Method and apparatus for pyrolytically decomposing waste plastic

Abstract

Disclosed is a method and an apparatus for pyrolytically decomposing waste plastic, e.g. PVC, to recover light fuel oil. The invention enables to prevent the product from contamination by halogen compounds. The plastic is first thermally decomposed in an atmosphere of a normal or reduced pressure to produce a primary decomposition product in the form of gas and a decomposition residue. The primary decomposition product is cooled at a first cooling temperature to separate the primary decomposition product into a relatively light fraction containing a desired light constituent and a relatively heavy fraction by condensation of the relatively heavy fraction, and the relatively heavy fraction is then thermally decomposed in an atmosphere pressurized at a predetermined pressure to produce a secondary decomposition product containing the desired light constituent in the form of gas. The relatively light fraction and the secondary decomposition product are cooled at a second cooling temperature to condense a fraction containing the desired light constituent. This method may be changed so that the first and second thermal decomposition steps are performed at the same high pressure in one vessel and the heavy fraction is circulated. Additionally, alkali treatment of time plastic to be decomposed or the decomposition gas, thermal pretreatment of the plastic and addition of water or catalyst to the plastic can be used. The decomposition apparatus which is so systematized that the decomposition can be continuously performed is shown.