Comparative study of carbon dioxide and nitrogen atmospheric effects on the chemical structure changes during pyrolysis of phenol–formaldehyde spheres

Gasification of Coal by CO2: The Impact of the Heat Transfer Limitation on the Progress, Reaction Rate and Kinetics of the Process

This paper presents the impact of thermal lag on the progress of different coal types’ gasification by CO2. The analysis was performed using thermogravimetry and numerical modeling. Experiments were carried out at a heating rate of 1–50 Kmin−1 and a temperature ranging from 383 to 1173 K. The developed numerical model enabled the determination of a true sample temperature considering the gasification process to consist of two single-step consecutive reactions. Analysis revealed that the average thermal lag in CO2 is about 11% greater than that in N2, which is related to the properties of CO2 itself and the occurrence of the char–CO2 reaction. The onset temperature of the reverse Boudouard reaction depends on the type of fuel; however, no simple relationship with the coal rank was found. Thermal lag has an impact on the kinetic parameter Aα0.5 describing devolatilization, up to 19.8%, while in the case of the char–CO2 reaction, this influence is expected to be even greater. The performed analysis proved that disregarding thermal lag may significantly hinder the interpretation of the analyzed processes; thus, TG experiments should be carried out with a low heating rate, or at the post-processing stage, a thermal lag model needs to be employed.

CO2 -Enabled Biomass Fractionation/Depolymerization: A Highly Versatile Pre-Step for Downstream Processing

Lignocellulosic biomass is inevitably subject to fractionation and depolymerization processes for enhanced selectivity toward specific products, in most cases prior to catalytic upgrading of the three main fractions-cellulose, hemicellulose, and lignin. Among the developed pretreatment techniques, CO₂ -assisted biomass processing exhibits some unique advantages such as the lowest critical temperature (31.0 °C) with moderate critical pressure, low cost, nontoxicity, nonflammability, ready availability, and the addition of acidity, alongside easy recovery by pressure release. This Review showcases progress in the study of sub- or supercritical CO₂ -mediated thermal processing of lignocellulosic biomass-the key pre-step for downstream conversion processes. The auxo-action of CO₂ in biomass pretreatment and fractionation, along with the involved variables, direct degradation of untreated biomass in CO₂ by gasification, pyrolysis, and liquefaction with relevant conversion mechanisms, and CO₂ -enabled depolymerization of lignocellulosic fractions with representative reaction pathways are summarized. Moreover, future prospects for the practical application of CO₂ -assisted up- and downstream biomass-to-bioproduct conversion are also briefly discussed.

Comprehending adsorption of methylethylketone and toluene and microwave regeneration effectiveness for beaded activated carbon derived from recycled waste bamboo tar

Beaded activated carbons (BACs) were derived from waste bamboo tar through carbonization (500°C for 2 hr) followed by physical activation using carbon dioxide (800-900°C for 2-4 hr). The adsorbent was examined for their physical and chemical properties, adsorption capacities toward methylethylketone (MEK) and toluene, and regenerabilities under microwave heating. It was found that the maximum total surface area reached for bamboo-tar-derived BAC after physical activation was 1364 m² g^-1, and more than 95% of the area was attributed to the microporous structures. Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models were applied to the adsorption isotherm fitting, and the minimum R² for each model was 0.986, 0.915, and 0.943, respectively. The isosteric heats of adsorption calculated based on D-R parameters for methylethylketone and toluene were 44.04 to 51.50 and 45.88 to 73.27 KJ mol^-1, respectively. They were slightly over the range of physisorption and increased with adsorbate loading, which might be related to the micropore filling mechanism. Microwave regeneration under 600 W of power output removed most of the adsorbate (>93.03%) within 8 min. The results of this study are intended to benefit future study on waste-derived adsorbent in environmental applications.

IMPLICATIONS

Recycling waste bamboo tar for the novel adsorbent preparation is shown feasible in this study. Beaded activated carbon (BAC) synthesized from this waste bamboo tar possessed a high specific surface area, which aided in the capturing of volatile organic compounds (VOCs). Three adsorption isotherms, Langmuir, Freundlich, Dubinin-Radushkevich (D-R) models can be applied in interpreting the experimental adsorption data, providing information on adsorption heat and possible adsorption mechanism. A potential microwave regeneration method for BAC is tested, showing high desorption efficiencies with minimum heel formation. These findings can provide a new pathway for waste bamboo tar management and VOC abatement using adsorbents.

Enhanced Thermal Decomposition Properties of CL-20 through Space-Confining in Three-Dimensional Hierarchically Ordered Porous Carbon

High energy and low signature properties are the future trend of solid propellant development. As a new and promising oxidizer, hexanitrohexaazaisowurtzitane (CL-20) is expected to replace the conventional oxidizer ammonium perchlorate to reach above goals. However, the high pressure exponent of CL-20 hinders its application in solid propellants so that the development of effective catalysts to improve the thermal decomposition properties of CL-20 still remains challenging. Here, 3D hierarchically ordered porous carbon (3D HOPC) is presented as a catalyst for the thermal decomposition of CL-20 via synthesizing a series of nanostructured CL-20/HOPC composites. In these nanocomposites, CL-20 is homogeneously space-confined into the 3D HOPC scaffold as nanocrystals 9.2-26.5 nm in diameter. The effect of the pore textural parameters and surface modification of 3D HOPC as well as CL-20 loading amount on the thermal decomposition of CL-20 is discussed. A significant improvement of the thermal decomposition properties of CL-20 is achieved with remarkable decrease in decomposition peak temperature (from 247.0 to 174.8 °C) and activation energy (from 165.5 to 115.3 kJ/mol). The exceptional performance of 3D HOPC could be attributed to its well-connected 3D hierarchically ordered porous structure, high surface area, and the confined CL-20 nanocrystals. This work clearly demonstrates that 3D HOPC is a superior catalyst for CL-20 thermal decomposition and opens new potential for further applications of CL-20 in solid propellants.

