Gas-phase Pyrolysis Research Articles

INVESTIGATION OF THE DENSITY OF CCCM AND ITS INFLUENCE ON SPECIFIC VOLUME ELECTRICAL RESISTIVITY

This article investigates the structure and properties of carbon-carbon composite materials (CCCM), where the carbon matrix is formed by the deposition of pyrolytic carbon in the porous volume of a carbon fiber preform using thermogradient gas-phase pyrolysis densification technologies. The results of studying the apparent density of CCCM by hydrostatic methods and its influence on the specific volume electrical resistivity of the material are presented. The conducted study established that the specific volume electrical resistivity of CCCM significantly depends on a number of factors, one of which is the material density. An increase in the apparent density of the material leads to a decrease in its porosity, which, in turn, affects the decrease in electrical resistance. It is emphasized that density control becomes a key factor in ensuring optimal electrical conductivity of carbon-carbon composite materials. It is shown that the densification of CCCM significantly improves the structure of blanks and crucibles, increasing their physical and operational characteristics. This makes them more suitable for use in high-temperature conditions, aggressive environments, in the production of heat-resistant components and other high-tech areas. Repeated densification of CCCM revealed a significant impact on the quality of the material. It is shown that an increase in density after additional densification leads to a decrease in porosity, improvement of mechanical properties and a change in the pore distribution in the material, which positively affects its porosity and strength. Bench tests of model samples made of CCCM showed that an increase in the apparent density of the material leads to a decrease in its electrical resistance. To ensure control in industrial practice, an effective and affordable method for assessing the degree of completion of crystalline transformations and determining the degree of graphitization during high-temperature treatment of carbon materials is recommended to compare the specific volume electrical resistivity of the working sample with the reference one. The importance of controlling the parameters of density, porosity, and electrical resistance to optimize technological processes and ensure high quality of final products is emphasized. The obtained data can be useful for applications in various industries.

The intramolecular aggregation of phosphaphenanthrene groups and benzene-terminated effect within linear phosphonate oligomers effectively enhanced the flame retardancy and toughness of epoxy resin

To explore the potential of a flame retardant molecular structure that simultaneously enhances the flame retardancy and physical properties of epoxy resin (EP), benzene-terminated linear phosphonate oligomers Bz-DQPC-n were synthesized. Compared with the previously prepared linear bisphenol phosphonate oligomers DQPC-n, the benzene-terminated effect of Bz-DQPC-n molecules endows EP composites with better flame retardancy and toughness. In the vertical combustion (UL 94) test, Bz-DQPC-n/EP reached a V-0 rating. For the Bz-DQPC-2 molecule, the results revealed that under the same phosphorus contents, the limiting oxygen index (LOI) value of the Bz-DQPC-2/EP reached 38.2 %, which was higher than that of DQPC-2/EP. Furthermore, the peak heat release rate (pk-HRR) and total heat release rate (THR) of Bz-DQPC-2/EP were 677 kW/m2 and 83 MJ/m2. These values decreased by 54.7 % and 27.2 % in comparison to pure EP, respectively. In addition, the incorporation of Bz-DQPC-n can enhance the glass transition temperature (Tg) of EP composites. The flame retardant mechanism research demonstrated that Bz-DQPC-n molecules produced phosphorus-containing free radicals and aromatic compound fragments during gas-phase pyrolysis. These phosphorus-containing free radicals can interrupt or inhibit the combustion chain reaction process. A proportion of the aggregated phosphaphenanthrene groups decomposed to produce aromatic compounds that remained in the condensed phase, thereby enhancing the quality of the char layer. The investigation of the impact of the end-capping effect within Bz-DQPC-n molecules on the flame retardant behavior of EP composites offers a valuable reference for designing phosphaphenanthrene compounds with high flame retardant efficiency.

Thermal Decomposition of 2-Cyclopentenone.

