INEOS Zhuhai (ex BP Zhuhai) PTA

INEOS Zhuhai (ex BP Zhuhai) PTA refers to purified terephthalic acid produced at the former BP Zhuhai Chemical Co., Ltd. aromatics site in Guangdong Province, China, which transferred to INEOS ownership on 1 January 2021 as part of the acquisition of BP’s global aromatics and acetyls business. The product is a crystalline aromatic dicarboxylic acid with CAS 100-21-0, molecular formula C₈H₆O₄, and molar mass 166.13 g/mol. Synthesis follows the continuous catalytic air oxidation of p-xylene in acetic acid solvent under cobalt-manganese-bromide catalysis, followed by crude terephthalic acid hydrogenation and multi-stage crystallization. That hydrogenation step distinguishes this material from crude terephthalic acid and from less-refined technical-grade terephthalic acid streams. The theoretical acid number for the molecular structure is 675 ± 2 mg KOH/g, based on two carboxylic acid groups per molecule. This value provides a rapid gross purity control point, although it is not sufficiently sensitive to detect trace monofunctional impurities at the part-per-million level.

What specification envelope separates this PTA from general technical-grade terephthalic acid?

Polymer-grade PTA from the Zhuhai asset is controlled by parameters that directly affect esterification kinetics, polycondensation chain growth, and optical clarity. The dominant purity index is 4-carboxybenzaldehyde content. Residual 4-CBA is an aldehyde-functional impurity that can terminate chain extension in polyethylene terephthalate melt polymerization and contributes to yellowing. Typical polymer-grade control for this impurity is ≤ 25 mg/kg, whereas non-hydrogenation terephthalic acid products may contain significantly higher aldehyde-bearing impurities. p-Toluic acid is limited to ≤ 150 mg/kg because the monofunctional carboxylic acid can act as an end-capping species during polycondensation. Moisture is routinely controlled to ≤ 0.2 wt% by Karl Fischer titration according to ISO 15512:2016; the limit is intended to reduce feeding variability and hydrolysis of esterification intermediates. Ash content is limited to ≤ 10 mg/kg, reflecting the importance of residual cobalt, manganese, iron, and other catalyst-related metals in downstream processing. The optical parameter b*, measured by reflectance spectrophotometry in the CIE L*a*b* system, is typically controlled below 1.0 to maintain whiteness in bottle resin, continuous filament, and biaxially oriented film. Particle size distribution is controlled such that the laser diffraction median D50 falls in the range 100–140 μm and the mass fraction below 45 μm remains below 5 wt%. The measurement framework is described in GB/T 32685-2016 for polyester-grade PTA, supplemented by ISO 13320:2020 for particle size analysis and ISO 15512:2016 for moisture. Published asset-specific lot data are limited; the stated ranges should be read as the typical polymer-grade envelope rather than a guaranteed certificate of analysis for every shipment.

In melt-phase polyester production, the principal impurity effects are observed at low concentrations because chain-stopper molecules are not distinguishable from PTA during esterification. At a 4-CBA content of 25 mg/kg, the molar impurity fraction relative to PTA is approximately 2.8 × 10⁻⁵ mol/mol, based on a 4-CBA molar mass of 150.13 g/mol. At a p-toluic acid content of 150 mg/kg, the corresponding fraction is approximately 1.8 × 10⁻⁴ mol/mol, based on a p-toluic acid molar mass of 136.15 g/mol. These levels are not the primary direct determinant of number-average degree of polymerization, but they remain relevant to color-body formation, thermal oxidative stability, and long-term accumulation in recycled glycol loop streams. The low residual metal content in the Zhuhai product is therefore operationally significant because cobalt and manganese residues can catalyze thermal oxidative degradation during drying and injection molding, shifting acetaldehyde regeneration rate and increasing yellowing under barrel residence times above 5 min.

In continuous polyethylene terephthalate production, PTA from this asset is fed as a paste with ethylene glycol at a molar ratio typically in the range 1.1–1.3 glycol to PTA. The esterification stage operates at 240–270 °C and 1–3 bar g, with water removed through a rectification column. Under these conditions, the esterification of PTA and ethylene glycol is temperature-sensitive and dependent on effective removal of water from the paste. The low 4-CBA and p-toluic acid limits are necessary to achieve a melt-phase intrinsic viscosity of 0.60–0.65 dL/g before solid-state polymerization. Intrinsic viscosity is measured by capillary viscometry according to ASTM D4603-18. For bottle resin, subsequent solid-state polycondensation raises intrinsic viscosity to 0.80–0.84 dL/g, at which point acetaldehyde generation, crystallinity, and melt strength become critical. In film-grade and textile-filament operations, the emphasis shifts from acetaldehyde control toward particle size uniformity and fines control, because slurry feed stability in high-throughput lines depends on avoiding particle segregation in day bins and screw feeders.

