Start-up of a methanol-to-olefin process

A method of starting up a catalytic MTO process comprising a fluidized MTO reactor zone containing one or more cyclones requiring a minimum superficial gas velocity in order to function properly, an effluent quench zone, a motor-driven product compression zone that is sized to handle only about 20 to 60 vol-% of the MTO reaction zone effluent gas stream at design capacity and that cannot provide the required superficial linear velocity for the fluidized MTO reaction zone and a light olefin and oxygenate recovery zone, where the start-up is-conducted without the use of an additional motor-driven start-up compressor and with the use of a thermal compressor having a motive gas inlet, a suction gas inlet, and a discharge gas outlet, the start-up method comprising the steps of:

• a) charging the MTO reaction zone with an inert start-up gas in an amount sufficient to provide effluent gas stream for recirculation;
• b) passing a first portion of the resulting effluent gas stream to the product compression zone and compressing it therein to provide a high pressure gas stream;
• c) heating at least a first portion of the high pressure gas stream, charging the resulting heated high pressure gas stream to the motive gas inlet of the thermal compressor to produce a discharge gas stream and recycling the resulting discharge gas stream from the thermal compressor back to the MTO reaction zone thereby establishing a first start-up gas circuit;
• d) passing a second portion of the effluent gas stream from step a) directly to the suction gas inlet of the thermal compressor, compressing the second portion using energy contained in the motive gas and passing the resulting compressed gas into the discharge gas stream thereby establishing a second start-up gas circuit;
• e) increasing the temperature of the heated high pressured gas stream until the temperature of the MTO reaction zone reaches at least about 300° to 400° C. (572° to 752° F.);
• f) increasing the pressure of the discharge gas stream until the pressure differential across the MTO reaction zone is sufficient to drive the discharge gas stream there through at a velocity which meets or exceeds the minimum cyclone superficial gas velocity;
• g) start circulating catalyst particles in the MTO reactor zone using the discharge gas stream from the thermal compressor as the fluidizing gas and charging a minor amount of the methanol feed to the MTO reaction zone while contacting a quenching medium in the quench zone with the effluent gas stream in order to condense stream contained therein and while-passing a commensurate second portion of the high pressure gas stream produced in step b) into the light olefin and oxygenate recovery zone;
• and
• h) increasing the amount of the methanol feed charged to the MTO reaction zone while simultaneously decreasing the amount of the first portion of the high pressure gas stream passed into the first start-up gas circuit until the desired flow rate of the methanol feed into the MTO reaction zone is established and the thermal compressor is blocked off.