Direct answer
What are the different ways to do pyrolysis?
All of them starve oxygen. They differ by heating rate, solids time, vapour time, pressure, catalyst and how heat is delivered. Those six knobs set oil vs char vs gas more than the logo on the skid.
| Technique | Heating rate | Peak T | Vapour time | Typical intent | Typical split (biomass) |
|---|---|---|---|---|---|
| Torrefaction | slow | 200–300 °C | long | Dried, brittle solid | Solid 70–90% |
| Slow / carbonisation | ≲ 1 °C/s | 300–700 °C | minutes–hours | Char | Char 30–40, oil 20–45, gas 25–40 |
| Intermediate | ~1–10 °C/s | 400–550 °C | seconds–minutes | Balanced, dirty feeds | Oil 40–50 |
| Fast | 10–1000 °C/s | 450–550 °C typical | 0.1–2 s target | Bio-oil | Oil 50–75, char 10–20, gas 10–25 |
| Flash | 10³–10⁴ °C/s | 600–1400 °C | <0.5 s | Max liquid (lab) | Oil 60–80 |
| Vacuum | slow–medium | lower than 1 atm equivalent | vapours pulled away | Less secondary cracking | Higher oil at lower T (tires 45–55%) |
| Catalytic (in situ / ex situ) | as host reactor | often 400–550 °C | catalyst contact | Better oil, more gas | Oil down, quality up |
| Hydropyrolysis / H2 | fast or medium | ~400–500 °C | short + H2 | Deoxygenated oil | Oil quality, not max mass |
| Microwave-assisted | volumetric | feed-specific | seconds–minutes | Electrified, selective carbons | Can match fast oil in lab |
| Plasma (thermal) | extreme local T | 10³–10⁴ °C | ms | Syngas, slag, H2 | Not an oil table |
| Co-pyrolysis | as host | as host | as host | Synergy (H-donor plastics) | Non-linear blend |
| Carbothermal (batteries) | medium | 550–700 °C | minutes–hours | Reduce cathode, free Li | Solid BM remains |
Atmosphere is not optional
Nitrogen or recycled syngas keeps oxygen out. A little tramp air turns pyrolysis into combustion: you lose oil, oxidise copper in battery black mass, and can form dioxins if chlorine is present. Steam can be used deliberately (steam pyrolysis) to lift hydrogen and cut char. Hydrogen is a different plant (hydro). Vacuum is a third.
Catalytic vs thermal for plastics
Thermal PE/PP at ~500 °C maximises liquid mass, often waxy. Zeolites (ZSM-5, FCC, USY) crack wax to gasoline-range aromatics and raise gas. That is a quality vs quantity trade. For tires, ZSM-5 oil yields in the literature swing from ~30% to ~56% at 500 °C — catalyst loading and reactor dominate, so do not copy a single paper into a bank model.
Microwave and plasma, without the brochure
Microwave-assisted pyrolysis (MAP) has a pre-industrial plastic prototype at tens of kg/h (TRL ~7 in Italian work). Penetration depth and absorbers (carbon, SiC) limit mixed wet waste. Thermal plasma is excellent at destroying organics and vitrifying ash; it is the wrong tool if your KPI is diesel-range oil. Methane plasma pyrolysis (Monolith-class turquoise hydrogen + carbon black) is a different industry that happens to share the word.