Search Results (78)

The global shift toward carbon-neutral energy systems has renewed interest in biorefineries as integrated platforms for the sustainable production of fuels, chemicals, and materials. In this context, lignin, the second most abundant natural polymer and the only renewable source of aromatic carbon, has gained attention as a promising feedstock for high-value applications. Despite its high energy density and chemically complex structure, lignin is primarily used as a low-value fuel through combustion, a practice that fails to capitalize on its molecular potential and offers minimal energetic and economic benefits to the industry. Unlocking its value requires a fundamental shift toward energy-efficient valorization strategies that minimize external energy input while retaining carbon in marketable products. To enable a comprehensive evaluation of this shift, this perspective introduces a three-criterion framework—operating below 250 °C and 50 bar, achieving a fossil energy ratio above one across all process steps, and retaining more than 40% of lignin carbon in recoverable products—and applies it to critically evaluate four lignin valorization pathways: catalytic depolymerization, solvent-assisted fractionation, biological and electrochemical conversion, and material-based applications. Across all pathways, system-level integration, namely, separation, solvent recycling, and catalyst generation, constantly influences the overall energy balance and represents the field’s unresolved challenge. To address these barriers, this perspective discusses several future research directions spanning advanced catalyst design, biotechnology, computational tools, and process intensification, alongside the policy and economic measures needed to enable the commercial deployment of integrating lignin valorization with existing biorefinery operations. Collectively, these insights aim to elevate lignin from an underutilized by-product to a foundational resource for circular, low-carbon bioeconomy. Full article

The sustainable conversion of agricultural waste biomass, particularly crop residues such as corn stover, into high-value products is vital for reducing their open-field burning and mitigating environmental hazards. The hydrothermal carbonization (HTC) process integrated with natural deep eutectic solvents (NADES) presents an alternative approach for valorizing biomass into lignin-rich solid fuels and fermentable sugars for bioethanol production. In this study, corn stover was subjected to HTC using deionized (DI) water, a xylose-based NADES (ChCl:Xy:W), and an oxalic acid-based NADES (ChCl:OA:W) in a 150–300 °C temperature range to optimize both solid fuel and sugar stream yields. Characterization, including fiber analysis, SEM, FTIR, EDS, and bomb calorimetry, was conducted to evaluate structural, compositional, and energetic transformations. The results explored the HTC process, restructuring the biomass, promoting extensive hemicellulose solubilization and cellulose depolymerization, as well as substantially enriching lignin and polymerized compounds with increasing temperature. In addition, the DI water at 300 °C generated a lignin-rich residue, the Xy-based NADES effectively removed ash and extractives, and the OA-based NADES produced the most carbon-dense hydrochar with the highest calorific value. Collectively, these findings demonstrate that solvent-assisted HTC may be employed as a possible strategy for the valorization of agricultural residues into high-energy solid fuels. Full article

Organic residues from households and food-service facilities, such as orange peels, spent coffee grounds, banana peels and potato skins, represent abundant biomass resources that can release undesirable compounds during degradation. Their conversion into carbonized materials through thermochemical processes offers a sustainable route for waste valorization. In this study, residues were characterized by proximate and elemental analyses, density, porosity, and calorific value. Valorization was performed using microwave-assisted pyrolysis and two hydrothermal carbonization (HTC) routes. Pyrolysis experiments were conducted at 450, 600 and 800 W with residence times of 20–70 min. Conventional HTC was carried out at 180, 200 and 220 °C for 20 h, while autoclave HTC was performed at 134 °C for 2 and 4 h. The resulting biochars and hydrochars were evaluated for their physicochemical and energetic properties and ANOVA was applied to assess the influence of operating conditions. Conventional HTC at higher temperatures produced the highest calorific values, whereas microwave-assisted pyrolysis at 800 W provided competitive HHVs with high solid yields. Autoclave HTC enhanced solid retention and carbon preservation. Among the investigated residues, spent coffee grounds exhibited the most favorable solid-phase energetic performance. These findings demonstrate that thermochemical conversion enables the transformation of common residues into carbon-rich materials with physicochemical and energetic properties relevant for comparative assessment and future application-oriented studies. It should be noted that conventional hydrothermal carbonization experiments were conducted using pre-dried biomass, which represents a methodological limitation of the comparative assessment. Full article

