Analysis of PET pollymerization reactor with surface renewal

Abstract

For high efficiency polymerization of polyethylene terephthalate (PET), the development of polymerization catalysts, the elevation of monomer``s (bis-2-hydroxyethyl terephthalate, BHET) reactivity and the modeling of polymerization process have been continuously studied. In order to increase the molecular weight of PET, it has been reported that the removal of volatile byproduct in a final stage reactor is one of the most important factors to obtain the degree of polymerization wanted and the film renewal action is most important for the removal of volatile byproducts. Hence a reactor with film renewal was designed as a laboratory scale and tested as a batch reactor. At the same time comprehensive mathematical model was developed and compared with the experimental results to show a clear analysis of the influence of pertinent operating variables. The diffusivity of ethylene glycol (EG) in PET melt has a very important role to determine the overall polymerization profiles, which was separately obtained from desorption experiment. Reactants (BHET monomer, oligomer, prepolymer) were fed into the reactor at room temperature. After the reaction temperature reaching 255℃ by heating the silicone oil in the jacket with electric wire, the polymerization reaction was started by rotating the cylindrical screw within the reactor to generate the film continuously with the film exposure time 1.0 sec or others and pressure was gradually reduced. When reaction temperature reaches 285℃ (or specified levels) and the reduced pressure was set to be 2.5 torr (or a specified pressure level) and these were maintained throughout the experiment. Catalysts used were $Sb_2O_3$, Sn-Sb complex, KR41B and titanium tetrabutoxide. By comparing the modeling with experimental results, polycondensation reaction rate constant $k_1(=k_8)$ and diester group degradation reaction rate constant $k_7$ for $Sb_2O_3$ were obtained as follows: $k_1(=k_8) = 3.4\times 10^9 exp(-18500/RT)$, ㎤/mol-min a...