Purified terephthalic acid manufactured by Hainan Yisheng Petrochemical Co., Ltd. at the Yangpu, Hainan petrochemical complex is a single polyester-grade aromatic dicarboxylic acid stream supplied without model sub-designations. The material carries CAS 100-21-0, has the condensed formula C₈H₆O₄, and has a molecular weight of 166.13 g/mol. It is produced by continuous liquid-phase oxidation of para-xylene in acetic acid under a cobalt/manganese/bromine catalytic system, followed by hydrogenation of the crude oxidation product, crystallization, and drying. The output is a white crystalline powder intended for melt-phase polyethylene terephthalate polymerization, with secondary application in polybutylene terephthalate and certain copolyester systems.

The product is typically released against SH/T 1612.1-2005 and/or GB/T 32685-2016 polyester-grade PTA specifications. Because the powder is sensitive to moisture and forms wall scale in dense-phase conveying when relative humidity exceeds 60%, receiving silos are maintained under dried air at dew point below -20 °C. Contact surfaces should be stainless steel or aluminum; copper-alloy lines are avoided because residual acetic acid vapors and wet product can create local corrosion and metal contamination. The absence of sub-model designations means that differentiation from other PTA products is based on certificate-of-analysis impurity data and particle-size behavior rather than product identifiers.

Analytical release profile and standardized limits

The primary specification values are given in Table 1. These values are polyester-grade release windows reported for hydrogenation-refined PTA of this class; the producer’s certificate of analysis should be used for final acceptance. The most sensitive value is 4-carboxybenzaldehyde, which functions as a chain-stopping impurity and chromophore precursor during downstream molten polymerization.

On a 600 t/day continuous PET melt-phase line producing bottle-grade chip, the PTA is mixed with ethylene glycol as a high-solids paste. Esterification is operated between 255 °C and 270 °C at 0.15–0.30 MPa; the oligomer is then forwarded to a finisher at 278–288 °C under vacuum below 1 mbar. In this operating window, a 4-CBA value near 20 mg/kg can raise oligomer color only modestly if antimony trioxide catalyst is held at 140–190 mg Sb/kg PET, but higher 4-CBA concentrations increase the risk of conjugated aldehyde end groups and b* drift. The particle-size window is operationally significant: fines below 45 µm can bridge hoppers and produce dust, while particles above 250 µm may reduce esterification mass transfer and raise screen-pack pressure. Plants with high-shear slurry mixers typically monitor the 45–250 µm mass fraction and the laser diffraction span rather than relying on a single D50 value.

The acid value of 675 mg KOH/g is derived from the two carboxylic acid functions of terephthalic acid. A significantly lower value indicates partial esterification or contamination, while a higher value may reflect residual acidic synthesis impurities. Because PTA is a weak organic acid, wet powder in prolonged contact with carbon steel can produce iron contamination; this is why stainless steel or aluminum contact surfaces are specified for storage and conveying equipment. Sampling from bulk tankers and silos should be performed under dry-air protection to avoid moisture condensation on the product surface.

What Does the Hydrogenation Refining Stage Change in Polyester Chemistry?

The hydrogenation purification step distinguishes this product from unrefined crude terephthalic acid and older oxidation-only PTA streams. In the hydrogenation circuit, 4-carboxybenzaldehyde is reduced to p-toluic acid over a supported palladium catalyst in aqueous solution. The reduction lowers 4-CBA by one to two orders of magnitude relative to crude oxidation cake. The p-toluic acid that remains is monofunctional and less chromophoric, but it still must be controlled because high p-toluic acid can modify terminal acid end groups and oligomerization kinetics. For converter operations, the low 4-CBA value translates into a narrower melt-color trajectory during finisher residence times above 90 min and a more predictable carboxyl end-group response in solid-state PET.

Residual cobalt, manganese, and bromine values are not zero in refined PTA; they are reduced to low milligrams-per-kilogram levels but can still influence downstream catalyst selection. Antimony-based polycondensation catalysts tolerate moderate traces of these metals without major kinetic shift. Titanium-based polyester catalysts, particularly hydrolytically sensitive organotitanates, may require a tighter incoming metal profile because iron and cobalt can promote hydrolysis and yellowing in the presence of residual oxygen. Users switching to titanium catalyst packages should compare certificate-of-analysis total heavy metals and iron values against the catalyst supplier’s upper metal tolerance. When published data for Hainan Yisheng PTA in a specific titanium formulation is limited, the formulation should be qualified by a pilot esterification run followed by ASTM D4603 intrinsic viscosity and ASTM D6290 color measurements.

