Heavy Naphtha (Heavy Straight-Run / HSR Atmospheric Distillation Heavy Cut and Catalytic Reformer Feedstock) Storage — C7-C10 Naphthenic + Paraffinic Tank Selection

Heavy Naphtha (Heavy Straight-Run / HSR Atmospheric Distillation Heavy Cut and Catalytic Reformer Feedstock) Storage — C7-C10 Naphthenic + Paraffinic Tank Selection at Refinery Crude Unit Outlets and Reformer Unit Feed Pools

Heavy naphtha (also called heavy straight-run naphtha, HSR; or heavy virgin naphtha, HVN; or simply naphtha hydrotreater feed) is the C7-C10 heavier naphtha cut drawn from the atmospheric crude distillation tower (CDU) heavy-naphtha splitter outlet. Boiling range 90-180°C (195-355°F) at atmospheric-equivalent boiling point, heavy naphtha is dominated by C7-C10 paraffins (n-heptane, iso-heptanes, n-octane, iso-octanes, n-nonane, n-decane) + naphthenes (methylcyclohexane, ethylcyclohexane, dimethylcyclohexanes, methylcyclopentane homologs) + minor aromatics (5-15 wt%, mostly toluene, ethylbenzene, xylenes, C9 alkylaromatics). The chemistry is paraffinic + naphthenic + low-aromatic + low-olefin + low-sulfur (post-hydrotreating to remove crude-derived sulfur), making heavy naphtha the principal feedstock to the catalytic reformer where it converts to high-octane aromatic reformate plus hydrogen co-product.

Heavy naphtha physical properties: density 0.72-0.76 g/cm³; specific gravity 0.72-0.76; RVP (Reid Vapor Pressure) 1-3 psi (much lower than light naphtha because of negligible C5 + minor C6 content); RON (Research Octane Number) 35-55 in the straight-run form (very low; the catalytic reformer is required to upgrade to gasoline-pool octane); MON 35-50; sulfur under 0.5 ppm post-naphtha-hydrotreater (essential to protect the platinum reformer catalyst from sulfur poisoning; reformer catalyst is irreversibly poisoned by sulfur exposure above 0.5 ppm); flash point 0-30°C; pour point typically -50°C or lower; ASTM D86 distillation 90-180°C; nitrogen under 0.5 ppm post-hydrotreater (also a reformer catalyst poison). Heavy naphtha is stored at refinery crude-unit outlets + naphtha hydrotreater feed pools + catalytic reformer feed day-tanks in API 650 atmospheric carbon-steel tanks with floating-roof or internal-floating-roof construction.

The eight sections below cite Honeywell UOP (CCR Platforming + naphtha hydrotreater technology), Axens / IFP (Octanizing + naphtha hydrotreater), Chevron Lummus Global (Rheniforming + Aromax + CLG hydroprocessing), ExxonMobil Powerformer + naphtha hydrotreater, API 650, NFPA 30, NFPA 30A, OSHA 29 CFR 1910.119 PSM, EPA 40 CFR 60 Subpart Kb, 40 CFR 63 Subpart CC Petroleum Refinery MACT, EPA 40 CFR 80 gasoline regulations, and operating refinery practice at Marathon, Phillips 66, Valero, ExxonMobil, Chevron, BP, Shell, and CITGO U.S. refineries for heavy naphtha storage and tank selection.

1. Material Compatibility Matrix

Refinery heavy naphtha is a clean low-sulfur low-aromatic paraffinic + naphthenic light-to-middle hydrocarbon stream. Material selection mirrors clean light-distillate service.

The dominant industrial pattern at U.S. refineries is API 650 carbon-steel atmospheric storage with welded floating-roof or internal-floating-roof (IFR) construction, primary + secondary peripheral seals, full epoxy-novolac internal floor coating, and 316L stainless trim at high-velocity blending headers + flow meters. HDPE and FRP are never specified at refinery heavy naphtha or finished-gasoline blendstock storage.

2. Real-World Industrial Use Cases

Catalytic Reformer Feedstock. The dominant single end use of heavy naphtha is feedstock to the refinery catalytic reformer (Honeywell UOP CCR Platforming, Axens / IFP Octanizing, Chevron Rheniforming, ExxonMobil Powerformer) where the C7-C10 paraffins + naphthenes are converted to high-octane aromatics over a Pt-Re/Al₂O₃ or Pt-Sn/Al₂O₃ bifunctional catalyst at 480-540°C and 5-30 bar. The reformer produces reformate (the high-octane aromatic gasoline blendstock) plus hydrogen as primary co-product (the largest single hydrogen source at most refineries). Reformer severity (Octane Number target 95-103 RON) is set by reactor temperature + recycle ratio, balancing octane uplift against yield + aromatic + benzene production.

