Sept 1 (Reuters) - German billionaire Klaus-Michael Kuehne has doubled his stake in chemicals distributor Brenntag , according to a disclosure announcement released by the company after the market close on Friday.

Kuehne, who also owns the biggest share in German airline Lufthansa, has raised his stake in Brenntag to 10% from 5.18% via his Kuehne Holding, the release said.

At Brenntag's annual shareholder meeting in June, Kuehne Holding was among shareholders that supported the company's nominations for its supervisory board, rejecting counter-motions submitted by activist investor PrimeStone Capital, which is seeking a break up of the company.

Brenntag is facing calls from Engine Capital and PrimeStone to spin off its specialties business, joining other German companies such as Bayer and Thyssenkrupp in facing similar demands from activist investors. (Reporting by Andrey Sychev Editing by Emma-Victoria Farr and Mark Potter)