KINETICS AND MECHANISMS OF THE PYROLYSIS OF n-BUTANE: PART II. THE REACTION INHIBITED BY NITRIC OXIDE

1963 ◽  
Vol 41 (4) ◽  
pp. 848-857 ◽  
Author(s):  
N. H. Sagert ◽  
K. J. Laidler
Keyword(s):  
Nitric Oxide ◽  
Main Chain ◽  
Frequency Factor ◽  
Radical Mechanism ◽  
Quantitative Interpretation ◽  
Kcal Mole ◽  
Free Radical Mechanism ◽  
Initiation Step ◽  
Kinetics Of ◽  
Short Induction Period

The kinetics of the pyrolysis of n-butane, when maximally inhibited by nitric oxide, were studied at temperatures from 540° to 610 °C, and at pressures from 30 to 550 mm Hg. The reaction has a short induction period and is accurately of the three-halves order; the activation energy was 65.9 kcal mole−1 and the frequency factor 5.3 × 1016 cc1/2 mole−1/2 sec−1. The reaction was somewhat less inhibited by surface than was the uninhibited reaction. Excess of carbon dioxide had no effect on the rate. The results are explained in terms of a free-radical mechanism for the maximally inhibited decomposition. It is proposed that the initiation step in the inhibited decomposition is mainly C4H10 + NO → C4H9 + HNO. This is followed by the ordinary chain-propagating reactions, and by processes such as C2H5 + NO → C2H5NO. The main chain-terminating step, of the type β + βNO, is concluded to be C2H5 + C2H5NO → C4H10 + NO or C2H6 + C2H4 + NO. This scheme leads to three-halves-order kinetics, and provides a satisfactory quantitative interpretation of the experimental behavior.

KINETICS AND MECHANISMS OF THE PYROLYSIS OF n-BUTANE: PART I. THE UNINHIBITED DECOMPOSITION

1963 ◽  
Vol 41 (4) ◽  
pp. 838-847 ◽  
Author(s):  
N. H. Sagert ◽  
K. J. Laidler
Keyword(s):  
Activation Energy ◽  
Surface Effect ◽  
Frequency Factor ◽  
Radical Mechanism ◽  
Free Radical Mechanism ◽  
Surface Catalysis ◽  
Initiation Reaction ◽  
Pressure Changes ◽  
Ethyl Radicals ◽  
Kinetics Of

The kinetics of the pyrolysis of n-butane have been studied at temperatures from 520° to 590 °C, and at pressures from 30 to 600 mm Hg; the rate was followed from pressure changes and by gas chromatography. The reaction was accurately of the three-halves order; the activation energy was found to be 59.9 kcal mole−1, and the frequency factor 3.24 × 1015 cc1/2 mole−1/2 sec−1. The reaction is sensitive to surface; packing the vessel and 'conditioning' it usually led to a decrease in rate and an increase in activation energy. The reaction is concluded to be largely homogeneous, and to occur almost entirely by a free-radical mechanism; the initiation reaction is considered to be the dissociation of a butane molecule into two ethyl radicals, in its first-order region, and termination is believed to be the second-order combination of ethyl radicals. The mechanism proposed is shown to account satisfactorily for the observed behavior. The surface effect is attributed to a certain amount of initiation by abstraction, by a surface atom, of a hydrogen atom from butane, and to surface catalysis of the recombination of ethyl radicals.

Copper Catalyzed Autoxidation of Sulphur Dioxide and Inhibition by Methanoic Acid

2020 ◽  
Vol 10 (1) ◽  
pp. 33-46
Author(s):  
Arun Kumar Sharma ◽  
Devarkonda Satay Narayan Prasad
Keyword(s):  
Acid Rain ◽  
Atmospheric Chemistry ◽  
Harmful Effect ◽  
Frequency Factor ◽  
Rain Water ◽  
Radical Mechanism ◽  
Gravimetric Analysis ◽  
Free Radical Mechanism ◽  
Organic Inhibitors ◽  
Methanoic Acid

Background:: Today, acid rain problem is one of the serious global problems to the environment in which pH of the rain water decreases, causing harmful effect to nature, buildings, monuments, vegetation and human being as well. Therefore, the objective of the paper to find out some organic inhibitors present in the atmosphere that inhibited the acid rain. Objective:: In this paper, we studied the chemistry of Cu (II)-methanoic acid-S(IV)-O2 in acetate buffered medium by earlier reported methods in literature. Gravimetric analysis was carried out to find the end product and confirmed that it was sulphate with 98 % recovery. Methods:: Experiments were carried out at 303 ≤ T/K ≤ 313, 4.0 ≤ pH ≤ 5.35, 1.0×10−3 mol/dm3 ≤ S(IV) ≤ 10.0×10−3 mol/dm3, 5×10−6 mol/dm3 ≤ [Cu(II)] ≤ 2.5×10−5 mol/dm3, 6×10−6 mol/dm3≤[methanoic acid]≤7×10-4 mol/dm3. The value of apparent activation energy and inhibition parameter B was calculated in the presence of methanoic acid found as 29.07 kJ mol-1and 3.18 x 103 mol dm-3, respectively. The thermodynamic parameters were found as frequency factor (1.59 x 10-6s-1), entropy (-358.92 J K-1 mol-1), enthalpy (20.97 k J mol-1), and Gibbs free energy (172.83k J mol-1), respectively. Results:: We observed that methanoic acid acts as an inhibitor in copper catalyzed autoxidation of SO2 in acidic medium. Therefore, on the basis of the observed results a free radical mechanism has been identified. The results are useful for modeling rain water acidity and therefore a great use of meteorology and atmospheric chemistry. This study is important in understanding the mechanism of the oxidation of S(IV) by O2. Conclusion:: This study suggests that since organic inhibitors are found in the atmosphere, their concentrations and their influence on the oxidation of aqueous SO2 should be taken into account. The intervention of methanoic acid in the autoxidation of aqueous SO2 plays a role in deciding the fate of both methanoic acid and SO2. The influence of inhibitors may be used to calculate the lifetime of SO2, Methanoic acid has high values of kinh and, therefore, it would be degraded by sulfate radical anions in atmospheric waters.

