Improving bench scale pilot reactor design for polymerisation of green CO2-polymers

Abstract

Plastic has become the most common material since the beginning of the 20th century and has become almost indispensable due to its durability, light weight and low costs. However, some of the characteristics also make the plastic problematic when it comes to the end of its life phase. Norner Research AS, a polymer research institute performing extensive independent or funded research in the plastic value chain from process technology to final product and application, has during the last ten years been active in developing biodegradable green plastic that can replace up to 40% of the fossil raw materials with industrial captured CO2. The green plastic, poly(propylene carbonate) (PPC), is produced by reacting propylene oxide (PO) with CO2. The aim of this paper is to study the effect of static mixer on production of PPC and improve the catalytic process by reducing the reaction time and increasing the yield. The process includes multiphase gas-liquid flow, and good mixing is one of the key factors to succeed in improving the process. The flow behavior of the components in the multi-phase bench scale reactor is studied in order to investigate the potential of reducing the reaction time by using static mixers to increase mass transfer. A static mixer is a device for the continuous mixing of fluids, and can be used to mix liquids, gases or to mix a gas into a liquid. The energy needed for mixing comes from a loss in pressure as the fluids flow through the static mixer. Computational fluid dynamic (CFD) is an important tool in order to simulate and optimize the polymerization process. In this study, the CFD software Ansys/Fluent is used to investigate the multiphase flow through the static mixer. The static mixer is simulated to study the effect on the gas-liquid mixing. The simulations were performed with mixtures of 17% and 34% PPC in PO under CO2 pressure. The simulations showed that the required number of mixing elements (L) to obtain a uniform mixing of CO2, PO and PPC in the liquid phase is estimated to be 6.5L for the 17% PPC case and 5.25L for the 34% PPC case. Consequently, using more than the required number of mixing elements would increase the pressure drop without increasing the mixing. It was observed that the required mixer length decreased when the composition of PPC in the inlet liquid phase was increased from 17% to 34%.