ABSTRACT. Carbonaceous wastes including biomass is envisaged to plan an important role in future sustainable energy transition for achieving circular economy. This talk starts with the key biomass features that must be considered in biomass utilisation. Biomass is widely dispersed, available locally, bulky, of high moisture content and low-energy-density, leading to its high logistic cost in practical applications. Biomass is also of a fibrous nature and has a poor grindability. Therefore, a bioenergy plant, which directly takes biomass as feedstock, needs to be distributed, of small scale, and flexible to handle large particles. During thermochemical processing, biomass conversion is dominated by gaseous phase reactions as results of its high moisture and volatile contents, leading to mismatch in fuel properties when co-processed in existing stationary plants. This talk further recognises pyrolysis as a flexible thermochemical technology for local processing. Pyrolysis can be used to convert biomass into solid (biochar), liquid (bio-oil) and pyrolytic gas that can be used to supply the energy for drying and pyrolyser operation. Biochar and bio-oil, a mixture of these two, or other bioproducts derived, are high-energy-density fuels/products that are favourable for transport. The yields and properties of these bioproducts are highly dependent on feedstock properties, processing conditions and the underlying reaction mechanisms. This enables a favourable concept based on a combination of many distributed small-scale pyrolysers to produce these high-energy-density products locally in areas where biomass is available, and centralized applications of such products that are produced and transported from many of these distributed pyrolysers. This talk further discusses the potential opportunities for establishing a favourable supply chain based on some of these key bioproducts, the roles of fundamental reaction mechanisms, the optimisation required for targeted applications, the associated challenges, and potential R&D needed.

ABSTRACT. The fundamental investigation of thermochemistry demands for a reliable analytical tool for comparison of processes from a chemical point of view. There is a large consensus that identification of all (up to ten thousand compounds) molecular constituents of pyrolysis (Py) and hydrothermal treatment (HT) liquid requires a combination of different analytical procedures and advanced spectroscopic techniques (e.g., high resolution mass spectrometry, HRMS or GCxGC-MS techniques). This approach needs specific analytical skills, costly dedicated equipment, and it is time-intensive. This implies sub-optimal or slow feedback from chemical analysis and missed opportunities for applied thermochemistry research. For that reason, we evaluated if it would be possible to identify just one analytical procedure, potentially applicable in most of the research labs, which allows the identification/quantification of more than half (mass basis) of organic compounds in liquids. GC-MS is one of the few techniques that can be applied in almost every lab, which typically allows quantifying/identifying up to 10-20% of organics in HT and Py liquids. Derivatization increases the share of detected organic by a factor of 3 (reaching 30-45%, mainly thanks to improved separation efficiency and stabilization of reactive analytes), allowing to resolve up to 300 compounds, which is close to the theoretical limit of capillary GC. Peak deconvolution using independent GC runs (e.g., analyzing a large number of independent samples with appropriate computational capability) increases the number of resolved compounds to a value close to that detectable with FT-ICR MS [1]. Derivatization and automated deconvolution allow, in practice, to deliver information that can entirely describe pyrolysis products from a molecular point of view, but (especially for silylated derivatives) library-based identification of MS spectra is ineffective and somewhat misleading. To address this problem, a complete library of fragmentation patterns for pyrolysis products was created, providing a standardized identification strategy for unknown silylated derivatives. Although automated identification of unknown spectra is not possible at present, the presence of a silyl group provides several deterministic fragmentation patterns, which have been identified and incorporated into a semi-automatic, human-assisted algorithm that resolves and provides partial identification of the products. This procedure was validated by HRMS, demonstrating that it is possible to obtain a molecular picture of complex materials easily and, in some cases, to identify novel, relevant pyrolysis products (e.g., cyclic dipeptides and anhydrodisaccharides). The final automated procedure allowed, just with standard GC-MS equipment and without advanced analytical skills, to quantify and tentatively identify about 65% of the organics into liquid products from fast/intermediate pyrolysis and hydrothermal treatment of various representative feedstock such as cellulose, switchgrass, wood, sewage sludge and water-soluble derivatives arising from biological upgrading of thereof. Aim of this contribution is to show the potential of the approach and deliver an open-source methodology that scientists/engineers can use without a specific analytical background to obtain a molecular picture of liquids from thermochemical treatment.

ABSTRACT. The integration of carbon capture by dry reforming can offer a promising solution to both reduce the carbon dioxide emissions, thus achieving the goals of reducing global warming, and to produce valuable gases. In general, dry reforming is a catalytic process converting hydrocarbon feeds, mainly methane (CH4), into syngas over a metal-based catalyst (e.g. nickel, platinum or rhodium). Although the use of catalysts allows to increase the process performance and moderate the operating conditions, deactivation phenomena represent a critical issue, even more if bio-oils, hydrocarbon by-products or heavy hydrocarbon mixtures are considered as feedstocks, due to their higher tendency to form coke. This requires other strategies, such as non-catalytic dry reforming. Pyrolysis bio-oils are gaining increasing attention as feedstock for the dry reforming process. However, for complex mixtures as bio-oils, it is necessary to develop systematic studies using representative chemical components to gain insight into the reaction mechanism and the optimal operating condition for the non-catalytic dry reforming. In this framework, this study reports an experimental investigation of the non-catalytic dry reforming and oxidation of selected chemicals commonly present in bio-oils, providing a systematic analysis of the effect of molecular structure (i.e., carbon chain length and the presence of oxygenated functional groups) on process reactivity. To study the dry reforming of the bio-oil components, the experimental tests were carried out in a spiral-shaped tubular laminar-flow reactor, with a total length of 4 m, fixing the mixture residence time equal to 2.5 s. Experiments were performed for diluted stoichiometric fuel/CO2 mixture, with stoichiometry defined according to the dry reforming reaction for each component. The mixtures were diluted at 92%vol. in N2 and the tests were performed in the temperature range 600-1350 K. Several pure compounds and binary mixtures have been tested, such as furfural, acetol, furfural-syringol, acetol-phenol and acetol-guaiacol. The exhaust gases are fed to a condenser and cooled down to 10°C. The produced gases were analyzed online with micro-gas chromatography and FTIR, while the condensed liquids were analyzed with GC-MS and Karl Fischer titration. The obtained results showed that at temperatures below 1150 K, thermal decomposition of the fuel dominates, leading to the formation of CO, H2, CH4, and light hydrocarbons, while CO2 is only weakly affected. At higher temperatures, dry reforming reactions become increasingly important, as evidenced by the marked consumption of CO2, the higher concentration of CO and H2, and the decrease in CH4 concentration. Overall, the selected bio-oil components can be effectively converted into syngas via a non-catalytic dry reforming process, which becomes active at temperatures above 1200 K. This activation temperature remains essentially unchanged when considering either pure compounds or mixtures of different compounds.

ABSTRACT. The production of condensates from pyrolysis, such as ‘fast pyrolysis bio-oil’ and ‘wood vinegar’ demands for control of decisive quality parameters, which are determined by their composition. Prediction of phase equilibria is of fundamental importance to achieve this aim, since it allows to design condensate composition through the choice of condensation temperature. It also opens up the opportunity to design a strategy for further downstream separation of condensate fractions or even single compounds. While phase equilibria prediction is a well established tool in chemical engineering in general, it lacks application for pyrolysis products due to several fundamental challenges: 1) A large part of pyrolysis products consists of oligomers, which are largely unknown in composition/ structure, 2) most of the compounds observed after pyrolysis (of biomass) are not used in chemical engineering, yet, and thus lack well established knowledge of their thermophysical properties, 3) consequently, surrogate mixtures need to be developed to describe the behavior of the bulk fractions in phase equilibria with adequate precision, and 4) it is largely unclear how well the various models perform for the case of phase equilibria calculation of pyrolysis products.

This contribution focusses on the first of above-mentioned challenges with the aim to achieve a better representation of oligomers produced from biomass pyrolysis in phase equilibria prediction. A specific focus was set on vapor-liquid-equilibria (VLE) since they form the fundamentals for the design of the condensation step of pyrolysis liquids. It is hypothesized that an important share of oligomers is derived from lignin and, consequently, a dedicated study was conducted which aimed at producing pyrolysis condensates enriched in lignin derived oligomers. Measurements of VLE for this lignin-derived pyrolysis oil were conducted in an advanced distillation curve setup to investigate the use of varying oligomers as potential products from lignin pyrolysis. It is shown that oligomers require consideration in the prediction of VLE, not only due to their low boiling pressure but also due to their interaction with other molecules, such as e.g. water as the main compound of many pyrolysis condensates. Dimers of the biphenyl type showed good performance across various indicators, especially as compared to the larger tetramers tested in this study. These results are further supported by GC-MS/FID analyses combined with results from advanced analyses such as e.g. ultra-high resolution mass spectrometry, which reveal that a large share of these oligomers are characterized by highly oxygenated dimers/trimers. Despite the fact that including such lignin oligomer representatives in surrogate mixtures leads to an important improvement in VLE prediction, overall precision of prediction still requires optimization. Focus of future work could be on the influence of cellulose derived oligomers, which can now be efficiently studied based on the presented results.

