Relative Yields Of Products Research Articles

Catalytic Pyrolysis of Polypropylene for Cable Semiconductive Buffer Layers.

With the progress of the power grid system, the coverage area of cables is widening, and the problem of cable faults is gradually coming to affect people's daily lives. While the vast majority of cable faults are caused by the ablation of the cable buffer layer, polypropylene (PP), as a common cable buffer material, has pyrolysis properties that critically impact cable faults. Studying the semiconductive buffer layer of polypropylene (PP) and its pyrolysis properties allows us to obtain a clearer picture of the pyrolysis products formed during PP ablation. This understanding aids in the accurate diagnosis of cable faults and the identification of ablation events. In this study, the effects of temperature and catalyst (H-Zeolite Standard Oil Corporation Of New York (Socony) Mobil-Five (HZSM-5)) content on the PP thermolysis product distribution were studied by using an online tubular pyrolysis furnace-mass spectrometry (MS) experimental platform. The results showed that PP/40% HZSM-5 presented the highest thermolytic efficiency and relative yield of the main products at 400 °C.

Exploring the ultrafast and isomer-dependent photodissociation of iodothiophenes via site-selective ionization.

C-I bond extension and fission following ultraviolet (UV, 262 nm) photoexcitation of 2- and 3-iodothiophene is studied using ultrafast time-resolved extreme ultraviolet (XUV) ionization in conjunction with velocity map ion imaging. The photoexcited molecules and eventual I atom products are probed by site-selective ionization at the I 4d edge using intense XUV pulses, which induce multiple charges initially localized to the iodine atom. At C-I separations below the critical distance for charge transfer (CT), charge can redistribute around the molecule leading to Coulomb explosion and charged fragments with high kinetic energy. At greater C-I separations, beyond the critical distance, CT is no longer possible and the measured kinetic energies of the charged iodine atoms report on the neutral dissociation process. The time and momentum resolved measurements allow determination of the timescales and the respective product momentum and kinetic energy distributions for both isomers, which are interpreted in terms of rival 'direct' and 'indirect' dissociation pathways. The measurements are compared with a classical over the barrier model, which reveals that the onset of the indirect dissociation process is delayed by ∼1 ps relative to the direct process. The kinetics of the two processes show no discernible difference between the two parent isomers, but the branching between the direct and indirect dissociation channels and the respective product momentum distributions show isomer dependencies. The greater relative yield of indirect dissociation products from 262 nm photolysis of 3-iodothiophene (cf. 2-iodothiophene) is attributed to the different partial cross-sections for (ring-centred) π∗ ← π and (C-I bond localized) σ∗ ← (n/π) excitation in the respective parent isomers.

Exploring the selectivity of cytochrome P450 for enhanced novel anticancer agent synthesis.

Cytochrome P450 monooxygenases are an extensive and unique class of enzymes, which can regio- and stereo-selectively functionalise hydrocarbons by way of oxidation reactions. These enzymes are naturally occurring but have also been extensively applied in a synthesis context, where they are used as efficient biocatalysts. Recently, a biosynthetic pathway where a cytochrome P450 monooxygenase catalyses a critical step of the pathway was uncovered, leading to the production of a number of products that display high antitumour potency. In this work, we use computational techniques to gain insight into the factors that determine the relative yields of the different products. We use conformational search algorithms to understand the substrate stereochemistry. On a machine-learned 3D protein structure, we use molecular docking to obtain a library of favourable poses for substrate-protein interaction. With molecular dynamics, we investigate the most favourable poses for reactivity on a molecular level, allowing us to investigate which protein-substrate interactions favour a given product and thus gain insight into the product selectivity.

Cold reactions of He+ with OCS and CO2: competitive kinetics and the effects of the molecular multipole moments.