The kinetics of the oxidation of ammonia by nitrous oxide

1964 ◽  
Vol 17 (2) ◽  
pp. 202 ◽  
Author(s):  
TN Bell ◽  
JW Hedger
Keyword(s):  
Thermal Decomposition ◽  
Nitrous Oxide ◽  
Free Radical ◽  
Rate Equation ◽  
Radical Mechanism ◽  
15N Isotope ◽  
Free Radical Mechanism ◽  
Products Of Reaction ◽  
Kinetics Of ◽  
Decomposition Of Nitrous Oxide

Ammonia is oxidized by nitrous oxide smoothly and homogeneously at temperatures between 658 and 730� and total pressures up to 250 mm. The products of reaction, nitrogen, water, and hydrazine are accounted for by a free-radical mechanism initiated by oxygen atoms which result from the thermal decomposition of nitrous oxide. Ammonia labelled with the 15N-isotope was used to distinguish between the nitrogen formed from the nitrous oxide and that from the ammonia. The kinetics follow an empirical rate equation, ������������� Rate = k'[N2O]1.56 + k"[N2O]0.61[NH3]. This is of a form which shows the importance of the ammonia molecule participating in the activation of nitrous oxide through bimolecular collision. Assigning a collisional efficiency of unity for like N2O-N2O collisions, the efficiency of ammonia in the process ������������ NH3 + N2O → NH3 + N2O* is determined as 0.85.

The pyrolysis of propylene

1967 ◽  
Vol 300 (1460) ◽  
pp. 120-139 ◽  
Keyword(s):  
Main Chain ◽  
Initial Pressure ◽  
Pressure Change ◽  
Chain Termination ◽  
Radical Mechanism ◽  
Reaction Products ◽  
Secondary Products ◽  
Free Radical Mechanism ◽  
Chain Termination Reaction ◽  
The Many

Detailed analyses of the reaction products of the pyrolysis carried out in the temperature range 555 to 640°C, at initial pressures between 7 and 300 mmHg, and measurements of overall pressure change have shown that the overall pyrolysis may be described by the expression -d[C 3 H 6 ]/d t = 10 14.06 [C 3 H 6 ] 1.4 exp (-58600/ RT ) mole ml. -1 s -1 . Twenty three primary and three secondary products of the pyrolysis at 600°C and an initial pressure of 103 mmHg have been determined at six extents of reaction up to 12%. On the basis of these measurements a long chain free radical mechanism is proposed in which reactions of the 1-methyl-4-pentenyl radical are of prime importance. The main chain termination reaction is found to be combination of methyl and allyl radicals. It is concluded that radical combination reactions involving allyl are considerably slower than those involving alkyls. Steady-state treatment of the data is precluded by their complexity. Speculative routes to the formation of the many higher products are suggested.

The kinetics of the thermal polymerization of acetylene

1957 ◽  
Vol 242 (1231) ◽  
pp. 411-429 ◽  
Keyword(s):  
Nitric Oxide ◽  
Chain Length ◽  
Thermal Polymerization ◽  
High Rate ◽  
Polymerization Reaction ◽  
Radical Mechanism ◽  
Radical Chain ◽  
The Mean ◽  
Direct Hydrogenation ◽  
Kinetics Of

The thermal reactions of acetylene in Pyrex tubes at 352 to 472°C have been studied by analysis of the amounts of acetylene and the simpler products at definite time intervals; the mean composition of the polymer was also found from pressure measurements com­bined with the analytical results. Increase in surface area caused a marked increase in the rate of the reaction. By comparing the results obtained in normal and packed tubes, the kinetics of both the homogeneous and the surface reactions have been elucidated. The former is almost entirely a polymerization reaction, and is second order with a velocity constant k = 3.72 x 10 13 e -50 200/ RT . Nitric oxide (0.3%) completely inhibits this reaction, which is a radical process with a chain length of about 100. The polymer is initially C 4 H 4 , and the mean molecular weight increases slowly as the reaction proceeds. A radical chain mechanism with a high rate of chain transfer is proposed. The surface reaction is first order with respect to the acetylene concentration in the gas phase, with an activation energy of 42.7 kcal, and is also completely inhibited by nitric oxide (25%), the chain length being about 5. The mean initial composition of the polymer from this reaction is C 4 H 2.8 ; hydrogen and ethylene are also important products. A radical mechanism is proposed for the formation of polymer and hydrogen; the ethylene is considered to come from direct hydrogenation of acetylene. The kinetics of the reaction between nitric oxide and acetylene, which is largely heterogeneous, have also been studied.