ABSTRACT. In this study, a Microfluidized Bed Reactor (MFBR) was employed to mimic the residence time and kinetics of reactions found in an industrial reactor. The novelty of this research lies in its investigation on biomass conversion with diverse carrier gases (either pure N2 or N2+H2O). The study aims to clarify the influence of these gases on both the pyrolysis mechanism and the char gasification mechanism. Beech wood pellets, measuring 6 mm in diameter and height, were employed to compare reactions and results for pyrolysis and steam-gasification at 850°C (using a mixture comprising 80% H2O vapours and 20% N2), 3.7s gas phase residence, with varying solid residence time (1, 2.5, 5, 10, 15, and 20 minutes) and varying the nature of bed (sands of Fontainebleau and Olivine). The products were characterized using advanced analytical techniques, including micro-GC and online mass spectrometry for gases, gas chromatography coupled with mass spectrometry and flame ionization detection (GC-MS-FID) for bio-oils, proximate and ultimate analysis (CHNS-O), and surface functional group analysis (IR) for biochars. This investigation confirmed that H₂O has a limited effect on methane gas-phase reforming, while emphasizing the key role of char gasification. Char gasification led to a significant increase in CO₂ and H₂ yields, with no noticeable effect on CO production.

ABSTRACT. The co-thermal conversion process of biomass and coal, such as co-pyrolysis and co-gasification, is considered to be a promising technology for the clean and efficient co-utilization of coal and biomass. However, the volatilization of high content alkali metals in biomass will cause the equipment corrosion, which seriously restricts the development of these co-utilization technology. Understanding on the release and migration mechanisms of alkali metals deeply especially the in-situ release is crucial to control the volatilization of alkali metals, but the lack of in-situ detection technique limits the fully understanding on this. In this work, a self-designed visual fixed bed (VFB) combined with laser-induced breakdown spectroscopy (LIBS) was used to investigate the in-situ release characteristics and the migration mechanisms of alkali metals during co-pyrolysis/co-gasification of coal and biomass. The results showed that the temporal release of alkali metals during the biomass pyrolysis and co-pyrolysis first increased and then decreased over time, independent of pyrolysis temperature, mass ratio of biomass to coal, and minerals in coal. Besides, pyrolysis temperature had a decisive effect on the maximum release concentration and ratio of alkali metals, while the co-pyrolysis limited the volatilization of alkali metals via the interaction between coal and biomass. The presence of minerals, such as SiO2 and Al2O3, and O-containing functional group in coal reduced the maximum release concentra-tion and release ratio of potassium and sodium. Furthermore, a good negative correlation was obtained between the disorder degree of char and the temporal release concentration of alkali metals. This work provided the theoretical basis for alleviating the equipment corrosion problem caused by alkali metals in industrial application.

ABSTRACT. Brazil established a target to reduce greenhouse gas emissions by up to 67% by 2035 compared to 2005. In this context, the incorporation of residues from forest biomass into refining processes represents a promising pathway to produce renewable products while utilizing existing refinery infrastructure and reducing fossil CO₂ emissions, which aligns with Sustainable Development Goals (SDGs) 7, 12, 13, and 9. Thus, the objective of this work is the chemical speciation of the liquid products generated in this process, an essential step for assessing the feasibility of this coprocessing route. Three delayed coking liquid products (100% petrogenic-based, PP) co-processed with 5% (BO5) and 10% bio-oil (BO10) were characterized by comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOFMS). The liquid products were fractionated, derivatized, and analyzed by GC×GC-TOFMS using DB-5MS (1D) and HP-17HT (2D) column set. Data processing was performed using ChromaTOF Tile software, applying a signal-to-noise ratio of 10:1 and a minimum mass spectral similarity of 70% for compound identification. GC×GC-TOFMS data showed the presence of oxygenated classes such as acids, phenols, and alcohols identified in their derivatized form by ions m/z 73, m/z 91, m/z 105, and m/z 117 in PP, BO5, and BO10. Methoxyphenols and dimethoxyphenols classes and thirteen biogenic compounds were identified only in BO5 and B010, such as syringol, 5-methyl guaiacol, o-cresol, catechol, and 1,6-hexanediol, which originate from the pyrolysis of cellulose, hemicellulose, and lignin, the main components of eucalyptus biomass. The application of the GC×GC-TOFMS to elucidate the individual molecular chemical composition of the samples revealed an increase in phenolic derivatives after the inclusion of bio-oil. These compounds have antioxidant activity and have potential as additives for fuels and biofuels. The liquid products generated can also be reintroduced as feedstock in delayed coking or other routes (e.g., catalytic cracking and hydrotreating), to convert these products into higher value-added compounds, with a significant biogenic contribution. Thus, the inclusion of eucalyptus bio-oil offers new perspectives for the industry integrated with the SDGs concepts, by decarbonization and the generation of renewable products.

ABSTRACT. The tandem micro reactor–gas chromatography/mass spectrometry (TMR-GC/MS) system provides a powerful and flexible analytical platform for investigating the reaction mechanisms of biomass pyrolysis and catalytic upgrading under precisely controlled conditions. By employing two independently controlled micro-furnaces arranged in series, the system allows the separation or integration of primary pyrolysis and secondary catalytic upgrading reactions. This configuration enables detailed mechanistic understanding of the effects of reaction atmosphere, catalyst properties, contact mode, and pressure, which are often difficult to isolate in conventional fixed-bed or fluidized-bed reactors. In this presentation, the applicability of the tandem micro reactor for in-situ catalytic pyrolysis, ex-situ catalytic pyrolysis, and high-pressure hydropyrolysis is demonstrated using representative publication examples. Ex-situ catalytic pyrolysis of Citrus unshiu peel illustrates the effectiveness of separating pyrolysis and catalytic upgrading steps within the tandem reactor configuration. Oxygenated pyrolyzates, including alcohols, ketones, and furan compounds, generated in the primary pyrolysis furnace were efficiently converted into aromatic hydrocarbons in the secondary catalytic furnace. Among the catalysts examined, HZSM-5 exhibited superior catalytic stability and lower formation of polycyclic aromatic hydrocarbons (PAHs) compared to HBETA, although HBETA showed higher initial aromatic yields. Sequential catalytic upgrading experiments further revealed that the slower deactivation of HZSM-5 resulted in more sustained production of BTEX (benzene, toluene, ethylbenzene, and xylenes), highlighting the importance of catalyst stability and selectivity in ex-situ catalytic pyrolysis. In contrast, studies on the catalytic pyrolysis of wood plastic composites (WPCs) emphasized the critical role of catalyst–reactant contact mode. In-situ catalytic pyrolysis, in which the catalyst is physically mixed with the feedstock, resulted in higher aromatic formation efficiency than ex-situ operation due to enhanced interaction between pyrolysis intermediates and active catalytic sites. However, aromatic yields were strongly influenced by catalyst pore architecture and coke accumulation behavior. Microporous HZSM-5 suffered from diffusion limitations, while HY experienced severe coke deposition within its larger pores, both leading to catalyst deactivation. These findings suggest that hierarchical or mesoporous zeolite structures may improve mass transfer and catalyst lifetime. The tandem micro reactor platform was further extended to high-pressure hydropyrolysis, enabling investigation of hydrogen-assisted thermal cracking and catalytic upgrading of lignin under elevated H₂ pressures. Hydropyrolysis significantly suppressed char formation and promoted the formation of monoaromatic hydrocarbons, particularly BTX, through hydrogen radical-mediated reactions that enhanced bond cleavage and inhibited condensation reactions. The presence of HZSM-5 further facilitated hydrocracking and aromatization of lignin-derived vapors; however, excessive reaction temperatures and hydrogen pressures favored hydrocarbon pool coupling reactions, leading to increased PAH formation and underscoring the need for careful optimization. Finally, integration of catalytic hydropyrolysis with downstream hydrodeoxygenation over Ni/desilicated HZSM-5 demonstrates a viable two-step upgrading strategy for biomass-derived pyrolysis vapors and oils. Overall, this presentation highlights the tandem micro reactor as a versatile analytical reactor that bridges fundamental reaction chemistry and practical catalytic process design in advanced pyrolysis and hydropyrolysis research.

