Yisheng Petrochemical PTA is a purified terephthalic acid product recovered from continuous catalytic oxidation of p-xylene and subsequent fixed-bed hydrogenation purification. The product is identified by CAS 100-21-0 and has a molecular weight of 166.13 g/mol. In the production route, p-xylene is oxidized in acetic acid at 190–205 °C and 1.4–1.6 MPa gauge using cobalt-manganese-bromide catalysis; the crude terephthalic acid is then dissolved and hydrogenated over a palladium-carbon fixed bed to reduce 4-carboxybenzaldehyde to p-toluic acid. Final product is crystallized, filtered, and dried to a white crystalline powder. The purification step is critical because residual 4-CBA acts as a difunctional aldehyde impurity that can form crosslinks and chromophores in polyester resins. Yisheng Petrochemical supplies standard polyester-grade PTA without published sub-model designations; the material is sold against impurity-based specifications rather than differentiated product lines. Bulk density is typically 0.95–1.05 g/cm³, and median particle size D50 is commonly controlled between 100 µm and 130 µm. No external slip agent, nucleator, or processing aid is added in the PTA itself.

Oxidation and purification conditions also determine crystal habit and surface fines. PTA crystallized under controlled agitation produces particles with D50 in the 100–130 µm range; excessive fines below 45 µm are typically held below 5 wt% because they increase dust generation and can segregate during railcar unloading. The acid number of the dried product, measured by titration, corresponds to the dibasic acid content; for PTA of ≥ 99.5 wt% purity, the theoretical acid number is approximately 676 mg KOH/g, but commercial PTA is not sold on acid number because p-toluic acid and moisture skew the value. Residual acetic acid from the oxidation solvent is monitored as part of odor control; purchasers should confirm the lot certificate limit. Users handling bulk PTA in humid coastal terminals report that moisture gain occurs faster in hopper cars than in closed silos; therefore nitrogen blanketing or dry-air purge is applied to outdoor storage vessels.

What specification boundaries apply to polyester-grade PTA?

Polyester-grade PTA is controlled primarily through impurity limits because residual monofunctional carboxylic acids and metal residues influence molten-state polycondensation kinetics, melt filtration, and final resin color. The following table summarizes typical product control boundaries used for Yisheng Petrochemical PTA and aligned with GB/T 32685-2016 polyester-grade PTA requirements. Values represent standard commercial limits and should be confirmed on each lot certificate.

Each boundary has a distinct function in polymer production. The ≤ 25 mg/kg 4-CBA limit protects against aldehyde-induced branching and yellowing; the ≤ 150 mg/kg p-toluic acid limit controls chain termination because each molecule is a monofunctional aromatic acid. Ash and iron controls below 15 mg/kg and 2 mg/kg respectively reduce spinneret pack plugging and catalyst deactivation. Moisture above 0.5 wt% can shift the esterification equilibrium toward hydrolysis during melt processing and must be removed from stored material. The b* color limit is monitored because even small yellowing in PTA transfers to bottle preforms and film. The test methods are high-performance liquid chromatography for 4-CBA and p-toluic acid, Karl Fischer titration for moisture, combustion at 800 °C for ash, and HunterLab reflectance for b* color. The analytical method for intrinsic viscosity of the downstream polymer is ASTM D4603; melt flow characterization of PET formulations is performed according to ISO 1133-1:2022. Lot certificates normally report these parameters, and buyers with optical requirements should specify b* color and 4-CBA limits on the certificate of analysis.

For context, the 4-CBA boundary of ≤ 25 mg/kg is equivalent to 0.0025 wt%. Because residual 4-CBA contains both an aldehyde and a carboxylic acid group, it can act as a difunctional impurity and create branched structures. The p-toluic acid limit of ≤ 150 mg/kg is a monofunctional acid limit; at this concentration, approximately 0.015 wt% of the feed can cap chain ends. In a PET homopolymer with number-average molecular weight near 20,000 g/mol, the degree of polymerization is about 104 repeat units. A molecule of p-toluic acid consumes one reactive end group, so excess terminator lowers the attainable molecular weight at fixed finisher vacuum and residence time. These relations explain why polyester-grade PTA is traded on impurity levels rather than only total composition.

Bulk handling of Yisheng PTA is configured for dilute-phase vacuum conveying, dense-phase pressure conveying, and flexible intermediate bulk containers. Typical design values for dilute-phase conveying place air velocity between 18 m/s and 25 m/s to avoid attrition or dust generation; dense-phase systems reduce fines and are used for long transfer lines. PTA dust clouds can be combustible, so transfer lines should be bonded and grounded, and silos equipped with deflagration vents or suppression systems following local combustible dust regulations. Storage in closed dry silos at ambient temperature and relative humidity below 60% minimizes moisture pickup and caking. If moisture exceeds 0.5 wt%, the powder can form cohesive bridges in hoppers and loss-in-weight feeders. In high-humidity operations, pre-drying with dry air at 80–100 °C is used before feeding. The product is not classified as a dangerous good for transport under GB 12268-2012; however, the dust explosion risk must be assessed separately. Prolonged contact with strong alkalis is exothermic because PTA is a dibasic aromatic acid. Contact with strong oxidizers should be avoided. Spills should be vacuumed with explosion-rated equipment rather than swept dry because sweeping increases dust suspension.

