Hydrodynamics of gas–liquid flow in a capillary at elevated pressure: Implications for the fixation of CO2 into propylene carbonate in microreaction systems

It is an effective method to capture and utilize carbon dioxide (CO2) by using a microreactor to fix CO2 into propylene carbonate (PC). It is important to investigate the hydrodynamics of gas–liquid flow in order to ensure that the CO2 fixation in microreactor is operated under suitable conditions to obtain efficient mass transfer performance. However, few studies have been concerned with PC-CO2 two-phase flow in microreactors, especially at elevated pressures. Therefore, a high-pressure microreactor observation platform is established in this work to explore the hydrodynamics of PC-CO2 two-phase flow at a pressure range of 0.5–3.0 MPa. Three typical patterns such as bubbly flow, slug flow, and slug-annular flow were observed, and the flow pattern diagram at different pressures was plotted using WeG and WeL. The influence of the pressure on flow pattern transition lines was further discussed. Moreover, the effects of pressure on bubble size, liquid film thickness, bubble frequency, and gas volume fraction were investigated, as well as the corresponding correlation models. This work may provide guidance for the operation of gas–liquid microreactor at elevated pressure, especially for the fixation of CO2 into PC.