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Title: Dispersion of a highly viscous surfactant binder in a high shear batch mixer for detergent granulation
Author: Balashanmugam, Menan
ISNI:       0000 0004 6058 6613
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2017
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A key difference in detergent granulation, compared to most granulation processes conducted in the pharmaceutical and food industries is the high viscosity of the surfactant binder. These surfactants are approximately ×104 more viscous than water and this makes handling the substance a challenge. Previous studies have primarily focused on systems using liquid binders that are of a lower viscosity. This research aims to understand the initial dispersion of a highly viscous, semi or soft-solid binder (surfactant) in a high shear wet agglomeration process. Experiments were conducted with a view to outlining a mechanism for binder dispersion, which involves the breakup of lumps of binder, as a result of the mechanical action of the impeller and the powder bed. The mechanistic understanding was subsequently used to create and validate a model that describes binder breakage. Another key deliverable of this research was to develop a technique for monitoring the dispersion of a binder in situ. The influence of the method of binder delivery on granule attributes such as size, binder content and granule strength were investigated in a vertical shaft 10 L high shear granulator. A typical powdered detergent formulation was used for this study, and consists of a mixture of surfactant (binder), zeolite (powder) and soda ash (powder). The binder was either injected (as a continuous stream) or preloaded into the mixer (as one large blob). Varying the method of binder delivery changes both the rate of binder addition and initial size of the semi-solid binder. At low to moderate agitation intensities, the results suggest that injection improves initial dispersion and subsequent distribution of binder in a moving bed of powder. In order to develop a mechanistic understanding of the binder dispersion process, small scale experiments were conducted in a 100 ml high shear mixer (this equipment is a scaled down replica of the 10 L high shear mixer). This is the first study to introduce the concept of "breakage" of lumps of binder, during its initial dispersion. In other words, binder dispersion occurs when lumps of binder get coated with powder and are subsequently broken up within the mixer. The coated lumps of binder are referred to as powder coated binder particles (PCBPs). Scaling down the operation enables binder breakage to be monitored in more detail. These PCBPs undergo a size reduction process. Experiments were conducted using zeolite and soda ash (of two different sizes), and the mixer was operated at different speeds. Results reveal that larger and rougher primary particles disperse the binder more effectively in a moving bed of powder, and also a high impeller speed is required for better initial dispersion of the binder into powder formulations that consist of a large proportion of fine material. A population balance model that describes the breakage of the semi-solid binder was also developed. The model predicts the change in the length of the binder particles, as a function of time. Other features of the model include a selection function for the binder particles based on their initial length (larger binder particles are more likely to undergo breakage than smaller ones). There are two parameters which could be changed in the model: the initial length of the parent binder particle and the selection constant. The analytical solution to the population balance equation indicates that the variation in the size distribution is self-similar with time. It was also found that the mean length of the PCBPs predicted using the model is in good agreement with the experimentally determined mean length. A population balance model, coupled with a kinetics approach has, therefore, been used to successfully describe the binder dispersion (breakage) process. This is the first study to also introduce a non-invasive technique (thermal imaging) for online monitoring of binder dispersion in a moving bed of powder. Experiments were conducted in a 10 L high shear mixer and a pilot scale 32 L paddle mixer. Thermal imaging was used to study the influence of the method of binder delivery on its subsequent dispersion for a non-reactive system. Results suggest injecting the binder leads to a more rapid and even distribution throughout the powder bed. The thermal imaging technique was also used to understand binder dispersion in a reactive granulation process. The exothermic reaction between the acidic binder and basic powder produces a heat signature that could be traced. The effect of particle size and impeller speed on the dispersion of the reactive binder was monitored and the results suggest that larger particles disperse the binder more evenly, and higher impeller speeds promote improved dispersion too.
Supervisor: Salman, Agba D. ; Hounslow, Michael J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available