Alkylate (Refinery Alkylation Unit High-Octane Gasoline Blendstock) Storage — Iso-Paraffinic Trimethylpentane Blendstock Tank Selection

Alkylate (Refinery Alkylation Unit High-Octane Gasoline Blendstock) Storage — Iso-Paraffinic Trimethylpentane Blendstock Tank Selection at Petroleum Refinery Blending Tank Farms

Alkylate is the highest-quality light gasoline blendstock produced inside a petroleum refinery: a clean, low-sulfur, low-aromatics, low-olefin iso-paraffinic stream consisting primarily of branched C7-C8 hydrocarbons (predominantly 2,2,4-trimethylpentane / iso-octane plus 2,3,3- and 2,3,4-trimethylpentane plus 2,2-dimethylhexane). Refineries produce alkylate by reacting isobutane with light olefins (propylene, n-butylenes, isobutylene, isoamylenes) at low temperature in the presence of a strong-acid catalyst, either liquid hydrofluoric acid (HF alkylation, ConocoPhillips / Phillips 66 process) or concentrated sulfuric acid (H2SO4 alkylation, Stratco / DuPont and Exxon-Mobil processes). The product blendstock has Research Octane Number (RON) 90-98, Motor Octane Number (MON) 88-95, Reid Vapor Pressure (RVP) 4-7 psi, sulfur under 10 ppm, aromatics under 1%, and olefins effectively zero, making it the cleanest, highest-octane gasoline blendstock available from a refinery and a critical component of every modern reformulated gasoline (RFG) recipe and of premium-grade finished gasoline pools.

Alkylate is stored at refinery blendstock tank farms in atmospheric API 650 floating-roof or internal-floating-roof tanks at typical inventories of 50,000-500,000 barrels per blendstock day-tank service. Flash point at -40°C or lower, autoignition 410-450°C, vapor pressure 4-7 psi RVP at summer-grade and 7-12 psi at winter-grade specifications place alkylate firmly inside Class IB Flammable Liquid service per NFPA 30 Flammable and Combustible Liquids Code with mandatory floating-roof / internal-floating-roof vapor-control construction at the storage tank, vapor-recovery loading facilities at truck and rail loading racks, and full API RP 752 Process Hazard Analysis under OSHA 29 CFR 1910.119 Process Safety Management of Highly Hazardous Chemicals. Density 0.69-0.71 g/cm³; specific gravity 0.69-0.71; pour point typically -60°C.

The eight sections below cite ExxonMobil Research and Engineering, Honeywell UOP (HF Alkylation licensor), DuPont / Stratco (sulfuric-acid alkylation licensor), API 650 (welded steel tanks for oil storage), API RP 752, NFPA 30, NFPA 30A, OSHA 29 CFR 1910.119 PSM, EPA 40 CFR 60 Subpart Kb (volatile organic liquid storage NSPS), 40 CFR 63 Subpart CC Petroleum Refinery MACT, EPA 40 CFR 80 (gasoline reformulation specifications), and operating refinery practice at Marathon Petroleum, Phillips 66, Valero, ExxonMobil, Chevron, BP, and Shell U.S. refineries for alkylate storage, blending, and tank-selection practice at modern alkylation-equipped refineries.

1. Material Compatibility Matrix

Refinery-grade alkylate is a clean iso-paraffinic light hydrocarbon stream with no acid carryover (downstream caustic wash and water wash remove residual HF or sulfuric-acid catalyst before product blendstock storage), no aromatics, no olefins, low sulfur, and very low water solubility. Material selection mirrors clean light-gasoline blendstock service.

The dominant industrial pattern at U.S. refineries is API 650 carbon-steel atmospheric storage with welded floating-roof (external) 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 + custody-transfer measurement points. HDPE and FRP are never specified at refinery alkylate or finished-gasoline blendstock storage; rotomolded HDPE has no role in active hydrocarbon service. OneSource Plastics' 5-brand HDPE network supports refinery-adjacent service envelopes only: aqueous wastewater holding, glycol-based heat-transfer makeup, ammonium-thiosulfate scrubber-makeup, sodium-hydroxide neutralization makeup at the alkylation acid-wash + caustic-wash circuits, and similar non-hydrocarbon service points around the unit battery limits.

