Polymorph control of glycine by antisolvent crystallization using nitrogen minute-bubbles

Some current challenges in clathrate hydrate science: Nucleation, decomposition and the memory effect

“…Nanobubbles still provide regions of high concentration of gas (thus solving the mass transfer process during hydrate formation) and, by the formation of gas-solution interfaces they also will have an effect on the thermodynamic state of the solution. Interestingly, nanobubbles have also been observed to act as nucleation centers for crystal formation in various experiments [60,61] and simulations [59] as presumably, the gas-liquid interfaces can act as surfaces for heterogeneous nucleation. This is shown in Fig.…”

Change in glycine polymorphs induced by minute-bubble injection during antisolvent crystallisation

“…Furthermore, to investigate the effects of the presence of glycine and/or methanol on the electric charge on the minute-bubble surface, the zeta potential in the boundary area of the gas-liquid interface was measured when N 2 minute-bubbles were supplied to a 2.0 mol/l glycine solution, a 40 vol% methanol solution, or a glycine-methanol mixed solution. The results showed that the zeta potential in all cases approached 0 mV, although the potential difference between three cases was small [15]. Fig.…”

“…The results obtained in the two systems indicated that local supersaturation in the regions around the minute gas-liquid interfaces increased approximately twice compared with the supersaturation of the surrounding bulk solution, and the generation of numerous local supersaturation regions near the gas-liquid interfaces decreased the r C/CS necessary for the selective crystallisation of the metastable a-form and unstable b-form. Examination of the electrification of minute-bubbles was conducted by the zeta potential measurement to clarify the occurrence of interactions at the gas-liquid interfaces [13][14][15]. The zeta potential of the minutebubbles in water was negative, from À40 to À90 mV, at an average bubble diameter of 10-30 lm.…”

“…In this study, a micron-scale bubble formation technique that enables the generation of local supersaturation in the regions around the gas-liquid interfaces was applied to the antisolvent crystallisation of glycine to control polymorphism. Minimising the bubble diameter in the gas-liquid systems helps achieve the following: (i) acceleration of mass transfer and reactive absorption with an increase in the gas-liquid interfacial area, (ii) an increase in the average residence time of the bubbles with a decrease in buoyancy, and (iii) the occurrence of interactions at the gas-liquid interface caused by electrification of minute-bubbles [13][14][15]. When minute-bubbles with the above properties are introduced into the antisolvent crystallisation of glycine, the local supersaturation at the minute gas-liquid interfaces increases due to the accumulation of glycine and antisolvent caused by the residence of minute-bubbles with surface potential in the liquid phase for a long period of time.…”

“…In our previous study, N 2 bubbles with different average diameters were injected into the antisolvent crystallisation of glycine at the methanol mixture ratio of 50 vol%. As a consequence, minimisation of bubble formation led to the enhanced production of the unstable b-form at the crystallisation time of 0.5 min, and the inhibition of the polymorphic transformation from the b-form to the a-form with an increase in the crystallisation time [15]. In the present study, the crystallisation of glycine polymorphs was conducted by mixing two liquids (the saturated glycine solution and methanol as an antisolvent) under two different schemes: by adding methanol into the saturated glycine solution (Gly solution/MeOH system) and by adding the saturated glycine solution into methanol (MeOH/Gly solution system).…”