La décomposition thermique du propane

Martin, René; Dzierzynski, M.; Niclause, Michel

doi:10.1051/jcp/1964610286

Cited by 12 publications

(15 citation statements)

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“…In contrast, results in Pyrex vessels after surface treatments with HF or deposition of KCI were identical to those obtained with clean Pyrex vessels (washed with nitric acid and then with water). Irreproducible results were obtained with magnesium perchlorate coatings, which were found to give off chlorine and oxygen, presumably to leave a mixture of MgO and MgCb This observation almost certainly explains Voevodsky's results for propane (14) with Mg(Cl04h surfaces, and is similar to that found by Ni clause et al (19) when preparing PbO surfaces from Pb(NO a h. Niclause et al (3,11) found that the initial rate in isopentane pyrolysis at 480°C and 25 mm Hg in Pyrex vessels was independent of Sj V in the range 0.8 to 12 cm-l , and that deposition of KCI or PbO had no significant effect on the rate. In quartz vessels at 490°C and isopentane pressures of 10 to 100 mm Hg, they found, however, a slight reduction in rate on increasing Sj V from 0.8 to 14 cm-1 (11) .…”

Section: Surface Effectssupporting

confidence: 81%

“…Similarly, erynes & Albright (17) found no effect on the rate of propane pyrolysis in the temperature range 600-750oe in untreated stainless steel flow tubes when SjV was changed by a factor of 2.6, but they observed significant wall effects after surface treatments with a variety of gases, notably oxygen. Finally, at 503°C, provided oxygen has been rigorously excluded, identical rates have been observed in vessels of quartz, of Pyrex, and of Pyrex coated with KCl (18), while similarly, surface pretreat ments with HF or with chromic acid followed by deposition of KCl or PbO have been shown to have no significant effect on the rate of propane pyrolysis at 546°e (19). This removal of oxygen is crucial, and in fact after laying down PbO by decomposition of Pb (N03h it is necessary to evacuate the vessel at high temperature for several days to remove all traces of oxygen and oxides of nitrogen (19).…”

Section: Surface Effectsmentioning

confidence: 82%

“…Finally, at 503°C, provided oxygen has been rigorously excluded, identical rates have been observed in vessels of quartz, of Pyrex, and of Pyrex coated with KCl (18), while similarly, surface pretreat ments with HF or with chromic acid followed by deposition of KCl or PbO have been shown to have no significant effect on the rate of propane pyrolysis at 546°e (19). This removal of oxygen is crucial, and in fact after laying down PbO by decomposition of Pb (N03h it is necessary to evacuate the vessel at high temperature for several days to remove all traces of oxygen and oxides of nitrogen (19). The balance of evidence clearly supports the view that above soooe at least.…”

Section: Surface Effectsmentioning

confidence: 82%

“…Rates in a conditioned packed vessel. however, are invariably lower than in the corresponding clean, packed vessel (19). Purnell & Quinn (9) also found that conditioning by prolonged pyrolysis of n-butane led to a significant fall in the rate of subsequent n-butane pyrolyses, and that the effect of successive conditioning was cumulative; after three conditionings, the rate in a Pyrex vessel was found to fall by about 40%.…”

Section: Surface Effectsmentioning

confidence: 99%

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Paraffin Pyrolysis

Leathard¹,

Purnell²

1970

Annu. Rev. Phys. Chem.

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Paraffin pyrolyses have occupied a central role in the development of gas kinetics: first, because of their great economic potential and, sec ondly, be cause their relative molecular simplicity has been thought to offer the pros pect of reasonably straightforward elucidation of the processes involved. Unhappily, for a long period the issues were totally confused by the results of inhibition experiments, notably those involving additions of NO or CaRs. The findings were widely, though not everywhere, taken to prove the occurrence of concurrent molecular and radical chain routes to decomposition. Belief in the validity of the arguments underlying such gaseous inhibitor action was so unquestioned that diagnostic use of inhibitors became standard practice and is stilI common. That there is, in fact, no significant molecular component in paraffin pyrolyses took long to establish but cannot now be questioned. The main body of evidence, accumulated mainly in the period 1957-1965, has already bee n reviewed in depth (1). Its validity has recently received strik ing confirmation in the observations of Martin, Niclause, and their co workers (2-4) that the pyrolyses of propane, of isobutane, and of isopen tane are effectively totally suppressed in PbO-coated vessels of high surface/ volume ratio (S/ V) if a trace of oxygen is present. Since molecular processes could hardly be inhibited in these conditions, it follows that the reactions are entirely free radical in nature.Most recent studies relate to reaction conditions within the ranges 400-625°C and 10 -700 mm Hg. The most comprehensive and reliable are in addi tion restricted to at most 10% decomposition and frequently to as little as 2% reaction. In the most detailed work, analytical measurements have been conducted down to about 0.0 1 % reaction in static systems. All in this field are now agreed that the reactions can basically be described in terms of Rice-Herzfeld radical chain mechanisms (15) and that, in general, chains are long. However, the increasing application of gas chromatography has re vealed that the appropriate Rice-Herzfeld scheme must always be extended and modified and that the complicating factors responsible may dominate the kinetic picture sufficiently that no very reliable predictions of order or rate parameters may be made from simple Rice-Herzfeld ideas. Thus, while par affin pyrolyses may be among the most simple, they are not necessarily

