Air Blown Bitumen Process
Last updated: 2026-09-29
Air Blown Bitumen Process: Complete Technical & Commercial Guide
The bitumen blowing process converts soft penetration-grade bitumen (typically 80/100 or 200/300 pen) into harder, oxidised bitumen by injecting air at 230–280°C for 4–12 hours, producing grades such as 10/20, 20/30, 30/40, and industrial 115/15. A standard 40 TPH batch oxidiser produces roughly 800–960 tonnes per day, while global oxidised bitumen prices range from USD 380–520 per tonne FOB depending on grade, penetration value, and origin port. This article breaks down the chemistry, process parameters, equipment, and commercial economics of air blowing bitumen, with data tables exporters and buyers can use for procurement planning.
What Is the Bitumen Blowing Process?
The bitumen blowing process (also called oxidation, air rectification, or the Shell blowing process) is a controlled chemical reaction in which compressed air is bubbled through hot bitumen at 230–280°C. Oxygen from the air reacts with the hydrocarbon molecules, dehydrogenating them and forming larger asphaltene aggregates. This increases viscosity, raises softening point, lowers penetration, and improves temperature susceptibility — turning a soft feedstock into a durable oxidised grade used in roofing, waterproofing, pipe coating, and mastic.
Three reaction mechanisms dominate:
- Dehydrogenation — hydrogen is stripped from hydrocarbon chains, forming water vapour as a by-product
- Polymerisation/condensation — smaller molecules combine into larger asphaltenes
- Oxidation — oxygen bonds form carbonyl and carboxyl groups, increasing polarity and adhesion
The net effect is measurable: penetration drops from ~90 dmm to 20 dmm, softening point rises from ~45°C to 60–95°C, and viscosity increases by a factor of 10–500 depending on blow time.
| Parameter | Feedstock (Soft Bitumen) | Blown Bitumen (30/40) | Blown Bitumen (115/15) |
|---|---|---|---|
| Penetration @25°C (dmm) | 80–200 | 30–40 | 10–20 |
| Softening point (°C) | 40–48 | 52–58 | 95–115 |
| Viscosity @135°C (cSt) | 100–200 | 400–700 | 1,800–3,500 |
| Flash point (°C) | 220–250 | >250 | >250 |
| Solubility in TCE (%) | 99.5 | 99.0 | 99.0 |
| Typical use | Paving | Waterproofing, pipe coating | Roofing, battery cases |
Process Parameters That Control Bitumen Quality
Four variables determine the final grade in the air blown bitumen process: temperature, air rate, residence time, and feedstock composition. Get these wrong and you either under-blow (grade fails pen test) or over-blow (brittle product, cracking risk).
| Variable | Typical Range | Effect of Increase |
|---|---|---|
| Reaction temperature | 230–280°C | Faster reaction, higher softening point, risk of coking >290°C |
| Air flow rate | 50–150 m³/hour per tonne | Increases oxidation rate, shortens cycle time |
| Blowing time | 4–12 hours | Higher softening point, lower penetration |
| Pressure | Atmospheric to 5 bar | Higher pressure = better O₂ transfer, faster reaction |
| Catalyst (optional) | 0.05–0.5% FeCl₃ or P₂O₅ | Cuts cycle time 20–40% |
At 250°C with 100 m³/h/tonne air flow, a typical batch reaches 30/40 grade in 6–8 hours. Pushing to 115/15 industrial grade requires 10–12 hours and careful temperature control to prevent thermal cracking.
| Time (hours) | Penetration (dmm) | Softening Point (°C) | Grade Achieved |
|---|---|---|---|
| 0 | 90 | 45 | Feedstock |
| 3 | 55 | 50 | 50/60 |
| 5 | 40 | 55 | 40/50 |
| 7 | 32 | 57 | 30/40 |
| 9 | 22 | 65 | 20/30 |
| 12 | 14 | 98 | 10/20 |
Data typical for Middle East feedstock at 250°C, 100 m³/h/tonne air rate.
Equipment and Reactor Types
Two reactor designs dominate commercial production: vertical batch oxidisers and continuous horizontal/column blowers.
| Feature | Batch Oxidiser | Continuous Blower |
|---|---|---|
| Capacity | 20–200 tonnes/batch | 500–3,000 tonnes/day |
| Cycle time | 6–12 hours + heating | Continuous, 8–24 h residence |
| Product flexibility | High — change grade per batch | Low — fixed grade |
| Capex | Lower (USD 1.5–4 M) | Higher (USD 8–25 M) |
| Energy use | 180–250 MJ/tonne | 140–200 MJ/tonne |
| Best for | Small exporters, custom grades | Refineries, large-scale export |
A complete blowing unit includes:
- Feedstock storage tanks (heated to 150–180°C)
- Blowing reactor with air spargers and cooling coils
- Air compressor (screw type, 7–10 bar, 500–2,000 m³/h)
- Off-gas treatment — thermal oxidiser or scrubber for H₂S, SO₂, VOCs
- Product cooler and drum filling line
- Control system — PLC with temperature, air flow, and pen trending
Off-gas handling is critical: blowing generates 5–15 kg of VOCs and 1–3 kg of H₂S per tonne of bitumen, requiring thermal oxidation at 700–850°C to meet emission norms.
