Small Hydrocarbon Molecules Research Articles

Experimental study of the co-hydrocracking mechanism of polyolefin plastics and atmospheric residue

The recycling and upcycling of plastic waste is a significant challenge owing to its inherent resource attribute and the resulting environmental issues. Slurry-phase hydrocracking technology, which employs a dispersed catalyst with high dispersion and catalytic activities, is a promising technology to process mixed feedstocks of inferior heavy oils and plastic powders. Herein, the slurry-phase co-hydrocracking of polyolefin plastics and atmospheric residue (AR) using a dispersed Mo-based catalyst is investigated in detail. Experimental results indicate that the cracking of polyolefin plastics generates free radicals, leading to the formation of gas and naphtha, as well as condensing with residue macromolecular free radicals to produce AR and coke products. Therefore, the distribution and composition of the co-hydrocracking products are influenced by the addition of polyolefin plastics, particularly highly reactive polypropylene (PP). Furthermore, the saturate, aromatic, resin, and C7-asphaltene (SARA) of the co-hydrocracking AR products are separated and systematically analyzed to investigate the synergistic reaction mechanism of polyolefin plastics and heavy oil at the molecular level. For the heavy products, the results show that the polyolefin-derived small molecule hydrocarbon free radicals will combine with the hydrocarbon free radicals generated by heavy oil, thereby leading to an increase in both the side chain number and branching degree of the AR product.

Effects of metal-loaded ZSM-5 catalysts on gas-phase products and PAHs formation characteristics during the co-pyrolysis of plastic with biomass

With the urbanization and population growth, the disposal of plastic waste has become a significant challenge, as the traditional methods often result in pollution and resource wastage. Pyrolysis technology offers a sustainable solution by converting the waste plastics into valuable gas or liquid fuels. The co-pyrolysis of plastics and biomass is an effective approach for synergistically managing these two types of solid waste. The polyethylene (PE) and salix psammophila (SP) was used to investigate the gas production characteristics and polycyclic aromatic hydrocarbons (PAHs) formation during the co-pyrolysis. Additionally, Cu/ZSM-5, Co/ZSM-5, and Ni/ZSM-5 catalysts were employed to investigate the effects of different metal-loaded catalysts on the co-pyrolysis process. The results indicate that, with the increase of the pyrolysis temperature, the yield of gas-phase products gradually increases, solid residue decreases, and liquid-phase products initially increase before declining, reaching their maximum at 500 °C. The synergistic effect promotes the formation of C2Hm (C2H2, C2H4, C2H6) and CH4, leading to the increase of the gas-phase product yields compared to the individual pyrolysis. The addition of catalysts further enhances the gas production: Cu/ZSM-5 boosts H2 yield, Co/ZSM-5 shows selectivity for CH4 and C2Hm, and Ni/ZSM-5 exhibits better selectivity for CO and H2. Under the various pyrolysis conditions, aromatic compounds and aliphatic hydrocarbons consistently dominate the liquid-phase products. With the increase of the pyrolysis temperature, the proportion of aliphatic hydrocarbons decreases, while the proportion of aromatic compounds increases. The addition of catalysts reduces the proportions of both aliphatic and aromatic compounds. PAHs generation is temperature-dependent, significantly increasing at 700 °C. At the low pyrolysis temperatures, the co-pyrolysis reduces PAHs yield, but at high temperatures, PAHs formation increases. The addition of catalysts decreases PAHs yield and toxicity equivalency. Cu/ZSM-5 promotes the cracking of two-ring PAHs, reducing two-ring PAHs yield. Co and Ni catalysts enhance the selective aromatization of small hydrocarbon molecules, forming low-ring PAHs and limiting PAHs aggregation. Overall, Ni/ZSM-5 demonstrates the best performance in enhancing gas production and reducing PAHs emissions, followed by Co/ZSM-5 and Cu/ZSM-5.

