Thermodynamic Data For Reaction Research Articles

Study on the mechanism of free radical scavenger TEMPO blocking in coal oxidation chain reaction

The inhibitory effect of free radical scavenger 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) on the spontaneous combustion process of coal has been experimentally confirmed. However, the mechanism of free radical trapping in coal by TEMPO is not clear. This paper revealed the mechanism of free radical capture in coal by TEMPO from three perspectives by quantum chemistry method, including capture radicals directly, regenerative cycle chain and hydrogen transfer. It was regarded as a beginning that the formation of free radicals (R-CH2∙, CH3∙) by breaking alkane groups in the side chain of the coal molecule. The oxidation process of these free radicals was analyzed and the capturing models of radicals were described. The thermodynamic data for reactions (R2 ∼ R5) are calculated to reveal the initial reaction process of coal. The adsorption energy and thermodynamic data for reactions (Process1 ∼ 4, R6 ∼ R10, R12 ∼ R13) are computed to illustrate spontaneity and difficulty of traps free radicals by TEMPO. The results indicate that the initial reaction (R2, R4) of free radicals with oxygen in coal is exothermic and some other reactions (R3, R5) need to overcome large reaction energy barriers. TEMPO can capture free radicals in coal directly, reducing the concentration of free radicals, and is most effective in capturing ∙OH and alkyl radicals. At the same time, TEMPO can capture peroxide radicals and alkyl radicals in coal through regenerative cycle chains and keep reborn to maintain the efficiency of its capture. For coals under acidic conditions, TEMPO can bind to H+ first, then transfers hydrogen with oxygen-containing radicals in the coal. This process is prone to occur due to the presence of hydrogen bonds. In future applications, the pH value of TEMPO can be appropriately reduced to enhance the effect of capturing free radicals in coal.

Reaction pathways and cyclic chain model of free radicals during coal spontaneous combustion

Reactions of free radicals play essential roles in the evolution of the spontaneous combustion of coal. However, their elementary reaction pathways and details during this process have not been revealed by far. This paper established reaction pathways of free radicals during coal spontaneous combustion based on typical active free radicals by quantum chemistry method. The specific structural parameters and thermodynamic data for reactions (R1 ~ R9) are calculated to reveal the reaction process. The cyclic model of free radicals during coal self-heating has been proposed for the first time. The results indicate that most of the reactions involved in free radicals are exothermic reactions with heat release ranging from 7.568 ~ 167.113 kJ/mol. The initial reactions (R1 and R2) can accumulate heat and generate active peroxide free radical (R-O-O) as well as hydroxyl radical (OH). Both of them can occur easily at the normal temperature. The heat release increases the ambient temperature, which causes non-spontaneous reactions to proceed successively. The decomposition of peroxide free radicals triggers the reaction pathways of the cyclic model. The hydroxyl radical can lead to the reaction with active sites in coal, which can accumulate plenty of heat and supply the R for initiating reaction R(1) in the cycle. Both hydroxyl radicals and hydrocarbon radicals play vital roles in consuming active groups in coal and oxygen continuously. The results demonstrate that to fundamentally prevent coal spontaneous combustion, it is necessary to eliminate the key active free radicals (R, R-O-O, and OH) to terminate the cyclic chain reaction.

Sulfide catalysts for hydrogenating carbon monoxide

We use gas chromatography to identify and measure the amounts of carbonyl sulfide (OCS) formed in a gas-flow system via the net thermochemical reactionsSO2+3 CO=OCS+2 CO2 (1)3 FeS2(pyrite)+4 CO2+ 2 CO=Fe3O4(magnetite)+6 OCS (2)2 CO+S2=2 OCS (3)at temperatures of 470–612°C and ambient atmospheric pressure. The goal of our work is to evaluate the importance of reactions (1) to (3), which have been proposed as potential sources of OCS in Venus' lower atmosphere. Our results show OCS formation by reaction (3), but not by reactions (1) or (2) under our experimental conditions. Based on our results, experimental data from the literature, and theoretical models in the literature, we conclude that (1) the reaction of S2and CO is an important source of OCS in Venus' lower atmosphere, and (2) probably neither reaction (1) nor reaction (2) is an important source of OCS on Venus. Finally, we use thermodynamic data for reaction (3) and Venera spacecraft observations of CO and sulfur vapor at 0–12-km altitude to calculate an OCS equilibrium abundance of 1–14 ppmv, with a nominal value of 5 ppmv, for reaction (3) near Venus' surface.

Formation of Carbonyl Sulfide (OCS) from Carbon Monoxide and Sulfur Vapor and Applications to Venus

We use gas chromatography to identify and measure the amounts of carbonyl sulfide (OCS) formed in a gas-flow system via the net thermochemical reactionsSO2+3 CO=OCS+2 CO2 (1)3 FeS2(pyrite)+4 CO2+ 2 CO=Fe3O4(magnetite)+6 OCS (2)2 CO+S2=2 OCS (3)at temperatures of 470–612°C and ambient atmospheric pressure. The goal of our work is to evaluate the importance of reactions (1) to (3), which have been proposed as potential sources of OCS in Venus' lower atmosphere. Our results show OCS formation by reaction (3), but not by reactions (1) or (2) under our experimental conditions. Based on our results, experimental data from the literature, and theoretical models in the literature, we conclude that (1) the reaction of S2and CO is an important source of OCS in Venus' lower atmosphere, and (2) probably neither reaction (1) nor reaction (2) is an important source of OCS on Venus. Finally, we use thermodynamic data for reaction (3) and Venera spacecraft observations of CO and sulfur vapor at 0–12-km altitude to calculate an OCS equilibrium abundance of 1–14 ppmv, with a nominal value of 5 ppmv, for reaction (3) near Venus' surface.

