Synthesis Of Xylitol By Single Cation-Exchange Membrane Technology

Corncob is a kind of plant stalks which contains the most abundant hemicellulose. It is also a low-cost renewable resource. In this research, xylose was firstly extracted by acid hydrolysis under the conditions of the ultrasonic. Xylitol was then synthesized from xylose by a single-yang membrane technology. Compared with the current catalytic hydrogenation process, this method has many advantages, such as no need to add special chemical reagents, the low production cost, the mild reaction conditions, and the simpleness of process and so on.The xylose purity was improved with hot water to get rid of a small amount of tannin, vegetable base, colloid, pigment, etc. With self-made device ultrasound-assisted acid hydrolysis corncob, the solid-liquid ratio, time, temperature, acid concentration and other experimental conditions were studies respectively. When they were got a good yield of reducing sugar and xylose, the range of the above factors was obtained. The best parameters of xylose by L₉ (3⁴) orthogonal optimized test was got. It showed that when the solid-liquid ratio was 1:20, the time was 40min, the temperature was 70℃, the acid concentration was 0.8%, the reducing sugar and xylose extraction rates were 18.1% and 17.6% respectively.With self-made experimental device, the foam nickel electrode as a cathode, the titanium-based ruthenium dioxide electrodes as the anode, the xylitol was synthesized from the extractive xylose by the single-yang membrane electrochemical. The reaction temperature, the reaction time, the electrical current, the pH value of cathode solution, the initial concentration of xylose and other factors were studied. The optimum parameters of the single-yang membrane electrochemical synthesis of the xylitol were obtained by L₁₆(4⁵) orthogonal experiment. It showed that when the reaction temperature was 60℃, the current was 2A, the pH value was 10, the reaction time was 2h, the initial xylose concentration was 0.75mol/L, and the xylose conversion rate was upper to 99%. The obtained products were characterized by the infrared spectroscopy, the 1H-NMR and C13-NMR. The purity of xylitol was 99.4%. The single-yang membrane technology synthesis of xylitol was preliminarily studied on kinetic characteristics, which is first order reaction kinetics. Cathode reaction mechanism of single-membrane electrochemical reduction was researched.