Pyrolysis Mechanism Research Articles

Research on the pyrolysis mechanism of tobacco based on low temperature torrefaction

The temperature range of 100–220 °C is known to cause the volatilization of some volatile components and the pyrolysis of some unstable components in tobacco. However, there is a lack of research on the pyrolysis mechanism of tobacco at this temperature range. To address this gap, the present study employed an innovative cascade pyrolysis method based on stepwise heating to analyze the composition of tobacco's rapid pyrolysis products within this temperature range. The analysis was conducted at intervals of 30 °C. The study summarized the release characteristics of organics at different temperatures and analyzed the representative substances of various organic families. In addition, considering that tobacco has a unique composition compared to most biomass, the same five temperature points as they do in the cascade pyrolysis process were selected to torrefy the tobacco samples. These temperatures are lower than the conventional torrefaction temperatures typically used for biomass pretreatment. Multiple techniques were used to systematically analyze the composition, functional group structure, and thermal degradation characteristics of tobacco torrefied at different temperatures. Subsequently, the effect of torrefaction temperature on the release performance of products from tobacco pyrolysis at 650 °C was also studied. The results of this study not only contribute to a more comprehensive understanding of the pyrolysis mechanism of tobacco but also provide theoretical support for cigarette processing and tobacco waste utilization.

Product distribution and conversion mechanism of fossil-based biodegradable plastics during rapid pyrolysis

Fast pyrolysis has emerged as a promising technology for converting fossil-based biodegradable plastics (FBBPs) into clean energy and high-value products with rapid volume reduction and efficient utilisation. The degradation mechanism during pyrolysis is crucial, and different chemical structures and reaction processes directly affect the treatment efficiency and economic benefits. In this study, three typical FBBPs, including poly(butylene adipate-co-terephthalate) (PBAT), polybutylene succinate (PBS) and poly(epsilon-caprolactone) (PCL), have been analyzed in rapid pyrolysis experiments and corresponding products. Being pyrolyzed at 550℃, three kinds of FBBPs exhibited distinctly different decomposition behaviors and characteristics. These differences can be attributed to the bond-breaking ways and pyrolysis mechanisms, which enhance the value of products. Specifically, PBS exhibited the highest abundance of bio-oils and particulate matter (total 90.58%) compared to PBAT and PCL, mainly converted to ketones and acids with a homogeneous component distribution, which was likely to help facilitate further utilisation. In addition, the oxygen of PBS remained in the bio-oil fraction while showing high levels of CO in the bio-gas. Moreover, PCL had the highest amount of bio-gas (21.76%) among the three FBBPs, indicating that it was more likely to break into small molecule products. Notably, the broken chains or macro-molecules of PCL were primarily converted into esters, with di(but-2-en-1-yl) adipate accounting for 57.5% of bio-oils. This work elucidated the transformation pathways and mechanism of FBBP pyrolysis, providing guidance for the treatment and resource utilisation of FBBPs.

Evaluation of the thermal hazard and pyrolysis mechanism of 1-allyl-3-methylimidazole nitrate and 1-propyl-3-methylimidazole nitrate via thermal analysis and DFT calculation: Effect of structural characteristics

Imidazole ionic liquid, as a green solvent, is one of the most widely used ionic liquids. Understanding its thermal safety characteristics and mechanism is the essential basis for its safe application. In this paper, the thermal hazard characteristics of two ionic liquids with typical structural characteristics are systematically studied, which were 1-allyl-3-methylimidazole nitrate and 1-propyl-3-methylimidazole nitrate ionic liquids. The thermal decomposition peculiarities of two ionic liquids were systematically analyzed by thermogravimetric analyzer, differential scanning calorimetry and accelerating rate calorimeter techniques, and the risk of thermal runaway is also evaluated. In addition, the pyrolysis products and microscopic pyrolysis mechanism of ionic liquids were studied via thermogravimetry-Fourier transform infrared spectroscopy, thermogravimetric mass spectrometry and density functional theory calculation, and the essential mechanism of thermal hazard were determined. The influence of substituent structure on the thermal hazard characteristics of imidazole nitrate ionic liquid was preliminarily analyzed from macroscopic experiment and microscopic mechanism two aspects. This study provides a theoretical basis for the safe application, design and development of imidazole nitrate ionic liquids.

