thyssenkrupp AG (XTRA:TKA) has started a structured process to look for potential buyers of all or parts of its elevator unit, its most profitable division. Letters asking for expressions of interest for the unit, valued anywhere between $13 billion -$19 billion, were sent out to private equity and strategic investors, three people familiar with the matter said. Recipients included private equity groups KKR & Co.

Inc. (NYSE:KKR), Bain Ca[pital, LP, Advent International Corporation, CVC Capital Partners Limited, EQT Partners AB, The Blackstone Group Inc. (NYSE:BX), Partners Group Holding AG (SWX:PGHN) and Apollo Global Management, LLC (NYSE:APO) as well as Kone Oyj (HLSE:KNEBV), Schindler Holding AG (SWX:SCHN), Otis Gold Corp. (TSXV:OOO) and Hitachi, Ltd. (TSE:6501), the people said. The parties declined to comment or were not immediately available for comment.

Sources had told Reuters last week that Thyssenkrupp had launched a formal auction process in addition to plans for an initial public offering (IPO), adding chief executive Guido Kerkhoff might be forced to sell the whole unit. Interested parties are expected to respond to the letters within two weeks, the people said. “We have clearly stated that, in addition to preparing for the IPO, we are also examining expressions of interest from potentially interested parties,” a spokesman for Thyssenkrupp said, adding a structured process had been started.