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Section: Surface Effectssupporting

confidence: 81%

Section: Surface Effectsmentioning

confidence: 82%

Section: Surface Effectsmentioning

confidence: 82%

Section: Surface Effectsmentioning

confidence: 99%

See 2 more Smart Citations

Paraffin Pyrolysis

Leathard¹,

Purnell²

1970

Annu. Rev. Phys. Chem.

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“…The initial rates of methane and ethylene production are thus multiplied by a factor larger than 5 Table I). …”

Section: Resultsmentioning

confidence: 99%

The hetero‐homogeneous pyrolysis of propane, in the presence or in the absence of dihydrogen, and the measurement of uptake coefficients of hydrogen atoms

Perrin¹,

Martin²

2000

Int J of Chemical Kinetics

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Propane pyrolysis is studied in the presence and the absence of dihydrogen between 743 and 803 K, in the propane pressure range 10-100 Torr, and at 20-254 Torr dihydrogen pressure. In unpacked Pyrex reactors, dihydrogen accelerates propane dehydrogenation and demethanation. The reaction is modeled by a conventional homogeneous free-radical chain mechanism.Propane pyrolysis is strongly inhibited by the walls of reactors packed with stainless steel, zirconium, or palladium foils. Adding dihydrogen to propane still increases the rates of product formation. The reaction in these packed reactors is modeled by the kinetic scheme proposed for the homogeneous reaction and by the heterogeneous process THE HETERO-HOMOGENEOUS PYROLYSIS OF PROPANE 341In the presence of dihydrogen, steps (w 2 ) and (Ϫw 2 ) are instantaneously at equilibrium. The latter system should be useful to study any reaction of hydrogen atoms in the temperature range.

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Kinetics of the nonisothermal pyrolysis of propane

Kershenbaum

Martin

1967

AIChE Journal

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A method was devised to yield chemical reaction kinetic parameters from nonisothermal, nonisobaric flow experiments. The system studied was the pyrolysis of propane a t high temperatures (800" to 1,OOO"C.). A t these temperatures the rates of the various reactions are so high that a batch or even an isothermal flow experiment is impossible. To keep the conversions low so that the initial stages of decomposition could be studied, the feed gas was diluted with varying amounts of nitrogen. Residence times in the reactor were in the millisecond range. The reactor exit gas was analyzed by mass spectrometry. The method developed in this work is not limited to simple kinetic studies, but can be useful in complicated series and parallel reactions which often require nonisothermal conditions.As reaction temperatures are raised, it becomes increasingly difficult to measure kinetic rate constants experimentally. In this work, the pyrolysis of propane was studied at 800" to 1,OOO"C. where the reactions are extremely rapid. Furthermore, the products of reaction themselves decompose under these conditions, tending to mask the primary kinetics. Conversions, therefore, were kept low through the use of a steady state flow system, where residence times can be shorter than in batch systems; the concentration of the reaction products was minimized by diluting the feed gas with nitrogen to about 5% propane.The extent of this dilution was limited however, because the higher the concentration of diluent and the lower the conversion, the more difficult becomes the exit gas analysis.Since rate constants are strongly dependent upon temperature, it would be most convenient to conduct kinetic experiments isothermally. However, because of the low residence times required and the physical limitations on heat transfer rates, a 'nonisothermal experiment results. Some previous workers have chosen an equivalent, average temperature for all or a fraction of the reactor, but this procedure leads to only partially satisfactory results. An alternative is to measure the gas temperature profile throughout the reactor and to devise some method of treating the data to yield the desired rate constants. Such was the method used in this study.Once the rate constants are obtained as functions of temperature, the kinetic model can be programmed on an analog computer; it is then possible to test the consistency of the data and to predict product distributions, conversions, etc., for any arbitrary set of conditions. This is extremely valuable if similar studies are made for the other low hydrocarbons which are products of propane pyrolysis. Then the entire series could be studied simultaneously; that is, product distributions could be predicted not only for the simple case of low conversions but also for the more complicated cases of consecutive reactions where reaction products themselves react further.There is much ublished information in the literature in general and propane in particular. While much kinetic work has been done with propane at lower temperatu...

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La décomposition thermique du propane

Cited by 12 publications

References 0 publications

Paraffin Pyrolysis

Paraffin Pyrolysis

The hetero‐homogeneous pyrolysis of propane, in the presence or in the absence of dihydrogen, and the measurement of uptake coefficients of hydrogen atoms

Kinetics of the nonisothermal pyrolysis of propane

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