Removal of polystyrene microplastic from aqueous solutions with London Plane bark biochar: Pyrolysis temperature, performance and mechanism

The seasonally shed bark of London Plane tree is an ideal source for biochar due to its high lignin content. Microplastics derived from plastic wastes has become a hot topic due to its potential threats to ecosystems. The aim of this work is to convert the shed bark into efficient London Plane bark biochar (LBC) adsorbents and investigate its application in microplastics adsorption. The effects of pyrolysis temperature on LBC structure, surface properties and microplastic adsorption were investigated and the best adsorption performance of 60.05 mg/L was found at the 550 °C-pyrolyzed LBC. The wet sieve-weighing method was applied to assess the adsorption effect of LBC and verified with thermogravimetric analysis. The adsorption of polystyrene (PS) particles on LBC was in accordance with the Sips isothermal model and the second-order-kinetics model. The robustness of LBCs and the adsorption mechanism were investigated. With the analysis from pore size distribution, SEM images, FTIR and XPS spectra, physical trapping, surface complexation, hydrogen bonding and π-π interaction all play key roles in the adsorption of PS onto the LBC surface. This study not only provides a new approach for the removal of microplastics, but also offers a broad perspective on the treatment of biomass waste.

Experimental and theoretical study on the thermal stability and pyrolysis mechanism of octamethyltrisiloxane (MDM) with lubricating oil

In actual organic Rankine cycle systems (ORCs), the inclusion of lubricating oil in the working fluid is nearly unavoidable. Under the condition of high-temperature operation, the presence of lubricating oil can potentially exacerbate the thermal stability of the working fluid. The impact of polyol ester (POE) and mineral lubricant on the thermal stability of octadethyltrisiloxane (MDM) is studied. Results indicate that both POE and mineral lubricant contribute to the decomposition of MDM to a certain extent. Specifically, at a 5.0% mass fraction of POE and mineral lubricant, MDM remains its stable at 230 °C and 210 ℃, respectively. However, as the mass fraction of lubricant increases, the decomposition of MDM intensifies, with mineral lubricant exhibiting a more pronounced effect compared to POE lubricant. Regarding pyrolysis products, the presence of lubricants leads to an increase in CH4, C2H6 and C2H4 gases. Furthermore, the addition of lubricant promotes the formation of siloxane oligomers, particularly MD5M to MD9M, and enhances the production of unidentified products. Compared to MDM, both POE and mineral lubricant molecules exhibit lower bond dissociation Gibbs free energies. The free radicals generated from lubricant decomposition are prone to hydrogen abstraction reactions with MDM to promote MDM decomposition. Moreover, ReaxFF simulation results demonstrate that lubricant molecules also enhanced the activation of MDM and increased its susceptibility to Si-C bond cleavage. Following the removal of the methyl group, the Si-O bonds in the radicals are more likely to break, leading to the formation of additional siloxane oligomers through Si-O bond recombination. Kinetic analysis reveals that the apparent activation energy of MDM decomposition drops from 134.4 kJ∙mol−1 to 110.8 kJ∙mol−1 as the mass fraction of n-hexadecane (model compounds for mineral lubricant) rises from 0% to 10.30%.

Cure Kinetics and Thermal Decomposition Behavior of Novel Phenylacetylene-Capped Polyimide Resins.

