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| HS Code | 352429 |
| Chemical Formula | C6H12 |
| Molecular Weight | 84.16 g/mol |
| Cas Number | 110-82-7 |
| Appearance | Colorless liquid |
| Melting Point | 6.55 °C |
| Boiling Point | 80.75 °C |
| Density | 0.7781 g/cm³ at 20 °C |
| Flash Point | -18 °C (closed cup) |
| Autoignition Temperature | 245 °C |
| Vapor Pressure | 77.3 mmHg at 20 °C |
| Water Solubility | 0.055 g/L at 25 °C |
| Refractive Index | 1.4262 at 20 °C |
As an accredited Cyclohexane factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Cyclohexane, 1 liter, in a tightly sealed, labeled glass bottle resistant to solvents, with clear flammability warnings and child-resistant closure. |
| Container Loading (20′ FCL) | Cyclohexane (flammable liquid) is loaded into a 20′ FCL using UN-approved drums or ISO tanks, secured and labeled for safe transport. |
| Shipping | Cyclohexane is a flammable liquid requiring careful transport. Ship in approved containers, away from oxidizers and ignition sources. Use grounded, vented equipment and clearly label packages. Ensure proper hazardous material documentation, segregation, and temperature control. Follow all regulations for flammable liquids to prevent leaks, vapors, or fire risk during transit. |
| Storage | Store cyclohexane in tightly sealed, appropriately labeled containers in a cool, dry, well-ventilated area away from direct sunlight. Keep it separated from strong oxidizers and ignition sources. Use approved flammable-liquid storage cabinets and ensure proper grounding and bonding during transfer. Follow all relevant safety regulations. |
| Shelf Life | Shelf life is generally indefinite when stored properly in sealed containers, away from heat, ignition sources, and oxidizers. |
In the liquid-phase air oxidation train for KA oil, cyclohexane is contacted with oxygen-lean air or nitrogen-diluted air at 0.8–1.5 MPa and 150–170°C in a continuous stirred cascade. The feedstock has a density of 0.779 g/mL at 20°C, a boiling point of 80.7°C, and a freezing point of 6.5°C; storage and transfer lines are heat-traced when ambient temperature approaches the freezing point. The oxidation is intentionally arrested at cyclohexane conversion below 10%, typically 4–8%, because the cyclohexyl hydroperoxide intermediate is thermally unstable and the C6 oxidation products are more susceptible to further oxidation than the parent hydrocarbon. A cobalt naphthenate or cobalt–manganese salt package is fed at 0.1–10 ppmw metal basis relative to cyclohexane; boric acid additions in a second oxidation stage esterify cyclohexanol and protect it from oxidative ring opening, lifting selectivity toward cyclohexane-derived C6 products to 85–90%. Off-gas from the oxidation reactor is scrubbed to recover entrained cyclohexane before thermal oxidation, and the liquid product is quenched with water to hydrolyze the boric acid esters. Equipment on production lines includes multi-stage bubble columns and vertical stirred autoclaves with interstage coolers; batch-to-batch selectivity variation is commonly observed when unconsumed hydroperoxide is not reduced with sodium hydroxide or water wash before distillation. Distillation of KA oil requires high vacuum because cyclohexanone and cyclohexanol form a close-boiling mixture with cyclohexane; unconverted cyclohexane is recovered overhead and recycled, while the bottoms containing cyclohexanol, cyclohexanone, and boron residue are separated. The process is governed by API 510 and API 570 for pressure vessels and piping; reactor metallurgy is typically AISI 316L or higher due to trace organic acids. Published data for plant-specific catalyst half-life in the oxidizer is limited; however, cobalt deactivation by trace sulfur and iron scale is an established bottleneck.
| Parameter | Conventional air oxidation | Boric-acid-assisted oxidation |
|---|---|---|
| Reactor temperature | 150–170°C | 165–175°C |
| Operating pressure | 0.8–1.5 MPa | 0.7–1.0 MPa |
| Cyclohexane conversion per pass | 4–8% | 3–5% |
| Selectivity to cyclohexanone + cyclohexanol | 75–85% | 85–90% |
| Catalyst package | Cobalt or cobalt–manganese salts | Cobalt salt plus boric acid |
Cyclohexanol recovered from KA oil is converted to cyclohexanone in a fixed-bed catalytic dehydrogenation unit over copper chromite or copper–zinc oxide catalysts at 220–260°C and near atmospheric pressure. The reaction is endothermic and requires tubular reactor heat input; excursions above 300°C promote ring dehydrogenation to phenol and cracking to cyclohexene and lower hydrocarbons, reducing cyclohexanone yield. The per-pass equilibrium conversion of cyclohexanol is limited to approximately 70–85%; unreacted cyclohexanol is separated from cyclohexanone under vacuum and recycled to the reactor. The dehydrogenation effluent is cooled, non-condensable hydrogen is vented through a pressure swing adsorption or hydrogen recovery unit, and the crude cyclohexanone is distilled to a purity of 99.5% or better for downstream adipic acid or caprolactam synthesis. Purity is monitored by gas chromatography using ASTM D3760. The main operational boundary is catalyst deactivation by heavy boilers and residual sulfur; a guard bed of zinc oxide or activated carbon is installed upstream when KA oil is not sufficiently washed. Because the reaction operates at low pressure, any air ingress into the reactor creates a flammable mixture; the system is blanketed with nitrogen and equipped with flame arrestors.
