| HS Code | 601053 |
| Chemical Formula | C7H8 |
| Molar Mass | 92.14 g/mol |
| Appearance | colorless liquid |
| Odor | sweet, pungent, benzene-like |
| Density | 0.867 g/cm3 at 20°C |
| Melting Point | -95°C |
| Boiling Point | 110.6°C |
| Water Solubility | 0.52 g/L at 20°C |
| Vapor Pressure | 2.8 kPa at 20°C |
| Viscosity | 0.590 cP at 20°C |
| Flash Point | 4°C |
| Autoignition Temperature | 480°C |
| Refractive Index | 1.496 |
| Dipole Moment | 0.375 D |
As an accredited Toluene factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Toluene, 1 L, supplied in a sealed amber glass bottle with a leak-proof cap and full hazard labeling. |
| Container Loading (20′ FCL) | Loading toluene into a 20′ FCL involves securing drums/pails, proper ventilation, grounding against static, and spill containment for safe transport. |
| Shipping | Toluene (UN 1294, Class 3, PG II) is a flammable, toxic liquid shipped in properly labeled, grounded containers, such as steel drums or ISO tanks. Transport requires segregation from oxidizers, ventilation, and strict adherence to hazardous materials regulations to prevent fire, inhalation exposure, and environmental contamination. |
| Storage | Store toluene in clearly labeled, approved containers in a cool, well-ventilated area away from heat, sparks, and open flames. Keep containers tightly closed and grounded to prevent static discharge. Use a dedicated flammable-liquid storage cabinet, and separate from strong oxidizers. Ensure spill containment and access to fire extinguishing equipment nearby. |
| Shelf Life | Toluene has a shelf life of several years when stored in a sealed container, away from light, heat, and air. |
In continuous flexible polyether slabstock production, toluene enters the supply chain not as a process solvent but as the upstream aromatic precursor for toluene diisocyanate via mixed-acid nitration, dinitrotoluene hydrogenation, and phosgenation. The hydrogenation stage is carried out in methanol or water over Raney nickel at 120–170 °C and 30–80 bar. The resulting toluenediamine stream typically contains 75–82% 2,4-isomer and 18–25% 2,6-isomer and is then phosgenated in o-dichlorobenzene or monochlorobenzene at 80–180 °C. Hydrogen chloride is recovered from the overhead system and crude toluene diisocyanate is vacuum-distilled before blending into the standard 80/20 2,4-/2,6-isomer product. On the foam line, the toluene diisocyanate blend is metered into a high-shear pin mixer against a polyol component containing a polyether triol with an OH number of 28–56 mg KOH/g, water at 2.0–5.0 parts per hundred polyol, an amine catalyst at 0.05–0.4 php, and a tin catalyst at 0.05–0.3 php. The isocyanate index on conventional slabstock lines is held at 100–115. Water content in the polyol blend is not a minor adjustment; an uncontrolled increase of 0.1 php water shifts foam density and increases exotherm, which changes blow-off timing and can alter cell structure. Production-scale failure modes include foam collapse when the index falls below 95 at high water loading and scorch when the index is pushed above 120 without sufficient stabiliser. Foam rise is checked in a laboratory box before production width is increased, and physical properties are measured according to ISO 845, ISO 1798, and ISO 1856. In the United States, flexible foam physical testing frequently maps to ASTM D3574. TDI viscosity at 25 °C is approximately 3 mPa·s, and changes in tank heating alter metering calibration at the mixing head. TDI transfer is conducted under closed systems to limit dermal and respiratory exposure, and the storage temperature is normally maintained at 20–28 °C to reduce dimer formation.
Representative slabstock production-starting ranges and the corresponding test methods are tabulated below.
