The Brazilian conglomerate Novonor has received a nonbinding offer from Abu Dhabi National Oil (ADNOC) for its controlling interest in Braskem. ADNOC is offering to pay more than $2.2 billion for the 38.3% stake, which would value Braskem at about $5.6 billion. The offer is the latest in a string of proposals that Novonor has entertained from petrochemical rivals and other suitors. ADNOC’s new proposal would also allow Novonor to retain a 3% interest. Braskem’s other major shareholder is the government-controlled oil company Petrobras, which would have to approve any deal.