The reactions of He+ with OCS and CO2 have been studied at collision energies between ∼kB ⋅ 200 mK and ∼kB ⋅ 30 K by merging a beam of Rydberg He atoms with rotationally cold (∼3.5 K) seeded supersonic expansions containing either OCS or 13CO2 or a mixture of OCS (mole fraction 23.2%) and 13CO2 (76.8%). The observed product ions of the He+ + 13CO2 and He+ + OCS reactions are 13CO+, and CS+ and CO+, respectively. The He+ + OCS capture rate coefficient increases by ∼75% with decreasing collision energy over the investigated range, whereas that of He+ + 13CO2 decreases by ∼40%. The analysis of the experimental results using an adiabatic-channel capture model indicates that these opposite collision-energy dependences of the rate coefficients arise from the interaction between the charge of the ion and the electric multipole moments of OCS and 13CO2. From the relative product-ion yields observed when using the mixture of OCS and 13CO2, the He+ + OCS collisions are inferred to be ∼20% more reactive than those between He+ and 13CO2. The comparison of the calculated thermal rate coefficients with earlier experiments suggests that about half of the He+ + 13CO2 collisions are reactive.

Industrial-era decline in Arctic methanesulfonic acid is offset by increased biogenic sulfate aerosol.

Marine phytoplankton are primary producers in ocean ecosystems and emit dimethyl sulfide (DMS) into the atmosphere. DMS emissions are the largest biological source of atmospheric sulfur and are one of the largest uncertainties in global climate modeling. DMS is oxidized to methanesulfonic acid (MSA), sulfur dioxide, and hydroperoxymethyl thioformate, all of which can be oxidized to sulfate. Ice core records of MSA are used to investigate past DMS emissions but rely on the implicit assumption that the relative yield of oxidation products from DMS remains constant. However, this assumption is uncertain because there are no long-term records that compare MSA to other DMS oxidation products. Here, we share the first long-term record of both MSA and DMS-derived biogenic sulfate concentration in Greenland ice core samples from 1200 to 2006 CE. While MSA declines on average by 0.2 µg S kg-1 over the industrial era, biogenic sulfate from DMS increases by 0.8 µg S kg-1. This increasing biogenic sulfate contradicts previous assertions of declining North Atlantic primary productivity inferred from decreasing MSA concentrations in Greenland ice cores over the industrial era. The changing ratio of MSA to biogenic sulfate suggests that trends in MSA could be caused by time-varying atmospheric chemistry and that MSA concentrations alone should not be used to infer past primary productivity.

Экспериментально-аналитические исследования токсичности продуктов горения, обнаружения и тушения пожаров в гермобарокамерах в средах, обогащенных кислородом и при повышенном давлении

Experimental and analytical studies were carried out related to the detection and extinguishing of fires, the toxicity of products in equipment with oxygen-enriched media and at elevated pressure. Toxicity of combustion products in the pressurized pressure chambers is due to the release of aerosol particles and gaseous products of thermal-oxidative destruction of materials, for which empirical dependences are presented over a wide temperature range allowing calculations to determine the integral relative yields of reaction products. Analysis of the experimental results shows that the increase in the mass yield of aerosol particles occurs more intensely than that of toxic gases, and a noticeable release of gases begins at a temperature of about 523 K, while the release of dispersed particles occurs already at a temperature of approximately 473 K. At the early stage of thermal destruction in the temperature range 473–623 K, the yield of aerosols is 5 times higher than the yield of gases by mass. When the temperature rises close to the ignition temperature, the combustion source can be detected using gaseous products, in particular CO and CO2. Justification for the methodology for assessing the main parameters of fire extinguishing in the pressurized chambers is given. The most important elements of the main components, elements and installation as a whole are: inertia, intensity of supply of fire extinguishing agent. Dependence obtained analytically, which was confirmed in experiments, between the extinguishing time and the intensity of the supply of fire extinguishing agent is presented, which considers the characteristics of the environmental parameters in the chamber and the thermophysical properties of the flame. Dependences were obtained related to the extinguishing time on the intensity of the supply of sprayed water, on the size of the sample, and on the oxygen content in the chamber atmosphere. Results of the experimental studies indicate that changes in oxygen concentration in the atmosphere have a more noticeable effect on extinguishing parameters than changes in gas pressure.

