Cellulose derivative polymers for demulsification of lagoon wastewater-in-crude oil systems: An efficient water reuse strategy

Abstract

Removal of ions from produced crude oil necessitates desalting with water. During desalting it is essential to remove aqueous impurities from oil to avoid corrosion and fouling in upstream oil industry as well as catalyst deactivation in downstream processing. It is also important to simultaneously minimize the environmental impact of produced wastewater by cost-effective industrially feasible techniques. Since the ion content of wastewater discharge of oil desalter unit is far from saturation, its reuse for further desalting of crude oil is proposed in this study. Biocompatible carboxymethyl cellulose (Walocel), two methyl cellulose with different methyl and 2-hydroxypropyl derivative contents (Methocel K3 and Methocel E5), and cellulose acetate, are used to promote demulsification of well water- and lagoon wastewater-in-crude oil emulsion. Screening bottle tests revealed that Walocel and Methocel E5 are more suitable. Walocel and Methocel E5 at 3000 ppm could remove 97.6% and 91.7% of well water from oil at 80 °C. It was observed that presence of hydrocarbon impurities and previously added demulsifier in lagoon wastewater greatly enhances initial demulsification rate for Walocel and Methocel E5 up to 5.5 and 19.6 times, respectively. Walocel and Methocel E5 at a final concentration of 3000 ppm could remove 93.5 ± 3.6% and 95.8 ± 4.2% of lagoon wastewater within 60 min at 80 °C and finally remove all oil content of the emulsion. Superior performance of Methocel E5 in complete demulsification of lagoon wastewater-in-oil is attributed to abundance of hydrogen bond forming oxygen atoms in its cellulosic backbone as well as amphiphilic 2-hydroxypropyl and hydrophobic methyl side chains which constructively interact with water molecules and hydrocarbon impurities in the lagoon wastewater. The results of this study revealed that reuse of oily wastewater in crude oil desalting may be practical and such demulsification could be fast.