Abstract: Method for depolymerising terephthalate polymer into reusable raw material, the method comprising steps of: depolymerizing terephthalate polymer by using ethylene glycol into a depolymerised mixture comprising at least one monomer and at least one dimer, wherein said at least one monomer comprises bis (2-hydroxyethyl) terephthalate (BHET), and said at least one dimer comprises dimer of bis (2-hydroxyethyl) terephthalate (BHET-dimer); removing solid compounds from said depolymerised mixture in a first separator to obtain a composition comprising the at least one dimer and the at least one monomer as solutes in a mixture of ethylene glycol and water; crystallizing BHET-dimer from said solution, thereby obtaining a mixture of BHET-dimer crystals and a first mother liquid; separating the crystallized BHET-dimer from the first mother liquid, and thereafter: forming BHET crystals from said first mother liquid, thereby obtaining a mixture of BHET crystals and a second mother liquid; and recovering the BHET crystals.