Systems and methods for the oxidative coupling of methane

A method for producing an olefin, the method comprising:

• (a) providing a reactor comprising two sections:
• an isothermal tubular section and a substantially adiabatic section, wherein said isothermal tubular section contains a first oxidative coupling of methane (OCM) catalyst configured to promote a first OCM reaction and is in thermal communication with a heat transfer medium;
• (b) introducing a gas mixture into the isothermal tubular section of the reactor, which gas mixture comprises oxygen (O2) and methane (CH4), whereby at least about 75 mol % of the O2 reacts with the CH4 to produce an intermediate gas stream comprising hydrocarbon compounds having two or more carbon atoms (C2+ compounds) and non-C2+ impurities, wherein said first OCM catalyst undergoes deactivation over time such that (i) an outlet temperature of the isothermal tubular section decreases over time, (ii) an oxygen concentration at the outlet of the isothermal tubular section increases over time, and (iii) the oxygen concentration at the outlet of the isothermal tubular section is at least about 500 parts per million (ppm);
• (c) injecting the intermediate gas stream into said substantially adiabatic section, wherein said substantially adiabatic section contains a second OCM catalyst to promote a second OCM reaction, wherein said second OCM catalyst undergoes deactivation over time such that (i) an outlet temperature of said substantially adiabatic section increases over time and (ii) an oxygen concentration at an outlet of said substantially adiabatic section is less than about 100 ppm;
• and
• (d) generating a reactor effluent gas stream from said intermediate gas stream, wherein the reactor effluent gas stream comprises hydrocarbon compounds having C2+ compounds and non-C2+ impurities.