Acrylonitrile (2-propenenitrile, CAS 107-13-1) is a commodity unsaturated nitrile monomer with a molecular weight of 53.06 g/mol and a normal boiling point of 77.3 °C. It is the principal co-monomer in ABS and SAN resins, acrylic fibre, nitrile rubber, and adiponitrile production. Conventional manufacture is dominated by the Sohio ammoxidation of propylene over bismuth-molybdenum mixed-oxide catalysts in fluidized-bed reactors. An evaluation of bio-based acrylonitrile routes, ISCC mass balance and real supply timelines therefore centres on replacement of the fossil propylene input and on site-level chain-of-custody allocation, not on replacement of the Sohio unit itself. The result is a drop-in monomer in which the renewable attribute is assigned by certified inventory records rather than by segregated molecular identity.

Which Bio-Based Acrylonitrile Routes Reach Commercial Production?

Two bio-feedstock routes have moved beyond laboratory and pilot scale. The most commercially established is bio-propylene derived from renewable ethanol. Bioethanol is first dehydrated to ethylene over γ-alumina at 300–500 °C. The ethylene is then reacted with 2-butene in an olefin metathesis unit over WO₃/SiO₂ or MoO₃/Al₂O₃ at 300–400 °C and 1–3 MPa, producing polymer-grade propylene. This bio-propylene is subsequently supplied to a conventional ammoxidation train. A second route uses hydrotreated vegetable oil bio-naphtha in an existing steam cracker; the cracker yields bio-ethylene, bio-propylene, and heavier olefins, with renewable carbon allocated across multiple products. Glycerol-to-acrolein ammoxidation remains a research route with published fluidized-bed studies, but commercial catalyst lifetime data and economics for this specific configuration are limited.

The Sohio reaction stoichiometry is 2 C3H6 + 2 NH3 + 3 O2 → 2 C3H3N + 6 H2O. The reaction is exothermic and requires controlled air-to-propylene ratios to maintain operation outside flammable regimes. Industrial fluidized-bed reactors operate at 430–450 °C and 0.5–1.5 bar gauge, with ammonia-to-propylene molar ratios between 1.05:1 and 1.20:1. Reported molar selectivity to acrylonitrile is 80–84%, with acetonitrile, hydrogen cyanide, acrolein, and carbon oxides as principal side products. Because bio-propylene is chemically identical to fossil propylene, catalyst activity, pressure drop, and product distillation profiles remain unchanged. The critical interface is feedstock quality: certified bio-propylene must meet the same polymer-grade propylene limits for sulfur, water, and C3H6 purity as fossil propylene, and the receiving site must maintain ISCC PLUS mass-balance records from feedstock receipt through acrylonitrile storage.

Mass Balance Attribution Under ISCC PLUS Defines Current Bio-ACN Volumes

ISCC PLUS is a chain-of-custody certification system, not a chemical product specification. Under mass-balance accounting, renewable feedstock quantities are recorded into a site-level inventory and allocated to selected outputs within a defined mass-balance period, commonly 3 months for chemical operations. ISCC PLUS 3.4 permits bio-propylene and fossil propylene to be co-processed in the same reactor and distillation train, provided the site reconciles certified inputs with attributed outputs and applies approved conversion factors for yield losses and process waste. The bio-carbon content of the final acrylonitrile can be verified by radiocarbon analysis according to ASTM D6866 or ISO 16620-2, because renewable biomass retains a contemporary 14C signature while fossil feedstock does not.

Mass-balance acrylonitrile therefore has identical CAS registry, vapour density, and polymerisation kinetics to fossil acrylonitrile. The renewable attribute is an accounting allocation, not a molecular difference. This mechanism is not book-and-claim: ISCC PLUS requires physical delivery of certified feedstock to the certified site and third-party verification of inventory. However, it does not guarantee that each drum, isotainer, or marine parcel contains only biogenic carbon. A buyer requiring physical separation must specify ISCC PLUS identity-preserved or segregated chain-of-custody. For acrylonitrile, segregated supply involves dedicated storage tanks, loading lines, and documentation, which carries materially higher logistics cost and is not the default commercial model.

Because the substance is identical, bio-attributed acrylonitrile remains covered by the same REACH registration as fossil acrylonitrile under Regulation (EC) No 1907/2006. The product specification lists the same purity, inhibitor formulation, water content, and distillation range as fossil material, with the addition of a lot-specific bio-carbon content and a third-party audit certificate. In the absence of an analytical method to distinguish bio-attributed ACN from fossil ACN after mass-balance allocation, the certification ledger and ASTM D6866 result are the operative quality documents.

Real supply timelines for bio-based acrylonitrile are governed by certified bio-propylene lot availability and the site-level mass-balance window rather than by new reactor construction. Public production disclosures indicate commercial shipments of ISCC PLUS bio-attributed acrylonitrile in Europe from 2022 onward, with a second European monomer source appearing in the Netherlands in 2023. Published nameplate capacity remains a small fraction of total acrylonitrile demand, and most supply is allocated under multi-year offtake agreements for bio-attributed ABS, SAN, and acrylic fibre rather than sold as general-purpose spot monomer. Supply is lot-certified at the inventory level. This means a polymer plant may receive a marine parcel or tank truck from the same continuous Sohio distillation train that also produces fossil acrylonitrile. For bio-attributed ABS, the acrylonitrile mass fraction typically ranges from 15% to 35%, so the ACN lot is the enabling monomer for the resin producer’s certified renewable content claim.

When the Sohio Train Is Mass-Balanced, Documentation Becomes the Product

At production scale, the principal allocation point is the propylene feed drum and the acrylonitrile product tankage. A Sohio unit receiving a certified bio-propylene parcel into a shared feed drum must record the mass and carbon balance before and after injection, then allocate a corresponding mass of acrylonitrile output within the approved ISCC PLUS mass-balance period. For a continuous train with production capacity above 100,000 t/a, bio-attributed supply is therefore an accounting period aligned with monthly tank loading and marine parcel schedules, not a short reactor campaign. The limiting constraints include the availability of ISCC-certified propylene lots, cracker turnaround schedules, and the requirement that the site inventory never become negative during the allocation period.

Ammonia contributes no carbon to acrylonitrile, so the bio-carbon claim resides almost entirely in the propylene feed. All three carbon atoms of acrylonitrile derive from propylene; therefore, fully renewable propylene yields acrylonitrile with 100% bio-carbon by ASTM D6866. In mass-balance production, the declared bio-content is a fraction of the total ACN output based on certified input, not an assay of molecular purity. This makes the mass-balance ledger, raw-material sustainability declaration, greenhouse-gas emission calculation, and audit certificate the only documentable differences from fossil acrylonitrile. Physical properties, polymerisation behaviour, and downstream processing performance remain analytically indistinguishable from fossil monomer under conventional ISO and ASTM test methods.