This study evaluated the impact of hydrodynamic cavitation (HC) versus conventional thermal processing (TT) for the valorization of fruit and vegetable surpluses, using optimized purees of carrot, banana, yacón, beetroot, and gulupa. HC-treated purees consistently preserved bioactive compounds, with vitamin C retention in purple carrot puree reaching 6.8 ± 0.6 mg/100 g, compared to only 0.6 ± 0.0 mg/100 g after thermal treatment. Total polyphenol content and antioxidant capacity (FRAP up to 2580 ± 126 μmol Eq-Trolox/100 g, DPPH inhibition up to 88.72% ± 0.80) were similarly superior with HC. While HC resulted in noticeably higher grumosity and fibrosity, limiting acceptance, TT improved sensory sweetness but degraded nutritional quality, causing up to 80% losses of vitamin C and bioactives. The findings confirm that HC is an effective non-thermal strategy for converting agri-food surpluses into functional ingredient bases, maximizing nutritional retention and energetic efficiency and supporting sustainable circular food systems. Full article

The present study investigates the potential of poplar (Populus spp.) biomass from phytoremediation plantations as a feedstock for downdraft fixed bed gasification. The biomass was characterized in terms of moisture, ash content, elemental composition (C, H, N, O), and calorific values (HHV and LHV), confirming its suitability for thermochemical conversion. Gasification tests yielded a volumetric syngas production of 1.79 Nm³ kg⁻¹ biomass with an average composition of H₂ 14.58 vol%, CO 16.68 vol%, and CH₄ 4.74 vol%, demonstrating energy content appropriate for both thermal and chemical applications. Alkali and alkaline earth metals (AAEM), particularly Ca (273 mg kg⁻¹) and Mg (731 mg kg⁻¹), naturally present enhanced tar reforming and promoted reactive gas formation, whereas heavy metals such as Cd (0.27 mg kg⁻¹), Pb (0.02 mg kg⁻¹), and Bi (0.01 mg kg⁻¹) were detected only in trace amounts, posing minimal environmental risk. The results indicate that poplar pruning residues from phytoremediation sites can be a renewable and sustainable energy resource, transforming a waste stream into a process input. In this perspective, the integration of soil remediation with syngas production constitutes a tangible model of circular economy, based on the efficient use of resources through the synergy between environmental remediation and the valorization and sustainable management of marginal biomass—i.e., pruning residues—generating environmental, energetic, and economic benefits along the entire value chain. Full article

The leather industry generates large amounts of solid waste, creating environmental concerns for the presence of hazardous compounds such as chromium. In fact, conventional disposal practices, including landfill and incineration, promote the formation of hexavalent chromium (Cr⁶⁺) and polluting emissions. This work reviews biochemical and thermochemical processes for the energetic valorization of different leather solid wastes, namely untanned, tanned with chromium or vegetable tanning agents, and post-consumer leather. Thermochemical routes, i.e., pyrolysis, gasification, and hydrothermal treatment (HT), can convert leather waste into energy carriers including bio-oil, syngas, and char, while anaerobic digestion (AD) is a biochemical method used to produce biogas. Particularly, pyrolysis is promising for fuel precursors and chromium stabilization, HT suits wet, raw waste, while gasification enables syngas recovery. In AD, microbial chromium inhibition is mitigated through the co-digestion of degradable substrates. This review takes a waste-type-driven rather than process-driven approach to provide new insights into the conversion of leather solid waste into value-added products, showing that the optimal recycling route depends on the waste characteristics. Moreover, these methods have not yet been directly compared in terms of their energy production performance with regard to leather waste. Future work should improve process conditions, evaluate chromium and finishing additive impacts, and assess scalability. Full article

