Hydrogenation of Lactose over Sponge Nickel CatalystsKinetics and Modeling

Abstract

Kinetics of lactose hydrogenation to lactitol, an alternative sweetener, over Mo-promoted sponge nickel slurry catalyst in aqueous solutions was studied. Hydrogenation experiments were carried out batchwise in a three-phase laboratory-scale reactor (300 mL, Parr Co.), operating at 20−70 bar and between 110 and 130 °C. The main hydrogenation product was lactitol, while small amounts of lactobionic acid, lactulose, lactulitol, sorbitol, and galactitol were detected as byproducts. The lactitol selectivity within the experimental range varied from 90 to 99%. The selectivity values improved as the hydrogen pressure increased and the reaction temperature decreased. The effect of catalyst loading and catalyst deactivation during consecutive hydrogenation batches was also studied. Fresh and recycled catalysts were characterized by nitrogen adsorption, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), hydrogen temperature-programmed desorption (TPD), and particle-size analysis. Recycled sponge nickel catalyst was able to adsorb less hydrogen compared to fresh one, indicating active site poisoning. Of all byproducts, only lactobionic acid had an inhibiting effect on lactose conversion rate and deactivated the catalyst. By lactobionic acid, deactivated catalyst can be regenerated by controlled alkali wash. The kinetic data were modeled by Langmuir−Hinshelwood−Hougen−Watson (LHHW) kinetics, assuming surface reaction steps are rate determining. Noncompetitive adsorption of molecular hydrogen and lactose was assumed. The fitting of the experimental data to the kinetic model was carried out by a combined Simplex−Levenberg−Marquardt method. The model predicted the experimental concentrations of lactose and lactitol very well. A reasonably good description of the byproducts was obtained.

Sugar Hydrogenation Over Supported Ru/C—Kinetics and Physical Properties

“…The sugar solution was saturated with hydrogen and preheated in a separate vessel before it was fed into the reactor. High stirring rates (1800 rpm) were used to ensure the operation under kinetic regime since our previous experiments with varying stirring rates showed that a rate of 1800 rpm was enough to suppress external mass transfer limitations [3]. Samples were withdrawn and analysed with HPLC.…”

“…The selective catalytic hydrogenation of naturally appearing sugar molecules to their corresponding sugar alcohols is an environmentally friendly route to the production of alternative sweeteners: solid metal-based catalysts are used in an aqueous environment and the hydrogen addition is materialized through catalytic reactions, thus avoiding the use of stoichiometric reducing agents and the subsequent production of inorganic salts as waste material [1][2][3]. The current production technology of sugar alcohols is based on the use of batchwise operating slurry reactors: finely dispersed, supported or sponge metal catalyst (catalyst particles smaller than 0.1 mm) are immersed in a batch of aqueous sugar solution, to which hydrogen is continuously added.…”

“…The current production technology of sugar alcohols is based on the use of batchwise operating slurry reactors: finely dispersed, supported or sponge metal catalyst (catalyst particles smaller than 0.1 mm) are immersed in a batch of aqueous sugar solution, to which hydrogen is continuously added. Sponge nickel is the traditional catalyst [2,3], which has been used for sugar hydrogenation, such as hydrogenation of glucose to sorbitol and xylose to xylitol, but in recent years [1,4], supported ruthenium catalysts have attracted growing interest, since they provide a very good selectivity towards sugar alcohols and they have a better durability-less deactivation-than nickel-based catalysts. The basics of the new technology development are the reaction kinetics and studies on product selectivity.…”

Chemical Reaction Engineering of Biomass Conversion

“…Elevated pressures and temperatures are needed to have a high enough reaction rate. On the other hand, too high a temperature impairs the selectivity of the desired product, as has been demonstrated by Kuusisto et al (2006). An overview of some feasible processes and catalysts is provided by Kinetic experiments were carried out isothermally in autoclave reactors of sizes 300 and 600 ml.…”

Influence of the Mesoporous Polymer Matrix Nature on the Formation of Catalytically Active Ruthenium Nanoparticles

“…Moreover, synthesized polyols can play a key role in the production of biofuels from renewable sources [15]. The most important saccharide hydrogenation processes are glucose, xylose, maltose, and lactose hydrogenation to the corresponding alcohols [15][16][17][18][19]. The catalytic method of D-glucose hydrogenation to D-sorbitol is a complex process ( Figure 1) providing several reaction routes.…”