STRUCTURE OF MASS DISTRIBUTIONS OF PHOTOFISSION PRODUCT YIELDS OF 238U AT 17.5 MeV BREMSSTRAHLUNG ENERGY

The values of 29 relative yields of products belonging to 26 mass chains of photofission of 238U were obtained at a maximum bremsstrahlung energy of 17.5 MeV (near the second chance fission threshold). The stimulation of the 238U photofission reaction was performed at the electron accelerator of the Institute of Electron Physics of the National Academy of Sciences of Ukraine, the M-30 microtron. The GEANT4 toolkit was used to model the components of the bremsstrahlung spectrum. The presence of a fine structure in the mass distribution of heavy product yields was found to be localized in the mass range 133-134, 138-139, and 143-144. A multi gaussian model (superposition of three Gaussians) was used to theoretically describe the structure. The calculated values of product yields using the GEF code describe in general terms and predict the fine structure of the mass distribution of photofission products of 238U.

POPTARTS: A New Method to Determine Quantum Yields in a Molecular Beam.

A new technique is reported to determine absolute photodissociation quantum yields, ϕdiss, in a molecular beam. The technique relies on a molecule having two available product channels, where a species in channel A can be converted photolytically to a species in channel B. The relative decrease in the species from channel A and the relative increase in species from B provide a direct measure of the relative product yield of each channel, with no external calibration required. In the event that only channels A and B exist, or at least dominate, then the sum rule ϕA + ϕB = 1 can be used to convert relative quantum yields into absolute yields. The technique is demonstrated using the well-understood and characterized photochemistry of HCHO. Formaldehyde photolysis at wavelengths near 310 nm produces either H + HCO (channel A) or H2 + CO (channel B). HCO can then be photolyzed with high efficiency into H + CO. The product state distributions for HCO from channel A, CO from channel B, and CO from the secondary HCO photolysis event are all well-known; this is not a requirement but is utilized here to demonstrate the veracity of the technique. The zero-pressure quantum yields of HCO from HCHO photolysis via the 2341 and 2151 states of HCHO are determined to be 0.66 and 0.74, respectively, which are in excellent agreement with the established quantum yields at atmospheric pressure and support the conclusion that HCHO quantum yields at these photolysis energies are not pressure dependent.

Biodiesel production from Chlorella Vulgaris microalgal-derived oil via electrochemical and thermal processes

Chlorella Vulgaris microalgal as a renewable and economically feasible oil feedstock is used in this study for producing biodiesel through electrochemical and thermal processes. The effect of operating parameters on non-catalytic and catalytic biodiesel production from the derived-oil is investigated and compared in a wide range of condition. According to the revealed data, during non-catalytic processes, electrochemical process proposed higher biodiesel production yield in comparison to thermal process with relative biodiesel production yield of 25% and 18%, respectively. According to the experimental results, although biodiesel production is restricted in presence of water in thermal process, electrochemical method enables biodiesel production in presence of water. Addition of H2SO4 in the range of 1–15 wt% through electrochemical process at the obtained optimum condition results in gradual increase in the biodiesel production yield to 95%. The optimum operating condition in electrochemical process are as follows: methanol to oil molar ratio of 20:1, tetrahydrofuran (THF) to methanol molar ratio of 0.25:1, reaction time of 2 h, voltage of 20 V/cm, water content of 2 wt% and H2SO4 loading of 15 wt%.

Multipole-moment effects in ion-molecule reactions at low temperatures: part II - charge-quadrupole-interaction-induced suppression of the He+ + N2 reaction at collision energies below kB·10 K.

