Moisture sorption, thermal, and caking characteristics of l-lysine-carbonate granules

l-Lysine, an essential amino acid, is often produced in the granular form of l-lysine-monohydrochloride (l-lysine-HCl). To address chemical waste and processing cost concerns associated with the production of l-lysine-HCl granules, an alternative process has been recently developed for the production of l-lysine as granules of l-lysine-carbonate (l-lysine-CO3). In the present study, the moisture sorption, thermal, and caking properties of l-lysine-CO3 granules were investigated in comparison with commercial l-lysine-HCl granules. l-Lysine-CO3 granules showed a popcorn-like surface structure (59.0% crystallinity), while l-lysine-HCl granules exhibited an angular crystalline structure (72.9% crystallinity). l-Lysine-CO3 granules had a less compact structure than l-lysine-HCl granules and showed excellent initial flowability comparable to l-lysine-HCl granules. l-Lysine-CO3 granules were more hygroscopic than l-lysine-HCl granules, probably due to their lower crystallinity and less compact structure. l-Lysine-CO3 granules began to undergo thermal decomposition at 192 °C, probably due to CO2 release, followed by melting at 234 °C and further decomposition, while l-lysine-HCl granules underwent melting at 251 °C, and then began to undergo thermal decomposition at 260 °C. No glass transition was observed for either lysine-CO3 or l-lysine-HCl granules. Storage test under pressurized and accelerated conditions showed that l-lysine-CO3 granules were more prone to caking and formed harder agglomerates than l-lysine-HCl granules. The results showed that l-lysine-CO3 granules were more hygroscopic, less thermally stable, and more prone to caking, compared to commercial l-lysine-HCl granules. However, these properties of l-lysine-CO3 granules were at acceptable levels for commercial use, thus l-lysine-CO3 granules have high potential for commercial development.