Verifying Chemical Conversion Yield Deductions under ISO 22095 Standards
Chemical conversion yield deductions under ISO 22095 mandate subtracting process gas, char, and hydrotreating losses from input mass before awarding credits.
Char Formation
Meaning
Thermal degradation during high-temperature polymer pyrolysis converts solid plastic scrap into an insoluble, carbon-rich solid residue alongside condensable liquid fuels. Liquid fuel yields decline when char formation occurs inside reactors because fixed carbon ties up hydrocarbon chains that would otherwise form monomeric or aromatic feedstocks. Solid deposit accumulation on reactor walls fouls heat transfer surfaces and disrupts continuous thermal cracking.
High filler loadings in post-consumer scrap accelerate this solid accumulation, forcing operators to adjust residence times and temperature profiles.
Thermal Carbonization
Temperature spikes above the target cracking point shift depolymerization reactions toward aromatic condensation and dehydrogenation. Cross-linking between unzipped polymer chains yields polycyclic aromatic networks that drop out of the vapor stream. Lowering peak reactor temperature minimizes these secondary reactions, preserving liquid hydrocarbon fractions.
Catalytic additives alter reaction pathways to inhibit radical recombination, reducing coke deposition on internal surfaces.
Reactor Fouling
Layering of solid carbon along heat transfer tubes reduces thermal conductivity. Heat transfer efficiency drops sharply, requiring elevated burner output to maintain bulk fluid temperatures.
Yield Penalty
Mass balance accounting treats non-volatile solid residue as an unallocated loss that reduces usable circular output. Processors deduct this unrecovered fraction before calculating the volume of circular oil eligible for chemical allocation. High char formation reduces conversion efficiency from ninety percent down to seventy percent, increasing the unit cost of certified circular polymer resins.