Increasing Carbon Number Research Articles

Turbulent burning rates of gasoline components, Part 2 – Effect of carbon number

Experimental measurements of turbulent and laminar burning velocities have been made for premixed hydrocarbon–air flames of straight chain molecules of increasing carbon number (from n-pentane to n-octane). Measurements were performed at 0.5MPa, 360K and rms turbulent velocities of 2 and 6m/s, for a range of equivalence ratios. The laminar burning velocities were used to interpret the turbulent data, but were also found to be broadly in line with those of previous workers. At lean conditions the turbulent burning velocity was measured to be similar between the four alkanes studied. However, at rich conditions there were notable differences between the turbulent burn rates of the fuels. The equivalence ratio of the mixtures at which the maximum burning velocities occurred in the turbulent flames was richer than that under laminar conditions. The equivalence ratio of the peak turbulent burning velocity was found to be a function of the carbon number of the fuel and the turbulent intensity and became gradually fuel rich with increases in each of these values.

Action of biosurfactant producing thermophilic Bacillus subtilis on waxy crude oil and long chain paraffins

The study has been carried out to investigate the production of biosurfactant by a thermophilic strain of Bacillus subtilis on various hydrocarbon substrates, such as waxy crude oil, model crude oil and six long chain paraffins (C16H34 to C36H74) at 35, 50 and 75 °C. Model crude oil represents the mixture of the six long chain paraffins. The maximum biosurfactant production has been found to occur at 50 °C with n-hexadecane (C16H34) as a substrate. It has also been inferred that the physico-chemical properties of the biosurfactant is reduced with an increase in carbon number in the hydrocarbon substrate. Biosurfactant production is observed to be higher in the presence of waxy crude oil than the model crude oil, which is due to the presence of short chain paraffins with fewer carbon numbers in the former. B. subtilis in the presence of waxy crude oil has been observed to show high microbial adherence, improved surface tension reduction and emulsification activity, production of higher amount of biosurfactant ‘surfactin’, and improved biosurfactant stability upto 120 °C at 10 MPa, 10% (w/v) salinity and pH 8–14. This indicates the potential of microorganism in tackling oil-spill, wax degradation, flow assurance and enhanced oil recovery.

Re-examination of C1–C5 alkyl nitrates in Hong Kong using an observation-based model

The photochemical formation of alkyl nitrates (RONO2) and their impact on ozone (O3) formation were investigated using a Photochemical Box Model incorporating the Master Chemical Mechanism (PBM-MCM). The model was constrained with field measurement data collected on selected O3 episode days at Tai O, a rural-coastal site in southwestern Hong Kong, from August 2001–December 2002. The in-situ observations showed that the sum of C1–C5 RONO2 varied from 30.7 ± 14.8 pptv in spring to 120.7 ± 10.4 pptv in autumn, of which 2-butyl nitrate dominated with the highest average concentration of 30.8 ± 2.6 pptv. Model simulations indicated that the pathway of CH3O reacting with NO2, proposed in our previous study, made minor contributions (11.3 ± 0.7%) to methyl nitrate formation. Indeed, 51.8 ± 3.1% and 36.5 ± 6.3% of the methyl nitrate was attributed to the reaction of CH3O2+NO and to oceanic emissions/biomass burning, respectively. For the C2–C5 alkyl nitrates, the contribution of photochemical formation increased with increasing carbon number, ranging from 64.4 ± 4.0% for ethyl nitrate (EtONO2) to 72.6 ± 4.2% for 2-pentyl nitrate (2-PenONO2), while the contribution of oceanic emissions/biomass burning decreased from 35.1 ± 6.5% for EtONO2 to 26.8 ± 6.8% for 2-PenONO2. Model simulations of photochemical O3 levels influenced by RONO2 chemistry showed that the formation of methyl-, ethyl-, i-propyl-, n-propyl-, 2-butyl-, 2-pentyl-, and 3-pentyl-nitrates led to O3 reduction of 0.05 ± 0.03, 0.05 ± 0.03, 0.06 ± 0.02, 0.02 ± 0.02, 0.18 ± 0.04, 0.09 ± 0.02 and 0.06 ± 0.02 ppbv, respectively, with an average reduction rate of 11.0 ± 3.2 ppbv O3 per 1 ppbv RONO2 formation. The C1–C5 RONO2 constituted 18.6 ± 1.9% of the entire RONO2, and had a nitrogen reserve of 4.1 ± 0.2%, implying their potential influence on O3 production in downwind areas.

