The C$4 billion ($3.20 billion) Heartland Petrochemical Project has emerged as a central asset in Brookfield's bid to buy the Calgary-based energy infrastructure company. Inter says the Heartland plant will open up new markets and boost earnings, but cost overruns and slow progress in securing buyers for the polypropylene pellets it will produce have weighed on the company's stock.

Chief Executive Christian Bayle said the contract announcement made Inter more valuable.

"The missing component in shareholders' minds was how to value Heartland," Bayle told Reuters in an interview. "We are bringing a lot more certainty to the project today."

Heartland, which will convert propane into 525,000 tonnes per year of polypropylene, a plastic used in the manufacturing of a wide range of finished products, is scheduled to start operating in early 2022 and take two years to ramp up to full output.

Inter said 60% of production capacity is now covered by long-term contracts with seven Canadian and multinational buyers. It did not name them.

That is slightly below the company's target of 70% of production contracted, but likely above market expectations, Stifel GMP analyst Ian Gillies said in a note.

Inter said it expects adjusted EBITDA, which are earnings before certain items are taken into account, from the project to be around C$300 million in 2022 and C$400-C$450 million in 2023. Previously the company said Heartland would contribute C$500 million to adjusted annual EBITDA.

"Overall, we expect the stock reaction to be muted given the ongoing strategic review process," Gillies added.

Inter shares were last down 0.1% at C$18.04 on the Toronto Stock Exchange.

Brookfield launched its hostile bid for Inter in February with a C$16.50 per share offer that valued the company at C$7.08 billion. Inter rejected that bid as too low and launched a strategic review process that will conclude before Brookfield's bid expires in early June.

(Reporting by Nia Williams; Editing by Marguerita Choy)

By Nia Williams