In continuous bottle-resin production based on SASA Polyester PTA, slurry formulation for PET esterification uses a molar ratio of ethylene glycol to purified terephthalic acid between 1 : 1.08 and 1 : 1.15, equivalent to approximately 40–43 parts by mass ethylene glycol per 100 parts PTA. In the paste preparation vessel, PTA with a mean particle size of 110–140 µm and residual 4-carboxybenzaldehyde below 25 mg/kg is mixed at 60–80 °C under nitrogen to suppress diethylene glycol formation. The slurry is discharged to a continuous esterification reactor operating at 260–270 °C and 1–2 bar(g); water of reaction is removed overhead and esterification conversion reaches 96–98% before the oligomer is transferred to a pre-polycondensation vessel. Polycondensation proceeds under pressure reduction from atmospheric to 0.5–1.0 mbar at 285–295 °C, with antimony trioxide catalyst at 150–300 ppm Sb and phosphoric acid stabilizer at 20–80 ppm P to suppress catalyst reduction and grey discoloration. The resulting amorphous melt is cooled, cut, and then subjected to solid-state polycondensation at 210–220 °C under continuous nitrogen flow until intrinsic viscosity reaches 0.80–0.85 dL/g. Before injection moulding, the pellets are dried at 170–180 °C to below 0.004 wt% moisture when ambient relative humidity exceeds 60%, preventing hydrolytic IV loss and acetaldehyde regeneration. For food-contact use, compliance is governed by FDA 21 CFR 177.1630 and EU Regulation (EU) No 10/2011; preform validation typically measures acetaldehyde below 1.0 µg/L in wall-section testing to prevent sensory degradation. Bottle-grade resin with this specification is injection-moulded at clamp forces from 250 to 450 t on multi-cavity preform systems, reheated, and blow-moulded into carbonated soft drink and still water bottles.

What Limits Melt Dewatering Efficiency in PTA-Based PBT Polycondensation?

In polybutylene terephthalate production based on SASA Polyester PTA, the purified terephthalic acid is slurry-fed with 1,4-butanediol at a molar ratio of BDO to PTA between 1.20 : 1 and 1.40 : 1, a deliberate excess over the theoretical 1 : 1 stoichiometry required to offset irreversible dehydration of BDO to tetrahydrofuran under acidic esterification conditions. Titanium alkoxide catalysts, typically tetra-n-butyl titanate added at 50–200 ppm Ti, accelerate esterification at 170–230 °C, but elevated residence time above 230 °C increases THF formation and consumes BDO, shifting the oligomer acid value and requiring downstream compensation in the precondensation reactor. The melt is then processed through a thin-film or disc-ring polycondensation unit at 245–260 °C under vacuum of 0.5–1.0 mbar, where 1,4-butanediol is removed and molecular weight builds to an intrinsic viscosity of 0.85–1.10 dL/g for injection-grade PBT. The processing window is narrow: melt temperatures above 260 °C accelerate degradation of the tetramethylene segment, while temperatures below 240 °C increase melt viscosity and restrict discharge through melt pumps. The final resin is normally compounded with 30 wt% glass fibre, flame-retardant synergists, and heat stabilizers; compliance testing follows UL 94 for vertical burning classification, ISO 527-2:2012 for tensile properties, and ISO 178:2019 for flexural modulus. Terminal products include electrical connectors, automotive sensor housings, relay bobbins, and encapsulant shells where heat deflection temperature above 200 °C is required. Published data for optimum THF suppressant feed strategies is limited, but production-scale experience indicates that staged BDO injection and rapid removal of water below 180 °C reduce THF-related yield loss.

Biaxially oriented polyester film made from SASA Polyester PTA requires high-purity feedstock with 4-carboxybenzaldehyde content below 20 mg/kg and total metal content below 30 mg/kg to reduce haze and gate-line deposits during extrusion. The PTA–ethylene glycol slurry is formulated at a molar ratio of 1 : 1.02 to 1 : 1.05, with silica anti-block particles added at 0.08–0.3 wt% as a dispersion in ethylene glycol to prevent film blocking without degrading optical clarity. After esterification and polycondensation to an intrinsic viscosity of 0.62–0.68 dL/g, the melt is extruded at 275–285 °C through a slot die onto a chilled casting drum held at 15–40 °C, where electrostatic pinning stabilizes the amorphous sheet. The cast sheet must remain below 40 °C before stretching; premature spherulitic crystallization above this temperature impairs uniform orientation. The sheet is then stretched in the machine direction at 90–110 °C by a factor of 3.0–3.5, followed by transverse stretching in a tenter frame at 100–120 °C by a factor of 3.0–4.0. Heat setting under tension at 200–240 °C crystallizes the film and locks in dimensional stability. Compliance for food-contact packaging is verified against EU Regulation (EU) No 10/2011, while film mechanical properties are tested according to ASTM D882-18 and haze by ASTM D1003-21. The end product categories include metallized barrier films, photovoltaic backsheet core layers, release liner substrates, and flexible electronic insulation.