Impurity, Particle Morphology, and Downstream Viscosity Effects

The distinction between INEOS Zhuhai PTA and other PTA sources lies primarily in the fixed-bed hydrogenation step and crystallization train. Some PTA assets produce powder with a broader span of particle size distribution because of differences in crystallizer agitation, slurry density, and rotary vacuum filtration. A broader span raises the fines fraction and creates feeding discontinuities in continuous PET plants that do not re-blend incoming material. The former BP Zhuhai asset has historically emphasized p-xylene oxidation selectivity and hydrogenation reactor performance; this is reflected in the low 4-CBA limit and in the low total aldehyde content, which is often below 10 mg/kg as terephthalic acid equivalents for polymer-grade lots. In contrast, crude terephthalic acid and non-hydrogenation PTA routes may contain 4-CBA in the range 200–2,500 mg/kg and require additional purification before polyester use. The particle morphology of the Zhuhai product is controlled by the crystallization temperature profile and the ratio of mother liquor recycle. This affects the specific surface area of the powder, typically measured by nitrogen adsorption with a range of 0.5–1.5 m²/g for commercial PTA, and influences slurry rheology. A lower specific surface area reduces ethylene glycol absorption into particle voids, while excessive surface area can increase paste viscosity and reduce slurry uniformity. The dissolution behavior of PTA in ethylene glycol is not a simple solubility-limited process; it is affected by particle size distribution, crystal habit, and residual p-toluic acid. Therefore, two PTA shipments with identical purity may not deliver the same esterification rate if their particle size distributions differ. For this reason, some downstream converters specify not only chemical composition but also a particle size ratio such as D90/D10 ≤ 3.0. The Zhuhai asset’s product is supplied as a free-flowing crystalline powder; bridging and ratholing in silos are controlled by limiting moisture to the stated maximum and by maintaining silo walls above dew point.

For bottle-grade PET, the operational emphasis shifts to acetaldehyde control, preform haze, and melt color stability. Acetaldehyde in the final preform is frequently controlled at ≤ 1 ppm, with haze measured according to ASTM D1003-21. The contribution of PTA to these values is indirect but measurable through residual aldehydes and metal residues. For biaxially oriented polyester film, the contribution of PTA impurities is evaluated through thermal stability after casting, and through the frequency of melt filtration pressure rise. The small particle size tail of the PTA powder affects melt filtration only after polymerization, but poor slurry wetting of high-fines PTA can produce localized oligomer-rich zones in the esterification vessel. In textile filament operations, the practical consequence of high fines is often observed as increased spinning pack pressure rise and greater filament break frequency in high-speed winding. These effects are not unique to PTA produced at the former BP Zhuhai site, but they explain why the particle size distribution of this product is specified with the same rigor as its chemical purity.

When slurry moisture and fine-particle migration reach the esterification stage

Slurry preparation in continuous PET lines commonly targets solids concentrations of 65–70 wt% PTA in ethylene glycol. Above 70 wt%, paste viscosity increases sharply and the mixture can exhibit shear-thinning behavior; this makes pump speed and pressure relationships non-linear during esterification feed control. If the D90/D10 ratio exceeds 3.5, size segregation in day bins can lead to a fines-rich lot discharged first and a coarse-rich lot discharged last. Downstream, this segregation can produce measurable esterification pressure fluctuations and require compensating paste heater duty adjustments. The particle size envelope for the Zhuhai PTA product is therefore relevant to slurry pump selection and to the design of recirculation loops. The product should be conveyed in closed pneumatic systems with dry, oil-free compressed air. Pre-drying is not normally required below ambient relative humidity of 60%; above this value, moisture pick-up during prolonged storage may alter feed composition and should be monitored before bulk unloading. Contact with strong bases, strong oxidizers, and reducing agents is not recommended. Neutralization with sodium hydroxide is exothermic and may produce soluble terephthalate salts that alter waste-stream pH. The dust is combustible as an organic powder, and ignition sources should be controlled; protection design generally follows ATEX or Chinese GB 15577 requirements for combustible dust. Intimate mixing with primary or secondary amines in the solid state should be avoided because exothermic salt formation and localized agglomeration can occur.

From a regulatory compliance standpoint, the material is notified under the relevant chemical inventories. The CAS 100-21-0 entry aligns with the EU REACH registration by the responsible INEOS legal entity, and the product can be used as a monomer for food-contact polyethylene terephthalate when the final polymer meets European Commission Regulation (EU) No 10/2011 and U.S. FDA 21 CFR 177.1630 requirements for PET. Compliance under Chinese food-contact standards requires conformance with the applicable positive list and migration limits. RoHS obligations do not apply because PTA is not an electrical or electronic equipment article, but heavy-metal limits such as ≤ 10 mg/kg ash and low iron content are often verified to safeguard downstream catalyst performance. The product does not contain intentionally added substances of very high concern above the concentration threshold 0.1 wt% under EU REACH Article 57. Shipment-specific certificates of analysis and regulatory conformance statements from the producing legal entity remain the operative documents.