Plastic pollution, driven by the durability and widespread use of polyolefins such as polypropylene (PP) and high-density polyethylene (HDPE), poses a formidable environmental challenge. To address this issue, we have developed an integrated multiscale framework that combines thermocatalytic experimentation, process-scale simulation, and molecular-level modeling to optimize the catalytic pyrolysis of PP and HDPE waste. Under the identified optimal conditions (300 °C, 10 wt % HMOR zeolite), liquid-oil yields of 60.8% for PP and 87.3% for HDPE were achieved, accompanied by high energy densities (44.2 MJ/kg, RON 97.5 for PP; 43.7 MJ/kg, RON 115.2 for HDPE). These values significantly surpass those typically reported for uncatalyzed pyrolysis, demonstrating the efficacy of HMOR in directing product selectivity toward valuable liquids. Above 400 °C, the process undergoes a pronounced shift toward gas generation, with gas fractions exceeding 50 wt % by 441 °C, underscoring the critical influence of temperature on product distribution. Gas-phase analysis revealed that PP-derived syngas contains primarily methane (20%) and ethylene (19.5%), whereas HDPE-derived gas features propylene (1.9%) and hydrogen (1.5%), highlighting intrinsic differences in bond-scission pathways governed by polymer architectures. Aspen Plus process simulations, calibrated against experimental data, reliably predict product distributions with deviations below 20%, offering a rapid, cost-effective tool for reactor design and scale-up. Complementary density functional theory (DFT) calculations elucidate the temperature-dependent energetics of C–C bond cleavage and radical formation, revealing that system entropy increases sharply at 500–550 °C, favoring the generation of both liquid and gaseous intermediates. By directly correlating catalyst acidity, molecular reaction mechanisms, and process-scale performance, this study fills a critical gap in plastic-waste valorization research. The resulting predictive platform enables rational design of catalysts and operating conditions for circular economy applications, paving the way for scalable, efficient recovery of fuels and chemicals from mixed polyolefin waste. Full article

Residual and waste materials such as biowaste and the perennial energy crop Silphium perfoliatum (cup-plant) contain high fiber contents, which limit their energetic utilization in biogas plants. Pre-separating the fiber fraction can improve overall valorization. The recovered natural fibers can be further used as raw materials, e.g., in paper production or fiber-reinforced composites. This study aimed to optimize fiber extraction from biogenic residues and renewable raw materials using pilot-scale Thermal-pressure hydrolysis (TPH). Biowaste and cup-plant were used as substrates. Process parameters (150, 160, 170 °C; 15, 30, 60 min) were systematically varied to evaluate their influence on process efficiency, chemical composition, and functional properties of the resulting fiber and pulp fractions. Biowaste and cup-plant produced final products with similar dry matter (DM) contents—fibers (~36% DM) and pulp (~3.2% DM)—but differed markedly in chemical composition: biowaste was richer in nutrients, whereas the cup plant contained more fiber. Sugar release from the cup-plant increased by over 1900% during TPH and, like the organic acids, was largely relocated to the pulp fraction. Methane yields of the resulting pulps ranged between 310 and 375 L_CH4kg_ODM⁻¹, significantly higher than those measured in the fiber fractions, which ranged from 180 to 250 L_CH4kg_ODM⁻¹. Approximately 55% of the total energy potential was transferred into the pulp. Despite the formation of organic acids and potential inhibitors during TPH, no critical threshold values were exceeded. The energy balance of the Biowaste fiber processing was neutral (biowaste: energy demand 475 kWh/t, energy yield from biogas 484 kWh/t). For papermaking applications, the cup-plant proved to be significantly more suitable, as the heterogeneity and contamination of biowaste limited its material usability. The results highlight the potential of TPH for the combined energetic and material utilization of biogenic residues. Full article

In light of the exponential rise in feed costs within the livestock sector, the scientific research and valorization of novel agro-industrial by-products have essential strategies in animal nutrition. The overall objective of this study was to characterize and evaluate the inclusion of a novel olive pulp included at 12% of the concentrate on a dry matter basis in the diet of Murciano–Granadina goats to assess its effects on ruminal fermentation, nutrient digestibility, energy and nitrogen metabolism, and milk yield and composition. Two experiments were conducted, taking into account two groups (control group, CTL, and an experimental group) with the inclusion of 12% olive pulp in the concentrate (OPD): one in vivo trial in metabolic cages (n = 10 nulliparous female goats (34.1 ± 0.70 kg) per treatment) was conducted to evaluate digestibility, nitrogen balance, and energetic utilization; and a second on-farm production trial (n = 24 adult dairy goats (53.6 ± 1.14 kg) per treatment). The results showed no significant differences in energy balance or microbial protein synthesis between CTL and OPD (p > 0.05). However, the OPD exhibited higher digestibility of dry matter (71.2 vs. 68.8%; p = 0.028), organic matter (70.8 vs. 68.4%; p = 0.026), and crude fat (85.9 vs. 83.4%; p = 0.024), but lower crude protein digestibility (70.7 vs. 73.4%; p = 0.012) and nitrogen excretion (1.24 vs. 1.44 g/kg^0.75; p < 0.001). Additionally, ruminal butyrate concentrations were higher in OPD goats (13.5 vs. 11.3 mol/100 mol of total short-chain fatty acids; p = 0.020). Although milk yield remained unaffected, the OPD exhibited higher milk protein (4.17 vs. 3.79%; p = 0.036) and conjugated linoleic acid (0.620 vs. 0.400%; p < 0.001) concentrations compared to CTL. These findings demonstrate that the inclusion of 12% of the novel olive pulp in goat concentrate is a viable feeding strategy that maintains productive performance while enhancing the nutritional quality of milk. Full article