When low 4-CBA content shifts end-group balance in bottle-grade PET

In continuous bottle-grade PET production, PTA and monoethylene glycol are reacted at esterification temperatures from 260 °C to 280 °C with molar EG/PTA ratio between 1.10:1 and 1.20:1. Esterification is usually conducted in a paste of approximately 70 wt% PTA in glycol; the paste is transferred by gear pumps to a sequence of esterification and polycondensation reactors operating under progressive vacuum. If residual 4-CBA exceeds the polyester-grade PTA boundary of ≤ 25 mg/kg, aldehyde-derived byproducts can introduce branching and color bodies that alter both melt-phase polycondensation kinetics and solid-state polymerization behaviour. Because Yisheng Petrochemical PTA is controlled at or below this 4-CBA ceiling, the feed stream maintains a low concentration of aldehyde-terminated species during esterification. The p-toluic acid content is a second end-group variable: each molecule acts as monofunctional chain stopper, so concentrations above 150 mg/kg reduce the number-average molecular weight achievable in the finisher at fixed residence time, observed as lower intrinsic viscosity before solid-state polymerization. In solid-state polymerization, pellets are heated to 205–220 °C under nitrogen to raise intrinsic viscosity from approximately 0.63 dL/g to 0.82 dL/g; the measurement follows ASTM D4603. Bottle-grade resin produced from PTA with stable 4-CBA and p-toluic acid values displays less lot-to-lot variation in carboxyl end groups. This directly affects acetaldehyde generation during injection molding of preforms; acetaldehyde is monitored by headspace gas chromatography, and published target concentrations in water-bottle preforms are commonly below 5 mg/kg. The residual aldehyde and carboxyl end groups also influence the final intrinsic viscosity after solid-state polymerization.

Process analytical control in the PTA plant includes continuous crystallizer temperature and pressure monitoring; crystallizer temperature shifts of even 5 °C can alter particle size distribution and the fraction of fines. Users that feed PTA through loss-in-weight feeders with double-concave screws should verify feeder fill factor because bulk density changes above 0.05 g/cm³ can disturb gravimetric output. In direct esterification pilot units, PTA paste viscosity at 70 wt% solids is sensitive to particle size; a reduction in D50 below 80 µm can increase paste viscosity by more than 20% because of higher particle surface area. These operational boundaries are more significant in humid climates and in rail-to-silo transfer systems.

Fiber-grade PET spinning lines impose additional constraints on particle size and metal residues. Spinneret packs with filtration grades from 20 µm to 40 µm are used in direct melt spinning; high ash or agglomerated particles increase pack pressure and shorten filter service. The low iron and ash limits for Yisheng Petrochemical PTA reduce coagulation of catalyst residues in the melt filter. In polyester film applications, p-toluic acid and color are monitored because optical defects and surface roughness can originate from monofunctional impurities that modify crystallization rate. Tensile properties of PET film are tested per ASTM D882, and haze is tested per ASTM D1003. The material is also used in polybutylene terephthalate production with 1,4-butanediol on twin-screw reactors with L/D ratio of 36:1 to 44:1 and barrel temperatures in the 240–260 °C range; titanium-based catalysts used in PBT are sensitive to cobalt and manganese residues, so ash and metal specifications are tighter than for commodity PET. In polyester polyol production, moisture input must be limited because water reacts with isocyanate in downstream polyurethane systems, generating carbon dioxide and reducing dimensional stability. The moisture ceiling of 0.5 wt% is therefore not only a storage specification but also a formulation boundary for moisture-sensitive polyol synthesis.

Compared with crude terephthalic acid, Yisheng Petrochemical PTA contains much lower 4-CBA because of the hydrogenation purification stage. Crude terephthalic acid may retain 4-CBA levels several orders of magnitude higher; medium-purity terephthalic acid sits between crude and purified streams with higher p-toluic acid and color. Compared with recycled PET flake, PTA offers a consistent acid value, median particle size, and optical property; published data for recycled streams often show intrinsic viscosity lot variation above 0.03 dL/g and color b* variation above 0.5. Published data comparing Yisheng PTA to other specific producer lots under identical polycondensation conditions is limited; lot-to-lot comparisons should be based on certificate values for 4-CBA, p-toluic acid, ash, and b* color. Differences from competitive PTA sources are generally limited to particle size distribution, bulk density, trace metal profile, and certificate consistency because the chemical identity is identical. Yisheng Petrochemical PTA is characterized by single-product continuous-line supply with no sub-model differentiation for standard polyester-grade material. Purchasers requiring exact optical properties should set certificate limits for b* color, 4-CBA, and p-toluic acid rather than assuming interchangeability across producers.

Regulatory status applies to the PTA monomer. Yisheng Petrochemical PTA is not intended for direct food contact; food-contact compliance applies to the final polymer after conversion. Customers using final PET for food packaging must verify compliance under FDA 21 CFR 177.1630 or European regulations for plastic materials and articles intended for food contact. The PTA monomer is registered under REACH; users in the European Economic Area should confirm substance registration and exposure scenarios. RoHS is not applicable to PTA itself but may apply to finished articles containing polyester. Sulfated ash and metal residues documented in the lot certificate are used for supplier qualification.