The potential of recycling carbon fiber reinforced polymers (CFRP) as a sustainable solution for waste management is yet to be fully understood. This study reports on the evolution of mechanical, and chemical properties of reclaimed carbon fibers when recycled multiple times via pyrolysis and partial oxidation. The performed work aims at filling the knowledge gap related to repetitive recycling when moving towards a circular flow of resources. A recycling process existing at industrial scale is used to ensure the relevance and usefulness of the results in the current industry scene. Two sets of three identical model composites are recycled using distinct recycling parameters, and their properties are characterized at the end of each recycling cycle. Results show that recycling can lead to an increase in stiffness but can have a negative impact on strength of recovered fibers. Mechanical behaviour shows recovered fibers suitable for secondary applications with medium performance requirements after two recycling cycles. The findings highlight the importance of understanding the material properties evolution during recycling processes. This research contributes to the development of sustainable waste management strategies and a more environmentally friendly future.

To address the impacts of climate change, it is imperative to significantly decrease anthropogenic greenhouse gas emissions. Biomass-based chemicals and fuels will play a crucial role in substituting fossil-based feedstocks and reducing emissions. Gasification-based biomass conversion processes with catalytic synthesis producing chemicals and fuels (Biomass-to-X, BtX) are an innovative and well-proven process route. Since biomass is a scarce resource, its efficient utilization by maximizing product yield is key. In this review, the electrification of BtX processes is presented and discussed as a technological option to enhance chemical and fuel production from biomass. Electrified processes show many advantages compared to BtX and electricity-based processes (Power-to-X, PtX). Electrification options are classified into direct and indirect processes. While indirect electrification comprises mostly the addition of H2 from water electrolysis (Power-and-Biomass-to-X, PBtX), direct electrification refers to power integration into specific processing steps by converting electricity into the required form of energy such as heat, electrochemical energy or plasma used (eBtX). After the in-depth review of state-of-the-art technologies, all technologies are discussed in terms of process performance, maturity, feasibility, plant location, land requirement, and dynamic operation. H2 addition in PBtX processes has been widely investigated in the literature with process simulations showing significantly increased carbon efficiency and product yield. Similar studies on direct electrification (eBtX) are limited in the literature due to low technological maturity. Further research is required on both, equipment level technology development, as well as process and system level, to compare process options and evaluate performance, economics, environmental impact and future legislation.

Oxygen-enriched air combustion of pulverized biomass fuel is an effective method to improve char combustion and improve flame stability. Moreover, understanding the impact of O2 addition is an important step toward oxyfuel combustion, one of the most promising technologies for bioenergy with carbon capture and storage (BECCS). Our previous studies focused on flow manipulation methods, e.g., swirling co-flow and acoustic forcing, to enhance particle dispersion during biomass combustion and gasification. This work aims to extend the understanding of the effect of different manipulation methods on oxygen-enriched combustion at different levels in a lab-scale entrained flow reactor. This methodology combines the analysis of visible flame characteristics, CO and NO gas emissions, and coarse particle emissions characterization with thermogravimetric analysis and particle size distribution by dynamic imaging. The results indicated that oxygen-enriched combustion leads to lower liftoff distance and higher flame brightness. Moreover, oxygen-enriched combustion presented coarse particle emissions with finer particle size distribution and lower carbon content. The acoustic forcing further decreased the flame liftoff and decreased CO emissions, increasing combustion efficiency under conditions with similar equivalence ratios and lower momentum flux at the secondary air.

