Purified Terephthalic Acid CAS 100-21-0
Chelora Chemicals supplies bottle-grade and fibre-grade purified terephthalic acid to PET resin, polyester fibre and film producers worldwide. Every consignment leaves with a batch-specific COA covering purity, 4-CBA, p-toluic acid, colour and metals, the current SDS and full export documentation.
Also known as: PTA · Terephthalic acid · 1,4-Benzenedicarboxylic acid · TPA · Purified TA
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Price, lead time and a sample COA for Purified Terephthalic Acid, usually within one working day. We ship worldwide.
Request a Quote Email the DeskDocumentation
- Batch-specific COA (purity, 4-CBA, colour, metals)
- Safety Data Sheet (SDS)
- Transport and export documents
- Third-party inspection on request
- Certificate of origin
What is Purified Terephthalic Acid?
Purified terephthalic acid is the symmetric aromatic diacid, C₈H₆O₄, a white crystalline powder that sublimes rather than melts and is almost insoluble in water and common solvents.
That insolubility is why purification is difficult and why the product is defined by its impurity profile. Crude terephthalic acid is hydrogenated and recrystallised to remove 4-carboxybenzaldehyde, the impurity that terminates polyester chains.
Essentially all PTA goes to polyester: PET bottle resin, polyester staple and filament fibre, BOPET film and PBT engineering resin.
It is a benign solid in handling terms — not classified as dangerous goods — but its dust is combustible and the specification tolerances are among the tightest of any bulk commodity.
Why Purified Terephthalic Acid specifically
- A rigid linear diacid. The 1,4 geometry gives polyester its crystallinity, strength and barrier properties.
- Chain-terminator free. The purification step removes 4-CBA, which would cap growing chains and limit molecular weight.
- Direct esterification. Reacts with MEG without a catalyst in modern PET plants, replacing the older DMT ester-interchange route.
- Produced at enormous scale. World-scale plants keep polyester affordable for packaging and textiles.
How Purified Terephthalic Acid is Manufactured
PTA is made by oxidising para-xylene and then purifying the crude acid by hydrogenation and recrystallisation.
- Para-xylene feed. Fibre-grade PX at 99.7% or better is the starting material.
- Air oxidation. PX is oxidised in acetic acid solvent over a cobalt-manganese-bromide catalyst at about 190 °C and 15 bar.
- Crude TA recovery. Crude terephthalic acid precipitates and is separated by centrifuge or filtration.
- Hydrogenation. Crude TA is dissolved in hot water and hydrogenated over palladium on carbon to convert 4-CBA to p-toluic acid.
- Recrystallisation. Successive crystallisation stages remove p-toluic acid and colour bodies to reach bottle grade.
- Drying and conveying. The purified crystals are dried and conveyed to silos or packing under controlled conditions.
Typical Commercial Specification
Figures below are representative of commercial bottle-grade PTA. Fibre grade carries slightly wider limits — tell us the application and we will send the matching sheet.
| Parameter | Typical Value |
|---|---|
| Appearance | White crystalline powder, free flowing |
| Terephthalic acid purity | 99.9% min by weight |
| 4-Carboxybenzaldehyde (4-CBA) | 25 ppm max |
| p-Toluic acid | 150 ppm max |
| Colour (APHA, in solution) | 10 max |
| Acid value | 675 to 677 mg KOH/g |
| Moisture | 0.2% max |
| Ash | 15 ppm max |
| Total metals (Fe, Co, Mn, Cr) | To grade, typically 10 ppm max combined |
| Particle size | To grade, typically 50 to 150 µm median |
Physical & Chemical Properties
| Property | Value |
|---|---|
| Chemical formula | C₈H₆O₄ |
| Molecular weight | 166.13 g/mol |
| Appearance | White crystalline powder, odourless |
| Sublimation point | About 402 °C — sublimes rather than melts at atmospheric pressure |
| Bulk density | About 0.8 to 1.0 g/cm³ |
| Solubility in water | Very low, about 0.017 g/L at 25 °C |
| Solubility in organics | Soluble in DMSO and DMF; poorly soluble in most solvents |
| pKa | 3.51 and 4.82 |
| Dust explosion | Combustible dust requiring ignition control |
| Thermal stability | Stable to high temperature; decomposes above sublimation |
| Incompatibilities | Strong oxidisers and strong bases |
Behaviour in the process
PTA behaves predictably as a solid, and the handling questions are about dust and flow:
- Does not melt. Sublimes at about 402 °C, so PET esterification runs as a paste or slurry with glycol rather than as a melt.
