Separation by Size Exclusion: Selective Liquid-Phase Adsorption of l-Lysine from Lysine–Glucose Mixtures on Zeolites

Abstract

l-Lysine is an essential amino acid of great importance for the pharmaceutical and nutrition industries and is mainly produced by the fermentative conversion of d-glucose. The technological bottleneck for an efficient process is often the development of separation and purification technologies as they can account for 20–50% of the overall operation costs. Liquid-phase adsorption on zeolites is an energy-, resource-, and cost-saving alternative. Zeolites are a well-established and widely available class of adsorbents. In this research, a variety of commercial zeolites of different framework types with varying Si/Al ratios were used to investigate the adsorption of l-lysine from single-component solutions and lysine–glucose mixtures. l-Lysine recovery resulted in adsorption capacities of up to 169 mg g–1 on Hβ-30 in batch experiments. Zeolites showed high l-lysine selectivity in competitive adsorptions from lysine–glucose mixtures, outperforming previously reported adsorbents. Based on the analysis of adsorbent and adsorbate dimensions, a size-exclusion-based separation of l-lysine from d-glucose was proposed, which was found to be primarily responsible for the high l-lysine selectivity. Fourier transform infrared spectroscopy analysis allowed proposing a structure–adsorption relationship for l-lysine on zeolites. The transferability of the batch results to a continuous process was shown. In addition, a high desorption efficiency of up to 90% using water as the desorption solution could be achieved, complemented by successful recyclability tests over five consecutive adsorption–desorption cycles.