Autoignition of Hydrocarbons

Heavy hydrocarbons, such as vacuum tower bottom products, tar, and pitch, are frequently pumped and stored in tanks above their autoignition temperatures. The process reason for this is to prevent these fluids from setting up or solidifying in the pipelines or tanks. At ambient temperatures, even in hot climates, these fluids would normally be either solid or extremely viscous. 

Sections of piping that contain a pair of alternate 90-degree elbows or alternate right-angled bends are hazardous. These should be avoided when designing pipe work because  

Outages and some serious incidents have occurred as a result of the use of this type of piping configuration (see Fig. 38.2). 

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M.P. Halstead, L.J. Kirsch and C.P. Quinn, The Autoignition of Hydrocarbon Fuels at High Temperatures and Pressures Fitting of a Mathematical Model, Comb, and Flame 30 (1977) 45-60. 

N. Blin-Simiand, R. Rigny, V. Viossat, S. Circan and K. Sahetchian, Autoignition of Hydrocarbon/Air Mixtures in a CFR Engine Experimental and Modeling Study, Comb. Sci. Tech. 88 (1993) 329. 

D. Bradley and J. Yeo, A Five-Equation, Four Species Scheme for Modelling Autoignition of Hydrocarbons, Proceedings of the Anglo-German Combustion Symposium 1993 (British Section of the Combustion Institute, 1993) p. 356. 

M. Halstead, L. Kirsh, and C. Quinn. The autoignition of hydrocarbon fuels at high temperatures and pressures - fitting of a mathematical model. Combust. Flame, 30 45-60, 1977. 

Autoignition temperature of hydrocarbons decreases with the length of the hydrocarbon chain. 

Diesel fuel is produced by distilling raw oil, which is extracted from bedrock. Diesel is a fossil fuel, consisting of hydrocarbons with between 9 and 27 carbon atoms in a chain, as well as a smaller amount of sulfur, nitrogen, oxygen and metal compounds. It is a general properly of hydrocarbons that the autoignition temperature is higher for more volatile hydrocaibons. The hydrocarbons present in the diesel fuels include alkanes, naphthenes, olefins and aromatics. 

The first attempts to understand quantitatively the high-temperature chemical processes were related to combustion. They took place in the first part of the last century, partly with the development of thermal theories and theories for chain reactions and partly with work on high-temperature oxidation of hydrocarbons (to understand flame propagation) and low-temperature oxidation (to understand autoignition and knock in internal combustion engines). 

Conversion of the original hydrocarbon to other compounds appears to be extensive in the reactions preceding autoignition, as found in one investigation in which 70% or more of the inducted n-heptane was degraded to other products prior to autoignition (105). Hydrocarbon structure has an important bearing on the amount of conversion,... 

The photo-oxidation of n-butane has been modelled by ab initio and DFT computational methods, in which the key role of 1- and 2-butoxyl radicals was confirmed.52 These radicals, formed from the reaction of the corresponding butyl radicals with molecular oxygen, account for the formation of the major oxidation products including hydrocarbons, peroxides, aldehydes, and peroxyaldehydes. The differing behaviour of n-pentane and cyclopentane towards autoignition at 873 K has been found to depend on the relative concentrations of resonance-stabilized radicals in the reaction medium.53 The manganese-mediated oxidation of dihydroanthracene to anthracene has been reported via hydrogen atom abstraction.54 The oxidation reactions of hydrocarbon radicals and their OH adducts are reported.55... 

Egolf, L.M. and Jurs, P.C. (1992). Estimation of Autoignition Temperatures of Hydrocarbons, Alcohols and Esters from Molecular Structure. Ind.Eng.Chem.Res., 31,1798-1807. 

Horning, D. C. 2001. A study of the high-temperature autoignition and thermal decomposition of hydrocarbons. Ph.D. Thesis. Stanford, CA Stanford University. 

Ethylene - An alkene (unsaturated aliphatic hydrocarbon) with two carbon atoms, CH2=CH2. A colorless, highly flammable gas with a sweet odor. Autoignition point 543°C. Derived by thermal cracking of hydrocarbon gases or from gas synthesis. Used as monomer in polymer synthesis, refrigerants, and anesthetics. Also called ethene. 

Gas-phase thermal reactions and, more particularly, the oxidation of hydrocarbons exhibit a wide variety of macroscopic behaviour patterns slow reactions which are strongly inhibited or accelerated by the addition of small quantities of additives, cool flames and oscillations, isothermal explosions, two stage autoignitions, thermal explosions and flames. 

The oxidation of hydrocarbons at low temperatures, between 500 and 900 K, is of great importance as these reactions are responsible for the engine knock in spark-ignition engines and the autoignition of diesel fuel in Diesel engines and contribute to the formation of pollutants. 

Synonyms Heavy hydrotreated naphtha (petroleum) Hydrotreated heavy naphtha Naphtha, heavy hydrotreated Naphtha (petroleum), hydrotreated heavy Definition Complex combination of hydrocarbons obtained by treating a petrol, fraction with hydrogen in the presence of a catalyst consists predominantly of C6-13 hydrocarbons mixt. of C9-13 naphthenes, iso- and n-paraffins Properties Colorless liq. insol. in water dens. 0.76-0.79 g/cm vapor pressure 0.1-0.3 kPa (20 C) m.p. 0 C b.p. 155-217 C flash pt. (CC) 40-62 C autoignition temp. 255-270 C Toxicoiogy Inh. may cause dizziness, headache, drowsiness, nausea, unconsciousness contact may cause dry skin, eye redness ing. may cause cough, diarrhea, sore throat, vomiting if aspirated, may cause chem. pneumonitis Environmentai Toxic to aquatic organisms ... 

A special feature of the autoignition of many organic solvent vapours, including those from hydrocarbons, alcohols, ethers, aldehydes and acids is their ability to form cool flames at temperatures well below their autoignition temperature as measured in the standard apparatus [10]. A cool flame is a form of incomplete combustion, usually involving the formation of an unstable peroxide and its decomposition to an aldehyde. Cool flames emit a pale blue light which is visible only in the dark and on their own produce a relatively modest ca. 20-50 K) temperature rise, hence their name. The main hazard with cool flames lies in their potential for transition into true combustion, and that their products are often less stable and more reactive than the original compound. 

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