(473f) Packed Bed Reactor for Continuous Enzymatic Ring Opening Polymerization of Lactones

Enzymatic Ring-opening Polymerization of lactones permits the production of polylactones at atmospheric pressures, low temperatures, and without the use of toxic tin catalyst. Because of these attributes this polymerization process has often been regarded as a more environmentally friendly route to the production of polyesters as compared to classical condensation chemistry. Enzymatic polymerizations however suffer from low reaction rates and as a result require the use of high supported catalyst loadings (10 wt% vs. monomer) in batch processes. Further increases in the catalyst concentrations add cost to the process, reduce batch throughput, and further complicate the downstream catalyst-product separation step given the economic need to recover and re-use the catalyst. When we examine these challenges closely we note that the separation step itself markedly deteriorates the environmental benefits of enzymatic polymerization over condensation polymerization. Large volumes of solvent are required to dilute the viscous reaction product sufficiently to permit filtration for catalyst recovery. To overcome this challenge we examined a number of possible reactor technologies and specifically studied the use of packed-bed continuous reactors to replace the batch process. Monomer solutions are fed through the reactor to produce, at the bed's exit, a catalyst-free polymer product. In addition, because of the higher enzyme concentrations in the packed-bed, reaction rates observed with this reactor configuration are substantially higher than those observed in batch. This permits the high throughput production of polymers and intensified experimentation at the small scale. As a result of this successful technology the sustainability of the enzymatic polymerization process has been greatly improved allowing the production of a wide range of co-polymers with 0.5% of the catalyst and 20% of the solvent originally used in the batch process.