Bottle-grade PET resin production from Sinopec Luoyang PTA is typically initiated in a paste mixer where ethylene glycol and PTA are metered at an EG/PTA molar ratio of 1.15–1.25:1. The slurry is held below 90 °C; PTA powder with mean particle size 100–160 μm and bulk density 0.80–0.95 g/cm³ can segregate in storage hoppers, so agitator torque is used to confirm paste uniformity. The two-stage esterification system operates at 245–265 °C and 0.10–0.30 MPa gauge, with primary and secondary residence times of 2.5–4.0 h and 1.0–2.0 h respectively; liberated water is removed through a reflux column. PTA quality is monitored with 4-CBA ≤25 mg/kg and ash ≤10 mg/kg because residual p-carboxybenzaldehyde can conjugate during esterification and shift clear-resin CIE b* into the 1.5–2.0 range. Antimony trioxide is metered at 150–250 ppm Sb, and phosphorus stabiliser at 10–50 ppm P is added after esterification. The finisher operates at 270–285 °C under 20–200 Pa absolute, producing amorphous pellets with intrinsic viscosity 0.60–0.65 dL/g by ASTM D4603-18. Pellets are crystallised at 150–180 °C for 30–60 min and solid-state polymerised at 205–215 °C under nitrogen at 20–100 Pa absolute for 12–20 h to reach 0.80–0.84 dL/g. Residual acetaldehyde is reduced to <1 μg/g for carbonated-soft-drink preforms under FDA 21 CFR 177.1630 and EU Regulation No 10/2011. Terminal products include beverage bottles, food jars and edible-oil containers; pre-drying at 160–170 °C to <50 ppm moisture is required before injection stretch-blow moulding.

Polyester Staple Fibre Spinning and Draw Ratio Control

Textile-grade PET from the same PTA source is polymerised to an intrinsic viscosity of 0.62–0.68 dL/g at 280–290 °C under high vacuum; the melt enters a manifold and is dosed with a TiO₂ delustrant masterbatch at 0.3–0.5 wt% through high-shear static mixer elements with shear rates of 200–500 s⁻¹. A 20–40 μm rated filter pack removes oligomer gels. Spinning packs with capillary diameters of 0.15–0.25 mm deliver partially oriented yarn at 2,800–3,500 m/min for POY or fully drawn yarn at 4,000–5,000 m/min for FDY. Draw ratio on POY lines is held between 1.4 and 1.6, and hot rolls at 80–140 °C control crystallinity. Tenacity at break for FDY is 4.0–4.8 cN/dtex under ISO 2062:2009, elongation at break 20–35%. Batch-to-batch variance in PTA bulk density can shift dosing accuracy on volumetric feeders, so gravimetric loss-in-weight feeding is specified for 0.3 wt% additive masterbatches. Finishing oil application at 0.3–0.7 wt% and spin finish selection adjust inter-fibre friction; high 4-CBA carryover raises melt colour and limits whiteness in hygiene-grade fibre. Terminal products include sportswear, fleece, nonwoven geotextiles, automotive carpet face yarn and filling fibre.

Film-Grade Extrusion Casting Demands Tight Oligomer and Moisture Control

Cast film from Luoyang PTA-based PET is processed at 260–280 °C through a two-stage vented extruder with melt filtration at 10–20 μm; the resin is pre-dried at 160–175 °C to <30 ppm moisture. Extrudate is quenched on a chill roll at 15–30 °C to form an amorphous sheet, then machine-direction stretched 3.0–3.6:1 at 85–100 °C and transverse-direction stretched 3.5–4.0:1 at 100–120 °C. Heat setting at 200–220 °C stabilises dimensional shrinkage to <0.5% at 150 °C for 30 min under ASTM D1204. PTA fines and ash above 10 mg/kg generate surface defects; users specify average particle size 100–160 μm and 4-CBA ≤25 mg/kg to avoid yellowing and haze. Silica slip agent at 0.1–0.3 wt% is added to control handling. Terminal products include flexible food packaging, capacitor dielectric film, thermal transfer ribbons and photovoltaic backsheet base film. Direct food contact compliance follows EU No 10/2011 with overall migration <10 mg/dm²; solar backsheet damp-heat testing at 85 °C/85% RH for 1,000 h is controlled by low diethylene glycol content in the base polymer.

