(494h) On the Dynamic Behaviour of Industrial Plant for the Production of PLA By Ring-Opening Polymerization of Lactides

Due to increasing importance of sustainability of petrochemical based polymers in the market, polymers from renewable resources have obtained large interest from both academia and industrial sides.[1,2] One of the most successful biopolymers to replace petroleum-based polymers currently is polylactic acid (PLA). Sulzer has developed a continuous process for the ring opening polymerization (ROP) of lactide (LT) to high molecular weight PLA, suitable for the production of polymer grades with tailor-made properties. In cooperation with Purac Biochem, various PLA grades for applications such as packaging, fiber spinning and injection molding have been developed.

In the first part of this work, the concept of the Sulzer polymerization process is discussed. The reaction is carried out in a loop reactor followed by a plug-flow section [3]. Both sections are built using Sulzer's proprietary equipments, i.e. static mixers and heat exchangers, that ensure cross-sectional homogeneity of the reacting mixture and high heat transfer efficiency, which are fundamental for the production of thermo-sensitive polymers. Finally, after the reaction section, a multi-stage devolatilization section is applied to remove unreacted monomer from the final product in order to reach the requirements for residual volatiles.

In the second part, the mathematical model used for the industrial plant design is described and model predictions are compared with experimental data collected on plants with different production scales for monomer conversion, polymer molecular weight and pressure drops. In particular, the model consist of a kinetic model proposed in the literature[4], which accounts for the impact of acid impurities, alcohol and catalyst on the reaction kinetics, a viscosity model, accounting for temperature, shear rate and polymer molecular weight dependence, and heat transfer equations.

Finally, the dynamic behaviour of different plant configurations is discussed.

Literature

[1] A. Gandini, Macromolecules, 41, 9491-9504, 2008.

[2] Bioplastics, 6, 22-25, 5/2011.

[3] N. K. Tien, E. Flashel, A. Renken, Chem. Eng. Commun, 36, 251-267, 1984.

[4] Y. Yu, G. Storti, M. Morbidelli, Ind.&Eng. Chem. Res., 50, 7927-7940, 2011.