Upcycling of waste disposable medical masks to high value-added gasoline fuel and surfactants products by sub/supercritical water degradation and partial oxidation

The amount of waste disposable medical masks (DMMs) and the potential environmental risk increased significantly due to the huge demand of disposable medical surgical masks. In this study, two effective and environmentally friendly processes, supercritical water degradation (SCWD) and subcritical water partial oxidation (SubCWPO), were proposed for the upcycling of DMMs. The optimal conditions for the SCWD process (conversion ratio>98 %) were 410 ℃, 15 min, and 1:5 g/mL. The oil products obtained from the SCWD process were mainly small molecule hydrocarbons (C7-C12) with a content of 86 % and could be recycled as fuel feedstock for gasoline. Alkyl radicals in the SCWD reaction formed double bonds and ring structures through hydrogen capture reactions, β-scission, and dehydrogenation reactions, and aromatic hydrocarbons were formed by olefin cyclization and cycloalkane dehydrogenation. The introduction of an oxidant (H2O2) to the reaction system could significantly reduce the reaction temperature and shorten the reaction time. At 350 ℃, 15 min, 1:20 g/mL, V(H2O2): V (H2O) of 1:1, the conversion ratio of the SubCWPO process was 88 %, which was higher than that of the SCWD process at 400 ℃ (71.49 %). Oil products produced from the SubCWPO process were rich in alcohols and esters, which could be used as raw materials for nonionic surfactant of polyol and fatty acid ester. The abundant hydroxyl radical in the SubCWPO system trapped hydrogen atoms on PP and reacted with the resulting alkyl radical to form alkanols, which was oxidized to form acids. The esterification of acids and alkanols formed high level of esters. The SCWD and SubCWPO processes proposed in this study are believed to be promising strategies for DMMs degradation and the recovery of high value-added hydrocarbons.

Hydrogels based on crosslinked polyethylene glycol diacrylate and fish skin gelatin

The aim of this work was to develop hydrogels based on poly(ethylene glycol diacrylate) (PEGDA) and fish gelatin for potential biomedical applications such as wound healing, drug delivery and biosensors. The hydrogels were prepared via in situ Michael addition of ammonia crosslinker to PEGDA in the presence of cold-water fish skin gelatin that was used as an additive. The fabrication conditions and properties of the hydrogels were examined using various amounts of fish gelatin to evaluate the influence of its concentration on gelation time, crosslinking density and swelling behavior of the hydrogels. FTIR spectra confirmed the formation of the crosslinked hydrogels and the degree of conversion (DC) of the double bonds for the hydrogels containing 5, 7.5 and 10 % w/v of gelatin was between 72 and 80 %. Fish skin gelatin had a strong effect on the dimentional stability and water absorbing properties of the hydrogels and the system containing 7.5 % w/v gelatin exhibited the longest swelling time of 18 h. The hydrophobicity of the hydrogels was achieved by covalent grafting of the residual double bonds with thiol-containing small hydrocarbon molecules using thiol-ene click chemistry reaction conditions, leading to the increase of the water contact angle from 0° to 60-73°.

How to Set the “Chirality” of Polyhedral Small Molecule Hydrocarbons: Decoration and Editing of Cubane Skeleton

AbstractSmall polyhedral hydrocarbons represented by cubane have attracted attention as potential molecular scaffolds for pharmaceuticals as benzene bioisoster. Cubane is also expected to be used as a chiral scaffold, but due to its high symmetry, it is necessary to introduce chirality by sequential site‐selective introduction of substituents. Furthermore, polyhedral desymmetrized isomers of cubane, such as cuneane and semibullvalene, and extended cage compounds, such as bishomocubane and homocuneane, exhibit chirality and are also expected to be used as new optically active scaffolds. In this concept, we would like to explain the synthetic routes we have planned, specifically, the decoration and editing of the cubane skeleton.

