SELECTIVE NAPHTHENE PYROLYSIS FOR ETHYLENE WITH HYDROGEN AS DILUENT

Thermal decomposition of a heavy Nigerian naphthenic naphtha and cyclohexane was investigated in a flow system with stainless steel tubular reactors in the presence of hydrogen. The pyrolysis conditions were: atmospheric pressure, temperatures ranging between 630 and 900°C, constant space time of 0.03 sec, hydrogen: liquid ratio of 7 and 28 for naphtha and 20 for cyclohexane, and surface to volume ratios of 8 and 21.5 cm-1. The main products of the pyrolysis reaction were ethylene, propylene, butadiene and methane. The ethylene yield was enhanced in the presence of hydrogen. At temperatures between 820 and 850°C, the ethylene yield was increased from 0.238 to 0.528 for a four-fold increase in hydrogen to naphtha ratio. The coke yield was found to go through a maximum at temperatures between 780 and 800°C, depending on the hydrogen: naphtha ratio. As the effect of surface was minimized by increasing tube size or the addition of CS2 to a given tube size, both ethylene and coke yield were reduced while methane yield was increased. © 1979.