Effects Of Secondary Reactions Research Articles

Differential Global Reaction Model with Variable Stoichiometric Coefficients for Thermal Cracking of n-Decane at Supercritical Pressures

This study presents a new modeling approach for the thermal cracking of hydrocarbon fuels at supercritical pressures. The thermal cracking process is treated as an infinite number of continuous microreactions at different fuel conversions, in which the stoichiometric coefficients of each species are expressed by continuous differentiable functions of the fuel conversion to consider the effects of secondary reactions. A set of thermal cracking experimental results involving n-decane was used as an example to show how to establish the differential global reaction (DGR) model with variable stoichiometric coefficients. The DGR model was implemented in a computational fluid dynamics simulation to predict n-decane thermal cracking coupled with flow, heat transfer, and wall thermal conduction. The results showed that the DGR model can more accurately predict the species mass fractions than existing global reaction models, especially for conditions when the secondary reactions strongly impact the thermal cracking...

Thermal Decomposition of Diphenyl Tetroxane in Chlorobenzene Solution

The thermal decomposition of Cyclic Diperoxide of Benzaldehyde 3,6-diphenyl-1,2,4,5-tetroxane, (DFT) in chlorobenzene solution in the studied temperature range (130°C - 166°C) satisfactorily satisfies a first order law up to 60% conversions of diperoxide. DFT would decompose through a mechanism in stages and initiated by the homolytic breakdown of one of the peroxidic bonds of the molecule, with the formation of the corresponding intermediate biradical. The concentration studied was very low, so that the effects of secondary reactions of decomposition induced by free radicals originated in the reaction medium can be considered minimal or negligible. The activation parameters for the unimolecular thermal decomposition reaction of the DFT are ΔH# = 30.52 ± 0.3 kcal·mol-1 and ΔS# = -6.38 ± 0.6 cal·mol-1 K-1. The support for a step-by-step mechanism instead of a process concerted is made by comparison with the theoretically calculated activation energy for the thermal decomposition of 1,2,4,5-tetroxane.

Effects of Secondary Reactions on the Destruction of Cellulose-Derived Volatiles during Biomass/Coal Co-gasification

The purpose of this study was to reveal the structural evolution of cellulose-derived tars in the biomass/coal co-gasification environment. A two-stage reactor was employed, where the pyrolytic vapors of cellulose were produced in the top stage and the secondary reactions of these vapors took place in the bottom stage under a range of conditions. The roles of anthracite char and steam were examined by implementing three operational modes in the bottom stage: thermal cracking (TC), catalytic cracking (CC), and catalytic reforming (CR), over a temperature range from 600 to 900 °C. Anthracite char was effective in enhancing tar reduction at lower temperatures (≤700 °C), above which its effect diminished. Tar yields under the CC and CR modes were comparable in the studied temperature range, suggesting the minimum effects of steam on the tar amount. However, gel permeation chromatography coupled with a diode array detector (GPC–DAD) and gas chromatography–mass spectrometry (GC–MS) characterization of tars show...

Secondary reactions in oil shale pyrolysis by solid heat carrier in a moving bed with internals

The secondary reactions occurring during the formation of shale oil are investigated with Huadian oil shale pyrolysis by solid heat carrier in a newly devised moving bed with internals (MBI). The effect of secondary reactions, which are mainly vapor-phase cracking, on shale oil property and yield at different temperatures is characterized on the basis of ultimate, 13C NMR and GC–MS analyses of the produced oil. The increases in the production rate of hydrocarbon gas species and related molar ratios clarify that the oil vapor cracking, rather than coking, is the main secondary reactions at pyrolysis temperature over 495°C. Ultimate analysis of shale oil shows that cracking increases the carbon and nitrogen contents of oil but decreases its hydrogen and oxygen contents. There are obvious decreases in the atomic H/C and O/C ratios of shale oil with increasing the pyrolysis temperature. NMR analysis shows that the aromaticity of shale oil increases considerably due to secondary reactions. Selective concentration of existing aromatics and aromatization of aliphatics are of roughly equal importance. The GC–MS results indicate that the aliphatic hydrocarbons (alkanes and alkenes) are the main detected components in shale oil and represent 75% of the detected peak areas. Via oil vapor cracking, a part of long-chain aliphatics is transformed into short-chain alkanes, alkenes and gas species to increase the low-carbon hydrocarbons. The increase in aromatic proportion with raising temperature is due to the selective concentration by cracking aliphatics and aromatization reactions such as dehydrogenation and their subsequent reactions.

