Gaseous Product Distribution in Hydrocarbon Pyrolysis

Abstract

ARLIER studies of hydrocarbon pyrolysis (12, 14, 4 6 ) were E usually conducted at temperatures below 650" C. (1202" F.), or, when higher temperatures were used, at extremely short reaction times, t o obtain data suitable for kinetic interpretation. Because of the emphasis given to these relatively mild pyrolysis conditions, the interpretation of results generally stressed dissimilarity in the behavior of individual or groups of hydrocarbons. However, except in the production of acetylene, practical operating conditions for hydrocarbon pyrolysis fall in the temperature range of 1200" t o 2000" F. at reaction time well above 0.1 second.In this range of pyrolysis conditions the gaseous product distribution for most feed hydrocarbons other than methane shows a striking similarity, only slightly affected by the composition, structure, or molecular weight of the feed hydrocarbon when cracked at equivalent temperatures, reaction times, and partial pressures (14, 28).I n the first part of this study, empirical relationships for the prediction of gaseous product distribution are developed for a wide range of feed hydrocarbons by the use of a simple and general approach t o the analysis of the behavior of the complex gaseous reaction systems encountered in high-temperature, vapor-phase cracking. Pyrolysis data show similiar gaseous product distributionsPrevious studies have shown that hydrocarbons of equal carbon-hydrogen weight (C/H) ratio will yield approximately equal quantities of gas of similar composition (26-28, $3) independently of their molecular weight or structure as long as the severity of cracking is sufficient to eliminate the effects of the primary decornnosition reactions. The composition, although not the total yield, of the nongaseous products was shown to be affected by feed hydrocarbon properties other than carbon-hydrogen ratio because of the tendency of feed hydrocarbons of higher molecular weight t o form nongaseous cracking products through primary reactions-that is, those specific to the feed hydrocarbons, such as dehydrogenation, cyclization and dehydrocyclization, and polymerization.As illustrated in Table I, the influence of carbonhydrogen ratio on gaseous product distribution is small for natural gas liquids, and for petroleum and shale oils, so that only minor changes in cracking conditions will compensate for the tendency of hydrocarbons of higher carbon-hydrogen ratio to form gases of higher hydrogen content and higher paraffinolefin ratio (26, 28). This similarity in gaseous product distribution tends to be masked by the relatively slow rates of the primary cracking reactions for hydrocarbons of low molecular weight such as methane, ethane, and ethylene.From the data on pyrolysis obtained in this and earlier studies, any reaction schemes attempting t o interpret gaseous product distributions-by the assumption of dehydrogenation or carbon-carbon bond scission reactions specific to a given hydrocarbon (14, 38) did not appear applicable for reaction temperatures above 1300' F. and reaction ti...

Coke Formation during Thermal Cracking of n-Octane

“…(C) Severity Correlation of the Rate Data. Because of the lack of knowledge of an exact mechanism of cracking of hydrocarbons, yields of products from cracking furnaces have often been correlated by a severity factor (Linden and Peck, 1955;White et al, 1970). For the present study the severity factor is defined as S = TmTn where T is the absolute temperature (K) and is the space time (seconds).…”

“…Because of the lack of knowledge of' an exact mechanism of cracking of hydrocarbons, yields of products from cracking furnaces have often been correlated by a severity factor (Linden and Peck, 1955;White et al, 1970). Because of the lack of knowledge of' an exact mechanism of cracking of hydrocarbons, yields of products from cracking furnaces have often been correlated by a severity factor (Linden and Peck, 1955;White et al, 1970).…”

Thermal Cracking of n-Nonane

“…Due to the lack of data on intermediate free radical reactions, it is not yet possible to postulate a detailed step-by-step free radical mechanism for the cracking of large hydrocarbons. To overcome this, products from cracking furnaces usually have been correlated with the so-called severity function (Schultz, 1954;Linden et al, 1955;White etal., 1970).…”

Computer simulation of an industrial ethane-cracking furnace operation

“…Experts launched the Severity factor instead that is a simple method for complex pyrolysis reaction-system, which was introduced by Linden and Peck [12] 06 , 0 τ ⋅ = t S (6) Modeling: To build-up the furnace model, a simulation program is also needed. According to this, the strategy of the calculation of reactor processes with the application of modeling programs in the construction of computer models for complete flowsheets of industrial chemical processes consists of the following:…”