ABSTRACT. To increase the recycling rates of plastic waste, thermochemical recycling processes have been investigated for decades as a complement to mechanical recycling. Previous studies at the KIT have shown that the catalytic pyrolysis of polyolefin-rich plastic waste using microporous zeolites presents a promising pathway, as it yields high amounts of C2 to C4 olefins and valuable by-products such as BETX [1]. However, when heterogeneous plastic waste streams containing polyamides are pyrolyzed, the catalytic pyrolysis products begin to resemble those of non-catalytic pyrolysis, accompanied by a pronounced increase in coke formation. This behavior is attributed to catalyst deactivation [1]. To develop effective strategies mitigating this deactivation, it is crucial to elucidate the underlying mechanisms. In this study, these deactivation mechanisms were investigated through systematic and comparative catalytic pyrolysis experiments conducted on the milligram, gram, and kilogram scale. Low-density polyethylene (LDPE) was pyrolyzed in a gram scale batch reactor at 500 °C, either on its own or with the addition of 5 wt% polyamide-6 (PA-6) or ammonia as an inorganic basic nitrogen compound. The resulting pyrolysis vapors were subsequently catalytically cracked in a downstream fixed bed loaded with a microporous zeolite with a catalyst-to-plastic ratio of 0.08, and gaseous and liquid products were separated in a condenser. The gaseous products were identified and quantified using a gas chromatograph (GC) coupled with thermal conductivity (TCD) and flame ionization detector (FID), as well as a mass spectrometer (MS), while the liquid products were identified and quantified using proton nuclear magnetic resonance spectroscopy (1H-NMR) and a two-dimensional-GC coupled with a FID and MS. The resulting mass balances and the detailed gas and liquid product compositions reveal distinct shifts in product distribution toward non-catalytic products associated with catalyst deactivation when 5 wt% PA-6 or ammonia was added. Additionally, thermogravimetric analyses were carried out in which the PA-6 content in LDPE varied from 0 to 100 wt% along with the catalyst loading. A correlation between the PA-6 content and the coke deposited on the catalyst was observed. PA-6 also altered the decomposition behavior of LDPE, resulting in a three-step decomposition. The combined findings from both the gram-scale experiments and the thermogravimetric analyses reveal that coke formation alone cannot account for the observed catalyst deactivation. The results further indicate that nitrogen-containing species, which are formed by the decomposition of PA-6 are adsorbed and retained on the catalyst surface, providing an additional deactivation pathway that significantly contributes to the deterioration of catalytic performance. The findings were validated using a screw pyrolysis pilot plant operating at the kilogram scale with an integrated downstream fixed-bed reactor, demonstrating the relevance of these deactivation pathways under practical process conditions.

[1]: Netsch et al. Chemical Recycling of Polyolefinic Waste to Light Olefins by Catalytic Pyrolysis. Chemie Ingenieur Technik. 2023. 95(8).1305-1313. DOI: 10.1002/cite.202300078

ABSTRACT. In the feedstock recycling of plastics containing brominated flame retardants (BFRs), evaluation of brominated compounds in the products is essential for assessing both product quality as chemical feedstocks and overall process performance. Brominated compounds formed during pyrolysis are diverse and often present at trace levels, making their detection challenging because they are masked by abundant non-brominated pyrolysates. Negative ion chemical ionization (NICI), a mass-spectrometric ionization technique, enables highly sensitive and selective detection of compounds with high electron affinity, such as halogenated species.

In this study, we newly constructed a pyrolysis–gas chromatography/NICI–mass spectrometry (Py-GC/NICI-MS) system and investigated a high-sensitivity method for analyzing brominated compounds in pyrolysis products using polystyrene (PS) and tetrabromobisphenol A (TBBPA), a representative BFR, as model materials. PS containing 1 wt% TBBPA (TBBPA–PS) was pyrolyzed at 800 °C and analyzed using conventional Py-GC/electron ionization (EI)-MS and the newly constructed Py-GC/NICI-MS. The pyrolyzer was a EGA/PY-3030D (Frontier Laboratories). The GC/EI-MS system comprised an Agilent 6890N GC and an Agilent 5975C MS, while the GC/NICI-MS system comprised an Agilent 8890 GC and an Agilent 5977C MS. Pyrolysates were separated on a metal capillary column (Ultra ALLOY-1 (MS/HT), Frontier Laboratories) and then introduced into the MS.

With EI, no peaks could be unambiguously assigned to brominated compounds, and the pyrogram was dominated by PS-derived aromatic hydrocarbons. In contrast, NICI detected more than 70 brominated-compound peaks with S/N ≥ 3, demonstrating the superior sensitivity of GC/NICI-MS for brominated compounds. We further examined the effect of ion source temperature on ionization behavior. At an ion source temperature of 300 °C or higher, the molecular ion of TBBPA was not observed and only bromine-derived ions at m/z 79 and 81 were detected. In contrast, at 200 °C or lower, the molecular ion was clearly observed, indicating that lower ion source temperatures are more suitable for compound identification. Overall, Py-GC/NICI-MS was confirmed to be highly effective for the sensitive detection of brominated compounds in pyrolysis products.

ABSTRACT. In our work hyphenated techniques have been applied for the analysis of pyrolytic processes of non-isocyanate polyurethanes (NIPUs) to provide an understanding of the degradation mechanism and their chemical recycling potential. The thermal stability and volatile degradation products composition were investigated by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy (TGA–FTIR) and pyrolysis–gas chromatography–mass spectrometry (Py–GC/MS) techniques. NIPUs, a novel class of polymers synthesized – contrary to the classical polyurethanes - without the use of toxic diisocyanates, have been extensively investigated with respect to their synthesis and sustainability. However, their thermal degradation behavior remains insufficiently explored, particularly regarding degradation mechanisms and the identification and characterization of volatile decomposition products. We studied NIPUs with varying amine content and chemical structure, as well as hybrid composite materials, which were subjected to pyrolytic degradation. The effect of the chemical environment of the hydroxyurethane group on polymer thermal stability was analyzed, as well as kinetic analysis of the pyrolytic degradation process was performed. Finally, the decomposition pathways were proposed, and, based on these complementary results, the potential of pyrolysis as a chemical recycling route for non-isocyanate polyurethanes was assessed in the context of a closed-loop recycling strategies.

ABSTRACT. Thermochemical treatment of waste wind turbine blades (WTBs) is regarded as a promising approach for resource utilization, enabling the production of high-value byproducts. While the pyrolysis process allows for the recovery of valuable chemicals, the residual char could compromise the properties of recycled fibers. In this study, a one-step oxidation treatment of WTBs was conducted under steam/air conditions. The effects of various reaction parameters on the degradation behavior of WTBs were systematically investigated. Reactive force field molecular dynamics (ReaxFF MD) simulations were employed to elucidate the thermo-oxidative degradation mechanisms of epoxy resin matrix. The results indicated that under a N2 atmosphere, high temperature and elevated heating rate facilitated the reduction of char yield to 9.4 wt% at 550 °C. The liquid yield ranged from 83 to 84 wt%, with the maximum bisphenol A yield reaching 128.40 mg g-1 at 550 °C. Under an air atmosphere, 2.14 wt% residual char was obtained at 550 °C. However, when 25% steam was introduced into the air stream, the synergistic effect between air and steam enabled complete elimination of char at 550 °C while preserving 87.4 wt% of liquid product containing 117.78 mg g-1 of bisphenol A. Increasing the reactant gas flow rate from 200 to 400 ml min-1 resulted in only 0.35 wt% residual char at 500°C. SEM analysis demonstrated the clean and smooth fibers recovered under the mixture atmosphere of air and steam. ReaxFF MD simulations revealed that the degradation of the epoxy resin matrix initiated with the cleavage of the cross-linked C-N and ether bonds, followed by hydrogenation of the generated terminal phenoxy groups to produce phenolic derivatives as primary degradation products. The presence of O2 facilitated the generation of reactive radicals (•HO, •HO2, •H2O2, and •CHO2), accelerating the polymer backbone cleavage via radical chain reactions and intermediate oxidation. This research reveals the synergistic effects of air and steam for the degradation of WTBs and provides theoretical insights for chemical and clean fiber recovery from WTBs.

ABSTRACT. Thermochemical conversion routes, such as fast pyrolysis (FP) of lignocellulosic biomass or lignin, produce highly complex liquids (fast pyrolysis bio-oil, FPBO) and heavy fractions, including pyrolignin (PL). Detailed characterisation of these materials remains challenging, particularly for the high-molecular-weight fraction, owing to their oligomeric nature, the absence of appropriate reference spectra in MS/NMR libraries, and the scarcity of dedicated standards. In this contribution, we explore the use of synthetic lignin oligomers (SLOs) and curated model compounds as a practical means to improve the molecular interpretation of 1H and 13C NMR spectra of FPBO and PL fractions. We first digitised and standardised the structures and experimental NMR data in the NMR Database (University of Wisconsin/USDA) and generated predicted 1H and 13C spectra and shifts for each entry using ACD/Labs NMR Predictor (v2024.2.3). The theoretical shifts were systematically compared with the experimental values reported in the database. The spectra and shifts of the commercial pinoresinol standard (β–β linkage) and a laboratory-synthesised β-O-4 oligomer were also validated, with measurements in different NMR solvents. In parallel, the thermophysical properties of the same set of LigninOMICS molecules were estimated using Aspen Plus v14, providing a consistent property layer to support subsequent process modelling. These selected spectral and property data form the initial core of a lignin-centric reference library: LigninOMICS. On this basis, we developed a Python-based linear-additive model that simulates NMR mixture spectra by combining individual reference spectra from LigninOMICS with composition constraints derived from ultra-high-resolution mass spectrometry (UHRMS). The algorithm estimates plausible surrogate compositions for FPBO, solid and liquid PL (BTG), and column-chromatography sub-fractions of PL by minimising the deviation between simulated and experimental spectra under physically consistent constraints. Preliminary results show that the approach reproduces key spectral features of FPBO and PL and yields chemically reasonable compositions for their heavy fractions. These estimated compositions, together with the expanding LigninOMICS database and Aspen-based property predictions, open the way to rigorous liquid–liquid equilibrium modelling (e.g. UNIFAC-Dortmund) and to a more mechanistic understanding of fractionation and upgrading strategies for lignin-derived bio-oils.

