Radical Recombination Reactions Research Articles

A Hexaarylbiimidazole-Terarylene Hybrid: Visible-to-NIR-II Absorption via Sequential Photochromic Reactions.

A synergetic interaction between two or more photochromic chromophores has a potential to achieve advanced photochemical properties beyond conventional photochromic molecules and to realize photochemical control of complex systems using only a single molecule. Herein, we report a hybrid photochromic molecule consisting of hexaarylbiimidazole (HABI) and terarylene that exhibits multi-state photochromism. The biphotochrome hybrid shows four-state photochromic reaction involving sequentially proceeding photoreactions. The UV or visible light irradiation to the biphotochrome leads to the C-N bond breaking reaction of the HABI in preference to the ring-closing reaction of the 6π-electron system in the terarylene unit, leading two terarylene radical molecules. The photogenerated terarylene radical further exhibits the 6π-electrocyclization reaction by UV irradiation. The delocalized π-radical on the closed-ring form of the terarylene is efficient to enhance the photosensitivity to the NIR-I and -II region. Furthermore, a recombination reaction of radicals between the open- and closed-ring isomers of terarylene affords an unprecedented photochromic dimer as a structural isomer of the initial molecule. This is a consequence of the sequential hybrid photochromic system involving the HABI and terarylene units.

Drastically Accelerated Radical Recombination Kinetics of a Hexaarylbiimidazole Derivative.

More than 60 years have passed since the discovery of hexaarylbiimidazole (HABI), which exhibits a characteristic photochromism that produces colored lophyl radicals through a radical dissociation reaction induced by light irradiation and reverts to its original state through a radical recombination reaction in the dark. Lophyl radicals are relatively stable among organic radicals, have low reactivity with oxygen, and have a very slow radical recombination reaction rate. HABI has been used industrially as a photoinitiator to date. However, the guidelines for molecular design to accelerate the thermal reverse reaction of HABI are still unknown and remain a challenge. We found that suppressing the rotation of the phenyl groups attached to the 4- and 5-positions of the imidazole ring of HABI is effective in accelerating the radical recombination reaction. The simple molecular design strategy to accelerate the thermal reverse reaction of HABI is expected to improve the performance of photoinitiators and photoresponsive materials that utilize HABI as a photoresponsive unit.

Kinetic effects of methanol addition on benzene formation in methyl decanoate/air counterflow nonpremixed flames

In this study, counterflow nonpremixed flame modeling was conducted to examine the effects of methanol addition on benzene (A1) formation in methyl decanoate (MD) /air flames. Methanol was added to either the fuel side or oxidant side of the counterflow flames, to explore the chemistry difference in A1 formation when different methanol addition strategies were adopted. The formation routes of A1 were emphatically analyzed, and some important polycyclic aromatic hydrocarbons (PAHs), such as naphthalene (A2) and phenanthrene (A3) were also evaluated in terms of emission index. Results show that most of A1 is produced at the downstream of MD pyrolysis zone, through the recombination reactions of C3 radicals, while methanol is primarily to produce methyl groups within a relatively higher temperature zone. Both the air-side and fuel-side additions of methanol can decrease A1 concentration, but the former shows a more significant inhibiting effect. Methanol addition featured both dilution and chemical inhibitory effects on the formation of A1 precursors, and the dilution effect was superior to the chemical effects. The chemical inhibition on A1 formation was mainly achieved through the enhancement in the generation trend of active groups and the H-addition reaction of methyl groups. The air-side addition of methanol featured a minimal effect on A1 formation, and the reduced A1 concentration within the flames was mainly attributed to the increased radial leakages of reactive species. Besides, both addition strategies of methanol show the inhibitory effect on A2 and A3 formation, but the change in flames with the air-side addition is relatively weaker than that of the fuel-side addition flames.