The thermal decomposition of 2-cyclopentenone, a cyclic oxygenated hydrocarbon that occurs in the pyrolysis of biomass, has been studied in a combined experimental and theoretical approach. Gas-phase pyrolysis was performed at temperatures ranging from 1000 to 1400 K in a pulsed, microtubular reactor. Products were identified by FTIR spectroscopy following their isolation in a low-temperature argon matrix. The following products were identified: carbon monoxide, ketene, propenylketene, vinylacetylene, ethylene, propene, acrolein, acetylene, propyne, and propargyl radical. Computational results identify three different decomposition channels involving a H atom migration, and producing prop-2-enylketene (Pathway 1), prop-1-enylketene (Pathway 2), and a second conformation of prop-2-enylketene (Pathway 3). A fourth decomposition pathway involves simultaneous rupture of two C-C bonds forming a high energy cyclopropenone intermediate that further reacts to form ethylene, acetylene, and carbon monoxide. Finally, a fifth pathway to the formation of acrolein and acetylene was identified that proceeds via a multistep mechanism, and an interconversion from 2-cyclopentenone to 3-cyclopentenone was identified computationally, but not observed experimentally.

Mixing and ignition characteristics of laser-induced solid fuel pyrolysis under wide-range variation of crossflow

A theoretical model has been developed to elucidate the thermal initiation laser ignition process of solid fuel. This model comprehensively explores both the heating process of solid fuel and the mixing process of gas-phase pyrolysis gases with crossflow conditions. A two-dimensional transient numerical model has been established and validated through experimental investigations across a spectrum of crossflow fluxes (ranging from 20 to 150 kg/m2/s) and pressures (ranging from 0.15 to 1.83 MPa). The study involves a quantitative analysis of the influence of key macroscopic parameters, including laser energy levels, combustion pressure, and flow rates, on essential mixing characteristics. The solid fuel heating process is segmented into two distinct phases: a preheating phase and a pyrolysis phase, with the latter exhibiting considerably higher heating rates. Notably, a direct linear relationship is observed between the laser energy levels and the rate of heating. It reveals that the dynamics of pyrolysis product mixing are primarily determined by the solid fuel pyrolysis rate and the prevailing crossflow conditions. The dimensionless penetration depth, which measures the extent of pyrolysis product mixing with crossflow, demonstrates an exponential positive correlation with pyrolysis rates and oxidizer flow rates while displaying a negative correlation with combustion pressure. This analysis includes the quantitative determination of proportionality constants and power exponents within the correlations. Finally, the study delves into the intricate interplay between crossflow conditions and the criteria for laser ignition, specifically ignition temperature and the flammable lower limit.

Carbon nanotube interweaved Fe7Se8 nanosheet/nanorod hybrids on expanded graphite for high-performance sodium storage

The construction of nano-micro scale hybrid structures by carbon materials is an effective strategy to address the issues of metal chalcogenides when used as anodes of sodium-ion batteries. Herein, we develop a carbon nanotube (CNT)-interweaved Fe7Se8/expanded graphite (EG) composite by means of a facile one-step gas-phase pyrolysis route with ferrocene, selenium and EG as the starting materials. The ex-situ monitoring of the pyrolysis process indicates that the selenium as a promoter facilitates the formation of CNTs and the carbon coated Fe7Se8 nanosheet/nanorod mixture. A competing reaction between CNT growth and the evolution of Fe7Se8 nanostructures occurs, which could be dominated by the concentration of selenium vapor. By optimizing the feeding ratio and the pyrolysis condition, the nanocomponents are homogeneously deposited on the surface of the EG matrix to realize a well-developed nano-micro hybrid configuration. The constructed three-dimensional conductive network, rich mesopores and high specific surface area (107.1 m2 g−1) contribute to substantially enhanced sodium-storage performance in ester electrolyte. Remarkably, the optimized composite electrode exhibits high reversible capacity retention of 97.5 % after 1000 cycles at 1.0 A g−1 and improved rate performance of 325 mAh g−1 at 2.0 A g−1. This study provides new avenues to develop high-performance metal chalcogenide electrodes for electrochemical energy storage.

