{"id":11646,"date":"2026-10-19T14:59:20","date_gmt":"2026-10-19T14:59:20","guid":{"rendered":"https:\/\/nantek.es\/mass-balance-chemical-recycling\/"},"modified":"2026-10-19T15:05:13","modified_gmt":"2026-10-19T15:05:13","slug":"mass-balance-chemical-recycling","status":"publish","type":"post","link":"https:\/\/nantek.es\/en\/mass-balance-chemical-recycling\/","title":{"rendered":"Mass balance in chemical recycling: how it works"},"content":{"rendered":"

Mass balance<\/strong> is the accounting method that makes it possible to attribute recycled content to a new plastic when pyrolysis oil has been processed mixed with fossil feedstock and can no longer be separated. It does not track molecules but quantities: what goes in as plastic waste is allocated, under rules and audits, to what comes out. Since July 2026 the EU has had its own rules for doing this in PET bottles, and the PPWR is preparing its own for all other packaging.<\/p>\n

Why chemical recycling needs mass balance<\/h2>\n

In mechanical recycling, recycled flake can be physically traced through to the bottle or film. In chemical recycling<\/a> that is not possible.<\/p>\n

Pyrolysis oil enters a steam cracker together with fossil naphtha. Both streams mix, are broken down into small molecules such as ethylene and propylene, and leave through the same pipes. Nobody can say which molecule comes from waste and which from crude oil.<\/p>\n

Mass balance records how much recycled material has gone in, deducts losses and shares that quantity out among the outputs. The basic logic and the steps for certifying a plant are covered in ISCC PLUS and environmental credits<\/a>. Here we go further: chain of custody, attribution and EU regulation.<\/p>\n

The five chain of custody models under ISO 22095<\/h2>\n

ISO 22095:2020 ranks chain of custody models by how physically present the claimed characteristic is, in this case recycled origin. January 2026 saw the publication of ISO 22095-2:2026, devoted solely to mass balance: geographical and time boundaries, conversion factors, the average percentage method and the credit method, and communication rules.<\/p>\n\n\n\n\n\n\n\n\n\n
Model<\/th>\nHow it works<\/th>\nPhysical link to the waste<\/th>\nFit with chemical recycling<\/th>\n<\/tr>\n<\/thead>\n
Identity preservation<\/td>\nSeparate material from a specific source, batch by batch<\/td>\nFull<\/td>\nImpractical in a cracker<\/td>\n<\/tr>\n
Segregation<\/td>\nOnly mixed with other certified material<\/td>\nFull<\/td>\nRequires dedicated units<\/td>\n<\/tr>\n
Controlled blending<\/td>\nBlend in a known proportion carried by each product<\/td>\nProportional in each product<\/td>\nPossible in simple stages<\/td>\n<\/tr>\n
Mass balance<\/td>\nPhysical mixing; accounting allocation never exceeding what went in<\/td>\nIn the system, not in each product<\/td>\nThe usual model<\/td>\n<\/tr>\n
Book and claim<\/td>\nCertificates decoupled from the product<\/td>\nNone<\/td>\nDoes not demonstrate recycled content<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

ISCC PLUS accepts physical segregation, controlled blending and mass balance, and within the latter it distinguishes between the rolling average percentage and the credit method. Only controlled blending allows a physical percentage of recycled content in the product to be claimed.<\/p>\n

Attribution rules: where the debate lies<\/h2>\n

Mass balance tells you how much recycled material there is. Attribution decides which products it is allocated to. A cracker produces polymers, chemicals, fuels and losses, and the rule chosen makes a big difference to the content each one can claim.<\/p>\n

Proportional attribution<\/h3>\n

All outputs receive the recycled percentage of the input mix, fuel included. It is the simplest and least disputed rule, but it dilutes the recycled content into products that are not plastic.<\/p>\n

Free or credit-based attribution<\/h3>\n

Recycled content is freely allocated to any output, within certain limits. It is the most flexible rule and the most criticised, because it can assign recycled content to a polymer even when part of the waste has ended up as fuel.<\/p>\n

Fuel-use excluded (fuel-exempt)<\/h3>\n

Whatever ends up as fuel or as loss is deducted, and the rest is shared among the outputs that remain materials. It is consistent with the legal definition of recycling, which excludes energy recovery.<\/p>\n

Polymers only<\/h3>\n

Only polymers can receive recycled content; chemicals and fuels are left out. It is the most restrictive rule, advocated by part of the mechanical recycling sector and by some NGOs.<\/p>\n

The ISCC PLUS mass balance guidance, published for consultation in December 2025, covers free attribution, fuel exemption, proportional attribution and “trace-the-atom”, and leaves the detailed fuel-exemption rules until legislation is settled.<\/p>\n

What the EU has decided: Implementing Decision (EU) 2026\/1425<\/h2>\n

Directive (EU) 2019\/904 on single-use plastics requires 25 % recycled plastic in PET beverage bottles from 2025 and 30 % in all plastic bottles from 2030. On 30 June 2026 the Commission adopted Implementing Decision (EU) 2026\/1425, in force since 23 July 2026. It replaces Decision 2023\/2683 and lays down, for the first time, how to calculate and verify recycled content obtained through chemical recycling. Its key points:<\/p>\n