Phase formation agent for liquid-liquid-liquid tri-phase system

The invention relates the phase former of liquid-liquid-liquid triple systems, comprising 7-20wt% copolymer of epoxyethane and epoxypropane, 7-20wt% inorganic salt and 10-40wt% organic solvent. The copolymer is block copolymer the weight average molecular weight of which is 1000-10000, comprising 40-85úÑ epoxyethane block, or random copolymer the weight average molecular weight of which is 800-10000, comprising 50-85úÑ epoxyethane. The invention can be used in separating filter liquor containing the biofermentation system, industrial waste water, and the complicated system containing the miscible liquids of organic synthesis product. The invention reaches the purification of phase-forming polyaromatics, reduces the cost, shortens the nature difference of organic phase and intermediate phase, and simplifies the technology.