Based on a novel phenylacetylene capped polyimide (PI) with unique high-temperature resistance, its curing kinetics and thermal decomposition behavior were investigated. The curing mechanism and kinetics were studied by differential scanning calorimetry (DSC), and the activation energy (Ea) and pre-exponential factor (A) of the curing reaction were calculated based on the Kissinger equation, Ozawa equation, and Crane equation. According to the curve of conversion rate changing with temperature, the relationship between the dynamic reaction Ea and conversion rate (α) was calculated by the Friedman equation, Starink equation, and Ozawa-Flynn-Wall (O-F-W) equation, and the reaction Ea in different stages was compared with the results of molecular dynamics. Thermogravimetric analysis (TGA) and a scanning electron microscope (SEM) were used to analyze the thermal decomposition behavior of PI resins before and after curing. Temperatures at 5% and 20% mass loss (T5%, T20%), peak decomposition temperature (Tmax), residual carbon rate (RW), and integral process decomposition temperature (IPDT) were used to compare the thermal stability of PI resins and cured PI resins. The results display that the cured PI has excellent thermal stability. The Ea of the thermal decomposition reaction was calculated by the Coats-Redfern method, and the thermal decomposition behavior was analyzed. The thermal decomposition reaction of PI resins at different temperatures was simulated by molecular dynamics, the initial thermal decomposition reaction was studied, and the pyrolysis mechanism was analyzed more comprehensively and intuitively.

The effect of H2 and NH3 on the pyrolysis of coal model compounds based on reactive molecular dynamics simulation

The co-combustion of coal and ammonia (NH3) has been receiving considerable attention due to its potential for mitigating CO2 emissions. Consequently, comprehending the pyrolysis mechanism of coal under the NH3 atmosphere is of paramount significance. Using pyrrole and pyridine, which are crucial model compounds of coal, the pyrolysis mechanisms within N2/H2/NH3 is systematacially investigated with the help of chemical reaction kinetics simulations (ReaxFF MD). The results revealed that pyrrole performs inferior structural stability compared to pyridine, resulting in accelerated and shorter pyrolysis, alongside a lower activation energy for the reaction. As a result, the pyrolysis process of pyrrole is more prone to C-C and C-N bond cleavage, ultimately producing more HCN. Moreover, this investigation revealed that both H2 and NH3 atmospheres promote the pyrolysis of pyrrole and pyridine, with the NH3 atmosphere having a more pronounced influence. The presence of an NH3/H2 atmosphere increased the production of HCN, lowered the activation energy required for the pyrolysis of pyrrole and pyridine, and aided in the cleavage of C-C and C-N bonds. Additionally, this study demonstrated the reaction network of pyrrole and pyridine in N2/H2/NH3 atmospheres, focusing on the observation that NH2 radicals, during the initial phases of the reaction, stimulate the production of low-carbon fragments and assist the fracture process of the model compounds. Furthermore, this study presents the reaction network of pyrrole and pyridine in N2/H2/NH3 atmospheres, with a particular focus on the NH3 atmosphere. The existence of NH3 in the atmosphere facilitates the formation of low-carbon fragments during the cleavage phase of the model compounds. This leads to the production of low-carbon intermediates and an increase in the generation of HCN during the subsequent condensation stage. These findings highlight the significant impact of the ammonia atmosphere on the pyrolysis of the model compounds. The outcomes of this study elucidate the fundamental principles of nitrogen-containing compound pyrolysis at the mechanistic level, providing critical insights for subsequent experimental and computational research.

Thermal stability of trifluoroiodomethane (R13I1) as an environmentally friendly working fluid for refrigeration and heat pump systems: Investigations and improvement strategies

