Ineos said TGE is the preferred bidder to build a huge ethane tank at the site in Scotland, with completion due in 2016.
Two plants dating from the 1960s will close, but Ineos said there will be no job losses from the changes, which are part of its £300 million survival plan agreed last year.
The firm had threatened to close part of the site because of industrial relations problems.
Ineos said the ethane gas terminal was essential as it looked to replace existing North Sea feedstocks that were running out. MORE