We report on an experimental and theoretical investigation of the He+ + N2 reaction at collision energies in the range between 0 and kB·10 K. The reaction is studied within the orbit of a highly excited Rydberg electron after merging a beam of He Rydberg atoms (He(n), n is the principal quantum number), with a supersonic beam of ground-state N2 molecules using a surface-electrode Rydberg–Stark decelerator and deflector. The collision energy Ecoll is varied by changing the velocity of the He(n) atoms for a fixed velocity of the N2 beam and the relative yields of the ionic reaction products N+ and N2+ are monitored in a time-of-flight mass spectrometer. We observe a reduction of the total reaction-product yield of ∼30% as Ecoll is reduced from ≈kB·10 K to zero. An adiabatic capture model is used to calculate the rotational-state-dependent interaction potentials experienced by the N2 molecules in the electric field of the He+ ion and the corresponding collision-energy-dependent capture rate coefficients. The total collision-energy-dependent capture rate coefficient is then determined by summing over the contributions of the N2 rotational states populated at the 7.0 K rotational temperature of the supersonic beam. The measured and calculated rate coefficients are in good agreement, which enables us to attribute the observed reduction of the reaction rate at low collision energies to the negative quadrupole moment, Qzz, of the N2 molecules. The effect of the sign of the quadrupole moment is illustrated by calculations of the rotational-state-dependent capture rate coefficients for ion–molecule reactions involving N2 (negative Qzz value) and H2 (positive Qzz value) for |J, M〉 rotational states with J ≤ 5 (M is the quantum number associated with the projection of the rotational angular momentum vector J⃑ on the collision axis). With decreasing value of |M|, J⃑ gradually aligns perpendicularly to the collision axis, leading to increasingly repulsive (attractive) interaction potentials for diatomic molecules with positive (negative) Qzz values and to reaction rate coefficients that decrease (increase) with decreasing collision energies.

Progress of the Pyrolyzer Reactors and Advanced Technologies for Biomass Pyrolysis Processing

In the future, renewable energy technologies will have a significant role in catering to energy security concerns and a safe environment. Among the various renewable energy sources available, biomass has high accessibility and is considered a carbon-neutral source. Pyrolysis technology is a thermo-chemical route for converting biomass to many useful products (biochar, bio-oil, and combustible pyrolysis gases). The composition and relative product yield depend on the pyrolysis technology adopted. The present review paper evaluates various types of biomass pyrolysis. Fast pyrolysis, slow pyrolysis, and advanced pyrolysis techniques concerning different pyrolyzer reactors have been reviewed from the literature and are presented to broaden the scope of its selection and application for future studies and research. Slow pyrolysis can deliver superior ecological welfare because it provides additional bio-char yield using auger and rotary kiln reactors. Fast pyrolysis can produce bio-oil, primarily via bubbling and circulating fluidized bed reactors. Advanced pyrolysis processes have good potential to provide high prosperity for specific applications. The success of pyrolysis depends strongly on the selection of a specific reactor as a pyrolyzer based on the desired product and feedstock specifications.

Mechanistic Study of the Aqueous Reaction of Organic Peroxides with HSO3− on the Surface of a Water Droplet

AbstractAqueous reactions between organic peroxides and SO2 are of intense interest in atmospheric science because of their ubiquitous implications for sulfate formation in secondary aerosols. However, the relative yields of the reaction products (inorganic vs. organic sulfates) remain controversial (i.e., 90 % vs. 40–70 % for inorganic sulfate) due in part to the lack of understanding of the underlying reaction mechanisms. Here, our computational results suggest that the reactions of HSO3− (dissolved SO2) with organic peroxides are initiated on the surface of water nanodroplets and then proceed under two reaction pathways, in which the S atom of HSO3− attacks either the O1 or O2 atom of the peroxide group ‐O(O2)O(O1)H, leading to the formation of inorganic and organic sulfates, respectively. Notably, we find that thse reaction initiated by O1 atom exhibits a relatively low energy barrier and high reaction rate, which favours the formation of inorganic sulfate.

Mechanistic Study of the Aqueous Reaction of Organic Peroxides with HSO3 - on the Surface of a Water Droplet.

Aqueous reactions between organic peroxides and SO2 are of intense interest in atmospheric science because of their ubiquitous implications for sulfate formation in secondary aerosols. However, the relative yields of the reaction products (inorganic vs. organic sulfates) remain controversial (i.e., 90 % vs. 40-70 % for inorganic sulfate) due in part to the lack of understanding of the underlying reaction mechanisms. Here, our computational results suggest that the reactions of HSO3 - (dissolved SO2 ) with organic peroxides are initiated on the surface of water nanodroplets and then proceed under two reaction pathways, in which the S atom of HSO3 - attacks either the O1 or O2 atom of the peroxide group -O(O2)O(O1)H, leading to the formation of inorganic and organic sulfates, respectively. Notably, we find that thse reaction initiated by O1 atom exhibits a relatively low energy barrier and high reaction rate, which favours the formation of inorganic sulfate.