A numerical study on premixed laminar ammonia/air flames enriched with hydrogen: An analysis on flame–wall interaction

Ammonia (NH3) has been recognized as a potential carbon-free synthetic fuel of the near future. To enhance its low reactivity, one practical option is to blend it with hydrogen (H2). In this study, the transient head-on quenching of premixed laminar ammonia/air flames enriched with hydrogen is explored based on numerical simulations using detailed chemistry and the mixture-averaged transport model. In this respect, nine different test cases are studied for blending ratios (the molar ratio of hydrogen to the ammonia/hydrogen mixture) of 0.0, 0.2, and 0.4, equivalence ratios of 0.8, 1.0, and 1.2, wall temperatures of 300, 500, and 750 K, and pressures of 1, 2, and 5 atm. The results reveal that the quenching distance (maximum absolute wall heat flux) decreases (increases) with increasing the blending ratio, the equivalence ratio, the wall temperature, and the pressure. For all the test cases, the quenching Peclet number changes between 1 and 3.5. In addition, the local heat release rate enhancement and the role of radical recombination reactions are highlighted at the time of quenching in the vicinity of the wall. This effect is augmented as the blending ratio, the equivalence ratio, and the wall temperature increase. Furthermore, the results show that the N2 pathway is the dominant pathway in consumption of NO near the wall at the time of quenching, in which R76 (NH2+NO⇔N2+H2O) poses the rate controlling role. In addition, the leading role of R85 (NH+NO⇔N2O+H) in consuming NO and converting it to N2O is highlighted at the time of quenching near the wall. Moreover, the significant roles of molecular diffusion and reaction source terms over convection are discussed for both NO and N2O species transport in the vicinity of the wall.Novelty and significance statement: The significance of this work is that using ammonia and its blends with hydrogen as promising carbon-free fuels for the future has several technical issues/uncertainties, which needs to be addressed fundamentally. One of the relatively unexplored issues in the combustion devices for ammonia/hydrogen/air flames is the head-on quenching phenomenon, which is investigated in detail in this study. The novelty of this work is that, for the first time, (1) the head-on quenching of various ammonia/hydrogen blends is systematically studied numerically, employing detailed chemistry, (2) effect of wall on the heat release rate chemistry is discussed wherein the role of radical recombination reactions is highlighted, and (3) the formation pathways of pollutant emissions (NO and N2O) for such flames are thoroughly investigated in the freely propagating flame scenario and in the vicinity of the wall at the time of quenching.

Evaluation and Modeling of Polylactide Photodegradation under Ultraviolet Irradiation: Bio-Based Polyester Photolysis Mechanism.

In our study, we investigated the accelerated aging process of PLA under 253.7 nm UV-C irradiation with the use of the GPC, NMR, FTIR, and DSC methods and formal kinetic analysis. The results of GPC and DSC indicated a significant degree of destructive changes in the PLA macromolecules, while spectroscopic methods NMR and FTIR showed maintenance of the PLA main structural elements even after a long time of UV exposure. In addition to that, the GPC method displayed the formation of a high molecular weight fraction starting from 24 h of irradiation, and an increase in its content after 144 h of irradiation. It has been shown for the first time that a distinctive feature of prolonged UV exposure is the occurrence of intra- and intermolecular radical recombination reactions, leading to the formation of a high molecular weight fraction of PLA decomposition products. This causes the observed slowdown of the photolysis process. It was concluded that photolysis of PLA is a complex physicochemical process, the mechanism of which depends on morphological changes in the solid phase of the polymer under UV radiation.

Rotational Spectrum and First Interstellar Detection of 2-methoxyethanol Using ALMA Observations of NGC 6334I

We use both chirped-pulse Fourier transform and frequency-modulated absorption spectroscopy to study the rotational spectrum of 2-methoxyethanol (CH3OCH2CH2OH) in several frequency regions ranging from 8.7 to 500 GHz. The resulting rotational parameters permitted a search for this molecule in Atacama Large Millimeter/submillimeter Array (ALMA) observations toward the massive protocluster NGC 6334I, as well as source B of the low-mass protostellar system IRAS 16293−2422. A total of 25 rotational transitions are observed in the ALMA Band 4 data toward NGC 6334I, resulting in the first interstellar detection of 2-methoxyethanol. A column density of 1.3−0.9+1.4×1017 cm−2 is derived at an excitation temperature of 143−39+31 K. However, molecular signal is not observed in the Band 7 data toward IRAS 16293−2422B, and an upper-limit column density of 2.5 × 1015 cm−2 is determined. Various possible formation pathways—including radical recombination and insertion reactions—are discussed. We also investigate physical differences between the two interstellar sources that could result in the observed abundance variations.