Chemical upcycling of PVC-containing plastic wastes by thermal degradation and catalysis in a chlorine-rich environment

Chlorine (Cl)-containing chemicals, including hydrogen chloride, generated during thermal degradation of polyvinyl chloride (PVC) and corresponding mixture impede the chemical recycling of PVC-containing plastic wastes. While upgrading plastic-derived vapors, the presence of Cl-containing chemicals may deactivate the catalysts. Accordingly, herein, catalytic upgrading of pyrolysis vapor prepared from a mixture of PVC and polyolefins is performed using a fixed-bed reactor comprising zeolites. Among the H-forms of zeolites (namely, ZSM-5, Y, β, and chabazite) used in this study, a higher yield of gas products composed of hydrocarbons with lower carbon numbers is obtained using H-ZSM-5, thus indicating further decomposition of the pyrolysis vapor to C1–C4 hydrocarbons on it. Although the formation of aromatic compounds is better on H-ZSM-5, product distributions can be adjusted by further modifying the acidic properties via the alteration of the Si/Al molar ratio, and maximum yields of C1–C4 compounds (60.8%) and olefins (64.7%) are achieved using a Si/Al molar ratio of 50. Additionally, metal ion exchange on H-ZSM-5 is conducted, and upgrading of PVC-containing waste-derived vapor to aromatic chemicals and small hydrocarbon molecules was successfully performed using Co-substituted H-ZSM-5. It reveals that the highest yield of gas products on 1.74 wt% cobalt (Co)-substituted H-ZSM-5 is acquired via the selection of an appropriate metal and metal ion concentration adjustment. Nevertheless, introduction of excess Co into the H-ZSM-5 surface decreases the cracking activity, thereby implying that highly distributed Co is required to achieve excellent cracking activity. The addition of Co also adjusted the acid types of H-ZSM-5, and more Lewis acid sites compared to Brønsted acid sites selectively produced olefins and naphthenes over paraffins and aromatics. The proposed approach can be a feasible process to produce valuable petroleum-replacing chemicals from Cl-containing mixed plastic wastes, contributing to the closed loops for upcycling plastic wastes.

Taming semi-empirical methods for PAHs and vibrational spectra

Semi-empirical methods offer a cost-effective means of computing explicit, anharmonic vibrational frequencies for large molecules, such as polycyclic aromatic hydrocarbons (PAHs), but their default parameters produce insufficiently accurate results for comparison to experiment, especially in the hydride stretching region where the NIRSpec instrument on JWST is most effective. This work delivers several reparameterized variants of the PM6 semi-empirical method trained to reproduce the experimental vibrational frequencies of 5 small hydrocarbon molecules. When benchmarked on the experimental frequencies of benzene and naphthalene, these reparameterized methods match the empirical values to within 38.7 cm−1 on average. Combining these values with the default PM6 frequencies below 3000 cm−1 brings the average deviation below 22 cm−1 for naphthalene, comparing favorably with the existing state of the art in B3LYP/4-31G, for a two order of magnitude decrease in the computational cost. As such, the present work offers a promising means of extending the computation of explicit, anharmonic vibrational frequencies to PAHs larger than those that can be examined anharmonically via B3LYP. Such large and accurate data sets are necessary to disentangle the unidentified spectral features observed around myriad astronomical bodies and the influx of observational data from JWST.

Expulsion of small molecule hydrocarbons and expansion of nanopores effect in tectonically deformed coal evolution

This work aimed to investigate the impact of the evolution of small molecular structures during the deformation of coal on the constraints imposed on nanoscale pores and adsorption behaviors. Both undeformed and tectonically deformed coal (TDC) from the Huaibei mining area in China were collected for analysis. The pyridine was employed for the extraction of small molecules from coal, which was further complemented by Fourier-transform infrared spectroscopy (FTIR) and low-pressure CO2 and N2 adsorption experiments (LP-CO2/N2AD). The study yielded the following results: (1) Intense tectonic stresses facilitate the removal and recombination of small molecular side chains within the basic structural units (BSU) of coal. As deformation occurs, hydroxyl groups, aliphatic hydrocarbons, C=O, C=C, aromatic hydrocarbons, and 'C' structures tend to accumulate, resulting in an enhanced extraction rate. (2) The deformation process of the coal demonstrates a significant pore-expansion effect, with the most substantial increase observed in micropores (surface area increased by over 70 %), followed by mesopores and macropores. This enlargement facilitates the aggregation of small molecules and gas storage. (3) Intense deformation stages involving shear slip, ductile deformation, and maceral fragmentation result in small molecular fractures and an increased number of micropores. The removal and recombination of I, DOC, and CH2/CH3 within BSUs lead to the formation of larger interconnected pores accompanied by the aggregation of hydroxyl groups (OH–), C=O, C=C, aliphatic hydrocarbons, and 'C' structures. (4) The adsorption capacity of residual coal is lower than that of the raw coal before extraction, indicating that small molecular structures contribute to increased adsorption. This likely plays a significant role in the higher gas content observed in structurally deformed coal. The removal of small molecular structures effectively diminishes the adsorption capacity, providing novel perspectives for coalbed methane development and gas extraction in TDC areas.