Determination and prediction of solubilities of active pharmaceutical ingredients in selected organic solvents

The aim of this work was to measure the solubilities of active pharmaceutical ingredients (APIs) in various organic solvents using the synthetic-visual method. Two non-steroidal anti-inflammatory drugs, i.e., acetylsalicylic acid and acetaminophen, and two histamine H2 receptor antagonists, i.e., cimetidine and famotidine, were selected as the APIs. The solubilities of these APIs in different organic solvents, namely methanol, ethanol, 2-propanol, 1-octanol, and poly(ethylene glycol) 400, were determined in the temperature range of 260–360K. Cimetidine and famotidine, which have several polymorphs, were characterized using powder X-ray diffraction, scanning electron microscopy, and differential scanning calorimetry before the solubility measurements. The experimental results for the APIs except famotidine show that the solubilities at a given temperature decreased with increasing carbon number of the alcohol. The solubility data were represented by two activity coefficient models: NRTL and UNIQUAC. In addition, predictions of the solubilities using the group contribution models Pharma Modified UNIFAC and modified UNIFAC (Dortmund) were also performed. The predictions obtained using Pharma Modified UNIFAC were better than those obtained using modified UNIFAC (Dortmund).

Liquid jet breakup regimes at supercritical pressures

Previously, a theory has been presented that explains how discrete vapor–liquid interfaces become diminished at certain high-pressure conditions in a manner that leads to well known qualitative trends observed from imaging in a variety of experiments. Rather than surface tension forces, transport processes can dominate over relevant ranges of conditions. In this paper, this framework is now generalized to treat a wide range of fuel-oxidizer combinations in a manner consistent with theories of capillary flows and extended corresponding states theory. Different flow conditions and species-specific molecular properties are shown to produce distinct variations of interfacial structures and local free molecular paths. These variations are shown to occur over the operating ranges in a variety of propulsion and power systems. Despite these variations, the generalized analysis reveals that the envelope of flow conditions at which the transition from classical sprays to diffusion-dominated mixing occurs exhibits a characteristic shape for all liquid–gas combinations. For alkane-oxidizer mixtures, it explains that these conditions shift to higher pressure flow conditions with increasing carbon number and demonstrates that, instead of widely assumed classical spray atomization, diffusion-dominated mixing may occur under relevant high-pressure conditions in many modern devices.

Gas-Wall Partitioning of Oxygenated Organic Compounds: Measurements, Structure–Activity Relationships, and Correlation with Gas Chromatographic Retention Factor

Gas-wall partitioning of 50 oxygenated organic compounds was investigated by using gas chromatography to monitor time-dependent gas-phase concentrations of authentic standards added to a large Teflon environmental chamber. Compounds included C8–C14 monofunctional ketones and alcohols, C5–C9 monoacids, and C4–C10 diols with linear and cyclic structures. Measured time constants for reaching gas-wall partitioning equilibrium ranged from ∼10 to 100 min with an average value of ∼30 min and exhibited no obvious trend with compound structure, whereas the extent of equilibrium partitioning to the walls ranged from ∼0 to 100% and increased with increasing carbon number and with functional group composition in the order ketones < alcohols < monoacids < diols. When results were modeled using an approach analogous to one commonly used to describe absorptive gas-particle partitioning in terms of compound vapor pressure and aerosol mass loading it was determined that the absorptive properties of the Teflon film walls w...

Thermal decomposition of alkane hydrocarbons inside a porous Ni anode for fuel supply of direct carbon fuel cell: Effects of morphology and crystallinity of carbon

This study improved the physical contact between anode and fuel in a direct carbon fuel cell (DCFC) by directly generating carbon in a porous Ni anode through thermal decomposition of three kinds of hydrocarbons (CH4, C2H6, C3H8). From electron microscope observations of the carbon particles generated from each hydrocarbon, carbon spheres (CS), carbon nanotubes (CNT) and carbon nanofibers (CNF) were identified with increasing carbon number. Raman scattering analysis was performed to determine the crystallinity of the carbon samples. As a result, the carbon samples (CS, CNT, and CNF) produced from CH4, C2H6 and C3H8 were found to be less crystalline and more flexible with increasing the carbon number. DCFC performance was measured at 700 °C for the anode fueled with the same mass of the carbon sample. It was found that the 1-dimensional CNT and CNF were more active to produce 148% and 210% times higher power density than the CS. The difference was partly attributed to the finding that the less-crystalline CNT and CNF had much lower charge transfer resistances than the CS. A lifetime test found that the CNT and CNF, which are capable of transporting electrons for much longer periods, maintained the power density much longer, as compared to the CS which can lose their point contacts between the particles shortly at high current density.

