Search Results (273)

The development of low-cost and sustainable adsorbents for carbon dioxide (CO₂) capture has gained increasing attention as a strategy to mitigate greenhouse gas emissions. In this study, activated biochars produced from babassu, elephant grass, and Pinus elliottii were evaluated as CO₂ adsorbents after different activation treatments. The biochars were produced by slow pyrolysis at 400 °C and subsequently modified using three activation routes: steam activation, chemical activation with KOH, and KOH activation followed by acid washing. The materials were characterized by proximate analysis, specific surface area measurements, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, and CO₂ adsorption tests. Steam activation produced the highest specific surface areas, reaching 1270.53, 1027.28, and 907.87 m² g⁻¹ for babassu, elephant grass and Pinus, respectively. Despite the superior textural properties achieved through steam activation, the highest CO₂ adsorption capacities were obtained for the samples subjected to chemical activation followed by acid washing. These results indicate that adsorption performance is governed not only by the development of surface area but also by pore accessibility and the surface chemistry of the adsorbent. Maximum adsorption capacities of 82.78, 81.19, and 85.24 mg g⁻¹ were obtained for ACKAW B, ACKAW CE, and ACKAW P, respectively. Adsorption–desorption cycling experiments demonstrated regenerability and stable performance over repeated cycles. The results indicate that KOH activation followed by acid washing is an effective strategy for producing high-performance biochar-based adsorbents for CO₂ capture. Full article

Biochar (BC) and hydrochar (HC) have attracted increasing attention as sustainable soil amendments for improving soil water retention and mitigating agricultural water stress. This review synthesizes and compares the current state of knowledge on the production, physicochemical properties, and hydraulic performance of slow-pyrolysis BC, hydrothermal carbonization hydrochar (HTC HC), and hydrothermal liquefaction hydrochar (HTL HC). The mechanisms governing soil water retention are first examined, followed by a comprehensive review of the effects of amendment properties, feedstock type, thermochemical conversion conditions, particle size, application rate, and soil characteristics on field capacity, permanent wilting point, plant-available water, and water-holding capacity. The available evidence demonstrates that BC generally provides the most consistent improvement in soil hydraulic properties, particularly in coarse-textured soils, whereas the performance of HTC HC is considerably more variable and strongly dependent on hydrothermal conversion conditions and soil characteristics. HTL HC remains largely unexplored but shows promising hydraulic performance and exceptional resistance to biodegradation. Apparently contradictory findings among published studies are shown to arise largely from interactions among feedstock and conversion conditions, resulting amendment properties, soil characteristics, application conditions, and differences in hydraulic evaluation, highlighting the need for integrated mechanistic frameworks rather than interpretation based on individual factors. A comparative assessment of the three materials further considers ecotoxicity, biodegradation, life-cycle assessment, and techno-economic analysis. Overall, BC is currently the most mature soil amendment technology, HTC HC offers important advantages for wet biomass utilization, and HTL HC represents a promising but underdeveloped alternative. Future research should emphasize standardized evaluation methods, long-term field validation, and integrated mechanistic approaches linking production conditions, amendment properties, soil characteristics, and application conditions to enable predictive, application-specific design of carbonaceous soil amendments for sustainable soil water management. Full article

Wood vinegar (WV), also known as pyroligneous acid, is the aqueous condensate produced during lignocellulosic biomass pyrolysis, generated alongside biochar and non-condensable gases. In forest biorefineries, it represents a promising value-added coproduct capable of transforming forestry and agroforestry residues into a multifunctional bioproduct. Its composition, dominated by water, organic acids, phenolic compounds, aldehydes, and ketones, confers antimicrobial, antioxidant, biostimulant, herbicidal, and preservative properties. This review critically examines WV production, chemical composition, purification strategies, mechanisms of action, and applications, explicitly distinguishing evidence-based uses from prospective ones. Current evidence supports applications in agriculture, wood preservation, environmental management, and forestry, including forest nursery production and clonal propagation of Eucalyptus and Pinus. However, the literature remains fragmented by compositional variability, non-standardized terminology, limited mechanistic understanding, and scarce long-term toxicological and techno-economic assessments. WV holds significant potential for sustainable biomass valorization and circular bioeconomy strategies. Realizing this potential requires harmonized analytical protocols, standardized formulations, rigorous mechanistic studies, life-cycle assessments, and regulatory frameworks that support the transition of this heterogeneous pyrolysis byproduct into a reliable commodity within integrated forest biorefineries. Full article

