(206b) Effect of Process Variables on Fluid Bed Granulation and Coating - in-Line Monitoring of Granule Size and Population

The granulation of fine powders is a key unit operation in many process industries. It is used extensively in the pharmaceutical industry as a precursor to tablet making and in other industries such as agricultural chemicals, catalyst manufacture and food flavorings. In a typical granulation process, a mix of fine dry powder ingredients is combined together using a water soluble binder to create larger granules. The resulting granulated product is free-flowing and easier to handle and post process than the starting fine powder. Additionally, health and safety risks associated with fine dusts are significantly reduced. Coating of particles in fluidized beds is of high interest especially in pharmaceutical and agricultural applications to obtain controlled-release or delayed released particles.

In order to achieve proper downstream processing and for consistent product quality, it is essential that the granulation and coating processes are effectively controlled, such that a consistent granule/pellet size distribution is obtained. This is often very difficult to achieve, since a great many variables affect the nature of the processes: equipment design and scale, the formulation used, water content, water addition rate and for fluid bed granulators, the air flow and humidity. Typically, the effect of these variables on granule/pellet size distribution is at best only qualitatively understood. This makes the optimization and control of a granulation process a considerable challenge.

Traditional methods of determining the granule/pellet size distribution rely on off line after-the-event particle size analysis. While this approach is acceptable for a final product QA perspective, it is inappropriate for real-time monitoring or control, since the time taken to acquire the data is longer than the process itself. In addition, repeat sampling during a run is inadvisable, since the act of sampling often influences the course of the process.

In this poster we describe how two in-process real-time particle characterization tools have been used to monitor and quantify granule size and granule/pellet number during fluid bed granulation processes. The first technique, FBRM (Focused Beam Reflectance Measurement), provides a real-time track of granule/pellet size and number during the granulation process. The second technique, PVM (Particle Vision Measurement), provides high quality, high resolution digital video images during the granulation and coating process.

Data here is presented from two types of fluid bed process: firstly from a top-down spray process, and secondly from a co-current bottom-up spray process using a segregated dilute phase powder stream. The influence of spray rate and air flow rate on the granulation process and on the resultant granule size distribution is quantified. In addition, the effect of process events such as filter back-flushing is quantified.