Alpek Polyester Brazil (Petroquimica Suape) PTA is purified terephthalic acid manufactured at the Suape petrochemical complex in Ipojuca, Pernambuco, Brazil. The material is a white crystalline powder with the chemical formula C₈H₆O₄, CAS registry number 100-21-0, and relative molecular mass 166.13 g/mol. The product is sold as a polymer-grade aromatic diacid rather than a family of model-differentiated grades; no separate public grade code is consistently assigned in technical literature beyond the Suape unit designation. It is used primarily in the esterification of monoethylene glycol to bis(2-hydroxyethyl) terephthalate, followed by continuous melt-phase polycondensation to polyethylene terephthalate resin. Downstream outlets include carbonated soft drink bottle preforms, hot-fill containers, polyester staple fibre, partially oriented yarn, biaxially oriented film, and lower-volume polyester polyol synthesis.

For melt-phase polyester producers, the critical quality boundary is not total acidity but the population of monofunctional impurities that terminate chain extension. 4-Carboxybenzaldehyde is controlled at ≤ 25 mg/kg in conventional polymer-grade PTA; p-toluic acid is typically held at ≤ 150 mg/kg. Both compounds introduce chain ends that reduce number-average molecular weight at a fixed polycondensation residence time. The aldehyde group in 4-carboxybenzaldehyde also acts as a colour-body precursor under high-temperature esterification at 240–270 °C. Published certificate-of-analysis data specifically for the Suape unit remain limited; the following matrix is representative of polymer-grade PTA quality-control bands rather than a site-specific guarantee.

How Does Impurity Loading in Suape PTA Influence Melt-Phase Polycondensation?

In continuous esterification, PTA powder is dispersed in molten monoethylene glycol at a molar ratio of approximately 1.15–1.40:1 ethylene glycol to PTA. The resulting oligomeric mixture contains bis(2-hydroxyethyl) terephthalate and low molecular weight esters, while water is removed under vacuum. Residual 4-carboxybenzaldehyde is monoesterified and cannot support further chain extension at the same effective rate, acting as an irreversible chain terminator. p-Toluic acid enters the polymer chain as a dead end after one ester linkage, reducing the ester interchange equilibrium and increasing the time required to reach a given intrinsic viscosity. For bottle-grade resin, intrinsic viscosity after solid-state polycondensation is commonly specified at 0.80–0.84 dL/g per ASTM D4603-18; for fibre-grade resin, melt-phase intrinsic viscosity is typically 0.62–0.68 dL/g. European plants may express the same property as viscosity number under ISO 1628-1:2021.

Pneumatic conveying of the powder into day silos is arranged with dry air purge when ambient relative humidity exceeds 60%; moisture uptake beyond 0.2 % w/w can accelerate caking in storage hoppers and block rotary valves. PTA dust is classified as a combustible dust, and area classification is governed by NFPA 652 and, within the European regulatory sphere, ATEX Directive 2014/34/EU. Published K_st and minimum ignition energy data for this specific Suape product configuration are not consistently available in public technical literature, so converter-specific dust-hazard testing should be performed when designing silo protection systems. The material is incompatible with strong bases, which can form terephthalate salts, and with reducing agents under abnormal thermal exposure.

Packaging, Discharge, and Intrinsic Viscosity Response in Downstream Processing

Commercial movement of Suape PTA is arranged as bulk pneumatic delivery or in intermediate bulk containers with internal polyethylene liners. No single packaging configuration defines the product because supply mode is negotiated against the receiving plant’s day-silo configuration. Compared with merchant PTA sourced from geographically distant depots, Suape supply reduces transfer steps from production to PET polymerization, lowering moisture regain and particle attrition. This integration is a physical distribution difference rather than an absolute purity difference. In high-humidity coastal regions, closed-loop conveying with dry air is specified; the operational boundary for receiving is normally ≤ 0.2 % w/w moisture.

Intrinsic viscosity of finished PET is measured in 60/40 w/w phenol/1,1,2,2-tetrachloroethane at 30 °C with a solution concentration of 0.5 g/dL according to ASTM D4603-18. Melt mass-flow rate is compared under ISO 1133-1:2022 at 280 °C with a nominal load of 2.16 kg. The relationship between melt viscosity and intrinsic viscosity is exploited on twin-screw extruders with L/D ratios of 32:1 or higher to homogenize additives before injection moulding. PTA lot-to-lot shifts in particle size and fines can alter feeding uniformity in loss-in-weight gravimetric systems; high fines fractions raise dust exposure and can segregate in silo discharge. Published particle-size-distribution data for the Suape unit itself are limited, so incoming inspection should verify bulk density and fines content against the receiving system design.

When Bottle-Grade Preforms Demand Controlled Acetaldehyde and Clarity

In bottle applications, the conversion path is melt-phase polycondensation to amorphous pellets with an intrinsic viscosity near 0.60 dL/g, followed by solid-state polycondensation at 210–220 °C under nitrogen to raise intrinsic viscosity to 0.80–0.84 dL/g. During injection moulding of preforms, barrel temperatures are maintained between 270 °C and 285 °C; excessive thermal history raises acetaldehyde. Preform acetaldehyde is measured by static headspace gas chromatography per ASTM D4526-20, with common release criteria below 5 µg/kg in the preform and below 1 µg/kg in pellet after solid-state processing. The Suape PTA lot certificate is expected to report colour parameters derived from diffuse reflectance; b* values above 1.5 translate into higher yellowness index in preforms measured under ASTM E313-20. High p-toluic acid and residual 4-carboxybenzaldehyde can shift the vinyl end-group population and increase acetaldehyde generation during melt processing, which is why bottle-grade converters impose tighter incoming PTA limits than fibre producers.

The practical distinction between Suape PTA and commodity PTA from non-integrated facilities emerges most clearly in bottle-grade production: direct integration with PET polymerization at the same complex allows faster quality feedback when preform colour or acetaldehyde drifts. This does not eliminate incoming inspection but reduces the delay between upstream lot change and downstream detection. Converters using high-cavitation preform moulds with 96 or more cavities are especially sensitive to lot-to-lot colour consistency because residence-time differences magnify thermal degradation.

Biaxially Oriented Film Converters Require Low Cyclic Trimer Drift, Not Just Low 4-CBA

In biaxially oriented polyester film production, cyclic trimer and diethylene glycol content are processing variables influenced by PTA purity and esterification stoichiometry. Residual p-toluic acid tends to remain in the amorphous phase and can modify surface properties after stretching; film producers therefore request tight lot-to-lot consistency more than exceptionally low values. Typical film-grade resin is polymerized to intrinsic viscosity 0.58–0.64 dL/g and then dried to moisture below 50 ppm before extrusion at 275–285 °C. Film haze is assessed using ASTM D1003-21; tensile properties are evaluated under ASTM D882-18. Suape PTA used in this segment must provide a stable acid-end equilibrium so that cast film and machine-direction orientation do not generate gel-like defects from high-viscosity agglomerates.

Polyester polyol producers react PTA with diethylene glycol, adipic acid, and trimethylolpropane in nitrogen-blanketed reactors at 220–240 °C to acid numbers below 2 mg KOH/g. In these systems, PTA contributes rigidity and hydrolytic stability to polyurethane foams and coil-coating resins. The material is not intended for direct consumer use; polycondensation plants should avoid contamination with amines or strong bases, which can form salts and reduce monomer availability. Because published lot-level trace metal distributions for the Suape unit are limited, converters should request a supplier certificate of analysis and confirm that total ash and metal limits match the catalyst requirements of their continuous polycondensation operation.