Preparation and properties of the biogas decarbonization byproduct of nano-CaCO₃ in a microfluidic device and computational fluid dynamics simulation

Biogas decarbonization is a key step in increasing the calorific value of biogas to meet demand. However, the release of CO₂ into the atmosphere from the biogas decarbonization process increases carbon emissions. The use of Ca(OH)₂ slurry to absorb and remove CO₂ can achieve a carbon-free biogas purification process, and it is also an effective method for preparing CaCO₃. This study prepared biogenic nano-CaCO₃ using CO₂ from biogas decarbonization with a newly fabricated microfluidic device and novel microfluidic chips were also made. The reaction pH, microfluidic chips, and total flow rate were parameters varied and studied for optimization. In addition, computational fluid dynamics (CFD) simulated the flow mixing and mass transfer of Ca(OH)₂ solution and CO₂-rich water in the microfluidic chips. Results showed the weakly alkaline condition (pH = 7.5), microfluidic chips with < 10 μm gaps, and > 100 mL/min total flow rate enhance CO₂ absorption. At those conditions, the microfluidic device prepared 30 nm-sized nano-CaCO₃ abundantly. Further, the CFD simulation proved the necessity to select the appropriate ratio of Ca(OH)₂ solution and CO₂-rich water to obtain nano-CaCO₃ with stable particle size. CFD also informed that increasing the length of the inlet and outlet of the reaction chamber and changing the chip shape can effectively improve CaCO₃ production.