Secondary use in polybutylene terephthalate relies on direct esterification with 1,4-butanediol at 150–170 °C, followed by polycondensation at 250–260 °C under vacuum, typically with a titanium tetrabutoxide catalyst. In this application, ash control is more critical than in PET because titanium butoxide is hydrolytically active and metal residues can shift melt viscosity and hydrolytic stability. The product’s low iron and total heavy metal windows reduce the risk of excessive catalytic side reactions. Copolyester manufacture using isophthalic acid, cyclohexanedimethanol, or diethylene glycol also benefits from controlled 4-CBA because these copolymers are more sensitive to color shift at high finisher temperatures.

When Moisture and Aldehyde Control Govern Bottle-Resin Solid-State Processing

For bottle-grade resins that are further polymerized in the solid state, the PTA specification intersects with final pellet quality in three process zones. First, melt-phase prepolymer exiting the finisher is pelletized and then heated under nitrogen at 205–215 °C; residual aldehyde and acid impurities can form acetaldehyde and free carboxyls during this heating. Second, any moisture ingress from PTA above 0.2% feed moisture can alter the esterification water balance and produce oligomer with irregular end groups, which later affects solid-state reactivity. Third, the final intrinsic viscosity target of 0.80–0.85 dL/g under ASTM D4603 requires stable stoichiometry and limited side reactions from residual impurities. The refinery-controlled 4-CBA, ash, and moisture window makes the product suitable for this application class, but actual solid-state response must be established with the site’s pellet geometry, crystallizer temperature, and nitrogen dew point.

Comparative impurity phenotype across PTA sources

Table 2 provides representative published ranges for impurity phenotypes across three PTA-like materials. The values are not a substitute for the certificate of analysis but are useful for understanding why a hydrogenation-refined product behaves differently from unrefined CTA or mechanically recovered material.

In a direct comparison, the ≤20 mg/kg 4-CBA window is the primary specification differentiator. Unrefined CTA containing 200–3500 mg/kg 4-CBA cannot be used directly in high-clarity PET because the aldehyde groups introduce chromophoric structures and chain termination during finisher operation. Mechanically recovered PTA can be blended with virgin PTA only when 4-CBA and metal contamination are measured lot-by-lot; otherwise spinneret pressure increases and sheet color variation may occur. Hainan Yisheng PTA therefore enters the supply chain as a direct-replacement polyester-grade intermediate rather than a blend stock, subject to the user’s incoming-particle-size and moisture checks.

Bulk-handling, moisture ingress, and operational boundaries

The product is transported in bulk road tankers, railcars, and marine containers. The Hainan coastal location makes moisture protection during marine transit a key receiving requirement; packaging is not used for typical large-scale polyester operations. Receiving silos should be purged with dried air at a dew point below -20 °C and vented through filters that prevent dust release. Dense-phase conveying should use oil-free air or nitrogen, and line velocities should be kept below the saltation velocity for fine fractions to reduce pipe wear. The material should be segregated from strong bases, volatile amines, and sources of polyethylene or polypropylene fines; amine bases can form terephthalate salts, while polymer fines may reduce melt purity and create black specks.

PTA dust clouds present a combustible dust hazard. Housekeeping, bonding, and grounding should follow NFPA 652 and, where applicable, IEC 60079-10-2. The product should be stored away from direct sunlight and high-temperature surfaces to prevent localized sintering of fines. If exposed to moisture and then compressed in a hopper, the powder can form crusts that release unevenly into the slurry mixer. These crusts are removed mechanically and should not be forced through pneumatic lines, because the resulting surge can alter esterification feed ratio and downstream melt viscosity.

Safety and compliance documentation should include the product safety data sheet, REACH registration or equivalent regional chemical inventory status, and food-contact clearance of the final polyester article. In the United States, PET resins made from this monomer are normally evaluated under 21 CFR 177.1630; in the European Union, the finished plastic is assessed under EU Regulation (EC) No 1935/2004 and the specific migration limits of EU 10/2011. These clearances apply to the final article rather than the PTA intermediate. Users selecting PTA for food-grade PET should perform migration testing on the finished container or film according to GB 4806.6-2016 or GB 31604.1-2015 where Chinese food-contact requirements apply.

Because Hainan Yisheng Petrochemical PTA is released as a single polyester-grade stream, supplier qualification is controlled by the certificate of analysis, not by a model number. The operational comparators are 4-CBA, p-toluic acid, ash, moisture, particle-size distribution, and the trace metal signature. A change of supplier to this product, or from this product to another PTA, should be executed under a measured transition protocol on the downstream line, with attention to esterification pressure, slurry mixer power, finisher vacuum, and the 45–250 µm coarse-laden fraction. That measured transition is the only reliable basis for confirming interchangeability.