Applications of Oxidized Chitosan for Scale Prevention in Sugar Evaporators

Abstract

This study explores the potential use of oxidized chitosan (O.C) as an antiscalant for calcium oxalate (CaOx) and calcium sulfate (CaSO4), which are the main components of scales during sugar processing. Chitosan was selectively oxidized by NaClO/NaBr/TEMPO at pH 10.8 and 30 °C following the procedure by Yoo et al. [1]. The products have oxidation degrees ranging from 31 % to 77 % (by conductivity titration). The antiscaling performance of the O.C. was observed in comparison with a commercial antiscalant, Acumer1050, at the same antiscalant concentration (10 ppm) for two types of scales: CaOx and CaSO4. For CaOx scales, the O.C with 77 % degree of oxidation (O.C-77) shows the highest inhibition (72 %), whereas Acumer1050 and O.C-31 exhibit similar percent inhibition, 46 % and 36 %, respectively. However, in the presence of 13 % sugar (w/v), O.C-77 experiences a dramatic drop in performance to 30 % inhibition, but Acumer1050 only slightly decreases to 40 %. For CaSO4 scales, the results also show that the higher the oxidation degree, the better the antiscaling performance, with O.C-77 showing the highest percent inhibition (80 %) in aqueous solution, whereas Acumer1050 shows the best performance with 90 % inhibition. In 15 % sugar (w/v), the performance slightly drops to 75 % for Acumer1050 and 62 % for O.C-77. For CaOx, sugar strongly affects antiscaling performance of the high molecular weight O.C (O.C HMW), whereas the low molecular weight O.C (O.C LMW) shows consistent performance with increasing sugar concentration. For CaSO4, O.C HMW exhibits better performance, although for both, antiscaling performance is reduced with increasing sugar concentration. The different antiscaling performance may come from the different antiscaling mechanisms involved for CaOx and CaSO4. The results from SEM and XRD suggest that O.C binds with calcium ions to form a metal ion-polymer complex to prevent CaOx scales. On the other hand, O.C prefers to adsorb onto nuclei to prevent CaSO4 crystal growth. The results show that O.C can be a green alternative to the commercial antiscalant from a petroleum-based product.