(Invited) Optical Investigation of Single Nanographenes

Carbon based light emitters ranging from small organic molecules to carbon nanotubes have been subject of a great attention in the framework of diverse applications such as optoelectronics, bio-imaging, and quantum technologies. In this context, graphene quantum dots (GQD) whose size is between that of small polycyclic aromatic hydrocarbon molecules and of carbon nanotubes, have important assets. In particular the complete control of the structure allowed by their synthesis through bottom-up chemistry opens the way to a wide customization of their electronic, optical, and spin properties [1-3].The full benefit from these opportunities requires addressing GQD’s intrinsic photophysical properties. To do so, single molecule photoluminescence experiment is a powerful tool [4-6]. Nevertheless, until now, GQDs faced a problem of solubility that has complexified both the study of their intrinsic properties and their use for applications. In this presentation, we will report on the study of new structures that show a quasi-perfect solubility. We will show how this breakthrough allows us studying in depth their photophysics. Finally, we will see that the theoretical predictions of the evolution of the electronic properties of the GQDs with their structure are fully confirmed by the experiments.[1] M. G. Debije, J. Am. Chem. Soc. 2004, 126, 4641[2] X. Yan, X. Cui, and L.-s. Li, J. Am. Chem. Soc. 2010 132, 5944[3] A. Konishi et al, J. Am. Chem. Soc. 2010, 132, 11021[4] S. Zhao et al, Nature Communications, 2018, 9, 3470[5] T. Liu et al, Nanoscale, 14, 3826 – 3833 (2022)[6] T. Liu et al, Journal of Chemical Physics 156, 104302 (2022)[7] D. Medina-Lopez et al, in preparation

The critical role of swirl in high-specific-output diesel engines

In-cylinder flows are critical for the understanding of the combustion process in internal combustion engines. Although swirl flow has been extensively employed as the primary in-cylinder flow motion in diesel engines, it is usually accompanied with reduced intake mass, and the necessity and the role of swirl flow in high-specific-output diesel engines still remain inadequately understood. In this work, the combustion process of a high-specific-output diesel engine is numerically investigated under different swirl ratios (SR). Results show that the indicated work exhibits a nonmonotonic variation of “increase–decrease” with increasing SR, peaking at SR = 1 with the shortest combustion duration yet slightly higher heat loss compared to the non-swirl condition. The introduction of swirl is capable of reducing high-equivalence-ratio regions through enhanced transport and turbulent diffusion, while the spray-spray interaction may be too strong to yield a rich region in the central cylinder when the swirl is excessively high. The chemical reaction pathway analysis indicates that a moderate swirl ratio could promote mixing, yielding an improved utilization of fresh O2 that further affect the reactions. Specifically, the highly reactive mixture enlarges the radical pool and yields a higher reaction rate during the mixing-controlled combustion stage; While an overlarge swirl ratio may cause excessive mixing, leading to reduced local availability of fresh O2 in the mixing-controlled combustion stage, thereby suppressing the oxidation of small molecule hydrocarbon and hence reducing the global heat release rate. Compared to the spray-induced turbulent mixing for the non-swirl case, the turbulence intensity is significantly increased through swirl-spray interaction under a moderate SR, which could preserve throughout late-cycle combustion and yield improved soot oxidation rate, while an excessive swirl would trap some soot within the central cylinder region and suppress late-cycle soot oxidation. According to the present results, solely high-pressure injection is not sufficient to control the combustion, particularly due to the poor late-cycle mixing and combustion, and an adequate swirl flow is still indispensable in high-specific-output diesel engines.