Char conversion is a complex phenomenon that involves not only heterogeneous reactions but also external and internal heat and mass transfer. Reactor-scale simulations often use a point-particle approach (PP approach) as sub-models for char conversion because of its low computational cost. Despite a number of simplifications involved in the PP approach, there are very few studies that systematically investigate the inaccuracies of the PP approach. This study aims to compare and identify when and why the PP approach deviates from resolved-particle simulations (RP approach). Simulations have been carried out for CO2 gasification of a char particle under zone II conditions (i.e., pore diffusion control) using both PP and RP approaches. Results showed significant deviations between the two approaches for the effectiveness factor, gas compositions, particle temperature, and particle diameter. The most significant sources of inaccuracies in the PP approach are negligence of the non-uniform temperature inside the particle and the inability to accurately model external heat transfer. Under the conditions with low effectiveness factors, the errors of intra-particle processes were dominant while the errors of external processes became dominant when effectiveness factors were close to unity. Because it assumes uniform internal temperature, the models applying the PP approach always predict higher effectiveness factors than the RP approach, despite its accurate estimation of intra-particle mass diffusion effects. As a consequence, the PP approach failed to predict the particle size changes accurately. Meanwhile, no conventional term for external heat transfer could explain the inaccuracy, indicating the importance of other sources of errors such as 2D/3D asymmetry or penetration of external flows inside the particles.

Packed bed reactors play a crucial role in various industrial applications. This paper utilizes the Discrete Element Method (DEM), an efficient numerical technique for simulating the behavior of packed beds of particles as discrete phases. The focus is on generating densely packed particle beds. To ensure the model accuracy, specific DEM parameters were studied, including sub-step and rolling resistance. The analysis of the packed bed model extended to a detailed exploration of void fraction distribution along radial and vertical directions, considering the impact of wall interactions. Three different samples, spanning particle sizes from 0.3 mm to 6 mm, were used. Results indicated that the number of sub-steps significantly influences void fraction precision, a key criterion for comparing simulations with experimental results. Additionally, the study found that both loosely and densely packed beds of particles could be accurately represented by incorporating appropriate values for rolling friction. This value serves as an indicator of both inter-particle friction and friction between particles and the walls. An optimal rolling friction coefficient has been thereby suggested for the precise representation for the densely packed bed of spherical char particles.

Carbon fiber, despite its exceptional properties, remains underutilized due to monetary and environmental concerns. Concurrently, the imminent challenge associated with rising quantities of End-of-Life CFRP (carbon fiber reinforced polymer) demands the further development of recycling strategies. This study focuses on optimizing the recycling process parameters of pyrolysis and oxidation thermal treatment to maximize the retention of mechanical properties in the recycled fibers in the shortest process time. To assess the result of the pyrolysis, single fiber tensile tests were executed to measure strength and stiffness. Additionally, microscopy and spectroscopy studies were carried out to evaluate fiber geometry as well as surface quality. At the laboratory scale, experiments demonstrated that the combination of pyrolysis and oxidation yields clean, reusable fibers with mechanical properties suitable for secondary applications. The influence of various treatment parameters on the strength and stiffness of the recycled fibers was explored, establishing a clear correlation. The outcome is a set of optimized parameters that contribute to mechanical property retention, including a novel recycling method that allows for reduced processing times, as short as 10 min. This work paves the way for a more eco-friendly and cost-effective approach to harnessing the potential of carbon fiber in a wide range of applications while mitigating environmental concerns associated with landfill disposal.

Binary and ternary composites of BiOI with NH2-MIL-101(Fe) and a functionalized biochar were synthesized through an in situ approach, aimed at spurring the activity of the semiconductor as a photocatalyst for the removal of ciprofloxacin (CIP) from water. Experimental outcomes showed a drastic enhancement of the adsorption and the equilibrium (which increased from 39.31 mg g–1 of bare BiOI to 76.39 mg g–1 of the best ternary composite in 2 h time), while the kinetics of the process was not significantly changed. The photocatalytic performance was also significantly enhanced, and the complete removal of 10 ppm of CIP in 3 h reaction time was recorded under simulated solar light irradiation for the best catalyst of the investigated batch. Catalytic reactions supported by different materials obeyed different reaction orders, indicating the existence of different mechanisms. The use of scavengers for superoxide anion radicals, holes, and hydroxyl radicals showed that although all these species are involved in CIP photodegradation, the latter play the most crucial role, as also confirmed by carrying out the reaction at increasing pH conditions. A clear correlation between the reduction of BiOI crystallite sizes in the composites, as compared to the bare material, and the material performance as both adsorbers and photocatalyst was identified. 

