Mass Balance Accounting Rules for Chemical Recycled Polymers
Mass balance accounting requires rigorous yield loss deductions and fuel exclusion rules to legally defend circular resin claims during regulatory audits.
Organic Chlorine Contamination
Meaning
Halogenated organic compounds bound within plastic waste or pyrolysis oils represent hazardous chemical impurities that generate corrosive acids and toxic combustion byproducts during processing. Organic chlorine contamination originates from chlorinated polymers like polyvinyl chloride and polyvinylidene chloride, chlorinated solvents, or flame-retardant additives present in post-consumer resin streams. In chemical recycling and steam cracking operations, chlorinated species break down under heat to form hydrochloric acid gas, causing rapid equipment corrosion and poisoning downstream hydrogenation catalysts.
Operating temperatures above thermal decomposition thresholds dictate where unreacted organic chlorine converts completely into volatile acid gases.
Origin Mechanism
Post-consumer plastic sorting failures introduce small quantities of polyvinyl chloride packaging films into polyolefin recycling streams. Pyrolysis processing of mixed waste breaks down these chlorinated polymers, forming chloroalkanes and chlorobenzene compounds dissolved in liquid oil. Solvent residues from industrial degreasing operations add low boiling point organic chlorides to raw feedstock oils.
Corrosion Risk
Thermal cracking liberates anhydrous hydrochloric acid, which attacks stainless steel distillation columns and heat exchanger tubes. Acidic gas streams require immediate caustic scrubbing to prevent stress corrosion cracking in high-pressure reactor loops. Corrosion products such as iron chloride contaminate liquid streams, promoting unwanted polymerization side reactions and fouling heat transfer surfaces.
Dechlorination Boundary
Catalytic hydrodechlorination converts organic chlorine into hydrogen chloride gas and neutral hydrocarbons across noble metal catalysts. Sorbent guard beds trap volatile chlorides at lower temperatures before feedstocks enter sensitive hydrotreating or cracking reactors. High nitrogen content in mixed pyrolysis oils competes for active catalyst sites, reducing overall dechlorination efficiency.