Naphtha Hydrotreater Feed. Heavy naphtha is first routed through the refinery naphtha hydrotreater (Honeywell UOP Unionfining, Axens HR Series, Chevron Lummus Global ISOTREATING) where sulfur is reduced from typical crude-derived 100-2000 ppm to under 0.5 ppm, nitrogen reduced to under 0.5 ppm, and selected olefins saturated, all to protect the downstream platinum reformer catalyst. Naphtha hydrotreater operating conditions: 290-380°C, 25-45 bar hydrogen partial pressure, NiMo or CoMo sulfided catalyst.

Steam-Cracker Feedstock for Ethylene + Propylene. Heavy naphtha (especially the lighter portion) feeds petrochemical steam-crackers as a paraffin-rich naphtha-cracker feed at integrated petrochemical complexes producing ethylene + propylene + butadiene + pyrolysis gasoline. Heavy naphtha cracker yields are 25-30 wt% ethylene + 14-17 wt% propylene + 4-6 wt% butadiene + 18-22 wt% pyrolysis gasoline.

Refinery Gasoline Blending. Heavy naphtha can blend directly into the gasoline pool as a low-octane low-RVP component, but in practice almost all heavy naphtha is reformed to higher octane reformate before gasoline blending because the straight-run RON 35-55 is far below the gasoline pool target. Selected refineries operate hydrocrackate splitters that route a portion of heavy naphtha directly to gasoline blending where the cut has acceptable octane and the refinery economics favor blending over reforming.

Specialty Aliphatic Solvent Production. Heavy naphtha feeds specialty hydrocarbon solvent production: high-purity heptane (chemical synthesis solvent + chromatography mobile phase + specialty degreasing solvent), Stoddard solvent (ASTM D235 mineral spirits, used in dry cleaning + degreasing), and varnish makers' & painters' (VM&P) naphtha. Specialty solvent producers (ExxonMobil ExxsolTM, Shell ShellSolTM, Total Energies SpecialFluids, Idemitsu IPSolventsTM) source heavy-naphtha-derived feedstocks for hydrotreating + fractionation.

Refinery Crude Unit + Splitter Storage. Atmospheric crude distillation outlets at U.S. refineries store heavy naphtha at typical inventories of 100,000-500,000 barrels per crude-unit outlet position, with tankage feeding the naphtha hydrotreater + catalytic reformer + gasoline blender + steam-cracker complex depending on refinery configuration.

3. Regulatory Hazard Communication

OSHA HazCom GHS Classification. Refinery heavy naphtha is classified as Flammable Liquid Category 2 or 3 (flash point 0-30°C; classification depends on cut). Hazard statements: H225 or H226 (flammable liquid and vapour), H304 May be fatal if swallowed and enters airways, H315 Causes skin irritation, H336 May cause drowsiness or dizziness, H373 May cause damage to organs through prolonged or repeated exposure, H361 Suspected of damaging fertility or the unborn child, H411 Toxic to aquatic life with long-lasting effects.

NFPA 704 Diamond. Health 1, Flammability 3 (NFPA 30 Class IB Flammable Liquid; flash 22.8-37.8°C, BP above 38°C), Instability 0.

DOT and Shipping. Heavy naphtha is shipped under UN1268 Petroleum distillates, n.o.s. or Petroleum products, n.o.s. Hazard Class 3 Flammable Liquid Packing Group II (most cuts) or PG III (heavier-end cuts with flash above 23°C) per 49 CFR 173.121 assignment of packing group. Bulk shipment by tank truck (DOT 406 spec), rail tank car (DOT 111 / TC 117), pipeline, or marine vessel.

EPA Air Regulations. Heavy naphtha storage tanks are Volatile Organic Liquid Storage Vessels under 40 CFR Part 60 Subpart Kb NSPS where true vapor pressure exceeds 0.75 psi at storage temperature (typical heavy naphtha at 1-3 psi RVP; warmer storage exceeds the threshold). Floating-roof or IFR construction with primary + secondary seals is required, or fixed-roof tank with vapor recovery to control device.

EPA Gasoline Specifications. Heavy naphtha as a gasoline blendstock or reformer feed falls under EPA gasoline regulations at 40 CFR Part 80 Tier 3 sulfur cap, MSAT2 benzene cap, and seasonal RVP limits. Heavy naphtha's low aromatics + low sulfur post-hydrotreating supports gasoline pool compliance.

OSHA Process Safety Management. Refinery crude unit + naphtha hydrotreater + catalytic reformer units are covered under OSHA 29 CFR 1910.119 PSM. Heavy naphtha storage at the refinery tank farm is generally covered under the broader refinery PSM scope.

n-Heptane and Hydrocarbon Health Hazard. Heavy naphtha contains 5-15 wt% n-heptane plus iso-heptanes; n-heptane has lower neurotoxicity than n-hexane (no peripheral neuropathy at chronic exposure) but the broader paraffin + naphthene mixture carries acute CNS depression hazard at high vapor concentrations. OSHA PEL n-heptane 500 ppm 8-hour TWA; ACGIH TLV 400 ppm 8-hour TWA.

