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Purified Terephthalic Acid (PTA), also known as benzene-1,4-dicarboxylic acid and identified by CAS No. 100-21-0, is an organic compound with the formula C₆H₄(CO₂H)₂ that occurs as a white crystalline powder with a slightly acidic odour and is obtained from crude terephthalic acid through the oxidation of paraxylene followed by purification. PTA is the main raw material for polyethylene terephthalate (PET) and polyester fibres and is used as an important chemical intermediate in the production of polyester for clothing, plastic bottles and other materials.
PTA is an aromatic dicarboxylic acid with a molecular weight of 166.13 g/mol that carries two carboxyl groups in opposite (para) positions on the benzene ring, is only very slightly soluble in water and sublimes without melting when heated. The acid groups at both ends of PTA undergo esterification and polycondensation reactions with diols such as ethylene glycol, enabling the formation of long, linear polyester chains.
PTA accounts for approximately 90% of global polyester production and is used in PET bottles and packaging, polyester fibres and films, engineering plastics such as PBT, alkyd and polyester coating resins, and certain terephthalate-based plasticizers. Thanks to its high purity, PTA helps reduce problems such as interrupted chain growth during polymerization, yellowing of the polymer and low molecular weight.
The purity, 4-carboxybenzaldehyde (4-CBA) impurity, moisture, ash, heavy metal content and colour values of PTA are critical parameters that determine polymer quality and should be checked for each batch using the TDS and COA. Although PTA is a stable solid under normal conditions, it can form explosive mixtures with air as a fine dust; it should therefore be stored in cool, dry, well-ventilated areas away from strong bases and combustible materials, and handled on the basis of the current SDS.
WHAT IS PTA (PURIFIED TEREPHTHALIC ACID)?
Purified Terephthalic Acid (PTA), also known as benzene-1,4-dicarboxylic acid, is an organic compound with the formula C₆H₄(CO₂H)₂.
It is a white crystalline powder with a slightly acidic odor. It is obtained from crude terephthalic acid through the oxidation and purification of paraxylene.
PTA is the main raw material for polyethylene terephthalate (PET) and polyester fibers. It is a key chemical intermediate in the production of polyester, which is primarily used to make clothing, plastic bottles, and other materials. Unlike isophthalic acid, which is used in specialty polyesters, PTA is the main component of PET and contributes to approximately 90% of global polyester production.
This makes PTA an indispensable raw material in industries ranging from packaging and textiles to automotive and construction.
PTA's high purity ensures consistency in polymer reactions, making it valuable for producing high-quality resins used in various applications.
The manufacturing process of PTA involves catalytic liquid-phase oxidation of paraxylene (PX) in a solvent such as acetic acid, in the presence of air.
In this oxidation, paraxylene is transformed into crude terephthalic acid (CTA) by oxygen present in compressed air. In the next step, the impurities present in CTA are removed by catalytic hydrogenation and PTA is obtained.
PTA is then reacted with monoethylene glycol to obtain polyester melt resin.
Produced with different intrinsic viscosities and molecular weights, this polyester resin is manufactured for different end uses, such as polyester bottle resin, thermoforming sheet food packaging, polyester film and continuous, textile and industrial filament or fiber.
Polyester fibers are predominantly used in carpets, clothing, furniture, and industrial applications, as well as other consumer products.
Polyester products are also involved in a wide range of consumer applications, such as PET bottles, food packaging, clothing, carpets, and home furnishings.
COMMON PRODUCT and CHEMICAL NAMES:
Purified Terephthalic Acid (PTA)
Purified Terephthalic Acid
Pure Terephthalic Acid
Terephthalic Acid
Terephthalic Acid (INCI)
PTA
TPA
BDC
1,4-Benzenedicarboxylic Acid
Benzene-1,4-dicarboxylic Acid
1,4-Dicarboxybenzene
p-Phthalic Acid
para-Phthalic Acid
p-Benzenedicarboxylic Acid
C₆H₄(CO₂H)₂
C₈H₆O₄
Some of these names refer to chemical designation, some to abbreviation, and some to trade name. For example, Benzene-1,4-dicarboxylic Acid and 1,4-Benzenedicarboxylic Acid are chemical names, while C₆H₄(CO₂H)₂ and C₈H₆O₄ are chemical formulas. PTA and TPA are abbreviations. Purified Terephthalic Acid and Pure Terephthalic Acid are trade names. p-Phthalic Acid and para-Phthalic Acid are synonyms. Terephthalic Acid is also the INCI name.
It is important to evaluate the CAS number used for PTA together with the actual description of the product. For terephthalic acid, CAS No 100-21-0 and EC No 202-830-0 are listed in the sources. Isophthalic acid (CAS No 121-91-5) and dimethyl terephthalate (CAS No 120-61-6) are separate substances with different CAS numbers. For this reason, it should be checked on the documents whether the product is purified terephthalic acid or a different substance during the purchase.
CAS NO, EC / EINECS NO AND CHEMICAL IDENTIFICATION
Product Name: Pure Terephthalic Acid (PTA) / Purified Terephthalic Acid
Common abbreviation: PTA
Chemical name: Benzene-1,4-dicarboxylic acid
INCI name: Terephthalic Acid
CAS No: 100-21-0
EC/EINECS No: 202-830-0
Molecular formula: C₆H₄(CO₂H)₂ (Hill formula: C₈H₆O₄)
Molecular weight: 166.13 g/mol
Chemical class: Organic compound/aromatic dicarboxylic acid
Its main functions: main raw material for PET and polyester fiber production, terephthalate source in PBT production, chemical intermediate in polyester and resin production
Purified Terephthalic Acid is a dicarboxylic acid with the molecular formula C₈H₆O₄, containing two carboxyl groups attached to the benzene core. The two acid groups are in the para position relative to each other on the benzene ring; other possible structural isomers are phthalic acid (ortho) and isophthalic acid (meta). The high purity of PTA ensures consistency in polymer reactions.
For terephthalic acid, CAS No 100-21-0 and EC No 202-830-0 are listed in various official and technical sources. This registration is the general chemical designation that identifies terephthalic acid.
CHEMICAL STRUCTURE AND MOLECULAR PROPERTIES OF PTA
Purified Terephthalic Acid is an organic dicarboxylic acid with the molecular formula C₈H₆O₄, containing two carboxyl groups (–COOH) attached to the benzene ring.