- Combustible dust. Fine PTA dust forms explosible clouds; earthing, extraction and housekeeping are standard requirements.
- Low solubility. Insoluble in most solvents, which is what makes purification by recrystallisation from water necessary.
- Flow sensitive to moisture. Moisture pick-up causes bridging in silos and inconsistent paste preparation.
PTA Grades and Polyester Alternatives
PTA is bought by grade, and the differences are 4-CBA, colour and metals rather than bulk purity.
| Material | Origin / type | When it is the right choice |
|---|---|---|
| Bottle-grade PTA | 4-CBA 25 ppm max, APHA 10 max | PET bottle resin and high-clarity applications |
| Fibre-grade PTA | Slightly wider 4-CBA and colour | Polyester staple, filament and industrial yarn |
| Dimethyl terephthalate | The ester route, CAS 120-61-6 | Older polyester plants and specialty polyesters |
| Isophthalic acid | The meta isomer, CAS 121-91-5 | Copolymer modifier for clarity and toughness |
| Recycled PET flake | From post-consumer bottles | Where recycled content targets apply |
Stated plainly: PTA has displaced DMT on nearly all new polyester capacity because it avoids the methanol loop and gives higher yield. DMT survives where existing plants are built for it or where specialty polyesters need the ester route.
Industries We Supply Purified Terephthalic Acid To
PTA has few but very large customers, all in the polyester chain.
Where Purified Terephthalic Acid is Used
PET resin and polyester fibre together take nearly all PTA production.
In PET manufacture
PTA is slurried with MEG and esterified directly without catalyst at about 250 °C, releasing water, then polycondensed under vacuum with antimony or titanium catalyst. Intrinsic viscosity is the controlling property, and 4-CBA in the feed caps chains and limits the IV that can be reached — which is why bottle grade and fibre grade are specified differently.
Dust and conveying
PTA is conveyed pneumatically in large volumes and generates fines through attrition. Because the dust is combustible, conveying systems are inerted or earthed and extraction is designed in. Moisture control matters too, as damp PTA bridges in silos and gives inconsistent paste density.
Need a specific grade, purity and packing format?
Tell us the grade, the 4-CBA and colour limits your polyester grade requires, the packing format you can receive and the annual quantity. We will come back with a price, a lead time, a sample COA and the full documentation set.
Quality Control & Testing
Every lot is released against a batch-specific Certificate of Analysis, with 4-CBA and colour reported because they define which polyester grades the lot can serve.
- Terephthalic acid purity and acid value — confirming identity and bulk quality.
- 4-CBA content — by HPLC, the defining specification for polymerisation performance.
- p-Toluic acid — reported as the hydrogenation product and a secondary chain terminator.
- Colour in solution — by APHA, predicting polymer appearance.
- Metals — iron, cobalt, manganese and chromium measured because they affect polymer colour and catalyst behaviour.
- Moisture and particle size — confirming handling and paste preparation behaviour.
Common Process Problems & Likely Causes
When PTA causes trouble, it is usually 4-CBA, metals, moisture or particle size. This table is the shortcut our technical desk works through before anyone opens a complaint file.
| Symptom | Likely cause | What to check |
|---|---|---|
| Intrinsic viscosity below target | 4-CBA capping polyester chains | 4-CBA figure on the COA |
| Yellow colour in the resin | Metals or colour bodies in the PTA | Colour and metals results |
| Paste density inconsistent | Moisture or particle size variation | Moisture and particle size figures |
| Bridging in silos | Moisture pick-up in humid storage or conveying | Moisture result and silo aeration |
| Esterification rate slow | Particle size coarser than usual | Particle size distribution against the previous COA |
| Dust accumulation in conveying | Attrition through pneumatic transfer | Conveying velocity, extraction and housekeeping |
Packaging, Storage & Shipping
- Standard packing. 1000 to 1250 kg jumbo bags, 25 kg bags and bulk containers or silo trucks.
