Preparation of oil-brine emulsions
Saltwater (brine) was prepared by mixing NaCl and deionized water at 600 rpm and a temperature of 298 K to obtain a concentration of 500 mg/L. Oil-brine emulsions were prepared by mixing crude oil and brine at 16,000 rpm for 20 min. Neutral emulsions were acidified and basified by adding aliquots of 0.1 N HNO3 and 0.1 N NaOH, respectively. The stability of the emulsions was monitored for 72 h by observing changes in the size of oil drops using a RPL3B optical microscope Rotating Stage Bertrand Lens Mica and Gypsum Plates (Microscopes INDIA, India) [33] and changes in absorbance using UV–vis spectrophotometer Genesys 10S (Thermo scientific, United States). Properties of crude oil, brine and oil-brine emulsion were reported in our previous study [32] and are presented in Table 1 as a reference.