Three-phase catalytic hydrogenation of xylose to xylitol prolonging the catalyst activity by means of on-line ultrasonic treatment

A novel concept fur improvement of the activity of recirculated Raney nickel catalyst by means of on-line ultrasonic irradiation was studied. Qualitatively, acoustic irradiation was clearly found to retard the catalyst deactivation in the three-phase hydrogenation of xylose to xylitol. Two different intensities of the ultrasonic field were utilized in the experiments. The hydrogenation kinetics was modeled with a semi-competitive reaction-adsorption model accounting for interstitital adsorption sites for hydrogen located between larger organic molecules. The deactivation of the Raney nickel catalyst was found to diminish notably upon the use of on-line acoustic irradiation. Also, the selectivity of the system was found to be improved by the use of ultrasound in comparison to the case when no acoustic energy was dispatched to the system. The kinetic model used in the fitting of the data was able to explain the experimental concentrations fairly well. (C) 2001 Elsevier Science B.V. All rights reserved.