- Storage. Dry, covered warehousing or sealed silos; PTA picks up moisture and bridges in humid conditions.
- Dust control. Combustible dust. Use earthed, enclosed conveying with extraction and strict housekeeping.
- Moisture control. Keep bags sealed and silos dry; moisture causes bridging and inconsistent paste preparation.
- Material compatibility. Stainless steel preferred in slurry service; carbon steel contributes iron that colours polymer.
- Segregation. Keep apart from strong oxidisers and bases.
- Shelf life. Typically 24 months in sealed bags in dry storage.
- Transport classification. Not classified as dangerous goods for transport.
Hazards & Safe Handling
PTA has very low toxicity and is not classified as dangerous goods. The real hazards are combustible dust and mechanical handling rather than chemical exposure.
- Low toxicity. PTA is not classified as hazardous to health in most jurisdictions and is handled routinely in very large volume.
- Combustible dust. Fine dust forms explosible clouds. Earthing, enclosed conveying, extraction and housekeeping are required.
- Eye and respiratory irritation. Dust irritates eyes and the respiratory tract; use goggles and dust masks during bag handling.
- Skin contact. Mild irritant on prolonged contact; use gloves.
- Manual handling. Jumbo bags present a mechanical rather than chemical hazard; use proper lifting equipment.
- Environment. Low aquatic toxicity and poorly soluble; contain spills as a housekeeping matter.
Regulatory & Compliance Notes
PTA is unregulated for transport, with food contact documentation required down the chain. The notes below are orientation rather than legal advice.
- GHS classification. Not classified as hazardous in most jurisdictions; some classifications apply eye irritation.
- Transport. Not classified as dangerous goods. Standard packaged and bulk cargo documentation applies.
- Food contact. PET for food packaging requires compliance documentation under EU, FDA and other regimes, which traces back to monomer purity and catalyst residues.
- Dust explosion regulation. Handling and conveying systems fall under ATEX, NFPA or equivalent combustible dust requirements.
- REACH and inventories. Registered under EU REACH and listed on the major chemical inventories.
- Quality agreements. PET producers commonly expect documented 4-CBA, colour and metals limits with change control.
We Supply Purified Terephthalic Acid Worldwide
Chelora Chemicals is a supplier and export partner, not a single-plant trader. We ship Purified Terephthalic Acid from India and from partner sources to customers across Asia, Europe, the Middle East, Africa, and North and South America, handling the export documentation, transport paperwork and freight so the material arrives ready to use.
- Incoterms. EXW, FOB, CIF, CFR and DAP quoted to suit your purchasing terms and freight arrangements.
- Ports. Regular shipments through Nhava Sheva (JNPT) and Mundra, with other ports arranged where routing and cargo rules allow.
- Documentation. Commercial invoice, packing list, certificate of origin, COA, SDS and the transport declaration issued as a complete set.
- Flexible volumes. From a container of jumbo bags up to repeat bulk shipments on a supply contract.
- Supply continuity. Because we are independent of any one producer, a plant turnaround or a shipping disruption at one source does not have to become your stock-out.
Buying Purified Terephthalic Acid from Chelora
We are an independent sourcing and supply partner. For PTA that means settling three things at enquiry: bottle or fibre grade and the 4-CBA ceiling, the packing and conveying format your plant receives, and the volume and schedule against a market that moves in large contracted parcels.
- Documentation on every lot. Batch-specific COA (purity, 4-CBA, colour, metals), plus SDS and the full transport paperwork.
- Analysis before commitment. Representative analysis shared ahead of a commercial order so your lab can qualify the material.
- Quantities. From a container of jumbo bags through to full bulk shipments on contract supply.
