US speciality chemicals group Lubrizol has approached Cognis about a potential takeover which could value its German rival at about €3bn (£2.7bn). Other interested bidders for Cognis include BASF, the world’s largest chemicals group. Goldman Sachs and Permira, the private equity group, the owners of Cognis, have not started a formal sales process. Lubrizol manufactures chemical solutions ranging from engine oil additives to pharmaceuticals and food ingredients. Its last big purchase was Noveon for $1.84bn.