| HS Code | 423006 |
| Chemical Formula | C8H10 |
| Molecular Weight | 106.17 g/mol |
| Cas Number | 108-38-3 |
| Appearance | Colorless liquid |
| Odor | Sweet, aromatic |
| Density | 0.864 g/cm3 at 20°C |
| Melting Point | -47.4°C |
| Boiling Point | 139°C |
| Flash Point | 25°C (closed cup) |
| Solubility In Water | 0.1 g/L at 25°C |
| Vapor Pressure | 8.3 mmHg at 25°C |
| Autoignition Temperature | 527°C |
| Refractive Index | 1.4973 at 20°C |
As an accredited M-Xylene factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | M-Xylene is packaged in 200-liter steel drums, net weight 180 kg, with secure seals and hazardous material labeling. |
| Container Loading (20′ FCL) | Loading M-Xylene in 20′ FCL: use sealed drums/IBCs, secure bracing, proper hazardous labels, ventilation, and segregation from incompatible goods. |
| Shipping | M-Xylene is shipped as a flammable liquid, classified as UN 1307, Hazard Class 3, Packing Group II. It requires approved packaging, designated labeling, and segregation from oxidizers. Transport by road, rail, or sea must follow dangerous goods regulations, with adequate ventilation, grounding, and spill containment for safe handling. |
| Storage | Store m-xylene in a cool, dry, well-ventilated area away from heat, sparks, open flames, and strong oxidizers. Keep containers tightly closed and properly labeled. Use grounded or bonded containers during transfer to prevent static discharge. Store in approved flammable-liquid cabinets, protected from direct sunlight, and ensure spill containment measures are readily available. |
| Shelf Life | Shelf life is typically 3–5 years when stored tightly sealed, away from heat, ignition sources, and sunlight. |
Purified isophthalic acid production from meta-xylene proceeds through a continuous liquid-phase oxidation train in which the aromatic hydrocarbon is oxidized by compressed air in a recirculating acetic acid reaction medium. A 316L mechanically agitated continuous stirred-tank reactor with a radial turbine impeller and internal cooling coils is operated at 180–205 °C and 1.5–2.5 MPa; the feed mixture contains 12–18 wt% meta-xylene, 85–90 wt% acetic acid, 4–8 wt% water, and homogeneous Co/Mn/Br catalyst at 100–400 ppm cobalt, 200–800 ppm manganese, and 300–1200 ppm bromide based on total reactor charge. Air is introduced through a sparger at a rate controlled to keep oxygen content in the off-gas below 4 vol%, below the flammability limit of the acetic acid/meta-xylene system. Addition ratios across the three-stage oxidation are set so that meta-xylene concentration in the first reactor is held at the lower end of the range to limit decarboxylation and carbon dioxide formation, while the second and third reactors complete conversion at progressively higher temperature. Stoichiometric mass demand is approximately 0.64 kg meta-xylene per kilogram of isophthalic acid; industrial yields of 88–92 mol% correspond to a practical consumption of 0.71–0.75 kg meta-xylene per kilogram of purified isophthalic acid. Crude isophthalic acid is separated in a pressure crystallizer train, washed with acetic acid, redissolved in water, and hydrogenated over a palladium-on-carbon fixed bed at 220–280 °C and 2.0–3.5 MPa to reduce 3-formylbenzoic acid and color-forming impurities before final crystallization and rotary steam-tube drying.
Compliance boundaries for purified isophthalic acid entering PET bottle resin and coating intermediates include FDA 21 CFR 177.1630 and EU Regulation (EU) No 10/2011 for food-contact plastics; the PET copolymer is tested for intrinsic viscosity under ASTM D4603-18, and the isophthalic acid shipment is typically specified by acid number 670–676 mg KOH/g and moisture <0.1 wt%. Terminal production sectors supplied by this material include copolymerized bottle-grade PET containing 2–12 mol% isophthalic acid, high-heat unsaturated polyester resins for corrosion-resistant equipment, isophthalic alkyd coatings, and isophthaloyl chloride for high-temperature polymers.