Sensitivity enhancement of radical-pair magnetoreceptors as a result of spin decoherence.

Electron spin relaxation is, on many occasions, considered an elephant in the room that challenges the idea of a radical-pair compass, a leading hypothesis for the navigation of migratory avian species. It has been widely recognized that an effective radical-pair magnetoreceptor requires a relaxation time that is long enough for an external magnetic field as weak as the geomagnetic field to significantly modify the coherent spin dynamics. However, previous studies proposed that certain spin relaxation, far quicker than the radical recombination reactions, could enhance, rather than degrade, the directional sensitivity of a radical-pair magnetoreceptor. Here, I investigate relaxation effects on the singlet-triplet interconversion of a model radical pair and find that the enhancement effect originates from population relaxation over a period of several microseconds as a result of efficient spin decoherence. Insights into the truncated spin systems shed light on the physics behind them. I further investigate the possibilities of such enhancement in cryptochrome-based magnetoreception, in which electron hopping takes place between tryptophan residues.

Understanding the Reaction Chemistry of 1,1,3,3-Tetramethyldisilazane as a Precursor Gas in a Catalytic Chemical Vapor Deposition Process.

The reaction chemistry of 1,1,3,3-tetramethyldisilazane (TMDSZ) in catalytic chemical vapor deposition (Cat-CVD), including its primary decomposition on a heated W filament and secondary gas-phase reactions in a Cat-CVD reactor, was studied using 10.5 eV vacuum ultraviolet single-photon ionization and/or laser-induced electron ionization in tandem with time-of-flight mass spectrometry. It has been demonstrated that TMDSZ initially breaks down to form various species, including methyl radical (•CH3), ammonia (NH3), and 1,1-dimethylsilanimine (DMSA). The activation energies (Ea) for the formation of •CH3 and NH3 were determined to be 61.2 ± 1.0 and 42.1 ± 0.9 kJ mol-1, respectively, in the temperature range of 1400-2000 and 900-2400 °C. It was found that the formation of DMSA may have two different contributing routes, i.e., a concerted one (Ea = 33.6 ± 2.3 kJ mol-1) at lower temperatures of 900-1500 °C and a stepwise one (Ea = 155.0 ± 7.8 kJ mol-1) at higher temperatures of 2100-2400 °C. The secondary gas-phase reactions occurring in the Cat-CVD reactor environment were found to stem from two competing processes. The first one, free-radical short-chain reactions initiated by •CH3 formation and propagated by H abstraction reactions, is the dominating chemical process, producing many high-mass stable alkyl-substituted or silyl-substituted disilazane or trisilazane products via radical recombination reactions. Head-to-tail cycloaddition of unstable DMSA is the second contributing chemical process, which forms cyclodisilazane species. In addition, evidence was found for the conversion of NH3 into H2 and N2 in the Cat-CVD reactor.

Nanosecond time-resolved infrared spectroscopy for the study of electron transfer in photosystem I.

Microsecond time-resolved step-scan FTIR difference spectroscopy was used to study photosystem I (PSI) from Thermosynechococcus vestitus BP-1 (T. vestitus, formerly known as T. elongatus) at 77K. In addition,photoaccumulated (P700+-P700) FTIR difference spectra were obtained at both 77 and 293K. The FTIR difference spectra are presented here for the first time. To extend upon these FTIR studies nanosecond time-resolved infrared difference spectroscopy was also used to study PSI from T. vestitus at 296K. Nanosecond infrared spectroscopy has never been used to study PSI samples at physiological temperatures, and here it is shown that such an approach has great value as it allows a direct probe of electron transfer down both branches in PSI. In PSI at 296K, the infrared flash-induced absorption changes indicate electron transfer down the B- and A-branches is characterized by time constants of 33 and 364ns, respectively, in good agreement with visible spectroscopy studies. These time constants are associated with forward electron transfer from A1- to FX on the B- and A-branches, respectively. At several infrared wavelengths flash-induced absorption changes at 296K recover in tens to hundreds of milliseconds. The dominant decay phase is characterized by a lifetime of 128ms. These millisecond changes are assigned to radical pair recombination reactions, with the changes being associated primarily with P700+ rereduction. This conclusion follows from the observation that the millisecond infrared spectrum is very similar to the photoaccumulated (P700+-P700) FTIR difference spectrum.

