Process intensification: Monolitic stirred reactor for the selective lactose oxidation

BIANCHI, G.S.; MEYER, C.I.; DUARTE, H.A.; SANZ, O.; MARCHI, A.J.; REGENHARDT, S.A.

Buenos Aires

Congreso; WCCE 11th World Congress of Chemical Engineering; 2023

The recovery of waste from the agri-food industry is a highly strategic way of meeting the challenge of the circular economy. A case of high interest is whey, the liquid effluent from the cheese production and casein manufacture, with an important lactose (LA) content. Obtaining higher value-added products through catalytic processes, using LA from the cheese whey as raw material, is a challenging task. Lactobionic acid (LBA) can be obtained by selective oxidation of LA. This acid has antioxidant, humectant and emollient properties, so it is widely used in formulations of the pharmaceutical, cosmetic and medicinal industry [1].In this work, the performance of rotating metallic monolith stirrer reactor was studied for selective lactose oxidation in liquid phase at 65 °C, atmospheric pressure and with air as oxidant agent. An Au(2%)/Al2O3 solid catalyst, prepared by precipitation-deposition, was washcoated on metallic substrates (monoliths), producing catalyst coating thicknesses between 5 and 20 μm. These washcoated monoliths with different configuration (channel size between 0.36 and 1.06 mm) were used as stirrer blades in aqueous phase batch reactor. Internal and external mass transfer limitations were observed during liquid phase lactose oxidation. For stirring rates equal or higher than 600 rpm there were no important external diffusional restrictions. Coating with thickness higher than 15 μm presents loss of catalyst effectiveness due to internal diffusional restrictions. Excellent stability in the catalytic tests was obtained after three regeneration-reaction cycle carried out at 400 °C in air flow. Gold particle size distribution in the monolith before and after reaction, was determined by TEM obtaining a homogeneous size distribution with a medium particle diameter of around 5 nm.In all of the cases, the selectivity to LBA was always 100 %. Experimental data obtained under kinetic control, in absence of external and internal mas transfer limitations, were interpreted by kinetic modelling applying pseudo-homogeneous and Langmuir-Hinshelwood-Hougen-Watson (LHHW) models. It was observed that the trends for the LA conversion with time depends on the ratio of catalyst weight to initial LA moles and the initial LA concentration.The use of a structured catalyst as stirred blades combines the advantages of a structured substrate and catalytic stirrer. As structured substrates, monoliths have a promising application for liquid phase reaction due to their high geometric surface area and high void fraction, which provides accessibility of reactants to the catalyst particles with low pressure drop. It is concluded that metallic monolith stirrer reactors are a promising application for process intensification in selective lactose oxidation in liquid phase.