation of L-lysine to cadaverine, is of both industrial and economic significance. Here, we reported the synthesis of RuO₂ well-confined in the supercage of FAU zeolite (RuO₂@FAU) through in situ hydrothermal strategies. A set of characterizations, such as XRD, Raman, TEM, XPS, NH₃-TPD and N₂ physical adsorption, confirmed the successful encapsulation of RuO₂ clusters (~1.5 nm) inside the FAU zeolite. RuO₂@FAU had the higher cadaverine productivity of 120.9 g/L/h/mmol cat., which was almost six times that of traditionally supported ruthenium oxide catalysts (21.2 g/L/h/mmol cat.). RuO₂@FAU catalysts with different ammonia exchange degrees, as well as different Si/Al ratios were further evaluated. After optimization, the highest cadaverine productivity of 480.3 g/L/h/mmol cat. was obtained. Deep analysis of the electronic properties of RuO₂@FAU indicated that the surface defect structures, such as oxygen vacancies, played a vital role in the adsorption or activation of L-lysine which finally led to a boosted performance. Furthermore, the mechanism of decarboxylation of L-lysine to cadaverine was proposed. Full article