Effect of nitrogenous promotors on the low-temperature ignition lag of methane mixtures

Slutskii, V. G.

doi:10.1007/bf01463724

Cited by 4 publications

(5 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Without NO x , CH 4 −O 2 reactions proceed mostly (>90%) via H-abstraction from CH 4 using OH radicals (Figure a): with small contributions from H-abstraction by H radicals. With NO (5 kPa NO; Figure b), H-abstraction by OH also accounts for >90% of the CH 4 converted; abstraction by NO 2 (formed from NO) is involved in ∼4% of CH 4 conversion events: Reaction 3, however, provides an efficient route for activating C−H bonds during the initial induction period, − consistent with the shorter induction observed when NO 2 is used instead of NO; NO forms NO 2 during CH 4 −O 2 −NO reactions only after a finite residence time. Two maxima in CH 4 conversion rates occur with NO (5 kPa NO; at ∼0.4 s and ∼2.7 s); the latter one reflects CH 3 O dissociation to HCHO and H, as NO x is depleted with increasing residence time.…”

Section: Resultsmentioning

confidence: 62%

“…Reaction 3, however, provides an efficient route for activating C-H bonds during the initial induction period, 40 HCHO formation rates are shown in Figure 5 at 873 K for equimolar CH 4 -O 2 mixtures with 0 kPa (a) and 5 kPa (b) NO. Without NO, HCHO forms predominantly via These steps account for 95% of the HCHO molecules formed.…”

Section: Pathways For Hcho Synthesis and Consumption With And Without Nomentioning

confidence: 97%

“…Without NO x , CH 4 -O 2 reactions proceed mostly (>90%) via H-abstraction from CH 4 using OH radicals (Figure 4a): with small contributions from H-abstraction by H radicals. With NO (5 kPa NO; Figure 4b), H-abstraction by OH also accounts for >90% of the CH 4 converted; abstraction by NO 2 (formed from NO) is involved in ∼4% of CH 4 conversion events: Reaction 3, however, provides an efficient route for activating C-H bonds during the initial induction period, [40][41][42] which account for 22% and 5%, respectively, of all HCHO formed. Tabata et al 17,34 suggested that NO x provides faster routes for CH 3 O conversion to HCHO.…”

Section: Simulations Of Nomentioning

confidence: 99%

See 2 more Smart Citations

NO_x-Mediated Homogeneous Pathways for the Synthesis of Formaldehyde from CH₄−O₂ Mixtures

Zalc

Green

Iglesia

2006

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

A detailed kinetic network for homogeneous CH 4 -O 2 -NO x reactions is used to estimate maximum attainable formaldehyde (and methanol) yields and to identify elementary steps that lead to the observed enhancement effects of NO x on CH 4 oxidation rates, to HCHO yield limits, and to NO x losses to unreactive N-compounds. NO x was shown previously to increase CH 4 oxidation rates and HCHO yields in CH 4 -O 2 reactions, but maximum yields were low (<10%) and intrinsic kinetic limits were not rigorously examined. We show here that the CH 4 oxidation rate increases because NO 2 reacts with CH 4 during an initial induction period. NO and NO 2 lead to similar effects, except that residence times required for a given yield are higher for NO feeds because NO-NO 2 interconversion must first occur. CH 4 leads to supra-equilibrium NO 2 concentrations because HO 2 formed during HCHO oxidation reacts with NO to form OH and NO 2 faster than NO 2 can decompose to NO. Oxygenate selectivities decrease with increasing CH 4 conversion, because weaker C-H bonds in HCHO and CH 3 OH relative to CH 4 lead to their fast sequential oxidation to CO and CO 2 . Rate-of-formation analyses show that NO x molecules introduce more effective elementary steps for the formation of CH 3 O intermediates and for its conversion to HCHO, but H-abstraction from CH 4 and HCHO remains the predominant step in controlling rates and selectivities in the presence or absence of NO x . Without NO x , OH radicals account for all H-abstraction reactions from CH 4 , while HCHO reacts with OH but also with less reactive H and HO 2 radicals. NO x increases HCHO yields by converting these less reactive H and HO 2 radicals to OH radicals, which become the predominant H-abstractor for both CH 4 and HCHO and which react less selectively with HCHO than do H and HO 2 . Kinetic selectivity, based on C-H bond energy differences between CH 4 and HCHO, becomes weaker with increasing radical reactivity and increasing reaction temperature. Maximum HCHO yields of 37% are theoretically possible for radicals that abstract H from CH 4 and HCHO at equal rates, but radical species prevalent during CH 4 -O 2 -NO x reactions lead to maximum HCHO yields below 10% under all conditions. Higher yields appear unlikely with more reactive radicals, because their reactivity would lead to cascade reactions that form species with greater kinetic sensitivity to C-H bond energies. Maximum C 1 -oxygenate yields increase with increasing O 2 pressure, suggesting that the O 2 distribution along a reactor will not improve HCHO yields but may prove useful to inhibit NO x losses to less reactive N-compounds.

show abstract

Section: Resultsmentioning

confidence: 62%

Section: Pathways For Hcho Synthesis and Consumption With And Without Nomentioning

confidence: 97%

Section: Simulations Of Nomentioning

confidence: 99%

See 1 more Smart Citation

NO_x-Mediated Homogeneous Pathways for the Synthesis of Formaldehyde from CH₄−O₂ Mixtures

