Chemical Engineering Journal 145 (2009) 505–513 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Exploring the regime map for high-shear mixer granulation Wei-Da Tu a , Andy Ingram b , Jonathan Seville c , Shu-San Hsiau a,∗ a Department of Mechanical Engineering, National Central University, Taiwan 32001, R.O.C b Centre for Formulation Engineering, Department of Chemical Engineering, University of Birmingham, Birmingham B15 2TT, UK c School of Engineering, University of Warwick, Coventry CV4 7AL, UK article info Article history: Received 21 March 2008 Received in revised form 11 September 2008 Accepted 23 September 2008 Keywords: Granule size distribution GSD High-shear mixer Growth behaviour Regime map Sieving Agglomeration abstract The aim of this study was to investigate the applicability of the regime map approach proposed by Lit- ster/Iveson and co-workers [S.M. Iveson, J.D. Litster, Growth regime map for liquid-bound granules, AIChE Journal 44 (1998) 1510–1518; S.M. Iveson, P.A.L. Wauters, S. Forrest, J.D. Litster, G.M.H. Meesters, B. Scarlett, Growth regime map for liquid-bound granules: further development and experimental validation, Powder Technology 117 (2001) 83–97] over the whole parameter range, for a given material and agglomeration method. Agglomeration behaviour in a high-shear mixer granulator was investigated and categorised using the evolution of granule size distribution (GSD). MCC 102 (Microcrystalline cellulose, Avicel 102) and aqueous PEG 6k (Polyethylene Glycol 6000) were employed as solid and liquid materials. Different operating conditions were applied by changing impeller speeds and L/S (liquid-to-solid) ratios (weight of liquid/weight of solid). 12 representative settings were selected and typical agglomeration behaviours were identified, forming a regime map for the system. The effect of impeller speed was found to depend on the L/S ratio, very little effect being seen at low L/S ratio (L/S = 85/150), but much more effect at higher binder ratios. In general, the effect of L/S ratio is of paramount importance in these systems and usually determines the growth behaviour. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Wet agglomeration is a widely applied process in which fine par- ticles are combined to form larger, more easily handled, granules by mixing with a suitable binder. It is a fundamental technique for many industries, particularly pharmaceutical materials handling, mining processes and advanced materials processing, because it can greatly influence the granule properties. For example, in catal- ysis/absorbents industry, high-shear granulation is used to modify the properties of products (strength, attrition resistance, porosity, and surface area) and thereby to control the efficiency of a chemical reaction [3]. In the pharmaceutical industry, Lee and his co-workers [4,5] have also revealed correlations between drug dissolution rate and the properties of granules (Carr’s index, mixing index, surface area, and particle size distribution) in wet granulation. There are, however, many operating variables and these interact with each other, leading to complex behaviour and it is often a challenge to manufacture products consistently to specification [3,6,7]. There- fore a better understanding of granulation mechanisms is required ∗ Corresponding author. Tel.: +886 3 426 7341; fax: +886 3 425 4501. E-mail address: sshsiau@cc.ncu.edu.tw (S.-S. Hsiau). for predicting growth behaviour, as well as to achieve optimal con- trol. Since 1998, work has been directed to produce regime maps that describe and enable prediction of granule growth in equipment such as rotating drums and high-shear mixers [1,2,8]. These maps show how growth behaviour (changing rate of growth with time) is determined by the work done to deform the granules relative to their deformability (characterized by a Stokes deformation number (St def )) and the maximum saturation states of granules (character- ized by the maximum pore saturation (S max )). The map from Litster et al. [1,2,8], shown in Fig. 1, identifies four classes of agglomeration growth behaviour: nucleation, steady growth, induction and rapid growth. Nucleation occurs when the binder is brought into contact with a powder bed and granule nuclei are formed, but there is not enough binder to promote further growth. With more binder addi- tion, granules will start to grow and the rate of growth will depend on the deformability of the granules and/or the rate of work done. At the start of granulation, binder tends to get trapped in pockets within granules. The key to growth is redistribution of binder to the surface so that granules can stick together. If the granules are weak or deformable then the process of redistribution is rapid and gran- ules tend to grow immediately and at a steady rate (steady growth). With stronger granules, or less powerful agglomeration processes, 1385-8947/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2008.09.033