ABSTRACT. Pyrolysis is a central process in thermal conversion technologies and plays a governing role in solid-fuel aerospace propulsion systems. In both solid and hybrid rocket motors, pyrolysis constitutes the primary mechanism by which condensed-phase materials are transformed into gaseous species that sustain gas-phase combustion. The characteristics of pyrolysis—namely decomposition pathways, kinetics, and product distribution—directly affect fuel regression rates, flame structure, and combustion efficiency. For this reason, a detailed thermo-chemical characterization of solid fuels, with specific focus on pyrolysis phenomena, is essential for the development of advanced propulsion concepts. In hybrid rocket propulsion, the coupling between heat feedback from the flame and pyrolysis at the solid fuel surface controls the generation rate and composition of gaseous fuel species. Unlike conventional solid propellants, where oxidizer and fuel are premixed, hybrid systems rely entirely on pyrolysis-driven mass transfer from the solid phase to the reacting flow. Consequently, the efficiency and stability of hybrid combustion are intrinsically linked to the thermal degradation behavior of the solid fuel. Insufficient pyrolysis rates, unfavorable melting/decomposition windows or volatiles composition may result in reduced regression rates and incomplete combustion. Recent research has increasingly focused on the pyrolysis of non-traditional polymeric materials, including thermoplastics and bio-based polymers, as alternative solid fuels. These materials offer advantages in terms of processability, reduced toxicity, and compatibility with additive manufacturing, while also enabling more sustainable material sourcing. Polylactic acid (PLA) is a biodegradable thermoplastic polymer extensively used in additive manufacturing that has recently emerged as a candidate solid fuel for hybrid aerospace propulsion. Its molecular structure suggests a well-defined thermal response, making it a suitable model material for investigating the interplay between thermal transitions, pyrolysis onset, and volatile release. In this work, PLA is characterized through a combination of differential scanning calorimetry (DSC), thermogravimetric analysis (TG/DTG), and analytical pyrolysis coupled with gas chromatography–mass spectrometry (Py-GC/MS). DSC measurements were performed to identify thermal transitions such as melting behavior, and possible pre-decomposition phenomena, providing insight into the thermal stability and heat flow associated with structural changes in the polymer. TG/DTG analysis was used to determine mass loss profiles, decomposition onset temperatures, and apparent reaction rates under controlled heating conditions. Py-GC/MS enabled the identification and quantification of volatile and condensable species released during thermal degradation, offering detailed information on pyrolysis pathways and product distribution. The results indicate that PLA undergoes a reproducible pyrolytic decomposition over a relatively narrow temperature range, preceded by well-defined thermal transitions. The pyrolysis process yields a significant fraction of low-molecular-weight combustible species, including acetaldehyde, which are expected to play a key role in sustaining homogeneous combustion when adequately mixed with common hybrid rocket oxidizers. While these laboratory-scale experiments do not directly reproduce the complex thermo-fluid-dynamic conditions of an operating hybrid rocket motor, they represent essential input for pyrolysis-driven combustion modeling. Overall, this study emphasizes pyrolysis as the key link between material properties and combustion behavior, supporting the assessment of PLA as a solid fuel for hybrid propulsion systems governed by pyrolysis-controlled mass transfer.

ABSTRACT. Selective carbonization aims to maximize carbon retention during biomass pyrolysis by steering oxygen removal toward dehydration (H2O) rather than decarbonylation/decarboxylation (CO/CO2) or fragmentation into small oxygenated volatiles. Because dehydration preserves the carbon backbone, promoting this pathway is central to improving biochar yield, sustainability, and process economics. Here, controlled experiments with atomistic–molecular modeling were integrated to quantify how acid pretreatments and pressure can be leveraged to tune dehydration and secondary reactions that ultimately define char yield and properties. Hybrid poplar wood was pretreated with inorganic acids (sulfuric and phosphoric) and organic acids (acetic and formic) across multiple concentrations, then carbonized under varied pressure conditions. Acid pretreatment acted as a catalyst for dehydration reactions, reducing oxygen content before and during pyrolysis and shifting product distributions toward higher solid yields. Pressure further enhanced selective carbonization by retaining tarry vapors at the reacting biomass surface, increasing the opportunity for secondary reactions that deposit carbon and reduce volatilization losses. Optimized combinations of pretreatment and pressure achieved up to 78% carbon conversion efficiency and demonstrated that selective carbonization can boost biochar yields by more than 50%. Inorganic acids additionally produced phosphorus- and sulfur-doped biochars, emphasizing that carbon yield must be considered together with resulting elemental composition and surface functionality. Because application performance depends on intrinsic properties beyond yield, the produced chars were comprehensively characterized to resolve aromaticity, heteroatom functionalities, density, surface area, and pore structure across micro- and nanoscale features. To translate characterization into molecular-scale understanding, an automated “data-into-structure” workflow that constructs molecular building blocks directly from experimental observables and assembles large-scale atomistic representations of biochar was employed. The methodology was validated against independent measurements, including 13C NMR, aromatic cluster size distributions, elemental analysis, X-ray diffraction, helium density, surface area, and porosity, achieving greater than 90% agreement with measured values across these observables. The resulting models explicitly capture how pretreatment chemistry, pressure, and temperature reshape the carbon skeleton topology, heteroatom functionalities, and pore networks that govern interactions with water, nutrients, and pollutants. Beyond explaining experimental trends, these representations provide predictive capability that reduces trial-and-error experimentation and supports hypothesis-driven biochar engineering for targeted environmental and industrial end uses. Modeling also enables questions that cannot be answered by experimentation alone, including the molecular origins of biochar recalcitrance, plausible soil degradation pathways, and which functional groups or environmental factors most strongly control long-term stability and carbon storage potential. In addition, modeling supports contaminant risk management for thermally persistent species that may concentrate during pyrolysis (e.g., PAHs, VOCs, and PFAS) by simulating adsorption and desorption within realistic pore environments and surface chemistries, guiding choices of feedstock, pretreatments, and operating windows that minimize contaminant loading. We emphasize a fit-for-purpose philosophy: model complexity should increase only as needed for the question at hand. Workflows and representative biochar models are released openly in GitHub to accelerate reuse, benchmarking, and collaboration. This integrated framework shortens design cycles and supports reproducible, data-driven biochar optimization across diverse feedstocks.

Figure 1. Methodology for engineering biochar using experimental and atomic-molecular modeling data.

ABSTRACT. The plastics industry must adopt sustainable alternatives to conventional materials to reduce CO2 emissions, which reached 208 million tons in the EU in 2018. Biochar presents a promising filler material with negative greenhouse potential, significantly improving the CO2 balance of polymers like polypropylene (PP). The biocharPP project focuses on developing CO2-optimized compounds using biochar, addressing functionalization, processing, and ecological and as well as technical evaluation. Critical challenges include optimizing biochar surface properties, ensuring compatibility with polymers while at the same time, and scaling the technology from TRL 2-3 to industrial levels. Fraunhofer UMSICHT evaluated various feedstocks for its suitability to produce high-quality biochar, including walnut shells, wine pruning, waste wood, and green waste, For this, through an advanced pyrolytic conversion process using thermochemical conversioncalled the thermo-chemical reforming (TCR)-technology was used. Elemental composition, pH, porosity, and thermogravimetric behavior of the produced biochar were analyzed to assess suitability as fillers. An integrated, scalable activation module was developed to optimize biochar properties for PP applications. Activation trials were conducted in a 1.5 L model reactor simulating pilot plant flow conditions, with plans to transfer findings to a pilot plant capable of processing 30 kg/h of biochar. The objective was to achieve maximum activation effects under mild reaction conditions to ensure a cost-efficient process. For this purpose steam and CO2 introduction in the pyrolysis process were tested in several steps. Results show that all activation methods increase the BET surface area, enhancing biochar performance. A 100°C temperature increase nearly tripled surface area, while using CO2 as a mild oxidizing agent further increased surface area by 50% under identical conditions. Doubling CO2 input from 1.5 to 3 kg did not significantly affect the surface area but slightly improved the water holding capacity by altering the surface chemistry of the biochar material. Both steam and CO2 activation were included in the pyrolysis pilot plants at Fraunhofer UMSICHT allowing the production of surface optimized biochars within one process. The respective chars were tested in polypropylene compounds as filler material and could be introduced up to 30 Ma% resulting in competable biochar-polypropylene composit materials.

ABSTRACT. Cellulose is a major structural component of biomass, and developing a reliable cellulose pyrolysis model is essential for advancing high-value product extraction. The degradation behavior of cellulose is influenced by its crystal structure, initial degree of polymerization (DP), and vaporization dynamics of degradation products. The bio-CPD model [1], a biomass-extended version of the chemical percolation devolatilization model, describes biomass as a three-dimensional macromolecular network, where monomer units are connected by breakable crosslinks, solving the kinetics of their breakage, molecular size distribution via lattice statistics, and bio-oil release via vapor-liquid equilibrium. While the bio-CPD model is one of the most advanced and reliable models currently available for describing biomass pyrolysis, it has key limitations when applied to cellulose. The assumption of a three-dimensional crosslinked network is not completely consistent with individual cellulose chain which has a one-dimensional linear structure, where the chain degradation is dominated by chain scission rather than network percolation. In addition, it does not explicitly account for the DP, which influences cellulose degradation behavior. The vapor-liquid equilibrium formulation is based on coal-derived compounds and does not accurately represent the volatilization dynamics of oxygen-rich pyrolysis products [2]. Finally, it lacks mechanisms to predict or optimize the formation of specific targeted products.