| Parameter | Production-starting range or target | Test method or equipment basis |
|---|---|---|
| Polyether triol blend | 100 parts | Formulation basis |
| Total water | 2.0–5.0 parts per hundred polyol | Karl Fischer titration on polyol blend |
| TDI index | 100–115 | Continuous slabstock mixing head |
| Amine catalyst | 0.05–0.4 php | Formulation basis |
| Tin catalyst | 0.05–0.3 php | Formulation basis |
| Density | 18–35 kg/m³ | ISO 845 |
| Tensile strength | 70–150 kPa | ISO 1798 |
| Compression set | ≤10% | ISO 1856 |
Thermal hydrodealkylation units convert toluene to benzene in a fired heater and adiabatic reactor at 650–750 °C and 35–50 bar. The hydrogen-to-toluene molecular feed ratio is maintained at 4:1–6:1 because lower ratios increase polycondensation to biphenyl and heavy aromatics, which accelerates coke deposition in the reactor outlet and quench exchanger. Single-pass conversion is typically limited to 75–85% with benzene selectivity above 95%; unconverted toluene is recycled, while higher conversion increases ring-opening to methane. Catalytic hydrodealkylation using chromia-alumina can operate at lower temperature, but thermal units dominate benzene supply because they avoid catalyst regeneration and tolerate feed variation. The product benzene stream is stabilised, clay-treated, and distilled to remove thiophene, toluene, and non-aromatic hydrocarbons. Refined benzene is tested against ASTM D2359 grade criteria, with sulfur limits as low as 0.5 mg/kg for some nitration-grade deliveries, and aromatic purity is checked by ASTM D4492. Downstream, benzene feeds ethylbenzene alkylation using a zeolite catalyst, and the ethylbenzene is dehydrogenated to styrene for polystyrene and acrylonitrile-butadiene-styrene copolymer. Benzene is also consumed in cumene production for phenol and acetone. Equipment on the hydrodealkylation charge side includes a fired heater with alloy supporting high-temperature hydrogen service, a quench boiler, and a recycle gas compressor that must tolerate hydrogen and methane fractions above 80 mol%. Furnace tube skin temperatures are monitored because carburisation and metal dusting can occur when sulfur in the toluene feed drops below 0.5 ppm and the protective iron sulfide scale is not maintained.
In anionic solution polymerisation of styrene and butadiene, toluene that contains water above 50 ppm or oxygen above 5 ppm consumes the n-butyllithium initiator before the target molecular weight is reached. Operators dry toluene over molecular sieves or silica gel, store it under a nitrogen pad, and measure water by Karl Fischer titration before the solvent is charged to the polymerisation train. A typical solvent blend includes toluene and cyclohexane in mass ratios between 20:80 and 80:20; the selected ratio shifts the vinyl content of the polybutadiene portion through solvent polarity. Styrene is charged at 15–35 wt% of total monomer, with tetrahydrofuran or tetramethylethylenediamine added as a randomiser to limit styrene blockiness. Reaction temperature is held at 40–80 °C and reactor pressure at 2–6 bar. After polymerisation, the cement is discharged into steam-heated coagulation, and toluene is recovered from the overhead decanter for drying and reuse. The dried solution SBR crumb is tested for Mooney viscosity according to ASTM D1646, and bound styrene is checked by ASTM D5775. End-use mixing in tire tread compounds uses silica coupling agents and solution SBR with 35–50 mass% vinyl polybutadiene to balance wet grip and rolling resistance. Solvent purity constraints are stricter than those of ordinary aromatic diluents because living chain ends remain active throughout the reaction; water, carbon dioxide, alcohols, and sulfur compounds act as termination or chain-transfer agents. Start-up after solvent change is a sensitive control point because a batch of toluene with water above 50 ppm can depress the number-average molecular weight before the first viscosity check, and polydispersity control is verified by gel-permeation chromatography against polystyrene standards.
Liquid-phase oxidation of toluene to benzoic acid uses dissolved cobalt and manganese acetates with a bromide promoter in a stirred bubble column or agitated autoclave at 140–170 °C and 5–10 bar air pressure. The reaction is deliberately stopped at 30–40% toluene conversion per pass because higher conversion accelerates decarboxylation to carbon dioxide and increases tar. Benzaldehyde is the main intermediate and is recovered from the reactor overhead and oxidate distillation; excessive benzaldehyde carryover in the crude benzoic acid shifts the odour and colour profile of downstream sodium benzoate. Industrial units often use a falling-film or thin-film evaporator to recover benzoic acid from the oxidate before recrystallisation or melt flaking. Sodium benzoate produced from the benzoic acid is controlled under food chemical specifications, and production for preservative use requires limits on chloride, heavy metals, and residual toluene. Benzoate plasticizers such as diethylene glycol dibenzoate or dipropylene glycol dibenzoate use benzoic acid as the esterification acid; these esters are used in polyvinyl acetate adhesives and water-based coatings. The compliance framework for food-grade sodium benzoate includes FCC and USP monographs, while industrial-grade benzoic acid is traded under CAS 65-85-0 and is subject to REACH registration. Published data for optimum bromide-to-cobalt ratios vary by licensor; the process window is narrow because insufficient bromide reduces radical chain initiation and excess bromide increases corrosion in the stainless steel reactor and condenser train. The limiting operational boundary is not the air compressor capacity but the heat removal from the exothermic oxidation, which sets the maximum bubble column diameter on production-scale trains.