The adipic acid route oxidizes cyclohexanone/cyclohexanol mixtures with 50–60 wt% nitric acid at 60–80°C and 0.1–0.4 MPa in a stirred reactor cascade. Copper metal and ammonium metavanadate are added as homogeneous catalysts to suppress nitrous oxide and improve dicarboxylic acid selectivity; typical yield of adipic acid from cyclohexanone is 92–94 mol%. The exotherm is managed by staged nitric acid feed and external cooling because a temperature excursion above 85°C accelerates oxidative cleavage to glutaric and succinic acids. The off-gas containing NOx is recovered as nitric acid or decomposed in a tail-gas unit, and the crude adipic acid is crystallized from water. Mother liquor contains dibasic acids and heavy metal catalyst residues and is recycled or treated before discharge. Product purity is controlled to 99.7 wt% minimum for polymer-grade adipic acid under ISO 9001 batch release. Process safety obligations follow Seveso III Directive 2012/18/EU for nitric acid inventories and NFPA 30 for combustible liquid handling. This operation is a lower-purity-tolerant step compared with fibre-grade caprolactam, but trace hydrocarbon carryover into nitric acid oxidation is strictly limited because unreacted cyclohexane can form flammable vapour in the vent system.
Cyclohexanone diverted to caprolactam synthesis is reacted with hydroxylamine sulfate to produce cyclohexanone oxime under weak acid conditions at 80–90°C, then the oxime is rearranged in oleum or concentrated sulphuric acid at 80–120°C. The Beckmann rearrangement is highly exothermic and requires external cooling; local overheating above 130°C leads to tar formation and caprolactam colour degradation. Neutralisation with ammonia yields ammonium sulfate as co-product, typically 1.8–2.2 kg per kg caprolactam depending on the route. The caprolactam melt is extracted, then distilled under vacuum to fibre-grade specifications. The main cyclohexane-related quality constraint is residual cyclohexanone in the oxime feed, which must be controlled to low ppm levels to prevent polymerisation defects in the resulting polyamide 6. Published data for specific plant extraction solvent losses in caprolactam purification is limited, but recovery units are designed for high solvent recovery. This outlet competes with the adipic acid route for cyclohexanone; split decisions are driven by nylon 6 versus nylon 66 demand rather than by solvent performance.
Cyclohexane is used as a non-polar, chain-stable solvent in anionic polymerisation of butadiene and styrene initiated by n-butyllithium. The solvent must be dried to below 5 ppmw water and purged with nitrogen to avoid termination of the living chain end. Cyclohexane offers a boiling point of 80.7°C and lower vapour pressure than n-hexane, allowing reactor operation at 80–110°C under 0.4–0.8 MPa pressure without excessive vapour loss. The solvent dissolves high-cis and random styrene-butadiene copolymer at polymer concentrations up to 15–20 wt% while maintaining reactor viscosity below 5,000 mPa·s. The absence of unsaturation and heteroatoms reduces termination by proton abstraction; gel permeation chromatography with polystyrene calibration shows polydispersity indices below 1.05. The solvent is removed by steam stripping or devolatilisation extruders; residual cyclohexane in the crumb is controlled to 50 ppm or lower under supplier specification and REACH exposure-scenario obligations. The main operational limitation is solvent purification over molecular sieves and activated alumina beds, because oxygenated impurities such as tetrahydrofuran or water alter initiation efficiency and vinyl content. Published data for specific anionic styrene–butadiene grades using cyclohexane is limited; the above ranges reflect general solvent polymerisation practice rather than a single validated campaign.
