Estimation of the Growth and the Dissolution Kinetics of Ammonium Bicarbonate in Aqueous Ammonia Solutions from Batch Crystallization Experiments

In this work, we estimate the macroscopic crystal growth and dissolution rates of ammonium bicarbonate in aqueous ammonia solutions as a function of the solution supersaturation in a range of process conditions of industrial relevance. The electrolytic and reactive nature of the mixtures requires the computation of the driving force for crystallization using an activity-based speciation model. The model parameters have been estimated based on experimental speciation data obtained by applying tailored multivariate data analyses on the measured ATR-FTIR spectra of the solutions. Moreover, the volatility of CO₂(aq) and NH₃(aq) requires operating the system under its vapor pressure in order to avoid depletion of the solute in the liquid phase. For this reason, a sealed crystallizer equipped with custom-made connections for the online monitoring tools, such as FBRM and ATR-FTIR probes, has been used during the experiments. In addition to estimating the crystallization kinetics, it has been found that the speciation in solution and the supersaturation can affect the relative growth of the ammonium bicarbonate crystal facets, thus leading to different crystal habits. Finally, this work provides a sound thermodynamic framework in which the kinetics models for crystal growth and dissolution of ammonium bicarbonate can be applied to the design and optimization of ammonia-based CO₂ capture absorption processes that exploit solid formation.