Toluene is sulfonated with 98% sulfuric acid or sulfur trioxide at 95–110 °C, and the para-toluenesulfonic acid content is enriched to above 85% by crystallisation or extraction before the monohydrate is sold as an esterification catalyst. Unsaturated polyester resin producers charge the monohydrate at 0.1–1.0 wt% of the reactor mass during the polycondensation step, where it accelerates esterification at 180–220 °C while water is removed via a xylene azeotrope. The same sulfonation intermediate is converted to para-toluenesulfonyl chloride for pharmaceutical and agrochemical intermediates, a route that uses chlorosulfonic acid and requires strict control of residual sulfur compounds in the waste stream.
Publication gravure ink systems use toluene as a fast-evaporating diluent in nitrocellulose-based and polyamide-based inks, where it adjusts evaporation rate and substrate wetting on coated paper. The toluene fraction in the diluent can range from 30–50 wt%, with isopropanol and ethyl acetate used as co-solvents to control drying profile. Enclosed doctor blade chambers and press-side solvent recovery are standard because the European Union VOC framework under Directive 2004/42/CE caps volatile organic compound emissions from printing activities, and toluene is classified as a hazardous air pollutant under US EPA rules. Production-scale ink plants recover toluene by activated carbon adsorption or distillation and return it to the ink let-down tank, but recovered toluene must be monitored for nitrocellulose decomposition products and high-boiling resin residues that raise viscosity drift. Ink viscosity is checked by efflux cups such as DIN 53211, and the press-side temperature is held between 20–25 °C to prevent solvent imbalance at high printing speeds. The operational boundary for toluene replacement in gravure inks is not solvency alone but the combination of evaporation rate, surface tension, and the explosion limit range in the enclosed press room; inks formulated with slow solvents fail to dry at speeds above 300 m/min, while overly fast blends destabilise print gloss on coated stock.
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Toluene, CAS 108-88-3, IUPAC name methylbenzene, is an aromatic hydrocarbon with molecular formula C₇H₈ and molar mass 92.14 g/mol. Commercial product models are identified by specification grade rather than machine designation: ASTM D841-19 nitration grade, TDI-grade feedstock, and high-purity benzene-controlled grade for solvent and pharmaceutical applications. Physical properties are determined using ASTM D4052 for density (0.867 g/cm³ at 20 °C), ASTM D86 for boiling point (110.6 °C at 101.325 kPa), and ISO 13736 for closed-cup flash point (4.4 °C). The liquid has a refractive index of 1.496 at 20 °C, dynamic viscosity 0.59 mPa·s at 20 °C, vapour pressure 2.8 kPa at 20 °C, lower and upper flammability limits 1.2 vol% and 7.1 vol%, autoignition temperature 480 °C, and water solubility 0.52 g/L at 20 °C. Transport classification is UN 1294, ADR/RID class 3, packing group II. Under EC 1272/2008, the substance carries H225, H304, H315, H336, and H361d hazard statements. Storage systems use conductive piping, nitrogen blanketing, and flame-arrestor vents because vapour can form flammable mixtures at ambient temperatures. Toluene is incompatible with strong oxidizers, concentrated nitric acid, sulfur trioxide, and certain halogenated agents; separate containment is required where mixed-acid nitration feed tanks are located on the same process plot.