Slow pyrolysis of a plastic fraction isolated from municipal waste produced a char, which was then used as a precursor for the synthesis of activated carbon. The process involved thermal conversion at 800 °C and chemical activation using K₂CO₃. The resulting activated carbon was used to remove Pb(II), Cd(II), and Co(II) from aqueous solutions. Physicochemical, structural, and granulometric characterizations of the resulting adsorbent were performed. The obtained material had a specific surface area of 562 m²/g, a total pore volume of 0.328 cm³/g, and a micropore volume of 0.146 cm³/g. To determine the optimal adsorption conditions, the Box–Behnken experiment planning method was used, assuming solution pH, adsorbent mass, and initial metal ion concentration as independent variables, and the percentage removal of the contaminant as the response. Studies on sorption isotherms were conducted using a static method in a periodic system for initial metal ion concentrations ranging from 10 to 250 mg/dm³. The effect of temperature on the adsorption process was analyzed, and the kinetics sorption was investigated. Several adsorption isotherm models were used to describe the adsorption equilibrium. The maximum sorption capacity was 35.5 mg/g for Pb(II), 14.7 mg/g for Cd(II), and 11.6 mg/g for Co(II). The obtained results indicate that the plastic waste based adsorbent exhibits favorable sorption properties for the tested heavy metal ions and may be useful in water and wastewater treatment processes. Full article

The excessive use of conventional NPK fertilizers can reduce nutrient use efficiency due to nutrient losses, emphasizing the need for controlled-release fertilizer systems. This study aimed to prepare and evaluate olive pomace-derived biochar (BC) as a carrier for nitrogen–phosphorus–potassium (NPK) fertilizer and assess its effects on nutrient release and lettuce performance. Biochar was produced by pyrolysis at 400 °C and loaded with NPK fertilizer. The BC/NPK composite was characterized using Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), nutrient-release behavior was evaluated in deionized water and soil. The cumulative nutrient release reached 64% in deionized water and 91% in soil. Under greenhouse conditions, BC/NPK applied at 100% and 75% NPK rates increased lettuce fresh weight, plant height and leaf number to 163.33 and 183.67 g, 23.00 and 23.67 cm, 34 and 36, respectively. Moreover, BC/NPK reduced nitrate accumulation in lettuce leaves, with nitrate concentrations decreasing in outer leaves to 10 and 0.73 mg g⁻¹ and in inner leaves to 2 and 1.33 mg g⁻¹ at the 100% and 75% rates, respectively. These findings demonstrate that olive pomace-derived BC/NPK is a promising slow-release fertilizer capable of improving crop performance while supporting sustainable nutrient management and agricultural waste valorization. Full article

The valorisation of textile wool waste through sustainable conversion technologies such as pyrolysis has gained increasing attention as an effective strategy to reduce textile waste, recover valuable resources, and support the transition toward a circular economy. Herein, we investigated the pyrolysis of processed wool textile waste in CO₂ and N₂ atmospheres to recover valuable products and reduce the environmental impact. Key factors such as the temperature, carrier gas type, feed size, condensation set-up, and reactor configuration were evaluated for their influence on product distribution and quality. Pyrolysis at 900 °C in the presence of CO₂ led to greater gas formation (79 wt%), enhanced the stability and BET surface area of the char (10–12 wt%), and increased byproducts including phenol and indole in the bio-oil (13 wt%) product. CO made up over 65% of the gas at 900 °C due to the prevalence of the reverse (endothermic) Boudouard reaction, with the remnant gas made of CO₂ (21%) and small amounts of NH₃ (2%), HCN (0.8%) and SO₂ (0.3%). This CO-rich gas could have industrial applications such as Fischer–Tropsch after conditioning and N/S removal. Moreover, the higher carbon content (82.5% at 900 °C) increased the stability of char produced with CO₂ (compared to N₂), making it suitable for soil enhancement (~10% N at 900 °C) or pollutant removal and allowing it to be categorised and marketed as biochar. Despite low-temperature pyrolysis (350 °C) not being efficient in decomposing the whole wool waste, a staged pyrolysis with an initial low-temperature stage was shown to be effective in separately removing bromine-rich compounds. In summary, this study provides insights into the thermal decomposition behaviour of wool and the influence of the reaction conditions and reactor type on product distribution. Full article

