Arco Chemical Co. persuaded a Delaware Chancery Court judge to throw out a lawsuit filed by a former stock owner who said she’d been shortchanged in a $1.15 billion acquisition by rival Lyondell Chemical Co.

Newtown Square, Pa.-based Arco Chemical, maker of antifreeze, paint and engine-fuel compounds, agreed in 1998 to be acquired by Houston-based plastics and petroleum chemical-maker Lyondell for $57.75 per share — 14 percent over the market price of the shares at the time.