Most products we hold in our hands, consume and dispose of are the result of complex chemical manufacturing processes that combine a variety of different materials. The input ranges from distinct fossil-based to emerging non-conventional feedstock that include bio-based, renewable and recycled materials and can substitute fossil-based resources. While we see more products claiming 100% bio-based or recycled content on the market, the volume of fossil-based materials continues to surpass the amount of more sustainable alternatives in other applications. Still, they are gradually becoming substituted by less carbon-intense and sustainable alternatives. For a good reason.

Driven by legislation, individual corporate commitments and consumer awareness, the shift to a circular economy and bioeconomy is gaining ever more momentum and has turned into a priority across industries. The petrochemical industry, one of the largest industries relying primarily on fossil-based oil and gas globally, is a key player in this transition. Aiming to scale up the use of recycled and bio-based materials and track those as they move along the value chain, chemical companies increasingly add recycled or bio-based feedstock to the manufacturing process and apply a stringent chain of custody option. 

To demonstrate compliance with recognised certification systems, many companies opt for third-party certification for the applied chain of custody model and source certified materials. Based on certified biomass that meets distinct sustainability criteria, renewable resources, waste or residues, certified feedstock can help decouple production from fossil-based resources. Hereafter, we will refer to certified materials or feedstock, regardless of their origin. 

The chain of custody model prevailing today in the chemical industry is mass balance. It is a  proven method that helps gradually grow the share of certified materials in existing infrastructures. Moreover, it makes it possible to reflect the ratio of certified materials attributed to the manufactured product and eventually making credible claims on the finished goods. 

The rationale behind mass balance

In chemical production processes, input materials of different origins and characteristics, such as certified recycled materials and fossil feedstocks, are often mixed. That is particularly the case in industries with assets with complex manufacturing processes where certified and non-certified materials cannot be processed in separate production lines.

Mixing inputs requires companies to state the share of certified materials incorporated in the end product. Unfortunately, the amount of certified materials entering the chemical process is still low and so is its physical share in the finished product. This leaves little room for incentives to increase the use of certified feedstocks. Fortunately, mass balance can help. 

Mass balance provides manufacturers with a methodology to track the certified materials as they move along the value chain and attribute the inputs of a production process, like certified recycled plastic, to outputs of that production process through certified bookkeeping. Although the material’s physical features are mixed and cannot be told apart within the mix anymore, their sustainability and GHG emission data remain assigned to the batches of materials in the bookkeeping. 

This distinct accounting method verifies that the certified feedstock has replaced an equivalent quantity of fossil raw materials at the beginning of the supply chain and can be attributed to the product-to-be-sold, ensuring that both input and output are balanced. 

A set of rules governing mass balance

The attribution underlies generally applicable and robust rules. Developed by third-party multi-stakeholder certification systems these proven and robust rules ensure the methodology is applied in a correct and reliable way. They define how to get from input to an equivalent share of outputs taking the production process into account and require the application of conversion factors to take process losses into account. Applying this set of rules in mass balance, allows brand owners and the industry to make transparent and credible on and off-product claims.  

In practice

Let’s take an example to see how mass balance works. Imagine 70% of fossil-based (700 kg) and 30% (300 kg) of certified recycled feedstock are mixed in a processing unit. The operator of the processing unit conducts the first mass-balance, deduces processes losses, and supplies a certain volume of the mixture to a polyolefin producer. Although the polyolefin producer receives mass-balanced materials, it is not guaranteed that the certified recycled materials attributed to his batch are “physically” there. However, the polyolefin manufacturer attributes the certified feedstock to his outputs in the bookkeeping. In the next processing step, a converter turns the mass-balanced materials into one metric ton of finished goods. Considering processes losses of 10%, for instance, the converter could claim 270 kg of the output as linked to 100% certified recycled feedstock based on the mass balance approach. Alternatively, 540 kg of output could be claimed as linked to 50% certified materials. We cannot say for certain that the finished good in our hands physically contains certified recycled content. What is evident is that the certified input has substituted fossil resources at the beginning of the supply chain and contributed to bringing more circularity to the process.

Benefits at a glance

Mass balance comes with a myriad of advantages that benefit all participants across the value chain and boosts recycling rates. First and foremost, it helps gradually leverage non-conventional feedstock in existing infrastructures and supply chains. Chemical companies aiming to incorporate non-conventional feedstock into their products can flexibly feed the desired volumes into their processes and keep the different feedstock separate through detailed accounting. This makes investment in new infrastructure or the building of entirely new production lines redundant, increases incentives to incorporate non-conventional feedstock and enables large-scale operations to transition to more sustainable operations. 

One of the concept’s core tasks is tracing materials through the supply chain and multiple processing steps to bring greater transparency to global supply chains. Moreover, the concept finds widespread use as complementary concept in chemical plastic recycling processes. When mechanical recycling reaches its limits in plastic recycling, chemical recycling is the complementary go-to-process to prevent a loss of recyclable materials. It enables the recycling of hard-to-recycle products and brings high-quality recyclates, including those suitable for food-contact applications, back into the economy. Employing the mass balance approach, companies downstream chemical recycling are given a means to increase recycling rates, verify the use of certified recycled content and thereby meet recycled content targets.   

The role of certification

Certifications take on an imperative role in supply chain traceability and leveraging the use of non-conventional raw materials. ISCC, as one of the leading multi-stakeholder sustainability and carbon certification systems, certifies various non-conventional feedstocks, mechanical and chemical recycling processes and different chain of custody options based on the standards set out in its ISCC PLUS system. As it stands, it is a system of choice in non-regulated markets, but is expected to find application in distinct regulated markets and will undergo further development based on global market trends. Providing full transparency along the value chain, it allows brand owners to make credible claims about their product’s contribution to the circular or bioeconomy.  

A key lever for circularity

Mass balance is an enabler for transitioning to a bio- and circular economy. As a cost-efficient solution, it is a means to scale up the volumes of recycled and bio-based materials used alongside fossil feedstock and to gradually phase out primary resource use in chemical production processes. If applied widely, mass balance can be a key lever to accelerate the substitution of fossil raw materials and scale-up recycling within existing infrastructures.