Comparative performance of in-line rotor-stators for deagglomeration processes

Abstract

In-line rotor-stators are used for a wide range of power intensive dispersion applications, including the breakup of immiscible liquid droplets or agglomerates. This study, performed within the DOMINO project at BHR Group, aimed at studying the performance of three different rotor-stator head designs for deagglomeration processes. A given test system, nanoscale silica particles-in-water, was used to identify the mechanism and kinetics of break-up and determine the smallest attainable size. Three rotorstator head designs used were the GPDH-SQHS and EMSC screens from Silverson and Ytron Z-Lab from Ytron. These in-line rotor-stators were used in the recirculation loop of a stirred tank with a total dispersion volume of 100 litres. Power input and residence time were varied by changing the rotor speed and dispersion flow rate. Breakup was found to occur through erosion regardless of the operating conditions or rotor-stator design. The smallest fragments obtained were aggregates, rather than primary particles, and these were of a mean diameter of 150-200 nm; also independent of the operating conditions or rotor-stator head design. With a given rotor-stator operated at a given flow rate, increasing the rotor speed and hence the power input increased the break up kinetics. For a given design at a given specific power input, whilst the break up rate per tank turnover decreased when the flow rate was increased, the total processing time could be reduced. There were differences in the volume of the mixer head and chamber volumes; in addition, a smaller flow rate range could be covered with the Ytron design. Comparison of the different designs was therefore not straightforward. It could however be shown that the rotor-stator designs with a high number and small size of holes and/or gaps have a faster break up rate.

Dispersion of clusters of nanoscale silica particles using batch rotor-stators

“…In addition to the evolution of the Sauter mean diameters of fines and coarse material, rates of fines generation and size reduction of coarse material are presented and discussed in the following Sections. It is also in agreement with findings using in-line rotor-stators with this particle-liquid pair (Özcan-Taşkın, 2009(Özcan-Taşkın, , 2016.…”

“…This overall trend of rotor-stator designs with smaller holes or narrower gaps having a higher break up kinetics was also reported by Özcan-Taşkın et al (2016) for different in-line rotorstator designs.…”

“…Different process devices used for the purpose include the stirred bead mill (Stenger et al, 2005;Kowalski et al, 2008;Schilde et al, 2010), ultrasonic dispersers (Baldyga et al, 2008b(Baldyga et al, , 2009Quarch et al, 2010) in-line rotor-stators (Baldyga et al, 2008a;Padron et al, 2008;Özcan-Taşkın et al, 2016), a batch rotor-stator or high pressure devices (Sauter and Schuchmann, 2007;Seekkuarachchi et al, 2008 andXie et al, 2008). Local energy dissipation rate in these devices, responsible for the breakup of agglomerates, can be orders of magnitude higher than the average energy dissipation rate.…”

Particle de-agglomeration with an in-line rotor-stator mixer at different solids loadings and viscosities

“…Therefore, they are used in applications that require high levels of local energy dissipation, such as liquid-liquid dispersions (Carrillo De Hert and Rodgers, 2017;Håkansson et al, 2016;Jasińska and Bałdyga, 2017;O'Sullivan et al, 2018), de-agglomeration of particles (Bałdyga et al, 2008a;Özcan-Taşkın et al, 2016;Padron et al, 2008), chemical reactions (Bałdyga et al, 2007;Jasińska et al, 2016). These devices have attracted more attention in the recent decades with more focus on the flow field in the mixer head and\or solid-liquid and liquid-liquid dispersion processes through both experimental (Padron et al, 2008;Özcan-Taşkin et al, 2011;Hall et al, 2013;O'Sullivan et al, 2017) and numerical studies (Orciuch et al, 2006;Bałdyga et al, 2008b;Özcan-Taşkın, et al 2011;Hakansson and Innings, 2017;Zhang et al, 2017).…”

“…The deagglomeration of nanoscale silica particle clusters was reported in a comparative study using three rotor-stator head designs for a dilute system: 1% wt. Aerosil ® 200V in water (Özcan-Taşkın et al, 2016). As higher solid concentrations are of more interest in industrial practice due to the advantages of preparing a master batch, or the products may have a higher viscosity continuous phase, this study has been conducted to establish the effects of solids loading (up to 15%wt) in water and continuous phase viscosity (up to 100 mPa•s) for 1%wt particle concentration.…”