| HS Code | |
| Chemical Formula | C8H10 (mixed isomers) |
| Molecular Weight | 106.16 g/mol |
| Appearance | Colorless liquid |
| Odor | Aromatic, sweet |
| Boiling Point | 137-144 °C |
| Melting Point | < -25 °C |
| Flash Point | 25 °C (closed cup) |
| Autoignition Temperature | 463 °C |
| Flammable Limits | 1.0-7.0 % v/v |
| Density | 0.86-0.88 g/cm³ at 20 °C |
| Vapor Pressure | 0.9 kPa at 20 °C |
| Solubility | Insoluble in water; miscible with common organic solvents |
| Refractive Index | 1.497 at 20 °C |
| Viscosity | 0.62 mPa·s at 25 °C |
| State At 20 C | Liquid |
As an accredited Mixed Xylenes factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Mixed Xylenes packaged in 200-liter UN-approved steel drums, sealed and labeled flammable, with safety data sheets and batch traceability. |
| Container Loading (20′ FCL) | Mixed Xylenes, UN1307, Class 3 flammable liquid, loaded in a 20′ FCL container using approved drums/IBCs with secure stowage and IMDG labeling. |
| Shipping | Mixed Xylenes are shipped as a flammable liquid, UN1307, Class 3, Packing Group II or III depending on flash point. They require UN-approved steel drums, tank trucks, or ISO tanks, with flammable-liquid labels, placards, shipping papers, and emergency response information. Keep away from ignition sources and ensure ventilation. |
| Storage | Store Mixed Xylenes in a cool, dry, well-ventilated, fire-resistant area away from heat, sparks, flames, strong oxidizers, and incompatible materials. Keep containers tightly closed, properly labeled, and grounded when dispensing. Use secondary containment to control spills and leaks. Limit access, avoid inhalation, and provide suitable PPE and emergency equipment. Follow local regulations for flammable liquid storage. |
| Shelf Life | Mixed xylenes are stable and have an indefinite shelf life when stored sealed in a cool, dry, well-ventilated area away from ignition sources. |
Within a C8 aromatic separation block, mixed xylenes from reformate or pyrolysis gasoline are routed through clay treating and hydrotreating to reduce olefins, sulfur, and nitrogen compounds before entering the separation feed tank. A typical reformate-derived mixed xylene stream contains ethylbenzene 15–20 wt%, p-xylene 18–20 wt%, m-xylene 40–45 wt%, and o-xylene 20–25 wt%. The boiling point gap between p-xylene and m-xylene is 0.7°C, so fractionation cannot produce polymer-grade p-xylene. Commercial units therefore operate simulated moving bed adsorption loops, such as UOP Parex or Axens Eluxyl, using zeolitic adsorbent and paradiethylbenzene or toluene desorbent. The rotary valve in a Parex unit is a high-maintenance equipment item because seal wear produces cross-leakage and reduces extract purity. Normal extract purity is controlled at 99.7–99.9 wt%, with recovery in the 90–97% range depending on feed impurities and adsorbent ageing. The p-xylene extract is then sent to oxidation by air in acetic acid with cobalt-manganese-bromide catalysis at 175–220°C and 1.5–3.0 MPa. The crude terephthalic acid slurry is hydrogenated to reduce 4-carboxybenzaldehyde to ≤25 mg/kg in purified terephthalic acid. This limit is process-critical because 4-carboxybenzaldehyde acts as a chain terminator in PET polycondensation and lowers intrinsic viscosity. The purified terephthalic acid is esterified with ethylene glycol and polymerized under antimony or titanium catalysis to bottle-grade PET. Terminal products include PET bottle resin, fiber, and film. Food-contact PET is evaluated under 21 CFR 177.1630 and EU Regulation 10/2011. Production-scale bottlenecks include rotary valve seal leakage, oxidation reactor sparger plugging, and fines generation in crude TPA slurry filtration.
