Cyclohexanone (CAS 108-94-1) is a six-carbon cyclic ketone produced predominantly as an intermediate for caprolactam and adipic acid, with merchant-grade material also entering solvent, thinner, and coatings formulations. Cyclohexanone Carbon Footprint & Scope 3 Data are typically developed under ISO 14067:2018 using life-cycle inventory methods from ISO 14040:2006 and ISO 14044:2006. In a corporate greenhouse-gas inventory, upstream emissions from purchased feedstocks, purchased energy, transportation, and waste handling fall under the GHG Protocol Corporate Value Chain (Scope 3) Standard, Categories 1, 3, 4, and 5. The dominant mass-flow route is cyclohexane oxidation to a cyclohexanol–cyclohexanone mixture known as KA oil, followed by dehydrogenation of cyclohexanol; a smaller but commercially significant route is phenol hydrogenation. The carbon footprint of cyclohexanone is therefore process-resolved and feedstock-sensitive: a facility switching from natural-gas-derived steam to coal-derived steam, or from merchant hydrogen to by-product hydrogen, can shift cradle-to-gate intensity by more than 1 kg CO₂e/kg.

The functional unit for a product carbon footprint is normally 1 kg of merchant cyclohexanone at minimum purity 99.8%, measured at the plant gate. System boundaries include raw-material extraction, feedstock transport, process energy, catalyst manufacture, waste treatment, and on-site emissions. Downstream conversion to caprolactam, adipic acid, or solvent applications is excluded from a cradle-to-gate study unless the reporting entity is also responsible for those downstream operations. Any exclusion must be justified and quantified if material under ISO 14067:2018.

What Process Conditions Drive the Cradle-to-Gate Carbon Intensity of Cyclohexanone?

In the air-oxidation process, liquid cyclohexane is contacted with molecular oxygen at 150–170 °C and 0.8–1.2 MPa in a bubble-column or stirred autoclave reactor. Cobalt(II) salts or boric acid are used as homogeneous oxidation promoters. Per-pass conversion is deliberately limited to 4–8% to suppress ring-opening acids and esters; selectivity to KA oil under these conditions is typically 80–85%. The unconverted cyclohexane is recovered in a multi-column distillation train. The carbon footprint penalty from this route is not only feedstock loss but also reboiler steam demand for cyclohexane recycle and the caustic saponification of ester by-products before final product purification. Published cradle-to-gate inventories for conventional cyclohexane-based cyclohexanone generally fall between 3.0 and 5.4 kg CO₂e/kg when steam and electricity are supplied by a natural-gas-fired cogeneration unit. If coal-fired steam is used, the upper bound can exceed 6.0 kg CO₂e/kg; such configurations are less common in modern merchant plants but remain relevant for captive capacity.

Production-scale distillation trains in cyclohexane oxidation units commonly record batch-to-batch variation in the cyclohexanol-to-cyclohexanone ratio of KA oil from 1.5:1 to 2.5:1. This variation shifts the downstream dehydrogenator feed composition and can increase natural-gas firing by 5–10% during high cyclohexanol campaigns. Utility log review is therefore a necessary check when converting monthly natural-gas metered data into Scope 1 and Scope 3 Category 3 emission factors.

In the phenol hydrogenation route, phenol is fed with hydrogen over a palladium or nickel catalyst in a fixed-bed reactor at 120–180 °C and 0.5–1.5 MPa. The stoichiometric phenol requirement is 0.959 kg per kg cyclohexanone and hydrogen demand is 0.041 kg per kg cyclohexanone. At 99% yield, practical phenol consumption rises to approximately 0.97 kg/kg. The carbon footprint of phenol dominates the feedstock burden. Phenol itself is produced from benzene and propylene via cumene oxidation, with published cradle-to-gate values often in the range 2.0–3.5 kg CO₂e/kg depending on steam and propylene supply. This can place phenol-based cyclohexanone between 2.4 and 4.0 kg CO₂e/kg if hydrogen is supplied by steam methane reforming without carbon capture.

Hydrogen supply is a critical variable. Steam methane reforming produces approximately 8–12 kg CO₂e/kg H₂ without carbon capture; electrolysis using average grid electricity can be higher, while by-product hydrogen from catalytic reforming may be allocated downward. If a phenol hydrogenation unit consumes 0.041 kg H₂ per kg cyclohexanone at stoichiometric conditions, the hydrogen contribution alone ranges from 0.33 to 0.49 kg CO₂e/kg for steam methane-reforming hydrogen without carbon capture. With certified low-carbon hydrogen, that component can be significantly lower, but inventory standards require clear evidence of physical or contractual tracking rather than an unverified emission factor.

Within both routes, the final purification step is a major energy consumer. Cyclohexanone is usually refined by vacuum distillation because it is thermally sensitive and can form aldol condensation products at elevated temperature. The vacuum distillation column typically operates at 80–120 °C reboiler temperature and 20–100 mbar head pressure, depending on product grade. At these conditions, reboiler steam demand can account for 25–40% of total thermal energy use in the purification train. Production-scale shell-and-tube condensers and vacuum ejectors contribute to electricity consumption, and regular cleaning is required to manage fouling from residual organic acids. Published data for the exact split between distillation steam and oxidation air compression in a specific plant is limited because process flow diagrams and utility logs are usually proprietary.

Scope 3 Category Materiality and Supplier-Data Exchange

Scope 3 screening for cyclohexanone should follow the GHG Protocol Corporate Value Chain (Scope 3) Standard. The material categories for a non-integrated merchant producer are usually Category 1 purchased goods, Category 3 fuel- and energy-related activities not included in Scope 1 or Scope 2, Category 4 upstream transportation and distribution, Category 5 waste generated in operations, and in some reporting structures Category 12 end-of-life treatment of sold products. Category 2 capital goods and Category 11 use of sold products are typically excluded because cyclohexanone is an intermediate that is chemically transformed. In practice, Category 1 plus Category 3 often represent 70–90% of total Scope 3 emissions for cyclohexanone production; the remainder arises from barge, rail, and truck movements and from off-site treatment of distillation bottoms.

