Gas To Liquids - Mobil Process

Mobil Process

An alternative path starts by conversion of the natural gas to syngas, conversion of the syngas to methanol which is subsequently polymerized into alkanes over a zeolite catalyst. It was developed by Mobil in early 1970s.

Methanol is made from methane (natural gas) in a series of three reactions:

1. Steam reforming: CH₄ + H₂O → CO + 3 H₂ ΔrH = +206 kJ mol-1
2. Water shift reaction: CO + H₂O → CO₂ + H₂ ΔrH = -41 kJ mol-1
3. Synthesis: 2 H₂ + CO → CH₃OH ΔrH = -92 kJ mol-1

The methanol thus formed may be converted to gasoline by the Mobil process. First methanol is dehydrated to give dimethyl ether:

2 CH₃OH → CH₃OCH₃ + H₂O

This is then further dehydrated over a zeolite catalyst, ZSM-5, to give a gasoline with 80% (by weight based on the organics in the product stream) C5+ hydrocarbon products.

ZSM-5 is deactivated by a carbon build-up ("coking") over time in converting methanol to gasoline. The catalyst can be re-activated by burning off the coke in a stream of hot (500 °C (930 °F)) air; however, the number of re-activation cycles is limited.