Kinetic Model of Heavy Paraffins Dehydrogenation

Kinetics of reaction and catalyst deactivation were determined based on the dehydrogenation of C10 − C13 heavy paraffins to the corresponding mono-olefins, and Powell method was used to optimize the parameters. Activation energy and pre-exponential factor presented linear relationship with carbon number. The results showed that dehydrogenation became easier with the increase of carbon number of heavy paraffin and the deactivation of catalyst became slower with the increase of LHSV and pressure. The validation of kinetic model showed it was in good accordance with experimental data.

다공성 니켈 연료 전극 내부에서 탄화수소의 열분해를 통한 직접 탄소 연료 전지의 연료공급

This study offers a novel method for improving the physical contact between the anode and fuel in a direct carbon fuel cell (DCFC): a direct generation of carbon in a porous Ni anode through the thermal decomposition of gaseous hydrocarbons. Three kinds of alkane hydrocarbons with different carbon numbers (CH4, C2H6, and C3H8) are tested. From electron microscope observations of the carbon particles generated from each hydrocarbon, we confirm that more carbon spheres (CS), carbon nanotubes (CNT), and carbon nanofibers (CNF) were identified with increasing carbon number. Raman scattering results revealed that the carbon samples became less crystalline and more flexible with increasing carbon number. DCFC performance was measured at with the anode fueled by the same mass of each carbon sample. One-dimensional carbon fuels of CNT and CNF more actively produced and had power densities 148 and 210 times higher than that of the CS, respectively. This difference is partly attributed to the findings that the less-crystalline CNT and CNF have much lower charge transfer resistances than the CS.

Characteristics and origin of carbon isotopes of n-alkanes in crude oils from the western Pearl River Mouth Basin, South China sea

The quantitative characterization of carbon isotopes of n-alkanes is commonly carried out in organic geochemical studies. Possible controls on carbon isotopes include source organic matter, maturity, fractionation during oil expulsion and migration, and the mixing of different oils. In this study of the origin of crude oils in the western Pearl River Mouth Basin, the influences of all of these factors have been considered in reaching a conclusion. Carbon isotopes of n-alkanes in the crude oils, and the extracts of the two effective source rocks (the Wenchang and Enping formations) in the basin, exhibit clear differences. The Wenchang source rocks have heavy δ13C values that remain almost constant or become slightly heavier with increasing carbon number. The Enping source rocks have light δ13C values that become lighter with increasing carbon number. Two groups of oils in this area were identified based on the carbon isotopes of the n-alkanes; groupIoils are similar to extracts of the Wenchang source rocks. However, the groupIIoils are different from both the Wenchang and Enping source rocks and the carbon isotopic profiles of their n-alkanes exhibit a “V” feature with increasing carbon number. The results of artificial thermal maturation experiments indicate that, from the early stage to the peak stage of oil generation (with EasyRo between 0.64% and 1.02%), the δ13C values of n-alkanes in the pyrolysis oils become heavier by about 3‰ with increasing thermal maturity, but the shape of the carbon isotopic profiles are not significantly changed. Calculated δ13C values of n-alkanes in “mixed” artificial pyrolysis oils indicate that the mixture of oils generated from the same source rocks with different maturities could not change the carbon isotopic profile of the n-alkanes, however, a mixing of the Wenchang and Enping oils could give the “V” feature in the profiles, similar to the groupIIoils in this area. The groupIIoils appear to be mixed Wenchang and Enping oils, the latter being the dominant component in the mixture. We conclude that the source organic matter and the degree of mixing are the main factors controlling the carbon isotopic characteristics of n-alkanes in crude oils in the western Pearl River Mouth Basin.

Clean synthesis of biolubricant range esters using novel liquid lipase enzyme in solvent free medium.