Comparative study on the flame retardancy, pyrolysis behavior, and flame retardant pathways of black phosphorus in polyurethane and polypropylene

Black phosphorus nanosheets (BPns) have gained widespread attention in the field of flame retardancy due to their highly efficient flame-retardant properties achieved with a low addition rate (e.g., 0.4%). However, the pyrolysis pathways of BP in polymers have not yet been elucidated. This work systematically studies the flame retardancy and pyrolysis behavior of BP in oxygen-containing (polyurethane, PU) and oxygen-free (polypropylene, PP) polymers, distinguishing between the gas-phase and the condensed-phase flame retardant effect of BP. Through slow heating and staged heating methods, the condensed phase and gas phase pyrolysis products of BP in PU and PP at different temperatures are compared in detail. The distinct flame retardant pathways of BP in PU and PP are revealed. The results indicate that the oxidation of BP commences with its reaction with atmospheric oxygen, implying that the condensed-phase flame-retardant effect of BP primarily occurs at the polymer surface. In PP, BP mainly functions as a gas-phase flame retardant. In the condensed phase, BP generates phosphate derivatives that cover the substrate surface, providing solely a physical barrier effect. In PU, while BP demonstrates an outstanding gas-phase flame-retardant effect, it also accelerates the early dehydration carbonization of alcohols within the substrate, resulting in the formation of phosphate ester compounds (P–O–C structure) to bolster the thermal stability of residual carbon. Additionally, the side reactions of BP during catalytic carbonization will decrease the thermal stability of ester bonds in PU. This work lays a theoretical foundation for the development and application of BP-based flame retardant systems.

A lava-inspired design strategy based on combustion characteristics of PFRP for excellent flame retardancy via dual action mechanism at wide temperature range

Although plant fiber reinforced composite (PFRP) with environmental-friendly and biodegradable matches with society development requirements and carbon neutral strategy, the inherent flammability limits application in the engineering field, especially in rail transit and aerospace with strict fire standards. In this work, based on combustion behaviors of PFRP, the flame-retardant strategy inspired by the characteristics of volcanic lava in nature which could flow along rock crevices or valleys and form dense ceramic protective layer with outstanding heat insulation on the surface after cooling is designed. Compared with neat PFRP, the LOI of the PFRP/APP@PTNi20-GP10 (7.7 wt% FR contents) reaches 35.8 %, and UL-94 achieves V-0, showing excellent self-extinguishing performance. Meanwhile, the peak heat release rate (PHRR), total heat release (THR), total smoke release (TSR) and CO production (COP) decrease by 70.1 % and 51.7 %, 60.3 % and 65.5 % respectively. More importantly, the char layer formed after the combustion process retains excellent strength and compactness, which provides better protection for the undecomposed composite. Furthermore, the release of toxic volatiles including aromatic compounds, esters and carbonyl compounds in gas-phase pyrolysis products decrease significantly. The mechanism of lava-inspired flame-retardant system can be attributed to the dual action mechanism where different components play corresponding flame-retardant role under wide temperature range. And it is noted that the designed strategy endows PFRP with excellent fire resistance without deteriorating mechanical properties. This work provides a novel design idea for realizing the flame retardancy of PFRP and broadens the application field of PFRP.

Bottom-up gas phase construction of carbon coated Fe7Se8 nanosheet/carbon nanotube hybrid as ultrastable anode material for sodium-ion half/full batteries

Transition metal selenide/carbon nanotube (TMS/CNT) composites as one important category of anode material for rechargeable alkali metal ion batteries are always troubled by the high-quality combination between active matter and inert CNT matrices. Herein, a bottom-up gas phase pyrolysis strategy is introduced to avoid the tedious and time-consuming loading process of active nanostructures. With ferrocene and selenium powders as the raw materials, a carbon coated Fe7Se8 nanosheet/carbon nanotube (Fe7Se8@C/CNT) hybrid is synthesized. The critical role of selenium in the mass growth of CNTs at low deposition temperature is demonstrated for the first time. Benefiting from the molecular-level synthesis process, the carbon coated Fe7Se8 nanosheets are uniformly anchored on CNTs, and a porous hybrid network architecture is constructed. When tested in sodium-ion batteries (SIBs), the Fe7Se8@C/CNT electrode exhibits high reversible capacity (485 mA h g−1 at 0.1 A g−1), high initial Coulombic efficiency (97.4 %), superior long-term cycling stability upon 1000 cycles and excellent rate capability (397 mA h g−1 at 10.0 A g−1). Moreover, the full cell that coupled with a Na3V2(PO4)3 cathode also retains an undiscounted long-term cycling ability and high rate performance, reflecting its great potential for practical SIBs. The detail kinetics analyses including capacitive contribution, EIS and GITT are carried out. This work provides a new avenue for developing high-performance TMS/CNT electrode materials in electrochemical energy storage applications.