| Component | Boiling point at 101.3 kPa | Freezing point | Typical reformate content |
|---|---|---|---|
| Ethylbenzene | 136.2°C | -95.0°C | 15–20 wt% |
| p-Xylene | 138.4°C | 13.3°C | 18–20 wt% |
| m-Xylene | 139.1°C | -47.9°C | 40–45 wt% |
| o-Xylene | 144.4°C | -25.2°C | 20–25 wt% |
The fixed-bed oxidation of ortho-xylene to phthalic anhydride is exothermic and is constrained by hot-spot control rather than equilibrium conversion. ortho-Xylene is first recovered from a mixed xylene stream by superfractionation because its boiling point is 5.3–6.0°C higher than that of the para and meta isomers. The oxidation feed is a 95–99 wt% ortho-xylene cut to limit the excess heat load contributed by meta-xylene and ethylbenzene impurities. Reaction is carried out over vanadium pentoxide-titanium dioxide catalyst packed in tubular fixed-bed reactors cooled by a molten salt bath. The salt bath inlet temperature is maintained at 340–375°C, while a hot spot can exceed 400°C when ortho-xylene loading rises above 80 g/Nm³ air. Useful phthalic anhydride yield is generally in the 78–82 mol% range, with the balance lost to maleic anhydride and carbon oxides. Oxygen analyzers are placed after each reactor pass to hold excess oxygen within a narrow band, because an oxygen-lean condition shifts the catalyst oxidation state and an oxygen-rich condition promotes total combustion. The crude phthalic anhydride is distilled under vacuum to separate maleic anhydride and benzoic acid, then flaked or stored in heated tanks above 131°C. Phthalic anhydride should not be stored with amines because exothermic imide formation can pressurize a closed vessel. Compliance for product quality is assessed under ISO 1389 methods. Downstream conversion to plasticizers such as DEHP or DOP connects to EU REACH Annex XIV authorisation for certain phthalates. Terminal products include plasticized PVC compounds for cables, footwear, and films, as well as alkyd resins and unsaturated polyester resins. In production-scale operation, salt bath pump failure is a severe excursion risk, and ortho-xylene feed with >5 wt% meta-xylene raises hot-spot frequency and shortens catalyst life.
Because metaxylene content in mixed xylenes is the largest single C8 aromatic fraction in most reformate streams, the production of isophthalic acid starts from a meta-xylene-rich raffinate or from isomerisation output rather than direct distillation. Meta-xylene is oxidized with air in acetic acid using cobalt-manganese-bromide catalysis, but the process control loops differ from PTA because the intermediate oxidation products show higher solubility in the reaction matrix. The resulting isophthalic acid is purified by hydrogenation and crystallisation to reduce 3-carboxybenzaldehyde and color bodies. PIA is incorporated into unsaturated polyester resins where it replaces a portion of the ortho-phthalic or maleic anhydride in the acid charge to improve hydrolysis resistance and thermal stability. In PET copolyesters, isophthalic acid is used at low addition levels to reduce crystallinity and widen the processing window for thermoformed trays and clear containers. Residual cobalt and manganese species in PIA are controlled because they contribute to oxidative yellowing in powder coating overbake cycles. PIA is a combustible dust, so transfer lines are grounded and baghouses are fitted with deflagration venting. Acid value and viscosity of PIA-modified unsaturated polyester resins are measured under ISO 2114 and ISO 3219. Terminal products include corrosion-resistant UPR tanks, gel coats, powder coatings, and low-crystallinity PET packaging. Published data for this specific oxidation configuration is limited, so final reactor geometry is normally fixed only after pilot oxidizer testing.
Industrial mixed-xylene solvent grades are sold under ASTM D843 for nitration-grade material and under broader industrial specifications for lower-purity blends. A typical commercial mixed-xylene solvent has an initial boiling point near 137°C and a dry point near 143°C, with total C8 aromatic content not less than 99.0 wt%. Distillation range is measured by ASTM D1078 or ASTM D86. Kauri-butanol value is tested under ASTM D1133 and is normally in the 93–100 range. These solvents are used as the continuous phase in alkyd paints, phenol-formaldehyde varnishes, rubber tackifying sprays, and agricultural emulsifiable concentrates. In crop protection emulsifiable concentrates, the xylene carrier is blended with surfactant packages at 20–50 wt% of the formulation, but the exact ratio is active-ingredient specific. Storage equipment for xylene solvent should be nitrogen padded and grounded because the flash point is approximately 25–27°C and the autoignition temperature is 464–470°C. Under EU Directive 2004/42/EC, solventborne decorative coatings are restricted by maximum VOC content per liter, so reformulators shift to high solids or waterborne systems when compliant xylene level cannot be maintained. Mixed xylene should not be blended with strong oxidizers or stored in galvanized tanks where a water bottom can form zinc corrosion products. Terminal products include industrial wood coatings, marine coatings, crop protection formulations, and metal cleaning agents. For food-contact can coatings, residual xylene is controlled by migration or extraction testing, but mixed xylene is not acceptable in direct food-contact materials.