Nitration-grade product is governed by ASTM D841-19, which requires benzene not exceeding 0.05 wt%, non-aromatic hydrocarbons not exceeding 0.10 wt%, sulfur not exceeding 0.003 wt%, distillation range not exceeding 1.0 °C including 110.6 °C, acid wash colour no greater than 2, and copper corrosion classification 1A. Laboratory release testing uses ASTM D2360 for trace benzene by gas chromatography and ASTM D4045 for sulfur. TDI-grade feedstock is controlled more tightly, with benzene and olefin ceilings reduced because benzene in mixed-acid nitration contributes to undesirable nitrophenol and tar formation, while olefins consume nitric acid and raise exotherm. Published public standards for TDI-grade toluene are limited; procurement documents commonly specify benzene below 0.02 wt%, olefins below 0.01 wt% by GC-FID, and water below 0.01 wt% to prevent acid dilution and local hot spots in cascade nitrators. Batch-to-batch isomer ratio in downstream mononitrotoluene is maintained within ±3% on production-scale nitrators by controlling mixed-acid feed rate and agitator tip speed. The distinction is operational: tanks allocated to TDI-grade product are not returned to solvent service without dedicated cleaning because dissolved iron above 0.1 mg/kg accelerates colour development and by-product yield in nitration.
| Attribute | ASTM D841-19 nitration grade | TDI-grade supplier certificate |
|---|---|---|
| Benzene | ≤0.05 wt% | ≤0.02 wt% |
| Non-aromatic hydrocarbons | ≤0.10 wt% | ≤0.05 wt% |
| Sulfur | ≤0.003 wt% | ≤0.001 wt% |
| Water | not specified | ≤0.01 wt% |
| Distillation range | ≤1.0 °C including 110.6 °C | ≤1.0 °C including 110.6 °C |
| Acid wash colour | max 2 | max 1 |
In solventborne flexographic and gravure packaging inks, toluene is used as a medium-evaporating aromatic diluent that dissolves high-molecular-weight acrylic, chlorinated rubber, and maleic-modified rosin binders. The relative evaporation rate is 2.0 based on n-butyl acetate = 1.0; drying hoods on 8-colour gravure presses are operated at 60–80 °C supply air temperature and air velocity 12–18 m/s to keep retained solvent below customer-specific limits. Hansen solubility parameters are δD = 18.0 MPa0.5, δP = 1.4 MPa0.5, δH = 2.0 MPa0.5, placing toluene within the solubility sphere of alkyd and polystyrene resins while excluding polyolefins. Vapour pressure of 2.8 kPa at 20 °C permits longer film leveling than ethyl acetate (10.1 kPa) but requires lower web speed in high-coverage ink layers. Residual solvent in printed and laminated film is measured by headspace gas chromatography using ASTM F1884-04; retort pouch converters reject reels where toluene retention exceeds 0.5 mg/m² because foil-seal heating at 180–220 °C releases vapours into the food-contact headspace. In coil coatings, addition of n-butanol at 5–10 wt% raises flash point and adjusts electrical resistivity for electrostatic bell applicators, but aromatic solvency decreases as the Hildebrand parameter shifts. Production-scale batch tanks require nitrogen padding and closed-loop vapour recovery because the liquid is flammable at process temperatures.
| Parameter | Test method | Toluene | Mixed xylene | Methyl ethyl ketone |
|---|---|---|---|---|
| Boiling point at 101.325 kPa | ASTM D86 | 110.6 °C | 137–140 °C | 79.6 °C |
| Closed-cup flash point | ISO 13736 | 4.4 °C | 27 °C | -9 °C |
| Density at 20 °C | ASTM D4052 | 0.867 g/cm³ | 0.865 g/cm³ | 0.805 g/cm³ |
| Vapour pressure at 20 °C | ASTM D5482 | 2.8 kPa | 0.8 kPa | 10.5 kPa |
| Hansen dispersion parameter | — | 18.0 MPa0.5 | 17.8 MPa0.5 | 16.0 MPa0.5 |
| Hansen polar parameter | — | 1.4 MPa0.5 | 1.0 MPa0.5 | 9.0 MPa0.5 |
| Hansen hydrogen-bonding parameter | — | 2.0 MPa0.5 | 3.1 MPa0.5 | 5.1 MPa0.5 |
| Water solubility at 20 °C | shake-flask | 0.52 g/L | 0.18 g/L | 275 g/L |
Differences from benzene and mixed xylene are defined by freezing point, flash point, and evaporation rate. Benzene freezes at 5.5 °C; toluene remains liquid to -95 °C, allowing outdoor storage in logistic networks where benzene requires heat tracing. Mixed xylene has a closed-cup flash point of 27 °C, higher than toluene at 4.4 °C, but lower vapour pressure at 20 °C; toluene therefore requires more aggressive condenser and vapour-recovery design during tanker loading. Methyl ethyl ketone has higher polar solubility and water miscibility, leading to different resin compatibility and higher risk of moisture pickup from humid air. These distinctions are selected in formulation databases by Hansen parameter matching and by coating open-time requirements.