A Mechanistic Study on the Formation of Acetone (CH3COCH3), Propanal (CH3CH2CHO), Propylene Oxide (c-CH3CHOCH2) along with Their Propenol Enols (CH3CHCHOH/CH3C(OH)CH2) in Interstellar Analog Ices

Carbonyl-bearing complex organic molecules (COMs) in the interstellar medium (ISM) are of significant importance due to their role as potential precursors to biomolecules. Simple aldehydes and ketones like acetaldehyde, acetone, and propanal have been recognized as fundamental molecular building blocks and tracers of chemical processes involved in the formation of distinct COMs in molecular clouds and star-forming regions. Although previous laboratory simulation experiments and modeling established the potential formation pathways of interstellar acetaldehyde and propanal, the underlying formation routes to the simplest ketone—acetone—in the ISM are still elusive. Herein, we performed a systematic study to unravel the synthesis of acetone, its propanal and propylene oxide isomers, as well as the propenol tautomers in interstellar analog ices composed of methane and acetaldehyde along with isotopic-substitution studies to trace the reaction pathways of the reactive intermediates. Chemical processes in the ices were triggered at 5.0 K upon exposure to proxies of Galactic cosmic rays in the form of energetic electrons. The products were detected isomer-selectively via vacuum ultraviolet (VUV) photoionization reflectron time-of-flight mass spectrometry. In our experiments, the branching ratio of acetone (CH3COCH3):propylene oxide (c-CH3CHOCH2):propanal (CH3CH2CHO) was determined to be (4.82 ± 0.05):(2.86 ± 0.13):1. The radical–radical recombination reaction leading to acetone emerged as the dominant channel. The propenols appeared only at a higher radiation dose via keto–enol tautomerization. The current study provides mechanistic information on the fundamental nonequilibrium pathways that may be responsible for the formation of acetone and its (enol) isomers inside the interstellar icy grains.

Identification and mechanistic analysis of a bifunctional enzyme involved in the C-N and N-N bond formation

N–N bonded compounds are a relatively small but valuable group of natural products with a variety of important biological activities, including anti-inflammatory, anti-tumor, anti-bacterial and anti-oxidant activities. Currently, the synthesis of natural products containing N–N bonds is mainly based on chemical synthesis, but the chemical synthesis of N–N bonds may have safety issues and raw material sustainability problems. A variety of N–N bond biosynthetic mechanisms exist in nature, including comproportionation, rearrangement, and radical recombination reactions, which provide ideas for the biosynthesis of many N–N bond compounds. But at this stage, only a few N–N bond synthases have been reported, and difficulties exist in the biosynthesis of N–N bond-containing compounds. The new N–N-bond synthase PAI2, which was found to catalyze the synthesis of piperazinic acid, expands the family of N–N-bond synthases and provides better catalytic activity and different enzymatic properties for the substrate L-N5-hydroxyornithine than the known enzyme KtzT derived from the piperazinic acid biosynthetic gene cluster of Kutzneria sp. 744. Moreover, PAI2 was found to have the ability to catalyze the formation of C–N bonds in Pro.

A Study of the Ceramicisation of Allylhydridopolycarbosilane by Thermal Volatilisation Analysis and Solid-State Nuclear Magnetic Resonance