Trifluoroiodomethane (R13I1) has attracted extensive attention because of its excellent environmental protection performance and flame retardant effect. However, R13I1 has poor thermal stability due to the presence of C-I bonds, which greatly limits its application in refrigeration and heat pump systems. At present, there are few theoretical and experimental studies on the thermal stability of R13I1 and its improvement methods. In order to solve these problems, the thermal stability and pyrolysis mechanism of R13I1 and its mixture with lubricants and stabilizers were investigated using experiments, DFT calculations, and ReaxFF simulations in this study. Firstly, the pyrolysis temperature and pyrolysis products of R13I1 were measured using the reactor method. The initial pyrolysis temperature range of R13I1 was 110–120 °C. C2F6 and I2 are the main pyrolysis products of R13I1. Then, the effect of polyol ester (POE) oil on the thermal stability of R13I1 was analyzed. The results showed that the addition of POE oil significantly promoted the decomposition of R13I1 and the generation of the pyrolysis product CHF3. Circulation systems containing R13I1/POE oil were not suitable for long-term operation at temperatures above 120 °C. The active radicals generated by the pyrolysis of lubricant were the key factor in the deterioration of the thermal stability of R13I1. Finally, a stabilizer addition to the lubricant was used to improve the thermal stability of the R13I1/POE oil, and the optimal stabilizer was determined to be 5 % AN5/0.15 % 2-ethylhexyl glycidyl ether. The thermal stability of R13I1/POE oil before and after the addition of the optimal stabilizer was compared. The experimental results showed that when the reaction temperature was 160 °C, the concentration of R13I1 increased from 98.94 % to 99.85 %, the concentration of CHF3 decreased from 0.89 % to 0.08 %, and the pyrolysis rate of R13I1 was only 3.86 × 10−9 s−1 with the addition of the optimal stabilizer. The optimal stabilizer achieved excellent improvements. This study not only provides basic thermal stability data for R13I1 and its mixtures, but also proposes effective methods to improve the thermal stability, which is of great significance for the safe and reliable application of R13I1 in refrigeration and heat pump systems.

Effect of heating rate on the secondary reaction in low-rank coals pyrolysis with the real-time evolution analysis of in-situ tar

Performing online evolution analysis of tar in actual pyrolysis process is a major challenge. In this work, the effects of heating rate (HR) on evolution curves of in-situ tar for low-rank coals pyrolysis were investigated in a novel laboratory bench. The escape law of volatiles was obtained, the influence of HR on secondary reactions was analyzed, the association between products and molecular structures was constructed, and pyrolysis mechanism was deduced. Aliphatic hydrocarbons (except dienes), phenols, and oxygenated compounds have only one peak, while dienes and aromatics have multiple peaks throughout the pyrolysis process. The first peak is attributed to coal primary pyrolysis. At increased HRs, the second peak for 1∼2ring aromatics is from the cracking of primary volatiles, and that for 3∼4ring aromatics from coal continued cracking. The proportion of phenols and oxygenated compounds decreases, aromatics increases, and aliphatic hydrocarbons varies for different coals. Generally, HR increases the yield of primary volatiles by enhancing coal primary pyrolysis, elevates the proportion of light aromatics by promoting secondary cracking and aromatization of primary volatiles, reduces char yield by inhibiting condensation reactions throughout the pyrolysis process. The similar macromolecular structures of different coals make the evolution curve versus HRs follow a common law.

Reaction path identification and validation from molecular dynamics simulations of hydrocarbon pyrolysis

AbstractCreation of complex chemical mechanisms for hydrocarbon pyrolysis and combustion is challenging due to the large number of species and reactions involved. Reactive molecular dynamics (RMD) enables the simulation of thousands of reactions and the discovery of previously unknown components of the reaction network. However, due to the inherent imprecision of reactive force fields, it is necessary to verify RMD‐obtained reaction paths using more accurate methods such as Density Functional Theory (DFT). We demonstrate a method for identification and confirmation of reaction pathways from RMD that supplement an established mechanism, using the example of benzene formation from n‐heptane and iso‐octane pyrolysis. We establish a validation workflow to extract reaction geometries from RMD and optimize transition states using the Nudged‐Elastic‐Band method on semi‐empirical and quantum mechanical levels of theory. Our findings demonstrate that the widely recognized ReaxFF parameterization, CHO2016, can identify known pathways from a established soot formation mechanism while also indicating new ones. We also show that CHO2016 underestimates hydrogen migration barriers by up to as compared to DFT and can lower activation barriers significantly for spin‐forbidden reactions. This highlights the necessity for validation or potentially even reparametrization of CHO2016.

