PURPOSE: To prevent degradation or the like of a product, by completely removing inorganic scales deposited on the inside wall within a short time by cleaning the reaction apparatus with a glycol containing phosphorous acid after finishing the polyester production.
CONSTITUTION: A reaction apparatus used in the production of an ethylene terephthalate-based polyester is charged with a glycol (e.g., ethylene glycol, triethylene glycol), and the high-melting polyester deposited on the wall of the apparatus is washed under pressure and depolymerized. Then, phosphorous acid in an amount of above 0.001wt% based on glycol is added and, by washing at a temperature at above about 70°C, the inorganic black scales strongly adhering on the wall of the apparatus can be removed. It is of economic advantage to employ, directly as the glycol, an impure glycol formed and distilled off in the transesterification and/or polycondensation.
YASUJIMA YASUO
KOJIYOU KOUZOU
