Mechanism of Formation of Aromatics from Lower Paraffins^1,2

Equilibrium constants of some reactions involved in the production of 1,3-butadiene

“…In the pyrolysis of ethylene at .725° C (1,000° ~ K) Schneider and Frolich [56] found that 72 per-~l cent of the product initially formed is C4H 6 and ..t H 2. According to these authors the rate of the reaction is first order or less, indicating an intermediate reaction, possibly that of formation of an J excited ethylene molecule or a free vinyl radical.…”

“…For the same concentration of H2 and C,H6 this means that the concentration of CZH4 is about 5 times that of butadiene. Schneider and Frolich [56] have shown that butadiene and hydrogen are the principal initial products resulting from the pyrolysis of etheylene, from which it would be inferred that the rate of cracking of butadiene to form ethylene must be appreciable. Hence in the production of butadiene from cyclohexane, the temperature of a cracked cyclohexane product high in butadiene should be lowered in a reasonably short time.…”

“…In table 27 are given the equilibrium constants for the separate reactions forming I-butene, cis-2-butene, trans-2-butene and an equilibrium mixture of n-butenes. The thermodynamic data on the butenes used in the calculation of these equilibrium constants were taken from reference [ ---------~--~------------------------------~-------~----=.~=~-- [56] suggest that benzene may be formed as a result of a coalescence of two butadiene molecules. …”

Conversion of Hydrocarbons into Butadiene.

“…Thermal condensation of ethene (52,63,110,114,138,142,144,155,157,158,164) also yields butadiene, so that the latter could be a secondary or tertiary product from ethane, propane, n-butane, npentane, and 2-methylbutane. Whenever ethene dehydrogenates to vinyl radicals and then condenses, butadiene is a secondary product.…”

THE THERMAL DECOMPOSITION OF n-BUTANE

“…In order to identify the initial products, recourse is usually had to a proceclure which involves extrapolation of the products formed a t real conditions to their values a t zero decon~position (9). Although it is possible in principle to decrease the extent of decomposition until primary proclucts only are formed, excessive dilution of the products with undecomposed paraffin presents a formidable analytical problem.…”