The body of the worker, whose name was not released, was found under debris about seven hours after the 7:30 a.m. blast in a heat exchange unit, company spokesman Scott Baughman said.
The explosion also caused a small release of ammonia, which is used to cool processed liquids.
The six injured workers were treated by the plant's medical team, then taken to hospitals for evaluation. Baughman said the damage and ammonia release were contained in a small area of the plant, which makes synthetic rubber for tires.
The plant was evacuated for several hours. About 200 people were in the plant at the time.
There was no danger to the public, plant officials said.
The cause of the explosion was under investigation.