Precipitating Characteristics of Potassium Bicarbonate Using Concentrated Potassium Carbonate Solvent for Carbon Dioxide Capture. Part 2: Crystal Growth

Crystallization kinetics of potassium bicarbonate in the potassium carbonate (K2CO3)–potassium bicarbonate (KHCO3)–water (H2O) ternary solvent system were estimated using focused beam reflectance measurement (FBRM) in unseeded batch cooling experiments. Two groups of experiments including apparent K2CO3 concentrations of 35 and 40 wt %, both with 0.4 loading, at different constant cooling rates were conducted. KHCO3 was the only precipitate in the ternary system. The concentration of KHCO3 measured by autotitration and chord length distribution collected from FBRM were used to estimate the parameters required for the primary nucleation, secondary nucleation, and growth rate models through mass balance, population balance using the method of moments, and least-squares minimization in MATLAB. The solubility of the ternary solvent system was successfully predicted using the regressed electrolyte nonrandom two-liquids (ENRTL) activity model in Aspen Plus. The crystallization of KHCO3 was impacted by KHCO3 supersaturation and K2CO3 concentration. Primary nucleation was found to dominate the system including both homogeneous and heterogeneous nucleation, whereas secondary nucleation was inhibited to a great extent. The model developed was able to predict the average particle size within 20%, the results obtained from the model were consistent with the conclusion that primary nucleation dominates the K2CO3–KHCO3–H2O solvent system.