Zalc

Green

Iglesia

2006

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

show abstract

“…While there is no experimental value available for the calculated activation energy to compare with directly, the values of related systems can be obtained. The activation energy of H-abstraction of nitro with CH 4 was 120–126 kJ/mol, , and for the reaction of nitro with propane, the activation energy was reported to be 95–126 kJ/mol. , It is found that the DFT results are close to experimental analogues. As indicated in Table , the activation energies for the three possible reaction pathways are predicted to be in the order 6C 1 > 6C 3 > 6C 2 , which agrees with the calculated results of Chan et al By comparing alkyl radicals acting on n -heptane, nitro abstracting an H atom from n -heptane is characterized with higher activation energy by about 50 kJ/mol.…”

Section: Resultsmentioning

confidence: 78%

Section: Further Reaction Of N-propylmentioning

confidence: 99%

Kinetic Modeling of the Free-Radical Process during the Initiated Thermal Cracking of Normal Alkanes with 1-Nitropropane as an Initiator

Guan

Yang

et al. 2011

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

To elucidate the accelerating effect of 1-nitropropane on the thermal cracking of normal alkanes, ab initio and density functional theory calculations were performed to investigate the elementary reactions involved in the initiated thermal cracking of a 1-nitropropane/n-heptane mixture. The kinetic parameters were evaluated on the basis of standard transition state theory (TST) or variational transition state theory (VTST) with Wigner tunneling correction. The activation energy for the C–N bond rupture of 1-nitropropane to produce primary n-propyl and nitro radicals is calculated to be 234–269 kJ/mol, while the bond dissociation energy of the C–C bond within the n-heptane molecule is predicted to be at least 335 kJ/mol. These calculated results demonstrate that the presence of 1-nitropropane makes the free radical formation become relatively easier compared with single n-heptane cracking. Furthermore, compared with the C–H bond cleavage and 1,3-H intramolecular transfer, the unstable n-propyl radical mainly follows the C–C bond cleavage pathway to produce ethylene and secondary ĊH3 radical. After formation of these free radicals, the H-abstraction of n-heptane with radicals occurs readily with considerably lower activation energy than the radical formation step to initiate the chain reaction. The analysis result indicates that the thermal cracking of n-heptane is accelerated mainly due to the change of the initial step from the C–C bond cleavage of n-heptane to the C–N bond rupture of 1-nitropropane.

show abstract

Kinetics for the hydrogen‐abstraction of CH₄ with NO₂

Guan

Yang

2012

J Comput Chem

View full text Add to dashboard Cite

The detailed mechanism of the NO(2)+CH(4) reaction has been computationally investigated at the M06-2X/MG3S, B3LYP/6-311G(2d,d,p), and MP2/6-311+G(2df,p) levels. The direct dynamics calculations were preformed using canonical transition state theory with tunneling correction and scaled generalized normal-mode frequencies including anharmonic torsion. The calculated results indicate that the NO(2)+CH(4) reaction proceeds by three distinct channels simultaneously, leading to the formation of trans-HONO (1a), cis-HONO (1b), and HNO(2) (1c), and each channel involves the formation of intermediate having lower energy than the final product. The anti-Hammond behavior observed in channel 1a is well analyzed. Proper treatment of anharmonic torsions about the C···H···O (or N) axis in the transition structures greatly improves the accuracy of kinetics predictions. The activation energy for each channel increases substantially with temperature, but is not strictly a linear function of temperature. Therefore, the thermal rate constants are fitted to the four-parameter expression recommended for this case over the wide temperature range 400-4000 K.

show abstract

Effect of nitrogenous promotors on the low-temperature ignition lag of methane mixtures

Cited by 4 publications

References 7 publications

NO_x-Mediated Homogeneous Pathways for the Synthesis of Formaldehyde from CH₄−O₂ Mixtures

NO_x-Mediated Homogeneous Pathways for the Synthesis of Formaldehyde from CH₄−O₂ Mixtures

Kinetic Modeling of the Free-Radical Process during the Initiated Thermal Cracking of Normal Alkanes with 1-Nitropropane as an Initiator

Kinetics for the hydrogen‐abstraction of CH₄ with NO₂

Contact Info

Product

Resources

About

Effect of nitrogenous promotors on the low-temperature ignition lag of methane mixtures

Cited by 4 publications

References 7 publications

NOx-Mediated Homogeneous Pathways for the Synthesis of Formaldehyde from CH4−O2 Mixtures

NOx-Mediated Homogeneous Pathways for the Synthesis of Formaldehyde from CH4−O2 Mixtures

Kinetic Modeling of the Free-Radical Process during the Initiated Thermal Cracking of Normal Alkanes with 1-Nitropropane as an Initiator

Kinetics for the hydrogen‐abstraction of CH4 with NO2

Contact Info

Product

Resources

About

NO_x-Mediated Homogeneous Pathways for the Synthesis of Formaldehyde from CH₄−O₂ Mixtures

NO_x-Mediated Homogeneous Pathways for the Synthesis of Formaldehyde from CH₄−O₂ Mixtures

Kinetics for the hydrogen‐abstraction of CH₄ with NO₂