Crossing the Traditional Boundaries: Salen-Based Schiff Bases for Thermal Protective Applications

A broad spectrum of applications of "Salen"-based Schiff bases tagged them as versatile multifunctional materials. However, their applicability is often bounded by a temperature threshold and, thus, they have rarely been used for high temperature applications. Our investigation of a classical Schiff base, N,N'-bis(4-hydroxysalicylidene)ethylenediamine (L2), reveals that it displays an intriguingly combative response to an elevated temperature/fire scenario. L2 resists and regulates thermal degradation by forming an ablative surface, and acts as a thermal shield. A polycondensation via covalent cross-linking, which forms a hyperbranched cross-linked resin is found to constitute the origin of the ablative surface. This is a unique example of a resin formation produced with a Schiff base, that mimicks the operational strategy of a high-heat resistant phenolic resin. Further applicability of L2, as a flame retardant, was tested in an engineering polymer, polyamide-6. It was found that it reinforces the polymer against fire risks by the formation of an intumescent coating. This paves the way for a new strategic avenue in safeguarding polymeric materials toward fire risks. Further, this material represents a promising start for thermal protective applications.

Photonic patterns printed in chiral nematic mesoporous resins

Chiral nematic mesoporous phenol-formaldehyde resins, which were prepared using cellulose nanocrystals as a template, can be used as a substrate to produce latent photonic images. These resins undergo swelling, which changes their reflected color. By writing on the films with chemical inks, the density of methylol groups in the resin changes, subsequently affecting their degree of swelling and, consequently, their color. Writing on the films gives latent images that are revealed only upon swelling of the films. Using inkjet printing, it is possible to make higher resolution photonic patterns both as text and images that can be visualized by swelling and erased by drying. This novel approach to printing photonic patterns in resin films may be applied to anti-counterfeit tags, signage, and decorative applications.

Aerosol synthesis of self-organized nanostructured hollow and porous carbon particles using a dual polymer system

A facile method for designing and synthesizing nanostructured carbon particles via ultrasonic spray pyrolysis of a self-organized dual polymer system comprising phenolic resin and charged polystyrene latex is reported. The method produces either hollow carbon particles, whose CO2 adsorption capacity is 3.0 mmol g(-1), or porous carbon particles whose CO2 adsorption capacity is 4.8 mmol g(-1), although the two particle types had similar diameters of about 360 nm. We investigate how the zeta potential of the polystyrene latex particles, and the resulting electrostatic interaction with the negatively charged phenolic resin, influences the particle morphology, pore structure, and CO2 adsorption capacity.

Self-organized macroporous carbon structure derived from phenolic resin via spray pyrolysis for high-performance electrocatalyst

The synthesis and evaluation of porous carbon derived from phenolic resin using a fast and facile spray pyrolysis method has been studied for use as a new electrocatalyst support material. By adding polystyrene latex nanoparticles as a template to the phenolic resin precursor, self-organized macroporous carbon structure was first developed. The mass ratio of phenolic resin to PSL at 0.625 gave the optimum porous morphology. Pt nanoparticles (∼20 wt %) were grown on the carbon surface using a standard industrial impregnation method. Well-dispersed Pt nanoparticles of average size 3.91 nm were observed on the surface of porous carbon particles. The high catalytic performance of porous Pt/C electrocatalyst was confirmed by the high mass activity and electrochemically active surface area, which were 450.81 mA mg(-1)-Pt and 81.78 m(2) g(-1)-Pt, respectively. The porous Pt/C catalyst obtains two times higher mass activity than that of the commercial Pt/C catalyst and performs excellent durability under acid conditions.

Thermochemical decomposition of sewage sludge in CO2 and N2 atmosphere

In this study, the effect of CO(2) on the thermal conversion of sewage sludge was investigated by means of the thermogravimetric analysis and the batch-type thermal process. The results showed that the kinetics of sewage sludge during thermal treatment under both N(2) and CO(2) atmospheres are quite similar and can be described by a pseudo bi-component separated state model (PBSM). It was, however, noticed that under CO(2) atmosphere, the first reaction was significantly accelerated whereas the secondary reaction temperature was shifted to a lower temperature. The apparent activation energies for the first decomposition reaction under both N(2) and CO(2) atmosphere, corresponding to the main decomposition typically at 305 degrees C were similarly attained at ca. 72 kJ mol(-1), while that of the second decomposition reaction was found to decrease from 154 to 104 kJ mol(-1) under CO(2) atmosphere. The typical reaction order of the decomposition under both N(2) and CO(2) atmosphere was in the range of 1.0-1.5. The solid yield was slightly reduced while the gas and liquid yields were somewhat improved in the presence of CO(2). Furthermore, CO(2) was found to influence the liquid product by increasing the oxygenated compounds and lessening the aliphatic compounds through the insertion of CO(2) to the unsaturated compounds resulting in the carboxylics and the ketones formation.