Commercial Data: Pricing, Logistics, and Export Economics
For exporters, the blowing process adds value through grade upgrading. A 60/70 paving bitumen at USD 420/tonne FOB can be oxidised to 30/40 waterproofing grade selling at USD 460–500/tonne, capturing a USD 40–80/tonne margin minus conversion cost of USD 15–28/tonne.
| Cost Component | Batch Plant | Continuous Plant |
|---|---|---|
| Fuel/gas for heating | USD 6–10 | USD 4–7 |
| Electricity (compressor) | USD 4–7 | USD 3–5 |
| Catalyst (if used) | USD 1–3 | USD 0.5–2 |
| Labour | USD 3–5 | USD 1–2 |
| Off-gas treatment | USD 2–4 | USD 1–3 |
| Total conversion cost | USD 16–29 | USD 9.5–19 |
| Route | Mode | Cost (USD/tonne) | Transit Time |
|---|---|---|---|
| Iran → India (JNPT) | Bulk vessel | 28–42 | 7–12 days |
| UAE → Kenya (Mombasa) | Flexitank/ISO | 55–75 | 18–25 days |
| Saudi → Bangladesh | Bulk vessel | 35–50 | 10–16 days |
| South Korea → Vietnam | ISO tank | 40–60 | 5–9 days |
Typical MOQ for drummed oxidised bitumen is 20–26 tonnes (one 20-ft container), while bulk shipments start at 1,000–3,000 tonnes and flexitank lots at 20–24 tonnes. Drum packaging adds USD 18–28/tonne, while bulk saves cost but requires port discharge infrastructure.
Quality Control and Standards
Blown bitumen must meet standards such as ASTM D312 (roofing), ASTM D449 (waterproofing), BS 3690, and IS 702. Core QC tests run every batch or every 2 hours in continuous operation:
- Penetration — ASTM D5, 25°C, 100 g, 5 s
- Softening point — ASTM D36 (ring & ball)
- Viscosity — ASTM D4402 (Brookfield, 135°C or 160°C)
- Flash point — ASTM D92 (Cleveland open cup)
- Solubility — ASTM D2042 (trichloroethylene)
- Ductility — ASTM D113 (some grades)
A batch failing penetration by more than 5 dmm is typically re-blown or blended with feedstock. AI-assisted process control using near-infrared (NIR) spectroscopy can predict softening point within ±1.5°C in real time, cutting off-spec batches by up to 30%.
Frequently Asked Questions
Q1: How long does the bitumen blowing process take?
A standard batch at 250°C with 100 m³/h/tonne air flow takes 6–8 hours to reach 30/40 grade and 10–12 hours for 115/15 industrial grade. Continuous blowers maintain a stable residence time of 8–24 hours depending on reactor volume and target penetration.
Q2: What temperature is used in air blowing bitumen?
The reaction runs at 230–280°C, with the sweet spot at 250–260°C for most grades. Above 290°C, thermal cracking and coke formation increase sharply, damaging product quality and requiring reactor cleaning.
Q3: What is the difference between blown bitumen and paving bitumen?
Blown (oxidised) bitumen has lower penetration, higher softening point, and higher viscosity than paving bitumen, making it suitable for roofing, waterproofing, and pipe coating. Paving bitumen (60/70, 80/100) is designed for road construction with better low-temperature flexibility.
Q4: How much does it cost to produce blown bitumen?
Conversion cost is USD 9.5–19/tonne in continuous plants and USD 16–29/tonne in batch plants, excluding feedstock. Feedstock itself trades at USD 380–450/tonne FOB, so total production cost lands at USD 400–470/tonne before packaging.
Q5: What are the main export grades of blown bitumen?
The most traded grades are 10/20, 20/30, 30/40, and 115/15, with 30/40 dominating waterproofing markets and 115/15 serving roofing and industrial applications. Standard export packaging is 150–200 kg steel drums, 20-ft flexitanks, or bulk vessel parcels of 1,000–3,000 tonnes.
Calculate Your Blown Bitumen Cost Instantly
Whether you are an exporter pricing a 2,000-tonne oxidised bitumen parcel or a buyer verifying CIF landed cost, manual calculations leave money on the table. Use the 6Tar cost calculator to model feedstock, conversion, packaging, freight, and duty in seconds — across every grade from 10/20 to 115/15. Get accurate per-tonne landed cost, compare supplier quotes side by side, and lock in your margin before the market moves.