Isophthalic acid confers chain rigidity and reduces the free volume of the cured network in unsaturated polyester resins, which raises the deflection temperature under load relative to orthophthalic formulations at equivalent crosslink density. In a two-stage stainless steel resin kettle fitted with a packed column and decanter, isophthalic acid is first reacted with propylene glycol or neopentyl glycol at 200–240 °C until the acid value falls to 20–40 mg KOH/g; maleic anhydride is then charged at 180–200 °C and the melt is condensed to a final acid value of 15–30 mg KOH/g and a cone-and-plate viscosity of 800–1500 mPa·s at 125 °C. Formulation addition ratios in a corrosion-grade isophthalic resin commonly place isophthalic acid at 30–50 mol% of total dibasic acid, maleic anhydride at 40–60 mol%, and phthalic anhydride or adipic acid in the balance; glycol excess over total acid is maintained at 5–10 mol%, and hydroquinone or tert-butylcatechol is added at 50–150 ppm before letdown in styrene to 35–45 wt%. During letdown, the resin mass is cooled below 90 °C before styrene addition to prevent thermally initiated polymerization; the resultant liquid resin is then accelerated with cobalt octoate 0.2–0.5 phr and cured with methyl ethyl ketone peroxide 1.0–2.0 phr.
Compliance testing for the finished fiber-reinforced plastic includes tensile properties under ISO 527-2, heat deflection temperature under ISO 75-2, and Barcol hardness under ASTM D2583-13a; fabrication of above-ground chemical storage tanks follows EN 13121-3. Terminal finished product types include corrosion-resistant chemical storage tanks, fume scrubbers, process piping and ductwork, marine hulls and deck components, and weathering-resistant gel coats applied to composite surfaces.
From the same meta-xylene backbone, meta-xylylenediamine is produced by a two-step route in which fluidized-bed ammoxidation to isophthalonitrile is followed by hydrogenation over a supported nickel catalyst in the liquid phase. The ammoxidation reactor operates at 370–430 °C using a vanadium-chromium oxide catalyst with particle diameter 40–80 µm and a gas residence time of 1–5 s; selectivity to isophthalonitrile above 80 mol% is typical. The nitrile is then hydrogenated at 80–120 °C and 4–8 MPa in a continuous fixed-bed reactor, after which vacuum distillation at 10–50 kPa yields meta-xylylenediamine with purity above 99.5 wt%. For room-temperature epoxy curing, meta-xylylenediamine has an amine hydrogen equivalent weight of 34.1 g/eq; when bisphenol A diglycidyl ether has an epoxide equivalent weight of 188 g/eq, the stoichiometric loading is 18.1 parts per 100 parts resin. Commercial formulations use 16–20 phr meta-xylylenediamine or its epoxy-adduct to control carbamation blush, with accelerators such as benzyl alcohol at 2–4 phr or salicylic acid at 0.5–2 phr for cure at 10–25 °C. Pot life at 25 °C for unmodified meta-xylylenediamine is 25–40 min, and the cured film reaches handling hardness within 4–6 h at 23 °C.
Operational boundaries are significant: meta-xylylenediamine reacts rapidly with atmospheric carbon dioxide and moisture, so storage under dry nitrogen and processing at relative humidity below 60% are required; direct contact with amine-sensitive substrates must be avoided. Compliance for the resulting coatings and flooring systems is evaluated by ISO 9227 salt spray resistance and ISO 527-2 mechanical testing of castings; end-use finished product types include industrial concrete flooring, secondary containment linings, tank and pipe coatings, structural epoxy adhesives, and wet lay-up composite laminates.
A selective liquid-phase oxidation window is used when the intended downstream product is m-toluic acid rather than purified isophthalic acid, because excessive conversion of the second methyl group must be avoided. The reactor, typically a glass-lined or 316L stirred autoclave, is operated at 120–160 °C and 0.5–1.5 MPa air partial pressure; meta-xylene is charged at 15–25 wt% in acetic acid, with cobalt acetate at 0.05–0.3 wt% and sodium bromide at 0.05–0.2 wt% based on solvent mass. To keep selectivity to m-toluic acid above 80 mol%, per-pass meta-xylene conversion is maintained at 15–25%, water is restricted to 3–6 wt% of the liquid phase, and the reactor is stopped before over-oxidation to isophthalic acid becomes significant. The m-toluic acid is isolated by cooling the reaction mass to 30–50 °C, followed by centrifugation, washing with cold acetic acid, and drying. Conversion to N,N-diethyl-meta-toluamide proceeds through m-toluoyl chloride: the dry acid is reacted with thionyl chloride at 60–85 °C in the presence of dimethylformamide at 0.1–0.5 wt%, with hydrogen chloride and sulfur dioxide routed to caustic scrubbing; vacuum distillation at 2–5 kPa purifies the acid chloride. The acid chloride is then added to a mixture of diethylamine and aqueous sodium carbonate in toluene at 5–25 °C, maintaining pH 8–10 to capture hydrogen chloride; the organic layer yields technical DEET at 95–97 wt%.