Polybutylene terephthalate polymerisation from PTA and 1,4-butanediol is run at an alcohol/acid molar ratio of 1.1–1.3:1 in a two-stage esterification train at 220–235 °C, with tetrabutyl titanate at 50–150 ppm Ti and tetrahydrofuran removal as overhead. Compared with the dimethyl terephthalate route, PTA esterification releases water rather than methanol, simplifying rectification but requiring tighter control of THF formation. The prepolymer is advanced at 245–260 °C below 100 Pa absolute to intrinsic viscosity 0.85–1.20 dL/g for injection-moulding grades. Granules are pre-dried at 120–140 °C for 3–4 h to <0.02% moisture; injection-moulding barrel temperatures are 240–260 °C, mould temperatures 60–100 °C, and filling pressures 60–100 MPa. Shot sizes above 60% of barrel capacity and melt residence below 5 min limit thermal degradation. Tensile modulus is evaluated under ISO 527-2 and melt volume-flow rate under ISO 1133-1:2022 at 250 °C/2.16 kg. In electrical connector applications, UL 94 V-0 formulations based on halogenated or phosphinate flame retardants are used, but acidic PTA residuals above target can reduce retention after hydrolytic ageing; carboxyl end-group content is therefore monitored. Terminal products include automotive engine-compartment connectors, relay housings, bobbins, pump casings and appliance components.

Why Does Acid Number Drift in Aromatic Polyol Esterification?

Aromatic polyester polyols use PTA as a rigid aromatic segment donor in combination with diethylene glycol, neopentyl glycol, dipropylene glycol and small additions of adipic or phthalic anhydride. Single-stage cook at 210–230 °C with nitrogen sparge at 0.5–1.0 L/min per metric tonne is used; water of esterification is removed through a packed column or partial condenser. Acid number is driven to 1.5–3.0 mg KOH/g and hydroxyl number to 230–320 mg KOH/g, measured under ASTM D4662 and ASTM D4274 respectively; viscosity at 25 °C is usually 2,000–8,000 mPa·s. Higher PTA content increases viscosity from 35% aromaticity upward, which can require anchor agitators and larger reflux capacity beyond 50 mol% PTA on total dibasic acid. Drift in acid number occurs when PTA sublimes into the reflux leg or when batch temperature exceeds 235 °C, causing diethylene glycol degradation to dioxane and viscosity loss. The product is reacted with polymeric MDI at isocyanate index 100–115 in rigid polyurethane foam, with pentane or hydrofluoroolefin blowing agents. Terminal products include metal-faced insulation panel cores, pour-in-place appliance insulation and spray foam. Compressive strength is tested under ASTM D1621; blowing-agent solubility and cell structure are controlled through water content below 0.05%.

When PTA Replaces Phthalic Anhydride in Short-Oil Alkyd Bake Systems

In short-oil alkyds for coil coatings and automotive bake systems, PTA can displace 20–40 mol% of phthalic anhydride when a staged addition program compensates for its high melting point and low initial solubility. Esterification is run at 230–250 °C with xylene azeotrope recirculation and a two-step acid feed: PTA is charged with the polyol at 180–200 °C and held until clear before adding phthalic anhydride and fatty acid. Target acid value is <10 mg KOH/g at 60% solids, with Gardner colour <4 under ASTM D1544. Polyol excess of 10–20% on equivalents is held to prevent gelation during the high-temperature bodying phase. PTA-derived alkyds show faster bodying and higher aromatic ring density, improving hardness and chemical resistance but reducing flexibility; rapid deformation impact is tested under ASTM D2794. Terminal products include coil coating primers, interior can coatings and heat-cured appliance finishes. The polyester binder must remain soluble in high-flash naphtha; excessive terephthalate content can raise viscosity and cause hazing, so cloud point is controlled. For can coating use, migration limits are assessed under 21 CFR 175.300.