This study proposes a new approach to model pyrolysis kinetics of cellulose, addressing the above issues. Specifically, we focused on the investigation on the effect of DP and improved vapor-liquid equilibrium formulations. Cellulose depolymerization is modeled through detailed mechanistic pathways, including transglycosylation, dehydration, and hydrolysis reactions that generate characteristic reducing, levoglucosan, and dehydrated glucose chain ends. Density functional theory (DFT) derived kinetic parameters are incorporated to capture the effects of DP and chain-end chemistry on β-1,4-glycosidic bond scission and subsequent fragmentation reactions which results in the formation of products such as levoglucosan, levoglucosenone, glycoaldehyde, furans, and other light oxygenates. A kinetic Monte Carlo simulation tracks the stochastic evolution of the population balance of cellulose chains, accounting for changes in DP and end-type distributions, and fragment formation under non-isothermal conditions. Additionally, we revise the vapor liquid equilibrium parameters to better represent the volatilization dynamics of cellulose-derived oxygenated species, including glucose, levoglucosan, dehydrated glucose, and their oligomers. The new parameters account for the distinct thermodynamic behavior of these species, as the current formulations based on coal-derived aromatic compounds are insufficient for cellulose derived feedstocks.

The model was validated using available experimental data from the literature, resulting in a more mechanistically sound and predictive pyrolysis kinetic model that can better describe cellulose decomposition. This work not only advances the modeling of cellulose pyrolysis but also provides insights that could be applied to improve thermochemical conversion processes and optimize the production of specific targeted products.

Figure 1: Scheme of the model

References

[1] Lewis, A.D. and Fletcher, T.H., 2013. Prediction of sawdust pyrolysis yields from a flat-flame burner using the CPD model. Energy & Fuels, 27(2). [2] Oja, V. and Suuberg, E.M., 1999. Vapor pressures and enthalpies of sublimation of D-glucose, D-xylose, cellobiose, and levoglucosan. Journal of Chemical & Engineering Data, 44(1).

ABSTRACT. In recent years, alternative thermochemical conversion processes for energy recovery from agricultural residues and digestate have been increasingly investigated [1]. Gasification of these by-products, instead of being discarded, incinerated or applied in agriculture, can be used to produce synthesis gas (syngas), mainly containing hydrogen and carbon monoxide, under partial oxidation conditions. On the basis of ongoing research [2, 3], experimental investigations were conducted using a thermogravimetric analyser (TGA) coupled with micro-gas chromatography (MicroGC) to investigate the suitability of using gasification process of digestates after anaerobic digestion (AD) of agricultural waste, in order to produce hydrogen-rich syngas.

Two feedstocks were examined as fuels for gasification experiments: (i) raw digestates after AD of agricultural residues, and (ii) chars produced from digestate pyrolysis. Raw digestates were first pyrolyzed under nitrogen atmosphere at about 500° C by using a pre-heated autoclave and the resulting chars were subsequently gasified. A parametric study was conducted to evaluate the effect of varying selected gasification parameters on the overall process performance. The parameters considered were the heating rate, the gasification agent, the oxidant flow rate, the reaction temperature and the type of feedstock (e.g., raw digestate and char).

Pyrolysis experiments were carried out under inert (N₂) conditions and gasification tests were performed under oxygen-enriched (O₂/N₂) or CO₂ atmospheres. The main indicators of the gasification process were determined at oxygen to fuel ratios from 0.1 to 0.5. Product distributions were quantified in terms of solid residues (char and ash), liquid condensates (tar), and gaseous products. The syngas composition was analysed both qualitatively and quantitatively. The main gaseous components identified were CO, CO₂, CH4, and H₂, which were released sequentially during the pyrolysis–gasification process. The syngas obtained by air gasification of digestates in the temperature range of 40–800 °C, and after a 30 min isothermal step, contained up to 29.9% H₂ and up to 30.1% CO, with H₂/CO molar ratios between 0.7 and 1.0. The corresponding lower heating value ranged from 6.2 to 7.5 MJ/m3.

In addition, char gasification experiments were performed under CO₂/N₂ mixtures containing 10–90% CO₂ at temperatures of 850, 900, and 950 °C. The influence of CO₂ concentration and temperature on char reactivity and syngas composition will be discussed and some examples will illustrate the results.

[1] M. H. Aissaoui, J. Hertzog, C. Sambusiti, P. Gauthier-Maradei, M.-N. Pons, V. Carré, Y. Le Brech, A. Dufour. J. Anal. Appl. Pyrolysis, 2025, 186, pp.106928. [2] D. Sangaré, S. Bostyn, M. Moscosa-Santillan, V. Belandria, I., P. García-Alamilla, I. Gökalp. Bioresour. Technol. 2022, 346, pp.126598. [3] D. Sangaré, V. Belandria, S. Bostyn, M. Moscosa-Santillan, I. Gökalp. Biomass Conv. Bioref., 2024, 14, pp. 9763–9775.

ABSTRACT. The insertion of biogenic raw materials into conventional refineries is a promising option to increasing the green carbon content of traditional fuels and products. Co-processing low carbon footprint bio-oils with petroleum derivatives can be a faster way to decrease greenhouse gases emissions through small modifications in the oil refining existing infrastructure. However, the influence of bio-oil inclusion in the typical processes of conventional oil refineries is still understudied. This work aimed to perform individual chemical structural elucidation via comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS) of liquid products from wood pyrolysis bio-oils (BO) co-processed with vacuum residue (VR) in two units: the delayed coking process and the pentane solvent deasphalting process. Effluents from delayed coking were obtained using three batch loadings: (A) 100% VR, (B) 95% VR and 5 % BO; and (C) 90% VR and 10 % BO. The effluents were then distilled, and three cuts were obtained: naphtha (up to 150 °C), light gasoil (150-380 °C), and heavy gasoil (+380 °C). The solvent deasphalting process was made by liquid-liquid extraction of BO and VR blend (1:1) with pentane at 65 ◦C and 200 psi, and two fractions were produced: deasphalted oil and asphaltic residue. Using GC×GC-TOFMS, an advanced analytical tool, it was possible to identify at the molecular level the contribution of bio-oil in different traditional fossil streams. The biomass-derived carbon inclusion in the delayed coking batch promoted the reduction of alkane, olefin, and alkyl-thiophene concentrations in the effluents. Biogenic C1-alkyl-cyclopentenones (42.7 µg g-1) and C1-C3 alkyl-cyclopentenones (392.3 µg g-1) were detected in effluents B and C, respectively. These cyclic ketones from BO can be a good additive for fossil fuels, due to their high resistance to auto-ignition characteristics. After distillation, a greater BO contribution was observed in light gasoils. The pentane solvent deasphalting process extracts mainly the apolar compounds as aliphatic and aromatic hydrocarbons, whereas the mid-polar to polar ones are partitioned in both phases, with the low molecular mass polar compounds observed in a greater proportion in deasphalted oil. Thus, coprocessing BO with the VR inserted renewable molecules in the deasphalting fraction, which aims to recover lower molecular-weight fractions that can be used to produce valuable byproducts. Deasphalted oil containing green (or biogenic) carbon can be readily co-processed in FCC units, whereas the presence of renewable molecules in the asphaltic residue demonstrated an improvement in bioasphalt stability compared to petroleum asphalt cement. Thus, co-processing biomass-derived carbon in conventional oil refining steps increases the green carbon content and represents a viable pathway for a sustainable energy transition.

ABSTRACT. There is currently no definitive consensus on whether lignocellulosic biopolymers interact during pyrolysis, with the literature presenting contradictory conclusions. In this study, we show that these discrepancies largely stem from differences in experimental design—particularly the degree of mixing between cellulose and lignin. We demonstrate that the spatial scale of mixing—macroscale versus nanoscale—fundamentally alters the observed interactions between cellulose and lignin during slow pyrolysis within the heating rate range of 2.5–40 °C/min. Macroscale mixtures, prepared as physical blends of regenerated cellulose II fibres and Organosolv beech lignin (OSBL) particles, undergo pyrolysis independently, with no significant interactions detected in thermogravimetric measurements. In contrast, nanoscale mixtures—produced through the regeneration of hybrid fibres containing nanoscale co-localized cellulose II and OSBL—exhibit clear evidence of interactions between the two components. These interactions manifest in altered mass loss dynamics and evolved gas profiles, indicating that the pyrolysis pathways of each biopolymer are influenced by their proximity at the nanoscale. Notably, while OSBL alone undergoes softening and extensive foaming during pyrolysis, this behaviour is entirely suppressed in the nanoscale mixture, suggesting that thermal softening and gas-driven expansion are inhibited by confinement within the cellulosic matrix. This suppression points to a reduction in lignin’s mobility when restricted between cellulose domains. Molecular simulations on lignin dynamics under confinement support this interpretation. Additionally, the reactivity of carbonized OSBL toward CO₂ is significantly enhanced when lignin is confined within nanoscale domains in the hybrid cellulose-lignin fibres. This finding suggests that nanoscale confinement not only affects the pyrolytic transformation of lignin but also modifies the structure and accessibility of the resulting carbon composite materials. Collectively, these results underscore the importance of considering the morphological scale when evaluating biopolymer interactions during thermochemical conversion. Additionally, they prompt a re-evaluation of how synergistic effects are understood—particularly in naturally occurring composite systems such as wood, where cellulose and lignin are inherently mixed at the nanoscale, unlike the macroscale physical blends commonly used in experimental studies.