In view of the rising global problems of environment pollution and degradation, the present process provides a ‘green solution’ to the synthesis of higher esters of lubricant range, more specifically in the range C12-C36, using different combinations of acids and alcohols, in a single step reaction. The esters produced are biodegradable in nature and have a plethora of uses, such as in additives, as lubricating oils and other hydraulic fluids. The enzymatic esterification was performed using liquid (non-immobilized or free) lipase enzyme, without any additional organic solvent. Soluble lipase proves to be superior to immobilized enzymes as it is more cost effective and provides a faster process for the production of higher esters of lubricant range. An interesting finding was, that the lipase enzyme showed higher conversion rates with increasing carbon number of straight chain alcohols and acids. Reactions were carried out for the optimization of initial water concentration, temperature, pH of the substrate mixture and the chain length of the substrates. Under optimized conditions, the method was suitable to achieve ~ 99% conversion. Thus, the process provides an environment friendly, enzymatic alternative to the chemical route which is currently used in the industrial synthesis of lubricant components.

Adsorption thermodynamics of C1–C4 alcohols in H-FAU, H-MOR, H-ZSM-5, and H-ZSM-22

The adsorption thermodynamics of C1–C4 primary alcohols in large-pore (H-FAU and H-MOR) and medium-pore (H-ZSM-5 and H-ZSM-22) zeolites is quantified using combined periodic DFT-D – statistical thermodynamic calculations. The increase of adsorption equilibrium coefficients with increasing carbon number of the alcohol and with decreasing pore size of the zeolite is attributed to the well-known dispersive van der Waals interactions. Although electrostatic interactions increase in the order: H-FAU<H-ZSM-5≈H-MOR<H-ZSM-22, an interplay with other factors including zeolite acid strength, framework flexibility, and steric constraints globally renders non-dispersive interactions largely similar among the four zeolites. Also, the shape selectivity is probed for adsorption of n-butanol, i-butanol, 2-butanol, and t-butanol at the straight and zigzag channels of H-ZSM-5. A compensation between entropy and enthalpy leads to a difference of at most two orders of magnitude in the adsorption equilibrium coefficient between the two channels.

Identification and yields of 1,4-hydroxynitrates formed from the reactions of C8-C16 n-alkanes with OH radicals in the presence of NO(x).

A series of C8-C16 n-alkanes were reacted with OH radicals in the presence of NOx in an environmental chamber and particulate 1,4-hydroxynitrate reaction products were collected by filtration, extracted, and analyzed by high-performance liquid chromatography with UV absorption and electron ionization mass spectrometry (HPLC/UV/MS). Observed mass spectral patterns can be explained by using proposed ion fragmentation mechanisms, permitting the identification of each hydroxynitrate isomer. Reversed-phase retention of these compounds was dictated by the length of the longer of two alkyl chains attached to the 1,4-hydroxynitrate subunit. 1,4-Hydroxynitrates were quantified in particles using an authentic analytical standard for calibration, and the results were combined with gas chromatography measurements of the n-alkanes to determine the molar yields. Yields based on analyses of particles increased with increasing carbon number from 0.00 for C8 to an average plateau value of 0.130 ± 0.008 for C14-C16, due primarily to corresponding increases in gas-to-particle partitioning. The value at the plateau, where essentially all 1,4-hydroxynitrates were in particles, was equal to the average total yield of C14-C16 1,4-hydroxynitrates. The average branching ratio for the formation of C14-C16 1,4-hydroxynitrates from the reaction of NO with the corresponding 1,4-hydroxyperoxy radicals was 0.184 ± 0.011. This value is ∼20% higher than the plateau value of 0.15 for reactions of secondary 1,2-hydroxyperoxy radicals and ∼40% lower than the plateau value of 0.29 for reactions of secondary alkyl peroxy radicals, both of which were reported previously. The branching ratios determined here were used with values reported previously to calculate the yields of C7-C18 alkyl nitrates, 1,4-hydroxynitrates, and 1,4-hydroxycarbonyls, the three products formed from the reactions of these n-alkanes.

Synthesis of a new cyclosporine-based stationary phase and separation behaviors toward aromatic positional isomers by high-performance liquid chromatography.

