M-Xylene Supplier: Bulk M-Xylene for Industrial Applications

Bulk m-xylene that reaches polymer and solvent markets from catalytic reformate streams is a single aromatic isomer with CAS registry number 108-38-3, molar mass 106.17 g/mol, and a boiling point of 139.1 °C at 101.3 kPa. Because the boiling point separation from p-xylene is narrower than 1 °C, conventional fractionation alone cannot deliver high-purity m-xylene economically; commercial suppliers therefore rely on extractive distillation, fractional crystallisation, or simulated moving-bed adsorption after removing o-xylene and ethylbenzene. Density at 20 °C is 0.864 g/cm³ when measured by ASTM D4052, and freezing at -47.8 °C permits outdoor storage in temperate climates without extensive heat tracing. The flash point is approximately 27 °C closed cup, which places the material in NFPA 30 Class IC flammable liquid category. Transport documentation uses UN 1307, Class 3, Packing Group III, and the same entries apply under ADR/RID and IMDG when shipped via road, rail, or marine container. Certificates of analysis for polymer-grade m-xylene commonly specify a minimum purity of 99.0% by mass, with tighter 99.5% or 99.7% by mass required for oxidation to isophthalic acid. The primary organic contaminants in single-isomer m-xylene are ethylbenzene, p-xylene, and o-xylene; their combined concentration is typically kept below 0.5% by mass because ethylbenzene and p-xylene residues can persist through downstream oxidation and affect purified product color or isomer purity. Analytical enforcement of purity uses capillary gas chromatography under ASTM D7504, while water content is determined by Karl Fischer coulometry per ASTM E1064. Sulfur and nitrogen contaminants are controlled at low parts-per-million levels because they act as catalyst poisons in catalytic oxidation and hydrogenation operations. Occupational exposure limits for xylene vapor, including m-xylene, are 100 ppm as an 8-hour time-weighted average under OSHA 29 CFR 1910.1000 Table Z-1, with an equivalent limit of 435 mg/m³. ACGIH assigns a TLV-TWA of 100 ppm and a short-term exposure limit of 150 ppm. The odor threshold is reported as lower than 1 ppm; dependence on odor alone is not sufficient for exposure control because olfactory fatigue occurs at sustained low-level exposure. For loading and unloading enclosures, continuous photoionisation detection with alarm setpoints not above 10% of the lower explosive limit is used, and confined-space entry follows OSHA 29 CFR 1910.146 with pre-entry measurement for oxygen and flammable vapor. Industrial demand for m-xylene is concentrated in oxidation to isophthalic acid, manufacture of m-xylylenediamine, and a narrower segment of solvent use where single-isomer aromatic content is required. These applications impose different purity constraints: oxidation units tolerate small quantities of o-xylene but are sensitive to metals and sulfur; hydrogenation to m-xylylenediamine demands low sulfur and halide levels to protect nickel and cobalt catalysts; solvent applications are controlled by flash point, distillation range, and color. The selection of a bulk supplier therefore depends less on the base hydrocarbon than on the analytical reproducibility of low-level impurities and the consistency of lot-to-lot physical properties after transport.

Property	Test method	m-Xylene	Mixed xylene
Boiling point or distillation range	ASTM D850	139.1 °C at 101.3 kPa	137–143 °C
Density at 20 °C	ASTM D4052	0.864 g/cm³	0.865–0.875 g/cm³
Flash point Tag closed cup	ASTM D56	27 °C	25 °C
Molar mass	Calculated	106.17 g/mol	Mixture
Vapour pressure at 20 °C	ASTM D2879	0.8 kPa	0.7–0.9 kPa

What Process Limits Govern Catalytic Air Oxidation of m-Xylene to Isophthalic Acid?

