Hanbang (Jiangyin) Petrochemical PTA is supplied as bulk purified terephthalic acid manufactured in Jiangyin, Jiangsu Province, via continuous catalytic air oxidation of p-xylene in an acetic acid reaction medium, followed by selective hydrogenation purification. The product is a free-flowing crystalline aromatic dicarboxylic acid with molecular formula C8H6O4, molecular weight 166.13 g/mol, and a theoretical dibasic acid number of 675 mg KOH/g. The powder is specified as a single polymer-grade feedstock rather than as separate melt-grade, bottle-grade, or fibre-grade product codes. Its primary use is as the acid monomer for continuous polyethylene terephthalate melt-phase polymerization, solid-state polycondensation, polyester staple and filament spinning, biaxially oriented film, and related copolyester and engineering polymer formulations. The oxidation platform uses cobalt, manganese, and bromide catalyst components in acetic acid; the subsequent hydrogenation stage reduces 4-carboxybenzaldehyde to p-toluic acid and suppresses colour-forming aromatic intermediates. Published polyester-grade PTA specifications, including GB/T 32685-2016, position residual 4-carboxybenzaldehyde near 25 mg/kg and p-toluic acid near 150 mg/kg. The material therefore differs from crude terephthalic acid primarily by the removal of aldehyde-terminated and coloured impurities that would otherwise behave as chain stoppers during direct esterification with ethylene glycol.

What Separates Hanbang PTA From Less Purified Terephthalic Acid Streams?

Crude terephthalic acid exiting the oxidizer typically contains 4-carboxybenzaldehyde in the 200–300 mg/kg range before hydrogenation. Polymer-grade PTA supplied to continuous polyester systems is controlled below 25 mg/kg when measured by high-performance liquid chromatography; ASTM D7884-13 provides a comparable HPLC method for 4-carboxybenzaldehyde and p-toluic acid in purified terephthalic acid. The distinction is not merely numeric. Residual 4-carboxybenzaldehyde introduces an aldehyde functionality that competes with carboxylic acid groups during esterification, caps chain ends, and lowers number-average molecular weight at fixed reactor residence time. p-Toluic acid, generally limited to 150 mg/kg, is a monofunctional aromatic acid and reduces the maximum attainable intrinsic viscosity in batch melt-phase trials. The purification train also reduces colour bodies such as 2,6-dicarboxybenzaldehyde and benzil, keeping powder b* values at or below 1.5. Ash is controlled below 10 mg/kg because residual cobalt, manganese, and iron from oxidation can catalyse thermal degradation and increase diethylene glycol formation. The moisture limit of 0.2 wt% is relevant for dry-bulk storage and for preventing premature hydrolysis of bis(2-hydroxyethyl) terephthalate in the melt phase.

Published data for the specific Hanbang Jiangyin lot-to-lot distribution is limited; the tabulated values are benchmark limits for polyester-grade PTA rather than guaranteed certificate-of-analysis targets. Converter qualification therefore includes arrival sampling and melt-performance trials.

Compared with imported PTA delivered by ocean vessel and transloaded through coastal terminals, the Jiangyin product’s Yangtze River logistics corridor can reduce inland transloading steps. In bulk powder logistics, each transfer point introduces fines generation, moisture uptake, and contamination risk. The technical comparison between Hanbang PTA and other polymer-grade PTA sources is therefore conducted on arrival samples rather than on origin alone. Customers receiving the material by bulk tanker often report no chemical identity difference, but may observe differences in bulk density, angle of repose, or flowability due to transport compaction. Such differences are operational and require feeder and silo setting adjustments rather than reformulation.