4. Storage System Specification

Refinery Crude Unit + Naphtha Splitter Storage. Heavy naphtha is stored at refinery crude unit + naphtha splitter outlet tank farms in API 650 atmospheric carbon-steel tanks with welded floating-roof (external) or internal-floating-roof (IFR) construction. Typical tank size 50,000-300,000 barrels (8,000-50,000 m³); tank diameter 100-250 ft; height 40-60 ft. The IFR retrofit pattern with aluminum-honeycomb deck panels and dual peripheral seals is the modernization standard.

Naphtha Hydrotreater + Catalytic Reformer Feed Storage. Naphtha hydrotreater units maintain feed-pool storage of 30,000-150,000 barrels at the unit battery limits feeding the reactor pre-heat train. Catalytic reformer units maintain treated naphtha (post-hydrotreating) feed-pool storage of 30,000-150,000 barrels feeding the reformer reactor train. Day-tank construction is bare carbon steel with insulation matching the main feed-pool tank.

Vapor Recovery and Loading. Truck and rail loading racks at the refinery for heavy naphtha are equipped with bottom-loading vapor balance, vapor-recovery to thermal oxidizer or carbon-bed adsorber, and grounding + bonding per API RP 2003.

Tank-Bottom Water Drainage. Heavy naphtha has very low water solubility (under 100 ppm at typical storage temperatures), so water settles to the tank bottom. Refinery operating practice drains tank-bottom water on a scheduled cadence to a slop oil + water sump.

Refinery-Adjacent OneSource Service. Aqueous service points around the crude unit + naphtha splitter + naphtha hydrotreater + catalytic reformer + heavy naphtha tank farm where rotomolded HDPE day-tanks are appropriate include caustic-wash makeup at the naphtha hydrotreater + amine-treater (50% NaOH carbon-steel main; HDPE day-tank dilute neutralization), demineralized water makeup, glycol heat-transfer makeup, water-treatment polymer feed, MEA / DEA / MDEA amine-makeup at the naphtha hydrotreater amine absorber (where applicable; aliphatic amines are highly compatible with HDPE at ambient conditions), and emergency-spill containment retention.

5. Field Handling Reality

Operator PPE. Refinery operators handling heavy naphtha sample draw, blending-header valve operation, custody-transfer flow-meter inspection, and tank-roof maintenance require Nomex or comparable FRC per API RP 2030 + OSHA 29 CFR 1910.269; chemical splash safety glasses + face shield at sample-port and valve operation; nitrile or Viton gloves rated for hydrocarbon contact; H₂S monitor at refinery storage areas; full-face APR or supplied-air respirator at confined-space entry into degassed storage tanks; static-dissipative footwear + grounding wrist-strap at flammable-liquid sample-draw.

Fire and Explosion Hazard. Heavy naphtha at flash point 0-30°C is NFPA 30 Class IB Flammable Liquid; vapor ignition energies under 0.30 mJ make static-discharge ignition the dominant mechanism in tank-roof, sample-draw, loading-rack, and small-vessel operations. NFPA 77 + API RP 2003 + refinery-specific bonding + grounding programs are mandatory. LFL approximately 1.0-1.4 vol%; UFL approximately 6-7 vol%.

Spill Response. Heavy naphtha spill response: (1) evacuate area + activate refinery emergency response + isolate ignition sources, (2) PPE-equipped responders deploy AFFF or fluorine-free F3 alternative foam blanket, (3) recover liquid via vacuum truck to slop oil tank, (4) decontaminate concrete and gravel surfaces with absorbent (vermiculite, oil-only sorbent pads), (5) document spill volume + report under EPA NRC + state environmental agency reporting + CERCLA Section 103 + CWA Section 311 reportable quantities.

Tank Maintenance and Confined-Space Entry. Heavy naphtha storage tank inspection per API 653; internal entry requires confined-space permit under OSHA 29 CFR 1910.146 with full degassing + LEL monitoring + supplied-air respirator + standby attendant.

Catalytic Reformer Feed Quality Control. Heavy naphtha quality control at the catalytic reformer feed pool is mission-critical: sulfur above 0.5 ppm or nitrogen above 0.5 ppm rapidly poisons the platinum reformer catalyst; halide carryover (organic chlorides from upstream desalter or tank-bottom water emulsification) attacks the chlorinated alumina catalyst support. Online sulfur + nitrogen + chloride analyzers + grab-sample wet-chemistry confirmation are standard at the reformer feed pool. Feed pool tank-bottom water management is critical to prevent halide carryover.

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