Available online at www.sciencedirect.com Chemical Engineering and Processing 47 (2008) 2238–2246 Effect of process variables on fluiddynamics and adhesion efficiency during spouted bed coating of hard gelatine capsules Gilmarcio Z. Martins, Claudia R.F. Souza, Tumuluru J. Shankar, Wanderley P. Oliveira ∗ Faculdade de Ciˆ encias Farmacˆ euticas de Ribeir ˜ ao Preto, Universidade de S˜ ao Paulo Av. do Caf´ e s/no, Bl. Q, Bairro Monte Alegre, Ribeir˜ ao Preto, SP 14040-903, Brazil Received 2 July 2007; received in revised form 25 November 2007; accepted 5 December 2007 Available online 16 January 2008 Abstract This article presents an evaluation of the effects of the spouted bed design and operating conditions on system fluiddynamics and process performance during enteric coating of hard gelatine capsules. The design parameters studied were the column diameter (150 mm and 200 mm), the included angle of the conical base, γ (60 ◦ or 40 ◦ ) and the presence or absence of a Venturi inserted before the inlet air orifice. The process variables studied were the ratio between the feed flow rate of the coating suspension to the spouting gas flow rate (W s /W g ), the mass of capsules loaded to the equipment (M 0 ), and the ratio between the spouting gas flow rate to the gas flow rate at minimum spouting condition (Q/Q ms ). The response variables were the rate of increase of the capsules mass (K 1 ), and the adhesion efficiency (η). The linear regression equation for the dependent variable K 1 in terms of the independent variables adequately described the process with an r 2 value of 0.872. Analysis of variance (ANOVA) revealed that increasing of W s /W g , Q/Q ms and γ significantly increased the adhesion efficiency. Adhesion efficiencies higher than 90% were achieved by selecting precise coating conditions, indicating the feasibility of the process for coating of hard gelatine capsules. © 2008 Elsevier B.V. All rights reserved. Keywords: Spouted bed; Enteric coating; Hard gelatine capsule; Experimental design 1. Introduction Currently, hard gelatine capsules have a remarkable com- mercial significance being, together with tablets, an important pharmaceutical solid dosage form for oral administration [1,2]. Enteric coating of hard gelatine capsules can be useful in situ- ations in which the drug may be degraded by the gastric juice and/or can cause irritation to stomach. However, the coating application is not an easy task due to physical characteristics of the hard gelatine capsules, such as shape, size, shell fragility and smooth surface [1]. In recent years, some studies related to the feasibility of the spouted beds for coating application on hard and soft gelatine capsules have been reported in the literature [3–7]. Coating in spouted beds have a distinct advantage of formation of uniform layers in relatively short period of time mainly due to excellent ∗ Corresponding author. Tel.: +55 16 36024185; fax: +55 16 36024879. E-mail address: wpoliv@fcfrp.usp.br (W.P. Oliveira). heat and mass transfer within the bed [8–11]. However, attri- tion and elutriation of fines are limitations that severely confine this technique to materials with adequate physical and chemical properties [12]. In addition, the control of the operation variables plays a vital role to prevent bed collapse due to overfeeding or under drying of the coating material [13]. The aim of this work was to study the effects of the spouted bed configuration and operating conditions on spouting fluiddy- namics (dry bed) and system performance during film coating of hard gelatine capsules. 2. Materials and methods The coating formulation was composed of 0.15% of sodium croscarmellose (Blanver, S˜ ao Paulo, Brazil), 4.75% of talc (Henrifarma, S˜ ao Paulo, Brazil), 15.0% of the enteric polymer Eudragit L30-D55 ® (dry basis—Degussa, Darmstadt, Ger- many), 20.0% of triethyl-citrate, related to the concentration of the polymer, as plastifying material (Sigma Chemical Co., St. Louis, MO, USA), and distilled water. Table 1 presents the den- 0255-2701/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2007.12.014