A new cyclosporine-bonded stationary phase has been synthesized through the Staudinger reaction between azido cyclosporine A (CsA) and aminopropyl silica gel and applied in separations of six disubstituted aromatic analytes by high-performance liquid chromatography. For dimethyl phthalate, nitroaniline and chloronitrobenzene, their positional isomers were well-separated on this CsA stationary phase, in which the separation factor for m-/o-dimethyl phthalates was the biggest. For nitrotoluene, dichlorobenzene and benzenediol, the m-/o-isomers were co-eluted. Then, effects of chromatographic conditions (such as types and content of alcoholic modifiers) on separation of nitroaniline positional isomers have been investigated. Retention behaviors of nitroaniline isomers on the column exhibited the strengthening trend along with increasing carbon number of alcohols, from ethanol to 1-propanol, and to 1-butanol. A similar phenomenon was observed by lowering the content of alcohol.

Product distributions and olefin-to-paraffin ratio over an iron-based catalyst for Fischer–Tropsch synthesis

An iron-based catalyst was prepared by the co-precipitation method. The product distributions and olefin-to-paraffin ratio (O/P ratio) with chain length of Fischer–Tropsch synthesis over the iron-based catalyst were investigated under different reaction conditions in an integral fixed bed reactor. It is found that the product distributions are non-ASF situation, and the deviation from ASF law was analyzed by taking the physisorption, solubility, volatility of products and the subsequent secondary reactions into consideration. It is noted that the contents of hydrocarbons decline with increasing carbon number and higher temperature, space velocity, H2/CO in feed gas and lower pressure is preferential for the formation of light hydrocarbons but against the chain propagation. The O/P ratio shows an exponential decrease with chain length except for ethylene and ethane because of the special adsorption character of ethylene. The O/P ratio is also affected by operating conditions. The results indicate that higher reaction temperature, space velocity of feed gas, lower pressure and higher H2/CO in the feed gas are preferential for the formation of olefins and the enhancement of O/P ratio.

Assessing the origins of aliphatic amines in the Murchison meteorite from their compound-specific carbon isotopic ratios and enantiomeric composition

The study of meteoritic organic compounds provides a unique window into the chemical inventory of the early Solar System and prebiotic chemistry that may have been important for the origin of life on Earth. Multiple families of organic compounds have been extracted from the Murchison meteorite, which is one of the most thoroughly studied carbonaceous chondrites. The amino acids extracted from Murchison have been extensively analyzed, including measurements of non-terrestrial stable isotopic ratios and discoveries of l-enantiomeric excesses for α-dialkyl amino acids, notably isovaline. However, although the isotopic signatures of bulk amine-containing fractions have been measured, the isotopic ratios and enantiomeric composition of individual aliphatic amines, compounds that are structurally related to amino acids, remain unknown. Here, we report a novel method for the extraction, separation, identification and quantitation of aliphatic monoamines extracted from the Murchison meteorite. Our results show a complete suite of structural isomers, with a larger concentration of methylamine and ethylamine and decreasing amine concentrations with increasing carbon number. The carbon isotopic compositions of fourteen meteoritic aliphatic monoamines were measured, with δ13C values ranging from +21‰ to +129‰, showing a decrease in 13C with increasing carbon number, a relationship that may be consistent with the chain elongation mechanism under kinetic control previously proposed for meteoritic amino acids. We also found the enantiomeric composition of sec-butylamine, a structural analog to isovaline, was racemic within error, while the isovaline extracted from the same Murchison piece showed an l-enantiomeric excess of 9.7%; this result suggested that processes leading to enantiomeric excess in the amino acid did not affect the amine. We used these collective data to assess the primordial synthetic origins of these meteoritic aliphatic amines and their potential linkage to meteoritic amino acids.

Reactivities of C6–8 hydrocarbons and effect of coexistence of another hydrocarbon in cracking on H-ZSM-5 catalyst at high temperatures

The cracking of C6–8 hydrocarbons on H-ZSM-5 (Si/Al=51) at high temperatures was carried out as a model reaction of naphtha cracking to produce light olefins. The reactivity of n-paraffin increased with an increase in carbon number, while the selectivities for light olefins were almost constant. In the cracking of cycloparaffin, the selectivity for the corresponding aromatics was very high, indicating that the dehydrogenation occurred directly without C-C bond cleavage. In the case of cycloparaffin cracking, the deactivation of H-ZSM-5 with time-on-stream (TOS) was fast due to high BTX (benzene, toluene, and xylene) selectivity. The deactivation of H-ZSM-5 in the cracking of methylcyclohexane was especially fast due to very high toluene selectivity. Coexistent 1-hexene did not affect the cracking rate of n-heptane, cyclohexane, or methylcyclohexane, indicating that monomolecular cracking was predominant at as high a temperature as 923K. In contrast, coexistent cyclohexane and methylcyclohexane considerably affected the cracking rate of n-heptane because of their slow diffusion in the pores of H-ZSM-5.