ReaxFF MD simulation of microwave catalytic pyrolysis of polypropylene over Fe catalyst for hydrogen

Microwave-assisted catalytic pyrolysis of waste plastics is promising for hydrogen generation. To study the mechanism of microwave in Fe catalyzed pyrolysis of plastics. Molecular dynamics (MD) simulation was carried out using the ReaxFF method to compare the bonded and non-bonded interatomic interactions at the same temperature under conventional heating and microwave heating at different powers. The results show that the microwave improves the adsorption capacity of Fe clusters, reduces the dissociation energy of CH bonds, and promotes the cleavage of CC bonds due to H radicals at low temperature. Therefore, microwave enhances the generation of H2, reduces the required reaction temperature, and suppresses the generation of small gaseous hydrocarbon molecules and tar. These results prove the reliability of ReaxFF MD and provide a theoretical basis for valorising waste plastics aided by microwave.

Reparameterized semi-empirical methods for computing anharmonic vibrational frequencies of multiply-bonded hydrocarbons

Abstract Reparameterized semi-empirical methods can reproduce gas-phase experimental vibrational frequencies to within 24 cm−1 or better for a 100-fold decrease in computational cost in the anharmonic fundamental vibrational frequencies. To achieve such accuracy and efficiency, the default parameters in the PM6 semi-empirical model are herein optimized to reproduce the experimental and high-level theoretical vibrational spectra of three small hydrocarbon molecules, C2H2, c-C3H2, and C2H4, with the hope that these same parameters will be applicable to large polycyclic aromatic hydrocarbons (PAHs). This massive cost reduction allows for the computation of explicit anharmonic frequencies and the inclusion of resonance corrections that have been shown to be essential for accurate predictions of anharmonic frequencies. Such accurate predictions are necessary to help to disentangle the heretofore unidentified infrared spectral features observed around diverse astronomical bodies and hypothesized to be caused by PAHs, especially with the upcoming influx of observational data from the James Webb Space Telescope. The optimized PM6 parameters presented herein represent a substantial step in this direction with those obtained for ethylene (C2H4) yielding a 37% reduction in the mean absolute error of the fundamental frequencies compared to the default PM6 parameters.

In Situ Observation of C-C Coupling and Step Poisoning During the Growth of Hydrocarbon Chains on Ni(111).

The synthesis of high-value fuels and plastics starting from small hydrocarbon molecules plays a central role in the current transition towards renewable energy. However, the detailed mechanisms driving the growth of hydrocarbon chains remain to a large extent unknown. Here we investigated the formation of hydrocarbon chains resulting from acetylene polymerization on a Ni(111) model catalyst surface. Exploiting X-ray photoelectron spectroscopy up to near-ambient pressures, the intermediate species and reaction products have been identified. Complementary in situ scanning tunneling microscopy observations shed light onto the C-C coupling mechanism. While the step edges of the metal catalyst are commonly assumed to be the active sites for the C-C coupling, we showed that the polymerization occurs instead on the flat terraces of the metallic surface.

In Situ Observation of C−C Coupling and Step Poisoning During the Growth of Hydrocarbon Chains on Ni(111)

AbstractThe synthesis of high‐value fuels and plastics starting from small hydrocarbon molecules plays a central role in the current transition towards renewable energy. However, the detailed mechanisms driving the growth of hydrocarbon chains remain to a large extent unknown. Here we investigated the formation of hydrocarbon chains resulting from acetylene polymerization on a Ni(111) model catalyst surface. Exploiting X‐ray photoelectron spectroscopy up to near‐ambient pressures, the intermediate species and reaction products have been identified. Complementary in situ scanning tunneling microscopy observations shed light onto the C−C coupling mechanism. While the step edges of the metal catalyst are commonly assumed to be the active sites for the C−C coupling, we showed that the polymerization occurs instead on the flat terraces of the metallic surface.

