Pyrolysis and partial oxidation of n-butane

A gas-chromatograph network capable of the analysis of possible products in the gas-phase pyrolysis, oxidative pyrolysis, and partial oxidation of n-butane was developed. Low-molecular-weight paraffins, olefins, alcohols, esters, aldehydes, ketones, organic acids, carbon oxides, fixed gases, and water could be identified and measured in the parts-per-mi1lion range of product mixtures. The pyrolysis of n-butane was examined in tubular-flow, gold microreactors having lengths of twelve inches and an inside diameter of 0.0625 inch. Partial pressures of butane were varied from 0.5 to 12 psia, with the total pressure being maintained at fifteen psia by use of an argon diluent. Conversions of butane were less than 2.5 per cent. The overall rate of reaction of the butane was accurately described by kinetics of three-halves order. An average activation energy of 65 kcal mole^(-1) was observed. Approximately equal molar quantities of methane and propylene were observed in the products. Formation of ethane, ethylene, and hydrogen varied with temperature and concentration of butane. The pyrolysis varied only slightly in untreated and in acid-treated reactors. The influence of trace quantities of oxygen on moderate-temperature (500 to 600°C) pyrolysis of butane was investigated using gold microreactors having lengths of twelve inches and inside diameters of 0.0625 and 0.125 inch. Partial pressures of butane from one to twelve psia were used, with the total pressure being maintained at fifteen psia. Oxygen, present from 7 to 800 parts-per-million in the reactants, inhibited the overall pyrolysis rate and increased the olefin content of the product mixture which was predominantly paraffins and olefins. The investigation of the oxidative dehydrogenation of n-butane was also examined from 460 to 595°C. Concentration of oxygen in the reactants was varied from 0.04 to 1.0 per cent by volume. At the lower temperatures, isomers of butene, 1,3-butadiene, water, and carbon dioxide comprised over 97 per cent of the products. At higher temperatures, formation of the cracked products of the pyrolysis increased. The overall rate of the disappearance of n-butane was correlated on the basis of a power-law expression of three-halves order with respect to the butane and one-half order with respect to oxygen. The Arrhenius activation energy of the overall dehydrogenation of n-butane was 23.1 kcal mole^(-1) compared to a value of 65 kcal mole^(-1) for the pyrolysis. The partial oxidation of n-butane to oxygenated-organic products was totally suppressed at temperatures of 400 and 440°C for contact times of 20 seconds and less