Fast pyrolysis of soybean hulls: analysis of bio-oil produced in a fluidized bed reactor and of vapor obtained in analytical pyrolysis

This research involved an investigation into the composition both of vapors produced in the analytical pyrolysis of soybean hulls and of the bio-oil produced in the fast pyrolysis of soybean hulls in a fluidized bed reactor. The reaction temperatures were 450, 550, 650 and 750 °C for analytical pyrolysis and 550 °C for the fluidized bed reactor. Product compositions were analyzed using a gas chromatograph coupled to a mass spectrometer. The main objectives of this work were to evaluate the chemical potential of the produced bio-oil and to study the extent and the effects of secondary reactions that occur in the fluidized bed pyrolysis apparatus. The bio-oil proved to be a complex mixture; rich in phenols, cyclopentene derivatives and tetradecane. The main compounds identified in the vapor were 1,3-pentadiene, acetic acid and tetradecane. The differences between the composition of bio-oil and vapor are probably due to the occurrence of secondary reactions, the distinct heating rates applied during analytical pyrolysis and in the fast pyrolysis pilot plant, and the vapor condensing process in the pyrolysis pilot unit.

Secondary Vapor Phase Reactions of Lignin-Derived Oligomers Obtained by Fast Pyrolysis of Pine Wood

In this paper, the effect of secondary reactions in vapor phase on the yield and composition of pyrolytic lignin (PL) oligomers was investigated. The Pine wood material was pyrolyzed at 500 °C in a fluidized bed reactor, and the vapors were transferred to a downstream tubular reactor operated at residence times between 0 and 15 s and temperatures of 400, 500, and 550 °C. Relatively small changes in yield and composition of PL oligomers were observed when the tubular reactor was operated at 400 °C. However, as the temperature in the tubular reactor increased (500 and 550 °C), the effect of residence time became more pronounced and the rate of thermal degradation of pyrolytic lignin increased. The pyrolytic lignin fraction was isolated from the bio-oil and analyzed by UV-fluorescence, TGA, Py-GC/MS, FTIR, ESI-MS, and 1H NMR. The main change observed in the composition of PL oligomers (by Py-GC/MS and 1H NMR) as a function of the vapor phase reaction time and temperature was the removal of methoxyl groups. F...

Influence of secondary reactions on the synthetic efficiency of DHAP‐aldolases

The effect of secondary reactions on DHAP-dependent aldolase stereoselective synthesis yields is reported. The fuculose-1-phosphate aldolase catalyzed synthesis between DHAP and Cbz-S-alaninal has been chosen as case study. It has been demonstrated that DHAP is not only chemically degraded in the reaction medium, but also enzymatically. The last reaction has been shown to take place when type II aldolases are used as biocatalysts. In order to minimize the effect of non-desired reactions, temperature reduction has been shown to be favorable, and operation at 4 degrees C has been chosen as appropriate. On the other hand, the fed-batch addition of DHAP also increased the synthesis yields and, combined with low temperature, led to almost quantitative conversion.

Investigation of pyrite-weathering processes in the vadose zone using optical oxygen sensors

Pyrite weathering in the unsaturated zone of overburden material was investigated in column experiments. Optodes were used to monitor changes in oxygen concentrations. Oxygen recharge in the vadose zone and effects of secondary reactions were investigated. Oxygen transport limits thickness and the rate of the depyritisation. The overburden material (thickness 0.6 m, initial pyrite content 1.2 wt%) was depyritised within 200 days. The position of the pyrite decomposition front, the momentary release of reaction products and the remaining acidification potential can be determined. Buffer capacity, speciation and seepage water velocity are crucial for the distribution of the reaction products and the resulting acidification (minimum pH 1.6). A total of 75% of the protons were consumed by buffering reactions and 15% were fixed to complexes. Only 10% of the protons are represented by the measured pH value. In oxygen-consuming environments optical oxygen measurements can be used to identify and quantify structures and processes.