The ranges in the table are screening values, not universal product carbon footprints. Comparative assertions between suppliers require critical review under ISO 14044:2006, Clause 6.1. A single deterministic carbon footprint should not be used for supplier benchmarking without reviewing the underlying allocation and cut-off choices.

Steam and electricity data from the distributed control system can be converted into Scope 2 and Scope 3 Category 3 footprints using supplier-specific or grid-specific emission factors. In a typical cyclohexane oxidation unit, the steam-to-feed ratio at the KA oil stripper is recorded in the process historian. A production campaign with high ester content in the oxidizer effluent will consume additional caustic in the saponifier and increase the organic load to the wastewater treatment plant, which in turn raises Scope 3 Category 5 off-site treatment emissions. The exact increase is facility-specific and should be quantified by mass balance rather than assumed from generic factors.

Upstream transportation of cyclohexane often occurs by pipeline or barge. Pipelines have lower emission factors per tonne-km, but data granularity is coarse because pipeline operators may allocate emissions across multiple products. For the Scope 3 inventory, the mass-distance method under EN 16258:2012 is commonly applied to road and rail legs, while a tonne-km emission factor from the GLEC Framework may be used for inland waterways. The exact factor depends on vehicle class, loading factor, and route; using a default factor without adjusting for empty returns can under-report Scope 3 emissions by more than 10%.

Double counting occurs when supplier-specific product carbon footprints already include upstream transport and waste, and the purchaser adds those categories again from secondary data. To avoid double counting, the inventory report should map the supplier’s declared system boundary to the GHG Protocol categories. If the phenol supplier reports a full cradle-to-gate product carbon footprint under ISO 14067:2018, the cyclohexanone producer should not add Category 4 transport for phenol delivery unless that transport was explicitly excluded. Many misstatements in Scope 3 reporting arise from boundary mismatches rather than from emission-factor error.

In the absence of audited supplier-specific product carbon footprints, procurement records may identify the mass of phenol or cyclohexane purchased, but secondary database values are frequently substituted. The uncertainty can be substantial: switching from a regional average phenol dataset to a supplier-specific product carbon footprint can change the result by 15–35% relative to the baseline. This is material for Scope 3 reporting because Category 1 purchased goods is typically the largest single category.

If Cyclohexanone Is Procured from Phenol Derived via Cumene Oxidation, Which Allocation Rules Apply?

Phenol feedstock carbon intensity is not a single value; it depends on how the cumene oxidation co-product acetone is treated. Under mass allocation, 62.0% of upstream cumene and utility burdens is assigned to phenol and 38.0% to acetone based on stoichiometric mass output. Under economic allocation, the phenol share can shift from approximately 58% to 68% depending on the phenol–acetone price ratio. This alone can change cyclohexanone cradle-to-gate intensity by 0.2–0.5 kg CO₂e/kg. ISO 14040:2006 and ISO 14044:2006 prefer subdivision or system expansion before allocation, but for publicly traded phenol this is usually impractical because process-level utility metering at the cumene cleavage unit is rarely available to downstream cyclohexanone producers.

Hydrogen allocation is a further boundary issue. If hydrogen is supplied over the fence from a refinery, the Scope 3 Category 1 burden of hydrogen should include refinery allocation for purge gas and flare gas. Using a generic steam methane-reforming hydrogen factor can under-report the carbon footprint when the supplier operates a high-flare refinery; conversely, by-product hydrogen from catalytic reforming can carry a lower allocated footprint. Supplier-specific data exchange under ISO 14025:2006 Type III environmental product declarations can reduce this uncertainty, but such declarations for phenol and hydrogen are not universally available.

For private supply contracts, a bespoke data request that includes the supplier’s Scope 1 and Scope 2 inventories, allocation method, and third-party assurance statement is the only reliable basis for a cyclohexanone Scope 3 submission. Where supplier-specific data is absent, the inventory report should disclose the secondary dataset version and its documented uncertainty range rather than presenting a single deterministic value. Spent dehydrogenation catalyst is typically sent to metals reclaimers; off-site transport and reclamation are reported in Scope 3 Category 5. Published data for this specific configuration is limited, but it is seldom a top-three category because catalyst consumption is on the order of 0.001–0.005 kg per kg cyclohexanone.

An operational boundary that is frequently overlooked is the treatment of purge gas and flare emissions in the hydrogen production unit supplying the phenol hydrogenation route. If hydrogen is supplied by a refinery or petrochemical complex, the allocation of refinery fuel gas, purge streams, and flaring must be consistent with the supplier’s corporate inventory under ISO 14064-1:2018. Otherwise, the cyclohexanone producer inherits an undetected truncation error in Category 1 purchased goods. This becomes especially relevant when hydrogen is sourced from multiple units with different carbon intensities and the supplier reports only a site-average factor.

Facility-specific Scope 3 data for cyclohexanone should be validated against material balance. The purchased mass of cyclohexane or phenol, the recorded production of cyclohexanone, the co-product and waste streams, and the utility consumption should reconcile within the plant’s monthly production report. A mismatch of more than 2–3% between the mass-balance output and the metered product quantity may indicate unrecorded purge losses, storage-tank breathing losses, or measurement bias in the level transmitter. These are not merely accounting errors; they affect the allocation of upstream feedstock burdens and therefore the reported Scope 3 emission intensity.