Continuous direct esterification trains processing Sinopec Yizheng Chemical Fibre purified terephthalic acid are typically configured for polyester staple and filament production at melt-phase intrinsic viscosity ranges of 0.62–0.68 dL/g measured to ASTM D4603. PTA is mixed with monoethylene glycol at a molar feed ratio of approximately 1:1.15 PTA to MEG before entering the first esterification vessel. The esterification stage operates at 255–265 °C and 0.15–0.25 MPa, while downstream polycondensation reactors require a vacuum below 100 Pa and temperatures of 278–288 °C. The resulting melt is fed through spinning beams with 0.15–0.30 mm diameter spinneret holes at 282–295 °C. Quench air velocities between 0.4–0.8 m/s and draw ratios of 3.5–4.5 are used depending on whether the line is producing high-tenacity industrial yarn or apparel-grade staple. Titanium dioxide delustrant is injected as a glycol slurry at 0.3–0.5 wt% for semi-dull fibre. The PTA specification for this route requires 4-carboxybenzaldehyde (4-CBA) content below 25 mg/kg, b* colour below 1.0, and ash content below 10 mg/kg, because residual impurities shift fibre brightness and increase spinneret pack pressure rise. Terminal products include ring-spun yarn, draw-textured yarn, nonwoven carded webs, and high-tenacity technical yarn used in tyre cord and geotextile fabric. Compliance for downstream trade rests on OEKO-TEX Standard 100 class-specific limits, REACH Annex XVII restrictions, and melt-spinning line acceptance tests conducted to ISO 2062 for yarn tenacity and ISO 1133-1 for melt flow control. Pack pressure rise exceeding 0.05 MPa/h on production spinnerets generally indicates filtration gel accumulation traceable to oxidation by-products in PTA, and is a routine batch acceptance parameter on continuous lines.

Why Does Solid-State Polymerisation Still Govern Bottle-Grade IV Requirements?

In PET bottle resin manufacture from Sinopec Yizheng Chemical Fibre PTA, melt-phase polycondensation alone rarely reaches the intrinsic viscosity of 0.80–0.84 dL/g needed for carbonated soft drink and water containers. The PTA-to-MEG ratio is held near 1:1.08–1:1.13 to control diethylene glycol formation and chain end balance. Antimony trioxide catalyst is added at 190–300 mg/kg as Sb, and a phosphorus stabiliser is introduced after esterification at 20–50 mg/kg as P. Melt-phase polymer is produced at 275–285 °C under a vacuum below 150 Pa to reach an IV of approximately 0.60 dL/g before chipping. Solid-state polymerisation increases IV to 0.82 dL/g at 205–215 °C in continuous shaft-dryer or tumble-dryer vessels with nitrogen flow and residence times of 14–24 h. Acetaldehyde content after SSP is typically below 1 ppm, measured by headspace gas chromatography. Injection moulding of preforms uses reciprocating screws with barrel zones of 270–290 °C, hot runner temperatures of 275–285 °C, and clamp force dependent on preform cavitation; a 48-cavity preform system commonly operates above 300 t. Blow moulding follows at 95–120 °C with stretch ratios of 2.5–3.0 longitudinal and 2.8–3.2 hoop. The ester content, residual heavy metals, and migration limits are evaluated under FDA 21 CFR 177.1630(b), EU Regulation 10/2011 as amended, and GB 4806.7. Processing deviations above 285 °C increase AA regeneration rates and require preform ventilation or storage time reductions. This route yields water bottles, CSD bottles, edible oil bottles, and hot-fill containers with panel weight reduced to 10–14 g for 500 mL formats.