2. Real-World Industrial Use Cases

Refinery Gasoline Blending Pool. Alkylate is the single highest-quality gasoline blendstock at a typical U.S. refinery, contributing 10-25% of the finished gasoline pool by volume at refineries with alkylation capacity. Marathon Petroleum (Galveston Bay TX, Garyville LA, Catlettsburg KY), Phillips 66 (Borger TX, Wood River IL, Sweeny TX), ExxonMobil (Baytown TX, Beaumont TX, Baton Rouge LA), Valero (Port Arthur TX, Corpus Christi TX, St. Charles LA), Chevron (Pascagoula MS, Richmond CA, Salt Lake City UT), and BP (Whiting IN, Cherry Point WA) all operate alkylation units feeding finished gasoline blending. Alkylate fills the high-octane + low-RVP + low-aromatics + low-sulfur corner of the gasoline blending property cube, especially valuable as benzene + aromatic + olefin restrictions tightened through the EPA Mobile Source Air Toxics (MSAT2) and Tier 3 gasoline rules.

Reformulated Gasoline (RFG) Compliance. EPA RFG and California CARB Phase 3 RFG specifications restrict aromatics (typical cap 25 vol%), olefins (typical cap 6-10 vol%), benzene (cap 0.62 vol%), sulfur (cap 10 ppm Tier 3), and Reid Vapor Pressure (cap 7.0-9.0 psi seasonal) at finished gasoline. Alkylate has effectively zero aromatics, zero olefins, zero benzene, sub-10-ppm sulfur, and 4-7 psi RVP, making it the ideal blendstock to maintain the gasoline pool inside RFG specifications without sacrificing octane.

Aviation Gasoline (Avgas 100LL) Production. Aviation gasoline 100LL (low-lead, 100-octane) production at a small number of refineries (Phillips 66 specialty avgas, ConocoPhillips Wood River legacy, Total petroleum specialty grades) uses alkylate as the primary base blendstock plus toluene + tetraethyl lead octane booster + dye to meet ASTM D910 specifications. Alkylate's high MON and low vapor pressure make it the dominant base for avgas, especially as global avgas refineries consolidate to a handful of producers.

Specialty High-Octane Racing and Engine-Test Fuels. Sunoco Race Fuels, VP Racing Fuels, and similar specialty blenders produce 100-114 octane racing and engine-development fuels using alkylate as a base blendstock with toluene, ethanol, methanol, and proprietary octane enhancers added depending on intended application (NASCAR, NHRA, sports-car series, OEM dyno-test programs).

Off-Highway and Marine Premium Fuels. Marine-grade premium gasoline for outboard and stern-drive engines, off-highway equipment requiring high octane, and selected industrial spark-ignition applications use higher alkylate content to combat the storage stability and gum-formation challenges of olefinic FCC gasoline blendstocks. Alkylate's chemical stability (no olefins to oxidize, no aromatics to gum) makes it the preferred light gasoline blendstock for long-storage applications.

Custody Transfer and Pipeline Movements. Alkylate moves from producing refineries to gasoline blending terminals via Colonial Pipeline, Magellan Midstream, Enterprise Products, and Plains All American product pipelines as a fungible high-octane blendstock. Custody-transfer specifications include ASTM D86 distillation, ASTM D5191 RVP, ASTM D2622 sulfur, ASTM D2699 RON + ASTM D2700 MON octane, ASTM D6730 detailed hydrocarbon analysis (DHA), and water + sediment via ASTM D4007. Tank-bottom water control is critical at custody-transfer storage: alkylate has very low water solubility (under 100 ppm), so any free water settles to the tank bottom and must be drained at scheduled maintenance.

3. Regulatory Hazard Communication

OSHA HazCom GHS Classification. Refinery alkylate is classified as a Flammable Liquid Category 1 (flash point under 23°C and initial boiling point at or below 35°C is Cat 1; flash under 23°C with IBP above 35°C is Cat 2). Typical alkylate at IBP 27-40°C, FBP 200-205°C, and flash under -40°C is GHS Cat 1 or Cat 2 depending on the specific refinery cut. Hazard statements: H224 Extremely flammable liquid and vapour (Cat 1) or H225 Highly flammable liquid and vapour (Cat 2), H304 May be fatal if swallowed and enters airways (aspiration hazard category 1), H315 Causes skin irritation, H336 May cause drowsiness or dizziness, H411 Toxic to aquatic life with long-lasting effects.