Derivation of rate constants for steps in the free-radical chain decomposition of paraffins

1962 ◽  
Vol 268 (1332) ◽  
pp. 36-45 ◽  
Keyword(s):  
Nitric Oxide ◽  
Free Radical ◽  
Rate Constants ◽  
High Pressures ◽  
Radical Mechanism ◽  
Methyl Radicals ◽  
Saturated Hydrocarbons ◽  
Radical Chain ◽  
Free Radical Mechanism ◽  
Standard Values

The Rice-Herzfeld free-radical mechanism for the thermal decomposition of saturated hydrocarbons, including both the uninhibited reaction and that partially inhibited by nitric oxide, involves the rate constants of various individual steps. If standard values are assumed for the rate constants of H -abstraction from n -pentane by methyl radicals, alkyl radical recombination, and addition of methyl to nitric oxide, then those of all the steps for a series of paraffins can be found. The method depends on measurements of the rate constant in the region where the chain reaction is of the first order, the inhibitory action of nitric oxide as a function of paraffin pressure, and the acceleration of paraffin decomposition rate produced by high pressures of nitric oxide. Values are derived for propane, three pentanes ( neo -, iso - and normal pentane) and three octanes ( normal octane, 2:3:4-trimethyl pentane and 2:2:4-trimethyl pentane), and the variations of the several rate constants with structure are discussed.

Kinetics of the gas-phase oxidation of methanol catalysed by nitric oxide

1964 ◽  
Vol 17 (2) ◽  
pp. 172 ◽  
Author(s):  
JJ Batten
Keyword(s):  
Nitric Oxide ◽  
Pressure Change ◽  
Product Distribution ◽  
Published Data ◽  
Static System ◽  
Oxides Of Nitrogen ◽  
Kcal Mole ◽  
Oxidation Of Methanol ◽  
Gas Phase Oxidation ◽  
Kinetics Of

The oxidation of methanol catalysed by nitric oxide has been studied in a static system in the temperature range 300-400°. The kinetics and product distribution were compared with previously published data on the uncatalysed reaction and shoum to dlffer significantly. The reaction vessel was of Pyrex glass and the maximum rate was found to be sensitive to the condition of its surface. The rate of pressure change was shown to be a valid measure of the reaction rate which accelerated rapidly to a maximum, remained constant for some time, and then decreased slowly. The overall activation energy was about 8 kcal mole-1 in the range 300-330°, and 25 kcal mole-1 between 360 and 400°. At 310° (d(Δp)/dt)max. ∝ [CH3OH]00.4[O2]0-1 [NO]01.7 and at 380° (d(Δp)/dt)max. ∝ [CH3OH]00.75[O2]0-1 [NO]00.75 provided that [O2]0 < [CH3OH]0 = 100 mmHg. At [O2]0 > [CH3OH]0, the maxi- mum rates were approximately independent of [O2]0 The pressure of the product, formaldehyde, always rose to a maximum and then decayed in the later stages of an experiment. Oxides of nitrogen appear to participate in the chain reaction.

Kinetics and mechanisms of the thermal decomposition of propane II. The reaction inhibited by nitric oxide

1962 ◽  
Vol 270 (1341) ◽  
pp. 254-266 ◽  
Keyword(s):  
Nitric Oxide ◽  
Volume Ratio ◽  
Inflexion Point ◽  
Kcal Mole ◽  
Large Excess ◽  
First Order ◽  
Partial Pressures ◽  
Pressure Time ◽  
Initiation Reaction ◽  
Kinetics Of

The kinetics of the pyrolysis of propane inhibited by nitric oxide were investigated from 640 to 560 °C and at partial pressures of propane from 25 to 550 mm Hg. The pressure-time curves were found to be S-shaped, and the induction period was lengthened considerably as the propane pressure was lowered. Complete inhibition by nitric oxide was obtained with 10 to 12% nitric oxide. The initial rates were found to be proportional to the 3/2 power of the pressure over most of the temperature range, and to a slightly lower power at the highest temperatures. The orders of reaction corresponding to the inflexion point are close to unity at the highest temperatures, and increase steadily as the temperature is lowered. The activation energy calculated from the inflexion rates in the first-order region was 69.4 kcal/ mole. The rates decreased with an increase in the surface to volume ratio. The addition of a large excess of carbon dioxide had no effect on the fully inhibited rates. The results are shown to be consistent with a mechanism in which the initiation reaction involves the abstraction of a hydrogen atom from propane by nitric oxide, and in which the termination reaction is between HNO and a propyl radical.

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