In a C8 aromatics complex, the raffinate stream after p-xylene adsorption is rich in meta-xylene and ethylbenzene. It is sent to a C8 isomerisation unit to restore the para-xylene concentration to thermodynamic equilibrium and prevent accumulation of meta-xylene in the recycle loop. Isomerisation reactors operate over platinum-containing zeolite catalysts in a hydrogen atmosphere at 380–450°C and 1.0–1.8 MPa. The units are radial-flow fixed-bed reactors with ceramic ball supports, and pressure drop is maintained below 0.5 bar to prevent channeling. Ethylbenzene dealkylation to benzene and ethane is a key side reaction, and unconverted ethylbenzene raises distillation load because it must be rejected or purged. The equilibrium C8 aromatic distribution at the reactor outlet is approximately 22–24 wt% p-xylene, 45–50 wt% m-xylene, 20–24 wt% o-xylene, with the balance ethylbenzene, but the exact split depends on catalyst age, space velocity, and feed composition. Hydrogen-to-hydrocarbon ratio is set to suppress coke, and chloride injection may be used on some bifunctional catalysts to maintain acid activity. Compliance for pressure equipment is governed by ASME BPVC Section VIII or PED 2014/68/EU. The product is cooled, separated from hydrogen-rich gas, and recycled to the p-xylene adsorption unit. This unit is a process bottleneck when ethylbenzene conversion falls because recycle flow increases and the para-xylene recovery loop becomes limited by adsorbent capacity. Terminal products remain tied to the p-xylene chain, but the isomerisation unit controls overall complex balance for downstream PTA and PET production.
Superfractionation of ethylbenzene from mixed xylenes requires a high-reflux column because the boiling point gap between ethylbenzene and p-xylene is only 2.2°C. The column may operate with 200–350 theoretical trays and reflux ratios above 50:1 in a tall trayed section. Recovered ethylbenzene at 99.5–99.8 wt% purity is then fed to a dehydrogenation unit. Dehydrogenation is carried out over potassium-promoted iron oxide catalysts at 600–650°C under vacuum or steam dilution. The steam-to-ethylbenzene mass ratio is typically 1.0–2.0:1, and the once-through conversion is limited to 55–70% by equilibrium. Unconverted ethylbenzene is separated from styrene in a vacuum distillation train and recycled. Styrene monomer is stabilized with 10–15 ppm 4-tert-butylcatechol to inhibit radical polymerization. The monomer purity is tested under ASTM D2827. Styrene production from this route is linked to downstream polymers such as polystyrene, acrylonitrile-butadiene-styrene, and styrene-butadiene rubber. In the distillation train, polymer fouling in the tower trays and reboilers is the dominant availability constraint. Compliance for the storage of styrene and ethylbenzene falls under Seveso III Directive 2012/18/EU for flammable liquid inventories. Higher xylene carryover into the ethylbenzene feed increases benzene and toluene byproducts in the dehydrogenation reactor and shortens catalyst cycle.
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Mixed xylenes are defined as a solvent-grade or chemical-grade blend of C8 aromatic hydrocarbons comprising meta-xylene, ortho-xylene, para-xylene, and ethylbenzene, assigned CAS registry number 1330-20-7. Commercial solvent-grade material typically contains ethylbenzene at 10–25 wt%, para-xylene at 10–20 wt%, meta-xylene at 35–50 wt%, and ortho-xylene at 10–25 wt%, with total aromatic content above 99 wt% when determined by ASTM D2360. The product is made available as a clear, low-viscosity liquid with a density of 0.865–0.875 g/cm³ at 15.6°C under ASTM D4052 and a closed-cup flash point of 25°C under ASTM D56. The vapor density relative to air is approximately 3.7, calculated from a mean molecular weight of 106.16 g/mol. Unlike para-xylene or ortho-xylene grades, mixed xylenes are not isolated for a single downstream molecule; the retained ethylbenzene and isomer distribution produce a broader boiling range and a different solvency balance relative to narrow-cut aromatic solvents.