Agricultural hazelnut shell waste was converted into biochar by slow pyrolysis at 500, 700, and 900 °C and evaluated as a sustainable adsorbent for waste frying oil purification. The biochars were characterized by proximate, thermal, spectroscopic, morphological, and elemental analyses, including Brunauer–Emmett–Teller (BET) surface-area measurement, and benchmarked against activated carbon and Magnesol. Pyrolysis markedly developed the pore structure, increasing the BET surface area from 1.68 m²/g in the raw shell to 666.05 m²/g at 900 °C, and an exploratory principal component analysis summarized 90.85% of the total variance. Acid-extractable element concentrations were screened against feed-grade biochar and oenological bentonite reference values, without establishing regulatory compliance or food-contact suitability. All three biochars significantly reduced free fatty acidity (27.6–37.8%) and p-anisidine value (23.3–27.5%), with no significant difference relative to activated carbon (Tukey’s test, p > 0.05); however, total polar material was not significantly reduced under these mild, short-contact conditions. Gas chromatography showed no significant changes in the major unsaturated fatty acids of the glyceride-bound fraction, and total color differences remained small (ΔE* = 0.71–1.82). Hazelnut-shell biochar therefore shows potential as a waste-derived, circular adsorbent for selected oil-degradation products. Full article

This study explores the utilization of local biomass through slow pyrolysis in a multifunctional domestic reactor, with a view to producing renewable energy and improving soil quality in arid regions. Four underutilized biomass sources were studied: millet stalks, cashew shells, cashew shell meal, and rumen contents. Thermal monitoring using thermocouples showed pyrolysis temperatures ranging from 270 to 350 °C, while the combustion chamber reached up to 800 °C depending on the biomass. Four thermal phases were identified (heating, devolatilization, stabilization, and cooling), confirming stable reactor operation. Gas analyses revealed a predominance of CO (approximately 1000 ppm) as well as variations in O₂, H₂S, and hydrocarbons, indicating a conversion process dependent on the type of biomass and interactions between chambers. Mass and energy balances show that performance depends heavily on the physicochemical properties of the feedstocks, particularly the content of volatiles, lignin, and ash. Cashew shells exhibited the highest energy efficiency (approximately 42.9%), followed by rumen contents (approximately 34.4%), while cashew shell meal showed lower performance due to prior extraction of volatiles. Biochar yields and energy distribution vary significantly depending on the biomass, highlighting the importance of feedstock selection in decentralized pyrolysis systems. Overall, household pyrolysis enables simultaneous energy recovery and biochar production under realistic, non-optimized conditions. These results provide new insights into biomass–reactor interactions and support the development of decentralized bioenergy solutions tailored to sub-Saharan regions. Full article

The escalating global accumulation of plastic waste (PW) poses a critical obstacle to environmental sustainability, necessitating the development of viable valorization strategies. Pyrolysis process offers a thermo-chemical conversion pathway capable of transforming waste plastics into a potentially functional liquid product. This work presents a systematic and comprehensive investigation of the physicochemical, wettability, thermal stability, rheological, and tribological properties of pyrolysis oil (i.e., pyro-oil) derived from virgin linear low-density polyethylene (LLDPE) pellets to mimic the behavior of common polymers in such thermo-chemical conversion processes. Pyro-oil was produced under controlled slow pyrolysis conditions in a fixed-bed reactor at 700 °C, and its properties were benchmarked against tire-derived pyro-oil and a commercial engine oil. Chemical and structural characterization was conducted via Fourier transform infrared spectroscopy (FTIR), wavelength dispersive X-ray fluorescence (WDXRF), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). Wettability was evaluated through temperature-dependent contact angle measurements, and thermal stability was assessed by thermogravimetric analysis (TGA). Rheological profiling of the plastic pyro-oil was investigated using a rheometer apparatus at different temperatures. Lastly, the tribological properties of plastic pyro-oils at various temperatures were examined using a tribometer instrument in a ball-on-disk configuration. Results demonstrate that plastic-derived pyro-oil exhibits a hydrocarbon-dominant chemical composition similar to that of tire pyro-oil and engine oil. Its absolute viscosity is nearly similar to that of the tire pyro-oil and is lower than that of engine oil across different temperatures. Tribological testing revealed that the plastic pyro-oil results in lower friction at elevated temperatures compared to both tire pyro-oil and commercial engine oil. However, the thermal examinations showed that plastic pyro-oil has lower thermal stability than tire pyro-oil and engine oil. Overall, these findings indicate that plastic pyro-oil holds promise as a functional lubricant for low-load and moderate-temperature industrial applications, positioning PW pyrolysis as a viable contributor to circular economy strategies in the lubricants sector. Full article

