Lime is widely utilized as a sorbent in dry and semidry sulfur removal processes. In this study limestone was calcined at high temperature and lime was produced by water vapor steam treatment at low temperature. Experiments were performed at conditions that also cover those usually present in coal-fired power plants. The investigation of the reaction of lime with synthetic flue gas showed that the relative humidity of the gas has a major impact on the reactivity. Also the presence of oxygen and/or carbon dioxide does not show a significant influence on the sulfur dioxide removal reaction though some intermediate formation of calcium carbonate cannot be excluded. Mainly calcium sulfite hemihydrate was found to be the reaction product, but some calcium sulfate hemihydrate was also formed when oxygen was present. Four regions with different prevailing reaction mechanisms can be defined: In the beginning the formation of a monolayer is mainly determined by the SO 2 concentration and to some smaller extent also by the relative humidity. This period is followed by the formation of the consecutive product layers which can initially be determined by a dissolving process of SO 2 . Afterward this formation is only determined by the relative humidity and most likely by product layer diffusion. Above a conversion of around 9% reaction rate drops significantly which can be due to pore closure.

A reverse-flow reactor (RFR)

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In product development, it is crucial to choose the appropriate drug manufacturing route accurately and timely and to ensure that the technique selected is suitable for achieving the desired product quality. Guided by the QbD principles, the pharmaceutical industry is currently transitioning from batch to continuous manufacturing. In this context, process understanding and prediction are becoming even more important. With regard to hot melt extrusion, the process setup, optimization and scale-up in early stages of product development are particularly challenging due to poor process understanding, complex product-process relationship and a small amount of premix available for extensive experimental studies. Hence, automated, quick and reliable process setup and scale-up requires simulation tools that are accurate enough to capture the process and determine the product-process relationships. To this end, the effect of process settings on the degradation of the active pharmaceutical ingredient (API) in a lab-scale Leistritz ZSE12 extruder was investigated. As part of the presented study, the limitations of traditional process analysis using integral process values were investigated, together with the potential that simulations may have in predicting the process performance and the product quality. The results of our investigation indicate that the average melt temperatures and the exposure times in specific zones along the screw configuration correlate well with the API degradation values and can be used as potent process design criteria to simplify the process development.

Highly potent active pharmaceutical ingredients (APIs) and low-dose excipients, or excipients with very low density, are notoriously hard to feed with currently available commercial technology. The micro-feeder system presented in this work is capable of feeding low-dose rates of powders with different particle sizes and flow properties. Two different grades of lactose, di-calcium phosphate, croscarmellose sodium, silicon dioxide, a spray-dried intermediate, and an active ingredient were studied to vary material properties to test performance of the system. The current micro-feeder system is a volumetric feeder combined with a weighing balance at the outlet that measures feeder output rates. Feeding results are shown as a so-called “displacement-feed factor” curve for each material. Since the powder mass and volume are known in the micro-feeder system, in this work, we characterized an observed density variation during processing via a “displacement-feed factor” profile for each of the fed powders. This curve can be later used for calibrating the system to ensure an accurate, constant feed rate and in addition predicting feeding performance for that material at any feed rate. There is a relation between powder properties and feeding performance. Powders with finer particles and higher compressibility show densification during their feeding process. However, powders with larger particles and lower compressibility show both “densification” and “powder bed expansion,” which is the manifestation of dilation and elastic recovery of particles during the micro-feeding process. Through the application of the displacement-feed factor, it is possible to provide precise feeding accuracy of low-dose materials. Graphical abstract

Multiple impeller reactors are widely used due to their advanced gas utilization and an increased volumetric mass transfer coefficient. However, with the application of Rushton impellers, gas dispersion efficiency varies between the bottom and the upper impeller levels. The present study analyzes the individual flow regime, power input, and gas hold-up in each compartment of a reactor equipped with four Rushton impellers. The results indicate that the pre-dispersion of the air introduced by the bottom impeller (up to 80%) plays a key role in a better gas retention efficiency of the upper impellers (>300%) and leads to a shift of the cavity and flooding lines in the flow map (Fr-vs Fl-Number) of the upper impellers. A novel analysis of the bubble flow in the dispersed state via a two-phase LES-based CFD model reveals that a more homogenous distribution of air bubbles in the upper compartments leads to high compartment gas hold-up values, but fewer bubbles in the vicinity of the impellers. The measured and simulated data of this study indicate that the upper impellers' efficiency mostly depends on the flow regime of and the pre-dispersion by the bottom impeller rather than on the upper impellers' flow regimes. These results contribute to the understanding of essential mixing processes and scaling of aerated bioreactors.