Extraction of heat-labile botanical oleoresins with cyclohexane is confined to non-food fragrance and industrial extract streams because Directive 2009/32/EC does not list cyclohexane among permitted extraction solvents for food ingredients. In a countercurrent extractor, milled spice or botanical matter is contacted with cyclohexane at a temperature above the solvent freezing point of 6.5°C and below its boiling point of 80.7°C; precise residence time and solvent-to-feed ratio are raw-material-dependent and published data for this configuration is limited. The miscella is desolventised in a falling-film evaporator under vacuum to limit thermal degradation of heat-sensitive monoterpenes and sesquiterpenes. Residual solvent in the non-food oleoresin is controlled to 10 ppm or less when the extract enters fragrance compounding under internal quality specifications. Cyclohexane is favoured over n-hexane only when a narrower boiling range and lower odour carryover are required, but its freezing point of 6.5°C complicates winter handling in unheated transfer lines.
Cyclohexane enters solvent blends for chlorinated rubber and alkyd maintenance coatings where xylene and toluene are restricted by hazard classifications. A typical solvent blend contains 30–60 wt% cyclohexane, 20–40 wt% methyl ethyl ketone, and 10–30 wt% aromatic 100, adjusted to an evaporation rate suitable for airless spray. The ketone-rich phase provides solvency, while cyclohexane reduces density and controls dry time. Flash point of the blend is below 23°C, so formulations are classified as flammable liquids under CLP Regulation (EC) No 1272/2008 and must be stored under Directive 1999/92/EC ATEX workplace requirements. With a solubility parameter of 8.2 (cal/cm³)^0.5 versus 9–10 (cal/cm³)^0.5 for epoxy resins, cyclohexane alone does not dissolve high molecular weight epoxy resin; formulators use cyclohexanone or ketone–aromatic blends instead. Application viscosity is measured by ISO 2431:2019 cup flow time, and sag resistance by ASTM D4400; batch viscosity tolerances of ±10% are used because cyclohexane evaporation from open mixing vessels shifts solids content.
| Downstream operation | Key standard or code | Controlled parameter |
|---|---|---|
| KA oil oxidation | ASTM D3760, API 510 | cyclohexane/cyclohexanone purity; vessel integrity |
| Adipic acid production | Seveso III Directive 2012/18/EU, ISO 9001 | nitric acid inventory; polymer-grade purity |
| Caprolactam synthesis | ISO 9001 | residual cyclohexanone in oxime feed |
| Anionic polymerisation solvent | REACH | residual cyclohexane in crumb; solvent purification |
| Non-food botanical extraction | Directive 2009/32/EC | non-food status; residual solvent in extract |
| Coatings solvent blends | CLP Regulation (EC) No 1272/2008, Directive 1999/92/EC | flammable liquid classification; ATEX storage |
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Cyclohexane (CAS 110-82-7, EC 203-806-2) is a saturated six-membered cycloalkane with molecular formula C6H12 and molar mass 84.16 g mol⁻¹. At 20 °C, the density is 0.7785 g cm⁻³, the refractive index is 1.4262, and the vapor pressure at 25 °C is 12.9 kPa. Industrial production is dominated by the catalytic hydrogenation of benzene, and the resulting solvent is supplied as bulk technical, high-purity, and anhydrous reagent grades. The largest use is liquid-phase oxidation to cyclohexanol/cyclohexanone for nylon 6 and nylon 66, followed by solvent and laboratory applications. Cyclohexane differs from aromatic toluene in that it provides no π-π solvation for polar resins; it differs from linear n-hexane in having higher density and lower vapor pressure; and it differs from methylcyclohexane in lacking a tertiary methyl substitution, which shifts oxidation selectivity and raises the freezing point to 6.5 °C.
Manufacturing of cyclohexane begins with benzene-rich refinery or steam-cracker hydrocarbon fractions. Benzene is hydrogenated in fixed-bed reactors over nickel or platinum catalysts at 150–200 °C and 2–4 MPa, with interstage cooling and hydrogen recycle to manage exothermicity. The crude product is fractionated, and cyclohexane is withdrawn as a narrow heart cut while unreacted benzene, methylcyclopentane, and C5–C7 paraffins are rejected. Bulk technical grade is commonly specified with cyclohexane content ≥99.5% by gas chromatography, benzene ≤0.1%, total sulfur ≤1 mg kg⁻¹, water ≤50 mg kg⁻¹, and distillation range 80.0–81.0 °C at 101.3 kPa by ASTM D86. Density at 15 °C is controlled to 0.780–0.784 g cm⁻³ by ASTM D4052. High-purity and anhydrous grades are available with cyclohexane content ≥99.9% and water ≤30 mg kg⁻¹, typically packaged under nitrogen in 1 L glass bottles, 200 L drums, or dedicated tank trucks.
