Concept:
Methane is the chief component of natural gas and an important raw material for synthesis of methanol.
Step 1:
Methane is abundantly available in natural gas.
Step 2:
Methane is first converted into synthesis gas containing CO and H$_2$.
Step 3:
Synthesis gas is catalytically converted into methanol.
Step 4:
Ethylene and propylene usually come from cracking of petroleum fractions, not directly from methane.
Step 5:
Therefore, the major petrochemical produced directly from methane is methanol.