Chromatographic separation of galactose, 5-Hydroxymethylfurfural, and levulinic acid

Abstract

Galactose, a versatile carbon source, has been studied for the production of bioethanol and other chemicals. Galactose can be obtained by hydrolysis of red algal galactan with acid. This particular process produces not only galactose but also two byproducts, levulinic acid (LA) and 5-hydroxymethylfurfural (5-HMF). The presence of LA or 5-HMF in a fermentation medium would inhibit microbial activity and thus reducing fermentation efficiency. Nevertheless, LA and 5-HMF are known as versatile building blocks in the chemical industry. Therefore, these two compounds need to be removed from the crude galactose solution and then separated from each other. In this study, chromatography was proposed to perform the separation task because it was known for high resolution and technical maturity. There had been no attempt on chromatographic separation of galactan hydrolysate. Two steps of experimental study were conducted: 1) adsorbent selection for chromatographic separation and 2) evaluation of the process performance at a preparative scale. A series of single component pulse injection experiments were conducted to select a suitable adsorbent. Dowex 50WX8 showed the best performance in terms of selectivity and resolution, being selected to be utilized in the preparative-scale chromatography experiments. We aimed to find the optimum conditions to 1) remove LA and 5-HMF and 2) perform ternary separation of galactose, LA, and 5-HMF by varying column loading (ratio of feed volume to bed volume) and flow rate. In overall, the performance of the chromatography process was satisfactory with high purities (≥98 %) and high yields (>95 %). For the first task, galactose can be obtained with a high productivity at a column loading of 18.8 vol % and a flow rate of 4 mL/min. For the second task, galactose, LA, and 5-HMF could be successfully separated from one another by varying the column loading and flow rate in the range of 9.4 - 57.6 vol % and 2 - 10 mL/min, respectively, satisf...