A shareholder of propylene specialist PetroLogistics LP, set to be sold by private equity and its management to Koch Industries subsidiary Flint Hills, is seeking to block the $2.1 billion deal, calling it "unfair and inadequate."

Tom Klemesrud filed a complaint in the state of Delaware's Chancery Court, charging that the proposed buyout will discourage rival offers for the Houston-based company.

Under the plan announced at the end of May, PetroLogistics has until July 6 to talk with other potential bidders, provided Flint Hills is allowed by Koch to match any other offers.

A Flint Hills spokesman told US media that on the basis of due diligence, the company believes the deal to be fair, based on historic market values and the level of future investment that will be required to maintain and grow the business.

He pointed also to the majority shareholders' agreement to provide remaining shareholders with "additional consideration," adding that PetroLogistics' financial advisors have also deemed the $14.00 per unit sale price is fair to the shareholders.