A high efficiency method combining metal chelate ionic liquid-based aqueous two-phase flotation with two-step precipitation process for bromelain purification

•Metal chelate ionic liquid-based aqueous two-phase flotation was designed to initially purify bromelain.•The bromelain was further purified using the two-step precipitation process.•The thermosensitive properties of the trapping agent are used to remove impurities again.•The recycling performance of the IL and the trapping agent used in the experiment was good.