Separation of crude oil-in-water emulsions using ethylenediamine modified rice husks

A large number of stable oil-in-water (O/W) emulsions are generated by the petroleum industry each year, resulting in a series of operational and environmental challenges. In this study, a RH-NH2 demulsifier was prepared for the separation of O/W emulsions by grafting ethylenediamine onto natural rice husk. RH-NH2 was characterized using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). When the dosage of RH-NH2 was 50 mg/L, the light transmittance (W-T) and corresponding oil removal efficiency (W-R) of the separated water were 90.2 +/- 1.8% and 94.82 +/- 0.95%, respectively, in the emulsion-0.2 (containing 0.2% crude oil). When the dosage was 200 mg/L, the W-T and W-R values of the emulsion-1 (with 1% crude oil) were 91.9 +/- 0.9% and 99.14 +/- 0.1%, respectively. In addition, dynamic interfacial tension (IFT), wettability, zeta potential, interfacial activity and adsorption capability of RH-NH2 at the interface were also investigated. The results showed that the IFT values of asphaltene and RH-NH2 (200 mg/L) was 22.58 mN/m and 16.42 mN/m, respectively. The zeta potential of the O/W emulsion was - 37 +/- 1.8 mV while that of RH-NH2 was 20.8 +/- 1.0 mV, which facilitated the electrostatic neutralization and reduced the electrostatic repulsion between oil droplets. A possible demulsification mechanism was proposed, which indicated that RH-NH2 was amphiphilic, with high interfacial activity and stronger capability to reduce IFT. It migrated rapidly to the oil-water interface and disrupted the interfacial film via synergistic effect of the pi-pi/n-pi interaction, leading to demulsification. RH-NH2 has a potential industrial application due to its low-cost and high demulsification efficiency.