Impact of Ultrasonic Energy on the Crystallization of Dextrose Monohydrate Surya Devarakonda, #,† James M. B. Evans, ⊥,‡ and Allan S. Myerson* ,⊥ Department of Chemical Engineering, Polytechnic University, 6 Metrotech Center, Brooklyn, New York 11201, and Department of Chemical Engineering, Illinois Institute of Technology, Chicago, Illinois 60616 Received April 9, 2003; Revised Manuscript Received June 25, 2003 ABSTRACT: In this paper, we investigate the potential of ultrasonic energy in assisting the crystallization of dextrose monohydrate, which is primarily manufactured via slow cool batch, lasting 48 h (0.5 °C/h), seeded crystallization; this cooling curve is designed to optimize the crystal growth and give rise to relatively large dextrose crystals. This study was interested in the impact of ultrasound on the nucleation, crystal breakage/size distribution, and rate of growth of the dextrose, while producing a product of the desired crystal size distribution. Experimental results show that ultrasonic energy can be used to induce nucleation and increase the overall mass rate of crystal growth while producing product with the desired crystal size distribution. 1. Introduction Dextrose monohydrate is primarily crystallized using a slow cool batch seeded approach. While the process yield is often acceptable (∼75%), it is a relatively slow process (48-h cooling cycle). The crystallization of the dextrose monohydrate is a slow process because a slow cooling cycle is required to prevent excessive nucleation, and in addition to this, the mass transfer and hence the growth rates within the system are limited because of the slow agitation rates. Increasing the rate of agitation within this system was deemed to be impracticable due to the high viscosity of the system (9.1 × 10 15 c.p. at ambient temperatures) and the need for variable power agitators. The use of ultrasonic energy as a means of altering a crystallization process has been reported for a number of systems 1-3 and might be suitable for enhancing the crystallization of dextrose monohydrate. Ultrasonic energy is thought to affect the crystalliza- tion process in two ways. Firstly, where ultrasound is creating heterogeneous nucleation sites, these nucle- ation sites are formed by cavitation where the applica- tion of ultrasound of an appropriate energy and fre- quency induces the formation and collapse of small bubbles. 4,5 The formation and destruction of these bubbles is thought to create extremely high levels of localized supersaturation, which trigger the nucleation. Ultrasound is also thought to impact the nucleation by the creation of container imperfections, which have been identified as a common source of heterogeneous sites. Support for ultrasound creating surface imperfections and hence heterogeneous nucleation sites comes from the fact that any strong interaction such as scraping or hitting will result in heterogeneous sites, 6,7 and if a corrosion token is placed into the system and the ultrasound is applied holes will be punched through the token (see for example Figure 1). Secondly, ultrasound is capable of inducing crystal breakage. 1 A primary effect of the crystal breakage is to increase the total surface area of the system, and from the mass growth rate equation (eq 1), it can be seen that this equates to an increase in the overall mass growth rate: 6 Another effect of the crystal breakage is to increase the overall rate of the nucleation via secondary nucle- ation, 6,7 as the crystal breakage and crystal/ultrasound collisions give rise to fragments that are considered to act as nuclei. The purpose of this study was to investigate the impact of ultrasound on the crystallization of dextrose monohydrate in a batch-seeded vessel. With regard to the crystallization process, the study was specifically interested in the impact of ultrasound on the nucleation, * To whom correspondence should be addressed. Tel: +1 312 567 3163. Fax: +1 312 567 5205. E-mail: myerson@iit.edu. # Polytechnic University. ⊥ Illinois Institute of Technology. † Current address: Wyeth Research, 401 N. Middletown Road, Pearl River, NY 10965, USA. ‡ Current address: GlaxoSmithKline, Cobden Street, Montrose, Angus, UK, DD10 8EA. Figure 1. Cavitation damage on metal token (picture taken from European Society of Sonochemistry website 8 ). dm dt ) Ak g ∆C (1) CRYSTAL GROWTH & DESIGN 2003 VOL. 3, NO. 5 741 - 746 10.1021/cg034056r CCC: $25.00 © 2003 American Chemical Society Published on Web 07/12/2003