The plant, belonging to joint UK-China venture Petroineos, has faced "significant challenges" amid market pressure and the energy transition, Sky News reported on Wednesday.
The Unite workers' union said the site would "primarily operate as an import and export oil terminal facility only."
Petroineos Refining CEO Franck Demay justified the move as "a necessary step in adapting our business to reflect the decline in demand for the type of fuels we produce." Meanwhile, trade unions and Scottish lawmakers have resented the future closure, the broadcaster said.