Formulation addition ratios in finished insect repellents vary by product type: pump sprays and aerosols commonly deliver DEET at 20–35 wt%, lotions and creams at 7–30 wt%, and impregnated wipes may be loaded to 15–30 wt% in the active formula. Regulatory compliance is governed by EPA 40 CFR Part 152 for registration in the United States and EU Biocidal Products Regulation (EU) No 528/2012 in the European Union; terminal finished product types include DEET-based pump sprays, aerosol repellents, lotions, creams, towelettes, and combined sunscreen/repellent formulations where national law permits.
Isophthaloyl chloride, produced from meta-xylene-derived isophthalic acid, is the diacid chloride monomer for poly(m-phenylene isophthalamide) and other high-temperature aromatic polyamides. The chlorination is performed in a glass-lined reactor with reflux condenser and hydrogen chloride scrubber: isophthalic acid is dispersed in chlorobenzene with dimethylformamide catalyst at 0.2–0.8 wt%, and thionyl chloride is fed in molar excess of 1.1–1.5:1 relative to carboxylic acid groups at 80–95 °C. After off-gas scrubbing and solvent removal, the isophthaloyl chloride is purified by vacuum distillation at 2–5 kPa, with a melting point specification above 43 °C and hydrolyzable chloride below 0.5 wt%. Low-temperature solution polycondensation with m-phenylene diamine is carried out in N,N-dimethylacetamide at −5 to +5 °C; the diamine is dissolved first, and isophthaloyl chloride is added as a solid or melt under high-shear mixing. The polymer stoichiometry is controlled at an isophthaloyl chloride to diamine molar ratio of 1:1.00–1:1.03; polymer solids are maintained at 15–20 wt%, and moisture in the solvent is kept below 50 ppm because water consumes isophthaloyl chloride and terminates chain growth. Molecular weight is adjusted with a small monofunctional end-capping agent such as benzoyl chloride at 0.1–0.5 mol% of total acid chloride.
The viscous dope is dry-jet wet spun through spinneret holes of 50–100 µm into a DMAc/water coagulation bath containing 20–40 wt% DMAc at 10–30 °C; filaments are drawn 3.5–4.5×, washed at 80–95 °C, and heat-set at 250–300 °C. Compliance for finished meta-aramid products includes NFPA 2112 for flash-fire protective garments, ISO 11612 for heat and flame protection, and ASTM D2863 for limiting oxygen index; terminal finished product types include flame-resistant turnout gear, industrial protective coveralls, electrical insulation paper, hot gas filter bags, and high-temperature pressboard.
Powder coating resins use isophthalic acid to shift the glass transition and melt viscosity of carboxyl-functional polyesters while maintaining exterior durability, because the meta substitution disrupts crystallinity without the embrittlement caused by para substitution. The resin is produced in a melt polycondensation reactor at 220–240 °C under vacuum of 20–50 kPa, using a glycol excess of 5–15 mol% to control molecular weight and a tin or titanium catalyst at 0.05–0.2 wt%. Isophthalic acid is charged at 20–35 mol% of total dibasic acid, with terephthalic acid or phthalic anhydride as the balance; the reaction is terminated at an acid value of 30–40 mg KOH/g for triglycidyl isocyanurate cure, or 20–24 mg KOH/g for β-hydroxyalkylamide cure, and the cooled resin has a glass transition of 55–65 °C. The finished powder is compounded in a co-rotating twin-screw extruder with L/D 40:1 at barrel temperature 100–120 °C, ground in an air classifier mill to a median particle size of 30–50 µm, and electrostatically sprayed onto aluminum or steel. Curing is performed at 180–200 °C for 10–15 min; the resulting crosslinked film resists UV degradation and hydrolysis, but process limits require the powder to be stored below 25 °C and 50% relative humidity to prevent particle sintering and moisture-induced craters.
Compliance matrices for exterior architectural powder coatings reference Qualicoat Class 2 and AAMA 2604 for weathering and corrosion resistance, with salt spray testing under ISO 9227 and cyclic weathering under ISO 16474-3; terminal finished product types include extruded aluminum window and curtain-wall profiles, automotive alloy wheel and trim coatings, appliance topcoats, outdoor furniture, and architectural cladding panels.
