Separation of scrap polyethylene pellets by density

A process is proposed for the separation of a mixture of polyethylene pellets scrap with different densities, contaminated with other impurities using a mixture of two or more miscible liquid components. The process is carried out at low pressure where one of these components is either a very volatile liquid (n-pentane) or a liquefied gas (n-butane, domestic gas) whilst the other component is a high density liquid such as glacial acetic acid or tetralin (1,2,3,4-tetrahydronaphthalene). The liquid mixture density can be decreased by increasing the concentration of the volatile component or gas pressure, or can be increased by aeration of the volatile liquid or lowering gas pressure. In this way all of the fractions of the polyethylene mixture can be separated according to their densities.