The transition to a low-carbon economy requires sustainable alternatives to fossil fuels. Up-recycling municipal solid waste and forestry biomass into solid biofuels presents a promising waste-to-energy strategy. This study aimed to develop a high-calorific, highly durable hybrid solid fuel without synthetic binders, utilizing the natural interlocking of lignocellulosic and plastic matrices under mild slow pyrolysis. Blends of Eucalyptus sawdust and municipal solid waste rejects (40 wt%) were densified with and without a glycerol binder. The optimal binder-free blend underwent slow pyrolysis at 400 °C and 500 °C to evaluate energy upgrading. Results showed that the binder-free formulation achieved mechanical durability of 99.67%, whereas glycerol severely compromised the dimensional stability of the pellets. Mild pyrolysis (400 °C, 30 min) increased the higher heating value to 27.75 MJ/kg—significantly outperforming local coal (18.3 MJ/kg)—while maintaining trace chloride levels, confirming the production of an environmentally safe, premium-grade energy vector. Full article

Biochar (BC) is widely utilised to enhance methane production from the anaerobic digestion (AD) process due to its physicochemical properties. This study investigates the influence of biochar pretreatment on its behaviour and performance in AD systems. Pre-treated biochar derived from different feedstocks via slow pyrolysis was applied in Biochemical Methane Potential (BMP) tests at a dosage of 0.25% (w/v), and its impact on both the methane yield and digestion kinetics during cellulose degradation was evaluated. Pre-treatment was performed via steam autoclaving, serving as both a sterilisation and surface-modification step aimed at improving the physicochemical characteristics of biochar, particularly its capacity for microbial immobilisation. The results demonstrated that the effect of autoclave pretreatment on methane production was strongly feedstock-dependent. Autoclaved rice husk biochar (AC-RH550) markedly inhibited methane production, whereas autoclaved softwood biochar (AC-SW550) exhibited the best performance among all biochars tested, achieving the highest methane yield of 382.2 (mL CH₄ g⁻¹ VS), corresponding to an increase of 18.3% compared to non-pretreated SW550 and 9.2% relative to the control. This improvement is attributed to the modifications in biochar surface properties, promoting improved microbial activity and biofilm formation potentially improving direct interspecies electron transfer (DIET). Additionally, biochar may act as a buffering agent and provide adsorption sites for inhibitory intermediates such as VFA. Cell immobilisation experiments further confirmed that autoclaving enhanced biochar porosity and hydrophilicity, encouraging better colonisation and biofilm formation. Scanning electron microscopy (SEM) and microbial analyses verified increased cell attachment on pretreated biochars. Overall, these findings highlight the critical role of pretreatment in optimising biochar functionality for anaerobic digestion applications and cell immobilisation. Full article

The aim of the work is to present a technologically feasible method for processing waste biomass into synthesis gas for further use, namely for the synthesis of bio-methanol, which is considered an important renewable fuel. Walnut shells were tested as lignocellulosic waste. Samples with an operating particle size (0.5–3 mm) were pyrolyzed under well-defined conditions in a sealed pressure reactor, using chromium (III) oxide particles and fine particles as a catalyst. The effect of particle size on the yield and composition of resulting synthesis gas and biochar was tested. It was found that slow, catalyzed pressure pyrolysis at a final temperature of 400 °C provides synthesis gas with a H₂/CO ratio of up to 0.9 or up to 1.8 and biochar (35–39 wt.%) useful as biofuel. These products were analyzed and their use described. The residual product was greywater (25–35 wt.%). Overall, under energy-saving conditions (slow pyrolysis, final temperature of 400 °C), pressure and catalyzed pyrolysis of biomass provide usable products and acceptable residuum. Full article

A computational model of anisotropic biomass particle pyrolysis was developed to evaluate the influence of particle properties and operating conditions during fast pyrolysis. The model integrates multicomponent CRECK kinetics with intraparticle heat and mass transfer. Simulations were performed at reactor temperatures between 400 and 700 °C and convective heat transfer coefficients from 50 to 1500 W·m⁻²·K⁻¹, representing conditions from slow to fast pyrolysis. Results showed that particle size and biomass composition strongly affect conversion time and product distribution, while aspect ratio becomes significant for larger particles. Increasing particle diameter from 3 to 8 mm more than doubled conversion times and increased char yield from approximately 16% to 23%. Lignin-rich biomass such as palm shell generated higher char yields and lower volatile production than cellulose-rich feedstocks such as oak or sugarcane bagasse. Higher reactor temperatures and heating rates reduced conversion times by up to 75%, with moderate effects on product yields. Analysis of Biot and pyrolysis numbers indicated that millimeter-scale particles operate in a transition regime where conduction, convection, and chemical kinetics occur on similar timescales. Therefore, accurate reactor design models must simultaneously consider coupled transport and reaction phenomena. Full article

