Mixed or isomer — say which
Xylene (C₈H₁₀, CAS 1330-20-7 for the mixed isomers) exists as three isomers plus ethylbenzene. Solvent users buy the mixture; chemical manufacturers buy separated isomers.
| Grade | Composition | Primary use |
|---|---|---|
| Industrial / solvent grade | ≥98.5% C₈ aromatics, mixed | Paints, coatings, adhesives, inks, rubber |
| Isomer grade, mixed | ≥99.0% C₈ aromatics | Feedstock for isomer separation |
| Ortho-xylene | ≥99.5% o-xylene | Phthalic anhydride production |
| Para-xylene | ≥99.7% p-xylene | PTA, and from there polyester fibre and PET resin |
| Pharmaceutical | ≥99.0%, benzene ≤2 ppm | Pharmaceutical solvent, histology |
| Histological | ≥99.0%, very low residue | Tissue processing and staining in pathology |
For a coatings, adhesive or printing operation, industrial mixed xylene is almost always the right answer. Isomer grades cost more and offer no benefit as a solvent.
Key physical properties
| Property | Value |
|---|---|
| Chemical formula | C₈H₁₀ |
| CAS number | 1330-20-7 (mixed isomers) |
| Molecular weight | 106.17 g/mol |
| Boiling range | 136–144 °C for mixed isomers |
| Flash point | 27–32 °C — flammable |
| Auto-ignition temperature | 463–528 °C, isomer-dependent |
| Density at 20 °C | 0.860–0.868 g/cm³ |
| Vapour pressure at 20 °C | 8–9 mmHg — slower evaporation than toluene |
| Explosive limits in air | 1.1–7.0% v/v |
Note the melting points of the individual isomers: para-xylene freezes at +13 °C while meta-xylene stays liquid to −48 °C. Mixed xylene does not freeze in normal Pakistani conditions, but a para-rich stream can start dropping crystals on a cold night, which is worth knowing if you are storing isomer-grade material.
Evaporation rate is why formulators choose it
Xylene evaporates roughly three times more slowly than toluene. That single property drives most of its use in coatings, and it is the reason the two are so often blended rather than substituted.
- Slower evaporation gives better flow and levelling, producing a smoother finished film
- It reduces blushing in humid conditions, which matters in coastal locations
- It extends open time for brush and roller application
- It slows drying, which can be a disadvantage on a fast production line
- The practical approach is blending: toluene for speed, xylene for finish, adjusted for ambient conditions
| Coating type | Xylene role | Typical share of formulation |
|---|---|---|
| Medium-oil alkyd gloss | Primary resin solvent | 20–35% |
| High-build epoxy | Resin component solvent | 15–25% |
| Two-pack polyurethane topcoat | Co-solvent for both components | 15–20% |
| Industrial enamel | Solvent and thinner | 20–30% |
| Wood varnish | Resin solvent and viscosity reducer | 15–25% |
Other applications
- Printing inks — gravure and flexographic formulations
- Adhesives and sealants — solvent and viscosity control
- Rubber and leather processing
- Chemical feedstock — phthalic anhydride from ortho-xylene, and PTA from para-xylene
- Histology and pathology laboratories — clearing agent in tissue processing, requiring histological grade
- Cleaning and degreasing where a slower-evaporating aromatic solvent is preferred
Storage and handling
- Flash point of 27–32 °C is higher than toluene or acetone, but still below Pakistani summer ambient temperatures — treat it as a flammable liquid all year
- Store bunded and ventilated in a designated flammables area, away from oxidising agents
- Bond and earth containers during transfer
- Suitable materials — carbon steel, stainless steel, PTFE; check elastomer compatibility, as xylene attacks many rubbers
- Provide low-level ventilation for the heavier-than-air vapour
- Chronic exposure control matters — the health risk from aromatic solvents is cumulative, not acute
What to put on the RFQ
- Grade — "industrial mixed xylene, ≥98.5% C₈ aromatics", not "xylene"
- Benzene limit, for the same reason it matters with toluene
- Water content, colour and non-volatile residue where the application is a clear coating
- Sulphur content where a downstream catalyst is involved
- Quantity per delivery and annual volume
- Pack — drum, IBC or tanker — and whether returnable
- Delivery city and confirmation of compliant flammables storage
What drives the price
- Crude oil and naphtha pricing, since xylene comes from refinery reforming and cracking streams
- Polyester demand, which is the large one — para-xylene feeds PTA and therefore polyester fibre and PET, and strong polyester demand pulls xylene away from the solvent market
- Grade, with separated isomers priced well above mixed solvent grade
- Pack format, freight and flammable-goods transport
- Exchange rate and duty, as Pakistan is supplied by import
- Coating season demand
Sourcing considerations in Pakistan
- Xylene is imported from regional refineries and petrochemical complexes; confirm origin where formulation consistency matters
- Pakistan has substantial polyester and PET manufacture, which competes for the same upstream xylene streams and can tighten solvent-grade availability
- It moves as a Class 3 flammable liquid and needs compliant transport and storage
- Where you blend with toluene, sourcing both together on one schedule keeps the blend ratio consistent batch to batch