The two acid groups are in the para position relative to each other on the benzene ring; other possible structural isomers are phthalic acid (ortho) and isophthalic acid (meta). This structure allows the product to be chemically stable.
The structural features of the molecule and the solution can be summarized as follows: since it contains two carboxyl groups, it shows two-stage ionization and its pKa₁ value is approximately 3.5 at 25 °C and its pKa₂ value is approximately 4.3–4.8; it is almost insoluble in water at room temperature due to the nonpolar character and crystal lattice energy that the benzene ring imparts to the molecule, and its solubility is approximately 15 mg/L at 20 °C; it dissolves well in strongly polar aprotic solvents such as DMSO and DMF; it dissolves in aqueous alkaline solutions by converting to terephthalate salts.
The solubility of PTA varies markedly with temperature, solvent, and pH of the medium.
Its water solubility increases markedly under hydrothermal conditions (above about 200–300 °C).
In organic solvents, it reaches a solubility of approximately 20 g/100 g in DMSO and approximately 6.7 g/100 g in DMF at 25 °C; in solvents such as NMP, its solubility increases at high temperatures.
Its solubility in acetic acid at room temperature is very low (about 0.035 g/100 g at 25 °C), but in industrial PTA production under 150–200 °C temperature and pressure, acetic acid is used as the main solvent and reaction medium.
In alcohols such as methanol and ethanol, solubility is limited although it increases partially when heated; in acetone, chloroform and diethyl ether, it is considered insoluble.
In aqueous solutions of strong bases such as sodium hydroxide or potassium hydroxide, PTA dissolves rapidly, transforming into salts that dissolve very well in water, such as disodium terephthalate; when the medium is reacidified, it precipitates again into a white solid.
The technical performance of PTA cannot be understood from its chemical structure alone. Purity, moisture, impurity profile, ash content, heavy metal content and color values are important parameters that determine the behavior of the product.
These parameters can affect the progress of the polymerization reaction, the quality of the polymer produced, and the color of the final product. Therefore, the process behavior of two PTA products sold under the same name may not be the same.
Current values should be checked from the supplier's TDS and COA documents.
PHYSICAL AND CHEMICAL PROPERTIES OF PTA
PTA is usually a white colored, free-flowing powder solid.
General technical specifications:
Physical appearance: White, free-flowing powder
Chemical character: Organic compound, aromatic dicarboxylic acid
Molecular formula: C₆H₄(CO₂H)₂ (Hill formula: C₈H₆O₄)
Molecular weight: Approximately 166.13 g/mol
CAS No: 100-21-0
EC/EINECS No: 202-830-0
Purity: It is a high purity product; the current value should be checked from TDS and COA
Acid value: Approximately 673–677 mg KOH/g
Density: Approximately 1.5 g/cm³
Vapor density: Approx. 5.74 (air = 1)
Bulk density: Current value should be checked from TDS
Water solubility: Very low; about 15 mg/L at 10 °C
Sublimation: Sublimates above 300 °C; sublimation point is reported to be approximately 402 °C
Melting point: About 425 °C (only in closed tube)
Flash point: About 260 °C
Autoignition temperature: Approx. 496 °C
Impurities: Impurities such as 4-Carboxybenzaldehyde (4-CBA) and p-toluic acid are usually limited to low ppm levels
Moisture: Usually specified with an upper limit
Ash content: Usually specified with an upper limit
Iron and total metals: Limited to low ppm levels
Color values (APHA): Usually specified by an upper limit
Reactivity: Chemically stable; should be kept away from strong oxidizing agents; can form explosive mixture with air under certain conditions (such as temperature, pressure, powder grain size, humidity, and flammable material concentration) in powder form; carbon monoxide and other harmful products may be formed as a result of incomplete combustion
PTA is only slightly soluble in water and sublimates without melting when heated in an open environment. Melting, at about 425 °C, can only be observed in a closed tube that prevents sublimation.
Impurity profile, ash, iron and other metal content, and color values are among the parameters that determine the quality of PTA. High metal content can lead to yellowing of the product.
These values are for general technical information; they should not be used as a binding specification of the product to be purchased. In particular, parameters such as purity, moisture, ash, iron and metals, impurities, color and grain size should be checked through the supplier's current TDS and COA documents.
HOW DOES PTA WORK AT THE MOLECULAR LEVEL?
The main effect of PTA in polymer systems is based on the two carboxyl groups (–COOH) in its structure undergoing an esterification (condensation) reaction with diols, the release of water in this reaction, and the formation of linear polyester chains with repeating ester bonds.
In PET production, PTA undergoes a direct esterification reaction with monoethylene glycol (MEG). At this stage, which usually runs in the range of 240–260 °C, PTA and MEG are converted into bis(2-hydroxyethyl) terephthalate (BHET) and low molecular weight oligomers; the released water is constantly removed from the system (PTA + 2 MEG → BHET + 2 H₂O).
Excess MEG and small molecules are then removed in the molten polycondensation stage, usually in the range of 270–285 °C and under high vacuum; in this way, the equilibrium shifts in the direction of high molecular weight PET and the chain is extended.
Antimony-based catalysts (e.g. antimony trioxide) can be used in these stages.
In bottle-grade PET, the viscosity can be further increased by solid-state polymerization after melt polymerization. This mechanism forms the basis for using PTA as the main raw material in the production of PET and polyester fibers.
In PBT production, PTA is esterified with 1,4-butanediol instead of MEG, resulting in polybutylene terephthalate (PBT), a high-performance engineering plastic.
The difunctional structure of PTA is the basis of these reactions. Since there is an acid group at each end of the molecule, PTA acts like a two-armed bridge; it is attached to one diol with one end and another diol with the other, forming an uninterrupted chain.
In a monomer containing a single carboxyl group, the reaction would stop at the first binding and the chain could not be extended.
The functions of PTA at the molecular level can differ based on the application:
Acting as the main monomer of PET and polyester fiber
Esterifying with MEG to form BHET and oligomers
Being a source of terephthalate in PBT production
To ensure the formation of linear polymer chains with its bifunctional structure
Enabling the production of thermoplastic, reformable polyesters
To form the building block of polyesters used as films, sheets and packaging materials
To be a building block in the production of polyester resin and polymer
The polymerization ability of PTA depends on the ability of the two carboxyl groups to form repeating ester bonds with the diol component. When used in conjunction with the diol, the bifunctional structure allows the chain to grow from both ends; unlike monomers with three or more functions, it does not form a side branching and cross-linked network structure.
