Performance Evaluation of Fly Ash as a Potential Demulsifier for Water-in-Crude-Oil Emulsion Stabilized by Asphaltenes

Abstract

Summary The quest for smart and cost–effective demulsification materials to separate water–in–crude–oil (W/O) emulsions is ongoing in the petroleum industry. We conducted an assessment study on the potency of coal fly ash (CFA) as a demulsifier for W/O emulsions. To our knowledge, this is the first study reporting CFA as a demulsifier for highly stable W/O emulsions. Samples of W/O emulsions were prepared without using any conventional emulsifier. Asphaltenes in the crude oil acted as an emulsifier, and stable emulsions were produced. Six W/O–emulsion samples of the same crude–oil/water volume ratio (4:6) were formulated. A reference sample was selected for comparison during demulsification. Demulsification tests were performed at room temperature (25°C). Demulsification results obtained using bottle tests showed that the reference sample (blank) without CFA remained stable without water separation after 48 hours, while the addition of various CFA quantities (1 to 7%) brought about the separation of water from the oil phase. Separation of water was observed to have increased with increasing CFA addition in the emulsion. Water separation continued for each sample until approximately 24 hours, when equilibrium was attained and water separation remained constant. The W/O emulsion containing 7% CFA displayed the highest performance with demulsification efficiency (DE) of 96.67%. Demulsification–comparison test results between CFA and a commercial demulsifier (poloxamer 407) using the same concentration and under room temperature showed that CFA was capable of separating water better than this commercial demulsifier. This observation indicates that CFA can compete favorably with many commercial demulsifiers available in the market. In addition, the outcome of DE of 7% CFA at elevated temperatures (i.e., 60 and 80°C) was approximately 98%. More importantly, the separated water at these elevated temperatures was clearer and contained fewer oil floccules than the separated water phase observed during demulsification tests conducted under room–temperature (25°C) conditions. Shear–rheology measurement reveals that adding CFA altered the viscoelastic characteristics at the crude–oil/water interface at an aging time of 10 hours and 55 minutes. The viscous modulus remained stagnant, whereas the elastic modulus dropped significantly. Interfacial–tension (IFT) results show that CFA particles often tend to diminish the interfacial films existing between crude oil and water. Optical morphology revealed the phase transformation in the as–prepared W/O emulsion before and after the addition of CFA particles. We propose a possible mechanism governing the demulsification of W/O emulsion driven by CFA particles. We believe that this work will be relevant to petroleum–exploration/refining operations.