Our team produced a detailed design of a chemical process to produce medical-grade polycaprolactone (PCL) on a large scale. These include the constraints on the project as well as decisions about reactor type, catalyst system, and separation methods. Engineering considerations, market factors, and design norms all influenced the results of this report. The medical grade polycaprolactone will be sold for $410 per kg, an economically profitable rate with an internal rate of return of 78% over 20 years.
A batch reactor was chosen carry out the polymerization reaction of the monomer caprolactone to PCL, because the PCL product needs a molecular weight of 75,000 g/mol, which translates into a viscosity of approximately 3×106 cP at the reaction temperature. Batch reactors are typically best for slow, highly viscous reaction systems. To reduce costs and promote stewardship of resources, the team designed the separations process to be continuous, thus eliminating most startup energy use for the separation units. Holding tanks were designed to join the batch reactor to the continuous separations process.
The primary use of the polycaprolactone will be in PCL-bioactive-glass composite, which can be used in medical procedures such as bone or cartilage repair. As a result, the biocompatibility and purity of the product was of utmost importance. Phenyllithium was determined to be the optimum initiator, for a system in which neither a solvent nor a traditional catalyst was needed. Separation and solidification methods included adsorption, falling strand devolatilization, extrusion, cooling, and pelletizing.