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

Abstract

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.