A new method for using pyrolysis-g.c.-m.s. to study the oxidative degradation of polymers or oils

The technique of pyrolysis-g.c.-m.s. has been extended to study oxidative degradation by a method which can deal with all types of samples. The method depends on the fact that when a pyrolysis filament unit is loaded into the pyrolysis chamber at the head of a g.c. column, it takes time (10 minutes or more) for the inert carrier gas to sweep away the air which has been admitted into the chamber during filament insertion. In normal thermal degradation work, the pyrolysis is not performed until all the air has been swept away. However, when it is desired to study oxidation, the pyrolysis may be performed whilst the air remains within the pyrolysis chamber, and during this time the concentration of air continuously monitored by the mass spectrometer. The use of this approach is illustrated by a study of the oxidation of a polyisobutylene oil. The pyrogram of the latter obtained in the presence of air shows distinct oxidation products which are not present in the thermolysis chromatogram obtained under inert atmosphere conditions. The results are also compared with those previously published for an enclosed Curie-point filament (ECP) study of the oxidation of this polymer. It is concluded that this new method is preferable to the ECP method, in that the latter method is more susceptible to the effects of secondary reactions occurring during this two-stage process.

Comparison of hydrocracking reactivities of coal extracts from a flowing-solvent reactor, a mini-bomb and a pilot plant

Hydrocracking reactivities of Point of Ayr coal liquefaction extracts prepared by several different liquefaction routes have been compared. Structural changes have been assessed by size exclusion chromatography (s.e.c.), u.v.-fluorescence (u.v.-f.) spectroscopy and t.g.a.-based boiling point determinations. In line with relatively short residence times of products in the reaction zone during the liquefaction stage, the extract prepared in the flowing solvent reactor (FSR) gave the largest molecular mass (MM) distribution and the greatest shift to smaller MMs during hydrocracking. The greater reactivity of this extract reflects that of material freshly released from the coal, with a minimum of thermal degradation. The use of primary coal extracts appear useful in providing a common baseline for the assessment of hydrocracking potentials of extracts from different coals. The order of hydrocracking reactivities of >450°C b.p. material contained in the set of extract samples was: FSR > mini-bomb (10 min) > pilot plant > mini bomb (60 min). For all samples, significant conversion of > 450°C b.p. material to lower-boiling fractions took place during the first 30 min; the slow-down in conversion with time appears at least partially due to a reduction in the reactivity of the extracts. The results suggest that high-boiling materials (> 450°C) in the coal extracts progressively tend to become less reactive and more resistant to further breakdown, due to loss of reactive groups such as alkyl side chains and hydroxyl groups and also possibly due to structural shifts of larger-MM material to stabler molecular configurations. Observed differences in hydrocracking reactivities of extracts from the same coal prepared under different reaction conditions highlight the need to consider the effects of secondary reactions during the coal extraction stage in assessing hydrocracking reactivities of coal extracts.

Liquefaction of coal in a flowing-solvent reactor

A flowing-solvent liquefaction reactor has been used to examine the primary solubilization potential of a range of coals. The reactor configuration allows the suppression of secondary reactions by sweeping the heated zone with a continuous flow of solvent. The design of the system combines low thermal inertia and direct electrical resistance heating to provide closely controlled time-temperature ramping, and a variable preset holding time at the target temperature. Heating rates of 0.1–15K s −1 up to temperatures of 450 °C and hold times of 0–1600 s can be achieved. Data are reported for a range of European and US coals with elemental carbon contents ranging from 74 to 91%. The effect on conversion of reactor pressure, heating rate, temperature, holding time at temperature and solvent flow rate have been determined. In contrast with pyrolysis, results suggest that liquefaction reactivities are relatively insensitive to changes in the heating rate. Comparison with results from micro-bomb reactors has shown that the continuous solvent sweep allows the relatively intact removal of primary solubilization products from the reaction zone. Molecular mass distributions of solubilized products thus obtained have been found to increase with increasing carbon content of the substrate coal (up to ~85%), and to decline with further increases up to 91% carbon content. In general, this reactor configuration appears to offer a promising avenue for analytically probing the more reactive structures of coals without interference from effects of secondary reactions.