AHPCS is a pre-ceramic polymer utilised as a precursor to SiC. An initial polymerisation to a cross-linked network is followed by a complex sequence of processes ultimately leading to amorphous SiC. Using thermal volatilisation analysis (TVA) accompanied with solid-state NMR (SSNMR), FTIR, MS, DSC and TGA the complete thermal profile was identified. Between 160 – 300 °C, AHPCS cross-links through the allyl group and undergoes some carbon-silicon rearrangement, with a volatilisation of low mass oligomeric material and significant volumes of hydrogen released from dehydrocoupling of SiH moieties. By 300 °C the allyl group is completely cross-linked but the polymer starts to undergo pyrolytic degradation of the network, with the release of chain fragments and low molar mass species such as methane, ethane, methanol, propane, propene and silane species. Hydrogen once again becomes the major volatile product above 400 °C due to higher proportion of dehydrocoupling forming Si–C and Si–Si bonds. Small chain fragments are seen in the form of larger alkyl silanes. These fragments come from the chain scission of the polymer at weaker parts of the network. The process of side group scission leads to further radical recombination reactions of silicon and carbon atoms to build the SiC network. By 500 °C higher proportion of dehydrocoupling occurs with recombination of Si–Si and Si–C species. The Si–H bonds in -SiH3 groups have completely cleaved along with C-H bonds in the CH3 and CH2 groups leaving SiC, -SiH and HCSi3 present in the material. This bond cleavage leads the silicon and carbon radical species to undergo radical recombination in the network with the volatile release being dominated by H2. By 650 °C the cleavage and recombination of remaining -SiH2-, -SiH- and HCSi3 groups ultimately form amorphous SiC. The volatiles released are mostly hydrogen with very few condensable products seen. Finally, SiC is then crystallised at higher temperatures forming β-SiC at 1100 °C and then subsequently α-SiC above 1500 °C.

Computed Pre-reactive Complex Association Lifetimes Explain Trends in Experimental Reaction Rates for Peroxy Radical Recombinations

The lifetimes of pre-reactive complexes, although implicitly part of the equations used to model many gas-phase bimolecular reactions, have seldom been included in quantitative calculations of rate coefficients. Here, we demonstrate the application of empirical molecular dynamics simulations of collisions between peroxy radicals to model association lifetimes. With the exception of the methyl peroxy–acetyl peroxy system, measurements of the lifetimes based on a phenomenological model are shown to correlate well with available experimental data for recombination reactions of peroxy radicals in cases where the rate-limiting transition state lies below the reactants in energy. Further, we predict reaction rates for larger α-pinene-derived peroxy radicals, and we interpret our results in tandem with available experimental data on these systems, which are of great relevance to improve our understanding of atmospheric aerosol formation.

Controlling Diradical Character of Photogenerated Colored Isomers of Phenoxyl-Imidazolyl Radical Complexes.

We propose a rational method for evaluating the diradical character of the photochromic phenoxyl-imidazolyl radical complex (PIC) derivatives based on their radical-radical coupling reaction rates. PIC consists of an imidazole ring, a phenoxyl ring, and a bridging unit that structurally connects them. The C-N bond formed between the imidazole and phenoxyl rings can be dissociated photochemically in a homolytic manner. The photochromism of PIC differs significantly from other photochromic molecules in that the transient colored open-ring isomer has a diradical character. The colored open-ring isomer returns promptly to the initial colorless closed-ring isomer by the intramolecular radical recombination reaction. By changing the aromaticity and substitution position of the bridging unit, it is possible to control the degree of contribution of the open-shell diradical and closed-shell quinoidal structures to the open-ring isomer. Systematic investigation of the photochromic reactions of several PIC derivatives revealed that the half-life of the open-ring isomers reflects the diradical character. Thus, the radical recombination reaction rate of the open-ring isomer of the PIC derivatives is an excellent parameter of the diradical character.

Formation of the Simplest Amide in Molecular Clouds: Formamide (NH2CHO) and Its Derivatives in H2O-rich and CO-rich Interstellar Ice Analogs upon VUV Irradiation

The astronomical detection of formamide (NH2CHO) toward various star-forming regions and in cometary material implies that the simplest amide might have an early origin in dark molecular clouds at low temperatures. Laboratory studies have proven the efficient NH2CHO formation in interstellar CO:NH3 ice analogs upon energetic processing. However, it is still under debate, whether the proposed radical–radical recombination reactions forming complex organic molecules remain valid in an abundant H2O environment. The aim of this work was to investigate the formation of NH2CHO in H2O- and CO-rich ices under conditions prevailing in molecular clouds. Therefore, different ice mixtures composed of H2O:CO:NH3 (10:5:1), CO:NH3 (4:1), and CO:NH3 (0.6:1) were exposed to vacuum ultraviolet photons in an ultra-high vacuum chamber at 10 K. Fourier-transform infrared spectroscopy was utilized to monitor in situ the initial and newly formed species as a function of photon fluence. The infrared spectral identifications are complementarily secured by a temperature-programmed desorption experiment combined with a quadrupole mass spectrometer. The energetic processing of CO:NH3 ice mixtures mainly leads to the formation of NH2CHO, along with its chemical derivatives such as isocyanic acid (HNCO) and cyanate ion (OCN−). The formation kinetics of NH2CHO shows an explicit dependency on ice ratios and compositions; the highest yield is found in H2O-rich ice. The astronomical relevance of the resulting reaction network is discussed.