Therefore, the resulting polymer is thermoplastic that can be melted and reshaped.
The polymerization rate and the molecular weight of the resulting polymer are directly related to temperature, vacuum level, catalyst type, diol/PTA ratio and impurities in the environment. For example, a small amount of diethylene glycol (DEG) can be formed by the self-assembly of MEG at high temperatures; this can affect melt viscosity and optical clarity.
Impurities in PTA, such as 4-carboxybenzaldehyde (4-CBA), can also adversely affect polymerization and the quality of the polymer. Therefore, PTA should not be evaluated alone, but in conjunction with the diol, catalyst, and process parameters with which it is used.
However, it should not be assumed that PTA will give the same performance in every system.
The PTA quality, diol type and ratio, catalyst, temperature, vacuum, and reactor design used should be evaluated by laboratory and production trials.
IN WHICH SECTORS IS PURE TEREPHTHALIC ACID USED?
Purified Terephthalic Acid is a versatile raw material used in various industrial fields, especially in the polyester, packaging, textile and paint-coating sectors, thanks to its bifunctional aromatic dicarboxylic acid structure, ability to form linear polymer chains and high thermal and chemical stability. The purpose of use may vary depending on the quality, purity and reaction system of the product.
Main areas of use:
Production of polyethylene terephthalate (PET) bottle and packaging resin,
Polyester fiber for textile and industrial purposes,
Filament and yarn production, woven fabric, clothing, carpet, home textile and filling fiber applications,
Production of food packaging, thermoforming sheets and packaging films,
Production of heat-resistant polyester films and technical sheets,
Polybutylene terephthalate (PBT) engineering plastic production,
Production of plastics for automotive components and electrical-electronic parts,
Alkyd resin production and resin modification,
Stoving industrial primers and industrial paints,
Coil coatings and high-temperature resistant exterior paints,
Unsaturated polyester resins and composite materials,
Special polyester film applications such as audio, video, x-ray and photographic film,
Cosmetic and personal care formulations (INCI: Terephthalic Acid),
Dicarboxylic acid component and intermediate raw material in chemical synthesis.
The most common use of Pure Terephthalic Acid is as the main raw material (monomer) of polyethylene terephthalate (PET) and polyester resins used in the production of beverage and water bottles, food packaging, polyester films and textile fibers.
These products are especially preferred in the packaging, textile, plastic, automotive, electrical-electronics, construction and paint-coating sectors.
The performance that each industry expects from Pure Terephthalic Acid is different.
For example, the textile and fiber manufacturer can focus on low color (APHA and $b^*$ yellowness value), high whiteness index and very low 4-CBA (4-carboxybenzaldehyde) content to prevent yellowing and ensure uniform dyeability in the fabric, while the PET bottle and packaging manufacturer can focus on high purity, low metal and ash content and intrinsic viscosity consistency, and the alkyd resin and paint manufacturer can focus on acid value, esterification reaction control and no haze in the paint film.
USE OF PURE TEREPHTHALIC ACID IN POLYESTER AND PET PRODUCTION
In polyester and polyethylene terephthalate (PET) formulations, Pure Terephthalic Acid is used as a difunctional dicarboxylic acid monomer with monoethylene glycol (MEG/EG), usually combined in a molar ratio of approximately 1.5 to 2.0. This production process, which is carried out through the purified terephthalic acid (PTA) and monoethylene glycol (MEG/EG) route, consists of two main chemical stages, referred to in the industry as direct esterification and melt polycondensation.
Possible functions of Pure Terephthalic Acid in the production of polyester and PET include:
To act as a two-armed bridge with two carboxylic acid (-COOH) groups in its structure, ensuring the formation of uninterrupted, long and linear polymer chains
Reacting directly with ethylene glycol to form ester bonds and bis(2-hydroxyethyl) terephthalate (BHET) oligomers
To ensure that the plastic produced can be melted and reshaped and is recyclable (thermoplastic) by not branching or forming three-dimensional cross-linked networks
To act as a source of terephthalate in the production of polybutylene terephthalate (PBT), a high-performance engineering plastic, by esterification reaction with 1,4-butanediol (BDO)
To give hardness, thermal stability and water resistance to the coating as a chain-forming acid component by reacting with polyol and fatty acids in the production of alkyd resin
To ensure consistency in polymerization reactions and obtain high-quality resin thanks to its high purity (99.9% and above)
To support brightness, non-yellowing and clear dyeability in textile fibers thanks to low color (APHA and b* yellowness value) and high whiteness index
Pure terephthalic acid-based polymerization programs can be used especially in the production of PET beverage bottles, food packaging, thermoforming sheets, heat-resistant polyester films, textile and industrial polyester fibers (yarn, carpet, woven fabric, filling fiber), PBT engineering plastics and alkyd-based industrial coatings.
In the production of polyethylene terephthalate, PTA powder and ethylene glycol (EG) are mixed into a pumpable paste (slurry) before entering the reaction system.
In the direct esterification stage, PTA reacts with ethylene glycol for 2 to 4 hours under moderate pressure at temperatures of 240 °C to 260 °C, releasing water as a by-product, and the resulting water is continuously distilled and removed from the system. Antimony-based catalysts such as antimony trioxide (Sb₂O₃) are added to drive the reaction; the BHET oligomers are then transferred to the pre-polycondensation reactor under vacuum to remove excess ethylene glycol and water, and then to the high vacuum finishing reactor (molten polycondensation) at temperatures ranging from 270 °C to 285 °C (or up to 300 °C).
As the reaction conditions, temperature, moisture, and amount of impurities change, the polymer's chain length, melt viscosity, and optical properties are directly affected.
Diethylene glycol (DEG) by-product can be formed through self-condensation of ethylene glycol at high temperatures, affecting melt viscosity and optical clarity, as well as 4-carboxybenzaldehyde (4-CBA) impurity in PTA exerts a chain-terminating effect, reducing polymer quality and leading to yellowing; therefore, the EG/PTA molar ratio, vacuum, and temperature parameters must be carefully optimized.
In bottle grade PET production, melt-polymerized chips are heated under an inert gas stream at temperatures below their melting point (around 200 °C – 230 °C) for 12 to 20 hours and subjected to Solid State Polymerization (SSP), thereby reducing the acetaldehyde content and increasing the intrinsic viscosity (IV) to levels suitable for beverage bottles (≥ 0.85 dL/g).
