Pyrolysis, examined as a system.
Pyrolysis is a family of thermochemical processes in which material undergoes thermal decomposition under conditions involving the substantial absence of oxygen. That definition describes a process family, not a guaranteed environmental outcome.
There is no single pyrolysis outcome
Performance depends on feedstock, reactor configuration, temperature, heating rate, residence time, product handling, gas treatment, pollution control, energy integration and operating stability.
Material before machinery
Polyolefins, PVC, tyres, biomass, wet bio-organics and medical waste are not interchangeable feedstocks. Moisture, ash, chlorine, sulphur, metals, additives and contamination can change process behaviour substantially.
Products require qualification
Gas, liquids and carbonaceous solids are product families, not proof of value. Composition, contamination, upgrading requirements, actual use, displacement and final fate determine whether recovery creates a genuine environmental benefit.
Energy and emissions
Gross energy, internal process energy, net exported energy and energy actually displaced must be distinguished. Environmental assessment includes reactor leakage, gas handling, combustion, filtration, acid-gas treatment, wastewater, residues, startup, shutdown and upset conditions.
Comparison
Pyrolysis should be compared with the realistic alternative for the same material on equivalent boundaries. It is not automatically circular and it is not automatically environmentally superior.
The governing question is: for this material, under these conditions and controls, producing these outputs, compared with this alternative, what does the evidence show?