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.
Hydrotreating Yield Loss
Meaning
Conversion mass reduction occurring when plastic pyrolysis oils undergo catalytic hydrogenation measures the transformation of heteroatoms and olefins into saturated hydrocarbons. Hydrotreating yield loss accounts for light hydrocarbon gas formation, water production, ammonia release, and hydrogen sulfide generation as oxygen, nitrogen, and sulfur exit the liquid oil. In circular polymer feedstocks, this mass reduction dictates net naphtha output for steam cracking into fresh plastic monomers.
High contaminant concentrations shift reaction equilibrium toward light paraffin gas production, reducing target liquid product volume.
Saturation Mechanism
Heteroatom removal breaks chemical bonds within hetero-atomic molecules, converting organic oxygen into water vapor and organic nitrogen into ammonia gas. Olefin saturation proceeds exothermically across nickel-molybdenum or cobalt-molybdenum catalyst beds. Deoxygenation of fatty acid methyl esters derived from plastic pyrolysis generates propane, carbon dioxide, and water mass losses.
Hydrogen Consumption
High double-bond density elevates stoichiometric hydrogen demand, increasing light gas formation through hydrocracking side reactions. Reactor bed temperatures rising beyond design limits accelerate thermal cracking, converting naphtha-range liquids into methane or ethane fuel gas. Optimized temperature control preserves liquid hydrocarbon yield while eliminating gum-forming diolefins.
Feedstock Boundary
Contaminant thresholds in raw pyrolysis oil dictate hydrotreater mass balance efficiency and bed lifespan. Halogenated compounds cause severe catalyst poisoning and overhead hardware corrosion, demanding pre-treatment guard beds. High iron or silicon levels form foulant crusts, increasing pressure drop across reactor beds.