Polyethylenterephthalat - PET PET = Poly(oxy-1,2-ethanediyloxycarbonyl-1,4-phenylenecarbonyl) Patents concerning PET-Synthesis go back to the 40th of the 20 th century Research on esterification and transesterification since 19 th century Production 2002 world wide approximately 35 x 10 6 t/a Plant capacities per line up to 1,200 t/d or 400 kt/a 1
Products Made from PET Man-Made Fibres Bottles and Bins Packaging Tapes staple fibres, micro fibres, tyre cord, spun bond soft drinks, still water, hot-fill, beer sheets and blisters, microwave trays (C-PET) audio and video (biaxially oriented PET) Huge Potential PET-Recycling bottles for beer, wine, and sparkling wine global market place for bottles and staple fibres 2
Polykondensation Polycarbonate 3 Polyester
Polycondensation - PET Monomer and Polymer Terephthalic Acid (TPA) 1,2-Ethanediol (EG) H H H C H 2 H C H 2 Poly(ethylene Terephthalate) (PET) * CH 2 CH 2 * n 4
PET Synthesis - Kinetic Concept, Chain Length Distribution Reactions of functional groups Equal reactivity hypothesis Reaction rate law, temperature dependency Catalysis by metal compounds and by H + from terminal CH groups Equilibrium reactions and irreversible reactions Redistribution of chain lengths 5 Flory-Schulz distribution
PET Synthesis - Molecules EG H H W H H TPA H H DEG H H AA C H 3 Dioxane 6
PET Synthesis - Functional Groups R3 R1 " n R2 t = terminal b = bound teg R1 H beg R2 R1 ttpa R1 H btpa R1 R2 tdeg R1 H bdeg R1 R2 tv R1 7
PET Synthesis - Molecules and Functional Groups for Kinetic Modelling Symbol Description Molecular Structure 8 EG ethylene glycol HCH 2 CH 2 H TPA terephthalic acid HC-C 6 H 4 -CH DEG diethylene glycol H(CH 2 ) 2 (CH 2 ) 2 H AA acetaldehyde CH 3 CH W water H 2 teg EG end group R-CH 2 CH 2 H beg EG repeat unit R-CH 2 CH 2 -R ttpa TPA end group R-C 6 H 4 -CH btpa TPA repeat unit R-C 6 H 4 -R tdeg DEG end group R-(CH 2 ) 2 (CH 2 ) 2 H bdeg DEG repeat unit R-(CH 2 ) 2 (CH 2 ) 2 -R tv vinyl end group R-C 6 H 4 -CCH=CH 2
Polycondensation - PET Synthesis Transesterification Transesterification / Methanolysis DMT + 2 EG = BHET + 2 CH3H Direct Esterification Esterification / Hydrolysis TPA + 2 EG = BHET + 2 H2 Melt Phase Polycondensation 2 BHET = PET + 2 EG ( ) EG Transesterification / Glycolysis n (PET) m = PET n x m + n 1 Solid State Polycondensation Transesterification / Glycolysis PETn + PETm = PETn+ m + EG 9
Polymer Kinetics - Equal Reactivity Hypothesis The reaction rate is independent from the degree of polycondensation or the molecular weight. Reactions of functional groups 10 ne parameter set for each reaction
Polymer Kinetics - Equal Reactivity Hypothesis 11 Flory, P.J., Principles of polymer chemistry, Cornell University Press, Ithaca, New York (1953)
PET Synthesis - Reversible and Irreversible Reactions Reversible Reactions with Low Equilibrium Constant Esterification Transesterification ligomer formation Significant Back Reaction Reversible Reactions with High Equilibrium Constant Formation of DEG 12 Formation of dioxane Irreversible Reactions Thermal degradation Acetaldehyde formation Colour formation Insignificant Back Reaction No Back Reaction
PET Synthesis - Esterification / Hydrolysis Esterification is the first step in PET synthesis, but also occurs in all subsequent stages Esterification is an equilibrium reaction The equilibrium constant is close to unity The esterification process involves three phases - gas / liquid / solid Esterification reactions are acid catalyzed, TPA behaves both as reactant and as catalyst Polydispersity index (Flory): D = 2 vs. measured: D < 2 13 Reactors with high surface area to volume ratios reduce the esterification time Kinetic data mostly from model systems at low temperatures