The reverse water gas shift reaction (RWGS) is a key step in the valorization of CO₂ to value-added products such as fuel. Metal carbides, particularly molybdenum carbide (Mo₂C), supported on transition metal oxide supports have been reported as promising materials to be used as catalysts for the low-temperature RWGS reaction. A deeper understanding of catalyst support interactions can be greatly beneficial for the development of better and more efficient catalysts in the future. To this end, this study computationally investigated the effect of the interaction between the Mo₂C(001) surface and the MgO(001) surface on the RWGS mechanism. The RWGS mechanisms were explored at the Mo₂C/MgO interface, as well as on the bare surface of Mo₂C. While the pathway at the interface went through an associative-type mechanism and a carboxylate intermediate, the Mo₂C surface was found to go through a redox-type mechanism. Interestingly, both the kinetics and thermodynamics of each pathway were similar, suggesting that the observed differences in the CO₂ hydrogenation pathways were primarily limited by the diffusion of CO₂ across the MgO surface rather than inhibitory energetics resulting from the interplay of the Mo₂C material and MgO support. Full article

Almond hulls and shells, the byproducts of the almond industry, were analyzed to assess their potential valorization pathways. Shells showed a higher content in lignin and polysaccharides, but very low levels of extractives and inorganics. Hull’s high polar extractives fraction showed poor phenolic preponderance and antioxidant activity, but high sugar and mineral contents, and its lipophilic extracts were highly enriched in triterpenes (from 73.5% to 91.3%), while shells presented more fatty acids (27.4% to 34.2%) and sterols (17.4% to 29.1%). Shells exhibited much higher S/G ratio (syringyl to guaiacyl units) in their lignin polymer (1.0 to 1.4), compared to hulls (0.5 to 0.6). After mineral analyses, hulls showed high amounts of potassium (3.7–4.9%). Fixed carbon content was similar for both materials, but shells showed a higher energetic content, ~20 MJ/kg. Finally, both hulls and pellets increased the water holding capacity (WHC) of the soil by 50%, when added in weight percentages of 6.25% (hulls) and 25% (pellets). With these results, the range of possibilities for these waste materials is exciting: shells could be used to obtain hemicellulose oligosaccharides, while hulls could be used in sugar extraction for biotransformation or as a soil amendment. Full article

The decarbonization of hard-to-defossilize sectors, such as international maritime transport, requires innovative, and at times disruptive, energy solutions that combine efficiency, scalability, and climate benefits. Therefore, power-to-liquid (PtL) routes have stood out for their potential to use low-emission electricity for the production of synthetic fuels, via electrolytic hydrogen and CO₂ capture. However, the high energy demand inherent to these routes poses significant challenges to large-scale implementation. Moreover, PtL routes are usually at most neutral in terms of CO₂ emissions. This study evaluates, from a thermo-energetic perspective, the optimization potential of an e-methanol synthesis route through integration with a biomass oxy-fuel combustion process, making use of electrolytic oxygen as the oxidizing agent and the captured CO₂ as the carbon source. From the standpoint of a first-law thermodynamic analysis, mass and energy balances were developed considering the full oxygen supply for oxy-fuel combustion to be met through alkaline electrolysis, thus eliminating the energy penalty associated with conventional oxygen production via air separation units. The balance closure was based on a small-scale plant with a capacity of around 100 kta of methanol. In this integrated configuration, additional CO₂ surpluses beyond methanol synthesis demand can be directed to geological storage, which, when combined with bioenergy with carbon capture and storage (BECCS) strategies, may lead to net negative CO₂ emissions. The results demonstrate that electrolytic oxygen valorization is a promising pathway to enhance the efficiency and climate performance of PtL processes. Full article

