Ineos said it has successfully completed trials on the unit eight years after it was mothballed.
The KG ethylene cracker was unable to operate at full capacity but US ethane will be used as a supplementary feed when deliveries to the plant begin in the autumn.
Gordon Milne, operations director at Ineos Grangemouth, said the move will take the facility into the "premier league of European petrochemical plants".
He said: "With the successful completion of the Train 2 trial we are now in great shape to receive shale gas from the US and to finally run the Grangemouth plant at full rates."
The project will see Ineos acquire gas from the Marcellus Shale in Western Pennsylvania.
Eight Dragon class ships will deliver the gas to a new import terminal at Grangemouth featuring the biggest shale gas storage tank in Europe.
John McNally, chief executive of Ineos Grangemouth, said: "Bringing the site back into profitability is the best way to secure our future here in Scotland.
"We know that ethane from US shale gas has transformed US manufacturing and we are now a step closer to seeing this advantage being brought to here to Grangemouth."
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