It is also being considered in laboratory and research applications to perform esterification in a shorter reaction time compared to traditional heating methods through microwave-assisted synthesis (MAS) using ethylene glycol, terephthalic acid, and antimony trioxide catalyst.
It should not be assumed, based solely on the name "Pure Terephthalic Acid" or "PTA" that a pure terephthalic acid product will give the same result in every polymer reactor. Trial and production monitoring should be carried out based on diol composition, catalyst system, reactor design and process conditions.
RESIN, FILM, ENGINEERING PLASTIC AND COATING APPLICATIONS OF PURE TEREPHTHALIC ACID
Pure Terephthalic Acid can be used as a functional ingredient in packaging films, thermoforming sheets, polybutylene terephthalate (PBT) engineering plastics, alkyd and composite resins, stoving industrial paints and coil coatings with the appropriate quality grade.
In these systems, it serves as a dicarboxylic acid monomer and as the main raw material that forms linear chains. Functions for which Pure Terephthalic Acid can be considered in these applications include:
To create polyester resin for food packaging, thermoforming packaging and packaging sheets,
To enable the production of heat-resistant polyester films and audio, video, x-ray and photographic films,
Supporting the production of high-strength, bright and durable textile and industrial polyester fibers,
Esterifying with 1,4-butanediol (BDO) to form PBT engineering plastic for automotive and electrical-electronic parts,
Taking part in the production of thermoplastic polyesters and composite resins as an acid component,
To be a chain-forming acid component by reacting with polyol and fatty acids in the production of alkyd resin,
To provide higher hardness, mechanical strength and chemical resistance to paints and coatings thanks to the para-positioned benzene ring,
To increase the thermal stability of alkyd-based coatings at high temperatures and their resistance to water and moisture (hydrolysis),
To provide resistance to outdoor weathering in stoving industrial primers, industrial paints and coil coatings.
The following aspects should be checked when purchasing Pure Terephthalic Acid in resin, film, engineering plastic, and coating applications:
Purity (assay) and acid value
Moisture content
4-CBA (4-carboxybenzaldehyde) and p-toluic acid impurities
Iron and heavy metal content and ash ratio
Color values (APHA, whiteness index and b* yellowness value)
Grain size and flow characteristics
Current technical specification (TDS) and certificate of analysis (COA)
Safety data sheet (SDS) and batch traceability
Compliance and certification documents, when required
In the production of alkyd resin, Pure Terephthalic Acid is used as an alternative dicarboxylic acid to conventional phthalic anhydride.
However, it requires higher reaction temperatures and times because it sublimates above 300 °C and does not dissolve easily in organic solvents.
PTA residues that do not react fully can create roughness or haze in the paint film.
For this reason, pre-reaction (esterification) with glycols is generally preferred in production.
In engineering plastics, PTA is converted into PBT granules by reacting with 1,4-butanediol.
These resins are especially used in automotive components and electrical-electronic parts.
A pure terephthalic acid product suitable for the production of general resins or coatings cannot automatically be said to be suitable for a sensitive textile fiber or food packaging application.
Relevant quality requirements and manufacturer documentation should be checked for each application.
IS PURE TEREPHTHALIC ACID USED IN COSMETIC, FOOD AND PHARMACEUTICAL APPLICATIONS?
Pure terephthalic acid appears in the European Commission's cosmetic ingredient database CosIng under the name TEREPHTHALIC ACID, but it has not been directly assigned a specific cosmetic function.
It is defined in the international INCI system as a monomer and polymer building block rather than an active ingredient added directly to finished cosmetic formulas.
When converted into polymer form or when its derivatives and copolymers are used, it can participate in the structure of film-forming agents that form a smooth, durable, water- and smudge-resistant glossy layer on the skin or nail in hair fixatives, make-up, mascaras, and nail polishes.
In addition, in the cosmetics industry, it plays a role as the main raw material in the production of PET cosmetic packaging that requires high clarity, light weight, tight sealing and chemical resistance (such as shampoo, lotion, perfume and cream bottles), as well as wet wipes, cotton pads and synthetic makeup brush bristles (polyester fibers).
Terephthalic acid can lead to skin and eye irritation or physical abrasion, upper respiratory tract irritation at high dust concentrations, and allergic skin reactions.
Therefore, if Pure Terephthalic Acid is to be used in the production of polymers, packaging, or fibers associated with cosmetics, dust control, safety assessment, residual monomer limits, and current cosmetic legislation must be considered. However, Pure Terephthalic Acid produced for general industrial, resin, or technical purposes should not be used directly as a raw material in cosmetics, personal care, food, or pharmaceutical products.
Industrial grades may not be designed to meet the required heavy metal limits, impurity profile, and certification for these areas. In the food field, pure terephthalic acid does not have a defined E code (E number) because it is not a food additive and is not used directly as a food ingredient.
In pharmaceutical applications, Pure Terephthalic Acid is not considered as a direct active ingredient, but rather as a laboratory reagent, synthesis intermediate chemical, and raw material for pharmaceutical packaging polymers. In indirect food contact applications such as food packaging, PET beverage bottles, thermoformed food containers, or food contact plastics, terephthalic acid (CAS No 100-21-0) is listed in Annex I of the European Union's Regulation (EU) No 10/2011 on plastic food contact materials (FCM) and in Regulation (EU) 2022/1616 on recycled plastic FCM as an authorized monomer/starting substance under FCM No 785 and Ref No 24910.
In this context, a specific migration limit (SML(T)) of 7.5 mg/kg has been defined within the framework of the group restriction (G28) expressed as terephthalic acid, and the compliance of the final packaging material with the relevant food contact legislation should be evaluated separately.
INDUSTRIAL APPLICATIONS OF PURE TEREPHTHALIC ACID
Pure Terephthalic Acid is an important functional raw material used in numerous industrial systems due to its bifunctional aromatic dicarboxylic acid structure, linear polymer chain-forming capacity, high purity, and thermal stability.
