Ethylene tar is traded as a heavy aromatic by-product of naphtha/LPG steam cracking, containing alkylbenzenes, naphthalenes, indenes, anthracenes, and higher polycyclic aromatics. It is commonly characterized by density at 15°C in the 1.03–1.12 g/cm³ range, kinematic viscosity at 50°C from 30 mm²/s to several thousand mm²/s, sulfur by ASTM D4294, and BMCI. The selection of downstream routes is constrained by aromaticity, coking propensity, sulfur, ash, and boiling point distribution. The following application entries are limited to merchant processes for which ethylene tar is a recognized feedstock, with commercial substitution ratios stated as mass percentages of total feed unless otherwise noted.

Carbon Black Feedstock in Oil-Furnace Reactors

Carbon black furnaces consume ethylene tar as a high-BMCI liquid feed where the aromatic core is partially oxidized and thermally cracked to carbon microaggregates. The receiving specification is generally based on density at 15°C per ASTM D4052-23, kinematic viscosity at 50°C per ISO 3104:2023, sulfur per ASTM D4294-21, ash per ISO 6245:2001, and calculated BMCI. Ethylene tar from naphtha cracking commonly shows BMCI in the 125–155 range, which compares favorably with FCC decant oil and coal tar distillates; sulfur is typically 0.3–1.8 wt%, and asphaltene separation must be confirmed because some high-severity tars contain sludge that blinds preheaters. Commercial addition in carbon black oil blending is not a fixed recipe; furnace operators target a blended BMCI above 120 and a sulfur ceiling dictated by the final carbon black grade, so ethylene tar may be run neat or diluted with FCC decant oil at 15–100 wt% of the total liquid feed. Downstream processing uses a high-temperature oil-furnace reactor: the blended feedstock is preheated to 200–320°C and hot filtered before being atomized by steam or mechanical nozzles into the reactor, where preheated air at 800–1200°C maintains a cracking zone of approximately 1400–1800°C. The carbon black aerosol is quenched with water at 650–800°C, passed through primary cyclones and bag filters, then densified in wet pelletizers and dried in rotary dryers before packing. Yield to carbon black under these conditions is usually in the 45–65% range relative to fresh hydrocarbon feed, falling at the lower end when the tar contains high boiling point resinous fractions. End-product grades include N220, N330, N550, and N660 under ASTM D1765, supplied to tire carcass, sidewall, conveyor belt, extruded profile, and rubber masterbatch manufacturing. Carbon black from ethylene tar feedstock is registered under REACH (EC) 1907/2006; surface activity of these grades affects vulcanization kinetics in sulfur-cured rubber compounds, so outgoing lot certification includes iodine adsorption per ASTM D1510, oil absorption per ASTM D2414, and tint strength per ASTM D3265.

What Limits Ethylene Tar Use in Delayed Coking for Needle Coke?

In needle coke production, ethylene tar must be evaluated as a secondary aromatic feedstock rather than a primary coker feed because its resinous C9+ fraction can reduce mesophase alignment and raise sulfur in the green coke. The relevant incoming feedstock compliance parameters are sulfur by ASTM D4294, Ni+V by ASTM D5708, density by ASTM D4052, and C/H ratio. Needle coke buyers specify anisotropic texture and low coefficient of thermal expansion; calcined needle coke for electric-arc furnace electrodes is tested by ASTM E228 for CTE, with premium grades often required to be below 1.0×10⁻⁶ K⁻¹ over the 100–250°C interval. Ethylene tar can be incorporated at 5–30 wt% of the total delayed coker feed, typically into hydrotreated FCC decant oil; exceeding this range usually raises the coke sulfur above 0.5 wt% and can shorten the anisotropic domain, though the exact limit depends on tar distillation endpoint and prior hydrotreatment. The downstream process begins with preheating the blended feed in a delayed coker fired heater to 490–510°C, transferring it to coking drums at 0.3–0.8 MPa(g), and holding for 18–36 h while thermal cracking, polycondensation, and mesophase growth proceed. The green coke is cut with high-pressure water, stacked, and calcined in a rotary kiln or shaft calciner at 1250–1400°C under controlled oxygen to remove volatiles and shrink porosity. Finished product types are super-premium, premium, and intermediate needle coke for UHP graphite electrodes in electric-arc furnaces; lower anisotropy material may be sold as recarburizer for steel foundries. Published data for the specific CTE of ethylene tar-derived needle coke blends is limited; a pilot delayed coker test or bench-scale autoclave test is normally required before a long-term supply agreement can be qualified.