| Parameter | Standard designation | Typical limit |
|---|---|---|
| Density at 15 °C | ASTM D4052 | 0.780–0.784 g cm⁻³ |
| Distillation range | ASTM D86 | 80.0–81.0 °C |
| Water content | ISO 760 | ≤50 mg kg⁻¹ |
| Flash point closed cup | ASTM D56 | -18 °C |
| Benzene content | Internal GC-FID | ≤0.1% |
These specification limits are set by downstream catalytic tolerance. Benzene persists through oxidation and can form nitrated byproducts during the subsequent nitric acid oxidation to adipic acid. Sulfur compounds, even at trace level, inhibit radical initiation during cyclohexane oxidation and can deactivate noble-metal catalysts in hydrogenation units. Water is controlled because it partitions into recycled cyclohexane and promotes hydrolysis side reactions in ester-forming oxidation systems.
Batch-to-batch variation is usually observed in benzene and methylcyclopentane content, which depend on upstream reformer severity and hydrogenation temperature. When benzene exceeds 0.1%, integrated producers divert the product to the benzene recovery column or reduce feed rate rather than adjusting distillation pressure. Methylcyclopentane, a structural isomer, is the main difficult-to-separate impurity because its boiling point is close to that of cyclohexane; extractive distillation or azeotropic separation may be required for high-purity grades.
Substitution decisions between cyclohexane and other low-boiling hydrocarbon diluents depend on density, vapor pressure, flash point, and water solubility. Cyclohexane has a closed ring; n-hexane is linear; methylcyclohexane adds a methyl substituent; toluene is aromatic. Those structural differences produce measurable changes in evaporation and solvency. The table below contrasts key physical properties at ambient pressure.
| Property | Cyclohexane | n-Hexane | Methylcyclohexane | Toluene |
|---|---|---|---|---|
| CAS number | 110-82-7 | 110-54-3 | 108-87-2 | 108-88-3 |
| Molar mass | 84.16 g mol⁻¹ | 86.18 g mol⁻¹ | 98.19 g mol⁻¹ | 92.14 g mol⁻¹ |
| Density at 20 °C | 0.7785 g cm⁻³ | 0.659 g cm⁻³ | 0.7695 g cm⁻³ | 0.867 g cm⁻³ |
| Boiling point | 80.7 °C | 68.7 °C | 101.0 °C | 110.6 °C |
| Flash point closed cup | -18 °C | -22 °C | -4 °C | 4 °C |
| Vapor pressure at 25 °C | 12.9 kPa | 20.2 kPa | 5.1 kPa | 3.8 kPa |
| Water solubility at 25 °C | 55 mg L⁻¹ | 9.5 mg L⁻¹ | 14 mg L⁻¹ | 526 mg L⁻¹ |
Selecting cyclohexane over n-hexane reduces vapor pressure from 20.2 kPa to 12.9 kPa at 25 °C and raises density, which can reduce volatile loss during open mixing but can increase film retention after application. Selecting cyclohexane over toluene removes aromatic solvent hazard statements but reduces solvency for polar resins, plasticizers, and oils. Methylcyclohexane offers a higher flash point and lower vapor pressure, but it is less selective in oxidation-based nylon precursor routes because methyl group oxidation competes with ring C–H abstraction.
In nylon intermediate plants, cyclohexane is oxidized to KA oil in bubble-column reactors or mechanically agitated autoclaves constructed of 316L stainless steel. The liquid-phase air oxidation operates at 140–180 °C and 0.8–1.5 MPa. Per-pass conversion is held at 4–6% because cyclohexanone is more easily oxidized than cyclohexane; above 6%, over-oxidation to ring-opened diacids, hydroxy acids, and ester condensation products increases rapidly. Commercial KA oil selectivity is generally 70–85%, with the remainder consisting largely of adipic acid precursors, carbon dioxide, and low molecular weight carboxylates. Boric-acid-assisted oxidation improves selectivity by converting cyclohexanol to borate esters, but requires boric acid hydrolysis and recovery; most modern trains therefore use cobalt-catalyzed oxidation without boric acid. The reactor effluent is cooled, and unreacted cyclohexane is recovered in a distillation train. A purge stream removes water and light acid byproducts, which otherwise accumulate and increase separation load. The recovered cyclohexane is recycled to the oxidation reactor, while the KA oil is sent to storage for cyclohexanone hydrogenation or nitric acid oxidation to adipic acid.