Haze Formation in Warm H2-rich Exoplanet Atmospheres

Abstract New observing capabilities coming online over the next few years will provide opportunities for characterization of exoplanet atmospheres. However, clouds/hazes could be present in the atmospheres of many exoplanets, muting the amplitude of spectral features. We use laboratory simulations to explore photochemical haze formation in H2-rich exoplanet atmospheres at 800 K with metallicity either 100 or 1000 times solar. We find that haze particles are produced in both simulated atmospheres with small particle size (20–140 nm) and relatively low production rate (2.4 × 10−5 to 9.7 × 10−5 mg cm−3 hr−1), but the particle size and production rate is dependent on the initial gas mixtures and the energy sources used in the simulation experiments. The gas phase mass spectra show that complex chemical processes happen in these atmospheres and generate new gas products that can further react to form larger molecules and solid haze particles. Two H2-rich atmospheres with similar C/O ratios (∼0.5) yield different haze particle size, haze production rate, and gas products, suggesting that both the elemental abundances and their bonding environments in an atmosphere can significantly affect the photochemistry. There is no methane (CH4) in our initial gas mixtures, although CH4 is often believed to be required to generate organic hazes. However, haze production rates from our experiments with different initial gas mixtures indicate that CH4 is neither required to generate organic hazes nor necessary to promote the organic haze formation. The variety and relative yield of the gas products indicate that CO and N2 enrich chemical reactions in H2-rich atmospheres.

A circular microreaction method to the safe and efficient synthesis of 3-methylpyridine-N-oxide

3-Methylpyridine-N-oxide is an essential intermediate in the preparation of 2-chloro-5-methylpyridine, which can be used to synthesize nicotine insecticides such as imidacloprid and acetamiprid. The traditional method of production of 3-methylpyridine-N-oxide is catalytic oxidation of 3-methylpyridine in semi-batch reactors. Due to strong exothermic reaction and explosive property of 3-methylpyridine, the reaction efficiency and safety is low using batch technology. Therefore, the development of a safer and efficient 3-methylpyridine-N-oxide production process is very necessary in industrial production. In this paper, microreaction systems were introduced into the preparation of 3-methylpyridine-N-oxide. The comparison of three different methods (traditional semi-batch method, co-current microreaction method, and circular microreaction method) showed that the circular microreaction method was the most applicable, with relative higher product yield (~ 90%), less side reaction and better reaction control.

Conversion of acenaphthalene to phenalene via methylation: A theoretical study

Ab initio calculations of the C13H10 and C13H9 potential energy surfaces related to the reaction of 1-acenaphthyl and methyl radicals and secondary isomerization of C13H9 primary radical products have been performed at the chemically accurate G3(MP2,CC)//B3LYP/6-311G** level of theory to unravel the mechanism of conversion of acenaphthalene to phenalene or phenalenyl radical + H. The computed energetics and molecular parameters were utilized in Rice-Ramsperger-Kassel-Marcus Master Equation (RRKM-ME) calculations of reaction rate constants and relative product yields. The 1-acenaphthyl + CH3 reaction is predicted to proceed by a fast radical-radical recombination mechanism and to predominantly produce collisionally stabilized 1-methylacenaphthalene B1 or a C13H9 benzylic radical A1 + H with exothermicities of 106.8 and 25.2 kcal/mol, respectively. The A1 + H channel is preferable at higher temperatures, whereas the stabilization of 1-methylacenaphthalene is favored at higher pressures. The radical A1 can nearly irreversibly interconvert to phenalenyl radical AP via a 22.7 kcal/mol exothermic isomerization process involving formal insertion of the CH2 group into a CC bond of the five-member ring leading to the expansion of this ring to a six-member ring. The rate constants for the H addition reaction to phenalenyl radical to form phenalene and the reverse H loss from phenalene were also computed and the strength of the weakest CH bond in the CH2 group of phenalene is evaluated as 62.2 kcal/mol. The analysis of the reaction kinetics allowed us to deduce a mechanism for the conversion of 1-acenaphthyl radical to phenalene or phenalenyl radical + H via methylation involving the formation of A1 via a well-skipping channel or stabilization and dissociation of (or H abstraction from) B1 followed by isomerization of A1 to phenalenyl AP, which can add an H atom producing phenalene. Rate constants for the significant elementary reactions are fitted to modified Arrhenius expressions and are proposed for kinetic modeling of the expansion of a five-member ring on a zigzag edge of PAH to a six-member ring by methylation.

