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Spray drying is one of the widely used manufacturing processes in pharmaceutical industry. While there are voluminous experimental studies pertaining to the impact of various process-formulation parameters on the quality attributes of spray dried powders such as particle size, morphology, density, and crystallinity, there is scant information available in the literature regarding process scale-up. Here, we first analyze salient features of scale-up attempts in literature. Then, spray drying process is analyzed considering the fundamental physical transformations involved, i.e., atomization, drying, and gas-solid separation. Each transformation is scrutinized from a scale-up perspective with non-dimensional parameters & multi-scale analysis, and comprehensively discussed in engineering context. Successful scale-up entails similar key response variables from each transformation across various scales. These variables are identified as droplet size distribution, outlet temperature, relative humidity, separator pressure loss coefficient, and collection efficiency. Instead of trial-and-error-based approaches, this review paper advocates the use of mechanistic models and scale-up rules for establishing design spaces for the process variables involved in each transformation of spray drying. While presenting a roadmap for process development and scale-up, the paper demonstrates how to bridge the current gap in spray drying scale-up via a rational understanding of the fundamental transformations. [ABSTRACT FROM AUTHOR]

The scaling-up of spray drying processes is an important and challenging step in commercializing specialty products with an ensured quality because it mandates a comprehensive understanding of several steps in the process such as atomization, efficient solvent removal, and particle segregation. The formation of needed particle sizes and shapes is impossible without appropriate atomization through spray dryer nozzles. Hence, research is discussed that investigates the atomization mechanism for a pilot scale externally-mixed, two-fluid nozzle spray dryer by using time resolved particle-image velocimetry to study the behavior of droplets in the near-field of the nozzle tip. Important near-field dynamics of droplets emanating from the nozzle are described, and particle formation characteristics are discussed for several formulations which are widely used in the pharmaceutical industry. Spray angle, droplet breakup length, and droplet sizes and velocity distributions are characterized. Understanding these parameters assists the interpretation of particle formation and enables the modeling of the spray drying process. [ABSTRACT FROM AUTHOR]

Spray drying as a commonly used process to produce amorphous solid dispersions of poorly water soluble active pharmaceutical ingredients (API) involves dissolution of the API and often a polymer, surfactant, and/or other functional excipient(s) into a volatile solvent. This feed solution is then pumped to an atomizing nozzle to produce droplets inside the drying chamber. The current paper aims to utilize non-scaled parameters to characterize the atomization process. A bi-fluid nozzle with two different designs commonly used in a lab-scale spray dryer was investigated under different operating conditions. The feed solutions were made of several excipients commonly used to produce amorphous solid dispersion composites. Atomization characterization is presented via both mean droplet size and size distribution. Various models are evaluated for predicting droplet mean diameter and span suitable for extrapolating atomization in the spray drying process. These approaches may be extended to other nozzles and across scales. [ABSTRACT FROM AUTHOR]

The article presents a literature review on modifications and the latest achievements in the field of spray drying (SD). Although the history of this method of drying dates back to more than a hundred years ago, and in the case of many products, the process is widely recognized and does not create problems, many others are still looking for new design and technological solutions to reduce energy expenditure, improve the process flow and improve properties of received products. Since early development SD system has evolved in its construction, and currently there are numerous system modifications already available in the market, apart from other being on early implementation or laboratory stage. This paper begins with a brief background of SD and existing technologies. The main part of the paper is devoted for the description of less developed approaches. As was presented, the particular drawbacks of conventional SD system can be overcome by innovative approaches. It is hoped that these added-value features/technologies will find their place in industrial systems to boost the process performance and/or powders properties. • Spray drying (SD) system has evolved since early development. • Drawbacks of conventional SD systems can be overcome by innovative approaches. • To reduce thermal degradation, vacuum, dehumidified air, or ultrasound SD can be applied. • Reduction of stickiness can be achieved by dehumidified air-assisted SD. • Particle size/morphology can be modified by foam, flame, ultrasound and nano SD. [ABSTRACT FROM AUTHOR]