Oxidation of m-xylene to isophthalic acid is conducted in continuous stirred-tank reactors where the feedstock is combined with acetic acid solvent, cobalt(II) acetate, manganese(II) acetate, and a bromide promoter. Air or oxygen-depleted air is sparged through the reactor at sufficient pressure to maintain dissolved oxygen partial pressure while keeping the vapour space outside the flammable envelope. The reaction is highly exothermic; published process descriptions for related methylbenzene oxidations report operating temperatures of 175–205 °C and total pressures of 1.5–2.0 MPa, but published data for this specific m-xylene configuration is limited. Reactor heat is removed through acetic acid/water reflux and external circulation loops because the oxidation rate is sensitive to temperature variations that affect both conversion and the concentration of 3-carboxybenzaldehyde intermediate. The main intermediate pathway proceeds through m-toluic acid and 3-formylbenzoic acid, with 3-formylbenzoic acid often abbreviated as 3-CBA in purified isophthalic acid analytical work. High residual 3-CBA in polymer-grade isophthalic acid can introduce branching or color in polyester resins, so purification trains rely on hydrogenation of the aqueous crude isophthalic acid solution over a supported palladium catalyst to convert 3-CBA to m-toluic acid, followed by crystallisation and solid-liquid separation. Polymer-grade purified isophthalic acid used as a PET copolymer modifier is usually specified for high purity, low moisture, and controlled particle size distribution, with analytical methods selected from the same general family used for purified terephthalic acid rather than from a single global product standard. The integration of an isophthalic acid train with mixed-xylene separation units affects the economic balance of m-xylene supply. Because m-xylene is a coproduct of p-xylene production in many aromatics complexes, its availability can be inversely related to p-xylene demand; when p-xylene pull is high, additional mixed-xylene processing makes more m-xylene available, but when p-xylene demand weakens, m-xylene supply may tighten despite stable isophthalic acid demand. This supply behavior is visible in published trade data for mixed-xylene isomer splits, where m-xylene content in reformate-derived C8 aromatic streams typically ranges from 40% to 45% by mass, with the precise value depending on reformer severity and feed naphtha composition. Safety and material selection in oxidation units reflect the corrosive mixture of acetic acid, bromide species, and high-pressure oxygen. Reactor internals and associated piping are specified with corrosion allowances appropriate for acetic acid service; product isolation centrifuges and filters are enclosed to control dust and solvent vapor. The off-gas from the oxidation reactor contains unreacted xylene, acetic acid, methyl acetate, carbon monoxide, and carbon dioxide; thermal oxidizers or activated carbon recovery systems are used before atmospheric release to meet site permits. Continuous emission monitoring is not a single universal standard for m-xylene oxidation, but site-level permits in many jurisdictions require demonstration of high destruction efficiency. In coil coating and high-solids alkyd topcoat formulations, the substitution of mixed xylene with high-purity m-xylene is evaluated against solvency parameters, evaporation rate, and regulatory VOC limits. The aromatic ring provides high solvency for short- and medium-oil alkyd resins, while the absence of heavier aliphatic tails lowers solution viscosity at equivalent solids. Formulators measure solvency by kauri-butanol value under ASTM D1133; xylene-range solvents typically produce KB values between 98 and 105, with m-xylene falling inside this band. Distillation range is set by ASTM D850, and flash point is controlled by ASTM D56; a flash point of 27 °C restricts storage and mixing rooms to Class I Division 2 electrical classification where open mixing occurs. Because m-xylene has vapor pressure near 0.8 kPa at 20 °C, it is classified as a volatile organic compound in most coating regulations. In U.S. architectural and industrial maintenance coatings, VOC content limits are category-specific and documented in 40 CFR Part 59 Subpart D; depending on the coating type and application method, a formulator may face limits as low as 250 g/L or 340 g/L. Aromatic hydrocarbon solvents with high solvency reduce resin viscosity at lower VOC content but their contribution to final VOC must be balanced against slower evaporating aliphatic or oxygenated solvents. The use of m-xylene in a topcoat is therefore not a direct one-for-one replacement but a reformulation exercise that adjusts resin molecular weight, pigment volume concentration, and rheology modifiers. Surface coating quality is influenced by the solvent evaporation profile. If the m-xylene fraction evaporates too quickly in a high-solids alkyd, film surface skin can trap remaining solvent, leading to solvent pop, loss of gloss, or microcracking in thick film applications. Conversely, retained aromatic solvent can plasticise the early film and raise initial adhesion on metal substrates. Laboratory drawdowns under ASTM D823 or spray application at defined wet-film thicknesses are used to compare film defects, with tack-free time measured manually or by rotary drum tester under ASTM D5895. These tests do not replace full-scale coil coating line trials because oven air flows, line speed, and metal surface temperature alter the solvent release rate.