Experimental and Kinetic Study on the Gas-Phase Pyrolysis of Syringol

Syringyl (3,5-dimethoxy-4-hydroxyphenyl) units are abundant in hardwood lignin, which explains the large amount of syringol present in bio-oils derived from these feeds. To improve understanding of the decomposition chemistry of these syringyl units, the gas-phase pyrolysis kinetics of syringol have been studied experimentally and theoretically under typical fast pyrolysis conditions. The experiments were performed at 673–923 K in a micropyrolyzer unit hyphenated with a gas chromatography (GC) × gas chromatography-flame ionization detection/time-of-flight mass spectrometry and a customized gas chromatograph, which allows to detect and quantify products with boiling points up to 823 K next to permanent gases and water. New obtained experimental data show that 2,3-dihydroxybenzaldehyde is the most important phenolic product, and a large amount of pyrolytic water was formed. The proposed decomposition pathways of syringol to these two products show two new features: (1) 2,3-dihydroxybenzaldehyde is formed from a unimolecular decomposition of syringol without any stable intermediates and (2) both pathways leading to 2,3-dihydroxybenzaldehyde and water involve one more H-atom migration step to form the more stable radicals. Potential energy surface calculations at the CBS-QB3 level of theory indicate that the new features are kinetically favorable. Furthermore, a detailed kinetic model for syringol pyrolysis including 361 reactions and 93 species was constructed. Thermodynamic data for important species and kinetics for crucial reactions were determined with ab initio calculations at the CBS-QB3 level of theory. The model predicts well the conversion of syringol and the formation of major products. A rate of production analysis shows that the new proposed pathway is the major decomposition pathway of syringol. These findings shed new light on the pyrolysis and oxidation chemistry of syringyl species.

The gas-phase pyrolysis of cyclopropylamine. A computational study on the kinetics and reaction mechanism

Small amines represent an accessible model to understand the reactivity of the nitrogenous components of biomass during combustion and pyrolysis processes. In this work, the kinetics and mechanism of the gas-phase pyrolysis of cyclopropylamine, c-C3H5NH2, have been studied by ab initio and density functional calculations. From the derived information high-pressure limit rate coefficients were estimated using the transition state theory over the 400 – 1400 K temperature range. The results support a stepwise process, in which the initial ring-opening stage determines the rate through competitive direct, biradical and carbene mechanisms to give 1-aminopropene, CH3CH=CHNH2, and 1-propanimine, CH3CH2CH=NH, as reactive intermediates. The Arrhenius equation obtained at the G3(MP2)//B3LYP/6–311++G(3df,3pd) level of theory, log10 (koverall,∞/s-1) = (15.47 ± 0.11) – (57.68 ± 0.32) kcal mol-1 (2.303 RT)-1, agrees very well with the experimental expression determined by Parry and Robinson. According to these findings, the carbenic pathway is most important up to ∼500 K, above which the biradical mechanism predominates. Subsequent reaction steps include the addition of the CH3CH=CHNH2 and CH3CH2CH=NH species to another c-C3H5NH2 molecule to produce c-C3H5NHCH(NH2)CH2CH3, which afterwards decomposes into c-C3H5N=CHCH2CH3 and NH3. The results also reveal relatively high electronic barriers for the interconversion between the geometric isomers of CH3CH=CHNH2 and CH3CH2CH=NH, suggesting that the contribution of these processes is negligible. Further calculations of the title reaction in the presence of selected aliphatic amines RNH2 (R = Me, Et,n-Pr, i-Pr, allyl) confirm that the unimolecular fission of the ring is the rate determining step.

