Dimethyl Terephthalate (DMT)
The route polyester started on. Terephthalic acid could not be purified by any conventional means, so the industry made the dimethyl ester instead — because unlike the acid, it melts, distils and recrystallises.
Molecular Structure
What is Dimethyl Terephthalate (DMT)?
DMT is terephthalic acid with both carboxyl groups esterified with methanol. Chemically that is a small change; commercially it was the change that made polyester possible. Terephthalic acid sublimes rather than melting and is essentially insoluble in ordinary solvents, so in the 1950s there was no practical way to purify it to polymer grade. Its dimethyl ester melts at 141 °C, distils under vacuum and recrystallises cleanly from methanol, which meant it could be purified to the standard the polymerisation demanded.
It is made from p-xylene by the Witten process — alternating stages of air oxidation and esterification with methanol, followed by distillation and crystallisation. Polymerisation runs by transesterification: DMT reacts with ethylene glycol, methanol is driven off and recovered, and the resulting bis-hydroxyethyl terephthalate is polycondensed to PET.
PTA displaced DMT once the hydrogenation purification route was commercialised, because direct esterification gives more polymer per tonne of raw material and produces water rather than methanol. DMT never disappeared, though. It remains the preferred feed for several copolyesters and PBT grades, for certain film and hot-melt applications, and it is what comes back when PET is chemically recycled by methanolysis.
DMT and PTA are not interchangeable on a plant that was built for one of them. The two routes differ in catalyst system, in reaction stoichiometry and in whether the plant has to recover methanol or water. Converting an esterification line between them is a capital project, not a feed switch.
Quick Reference
Key Physical & Chemical Properties
Structure & Bonding
The dimethyl diester of terephthalic acid. The same rigid para-substituted aromatic core that gives polyester its stiffness, but with both acid groups capped as methyl esters — which is precisely what makes the molecule meltable, distillable and therefore purifiable.
Skeletal structure — dimethyl diester of the para-dicarboxylic acid
Structural Identity
- IUPAC NameDimethyl benzene-1,4-dicarboxylate
- Common namesDMT, dimethyl terephthalate
- Molecular FormulaC₁₀H₁₀O₄
- Molecular Weight194.18 g/mol
- Functional groupsTwo aromatic methyl esters
- SubstitutionPara (1,4) — linear geometry
- Polymerises byTransesterification, releasing methanol
- Made fromp-Xylene, Witten oxidation–esterification
- Recycling roleThe product of PET methanolysis
- CAS Number120-61-6
- InChI KeyWOZVHXUHUFOZLK-UHFFFAOYSA-N
Product Specifications
Chelora supplies Dimethyl Terephthalate (DMT) in standard and custom grades. Contact us for specification sheets tailored to your process.
| Chemical name | Dimethyl terephthalate |
|---|---|
| CAS Number | 120-61-6 |
| Molecular formula | C₁₀H₁₀O₄ |
| Molecular weight | 194.18 g/mol |
| Purity (min) | ≥ 99.90 wt% |
| Freezing point (min) | ≥ 140.3 °C |
| Acid number (max) | ≤ 0.05 mg KOH/g |
| Saponification number | 577 – 579 mg KOH/g |
| Monomethyl terephthalate (max) | ≤ 50 ppm wt |
| Colour, molten (max) | ≤ 10 APHA |
| Methanol insolubles (max) | ≤ 10 ppm wt |
| Ash (max) | ≤ 10 ppm wt |
| Iron (max) | ≤ 0.50 ppm wt |
| Water (max) | ≤ 0.05 wt% |
| Dimethyl isophthalate (max) | ≤ 100 ppm wt |
| Dimethyl orthophthalate (max) | ≤ 50 ppm wt |
| Bulk density (flake) | ≈ 600 – 700 kg/m³ |
| Flash point | 153 °C (closed cup) |
| Autoignition temperature | 518 °C |
| Transport classification | Not regulated as dangerous goods; molten shipments as UN 3257 |
Downstream Applications & Derivatives
Key derivative chains and industrial uses of Dimethyl Terephthalate (DMT).