When m-Xylene Is Converted to m-Xylylenediamine for Ambient-Cure Epoxy Hardener Systems

When m-xylene is routed to m-xylylenediamine, the first step is catalytic ammoxidation to isophthalonitrile over a supported vanadium oxide catalyst in a fixed-bed reactor at elevated temperature. The nitrile is then hydrogenated over a nickel or cobalt catalyst to give m-xylylenediamine, often abbreviated MXDA. This bifunctional aliphatic amine has molecular weight 136.2 g/mol and contains two primary amine groups. The amine hydrogen equivalent weight is therefore approximately 34.0 g/eq, which means a stoichiometric epoxy formulation with DGEBA resin of epoxide equivalent weight 190 g/eq requires about 18 g of MXDA per 100 g of resin. Because MXDA is a low-viscosity liquid at room temperature, it is used in solvent-free concrete primers and self-leveling floor coatings where viscosity control is critical. Commercial MXDA-based hardeners are often modified with alkyl phenols, salicylic acid, or tertiary amines to adjust gel time, surface bloom, and cure speed. In unmodified systems, the reaction with DGEBA proceeds by amine-epoxide addition and is exothermic; the peak exotherm and pot life depend on mass, initial temperature, and container shape. For a 100 g mass at 25 °C, published data for this specific formulation is limited, and laboratory qualification under ASTM D2471 is used to define gel time and peak exotherm for a given mixer and mold configuration. The cured network produced by MXDA has relatively rigid aromatic ring segments separated by aminomethylene linkages, giving higher glass transition temperature and chemical resistance than many straight-chain aliphatic amines when measured by differential scanning calorimetry under ASTM E1356 and immersion testing under ISO 2812-1. Catalyst poisons in the upstream m-xylene feed can be carried into MXDA if the ammoxidation and hydrogenation trains are not protected. Sulfur, chloride, and heavy metals are therefore controlled to low parts-per-million levels before the m-xylene enters the ammoxidation reactor, because sulfur compounds can adsorb on nickel hydrogenation catalysts and reduce activity in the final step. The intermediate isophthalonitrile is also sensitive to hydrolysis; water in the ammoxidation effluent is controlled to avoid yield loss to amide and carboxylic acid by-products. The purification of crude MXDA by vacuum distillation removes high-boiling secondary amines and unreacted nitrile to achieve amine values of 99.5% or higher, as measured by gas chromatography or titration. Emulsifiable concentrate manufacturers in jurisdictions where aromatic hydrocarbon solvents remain registered for agricultural inert use evaluate m-xylene against compatibility, emulsion stability, and regulatory residue limits. The active ingredient is dissolved in the aromatic solvent with nonionic/anionic surfactant pairs; upon dilution in water, the concentrate must form a spontaneous emulsion with oil droplet sizes typically below 10 µm, as measured by laser diffraction under CIPAC MT 36.1 or equivalent. m-Xylene has low water solubility and sufficient density to reduce creaming of the emulsified oil phase, but its low flash point imposes restrictions during milling and filling. Storage tanks, transfer pumps, and mixing vessels are electrically classified and bonded, and packaging lines are interlocked with vapour detection. Regulatory acceptance of m-xylene in pesticide formulations is not uniform. In the United States, inert ingredient tolerances and exemptions are established under 40 CFR Part 180 Subpart D; formulators must verify current listing status for the specific product use pattern and crop group. The solvent may also be subject to reporting under SARA Title III, CERCLA, and VOC emission controls for pesticide manufacturing. In the European Union, plant protection product coformulants are evaluated under Regulation (EC) No 1107/2009 and Regulation (EU) No 540/2011; m-xylene is classified as a flammable liquid and as a specific target organ toxicant on repeated exposure under CLP, which affects both authorisation and worker exposure scenarios. Because coformulant acceptability is revised through active substance and product authorisation processes, a formulation chemist must consult the most current list rather than rely on historical use. Field experience in formulation plants indicates that batch-to-batch variation in m-xylene aromatic content affects active ingredient solubility and low-temperature stability. A batch with higher ethylbenzene or p-xylene content may require additional surfactant or cosolvent to keep the concentrate monophasic after 48 h at 0 °C, a common storage stability condition described in CIPAC MT 39.1. The same batch variation also shifts the density and refractive index used for in-process control, requiring densitometer and refractometer calibration against lot-specific values rather than fixed factory setpoints. Thus bulk supplies are often specified with narrow impurity bands and distillation ranges, and accepted only after pre-delivery sample retention under ASTM D4057 sampling protocols.