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Commercial m-xylene is the 1,3-dimethylbenzene isomer of the C8 aromatic hydrocarbon class, identified by CAS 108-38-3 and molecular formula C6H4(CH3)2. Commercial product descriptions differentiate polymer-grade m-xylene, refined solvent-grade m-xylene, and mixed-xylene feedstock containing m-xylene; the polymer-grade classification is applied when the material is intended as an isophthalic acid precursor. The substance exhibits a normal boiling point of 139.1 °C at 101.325 kPa, a normal freezing point of −47.8 °C, and a measured density of 0.864 g/mL at 20 °C under ASTM D4052. Its closed-cup flash point is 25 °C, autoignition temperature is 527 °C, and explosive limits in air are 1.1 vol% to 7.0 vol%. The 1,3-arrangement of the two methyl groups directs electrophilic substitution and catalytic oxidation toward derivatives that differ from those obtained from o-xylene or p-xylene.
The 0.7 K normal boiling point difference between m-xylene and p-xylene limits conventional distillation as a purification route. At atmospheric pressure, m-xylene boils at 139.1 °C, while p-xylene boils at 138.4 °C; the resulting relative volatility is close to 1.02 under ideal-solution assumptions. A practical high-purity split would require several hundred theoretical stages at high reflux ratios, which is not observed on industrial aromatic trains. Commercial separation therefore depends on selective adsorption, crystallization-assisted separation, or isomer-specific extraction. In catalytic reformate, m-xylene is usually the dominant xylene isomer, commonly reported in the range of 40–45 mol% of the C8 aromatic fraction; published data for specific high-purity m-xylene adsorption yields is limited. Because the freezing point of p-xylene is 13.2 °C, crystallization can remove p-xylene and leave m-xylene in the mother liquor, but the low freezing point of m-xylene at −47.8 °C makes direct crystallization recovery of m-xylene energy-intensive. Distillation remains practical for separating o-xylene from m-xylene because o-xylene has a normal boiling point of 144.4 °C, producing a 5.3 K gap. Industrial practice therefore sequences o-xylene recovery by fractionation and leaves m-xylene-rich streams for downstream conversion or selective separation.
A polymer-grade m-xylene certificate of analysis typically specifies purity, isomer distribution, distillation behavior, water content, sulfur content, and color. Representative specification values for material supplied as a chemical intermediate are tabulated below. Solvent-grade m-xylene may permit higher total ethylbenzene and sulfur limits, but the polymer-grade material intended for oxidation processes is controlled more tightly because residual o-xylene, p-xylene, ethylbenzene, and non-aromatic hydrocarbons affect downstream catalyst selectivity and final purified derivative quality.
| Parameter | Typical value or range | Test method |
|---|---|---|
| m-Xylene purity | ≥ 99.0 wt% | ASTM D5917 |
| Ethylbenzene | ≤ 0.30 wt% | ASTM D5917 |
| p-Xylene + o-xylene | ≤ 0.50 wt% total | ASTM D5917 |
| Non-aromatic hydrocarbons | ≤ 0.10 wt% | ASTM D5917 |
| Distillation range at 101.325 kPa | 138.8–139.3 °C | ASTM D850 |
| Color, platinum-cobalt scale | ≤ 10 | ASTM D1209 |
| Water | ≤ 200 mg/kg | ASTM E1064 |
| Total sulfur | ≤ 1 mg/kg | ASTM D5453 |
| Density at 20 °C | 0.864–0.866 g/mL | ASTM D4052 |
| Refractive index n20/D | 1.497–1.498 | ASTM D1218 |
Liquid-phase air oxidation of m-xylene to isophthalic acid is carried out in acetic acid using cobalt-manganese-bromide catalyst systems. Industrial reactors operate at temperatures from 150 °C to 210 °C and pressures from 15 bar to 30 bar, with continuous stirred-tank configurations and external heat removal to manage the exothermic oxidation. The meta-substituted methyl groups oxidize through m-toluic acid and 3-carboxybenzaldehyde intermediates. This intermediate profile creates a process conflict that is less severe in p-xylene oxidation to terephthalic acid: residual 3-carboxybenzaldehyde in crude isophthalic acid must be reduced before esterification to polyester-grade material. Commercial purified isophthalic acid specifications commonly require 3-carboxybenzaldehyde below 25 mg/kg. Incomplete oxidation or insufficient hydrogenation produces higher intermediate carryover, reduced thermal stability, and color formation in downstream resins. Crude isophthalic acid is typically dissolved in water and contacted with hydrogen over palladium-on-carbon at 80–120 °C and 5–10 bar to convert residual 3-carboxybenzaldehyde. Published data for specific catalyst metal loadings and residence-time distributions in commercial m-xylene oxidation reactors is limited; equipment performance depends on air sparger design, agitator power input, and acetic acid dehydration capacity.