ChemInform Abstract: BIMOLECULAR SELF‐REACTIONS OF PHENYL‐SUBSTITUTED PHENOXYL RADICALS STUDIED BY FLASH PHOTOLYSIS

AbstractDie Absorptionsspektren der Radikale (I) und (II) sowie die Kinetik, die Gleichgewichts‐ und thermodynamischen Daten ihrer Dimerenbildung werden 4untersucht.

Bimolecular self‐reactions of 2‐arylindandione‐ 1,3‐yl radicals studied by flash photolysis

AbstractKinetic and thermodynamic data for reaction (1) of certain C‐centered aromatic radicals (referred to in this paper by the numbers I to X) in chlorobenzene: equation image have been obtained. The k1 values of radicals varied between (1.1 ± 0.2) × 106M−1·sec−1 (radical VIII) and (3.6 ± 0.7) × 109M−1 sec−1 (radical VI) at 20°C. An investigation of the relationship between the recombination rates of radicals I–VIII and X and the solvent viscosity (mixture of toluene and dibutylphthalate, 0.6 < η < 18.4 cP) has shown that the recombination reactions involving radicals I–IV are limited by diffusion in solvents having a viscosity η> 10 cP and are activation reactions in solvents having a viscosity η < 10 cP. The recombination of radicals VIII and IX is an activation reaction, while that of radicals V–VII is diffusion‐controlled in the entire viscosity range. The recombination of radical X is limited, in the viscosity range of 18.4 to 2 cP, by intrusion into the first coordination sphere of the partner, the effect of viscosity on the radical X recombination rate in the specified range being the same as its effect on diffusion‐controlled reactions. The possible reasons of the discrepancies between the experimental fast recombination rate constants and the theoretical values calculated by the Debye–Smoluchowski theory are discussed. The equilibrium constant depends strongly on the nature of the substituent in the phenyl fragment: the substituents which increase unpaired electron delocalization in the radical intensify the dissociation of the respective dimer. Long‐wave absorption bands have been recorded for radicals I–X and their extinction coefficients obtained. Dimers I–V are thermo‐ and photochromic compounds.

Bimolecular self‐reactions of phenyl‐substituted phenoxyl radicals studied by flash photolysis

AbstractRate, equilibrium, and thermodynamic data for reaction (1) of 2,6‐diphenyl‐4R‐phenoxyl radicals, where R==OCH3 (I), Ph (II), OC2H5 (III), O‐n‐C18H37 (IV), and 2,6‐dicyclohexyl‐4‐phenylphenoxyl radical (V), equation image in various solvents are obtained. The k1 values of radicals I to V are within (5.5 ± 1.0) × 107‐(1.4 ± 0.3) × 109M−1·sec−1 in propanol. The solvent effect on k1 for radicals I and II was studied. The dimerization of radical I is diffusion‐controlled in all solvent studies. The dimerization of radical II is viscosity‐dependent but not diffusion‐controlled. Plots of k1 against ET have a V shape. Specific solvent–solute interactions are seeming to be responsible for numerical k1 values of radicals I and II. The solvent effect is more pronounced for “slow” dimerization of radicals II than for “fast” dimerization of radicals I. The minimum k1 values correspond to pyridine and chloroform. The reaction (1) rate strongly depends upon the composition of a chloroform (S)–cosolvent binary mixture. Besides reaction (1) the following reactions proceed in binary mixture: equation image (radical I, S‐CCL4 mixture) (radical II, S‐C6H14 mixture) (radical II, S‐CCL4 mixture)In all cases k16 ≪ k15. Factors influencing dimerization rates in strongly nonideal mixtures CH3OH‐CCL4 and CH3OH‐CHCl3 are discussed.

Reactions of the iso‐butyl radical during 1,1′‐azoisobutane pyrolysis

AbstractQuantitative analysis of the products formed in 1,1′‐azoisobutane pyrolyses in the temperature range of 553°–602°K has shown that the major reactions of the iso‐butyl radical are equation image Analysis of initial rate data gave log10k4/(kc)1/2(cm−3/2.mol 1/2.sec−1/2) = 7.54±0.44 − (136.5 + 4.8) kJ/mol/2.303RT, the Arrhenius parameters obtained being in good agreement with thermodynamic data for reaction (4). Measured values of ka/(kc)1/2 where ka is the rate constant of the reaction iC4H9 + AIB → iC4H10 +. AIB were consistent with published parameters determined by photolysis of 1,1′‐azoisobutane. Combination of photolysis and pyrolysis data gave log10 ka/(kc)1/2(cm3/2.mol−1/22.sec−1/2) = 3.68 ± 0.15 − (27.2 ± 1.2) kJ/mol/2.303RT. The crosscombination ratio for methyl and iso‐butyl radicals has been found to be 0.25, indicating that the geometric mean rule does not hold for methyl and iso‐butyl radicals.

四塩化珪素による金属珪化物の生成反応（第1報）四塩化珪素と鋼の反応

The chemical reactions of siliconizing of steel with silicon tetrachloride atmospheres were investigated. The effects of gas flow rate, temperature and time on weight change differed, whether the atmosphere was a reducing gas as hydrogen or neutral gas. The reaction rate of siliconizing of steel showed a discontinuity near 900°, and decreased rapidly by compound formation. On thermodynamic data of reactions between iron and silicon tetrachloride, the experimental results were discussed.