Table 1. Commercial solvent-grade mixed xylene specification profile.
| Property | Test method | Specification or typical value |
|---|---|---|
| Appearance | Visual | Clear, free of haze and suspended matter |
| Color, Pt-Co | ASTM D1209 | ≤20 |
| Density at 15.6°C | ASTM D4052 | 0.865–0.875 g/cm³ |
| Distillation range | ASTM D850 | Initial boiling point ≥137°C; dry point ≤143°C |
| Flash point, Tag closed cup | ASTM D56 | 25°C |
| Total aromatic content | ASTM D2360 | ≥99.0 wt% |
| Non-aromatic hydrocarbons | ASTM D2360 | ≤1.0 wt% |
| Water content | ASTM E1064 | ≤100 mg/kg |
Receiving laboratories verify composition using capillary gas chromatography under ASTM D2360 with flame ionization detection. A 60 m × 0.25 mm × 0.25 µm polyethylene glycol column is used to separate ethylbenzene, para-xylene, meta-xylene, and ortho-xylene; temperature programming from 40°C to 200°C at 5°C/min is typical for this separation. The analytical detail is significant because a 1 wt% shift in para-xylene or ethylbenzene content can alter downstream crystallization calculations and evaporation behavior in solvent formulations.
Solvency behavior in medium-oil alkyds is governed by aromatic content and boiling range rather than by single-isomer purity. In air-assisted airless spray lines operating at 0.7–1.4 MPa fluid pressure, mixed xylene is metered into resin at 5–15 wt%; viscosity is checked under ISO 2884-1, and sag resistance is assessed under ASTM D4400. The central process conflict is that solvent addition sufficient for atomization increases volatile organic content and reduces flash point. Closed-cup flash point should be retested after thinning because mixed xylene can lower the blended flash point below 25°C depending on co-solvent ratio and resin content.
Mixed xylene is not automatically interchangeable with nitration-grade xylene specified under ASTM D843. Nitration-grade material requires a narrower distillation interval and controlled sulfur and paraffin content because residual aliphatic hydrocarbons can generate odor and color in downstream nitration. In a nitration process using mixed acid at 30–40°C, the presence of ethylbenzene above the specification limit can undergo side-chain nitration and produce undesired nitroethylbenzene species, increasing purification load. The relevant specification is ASTM D843, which sets separate limits for paraffins, sulfur, and color; solvent-grade mixed xylene with a wider C8 distribution may fail these limits even when appearance and distillation range are acceptable. Process control relies on ASTM D850 for distillation, ASTM D1209 for color, and ASTM D2360 for hydrocarbon impurities. A solvent-grade shipment may exhibit a sulfur value of 3–5 mg/kg by ASTM D5453, whereas nitration-grade applications often require sulfur below 1 mg/kg; this difference alone prevents direct substitution without batch-specific verification.
Downstream isomer separation distinguishes mixed xylene from purified para-xylene and ortho-xylene streams. In a simulated moving-bed adsorption unit using zeolitic adsorbent, para-xylene is preferentially retained and recovered at 99.5 wt% purity; the raffinate contains meta-xylene and ortho-xylene, which are subsequently separated by distillation. Mixed xylene as a commercial product is often the unseparated C8 aromatic cut from catalytic reforming or toluene disproportionation, and its value as a solvent is lower than that of isolated para-xylene, which is oxidized to purified terephthalic acid. This composition difference means that solvent-grade mixed xylene cannot be used as a direct substitute for para-xylene in polyester feedstock without prior separation. Ortho-xylene separation by distillation at 144.4°C leaves a meta-rich stream that may be blended back into solvent-grade material; the ratio of para to ortho affects freezing point and crystallization behavior at low temperatures.
Table 2. Comparative boiling range, flash point, and application orientation for related aromatic products.
| Product | CAS registry number | Boiling range or point | Closed-cup flash point | Typical application orientation |
|---|---|---|---|---|
| Mixed xylenes | 1330-20-7 | 137–143°C | 25°C | Solvent, C8 aromatic feedstock |
| Para-xylene | 106-42-3 | 138.4°C | 25°C | Purified terephthalic acid feedstock |
| Ortho-xylene | 95-47-6 | 144.4°C | 32°C | Phthalic anhydride feedstock |
| Toluene | 108-88-3 | 110.6°C | 4°C | Fast-evaporating solvent |
| Aromatic 150 | 64742-94-5 | 180–210°C | 60°C | Slow-evaporating solvent |
Compared with toluene, mixed xylene has a higher flash point and a higher boiling range, which reduces open-top evaporative loss but extends bake schedules in coating ovens. The evaporation rate difference is measured by ASTM D3539; mixed xylene is slower than toluene and faster than Aromatic 150. Compared with Aromatic 150, mixed xylene evaporates more quickly and is more prone to evaporative loss from dip tanks, while Aromatic 150 is selected where slower release and lower vapor pressure are required. Compared with paraffinic solvents, mixed xylene provides stronger aromatic solvency for many resins and active ingredients, but the aromatic content triggers additional regulatory classification and labeling requirements under REACH and the U.S. Emergency Planning and Community Right-to-Know Act.
