Pyrolysis of n-butenes

The normal butenes were pyrolyzed in the presence of steam in a nonisothermal flow reactor at 730°-980°C and contact times between 0.04 and 0.15 sec to obtain conversion covering the range between 3% and 99%. Isomerization reactions accompanied the decomposition of these olefins however, the decomposition was the dominant reaction under these conditions. Pyrolysis of 1-butene is faster than that of either cis- or trans-2-butene. Methane, propylene, and butadiene are initial as well as major products from the pyrolysis of the n-butenes. Hydrogen is an initial product only from the 2-butenes. Ethylene appears to be an initial product only from 1-butene it becomes the most prominent product at high conversions. Over the range of conditions of potential practical interest, the experimental rate expressions for the disappearance of the respective butene isomers, have been derived. 

J.E. BLAKEMORE et al. (12) recently studied the pyrolysis of n-butane in the presence of trace quantities of oxygen, using a gold microreactor operated under plug-flow conditions, at 530-600 C and atmospheric pressure. For a given initial concentration of n-butane, increasingly larger fractions of 1- and 2-butenes,... 

Investigation of pyrolysis of the butenes was chosen here as a complement to previous work in this laboratory on pyrolysis and partial oxidation of n-butane (1)(2)(3). Previous investigations of butene pyrolysis typically have employed static systems and/or high conversions (4)(5)(6)(7)(8)(9). 

Because of the high pyrolysis temperature, the C4-fraction contains quantities of vinyl acetylene and ethyl acetylene, the removal of which prior to the recovery of butadiene is necessary in certain cases, particularly if butadiene of low acetylene content is desired. Similar considerations apply to effractions obtained by the dehydrogenation of n-butane and n-butenes. 

Over the range of conditions, 1-butene decomposes more rapidly than either of the 2-butene isomers. Double-bond shift and geometrical isomerization accompany the decomposition of the n-butenes however, skeletal isomerization does not occur, as isobutene is not found among the products of the pyrolysis. Isomerization reactions apparently are kinetically controlled, as equilibrium distributions are not generally observed. Trans cis ratios in the products do not correspond to equilibrium at either the maximum or the average reactor temperatures, and in some cases the ratio falls below equilibrium values based on American Petroleum Institute (API) data (14). However, none of these data exceed the equilibrium values based on more recent thermodynamic data (15). 

Here again, in the presence of small amounts of oxygen and as a consequence of the oxidation, we observe the formation of hydrogen peroxide (or water) and extra yields of the olefins which already appear in the decomposition reactions of the alkanes by loss of H, i.e. isobutene in isobutane pyrolysis, ethylene and n butenes in n-butane pyrolysis, ethylene, propene and isopentanes in isopentane pyrolysis (see Tables I, II and III). 

A method is discussed below for the determination of the composition of an ethylene-butene-1 copolymer containing up to about 10% butene. This technique has been applied to the pyrolysis gas chromatography of ethylene-butene copolymers. Pyrolysis were carried out at 410°C in an evacuated gas vial and the products swept into the gas chromatograph. Under these pyrolysis conditions, it is possible to analyse the pyrolysis gas components and obtain data within a range of about 10% relative. The peaks observed on the chromatogram were methane, ethylene, ethane, combined propylene and propane, isobutane, 1-butene, trans-2-butene, cis-2-butene, 2-methyl-butane and n-pentane. 

Sampling in inverse coannular diffusion flames [62] in which propene was the fuel has shown the presence of large quantities of allene. Schalla et al. [57] also have shown that propene is second to butene as the most prolific sooter of the n-olefins. Indeed, this result is consistent with the data for propene and allene in Ref. 72. Allene and its isomer methylacetylene exhibit what at first glance appears to be an unusually high tendency to soot. However, Wu and Kem [111] have shown that both pyrolyze relatively rapidly to form benzene. This pyrolysis step is represented as alternate route C in Fig. 8.23. 

N 13 59% oxygen-rich monomer no props are reported except 1R spectrum was prepd by reaction of ethyl methyl ketone with formaldehyde, hydrogenation of the product with Gi chromite catalyst, acetylation to the triacetate, pyrolysis, deacerylation, and nitration of 3,3"bis(hydroxymethyl) -butene-1. The subject compd was synthesized as a binder constituent, which might be polymer-... 

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