Scale-up of the enzymatic polymerization of polyesters

The aim of the ACTPAC project is to completely transform plastic waste into valuable materials like polyesters, taking this path all the way from academic research to industrial scale. Scaling-up from laboratory scale toward industrially relevant production is always a challenging task, as multiple parameters must be taken into consideration. In this article, we focus on the enzymatic production of polyesters from different diols and diacids obtained within the project.

The scale-up process will take the development from TRL 3-4 to TRL 5, using a 10 L reactor where critical parameters will be optimized to maximize degree of polymerization, yield, and purity. The resulting polyesters will then be characterized to ensure performance metrics suitable for further scaling at TRL 6.

Immobilized Candida antarctica lipase B is the enzyme that catalyses polyester formation via polycondensation. This biocatalytic route proceeds under relatively mild temperature and pressure compared with conventional metal-catalysed methods, reducing side reactions and avoiding toxic catalysts. This approach works well for a broad range of aliphatic monomers (diols and diacids), producing polyesters with molecular weights that can span from low oligomers up to tens of thousands of g/mol depending on conditions.

When transitioning from small-scale to a 10 L reactor, several critical parameters require careful control. First, it is essential to balance catalytic activity with enzyme stability to avoid enzyme deactivation. Also, due to the equilibrium of the reaction, water must be removed from the reaction mass using controlled vacuum or reduced pressure. The reactor design and procedures at 10 L scale will provide a robust basis for larger reactors (TRL-6), where reaction times, mixing and heat transfer effects become even more pronounced.