Toward a deep understanding of the difference between isotactic and syndiotactic polypropylene on the fire performance and degradation behavior

This work investigated the difference in flame retardancy and degradation behavior of polypropylene (PP) composites with different configurations. The piperazine pyrophosphate (PAPP) was combined with melamine polyphosphate (MPP) to construct an intumescent flame retardant system, before incorporating into the PP system by melt blending. It showed that by the introduction of equal amounts of flame retardant, isotactic polypropylene composites (iPP-IFR) can achieve better flame retardancy with a desirable UL-94 V-0 rating, whereas syndiotactic polypropylene (sPP-IFR) shows poor fire performance. Melt index tests show that sPP-IFR sample is easy to flow and prone to melt drops. Differential scanning calorimetry results show that iPP-IFR has a higher degree of crystallinity. The thermogravimetric infrared coupling results show that sPP-IFR produces more small molecule hydrocarbon gases during combustion, making the system more difficult to achieve satisfied flame retardancy. The burning properties of iPP-IFR have been proven to be somewhat better compared to that of sPP-IFR, and sPP is more difficult for flame retardant modification.

Nondestructive investigation on hydrocarbons occluded in asphaltene matrix: The evidence from the dispersive solid-phase extraction

Asphaltenes are the heaviest compound group in crude oil. The complex and porous macromolecular network of asphaltenes both adsorbs and occludes small hydrocarbon molecules, which are considered source-related petroleum biomarkers as they are shielded from secondary alterations. The current method to isolate the occluded content involves mild oxidative degradation of asphaltenes with CH3COOH/H2O2, but it is generally not suitable for quantitative studies, as side reactions that chemically alter the bound hydrocarbons are difficult to mitigate. In the current study, we compared the performance of dispersive solid-phase extraction (DSPE) and mild oxidative degradation in isolating asphaltene-occluded hydrocarbons, using Lower Cambrian solid bitumen from northwestern Sichuan and Ordovician crude oil from the Tazhong area of Xinjiang, China. We demonstrated that DSPE was effective in extracting occluded hydrocarbons from asphaltene aggregates without undesirable chemical alterations, thereby allowing subsequent quantitative analysis. Further investigations revealed that the chemical composition of the occluded n-alkanes provided useful information with regard to the origin of the petroleum. Importantly, the enrichment of aromatic hydrocarbons inside the asphaltene aggregates, particularly the relative abundance of different methylphenanthrene isomers, provided crucial experimental evidence in support of our earlier hypothesis that the occluded hydrocarbons were protected from secondary alterations, and therefore had remained relatively stable over a long geologic period.

Multiphoton ionization and dissociation of polycyclic aromatic hydrocarbon molecules of astrophysical interest

The photoprocessing of astrophysically relevant small polycyclic aromatic hydrocarbon (PAH) molecules, namely, anthracene, phenanthrene, and pentacene, under intense UV field is experimentally studied to explore the formation of smaller ions upon their dissociative ionization and the effect of their size and structure on the dynamics of dissociative ionization. The molecules are UV processed in the multiphoton regime using a 266-nm nanosecond laser pulse. The dissociative ionization spectra at different laser intensities reveal distinct dissociation dynamics of these PAHs based on their size and structures.

Cover Picture: Insight into Carbocation‐Induced Noncovalent Interactions in the Methanol‐to‐Olefins Reaction over ZSM‐5 Zeolite by Solid‐State NMR Spectroscopy (Angew. Chem. Int. Ed. 51/2021)

Cyclic carbocations are important intermediates in methanol-to-olefins (MTO) reaction over zeolite. In their Research Article on page 26847, Jun Xu and co-workers report that the carbocations formed in the MTO reaction can capture small hydrocarbon molecules via non-covalent interactions. Multiple non-covalent interactions have been identified by solid-state NMR spectroscopy and confirmed to be the key factors in modulating reaction properties.