- Grade matching. Bottle or fibre grade to the 4-CBA, colour and metals limits your polyester process requires.
- Inspection. Independent third-party inspection available at loading when the contract requires it.
- Related products. Mono Ethylene Glycol, Para-Xylene, Polyethylene Terephthalate Resin and other feedstocks alongside Purified Terephthalic Acid from one supplier.
How ordering works
- Send the enquiry. Product, grade or purity, quantity, destination port and the Incoterm you buy on. If you have a spec sheet, attach it — it saves a round trip.
- We quote. Price, lead time, packing format and a sample COA, normally within one working day.
- Qualify the supply. For first orders or critical applications, we share the analysis and handling documentation so your technical and safety teams can sign off before you commit.
- Confirm the order. Proforma invoice issued; payment terms agreed against the volume and the relationship.
- Allocation and QC. Material allocated and released against a batch-specific COA, with an independent inspection where the contract calls for it.
- Ship and document. Filled, labelled and loaded with the full export document set, and tracked through to arrival.
Purified Terephthalic Acid — Common Questions
The questions our technical desk is asked most often about Purified Terephthalic Acid. If yours isn't here, call or email and you will reach someone who knows the chemistry.
What is the CAS number of purified terephthalic acid?
The CAS number for terephthalic acid is 100-21-0, and its EC number is 202-830-0. Its molecular formula is C₈H₆O₄ with a molecular weight of 166.13 g/mol, and it is classified under HS code 2917.36.
What is PTA used for?
Almost entirely for polyester: PET bottle and sheet resin, polyester staple and filament fibre, BOPET film, PBT engineering resin and polyester powder coating resins.
Do you supply PTA worldwide?
Yes. Chelora Chemicals supplies and exports PTA worldwide — across Asia Pacific, Europe, the Middle East, Africa and the Americas, as well as throughout India, in jumbo bags, bags and bulk.
What is 4-CBA and why does it matter?
4-Carboxybenzaldehyde is a partial oxidation product of para-xylene. It is monofunctional, so it caps growing polyester chains and limits achievable molecular weight. The entire purification section of a PTA plant exists to control it, typically to 25 ppm or less.
How is PTA manufactured?
Para-xylene is oxidised with air in acetic acid over a cobalt-manganese-bromide catalyst to crude terephthalic acid, which is then dissolved in hot water, hydrogenated over palladium to convert 4-CBA, and recrystallised to bottle grade.
What is the difference between bottle grade and fibre grade?
Bottle grade carries tighter 4-CBA, colour and metals limits because bottle resin must be water-white and reach high intrinsic viscosity. Fibre grade allows slightly more and costs less.
Is PTA hazardous?
No, in chemical terms it is among the most benign products we supply and is not classified as dangerous goods. The real hazard is combustible dust, which requires earthing, extraction and housekeeping.
Should I buy PTA or DMT?
PTA for any modern plant: direct esterification avoids the methanol recovery loop and gives higher yield. DMT remains relevant only where existing plants were built for the ester-interchange route or for specialty polyesters.
How should PTA be stored?
In sealed jumbo bags or dry silos in covered storage. PTA picks up moisture, which causes bridging in silos and inconsistent paste density in esterification.
Why does PTA not melt?
It sublimes at about 402 °C rather than melting at atmospheric pressure, because the strong hydrogen bonding between the rigid diacid molecules holds the crystal together. That is why PET esterification runs as a glycol slurry rather than a melt.
What packing sizes and order quantities are available?
1000 to 1250 kg jumbo bags, 25 kg bags, bulk containers and silo trucks. Orders run from a container of jumbo bags up to repeat bulk cargoes on contract supply.
What is the typical shelf life?
Around 24 months in sealed bags in dry storage. PTA is chemically stable; moisture pick-up and bag integrity are the practical limits.
Ready to source Purified Terephthalic Acid?
Send us your specification, grade and annual volume. You will get a price, a realistic lead time and a sample COA from someone who understands what the material has to do in your process — delivered anywhere in the world.