In unsaturated polyester resin production, isophthalic acid obtained from m-xylene is reacted with maleic anhydride and propylene glycol in a two-stage polycondensation. The first stage is conducted at 180–220 °C to open the isophthalic acid structure and form low-acid-value prepolymer; the second stage incorporates maleic anhydride at 190–210 °C. Production-scale batch reactors use partial condensers and Dean-Stark separation to remove water while retaining glycol. The resulting isophthalic-based unsaturated polyester exhibits higher tensile strength and improved hydrolysis resistance relative to ortho-phthalic-based formulations, because the meta-substituted aromatic ester geometry reduces accessibility of ester carbonyl groups to water. Comparative mechanical testing under ASTM D638-14 and flexural testing under ASTM D790-17 show formulation-dependent differences; supplier technical bulletins report tensile modulus and flexural modulus shifts that depend on isophthalic acid content, maleic anhydride ratio, and glycol type. The processing window narrows when isophthalic acid replaces phthalic anhydride because higher first-stage temperature is required, but excessive temperature increases glycol loss and color. Published data for exact resin formulations is limited beyond producer technical literature.
Solvent applications of m-xylene require balancing evaporation rate, flash point, Hansen solubility parameters, and viscosity against application equipment. m-Xylene has a vapor pressure of approximately 1.1 kPa at 25 °C and a relative evaporation rate of approximately 0.7 relative to n-butyl acetate, placing it between toluene and o-xylene in drying behavior. Its Hansen solubility parameters are approximately δD 17.8 MPa0.5, δP 1.0 MPa0.5, and δH 3.1 MPa0.5, which support use in alkyd, epoxy, and urethane coating formulations. Dynamic viscosity of m-xylene at 25 °C is approximately 0.62 mPa·s, allowing low-shear transfer and spray atomization in air-assisted and airless equipment. In coil coating and high-solids alkyd systems, m-xylene is blended with o-xylene or ethylbenzene to adjust solvent strength and electrical resistivity; however, the flash point of 25 °C imposes maximum web temperatures and ventilation requirements. Coating formulations using m-xylene should be validated for retained solvent, cross-cut adhesion, and cure response under the relevant end-use specification because published data for specific solvent blend ratios is limited.
The separation and downstream chemistry of m-xylene differ from o-xylene, p-xylene, and ethylbenzene because the substitution pattern controls the primary derivative. m-Xylene is selectively oxidized to isophthalic acid; p-xylene is oxidized to terephthalic acid or dimethyl terephthalate; o-xylene is oxidized to phthalic anhydride; and ethylbenzene is dehydrogenated to styrene. The physical property differences relevant to product substitution and distillation sequencing are summarized below.
| Product | CAS | Normal boiling point | Normal freezing point | Density at 20 °C | Closed-cup flash point | Primary derivative |
|---|---|---|---|---|---|---|
| m-Xylene | 108-38-3 | 139.1 °C | −47.8 °C | 0.864 g/mL | 25 °C | Isophthalic acid |
| p-Xylene | 106-42-3 | 138.4 °C | 13.2 °C | 0.861 g/mL | 27 °C | Terephthalic acid / dimethyl terephthalate |
| o-Xylene | 95-47-6 | 144.4 °C | −25.2 °C | 0.880 g/mL | 32 °C | Phthalic anhydride |
| Ethylbenzene | 100-41-4 | 136.2 °C | −95.0 °C | 0.867 g/mL | 22 °C | Styrene |
Process safety for m-xylene storage and handling requires inert gas blanketing on atmospheric storage tanks, conservation vents set below design pressure and vacuum limits, and continuous lower-explosive-limit monitoring in process enclosures. The liquid has a closed-cup flash point of 25 °C, making it a flammable liquid classified as Flam. Liq. 3 under CLP. Electrical equipment in transfer areas is specified under IEC 60079-10-1 zone classification, and transfer piping is bonded and grounded with resistance to ground below 10 Ω as described in API RP 2003. Occupational exposure limits for xylene isomers include an OSHA PEL of 100 ppm 8-hour TWA (435 mg/m3), an ACGIH TLV of 100 ppm TWA with a 150 ppm STEL, and a NIOSH IDLH of 900 ppm. m-Xylene vapor is heavier than air and can collect in pits, trenches, and sumps. Storage incompatibilities include strong oxidizers, nitric acid, chlorine, and concentrated sulfuric acid, which can initiate exothermic oxidation, nitration, or sulfonation reactions. Free water in polymer-grade m-xylene above 200 mg/kg should be removed before oxidation use because excess water shifts catalyst activity and increases acetic acid dehydration load. Material transfers should be sampled and analyzed for water, sulfur, and isomer distribution before tank release.
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