Oligomer Deposition at the Die Lip Limits Biaxially Oriented Film Production Rates

When PTA-derived PET is cast into biaxially oriented film, the polymer typically enters the extruder with an IV of 0.62–0.68 dL/g and a moisture specification below 50 ppm. The resin is dried at 160–180 °C for 4–6 h in desiccant dryers to prevent hydrolytic degradation. Extruder barrel temperatures range from 260–285 °C, while the meltline and filter train are maintained below 285 °C to restrict cyclic trimer formation. Filtration screens of 25–40 µm are specified because gel and oligomer agglomerates create die-line streaks and voltage breakdown points in capacitor films. The melt is cast onto a chill roll held at 20–30 °C, then stretched in the machine direction at 3.0–3.5 and in the transverse direction at 3.5–4.0. Heat-setting at 220–230 °C for 5–15 s stabilises shrinkage. For packaging film, antiblock silica is added at 0.05–0.20 wt%; for electrical insulation film, particle addition is reduced and cleanliness standards are tightened. Terminal products include flexible packaging laminate base film, thermal transfer ribbon, photovoltaic backsheet film, and capacitor dielectric film with thickness below 2 µm in metallised grades. Qualification testing references IEC 60674-3 for thickness uniformity and breakdown voltage, ASTM D1004 for tear strength, and ASTM D882 for tensile properties. Operations data from film lines show that die lip deposit accumulation above 0.5 mm across the lip width increases film thickness variation by more than 0.3 µm and forces line stops for cleaning every 24–48 h on high-speed lines. The PTA 4-CBA content must remain below 25 mg/kg because elevated oxidation by-products correlate with higher melt oligomer content and faster filter pressure rise.

Crystallisation Half-Time and Injection Moulding Parameters in PBT Compounding

PBT produced from Sinopec Yizheng Chemical Fibre PTA and 1,4-butanediol is compounded when PTA is esterified at 230–245 °C with a molar ratio of diol to acid around 1.3–1.5:1.0. Tetrabutyl titanate catalyst is charged at 50–200 mg/kg as Ti after the esterification stage. The resulting PBT base resin reaches an intrinsic viscosity of 0.75–1.00 dL/g measured to ISO 1628-5, a melting point of 222–225 °C by ISO 11357-3, and a crystallisation half-time below 2 s at 180 °C. Reinforced grades are produced on twin-screw extruders with L/D ratios of 40:1–48:1, barrel temperatures of 240–270 °C, and glass fibre addition of 15–30 wt%. Injection moulding requires melt temperatures of 250–265 °C, mould surface temperatures of 60–90 °C, and holding pressures of 60–100 MPa. Unreinforced PBT is sensitive to alkaline cleaning agents and prolonged hot-water hydrolysis above 80 °C; hydrolysis stabilisers such as carbodiimides are added at 0.5–1.5 wt% where long-term coolant resistance is required. Terminal products include electrical connectors, relay housings, brush holders, automotive sensor brackets, and pump impellers. Compliance for global shipments normally includes IEC 60695-2-12 glow-wire tests, ISO 75-2 HDT values, ISO 527-2 tensile modulus, and RoHS Directive 2011/65/EU Annex II substance restrictions. A production-scale failure mode observed in thin-wall connectors is insufficient mould temperature causing premature freeze-off and a drop in weld-line strength below 70% of the base resin value; this is corrected by raising mould temperature to 90 °C, not by increasing melt temperature.

In resin reactors producing unsaturated polyester for continuous panel lamination, PTA functions as a high-melting aromatic diacid replacing part of the phthalic anhydride charge. A typical high-reactivity formulation charges maleic anhydride, PTA, propylene glycol, and diethylene glycol at a saturated-to-unsaturated acid molar ratio of 0.25–0.45:1.0 and a hydroxyl-to-carboxyl molar ratio of 1.05–1.15:1.0. The esterification cook proceeds at 190–210 °C under inert gas until the acid value falls to 20–30 mg KOH/g and the melt viscosity reaches 800–1,200 mPa·s at 125 °C. The cook is then inhibited and dissolved in styrene monomer at 35–40 wt% solids. PTA raises reactor torque and slows initial solubility compared with phthalic anhydride; operators compensate by stepwise addition or by using a longer cook time of 2–4 h after reaching 180 °C. The cured resin is used in fibreglass-reinforced panels, pultruded profiles, cast polymer concrete, and sheet moulding compound. Gel time is controlled to 8–15 min with methyl ethyl ketone peroxide at 1.0–1.5 wt%, and exotherm peak is routinely monitored between 180–220 °C in 100 g cup tests. Compliance for architectural and transportation applications includes EN 13501-1 reaction-to-fire classification, ASTM D2583 Barcol hardness, ISO 527-4 laminate tensile properties, and styrene monomer exposure limits under local occupational hygiene rules. Published data for Sinopec Yizheng PTA-specific performance differences in unsaturated polyester resin are limited; therefore plant-scale qualification generally includes acid value curves, colour measurements, and glass transition temperature checks after a reference cook. The end products are opaque or gel-coated building panels, tub-shower basins, vehicle body panels, and corrosion-resistant tanks.

