Organic matter in delayed coking wastewater: Molecular composition and its effect on emulsification

•Emulsified wastewater from a delayed coking unit was investigated.•Molecular composition of organics in the wastewater was characterized by FT-ICR MS.•Highly condensed heteroatoms were dominant in the emulsified wastewater.•Sulfonates and polyoxyethylene surfactants were found in the DOM.