Persistent weak demand amid a global financial meltdown has taken its toll on petrochem demand in Asia. Formosa Petrochemical Corp., plans to keep its No. 3 ethylene plant, closed on Sept. 3 for scheduled maintenance, shut this month. The shutters will be down despite completion of repair. Formosa posted the biggest profit decline in more than two years in Q3 as deteriorating prices hacked inventory values and slowed sales growth.