CFD simulation of CVD reactors in the CH3SiCl3(MTS)/H2 system using a two-step MTS decomposition and one-step SiC growth models

In this study, we report on a computational fluid dynamics (CFD) simulation of the chemical vapor deposition reactor of silicon carbide (SiC) in the methyltrichlorosilane (MTS, CH3SiCl3)/H2 system. The formation of SiC thin film is controlled by various process parameters, such as temperature and pressure. In this study, we propose a reaction mechanism of MTS decomposition to SiC growth on a substrate surface for CVD reactors in the CH3SiCl3(MTS)/H2 system. The reaction mechanism has two gas-phase pyrolysis reactions and one SiC film formation reaction. However, we individually build and validate MTS decomposition and SiC growth models to reduce uncertainty. An in-house version of reactingFoam, a reactive flow solver within OpenFOAM v2006, was used as the simulation tool. Our model accurately reproduced MTS decomposition for T = 1100–1350 K and [H2]/[MTS] = 2.65–14 at p = 101,325 Pa. Then, the MTS decomposition model was coupled with the SiC growth model, and the coupled model was applied to the SiC deposition data. The model could reproduce multiple datasets through validation studies.

Carbon Hybrid Materials-Design, Manufacturing, and Applications.

Carbon nanotubes (CNTs) have extraordinary properties and are used for applications in various fields of engineering and research. Due to their unique combination of properties, such as good electrical and thermal conductivity and mechanical strength, there is an increasing demand to produce CNTs with enhanced and customized properties. CNTs are produced using different synthesis methods and have extraordinary properties individually at the nanotube scale. However, it is challenging to achieve these properties when CNTs are used to form macroscopic sheets, tapes, and yarns. To further improve the properties of macroscale forms of CNTs, various types of nanoparticles and microfibers can be integrated into the CNT materials. The nanoparticles and microfibers can be chosen to selectively enhance the properties of CNT materials at the macroscopic level. In this paper, we propose a technique to manufacture carbon hybrid materials (CHMs) by combining CNT non-woven fabric (in the form of sheets or tapes) with microfibers to form CNT-CF hybrid materials with new/improved properties. CHMs are formed by integrating or adding nanoparticles, microparticles, or fibers into the CNT sheet. The additive materials can be incorporated into the synthesis process from the inlet or the outlet of the reactor system. This paper focuses on CHMs produced using the gas phase pyrolysis method with microparticles/fibers integrated at the outlet of the reactor and continuous microfiber tapes integrated into the CNT sheet at the outlet using a tape feeding machine. After synthesis, characterizations such as microscopy and thermogravimetric analysis were used to study the morphology and composition of the CNTs, and examples for potential applications are discussed in this paper.

CFD Simulation of a Hybrid Solar/Electric Reactor for Hydrogen and Carbon Production from Methane Cracking

Methane pyrolysis is a transitional technology for environmentally benign hydrogen production with zero greenhouse gas emissions, especially when concentrated solar energy is the heating source for supplying high-temperature process heat. This study is focused on solar methane pyrolysis as an attractive decarbonization process to produce both hydrogen gas and solid carbon with zero CO2 emissions. Direct normal irradiance (DNI) variations arising from inherent solar resource variability (clouds, fog, day-night cycle, etc.) generally hinder continuity and stability of the solar process. Therefore, a novel hybrid solar/electric reactor was designed at PROMES-CNRS laboratory to cope with DNI variations. Such a design features electric heating when the DNI is low and can potentially boost the thermochemical performance of the process when coupled solar/electric heating is applied thanks to an enlarged heated zone. Computational fluid dynamics (CFD) simulations through ANSYS Fluent were performed to investigate the performance of this reactor under different operating conditions. More particularly, the influence of various process parameters including temperature, gas residence time, methane dilution, and hybridization on the methane conversion was assessed. The model combined fluid flow hydrodynamics and heat and mass transfer coupled with gas-phase pyrolysis reactions. Increasing the heating temperature was found to boost methane conversion (91% at 1473 K against ~100% at 1573 K for a coupled solar-electric heating). The increase of inlet gas flow rate Q0 lowered methane conversion since it affected the gas space-time (91% at Q0 = 0.42 NL/min vs. 67% at Q0 = 0.84 NL/min). A coupled heating also resulted in significantly better performance than with only electric heating, because it broadened the hot zone (91% vs. 75% methane conversion for coupled heating and only electric heating, respectively). The model was further validated with experimental results of methane pyrolysis. This study demonstrates the potential of the hybrid reactor for solar-driven methane pyrolysis as a promising route toward clean hydrogen and carbon production and further highlights the role of key parameters to improve the process performance.

