Complex sentence: In 2012, the downstream assets of ConocoPhillips were split off to the newly reformed Phillips 66 who then in April of that year sold the refinery to Monroe Energy, LLC, a wholly owned subsidiary of Delta Air Lines.
Split into simpler sentences: In 2012, the downstream assets of ConocoPhillips were split off to the newly reformed Phillips 66. In April 2012, they sold the refinery to Monroe Energy, LLC, a wholly owned subsidiary of Delta Air Lines.