ABSTRACT. Decarbonizing metal production is a critical industrial challenge that necessitates a swift transition from fossil fuels to sustainable alternatives. Biocarbon holds immense potential to reduce the sector's carbon footprint; however, its success depends on expanding and diversifying biomass sourcing to meet high industrial demand. Bark, a high-volume waste stream from the forestry industry, is a promising candidate for biochar production. Nevertheless, bark often contains high ash content which, when retained in the biochar, is undesirable for metallurgical processes. In this study, water leaching was investigated as a method to reduce inorganic elements in pine, spruce, and birch bark. Biocarbons were produced from both untreated and leached barks and subsequently characterized using a suite of analytical techniques. Chemical composition analysis results indicated that biocarbons from water-leached barks possessed lower ash content, though they also exhibited slightly lower carbon content compared to untreated counterparts. Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) confirmed that concentrations of both total and individual inorganic elements were considerably lower in the leached samples. X-ray diffraction (XRD) identified calcium carbonate as the primary mineral phase in all samples. However, peak intensities for calcium carbonate were significantly reduced in biocarbons derived from leached bark. Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy (SEM-EDS) revealed that calcium-rich grains, prominent on the surface of untreated bark biocarbon, were rarely visible after leaching. Furthermore, leached biocarbons exhibited a coarser surface and a more open structure, suggesting that water leaching alters the physical matrix of the parental bark. Gasification reactivity was investigated using a Macro-TGA at 1100 °C in a CO2/CO gas mixture, simulating the conditions of an industrial closed submerged arc manganese alloy furnace. The Macro-TGA experiments demonstrated that biocarbons produced from leached barks had considerably lower reactivity than those from untreated barks. Post-test analysis of the conversion residues via SEM-EDS revealed significant differences; residues from untreated biocarbons contained substantial calcium-rich grains and aggregates. The presence of these inorganic elements catalyzes the gasification of the carbon matrix, thereby increasing carbon consumption. These findings suggest that water leaching is an effective pretreatment for producing high-quality, low reactivity biocarbon suitable for metallurgical applications.

ABSTRACT. Azaheterocycles are essential building blocks for high-value chemicals, traditionally derived from fossil fuel intermediates. This study fundamentally investigates the production of these compounds from cellulose as renewable resource, by means of fast pyrolysis at a micro-scale under a NH3-rich atmosphere. Herein is demonstrated for the first time a strategy to perform micropyrolysis under a NH3 atmosphere, while controlling the reaction time between cellulose’s pyrolysis products and NH3. This is achieved by using urea and ammonium carbamate as NH3 precursors within a specific on-line micro reaction sampler for micropyrolysis . Micropyrolysis experiments were conducted at 500 °C to elucidate the importance of N-source and determine the influence of nitrogen-to-biomass ratios and reaction time on product distribution. Under optimized conditions (30 s reaction time, nitrogen-to-biomass ratio of 10:1), a remarkable yield in azaheterocycles of 49 C-wt.% was achieved with a total azaheterocycle selectivity of 87%. The main contributor was pyrrole with a selectivity of 31%. Mechanistic pathways were elucidated by reacting key cellulose-derived intermediates (cellobiose, levoglucosan, glycolaldehyde and acetol) with ammonium carbamate. The results demonstrate three competing pathways: pyrroles are predominantly formed via furanic intermediates, while pyrazines and oxazoles originate from light oxygenates and pyridines were found to be associated with anhydrosugars. These findings suggest that the NH3 release mechanism and vapor-phase residence time are critical in governing nitrogen-incorporation pathways, establishing ammonium carbamate as an effective additive for the selective synthesis of bio-based azaheterocycles.

ABSTRACT. As the sole renewable carbon source, biomass can be pyrolyzed into bio‑oil, biochar, and syngas. However, bio‑oil suffers from inherently high oxygen content. Meanwhile, over 400 million tons of plastics are produced globally each year, with approximately 350 million tons ending up as waste. In the current waste treatment environment, bio‑oil and plastic wastes are often found as physically blended or even intermingled complex streams. Hence, the integrated catalytic conversion of biomass‑derived pyrolysis oil and polyester plastic waste into high‑value fuels and chemicals represents a sustainable and circular‑economy‑aligned resource recovery route. Hydrodeoxygenation (HDO) is considered one of the most effective approaches for simultaneously deoxygenating bio‑oil and upgrading plastic waste. However, the design of HDO catalysts that can synergistically process both feedstocks and simultaneously meet requirements for cost-effectiveness, high activity, stability, and selectivity remains a key challenge in this field. This study systematically demonstrates that the noble-metal-free bifunctional Co/HZSM 5 catalyst can directly and efficiently upgrade the mixed feedstock of bio-oil and polyester plastics into sustainable fuel components dominated by naphthenes under relatively mild reaction conditions, with a total yield as high as 94%. Moreover, the catalyst still maintains excellent catalytic activity after repeated uses, exhibiting good reusability and stability. In-depth mechanistic studies reveal that the highly dispersed metallic Co nanoparticles, serving as hydrogenation active sites, play an indispensable key role in catalyzing the cleavage of C–O bonds and C–C bonds as well as the hydrogenation of unsaturated bonds. In contrast, the abundant acidic sites provided by the HZSM 5 support effectively facilitate key tandem reaction steps such as dehydration and isomerization. Correlation analysis between catalytic performance and structural characterization further confirms that the metal-acid balance between metallic sites and acidic sites in the Co/HZSM 5 catalyst is the core factor that significantly affects its overall HDO activity, intermediate conversion pathways and final product distribution. Among them, the 10Co/HZSM 5(200) catalyst exhibits the optimal metal-acid balance . It demonstrates outstanding HDO performance in the co-conversion reaction of guaiacol and polyethylene terephthalate (PET). Under the reaction conditions of 260 °C, 4 MPa H₂ and 3 h, the yield of cyclohexane reaches 94%, the yield of 1,4-dimethylcyclohexane is as high as 86.6%, guaiacol is completely converted, and the conversion rate of PET exceeds 95%. In addition, the universality of this catalyst has been verified: it can effectively synergistically convert the mixture of heavy fractions of real bio-oil containing complex oxygenates (such as ethers, furans and furfural derivatives) and various engineering plastics (including polycarbonate and polyphenylene oxide), realizing efficient and directional conversion to naphthenic fuels while maintaining high structural stability and catalytic activity during long-term reactions. This bifunctional Co/HZSM 5 catalyst, featuring simple preparation process, low raw material cost and good reproducibility, provides a technical route with important industrial application prospects for the future synergistic, efficient and high-value chemical recycling of mixed biomass oil and complex waste plastics into valuable products.

ABSTRACT. Catalytic methane cracking is a heterogeneous reaction in which the gaseous hydrocarbon is converted into hydrogen and solid carbon particles over a catalyst bed. The advantage of this process lies in the ability to obtain carbon in a solid state rather than as CO2, which greatly facilitates its separation and sequestration. Both metal and carbon-based catalysts can be used for this purpose, with the latter offering higher thermal stability, greater sulfur resistance, and lower cost, despite lower methane conversion. Various studies were carried out at lab-scale to analyze the process and identify the effects of different parameters on the reaction efficiency and deactivation behavior. However, the number of studies on higher-maturity plants is limited. As part of an European-funded project (H2STEEL), a 20 kg/h moving-bed methane cracking reactor (Proof Of Concept, POC) was designed to study the reaction over a carbon-based catalyst. The work presents the first results of pilot-plant tests carried out at atmospheric pressure and temperatures in the range of 800-900°C, in order to assess the technical viability of sustainable hydrogen production together with solid-state carbon by-products. Different operational conditions were analyzed to compare and validate the results with lab-scale tests. Due to the POC limitation of a maximum 2 Nm3/h gas capacity and bed volume of 3-6L, a GHSV in the range of 126 to 313 h-1 was used. Methane was diluted with nitrogen at volume percentages ranging from 10% to 50%. Two commercial activated catalysts, with specific surface areas of 700 and 1000 m2/g, were initially used to test the plant and establish a fossil-based benchmark for the following materials. To evaluate catalyst deactivation and compare it with the experimental curve, residence times of 10, 20, and 30 minutes were used. The tests showed promising results from a technical standpoint, confirming the plant's ability to carry out the reaction at the desired operational conditions, with methane conversion ranging from 92% to 62%. The conversion decreased with increasing GHSV, methane concentration, and catalyst residence time. This behavior is consistent with the results of the lab-scale analysis, conducted on a wide range of carbon-based materials.