Exploring bioenergy prospects from malt bagasse: Insights through pyrolysis with multi-component kinetic analysis and thermodynamic parameter estimation

Malt bagasse is a by-product of little commercial value in the brewing industry. Under this scenario, the current study represents the first investigation aiming to determine the kinetic triplet and thermodynamic parameters for malt bagasse pyrolysis using a multi-component kinetic approach to elucidate its bioenergy prospects. The pyrolysis progress profiles of malt bagasse were obtained through slow pyrolysis experiments on a thermogravimetric scale in an inert atmosphere, employing four distinct heating rates (10, 15, 25, and 40 °C min−1). This investigation also used the Frazer-Suzuki deconvolution function to elucidate the relative contributions of hemicellulose, cellulose, and lignin to malt bagasse pyrolysis. Activation energies for devolatilization reactions were determined by the isoconversional methods of Friedman, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink, and revealed the lowest and highest mean values for pseudo-hemicelluloses (158.3−215.3 kJ mol−1) and pseudo-lignin (279.5−294.8 kJ mol−1), respectively. Frequency factors in malt bagasse pyrolysis ranging from 8.9 × 1016 and 2.2 × 1023 min−1 offer evidence of a simplified reaction chemistry pathway in the conversion towards bioenergy production. The integral master plot indicates the involvement of order-based and geometrical contraction-based mechanisms in malt bagasse pyrolysis. After defining multiple kinetic triplets, a differential equation encompassing contributions from all pseudo-components was formulated, and the simulated results aligned closely with experimental data, accurately describing pyrolysis progress profiles with at least 92.8% precision. The thermodynamic analysis reveals positive ΔH and ΔG values, indicating the non-spontaneous nature of malt bagasse pyrolysis. Higher disorder in the resultant products is attributed to volatile release and molecular rearrangement and is signified by positive ΔS values compared to the initial reactants. This study provided valuable insights into the valorization of malt bagasse, offering crucial information for optimizing pyrolysis reactors, scaling, and designing malt bagasse conversion into valuable biofuels, constituting an effort towards bio-circular economy principles based on the zero-waste concept.

Pyrolysis mechanism and evolved gas analysis of a promising energetic carbamate-functionalized microcrystalline cellulose nitrate

The present study aims to elucidate the decomposition mechanism and gas evolution characteristics of a promising energy-rich carbamated microcrystalline cellulose nitrate (M3CN). The molecular structure and morphological characteristics of starting microcrystalline cellulose carbamate (MCCC) and its nitrated derivative were examined using FTIR and SEM techniques. Thermal analysis using TGA and DSC revealed distinct decomposition behaviors for MCCC and M3CN. MCCC exhibited endothermic decomposition linked to the degradation of the cellulosic structure. In contrast, an exothermic decomposition event was observed for M3CN, attributed to the cleavage of energetic groups within the nitrated cellulosic chains. Furthermore, the hyphenated TG-FTIR analysis confirmed that the primary gaseous products emitted during the pyrolysis of M3CN included NO, N2O, NO2, CO2, H2O, CH4, HCHO, HCN, and CHNO. The findings of this study enhance our understanding of the pyrolysis mechanism in cellulose-based energetic materials, providing a significant reference for forthcoming research and explorations in this field.