Process of hydrogen discharge on the metal surface in the corrosion fissure of steel

The effects of secondary reactions in metal-medium systems on their initial properties have been analyzed, and the role of primary physical-chemical processes in creating conditions for the onset of the kinetic characteristics of hydrogen discharge on a metal surface has been evaluated. Based on the results of physical studies (using mass spectrometry, thermodesorption, and atomic absorption spectroscopy) the principal physical chemical aspects of the theory of electrochemical hydrogen discharge on a metal surface have been established, and the dynamics of hydrogen redistribution or partitioning between the interphase boundaries and the bulk phase have been investigated; the effects of these processes on the evolution of metal-medium systems have also been demonstrated. The primary act which determines the energetics of the entire process of the interaction of fluid media with a metal surface has been shown to be the adsorption and subsequent exothermic chemichemisorption of solvent molecules on active surface sites. This facilitates bond redistribution (including or up to complete dissociation of index groups of the solvent on the metal surface), which in turn delivers or supplies protons for the ensuing discharge, molization, and occlusions of hydrogen by the metal.

An electrochemical approach to chemically driven proton pumps: The effects of secondary reactions, uncouplers, inhibitors and ionophores

The concept of proton transfer in biological membranes in terms of proton-involved chemical reactions (R. Naumann, Bioelectrochem. Bioenerg., 16 (1986) 245) is pursued further. The vectorical character of proton flow is assumed to be caused by oscillations superimposed on a steady state. Oscillations are explained in terms of the theory of metastable states and hysteresis put forward by A. Katchalsky and R. Spangler (Q. Rev. Biophys., 1 (1968) 127). According to this theory, cooperative phenomena connected with permeability changes of membrane proteins are responsible for feedback control between the oscillations of proton flow and the electrostatic potential at the membrane/water interface, Δψ. Following the quasi-stationary state approach, the driving force of proton transfer is, however, taken to be the transmembrane Δ μ H + rather than Δψ. Proton flow as a function of Δ μ H + is treated in terms of the theory of electrochemical kinetics. Using computer calculations, this treatment is shown to be in qualitative agreement with experimental findings regarding the effects given in the title.

An electrochemical approach to chemically driven proton pumps: The effects of secondary reactions, uncouplers, inhibitors and ionophores

The concept of proton transfer in biological membranes in terms of proton-involved chemical reactions (R. Naumann, Bioelectrochem. Bioenerg., 16 (1986) 245) is pursued further. The vectorical character of proton flow is assumed to be caused by oscillations superimposed on a steady state. Oscillations are explained in terms of the theory of metastable states and hysteresis put forward by A. Katchalsky and R. Spangler (Q. Rev. Biophys., 1 (1968) 127). According to this theory, cooperative phenomena connected with permeability changes of membrane proteins are responsible for feedback control between the oscillations of proton flow and the electrostatic potential at the membrane/water interface, Δψ. Following the quasi-stationary state approach, the driving force of proton transfer is, however, taken to be the transmembrane Δ ▪ H + rather than Δψ. Proton flow as a function of Δ ▪ H + is treated in terms of the theory of electrochemical kinetics. Using computer calculations, this treatment is shown to be in qualitative agreement with experimental findings regarding the effects given in the title.

ChemInform Abstract: The O + NH3 Reaction: A Review

Experimental data for the reaction of O atoms with NH3 have been reviewed with particular attention to the possible effects of secondary reactions on the deduced rate coefficient. A reaction mechanism was assembled and computer calculations carried out to simulate several sets of experiments. The sensitivity of the calculations to uncertainties in the various rate coefficients was assessed. Transition-state theory calculations were carried out on the rate coefficient k1 for the O + NH3 → OH + NH2 reaction. These studies suggest that the reaction stoichiometry is dependent on temperature, initial reagent ratios, and extent of reaction; that available data are not sufficient to determine whether the initial step is H-atom abstraction (producing OH and NH2 radicals) or O-atom addition (producing an NH3O* complex): and that the low temperature values of k1 (T ⩽ 400 K) are not consistent with values deduced at higher temperatures if the reaction proceeds by H-atom abstraction. Taking all the evidence into account, it is recommended that the expression 1.1 × 103 T2.1 exp(−2620/T) L mol−1 s−1 be used for k1 until more definitive experimental measurements are made at low temperatures.

The O + NH3reaction: A review

AbstractExperimental data for the reaction of O atoms with NH3have been reviewed with particular attention to the possible effects of secondary reactions on the deduced rate coefficient. A reaction mechanism was assembled and computer calculations carried out to simulate several sets of experiments. The sensitivity of the calculations to uncertainties in the various rate coefficients was assessed. Transition‐state theory calculations were carried out on the rate coefficientk1for the O + NH3→ OH + NH2reaction. These studies suggest that the reaction stoichiometry is dependent on temperature, initial reagent ratios, and extent of reaction; that available data are not sufficient to determine whether the initial step is H‐atom abstraction (producing OH and NH2radicals) or O‐atom addition (producing an NH3O* complex): and that the low temperature values ofk1(T⩽ 400 K) are not consistent with values deduced at higher temperatures if the reaction proceeds by H‐atom abstraction. Taking all the evidence into account, it is recommended that the expression 1.1 × 103T2.1exp(−2620/T) L mol−1s−1be used fork1until more definitive experimental measurements are made at low temperatures.

