Patent ID: 7462649
Filing Date: 2008-12-09
Classification: C07C,C08G,C08J,Y02W

Abstract:
1. A method for recycling PET bottles characterized in that the wastes of resin bottles containing polyethylene terephthalate (PET) as the main component and further containing components different from it are passed sequentially through the following Processes (1) to (17): (1) a process for unpacking a packed bale of PET bottles which have been recovered through collection of classified refuse, (2) a process for removing iron and aluminum by a metal detector from the unpacked PET bottles, and subsequently crushing the PET bottles into flakes of 2-30 mm in sizes, (3) a process for separating polymer components different from PET consisting of polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC) from flaky pieces of PET bottles by winnowing, (4) a process for washing and gravity sorting having both the roles of washing out foreign materials attached inside and outside the crushed PET bottle pieces with water, and further removing sands, stones having specific gravities larger than water and PET, and foreign plastics having specific gravity smaller than water, (5) a depolymerization process for producing bis-β-hydroxyethyl terephthalate (BHET) by charging recovered PET flakes into ethylene glycol (EG) containing a PET depolymerization catalyst and treating the mixture at a temperature of 175-190° C. under a pressure of 0.1-0.5 MPa, (6) a solid-liquid separation process for removing solid foreign materials which have not dissolved in the above reaction solution, (7) a BHET concentration process for distilling and concentrating a solution fraction which has passed the solid-liquid separation process, (8) an ester interchange-recrystallization process for forming crude dimethyl terephthalate (DMT) and EG through an ester interchange reaction of the concentrated BHET in methanol (MeOH) in the presence of an ester interchange reaction catalyst, and subjecting the reaction mixture to recrystallization in a MeOH solvent, (9) a DMT distillation process for removing MeOH by distillation from the crude DMT to purify the DMT, (10) a hydrolysis process for subjecting the purified DMT obtained in the DMT distillation process to a hydrolysis reaction together with water which is supplied in an amount 0.5 to 5 times the weight of the DMT at a temperature of 230-250° C. to produce terephthalic acid (TA), (11) a process for cooling an aqueous slurry of the TA obtained in the hydrolysis process, (12) a process for obtaining TA cakes from the cooled aqueous slurry of TA through solid-liquid separation, (13) a slurry adjusting process in which the TA cakes obtained in Process (12) are added to a slurry preparation tank after the TA cakes are dried, and the mole ratio of TA/EG is adjusted to a range of 1:1 to 1:3, (14) a process in which TA cakes and EG are made to perform an esterification reaction to obtain a PET oligomer, (15) an initial melt-polycondensation process in which a polycondensation reaction catalyst and a stabilizer are added to the PET oligomer, the mixture is subjected to a melt polycondensation reaction in a weak vacuum of 1.3 kPa to 4.0 kPa at 260-300° C. to remove EG, and thus the degree of polymerization is increased, (16) a latter term melt-polycondensation process in which the product of the previous process is further subjected to a melt polycondensation in a high vacuum of 67 Pa to 0.7 kPa at 270-300° C. to remove EG by distillation, and thus the degree of polymerization is further increased, and (17) a solid phase polymerization process for further increasing the degree of polymerization in order to obtain a PET suitable for bottles.