Catalytic Hydrogenation of 4-Carboxybenzaldehyde During PTA Purification

The selective hydrogenation reactor receives a hot aqueous solution of oxidizer product and exposes it to a supported palladium catalyst under hydrogen partial pressure. The aldehyde group of 4-carboxybenzaldehyde is reduced to a methyl group, producing p-toluic acid, while the aromatic ring remains intact. The resulting p-toluic acid is separated in crystallisation and filtration because it is more water-soluble than terephthalic acid under the operating temperature profile. If this purification step is incomplete, residual 4-carboxybenzaldehyde acts as a monofunctional chain stopper in direct esterification with ethylene glycol. The effect is measured through solution intrinsic viscosity according to ISO 1628-1 and through melt mass-flow rate according to ISO 1133-1:2022. In a continuous esterification line with fixed residence time, residual 4-CBA above 25 mg/kg can shift the amorphous melt intrinsic viscosity below the target window for bottle-grade resin; the same effect is less critical in fibre-grade PET where lower intrinsic viscosity is accepted. The molar balance of the purification reaction is C8H6O3 plus hydrogen to C8H8O2. The reaction is selective for the aldehyde carbonyl; ring hydrogenation and decarboxylation side reactions are thermodynamically possible but kinetically suppressed on palladium under standard operating conditions. The hydrogenation step also reduces benzaldehyde-type colour bodies that produce yellowing in preforms and biaxially oriented polyester film. Reaction heat and hydrogen consumption are managed by continuous feed blending, and the catalyst bed is protected from iron and solids carryover. Operational boundaries include maintaining hydrogen purity and avoiding excessive oxygen in the feed to the hydrogenation reactor, as oxygen can degrade catalyst selectivity. Published data for the specific Hanbang catalyst life and hydrogen partial-pressure profile is limited.

At converter intake, the lot is sampled from bulk tankers or silo transfer lines. The certificate of analysis should include lot number, production date, residual 4-CBA, p-toluic acid, ash, colour, moisture, and particle-size distribution. Sampling requires attention to segregation because fines can migrate during pneumatic conveying and create localised high-ash pockets. The 4-CBA and p-toluic acid are determined by gradient HPLC with UV detection; ASTM D7884-13 provides a standard approach for purified terephthalic acid. Moisture is determined by Karl Fischer titration, with ISO 15512:2019 applicable to polymer-related raw materials. Powder colour is reported in CIELAB coordinates using a tristimulus colorimeter. Particle-size distribution is measured by laser diffraction with dry dispersion, typically covering a 0.1–2000 μm measurement range. Residual metals are quantified by inductively coupled plasma optical emission spectrometry after ashing. These methods are not specific to Hanbang but form the necessary qualification dataset for lot acceptance.

In continuous slurry-fed esterification, the Hanbang PTA powder is mixed with ethylene glycol in a thin-film paste mixer before entering the first reactor. The powder’s particle-size distribution and bulk density determine the stability of paste viscosity and the discharge accuracy of rotary feeders. Polymer-grade PTA commonly has a mean particle diameter of 100–130 μm, with fines below 45 μm controlled to avoid dust formation and feeder bridging. Bulk density is usually in the 0.9–1.0 g/cm³ range, although the exact value depends on particle packing and residual moisture. Slurry molar ratio of ethylene glycol to terephthalic acid is commonly in the range of 1.05–1.15:1 for direct esterification; variations in powder density and moisture can alter apparent mass flow but not molar ratio if feeders are calibrated by bulk density. If stored above 60% relative humidity, the powder can pick up moisture and shift paste viscosity, so silos are typically equipped with nitrogen blanketing or desiccant dryers. Moisture uptake above 0.2 wt% can promote hydrolysis of the resulting bis(2-hydroxyethyl) terephthalate and alter the esterification balance. Particle shape and fines content also affect slurry pump wear and nozzle clogging in continuous systems; narrowing the particle-size distribution reduces batch-to-batch paste rheology variation. Published data for the Jiangyin product’s specific sieve profile is limited, but converter qualification usually includes laser diffraction and loss-on-drying checks at intake.