The accumulation of non-recyclable construction, renovation, and demolition (CRD) wood waste necessitates sustainable management strategies, for which thermochemical valorization is a promising option. Slow pyrolysis is particularly suitable due to its high biochar yields and potential to partially replace fossil coal in energy, metallurgical, construction, and environmental applications. In this study, end-of-life CRD wood was converted into biochar using a pilot-scale vertical retort–kiln system at furnace set-point temperatures of 600 °C and 800 °C for 4 h. The biochar produced at 800 °C, which exhibited superior characteristics, was subsequently subjected to post-heat treatment at 600 °C for 30–90 min in the presence of nitrogen within a tightly sealed rotary retort-kiln assembly. Self-heating behavior was evaluated using adiabatic oven tests at 120–140 °C. Biochar properties were characterized by proximate and elemental analysis, TGA/DTG, R50, FTIR, and SEM–EDX. Increasing the pyrolysis temperature to 800 °C increased carbon content from 49.88% in the raw feedstock to 85.11% in biochar, while oxygen and hydrogen contents decreased to 5.91% and 1.52%, respectively. Van Krevelen ratios (H/C = 0.21; O/C = 0.05) indicated enhanced carbon stability, with the higher heating value reaching 30.81 MJ/kg. The thermostable fraction reached 75.18%, R50 recalcitrance index 0.57, fixed carbon 70.59%, volatile carbon 23.31%, pH 8.9, and surface area 188.33 m²/g. Post-heat treatment further enhanced aromaticity (H/C = 0.18; O/C = 0.02) of this higher pyrolysis temperature biochar, increasing its fixed carbon and stability, and reducing volatile content. Extending treatment time from 30 min to 90 min raised fixed carbon to 77–78% and thermostability to 84–85%, while volatile carbon decreased to 13–15%. Microporosity peaked at 350–380 m²/g by 75 min before declining due to pore widening. SEM and EDX analyses confirmed this structural evolution, increased carbon content, reduced oxygen, suppressed alkali metals, and enrichment of alkaline earth metals. Yield loss was highest at 90 min (20–21%), highlighting the need to balance treatment severity and biochar product yield. Both the 800 °C biochar and its post-heat-treated forms passed self-heating tests, confirming improved oxidative stability for energy and environmental applications. Full article

This study investigated carbonaceous materials prepared from Paulownia tomentosa leaves by hydrothermal carbonization, slow pyrolysis, and HCl post-treatment for the adsorption of metribuzin and tebuconazole from water. Hydrochars were prepared at 180–220 °C, pyrochars at 400–600 °C, and the pyrochar produced at 600 °C was further treated with HCl. The materials were characterized by yield, ash content, active and exchangeable pH, oxidizable organic carbon content, FTIR, SEM, and CO₂-derived surface and pore properties. Increasing processing temperature reduced the yield in both conversion routes. Hydrochars retained more oxygen-containing and oxidizable organic structures, whereas pyrochars showed stronger carbonization, higher ash content, and higher CO₂-derived surface area. HCl treatment decreased the ash residue, thereby resulting in improved CO₂-accessible surface and pore properties and more fragmented morphology. Metribuzin adsorption was better described by the pseudo-second-order kinetic model across all sorbents, with the highest fitted equilibrium adsorbed amount observed following HCl treatment. Tebuconazole showed higher initial uptake toward most untreated materials, but its kinetic profiles were non-monotonic, with a decrease in the adsorbed amount at longer contact times. Consequently, the conventional PFO and PSO models did not adequately describe its complete kinetic behavior. Nonlinear isotherm modeling showed predominantly Freundlich-type fitting for metribuzin, suggesting heterogeneous adsorption sites, whereas tebuconazole was formally better described by Langmuir-type fitting, although with poorer fit quality for several materials. The results show that Paulownia tomentosa leaves are a suitable precursor for carbonaceous sorbents and that HCl-treated pyrochar is the most promising material for metribuzin adsorption. Full article