Synthesis, characterization, and thermal pyrolysis mechanism of high temperature resistant phenolphthalein-based poly (arylene ether nitrile)

Phenolphthalein (PP) is usually used as a functional monomer to design novel high performance polymers with adjustable thermal, mechanical, and fluorescent properties. In this study, a soluble, amorphous, high temperature resistant PP-based poly (arylene ether nitrile) (PAEN) was synthesized and its corresponding thermal decomposition mechanism was reported via TGA/DTG, TGA/FTIR and TGA/MS analysis. PP-based PAEN showed a Tg of 250 °C a Tdmax of 503 °C and a char residue of 59.2 % at 800 °C, respectively. According to Kissinger and Flynn–Wall–Ozawa model, the activation energy of thermal pyrolysis was calculated as 225 ± 4 and 284 ± 17 kJ/mol respectively, higher than those of other poly arylene ethers. PP-based PAEN showed a three-stage thermal pyrolysis mechanism. Its initial degradation happened before 400 °C and liberated the inherent moisture. The latter backbone decomposition between 400 and 600 °C involved multiple routes mainly from the CO and CC cleavages of lactone ring, resulting in a Ph2CHPhOPh intermediate by releasing HCHO, HCOOH, CO2, H2O, CH4, C6H6, and C6H5OH. The third carbonization stage over 600 °C included the transformation from biphenyl linkages to aromatic graphite by dehydrogenation. This study not only gives a comprehensive understanding of the thermal pyrolysis behavior of PP-based PAEN, but also provides valuable references for the thermal behaviors of other PP-containing polymers.

Experimental and reactive molecular dynamics simulation of municipal sludge extract pyrolysis

The sludge extract obtained from degradation solvent extraction exhibits high carbon content, low oxygen content, and ash-free characteristics, making it an ideal fuel due to its excellent performance. In this study, the pyrolysis process of the extract was systematically studied by combining GC-MS experiment with ReaxFF molecular dynamics simulation. The comparison between GC-MS experimental results and ReaxFF-MD simulation shows a high degree of similarity, thus confirming the accuracy of the simulation. This study identified 2000 K as the turning temperature between initial pyrolysis and secondary pyrolysis. In the temperature range of 1200–2000 K, the extract mainly undergoes primary pyrolysis, while in the temperature range of 2000–3000 K, the secondary reaction is remarkable, which is characterized by the further decomposition of tar free radicals and the condensation reaction involving tar free radicals or char. The analysis of typical gas content shows that H2, CO, NH3 and HCN are by-products of the secondary reaction of tar, and there are a lot of reducing gases at high temperature, such as H2, CO and CH4. Finally, the migration patterns of carbon, hydrogen, oxygen and nitrogen are discussed. It is worth noting that hydrogen and nitrogen mainly migrate to the pyrolysis gas phase. This not only laid a foundation for the separation of nitrogen and hydrogen in the future, but also triggered thinking about the potential of “low-carbon emission resource” in future research work. When compared to raw municipal sludge, the initial pyrolysis temperature of municipal sludge extract is much lower, and its pyrolysis process becomes faster. The advantages of reactive gas components indicate that it is more reactive. This variance results in a distinct product distribution and pyrolysis mechanism.

Understanding hydropyrolysis mechanism of β-O-4 type lignin dimer

Hydropyrolysis has been demonstrated as a highly effective method in the production of fuels and high-value chemicals. However, limited research has been conducted on the reaction mechanism under hydrogen conditions, which necessitates further investigation. In order to examine the impact of hydrogen, experiments were conducted on a high-pressure pyrolyzer using 1-methoxy-2-phenethoxybenzenene with β-O-4 linkage. The results indicated that hydrogen promoted the depolymerization and reduced the formation of heavier compounds, leading to an increase in the production of the monomer phenols and aromatic compounds. Experiments were further conducted at different pressures. The results obtained from reactive molecular dynamics simulations exhibited the pyrolysis mechanisms. The cleavage of Cβ-O, Cph-O, and Cα-Cβ bonds, as well as demethylation and demethoxylation processes during hydropyrolysis were observed. The initial reaction commenced with Cβ-O bond cleavage, which was enhanced by the presence of hydrogen. Subsequent reactions were categorized into three types: decomposition or isomerization reaction, coupling with radical groups containing carbon, and combination with hydrogen molecules or hydrogen radicals. The direct reactions between the model compound molecules and hydrogen molecules or hydrogen radicals, as well as primary hydrogen abstraction reactions and hydrogen elimination reactions were explored. These simulations offer valuable insights into understanding the influence of hydrogen at the molecular level.

