Jp. Mikkola et al., Modelling or kinetics and mass transfer in the hydrogenation of xylose over Raney nickel catalyst, J CHEM TECH, 74(7), 1999, pp. 655-662
This paper discusses the modelling of xylose hydrogenation kinetics over Ra
ney nickel in aqueous solutions, the determination of the hydrogen solubili
ty in the reaction mixture as well as evaluation of mass transfer effects i
n the reaction system. The hydrogenation experiments were carried out batch
wise in an automatic laboratory-scale reactor. The reactor system operated
at a pressure range of 40-70 bar and at temperatures between 80 and 140 deg
rees C. The catalyst-to-xylose ratio was approximately 5wt-% of the xylose
weight normally. The reactor contents were analysed off-line with a high pe
rformance liquid chromatograph. Hydrogen solubility in the reaction medium
was determined with a gas-chromatographic system. The solubility was found
to remain fairly constant during the hydrogenation. Only a slight increase
in the hydrogen solubility was detected as xylose was hydrogenated to xylit
ol. The overall hydrogen solubility in the reaction mixture was significant
ly lower than in pure water, as expected. The main hydrogenation product wa
s xylitol, but small amounts of xylulose and arabinitol were detected as by
-products. A;semi-competitive kinetic model, based on hydrogen and xylose a
dsorption, was developed. The model accounts for the very different areas c
overed by a hydrogen atom and an organic species on the catalyst surface. T
he parameters of the kinetic model were determined with non-linear regressi
on analysis. It turned out that the kinetic model is able to describe the f
ormation of both xylitol and the by-products. The mass transfer effects in
the batch hydrogenation were evaluated by using measured viscosities and es
timated diffusion and mass transfer coefficients. A process simulator, util
izing the kinetic and mass transfer effects, was developed to predict the b
ehaviour of industrial reactors. (C) 1999 Society of Chemical Industry.