Medium-molecular-weight aromatic polyester polyols are prepared from PTA, diethylene glycol, and optional aliphatic acids in batch reactors equipped with rectification columns. The PTA charge is 20–40 wt% of the total reactor feed, while diethylene glycol serves as the main glycol at 40–60 wt%; the glycol excess and reaction water are removed by distillation to drive the esterification to a hydroxyl value of 250–350 mg KOH/g. The reaction temperature is kept at 210–230 °C, and vacuum is applied in the final stage to strip residual water until the acid value is below 1.0 mg KOH/g. The final polyester polyol exhibits a viscosity of 5,000–25,000 mPa·s at 25 °C and is used as a compatibilising polyol in rigid polyurethane and polyisocyanurate foam systems. In continuous foam lamination lines for metal-faced insulation panels, the PTA-based polyol is blended with blowing agents, silicone surfactants, catalysts, and polymethylene polyphenyl isocyanate at an isocyanate index of 250–350. The aromatic content from PTA improves dimensional stability and the onset of char formation, but compatibility with low-boiling pentane blowing agents must be verified by storage stability testing at 25 °C and 40 °C because viscosity drift above 10% after 7 days creates metering pump instability. Terminal products include continuous sandwich panels, pour-in-place insulation, and block foam cut into pipe sections. Fire performance is tested to EN 13501-1 or ASTM E84, and finished panel systems are supplied under regional construction product regulations such as CPR Regulation (EU) No 305/2011. Polyurethane systems containing PTA-derived polyester polyols are not suitable for prolonged contact with strongly alkaline aqueous media; polyester backbone hydrolysis becomes measurable above 60 °C in wet service.

When Phthalate-Free Plasticiser Specifications Require Di-2-Ethylhexyl Terephthalate

Diesters of PTA with 2-ethylhexanol are produced on continuous or batch esterification lines equipped with titanium or tin catalysts. A molar feed ratio of alcohol to PTA of 2.2–2.5:1 is used with the excess alcohol recovered by vacuum stripping. Esterification is carried out at 180–220 °C and completed under reduced pressure to achieve a final acid value below 0.05 mg KOH/g, ester content above 99.5%, colour below 20 Hazen, and water content below 500 mg/kg. The resulting di-2-ethylhexyl terephthalate has a density of 0.983–0.987 g/cm³ at 20 °C and a kinematic viscosity of approximately 70–80 mm²/s at 25 °C. Flexible PVC compounds containing DOTP typically achieve volume resistivity above 1×10¹² Ω·m when tested to IEC 60093. Compounding into flexible PVC uses plasticiser loadings of 50–100 phr in wire and cable insulation, flooring wear layers, and interior automotive skins. The low migration and low volatility profile is evaluated by ISO 177 or internal volatile loss methods and by extraction tests specified in ISO 3826 for blood bags or relevant regional food-contact legislation. Because DOTP is considered a non-phthalate plasticiser, downstream formulations are often submitted to REACH authorised use checks and RoHS Directive 2011/65/EU verification protocols, though no RoHS restriction applies specifically to DOTP. Batch scale-up issues on stripping columns include alcohol carryover into the vacuum system above 0.2 wt%; this raises final odour and requires a second thin-film evaporation pass. The terminal plasticised PVC articles are used for heat-resistant cable sheathing, upholstery, gasketing, and children’s articles where phthalate-based ortho-plasticiser exclusion is contractually required.