Destabilisation of water-in-crude oil emulsions using inorganic acids: The role of counter-ions and malonic acid

The quantitative role of pH with regards to the stabilisation of water-in-crude oil emulsions is not well established in literature. In this work, we report an observation wherein the prevention of stable emulsion formation occurs abruptly at a specific pH when water-in-crude oil emulsions are generated using inorganic acids (HCl, H₂SO₄ and HNO₃) and crude oils with comparatively low asphaltene contents. Subsequent analysis of the aqueous phase indicated the emulsion prevention coincided with both increasing partitioning of metal cations and total organic content (TOC). Analysis of the TOC highlighted the presence of elevated concentrations of malonic acid and its derivatives which emphasises its importance in the demulsification process. The effect of elevated concentrations of malonic acid was investigated and determined to increase the rate of emulsion destabilisation when initially dissolved in the aqueous phase. Therefore, the role of malonic acid on emulsion stability is hypothesised to be due to its partitioning into the aqueous phase as a counter-ion to dissolved metals. These results highlight malonic acid as being a key chemical species to consider when assessing the stability of a water in crude oil emulsion.