(167a) Population Balance Equation Modeling of Emulsion Drop Breakage and Coalescence in High Pressure Homogenization

Previously we have developed population balance equation (PBE) models of drop breakage in oil-in-water emulsions prepared with high pressure homogenization (Raikar et al., 2009; Raikar et al., 2010). These models were based on the assumption of negligible drop coalescence, which is reasonable for emulsions with low dispersed phase volume fractions and high surfactant loadings. However, many industrial emulsions do not satisfy these conditions and drop coalescence must be understood for rational emulsion design and processing. Other researchers have proposed inverse PBE methods for the extraction of the coalescence kernel from transient drop distribution measurements. The major shortcoming of inverse methods and many other PBE modeling techniques is that the coalescence functions do not depend explicitly on formulation and processing variables. Such coalescence kernels have limited predictive capabilities as the PBE model must be refit to each new set of experimental data in which formulation and/or processing variables were changed.

In this contribution, we demonstrate that drop distribution data from a high pressure homogenizer can be used to identify drop coalescence functions. Collision frequency and coalescence efficiency functions that depend explicitly on emulsion properties (interfacial tension and disperse phase volume fraction, density, and viscosity) and the homogenization pressure were considered. Drop volume distribution measurements for multiple homogenization passes were used to estimate adjustable parameters in the drop breakage and coalescence functions using nonlinear parameter estimation. We evaluated the ability of the PBE model to predict experimental results not used for parameter estimation by varying the homogenization pressure and the oil and surfactant concentrations. The resulting model yielded quantitatively accurate predictions over a wide range of operating conditions and provides a basis for model-based emulsion design.

Raikar N.B., Bhatia S.R., Malone M.F. and Henson M.A, ?Experimental Studies and Population Balance Equation Models for Breakage Prediction of Emulsion Drop Size Distributions?, Chemical Engineering Science, 64 (2009), 2433-2447.

Raikar N.B., Bhatia S.R., Malone M.F., McClements D.J., Almeida-Rivera C., Bongers P. and Henson M.A., ?Prediction of emulsion drop size distribution with population balance equation models of multiple drop breakage?,Colloids and surfaces A: Physicochemical and engineering Aspects, doi: 10.1016/j.colsurfa.2010.03.020