PET Synthesis - Molecular Weight Distribution of Prepolymer 446 638 830 1022 14 254
PET Synthesis - Transesterification / Glycolysis Transesterification is an equilibrium reaction Vacuum (p = 100... 1000 Pa) influences the (macro kinetic) rate of polycondensation Melt viscosity increases during polycondensation from approximately 0.01 Pas to 100-500 Pas Polydispersity index (Flory): D = 2 vs. measured: D = 3-6 Co-monomers (IPA, CHDM) increase the reaction time 15 Reactors with high surface area to volume ratios reduce the polycondensation time
PET Synthesis - Equilibrium Constants for Esterification and Polycondensation as Functions of Temperature 16 equilibrium constant K i 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Esterification free EG, Yamada, 1989 free EG, Reimschüssel, 1980 teg, Yamada, 1989 teg, Reimschüssel, 1980 TPA + 2 EG = BHET, Chemcad Polycondensation Yamada, 1980 Reimschüssel 1980 Challa, 1960 P n = 2, 3, 4 200 220 240 260 280 300 temperature / C
PET Synthesis - Rate Constants as Function of Temperature 17 rate constant k i / kg mol -1 h -1 30 esterification, EG hydrolysis, EG esterification, teg 25 hydrolysis, teg polycondensation glycolysis 20 15 10 5 0 230 240 250 260 270 280 temperature / C Rate constants calculated from data published by Yamada et al. 1989
Mass Transfer at PET Synthesis Esterification Esterification is the first step in PET synthesis, but also occurs in all subsequent stages 18 Esterification is an equilibrium reaction The equilibrium constant is close to unity The esterification process involves three phases - gas / liquid / solid Reactors with high surface area to volume ratios reduce the esterification time Polycondensation Transesterification is an equilibrium reaction Vacuum (p = 100... 1000 Pa) influences the (macro kinetic) rate of polycondensation Melt viscosity increases during polycondensation from approximately 0.01 Pas to 100-500 Pas Reactors with high surface area to volume ratios reduce the polycondensation time
Mass Transport at PET-Synthesis - Esterification 1 TPA dissolves 2 EG migrates to surface area of solid TPA particles by diffusion 3 Micro mixing vapour phase 4 Phase transition and evaporation phase boundary AA, water,eg, DEG, oligomer 4 liquid phase 19 TPA ( TPA S) 2 1 TPA ( dissolved ) + EG(l) prepolymer(l) + water(l) (dissolved) TPA ( S) + EG(l) prepolymer(l) + 3 water(l)
Mass Transport at PET-Synthesis - Polycondensation 1 Catalytic reaction in molten polymer 2 EG migrates to liquid / gas interphase by molecular diffusion 3 Phase transition and evaporation vapour phase phase boundary AA, water, EG, DEG, oligomer 3 liquid phase 1 teg + teg beg + EG 2 H H 2 C C H 2 H 20
Mass Transport at PET-Synthesis - verall Polycondensation Rate as Function of Polymer Film Thickness 200 P n 150 100 0.093 mm 0.185 mm 0.55 mm 1.28 mm 2.74 mm 50 21 0 0 30 60 90 120 time / min Rafler et al., 1979 (Sb catalyst)
Typical Process Parameters for Melt Phase Polycondensation Processes Esterification Pre-Polycondensation Finisher Temperature [ C] 250-265 265-275 275-295 Pressure [Pa] 1.2 1.8 x 10 5 2500 3000 50 150 Residence time [min] 180-360 50-70 90-150 22 P n [-] 4-6 15-20 100
Continuos PET Process Based on TPA with Five Reactors in Series 23
Slurry Preparation Plant 24
Esterification Plant 25
Pre-Polycondensation Plant 26
Polycondensation Plant - Finisher 27
Column System for EG Recovery 28
Solid State Polycondensation - Synthesis of PET PET bottle grade and technical yarn IV > 0.65 dl g -1 P > 100, n M n > 19,000 g mol 1 T G < T SSP < T M fi 220-235 C Residence time 8-12 h (0.015 dl g -1 h -1 ) Batch (tumbling dryer, vacuum) e.g. by HL Stehning 29 Continuous (tube type reactor, nitrogen) e.g. by Buhler, Sinco, Zimmer
Solid State Polycondensation - PET and PA 6 - Continuous SSP Process 30