Polyester Fibre & Resin
The original PET route, still operated where plants were built for transesterification. Produces the same polymer as the PTA route, with methanol rather than water as the condensate to recover.
PBT Engineering Resin
Widely preferred over PTA for polybutylene terephthalate. The transesterification route with 1,4-butanediol gives better control of tetrahydrofuran formation, which is a persistent side reaction on the direct acid route.
Speciality Film & Copolyester
Copolyesters and film grades where the very low acid number and tight isophthalate control of DMT give more consistent melt behaviour than acid-route feed.
PET Chemical Recycling
Methanolysis depolymerises PET back to DMT and ethylene glycol. Because DMT can then be distilled, the route strips out dyes, additives and contamination that mechanical recycling cannot touch.
Polyester Polyols & Coatings
DMT residues and DMT itself feed aromatic polyester polyols for rigid polyurethane and polyisocyanurate insulation foam, and saturated polyester resins for powder coatings.
Hot Melt & Adhesive Resins
A building block in copolyester hot melt adhesives and in speciality plasticisers, where the aromatic ring contributes heat resistance and cohesive strength.
Why source Dimethyl Terephthalate (DMT) through Chelora Petrochem?
Verified Origin
Full origin certification and asset-backed supply chain documentation — no grey-market supply.
Grade Flexibility
Fibre, resin and PBT grades supplied, as flake or molten. We specify against acid number, monomethyl terephthalate and isomeric phthalate content, since those govern transesterification behaviour more than the assay does.
Full Documentation
CoA, SDS, REACH compliance, transport documentation including elevated-temperature declarations, and destination-market certificates with every shipment.
Logistics Support
Experienced in both bagged and heated bulk logistics — 25 kg bags and jumbo bags of flake, and insulated, trace-heated ISO tanks for molten delivery, Indian and international.
Storage & Handling Guidelines
Always refer to the full SDS before handling. The following is a summary of key requirements.
- Hold molten material at 150–170 °C under a dry nitrogen pad. DMT freezes at about 141 °C, so the operating window between solidification and unnecessary thermal load is narrower than it looks.
- Trace-heat and insulate every line, valve and pump on molten service, including dead legs. A frozen line is the standard failure mode and DMT sets to a hard solid rather than a slush.
- Treat molten DMT as a thermal burn hazard first. At 150 °C and above, the burn risk substantially exceeds the chemical hazard, and splash protection should be specified for hot liquid.
- Keep flake dry and sealed. DMT is not strongly hygroscopic, but surface water hydrolyses ester groups back to acid and shows up directly as an acid number failure.
- Manage flake dust as an explosion risk — earth and bond conveying, and control accumulation at bag tipping and silo fill points.
- Use stainless steel for wetted parts in melt service; iron pickup drives colour in the finished polyester and is not recoverable downstream.
- Exclude strong acids, strong bases and strong oxidisers. Alkali contact hydrolyses the esters and destroys the acid number specification.
- Ventilate around heated handling points. DMT vapour condenses to a fine airborne solid that irritates the eyes and upper airways.
- Provide eyewash and washing facilities, label every container clearly, and declare molten shipments as elevated-temperature material where the receiving jurisdiction requires it.
Hazard Summary
Classification: DMT has no harmonised CLP classification and is generally not classified as hazardous. Acute toxicity is low by all routes. Self-classification for mild eye or respiratory irritation from dust and condensed vapour is common.
Thermal burns are the main acute hazard: DMT is handled molten at 150–170 °C, and a splash at that temperature causes serious burns made worse by the material solidifying on the skin. Personal protection at transfer connections should be selected for hot liquid, not for chemical contact.
Dust and condensed vapour: flake handling generates dust, and vapour above molten material recondenses as a fine solid that irritates eyes and airways. Extract at source around heated equipment.
