Measurement and enhancement of gas-liquid mass transfer in micro-scale reactors

Due to the limited availability of chemical components in the early process development of pharmaceuticals and fine chemicals, and sometimes the high-cost of catalyst, it is increasing popular to use micro-scale reactors with reaction volumes of less than 10ml to screen catalyst candidates for three-phase reactions. Micro-scale reactors not only allow one to use small amount of reactants in each experiment, but also enable parallel reactor setups so that large numbers of experiments can be performed simultaneously.; To ensure the success of catalyst screening, it is advantageous to run three-phase catalytic reactions under kinetically controlled conditions so that the activities of different catalysts can be compared. Because catalysts with small particle sizes are typically used, three-phase catalytic reactions in pharmaceutical and fine chemical synthesis are susceptible to gas-liquid mass transfer limitations. It is, thus, desirable for micro-scale reactors to have high gas-liquid mass transfer efficiencies in order to minimize the potential for mass-transfer limitations in screening experiments. This dissertation presents the first successful measurements of gas-liquid mass transfer coefficients in micro-scale reactors, which is two orders-of-magnitude smaller than systems for which mass transfer coefficients have been reported before. Both physical and chemical absorption techniques are used.; This dissertation also presents the finding of an efficient way of enhancing gasliquid mass transfer in micro-scale reactors. In the novel reactor described here, gas-liquid mass transfer coefficients can be doubled over those obtained with the agitation technique used in commercial micro-scale units. In addition, the reactor can achieve the top range of mass transfer coefficients obtained in a full-scale reactor.; Chemical absorption measurement in the new reactor showed that the variation of mass transfer efficiency with agitation speed was more likely caused by the variation in the mass transfer coefficient rather than the gas-liquid interfacial area.; This dissertation demonstrates that the gas-liquid mass transfer coefficient can be successfully measured, and can also be correlated with factors like catalyst loading, fill level and stirring speed, at the micro-scale. This opens up the possibility of performing process optimization and obtaining scale-up data directly at micro-scale in a parallel experimentation fashion. This possibility was supported by chemical reaction experiments using the new micro-scale reactor.