Catalyst retention in continuous flow with supercritical carbon dioxide

This review discusses the retention of organometallic catalysts in continuous flow processes utilizing supercritical carbon dioxide. Due to its innovative properties, supercritical carbon dioxide offers interesting possibilities for process intensification. As a result of safety and cost considerations, processes that use supercritical carbon dioxide are preferably done in continuous flow, as they require a pressure upwards of 74 bar. Many of the reactions that benefit from the application of supercritical carbon dioxide also involve the use of a homogeneous catalyst however, requiring efforts to recycle the catalyst when these are applied in continuous flow. Alternatively, the catalyst may be retained in the reactor by modifying the process or catalyst, such as by catalyst immobilization, membrane separation, or biphasic processing exploiting the properties of supercritical carbon dioxide. Each of these methods is discussed, including their advantages and drawbacks. Also discussed are milli- and micro-flow processes and their possibilities for integrated catalyst retention and handling supercritical carbon dioxide.