Organic matter evolution in pyrolysis experiments of oil shale under high pressure: Guidance for in situ conversion of oil shale in the Songliao Basin

To examine the evolution of shale oil and gas in different heating stages during in situ conversion in oil shale under high-pressure and high-temperature conditions and the hydrocarbon generation potential change in each reaction stage for application in theoretical guidance purposes, core samples are collected from an oil shale in situ mining area. Oil shale pyrolysis simulation tests are performed under the in situ bottom hole seepage pressure with a heating and insulation technique, and geochemical tests of the oil shale semi-coke and shale oil and gas products are conducted. The results show that the pyrolysis products form in three stages. At 300 ℃, water is mainly produced. From 300–475 ℃, shale oil and gas are the main products discharged from the oil shale, and the production greatly increases. From 475–520 ℃, oil and water production only slightly increases. Methane is the main hydrocarbon gas produced, and the methane percentage in the samples above 450 ℃ is higher than 90 %. Part of the shale oil produced by oil shale pyrolysis remains in the oil shale pores, while some is discharged from the oil shale pores and fractures. The proportions of the non-hydrocarbon components (nitrogen, sulphur and oxygen (NSO)) and asphaltenes in the shale oil remaining in oil shale exceed those of the saturated and aromatic hydrocarbons and reach a peak at 350 ℃. In the later stage of the kerogen transformation process, shale oil is rapidly generated and discharged, and the saturated hydrocarbon content in the discharged shale oil is the highest. Non-hydrocarbon components and asphaltenes may be intermediate products in the transformation process of kerogen into shale oil and may block oil shale pores at approximately 350 ℃. However, with increasing heating temperature during pyrolysis, pores reopen and expand, generating small-molecule hydrocarbons. Oil shale sample pyrolysis at low temperatures attains a good hydrocarbon generation potential, and 425–450 ℃ represents a turning point. Oil shale pyrolysis at temperatures above 450 ℃ exhibits a low hydrocarbon generation potential. This temperature threshold is very important for downhole temperature selection and control in oil shale mining engineering.

Green Fabrication of Polyimide Fibers with Phosphate Monoester Network to Reinforce Carbon Nanotube Polymer Composites: Simultaneously improving the Mechanical Properties and Flame Retardancy

To further enhance the reinforcing effect of polyimide (PI) fibers on carbon nanotube polymer composites, in this work, networks of long chains of phosphate monoester (PMOEs) were grown on the surface of PI fibers, and silanized multiwalled carbon nanotubes (Si-MWCNTs) were dispersed into the phenolic resin (PR) matrix. Subsequently, these two interpenetrating networks were entangled tightly at the PI-PMOEs fiber paper/PR matrix by vacuum-assisted wet papermaking technology and impregnation and vacuum curing technology. A novel type of PI-PMOEs fiber-reinforced carbon nanotube polymer composite was prepared. Structural observation and analysis revealed that the fiber surface activity and roughness were improved, resulting in enhanced interfacial adhesion. The Si-MWCNTs at the interface play an anchoring role, which leads to a strong mechanical interlock between the PI-PMOEs fibers and the matrix. Therefore, the generation and propagation of cracks encountered greater resistance, and the mechanical properties of the composites were improved. Compared with the Si-MWCNTs/PR composite with tensile strength of 20.29 MPa and elongation at break of 0.1%, the tensile strength and elongation at break of 80PI-PMOEs/Si-MWCNTs/PR (the basis weight of paper is 40 wt.%) composite are increased to 91.22 MPa and 2.0%, respectively. In addition, a tightly connected fiber "large skeleton" was provided by the PI-PMOEs fiber paper with a uniform pore size distribution. The Si-MWCNTs network and the thermally degraded carbides of the matrix formed a "small skeleton" based on the "large skeleton", resulting in a complete and dense protective barrier layer. The volatilization of pyrolysis products (CO, small-molecule hydrocarbons, aromatic compounds, etc.) was restricted, and heat and mass transfer were suppressed. Finally, the composites exhibited excellent flame retardancy.