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.
Distillation Tars
Meaning
Heavy hydrocarbon residues remaining in the reboiler after fractional distillation of pyrolysis oil represent high-molecular-weight oligomers and polycyclic compounds that fail to vaporize. Refining thermal cracking liquids into virgin-equivalent monomer streams separates light olefins from these dense distillation tars. The viscous liquid fraction gathers at column bottoms, dragging down total liquid recovery rates during chemical recycling.
Contaminants such as residual chlorine and organosilicones concentrate in this heavy phase.
Bottom Residue
High boiling points exceeding four hundred degrees Celsius prevent these heavy fractions from rising through fractional distillation trays. Viscosity increases continuously as volatile components boil off, creating pumping challenges in downstream piping. Adding light solvent diluents lowers fluid viscosity to maintain flow during tank transfers.
Removal Cost
Processing facilities relegate heavy distillation bottoms to industrial fuel blending or gasification feedstocks. High concentration of heteroatoms limits direct reuse in naphtha crackers.
Yield Impact
Polymer mass balance systems deduct the mass of distillation tars from total circular feed intake before assigning recycled content credits. Moulders buying circular polyethylene or polypropylene rely on this deduction to ensure that certified claims reflect actual monomer conversion rather than unrefined crude oil mass. High tar fractions force chemical recyclers to increase feedstock intake per kilogram of output resin, elevating virgin-replacement premiums across injection molding runs.