Gas-Phase Peroxyl Radical Recombination Reactions: AComputational Study of Formation and Decomposition of Tetroxides.

The recombination (“dimerization”) of peroxyl radicals (RO2•) is one of the pathways suggested in the literature for the formation of peroxides (ROOR′, often referred to as dimers or accretion products in the literature) in the atmosphere. It is generally accepted that these dimers play a major role in the first steps of the formation of submicron aerosol particles. However, the precise reaction pathways and energetics of RO2• + R′O2• reactions are still unknown. In this work, we have studied the formation of tetroxide intermediates (RO4R′): their formation from two peroxyl radicals and their decomposition to triplet molecular oxygen (3O2) and a triplet pair of alkoxyl radicals (RO•). We demonstrate this mechanism for several atmospherically relevant primary and secondary peroxyl radicals. The potential energy surface corresponds to an overall singlet state. The subsequent reaction channels of the alkoxyl radicals include, but are not limited to, their dimerization into ROOR′. Our work considers the multiconfigurational character of the tetroxides and the intermediate phases of the reaction, leading to reliable mechanistic insights for the formation and decomposition of the tetroxides. Despite substantial uncertainties in the computed energetics, our results demonstrate that the barrier heights along the reaction path are invariably small for these systems. This suggests that the reaction mechanism, previously validated at a multireference level only for methyl peroxyl radicals, is a plausible pathway for the formation of aerosol-relevant larger peroxides in the atmosphere.

Effective depolymerization of polyethylene plastic wastes under hydrothermal and solvothermal liquefaction conditions

Depolymerization of polyethylene (PE) is one of the most challenging tasks in the chemical upcycling of PE-based plastic wastes because the disassociation of the stable carbon–carbon bonds in PE is only possible at a very high reaction temperature. The thermal liquefaction of PE cable plastic waste in a stainless-steel batch reactor was thoroughly evaluated in this study. The effect of different liquefaction methods (hydrothermal liquefaction (HTL), ionic liquids catalyzed HTL, and solvothermal liquefaction (STL)) on the yields of product fractions (oil products, solid residue, and gas) and the properties of the oil products were examined. At 350 °C and 90 min reaction duration, the conversion (%) of 75.43%, the oil yield of 39.33%, the energy recovery rate of 39.7%, the higher heating values (HHV) of 43.83 MJ/kg for the oil samples, and the lower boiling range molecular distribution were obtained by the solvothermal liquefaction method with acetone as a solvent. The HHV of the oil samples obtained in the STL method (43.28–43.83 MJ/kg) is comparable to that of gasoline (HHV − 43.4 MJ/kg). The contribution of the solvent to the depolymerization reaction was mainly the dissolution and dispersion of feedstock by solvation, therefore reducing thermal cracking temperature through enhanced mass and thermal energy transfer. In thermal liquefaction, solvent and feedstock had a low level of solvolysis reactions, so the depolymerization reaction mainly follows thermal cracking. The main reaction path is the random scission of PE molecules during heat treatment, with a low level of polymerization, cyclization, and radical recombination reactions, which occurred through the free radical mechanisms. This work has demonstrated the feasibility of a very promising technique for effective chemical upcycling of polyethylene-based plastics.