Influence of the p-hydroxyphenyl/guaiacyl ratio on the biphenyl and β-5 contents in compression wood lignins

Abstract Reaction woods of three softwoods, Pinus merkusii, Cryptomeria japonica and Cedrus deodara, were investigated by alkaline nitrobenzene oxidation (NBO) to characterize the condensed-type structures in compression wood lignins. A novel biphenyl-type NBO product carrying guaiacyl (G)- and p-hydroxyphenyl (H)-units, dehydrovanillin-p-hydroxybenzaldehyde (HG-biphenyl product), was identified using the authentic standard compound. On the basis of the yield of this novel NBO product, as well as those of GG-biphenyl-, β-5-, and uncondensed-type products [e.g. dehydrodivanillin, 5-formylvanillin, vanillin and p-hydroxybenzaldehyde], the compression wood lignins contained more HG-type biphenyl and H-type β-5 structures than the opposite wood lignins. The increase in the condensed-type structure content was largely offset by the decreases in the content of GG-biphenyl and G-type β-5 structures. Consequently, the relative yields of biphenyl, β-5 and uncondensed-type NBO products were very similar between the compression wood and the opposite wood, even though the H-unit having no methoxy group on its aromatic ring can be assumed to have a greater probability to form condensed-type structures during lignin biosynthesis than the G-unit.

Enhanced CH4 Production from Corn-Stalk Pyrolysis Using Ni-5CeO2/MCM-41 as a Catalyst

Production of syngas from lignocellulosic biomass though pyrolysis is a promising solution for the large-scale utilization of biomass. However, current pyrolysis approaches suffer from the relative low product yield and selectivity, limiting their practical application. To solve this problem, a series of nickel-based catalysts including Ni/MCM-41, Ni-5CeO2/MCM-41, and Ni-5La2O3/MCM-41 were prepared and characterized by transmission electron microscopy (TEM), N2 adsorption–desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and H2-temperature-programmed reaction (TPR) analysis. It was observed that the simultaneous addition of Ni and CeO2 to MCM-41 could increase the reducibility of Ni and the number of active Ni0 sites on the surface of the catalyst. Consequently, Ni-5CeO2/MCM-41 gave a CH4 yield of 14.6 mmol/g, which is remarkably higher than that (10.5 mmol/g) obtained in the absence of the catalyst. Meanwhile, the CO and H2 yields increased slightly, while the CO2 yield decreased slightly. Therefore, the improved CH4 yield and selectivity was mainly due to the increased decomposition of tarry compounds catalyzed by Ni/MCM-41 with the assistance of CeO2.

2-Methyltetrahydrofuran as a Solvent of Choice for Spontaneous Metathesis/Isomerization Sequence.

A new protocol for ring-closing metathesis/isomerization sequence was developed. The reactions of selected dienes were performed in overheated 2-methyltetrahydrofuran at 120 °C and provided a wide range of cyclic vinyl ethers and amides with good yields and selectivities. Computational analysis suggests that the relative yield of products depends on a thermodynamically driven process on the basis of relative stabilities of isomers.

Hydrocarbon fuel from brown grease: Effects of reaction temperature profile on yields and product distribution

Pyrolysis of brown grease has been shown to produce kerosene-like hydrocarbons as well as ketones. The process involves several different chemical reactions of the saturated and unsaturated fatty acid components. The yields and product distributions are dependent on the reaction temperature profile, a factor that must be considered in reactor and process design. In this paper we investigated the parameters of reaction temperature and time as brown grease was preheated and held at a set of temperatures before distillation of the kerosene-like hydrocarbons. It was found that the heating and temperature profile has a significant effect on the relative yields of reaction products.