Durene (1,2,4,5-Tetramethylbenzene) — CAS 95-93-2, ≥96% PMDA-Grade White Crystal, Naphthalene Not Detected

Durene - 1,2,4,5-Tetramethylbenzene, CAS 95-93-2

≥96.00% assay · Melting range 77.0–78.8 °C · Naphthalene not detected (<0.002%) · Six-lot consistency data published below

About 100 °C of melting point spread against roughly 13 °C of boiling point spread. Durene's four methyl groups sit in the symmetric 1,2,4,5 arrangement, so the molecule packs into a crystal lattice far more efficiently than its lopsided siblings - and that symmetry is worth a hundred degrees.

The practical consequence: you enrich the C10 cut by rectification to get the tetramethylbenzenes together, then chill and let durene crystallise out while isodurene and prehnitene stay liquid, and separate the crystals. It is a cheap, low-energy operation compared with any distillation attempt - which is why "separation process" appears in every durene producer's description, and why the melting range on the COA is the single most informative number about what you are actually buying.

🚫 Naphthalene - the impurity that follows your product all the way to the drum

Of everything on a durene certificate, this is the number a PMDA producer should look at first. In gas-phase catalytic oxidation, naphthalene does not simply burn off - it co-oxidises to phthalic anhydride. PA and PMDA have broadly similar sublimation behaviour, so PA carries through the condensation train and lands in your dianhydride, where it is genuinely awkward to remove. Naphthalene also consumes oxidant and adds thermal load to a reactor that is already running a strongly exothermic reaction.

The specification allows 0.05%. These lots test below the 0.002% detection limit - roughly twenty-five times inside the limit. If you are comparing durene offers, ask every supplier for a naphthalene figure with a stated detection limit, and treat "≤0.05% (conforms)" without a number as no answer at all.

🌡️ Melting range - width matters more than position

Pure durene melts at about 79.2 °C. Every percent of dissolved isomer depresses that and, more tellingly, widens the range. These lots run 0.4–0.6 °C wide and sit at 77.0–78.8 °C, which is consistent with the 96–97.5% assay and indicates well-formed, uniformly grown crystals rather than a mechanically separated slurry. A lot showing a two- or three-degree melting range is telling you something the assay figure alone will not.

⚖️ 96% is standard grade - and you should price it as such

Let us be plain about this rather than let a data sheet imply otherwise. This is standard commercial durene to SH/T 1822-2019, not a 99% ultra-pure grade. The balance of roughly 3–4% is other C10 aromatics - principally isodurene and prehnitene, with minor tri- and pentamethylbenzenes.

Those isomers behave differently from naphthalene: on oxidation they yield their own acids and anhydrides or burn through to CO₂, so they do not contaminate PMDA the way phthalic anhydride does. What they do is consume oxidant and reduce PMDA yield per tonne of feed. So do your economics on the assay, not on the tonnage - a 96.24% lot and a 97.46% lot are not the same purchase, and a competitor quoting 98–99% durene at a higher price may still be the cheaper source of PMDA.

Higher-purity grades are reachable by repeated recrystallisation, at meaningfully higher cost. If your process genuinely needs 98%+, tell us and we will quote it separately rather than stretch this grade to fit.

🛢️ Petroleum C10 aromatics. Heavy reformate from catalytic reforming, rectified and crystallised. This is our source.

⛏️ Methanol-to-gasoline heavy ends. In MTG plants durene is a nuisance - its high freezing point causes cold-weather driveability problems, so it has to be stripped out of the gasoline pool and then becomes a saleable by-product. Volumes are real but the trace impurity profile differs from the refinery route.

01Crude oil - own import quota, tank farm, pipelines and transport fleet

02Integrated refining - in-house C10 aromatics production, not merchant feed

03Rectification & enrichment - tetramethylbenzene cut concentrated

04Crystallisation & separation - proprietary purification unit, own IPR

05Downstream - feeds the group's own PMDA oxidation plant, so the durene spec is set by a customer that cannot switch supplier

⚠️ Capacity, stated honestly. The durene unit is designed for 40,000 t/a. That is a design figure. Because a share of output is consumed internally by the group's own PMDA plant, merchant availability is a fraction of nameplate and varies with downstream run rates. Send us your target annual volume before we discuss price - we would rather tell you early that a tonnage is not available than quote it and disappoint you at contract time.

⚡ 1. Pyromellitic Dianhydride - effectively the entire market

There is no point pretending durene has a diversified demand base. The overwhelming majority of world production goes into one reaction: gas-phase catalytic oxidation of all four methyl groups to give pyromellitic dianhydride (PMDA), which is then condensed with aromatic diamines into polyimide - flexible circuit film, chip-on-film substrate, wire enamel, high-temperature tape and battery separator coating. Durene demand is therefore a derived demand: it tracks polyimide film, which tracks consumer electronics and flexible display.

