Scale-up of continuous microcapsule production

Abstract

The objective of this work is to establish an experimental approach to scale-up the production of melamine formaldehyde (MF) microcapsules from a batch lab-scale to a pilot-scale inline rotor stator mixer (RSM). The inline RSM is operated in a continuous recycle mode, allowing multiple passes of the emulsion through the intensive mixing zone during continuous production. The liquid is continuously recirculated directly to the RSM, without a holding vessel, as is the case in conventional batch recirculation emulsification. The setup is operated at feed flow rates of 0.24 kg/h - 20 kg/h. Parameters including the Weber number, tip speed and energy density are investigated to correlate the mean capsule size of the batch and flow process. Rotational speeds range from 3000 to 26,000 rpm. The dimensionless maximum diameter correlated well with the Weber number to the power -0.4, for both devices operated at the same residence time. Volume and number based mean diameters showed little influence of the feed flow rate in the continuous recycle mode of operation. This inline RSM setup is therefore an ideal tool to optimize emulsification processes at lab scale and increase production by increasing the feed flow rate, while maintaining rotor-stator geometry.