The use of adhesion of catalyst particles to gas bubbles to achieve enhancement of gas absorption in slurry reactors—I. Investigation of particle-to-bubble adhesion using the bubble pick-up method

Abstract

The adhesion between small catalyst particles (Pd/C, Pd/Al2O3 and activated carbon) and hydrogen bubbles, situated in aqueous electrolyte solutions or in ethanol/water mixtures, has been investigated with the Bubble Pick-up method. It was found that the adhesion between catalyst particles and hydrogen bubbles strongly depends on the properties of both catalyst particles and liquid. For solid particles adhering to a gas bubble rising in a liquid a model has been derived to estimate the fraction of the gas bubble surface area which is covered by solid particles. This model is based on a balance of forces exerted on a solid particle adhering to a gas bubble and has been applied for a bubble in a stagnant liquid, as used in the BPU method, and for a bubble rising in a liquid as occurs in slurry reactors. Considering the systems investigated, this model and the experimental results obtained with the BPU method lead to the conclusion that only Pd/C catalyst particles in an aqueous electrolyte solution show an adhesion to hydrogen bubbles which is so large that in a slurry reactor containing this system, gas bubbles will be covered partly by adhering catalyst particles. This phenomenon can result in an enhancement of the gas absorption rate and can consequently lead to a remarkable reduction of concentration and costs of expensive noble metal containing catalysts in slurry reactors.