Toluene is separated from catalytic reformate in aromatics recovery units where C₇ and C₈ fractions are split in extractive distillation or liquid-liquid extraction. Sulfolane and N-formylmorpholine are used as extraction solvents; process columns are operated with solvent-to-feed ratios between 3:1 and 8:1 by mass depending on reformate aromatic content. Reboiler outlet temperature is held below 205 °C to prevent solvent thermal degradation; vacuum stripping columns maintain overhead pressure at 10–20 kPa absolute. Tray fouling from polymerized olefins in cracked C₇ feed can reduce toluene recovery from 99.5% to below 98.0% within 30–60 days on unhydrotreated feeds. Production-scale failure is typically detected by increasing solvent regeneration load and rising chloride or sulfur carryover into the toluene product. Vapour-liquid equilibrium in the toluene-methylcyclohexane binary does not exhibit azeotropic behaviour, but separation requires high reflux ratios above 4:1 in the rerun column. Solvent carryover is controlled to below 1 mg/kg by steam stripping and coalescing filters.
As a chemical intermediate, toluene enters the methyl diisocyanate route through sequential nitration to mononitrotoluene and dinitrotoluene. Mixed-acid nitration is performed in cascade reactors with jacket and internal cooling; mononitrotoluene reaction temperature is maintained at 40–50 °C, and dinitrotoluene formation is controlled at 60–70 °C. The 2,4-dinitrotoluene/2,6-dinitrotoluene isomer ratio is adjusted to approximately 80:20 for TDI-grade production by controlling mixed-acid composition, agitation, and feed point distribution. Hydrogenation of dinitrotoluene to toluene diamine uses nickel or palladium catalysts in slurry bubble columns or fixed-bed reactors at 100–180 °C and 1.0–3.0 MPa hydrogen partial pressure. The exotherm is removed through external loop cooling; reaction mass temperature above 200 °C increases tar and azo by-product formation. Phosgenation of toluene diamine in ortho-dichlorobenzene at 30–80 °C followed by vacuum distillation yields toluene diisocyanate. Dissolved oxygen in toluene diamine is maintained below 0.1 mg/kg and storage is under nitrogen to hold APHA colour below 50.
When toluene is diverted from solvent markets to benzene production, thermal hydrodealkylation is conducted at 600–700 °C and 4–6 MPa hydrogen partial pressure in tubular reactors with radiant-coil outlet temperatures near 680 °C. Hydrogen-to-toluene molar ratio is maintained between 3:1 and 8:1; conversion per pass is 70–90%, with selectivity to benzene above 95% on molar basis. Methane is generated as co-product, and coking is controlled by adding steam at 2–5 wt% of feed and by maintaining turbulent plug flow. Turn-down below 60% of design capacity is avoided because residence-time distribution broadens, outlet benzene selectivity falls, and radiant tube skin temperatures increase due to lower heat-transfer coefficient. Catalytic hydrodealkylation on chromia-alumina or platinum catalysts operates at 500–650 °C but is limited by feed sulfur; therefore sulfur is hydrotreated to below 0.5 mg/kg upstream. This competing use reverses solvent-grade storage requirements: saturated hydrocarbons are permitted, while sulfur and oxygenates are removed to protect catalyst life. Published data for specific unit turndown limits is limited, but commercial fixed-bed licenses frequently specify minimum hydrogen partial pressure of 3.0 MPa to avoid rapid coke accumulation.
In REACH-registered supply chains, toluene is subject to registration under EC 1907/2006 and classification under EC 1272/2008; downstream users receive exposure scenarios that specify local exhaust ventilation rates of 10–20 air changes per hour for drum decanting and 0.5 m/s capture velocity at open vessels. Occupational exposure limits in some jurisdictions are set at 20 ppm as an 8-hour time-weighted average and 50 ppm short-term exposure limit; monitoring on production-scale mixing mezzanines uses photoionization detectors calibrated to 10.6 eV lamps. Transfer from tanker to storage uses vapour balancing or carbon adsorption because displaced vapour can exceed 1.5 vol% in the ullage. Waste toluene is recovered or incinerated in closed equipment with thermal oxidizer destruction efficiency above 99.9% when emission permits require hazardous air pollutant control.
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