Coupling of exothermic and endothermic reactions in oxidative conversion of natural gas into ethylene/olefins over diluted SrO/La₂O₃/SA5205 catalyst

Abstract

In the oxidative conversion of natural gas to ethylene/lower olefins over SrO (17.3 wt. %)/La₂O₃ (17.9 wt. %)/SA5205 catalyst diluted with inert solid particles (inerts/catalyst(w/w) = 2.0) in the presence of limited O₂, the exothermic oxidative conversion reactions of natural gas are coupled with the endothermic C₂₊ hydrocarbon thermal cracking reactions for avoiding hot spot formation and eliminating heat removal problems. Because of this, the process is operated in the most energy-efficient and safe manner. The influence of various process variables (viz. temperature, NG/O₂ and steam/NG ratios in feed, and space velocity) on the conversion of carbon and also of the individual hydrocarbons in natural gas, the selectivity for C₂-C₄ olefins, and also on the net heat of reactions in the process has been thoroughly investigated. By carrying out the process at 800-850°C in the presence of steam (H₂O/NG ≥ 0.2) and using limited O₂ in the feed (NG/O₂ = 12-18), high selectivity for ethylene (about 60%) or C₂-C₄ olefins (above 80%) at the carbon conversion (>15%) of practical interest could be achieved at high space velocity (≥34 000 cm³.g^-1(catalyst) h^-1], requiring no external energy and also without forming coke or tar-like products. The net heat of reactions can be controlled and the process can be made mildly exothermic or even close to thermoneutral by manipulating the O₂ concentration in the feed.