It serves as an essential monomer in industrial production due to its stable storage in powder form and its adaptability to high-volume polymerization lines. The following functions may come to the fore in industrial pure terephthalic acid applications:
PET production by direct esterification and melt polycondensation,
Creation of linear and thermoplastic polyester chains,
Textile and industrial polyester fiber and filament synthesis,
PET bottle resin and solid-state polymerization (SSP) applications,
Food packaging, thermoforming sheet and BOPET film production,
PBT engineering plastic synthesis with 1,4-butanediol,
Alkyd resin production and resin modification,
Stoving industrial paints and coil coating systems,
Production of unsaturated polyester and composite resin,
Chemical synthesis and production of terephthalate salts,
In the packaging and textile industry, Pure Terephthalic Acid is one of the basic chemicals of polyester systems that enable the production of beverage bottles, food containers, packaging films, clothing fabrics, carpets and industrial yarns.
For this reason, it is among the critical raw materials for facilities producing PET resin and polyester fibers. In the paint, coating, and engineering plastics sectors, pure terephthalic acid can be preferred because it imparts hardness, thermal resistance, and hydrolysis resistance to coatings and forms a source for PBT resins used in automotive and electrical-electronic parts.
Additionally, the fact that PET plastics produced using PTA are recyclable and that uncontaminated terephthalic acid can be recovered provides advantages in terms of industrial sustainability and waste management.
The following issues should be evaluated in the use of Pure Terephthalic Acid in industrial systems:
Product quality, purity (assay) and acid value
Impurities of 4-carboxybenzaldehyde (4-CBA) and p-toluic acid
Heavy metal (iron, cobalt, manganese, etc.) and ash content
Color values (APHA, CIE whiteness index and b* yellowness value)
Moisture content and grain size distribution
Ratio and homogeneity of the paste (slurry) prepared with ethylene glycol (MEG)
Esterification and polycondensation reaction temperatures and vacuum conditions
Catalyst selection and control of by-products such as diethylene glycol (DEG)
High sublimation temperature and solubility management in alkyd systems
Material and reactor compatibility
Dust control, ventilation and static electricity grounding measures
Compliance with waste management and local disposal legislation
WHAT PROBLEMS CAN PURE TEREPHTHALIC ACID HELP SOLVE?
Pure Terephthalic Acid can help solve a variety of problems associated with yellowing, low chain length, insufficient mechanical strength, thermal degradation, and hydrolysis in polyester, textile, packaging, engineering plastics, and paint-coating systems.
However, its effect depends on the product quality, purity, reaction ratio and system conditions used.
Yellowing, dullness and dyeing defects in textile and polyester fibers
Raw materials with high impurities and high color value can lead to the formation of undesirable dullness, graying and yellowish tones in the polyester fiber produced, making it difficult to dye light and pastel colors.
The use of textile-grade Pure Terephthalic Acid with low color (APHA ≤ 10 and b* ≤ 1.2), high whiteness index (WI ≥ 85), and low 4-CBA impurities can help achieve bright, white, and homogeneously dyeable fibers without the need for additional optical brightener. However, controlling the raw material color alone does not solve the problem under all circumstances. The polycondensation temperature, catalyst type, and thermal residence time in the reactor should be evaluated together.
Chain termination and low molecular weight in PET polymerization
Monomers of inadequate purity and a high content of 4-carboxybenzaldehyde (4-CBA) can exert a chain-terminating effect during the reaction, inhibiting the growth of polymer chains and reducing resin quality.
The use of Pure Terephthalic Acid with a very high purity (99.9% and above) and a limited 4-CBA (<25 ppm) and heavy metal content contributes to the uninterrupted growth of linear chains and the achievement of the target molecular weight.
Insufficient intrinsic viscosity and acetaldehyde formation in bottle and packaging resins
PET chips obtained after standard melt polycondensation may not meet the mechanical strength and low acetaldehyde level required for beverage bottles on their own.
Solid-state polymerization (SSP) treatment of PET chips produced with PTA of appropriate purity can help raise the intrinsic viscosity (IV ≥ 0.85 dL/g) and lower the acetaldehyde content.
Low hardness, low thermal resistance and moisture sensitivity in alkyd resins and industrial paints
Traditional phthalic anhydride-based alkyd coatings may not exhibit sufficient mechanical stiffness or water/moisture resistance under high temperature and harsh outdoor conditions.
Evaluation of Pure Terephthalic Acid as a chain-forming acid component in the formulation can improve the hardness, chemical resistance, thermal stability, and hydrolysis resistance of the coating due to the tight and linear structure imparted by the para-position benzene ring. However, due to the high sublimation temperature (> 300 °C) and low solubility of PTA, residues that do not react completely can create haze in the paint film.
Therefore, the reaction temperature, time, and pre-esterification step with glycols should be carefully controlled.
Moisture-induced hydrolysis and equilibrium disruption in esterification reactions
High moisture content in the raw material can disrupt the esterification reaction equilibrium during polyester production and lead to undesirable hydrolysis reactions.
The use of Pure Terephthalic Acid with a low moisture content (< 0.2%) and the continuous removal of water generated during the reaction helps to maintain the esterification yield. It should not be assumed that every Pure Terephthalic Acid product will exhibit the same process and performance behavior; the usage ratio and process conditions should be verified by laboratory and field trials.
THINGS TO CONSIDER WHEN USING PURE TEREPHTHALIC ACID
One of the most common mistakes in using Pure Terephthalic Acid is using terephthalic acid directly interchangeably with other monomers such as dimethyl terephthalate (DMT), isophthalic acid, or phthalic anhydride at the same weight and under the same temperature conditions.
However, since the molecular weights, acid values, solubilities and melting/sublimation behaviors of these compounds are different, the dosage calculation should be made based on moles or acid value equivalents and the reactor temperature should be adapted accordingly.
The following issues should be considered when using Pure Terephthalic Acid:
A PTA grade suitable for the intended use (textile fiber, bottle resin, film or alkyd resin) should be selected.
Reaction stoichiometry should be based on mole ratio and acid value (mg KOH/g).
Purity, moisture, ash and metal impurity values should be checked.
Limits for 4-CBA and p-toluic acid, which affect polymer chain growth and color, should be monitored.
In textile and transparent packaging applications, APHA color, whiteness index and b* yellowness value should be verified.
Homogeneous mixture and appropriate viscosity should be ensured during the preparation of paste (slurry) with ethylene glycol.
Water and excess glycol formed during esterification and polycondensation stages must be effectively removed from the system.
In the production of alkyd resin, pre-esterification with glycols should be carried out if necessary, taking into account the high sublimation temperature (> 300 °C) and low solubility.