Tank Farm Flammability and Static Discharge Control During Bulk Transfer

Bulk storage installations handling m-xylene under NFPA 30 and API RP 2003 must address vapour space flammability, static accumulation, and secondary containment. The material is a Class IC flammable liquid because its flash point is approximately 27 °C, which is above the 22.8 °C boundary for Class IB and below the 37.8 °C boundary for Class II. Fixed-roof tanks are maintained with inert gas padding or internal floating roofs to keep vapor concentrations below 25% of the lower flammable limit. The lower flammable limit for xylene-range aromatics is reported as 1.0% to 1.1% by volume, and the upper flammable limit is approximately 7.0% by volume; these limits vary with temperature and published sources, so site instruments should be calibrated against the specific isomer composition. Static charge accumulation during transfer is a critical failure mode because m-xylene has low electrical conductivity, typically below 2 pS/m in clean aromatic hydrocarbon streams when measured by ASTM D4308. Charge generated by pumping through filters, manifolds, and long transfer lines dissipates slowly; if the receiving tank contains an unbonded metal object or if the liquid free-falls into a tank, incendive sparks can occur. API RP 2003 recommends that initial fill velocities be limited to 1 m/s until the inlet is submerged at least two pipe diameters, after which velocity can be increased to 7 m/s for non-filtration service. Transfer hoses and piping are electrically continuous, and bonding cables with resistance below 10 Ω are verified before loading commences. Nitrogen blanketing does not eliminate static hazards; it only reduces the oxidant concentration. Emergency relief design for m-xylene storage tanks follows NFPA 30 and API 2000. Normal venting capacity must accommodate thermal breathing and pump-in displacement; emergency venting must handle fire exposure heat flux per API 2000 Annex C. Vapors of m-xylene are heavier than air and can travel along grade to ignition sources, so unloading stations are sloped to containment sumps with continuous flammable gas detection at the 10% LEL alarm setpoint. Dikes and remote impounding basins are sized for the largest tank volume plus rainfall, with valves and expansion joints specified for aromatic hydrocarbon service. Foam systems are designed under NFPA 11 with application rates for hydrocarbon fires, and tank spacing follows applicable tables in NFPA 30. Certificate-of-analysis compliance for polymer-grade m-xylene purchased in 20,000–30,000 L tank truck quantities typically includes gas chromatographic purity, distillation range, water content, sulfur content, and color. Sampling is performed after delivery by a composite method using ASTM D4057, and the laboratory data are compared against the supplier certificate before release to storage. The material is offloaded through a closed-loop vapour balance system to reduce loss and exposure; vapour return lines are routed to the delivery vessel and are equipped with detonation flame arresters. The batch is assigned a unique lot number, and retained samples are stored in amber glass under nitrogen headspace to support downstream quality investigations. Material release is conditional on meeting all specified limits. A representative polymer-grade m-xylene specification might require purity greater than 99.5% by GC, water below 100 mg/kg, sulfur below 1 mg/kg, and APHA color below 10 by ASTM D1209. Sulfur is quantified by ultraviolet fluorescence per ASTM D5453 or by trace sulfur analysis under ASTM D4045. Distillation range must fall between 138.0 °C and 140.0 °C under ASTM D850, with no more than 5% total residue or loss. These limits are not universally normalised; each plant establishes its own internal release criteria based on downstream process sensitivity and contractual terms. The final certification is reviewed against the purchase specification before the bulk m-xylene is transferred to day tanks serving oxidation, amine production, or solvent blending. If any parameter is outside the acceptance interval, the receiving site quarantines the tank and initiates investigative sampling of the retained sample. Because bulk aromatic shipments can stratify slightly after transport, mixing and sampling procedures are defined to ensure representative sampling; circular tanks with side-entering mixers or recirculation loops are used before sampling under ASTM D4057. Discrepancy resolution compares the supplier certificate, transport seal log, and retained sample under the same test methods to distinguish sampling error from product contamination. After acceptance, the lot is tracked to production batches through a mass-balance record that supports REACH and customer audit requirements.