Selective co-crystallization separation of sucrose-6-acetate from complicated sucrose acylation system and facile removal of co-former: Process optimizations and mechanisms

Abstract

The searching for the facial and highly efficient separation method of sucrose-6-acetate (SA-6) in the acylation process seems significant for the production of sucralose. In this work, an efficiently selective co-crystallization strategy of SA-6 from the complicated sucrose acylation mixture has been developed, i. e. firstly, selective co-crystallization using acetic acid (HAc) as a cheap and green co-former (operation I), and co-former removal by triethylamine (TEA) (operation II). The crystal structure of SA-6·HAc co-crystal in the operation I has been determined, it is a 3D hydrogen-bonding network with HAc inserting among the SA-6 layers, whose cavity size is 5.56 × 7.54 Å. And the optimization on two operations have been conducted, including HAc dosage, solvent/aliphatic amine types and dosage, separation time/temperature. Based on the optimal conditions, the high SA-6 separation efficiency of 90.33 % in 1.5 h can be achieved, during which relative selectivity coefficient (αX) is lower than 0.003, deacidification ratio (δ) is higher than 99.47 %, and the product purity is 99.86 % (wt). Furthermore, the selective co-crystallization and co-former removal mechanisms were proposed base on crystal structure and theoretical calculations, in which thermally stable co-crystals, proper solvent size and acid-base coupling drive these processes. This strategy can enhance the separation efficiency of acylation process in sucralose production greatly.