It should be ensured that there is no unreacted PTA residue in order to avoid haze formation in the paint film.
The product should not come into contact with strong oxidizing agents and should be kept away from incompatible substances.
Dust cloud formation should be prevented, and grounding should be done to dissipate static electricity charge in dry powder transfer equipment.
Dosage, catalyst ratio, and process conditions should be determined by laboratory and field trials.
Waste management and recovery processes should be carried out in accordance with local environmental legislation.
Manufacturer TDS and SDS documents should be examined.
Batch-based analysis results should be verified via the COA.
Pure Terephthalic Acid is an organic solid that can form explosive dust mixtures with air in certain conditions, and its dust may cause mild irritation or physical abrasion to the eyes, skin, and upper respiratory tract.
Appropriate dust mask (respiratory protection with P1/P2/P3 filter), nitrile gloves, safety glasses, appropriate work clothing and adequate ventilation should be used to prevent dust formation during weighing, transfer and feeding stages; safe working procedures should be determined according to the current SDS document.
Exposure to auxiliary raw materials used together in the processes, such as monoethylene glycol, 1,4-butanediol, catalysts like antimony trioxide, and organic solvents, should be evaluated separately.
In addition, necessary engineering measures should be taken against carbon monoxide and other irritating vapor and gas emissions that may occur during high-temperature reactions or incomplete combustion.
INITIAL FORMULATION APPROACHES FOR PURE TEREPHTHALIC ACID
The following examples are initial approaches to illustrate how Pure Terephthalic Acid can be evaluated in the formulation and process development process.
These are not verified commercial recipes, factory production instructions, or final formulas compliant with regulations. The ratios given are sample starting levels for laboratory pre-trials and R&D studies.
The purity of pure terephthalic acid to be used, 4-CBA impurity, moisture content, and other auxiliary raw materials can significantly change the final polymer performance.
Laboratory trials, performance tests, occupational safety and relevant legislation controls must be carried out in every application.
EXAMPLE 1: PET PREPOLYMERIZATION INITIAL APPROACH VIA DIRECT ESTERIFICATION
Objective: To investigate direct esterification and BHET oligomer production at laboratory scale using pure terephthalic acid and monoethylene glycol (MEG).
Starting ingredients:
Pure Terephthalic Acid: 1 mol (basis).
Monoethylene glycol (MEG): Approximately 1.5 to 2.0 molar ratio relative to PTA
Antimony trioxide (Sb₂O₃) catalyst: ppm level relative to the reaction mixture (e.g., 100-300 ppm)
Application approach:
PTA powder and monoethylene glycol (MEG) are formed into a homogeneous paste (slurry) in a suitable mixer and loaded into the reactor.
The reactor is purged with nitrogen gas to remove oxygen, and the mixture is heated to a temperature of 240 °C to 260 °C under moderate pressure.
The water released during esterification is continuously distilled and removed from the system, and the reaction is maintained for 2 to 4 hours.
The obtained BHET oligomers are transferred to pre-polycondensation and melt polycondensation reactors under vacuum to observe an increase in viscosity.
Dust masks and appropriate laboratory protective equipment should be used during work, and gases that may be released should be controlled under ventilation.
EXAMPLE 2: PTA MODIFICATION PRE-TRIAL IN ALKYD RESIN PRODUCTION
Objective: To investigate the effect of the use of Pure Terephthalic Acid instead of phthalic anhydride in alkyd resin formulation on resin hardness and thermal stability.
Starting ingredients:
Pure Terephthalic Acid: A certain percentage of the total dicarboxylic acid load (e.g., 10-25% initially as a partial substitution)
Phthalic anhydride (PA) or isophthalic acid: The remaining acid component
Polyol (glycerin or pentaerythritol): According to the stoichiometric ratio
Saturated/unsaturated fatty acid (or oil): According to the resin oil length
Application approach:
Considering the high melting and sublimation temperature (~300 °C), a pre-esterification step with glycols is planned to ensure complete reaction of PTA.
The esterification reaction is initiated by heating the polyol, fatty acid and acid components in a controlled manner under an inert atmosphere.
During the reaction, the acid value decrease is monitored and water is continuously removed.
The resulting alkyd resin is dissolved in solvent and samples are taken and film hardness, drying time and haze are tested.
Heat-resistant gloves and face shields should be used when working with acid and hot resin.
EXAMPLE 3: ESTERIFICATION APPROACH FOR PBT ENGINEERING PLASTIC
Objective: To evaluate the conditions for polybutylene terephthalate (PBT) prepolymerization using 1,4-butanediol (BDO) with pure terephthalic acid.
Starting ingredients:
Pure Terephthalic Acid: 1 mol
1,4-butanediol (BDO): Molar excess relative to PTA
Suitable esterification and polycondensation catalysts: According to laboratory optimization
Application approach:
PTA and 1,4-butanediol are combined in the reactor at the appropriate temperature and mixing speed.
During the esterification stage, the temperature is gradually increased, allowing water to escape.
Then, the polycondensation step is carried out under high vacuum to obtain PBT prepolymer.
The melting behavior and mechanical properties of the product are examined.
Appropriate local suction and respiratory protection against solvent vapors and dust should be provided during the procedure.
SIMILAR PRODUCTS AND ALTERNATIVES TO PURE TEREPHTHALIC ACID
The choice of alternative product for Pure Terephthalic Acid (PTA) depends on the type of polymer being targeted and the manufacturing process. Dimethyl Terephthalate (DMT) can be used as an alternative raw material to PTA in the production of PET and polyester, while Isophthalic Acid (IPA) and Phthalic Anhydride (PA) can be considered for different purposes in certain polyester, resin, and coating formulations.
2,5-Furandicarboxylic Acid (FDCA) is a monomer used in the production of a different polyester that is being investigated as an alternative to PET.
Not all of these chemicals are equivalent products that can directly replace PTA. When choosing an alternative, the targeted final product, polymer structure, reaction mechanism and process requirements should be evaluated together.
PURE TEREPHTHALIC ACID AND DIMETHYL TEREPHTHALATE (DMT)
Dimethyl Terephthalate (DMT) is the methyl ester of terephthalic acid, used in the production of PET and polyester. DMT can be used in the production of polyester by transesterification reaction with ethylene glycol. Therefore, it is one of the closest alternative raw material options to PTA, especially in terms of PET and polyester production.