Residual fuel blenders incorporate ethylene tar as an aromatic cutter stock and density adjuster in marine fuel oil pools. The addition ratio is not fixed; VLSFO blending may tolerate 3–12 wt% ethylene tar, while HSFO with scrubber operation can typically accept 5–18 wt%, subject to final deposit and asphaltene stability assessment. The governing fuel specification is ISO 8217:2024; for an RMG 380 grade the kinematic viscosity at 50°C must not exceed 380 mm²/s, density at 15°C must not exceed 991.0 kg/m³ for conventional grades, and sulfur must remain below 0.50 wt% for VLSFO under MARPOL Annex VI Regulation 14 when no exhaust gas cleaning system is used. The operation is performed in refinery or terminal in-line blenders with recirculation at 40–70°C; high-shear mixers or static mixers are commissioned if the tar contains polymers that reduce blend compatibility, and the product is then passed through centrifuges to remove water and sludge. Quality assurance includes total sediment potential by ISO 10307-2, with a maximum of 0.10 wt% for most merchant deliveries, and calculated carbon aromaticity index below 870 for medium-speed engines. Finished products are mostly ISO-F-RMG 380, ISO-F-RMG 180, and ECA-compliant VLSFO for two-stroke main engines and four-stroke auxiliary engines in oceangoing vessels.

Merchant chemical recovery units isolate a naphthalene-rich distillate from ethylene tar when the naphthalene content of the dry tar feed exceeds 8 wt%; typical naphthalene contents in naphtha-derived ethylene tar are in the 8–18 wt% range, while methylnaphthalenes and acenaphthene may contribute another 5–12 wt%. The compliance framework for the recovered naphthalene is driven by the CLP Regulation (EC) 1272/2008 classification as harmful if swallowed and very toxic to aquatic life, and the downstream use in phthalic anhydride requires producer-specific GC purity confirmation; no single ISO method covers all ethylene tar naphthalene fractions. The processing route begins with preflash vacuum distillation at 5–15 kPa absolute pressure, drawing the naphthalene-rich side stream at a column top temperature of 220–260°C; the distillate is then melt-crystallized in scraped-surface crystallizers at 60–75°C, with sweating and centrifugation separating naphthalene from methylnaphthalene-rich oil. The main finished product is refined naphthalene at 95–99 wt% purity for catalytic oxidation to phthalic anhydride, and the remaining methylnaphthalene-cut can be sold as a feedstock for SNF concrete superplasticizers or industrial solvent recovery. This route is sensitive to oxygen and must be operated under nitrogen blanketing to limit gum formation in the reboiler; batch-to-batch variance in naphthalene content requires continuous reflux adjustment, and tar with solids content above 1 wt% is generally filtered upstream to avoid fouling the thin-film evaporator.

When Ethylene Tar Is Thermally Polymerized into Carbon Binder Pitch

Thermal polymerization of ethylene tar can yield a carbon binder pitch for aluminium anodes and specialty graphite if the feed is low in ash, has limited quinoline-insoluble precursors, and is processed under inert gas. The formulation window is narrow: ethylene tar or its 280–360°C heart cut is charged to a stirred reactor at 350–420°C and 0.1–0.5 MPa(g) for 6–24 h, with continuous removal of naphthalene-rich light oil; the mass ratio of ethylene tar-derived polymerized residue in the final binder pitch can reach 10–100 wt%, but merchant anode plants frequently limit the substitute to 10–40 wt% when blending with coal tar pitch to protect anode density and air/CO₂ reactivity. Compliance testing uses softening point by ASTM D3104-14, quinoline insolubles by ISO 6791:1981, coking value by ISO 6998:1998, and sulfur by ASTM D4294; binder pitch for prebaked anodes is usually specified at a softening point of 105–120°C, QI of 8–16 wt%, and beta-resin content near 15–25 wt%. The downstream production step in the aluminium smelter is anode paste mixing: calcined petroleum coke, recycled butts, and binder pitch are mixed at 140–170°C in a high-intensity mixer, formed in a vacuum press, and baked at 1050–1250°C in ring furnaces. Finished product types include prebaked carbon anodes used in Hall-Héroult cells, ramming paste for cell linings, and specialty graphite binder for electrodes and structural graphite. Published anode performance data specific to ethylene tar-derived binder pitch is limited; plant qualification should include CO₂ reactivity oxidation data per ISO 12988-1 and air permeability per ISO 15906 before large-scale substitution.

High-pressure partial oxidation gasification represents a lower-value but technically real outlet for ethylene tar when refinery residue gasification is already installed and the tar cannot be economically distilled or sold as carbon black feedstock. The material is blended with vacuum residue at 5–25 wt% of total gasifier feed to raise carbon content and adjust syngas composition, though the upper limit is controlled by soot formation and burner pressure drop. Feed specification requires solids below 1 wt%, sodium plus potassium below 10 mg/kg, and viscosity below 200 mm²/s at pump suction. The process operates at 1200–1450°C and 3.0–8.0 MPa with oxygen and steam, converting hydrocarbons into raw syngas containing mostly H₂ and CO; acid gas removal units handle H₂S and COS. End products are hydrogen for hydroprocessing, methanol after catalytic synthesis, and carbon monoxide for oxo-alcohols or polycarbonate intermediates. Compliance is driven by the operating license under IED 2010/75/EU for gasification units and local CO/H₂S emission limits; no single commercial fuel specification covers ethylene tar for gasification.