Incineration is a widely adopted method for the disposal of waste energetic materials (SP). Nevertheless, this approach is associated with considerable thermal energy loss and significant environmental pollution. To address these limitations, this study proposes a co-pyrolysis process incorporating pine sawdust (SD) with SP. This technique utilizes the exothermic decomposition of energetic substances and the endothermic pyrolysis of biomass. Through this synergistic thermal interaction, the process enables efficient energy recovery and facilitates the resource valorization of SP. The pyrolysis kinetics and thermodynamics of SP, SD, and their blends were investigated. Synchronous thermal analysis examined the co-pyrolysis reaction heat at varying blend ratios, while the temperature’s effects on the gas–liquid–solid product distribution were explored. The results indicate that the apparent activation energy (E_a) required for co-pyrolysis of the SP and SD exhibits an initial increase followed by a decrease in both Stage 1 and Stage 2. Furthermore, the mean apparent activation energy (E_avg) during Stage 1 (FWO: 101.87 kJ/mol; KAS: 94.02 kJ/mol) is lower than that in Stage 2 (FWO: 110.44 kJ/mol; KAS: 100.86 kJ/mol). Co-pyrolysis reaction heat calculations indicated that SD addition significantly mitigates the exothermic intensity, shifts decomposition to higher temperatures (the primary exothermic zone shifted from 180–245 °C to 265–400 °C), and moderates heat release. Elevated temperatures increase the gas yield (CO and H₂ are dominant). High temperatures promote aromatic bond cleavage and organic component release; the char’s calorific value correlates positively with the carbon content. Higher co-pyrolysis temperatures increase the nitrogenous compounds in the oil, while the aldehyde content peaks then declines. This work proposes a resource recovery pathway for SP, providing fundamental data for co-pyrolysis valorization or the development of catalytic conversion precursors. Full article

Globally, winery wastewaters (WWWs) are estimated to account for about 62.5 billion L annually (2021), with COD levels up to 300,000 mg O₂/L primarily attributed to residual ethanol, posing serious environmental concerns. Conventional treatments are effective in COD removal, but they often miss opportunities for energy recovery and resource valorization. This study investigates the aqueous phase reforming (APR) of ethanol-rich wastewater as an alternative treatment for both COD reduction and energy generation. Two scenarios were assessed: electricity and heat cogeneration (S1) and hydrogen production (S2). Process simulations in Aspen Plus^® V14, based on lab-scale APR data, provided upscaled material and energy flows for techno-economic analysis, life cycle assessment, and energy sustainability analysis of a 2.5 m³/h plant. At 75% ethanol conversion, the minimum selling price (MSP) was USD0.80/kWh with a carbon footprint of 0.08 kg CO₂-eq/kWh for S1 and USD7.00/kg with 2.57 kg CO₂-eq/kg H₂ for S2. Interestingly, S1 revealed a non-linear trade-off between APR performance and energy integration, with higher ethanol conversion leading to a higher electricity selling price because of the increased heat reactor duty. In both cases, the main contributors to global warming potential (GWP) were platinum extraction/recovery and residual COD treatment. Both scenarios achieved a positive energy balance, with an energy return on investment (EROI) of 1.57 for S1 and 2.71 for S2. This study demonstrates the potential of APR as a strategy for self-sufficient energy valorization and additional revenue generation in wine-producing regions. Full article

The energetic valorization of digestate obtained from anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) was investigated via pyrolysis in a bench-scale rotary kiln. The mass rate of dried digestate to the rotary kiln pyrolyzer was fixed at 500 gr/h. The effect of the pyrolysis temperature was investigated at 600, 700, and 800 °C. The pyrolysis products, char, oil, and gas, were quantified and chemically analyzed. It was observed that with the increase in the temperature from 600 to 800 °C, the char decreased from 60.3% to 52.2% and the gas increased from 26.5% to 35.3%. With the aim of increasing the methane production and methane concentration in syngas, the effect of CaO addition to the pyrolysis process was investigated at the same temperature, too. The mass ratio CaO/dried digestate was set at 0.2. The addition of CaO sorbent has a clear effect on the yield and composition of pyrolysis products. Under the experimental conditions, CaO was observed to act both as a CO₂ sorbent and as a catalyst, promoting cracking and reforming reactions of volatile compounds. In more detail, at the investigated temperatures, a net reduction in CO₂ concentration was observed in syngas, accompanied by an increase in CH₄ concentration. The gas yield decreased with the CaO addition because of CO₂ chemisorption. The oil yield decreased as well, probably because of the cracking and reforming effect of the CaO on the volatiles. A very promising performance of the CaO sorbent was observed at 600 °C; at this temperature, the CO₂ concentration decreased from 32.2 to 13.9 mol %, and the methane concentration increased from 16.1 to 29.4 mol %. At the same temperature, the methane production increased from 34 to 63 g/kg_digestate. Full article