NFPA 704 Diamond. Health 1 (slight skin and respiratory irritation; aspiration hazard if swallowed), Flammability 4 (flash under 23°C, BP under 38°C-equivalent classification under NFPA 30 Class IB), Instability 0, no special hazard.

DOT and Shipping. Alkylate is shipped under UN1268 Petroleum distillates, n.o.s. or Petroleum products, n.o.s. Hazard Class 3 Flammable Liquid Packing Group II per 49 CFR 173.121 assignment of packing group. Bulk shipment is by tank truck (DOT 406 spec), rail tank car (DOT 111 / TC 117 specifications), pipeline, or marine barge. Refineries shipping alkylate as a finished blendstock comply with 49 CFR Part 172 Hazardous Materials Table, Part 173 packaging, Part 174 carriage by rail, Part 177 carriage by motor vehicle, and Part 195 PHMSA hazardous-liquid pipeline regulations.

EPA Air Regulations. Alkylate storage tanks are Volatile Organic Liquid (VOL) Storage Vessels under 40 CFR Part 60 Subpart Kb New Source Performance Standards for Storage Vessels for Volatile Organic Liquids (true vapor pressure above 0.75 psi triggers control requirements; alkylate at 4-7 psi is well within scope), with required floating-roof or internal-floating-roof construction with primary + secondary seals, or fixed-roof tank with vapor recovery to control device with 95% destruction efficiency. The Petroleum Refinery NESHAP at 40 CFR Part 63 Subpart CC additionally requires Leak Detection and Repair (LDAR) at storage tank gauging hatches, fittings, and rim seals; quarterly visual inspections of internal-floating-roof primary seal; and annual roof landings + degassing emissions reporting.

EPA Gasoline Specifications. Alkylate as a finished gasoline blendstock falls under EPA gasoline regulations at 40 CFR Part 80 (Tier 3 sulfur cap 10 ppm annual average refinery + 95 ppm per-gallon cap; benzene cap 0.62 vol% annual average; aromatics + olefins + RVP per RFG and conventional gasoline specifications) and CAA Section 211 Mobile Source Air Toxics Rule 2 (MSAT2). Alkylate is a critical compliance blendstock for refiners maintaining gasoline pool sulfur, aromatics, and benzene compliance.

OSHA Process Safety Management. The alkylation unit itself (HF or sulfuric-acid catalyst) is covered under OSHA 29 CFR 1910.119 Process Safety Management of Highly Hazardous Chemicals because of HF inventory thresholds (HF 1000 lb threshold) or because of the strong-acid alkylation reactor inventory. Alkylate finished blendstock storage at the refinery tank farm is generally not the PSM-covered process; the PSM scope ends at the alkylation unit battery limits. EPA RMP (40 CFR Part 68) Risk Management Plan applies in parallel for HF-alkylation refineries.

4. Storage System Specification

Refinery Blendstock Storage. Alkylate is stored at refinery tank farms in API 650 atmospheric carbon-steel tanks with floating-roof (external single-deck or double-deck pontoon) or internal-floating-roof (IFR) construction. Typical tank size 50,000-500,000 barrels (8,000-80,000 m³); tank diameter 100-300 ft; height 40-60 ft. Floating-roof construction limits vapor-space evaporative losses at the storage tank by collapsing vapor space to a thin annular gap between the floating deck and the tank shell, sealed by a primary mechanical-seal shoe (typically liquid-mounted or vapor-mounted) and a wiper-style secondary seal. IFR retrofit of legacy fixed-roof tanks is the dominant API 650 modernization pattern at U.S. refineries; aluminum honeycomb deck panels with stainless or aluminum truss support are the modern IFR construction standard.

Day-Tank and Blending-Header Service. Alkylate moves from main blendstock storage to the gasoline blending header at the refinery in-line blending control system (IBLC) or rotating-paddle blending tank by API-positive-displacement or Coriolis flow meter (Micro Motion CMF-series), with blending control via DCS (Honeywell, Emerson DeltaV, ABB, Yokogawa) holding the gasoline pool inside RVP, octane, sulfur, aromatics, benzene, and distillation property targets. Tank-piping is 6-24-inch carbon-steel ANSI 150 with PTFE-spirial-wound flange gaskets and Viton or FFKM valve stem packing.

