Preparation and characterization of a composite membrane based on the asphaltene component of coal

Abstract

Asphaltene–ceramic composite membranes were fabricated from ceramic supports and an asphaltene component, which was obtained from the separation of coal to give a kind of new carbonaceous precursor material. Using SEM and thermogravimetric analysis to measure the microstructure and properties of the asphaltene component allowed the porosity, permeability, and retention ratios to be determined. The results show that the asphaltene component can be regarded as a good carbon membrane precursor material because of its high carbon content and strong bonding capacity. When ceramic supports are impregnated with asphaltene colloid the asphaltene easily combines with the support surface and forms a good carbonaceous film after carbonization. Little of the asphaltene component permeates into the internal pores of the ceramic support. Although the number of coats applied to the substrate had little affect on the porosity of the asphaltene–ceramic composite membranes the permeability varied depending upon the number of times the substrate was treated. The way bubbles escape from the film, and the phenomenon of coalescence, as affected by different film thicknesses also seem closely related to the number of coats. A composite membrane carbonized at a final temperature of 600 °C is relatively dense and the permeability of Fe(OH)₃ colloid through it is very low. A membrane fired at 800 °C is porous and its permeability and retention of Fe(OH)₃ colloid are 88 L/(m² h MPa) and 85.3%, respectively when the trans-membrane pressure is 0.22 MPa.