Detailed insights of polydimethylsiloxane (PDMS) degradation mechanism via ReaxFF MD and experiments

Polydimethylsiloxane (PDMS) serves as a widely used silicone polymer in ablative thermal protection material. Nevertheless, the intricate degradation mechanism governing PDMS at ultra-high temperatures remains unclear. Herein, PDMS pyrolysis was in-depth investigated by employing a combination of experimental methodologies and ReaxFF molecular dynamics (ReaxFF-MD) simulations. PDMS model was firstly validated by product distribution analysis and kinetics analysis. Molecular reaction tracking unveils that the pyrolysis pathway primarily is triggered by the cleavage of the Si-C bond, leading to cyclization reactions and fractures within the Si-O framework at elevated temperatures. The pathways leading to the formation of gaseous, liquid, and solid products during thermal cracking are systematically unveiled. Drawing from these insights, DFT calculations reveal Si-C bond dissociation energies (BDEs) of 98.8, 102.2, and 108.2 kcal/mol for Si-CH3, Si-C2H3, and Si-C6H5, respectively. MD simulations further indicate that the heightened Si-C BDEs across various silicone rubbers impede their decomposition, thereby augmenting the thermal stability of the material. This study augments our comprehension of the PDMS pyrolysis mechanism and offers theoretical insights for enhancing its thermal stability.

Deduction of lignite liquefaction mechanism based on carbon structure analysis and free radical determination

The liquefaction performance of lignite is closely related to its structural evolution. The carbon structure and the free radical concentrations of Naomaohu (NMH) coal and liquefaction products were characterized by modified nuclear magnetic resonance (NMR) spectroscopy and electron paramagnetic resonance (EPR), respectively. The results showed that the oil yield increased gradually with the increase in temperature, and it reached a maximum of 64.91% at 430 °C. The carbon spectrum of the liquefied oil showed that the increase in temperature had little effect on the aromatic carbon connected with the aliphatic carbon, but had a greater effect on the aromatic proton carbon of the liquefied oil. The stability of aromatic carbon in asphaltene was greater than that of aliphatic carbon, and the temperature rise had a significant impact on the different types of aliphatic carbon of the asphaltene. The aromatic side chain of asphaltene gradually broke, and the bridgehead carbon content of the aromatic carbon increased due to the intensification of the condensation reaction at high temperature. On the other hand, the concentration of free radicals in liquefied oil increased with temperature, while the concentration of free radicals in asphaltene first increased and then decreased with temperature, indicating a positive correlation between its change trend and respective yield. With the increase in temperature, the aromatic ring substances with strong bond energy were gradually opened, the side chains were broken, thus forming more low molecular compounds. In summary, based on the above changes in the carbon structure and free radicals, the lignite pyrolysis and liquefaction mechanism have been deduced at the molecular level.

Construction of multidimensional structure model of the Mesoproterozoic Xiamaling shale kerogen, northern North China

