A comprehensive review on process and engineering aspects of pharmaceutical wet granulation

The spouted bed technique is an alternative to fluidization for handling particulate solids that are too coarse and uniform in size for good fluidization. Although the areas of application of spouted beds overlap with those of fluidized beds, the flow mechanisms in the two cases are very different. Agitation of particles in a spouted bed is caused by a steady axial jet and is regular and cyclic, as distinct from the more random and complex particle flow patterns in fluidized beds.

Spouting of Particulate Solids

Jianfeng LiSchool of Chemical Engineering, Purdue University, West Lafayette, IN 47907Ben FreireichSchool of Mechanical Engineering, Purdue University, West Lafayette, IN 47907Carl WassgrenSchool of Mechanical Engineering, Purdue University, West Lafayette, IN 47907Dept. of Industrial Physical Pharmacy, Purdue University, West Lafayette, IN 47907James D. LitsterSchool of Chemical Engineering, Purdue University, West Lafayette, IN 47907Dept. of Industrial Physical Pharmacy, Purdue University, West Lafayette, IN 47907DOI 10.1002/aic.12678Published online June 14, 2011 in Wiley Online Library (wileyonlinelibrary.com).In this work, a general multidimensional population balance (PB) model is developed topredict the coating volume distribution on polydisperse particles as a function of time duringparticle coating in a paddle mixer. The model adopts a compartmental approach to accountforcoatingvariationcausedbyparticleﬂowheterogeneity.Simulationsshowthatforarealis-tic range of seed particle size polydispersity and coating mass applied, the coating volumedistribution depends on the growth rate exponent and seed particle size distribute on, with thecoating volume coefﬁcient of variance (CoV) approaching an asymptotic value as the coat-ing-to-particle volume ratio increases. These effects cannot be predicted by simpler one-dimensional models. However, the full two-dimensional PB and simpler one-dimensionalmodels such as Mann’s equation do predict similar sensitivity of coating volume CoV to thevariation in the compartment model parameters, i.e., to changes in the particle mixing beha-viorinthe vessel.

A general compartment-based population balance model for particle coating and layered granulation

The aim of this work was to analyze the influences of operational variables on particle growth for urea coating in a conventional spouted bed (CSB). An aqueous polymeric suspension was the coating liquid sprayed on the spouted particles. The effects of inlet air temperature, coating suspension flow rate and atomizing air pressure on particle growth were analyzed by a central composite rotatable design (CCRD) of experiments. The results showed particle growth in the range of 1.1–2.6%, therefore, some results below the expected for a film coating (2–8%). A second-order polynomial model was obtained for estimating particle growth as a function of the statistically significant variables: air temperature, suspension flow rate and atomizing air pressure, with percentage of explained variation R2 = 90.72%. The urea growth kinetics during coating was analyzed for the optimal operating condition and a linear growth coefficient of 1.13 × 10−3 min−1 was obtained. The volatilization analyses showed that the polymer film coating provided a decrease of the nitrogen loss in the range of 3–57%. And, SEM analyses demonstrated a total, uniform and homogeneous covering of the urea particles surface.

A. Kmieć

Papers

Kinetics of granulation process during coating of tablets in a spouted bed