Dust explosion: DMT flake and fines are combustible and can form explosible clouds. Grounding, bonding and accumulation control apply to solid handling in the usual way.
Hydrolysis is a quality risk: water and alkali both convert ester groups back to acid, raising the acid number and upsetting transesterification stoichiometry. This is the most common cause of a compliant lot failing at the receiving plant.
Fire: a combustible material with a flash point of 153 °C and autoignition at 518 °C. Molten storage sits above the flash point in some operating regimes, so hot work control and vapour space management need specific assessment. Combustion produces carbon monoxide and carbon dioxide.
PPE minimum: safety goggles, gloves and coveralls for flake handling; face shield, heat-resistant gloves and full splash protection for molten service.
Consult the full SDS for exposure limits, spill containment, emergency response and disposal before any use.
Frequently Asked Questions
Technical and commercial questions about Dimethyl Terephthalate (DMT) sourcing and specifications.
What is DMT used for?
Its historic and largest use is as the feed for PET resin and polyester fibre on plants built for the transesterification route. It is also widely preferred for PBT engineering resin, used in speciality copolyesters and film, and it feeds aromatic polyester polyols for rigid insulation foam. Separately, DMT is what comes back out of PET chemical recycling by methanolysis, which has given it renewed relevance.
Why did DMT come first, and why did PTA replace it?
DMT came first because terephthalic acid could not be purified. It sublimes instead of melting and is nearly insoluble, so neither distillation nor recrystallisation works on it, and in the 1950s there was no route to polymer-grade acid. Esterifying it with methanol produced a compound that melts at 141 °C and distils cleanly, which solved the purification problem. PTA took over from the 1960s once catalytic hydrogenation made purified acid available, because direct esterification gives more polymer per tonne of feedstock, avoids carrying two methyl groups through the process, and produces water rather than methanol to recover.
When is DMT still preferable to PTA?
Three situations, mainly. First, on plants that were built for transesterification, where the reactor design, catalyst system and condensate recovery are all configured for methanol. Second, for PBT, where the DMT route gives better control over tetrahydrofuran formation from butanediol than the direct acid route does. Third, in speciality copolyesters and films where the very low acid number and tight isomeric phthalate control of distilled DMT produce more consistent melt behaviour than acid-route feed.
Why is DMT shipped molten?
For the same reason phenol is. DMT melts at 140–142 °C, and a plant that is going to melt it anyway for transesterification gains nothing from receiving it solid and paying twice for the heat. Molten delivery in insulated, trace-heated tanks avoids a full thermal cycle, avoids dust exposure and allows pumped transfer. It does require the receiving terminal to have heated storage and reliable offtake, so flake remains the practical choice for smaller or intermittent consumption. Molten shipments are declared as elevated-temperature material under UN 3257 in most jurisdictions.
What is DMT's role in PET chemical recycling?
Methanolysis is one of the main chemical recycling routes for PET. Treating the polymer with methanol under heat and pressure depolymerises it back to DMT and ethylene glycol, and because DMT can be distilled, the process strips out dyes, pigments, additives and contamination that mechanical recycling simply carries through. The recovered DMT is chemically indistinguishable from virgin material, which makes the route attractive for coloured, multilayer or heavily contaminated PET streams that mechanical recycling cannot handle to food-contact standard.
What documentation does Chelora provide?
Every shipment includes a Certificate of Analysis covering purity, freezing point, acid number, saponification number, monomethyl terephthalate, colour in the melt, methanol insolubles, ash, iron, water and isomeric phthalate content; a Safety Data Sheet to GHS and REACH format; transport documentation including elevated-temperature declaration for molten cargoes; an origin certificate; and food-contact or destination-market certificates where the application requires them.
Request a quote or specification sheet
Talk to Chelora's sourcing team about Dimethyl Terephthalate (DMT) grade, volume, logistics, documentation, and lead times. We respond within one business day.