In commercial cyclohexane oxidation reactors, liquid-hour space velocity is constrained by oxygen mass transfer, heat removal, and carboxylic acid accumulation. In a bubble-column reactor, superficial gas velocity is usually maintained between 0.02 m s⁻¹ and 0.05 m s⁻¹. Higher velocities increase gas holdup and back-mixing but shorten bubble residence time and reduce oxygen utilization. The oxygen supply must remain outside the flammable envelope while maintaining a dissolved oxygen concentration sufficient for radical-chain initiation. Off-gas oxygen is monitored continuously, and air feed is reduced or nitrogen inerting is increased when off-gas oxygen approaches 3–5 vol%. Heat removal is achieved by internal cooling coils or external recirculation through heat exchangers; local hot spots above 180 °C promote over-oxidation and increase carbon dioxide yield. Carboxylic acid byproducts are removed by water extraction or alkaline neutralization. If allowed to accumulate, they lower interfacial tension and can emulsify the organic and aqueous phases in the separator. Published operating data for specific bubble-column configurations is limited, but the indicated ranges are consistent with process licensor documentation and patent literature.
Laboratories and pilot plants requiring anhydrous aliphatic media often replace n-hexane with cyclohexane for higher boiling point and lower vapor pressure. The solvent is dried over molecular sieve 3A or 4A and transferred under argon or nitrogen through stainless steel cannulae. Water content is specified below 30 mg kg⁻¹ for pyrophoric organometallic synthesis; water above 50 mg kg⁻¹ can reduce initiator efficiency in organolithium-mediated anionic polymerizations. Unlike diethyl ether, cyclohexane is not effectively dried by sodium/benzophenone ketyl because the ketyl intermediate has low solubility in this non-polar medium. Karl Fischer titration per ISO 760 is used for release testing. The freezing point of cyclohexane is 6.5 °C, which imposes a low-temperature storage boundary not encountered with n-hexane, whose melting point is -95 °C. Consequently, unheated outdoor storage in temperate winter conditions is feasible for n-hexane but not for cyclohexane.
In analytical chemistry, high-purity cyclohexane is employed as a non-polar extraction solvent for petroleum-derived matrices and as a UV-transparent diluent for spectrophotometric methods. Its UV cutoff near 200 nm permits analysis of aromatic hydrocarbons without solvent absorption bands that interfere with toluene or benzene diluents.
Solventborne adhesive and coating systems using cyclohexane as a non-polar diluent are formulated for hydrocarbon resins, butyl rubber-based contact cements, and certain pressure-sensitive adhesives. The drying profile is slower than that of n-hexane because vapor pressure is 12.9 kPa at 25 °C, compared with 20.2 kPa for n-hexane. Forced-air ovens may need to operate 10–15 °C higher or residence time may need to be extended to satisfy residual volatile organic content standards such as ASTM D2369. Cyclohexane is not a VOC-exempt solvent in most regulatory jurisdictions and carries the aquatic chronic hazard H410, so substitution for toluene eliminates aromatic hazard statements but does not eliminate emission-control obligations. Mix tanks must be grounded and inerted to reduce the risk of flammable vapor accumulation.
Cyclohexane swells hydrocarbon elastomers less than toluene but is not compatible with EPDM, natural rubber, or butyl rubber in continuous dynamic sealing. Static seals in pumps, flange connections, and valve stems should be FFKM or PTFE-lined. Nitrile rubber may withstand short contact at ambient temperature, but continuous immersion above 40 °C can produce volume swell exceeding 15% in some formulations. Published swelling data for specific commercial elastomer grades is limited, so elastomer selection should be validated by ASTM D471 immersion testing. Dry cyclohexane is not aggressive to carbon steel, but wet cyclohexane containing dissolved oxygen causes rust generation at vapor-space condensation points. Bulk storage requires nitrogen blanketing, grounding and bonding, and vapor recovery. The flammable range is 1.3–8.3 vol% in air, and the autoignition temperature is 260 °C. Avoid contact with strong oxidizers, particularly concentrated nitric acid, because exothermic oxidation can initiate spontaneous ignition at elevated temperatures.
Under the EU CLP Regulation, cyclohexane is classified with hazard statements H225, H304, H315, H336, and H410. The substance has EC number 203-806-2 and is subject to REACH registration. For transport, it is assigned UN 1145, Class 3, Packing Group II. The NFPA 704 rating is typically 2-3-0: health 2, flammability 3, instability 0. Empty containers retain flammable vapor and should be inerted before hot work. Waste streams containing cyclohexane must not be discharged to surface water without treatment because the substance is classified as very toxic to aquatic life with long lasting effects.