Transport model for devolatilization of large nonplastic coal particles: the effect of secondary reactions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTransport model for devolatilization of large nonplastic coal particles: the effect of secondary reactionsNarasimhan Devanathan and Satish C. SaxenaCite this: Ind. Eng. Chem. Res. 1987, 26, 3, 539–548Publication Date (Print):March 1, 1987Publication History Published online1 May 2002Published inissue 1 March 1987https://doi.org/10.1021/ie00063a021RIGHTS & PERMISSIONSArticle Views73Altmetric-Citations14LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

A resonance fluorescence kinetic study of the O(3P)+CH4 reaction over the temperature range 474 K to 1156 K

The bimolecular rate constant for the reaction of O( 3 P) with CH 4 was measured directly over a wide range in temperature in a study that utilized two independent experimental technique. The flash photolysis-resonance fluorescence method was employed to obtain rate constants at 474 K and 520 K at total pressures (in argon diluent) of 100–200 torr. At higher temperatures (548 K to 1156K), a discharge flow-resonance fluorescence apparatus equipped with a quartz tube was employed. Rate data were obtained, using both techniques, not only under pseudo-first-order conditions but also free from the effects of secondary reactions. Stoichiometric conrrections were thus not applied to the derived rate constants. The results at twelve temperatures yield a linear Arrhenius plot that is described by the expression: k 1 (T)=(2.01±.34)×10 −10 exp (−10799±222/RT) cm 3 molec −1 s −1 . This result is compared to previous ones and an extrapolation to higher temperatures, based on a collision model, is discussed. Finally, the present data were combined with the shock tube results of Brabbs and Brokaw, and Roth and Just to obtain the following expression that fits the results of all three studies over the temperature range 475–2250 K: k 1 (T)=(5.24±.33)×10 −12 T 1/2 exp(−10290±108/RT) cm 3 molec −1 s −1 .

Identification of Elastomers in Tire Sections by Total Thermal Analysis. IV. Innerliner

Abstract Butyl and halogenated butyls are clearly indicated by both DSC and DTG in nitrogen. Binary NR/CIIR blends are also easily characterized by combined DSC and DTG techniques. In ternary SBR/CIIR/NR blends, only CIIR and NR show up in DTG curves when SBR occurs as a minor component. Minor indication of SBR is obtained from DSC curves. Thermal methods fail to distinguish between BUR and CIIR. In elastomer blends, DTG peak temperatures may vary over a wide range depending on the type of the second elastomer. The NR peak temperature (365°C), for example, is lowered by blending with SBR, BR (345–350°C) or CR (325–348°C). These latter elastomers degrade by exothermic reaction. An increase in peak temperature was observed in association with the polymers which degrade by endothermic reaction (EPDM, 369–374°C; CIIR, 373–377°C). This may be caused by abstraction of heat by the second elastomer in the overall decomposition process. Another important conclusion drawn from the blends studies in this series is that thermal stability of the polymers is not materially affected by the presence of another polymer, thus giving rise to the weight-loss peaks at well-defined temperatures, characteristic of each polymer. Thermooxidative stability, however, is very much dependent on the type and composition of the polymers present. The effect of secondary reactions on the degradation curves is also considerably greater in the oxidizing atmosphere. Thermooxidative degradation is very much dependent on sample size, characteristic of a diffusion-controlled reaction. However, it provides auxiliary evidence for idsntification. Except for SBR/BR blends, which show a single Tg changing with composition, all other elastomer blends show transitions at the respective temperatures, indicating the inherent incompatibility of elastomers. However, a second or third transition is not observed when (a) the proportion of the polymer is too small and (b) Tg'a are too close to each other. Thus, obtaining a single glass transition temperature in a polymer blend is not always a proof of its compatibility, as has been claimed so often.

Evaluation of the effect of secondary reactions in controlled potential coulometry.

Evaluation of the effect of secondary reactions in controlled potential coulometry.