Effect of Monoethylene Glycol on the Nucleation and Growth of Calcium Carbonate from Supersaturated Solutions in Microchannels of Varying Wettability

The control of calcium carbonate formation is of high importance for a wide range of applications in the pharmaceutical industry and membrane processes as well as in the oil and gas industry. Herein, for the first time, the effect of monoethylene glycol (MEG) on the formation of calcium carbonate (CaCO₃) crystals from supersaturated solutions flowing through microchannels (volume 0.36 mL) of varying wettability was investigated. The use of microdevices enabled the observation of the scaling phenomenon in the early stages. Solutions supersaturated with respect to calcite, containing MEG (10, 20, and 30% v/v), were injected into the microchannel under a constant total flow rate and under laminar flow conditions (Re = 0.052). The growth of calcium carbonate crystals was monitored by video recording. The effect of the wettability on crystal formation was tested using glass and silane-coated microchips. The microchannel walls were wet and neutral-wet by the supersaturated solutions with a low MEG concentration. In the presence of a high MEG concentration in the supersaturated solutions, the walls of both types of microchips were neutral-wet. The results showed that the addition of MEG at a concentration of 10% v/v in the supersaturated solutions decreased the time of observation of the first crystal, favored secondary nucleation, and in general decreased the crystal growth rates. Raman spectroscopy identified the formation of aragonite in most cases, while as SR values increased, the formation of aragonite aggregates was favored. Further increases of the MEG concentration in the supersaturated solutions to 20% v/v, at low supersaturation ratio (SR) values, favored the formation of amorphous calcium carbonate (ACC) while at higher SR values aragonite crystals and aragonite aggregates formed. Further increases in the MEG concentration in the supersaturated solutions up to 30% v/v completely inhibited the nucleation and crystal growth of calcium carbonate.