Membranas compósitas de paládio e óxido de grafeno para permeação de hidrogênio

Abstract

With the increase of greenhouse gases emission, alternative fuels such as hydrogen (H2) are increasingly needed. H2 has a high-energy potential; however, its production generates byproducts that need to be separated in order to achieve high purity. Palladium membrane purification is an alternative separation method due to its high efficiency and low energy consumption. However, the high cost of the metal requires studies around the reduction of the palladium membrane thickness, usually by depositing of thin layer of the metal on porous supports. Decreasing surface roughness of these supports also assists the deposition of ultra-thin palladium layers and decreases the chance of defects that may reduce selectivity. Graphene oxide (GO) is a carbonic compound with high mechanical strength capable of forming single layer films with low thickness, in this sense, the present work studied the influence of graphene oxide coatings to reduce the roughness of alumina hollow fibers for the deposition of H2 selective palladium membranes. For this purpose, alumina hollow fibers with controlled mesoporosity were produced, and were coated with graphene oxide layers, produced by the modified Hummer method, followed by the deposition of palladium membranes by electroless plating technique. The pure and coated fibers were characterized by scanning electron microscopy, water and nitrogen permeability and the roughness of their external surfaces. H2 permeation tests were performed at temperatures from 300 to 450 °C at pressures from 40 to 200 kPa. For the tested coatings, approximately 13.5% reduction in surface roughness was observed. The membrane produced without intermediate layer of OG (M1) presented a thickness of 1.6 µm, H2 permeability of 2x10-7 mol s-1m-2kPa-1 and infinite selectivity. Among the membranes produced with OG layer, M3 and M4 stood out, with thicknesses of approximately 1.0 µm and H2 permeabilities of 24x10-7 and 11x10-7 mol s-1m-2kPa-1, respectively. Through the analyzes carried out, it was verified that the graphene oxide coatings were able to provide the deposition of infinite selectivity palladium ultra-thin layers, reducing the production cost.