Surface properties of cellulose nanocrystal stabilized crude oil emulsions and their effect on petroleum biodegradation

Abstract

Crude oil biodegradation was improved after increasing the oil/water interfacial area via emulsification with cellulose nanocrystals (CNC) and no added surfactants. The extent of biodegradation of C15-C20 aliphatic hydrocarbons by Serratia marcescens after 5 days of incubation was increased from 1 to 12% to 6–19 %. Surface and physicochemical properties such as water salinity, presence of divalent ions and CNC concentration affect the extent of biodegradation due to their influence in emulsion stability. Stable oil in water (O/W) emulsions containing 5 v/v % crude oil and 95 v/v % brine were prepared with CNC at concentrations from 0.4 to 1.0 wt % in American Petroleum Institute (API) brine, synthetic seawater, and NaCl solutions. Creaming rate and droplet coalescence of emulsions were measured to study the impact of CNC concentration, divalent cations and ionic strength on emulsion stability. Results show a greater extent of droplet coalescence at CNC concentrations higher than 0.8 wt % for emulsions prepared in API. Coalescence was significant in API brine (ionic strength, I = 1.9 M); however, it was minimal in SSW (I = 0.65 M) and in NaCl solutions of the same ionic strength. Furthermore, no coalescence was observed in NaCl solutions at ionic strengths of 0.32, 0.65, 0.95, and 1.9 M.