Wettability Control Mechanism of Highly Contaminated Hydrophilic Silica/Alumina Surfaces by Ethyl Cellulose

Abstract

In a previous study (Feng et al. Langmuir2010, 26, 3050), a biodegradable ethyl cellulose (EC) was proven to be an effective demulsifier for water-in-diluted bitumen emulsions by flocculation-enhanced coalescence through the displacement of protective interfacial films. In the current study, the potential of EC in displacing the asphaltene or bitumen layers adsorbed on hydrophilic silica and alumina surfaces is investigated in an attempt to explore the applicability of EC as a chemical modifier to control the wettability of solids contaminated by heavy oils. The quartz crystal microbalance with dissipation (QCM-D) was used to determine the adsorption of EC on silica or alumina which has a thin layer of asphaltene contaminant (preadsorbed). For comparison, the adsorption of asphaltenes on silica or alumina which was preadsorbed with EC was also determined. The effect of EC on the wettability and morphology of the asphaltene- or bitumen-contaminated (coated) silica or alumina surfaces was determined by contact angle measurement and atomic force microscope (AFM) imaging. The measurements were conducted before and after soaking the asphaltene- or bitumen-coated silica and alumina wafers in EC-in-toluene solution. The results of QCM-D showed irreversible adsorption of asphaltenes on silica surface. However, EC was found to adsorb on and/or displace the irreversibly preadsorbed asphaltenes from silica and alumina surfaces. Atomic force microscope imaging confirmed a gradual displacement of the preadsorbed asphaltenes or bitumen by EC from silica wafer surfaces, in which the asphaltene/bitumen contaminants were forced into sporadic larger aggregates. After 7 h of contact with EC-in-toluene solutions, the majority of the silica substrate surfaces precontaminated by asphaltenes or bitumen were covered with EC. Correspondingly, the contact angle of water decreased from about 88° and 67° of the original asphaltene- and bitumen-coated surfaces, respectively, to final values in the range of 20–30° which are similar to that of the EC-coated surface. Effect of EC adsorption on increasing the wettability of chemically hydrophobized (silanized) silica surface with water contact angle from 80° to 100°, is more conservative, leading to an intermediate water contact angle of 60–70° due to its weak binding and different conformations of EC on hydrophobic surfaces from that on hydrophilic surfaces. These findings demonstrated the possibility of using EC to modify the wettability of hydrocarbon-contaminated inorganic solids (clays) to improve heavy oil processing.