The mechanism of superheated steam affecting the quality of in-situ pyrolysates of oil shale kerogen: Part A-saturation of pyrolytic organics

In this work, the effect of superheated steam on pyrolysates for in-situ pyrolysis of kerogen was investigated through ReaxFF molecular dynamics simulation in terms of the saturation of pyrolytic shale gas and light shale oil. The double bond equivalents were adopted to characterize the saturation of gas, light shale oil and the hydrocarbon. The existence form of H2O molecules, introduced by superheated steam (named the environmental H2O molecule, H2Owater), were obtained using python scripts to analyze bond order file. And the reaction pathways of several representative pyrolysates (propanol, methanol, phenols and H2), generated by the participation of H2Owater molecules, were analyzed. The results indicated that, compared with pyrolysis at nitrogen atmosphere, saturation of shale gas and light shale oil were both promoted at superheated steam atmosphere, especially for the light shale oil. Under superheated steam circumstance, the inhibited dehydrogenation of kerogen is the primary reason for the saturation improvement of products. The secondary cause is the bonding of Hwater and OHwater radicals to carbon-containing radicals, which may have a hampering effect on the radical recombination reaction of short chains. During pyrolysis of kerogen with superheated steam injection, H2Owater molecules could be involved in a serious of chemical reactions: the decomposition of char and heavy shale oil, opening reaction of heterocyclic rings, transmission and exchange of OH radicals and the formation of products (hydrocarbon, alcohols, NH3, H2S, H2, etc.), principally via attacking radicals or fragments. The typical reactions in which H2Owater molecules involved were given. This study would provide theoretical support for in-situ pyrolysis technology of oil shale with superheated steam injection.

Time-resolved measurements of HO2 radical in a heated plasma flow reactor

Time-resolved, absolute HO2 number density in diluted H2O2-Ar, CH4O2-Ar, and C2H4O2-Ar mixtures excited by a repetitive ns pulse discharge in a heated plasma flow reactor is measured by Cavity Ringdown Spectroscopy (CRDS). The experimental results are obtained at T = 300–600 K and P = 130 Torr, both during the discharge pulse burst and in the afterglow. The HO2 number density is inferred from the CRDS data using a spectral model exhibiting good agreement with previous measurements of absolute HO2 absorption cross sections. In the room-temperature H2O2 mixture, as well as in CH4O2 and C2H4O2 mixtures over the entire temperature range studied, HO2 is generated only during the discharge burst and decays in the afterglow. However, in the H2O2 mixture at elevated temperatures, T = 400–600 K, HO2 persists in the afterglow up to 10 ms after the discharge burst, comparable with the flow residence time in the reactor. Comparison with kinetic modeling shows that the sustained reactivity after the source of radicals is turned off is due to a chain propagation/ hydrogen oxidation process, which dominates the radical recombination reactions. The kinetic modeling predictions are in good agreement with the relative HO2 number density measured in all three mixtures, although the model underpredicts the absolute number densities in H2O2 at T = 400–600 K by up to a factor of two. Detection of the sustained low-temperature reactivity in H2O2, initiated by the radical generation in the plasma, suggests that the plasma excitation may also affect kinetics of oxidation and reforming of fuels exhibiting low-temperature chemistry below hot ignition point.

Synthesis of phosphazene‐triazine bi‐base sulfonate and its applications in flame‐retardant modified polycarbonate

AbstractA phosphazene‐triazine bi‐base sulfonate compound (CPNS) was synthesized using hexachlorocyclotriphosphazene, cyanuric chloride, and sodium p‐hydroxybenzene sulfonate as raw materials. The chemical structure was determined by FTIR, 1H NMR 31P NMR (NMR stands for nuclear magnetic resonance), and elemental analysis of P, Na. To study the flame retardant properties of CPNS, a series of modified polycarbonate (MPC) with different ratios of CPNS were prepared. The flame retardant performance and thermal stability of CPNS/MPC were characterized by limiting oxygen index (LOI), UL‐94 vertical burning test, cone calorimetry test, and TG. Results show that when CPNS is added to 0.3%, the CPNS/MPC can pass the UL94 V‐0 level with an LOI value of 35.3% and reduce the peak heat release rate by 16.89% during the combustion. TG results show that adding 0.1% CPNS can decrease the initial decomposition temperature of the MPC by 68°C in nitrogen and 27°C in air. The reduction of the initial decomposition temperature means that the flame retardant promotes the isomerization reaction of polycarbonate accelerates the formation of an intermediate char on the surface. Investigation of intermediate char residue's morphology and chemical structure demonstrates that CPNS promotes the formation of more complete and compact char residue, which acts not only there is increased opportunity for radical recombination reactions in the condensed phase but also as physical barriers to inhibit the transfer of heat and oxygen, resulting in good flame retardant properties.