When Purified Terephthalic Acid Replaces Phthalic Anhydride in Powder Coating Polyester Synthesis

When purified terephthalic acid replaces phthalic anhydride in carboxyl-functional polyester resin reactors, the initial esterification is slower because PTA has a melting point above 300 °C and low solubility in neopentyl glycol. This requires a staged monomer charge in a jacketed batch reactor with helical or anchor agitation, nitrogen sparge at 0.5–1.0 reactor volumes per hour, and temperature ramps from 180 °C to 245 °C to avoid sublimation of unreacted PTA in the overhead system. A typical monomer charge contains 30–55 wt% PTA based on total monomer weight, with the balance composed of neopentyl glycol, trimethylolpropane, and a small proportion of isophthalic acid or adipic acid to adjust glass transition and reactivity. The polycondensation is terminated when the acid value reaches 20–80 mg KOH/g and the softening point reaches 95–110 °C, depending on whether the resin will be crosslinked with triglycidyl isocyanurate or β-hydroxyalkylamide. For β-hydroxyalkylamide cure formulations, moisture control below 0.3 wt% residual water is required to avoid premature cure, and amine-based additives are incompatible because they promote premature crosslinking during extrusion. The hot resin is cooled to 90–100 °C and then combined with the curing agent and pigments in a double-screw extruder at 100–120 °C before being ground and classified to 10–100 µm particle size. Compliance for architectural powder coatings is established under ISO 8130-2:2019 for gas evolution, ASTM D3451-21 for coating powder testing, and REACH for monomer registration. Terminal products include anti-corrosion powder coatings for steel furniture, aluminium architectural profiles, and outdoor equipment, but formulations with high PTA content may have limited flow compared with conventional isophthalic acid systems.

Esterification of 2-Ethylhexanol Proceeds Through a Titanium-Alkoxide Intermediate

Continuous DOTP production from SASA Polyester PTA and 2-ethylhexanol is operated with a molar ratio of 2-ethylhexanol to PTA between 2.10 : 1 and 2.30 : 1, a slight excess over the theoretical 2 : 1 required to drive esterification toward the diester while suppressing acid-functional monoester carryover. The PTA is slurried in 2-ethylhexanol at 60–80 °C and transferred to an esterification reactor equipped with a reflux column and decanter, where titanium alkoxide catalyst at 50–150 ppm Ti initiates esterification at 180–220 °C. Reaction water is removed as a heteroazeotrope with 2-ethylhexanol, and the organic phase is returned to maintain the alcohol excess. The crude diester is then neutralized with dilute aqueous sodium carbonate, steamed under vacuum at 180–200 °C to strip unreacted alcohol, and filtered through plate-and-frame filter presses with diatomaceous earth to achieve an acid value below 0.05 mg KOH/g. The resulting bis(2-ethylhexyl) terephthalate typically exhibits a density of 0.983–0.985 g/cm³ at 20 °C and a viscosity of 63 mPa·s at 25 °C, with a flash point above 230 °C. For food-contact PVC applications, EU Regulation (EU) No 10/2011 establishes a specific migration limit of 60 mg/kg for the substance, and compliance with REACH and the absence of DOTP from the phthalate restrictions in RoHS Directive 2011/65/EU Annex II are routinely documented in extended safety data sheets. Terminal products include wire and cable jackets, vinyl flooring, synthetic leather, and food-contact PVC films where phthalate-free plasticizer demands are mandatory.

Staple Fiber Melt Spinning and Draw-Line Friction Profiles

In fiber-grade PET conversion, a slurry ratio of ethylene glycol to PTA of 1 : 1.10 to 1 : 1.15 is used, with ethylene glycol added in excess to compensate for diethylene glycol formation during esterification at 260–270 °C. A delustering agent, anatase titanium dioxide, is added as a 20–40 wt% suspension in ethylene glycol to achieve a final concentration of 0.3–0.5 wt% in the polymer; the suspension must be continuously recirculated through a high-shear mixer to prevent agglomeration and spinneret filter pressure rise. The polymerized melt with an intrinsic viscosity of 0.60–0.68 dL/g is conveyed to multi-position spinning beams and extruded through spinnerets at 285–295 °C, followed by cross-flow quench air at 0.4–0.7 m/s and a take-up speed of 1,200–1,600 m/min for partially oriented yarn. Staple fiber lines further draw the tow in a two-stage heated bath at draw ratios of 2.5–3.5, apply spin finish lubricant, crimp, and cut. When chipped polymer is used instead of direct melt-to-fibre conversion, drying at 170–180 °C for 4–6 h to less than 0.004 wt% moisture is required to prevent hydrolysis. Compliance for textile articles is verified under OEKO-TEX Standard 100, and melt flow characterization follows ISO 1133-1:2022. Terminal product categories include PET staple fiber for needle-punched nonwovens, geotextiles, automotive interior felt, hygiene coverstock, and carpet yarn or filling fibre.