Ortho-xylene is separated from the mixed C8 stream by fractional distillation and is produced at 99.0 wt% minimum purity. It is fed to fixed-bed oxidation reactors containing vanadium pentoxide/titanium dioxide catalyst at 350–400°C for phthalic anhydride manufacture. Mixed xylenes cannot meet this application because the other C8 isomers and ethylbenzene form different oxidation products, reducing phthalic anhydride yield and increasing maleic anhydride by-products. Published data for this specific configuration is limited; reactor catalyst hot-spot control and overall conversion vary with feed impurity levels.
Replacement of toluene with mixed xylene in a two-pack polyurethane topcoat changes pot life and film development because the evaporation rate is lower and the aromatic C8 blend remains in the wet film longer. In spray-applied topcoats over epoxy primers, the longer open time improves flow and reduces solvent popping, but the lower vapor pressure requires forced air circulation of 0.5–1.0 m/s across the part to achieve flash-off before force drying. The difference from toluene is measurable by ASTM D3539; mixed xylene has a lower evaporation rate than toluene, so film thickness per pass should be reduced to avoid solvent entrapment. When replacing toluene, the formulator should verify dry film adhesion under ASTM D4541 and recoat window under ASTM D3359 because retained solvent can soften the primer and alter intercoat adhesion. The shift from toluene to mixed xylene also changes the solubility parameter envelope; mixed xylene has higher aromatic content and lower hydrogen-bonding character than some polar solvents, which can improve wetting of certain epoxies but may reduce compatibility with high-acid acrylic resins.
Emulsifiable concentrate production uses mixed xylene as a solvent carrier for active ingredients that require aromatic solvency. In high-shear mixing vessels fitted with rotor-stator dispersers, the solvent is charged before active ingredient addition; hydration is controlled by Karl Fischer titration under ASTM E1064 to keep water content below 100 mg/kg and prevent hydrolysis of moisture-sensitive actives. The product’s flash point of 25°C under ASTM D56 imposes explosion-proof electrical classification and bonding and grounding under NFPA 77. Unlike paraffinic oils, mixed xylene provides higher solubility for many triazine and organophosphate actives, but its aromatic content triggers labeling and reporting obligations under REACH and the U.S. Emergency Planning and Community Right-to-Know Act. Emulsion stability after dilution in hard water should be tested under CIPAC MT 36.1; formulation adjustments may be required if the aromatic solvent destabilizes the emulsifier system.
Solvent-grade mixed xylene is controlled at the crude distillation tower and the aromatics extraction unit. The key process conflict occurs at the debutanizer and reformate splitter: a wider cut improves yield but raises the dry point above 143°C and drags C9 aromatics into the solvent, which slows evaporation and increases residue. For a packed column with 30–40 theoretical stages, the overhead C8 cut is maintained by controlling reflux ratio and reboiler steam flow; dry point is checked by ASTM D850. If the dry point exceeds specification, downstream users report slower film hardness development and higher residual solvent in coatings, as measured by ASTM D2369. C9 aromatic carryover above 1 wt% changes solubility parameter and can reduce compatibility with polar resins. The product is not a pure chemical; batch-to-batch variation is influenced by crude slate and reformer severity, and a shipment from a toluene disproportionation unit may contain higher ethylbenzene than a reformate-derived shipment.
Operational boundaries include storage in carbon steel or stainless steel, nitrogen blanketing if water content must remain below 100 mg/kg, and exclusion of natural rubber or EPDM seals due to solvent swelling; elastomer compatibility is verified under ASTM D471. The product should be segregated from strong oxidizers, peroxides, and open flames. Because the vapor density is heavier than air, floor-level ventilation is required. For transfer operations, low-velocity pumping below 1 m/s into a receiving vessel reduces static charge accumulation, and all equipment should be bonded and grounded in accordance with NFPA 77.
Paraffin wax dissolution in crude oil flowlines uses mixed xylene selected for its high aromatic solvent power. In batch soak treatments, the solvent is pumped at 0.2–0.6 m³/min through the flowline and shut in for 6–24 h; effectiveness is assessed by differential pressure decline across the line. Compared with toluene, mixed xylene has a higher boiling range and lower vapor pressure, reducing evaporative loss from open-top tanks but increasing the minimum flowline temperature required to avoid viscosity build-up. Published data for this specific configuration is limited; field evaluation should include compatibility with elastomer seals under ASTM D471 and flash-point monitoring under ASTM D56.
