20. Polymerization in Sprays: Atomization and Product Design of Reactive Polymer Solutions

The focus of this novel process is to polymerize a water-based solution in a spray with a conventional spray dryer to produce powder polymers. To achieve a successful process design, this project aims at the atomization of water-based polymer solutions, a novel device to measure reactivity and the design of a pre-reaction nozzle. To overcome the short residence time in a spray dryer a pre-reaction is necessary. It is done within the nozzle, which can be described as a combination of a laminar pipe reactor with a variable length and a twin-fluid nozzle in a lance shape in order to place it easily in a spray dryer. A model to optimize the progress of polymerization within the nozzle is based on kinetics from literature and a viscosity approach. That is made with the help of the novel measurement and the theory of rheokinetics. The increase of viscosity is dependent on the progress of chain growing and the conversion, respectively. A power law is presented to describe the viscosity with changing conversion at a constant initiator ratio. Another important aspect of optimizing the pre-reaction is the influence of the viscosity on the atomization. Investigations show the strong dependency of the molecular weight of the polymer on the drop formation because of its influence on the rheology of the solution. Sprays of different polymer water mixtures are measured by laser diffraction and a two parameter model, RRSB, is successfully used to describe the drop size distribution. The influence of the Sauter mean diameter \( {\overline{x}}_{1;2} \) is only able to be discussed if it is calculated by the RRSB fit. With increasing mass fractions of the high molecular weight polymer a turning point from drop to ligament formation is shown at low shear viscosity compared to lower molecular weight polymers. Finally a laboratory plant is presented that is producing polymer powders in one, but complex, process.