ABSTRACT. Valmet’s development of pyrolysis technology spans nearly two decades, beginning with the commercialization of a fast pyrolysis plant in Joensuu, Finland, in 2013. Building on this foundation, the company has intensified its focus on catalytic fast pyrolysis (CFP) to produce more refined, energy-dense, and stable bio oils suitable for advanced industrial applications. As part of this strategic shift, Valmet has comprehensively revamped its pilot facility in Tampere into a dedicated catalytic fast pyrolysis unit. Commissioned in 2023, the upgraded unit has since supported multiple test campaigns aimed at unit availability and performance, bio oil quality and production for downstream treatment. A key challenge for pyrolysis derived oils—particularly those originating from catalytic pathways—is their storage stability, which influences applicability in downstream upgrading, and logistics chains. In this study, we present results from recent CFP test campaigns conducted at Valmet’s Tampere pilot plant. The analysis focuses on the storage stability of bio oils produced under varying operating conditions. The primary emphasis is on understanding how the oxygen content of the produced oils correlates with their stability during storage. Bio oils were monitored over defined storage periods, and stability was evaluated using parameters such as viscosity development, phase behavior, and chemical aging indicators. Preliminary results show distinct relationships between oxygen content and aging behavior, highlighting critical thresholds beyond which storage stability deteriorates more rapidly. Process conditions that effectively affect oxygenation were found to significantly improve oil robustness over time. The findings contribute to a broader understanding of how catalytic fast pyrolysis can be steered toward higher quality, more storage-durable bio oils. These insights support the continued development of scalable, reliable CFP technologies and strengthen Valmet’s ongoing role in advancing thermochemical conversion processes for sustainable fuels and chemicals.

ABSTRACT. Integration of a waste pyrolysis unit at a cement plant can bring several advantages such as a decreased use of fossil fuel and the production of a liquid fuel product that can bring an extra revenue to the cement plant. In this study, laboratory fluid bed pyrolysis experiments of different waste types and applying a range of different operating conditions were conducted to investigate the influence on product yields and product liquid properties. The results obtained are important for the further industrial development of cement plant pyrolysis technology. Experiments were conducted on an electrically heated laboratory fluid bed reactor at a feeding rate of 0.35 kg/h using two waste types with different biomass contents and controlled fuel mixtures of wood and plastic. The investigated operating conditions included: Use of sand, cement raw meal and calcined cement raw meal as bed material; change of reactor temperature from 550 to 640℃, changes of freeboard residence time from 2 to 5 seconds and experiments with oxygen addition to simulate the extent of air ingress typically unavoidable in full scale plants. The optimal pyrolysis reactor temperature with respect to organic liquid yield for the waste samples were observed to be 550 to 570℃ where dry organic liquid yields of 44 to 49 wt. % were obtained. This optimal temperature is somewhat higher than typically observed value of 500 ℃ for biomass pyrolysis. At those conditions decreased liquid yield was observed for feeds with an increased biomass fraction. Increasing the temperature of the waste pyrolysis up to 640 ℃ led to a reduction in dry organic liquid yield down to 24 wt. %, an increased water and gas yield and also led to a large reduction in the dry oil oxygen content from 13 wt. % to 2 wt. %. Using calcined raw meal opposed to using sand as bed material led to a small decrease in the organic liquid yield and the liquid oxygen content. Reducing the freeboard gas residence time from 5 to 2 seconds only lead to a small reduction in gas yield and a small increase in oil oxygen content. Applying oxygen injection corresponding to λ = 0.1 led to a reduction in dry organic yield down to 22 wt. % and a reduction in oil TAN value. Selected oil samples were analyzed with respect to marine fuel relevant properties such as TAN, flash point and wax content. TAN analysis showed values from 25 to 80 mg KOH/g with oil produced at high temperatures, with calcined raw meal as bed material and with oxygen ingress applied leading to the lowest TAN values. Flash point values were mainly influenced by the waste type used, waste 1 (biomass lean) giving values from 38-47 ℃ and waste 2 (biomass rich) leading to values of 63-81℃. All oil samples had no visual wax content at 40℃ while samples produced at a pyrolysis temperature of 640 ℃ only showed traces of wax when cooled to 5℃ where wax appeared in all other samples.

ABSTRACT. From a circular economy perspective, polyolefin-rich plastic waste represents an important source of valuable chemicals and energy carriers. Thermochemical routes such as pyrolysis can valorize these heterogeneous feedstocks. To enable predictive reactor-scale modeling, a consistent kinetic description is needed to link condensed-phase polymer degradation with the subsequent gas-phase evolution of released volatiles.

In this work, we develop a multi-phase kinetic framework for low-density polyethylene (LDPE) pyrolysis, in which condensed-phase and gas-phase chemistries are represented by semi-detailed CHEMKIN mechanisms and simulated in OpenSMOKE++ (Cuoci et al., 2015). In the gas-phase mechanism, heavy fractions are treated via established lumping/surrogate representations (e.g., diesel-cut and wax representatives), while light products follow the CRECK semi-detailed description with updated light-olefin pathways based on recent speciation evidence (Locaspi et al., 2025).

Motivated by literature evidence that, once decomposition begins, polyethylene (PE) exhibits an endothermically buffered temperature plateau, with the particle-surface temperature stabilizing around 480–550 °C (Nakhaei et al., 2018), a two-stage modeling strategy is adopted. In Stage 1, a condensed-phase LDPE pyrolysis model provides the composition of the released volatiles, which is used to define the inlet mixture for Stage 2. In Stage 2, the released volatiles are simulated in a gas-phase plug-flow reactor (PFR) to describe secondary cracking, with the effective residence time (τ_eff) identified by iterative matching of the aromatic fraction, resulting in two candidate values. This simplified representation captures the measured phase split and its temperature trends across the investigated temperature range.

Within this framework, the gas-phase stage is used to evaluate product-class distributions under different gas-phase temperatures and two candidate values of τ_eff. Product classes are evaluated using both PIONA (Paraffins/Iso-paraffins/Olefins/Naphthenes/Aromatics) and carbon number ranges (Gas: C1-C4; Liquid: C5-C19; Wax: C20-C36; Tar: C37+). The framework is assessed by comparing simulated class distributions against flash pyrolysis experimental data reported in de Korte et al. (2025). The model reproduces the phase-split trends with temperature and matches the 800 °C distribution closely; deviations at 600–700 °C are primarily associated with the gas–liquid split, highlighting the role of τ_eff in secondary cracking. Figure 1. Phase-resolved product distributions for LDPE pyrolysis at 600,700 , and 800 °C: Comparison between experiment and model predictions. Key references

Cuoci, A. et al. "OpenSMOKE++: An object-oriented framework for the numerical modeling of reactive systems with detailed kinetic mechanisms", Computer Physics Communications 192 (2015) 237–264. DOI: 10.1016/j.cpc.2015.02.014

Locaspi, Andrea et al. "A semi-detailed pyrolytic gas-phase kinetic model for the volatiles of polyethylene thermal degradation", Proceedings of the Combustion Institute 41 (2025) 105912. DOI: 10.1016/j.proci.2025.105912

Nakhaei, M. et al. "Experiments and modeling of single plastic particle conversion in suspension", Fuel Processing Technology 178 (2018) 213–225. DOI: 10.1016/j.fuproc.2018.05.012

de Korte, R. J.et al. "Plastics pyrolysis: The impact of pyrolysis temperature on ethylene production and direct carbon dioxide footprint", Fuel Processing Technology, 267 (2025), 108148. DOI:10.1016/j.fuproc.2024.108148

ABSTRACT. Plastic waste includes diverse materials, ranging from single-resin plastics with minimal additives to complex multilayered composites like biaxially oriented polypropylene (BOPP). BOPP has excellent barrier and durability properties. However, because of its multi-layered composition, it poses significant environmental challenges due to the difficulties in its mechanical recycling and is often marked as “to be discarded”. Advanced recycling techniques, such as chemical recycling through pyrolysis, show promise in effectively processing these materials back into reusable raw materials, addressing the limitations of traditional recycling approaches, and reducing environmental impact. [1,2] Pyrolysis has emerged as a promising route for recycling complex plastic waste streams. This study researches the use of pyrolysis as a chemical recycling method for two commercially used BOPP samples, designated M and S, employing a hybrid reactive distillation lab-scale reactor. [3] The decomposition of this material was studied by thermogravimetric analysis with simultaneous differential scanning calorimetry under nitrogen, in the range of 40 to 800°C. Maximum degradation temperatures of 463 and 464°C were observed for samples M and S, respectively. These temperatures are consistent with the expected composition of the material, mainly polypropylene. Lab-scale pyrolysis experiments were conducted using sample masses between 4 and 8g. The reactions were carried out in a Schlenk-type glass vessel of around 0.1L under nitrogen. The temperature was set to rise from 20 to 500°C, after which it was held constant at 500°C for 90 minutes to complete the thermal degradation process. [4] During the pyrolysis process in the hybrid reactive distillation lab-scale reactor, both BOPP samples yielded approximately 36 % solid residue, with the remaining fraction consisting of gaseous and liquid hydrocarbons. The gas phase primarily contained hydrocarbons in the C2 to C6 range, while about 80% of the liquid phase comprised hydrocarbons between C5 and C10 for both samples. The solid residue of the reactor contained 81-87% of volatile matter (figure). These results highlight pyrolysis as a promising technique for the chemical recycling of BOPP plastics. Furthermore, thermogravimetric analysis of mixtures containing BOPP and simpler polyolefins such as HDPE, LDPE, and PP has yielded promising results. Ongoing experiments in the reactor are being carried out to further assess the co-pyrolysis performance and validate these findings.

