CO2-Switchable Oil/Water Emulsion for Pipeline Transport of Heavy Oil

By mixing an aqueous solution of tertiary amine, N,N-dimethylethanolamine (DMEA), with naphthenic acid (RCOOH) derived from heavy oil, a CO2 switchable zwitterionic surfactant (RCOO(-)DMEAH(+)) aqueous system was constructed. The CO2 switchability of this zwitterionic surfactant was confirmed by visual inspection, pH measurements, and conductivity tests, i.e., the RCOO(-)DMEAH(+) decomposed into RCOOH, DMEAH(+) and HCO3 (-) after bubbling CO2 through but switched back to its original state by subsequent bubbling N-2 through at 80 A degrees C to remove the CO2. The interfacial tension tests of heavy oil in DMEA aqueous solutions indicated that the solution containing 0.5 wt% of DMEA and 0.2 wt% of NaCl resulted in the lowest interfacial tension. The O/W emulsion formed when aqueous solutions of DMEA were used to emulsify heavy oil exhibited the best performance when the oil/water volume ratio, DMEA concentration, and NaCl concentration were 65:35, 0.5 and 0.2 wt%, respectively. The feasibility of pipeline transport of the O/W heavy oil emulsion was evaluated. The results illustrated that the demulsification of the O/W emulsion after transport could be easily realized by bubbling CO2 through. Although demulsification efficiency still needs to be improved, the recycling of the aqueous phase after demulsification by removal of CO2 looks promising.