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; WCCE11 - 11th WORLD CONGRESS OF CHEMICAL ENGINEERING; 2023

Asociación Argentina de Ingenieros Químicos

The recovery and use of waste from the agri-food industry is a highly strategic way of meeting the challenge of the circular economy. A high interesting case 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. An instance is the direct selective oxidation of LA to Lactobionic acid (LBA). 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 aqueous phase at 65 °C, atmospheric pressure and with air as oxidant agent. By washcoating technique, Au(2%)/Al2O3 powder catalyst prepared by precipitation-deposition, was deposited on the extended surface of metallic substrates: monoliths. These monoliths were made of Fecralloy® with different channel size, from 0.36 and 1.06 mm, and the catalyst coating thicknesses obtained were between 5 and 20 μm. The prepared monoliths were calcined in air and then were used as stirrer blades of a batch reactor. Internal and external mass transfer limitations were observed during aqueous phase lactose oxidation. Accordingly, for stirring rates equal or higher than 600 rpm and thickness coating lower than 15 μm, no important external or internal diffusional restrictions were observed. Excellent stability and reproducibility in the catalytic tests were obtained after three reaction-regeneration cycles carried out at 400 °C in air, probing the reusability of the used monoliths. Gold particle size distribution of the catalyst layer deposited on the monoliths, 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, as with the powder catalyst: Au(2%)/Al2O3, 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.