Impact of aspect ratio and crystal size distribution of l-glutamic acid formed by cooling crystallization on drying characteristics

Abstract

This study investigated the impact of aspect ratio and crystal size distribution on the mother liquor content and drying rate of L-glutamic acid (LGA). LGA cooling crystallization was performed using two methods: spontaneous nucleation and seeding. First, to identify various crystalline forms of LGA and obtain α-form seeds, cooling crystallization was carried out through spontaneous nucleation and seeding. Seeding improved the aspect ratio of the crystals, and both α- and β-form crystals had hexagonal shapes when their aspect ratio was enhanced. During seeding, the aspect ratio of α-form seeds improved under slow cooling rates and low supersaturation, while that of β-form seeds improved under fast cooling rates and high supersaturation. When assessing drying efficiency based on mother liquor content and drying rate, the highest efficiency was observed in crystals with an average aspect ratio of 1.25 and an average particle diameter of 416 μm, with a mother liquor content of 5.60%. Conversely, the lowest efficiency was found in crystals with an average aspect ratio of 16.40 and an average particle diameter of 170 μm, resulting in a mother liquor content of 25.21%. The time required for complete drying in these two cases showed a roughly twofold difference, taking approximately 120 minutes for the highest efficiency case and 240 minutes for the lowest. Consequently, this study was able to evaluate the drying efficiency of LGA crystals with varying aspect ratios and other crystal size distributions (CSD) in terms of mother liquor content and drying rate.