Synthesis, structure-activity relationships and biological activity of new isatin derivatives as tyrosinase inhibitors.

A newly series of isatin derivatives (6a-t) containing alkyl/aryl urea groups were synthesized and their inhibitory effects on the diphenolase activity of banana tyrosinase were evaluated. Tyrosinase was purified from banana on an affinity gel comprised of Sepharose 4B-L-tyrosine-p-aminobenzoic acid. The results showed that all the synthesized compounds inhibited the tyrosinase enzyme activity. Among them, 1-(2,3-dioxoindolin-5-yl)-3-(4-nitrophenyl)urea (6l) was found to be most active compound (Ki = 24.96 µM). The inhibition kinetics was analysed by Lineweaver-Burk double reciprocal plots. It revealed that compound 6l was a competitive inhibitor. According to results of structure-activity relationship, generally, the compounds electron-donating group bonded to the phenyl ring have higher inhibitory activity against tyrosinase than halogen group bonded to the phenyl ring. The inhibitory activities of alkyl urea substituted compounds decreased with increasing carbon number of the alkyl groups at urea moiety. The halogen series at the para position of the phenyl ring showed a qualitative relationship for higher inhibitory activity with increasing size and polarizability. HOMOLUMO energy levels and dipole moments of some selected compounds (6a, 6d, 6h, 6l and 6o) were also calculated by Gaussian software.

Chain length dependent olefin re-adsorption model for Fischer–Tropsch synthesis over Co-Al2O3 catalyst

Many models for describing the Fischer–Tropsch synthesis (FTS) over supported cobalt catalysts have been postulated but there is still much debate over its mechanisms and governing physio-chemical phenomena, particularly those relating to secondary reactions of olefins. In this work, a comprehensive kinetic model for the FTS over Co/Al2O3 catalyst, was developed to provide mechanistic explanations for deviations from Anderson–Schulz Flory (ASF) distributions.Experiments were conducted in a fixed bed reactor over a wide range of operating conditions (T=483–493 K, P=1.5–2MPa, feed ratio H2/CO=1.4–2.1 and CO conversion XCO=15–75%). Models were developed using, carbide, enolic and CO insertion mechanisms. The concept of 1-olefin re-adsorption and its chain length dependency was introduced. Chain length dependency was assumed to be due to an increased probability of 1-olefin interaction with the active site, with an increasing carbon number. Model results were analysed for statistical and physio-chemical robustness. The calculated apparent activation energies for the selected model were in good agreement with the values reported in the literature. It was found that FTS proceeded via the CO insertion mechanism and chain length dependent 1-olefin re-adsorption phenomena primarily governed the deviations from ASF distributions.

Alkyl Nitrate Formation from the Reactions of C8–C14n-Alkanes with OH Radicals in the Presence of NOx: Measured Yields with Essential Corrections for Gas–Wall Partitioning

In this study, C8-C14 n-alkanes were reacted with OH radicals in the presence of NO(x) in a Teflon film environmental chamber and isomer-specific yields of alkyl nitrates were determined using gas chromatography. Because results indicated significant losses of alkyl nitrates to chamber walls, gas-wall partitioning was investigated by monitoring the concentrations of a suite of synthesized alkyl nitrates added to the chamber. Gas-to-wall partitioning increased with increasing carbon number and with proximity of the nitrooxy group to the terminal carbon, with losses as high as 86%. The results were used to develop a structure-activity model to predict the effects of carbon number and isomer structure on gas-wall partitioning, which was used to correct the measured yields of alkyl nitrate isomers formed in chamber reactions. The resulting branching ratios for formation of secondary alkyl nitrates were similar for all isomers of a particular carbon number, and average values, which were almost identical to alkyl nitrate yields, were 0.219, 0.206, 0.254, 0.291, and 0.315 for reactions of n-octane, n-decane, n-dodecane, n-tridecane, and n-tetradecane, respectively. The increase in average branching ratios and alkyl nitrate yields with increasing carbon number to a plateau value of ∼0.30 at about C13-C14 is consistent with predictions of a previously developed model, indicating that the model is valid for alkane carbon numbers ≥C3.