[1] Chen, S., Rotaru, A.-E., Shrestha, P.M., Malvankar, N.S., Liu, F., Fan, W., Nevin, K.P., Lovley, D.R. (2014). Promoting interspecies electron transfer with biochar. Sci. Rep. 4, 5019. [2] Artūras Torkelis, Jolanta Dvarionienė, Gintaras Denafas. (2024). The Factors Influencing the Recycling of Plastic and Composite Packaging Waste. Sustainability, 16(21), 9515–9515. [3] Santos, E., Rijo, B., Lemos, F., Lemos, M. A. N. D. A. (2021). A catalytic reactive distillation approach to high density polyethylene pyrolysis – Part 2 – Middle olefin production. Catalysis Today, 379, 212–221. [4] Santos, E.R.F. Nanostructure Materials as Catalysts for the Degradation of Polyolefins. Ph.D. Thesis, Instituto Superior Técnico–University of Lisbon, Lisbon, Portugal, 2018.

ABSTRACT. Introduction: Plastic waste management is a crucial component of global sustainability initiatives, and the circular plastics economy promotes recycling. Pyrolysis can be a promising thermochemical process that recycles plastic waste into valuable products, such as fuel and chemical feedstocks [1]. Polyethylene pyrolysis is controlled by millisecond-scale intrinsic cracking kinetics, but conventional reactors often suffer from poor heat and mass transfer, resulting in temperature and concentration gradients. This extends effective residence time, promoting unselective conversion and secondary reactions that form aromatics and coke [2]. Pyrolysis in a vortex reactor (VR), which is built at LCT UGENT, provides intense gas–melt contact, very short residence times, and a narrow residence time distribution at high temperatures. Here, we evaluate a VR for the pyrolysis of polyethylene and quantify how operating conditions (temperature, sweep flow, and residence time) affect light olefin and pyrolysis oil selectivity. Experimental Details: The experiments were conducted in a pilot-scale vortex reactor (Figure 1). Polyethylene (PE) pellets with a density of 0.91 g/cm³ (from Total Energies) were continuously fed into the reactor at a rate of 1 kg/h via a twin-screw extruder. The melted PE was transferred through a melt pipe and injected into the reactor. Nitrogen, provided at a rate of 7 m³/h, served as the carrier gas and helped maintain a uniform reactor temperature of 600, 650, 700, 750, and 800 °C. A mixture of Nitrogen and melted plastic was introduced tangentially into the 79 ml vortex chamber through 12 inclined slots to establish a strong vortex flow. The reactor and downstream cyclones were housed in a furnace to maintain the desired temperature. Pyrolysis products exited through a central exhaust and passed through heated cyclones, followed by two condensers for char and condensable collection, while non-condensable gases were flared. Temperature and pressure were monitored using thermocouples and pressure sensors. The product stream from the sampling line at the top of the reactor is quantified using online refinery gas analysis (RGA) and two-dimensional gas chromatography (GC×GC). Yields are reported as weight percent of fed PE. Results and discussion: As expected, C2-C4 light olefins yield significantly increased with temperature (600, 650, 700 ℃) from 4.5 wt.%, 26 wt.%, and 44 wt.%, and reaching values substantially above 50 wt. % above 750°C. Ethylene and propylene yields contributed significantly to the increase in valuable products. The temperature‑driven selectivity shift could be attributed to the established radical‑cracking families for PE: initial random C–C scission and intramolecular H‑abstraction (backbiting) generate secondary radicals that undergo β‑scission to form light olefins. The VR’s short residence times, combined with rapid heat and mass transfer, limit slower secondary condensation/aromatization while permitting limited secondary cracking that further enriches C2-C4 light olefins. The carbon number distribution also highlights the kinetic dominance of end-chain β-scission and radical backbiting, which are thermally accelerated at elevated temperatures. Overall, coupling high-temperature with narrow residence-time distributions enhances light-olefin selectivity. References: [1] Costa et al., J. Anal. Appl. Pyrolysis 191, 107168 (2025). [2] Goshayeshi et al., J. Anal. Appl. Pyrolysis 187, 107016 (2025).

ABSTRACT. Global plastic waste generation continued its long-term upward trend, reaching an estimated 225 million tons in 20251. Among waste management technologies, pyrolysis is a viable chemical recycling route that converts plastic waste into valuable hydrocarbon fractions. However, post-consumer plastic waste is inherently heterogeneous, and compositional variability leads to the formation of oxygenated, nitrogenated, and chlorinated products during thermochemical conversion, which may limit the direct use of pyrolysis oils as steam cracker feedstocks2. Comprehensive characterization of pyrolysis products is necessary to assess the suitability of pyrolysis oil as a steam cracker feedstock, enabling closed-loop plastics circularity. In this study, three post-consumer plastic waste streams (PW1-PW3) were initially analyzed using FTIR, ICP-OES, and CIC to evaluate feedstock composition and heteroatom content. These polyolefin-rich waste mixtures contained heteroatom-containing plastics and additives, yielding measurable quantities of oxygen, nitrogen, metals, and halogens in the elemental profile. The thermal decomposition of three mixtures was investigated using a micropyrolysis unit coupled to an inline analytical section at 450 ℃ and 600 ℃. Product vapors were analyzed using comprehensive two-dimensional gas chromatography (GC×GC) with time-of-flight mass spectrometry (TOF-MS) for compound identification and a flame ionization detector (FID) for quantification. Pyrolysis products were classified into major hydrocarbon families, including paraffins, olefins, naphthenes, aromatics, as well as oxygenates and nitrogenates. The PIONA distribution exhibited a strong dependence on feedstock composition (Figure 1) and pyrolysis temperature. Across all feedstocks, the products were predominantly olefinic, comprising both linear and branched species. At 450 °C, the product distribution was dominated by heavier hydrocarbons (C21–C60), reflecting limited thermal cracking under mild conditions. Increasing the temperature to 600 ℃ significantly suppressed the formation of heavy wax fractions (C21+) while maximizing overall volatilization, primarily due to intensified secondary cracking and higher conversions. For PW1 and PW2, which contained substantial polypropylene fraction, characteristic PP derived fingerprints were observed, particularly the strong presence of branched C₉ olefins (Figure 1b, c), formed via β-scission of tertiary polypropylene radicals. PW3 exhibited distinctly different behavior due to its higher PET content, characterized by elevated levels of oxygenated pyrolysis products, including benzoic acid. The increased aromatic fraction in PW3 is consistent with PET’s aromatic backbone via the ester bond cleavage decomposition pathway, followed by decarboxylation and secondary aromatization reactions. Here, the formation of caprolactam, benzoic acid, and related derivatives confirmed the transfer of heteroatom-bearing contaminants originating from non-polyolefin plastics within the feed. By linking feedstock composition and temperature to PIONA distribution of pyrolysis products, the study provides insights into contaminant transfer and underscores the importance of detailed compositional analysis for integration into downstream chemical recycling pathways.

Figure 1. Two-dimensional GCxGC/FID/TOF-MS chromatogram of a)PW1 and PIONA distribution of the pyrolysis products, b)PW1, c)PW2, and d)PW3 at 450 °C.

References 1. Plastic Overshoot Day – Report 2025, EA-Earth Action, 2025. 2. M. Kusenberg, A. Eschenbacher, M.R. Djokic, A. Zayoud, K. Ragaert, S. De Meester, K.M. Van Geem, Opportunities and challenges for the application of post-consumer plastic waste pyrolysis oils as steam cracker feedstocks: To decontaminate or not to decontaminate?, Waste Manag 138 (2022) 83-115.

ABSTRACT. Pyrolysis offers a promising route for valorizing plastic and bituminous waste within a circular economy framework. This study examines the pyrolysis of polypropylene (PP), road asphalt waste and their mixtures to evaluate potential chemical synergies and optimize liquid product yields. Experiments were carried out in a glass semi-batch reflux reactor under nitrogen, heating from ambient temperature to 500°C at 10°C.min⁻¹. Product characterization was performed using GC–MS/FID, µ-GC, and ¹H-NMR analyses.

The addition of asphalt notably affected product yields, though the overall composition of the volatile fraction remained similar. Co-pyrolysis of PP with asphalt exhibited a clear synergistic effect, enhancing the oil yield by up to 6.3 ± 0.7 wt% at a PP/bitumen ratio of 2:1, compared with pure PP pyrolysis. This improvement is attributed to the stabilizing influence of bitumen, which mitigates catalytic degradation induced by mineral fraction. The resulting oils retained chemical characteristics comparable to PP-derived oils, with only minor changes in viscosity, confirming that asphalt incorporation does not compromise oil quality.

These findings highlight the potential of PP/asphalt co-pyrolysis as an effective pathway for the simultaneous conversion of plastic and bituminous waste into valuable hydrocarbons, contributing to sustainable chemical recycling strategies.