The aim of the work was to study the effects of neighboring particles with uniform Stefan flow in particle–fluid flows. Particle-resolved numerical simulations were carried out for particles emitting a uniform Stefan flow into the bulk fluid. The bulk fluid was uniform and isothermal. The Stefan flow volume emitted from the two particles is equal, such that it represents idealized conditions of reacting particles. Particles were located in tandem arrangement and particle distances were varied between 1.1 and 10 particle diameters (). Three particle Reynolds numbers were considered during the simulations ( and 14), which is similar to our previous studies. Three Stefan flow velocities were also considered during simulations to represent inward, outward, and no Stefan flow. The drag coefficient of the particles without Stefan flow showed that the results fit with previous studies on neighbor particle effects. When the particle distance is greater than 2.5 diameters (), the effects of Stefan flow and neighboring particles are independent of each other. I.e. an outward Stefan flow decreases the drag coefficient () while an inward Stefan flow increases it and the upstream particle experience a higher  than the downstream particle. When , the effect of Stefan flow is dominant, such that equal and opposite pressure forces act on the particles, resulting in a repelling force between the two neighboring particles. The pressure force showed a large increase compared to the viscous force at these distances. The effect of Stefan flow is weakened at higher Reynolds numbers. A model was developed for the calculation of the drag coefficient. The model, which reproduce the results from the numerical simulations presented above, is a product of independent models that describe the effects of both neighboring particles and two distinguished effects of the Stefan flow.

In most industrial applications, combustion and gasification of char progresses under regime II conditions. Unlike in other regimes, both particle size and density change simultaneously in regime II due to non-uniform consumption of carbon inside the particles. In this work, mathematical predictions of diameter changes in regime II were made by a one-dimensional simulation tool, where transient species balances are resolved locally inside the particle. This simulation is computationally expensive and usually not appropriate for the implementation in comprehensive CFD simulations of combustion or gasification processes. To overcome this restraint, an alternative shortcut method with affordable computation time has been developed and validated against the detailed model. This method allows the calculation of diameter changes during combustion and gasification from precalculated effectiveness factors. Additionally, the change of particle size has been investigated experimentally in a single particle converter setup. Therein, particles are fixed on a sample holder placed in the hot flue gas of a flat flame burner. Size and temperature trends are optically assessed by a 3CCD camera.

Despite a small proportion of mineral in coal, inherent alkali and alkaline earth metals (AAEM) catalytically affected thermal conversion of coal. The gasification of raw and leached coal char was investigated by using an operando microscopic Raman spectroscopy to explore the effect of content and chemical form of the inherent AAEM on morphology and carbon structure evolution of a single particle during in-situ char gasification. The removal of water-soluble and ion-exchangeable AAEM reduced the R_0.5 of SF, NM and YN char by 53.31%, 49.09% and 35.02%, respectively. As a result, the shrinkage of leached coal char progressed slower than that of the raw coal char. Besides, both water-soluble and ion-exchangeable AAEM accelerated char gasification because of an inhibition of the orderly evolution of carbon structure. Higher gasification temperature weakened the catalytic performance of ion-exchangeable AAEM. With the consumption of carbon, carbon microcrystalline structure of the residual char tended to be ordered, which led to a decrease in active free carbon sites for gasification reaction. Kinetic analysis indicated both water-soluble and ion-exchangeable AAEM reduced the activation energy of SF, NM and YN char by 20.97, 20.82 and 9.38kJ∙mol^-1, respectively, and the effect of ion-exchangeable AAEM was more significant.