When Hanbang PTA Is Evaluated for Solid-State Polycondensation Bottle Resin

Bottle-grade PET production places tighter constraints on residual aldehyde and colour bodies than fibre-grade or film-grade PET. The amorphous melt is pelletised and then subjected to solid-state polycondensation at temperatures below the pellet sticking point, with inert gas stripping to remove acetaldehyde and ethylene glycol. Residual impurities in PTA affect this process indirectly: 4-CBA lowers the preform intrinsic viscosity before solid-state polycondensation, and metal ash residues can catalyse acetaldehyde formation during melt processing. The relevant melt parameters include carboxyl end-group concentration, diethylene glycol content, and intrinsic viscosity. For carbonated soft drink preforms, the upstream PTA quality must permit a stable solid-state polycondensation rate and low acetaldehyde in the final preform. Hanbang PTA entering this chain is chemically equivalent to other polymer-grade PTA sources, but lot-level consistency in 4-CBA, p-toluic acid, and ash determines whether the same solid-state residence time reaches the required intrinsic viscosity of 0.80–0.85 dL/g without excess pellet agglomeration. Solid-state polycondensation is usually performed in a crystallizer and reactor cascade; prepolymer with intrinsic viscosity in the 0.60–0.65 dL/g range is crystallised above 140 °C and then heated to 200–210 °C under nitrogen or vacuum. Preform injection moulding is performed on high-clamp-force reciprocating-screw machines; melt residence time and screw L/D ratio determine shear heating. Residual ash above 10 mg/kg can increase filter pressure and contribute to thermal degradation at injection moulding temperatures. Qualification requires a full upstream-to-preform trial because published data for this specific configuration is limited.

In fine-denier polyester fibre spinning, the melt filtration behaviour of Hanbang PTA-derived polymer is more sensitive to coarse particles and catalyst residues. Fibre-grade PET is often polymerised to a lower intrinsic viscosity, but continuous spinning packs with high hole counts require low filter pressure rise; insoluble ash and agglomerated fines shorten pack life. Film-grade PET requires low gel counts and stable optical clarity, which are influenced by residual colour bodies in the PTA and by the esterification temperature profile. The material can be evaluated with differential scanning calorimetry for crystallisation behaviour and with ISO 1133-1:2022 for melt-flow stability. If the PTA contains excessive p-toluic acid, the molecular weight distribution broadens and film draw resonance may increase. The product is incompatible with intentional addition of amine-based additives during the esterification stage, as these can form salts with terephthalic acid and disrupt melt-phase stoichiometry. Storage should avoid condensation and prolonged residence in unheated outdoor silos.

Impurity Transfer Across Esterification and Melt-Phase Polymerization

Residual metals from oxidation, particularly cobalt and manganese, remain in the purified PTA at trace levels. During PET melt polymerization, these metals can accelerate thermal degradation and catalyse diethylene glycol formation from ethylene glycol. An ash limit of 10 mg/kg reduces but does not eliminate this effect. The metal speciation matters: dissolved cobalt has greater catalytic activity than inorganic particulates because it remains homogeneously distributed in the melt. Polyester producers often add a phosphorus-based stabilizer such as triphenyl phosphate or phosphoric acid to chelate trace metals and slow degradation. If the Hanbang PTA lot carries higher soluble manganese than an alternative source, stabilizer demand may shift; this is not visible from the certificate of analysis alone but appears in melt-stability trials under nitrogen and air. The powder b* value does not fully predict melt-phase colour because new chromophores form during high-temperature esterification. Therefore, the product must be evaluated against the converter’s specific stabilizer package and process temperature profile. Diethylene glycol content in PET is typically controlled between 0.8 wt% and 1.5 wt% depending on application; it arises from ethylene glycol dimerization catalysed by heat and trace metals. PTA itself does not contain diethylene glycol, but residual acidity and metal ash influence its formation. Thermal chain scission follows pseudo-first-order kinetics over the melt processing window; elevated metal residues increase the pre-exponential factor rather than the activation energy. Melt stability trials typically measure intrinsic viscosity loss after 30 min of residence at 280 °C under nitrogen. Lot-to-lot changes in PTA metal ash may require compensating adjustments in reactor temperature, pressure, or stabilizer addition. Published data for Hanbang PTA-specific diethylene glycol response is limited.