🔗 Downstream product: Pyromellitic Dianhydride (PMDA, CAS 89-32-7)

🧪 2. Pyromellitic Acid & Tetracarboxylate Derivatives

Liquid-phase oxidation gives pyromellitic acid directly, used in metal-organic framework synthesis, specialty chelants, corrosion-inhibiting coating resins and as an intermediate to pyromellitate esters. It is a much smaller outlet than the vapour-phase PMDA route but a real one.

🔬 3. Fine Chemical Intermediate & Analytical Use

Durene's symmetric, electron-rich ring makes it a convenient substrate for selective aromatic substitution - halogenation, nitration, sulfonation and Friedel-Crafts chemistry - en route to specialty intermediates and to durene-derived aldehydes and amines. High-purity zone-refined grades also serve as an aromatic reference standard in oxidation-catalysis research. These are low-volume applications; do not build a supply plan around them.

🐟 Do not overlook the aquatic hazard - it is the part most durene datasheets bury.

Durene is classified Aquatic Acute 1 / Aquatic Chronic 1 (H410 - very toxic to aquatic life with long lasting effects). Storage must be bunded, and no washings, spill residue or contaminated firewater may reach a surface drain or watercourse. This is a design requirement for the storage area, not a line in a procedure.

It also affects freight. Transport classification varies between suppliers' safety data sheets - some declare an environmentally hazardous substance entry on the strength of H410, others ship it unregulated, and treatment differs between sea and road. Confirm the DG status on our SDS against your carrier and destination before you book, because it changes container options and cost.

📁 Supplied with every consignment:

📄 EU CLP-format SDS, 16 sections, with the H410 aquatic section and transport classification stated explicitly

📄 Batch COA to SH/T 1822-2019 and GB/T 21781-2008 from a CNAS-accredited laboratory

📄 Extended GC impurity profile on request - beyond the standard three-parameter certificate

📄 REACH and TSCA inventory status confirmation

Q1. Is 96% durene good enough to make PMDA?

Yes - it is the industry standard feed, and virtually all commercial PMDA is made from durene in this range. What 96% costs you is yield per tonne of feed, not product quality, because the balance is other tetramethylbenzene isomers that oxidise to their own products rather than contaminating the dianhydride. The impurity that does reach your product is naphthalene, and that is why it carries a separate specification. Run your economics on assay, and negotiate on naphthalene.

Q2. Why can't durene simply be distilled out of the C10 cut?

Because the three tetramethylbenzene isomers boil within about 13 °C of one another - around 192, 198 and 205 °C. Separating that by distillation would need an impractical number of theoretical plates and enormous reflux. Their melting points, by contrast, span roughly 100 °C, so chilling the enriched cut crystallises durene out while the others remain liquid. Crystallisation is the economically viable route, and it is why melting range is such a meaningful quality indicator on the certificate.

Q3. My PMDA is showing phthalic anhydride contamination. Is the durene at fault?

Naphthalene in the feed is the usual suspect and the first thing to check - ask for the naphthalene figure with its detection limit on the exact lot you ran, not a generic "conforms". But it is not the only possibility: over-oxidation conditions, catalyst ageing and localised hot spots can also generate PA and other partial-oxidation products from durene itself. Send us the failing lot number with your PA figure and we will pull the retained sample and run the extended GC.

Q4. Should I take delivery as solid or molten?

It depends entirely on your intake. Solid in bags suits batch charging and smaller volumes, and avoids any heated-handling infrastructure. Molten in a heated ISO tank suits continuous feed at scale, removes bag-handling labour and dust, but commits you to heated storage, a melt-out procedure on arrival and vent management for sublimed vapour. Most established PMDA plants take molten; newcomers almost always start with bags. Tell us which and we will quote accordingly.

Q5. Does it matter whether durene comes from a refinery or an MTG plant?

For the three parameters on a standard certificate, usually not. For trace species below that certificate, it can - the two routes carry different minor-component histories, and oxidation catalysts are often tuned around a particular feed. In practice this means: do not treat durene as a fungible commodity you can switch mid-campaign on price alone. Qualify a new source on a trial run first. This material is the refinery C10 aromatics route.

Q6. Can you supply durene and PMDA from the same chain?

Yes - this durene feeds the group's own PMDA oxidation plant, so both are available from a single traceable chain running from the crude cargo forward. Buyers integrating backwards sometimes take durene; buyers who would rather not operate an oxidation reactor take the dianhydride. Tell us which end of the chain you want and we will quote both so you can compare the economics properly.

📩 Request Durene Price, Sample & Extended GC Profile

Tell us your target annual volume, destination port, whether you want solid or molten delivery, and the assay and naphthalene limits your process is written against. We reply within 24 hours with pricing, a representative batch COA, the EU CLP SDS with transport classification stated, and the extended GC impurity profile if you need it. Trial quantities available for source qualification.