Experimental and Theoretical Study of Oxolan-3-one Thermal Decomposition.

The thermal decomposition of oxolan-3-one, a common component of the bio-oil formed during biomass pyrolysis, has been studied using ab initio calculations and experiments employing pulsed gas-phase pyrolysis with matrix-isolation FTIR product detection. Four pathways for unimolecular decomposition were predicted using computational methods. The dominant reaction channel led to carbon monoxide, formaldehyde, and ethylene, all of which were observed experimentally. The other channels led to an assortment of products including ketene, water, propyne, and acetylene, which were all confirmed in the matrix-isolation FTIR spectra. There is also evidence for the production of substituted ketenes in pyrolysis, most likely hydroxyketene and methylketene.

Probing the Pyrolysis of Guaiacol and Dimethoxybenzenes Using Collision-Induced Dissociation Charge-Remote Fragmentation Mass Spectrometry

The dissociation of lignin model compounds has been examined using mass spectrometry and collision-induced dissociation charge-remote fragmentation (CID-CRF). The model compounds guaiacol and o- and m-dimethoxybenzene containing a remote sulfonate (SO3-) charge group undergo CID by dissociation without the involvement of the anionic group. The first dissociation for all three compounds is loss of methyl radical to form phenoxy radicals. Subsequent dissociation pathways depend on the specific structures being examined The dissociation pathways are compared to those observed upon gas-phase pyrolysis that have been reported previously. While the pathways are largely similar, there are some important differences that are explained by changes in dissociation barriers due to the effect of adding the charged group. This work shows that CID-CRF is an effective approach for tracking the thermolysis of lignin model compounds while eliminating secondary reactions that normally convolute such studies.

Thermochemical depolymerization of lignin: Process analysis with state-of-the-art soft ionization mass spectrometry

Lignin valorization via thermochemical approaches has the potential to produce renewable fuels and value-added chemicals, which are of great significance to the sustainable development of human beings. During the thermochemical depolymerization which involves acid-catalyzed, alkali-catalyzed, oxidative, reductive, pyrolytic, and other reactions, the lignin structure will undergo a series of bond cleavage, condensation, and functional group changes, while the mechanism is still unclear. To improve the efficiency, the analysis of the evolution of intermediates during depolymerization is very important, among which soft ionization mass spectrometry plays a vital role. This review aims to summarize the research progress of process analysis of lignin depolymerization in both gas-phase, typically thermal and catalytic pyrolysis, and liquid-phase via online mass spectrometry. The challenges and our insights into the future development of the lignin valorization as well as soft ionization mass spectrometry methods are also discussed.

Metal-Free Biomass-Derived Environmentally Persistent Free Radicals (Bio-EPFRs) from Lignin Pyrolysis.

To assess contribution of the radicals formed from biomass burning, our recent findings toward the formation of resonantly stabilized persistent radicals from hydrolytic lignin pyrolysis in a metal-free environment are presented in detail. Such radicals have particularly been identified during fast pyrolysis of lignin dispersed into the gas phase in a flow reactor. The trapped radicals were analyzed by X-band electron paramagnetic resonance (EPR) and high-frequency (HF) EPR spectroscopy. To conceptualize available data, the metal-free biogenic bulky stable radicals with extended conjugated backbones are suggested to categorize as a new type of metal-free environmentally persistent free radicals (EPFRs) (bio-EPFRs). They can be originated not only from lignin/biomass pyrolysis but also during various thermal processes in combustion reactors and media, including tobacco smoke, anthropogenic sources and wildfires (forest/bushfires), and so on. The persistency of bio-EPFRs from lignin gas-phase pyrolysis was outlined with the evaluated lifetime of two groups of radicals being 33 and 143 h, respectively. The experimental results from pyrolysis of coniferyl alcohol as a model compound of lignin in the same fast flow reactor, along with our detailed potential energy surface analyses using high-level DFT and ab initio methods toward decomposition of a few other model compounds reported earlier, provide a mechanistic view on the formation of C- and O-centered radicals during lignin gas-phase pyrolysis. The preliminary measurements using HF-EPR spectroscopy also support the existence of O-centered radicals in the radical mixtures from pyrolysis of lignin possessing a high g value (2.0048).