Vapor Recovery and Loading. Truck and rail loading racks at the refinery for alkylate blendstock or finished-gasoline are equipped with bottom-loading vapor balance, vapor-recovery to thermal oxidizer or carbon-bed adsorber with 95-99% destruction efficiency, and grounding + bonding per API RP 2003 Static Electricity in Petroleum Operations. Marine loading at refinery dock berths uses Marine Vapor Recovery Units (MVRU) per USCG 33 CFR 154 Subpart E.

Tank-Bottom Water Drainage. Alkylate has very low water solubility (under 100 ppm at typical storage temperatures), so water entering the tank from rainfall (through floating-roof deck drains), condensation, or process upsets settles to the tank bottom. Refinery operating practice drains tank-bottom water on a scheduled cadence (typically weekly) to a slop oil + water sump or wastewater treatment unit. Excessive water accumulation degrades product quality, accelerates floor corrosion, and creates microbial growth issues at the water-hydrocarbon interface.

Refinery-Adjacent OneSource Service. Aqueous-side service points around the alkylation + blendstock storage area where rotomolded HDPE day-tanks are appropriate include caustic-wash makeup (50% NaOH at carbon-steel main storage; HDPE day-tank at lower-strength caustic addition), ammonium-thiosulfate scrubber makeup, glycol heat-transfer makeup, and emergency-spill containment retention.

5. Field Handling Reality

Operator PPE. Refinery operators handling alkylate sample draw, blending-header valve operation, custody-transfer flow-meter inspection, and tank-roof maintenance require Nomex or comparable FRC (flame-resistant clothing) per API RP 2030 + OSHA 29 CFR 1910.269 hazard-zone requirements; chemical splash safety glasses + face shield at sample-port and valve operation; nitrile or Viton gloves rated for light hydrocarbon contact; H₂S monitor at tank-farm areas where sour-water carryover is possible; and full-face APR or supplied-air respirator at confined-space entry into degassed storage tanks. Static-dissipative footwear and grounding wrist-strap at flammable-liquid sample-draw operations.

Fire and Explosion Hazard. Alkylate at flash point under -40°C is among the most ignitable liquids on the refinery; vapor ignition energies are 0.20-0.25 mJ (typical static-discharge energy is 30-100 mJ from a charged person), making static-discharge ignition the dominant mechanism in tank-roof, sample-draw, loading-rack, and small-vessel applications. NFPA 77 Recommended Practice on Static Electricity, API RP 2003, and refinery-specific bonding + grounding programs are mandatory. Lower flammable limit (LFL) 1.0-1.2 vol% in air; upper flammable limit (UFL) 7.0-7.5 vol%; flammable-vapor cloud risk at floating-roof landed-position drainings, sample-draw, and tank-cleaning is documented in refinery PHA + JSA records.

Spill Response. Alkylate spill response at refinery tank farms: (1) evacuate area + activate refinery emergency response + isolate ignition sources within affected area, (2) PPE-equipped responders deploy foam blanket (Aqueous Film-Forming Foam, AFFF, or fluorine-free F3 alternative) to suppress flammable vapor, (3) recover liquid via vacuum truck to slop oil tank, (4) decontaminate concrete and gravel surfaces with absorbent (vermiculite, diatomaceous earth, oil-only sorbent pads), (5) document spill volume + decontamination + EPA NRC + state environmental agency reporting under CERCLA Section 103 + CWA Section 311 reportable quantities (refinery operator reports per facility-specific RMP and SPCC plan thresholds).

Tank Maintenance and Confined-Space Entry. Floating-roof tank inspection per API 653 Tank Inspection, Repair, Alteration, and Reconstruction is the dominant tank-integrity pattern: external visual + UT thickness inspection on 5-year cadence; internal inspection + floor scan + roof seal repair on 10-20-year cadence depending on service history. Internal entry requires confined-space permit under OSHA 29 CFR 1910.146 with full degassing + LEL monitoring + supplied-air respirator + standby attendant + entry rescue plan. Tank-cleaning contractors (Veolia, US Ecology, Clean Harbors) handle slurry and sludge removal under refinery-specific scope of work.

Talk to OneSource Plastics

Listed price covers tank + standard fitting package; LTL freight is quoted separately to your delivery ZIP. Call 866-418-1777, use our freight estimator, or try our chemical tank recommender to narrow material selection.