In the southeastern Xuanlong sag of Northern China, the organic-rich black shale of the Mesoproterozoic Xiamaling Formation holds significant potential as a source rock. Through advanced analytical techniques including elemental analysis, 13C NMR, XPS, FTIR, and XRD, the elemental composition and chemical structure were thoroughly characterized, and the molecular structure of the Xiamaling shale kerogen was established. The 13C NMR analysis revealed the carbon composition of kerogen, indicating 75.19 % aliphatic carbon, 22.06 % aromatic carbon, and 2.75 % carbonyl carbon, with quantitative support from FTIR and XRD spectra. The dominant methylene carbons exhibited a low average methylene chain length (Cn) of 3.87, suggesting that they are primarily short-branched or alicyclic compounds rather than long straight chains. This conclusion was verified by the absence of a sharp peak at a wavenumber of 719.95 cm−1 in the FTIR spectrum. Oxygen-containing functional groups observed in 13C NMR spectra were also identified in FTIR spectra at a wavenumber range of 3500–1000 cm−1. XPS analysis indicated that nitrogen-containing groups were amino, quaternary, pyridine, and primary pyrrole groups, and sulfur existed as sulfoxide, aromatic sulfur, aliphatic sulfur, and sulfone. Finally, a relatively rational 2D molecular structure with the chemical formula of C278H346N6O26S2 was established by comparing the predicted and experimental 13C NMR spectra. Using MD simulation, five optimized 2D molecules were combined to construct a robust 3D kerogen model with a physical density of 1.067 g/cm3. Comparatively, the aliphatic structure of the Mesoproterozoic Xiamaling kerogen model consists of some monocyclic alkanes and polycyclic saturated structures, resembling Paleozoic kerogen models but differing from Mesozoic counterparts. The constructed kerogen model addresses the gap in the Precambrian kerogen modeling and sets the stage for in-depth exploration of pyrolysis mechanisms in the future.

Elucidating the influence of metal oxides on pyrolytic behaviors and combustion performance of green gas generating agent 5-Aminotetrazole/Sr(NO3)2

5-Aminotetrazole/strontium nitrate (5AT/Sr(NO3)2) propellant is widely utilized as green gas generating agent in fire extinguishers. To enhance the combustion rate and modify the gas production performance of 5AT/Sr(NO3)2 propellant, this study investigated the catalytic effects of adding different metal oxides (Bi2O3, PbO, TiO2, and CoO) on its pyrolysis and combustion process. The pyrolysis behavior, pyrolysis mechanism and combustion performance of 5AT/Sr(NO3)2 propellants were studied by using thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning caborimetry (DSC), mass spectrometry (MS), fourier transform infrared spectroscopy (FTIR) analysis and closed bomb vessel tests. Experimental results indicated that Bi2O3 and PbO predominantly facilitated the thermal decomposition process of 5AT, while TiO2 and CoO primarily catalyzed the thermal decomposition of Sr(NO3)2. Certainly, the addition of metal oxides as catalysts to 5AT/Sr(NO3)2 propellant holds significant potential for improving the application as a gas generating agents in fire extinguishers.

Mechanistic insights into Ga-modified hollow ZSM-5 catalyzed fast pyrolysis of cassava residue

The preparation of valuable chemicals by catalytic fast pyrolysis (CFP) is a promising and environmentally-friendly approach for the selective upgrading of waste cassava residue (CR). This work systematically investigated the conversion mechanism and kinetic characteristics of CR pyrolysis over Ga-modified hollow ZSM-5, for the purpose of enhancing aromatics production. The hollow configuration significantly regulated the structural characteristics of ZSM-5, thus facilitating the diffusion, deoxygenation, and aromatization of pyrolysis intermediates. The incorporation of Ga species and generated Brønsted acid sites remarkably accelerated the reaction rate and suppressed the carbonization at high temperatures, through enhancing the end scission of starch and cellulose components. With the aid of 5Ga/ZSM-H, the relative content of aromatics achieved 95.4% at 700 °C, and still maintained over 92.5% even after 5 cycles. The ring-opening and retro-aldol degradation were identified as crucial steps for the production of ketones and aldehydes separately, which were further transformed into hydrocarbon pools by deoxygenation and subsequently converted into aromatics via Diels-Alder reaction. Kinetic analysis demonstrated that the use of 5Ga/ZSM-H lowered the average activation energy of CR pyrolysis by 14.8%, particularly for the initial pyrolysis stage. Moreover, the plausible mechanism for aromatics formation from Ga-modified hollow ZSM-5 catalyzed CR pyrolysis was proposed.