Experimental comparison of solar methane pyrolysis in gas-phase and molten-tin bubbling tubular reactors

This study experimentally compares solar methane pyrolysis in gas phase and molten tin for hydrogen and solid carbon production. Molten media are expected to facilitate carbon separation and to enhance solar-to-gas heat transfer. Effects of temperature (1000–1400 °C), gas feed flow rate (0.5–1.0 NL/min), and methane molar fraction in the feed (0.1–0.5) on methane decomposition were investigated in a tubular solar reactor. Methane conversion in molten tin was significantly lower than in gas phase at all temperatures (e.g., 64% vs. 92% at 1300 °C). It was justified by the negligible catalytic activity of tin, the small gas-liquid surface contact (bubble diameter ∼5 mm) and the reduced bubble-tin contact time, in comparison with gas-phase pyrolysis (e.g., 0.83 s vs. 0.5 s for 0.5 NL/min gas feed at 1300 °C). For both routes, a temperature increase (1000–1400 °C) improved methane conversion (gas phase: 2–98%, molten tin: 0–91%). Increasing gas feed flow rate (0.5–1.0 NL/min) decreased conversion (gas phase: 93-85%, molten tin: 64-48% at 1300 °C) by reducing space-time in gas phase (0.83–0.42 s) or by inducing bubbles coalescence in molten tin. Increasing methane molar fraction in the feed generally decreased methane conversion but energy efficiencies were enhanced. The carbon produced in gas-phase pyrolysis was carbon black powder (50–100 nm particle size) and carbon sheets in molten tin.

Reaction mechanism of the gas-phase pyrolysis of N – Acetylthiourea and N, N’–diacetylthiourea: A theoretical study based in density functional theory

In the present study, we propose a reaction mechanism for the decomposition of N -Acetylthiourea and N, N '-Diacetylthiourea using density functional quantum chemical calculations. For both reactions the level of theory that gave us the better agreement between theory and experiment was MPW1PW91/6-311G (d, p). Thermodynamic and kinetic parameters were evaluated at 600 K and 1 atm. For N -Acetylthiourea decomposition reaction, the products are ketene and thiourea, while for are N, N '-Diacetylthiourea, the product are ketene and N–Acetylthiourea. Our calculations suggest that the mechanism proceeds stepwise, where the rate-determining step is promoted by an intramolecular nucleophilic attack of the sulfur atom to the carbonyl carbon in the acetyl group. The kinetics of these reactions is influenced by the electron-withdrawing effect of the acetyl group. Population analysis shows that the mechanism is predominantly synchronous as demonstrated by the high values ​​of the Wiberg synchronicity index. A non-covalent interactions study was also carried out in each stage of the reaction, as well as the analysis of the binding forces of the structures was followed by the independent gradient model (IGM) and its descriptor δg.

Synthesis Tuning for Manufacturing Carbon Hybrid Materials

The overall hypothesis for this paper is that accurately tuning the gas phase pyrolysis synthesis process and using appropriate raw materials will enable manufacturing different types of carbon hybrid materials (CHM). Optimizing multiple variables including particle melting and vaporization temperatures, fuel flow rate, gas flow rates, gas velocity, and sock wind-up speed is needed to achieve reliability of the synthesis process. Results from our specific reactor are presented to show how the process variables interact and how they affect CNT sock yield and stability. Metal nanoparticle (NP) injection enables the formation of hybrid materials. Several types of CHM materials created by incorporating different types of NPs into the carbon nanotube (CNT) synthesis process and CNT sock are discussed. Many possible combinations of metal NPs can be used in the process to customize the properties of CHM. However, it is a complex problem to determine what metal compounds can chemically join with CNT. Some of the first results testing the new CHM process are presented in this paper.