In the PTA-based production route, direct esterification occurs, while in the DMT-based route, methanol is formed during transesterification. The presence of additional process requirements for the recovery of methanol has been effective in the spread of the PTA-based route. However, DMT remains important as an alternative raw material used in polyester production.
These two substances are not the same chemical and cannot be automatically used interchangeably under the same process conditions. Switching to DMT requires an assessment of the production route and associated process conditions.
PURE TEREPHTHALIC ACID AND ISOPHTHALIC ACID (IPA)
Isophthalic Acid (IPA) is an aromatic dicarboxylic acid structurally related to terephthalic acid that carries two carboxylic acid groups at different positions in the benzene ring. The structural difference between the two compounds allows different properties to be achieved in the production of polymers and resins.
IPA can be used in the modification of PET and copolyesters, unsaturated polyester resins, paint and coating systems, and adhesives. It is possible to evaluate it together with PTA in PET formulations. Therefore, IPA should be considered as a complementary component used to change the composition and properties of the polymer rather than as a raw material that completely substitutes PTA in some polyester applications.
PTA and IPA should not be considered the same chemical. Which compound to use should be determined by the targeted polymer structure and the requirements of the final product.
PURE TEREPHTHALIC ACID AND PHTHALIC ANHYDRIDE (PA)
Phthalic Anhydride (PA) is a chemical raw material used especially in the production of alkyd resins and various polyester resins. PA, which has an important place in the paint and coating industry, is one of the traditional building blocks used in certain resin formulations.
PTA can also be used in polyester coating resins and some unsaturated polyester systems. However, PTA and PA differ in their chemical structures and the way they participate in the reaction. Therefore, the use of PTA as a substitute for PA should not be considered as a directly applicable change for every formulation. The formulation needs to be re-evaluated based on the desired resin properties and process conditions.
The relationship between these two chemicals is important, especially in terms of alkyd resins, polyester resins and coating applications. However, it cannot be said that PA is a universal alternative to PTA or that PTA will give the same result in all PA applications.
PURE TEREPHTHALIC ACID AND 2,5-FURANDICARBOXYLIC ACID (FDCA)
2,5-Furandicarboxylic Acid (FDCA) can be used in the production of a polyester called Polyethylene Furanoate (PEF) by reacting with ethylene glycol. PEF is among the polymers being investigated as an alternative packaging material to PET.
There are studies on PEF's gas barrier properties and bio-based production potential. Therefore, FDCA is important in terms of developing an alternative to PET-based packaging materials.
However, FDCA is not a direct replacement for PTA in PET production. Using FDCA results in a different polyester, PEF. Therefore, this alternative is based on the production of a different polymer rather than the exchange of raw materials within the same PET production route.
GENERAL EVALUATION OF ALTERNATIVES
Alternatives for PTA differ according to their intended use. DMT offers an alternative feedstock route in the production of PET and polyester, while IPA can be used for modification in certain polyester and coating formulations. PA is an associated chemical, especially in terms of alkyd resins and coating systems. FDCA is used in the production of PEF, an alternative polyester to PET.
Therefore, when determining the alternative to PTA, only similar chemical structure or use in the same sector should not be considered. The properties of the targeted product, reaction path and process compatibility should be taken into account.
QUALITY CONTROL AND PURCHASING CRITERIA FOR PURE TEREPHTHALIC ACID
When purchasing Pure Terephthalic Acid (PTA), the chemical purity, physical properties and suitability of the product for its intended use should be evaluated. PTA is an important raw material used especially in the production of PET (polyethylene terephthalate), polyester fibers, films, engineering plastics and polyester coating resins. The consistent chemical quality of the product is important for the reliability of the production process and the performance of the final product.
Chemical Purity and Impurity Content
The purity of PTA is an important parameter in evaluating its suitability for polyester production. PTA is defined as a high-purity aromatic dicarboxylic acid, and consistent purity is important for the stability of polymerization reactions.
4-CBA (4-Carboxybenzaldehyde): One of the important impurities associated with PTA production. During the purification of crude terephthalic acid, impurities such as 4-CBA can be removed by hydrogenation and crystallization. The applicable ppm limit should be checked in the product specification.
Other impurities: When evaluating the chemical quality of PTA, the purity information of the product and the technical specifications announced by the manufacturer should be taken into account. Numerical acceptance limits for p-toluic acid, ash and metal content should be checked in the product’s TDS and COA
Physical and Chemical Properties
The physical properties of PTA are important for identifying the product and assessing its suitability for its intended use. These properties include white crystalline powder form, low water solubility, density and high-temperature behaviour.
Physical appearance: Described as a white crystalline powder.
Chemical formula: C₈H₆O₄.
Molecular weight: 166.13 g/mol.
Density: Approximately 1.58 g/cm³ at 25 °C
Solubility in water: Very slightly soluble in water. The page gives a value of approximately 0.017 g/L for 25 °C.
Behavior with temperature: It shows sublimation properties when heated.
These properties help define the physical and chemical identity of the PTA. However, the suitability of the product for a specific production process should not be evaluated solely on these general characteristics.
Color and Particle Characteristics
The color properties and particle structure of PTA can be considered in the evaluation of the product, especially in applications such as polyester coating resins, films and fiber production. The high chemical quality of PTA and its physical properties are important for production performance.
The particle size, powder flow and physical form of the product should be considered together with the intended use. Numerical acceptance limits for particle size distribution, sieve analysis, b* color value and APHA color value should be checked in the product specification.
Information to Check Before Purchase
During the PTA purchasing process, the product name, CAS number, chemical formula, physical form and intended use of the product must be compatible with each other. For PTA, CAS No. 100-21-0, EC No. 202-830-0 and the molecular formula C₈H₆O₄ are given.
PTA is used in areas such as polyester fiber, PET bottles, packaging film, engineering plastics and coating resins. Therefore, the suitability of the product for the targeted application and the features described in the available technical documentation should be evaluated together during purchase.
Ataman Chemical's product page states that PTA is used in areas such as polyester fiber, PET bottle, packaging film, engineering plastic, and coating resins. Therefore, the suitability of the product for the targeted application and the features described in the available technical documentation should be evaluated together during the purchase.
Overall Assessment
Chemical purity, impurity profile, and physical properties are key areas of evaluation in the quality control of PTA. However, it should not be assumed that every product has the same technical properties. The purchase decision should be based on the chemical identity of the product, the intended use, and product-specific technical information.
