Continuous Production of Polyester-Poly(Ethylene Terephthalate) Resins in Melt-Phase and Solid-State Reactors

A simple reaction model has applied net polycondensation rates to predict the steady-state performance of three distinct continuous processes for manufacturing polyester-PET resins. A net melt-phase polycondensation rate was described by the simple second-order kinetics. A net solid-state polycondensation rate was assumed to follow the modified second-order kinetics with respect to active end group concentration. A moving-packed bed requires a longer residence time to deal with the diffusion-limited SSP of standard pellets or challenging pastilles. The calculations and data showed low IV pastilles to have much slower diffusion-controlled SSP rates than medium IV pellets. The tanks-in-series model demonstrated a narrow RTD in a gas fluidization bed with five mixing stages. Higher reaction temperatures may significantly increase the low diffusion resistance SSP rates of smaller beads or micro-pellets in a gas-fluidized reactor. The reaction-controlled SSP of micro-beads becomes apparent at 230 degrees C. The high IV melt resins may challenge the slow reaction rates of Ti or Al-catalyzed SSP resins. The efficacy of catalyst promoters on Ti activity enhancement may depend upon various ligands in Ti glycolate, Ti citrate, or titanic acid. The thermo-oxidative stability of Ti or Al-catalyzed resins may decrease at higher hot air drying temperatures (188 degrees C or above). (C) 2016 Society of Plastics Engineers