Pyrolysis of Ethylbenzene with and without Oxygen Initiation

Abstract

BRIEFThe effect of small quantities of oxygen (0 to 10%) on the thermal decomposition of ethylbenzene in the temperature range of 570-650° c was investigated utilizing a flow reactor with residence times on the order of 0.1 second. The runs made,with oxygen excluded fit a half order rate expression with an activation energy of 69 kcal.jg.mole. Small quantities of oxygen increase the rate of thermal decomposition but this· effect tapers off as the oxygen concentration is increased. With an oxygen . concentration of around 3% the same level of conversion is achieved at a temperature 10° C :t:ow~r than that required when oxygen is excluded. The styrene yield selectivity increases from 74 mole % 'I· without oxygen to 81 mole %with 10% oxygen. The presence of "' oxygen also lowers the apparent activation energy. SHORT SUMMARYRates of thermal decomposition of ethylbenzene. were measured· ~-· .< in an C.l second flow reactor at 570-650° c and interpreted via a Rice-Herzfeld mechanism. The effect of small quantities of oxygen on rate and product selectivity was determined., .. A reviewof investigations of oxygen-initiated pyrolysis prior to 1956 has been given by Letort, who states that one part of oxygen in 100,000 doubles the initial deqomposition rate of · acetaldehyde at 4 77° c ( 13). Niclause, .Combe; and .Letort· ·have ·-·shown that the pyrolysis threshold· of acetaldehyde. is lowered·.from 450° C to 150° C by the addition of one part oxygen in 10,000 (16 ; .., . ' ' . ., ..... :The. hydrocarbon investigated· in this ·work ·was ethylbenzene .. · · · . .The tnermal decomposition rates of alkylated aromatics have not · 415-590° C with a residence time of 5 seconds and an oxygenethylbenzene mole ratio of 0.7-1.0 (10). They found that. styrene forms essentially all the non-oxygenated aromatic product. For example with 33% conversion of ethylbenzene at 530° C a carbon balance gives a selectivity of 65% to styrene, 15% to benzaldehyde~ 8% to acetophenone, 3%. to other aromatics and the remainder to gaseous products. This raises the possibility that at a much lower oxygen content the selectivity.of styrene formation might remain high without the simultan~ous appearance of oxygenated aromatics which present a separation problem. A qualitative analysis of the gaseous pyrolysis products was made using the gas chromatograph. Hydrogen was found to I • be present in the highest concentration. Methane, ethane and ethylene were also identl.fied as products of the pyrolysis.Approximately 10 times as much ethylene as ethane was produced.Exact quantitative analyses of the gaseous products were not made because of the large amount of nitrogen diluent. Webb andCorson found approximately equal yields of ethylene and parafinnic hydrocarbons; however they employed much higher conversion levels where secondary reactions would be more important (24). The.standard error of the resulting correlation is 23%. (1)( 2) can be seen the slope of this line is 35,000° K, which corresponds ! to an apparent activation energy, E, of 70,000 ca...

Thermal decomposition of ethylbenzene cations (C8H10+): experiments and modeling of falloff curves

“…The TIFT is similar to low-pressure flow tubes except that larger flow rates are used to achieve higher pressures and Reynolds numbers. The O 2 + precursor ions were created upstream by flowing a mixture of a few percent of O 2 diluted in Ar through an off-axis corona discharge source; the low [O 2 ] prevented unwanted side reactions and the falsification [32,33] of pyrolysis rate constant measurements. The ions flowed through a small orifice into a sidearm and were entrained by a large flow of nitrogen buffer gas (from liquid).…”

Investigation of the Kinetics of Ethylbenzene Pyrolysis Using a Temperature-Scanning Reactor

“…Deviations are greatest at low initial EB concentrations and high EB conversions. The simplicity of the model, its irreversibility, and unaccounted secondary reactions of the products probably account for the deviations at high conversions. , For EB conversions of less than 30%, the model equations predict the experimental partial pressures of the major components to within 10%.

10 EB mole fraction parity plot for all pressures, temperatures, τ's, and steam-to-oil ratios.

11 Toluene mole fraction parity plot for all pressures, temperatures, τ's, and steam-to-oil ratios.

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“…The literature values listed in the table were determined by different methods. Three of the authors used carrier gases in conventional flow systems (Clark and Price, toluene; Bruinsma et al, argon; Hausmann and King, nitrogen). Brooks et al used a conventional static reactor for their experiments.…”

“…The thermal cracking of EB was studied using a temperature-scanning plug-flow reactor (TS-PFR) at various temperatures, pressures, flow rates, and steam-to-oil ratios. EB pyrolysis has been studied extensively but not over such a wide range of conditions as presented here. − In addition, studies with steam dilution are limited. , The simplified thermal cracking model developed on the basis of this data is to be combined with our current catalytic models to provide a complete description of the reactor performance.…”

“…EB pyrolysis has been studied extensively but not over such a wide range of conditions as presented here. [4][5][6][7][8][9][10][11] In addition, studies with steam dilution are limited. 10,11 The simplified thermal cracking model developed on the basis of this data is to be combined with our current catalytic models to provide a complete description of the reactor performance.…”