Design and simulation of a single-stage SMB process for continuous separation of an agarose hydrolysate-derived ternary mixture under solvent-gradient conditions to prevent irreversible adsorption

Abstract

The growing demand for sustainable resource utilization has driven interest in producing 3,6-anhydrogalactose (AHG), galactose (GA), and 5-hydroxymethylfurfural (HMF) from agarose in red seaweeds. A major challenge is the development of an efficient, continuous, single-stage process to separate these three components from agarose hydrolysate, as HMF undergoes irreversible adsorption under typical conditions. This study proposes a solvent-gradient simulated moving bed (SG-SMB) process using two solvents: water as the main solvent for separation and 50% aqueous ethanol as a secondary solvent for regenerating the adsorbent and desorbing HMF. The column model incorporating the Snyder model was used to predict the adsorption and transport behaviors of HMF within a column where the ethanol content in the liquid phase is subject to variation along the axial direction. Based on these findings and the intrinsic parameters of AHG and GA, an optimized five-zone and open-loop SG-SMB system was designed, incorporating regeneration and solvent-replacement zones. Simulations and experiments confirmed that this system enables the continuous separation and recoveries of AHG, GA, and HMF with 100% purities and 100% yields through a single-stage process. Accordingly, the SG-SMB process developed in this study is anticipated to considerably enhance the economic feasibility of producing AHG, GA, and HMF via the hydrolysis of agarose in red seaweeds.