SUPPLY OF PURE TEREPHTHALIC ACID FROM ATAMAN KIMYA
Pure Terephthalic Acid (PTA) is an important chemical raw material used in PET and polyester production, polyester fibers, packaging films, engineering plastics and polyester coating resins.
Companies that want to obtain information about PTA from Ataman Kimya can specify their areas of use and technical requirements and request information about product suitability, current supply status, packaging options and a price offer.
Before ordering, the chemical description, intended use and necessary technical specifications of the product should be clarified. The current stock status, origin, quality features, packaging options and supply conditions of the product should be confirmed directly from Ataman Kimya.
Sharing the following information in the quote request facilitates the evaluation of the right PURE TEREPHTHALIC ACID product:
Use sector and end application
Requested product form and grain size
Requested minimum purity and maximum 4-CBA content
Iron and heavy metal limits
Knowledge of the formulation or process used
Requested quality standard
Estimated order quantity
Type of packaging requested
Requested technical documents
TDS or COA information of the current product, if applicable
FREQUENTLY ASKED QUESTIONS ABOUT PTA
What is Pure Terephthalic Acid (PTA)?
Pure Terephthalic Acid (PTA) is an organic compound in the class of aromatic dicarboxylic acids with the chemical formula C₈H₆O₄. It has the appearance of a white crystalline powder and is used in various industrial applications, particularly in the production of PET and polyester.
What is the CAS number of PTA?
The CAS number of PTA is 100-21-0.
What is the EC/EINECS number of PTA?
The EC/EINECS number for PTA is listed as 202-830-0.
What is the chemical formula and molecular weight of PTA?
Its chemical formula is C₈H₆O₄, and its molecular weight is approximately 166.13 g/mol.
In which areas is PTA used?
PTA is used in the production of PET bottles and packaging, polyester fiber and film production, engineering plastics, polyester resins and industrial paint-coating systems. It is also used as a raw material in the production of some terephthalate-based plasticizers.
Why is PTA used in PET production?
PTA is one of the basic raw materials used in the production of PET (polyethylene terephthalate). It contributes to the formation of the polyester chain by undergoing esterification and polycondensation reactions with ethylene glycol. PET is used in the production of products such as packaging materials, plastic bottles and polyester fibers.
Is PTA soluble in water?
PTA has low water solubility. Its solubility in water at room temperature (25 °C) is very limited; as the temperature increases, the solubility value in water increases.
What is the physical appearance of PTA?
PTA is a solid that exists in the form of a white crystalline powder. Its density is given as approximately 1.58 g/cm³ at 25 °C. It is odorless and tends to sublimate at high temperatures without melting.
Is PTA only used in the production of polyester?
No. Although the main use of PTA is polyester production, it is also used in the production of polyester coating resins, engineering plastics, plasticizers and resins used for some composite materials.
Are PTA and terephthalic acid the same substance?
PTA refers to purified terephthalic acid (Purified Terephthalic Acid). Terephthalic acid is the generic name for the same chemical compound; the high purity of the product (usually around 99.9%) and technical specifications define the PTA grade.
What other chemical names are used for PTA?
Terephthalic Acid is also known by names such as Benzene-1,4-dicarboxylic acid, 1,4-Benzenedicarboxylic Acid, p-Phthalic Acid and p-Dicarboxybenzene.
How is PTA produced industrially?
In the industrial field, PTA is usually produced by catalytic oxidation of p-xylene (Amoco process); in this process, the raw product is obtained using cobalt-manganese-bromide catalyst and acetic acid solvent and then undergoes purification steps.
What parameters are important for the polymer quality of PTA?
For polymer grade PTA, the purity grade, 4-formylbenzoic acid (4-CBA) impurity, moisture content, ash content and heavy metal contents are critical for process performance.
Is PTA a hazardous substance?
PTA is a stable solid under normal conditions; however, when mixed with air as a fine powder, it can form explosive dust mixtures. Inhalation may irritate the upper respiratory tract and cause mild irritation in contact with skin and eyes.
How should PTA be stored?
PTA should be stored in its original sealed packaging in a cool, dry, well-ventilated area, away from direct sunlight and moisture. It should be kept separate from strong bases and flammable materials.
What documents should be requested when purchasing PTA?
In PTA supply, Technical Data Sheet (TDS), Safety Data Sheet (SDS) and batch-based Certificate of Analysis (COA) must be examined and requested.
PTA (PURE TEREPHTHALIC ACID) – TECHNICAL SUMMARY
Pure Terephthalic Acid, also known as Purified Terephthalic Acid (Turkish: Saflaştırılmış Tereftalik Asit), is an organic compound in the aromatic dicarboxylic acid class with a white crystalline powder structure with the formula C₈H₆O₄. Terephthalic Acid can be referred to by different names such as Benzene-1,4-dicarboxylic acid, 1,4-Benzenedicarboxylic Acid, p-Phthalic Acid and p-Dicarboxybenzene.
PTA is produced to have a high degree of purity (usually around 99.9%), especially polymer quality (polyester grade). Purity, 4-CBA (4-formylbenzoic acid) impurity, moisture content, ash content and heavy metal contents are critical parameters for process performance and final product quality.
CAS No 100-21-0 and EC No 202-830-0 are used for PTA. In the industrial field, it is generally produced by catalytic oxidation of p-xylene; then the raw product obtained is passed through purification steps and made suitable for commercial use.
PTA is mainly used as a raw material in the production of PET (polyethylene terephthalate) bottles and packaging, polyester fiber and film production, engineering plastics, polyester resins, industrial paint-coating systems and some terephthalate-based plasticizers. It enters esterification and polycondensation reactions with ethylene glycol, allowing the formation of the polyester chain. Performance depends on product quality, purity degree, reaction conditions and system parameters.
PTA, which is a stable solid under normal conditions, can form explosive dust mixtures when mixed with air as a fine powder; inhalation may irritate the upper respiratory tract and cause mild irritation in contact with skin and eyes. For this reason, cool, dry, well-ventilated areas should be preferred during storage and processing, it should be kept away from strong bases and flammable materials, appropriate occupational safety measures should be taken and up-to-date SDS should be taken as a basis.
Companies planning to procure PTA from Ataman Kimya are recommended to confirm up-to-date product, stock, origin, packaging and offer information by sharing their usage area, requested product quality, purity, 4-CBA level, quantity and technical document needs.
